May 15, 2026 • 40 mins
We trace how autophagy keeps us alive by turning cells into disciplined self-recyclers when nutrients drop, then map the real control switches that wellness culture often gets wrong. We follow the story from lysosomes and yeast genetics to MTORC1, spermidine, and why the healthiest strategy is balance between building and cleaning.
• what autophagy is and why “self-eating” is survival, not a gimmick
• how lysosomes and autophagosomes work as an incinerator and garbage trucks
• how Ohsumi’s yeast experiments revealed ATG genes and proved conservation across species
• how MTORC1 senses nutrients and blocks autophagy through phosphorylation and TFEB control
• why constant snacking can keep MTORC1 stuck on and slow cellular cleanup
• how fasting triggers spermidine and why spermidine is required for autophagy induction
• how EIF5A hypusination prevents ribosome stalling on autophagy-related proteins
• why impaired autophagy links to protein aggregates, mitochondrial damage, inflammation, and metabolic disease
• the neonatal mouse evidence showing failure to trigger autophagy can be fatal
• Cleveland Clinic cautions on extreme fasting and who should avoid it
• where research is heading with caloric restriction mimetics such as spermidine and resveratrol pathways
This podcast is created by Ai for educational and entertainment purposes only and does not constitute professional medical or health advice. Please talk to your healthcare team for medical advice.
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Episode Transcript
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SPEAKER_01 (00:00):
If you stop eating right now, like literally put
down whatever you're snacking onand just don't eat for the next
24 hours, your cells, they arejust going to sit there
passively starving.
SPEAKER_00 (00:09):
Right.
They definitely don't just shutdown.
SPEAKER_01 (00:11):
Exactly.
They actually initiate thisimmediate, like highly
coordinated program to startcannibalizing their own internal
structures.
Which sounds bad, but here isthe craziest part.
If they couldn't do that, ifyour body somehow lacked this
specific self-eating mechanism,you wouldn't have just gotten a
little hungry.
(00:32):
You would have died on the exactday you were born.
SPEAKER_00 (00:35):
You absolutely would have.
I mean, within hours of theumbilical cord being cut,
actually, it leads to severefatal hypoglycemia.
SPEAKER_01 (00:42):
Right.
Which is just, I mean, when youreally think about the biology
of that, it completely reframeseverything we know about eating
and not eating.
So welcome to the deep dive.
SPEAKER_00 (00:50):
Glad to be here.
SPEAKER_01 (00:51):
Because today we are going way behind the incredibly
noisy, honestly kind of annoyingwellness hype surrounding
fasting.
And we're taking a massivemagnifying glass, the actual
hard cellular biology of how ourbodies clean themselves.
We're talking about autophagy.
SPEAKER_00 (01:05):
Autophagy, which, you know, if we look at the
Greek roots, you have autosmeaning self and phagomai
meaning to eat.
So it literally translates toself-devouring.
SPEAKER_01 (01:15):
Self-devouring.
Sounds like a metal band.
SPEAKER_00 (01:18):
It really does.
It's the cellular recyclingsystem, but honestly, even
calling it a recycling systemfeels a little too, I don't
know, passive for what'sactually happening at a
molecular level.
Aaron Powell Yeah.
SPEAKER_01 (01:29):
It's not like tossing a can in a blue bin.
It's more like a highlymilitarized city tearing down
its own dilapidated buildingsjust to forge weapons and fuel
to survive a siege.
SPEAKER_00 (01:39):
Aaron Powell That is a very dramatic but very
accurate way to put it.
SPEAKER_01 (01:42):
Aaron Powell And look, we have a massive stack of
literature to get through today.
I want to be super clear aboutour mission here with you guys.
Whether you are doingintermittent fasting or you're
deep into the longevity scienceworld, or you just find human
physiology fascinating, we'regoing to cut right through the
biohacking blocks.
SPEAKER_00 (02:00):
Aaron Powell Right.
We're looking at the rigorousdata today.
SPEAKER_01 (02:02):
Exactly.
We're pulling from the ClevelandClinic Guidelines, the 2016
Nobel Prize press release, aFrontiers paper on MTOR and
metabolism, a massive review onlifespan from the Journal of
Clinical Investigation, and thistotally paradigm-shifting paper
from Nature Cell Biology thatfocuses on polyamines.
SPEAKER_00 (02:22):
It is a phenomenal stack of sources, truly.
And I think to really understandwhy this is arguably one of the
most fundamental survivalmechanisms in all of biology, we
can't just jump straight intohow to, you know, hack it.
SPEAKER_01 (02:35):
Right.
Everyone just wants a hack.
SPEAKER_00 (02:36):
Exactly.
But we need to look at theliteral physical machinery
inside the cell first.
We really need to understand howscientists even figured out this
invisible process was happeningat all.
SPEAKER_01 (02:46):
Because it's not like you can just stick a tiny
GoPro inside a human cell andwatch it take out the trash.
The scale we are talking abouthere is just almost unfathomably
small.
SPEAKER_00 (02:54):
Aaron Ross Powell Exactly.
And our Nobel Prize source givesus this crucial timeline because
to find the machinery, weactually have to go all the way
back to the 1950s with a Belgianscientist named Christian de
Duvet.
SPEAKER_01 (03:05):
Okay, so mid-century biology.
What was de Duvet actuallylooking at?
SPEAKER_00 (03:09):
Well, he was doing these cell fractionation
experiments, which is basicallybreaking cells apart to see
what's inside.
And he ended up discovering acompletely new, specialized
organelle, like a brand newcompartment inside our cells.
He called it the lysosome.
SPEAKER_01 (03:23):
The lysosome, which is basically the cell's
incinerator, right?
SPEAKER_00 (03:26):
Incinerator, or you could think of it as a highly
acidic stomach.
It is a membrane-bound sac thatis absolutely packed with
destructive digestive enzymes.
SPEAKER_01 (03:35):
Just gnarly stuff.
SPEAKER_00 (03:36):
Oh, incredibly destructive.
Proteases, lipases, nucleases.
These are enzymes specificallydesigned to just rip apart
proteins, fats, and DNA.
SPEAKER_01 (03:46):
Aaron Powell, which obviously you have to keep
locked up.
Like if those enzymes justleaked out into the main body of
the cell, wouldn't they justmelt the cell from the inside
out?
SPEAKER_00 (03:53):
Yeah, precisely.
It would be catastrophic.
So they're safely quarantinedinside this lysosome.
And Deduve actually won a NobelPrize for this discovery in
1974.
But here is where the mysteryreally starts to pick up.
SPEAKER_01 (04:05):
Okay, I love a good science mystery.
SPEAKER_00 (04:06):
So in the 1960s, electron microscopes started
getting much, much morepowerful.
Scientists were finally zoomingin on these lysosomes, looking
inside the incinerators, andthey started noticing something
deeply weird.
SPEAKER_01 (04:19):
They were finding chunks of the cell inside his
own stomach.
SPEAKER_00 (04:22):
Right.
They were finding large, bulkycellular material.
We're talking whole, damagedmitochondria, massive protein
aggregates, just junk.
Right.
Which obviously raise a massivemechanical question.
SPEAKER_01 (04:34):
Aaron Powell How did the trash get into the
incinerator in the first place?
Because, like you said, thelysosome is sealed.
It's not like a gaping mouthjust swimming around the cell
eating thing.
SPEAKER_00 (04:43):
Exactly.
The cell had to have some sortof active transport system, a
way to bag up the garbage, sealit tightly, and physically haul
it over to the lysosome.
SPEAKER_01 (04:52):
And they found it.
SPEAKER_00 (04:52):
Eventually, yes.
Under the electron microscope,they spotted it.
They found this completely newtype of vesicle.
Essentially, it was a biologicalbubble, a double membrane that
would just form out of nowherearound the cellular junk,
swallow it completely, and thentravel through the cell to fuse
with the lysosome.
SPEAKER_01 (05:09):
Dump in the trash inside.
Okay, so the lysosome is theincinerator, and this double
membrane bubble is the garbagetruck.
SPEAKER_00 (05:16):
Aaron Powell That's the perfect analogy.
And De Duvet is actually the onewho coined the term autophagy
for the whole process.
And he named those specificgarbage trucks autophagosomes.
SPEAKER_01 (05:25):
Autophagosomes.
Okay, so by the 60s, they havethe visual evidence.
They know the incineratorexists, they know the garbage
trucks exist.
But reading through the Nobeltimeline we have, it seems like
the field just hit a massivebrick wall for like 30 years
after that.
SPEAKER_00 (05:43):
It really did.
It became an incrediblyfrustrating black box for
biologists.
Because seeing something happenunder a microscope is very
different from understanding howit actually happens
biochemically.
SPEAKER_01 (05:54):
Like what makes it tick.
SPEAKER_00 (05:55):
Right.
They didn't know which genescontrolled it.
They didn't know the moleculartriggers.
And if you don't know the genes,you can't design drugs to target
it.
You can't manipulate it.
SPEAKER_01 (06:04):
So it's just an observation at that point, like,
oh look, the cell is doing athing.
Cool.
SPEAKER_00 (06:08):
Yes.
It was basically stuck thereuntil the early 1990s.
And this is where our secondNobel Prize in the story comes
in.
A Japanese scientist namedYoshinoriosumi decided he was
going to finally crack thegenetic code of autophagy, but
he made a very, verycounterintuitive choice.
SPEAKER_01 (06:25):
What did he do?
SPEAKER_00 (06:26):
He didn't use human cells.
He decided to use baker's yeast.
Saccharomyces cerebisiae.
SPEAKER_01 (06:33):
Which honestly, on the surface, sounds kind of
wild.
Like if you're trying to figureout a mechanism that might cure
human neurodegeneration oraging, why are you messing
around with the stuff we use tomake sourdough bread?
SPEAKER_00 (06:45):
It's a totally fair question.
But yeast is actually aphenomenal model organism for
human cellular biology.
They are eukaryotes, meaningthey have a complex internal
architecture just like our cellsdo.
They have nucleus, they havemitochondria, and they have
their own version of a lysosome,which in yeast is called a
vacuole.
SPEAKER_01 (07:02):
Okay, sure.
They have the same parts.
But yeast cells are alsoincredibly tiny, right?
I was reading about Usumi'smethodology, and it seemed like
he had a huge physical problemright out of the gate.
SPEAKER_00 (07:11):
Yeah, he did.
Even with a really goodmicroscope, you couldn't
actually see autophagosomesforming in yeast because they
are just too small.
unknown (07:18):
Yeah.
SPEAKER_00 (07:18):
And the process is way too fast.
SPEAKER_01 (07:20):
Aaron Ross Powell Right, because think about the
life cycle of one of thesegarbage trucks.
The autophagosome forms, itgrabs the trash, it travels to
the vacuole, it fuses, and theenzymes inside the vacuole
destroy it almost instantly.
The turnover is so fast, it'svirtually invisible.
SPEAKER_00 (07:35):
That was the massive hurdle.
He wasn't even 100% sure thatautophagy happened in yeast at
all.
Because he couldn't see it.
SPEAKER_01 (07:42):
So how do you study a biological process that
destroys its own evidence theliteral second it finishes its
job?
SPEAKER_00 (07:50):
This is where Osumi's experimental design is
just breathtakingly elegant.
I mean it's brilliant.
He reasoned that if he couldsomehow stop the destruction
phase, he might be able to catchthe garbage trucks in the act.
So he genetically mutated aspecific strain of yeast.
SPEAKER_01 (08:04):
What did he mutate?
SPEAKER_00 (08:05):
He engineered them so that they lacked the
degradation enzymes inside theirvacuole.
SPEAKER_01 (08:09):
Oh wow.
So he basically broke theincinerator.
SPEAKER_00 (08:12):
He broke the incinerator.
The vacuole was still physicallythere, but it couldn't digest
anything.
Then he took these mutated yeastcells and he completely starved
them of nutrients.
SPEAKER_01 (08:23):
Just cut off their food supply entirely.
SPEAKER_00 (08:25):
Right.
He guessed that extremestarvation would force the yeast
to trigger its survivalmechanism, which he hoped was
autophagy.
SPEAKER_01 (08:33):
Wait, hold on.
So by breaking the enzymes butleaving the transport system
completely intact, he basicallygave the yeast cellular
constipation.
That's like the cell isstarting, so it starts
frantically bagging up its ownproteins to recycle them.
It sends all these trash bags tothe vacuole, but the vacuole
can't process them, so they justsit there.
SPEAKER_00 (08:51):
Yes.
And the result was spectacular.
Within just a few hours ofstarvation, the vacuoles of
these mutant yeast cells swelledup to massive proportions.
They were absolutely engorged,just stuffed full of tiny
vesicles, the autophagosomes,that had been delivered but
couldn't be destroyed.
SPEAKER_01 (09:07):
Because they just piled up.
Dude, that is amazing.
You lock the gates to thelandfill, you starve the city,
and suddenly there's amicroscopic traffic jam of
garbage trucks just backing uponto the highway.
SPEAKER_00 (09:19):
Exactly.
And now instead of thisinvisible fleeting process, you
have a massive swollen vacuolethat you can easily see under a
standard light microscope.
SPEAKER_01 (09:28):
That is so smart.
SPEAKER_00 (09:29):
Yeah.
SPEAKER_01 (09:29):
Because now he has a baseline.
Like if the traffic jam happens,he knows the autophagy machinery
works.
SPEAKER_00 (09:35):
Precisely.
So Osumi then took that baselineand ran with it.
He chemically mutated thousandsof other yeast strains at
random.
And he was specifically lookingfor mutants where when he
starved them and broke theirvacuoles, the traffic jam didn't
happen.
SPEAKER_01 (09:50):
Oh, I see.
Because if the vacuole is brokenand they are starving, but
there's no buildup of garbagebags, it means the cell
physically lost the ability tomanufacture the garbage bags in
the first place.
SPEAKER_00 (10:00):
He nailed it.
It means you found a yeast cellwith a broken autophagy gene.
He screened thousands ofcolonies this way.
And within a year, he hadidentified the very first
autophagy-related genes, whichwe now call the ATG genes.
And this discovery just blew thedoors off the entire field of
molecular biology.
SPEAKER_01 (10:19):
Aaron Powell Because once you have the actual genetic
sequence in yeast, you can justrun a search to see if humans
have it too.
SPEAKER_00 (10:25):
Exactly.
And they did.
They quickly discovered that thehuman genome contains almost
identical homologues to theseyeast ATG genes.
It proved that this machinery ishighly conserved across billions
of years of evolution.
Aliens.
Yes.
The core physical mechanism ofwrapping up cellular junk in a
double membrane and sending itto an incinerator is essentially
(10:46):
the exact same in asingle-celled yeast organism as
it is in the neurons of yourbrain right now.
SPEAKER_01 (10:52):
That kind of evolutionary conservation always
gets me.
Like if something hasn't changedin a billion years, it means it
is absolutely critical for life.
You just can't mess with it.
SPEAKER_00 (11:00):
It is fundamental to survival.
SPEAKER_01 (11:02):
But okay, this leads to a massive question for me.
And it's something the Frontiersand JCI papers go into deeply.
We know the garbage eggs existnow.
We know the genes that buildthem, but how does the cell
actually know when to buildthem?
Like, assume you literallystarve the yeast to trigger
this.
What is the actual biochemicalarchitecture of hunger?
SPEAKER_00 (11:21):
How does it detect the food is gone?
SPEAKER_01 (11:22):
Yeah.
How does a microscopic blob knowit's starving?
SPEAKER_00 (11:26):
To understand that, we have to introduce what is
arguably the most importantmaster switch in all of cellular
metabolism.
It's a massive protein complexcalled MTORC1.
SPEAKER_01 (11:37):
MTORC1.
Okay, let's unpack that.
Because I see this acronymthrown around in literally every
longevity article ever written.
SPEAKER_00 (11:44):
It stands for Mechanistic Target of Rapamycin
Complex 1.
SPEAKER_01 (11:47):
Mechanistic Target of Rapamycin.
Honestly, it sounds like aweapon from a sci-fi novel.
SPEAKER_00 (11:51):
It does, but its function is very grounded and
very real.
MTORC1 is the cell's masternutrient sensor and its primary
growth director.
I want you to picture MTORC1 asa highly sensitive, very
aggressive foreman on aconstruction site.
SPEAKER_01 (12:05):
Okay, I like that.
Formin.
SPEAKER_00 (12:07):
When nutrients are abundant in your bloodstream, so
when you have high levels ofamino acids, glucose, and growth
factors floating around, MTORC1is turned firmly into the on-end
position.
SPEAKER_01 (12:17):
And when the foreman is awake and active, what's he
doing?
SPEAKER_00 (12:20):
He is driving anabolism, building.
When MTORC1 is active, it floodsthe cell with signals to
synthesize new proteins, buildnew lipid membranes, create
nucleotides for DNA, andgenerally just grow and
multiply.
SPEAKER_01 (12:33):
It's just screaming, build, build, build.
SPEAKER_00 (12:35):
Exactly.
It is the ultimate biologicalsignal for times are good, we
have plenty of resources, let'sexpand.
SPEAKER_01 (12:42):
Okay, so if MTR is the growth boss driving all this
anabolic construction, how doesthat relate to the garbage
trucks?
SPEAKER_00 (12:48):
Aaron Powell Well, think about the basic energy
economics of a cell.
You cannot aggressively buildnew skyscrapers and
simultaneously demolish yourexisting buildings.
That would be a futile, chaoticwaste of cellular energy.
SPEAKER_01 (13:00):
Aaron Powell You'd just be spinning your wheels.
SPEAKER_00 (13:02):
Right.
You have to commit to one stateor the other.
So when MTRC1 is active anddriving growth, it actively
physically blocks the autophagypathway.
SPEAKER_01 (13:10):
Aaron Powell Well, physically.
I was looking at the Frontier'spaper and it talks about
phosphorylation, but I'm tryingto visualize what that actually
means in this context.
How does MTOR physically stopthe cleanup crew?
SPEAKER_00 (13:22):
Aaron Powell It's a really great mechanical
question.
So when nutrients are plentiful,the MTOR RC1 complex actually
travels to and physicallytethers itself to the outer
surface of the lysosome, theincinerator.
SPEAKER_01 (13:33):
Oh wow.
So it literally sits on the roofof the garbage dump.
SPEAKER_00 (13:36):
Yes.
It anchors there, and from thatperch, it acts as a kinase.
A kinase is just an enzyme thatattaches phosphate groups to
other proteins.
So MTORC1 grabs the initiationproteins that are required to
start building theautophagosome, specifically
these proteins, named ULK1 andATG13, and it phosphorylates
them.
SPEAKER_01 (13:56):
Okay, and adding that phosphate group, what does
that actually do?
Does it break them?
SPEAKER_00 (14:00):
It doesn't break them permanently, but it forces
a change in their 3D shape.
It's really like slapping abulky molecular padlock onto
them.
Because of that structuralchange, ULK1 and ATG-13 are
deactivated.
They cannot assemble themachinery needed to start
forming the double membrane.
SPEAKER_01 (14:16):
So the garbage trucks cannot be manufactured at
all.
SPEAKER_00 (14:18):
Exactly.
SPEAKER_01 (14:19):
That makes so much sense.
The foreman sits on theincinerator, slaughter padlocks
on the garbage trucks, and says,nobody cleans today.
We are only building.
SPEAKER_00 (14:27):
That's a great way to visualize it.
But it actually goes even deeperthan that.
MTORC1 also targets atranscription factor called TSB.
Now TFAB's entire job is totravel into the nucleus of the
cell, bind to the DNA, and turnon the genes that build more
lysosomes.
SPEAKER_01 (14:42):
To build more incinerators.
SPEAKER_00 (14:44):
Right.
But while MTORC1 is active, itphosphorylates TFE2, which
completely traps it in thecytoplasm.
It physically cannot enter thenucleus.
SPEAKER_01 (14:53):
Man, so MTOR is shutting down the recycling
program at every conceivablelevel.
It stops the trucks from formingand it stops the factory from
building new incinerators.
SPEAKER_00 (15:02):
Precisely.
It is a total systemic blockade.
Now, consider what happens whenthe food finally runs out.
When you stop eating, or whenOsumi starved his yeast.
SPEAKER_01 (15:11):
The amino acids in the blood drop.
SPEAKER_00 (15:12):
Right.
And without those amino acids,the biochemical signal that
keeps MTORC1 anchored to thelysosome just vanishes.
MTORC1 essentially detaches andshuts off.
SPEAKER_01 (15:22):
Aaron Ross Powell He goes to sleep.
SPEAKER_00 (15:23):
Exactly.
And at the exact same time, adifferent metabolic sensor
called AMPK, which acts like analarm system that detects low
cellular energy, turns on.
SPEAKER_01 (15:32):
Okay, so the day shift foreman clocks out, and
the night shift emergencysupervisor clocks in.
SPEAKER_00 (15:36):
That's a perfect analogy.
And the moment MTORC1 shuts off,all those molecular padlocks
fall off.
ULK1 and ATG13 are suddenlydephosphorylated and freed.
SPEAKER_01 (15:46):
They just wake up.
SPEAKER_00 (15:47):
They immediately spring into action.
They recruit other proteins tothe endoclasmic reticulum and
they begin physically weavingthe double membrane of the
autophagosome.
The garbage trucks are finallydispatched.
SPEAKER_01 (15:58):
And what about that transcription factor, TFEB?
SPEAKER_00 (16:01):
Without M2R holding it hostage, TFEB dives straight
into the nucleus, binds to theDNA, and initiates a massive
genetic program called lysosomalbiogenesis.
The cell literally prints newincinerators.
SPEAKER_01 (16:13):
It just goes into overdrive.
SPEAKER_00 (16:15):
It aggressively ramps up its capacity to break
things down.
Because remember, the cell isstarving.
It is desperate for rawmaterials.
So it starts engulfing its owndamaged proteins, its old lipid
droplets, and breaking them downinto basic amino acids and fatty
acids just to keep the cellularlights on.
SPEAKER_01 (16:31):
You know, I have to say, looking at it like this,
MTOR kind of seems like thevillain of the aging story.
SPEAKER_00 (16:37):
A lot of people think that.
SPEAKER_01 (16:38):
I mean, if MTOR stops the cleanup and allows all
this toxic junk to build up inour cells, shouldn't our goal
just be to turn MTORs as much asphysically possible?
I see people online trying tobasically biohack themselves
into like permanent autophagy.
SPEAKER_00 (16:53):
I completely understand the logic there, but
it is a massive, incrediblydangerous misconception.
We absolutely cannot vilify MTR.
Really?
You need MTR to live.
If you don't have active MTOR,you cannot build muscle mass.
Your immune system cannotproliferate white blood cells to
fight off an infection.
You can't heal a simple wound.
If you somehow force MTOR into achronically off F state, you
(17:16):
would suffer severe muscleatrophy, immune deficiency, and
eventual death.
SPEAKER_01 (17:20):
Okay, yeah.
Muscle mass is pretty importantfor, you know, not dying.
SPEAKER_00 (17:24):
Yeah.
SPEAKER_01 (17:25):
Especially as we age, faily is a huge killer.
SPEAKER_00 (17:28):
Exactly.
The magic of human metabolismisn't found in extremes.
It is found in the oscillation.
SPEAKER_01 (17:33):
The oscillation, like a pendulum swinging back
and forth.
SPEAKER_00 (17:36):
Yes.
True metabolic health requiresrobust periods of MTOR
activation when you are fed, soyou can build, repair, and
strengthen tissues, followed byperiods of low MTOR and high
autophagy when you are fasted,allowing the cell to
aggressively sweep out theaccumulated garbage.
SPEAKER_01 (17:53):
So you need both.
SPEAKER_00 (17:54):
You absolutely need both.
The pathology, the disease statewe see so much of today, occurs
when the pendulum gets stuck.
SPEAKER_01 (18:00):
Let me guess.
It gets stuck because we live inan environment where we're just
constantly eating.
SPEAKER_00 (18:05):
Right.
The modern dietary pattern.
Eating a heavy breakfast,snacking all day at your desk,
drinking caloric beverages,eating a late dinner, and then
having a midnight snack.
It means that your amino acidand glucose levels never truly
bottom out.
SPEAKER_01 (18:18):
So MTR is just jammed in the on-in position,
2004-7.
SPEAKER_00 (18:22):
Precisely.
The foreman never sleeps.
The cell never gets thebiochemical signal that it's
safe to halt construction andstart cleaning.
So the misfolded proteins startto pile up in the corners of the
cell, the damaged mitochondriaare left to rot.
That is grim.
And the accumulation of all thatmicroscopic trash is a primary
driver of metabolic dysfunctionand the aging process itself.
SPEAKER_01 (18:43):
Wow.
Okay, so the logic is incrediblytight.
Food is abundant, MTOR turns on,we build, food is scarce, MTOR
turns off, the pads fall off,ULK1 activates, and we clean.
It makes perfect sense.
But reading through the sourcematerials, particularly that
recent Nature Cell Biologypaper, it feels like this neat
little seesaw model is mything amassive piece of the puzzle.
SPEAKER_00 (19:05):
It absolutely is.
And this is where the biologytakes a really fascinating turn.
For a long time, the scientificconsensus was that the mere
absence of nutrients was thetrigger.
SPEAKER_01 (19:13):
Like just an empty tank.
SPEAKER_00 (19:14):
Right.
You take away the food, MTRshuts down, end of story.
The void itself is the signal.
But this new research completelyupends that idea.
SPEAKER_01 (19:23):
Because this paper shows that fasting isn't just an
empty void.
When you stop eating, theabsence of food actively causes
your body to synthesize a veryspecific molecule.
Like your body creates a newchemical signal in response to
starvation.
SPEAKER_00 (19:39):
Yes, and that molecule is not optional.
The researchers found that ifyou block the body's ability to
produce this specific molecule,fasting completely fails to
trigger autophagy.
SPEAKER_01 (19:50):
The whole thing just breaks.
SPEAKER_00 (19:51):
The entire cleanup system breaks down, even if the
cell is completely starving.
SPEAKER_01 (19:55):
Okay, we have to name the molecule, even though I
know the history here is alittle uh colorful.
What is this magic key?
SPEAKER_00 (20:01):
It is a naturally occurring polyme called
spermidine.
SPEAKER_01 (20:04):
Spermidine.
I mean, look, I know we're doingserious science here, but who
looked at this incrediblecellular longevity molecule and
said, yes, let's name itspermidine?
SPEAKER_00 (20:14):
Well, to be fair, it wasn't named recently.
The name comes from its initialdiscovery in the late 1600s by
Anthony van Leeuwenhoek.
He was the inventor of themicroscope, and he originally
isolated it from seminal fluid.
Right.
But we really need to look pastthe historical nomenclature
because spermidine isubiquitous.
It is found in almost all livingtissues, in plants, in animals,
(20:36):
and it is a master regulator ofcellular metabolism.
SPEAKER_01 (20:40):
All right, I'll put my middle school humor away.
Polyamine.
I know a polyamine is an organiccompound with multiple amino
groups, which usually means theyare positively charged and they
love to interact with negativelycharged things like DNA and RNA.
But what did this nature paperactually discover about it in
relation to fasting?
SPEAKER_00 (20:57):
So the research team led by the Tavernorakus lab,
along with prominent researcherslike Guido Kromer and Frank
Medeo, they asked a very elegantquestion.
They knew that fasting triggersautophagy, but they wanted to
know what happens to theinternal levels of polyamines
when an organism starves.
SPEAKER_01 (21:15):
Okay.
SPEAKER_00 (21:15):
And they didn't just look at one animal, they looked
across the entire evolutionarytree.
SPEAKER_01 (21:19):
So they went back to Osumi's yeast.
SPEAKER_00 (21:21):
They did.
They started by starving yeastcells, and they observed a
massive, sharp spike inspermidine production.
Then they moved up the tree,they starved fruit flies for 24
hours, again, a massive spike inspermidine.
They fasted mice overnight,which is actually a long time
for a mouse's fast metabolism.
They measured the serum andmultiple organs, spike in
(21:42):
spermidine.
SPEAKER_01 (21:43):
Okay, that shows evolutionary conservation,
definitely.
But mice and yeast aren'thumans.
Did they test this in actualpeople?
SPEAKER_00 (21:50):
They did.
They had four different humancohorts in this study, but the
most striking one involved aspecialized fasting clinic.
They monitored human volunteerswho underwent a medically
Supervised extreme fast for 7 to13 days.
SPEAKER_01 (22:03):
Wait, 7 to 13 days of zero food?
SPEAKER_00 (22:06):
Very close to zero.
They were allowed roughly 250calories a day.
Essentially just a little bit oforganic fruit juice, vegetable
soup broth, and a tiny bit ofhoney.
SPEAKER_01 (22:15):
That sounds miserable.
SPEAKER_00 (22:16):
It is a severe caloric restriction mimicking a
complete fast.
And when they analyzed the bloodof these human volunteers over
the course of the week, thelevels of spermidine surged.
And it was universal.
Didn't matter if the patient wasmale or female, old or young,
lean or obese.
Severe fasting fundamentallyaltered their polyamine
metabolism to pump outspermidine.
SPEAKER_01 (22:36):
Okay, so starvation correlates with a spike in
spermidine.
But we know correlation isn'tcausation.
How do we know spermidine isactually doing the work?
Maybe it's just a byproduct ofthe stress, you know, like an
exhaust coming out of a carengine.
If you take the spermidine away,does the car still drive?
Is the cleanup still happen justbecause MTOR is off?
SPEAKER_00 (22:57):
That is the exact critical experiment they
performed to prove causation.
They took yeast cells andgenetically knocked out a gene
called SPAY1.
This is the enzyme required tosynthesize spermidine.
So these mutant yeast physicallycannot make spermidine.
Okay.
When they starved these mutants,the entire starvation response
collapsed.
Autophagy was not induced.
(23:18):
They couldn't properly inhibitMTORC1.
Their energy metabolism wentcompletely haywire.
SPEAKER_01 (23:23):
Whoa.
So without this specificpolymer, taking away the food
does absolutely nothing totrigger the garbage trucks.
SPEAKER_00 (23:29):
Nothing.
And to prove it wasn't just aweird yeast quirk, they did the
exact same thing in microscopicworms, C.
elegans nematodes.
They used RNA interference tosilence the worm equivalent of
the gene, which is called oddC1.
SPEAKER_01 (23:41):
And what happened?
SPEAKER_00 (23:42):
When they starved the spermidine deficient worms,
the lifespan extension andautophagy induction that
normally comes from fasting werecompletely abolished.
SPEAKER_01 (23:50):
The mechanism is totally broken.
SPEAKER_00 (23:51):
Totally broken.
But here is the clincher.
When the researchers manuallysupplemented spermidine back
into the water of thesegenetically broken, starving
worms.
SPEAKER_01 (24:00):
Let me guess.
The pathway snapped back online.
SPEAKER_00 (24:03):
Completely rescued.
The metabolic flexibilityreturned, autophagy fired up,
and the worms' lifespans wereextended again.
SPEAKER_01 (24:10):
That is profoundly weird.
Why is this one molecule thelinchpin for this
billion-year-old process?
I was reading this section inthe paper about hypucination,
and my eyes kind of glazed over,honestly.
How does spermidine physicallyforce the cell to build the
autophagosomes?
SPEAKER_00 (24:27):
It is deeply technical, but if we break it
down, it's fascinating.
Spermidine is essentially therequired raw material for a very
unique post-translationalmodification called
hypucination.
In all of biology, there is onlyone specific protein that gets
hypucinated, and its name isEIF5A.
SPEAKER_01 (24:43):
EIF5A.
Another acronym, what does itdo?
SPEAKER_00 (24:47):
It's a translation factor.
When your cell's ribosomes arereading RNA to build new
proteins, they sometimes getstuck.
Specifically, if they have tostring together a bunch of
proline amino acids in a row, apolyproline tract, the ribosome,
literally jams.
It physically stalls out.
SPEAKER_01 (25:03):
Like a paper jam and a printer.
SPEAKER_00 (25:05):
Exactly like that.
EIF5A acts like a mechanicalgrease.
It binds to the stalled ribosomeand helps it push through that
difficult sequence.
SPEAKER_01 (25:13):
Okay, but what does a jammed ribosome have to do
with autophagy?
SPEAKER_00 (25:16):
Because the proteins required to build the
autophagosome, remember ULK1,and particularly a master
regulator called TFE, they areloaded with these difficult
polyproline sequences.
If EI5A isn't active, the cellphysically cannot manufacture
the proteins needed to executeautophagy.
The ribosomes just jam up andfail.
SPEAKER_01 (25:34):
Oh man.
I'm putting the pieces together.
An EIF5A can only be activatedif it gets hypucinated by
spermidine.
SPEAKER_00 (25:41):
Precisely.
Spermidine is the key in theignition.
When you fast, your body spikesspermidine production.
That spermidine hypucinatesEIF5A, which turns it green, so
to speak.
The active EIF5A then allows theribosomes to successfully
manufacture TFFB and the otherautophagy proteins without
jamming.
SPEAKER_01 (26:01):
That is wild.
SPEAKER_00 (26:02):
Right.
Without spermidane, EIF5A staysinactive, the ribosomes stall,
and the garbage trucks cannot bebuilt, no matter how hungry the
cell is.
SPEAKER_01 (26:11):
That is one of the most elegant biological cascades
I've ever heard.
It's not just food off,autophagy on.
Fasting is an active, demandinggenetic program.
SPEAKER_00 (26:20):
It is highly active.
SPEAKER_01 (26:21):
And this actually brings me to a really crucial
point.
We've talked a lot about themechanics, the incinerators, the
garbage trucks, the foreman, thejammed ribosomes.
But we need to zoom out for asecond for the listener.
Why does clearing out thismicroscopic junk matter so much
for the person listening to thisright now?
Like, what are the actual stakesfor human health ban and
disease?
SPEAKER_00 (26:38):
The stakes are incredibly high.
And it comes down tounderstanding that cellular junk
isn't just harmless cluttersitting in the corner, it is
actively toxic.
The JCI review and the Frontierspaper make it very clear that
failing to clear this debris isa root cause of age-related
decline.
SPEAKER_01 (26:56):
Toxic in what way?
Give me a concrete example ofthe trash.
SPEAKER_00 (27:00):
The most critical example is misfolded proteins.
Proteins are these highlycomplex three-dimensional
origami structures.
Their shape dictates theirfunction.
But over time, due to stress orjust the physics of the cellular
environment, they can foldincorrectly.
SPEAKER_01 (27:15):
In Menway.
SPEAKER_00 (27:16):
When they misfold, they expose sticky regions and
start clumping together intomassive, insoluble aggregates.
Aaron Powell, Jr.
SPEAKER_01 (27:22):
Which sounds exactly like the plaques and tangles you
hear about in neurodegenerativediseases.
SPEAKER_00 (27:26):
Aaron Powell Exactly.
Alzheimer's disease, Parkinson'sdisease, Huntington's, these are
all fundamentally characterizedby the accumulation of toxic
protein aggregates in neurons.
Neurons are postmitotic.
They generally don't divide.
SPEAKER_01 (27:38):
So they can't just dilute the trash by splitting
into two new cells.
SPEAKER_00 (27:41):
Aaron Powell Right.
They have to rely on autophagyto constantly sweep up these
misfolded proteins before theyclump together and destroy the
neuron.
SPEAKER_01 (27:50):
Wow.
So maintaining high levels ofautophagy in the brain isn't
just about general health, it'sliteral neuroprotection.
It is the frontline defenseagainst Alzheimer's.
SPEAKER_00 (27:59):
Yes.
And the second major target ofthe garbage trucks is your
mitochondria, the power plantsof the cell.
Yeah.
Mitochondria have a shelf life.
They undergo massivestress-generating ATP, and
eventually they get damaged.
And a damaged mitochondriondoesn't just quietly power down,
it becomes dangerously leaky.
SPEAKER_01 (28:17):
Leaking what?
Energy.
SPEAKER_00 (28:18):
Worse, it leaks toxic reactive oxygen species,
free radicals.
It starts violently oxidizingand destroying surrounding
cellular structures, mutatingDNA and driving massive
inflammation.
SPEAKER_01 (28:30):
That's terrifying.
SPEAKER_00 (28:31):
It's essentially a failing nuclear reactor
threatening to melt down insidethe cell.
SPEAKER_01 (28:34):
Okay, that sounds catastrophic.
SPEAKER_00 (28:36):
It is, which is why autophagy has a specialized,
targeted subroutine calledmitophagy.
The cell recognizes the leakypower plant, builds an
autophagosum specifically aroundit, and hauls it to the lysosome
for targeted destruction,eliminating the source of the
oxidative stress before itcauses irreversible DNA damage.
SPEAKER_01 (28:55):
It's so precise.
And I know there are othersubroutines too, right?
Because the GCI paper talkedabout lipophagy.
SPEAKER_00 (29:01):
Yes.
Lipophagy is the specifictargeting of lipid droplets,
stores of fat inside the cell.
As we age, our baseline rate ofautophagy naturally declines.
This is one of the primaryreasons we see a massive
increase in age-related hepaticlipid accumulation.
SPEAKER_01 (29:17):
Aaron Ross Powell Hepatic meaning in the liver.
So we're talking about fattyliver disease, metabolic
syndrome, insulin resistance.
SPEAKER_00 (29:23):
Aaron Powell Precisely.
The JCI paper sets a fascinatingexperiment regarding this.
Researchers engineered mice tohave a hyperactive version of T
heyday, that transcriptionfactor we talked about earlier
that drives the creation of newlysosomes.
SPEAKER_01 (29:34):
Okay, so they have extra incinerators.
SPEAKER_00 (29:36):
Right.
When they fed these mice aterrible high-fat
obesity-inducing diet, the micewere completely protected from
metabolic syndrome and obesity.
SPEAKER_01 (29:47):
Just because they had more incinerators.
SPEAKER_00 (29:48):
Yes.
Their enhanced autocogy clearedthe ectopic fat droplets so
efficiently that they remainedmetabolically healthy.
But crucially, if theresearchers knocked out the core
autophagy genes in those samemice, the protective effect of
TFAB vanished completely, andthe mice developed severe fatty
liver disease.
SPEAKER_01 (30:09):
That is incredible.
SPEAKER_00 (30:10):
It proves that the physical act of cellular eating
is the critical mechanismpreventing the metabolic
collapse.
SPEAKER_01 (30:16):
So we are talking about preventing Alzheimer's,
stopping mitochondrial meltdown,and staving off fatty liver
disease.
That's essentially the unholytrinity of aging.
SPEAKER_00 (30:25):
It really is.
SPEAKER_01 (30:26):
But if we want to talk about how absolute
non-negotiable this process isfor mammalian life, we have to
talk about the neonatal mouseexperiment from the Frontiers
paper, because this completelyblew my mind when I read it.
We mentioned it at the verybeginning of the deep dive.
SPEAKER_00 (30:38):
Yes, it is one of the most stark demonstrations of
biological necessity in theliterature.
SPEAKER_01 (30:43):
So break down the genetics of this experiment
because it's a little complex.
SPEAKER_00 (30:47):
The researchers genetically engineered a strain
of mice with a mutation in agene called RAGA.
Now, RAGA is an upstreamactivator of our old friend, the
MTORC1 complex.
The specific mutation theyintroduced rendered the RAGA A
protein permanently, irrevocablylocked in the on-end state.
SPEAKER_01 (31:05):
Which means the MTORC1 master switch is
permanently jammed on in.
SPEAKER_00 (31:09):
Exactly.
The genetic forman is screamingbuild, build, build 247.
The cell thinks it is constantlyat a massive all-you-can-eat
buffet, regardless of what theactual nutrient levels in the
blood are.
Now, while these geneticallyengineered pups are developing
in the mother's room, everythingseems perfectly fine.
SPEAKER_01 (31:27):
Right, because the placenta provides a constant
nonstop IV drip of glucose andamino acids.
The buffet is actually real.
SPEAKER_00 (31:34):
Exactly.
But then the pups are born, andthe moment of birth is arguably
the most severe metabolic shocka mammal ever experiences,
because the umbilical cord iscut.
SPEAKER_01 (31:44):
And suddenly the IV drip is gone?
I never thought about it likethat, but birth is basically a
forced extreme fasting state.
SPEAKER_00 (31:50):
It is our first true fast.
The constant supply of nutrientsplummets to zero instantly.
And it's going to be hoursbefore the mother's milk fully
comes in and the pup canactually feed.
In a normal, healthy mouse pup,the moment that cord is cut and
the amino acids in the blooddrop, MTORC1 instantly detects
the starvation and shuts off.
SPEAKER_01 (32:11):
And the pads fall off and autophagy fires up.
SPEAKER_00 (32:13):
Massively.
Within the very first hour oflife outside the womb, a normal
pup cells begin aggressivelycannibalizing their own internal
stores.
They break down stored glycogenand internal cellular proteins
to generate a massive surge offree amino acids.
Those raw materials are shippeddirectly to the liver to drive
gluconeogenesis, which is therapid synthesis of new glucose.
SPEAKER_01 (32:39):
They literally have to eat parts themselves to
survive their first day onEarth.
SPEAKER_00 (32:43):
Yes.
But what happens to thegenetically engineered mice, the
ones with the mutated ragae?
SPEAKER_01 (32:48):
Their MTOR is stuck on in.
The foreman refuses toacknowledge the famine.
SPEAKER_00 (32:52):
Right.
Even though the umbilical cordis cut and the blood nutrients
are crashing, their cells stillbiochemically believe there is
infinite food.
They never send the signal tostart cleanup.
They completely fail to triggerautophagy.
SPEAKER_01 (33:06):
And the result.
SPEAKER_00 (33:06):
They die almost immediately.
Because they cannot triggerautophagy, they cannot mobilize
those internal amino acids, theycannot produce new glucose in
the liver, and they succumb tosevere fatal hypoglycemia within
hours of birth.
The researchers noted that thephysical pathology of these
mice, mice with permanentlyactive MTOR, is virtually
indistinguishable from mice thathave had their core autophagy
(33:30):
genes completely deleted.
They both die as neonates.
SPEAKER_01 (33:33):
That is intense.
It really hammers home that thisisn't just some fringe
biohacking trick to look good onthe beach.
It is a foundational pillar ofhow eukaryotic life sustains
itself under stress.
SPEAKER_00 (33:43):
It is life and death.
SPEAKER_01 (33:45):
But okay, let's take a deep breath here because we
have covered a staggering amountof molecular biology.
We've gone from Daduvi'sincinerators to Osumi's yeast
traffic jams.
We've unpacked the MTOR seesaw,we've explored the wild spermine
hypesonation pathway, and we'velooked at the fatal consequences
in neonatal mice.
SPEAKER_00 (34:06):
I think we really need to bring this back down to
the practical reality for theperson listening.
SPEAKER_01 (34:10):
I agree, because the translation from cellular
biology to daily human health iswhere things get very
complicated.
SPEAKER_00 (34:16):
Yeah, because knowing how the internet works,
people are going to hearautophagy cures Alzheimer and
saves baby mice, and theirimmediate reaction is going to
be I need to stop eating for 30days straight so I can live
forever.
And our source from theCleveland Clinic has some very
explicit loud warnings aboutapplying this science
recklessly.
They do.
The Cleveland Clinic Guidelinesare very clear that while the
(34:36):
foundational biology is sound,the internet's interpretation of
autophagy as a magic youthbutton is deeply flawed.
Attempting to violently forceyour body into a state of hyper
autophagy through extremeprolonged fasting or severe
caloric restriction can beincredibly dangerous.
SPEAKER_01 (34:55):
Because you are fundamentally stressing the
system.
It's a survival response tostarvation.
SPEAKER_00 (35:00):
Exactly.
And for certain physiologicalstates, that level of systemic
stress is profoundly unsafe.
The medical guidelinesspecifically warn that pregnant
women, individuals who arebreastfeeding, or anyone with
diabetes or pre-existing bloodsugar regulation issues should
absolutely not attempt drasticfasting regimens to chase
autophagy.
SPEAKER_01 (35:19):
Right, because you can induce severe hypoglycemia,
pass out, or worse.
This is the classic rule ofbiology, right?
The dose makes the poison, alittle bit of stress hormesis
cleans out the cell and makes itmore resilient.
But an overwhelming amount ofstress just damages the tissue
and kills the organism.
SPEAKER_00 (35:33):
Precisely.
You have to respect thebiological limits.
You are trying to trigger anancient, highly tuned survival
mechanism, not win an internetsuffering contest.
Even attempting to force itthrough sudden extreme endurance
exercise without proper medicalsupervision is a bad idea.
SPEAKER_01 (35:51):
So if starving ourselves for a week straight
isn't a safe or practical dailyanswer for the vast majority of
people, where is this fieldactually heading?
Like what does the future ofthis research look like if we
want the benefits without theextreme starvation?
SPEAKER_00 (36:06):
This is where we get to one of the most provocative
and exciting areas in moderngerontology.
Let's look back in theintersection of the JCI paper
and the nature paper.
We know definitively thatcaloric restriction extends
lifespan across species.
But we also now know, thanks tothe spermidane data, that the
biological pathways activated byfasting are mediated by specific
identifiable molecules.
SPEAKER_01 (36:27):
Right.
Fasting is just the trigger.
The molecules are theexecutioners.
And the JCI paper also talkedheavily about another pathway,
right?
Something about acetyl-CoA andCzar T1.
I was trying to map that ontothe MTR story.
SPEAKER_00 (36:38):
Yes, and it fits together beautifully.
Acetyl-CoA is essentially thecentral currency of cellular
energy and fat metabolism.
When you are fully fed,acetyl-CoA levels are high.
That high energy state actuallycauses acetyl groups to be
physically attached to yourautophagy proteins, a process
called acetylation, whichinhibits them, just like M2R's
(36:59):
phosphorylation does.
SPEAKER_01 (37:00):
So it's just another molecular padlock.
SPEAKER_00 (37:02):
Exactly.
But when you fast, energy drops,and an enzyme called CERT1 gets
activated.
CERT1 is a diailase.
It physically strips thoseacetyl padlocks off the
autophagy machinery, helping totrigger the cleanup.
And here is the crucial partCERT1 can be powerfully
activated by certain naturalcompounds, most famously
resveratrol, which is found inthe skin of red grapes.
SPEAKER_01 (37:25):
Okay, so resveratrol triggers the Cirti1 pathway to
remove the acetyl padlocks.
And the nature paper showed thatspermidine triggers the EIF5A
pathway to build the machinery.
Both of these moleculesessentially trick the cell into
thinking it's starving, even ifit's not.
SPEAKER_00 (37:39):
You see exactly where this is going.
Scientists are asking a massivemulti-billion dollar question.
If naturally occurring moleculescan biochemically tap into the
exact same pathways as extremefasting, can we biomimic the
fast?
SPEAKER_01 (37:52):
Wait, are you saying the end goal of all this
research is a literal pill?
A supplement that givesyourselves the massive cleanup
signal of a five-day water fastwithout you actually having to
skip a single meal.
SPEAKER_00 (38:04):
They are called caloric restriction mimetics, or
CRMs.
It is a major heavily fundedarea of research.
Now, to be clear, the goal isn'tto create a magic pill that lets
you eat a box of donuts everyday and suffer zero
consequences.
SPEAKER_01 (38:17):
Damn, that'll be nice.
SPEAKER_00 (38:18):
The medical application is much more
profound than that.
Think about people whophysically cannot safely fast.
The frail, elderly, patientsundergoing certain disease
treatments, or individuals withsevere metabolic dysregulation.
What if we could give them alocalized, precise dose of a
polyamine like spermidine, or acombination therapy with a CERT
T1 activator like resveratrol?
SPEAKER_01 (38:40):
You could artificially lower the flag that
tells MTOR to shut off, stripthe acetyl padlocks, and force
EIF5A to turn green.
You're basically sending a fakebiochemical text message to the
cellular foreman saying, hey,the warehouse is empty, send the
construction crew home and bringin the deep cleaners, even if
the blood glucose is totallynormal.
SPEAKER_00 (39:00):
That is exactly the mechanism they are exploring.
The JCI paper even explicitlypoints out that combining
molecules like giving adeacetylase activator like
resveratrol concurrently with acompound that lowers acetyl-CoA
or hypucinates translationfactors might synergistically
induce massive therapeuticlevels of autophagy.
SPEAKER_01 (39:19):
Honestly, cellular biology is just the ultimate
hacker's playground.
The complexity is staggering.
But realistically, until thosehighly regulated, proven caloric
restriction memetic therapieshit the pharmacy, we have to
rely on the actual hardware andsoftware we were born with.
SPEAKER_00 (39:33):
And that biological hardware relies entirely on
respecting the balance.
SPEAKER_01 (39:36):
Right.
So to everyone listening to thisright now, I think the biggest
takeaway is to look at your ownlifestyle and think about your
balance of building andcleaning.
Are you keeping that MTOR switchjammed in the on-end position by
constantly grazing and snackingfrom 6 a.m.
until midnight?
Or are you intentionally givingyour body those quiet,
(39:57):
nutrient-free windows it sodesperately needs?
Because your cells want to fireup the incinerators, they want
to clear out the misfoldedproteins, and they want to take
out the toxic trash.
You just have to get out oftheir way and let them do it.
SPEAKER_00 (40:09):
It really does come down to just letting the
microscopic maintenance crew dotheir jobs.
SPEAKER_01 (40:13):
Exactly.
Because at the end of the day,you can build the most
beautiful, towering, anabolicskyscrapers in the world.
But if you never let the garbagetrucks run, the city is
eventually going to collapse.
SPEAKER_00 (40:25):
I couldn't have summarized it better.
SPEAKER_01 (40:27):
All right, that is our massive deep dive on the
science of autophagy.
Thank you so much for exploringthe microscopic world with us,
and we will catch you on thenext one.
If you stop eating right now, like literally put
down whatever you're snacking onand just don't eat for the next
24 hours, your cells, they arejust going to sit there
passively starving.
SPEAKER_00 (00:09):
Right.
They definitely don't just shutdown.
SPEAKER_01 (00:11):
Exactly.
They actually initiate thisimmediate, like highly
coordinated program to startcannibalizing their own internal
structures.
Which sounds bad, but here isthe craziest part.
If they couldn't do that, ifyour body somehow lacked this
specific self-eating mechanism,you wouldn't have just gotten a
little hungry.
(00:32):
You would have died on the exactday you were born.
SPEAKER_00 (00:35):
You absolutely would have.
I mean, within hours of theumbilical cord being cut,
actually, it leads to severefatal hypoglycemia.
SPEAKER_01 (00:42):
Right.
Which is just, I mean, when youreally think about the biology
of that, it completely reframeseverything we know about eating
and not eating.
So welcome to the deep dive.
SPEAKER_00 (00:50):
Glad to be here.
SPEAKER_01 (00:51):
Because today we are going way behind the incredibly
noisy, honestly kind of annoyingwellness hype surrounding
fasting.
And we're taking a massivemagnifying glass, the actual
hard cellular biology of how ourbodies clean themselves.
We're talking about autophagy.
SPEAKER_00 (01:05):
Autophagy, which, you know, if we look at the
Greek roots, you have autosmeaning self and phagomai
meaning to eat.
So it literally translates toself-devouring.
SPEAKER_01 (01:15):
Self-devouring.
Sounds like a metal band.
SPEAKER_00 (01:18):
It really does.
It's the cellular recyclingsystem, but honestly, even
calling it a recycling systemfeels a little too, I don't
know, passive for what'sactually happening at a
molecular level.
Aaron Powell Yeah.
SPEAKER_01 (01:29):
It's not like tossing a can in a blue bin.
It's more like a highlymilitarized city tearing down
its own dilapidated buildingsjust to forge weapons and fuel
to survive a siege.
SPEAKER_00 (01:39):
Aaron Powell That is a very dramatic but very
accurate way to put it.
SPEAKER_01 (01:42):
Aaron Powell And look, we have a massive stack of
literature to get through today.
I want to be super clear aboutour mission here with you guys.
Whether you are doingintermittent fasting or you're
deep into the longevity scienceworld, or you just find human
physiology fascinating, we'regoing to cut right through the
biohacking blocks.
SPEAKER_00 (02:00):
Aaron Powell Right.
We're looking at the rigorousdata today.
SPEAKER_01 (02:02):
Exactly.
We're pulling from the ClevelandClinic Guidelines, the 2016
Nobel Prize press release, aFrontiers paper on MTOR and
metabolism, a massive review onlifespan from the Journal of
Clinical Investigation, and thistotally paradigm-shifting paper
from Nature Cell Biology thatfocuses on polyamines.
SPEAKER_00 (02:22):
It is a phenomenal stack of sources, truly.
And I think to really understandwhy this is arguably one of the
most fundamental survivalmechanisms in all of biology, we
can't just jump straight intohow to, you know, hack it.
SPEAKER_01 (02:35):
Right.
Everyone just wants a hack.
SPEAKER_00 (02:36):
Exactly.
But we need to look at theliteral physical machinery
inside the cell first.
We really need to understand howscientists even figured out this
invisible process was happeningat all.
SPEAKER_01 (02:46):
Because it's not like you can just stick a tiny
GoPro inside a human cell andwatch it take out the trash.
The scale we are talking abouthere is just almost unfathomably
small.
SPEAKER_00 (02:54):
Aaron Ross Powell Exactly.
And our Nobel Prize source givesus this crucial timeline because
to find the machinery, weactually have to go all the way
back to the 1950s with a Belgianscientist named Christian de
Duvet.
SPEAKER_01 (03:05):
Okay, so mid-century biology.
What was de Duvet actuallylooking at?
SPEAKER_00 (03:09):
Well, he was doing these cell fractionation
experiments, which is basicallybreaking cells apart to see
what's inside.
And he ended up discovering acompletely new, specialized
organelle, like a brand newcompartment inside our cells.
He called it the lysosome.
SPEAKER_01 (03:23):
The lysosome, which is basically the cell's
incinerator, right?
SPEAKER_00 (03:26):
Incinerator, or you could think of it as a highly
acidic stomach.
It is a membrane-bound sac thatis absolutely packed with
destructive digestive enzymes.
SPEAKER_01 (03:35):
Just gnarly stuff.
SPEAKER_00 (03:36):
Oh, incredibly destructive.
Proteases, lipases, nucleases.
These are enzymes specificallydesigned to just rip apart
proteins, fats, and DNA.
SPEAKER_01 (03:46):
Aaron Powell, which obviously you have to keep
locked up.
Like if those enzymes justleaked out into the main body of
the cell, wouldn't they justmelt the cell from the inside
out?
SPEAKER_00 (03:53):
Yeah, precisely.
It would be catastrophic.
So they're safely quarantinedinside this lysosome.
And Deduve actually won a NobelPrize for this discovery in
1974.
But here is where the mysteryreally starts to pick up.
SPEAKER_01 (04:05):
Okay, I love a good science mystery.
SPEAKER_00 (04:06):
So in the 1960s, electron microscopes started
getting much, much morepowerful.
Scientists were finally zoomingin on these lysosomes, looking
inside the incinerators, andthey started noticing something
deeply weird.
SPEAKER_01 (04:19):
They were finding chunks of the cell inside his
own stomach.
SPEAKER_00 (04:22):
Right.
They were finding large, bulkycellular material.
We're talking whole, damagedmitochondria, massive protein
aggregates, just junk.
Right.
Which obviously raise a massivemechanical question.
SPEAKER_01 (04:34):
Aaron Powell How did the trash get into the
incinerator in the first place?
Because, like you said, thelysosome is sealed.
It's not like a gaping mouthjust swimming around the cell
eating thing.
SPEAKER_00 (04:43):
Exactly.
The cell had to have some sortof active transport system, a
way to bag up the garbage, sealit tightly, and physically haul
it over to the lysosome.
SPEAKER_01 (04:52):
And they found it.
SPEAKER_00 (04:52):
Eventually, yes.
Under the electron microscope,they spotted it.
They found this completely newtype of vesicle.
Essentially, it was a biologicalbubble, a double membrane that
would just form out of nowherearound the cellular junk,
swallow it completely, and thentravel through the cell to fuse
with the lysosome.
SPEAKER_01 (05:09):
Dump in the trash inside.
Okay, so the lysosome is theincinerator, and this double
membrane bubble is the garbagetruck.
SPEAKER_00 (05:16):
Aaron Powell That's the perfect analogy.
And De Duvet is actually the onewho coined the term autophagy
for the whole process.
And he named those specificgarbage trucks autophagosomes.
SPEAKER_01 (05:25):
Autophagosomes.
Okay, so by the 60s, they havethe visual evidence.
They know the incineratorexists, they know the garbage
trucks exist.
But reading through the Nobeltimeline we have, it seems like
the field just hit a massivebrick wall for like 30 years
after that.
SPEAKER_00 (05:43):
It really did.
It became an incrediblyfrustrating black box for
biologists.
Because seeing something happenunder a microscope is very
different from understanding howit actually happens
biochemically.
SPEAKER_01 (05:54):
Like what makes it tick.
SPEAKER_00 (05:55):
Right.
They didn't know which genescontrolled it.
They didn't know the moleculartriggers.
And if you don't know the genes,you can't design drugs to target
it.
You can't manipulate it.
SPEAKER_01 (06:04):
So it's just an observation at that point, like,
oh look, the cell is doing athing.
Cool.
SPEAKER_00 (06:08):
Yes.
It was basically stuck thereuntil the early 1990s.
And this is where our secondNobel Prize in the story comes
in.
A Japanese scientist namedYoshinoriosumi decided he was
going to finally crack thegenetic code of autophagy, but
he made a very, verycounterintuitive choice.
SPEAKER_01 (06:25):
What did he do?
SPEAKER_00 (06:26):
He didn't use human cells.
He decided to use baker's yeast.
Saccharomyces cerebisiae.
SPEAKER_01 (06:33):
Which honestly, on the surface, sounds kind of
wild.
Like if you're trying to figureout a mechanism that might cure
human neurodegeneration oraging, why are you messing
around with the stuff we use tomake sourdough bread?
SPEAKER_00 (06:45):
It's a totally fair question.
But yeast is actually aphenomenal model organism for
human cellular biology.
They are eukaryotes, meaningthey have a complex internal
architecture just like our cellsdo.
They have nucleus, they havemitochondria, and they have
their own version of a lysosome,which in yeast is called a
vacuole.
SPEAKER_01 (07:02):
Okay, sure.
They have the same parts.
But yeast cells are alsoincredibly tiny, right?
I was reading about Usumi'smethodology, and it seemed like
he had a huge physical problemright out of the gate.
SPEAKER_00 (07:11):
Yeah, he did.
Even with a really goodmicroscope, you couldn't
actually see autophagosomesforming in yeast because they
are just too small.
unknown (07:18):
Yeah.
SPEAKER_00 (07:18):
And the process is way too fast.
SPEAKER_01 (07:20):
Aaron Ross Powell Right, because think about the
life cycle of one of thesegarbage trucks.
The autophagosome forms, itgrabs the trash, it travels to
the vacuole, it fuses, and theenzymes inside the vacuole
destroy it almost instantly.
The turnover is so fast, it'svirtually invisible.
SPEAKER_00 (07:35):
That was the massive hurdle.
He wasn't even 100% sure thatautophagy happened in yeast at
all.
Because he couldn't see it.
SPEAKER_01 (07:42):
So how do you study a biological process that
destroys its own evidence theliteral second it finishes its
job?
SPEAKER_00 (07:50):
This is where Osumi's experimental design is
just breathtakingly elegant.
I mean it's brilliant.
He reasoned that if he couldsomehow stop the destruction
phase, he might be able to catchthe garbage trucks in the act.
So he genetically mutated aspecific strain of yeast.
SPEAKER_01 (08:04):
What did he mutate?
SPEAKER_00 (08:05):
He engineered them so that they lacked the
degradation enzymes inside theirvacuole.
SPEAKER_01 (08:09):
Oh wow.
So he basically broke theincinerator.
SPEAKER_00 (08:12):
He broke the incinerator.
The vacuole was still physicallythere, but it couldn't digest
anything.
Then he took these mutated yeastcells and he completely starved
them of nutrients.
SPEAKER_01 (08:23):
Just cut off their food supply entirely.
SPEAKER_00 (08:25):
Right.
He guessed that extremestarvation would force the yeast
to trigger its survivalmechanism, which he hoped was
autophagy.
SPEAKER_01 (08:33):
Wait, hold on.
So by breaking the enzymes butleaving the transport system
completely intact, he basicallygave the yeast cellular
constipation.
That's like the cell isstarting, so it starts
frantically bagging up its ownproteins to recycle them.
It sends all these trash bags tothe vacuole, but the vacuole
can't process them, so they justsit there.
SPEAKER_00 (08:51):
Yes.
And the result was spectacular.
Within just a few hours ofstarvation, the vacuoles of
these mutant yeast cells swelledup to massive proportions.
They were absolutely engorged,just stuffed full of tiny
vesicles, the autophagosomes,that had been delivered but
couldn't be destroyed.
SPEAKER_01 (09:07):
Because they just piled up.
Dude, that is amazing.
You lock the gates to thelandfill, you starve the city,
and suddenly there's amicroscopic traffic jam of
garbage trucks just backing uponto the highway.
SPEAKER_00 (09:19):
Exactly.
And now instead of thisinvisible fleeting process, you
have a massive swollen vacuolethat you can easily see under a
standard light microscope.
SPEAKER_01 (09:28):
That is so smart.
SPEAKER_00 (09:29):
Yeah.
SPEAKER_01 (09:29):
Because now he has a baseline.
Like if the traffic jam happens,he knows the autophagy machinery
works.
SPEAKER_00 (09:35):
Precisely.
So Osumi then took that baselineand ran with it.
He chemically mutated thousandsof other yeast strains at
random.
And he was specifically lookingfor mutants where when he
starved them and broke theirvacuoles, the traffic jam didn't
happen.
SPEAKER_01 (09:50):
Oh, I see.
Because if the vacuole is brokenand they are starving, but
there's no buildup of garbagebags, it means the cell
physically lost the ability tomanufacture the garbage bags in
the first place.
SPEAKER_00 (10:00):
He nailed it.
It means you found a yeast cellwith a broken autophagy gene.
He screened thousands ofcolonies this way.
And within a year, he hadidentified the very first
autophagy-related genes, whichwe now call the ATG genes.
And this discovery just blew thedoors off the entire field of
molecular biology.
SPEAKER_01 (10:19):
Aaron Powell Because once you have the actual genetic
sequence in yeast, you can justrun a search to see if humans
have it too.
SPEAKER_00 (10:25):
Exactly.
And they did.
They quickly discovered that thehuman genome contains almost
identical homologues to theseyeast ATG genes.
It proved that this machinery ishighly conserved across billions
of years of evolution.
Aliens.
Yes.
The core physical mechanism ofwrapping up cellular junk in a
double membrane and sending itto an incinerator is essentially
(10:46):
the exact same in asingle-celled yeast organism as
it is in the neurons of yourbrain right now.
SPEAKER_01 (10:52):
That kind of evolutionary conservation always
gets me.
Like if something hasn't changedin a billion years, it means it
is absolutely critical for life.
You just can't mess with it.
SPEAKER_00 (11:00):
It is fundamental to survival.
SPEAKER_01 (11:02):
But okay, this leads to a massive question for me.
And it's something the Frontiersand JCI papers go into deeply.
We know the garbage eggs existnow.
We know the genes that buildthem, but how does the cell
actually know when to buildthem?
Like, assume you literallystarve the yeast to trigger
this.
What is the actual biochemicalarchitecture of hunger?
SPEAKER_00 (11:21):
How does it detect the food is gone?
SPEAKER_01 (11:22):
Yeah.
How does a microscopic blob knowit's starving?
SPEAKER_00 (11:26):
To understand that, we have to introduce what is
arguably the most importantmaster switch in all of cellular
metabolism.
It's a massive protein complexcalled MTORC1.
SPEAKER_01 (11:37):
MTORC1.
Okay, let's unpack that.
Because I see this acronymthrown around in literally every
longevity article ever written.
SPEAKER_00 (11:44):
It stands for Mechanistic Target of Rapamycin
Complex 1.
SPEAKER_01 (11:47):
Mechanistic Target of Rapamycin.
Honestly, it sounds like aweapon from a sci-fi novel.
SPEAKER_00 (11:51):
It does, but its function is very grounded and
very real.
MTORC1 is the cell's masternutrient sensor and its primary
growth director.
I want you to picture MTORC1 asa highly sensitive, very
aggressive foreman on aconstruction site.
SPEAKER_01 (12:05):
Okay, I like that.
Formin.
SPEAKER_00 (12:07):
When nutrients are abundant in your bloodstream, so
when you have high levels ofamino acids, glucose, and growth
factors floating around, MTORC1is turned firmly into the on-end
position.
SPEAKER_01 (12:17):
And when the foreman is awake and active, what's he
doing?
SPEAKER_00 (12:20):
He is driving anabolism, building.
When MTORC1 is active, it floodsthe cell with signals to
synthesize new proteins, buildnew lipid membranes, create
nucleotides for DNA, andgenerally just grow and
multiply.
SPEAKER_01 (12:33):
It's just screaming, build, build, build.
SPEAKER_00 (12:35):
Exactly.
It is the ultimate biologicalsignal for times are good, we
have plenty of resources, let'sexpand.
SPEAKER_01 (12:42):
Okay, so if MTR is the growth boss driving all this
anabolic construction, how doesthat relate to the garbage
trucks?
SPEAKER_00 (12:48):
Aaron Powell Well, think about the basic energy
economics of a cell.
You cannot aggressively buildnew skyscrapers and
simultaneously demolish yourexisting buildings.
That would be a futile, chaoticwaste of cellular energy.
SPEAKER_01 (13:00):
Aaron Powell You'd just be spinning your wheels.
SPEAKER_00 (13:02):
Right.
You have to commit to one stateor the other.
So when MTRC1 is active anddriving growth, it actively
physically blocks the autophagypathway.
SPEAKER_01 (13:10):
Aaron Powell Well, physically.
I was looking at the Frontier'spaper and it talks about
phosphorylation, but I'm tryingto visualize what that actually
means in this context.
How does MTOR physically stopthe cleanup crew?
SPEAKER_00 (13:22):
Aaron Powell It's a really great mechanical
question.
So when nutrients are plentiful,the MTOR RC1 complex actually
travels to and physicallytethers itself to the outer
surface of the lysosome, theincinerator.
SPEAKER_01 (13:33):
Oh wow.
So it literally sits on the roofof the garbage dump.
SPEAKER_00 (13:36):
Yes.
It anchors there, and from thatperch, it acts as a kinase.
A kinase is just an enzyme thatattaches phosphate groups to
other proteins.
So MTORC1 grabs the initiationproteins that are required to
start building theautophagosome, specifically
these proteins, named ULK1 andATG13, and it phosphorylates
them.
SPEAKER_01 (13:56):
Okay, and adding that phosphate group, what does
that actually do?
Does it break them?
SPEAKER_00 (14:00):
It doesn't break them permanently, but it forces
a change in their 3D shape.
It's really like slapping abulky molecular padlock onto
them.
Because of that structuralchange, ULK1 and ATG-13 are
deactivated.
They cannot assemble themachinery needed to start
forming the double membrane.
SPEAKER_01 (14:16):
So the garbage trucks cannot be manufactured at
all.
SPEAKER_00 (14:18):
Exactly.
SPEAKER_01 (14:19):
That makes so much sense.
The foreman sits on theincinerator, slaughter padlocks
on the garbage trucks, and says,nobody cleans today.
We are only building.
SPEAKER_00 (14:27):
That's a great way to visualize it.
But it actually goes even deeperthan that.
MTORC1 also targets atranscription factor called TSB.
Now TFAB's entire job is totravel into the nucleus of the
cell, bind to the DNA, and turnon the genes that build more
lysosomes.
SPEAKER_01 (14:42):
To build more incinerators.
SPEAKER_00 (14:44):
Right.
But while MTORC1 is active, itphosphorylates TFE2, which
completely traps it in thecytoplasm.
It physically cannot enter thenucleus.
SPEAKER_01 (14:53):
Man, so MTOR is shutting down the recycling
program at every conceivablelevel.
It stops the trucks from formingand it stops the factory from
building new incinerators.
SPEAKER_00 (15:02):
Precisely.
It is a total systemic blockade.
Now, consider what happens whenthe food finally runs out.
When you stop eating, or whenOsumi starved his yeast.
SPEAKER_01 (15:11):
The amino acids in the blood drop.
SPEAKER_00 (15:12):
Right.
And without those amino acids,the biochemical signal that
keeps MTORC1 anchored to thelysosome just vanishes.
MTORC1 essentially detaches andshuts off.
SPEAKER_01 (15:22):
Aaron Ross Powell He goes to sleep.
SPEAKER_00 (15:23):
Exactly.
And at the exact same time, adifferent metabolic sensor
called AMPK, which acts like analarm system that detects low
cellular energy, turns on.
SPEAKER_01 (15:32):
Okay, so the day shift foreman clocks out, and
the night shift emergencysupervisor clocks in.
SPEAKER_00 (15:36):
That's a perfect analogy.
And the moment MTORC1 shuts off,all those molecular padlocks
fall off.
ULK1 and ATG13 are suddenlydephosphorylated and freed.
SPEAKER_01 (15:46):
They just wake up.
SPEAKER_00 (15:47):
They immediately spring into action.
They recruit other proteins tothe endoclasmic reticulum and
they begin physically weavingthe double membrane of the
autophagosome.
The garbage trucks are finallydispatched.
SPEAKER_01 (15:58):
And what about that transcription factor, TFEB?
SPEAKER_00 (16:01):
Without M2R holding it hostage, TFEB dives straight
into the nucleus, binds to theDNA, and initiates a massive
genetic program called lysosomalbiogenesis.
The cell literally prints newincinerators.
SPEAKER_01 (16:13):
It just goes into overdrive.
SPEAKER_00 (16:15):
It aggressively ramps up its capacity to break
things down.
Because remember, the cell isstarving.
It is desperate for rawmaterials.
So it starts engulfing its owndamaged proteins, its old lipid
droplets, and breaking them downinto basic amino acids and fatty
acids just to keep the cellularlights on.
SPEAKER_01 (16:31):
You know, I have to say, looking at it like this,
MTOR kind of seems like thevillain of the aging story.
SPEAKER_00 (16:37):
A lot of people think that.
SPEAKER_01 (16:38):
I mean, if MTOR stops the cleanup and allows all
this toxic junk to build up inour cells, shouldn't our goal
just be to turn MTORs as much asphysically possible?
I see people online trying tobasically biohack themselves
into like permanent autophagy.
SPEAKER_00 (16:53):
I completely understand the logic there, but
it is a massive, incrediblydangerous misconception.
We absolutely cannot vilify MTR.
Really?
You need MTR to live.
If you don't have active MTOR,you cannot build muscle mass.
Your immune system cannotproliferate white blood cells to
fight off an infection.
You can't heal a simple wound.
If you somehow force MTOR into achronically off F state, you
(17:16):
would suffer severe muscleatrophy, immune deficiency, and
eventual death.
SPEAKER_01 (17:20):
Okay, yeah.
Muscle mass is pretty importantfor, you know, not dying.
SPEAKER_00 (17:24):
Yeah.
SPEAKER_01 (17:25):
Especially as we age, faily is a huge killer.
SPEAKER_00 (17:28):
Exactly.
The magic of human metabolismisn't found in extremes.
It is found in the oscillation.
SPEAKER_01 (17:33):
The oscillation, like a pendulum swinging back
and forth.
SPEAKER_00 (17:36):
Yes.
True metabolic health requiresrobust periods of MTOR
activation when you are fed, soyou can build, repair, and
strengthen tissues, followed byperiods of low MTOR and high
autophagy when you are fasted,allowing the cell to
aggressively sweep out theaccumulated garbage.
SPEAKER_01 (17:53):
So you need both.
SPEAKER_00 (17:54):
You absolutely need both.
The pathology, the disease statewe see so much of today, occurs
when the pendulum gets stuck.
SPEAKER_01 (18:00):
Let me guess.
It gets stuck because we live inan environment where we're just
constantly eating.
SPEAKER_00 (18:05):
Right.
The modern dietary pattern.
Eating a heavy breakfast,snacking all day at your desk,
drinking caloric beverages,eating a late dinner, and then
having a midnight snack.
It means that your amino acidand glucose levels never truly
bottom out.
SPEAKER_01 (18:18):
So MTR is just jammed in the on-in position,
2004-7.
SPEAKER_00 (18:22):
Precisely.
The foreman never sleeps.
The cell never gets thebiochemical signal that it's
safe to halt construction andstart cleaning.
So the misfolded proteins startto pile up in the corners of the
cell, the damaged mitochondriaare left to rot.
That is grim.
And the accumulation of all thatmicroscopic trash is a primary
driver of metabolic dysfunctionand the aging process itself.
SPEAKER_01 (18:43):
Wow.
Okay, so the logic is incrediblytight.
Food is abundant, MTOR turns on,we build, food is scarce, MTOR
turns off, the pads fall off,ULK1 activates, and we clean.
It makes perfect sense.
But reading through the sourcematerials, particularly that
recent Nature Cell Biologypaper, it feels like this neat
little seesaw model is mything amassive piece of the puzzle.
SPEAKER_00 (19:05):
It absolutely is.
And this is where the biologytakes a really fascinating turn.
For a long time, the scientificconsensus was that the mere
absence of nutrients was thetrigger.
SPEAKER_01 (19:13):
Like just an empty tank.
SPEAKER_00 (19:14):
Right.
You take away the food, MTRshuts down, end of story.
The void itself is the signal.
But this new research completelyupends that idea.
SPEAKER_01 (19:23):
Because this paper shows that fasting isn't just an
empty void.
When you stop eating, theabsence of food actively causes
your body to synthesize a veryspecific molecule.
Like your body creates a newchemical signal in response to
starvation.
SPEAKER_00 (19:39):
Yes, and that molecule is not optional.
The researchers found that ifyou block the body's ability to
produce this specific molecule,fasting completely fails to
trigger autophagy.
SPEAKER_01 (19:50):
The whole thing just breaks.
SPEAKER_00 (19:51):
The entire cleanup system breaks down, even if the
cell is completely starving.
SPEAKER_01 (19:55):
Okay, we have to name the molecule, even though I
know the history here is alittle uh colorful.
What is this magic key?
SPEAKER_00 (20:01):
It is a naturally occurring polyme called
spermidine.
SPEAKER_01 (20:04):
Spermidine.
I mean, look, I know we're doingserious science here, but who
looked at this incrediblecellular longevity molecule and
said, yes, let's name itspermidine?
SPEAKER_00 (20:14):
Well, to be fair, it wasn't named recently.
The name comes from its initialdiscovery in the late 1600s by
Anthony van Leeuwenhoek.
He was the inventor of themicroscope, and he originally
isolated it from seminal fluid.
Right.
But we really need to look pastthe historical nomenclature
because spermidine isubiquitous.
It is found in almost all livingtissues, in plants, in animals,
(20:36):
and it is a master regulator ofcellular metabolism.
SPEAKER_01 (20:40):
All right, I'll put my middle school humor away.
Polyamine.
I know a polyamine is an organiccompound with multiple amino
groups, which usually means theyare positively charged and they
love to interact with negativelycharged things like DNA and RNA.
But what did this nature paperactually discover about it in
relation to fasting?
SPEAKER_00 (20:57):
So the research team led by the Tavernorakus lab,
along with prominent researcherslike Guido Kromer and Frank
Medeo, they asked a very elegantquestion.
They knew that fasting triggersautophagy, but they wanted to
know what happens to theinternal levels of polyamines
when an organism starves.
SPEAKER_01 (21:15):
Okay.
SPEAKER_00 (21:15):
And they didn't just look at one animal, they looked
across the entire evolutionarytree.
SPEAKER_01 (21:19):
So they went back to Osumi's yeast.
SPEAKER_00 (21:21):
They did.
They started by starving yeastcells, and they observed a
massive, sharp spike inspermidine production.
Then they moved up the tree,they starved fruit flies for 24
hours, again, a massive spike inspermidine.
They fasted mice overnight,which is actually a long time
for a mouse's fast metabolism.
They measured the serum andmultiple organs, spike in
(21:42):
spermidine.
SPEAKER_01 (21:43):
Okay, that shows evolutionary conservation,
definitely.
But mice and yeast aren'thumans.
Did they test this in actualpeople?
SPEAKER_00 (21:50):
They did.
They had four different humancohorts in this study, but the
most striking one involved aspecialized fasting clinic.
They monitored human volunteerswho underwent a medically
Supervised extreme fast for 7 to13 days.
SPEAKER_01 (22:03):
Wait, 7 to 13 days of zero food?
SPEAKER_00 (22:06):
Very close to zero.
They were allowed roughly 250calories a day.
Essentially just a little bit oforganic fruit juice, vegetable
soup broth, and a tiny bit ofhoney.
SPEAKER_01 (22:15):
That sounds miserable.
SPEAKER_00 (22:16):
It is a severe caloric restriction mimicking a
complete fast.
And when they analyzed the bloodof these human volunteers over
the course of the week, thelevels of spermidine surged.
And it was universal.
Didn't matter if the patient wasmale or female, old or young,
lean or obese.
Severe fasting fundamentallyaltered their polyamine
metabolism to pump outspermidine.
SPEAKER_01 (22:36):
Okay, so starvation correlates with a spike in
spermidine.
But we know correlation isn'tcausation.
How do we know spermidine isactually doing the work?
Maybe it's just a byproduct ofthe stress, you know, like an
exhaust coming out of a carengine.
If you take the spermidine away,does the car still drive?
Is the cleanup still happen justbecause MTOR is off?
SPEAKER_00 (22:57):
That is the exact critical experiment they
performed to prove causation.
They took yeast cells andgenetically knocked out a gene
called SPAY1.
This is the enzyme required tosynthesize spermidine.
So these mutant yeast physicallycannot make spermidine.
Okay.
When they starved these mutants,the entire starvation response
collapsed.
Autophagy was not induced.
(23:18):
They couldn't properly inhibitMTORC1.
Their energy metabolism wentcompletely haywire.
SPEAKER_01 (23:23):
Whoa.
So without this specificpolymer, taking away the food
does absolutely nothing totrigger the garbage trucks.
SPEAKER_00 (23:29):
Nothing.
And to prove it wasn't just aweird yeast quirk, they did the
exact same thing in microscopicworms, C.
elegans nematodes.
They used RNA interference tosilence the worm equivalent of
the gene, which is called oddC1.
SPEAKER_01 (23:41):
And what happened?
SPEAKER_00 (23:42):
When they starved the spermidine deficient worms,
the lifespan extension andautophagy induction that
normally comes from fasting werecompletely abolished.
SPEAKER_01 (23:50):
The mechanism is totally broken.
SPEAKER_00 (23:51):
Totally broken.
But here is the clincher.
When the researchers manuallysupplemented spermidine back
into the water of thesegenetically broken, starving
worms.
SPEAKER_01 (24:00):
Let me guess.
The pathway snapped back online.
SPEAKER_00 (24:03):
Completely rescued.
The metabolic flexibilityreturned, autophagy fired up,
and the worms' lifespans wereextended again.
SPEAKER_01 (24:10):
That is profoundly weird.
Why is this one molecule thelinchpin for this
billion-year-old process?
I was reading this section inthe paper about hypucination,
and my eyes kind of glazed over,honestly.
How does spermidine physicallyforce the cell to build the
autophagosomes?
SPEAKER_00 (24:27):
It is deeply technical, but if we break it
down, it's fascinating.
Spermidine is essentially therequired raw material for a very
unique post-translationalmodification called
hypucination.
In all of biology, there is onlyone specific protein that gets
hypucinated, and its name isEIF5A.
SPEAKER_01 (24:43):
EIF5A.
Another acronym, what does itdo?
SPEAKER_00 (24:47):
It's a translation factor.
When your cell's ribosomes arereading RNA to build new
proteins, they sometimes getstuck.
Specifically, if they have tostring together a bunch of
proline amino acids in a row, apolyproline tract, the ribosome,
literally jams.
It physically stalls out.
SPEAKER_01 (25:03):
Like a paper jam and a printer.
SPEAKER_00 (25:05):
Exactly like that.
EIF5A acts like a mechanicalgrease.
It binds to the stalled ribosomeand helps it push through that
difficult sequence.
SPEAKER_01 (25:13):
Okay, but what does a jammed ribosome have to do
with autophagy?
SPEAKER_00 (25:16):
Because the proteins required to build the
autophagosome, remember ULK1,and particularly a master
regulator called TFE, they areloaded with these difficult
polyproline sequences.
If EI5A isn't active, the cellphysically cannot manufacture
the proteins needed to executeautophagy.
The ribosomes just jam up andfail.
SPEAKER_01 (25:34):
Oh man.
I'm putting the pieces together.
An EIF5A can only be activatedif it gets hypucinated by
spermidine.
SPEAKER_00 (25:41):
Precisely.
Spermidine is the key in theignition.
When you fast, your body spikesspermidine production.
That spermidine hypucinatesEIF5A, which turns it green, so
to speak.
The active EIF5A then allows theribosomes to successfully
manufacture TFFB and the otherautophagy proteins without
jamming.
SPEAKER_01 (26:01):
That is wild.
SPEAKER_00 (26:02):
Right.
Without spermidane, EIF5A staysinactive, the ribosomes stall,
and the garbage trucks cannot bebuilt, no matter how hungry the
cell is.
SPEAKER_01 (26:11):
That is one of the most elegant biological cascades
I've ever heard.
It's not just food off,autophagy on.
Fasting is an active, demandinggenetic program.
SPEAKER_00 (26:20):
It is highly active.
SPEAKER_01 (26:21):
And this actually brings me to a really crucial
point.
We've talked a lot about themechanics, the incinerators, the
garbage trucks, the foreman, thejammed ribosomes.
But we need to zoom out for asecond for the listener.
Why does clearing out thismicroscopic junk matter so much
for the person listening to thisright now?
Like, what are the actual stakesfor human health ban and
disease?
SPEAKER_00 (26:38):
The stakes are incredibly high.
And it comes down tounderstanding that cellular junk
isn't just harmless cluttersitting in the corner, it is
actively toxic.
The JCI review and the Frontierspaper make it very clear that
failing to clear this debris isa root cause of age-related
decline.
SPEAKER_01 (26:56):
Toxic in what way?
Give me a concrete example ofthe trash.
SPEAKER_00 (27:00):
The most critical example is misfolded proteins.
Proteins are these highlycomplex three-dimensional
origami structures.
Their shape dictates theirfunction.
But over time, due to stress orjust the physics of the cellular
environment, they can foldincorrectly.
SPEAKER_01 (27:15):
In Menway.
SPEAKER_00 (27:16):
When they misfold, they expose sticky regions and
start clumping together intomassive, insoluble aggregates.
Aaron Powell, Jr.
SPEAKER_01 (27:22):
Which sounds exactly like the plaques and tangles you
hear about in neurodegenerativediseases.
SPEAKER_00 (27:26):
Aaron Powell Exactly.
Alzheimer's disease, Parkinson'sdisease, Huntington's, these are
all fundamentally characterizedby the accumulation of toxic
protein aggregates in neurons.
Neurons are postmitotic.
They generally don't divide.
SPEAKER_01 (27:38):
So they can't just dilute the trash by splitting
into two new cells.
SPEAKER_00 (27:41):
Aaron Powell Right.
They have to rely on autophagyto constantly sweep up these
misfolded proteins before theyclump together and destroy the
neuron.
SPEAKER_01 (27:50):
Wow.
So maintaining high levels ofautophagy in the brain isn't
just about general health, it'sliteral neuroprotection.
It is the frontline defenseagainst Alzheimer's.
SPEAKER_00 (27:59):
Yes.
And the second major target ofthe garbage trucks is your
mitochondria, the power plantsof the cell.
Yeah.
Mitochondria have a shelf life.
They undergo massivestress-generating ATP, and
eventually they get damaged.
And a damaged mitochondriondoesn't just quietly power down,
it becomes dangerously leaky.
SPEAKER_01 (28:17):
Leaking what?
Energy.
SPEAKER_00 (28:18):
Worse, it leaks toxic reactive oxygen species,
free radicals.
It starts violently oxidizingand destroying surrounding
cellular structures, mutatingDNA and driving massive
inflammation.
SPEAKER_01 (28:30):
That's terrifying.
SPEAKER_00 (28:31):
It's essentially a failing nuclear reactor
threatening to melt down insidethe cell.
SPEAKER_01 (28:34):
Okay, that sounds catastrophic.
SPEAKER_00 (28:36):
It is, which is why autophagy has a specialized,
targeted subroutine calledmitophagy.
The cell recognizes the leakypower plant, builds an
autophagosum specifically aroundit, and hauls it to the lysosome
for targeted destruction,eliminating the source of the
oxidative stress before itcauses irreversible DNA damage.
SPEAKER_01 (28:55):
It's so precise.
And I know there are othersubroutines too, right?
Because the GCI paper talkedabout lipophagy.
SPEAKER_00 (29:01):
Yes.
Lipophagy is the specifictargeting of lipid droplets,
stores of fat inside the cell.
As we age, our baseline rate ofautophagy naturally declines.
This is one of the primaryreasons we see a massive
increase in age-related hepaticlipid accumulation.
SPEAKER_01 (29:17):
Aaron Ross Powell Hepatic meaning in the liver.
So we're talking about fattyliver disease, metabolic
syndrome, insulin resistance.
SPEAKER_00 (29:23):
Aaron Powell Precisely.
The JCI paper sets a fascinatingexperiment regarding this.
Researchers engineered mice tohave a hyperactive version of T
heyday, that transcriptionfactor we talked about earlier
that drives the creation of newlysosomes.
SPEAKER_01 (29:34):
Okay, so they have extra incinerators.
SPEAKER_00 (29:36):
Right.
When they fed these mice aterrible high-fat
obesity-inducing diet, the micewere completely protected from
metabolic syndrome and obesity.
SPEAKER_01 (29:47):
Just because they had more incinerators.
SPEAKER_00 (29:48):
Yes.
Their enhanced autocogy clearedthe ectopic fat droplets so
efficiently that they remainedmetabolically healthy.
But crucially, if theresearchers knocked out the core
autophagy genes in those samemice, the protective effect of
TFAB vanished completely, andthe mice developed severe fatty
liver disease.
SPEAKER_01 (30:09):
That is incredible.
SPEAKER_00 (30:10):
It proves that the physical act of cellular eating
is the critical mechanismpreventing the metabolic
collapse.
SPEAKER_01 (30:16):
So we are talking about preventing Alzheimer's,
stopping mitochondrial meltdown,and staving off fatty liver
disease.
That's essentially the unholytrinity of aging.
SPEAKER_00 (30:25):
It really is.
SPEAKER_01 (30:26):
But if we want to talk about how absolute
non-negotiable this process isfor mammalian life, we have to
talk about the neonatal mouseexperiment from the Frontiers
paper, because this completelyblew my mind when I read it.
We mentioned it at the verybeginning of the deep dive.
SPEAKER_00 (30:38):
Yes, it is one of the most stark demonstrations of
biological necessity in theliterature.
SPEAKER_01 (30:43):
So break down the genetics of this experiment
because it's a little complex.
SPEAKER_00 (30:47):
The researchers genetically engineered a strain
of mice with a mutation in agene called RAGA.
Now, RAGA is an upstreamactivator of our old friend, the
MTORC1 complex.
The specific mutation theyintroduced rendered the RAGA A
protein permanently, irrevocablylocked in the on-end state.
SPEAKER_01 (31:05):
Which means the MTORC1 master switch is
permanently jammed on in.
SPEAKER_00 (31:09):
Exactly.
The genetic forman is screamingbuild, build, build 247.
The cell thinks it is constantlyat a massive all-you-can-eat
buffet, regardless of what theactual nutrient levels in the
blood are.
Now, while these geneticallyengineered pups are developing
in the mother's room, everythingseems perfectly fine.
SPEAKER_01 (31:27):
Right, because the placenta provides a constant
nonstop IV drip of glucose andamino acids.
The buffet is actually real.
SPEAKER_00 (31:34):
Exactly.
But then the pups are born, andthe moment of birth is arguably
the most severe metabolic shocka mammal ever experiences,
because the umbilical cord iscut.
SPEAKER_01 (31:44):
And suddenly the IV drip is gone?
I never thought about it likethat, but birth is basically a
forced extreme fasting state.
SPEAKER_00 (31:50):
It is our first true fast.
The constant supply of nutrientsplummets to zero instantly.
And it's going to be hoursbefore the mother's milk fully
comes in and the pup canactually feed.
In a normal, healthy mouse pup,the moment that cord is cut and
the amino acids in the blooddrop, MTORC1 instantly detects
the starvation and shuts off.
SPEAKER_01 (32:11):
And the pads fall off and autophagy fires up.
SPEAKER_00 (32:13):
Massively.
Within the very first hour oflife outside the womb, a normal
pup cells begin aggressivelycannibalizing their own internal
stores.
They break down stored glycogenand internal cellular proteins
to generate a massive surge offree amino acids.
Those raw materials are shippeddirectly to the liver to drive
gluconeogenesis, which is therapid synthesis of new glucose.
SPEAKER_01 (32:39):
They literally have to eat parts themselves to
survive their first day onEarth.
SPEAKER_00 (32:43):
Yes.
But what happens to thegenetically engineered mice, the
ones with the mutated ragae?
SPEAKER_01 (32:48):
Their MTOR is stuck on in.
The foreman refuses toacknowledge the famine.
SPEAKER_00 (32:52):
Right.
Even though the umbilical cordis cut and the blood nutrients
are crashing, their cells stillbiochemically believe there is
infinite food.
They never send the signal tostart cleanup.
They completely fail to triggerautophagy.
SPEAKER_01 (33:06):
And the result.
SPEAKER_00 (33:06):
They die almost immediately.
Because they cannot triggerautophagy, they cannot mobilize
those internal amino acids, theycannot produce new glucose in
the liver, and they succumb tosevere fatal hypoglycemia within
hours of birth.
The researchers noted that thephysical pathology of these
mice, mice with permanentlyactive MTOR, is virtually
indistinguishable from mice thathave had their core autophagy
(33:30):
genes completely deleted.
They both die as neonates.
SPEAKER_01 (33:33):
That is intense.
It really hammers home that thisisn't just some fringe
biohacking trick to look good onthe beach.
It is a foundational pillar ofhow eukaryotic life sustains
itself under stress.
SPEAKER_00 (33:43):
It is life and death.
SPEAKER_01 (33:45):
But okay, let's take a deep breath here because we
have covered a staggering amountof molecular biology.
We've gone from Daduvi'sincinerators to Osumi's yeast
traffic jams.
We've unpacked the MTOR seesaw,we've explored the wild spermine
hypesonation pathway, and we'velooked at the fatal consequences
in neonatal mice.
SPEAKER_00 (34:06):
I think we really need to bring this back down to
the practical reality for theperson listening.
SPEAKER_01 (34:10):
I agree, because the translation from cellular
biology to daily human health iswhere things get very
complicated.
SPEAKER_00 (34:16):
Yeah, because knowing how the internet works,
people are going to hearautophagy cures Alzheimer and
saves baby mice, and theirimmediate reaction is going to
be I need to stop eating for 30days straight so I can live
forever.
And our source from theCleveland Clinic has some very
explicit loud warnings aboutapplying this science
recklessly.
They do.
The Cleveland Clinic Guidelinesare very clear that while the
(34:36):
foundational biology is sound,the internet's interpretation of
autophagy as a magic youthbutton is deeply flawed.
Attempting to violently forceyour body into a state of hyper
autophagy through extremeprolonged fasting or severe
caloric restriction can beincredibly dangerous.
SPEAKER_01 (34:55):
Because you are fundamentally stressing the
system.
It's a survival response tostarvation.
SPEAKER_00 (35:00):
Exactly.
And for certain physiologicalstates, that level of systemic
stress is profoundly unsafe.
The medical guidelinesspecifically warn that pregnant
women, individuals who arebreastfeeding, or anyone with
diabetes or pre-existing bloodsugar regulation issues should
absolutely not attempt drasticfasting regimens to chase
autophagy.
SPEAKER_01 (35:19):
Right, because you can induce severe hypoglycemia,
pass out, or worse.
This is the classic rule ofbiology, right?
The dose makes the poison, alittle bit of stress hormesis
cleans out the cell and makes itmore resilient.
But an overwhelming amount ofstress just damages the tissue
and kills the organism.
SPEAKER_00 (35:33):
Precisely.
You have to respect thebiological limits.
You are trying to trigger anancient, highly tuned survival
mechanism, not win an internetsuffering contest.
Even attempting to force itthrough sudden extreme endurance
exercise without proper medicalsupervision is a bad idea.
SPEAKER_01 (35:51):
So if starving ourselves for a week straight
isn't a safe or practical dailyanswer for the vast majority of
people, where is this fieldactually heading?
Like what does the future ofthis research look like if we
want the benefits without theextreme starvation?
SPEAKER_00 (36:06):
This is where we get to one of the most provocative
and exciting areas in moderngerontology.
Let's look back in theintersection of the JCI paper
and the nature paper.
We know definitively thatcaloric restriction extends
lifespan across species.
But we also now know, thanks tothe spermidane data, that the
biological pathways activated byfasting are mediated by specific
identifiable molecules.
SPEAKER_01 (36:27):
Right.
Fasting is just the trigger.
The molecules are theexecutioners.
And the JCI paper also talkedheavily about another pathway,
right?
Something about acetyl-CoA andCzar T1.
I was trying to map that ontothe MTR story.
SPEAKER_00 (36:38):
Yes, and it fits together beautifully.
Acetyl-CoA is essentially thecentral currency of cellular
energy and fat metabolism.
When you are fully fed,acetyl-CoA levels are high.
That high energy state actuallycauses acetyl groups to be
physically attached to yourautophagy proteins, a process
called acetylation, whichinhibits them, just like M2R's
(36:59):
phosphorylation does.
SPEAKER_01 (37:00):
So it's just another molecular padlock.
SPEAKER_00 (37:02):
Exactly.
But when you fast, energy drops,and an enzyme called CERT1 gets
activated.
CERT1 is a diailase.
It physically strips thoseacetyl padlocks off the
autophagy machinery, helping totrigger the cleanup.
And here is the crucial partCERT1 can be powerfully
activated by certain naturalcompounds, most famously
resveratrol, which is found inthe skin of red grapes.
SPEAKER_01 (37:25):
Okay, so resveratrol triggers the Cirti1 pathway to
remove the acetyl padlocks.
And the nature paper showed thatspermidine triggers the EIF5A
pathway to build the machinery.
Both of these moleculesessentially trick the cell into
thinking it's starving, even ifit's not.
SPEAKER_00 (37:39):
You see exactly where this is going.
Scientists are asking a massivemulti-billion dollar question.
If naturally occurring moleculescan biochemically tap into the
exact same pathways as extremefasting, can we biomimic the
fast?
SPEAKER_01 (37:52):
Wait, are you saying the end goal of all this
research is a literal pill?
A supplement that givesyourselves the massive cleanup
signal of a five-day water fastwithout you actually having to
skip a single meal.
SPEAKER_00 (38:04):
They are called caloric restriction mimetics, or
CRMs.
It is a major heavily fundedarea of research.
Now, to be clear, the goal isn'tto create a magic pill that lets
you eat a box of donuts everyday and suffer zero
consequences.
SPEAKER_01 (38:17):
Damn, that'll be nice.
SPEAKER_00 (38:18):
The medical application is much more
profound than that.
Think about people whophysically cannot safely fast.
The frail, elderly, patientsundergoing certain disease
treatments, or individuals withsevere metabolic dysregulation.
What if we could give them alocalized, precise dose of a
polyamine like spermidine, or acombination therapy with a CERT
T1 activator like resveratrol?
SPEAKER_01 (38:40):
You could artificially lower the flag that
tells MTOR to shut off, stripthe acetyl padlocks, and force
EIF5A to turn green.
You're basically sending a fakebiochemical text message to the
cellular foreman saying, hey,the warehouse is empty, send the
construction crew home and bringin the deep cleaners, even if
the blood glucose is totallynormal.
SPEAKER_00 (39:00):
That is exactly the mechanism they are exploring.
The JCI paper even explicitlypoints out that combining
molecules like giving adeacetylase activator like
resveratrol concurrently with acompound that lowers acetyl-CoA
or hypucinates translationfactors might synergistically
induce massive therapeuticlevels of autophagy.
SPEAKER_01 (39:19):
Honestly, cellular biology is just the ultimate
hacker's playground.
The complexity is staggering.
But realistically, until thosehighly regulated, proven caloric
restriction memetic therapieshit the pharmacy, we have to
rely on the actual hardware andsoftware we were born with.
SPEAKER_00 (39:33):
And that biological hardware relies entirely on
respecting the balance.
SPEAKER_01 (39:36):
Right.
So to everyone listening to thisright now, I think the biggest
takeaway is to look at your ownlifestyle and think about your
balance of building andcleaning.
Are you keeping that MTOR switchjammed in the on-end position by
constantly grazing and snackingfrom 6 a.m.
until midnight?
Or are you intentionally givingyour body those quiet,
(39:57):
nutrient-free windows it sodesperately needs?
Because your cells want to fireup the incinerators, they want
to clear out the misfoldedproteins, and they want to take
out the toxic trash.
You just have to get out oftheir way and let them do it.
SPEAKER_00 (40:09):
It really does come down to just letting the
microscopic maintenance crew dotheir jobs.
SPEAKER_01 (40:13):
Exactly.
Because at the end of the day,you can build the most
beautiful, towering, anabolicskyscrapers in the world.
But if you never let the garbagetrucks run, the city is
eventually going to collapse.
SPEAKER_00 (40:25):
I couldn't have summarized it better.
SPEAKER_01 (40:27):
All right, that is our massive deep dive on the
science of autophagy.
Thank you so much for exploringthe microscopic world with us,
and we will catch you on thenext one.
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