This episode examines a PNAS study that identifies site-specific lactylation of HSP90α as a metabolic signal linking glycolysis to mitochondrial biogenesis in ovarian cells. Lactylation at K58 and K616 modulates HSP90α phosphorylation, enabling nuclear import of PGC1α and LRPGC1, boosting mitochondrial number, cholesterol import, estradiol synthesis, and follicle growth; CREBBP, ACSS2 and GTPSCS participate in the lactylation pathway.
0:00Welcome to Base by Base, the paper cast that brings genomics to you wherever you are. Thanks for listening, and don't forget to follow and rate us in your podcast app. Absolutely. tuning in. You know, when most of us hear the word lactate or lactic acid, our minds instantly go to one very specific place.
0:18Oh yeah. The gym? Right. We think of that deep, intense muscle burn you get during the last few reps of a really tough workout. Exactly. And for the longest time, biology has kind of taught us to view lactate as this, well, this annoying exhaust, a waste product of metabolism that your body just needs to clear out.
0:37Yeah, just metabolic trash essentially. Right. But what if we've had it completely backwards? Like if we picture a cell as a massive manufacturing factory, lactate isn't just the smoke blowing out the exhaust pipe.
0:48It's actually a work order sent back down to the foreman, telling them to build an entirely new assembly line. It's a master signaling key. That's great way to put it. And that raises a fascinating question for this deep dive.
1:01What really happens when the supposed waste product makes its way into the incredibly delicate, highly orchestrated world of reproductive cells? I mean, how could a simple metabolite drive something as complex as fertility?
1:15Well, today we celebrate the work of Gangwoo, Hungman Lee and the research team at Nanjing Agricultural University in China, who have advanced our understanding of how cellular energy metabolism directly controls a varian function.
1:29Yes, and to really grasp the magnitude of what this research team has discovered, we have to rethink how much energy it actually takes to create life. It's staggering honestly. Right. We need to at the ovary not just as a reproductive organ, but as a site of massive industrial output.
1:44Yeah, the energetic burden is just phenomenal. The ovary requires a constant, massive supply of energy to support the growth and maturation of a follicle. And the follicle is the fluid filled sac containing an immature egg, right?
1:57Exactly. And as that follicle grows, the cells surrounding it, the granulosis cells, they have to rapidly multiply and differentiate. Yeah, that process takes an immense amount of ATP. which you can think of as the basic energy currency of the cell.
2:09Right. And whenever we talk about ATP, we are immediately talking about mitochondria, you know, the classic cellular powerhouses. We are. But in the ovary, mitochondria have a 2nd job that is just as critical.
2:21Yeah, they aren't simply burning fuel to make energy. They operate as dual purpose factories. Wait, dual purpose? What's the other purpose? Well, yes, they generate ATP. But in these reproductive cells, mitochondria are also the primary manufacturing plants for steroid hormones.
2:38Wow, okay. They literally pull raw cholesterol inside their duddle membranes and convert it into the essential chemical precursors that eventually become estrogen. Specifically estradyle, right? Exactly.
2:50So if a follicle is trying to mature. It needs a vast network of these mitochondria. It does. It needs the ATP to physically grow, and it needs the manufacturing plants to pump out the hormones, orchestrating the entire reproductive cycle, which brings us to a fundamental biological logic puzzle.
3:07How does the cell actually know it's time to build more these factories? It needs some kind of sensor and a switch. Right. And the scientific community is actually known about this switch for a while. Okay, what is it?
3:18It's a protein called PGC one Alpha, along with a closely related partner called LRPGC one. PGC one Alpha. Got it. Yeah, and when these master switch proteins are activated, they trigger a massive program of mitochondrial biogenesis.
3:33Meaning they initiate the creation of brand new mitochondria from scratch. Exactly. But here's the catch. The switch isn't located anywhere near the blueprints. Ah. The master switch protein is floating out in the main body of the cell, the cytoplasm.
3:47But to actually turn on the factory production, it has to get inside the locked vault of the nucleus, where the DNA blueprints are kept. It has to physically cross that barrier. Right. And until this study, the exact transportation mechanism was essentially a black box.
4:02Yeah, we knew the switch moved from the cytoplasm into the nucleus in response to energy demands, but we didn't know how it navigated that journey. Or what was providing the specific molecular push to get it moving.
4:14Exactly. But that seems like a really tough thing to observe. I mean, you can't just throw a cell under a standard microscope and watch a tiny protein take a bus into the nucleus. No, definitely not. You'd have to chemically tear the cell apart to track where these molecules are residing at any given moment.
4:31And it is exactly what they did. The researchers approach this with a deeply elegant tool kit. They used a technique called nuclear cytoplasmic fractionation. By essentially breaking the cell open and separating the nucleus from the rest of the cellular soup, they could measure the exact location of those master switch proteins.
4:49Oh wow. And they found that when they introduced lactate to these ovarian cells, the master switch proteins suddenly rushed into the nucleus. But proteins rarely travel alone, right? They usually need a guide or a vehicle, especially to get through the highly guarded pores of the nucleus.
5:06You're spot on. The data showed they were being escorted by a chaperone protein, specifically one called HSP 90 Alpha. Right. And for anyone whose cellular biology is a little rusty. A chaperone protein is incredibly literal.
5:21It really is. It's a protein whose entire job is to bind to other proteins. stabilize them, make sure they don't fold into the wrong shape and safely escort them to their final destination. Exactly. But you know, science requires proof of absolute necessity.
5:36Sure. It wasn't enough to just see the chaperone hanging around the switch. They had to prove it was doing the work. So how did they do that? The researchers brought in CRISPR Cast 9, gene editing to completely knock out the gene responsible for creating this specific chaperone protein.
5:52Oh, wow. and the result. Definitive. Without that chaperone, the master switch proteins were stranded in the cytoplasm. No nuclear entry, no new mitochondria. Okay, so they've proven the chaperone protein is the necessary vehicle.
6:04But how does a simple lactate molecule actually turn the key in the ignition? Right. that's the big question Because it's not like the chaperone has eyes or ears to sense the lactate floating around. There has to be a physical interaction.
6:16Yes. The researcher suspected the chaperone was being physically modified by the lactate through a process called lactilation. Okay. But to prove this, they needed to find the specific writer enzyme. You know, the biological machine that actually attaches the lactape molecule onto the chaperone.
6:34And how do you find one specific machine in a whole cell? They used advanced mass spectrometry. They sifted through over a 1000 interacting proteins, ultimately isolating the exact writer enzyme responsible.
6:47And what was it? A protein known as CREBP. Wait, I want to pause on the sheer scale of that search. Because mass spectrometry is essentially looking at the weight and charge of chopped up protein fragments to identify them out of a massive cellular haystack.
7:02It is a massive undertaking. But what fascinates me is that they didn't stop at just identifying the enzyme. They wanted to find the exact amino acid parking spots on the chaperone where this lactate was being attached.
7:14Yes, the level of detail is amazing. They utilized site directed butogenesis. Okay, what does that mean in this context? Well, the mass spectrometry data indicated that lactate was being attached to specific amino acids called lycines.
7:26Right. So the researchers went in and genetically swapped out those specific lycines for a different amino acid arginine. Which is brilliant, because Argentine has a similar positive charge to lysine, keeping the overall protein structure somewhat stable, but it has a different shape that cannot accept a lactate molecule.
7:45Exactly. He essentially poured concrete into the molecular docking stations. That's a perfect analogy. And by breaking those docking stations, they prove that 2 very specific spots on the chaperoned protein, Lyscene 58 and Lyscene 616 are the absolute non-negotiable attachment points for lactate.
8:04Wait, really? Just 2 spots. Just those 2 spots. If you mutate those 2 spots, the entire process grinds to a halt. The chaperon can't bind the master switch, nothing goes to the nucleus, and the whole factory expansion is canceled.
8:16Okay, we have the actors on the stage now. We have the master switch, the chaperone vehicle, the right or enzyme, and the lactate itself. Let's look at how this sequence actually plays out because the mechanism they uncovered here is a masterclass in cellular engineering.
8:30It really is. So when lacate enters the cell, It is metabolically converted into a highly reactive molecule called lactyl coA. Okay. Then that writer enzyme we discussed, CREBBP, takes the lactyl group, and physically attaches it to the chaperoned protein at those 2 specific lycene spots.
8:49And adding a physical molecule to a protein isn't just a tiny decoration. It fundamentally changes the protein's physical reality, right? Absolutely. It changes the charge and the three-dimensional shape.
8:59Oh, so. Well, licines are naturally positively charged. When you attach a bulky, lactyl group to them. It neutralizes that charge. Okay. That forces the entire protein to fold differently. And the modifications that those 2 distinct spots do 2 opposite but entirely complementary things.
9:15It is a system of dual control. I love a good biological paradox. If one spot is doing one thing and the other is doing the opposite, how does that move the process forward? Let's look at the 1st spot.
9:26Lycene 58? When lactate attaches there and changes the shape of that region, it acts as a chemical invitation. An invitation for what? It specifically recruits a helpful kinase, an enzyme that adds phosphate groups called ULK1.
9:40Okay. That helpful enzyme comes in and adds an activating phosphate group to the chaperone. It helps the chaperone snap into the correct active confirmation. Got it. But if Lyscene 58 is the activating site, there must be a mechanism keeping the brakes off on the other side.
9:55That is exactly the role of the 2nd spot, Lycene 616. That region of the protein is all about physical blockades. Oh, interesting. Yeah, when lactate attaches there, the resulting shape change physically blocks a different unhelpful kines called CDK5.
10:09And what does CDK 5 usually do? Normally, TDK5 wants to add an inhibitory phosphate group. If it manages to do that, the chaperone shuts down entirely. Oh, wow. But the lactate tag acts as a physical shield, preventing the unhelpful enzyme from docking.
10:22It's like a bouncer at an exclusive club. Ah, yes. The modification at Spot 58 is essentially handing a VIP bracelet to the good guy, ULK1, saying, come on in, help us get this assembly line moving. Meanwhile, the modification at spot 616 is putting up a velvet rope to physically block the bad guy, CDK5 from getting inside and shutting the whole operation down.
10:45That is a very visual, perfect way to understand it. You have one modification, promoting an activating signal, and the other modification blocking an inhibitory signal. And the result. Because of this perfectly coordinated push and pull, the chaperone protein is locked into the absolute perfect three-dimensional shape.
11:02It becomes highly primed to grab onto our master switches. And once it grabs them, it acts as the shuttle, pulling them out of the cytoplasm and straight through those heavily guarded nuclear pores. Exactly.
11:13And what's inside the nucleus. those mattress switches are free to do their job. Which is to turn on the factory. Right. They bind to specific transcription factors, and they turn on the architectural blueprint genes.
11:23Specifically genes like TFB1 beater, TFB2 meter, and TFAM. These are the genes explicitly responsible for building the structural components of new mitochondria. Okay, I want to push back on something here, though.
11:35We are looking at a system that requires incredible precision. A velvet rope and a VIP bracelet, perfectly coordinating to build the most important energy factories in a reproductive cell. Yes. Isn't it incredibly risky for a cell to rely on a so-called waste product, like lactate to trigger something as important as fertility?
11:59I mean, why would evolution leave the keys to the factory in the hands of the exhaust pipe? See, that is the exact paradigm shift this paper highlights. We have to stop thinking of it as exhaust. Okay. From an evolutionary perspective, it is a brilliant system of resource sensing.
12:12Reproduction is incredibly energy intensive. Right, it takes a lot out of the body. Exactly. If a female mammal is starving or under severe metabolic stress, it is biologically dangerous to attempt to mature an egg and support a pregnancy.
12:25So the body uses metabolic flux as a real-time sensor. Precisely. High levels of glycolysis. The breaking down of glucose, which produces lactate signal to the cell, that energy is abundant. The cell is flush with resources.
12:40Yes. By linking the mitochondrial building program directly to lactate levels. The ovary ensures it only rams up hormone production and follicle maturation when the broader metabolic environment says it is safe to do so.
12:53Lactate is the green light. Wow, that makes so much sense. It bridges the gap between what a cell is eating and what a cell is building. Exactly. And we can see the physical result of that green light.
13:03The researchers measure the downstream effects, right? What happens to the cell once those blueprint genes are turned on? Oh, the physiological intact was massive. The researchers measured a significant increase in mitochondrial DNA, meaning the cells were literally multiplying their mitochondrial genome.
13:20Amazing. They also saw much higher levels of a protein called TOM 20, which is found in the outer mitochondrial membrane. So that's clear proof of increased mitochondrial mass. More mitochondria means more energy, but going back to our earlier point, it also means more manufacturing plants for steroid hormones.
13:37Right. Right. And they track the movement of cholesterol. They saw significantly more raw cholesterol being pulled into these newly formed mitochondria. And what's the downstream result of all that raw material entering the factory?
13:48A massive surge in estrogen production. The cells were suddenly churning out highly elevated levels of estrodeal. That is incredible. But, you know, it's one thing to see this intricate molecular ballet happening in a petri dish with cultured cells.
14:05Oh, sure. Biological systems and living organisms are infinitely more chaotic. Did they test this mechanism in a live animal model? They absolutely did. They took this entire hypothesis and injected living mice with sodium lactate.
14:18The results mirror the cellular data beautifully. The lactate injections directly led to elevated estradeal levels in the blood of the mice. Wow. Furthermore, when they examine the ovaries, they found a significantly higher count of healthy, mature antral follicles.
14:33That is just wild. A molecule we used to think was just the garbage from burning sugar is injected into a mouse, finds its way to the ovary, physically changes the shape of a chaperone protein by acting as a VIP bracelet and a velvet rope.
14:47Shuttles a master switch into the nucleus, builds new cellular power plants, pulls in cholesterol, synthesizes estrogen, and physically grows a healthy ovarian follicle. It completely redefines the hierarchy of cellular communication.
15:02Metabolic flux isn't just a background process supplying fuel. It is actively steering the epigenetic and genetic programming of the cell. If we zoom out from the ovary for a second, We really have to look at the broader implications of this deep dive.
15:15Yeah, we do that. For decades. Medicine has treated metabolism and genetics as 2 separate pillars. You have your metabolic pathways breaking down food, and your genetic pathways reading DNA, but this research provides a direct physical bridge between the two.
15:29It links glycolitic activity directly to stroidogenic capacity. And when you understand that link, you start to see totally new ways to approach reproductive health. I'm immediately thinking of conditions like polycystic ovary syndrome or PCOS.
15:43Yes, absolutely. It is a condition where metabolism, insulin resistance, and fertility are intimately entangled in ways we still struggle to fully treat. If lactate is a key trigger for building the mitochondria that make estrogen.
15:58This uncovers a huge potential metabolic target. The therapeutic potential is a very astute connection to make. If we can understand how to therapeutically modulate this specific lactulation pathway, we might be able to dial up or dial down mitochondrial function in the ovary without having to rely entirely on blunt force systemic hormonal therapies.
16:21Right. As much as we love the potential here, we always have to keep our feet on the ground, we have to impartially look at the boundaries of this specific paper, because this mechanism isn't a magic bullet ready for the fertility clinic tomorrow.
16:33No, and the researchers were very transparent about the limitations of their current findings. For instance, those live animal experiments with the mice. To prove the writer enzyme was responsible in Vivo, they relied on a pharmacological inhibitor.
16:48A chemical called C646, right? to shut the enzyme down. And chemical inhibitors are useful, but they can be notoriously messy. Yeah, they really can. They might block your target enzyme, but they might also quietly interfere with 3 other pathways you aren't looking at.
17:04Precisely. To be definitively certain, future studies need to move away from chemical inhibitors. What's the alternative? The field needs genetically precise, ovary specific knock in models. Okay. They need to breed mice that are genetically engineered to have those specific broken docking stations, the lysine mutations only in their ovarian cells.
17:26Oh that makes sense. Yeah, that would prove beyond a shadow of a doubt that this exact modification is responsible for the physiological changes without the off target effects of a chemical drug. They also mentioned a limitation in how we are visualizing this process, didn't they?
17:40They did, yeah. We've spent this entire deep dive talking about the velvet rope, the VIP bracelet, the protein folding and changing shape, but they haven't actually taken a physical picture of that happening.
17:50Well, the biochemical data is rock solid. We know the binding affinities change, the helpful enzyme binds better, the unhelpful one is blocked. But the researchers noted a critical need for high resolution structural biology.
18:02Specifically, tools like cryoelectron microscopy. Ah, cryo-EM. Exactly. To truly understand the mechanics of this, we need to physically see the three-dimensional conformational changes in the chaperone protein.
18:18We need the atomic blueprint of what happens the exact millisecond that lactate molecule attaches. And there's a broader physiological question hanging over this, too. Oh, definitely. This complex signaling pathway works beautifully in the granulosis cells of the ovary.
18:31But the ovary is not the only place in the body that relies on massive amounts of mitochondria to churn out steroid hormones. Right. It remains a complete mystery if this exact lactate driven pathway operates the same way in other steroid producing organs.
18:46Like the adrenal glands, which produce cortisol and adrenaline. Or the lighting cells in the testes, which produce testosterone. They all have similar metabolic and mitochondrial demands. Does lactate orchestrate their hormone production too?
18:58Or is this a bespoke mechanism entirely unique to the female reproductive system? We just don't have the data yet. It's fascinating to think that lactilation could be the universal language for all hormone production, or it could be a highly guarded secret of the ovary.
19:14We'll have to wait for the next wave of research to find out. Yeah, but when you synthesize everything we've explored today, the core insight is just profound, lactate is far more than a metabolic byproduct.
19:26It is a vital signaling molecule that links a cell's energy state directly to its genetic output. By physically modifying the chaperone protein HSP 90 alpha, Lactate controls the nuclear entry of key transcription regulators, driving mitochondrial expansion and ovarian hormone production.
19:41It completely flips the script on biology's waste products, and it makes you wonder, what does this mean for how we view the exhaust of our own metabolism. If lactate is secretly orchestrating fertility by changing the physical shape of cellular vehicles, what other hidden signals are buried in the byproducts of our energy hungry organs?
20:01What other biological work orders are being sent right now that we simply haven't learned how to read? It's a great question to leave off on. This episode was based on an open access article under the CCBY 4.0 license.
20:13You can find a direct link to the paper and the license in our episode description. If you enjoyed this, follow or subscribe in your podcast app and leave a 5 star rating. If you'd like to support our work, use the donation link in the description.
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