This episode summarizes a PNAS study showing that PARP1 activation links Aβ1-42 toxicity to DNA damage, amyloid accumulation, neuroinflammation, and cognitive deficits, and that genetic or pharmacologic PARP1 suppression reduces pathology in cells and 5XFAD mice.
0:00Welcome to Base by Base, the papercast that brings genomics to you, wherever you are. Thanks for listening, and don't forget to follow and rate us in your podcast app. Yeah, I am really excited for the deep dive today.
0:11We've got a fascinating one. We really do. But before we get into the heavy science. I want you to imagine a scenario. Imagine your house has this slow, persistent leak, like a pipe bursts deep inside the walls.
0:25Uh-huh, and water starts pooling on the hardwood floors, right? Right, exactly. Yeah, so you do the logical thing. You call an emergency response team. You expect them to come in, maybe patch the broken pipe, mop up the standing water and, you know, leave your house mostly intact.
0:39Which is what a normal repair crew would do. Right. But instead, this crew takes one look at the damp drywall, they pull out literal sledgehammers, and they decide to permanently tear down the entire foundation of your home.
0:51Oh, wow. So they just destroy everything. Yeah. You're less standing in the rubble of what used to be your living room. Realizing that the cure they offered was infinitely worse than the actual disease.
1:01That's a brutal analogy, but it's incredibly accurate for what we're talking about today. It really is, because when we look at neurodegenerative diseases, we are finding out that the human brain sometimes acts exactly like that overzealous demolition crew.
1:16Right, because the brain has its own internal DNA repair systems. Yeah, these systems are supposed to be the ultimate biological emergency responders, but toxic proteins can actually hijack these systems.
1:28It's kind of terrifying when you think about it. It really is. The cellar repair crew gets tricked into initiating a programmed self-destruct sequence, they completely wipe out the very neuron they were originally designed to save.
1:39And that completely reframes our entire approach to neurobiology. I mean, for decades, the focus has almost exclusively been on the initial leak, right? The toxic proteins themselves. But shifting our attention to the cellular mechanisms that disastrously overreact to those proteins, well, that opens up a completely new therapeutic avenue.
1:57And mapping out the precise biological wiring of that self-destruct pathway is, you know, a monumental task. But it is exactly what researchers have just accomplished. It's a massive shift in how we view the problem.
2:10It is. So today we celebrate the work of Anisha Haldiall, Ted M. Dawson, Velina L. Dawson, and a collaborative research team across the Johns Hopkins University School of Medicine, the Cleveland Clinic, and the University of Washington, who have advanced our understanding of Alzheimer's pathology.
2:26And to appreciate the sheer scale of the breakthrough this collaborative team achieved, we really need to ground ourselves in the traditional understanding of Alzheimer's disease. Right, so let's set the stage a bit.
2:38Well, historically, the primary hallmark of Alzheimer's has been the accumulation of amyloid beta, which is often just called a beta. And those are the proteins that misfold and clump together, right? Exactly.
2:49They form these sticky plaques in the brain. And over time, the presence of these plaques leads to a chronic progressive loss of neurons. But the exact mechanical steps linking those silent sticky plaques to the active death of a brain cell.
3:04Well, that's been a massive enduring puzzle in the field for a long time. Yeah, it's like we knew the plaques were there at the scene of the crime. But we didn't necessarily have the murder weapon. Precisely.
3:14We didn't have the weapon. And that brings us to the notorious enzyme at the center of this deep dive. Right, PRRP one, which stands for Poly ADP Rabot's Polymerase one. It's a mouthful. It is a mouthful, so we'll just stick with PRP one.
3:28Normally PRP one is actually one of the good guys, right? Oh, absolutely. It functions as a frontline DNA repair enzyme. So, if your cellular DNA gets nicked by environmental stress, PRP one is the 1st responder rushing to the site.
3:40And it synthesizes a molecule called P-AR. Right, P-AR, which essentially acts as a chemical flare to signal for the rest of the repair crew to come fix the damage. But, and this is the big butt. In scenarios of a key severe cellular injury, things change, like a stroke, where the brain is suddenly starved of oxygen, or there's a sudden flood of toxic neurotransmitters.
4:01Yeah, in those cases, PRA car one flips its behavior entirely. The transformation is just dramatic. How so? Well, under acute, overwhelming stress, PRP one gets massively overactivated. Instead of sending up a few chemical flares, it creates a blinding accumulation of PR molecules.
4:20So it just floods the zone. Exactly. And this massive stockpile of PR triggers a very specific programmed type of cell death called Parthonados. Parcinetos. Okay, and how is that different from regular cell death?
4:32It is fundamentally distinct from other quieter forms of cellular recycling like apoptosis. Apoptosis is neat and tidy. Parthenotos is, well, it's a violent execution of the cell, driven by this PAR overload.
4:45Wow. And we recently learned that Parthenatus plays a role in Parkinson's disease too. Right, we could. However, its exact role in driving the slow chronic neuronal loss we see in Alzheimer's disease was entirely unknown until the researchers publish this data.
4:59Okay, so if I'm picturing this correctly, PRP one is essentially an overly dramatic factory manager. I like that. on. On a normal day. The manager walks the factory floor, sees a broken gear on an assembly line, and issues a standard work order like, a little bit of PAR to fix it.
5:15Makes sense. But during Parthenado's, the manager sees the broken gear, completely panics, locks the doors, and permanently burns down the whole factory rather than trying to repair the machine. That is a perfect analogy.
5:28The manager's massive overreaction is what destroys the infrastructure, not the initially broken gear, that captures the essence of Parthenado's, perfectly. But I'm still caught on the timeline here. do you mean?
5:40Well, I completely understand why this dramatic response happens in a stroke. I mean a stroke is an acute injury. It's a sudden catastrophic loss of oxygen, the brain panics, but Alzheimer's disease is a slow, chronic burn.
5:53It takes decades for these plaques to build up, and for cognitive decline to show. It's a very slow process. So what made the researchers suspect that a biological panic button tied to an acute stroke was actively driving the slow decades long progression of Alzheimer's?
6:08That is the exact question the researchers asked. And, you know, they didn't look for the answer in a Petri dish first. They went straight to human patient data. Oh wow. Straight to human data. Yeah, they wanted to know if the biological footprint of that panicking factory manager was visible in real people who were actively suffering from cognitive decline.
6:27Which is a huge lead, but it makes sense. It does. And that decision to start with human biology naturally set the stage for their entire incredibly rigorous methodology. Right. So the human data showed us the smoke.
6:38But to prove PRP one was the fire. They had to design this massive 3 pronged approach. A huge undertaking. Yeah, they didn't just look at one biological model. They looked at human data, then cellular models, and then highly specialized animal models.
6:53So starting with the human data, they analyze samples using a highly sensitive technique called an enzyme linked immunosorbent assay, or an Elisa. Oh, Lisa. Okay. What exactly does that do? It's a biochemical test that relies on targeted antibodies to detect and measure specific proteins with incredible precision.
7:11And in the study, they were measuring PR levels. And PR is that direct chemical product created by our overactive manager, PARP1. Exactly, the chemical flare. They measured these PAR levels and the cerebrospinal fluid of patients from 2 entirely independent cohorts.
7:28One group from Johns Hopkins and another from the Cleveland Clinic. And just for anyone listening who isn't familiar, cerebrospinal fluid is the clear liquid that bathes the brain and spinal cord. It acts as a shock absorber, but it also carries away cellular waste, because it directly surrounds the brain, tapping into it, gives us a real-time biochemical window into what is happening deep inside this central nervous system.
7:51Which is exactly why it's such a valuable metric. So they have the human fluid data. Then for the 2nd prong, they move to in vitrocellular models. To recreate the environment in a controlled setting. Exactly.
8:01They took primary mouse cortical neurons, actual living brain cells, kept them in a dish, and introduced synthetic a beta oligomers. And these oligomers are the toxic free floating clumps of amyloid protein found in an Alzheimer's brain.
8:16Right. They wanted to observe in real time if hitting the cells with a beta would force PRP1 to hit the panic button. Did they just watch it happen? No. Furthermore, they didn't just watch the distraction happen.
8:27They intervened. They applied FDA approved PRP inhibitor drugs to the cellular models. Oh, so they brought in drugs that already exist. Yeah, specific compounds like velaparib, Rukuperrib, and Talziparib.
8:40Now, the way these drugs work is fascinating, they actually bind directly to the active site of the PRP1 enzyme. Like putting a lock on it. Exactly. By locking onto the enzyme, they physically block it from synthesizing the PRR molecules.
8:55The researchers wanted to see if chemically freezing the factory manager would shield the neurons from the toxic amyloid. That makes total sense. And finally, they move to the 3rd prong, which is arguably the heaviest lifting of the entire study.
9:06Oh, absolutely. The Invivo animal models. Right. They utilize what's known as the 5XFAD mouse model, and they systematically genetically crossed it with PRP1 knockout mice. And those knockout mice are genetically engineered from birth to completely lack the PRP1 enzyme in every cell of their bodies.
9:26But we really need to pause and emphasize why the 5X FED mouse model was chosen for this crossing. We do, because it speaks to a massive historical hurdle in Alzheimer's research. If you look back, dozens of different mouse models have been used over the years.
9:41Right, there are so many of them. And many of those models develop the signature amyloid plaques, and they even show signs of memory impairment. But surprisingly, they don't actually lose a significant number of brain cells.
9:52Wait, really? Their neurons get sick, but they don't actually die. Right. They don't die. Which is incredibly frustrating if you're trying to study a disease defined by brain tissue loss. Exactly. The 5XFAD model is fundamentally different, though.
10:05It is engineered to express 5 distinct human mutations associated with familial Alzheimer's disease. Okay, so it's a much more aggressive model. Because it carries these 5 specific mutations. It develops severe amyllidosis rapidly, and crucially, it exhibits significant visible neuron loss in key memory centers like the cortex and hippocampus by the time the mice are just 9 months old.
10:30Wow, 9 months. Yeah. If your entire study is focused on testing an enzyme like PRP one whose whole job is to trigger cell death, you absolutely must use an animal model where robust, measurable cell death actually occurs.
10:45Right. You can't test a cell death mechanism if the cells aren't dying. Exactly. So setting up this multi-layered methodology is enormous undertaking. But, you know, the setup is only as good as the results.
10:55Let's dig into what the researchers actually saw when they ran these tests. Let's start with the human cerebrospinal fluid. Okay, what did the Eliza show? The human data provided a striking confirmation, the PIR levels that chemical flair produced by PRP1 were significantly elevated in the cerebrospinal fluid of patients diagnosed with mild cognitive impairment.
11:14And in full-blown Alzheimer's too. Yes, as well as in patients with full-blown Alzheimer's disease compared to healthy individuals. Wait, there's a really specific detail here about the a beta 42 40 ratio that seems kind of counterintuitive at 1st glance.
11:28It does trick people up. Walk us through it. So for context, a beta 42 is a slightly longer, stickier, and far more toxic version of the amylly protein than a beta 40. Right. In a brain developing Alzheimer's, this sticky A beta 42 clumps up aggressively to form the plaques.
11:46Yeah, it binds together. Because it is all getting trapped and clumped up the physical brain tissue. The measurable levels of an 842 actually drop in the cerebrospinal fluid. Exactly, because it's stuck in the plaques.
11:58So if you see a lower A beta 42 to 40 ratio in the fluid, It's a well established clinical marker that the disease is actually progressing. Right. The plaques are essentially hoarding the toxic protein, pulling it out of the fluid.
12:11And the researchers found a direct negative correlation. As the a beta ratio and the fluid went down, indicating that the disease was worsening and plaques were forming, the PAR levels skyrocketed. Wow.
12:23So the human data proved the self-destruct mechanism was actively firing as the disease progressed. Exactly. So they took that correlation and moved to the cellular data to prove direct cause and effect.
12:34And what did the cells in the dish show? They discovered that only the highly neurotoxic clumpia beta 142 triggered the PRP1 activation. The slightly shorter, less toxic a beta 140 did absolutely nothing.
12:46That is so specific. Yeah. When the toxic A beta 42 hit the living neurons in the dish, it acted like a sledgehammer, causing visible physical damage to the cell's DNA. And they could actually measure that damage rate.
12:59Yes, using a specific biochemical marker called Gamma H2AX. The toxic protein damages the DNA, and that specific structural damage is what wakes up our dramatic factory manager, PARP1. But the most vital part of the cellular data was the drug intervention, wasn't it?
13:15Oh, absolutely. When they applied those FDA approved PRP inhibitor drugs, locking up the enzymes active site, or when they use neurons genetically engineered to lack PRP one entirely, it completely protected the neurons.
13:28Even with the toxic amyloids still there. Yeah. The toxica beta was still floating around in the dish, actively causing stress, but without PRP one, there to pull the self-destruct switch. The cells simply survived.
13:41Which is just incredible. And that brings us to the live Mel data. This is where the results cascaded far beyond just keeping individual cells alive in a dish. The Inviva results were staggering. Yeah, and the 5X FAD mice that were bred to lack PRP one, there was a staggering 50% reduction in Theo Flavin S positive plaque area.
14:01Let that sink in. Half of the physical amyloid plaques and the entire brain were simply gone. That is an unbelievable level of clearance, and the benefits just kept multiplying, didn't they? They did. They measured a critical protein called PSD 95.
14:14This protein serves as a marker for the density of synapses. The vital communication bridges between neurons. Right. In the mice without PRP one, that synaptic density was fully preserved. Furthermore, the actual physical death of neurons in the cortex and the sibiculum regions heavily involved in memory formation was entirely prevented.
14:32So the brain structure was saved. What about the inflammation? They analyzed the brain's immune system, too? Specifically, the support staff cells known as microglia and astrosytes? The cells that usually freak out during Alzheimer's.
14:45Right. Usually in an Alzheimer's brain, these support cells enter a state of hyper reactive panic, a condition called gliosis. They stop supporting the neurons and start pumping out inflammatory alarms.
14:58But without PRP1. Without PRP1, the markers for this reactive state plummeted. Chemical messengers driving inflammation in the brain were practically silenced. Okay, so if you're a listener wondering what all this cellular chemistry actually means for the living animal, we have to talk about the behavioral tests.
15:16Yes, the memory tests. The researchers didn't just look at brain slices. They tested the mice's memory using the Morris water maze. Which is where mice are placed in a small pool of opaque water, right?
15:27Yeah, and they have to rely on visual cues around the room to find a hidden platform just beneath the surface. It is a really rigorous test of spatial learning. And they use a Y maze too, right? Exactly, to test immediate working memory.
15:39Now, the 5XFAD mice, with intact PRP1, struggled immensely. They couldn't remember where the platform was. But the mice lacking PRP one. They regain their spatial learning and memory. They remembered exactly where to go.
15:53That is just incredible. It is. So we know the plaques cleared and the memory returned, but the researchers pushed even further to map out how it happened chemically. The mechanistic data. Yeah. They gathered data showing that deleting PRP1 actually altered how the amyloid precursor protein, or APP is metabolized in the 1st place.
16:12Okay, so the precursor protein is basically the raw material that gets cut up to form the toxic amyloid. Right. The researchers found that disabling PRP1 significantly reduced the levels of an enzyme called Bay AC1.
16:25And bas E1 is the biological machinery that makes the 1st crucial cut on the precursor protein. Exactly. They also noted changes in the gamma secretaste complex, which makes the 2nd cut. So the overall production machinery was dialed down.
16:37The system didn't stop there, did it? No, it didn't. While it reduced the enzymes that produce amyloid, the absence of PRP1 simultaneously increased the levels of NEP2 or Neprolison. What does that do?
16:51NEP2 is a completely different enzyme whose primary job is to degrade and clear away existing amyloid. Okay, we need another analogy here to visualize this dual mechanism, because finding something that works like this in biology is wild.
17:04Go for it. Imagine your bathroom is actively flooding because the sink is overflowing. Deleting PRP one is like fixing that flooded bathroom by simultaneously turning off the faucet. Which represents lowering the BACE one production of new amyloid.
17:20Right. And at the exact same time, unclogging the drain. Which represents increasing the NP2 degradation of the existing amyloid. Yes. How rare is it to find a single biological target that addresses both the faucet and the drain?
17:32In the landscape of pharmacology and drug development, it is exceptionally rare. Usually you are forced to target one specific pathway at a time. You design one drug for one thing. Right. You design one drug to slow down production, or you design a completely different drug to boost clearance, to find a single enzyme, a central node, like PRP1, that sits upstream, and regulates both the production and the degradation pathways.
17:57Well, simultaneously controlling the brain's inflammatory response and the ultimate cell death. Exactly. It is essentially the holy grail of Target discovery. It proves that PRP one orchestrates the entire pathogenic environment.
18:09Man, with these massive reductions in plaques, the preservation of synapses and the behavioral recovery. We really have to pivot to what this actually means for the future of human medicine. We do. The implications here feel enormous.
18:22The implications are profound. Because this study positions PRP1 as the missing bridge, linking amyde toxicity directly to neuroinflammation and cognitive decline. And what makes this infinitely more exciting than a typical lab discovery is the clinical translation aspect.
18:38Because PRP inhibitors are already being actively used in the clinic. Primarily oncology, right? Yeah. To treat specific cancers like breast and ovarian cancer. Right. So this positions PRP1 inhibition as a highly promising disease modifying therapeutic strategy for Alzheimer's disease.
18:55We aren't starting from absolute scratch with drug discovery. The physical drugs already exist. Okay, I have to challenge the translation timeline here. Sure, go ahead. Because if I'm listening to this, and you're telling me that PRP individors already exist, and they are literally sitting on pharmacy shelves right now.
19:10The obvious question is, why can't we just give them to Alzheimer's patients tomorrow? Why isn't this an immediate overnight cure? It is a completely valid question, and it's where we have to look soberly at the limitations of the study and the realities of human translation.
19:26Right, it's never that easy. No, it's not. We have to remember that a genetic knockout in a mouse where the animal is born without the PRP one enzyme in every single cell of its body is fundamentally different from administering a pharmacological dose of a chemical drug to an elderly human patient.
19:43The biology of an aging human brain is infinitely more complex than a laboratory mouse engineered for a specific trait. Significantly more complex. First, there is the formidable challenge of the blood brain barrier.
19:57Right, getting the drug where it needs to go. Exactly. Many oncology drugs are not designed to efficiently cross from the bloodstream into the brain tissue. We have to ensure that any PRP inhibitor used for Alzheimer's can actually reach the neurons in high enough concentrations to be effective.
20:13That makes sense. And what else? Second, and perhaps more critically, there is the issue of dosing and long-term side effects. We have to remember PRP one's day job. It repairs DNA. Right, the normal factory manager stuff.
20:25Exactly. In an oncology setting, doctors give these drugs, in short, aggressive bursts, specifically to stop cancer cells from repairing themselves, allowing the cancer to die. But for a chronic disease like Alzheimer's.
20:38A patient might need to take this drug continuously for years or even decades. So long-term safety is the massive hurdle here. You don't want to successfully stop the Alzheimer's progression, but inadvertently cause a host of other cellular damage because normal daily DNA wear and tear isn't getting repaired properly over a 10-year span.
20:58Precisely. We have to rigorously test what happens when you chronically suppress DNA repair in human cells. That is a big limitation to keep in mind. It is. Furthermore, this specific study utilized a global genetic deletion of PRP1, meaning it was missing everywhere in the mouse.
21:15Moving forward, the next logical step for research, must look at cell type specific manipulation. Like targeting only specific parts of the brain. Well, targeting specific cell types. We need to isolate exactly how PRP one functions distinctly in the neurons versus the glial cells, the immune support staff of the brain.
21:33Oh I see. Does chemically inhibiting PRP1 in a microglia cell have a vastly different effect than inhibiting it in a neuron. Understanding that cellular nuance will be absolutely crucial for developing therapies that are both targeted and safe.
21:47That's a great point. So we've covered the human fluid data showing the active mechanism. The cellular sledgehammer effect, the incredible recovery in the mouse models, and the very real clinical hurdles of bringing a cancer drug into the neurology ward.
22:01It's been a journey. It really has. Let's draw this conversation to a close by synthesizing these implications into a final consolidated takeaway for anyone listening. I think the central unifying insight here is that the PRP one enzyme acts as a master switch in Alzheimer's disease.
22:19A master switch for what exactly? It actively drives toxic amyloid production, brain inflammation, and ultimately neuronal death. All three. Yes. By disabling this single switch, researchers successfully protected delicate brain cells, cleared out existing claques, and restored spatial memory in a preclinical model.
22:36They really uncovered an incredibly powerful new therapeutic target for a devastating disease. They absolutely did. What does this mean for the future of Alzheimer's treatment? If a single therapeutic target can both defend the brain and help clean it up.
22:50It's a question that's going to drive the field forward for years. This episode was based on an open access article under the CCBY 4.0 license. You can find a direct link to the paper and the license in our episode description.
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