Elevated PCBP2 forms liquid-like condensates that sequester mitochondrial and RNA-binding proteins, stabilize BACE1 mRNA, and promote amyloid pathology while the small molecule CN-0928 reduces PCBP2 via INTS1 to lower Aβ and improve cognition in AD models
0:00Welcome to Base by Base, the papercast that brings genoics to you wherever you are. Thanks for listening, and don't forget to follow and rate us in your podcast app. I want you to imagine for a moment the um, the central villain in Alzheimer's disease.
0:14For decades, we've had a pretty clear picture, right? It's been all about these toxic garbage piles. Exactly. The amyloid plaques found outside the neurons, and then the twisted time tangles you find inside.
0:26We've spent so much time developing drugs to clean up those piles. And, you know, it's critical to say that those clinical trials have, well, they've mostly failed to reverse the cognitive decline. Right, which is force researchers to ask this really compelling question.
0:41What if those big aggregates, the plaques and tangles aren't the primary millons at all? What if they're just a symptom? And what if the real problem, the actual attack, happens much, much earlier, on a completely different level inside the cell?
0:54That's where we're going today. We're talking about these tiny dynamic compartments inside our cells called biomolecular condensates or BMCs. Hmm. You can think of them as these little temporary filing cabinets.
1:05They don't have a membrane, a wall around them. just form. They form through a physical process. It's called liquid, liquid phase separation or LLPS. They're essential for concentrating proteins and RNA right where they're needed.
1:17Like a little pop-up work bench. Exactly. But they're supposed to be transient liquid, flexible. In neurodegenitive diseases, that process goes robe. The liquid turns solid. It transitions into permanent solid aggregates.
1:31And in doing so, it traps vital cellular machinery and just grinds everything to a halt, this physical shift, this liquid to solid transition. That's the revolutionary new target. And this deep dive, it's all about a study that not only nails down the key protein that forms these condensates in Alzheimer's.
1:49But it also introduces a small molecule that can actually reverse the pathology. It dissolves these rogue assemblies, and the results and mouse models are pretty dramatic, a real rescue of cognitive function.
2:00It's about hitting the disease at its very foundation. So today, we celebrate the work of researchers primarily at the 1st affiliated hospital of shunking medical university and their collaborators. Their work is a huge advancement.
2:13It's really overwhelming proof of concept for the idea of um, the pharmacological modulation of PCBP 2 condensates as a real effective strategy for treating AD. Okay, let's set the stage a bit more because this is so important.
2:29We said that amyloid and Tao are the classic hallmarks. Right. But the drug pipeline targeting them has just been devastatingly dry. 1000000000s of dollars and very little to show for it in terms of real patient outcomes.
2:42It created this profound need to look further upstream, to find what actually kicks off this whole pathological cascade, long before the plaques and tangles are everywhere. And that search led them to a protein that was, frankly, a bit of a scientific mystery in Alzheimer's.
2:56PCBB2, policy binding protein, too. We knew it was an RNA binding protein and RBP, and we knew its levels were way up in the brains of AD patients. It's also found in stress granules, which are another kind of condizit.
3:07So we knew it was at the scene of the crime, you could say. It was likely involved in stress responses, but its actual role in driving the disease. was the mystery. So the central hypothesis was pretty elegant, actually.
3:20It was. Did this elevated level of PCBP2 protein actually promote this biomolecular condensation, this physical phase separation. And if it did, could that condensation be the actual driver of the disease?
3:32And they found out pretty quickly that it was. Oh, yeah. They confirmed that PCBP 2 condensation wasn't some rare event. It was a key pathological feature, right there in the neurons of human AD patients and in the standard animal models.
3:45So it wasn't a coincidence. It was a fundamental physical change in the diseased cell. Right. So the 1st thing they had to do, the 1st bit of detective work. was to prove that these things were genuinely liquid like condensates, not just, you know, random clumps of protein.
3:59And how do you do that? You do classic and vitro reconstitution essays. You take purified PCVP 2, mix it with some RNA in a dish and just watch. And they saw them form these beautiful little droplets. And these droplets behave like liquids.
4:12Absolutely. They showed all the core behaviors they'd fuse together when they touch, just like oil, droplets, and water. And then they did a technique called FRIP. Fluorescence recovery after photo bleaching.
4:23That's the one. They basically use a laser to bleach a tiny spot on one of the compensates, and then they watch to see if the fluorescence comes back. Okay, so for our listeners, what does that recovery actually tell us?
4:34It's the ultimate test of fluidity. If that spot recovers its fluorescence and it did very quickly. It means the molecules inside are constantly and rapidly swapping places with molecules outside. So it's dynamic.
4:47It's a liquid, not a solid gel. Exactly. The physics checked out. PCVP2 forms these pathological, dynamic liquid condensates. Okay, so the structure is confirmed. Now, for the really big question. Yeah. What was getting trapped inside this rogue filing cabinet?
5:03was it hiding? This is where they use a really sophisticated technique. It's called fluorescence activated particle sorting, or FAPS. That sounds complicated. It is, but the idea is brilliant. They tag the PCBP2 protein in cells with a fluorescent marker, and then use this advanced sorting technology to literally pull out the microscopic condensates themselves.
5:26They isolated them. They physically purified them. And once they had them, they ran the contents through a mass spectrometer, to identify every single protein that was trapped inside. That's amazing. It's like collecting the contents of a safe after a robbery to see what was stolen.
5:41And the manifest of stolen goods was stunning. It immediately linked 2 disease pathways that, before this, seemed pretty disconnected. What were they? Well, they found over a 1000 proteins enriched in there, but 2 categories just jumped out.
5:54First, they were trapping a huge number of mitochondrial proteins. The cells power plants. Right. And second, they were trapping key RNA binding proteins that are involved in cellular cleanup. Let's start with the power plants, the energy crisis.
6:07So this is finding A. The FPS analysis showed that PCBP2 condensates were sequestering a massive number of mitochondrial components, 140 of them. And not just any components. No, the really essential stuff.
6:20Part of the respiratory chain. Proteins needed for ATP synthesis. They were being physically pulled away from the mitochondria and locked inside these condensate traps. Wait, hold on. So you're saying this one protein, PCBP 2?
6:34By forming these condensates can disrupt the cell's physical organization and its energy production at the same time. Yes. With this level of direct physical evidence, it's a huge finding. This wasn't just a correlation.
6:48It was physical sequestration causing a functional breakdown. Which leads to finding B. Mitochondrial damage. By trapping all these essential parts, the structure of the mitochondria themselves just started to suffer.
6:59You could see it under the microscope. Structural damage, their internal ridges were reduced or even gone. The factory was falling apart. The function results were just as bad. Oh, absolutely. The cell went into measurable energy failure.
7:10They saw a big increase in damaging reactive oxygen species, ROS. And a drop in oxygen consumption and ATP production? A huge drop. This one condensation mechanism by hijacking mitochondrial parts directly causes the cellular energy collapse that is such a classic feature of Alzheimer's.
7:27Okay, so that's the energy crisis. How does the exact same mechanism drive the other classic AD symptom making amyloid? And that brings us to finding C amyloid regulation. Now, the condensate doesn't make amyloid directly.
7:41It controls the machinery that regulates amyloid production, specifically by stabilizing the MRNA blueprint for an enzyme called BCE one. ACE one. That's the big one. It's the molecular scissors that snipped the precursor protein to create the toxic AB peptide.
7:56So if you have more Bay AC one, you get more ammoid. You got it. And the compensates do this by trapping the cell's cleanup crew. They found that the PCBP 2 condensates were sequestering a key enzyme from the cell's waste disposal system.
8:07The nonsense mediated MRNA decay or MMD system. And specifically an enzyme called UPF1. So UPS one is supposed to be out in the cell, finding and degrading unstable MRNA blueprints, including the one for BACE one.
8:20But if UPF one gets locked away. Inside the rogue filing cabinet, exactly. By hoarding the UPF1 degradation enzyme inside the condensate, PCBP2 starves the rest of the cell of its cleanup crew. Which leaves the BECE one MRNA transcripts just floating around safe and found.
8:38Protected. Free to be translated into more and more BACE one protein, which in turn turns out more and more toxic apeptides. That is the conceptual leap. The disease isn't just a broken protein. It's a spatial dysfunction.
8:52It's the wrong things being in the wrong place, which triggers both energy failure and amyloid buildup. And they proved it. They made PCBP2 mutants that couldn't form condensates, and those mutants couldn't regulate BACE1.
9:05It proves that the physical condensation itself is the pathological step. It's the switch that flips the cell into a disease state. It is. Which logically brings us to the solution. If the problem is too much PCDP2 forming these traps, then the goal is simple.
9:19Get rid of the PCPP2. Reduce the levels and the condensates should dissolve. So they started screening for small molecules, looking for something they could get into the brain and do just that. And they found one.
9:29A small molecule called CN0928. It worked great in cell culture. Which sets up the biggest test of all, finding DCN 0928 efficacy in Vivo. This is the moment of truth. They gave CN 0928 to the 5 bifady mouse models, which are classic models for amyloid pathology.
9:49And the results. Highly encouraging. The treatment significantly dropped both PCBP2 and BACE1 protein levels in the brain, and that led to a major reduction in the number of pathological condensates, and a significant decrease in F deposit.
10:04That's the molecular result. But what about the mice themselves? Did it help them? It translated into a dramatic cognitive rescue. They use the Morris water maze? A standard test for memory and mice. Right, for spatial learning and memory.
10:16And the treated mice showed significantly reduced escape latency. They found the hidden platform faster. They spent more time searching in the right area. This wasn't just cleaning up plaques. This was reversing cognitive decline by hitting that upstream driver.
10:29This feels really significant. It shifts the entire focus from damage control to source control. It suggests PCBP2 condensation is the linchpin. The thing that connects mitochondrial dysfunction and amyloid production.
10:41It's a beautiful unified theory for a very complex disease. And crucially, it gives us a druggable target. A druggable mechanism. So let's talk about that mechanism. Because CN 0928 didn't just attack the common state directly, did it?
10:54No, and that's what's so fascinating. It has an indirect mechanism. They used chemical proteomics to figure out what the drug was actually binding to. And the target was. A protein called integrator complex subunit one or INTS one.
11:06INTS1. That's part of a bigger complex that regulates gene transcription, how genes are turned on and off. Exactly. It's a long range control system. The evidence suggests CN 0928 binds to INTS1. They even found the specific binding site, and this binding event somehow signals for the cell to down regulate PCBP2 expression.
11:25So you hit INTS one, which reduces how much PCBP2 protein is made, which in turn reduces the amount of condensation, and that alleviates the entire AD pathology. So this raises a really important question.
11:36Why is this approach better than, say, just targeting base CE1 directly? We have basic E1 inhibitors. Because direct BTCU one inhibition only tackles one downstream effect, the amyloid. By targeting INTS1 to reduce PCBP2, you're hitting the source.
11:53You're tackling both problems at once. You are. You're simultaneously protecting the mitochondria from being hijacked, and you're releasing the cleanup crew, UPF1, back into the cytoplasm to degrade base E1 MRNA naturally.
12:05You fix the energy crisis, and the amyloid problem with one drug. By modulating the fundamental physics of the cell. You're not just cleaning up the mess. You're fixing the organizational problem that made the mess in the 1st place.
12:17That is a much more robust approach, and it feels like a blueprint for other diseases too. ALS Parkinson's. They all have these aggregation problems. It opens up a whole new therapeutic class, really. One focused on regulating the physical state of proteins inside the cell.
12:32It's a huge step, but we always have to talk about limitations. What did the researchers themselves note? They pointed out 2 main things. First, the target identification was done using cell ice sates, basically a soup of cell parts, which might miss some of the dynamic interactions in a living neuron.
12:50And second, the special version of the drug they used for tracking, the biotin labeled one, it couldn't get into cells very well, which made it hard to directly confirm that CML 928 binds to INTS one in Vivo.
13:03But the fact that it works so well in the mouse model still gives you a lot of confidence in the overall mechanism. It absolutely does. It provides very strong evidence that if you reduce the abundance of this key condensate forming protein, you can reverse the whole disease cascade.
13:18Okay, let's try to synthesize this into our central insight for you, the listener. The central insight here is that Alzheimer's pathology can be driven by the pathological accumulation of this RNA binding protein, PCBP2, into liquid like condensates.
13:32And these condensates act as molecular traps. Exactly. They seize mitochondrial components and the cells cleanup machinery, like UPF1. This causes energy failure and increased BACE one translation all at the same time, which ends up creating that classic apathology.
13:47The breakthrough. The breakthrough is that you can use a small molecule, CN 0928 to target a completely different protein, INTS1, which in turn reduces PCBPK 2 levels. This indirect strategy effectively dissolves the pathological condensates and dramatically improves cognition in mouse models.
14:06It's just amazing to think that after decades of focusing on these big garbage piles, the real solution might be about just reducing the size of the internal filing cabinets. So if the fundamental issue here is this weird spatial clustering where things are located, their physical state, does this suggest that we should think of AD and other neurodegenerative disorders as fundamentally spatial diseases?
14:27I think it does. Absolutely. And if that's the new frontier, then what does this focus on spatial clustering mean for developing ultra early diagnostics? Could we develop ways to track that liquid to solid phase transition in living neurons?
14:41Maybe years before any widespread aggregation and permanent damage even begins? That transition point could be the key. It could be the next frontier for detection. A fascinating question to explore. This episode was based on an open access article under the CCBY 4.0 license.
14:58You 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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