Episode Transcript
[00:00:20] Speaker A: Welcome to Base by Base, the papercast that brings genomics to you wherever you are. Thanks for listening and don't forget to to follow and rate us in your podcast app. Base by Bass is now on YouTube too.
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[00:00:36] Speaker B: Glad to be here for another deep dive.
[00:00:38] Speaker A: So, to kick things off today, I want you to imagine a really bizarre biological paradox. Picture an animal that's just exhibiting wildly hyperactive behavior.
[00:00:48] Speaker B: Like constantly moving around.
[00:00:50] Speaker A: Yeah. Moving constantly, taking abnormal risks, showing almost zero anxiety. And logically, you know, if you were to peer inside the animal's brain, you would assume the neural circuitry is just running hot.
[00:01:01] Speaker B: Oh, absolutely. You'd picture the brain cells, the neurons, just firing out of control in this chaotic electrical storm.
[00:01:07] Speaker A: Right, exactly. But what if you look directly at those specific neurons and discover they are actually firing less? Like they are sluggish, they are diminished.
[00:01:17] Speaker B: It's a massive disconnect.
[00:01:19] Speaker A: It really is. We have this biological situation where a quiet underactive neuron is somehow driving an intensely noisy hyperactive behavioral state.
[00:01:28] Speaker B: And you know, that completely flips our standard assumptions about how the brain works. We have this natural tendency to think that loud behavior equals loud cells.
[00:01:38] Speaker A: Yeah. Which makes intuitive sense.
[00:01:39] Speaker B: Right. But to figure out how a quiet underactive neuron creates a manic like state, we have to kind of pull the camera back. We have to look past the electrical firing of the neurons themselves and look at the physical architecture of the brain.
[00:01:53] Speaker A: The structural stuff.
[00:01:54] Speaker B: Exactly. The scaffolding, the white matter insulation, and the literal cellular docking ports where these cells actually connect to each other.
[00:02:02] Speaker A: Well, today we celebrate the work of Se Yoon Yoon, Peter Penzes and their team at Northwestern University Feinberg School of Medicine, who have advanced our understanding of the genetic risk factors for neuropsychiatric conditions.
[00:02:13] Speaker B: Their recent research tackles this exact paradox we're talking about, and it centers on a specific gene called ANK3.
[00:02:21] Speaker A: Okay, let's unpack this, because ANK3 is a pretty big deal, right?
[00:02:25] Speaker B: Oh, in the world of psychiatric genetics, ANK3 is a heavy hitter. Like large scale global studies, genome wide association studies that look at hundreds of thousands of people have repeatedly flagged Ank3 as a major genetic risk factor for bipolar disorder and schizophrenia.
Wow. Yeah. And we'd known about this statistical link for years. But the barrier we keep running into is the mechanism. Because knowing a gene is associated with a condition tells you basically nothing about what that gene is actually doing on the factory floor of the brain.
[00:02:57] Speaker A: Right. It's just a correlation at that point. So if we look at that Factory floor, the Ank3 gene codes for a protein called anchirin G. Let's try to visualize what anchiron G actually does.
[00:03:09] Speaker B: I like to think of it structurally.
[00:03:11] Speaker A: Yeah. If a neuron is like a skyscraper, enchyrin G is the critical scaffolding, or like the rebar built into the foundation and the upper floors.
[00:03:19] Speaker B: That's a great analogy.
[00:03:21] Speaker A: It sits at the axon initial segment, which is the exact spot where the neuron decides to fire its electrical signal. And it sits at the synapses, the specialized ports, where it connects to other cells.
[00:03:32] Speaker B: It acts as a physical tether.
[00:03:34] Speaker A: Exactly. It holds the cell's machinery like the ion channels, which locked into their proper places. So, obviously, if you start ripping that structural rebar out of the building, the whole function of the skyscraper is going to warp.
[00:03:45] Speaker B: And you aren't just warping the one skyscraper. You might be altering the entire city block's infrastructure.
[00:03:52] Speaker A: Right.
[00:03:54] Speaker B: So to test what happens when that rebar is removed, the Northwestern team used mouse models. But before we get into the mechanics of how they did this, we really need to set a firm boundary on what we are looking at here.
[00:04:07] Speaker A: Important disclaimer time.
[00:04:08] Speaker B: Yes. They studied male mice, and these mice are modeling specific bipolar like traits, Specifically hyperactivity and a lack of normal anxiety.
[00:04:19] Speaker A: So we aren't saying these mice have bipolar disorder.
[00:04:22] Speaker B: No, we definitely aren't. Human psychiatric disorders involve, you know, incredibly complex cognitive and emotional and social dimensions.
[00:04:31] Speaker A: Things you can't see in a mouse.
[00:04:32] Speaker B: Right. It simply cannot be perfectly replicated in an animal model. But what we can do is study the biological roots of specific behavioral traits that are tied to those genetic risk factors.
[00:04:44] Speaker A: Okay, that makes sense. So we have these male mice, and the researchers want to rip the rebar out of the skyscraper. They want to delete the ank3 gene.
[00:04:53] Speaker B: Yes, but they didn't just knock it out globally across the whole body from conception.
[00:04:57] Speaker A: Right. They use something called CRE recombinase technology to be incredibly precise. Right.
[00:05:03] Speaker B: Yeah. CRE recombinase is essentially molecular wizardry. It's this genetic tool that acts like highly specific programmable molecular scissors. So the researchers can engineer the mouse so that the ANC3 gene is only deleted in a very specific type of
[00:05:19] Speaker A: cell, which in this case, is the forebrain excitatory neurons.
[00:05:23] Speaker B: Exactly. But even more crucially, they can control when those scissors activate. So they set up two distinct timelines for the mice.
[00:05:32] Speaker A: Okay, what were the timelines?
[00:05:33] Speaker B: Well, in One group, they used a driver called EMX1CRE to delete the gene prenatally, like, way before the mouse was even born. And in the second group, they used Cam2Alpha CRE to wait and delete the gene much later, when the mouse was in adolescence and adulthood.
[00:05:49] Speaker A: Wait, if the rebar's getting removed either way, why go through the immense effort of creating two completely different developmental timelines?
[00:05:56] Speaker B: Because the brain is not a static organ. I mean, building a house from scratch is very different from renovating a house that's already built and lived in.
[00:06:03] Speaker A: Oh, I see.
[00:06:04] Speaker B: Yeah. In developmental biology, if a gene is missing during fetal development, the brain might wire itself entirely differently to compensate. Losing a gene early often has these cascading severe effects.
[00:06:16] Speaker A: So they wanted to see if adult loss was different.
[00:06:19] Speaker B: Right. They hypothesized that pulling the rebar out before the skyscraper is built would yield a vastly different behavioral and cellular outcome compared to pulling it out in an adult brain where all the wiring is already established.
[00:06:31] Speaker A: So they have these two timelines. Early developmental loss versus adult loss. And they need to see how this changes the mice, starting with behavior. So they put them through several behavioral assays.
[00:06:41] Speaker B: The standard suite of tests.
[00:06:42] Speaker A: Yeah, like the open field test, the elevated zero maze, and the forced swim test. Let's break down what these actually measure for our listeners.
[00:06:49] Speaker B: Sure. So prey animals, like mice, have a natural instinct called thigmotaxis. They like to hug the walls because
[00:06:57] Speaker A: they don't want to be eaten.
[00:06:58] Speaker B: Exactly. They stay in dark, enclosed spaces because out in the open, they're vulnerable to predators.
So in an elevated zero maze, which is basically a raised circular track where two sections have high walls and. And two sections are totally exposed ledges,
[00:07:13] Speaker A: a typical mouse would just cautiously stick to the walled sections.
[00:07:16] Speaker B: Right, Right. So if a mouse is spending abnormal amounts of time running around on the exposed ledges, it's displaying a significant reduction in anxiety like behavior. It's basically taking massive risks.
[00:07:27] Speaker A: And the open field test is pretty similar. Just tracking how far and fast they run around a big empty box to measure basal locomotion, or hyperactivity.
[00:07:35] Speaker B: Exactly.
[00:07:36] Speaker A: And then the forced swim test evaluates how quickly they give up trying to escape water, which is a classic measure for depression like traits. So did the timeline actually matter? Did the mice who lost the gene before birth act differently than the mice who lost it as adults?
[00:07:51] Speaker B: Surprisingly, the timing didn't change the traits at all.
[00:07:54] Speaker A: Really?
[00:07:55] Speaker B: Yeah. We saw striking convergent behavioral abnormalities in both groups. Whether the gene was deleted prenatally or in Adulthood, the male mice became wildly hyperactive.
[00:08:05] Speaker A: So they were just running constantly?
[00:08:07] Speaker B: Yes. They traveled way further. In the open field test, they showed severely reduced anxiety in the zero maze, marching right out onto the exposed ledges. And they showed decreased depression like responses in the swim test.
[00:08:19] Speaker A: So basically, just maintaining this scaffolding in an adult brain is every bit as critical for regulating behavior as it is during early fetal development.
[00:08:28] Speaker B: Yeah. You can't just build the brain properly and assume it will run itself. It requires constant structural maintenance.
[00:08:34] Speaker A: Wow. But this brings us back to the paradox we opened with. The mice are running around like crazy. The behavioral output is extremely loud. So they decide to look at the cellular output using calcium imaging.
[00:08:48] Speaker B: Right. Calcium imaging lets researchers watch living neurons fire in real time. They introduce this floating fluorescent indicator called gcamp into the neurons.
[00:08:57] Speaker A: So it's essentially like installing a microscopic dimmer switch inside the cell that discloses neon green every time electrical current passes through it.
[00:09:05] Speaker B: That's a good way to picture it. When a neuron fires an action, potential calcium ions flood into the cell. This GCaMP sensor binds to that calcium, changes its shape, and emits light.
[00:09:17] Speaker A: So using two photon laser scanning microscopes on brain slices, you can physically watch the neural circuits lighting up.
[00:09:24] Speaker B: Exactly. And you'd assume, given the manic like behavior, that these brain slices were just glowing like a Christmas tree, but they weren't.
[00:09:32] Speaker A: What's fascinating here is they were dim.
[00:09:34] Speaker B: They were very dim. The spontaneous neuronal activity in cultured neurons just dropped. And when the researchers looked at acute brain slices and artificially stimulated the neurons to force them to fire, the peak calcium amplitude, the brightness and strength of that firing was significantly blunted.
[00:09:54] Speaker A: So the neurons missing the ANC3 gene became less active. Not overactive, but less active.
[00:10:01] Speaker B: Yes, absolutely less active. We have to be very clear on that. The loss of that rebar, that anchiron G scaffolding, clearly depressed the neuron's ability to fire effectively.
[00:10:13] Speaker A: The cell is basically physically struggling to depolarize and send a strong signal.
[00:10:17] Speaker B: Right. Because the structural integrity at the axon initial segment is fundamentally compromised. So the neuron goes quiet, but the behavior gets loud.
[00:10:27] Speaker A: It's so counterintuitive.
[00:10:30] Speaker B: So to figure out how a quiet cell causes this behavioral cascade, they had to look at what was happening to the actual molecular inventory of the brain.
[00:10:38] Speaker A: And to do that, they used a technique called TMT LC Ms. Proteomics to analyze the brain tissue.
[00:10:44] Speaker B: Okay, let's translate that for everyone.
[00:10:46] Speaker A: Mass spectrometry is basically taking the brain tissue, separating the different cellular Components in a centrifuge, chopping all the proteins up, tagging them with heavy molecular weights, and running them through a magnetic field. Right?
[00:10:58] Speaker B: Yep. It identifies exactly what proteins are present and in what quantities.
[00:11:02] Speaker A: And they specifically looked at the P2 fraction. Let's explain what that is, because it becomes incredibly important later in the deep dive.
[00:11:10] Speaker B: So when you spin brain tissue in a centrifuge, it separates out based on density. The p2 fraction is the membrane enriched fraction. It's basically the outer envelope of the cells and the general surrounding machinery.
[00:11:23] Speaker A: Got it.
[00:11:24] Speaker B: And when they analyzed this general P2 fraction in the brains of the mice, missing ANC3, they found massive proteomic remodeling. 75 different proteins were significantly altered.
[00:11:36] Speaker A: So the brain is clearly trying to adapt to the missing scaffolding. And some of the proteins that were upregulated, meaning the brain started manufacturing more of them, are known risk genes for entirely different disorders.
[00:11:48] Speaker B: Yeah, that was surprising.
[00:11:50] Speaker A: Like a protein called Ryr2, which is linked to schizophrenia, and Talc2, which is linked to autism spectrum disorder. Both of those just spiked concentration.
[00:11:59] Speaker B: It suggests the neural network is desperately trying to compensate for the missing anchiron G by leaning on these other structural and signaling pathways. But amidst all of this remodeling, there was one massive, unexpected drop.
[00:12:14] Speaker A: And here's where it gets really interesting. A protein called myelin basic protein, or mbp, was severely downregulated.
[00:12:23] Speaker B: Severely.
[00:12:23] Speaker A: Now, let me make sure I'm not jumping to conclusions here, because the name MBP is a dead giveaway. It's a critical structural component of myelin, which is the fatty insulation that wraps around nerve axons to help signals travel efficiently.
[00:12:36] Speaker B: Correct.
[00:12:37] Speaker A: But myelin isn't made by the excitatory neurons where they deleted the ANC3 gene.
[00:12:43] Speaker B: You've hit on the exact reason this was such a shock. MBP is produced by an entirely different class of support cells in the brain called oligodendrocytes.
[00:12:53] Speaker A: Wow.
[00:12:53] Speaker B: Yeah. The researchers deleted a gene inside a neuron, and a vital insulation protein produced by a completely different neighbor cell just crashed.
[00:13:02] Speaker A: So, wait, does that mean the insulation is literally melting away? Like, do these mice have less white matter? Are they experiencing active demyelination?
[00:13:11] Speaker B: We have to be incredibly careful here, because it is totally natural to assume that less MBP means the myelin sheath is degrading.
[00:13:19] Speaker A: Right.
[00:13:19] Speaker B: But when the researchers used super resolution microscopy to physically look at the structure, the myelin sheath diameter did not change significantly.
[00:13:27] Speaker A: Oh, really?
[00:13:28] Speaker B: Yeah, the physical insulation was still there, wrapping the nerves. What changed was the molecular composition.
Specifically, a massive reduction in the expression of the MBP protein inside that insulation.
And. But we still don't know the specific cell type behind that lower MBP signal.
[00:13:46] Speaker A: So we need to call it reduced MBP expression. Not proven. Myelin loss. The pipe isn't broken, but the material the pipe is made of is chemically altered.
[00:13:56] Speaker B: Exactly. And it wasn't even a global issue across the whole brain.
[00:14:00] Speaker A: It was hyperlocalized, wasn't it?
[00:14:02] Speaker B: Yes. Using immunofluorescence to map the brain, they found the drop in MBP was highly specific to layers 2, 3, 3 and 4 of the primary somatosensory cortex, which
[00:14:13] Speaker A: are the specific upper layers of the cortex responsible for processing touch and sensory input from the outside world.
[00:14:19] Speaker B: Right. The deeper layers, like layer five, and entirely different regions like the hippocampus were completely untouched. The MBP levels there were totally normal.
[00:14:29] Speaker A: So we have a highly localized, highly specific deficit in the molecular makeup of the brains. In the insulation.
Now, knowing that deleting inc3 causes this specific drop in MBP alongside these hyperactive traits, the researchers introduced a final clinical variable, which was Lithium.
[00:14:47] Speaker B: Right. Lithium, which is one of the oldest, most foundational mood stabilizers used in human psychiatry to treat bipolar disorder.
[00:14:55] Speaker A: So they fed the mice a diet enriched with lithium for three weeks. If they gave these hyperactive mice lithium, did it calm them down?
[00:15:03] Speaker B: Well, this specific paper actually didn't retest their behavior.
[00:15:07] Speaker A: Wait, they didn't?
[00:15:08] Speaker B: No, because they didn't really need to. An earlier study using this exact same mouse model already proved that chronic lithium treatment rescues the behavioral deficits. It reverses the hyperactivity.
[00:15:20] Speaker A: Oh, I see.
[00:15:21] Speaker B: The question this paper wanted to answer was, if we know lithium fixes the behavior behavior, what is it doing to the proteins to achieve that? Is it going in and fixing all 75 of those altered proteins?
[00:15:33] Speaker A: Right. Does it act like a biological factory reset? Like, does it just push the big red button and force the entire P2 membrane fraction back to factory settings?
[00:15:42] Speaker B: It absolutely does not. The effects of lithium were surgically precise when they analyzed that broad P2 membrane fraction. Again, lithium did. Didn't fix the MBP expression. It was still severely downregulated.
[00:15:56] Speaker C: Really?
[00:15:56] Speaker B: And it completely ignored those upregulated risk proteins we talked about, YR2 and Tauic 2. They remained totally elevated, untouched by the lithium.
[00:16:06] Speaker A: So we definitely shouldn't say lithium reversed the proteome. But if it didn't fix the general cell membrane, how is it fixing the behavior?
[00:16:14] Speaker B: They had to dig deeper into a totally different Cellular compartment.
They looked at the P3 fraction.
[00:16:20] Speaker A: Okay, remind us how that's different.
[00:16:22] Speaker B: Remember how P2 is the general membrane envelope? Well, the P3 fraction is much denser. It is the postsynaptic density enriched fraction.
[00:16:31] Speaker A: The synapses.
[00:16:32] Speaker B: Right. It represents the highly specialized docking ports. The exact microscopic junctions where two neurons physically connect and communicate.
[00:16:40] Speaker A: The actual point of contact.
[00:16:42] Speaker B: Exactly.
And in that highly specific P3 synaptic fraction, chronic lithium treatment completely restored MBP expression back to healthy, normal levels.
[00:16:52] Speaker A: That is wild. It selectively rescued the insulation protein strictly at the synaptic docking port, while completely ignoring the rest of the cellular membrane.
[00:17:02] Speaker B: It is wildly specific, but, you know,
[00:17:05] Speaker A: we still have a missing puzzle piece here. So what does this all mean? We. We have this cascade of events. You delete a gene in a neuron, the neuron gets quiet, and somehow a protein made by an oligodendrocyte neighbor drops in a specific cortical layer.
[00:17:19] Speaker B: Right.
[00:17:21] Speaker A: How does a quiet neuron cause a drop in an insulation protein made by a completely different cell?
[00:17:26] Speaker B: Well, this is the frontier of the research. The exact biological mechanism remains unknown, but the researchers put forward a highly compelling hypothesis.
[00:17:36] Speaker A: Okay, let's hear it.
[00:17:37] Speaker B: It relies on axoglial signaling. Oligodendrocytes don't just blindly wrap nerves in myelin. They actually rely on constant electrical and chemical text messages from the neurons to know how to maintain that insulation. It is a bidirectional communication loop.
[00:17:53] Speaker A: Oh, wow. And because the neurons missing ANC3 are firing less, you know, their peak calcium amplitudes are blunted. They simply aren't sending the text messages.
[00:18:03] Speaker B: That is the leading hypothesis. Because the excitatory neurons are sluggish and underactive, they fail to send the necessary signals that command the neighboring oligodendrocytes to maintain mpp.
[00:18:14] Speaker A: So the neuron's inability to fire properly creates a local communication breakdown in the sensory cortex.
[00:18:20] Speaker B: Exactly. Which leads to this targeted drop in the insulation protein.
[00:18:24] Speaker A: If we connect this to the bigger picture, what does that lithium finding tell us about. About how mood stabilizers actually work? I mean, we tend to think of psychiatric drugs as just broadly calming the brain down. Like turning down a global volume dial.
[00:18:38] Speaker B: Right, but this research challenges that global volume dial concept entirely. Lithium's highly selective compartment specific restoration of MBP specifically at the P3 synaptic fraction suggests something profound.
[00:18:52] Speaker A: Which is?
[00:18:53] Speaker B: It suggests that mood stabilizers might exert their therapeutic effects, at least in part, by targeting the health of the white matter and reinforcing the structural integrity of the synapse itself. It isn't just silencing noisy cells. It is physically repairing the axoglial communication infrastructure right at the site where neurons connect.
[00:19:14] Speaker A: It is repairing the city block, not just the skyscraper.
[00:19:17] Speaker B: That's a perfect way to put it.
[00:19:20] Speaker A: But as we navigate this, we definitely have to respect the boundaries of the data. For you listening, the limitations here are important markers for where the science goes next. First of all, they only studied male mice, right? And as we noted earlier, we are looking at specific behavioral traits, not the full spectrum of a human psychiatric disorder.
[00:19:39] Speaker B: Absolutely. And while that axoglial communication breakdown is a beautiful hypothesis, the exact molecular skill signals between the underactive neuron and the oligodendrocyte remain an open question for future studies to untangle.
[00:19:53] Speaker A: Those limitations are exactly what give the next generation of researchers their marching orders.
[00:19:58] Speaker B: Very true. But even with those boundaries firmly in place, I think the central insight we can extract from this deep dive is incredibly clear.
[00:20:06] Speaker A: Summarize it for us.
[00:20:08] Speaker B: Deleting the ANK3 risk gene in adult experience, excitatory neurons paradoxically reduces their cellular activity while driving a wildly hyperactive behavioral state.
This loss triggers a surprising targeted drop in myelin basic protein expression across specific cortical layers. And that highly specific deficit in the brain's insulation network is something that chronic lithium treatment can partially restore right at the synapse.
[00:20:34] Speaker A: We spent so much time looking at the number neurons trying to figure out why they are misfiring when the real culprit might be the physical environment they are sitting in.
[00:20:43] Speaker B: It changes the entire paradigm, which raises
[00:20:45] Speaker A: an important question to think what does this mean for how we design future psychiatric treatments? Should we be looking past the neurons themselves and focusing on the insulation that connects them?
This episode was based on an open Access article under the CC BY 4.0 license. You 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 five star rating. If you'd like to support our work, use the donation link in the description now. Stay with us for an original track created especially for this episode and inspired by the article you've just heard about. Thanks for listening and join us next time as we explore more science. Base by base.
[00:21:57] Speaker C: Held the current to the fire the rooms upstairs went quiet one switch at a time.
Still it's still humming just below the line on the street I'm moving faster than before Every door is open and I'm not afraid anymore the signal moing walls is running.
On.
Cool around the cable came and sparse and light on floors two, three and four, but five was wound up tight. The rappers spun by strangers in a different room and no one knows yet how the quiet reached them through the gloom, the pale solar glowing in a glass of Rayleigh. One strip of silver back a little on the lane, but the other pieces scattered on the floor stay right where they landed, Same as before, running on the surface dimmer underneath a city wide away.
The lower.
Sa.
