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. Glad to be here for another one So when we think about illness.
0:10I mean, we usually picture a siege, right? Like some pathogen scaling the walls, trying to breach our biological defenses. Right. Yeah. The entire architecture of our immune system evolved to repel those outside invaders.
0:25It's this beautifully orchestrated defense network that's just constantly patrolling for foreign elements. But systemic auto moon diseases kind of throw that whole siege metaphor completely out the window.
0:35You're looking at scenario where your body's internal security system suddenly declares like an all out war on your own biology. Yeah, exactly. It's friendly fire on a massive scale. And the trigger isn't a virus or a bacteria.
0:50It's simply because the cellular garbage disposal stopped working. Which is wild to think about. The mechanisms that are designed to keep you alive become the very forces tearing your tissues apart. It's a devastating internal betrayal, and historically, it's just been one of the most difficult puzzles in medicine to solve.
1:08Right. I picture the immune system here, like a highly sensitive, trigger happy security alarm. But this alarm isn't being tripped by an intruder. It's being triggered by a massive buildup of the cell's own unemptied trash.
1:22That's a great way to look at it. So the question we are exploring in this deep dive is, what really happens when this cellular trash piles up? And how could identifying one single broken molecular machine fundamentally rewrite our understanding of a complex devastating disease like lupus?
1:40Well, answering that takes us on a biological detective story straight down to the single cell level? I mean, it really shifts our entire perspective on the mechanical origins of autoimmunity. For sure.
1:49But before we start unpacking those molecular mechanics, we have to give credit where credit is due. Oh, absolutely. Today, we celebrate the work of the research teams at Liangzu Laboratory at Zedgeon University and the National Clinical Research Center of Kidney Diseases at Gin Ling Hospital, who have advanced our understanding of the genetic triggers behind systemic lupus arethmatosis.
2:09Yeah, their research really bridges the clinical reality of suffering patients with some of the most, uh, intricate genetic signaling pathways we've ever mapped. Let's start with that clinical reality.
2:21We are looking at systemic lupus array thermatosis or, you know, SLE. Right. It's a disease that is infamous for its complexity, and frankly, it's highly variable severity. Meaning it doesn't look the same at everyone.
2:34Exactly. One patient might present with, say, joint pain and a localized skin rash while another suffers catastrophic, rapid onset, kidney failure. Wow. Yeah, the global burden is immense. And untangling why the immune system mounts this massive, systemic inflammatory response is incredibly frustrating for rheumatologist.
2:52It's basically like trying to untangle a 100 different knotted fishing lines all at once. Right. And if regular SLE is a tangled mess of 100 fishing lines. Researchers usually look for simpler knots to figure out the underlying physics of the tangle right.
3:05They look at monogenic Lucas. Yes, exactly. By finding those rare cases where a single genetic mutation causes lupus-like symptoms, we get an unobstructed window into the specific pathways that can trigger the broader form of the disease.
3:20So in this study, the team focused their attention on the intracellular nucleic acid sensing pathways. Okay, so we're talking about the endosomes here. Like the biological sorting centers deep inside the cell.
3:31Right, right. Inside those endosomes sit specific receptors, TLR 7 and TLR 9, and their evolutionary purpose is to sense external viral or bacterial RNA and DNA. When they detect those foreign nucleic acids, they basically trip the wire.
3:47They trigger these massive inflammatory cascades, specifically the type I interfere on pathway and the NF Kappa B pathway. Wait, if TLR 7 and TLR 9 are looking for DNA and RNA to trigger an immune response, Isn't that incredibly dangerous?
4:02Since our own cells are full of our own DNA and RNA, How does the immune system avoid accidentally attacking us every day? That is the $1000000 question. And part of the answer lies in strict compartmentalization.
4:14Like keeping things in separate rooms. Exactly. Our genomic DNA is safely locked away in the nucleus. TLR 7 and 9 are localized in the endosomes. That's a totally different physical compartment where a material brought in from the outside environment is usually degraded.
4:30So it's a location protocol. If DNA is in the nucleus, it's ours, and it's ignored, if it ends up in the end of some sorting center, the alarm assumes it's an intruder. Right. But the problem arises when our own cellular debris, like our own worn out nucleic acids, ends up in those endosomes to be recycled or cleared out.
4:48Oh I see. If it stays there too long, those TLR sensors get confused by the accumulation and sound the alarm anyway. Which is bad. Very bad. Now, we have clearance mechanisms to prevent that buildup. But this deep dive really took off from a striking clinical observation of what happens when that exact clearance mechanism fails.
5:06Yeah, so the researchers identified 5 patients with SLE, who all presented with very severe distinct symptoms. Right. They all suffered from proliferative lupus nephritis, which involves severe inflammation and structural damage to the kidneys.
5:20That's rough It really is. They also showed significant blood abnormalities like leukopenia and anemia alongside various recurring skin rashes. So taking 5 patients with severe multi-organ autoimmune attacks, and hunting down a single broken gene out of our entire genome.
5:38I mean, that requires some heady diagnostic artillery. Oh, totally. They deployed whole XM sequencing to start. Okay. So they sequenced all the protein coating regions of the genomes of these patients and their family members too.
5:49But, you know, sequencing is just generating raw data. The real work is in the bioinformatics. sorting through the noise. Right. They ran inheritance filters, comparing the patient's exomes to their healthy parents to pinpoint variants that were shared among the affected individuals, but absent or heterozygous in the healthy relatives.
6:07Okay, so once they isolate that genetic suspect, they need to see how that specific typo is actually altering the immune system's behavior in real time, right? Exactly. So they moved to single cell RNA sequencing on the patient's peripheral blood modern nuclear cells.
6:23And this is where the sheer scale of the data becomes just staggering. Yeah, this is the massive technological leap compared to traditional bulk RNA sequencing. Because instead of blending all the circulating immune cells into a smoothie and looking at the average gene expression, you're mapping the exact inflammatory pathways, firing off in each individual cell type.
6:43You capture 1000s of individual cells and capsulate each one in a tiny microflutic droplet with a unique molecular barcode, and then you sequence the RNA. It's unbelievable that we can even do that. It really is.
6:54The data processing allows you to map out distinct clusters of cells. It's basically a needle in a haystack miracle. They could literally see which specific subpopulation of immune cells was driving the interferon overdrive.
7:08But they didn't stop at just looking at the RNA transcripts. They needed to measure the actual proteins, right? The chemical messengers of the immune system that are actually executing the attack. Right.
7:19So they utilize cytometry by time of flight, or cytuofus. I 2F, okay. Now, standard flow psychometry uses fluorescent tags to measure proteins, but you quickly run into spectral overlap. You can only measure so many colors before the light frequencies bleed into each other and the signals get muddy.
7:34Right. You just hit a physical limit on how many parameters you can observe at once. Exactly. So side 2F solves this by using heavy metal isotopes instead of fluorophores. Heavy metals. Yeah, you tag your antibodies with rare earth metals.
7:46Then you actually vaporize the cells into single ions and send them through a mass spectrometer. Wait, literally vaporize them? Literally vaporize them. The mass spectrometer then reads the distinct molecular weight of each metal tag.
8:01It allows you to measure over 40 different cellular parameters and cytokines simultaneously on 1000000s of single cells, with basically 0 signal overlap. Wow. That gives you an unprecedented high-definition map of the cytokine storm happening inside these patients.
8:19But I mean, mapping the storm is one thing. You still have to prove that the genetic typo you found in the blueprint is actually the thing causing the storm. Exactly. And that required moving from observing the patient's cells to testing the fundamental physics of the mutated protein itself.
8:33So they designed in vitro and X viva exenucleus assays. Okay, walk me through how you actually run that essay. Like, how do you measure a protein's ability to chop up DNA in a microscopic dish? So you synthesize the normal wild type version of the protein and you also synthesize the mutated version found of the patients.
8:51You place them in separate wells. Then you introduce a specific synthetic substrate, in this case, it's single stranded DNA that has a fluorescent tag attached to one end and a quenching molecule on the other.
9:01Ah, so as long as the DNA strand is physically intact, the quencher suppresses the fluorescence. The well stays dark. Exactly. But if the protein functions correctly as an exonucleus, it physically chops up the DNA strand.
9:15The fluorescent tag separates from the quencher, and the well suddenly emits light. Oh, that is so clever. Right. You put this in a fluorometer and measure the light emitted over time. By comparing the fluorescence of the wild type protein against the mutant, you get hard quantitative data on exactly how broken the machinery is.
9:35Okay, so whole XM sequencing finds the typo in the genetic blueprint. Single cell RNA sequencing shows us how the cellular factory workers are misinterpreting that blueprint, and the exonucleus essays prove that the machine they built is actually broken.
9:48That is a perfect summary. So let's reveal the culprit. What did that sequence of high tech diagnostics actually uncover? The sequencing data pinpointed biolillic misense mutations in a gene called PLD4.
10:00Okay, so a single letter change in the DNA code swapped out one crucial amino acid in the resulting protein. Yep. And that single amino acid swap fundamentally altered the 3 dimensional folding of the protein, which just destroyed its catalytic function.
10:14PLD 4 is normally an exonucleus that resides primarily in those endosomes we talked about earlier. Right, where the TLR 7 and TLR 9 security sensors are constantly monitoring. Exactly. PLD4's normal physiological role is to act as a molecular shredder.
10:30It actively cleaves single stranded DNA and RNA. By keeping the endosomes clean of this accumulating nucleic acid debris, PLD4 prevents the TLR 7 and TLR 9 sensors from getting overstimulated by our own cellular waste.
10:43I want to use an analogy here to lock this in. So think of PLD4 as a heavy-duty paper shredder in a highly secure office handling classified biological documents. Under normal circumstances, the Shredder constantly destroys the old documents, so the room stays clean.
10:57Yes. But when the PLD 4 shredder breaks, those sensitive biological documents, the single stranded DNA start piling up to the ceiling. Right. If the PLD 4 shredder brakes. The sensitive biological documents pile up.
11:10The TLR 7 and TLR 9 security cameras, see the pile, assume there's a massive security breach, and hit the panic button, flooding the body with inflammatory interferons. Exactly. And when they ran those exonucleus assays on the mutated PLD4, What happened?
11:26The wells stayed completely dark. The mutant peel before protein had completely lost its ability to cleave single stranded DNA. The catalytic activity was just obliterated. Wow. And without that molecular shredder, the downstream inflammatory pathways went into absolute overdrive.
11:42Single cell RNA sequencing data proved invaluable here too, right? Because it revealed exactly where this false alarm was originating. It was overwhelmingly concentrated in the patient's dendritic cells and monocytes.
11:54Right, which are the immune systems frontline sentinels. Dendritic cells are highly active antigen presenting cells. They interact with and activate so many other components of the adaptive immune system.
12:04So if they're panicking, everyone panics. Exactly. When a dendritic cell is locked in a hyperactive interferon state, that false alarm cascades outward, it drives the abnormal activation of B cells. D cells being the factories that produce antibodies.
12:20Right. And in this hyperactive environment, they lose their tolerance, they start producing auto antibodies, antibodies that mistakenly target the patient's own tissue. Yeah, that downstream cascade is what ultimately leads to the severe kidney damage, the skin rashes and the blood abnormality is seen in these 5 patients.
12:38Okay, so we found the broken shredder. We mapped the molecular alarm system. But having a brilliant mechanistic explanation doesn't automatically translate to a cure for the person sitting in the clinic.
12:50No, it doesn't, but it does provide the map needed to find the precise intervention point. The researchers didn't just isolate a mechanism. They essentially defined a new monogenic disease subset. Oh, right.
13:01They classified this condition as PLDD or PLD 4 deficiency disorder. Yeah. And defining the specific disorder is really the 1st step toward moving away from generalized blunt force treatments. Which is huge for autoimmute patients.
13:13Huge. Because they knew the hyperactive type I interfere on pathway was the main culprit, they could bypass broad immunosuppressants and turn to a highly targeted therapy. They focused on a drug called Bursatenib.
13:25I know birocytinib is used clinically for conditions like rheumatoid arthritis, but how does it actually help when the PLD4 shredder itself is fundamentally broken? It targets the communication relay. Interference don't just float around and magically cause inflammation.
13:40They bind to receptors on the outside of cells, which then activate a relay team of proteins inside the cell to carry the inflammatory message down to the nucleus. That relay team relies heavily on the Jexstat signaling pathway.
13:53So the J kindnesses are the runners passing the baton. Exactly. Bruceinum is a Jake inhibitor. It binds to the ATP binding site of those JK enzymes and physically blocks them from phosphorylating, meaning they can't pass the baton.
14:07You can't fix the broken POD 4 shredder, and you can't stop the TLR sensors from ringing the alarm bell inside the end of some. But by blocking the jackstat pathway, you effectively cut the wire between the alarm bell and the rest of the building.
14:21The siren is blaring, but nobody can hear it. Perfect analogy. Yes. And did it work? It did. They tested this approach on PLOV 4 deficient mouse models. They also took cells directly from the human patients, cultured them ex vivo, and treated them with barisa to nib.
14:38In both the Invivo mouse models and the human cellular models, the drug markedly suppressed the hyperactive interferon pathway. It successfully quieted the cytokine storm. It really did. I have to pause here though, because we need to look at the clinical reality.
14:53This sounds like an incredible silver bullet, but we are mostly talking about mouse models and cells in a dish here. We can't just start handing out bare sitinib to every loop as patient immediately, right?
15:02What are the limitations? Yeah, you hit the nail on the head. The leap from a lab bench to a human body is perilous, and the researchers explicitly acknowledge this. Mouse models of the immune system are incredibly sophisticated.
15:14But mice have distinct evolutionary divergences in how their immune pathways are regulated compared to humans. A mouse is not just a tiny human. No, it is not. Furthermore, suppressing an entire signaling pathway like Jack Stat, in isolated human cells, does not account for the systemic long-term side effects in a living patient.
15:34Because those pathways exist for a reason, right? Exactly, to fight off real viral infections. Broadly, cutting that alarm wire could leave the patient fatally vulnerable to opportunistic infections. It requires rigorous, structured clinical trials to find the exact therapeutic window.
15:52So it's a massive leap forward in our understanding of the mechanics, but it's not the finish line for treatment. No, but the most immediate clinical implication is diagnostic. How so? If a patient presents with severe undiagnosed systemic lupus, especially cases that manifest early in childhood with severe kidney involvement, PLD4 genetic screening could become standard practice.
16:12Oh, I see. If you run their XO and find that PLD 4 mutation, you are no longer guessing at the pathology. Right. You know the exact mechanical failure. Instead of relying immediately on broad spectrum therapies, like high dose corticosteroids that have devastating long-term side effects, and just wipe out the entire immune system.
16:31Clinicians could identify patients who would benefit specifically from targeted interventions. Exactly. They could intervene early before the systemic inflammation causes irreversible organ damage. It shifts the entire paradigm of autoimmune treatment from reacting to the downstream symptoms to intercepting the root genetic cause.
16:50It's absolutely fascinating. It really is a game changer. Let's synthesize all of this so you have the core takeaway from this deep dive. Mutations in the PLD 4 gene disable the body's ability to clear out single stranded nucleic acids, triggering a severe hyper-inflammatory autoimmune response now classified as PLDD.
17:09By identifying this precise genetic misstep, scientists can bypass blunt immunosuppressants and point directly toward targeted therapies like JJ inhibitors, offering a customized lifeline to patients. From a broken molecular shredder to a targeted pharmacological wire cutter.
17:23What does this mean for the future of diagnosing and treating mysterious autoimmune diseases? I think we're just scratching the surface, honestly. This episode was based on an open access article under the CCBY 4.0 license.
17:36You 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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