This episode summarizes a multi-modal study that integrates exome sequencing in 402,375 UK Biobank participants with CRISPR knockdown in human white adipocytes to nominate genes and pathways that alter overall adiposity and fat distribution.
0:10I'm reading signals in a quiet cold Welcome 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.
0:28Imagine for a moment that you're looking at 2 people standing right side by side. Okay, picture that. Right. And they have the exact same body weight. They might even have like the exact same body mass index, right?
0:40Same BMI. Sure. But there is a really crucial difference. One of them carries that weight primarily around their hips and thighs, while the other carries it mostly around their waist, like belly fat. Right, central adiposity.
0:54Yeah, exactly. Even though the scale reads the exact same number, the biological reality going on inside their bodies is entirely different. One of them has a significantly lower risk of heart disease and type 2 diabetes.
1:07And the other is basically at high risk for those exact same conditions. Exactly. It all comes down to, well, genetic real estate, you know, the old saying in property, right? location, location, location.
1:17Well, it turns out that where you carry weight is just as critical to your health as how much weight you actually carry. So what really happens when our bodies decide where to unpack our cellular moving boxes of fat.
1:30I mean, that is literally one of the most important questions in modern metabolic health. For decades, the medical community, we've really focused almost exclusively on just the total amount of fat a person carries.
1:42Like just the sheer volume on the scale. Exactly. just the raw volume. But what we're looking at in this deep dive is, uh, a massive genetic investigation into the actual blueprints of human fat distribution.
1:54We are finally moving beyond the bathroom scale. We want to understand the cellular instructions that tell fat exactly where to set up shop in your body. And to unpack those instructions. We are looking at some truly groundbreaking research today.
2:07Today we celebrate the work of Nicholas Abaya, Cecilia M. Lindgren, and their teams at the University of Oxford and the Broad Institute, who have advanced our understanding of the genetics behind obesity and fat distribution.
2:18Yeah, it's an incredible multiinstitutional effort. It really is. It was recently published in the American Journal of Human Genetics. And, you know, when you look at the sheer scale of what this team pulled off, it becomes so clear that they aren't just functioning as like data scientists crunching numbers.
2:34They're acting more like molecular detectives. Like they're trying to bridge this enormous gap between a statistical probability on a computer screen and the actual biological reality inside a living breathing cell.
2:49Right. And the global context for why this detective work matters is, frankly, it's staggering. I mean, one in 4 adults worldwide is either overweight or obese. Wow, one in four. Yeah. But as your opening scenario highlighted, not all fat is created equal.
3:06There's a fundamental biological difference between central adiposity belly fat and glutial adiposity. Which is the fat stored around the hips and thighs, right. Exactly. And that distinction, I mean, it isn't just about how your clothes fit, it's really an issue of life or death.
3:19Because when we talk about belly fat, we aren't just talking about, you know, the soft, pinchable layer right under the skin. No, we are talking about something far more aggressive. The real danger with central adiposity, is the visceral fat.
3:33visceral. Yeah. This is the fact that literally wraps itself deep inside your abdominal cavity. It surrounds internal organs like your liver, your pancreas, your intestines. Oh, wow. So it's right up against the vital organs.
3:48It's choking them, basically. Visceral fat isn't just some passive storage depot, right? It's biologically active tissue. What does that mean, active tissue? It means it constantly pumps out inflammatory markers and free fatty acids directly into your portal circulation.
4:03Okay, let me pause you there to make sure I'm visualizing this correctly. The portal circulation. That's basically the express blood highway that goes straight to your liver, right? Like it bypasses the rest of your search bar.
4:13That's the perfect way to picture it. Yeah. Because visceral fat. has direct access to that express highway. It just floods the liver with inflammatory signals and excess lipids. Yeah, it's a biological assault.
4:25And that assault is what drives insulin resistance, which directly increases the risk of cardiometabolic diseases. We're talking stroke, type 2 diabetes. Right. But then subcutaneous fat, the fat right under the skin, especially around the hips and thighs, that doesn't have that direct axe.
4:40Exactly. It doesn't pump those same inflammatory markers into the liver. In fact, gluteal fat is highly protective. The data actually shows that a standard deviation increase in hip circumference can reduce the risk of type 2 diabetes by roughly 40%.
4:55Wait, 40%? Yep, independent of a person's overall weight, too. That is an incredible number. And here is the piece of the puzzle that really blew my mind. Where your body puts that fat is heavily inherited.
5:08Like, the sources point out that fat distribution, which is usually measured by the waste to hip ratio, it has a heritability of up to 56% in women. Right. And about 32% in men. It's wild. Your genes are basically acting like a biological traffic cop, directing the fat trucks either to the safe parking lot in the hips or the highly dangerous parking lot around your organs.
5:31Which brings up a massive blind spot in how we currently treat obesity honestly. No. How so? Well, considered the blockbuster weight loss drugs dominating the market right now. Yeah. The GOP1 receptor agonists.
5:44Right. The ones everyone is talking about. Exactly. They are undeniably effective at reducing overall body weight. But here is the catch. They don't actually act on the fat tissue itself. Wait, really?
5:57Yeah. They work primarily in the central nervous system. They specifically target a region of the brain called the hypothalamus to suppress your appetite, so you eat less overall, and you lose weight everywhere.
6:09Okay, let's unpack this. If fat distribution is so heavily genetic, why haven't we just made a drug that tells the body to put fat in the hips instead of the belly? I mean, that is the $1000000 question.
6:20Right, because it feels like relying entirely on appetite suppressants is like, I don't know, turning off the main water valve to your entire house just because you have a leaky faucet in the kitchen. Yeah, when what you really want is just a wrench to tighten the specific pipe under the sink.
6:33But to build that wrench, we 1st need to know exactly which genes, build those pipes in the fat tissue. And historically, you know, we've only really had a statistical understanding of this. Like looking at population charts.
6:47Right. We could look at large populations and see that certain genetic markers correlate with belly fat. But correlation doesn't tell you how the mechanism actually works inside the cell. Which brings us to the core methodology of this study, and the scale of what these researchers did to find those mechanisms is just wild.
7:04really is. So step one is basically a genetic police lineup. You have 402,375 suspects from the UK biobank. All participants of European ancestry. Huge data set. Massive. And the researchers are looking at their XM sequencing data to find the ones like loitering around the scene of the crime.
7:23In this case, unusual fat distribution. Now, for those following along, the XOM is just the part of the genome that actually codes for proteins. It's only about, what, one to 2% of your entire DNA? Yeah, very small portion.
7:35But it's where most of the known hard-hitting disease mutations happen. And they narrowed this lineup down even further, actually, by only hunting for rare protein coating variants. So not the common stuff.
7:47No, we are talking about genetic mutations that occur in less than one% of the population. Why focus on the rare ones? Well, because while common variants might just gently nudge your risk for a disease up or down, rare variants also break a gene entirely.
8:04And a broken gene gives us a much clearer signal of what that gene actually does when it's functioning normally. Oh that makes total sense. Yeah. And so they cross-reference these rare variants against 9 different physical traits related to fat distribution.
8:20Right, and they use really specific measurements for that, didn't they? They did. This included highly detailed measurements from MRI and DXA scans so they could quantify the exact volume of visceral fat versus subcutaneous fat inside the body.
8:34Okay, but just because a suspect is at the scene of the crime doesn't mean they pulled the trigger. Like, that's just statistical correlation. To find the actual mechanism, they had to take the top 14 candidate genes from that data mining exercise and bring them into the interrogation room, which, in this study, was a petritus.
8:51Yeah, they executed a monumental pivot here, from data mining straight to physical cellular biology. Which is so cool. It really is. They took human white adipose tissue living human fat cells, and grew them in vitro.
9:05Then, they used CRISPR Cast 9, the precision gene editing tool, to selectively knock down those 14 candidate genes one by one. Wait, so they just snipped out these specific genes with CRISPR to see if the fat cells got skinnier or fatter in a dish?
9:21Is it really that direct? I know it sounds like science fiction. yes. It is that direct. And to measure the result, they used a fluorescent dye called BODIPY. BODIPY. Yeah. This specific dye binds directly to neutral lipids.
9:33When a cell accumulates fat, it literally lights up under a fluorescent microscope. Oh, wow. it's totally visual. Exactly. By measuring the brightness, they could visually quantify exactly how knocking out a specific gene changed that fat cell's ability to store lipids.
9:47That is so elegant. But, I mean, if you're listening to this and wondering why it takes decades to make a good localized drug, this right here is why, isn't it? Working with human fat cells outside the body is notoriously difficult.
10:01Oh, it's incredibly frustrating work. What we are talking about here are high throughput functional assays, meaning they are testing 1000s of cells simultaneously to see how they function, not just what their DNA looks like.
10:16Right. And manipulating human adipocytes in these assays is a nightmare because fat cells are fragile. And honestly, because they are full of lipids, they float. They float. Yeah. They don't stick to the bottom of standard laboratory plates like other cells do.
10:29Oh, man, that sounds like a huge headache. It is. And because of this mechanical difficulty, most genomic studies, just stop at the statistical correlation, they publish the math and move on. But this study took the rare and technically demanding step of actually proving the math in a living cell.
10:45And the interrogation worked. Let's dive into the results of this CRISPR test, because what they found completely changes how we understand the biology of obesity. Out of all that massive population data, they found 69 genes significantly associated with fat distribution.
11:02Right, with 19 of them being highly significant. And within those findings, they uncovered something crucial called a monotonic elilic series. In 22 of those genes. Yes. Okay, I love this concept. Let me try to explain this.
11:15Instead of a gene acting like a simple on and off switch, like, you know, you either have the belly fat gene or you don't. And the Lelic series is more like a dimmer switch. Yeah exactly. The study showed a dose response relationship.
11:27The more severely a genetic variant damaged the function of the gene, the more extreme the effect was on the person's body fat percentage or waste to hip ratio. That is the perfect analogy, the dimmer switch.
11:39It proves that the gene isn't just loosely hanging around the trait. It is directly driving the dial. And when they applied CRISPR to these genes. That dimmer switch analogy played out right under the microscope.
11:49Tell me about the PR gene. Oh, PPRG. So this gene acts like the ultimate foreman on a cellular construction site. It's a master regulator transcription factor for fad cell development. So when CRISPR knocks down PPR in the Petri dish, the workers literally lose the blueprints to build the lipid droplets inside the cell.
12:08Precisely. And the results were dramatic. When P Park was knocked down. There was a massive decrease in fat accumulation. The cells showed a .25 fold change. He knew what exactly. That means they were only able to store a quarter of the fat that a normal unedited cell would store.
12:25Wow, just a quarter. Yeah. The cellular machinery basically shut down. But then on the flip side, they knocked down an entirely different gene called COL 5A3. Right. And those fat cells went in the exact opposite direction.
12:37They just gorge themselves on lipids, showing a one. 72 full increase in fat accumulation. Almost double. Yeah. So by just turning down one specific gene, the researchers could dramatically control whether a human fat cell hoarded fat or rejected it entirely.
12:52Exactly. And the researchers also looked at longitudinal health records to see how these genes play out over a human lifetime. Oh, from the UK Biobank? Yes. They looked at the age of onset for obesity in those participants.
13:04They found that rare variants in certain genes, specifically MC4R, and a gene called SLTM are tied to a much earlier lifetime onset of obesity. So if you carry a variant that breaks the function of your MC4R or SLTM gene, you get obese earlier.
13:20Right. The data shows you are statistically likely to develop obesity much earlier in life than someone with intact copies of those genes. But the SLTM gene is where the story takes a really unexpected turn.
13:31Here's where it gets really interesting. If the SLTM gene acts differently in a human than in a petri dish, What does this all mean for actually making a medicine? Yeah, the SLTM paradox is one of those fascinating takeaways from the entire paper.
13:45It's so weird It is. So in the human population data, individuals who carry rare loss of function variants in SLTM, meaning the gene is broken and not doing its job, have a higher body mass index. So broken SLTM equals more overall fat on the human being.
14:00But in the Petri dish, when the researchers use CRISPR to knock down SLTM, those isolated fat cells actually decreased their lipid accumulation. See, that is wild. A broken gene makes the living, breathing human fatter, but makes the isolated cell in the dish skinnier.
14:16How does that make any biological sense? Well, it highlights the incredible complexity of scaling up from a single cell to a whole organism. SLTM encodes a protein that regulates other management level proteins, specifically the GLI family of transcription factors.
14:31Okay, GLI. Yeah. And these transcription factors control the expression of a vast network of metabolic genes. In an isolated cell floating in a dish, turning off SLTM might directly shut down the local lipid storage machinery.
14:44Right, but a human being isn't just a giant Petri dish of floating fat cells. Exactly. In a living human, SLTM is operating within a vast interconnected system. It is expressed in the brain, in the gut, and in the immune system.
14:58Most, it's everywhere. Yeah. So a broken SLTM gene might be causing systemic changes, perhaps altering hunger signals in the brain, or changing how the gut absorbs nutrients. Right, right. And those systemic changes might ultimately drive higher overall body weight, even if the individual fat cells themselves are theoretically less efficient at storing those lipids.
15:18But if we create a targeted therapy that stops fat from going to the belly, we have to make sure it safely goes to the hips instead. If the fat doesn't go to the belly and the patient is still overeating, doesn't it end up in dangerous places like the liver?
15:32Yes, that is the exact clinical risk, and it's known as ectopic fat. At topic fat. Right. Ectopic fat is fat stored where it absolutely doesn't belong, like marbling in a steak. Oof, not a great visual for a human organ.
15:46No, definitely not. If a drug blocks fat from entering adipocytes entirely, those lipids just stay in the bloodstream. They end up in the liver, leading to fatty liver disease, or in the muscles causing severe insulin resistance.
15:58That sounds worse than just being overweight. It is. A future therapy can't just be stop storing fat. It has to be stored this fat safely. And that brings up the crucial limitations explicitly noted by the researchers regarding their Petri dish models.
16:12Right, because an in vitro, fat cell lacks an immune system, and a nervous system. And we know from other research that adipose tissue is deeply intertwined with both of those in the real world. Adipose tissue is essentially an endocrine organ.
16:26There are resident immune cells inside human fat that control inflammation. Wow. And there's also tomato sensory innervation, actual nerve endings connecting directly to the fat tissue that regulates our metabolism.
16:39So a CRISPR edit and a sterile dish doesn't show us how the immune or nervous systems will react to that change in a living patient. Exactly. And there is also a major demographic limitation we have to point out here.
16:50This study relied almost entirely on EXM data from individuals of European ancestry. Yes, that's a very important point. The researchers are very clear that to truly understand the genetics of fat distribution for all of humanity.
17:03We urgently need larger, diverse population samples. Genetics can vary significantly across different ancestries, right? Absolutely. And creating localized therapies based solely on European data means those treatments might not be universally effective.
17:17It is a well-known blind spot in modern genomics, though massive efforts are currently underway globally to correct it. That's good to hear. Yeah. But even with these limitations. What this team accomplished is a monumental achievement.
17:32By successfully bridging the gap between massive population genetics and high throughput cellular biology, they have given us a validated physical map of the genetic pathways that control our fat. To bring it all together.
17:45This research proves that our genetics dictate not just how much fat we carry, but precisely where we store it. By combining massive population databases with CRISPR editing, science is uncovering the direct cellular pathways to safely rewrote fat.
17:58It's opening the door for therapies that target the fat tissue itself. Rather than just turning off hunger in the brain. What does this mean for the future of personalized medicine? Could we one day see treatments tailored not just to your weight, but to your unique genetic map of fat distribution?
18:14This 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. If you enjoyed this, follow or subscribe in your podcast app and leave a five-star rating.
18:28If 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.
18:38Thanks for listening and join us next time as we explore more science, base by base. I'm reading signals in a quiet cold Real little typos in the overload A thousand lives in a day to close Pointing where the hidden levers go.
19:16In addition in the bloodline thread. Two kinds of proof, say the same thing, say, turn one switch down the droplet's fade. turn another More gets laid. We're tracing the way to the pathways deep. With the body learns what to store what to keep.
19:42Cut the right wire, watch the pattern change from mastermind. Nothing stays the same. In white cells, learning how to hold their shine. Stained in green, like a warning sign. Park, quiet, less build up shows, SLT, M down.
20:14Still the lipid slows, but call 583 that arise hits fast. A matrix whisper that makes it last. Not one story fits every frame, age, and sex can. Bend the claim, but the method holds, it doesn't blur. Jeans to function like a guided spur from screens to sequences we narrow the aim.
20:47So tomorrow's targets have a real name. We're tracing the way to the pathways deep. Where the body learns what to store, what to keep. Bring the gene onto the bench, let the evidence sing. Find the knot that moves the whole damn thing from mastermind.
21:12Watch the pattern change. In the lipid light. We rearrange.
