Microbiome & Gut-Immune Interactions in Obesity & Metabolic Health | June Round | #178

About the guest: June Round, PhD is a microbiologist whose lab at the University of Utah studies microbiome-host interactions, gut microbiota, immunity, metabolism, obesity, and other disorders.

Episode summary: Nick and Dr. Round discuss: how the immune system and gut microbiome interact; dietary fiber & short-chain fatty acid production by gut microbes; nutrient absorption; obesity & metabolic syndrome; type I diabetes; cleanliness, development & the “hygiene hypothesis”; and more.

Related episodes:

* M&M #133: Infant Microbiome & Breast Milk, Oral Microbiome & Cavities, Gut Health, Fiber, Probiotics, Diet, Sex Hormones, Soy Foods & Estrogens | Carolina Tropini

* M&M #103: Connections Between Microbiome, Exercise, Diet, Metabolism, Circadian Rhythms, Endocannabinoids & Health | Christoph Thaiss

*This content is never meant to serve as medical advice.

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* Episode transcript below.

Full AI-generated transcript below. Beware of typos & mistranslations!

Nick Jikomes 0:25

Whether food, drugs or ideas, what you consume, influences, who you become. On the mind and matter podcast, we learn together from the best scientists and thinkers alive today about how your mind body reacts to what you feed it before starting mind and matter, I spent 10 years in academia doing scientific research. I got a PhD in neuroscience, where I focused on neuroendocrinology and the neurobiology of behavior, and before that, I specialized in molecular developmental and evolutionary genetics. I use my scientific background to help parse and translate the information that guests share on the podcast. In addition to the podcast, I write long form written content inspired by the show, where I integrate what I've learned across episodes. I also have a free weekly newsletter where I provide you with upcoming guests, share links and provide commentary on scientific studies and research that I'm reading and more, visit mindandmatter.substack.com to find all of my content. This episode is ad free, and I rely on my audience to support my efforts. If you're getting value from this content, please consider becoming a paid subscriber to the minded matter substack for just $5 a month, you'll get early access to episodes and other content, full episode transcripts, and I'll prioritize answering your questions in emails and the comments sections. You can also support me by checking out the links in the episode description to my affiliate partners who make various health and wellness products that I use and enjoy myself, you'll receive a discount and help support the podcast that way. And if you want the benefits of a paid subscription, but it's not in your budget, simply sign up for my free weekly newsletter. Send me an email, and I'll give you a complimentary paid subscription. Word of mouth is the best way to help the podcast grow. So if you like what I'm doing, please share your favorite episodes with family and friends. The purpose of the podcast is to provide you with information obtained largely from primary sources, the people doing the research and producing new knowledge. This content is never meant to serve as medical advice. And with that, enjoy the episode. Thanks

June Round 2:22

for watching. Appreciate it. Can you start

Nick Jikomes 2:24

off by just telling everyone a little bit about who you are and what your lab studies?

June Round 2:29

Sure. So I'm at the University of Utah. I'm in the Division of Microbiology and Immunology in the department of pathology, and my lab is interested in the interaction between the commensal microbes that live on your body and the immune system, and we're really interested in how these organisms promote health. So I think a lot of people, when they think about microbes, they think about disease. They think about pathogenesis. Of course, they equate microbes to the pandemic. They're always just thinking about getting rid of microbes. But we think about microbes in a very different way. We think that there's a lot of microbes that are present on a healthy body, and our real interest is identifying those microbes and how we might be able to utilize them to prevent diseases.

Nick Jikomes 3:24

And most people, you know, when you start talking about the microbiome, people talk about good versus bad bacteria. It's intuitive as to why they're doing that, right? Bad bacteria would be, you know, a pathogen, something that could make you sick or even kill you, potentially a good bacteria, you know, I guess, what's implied there is that it's contributing something to your health or to the functioning of the organism, potentially even something that's necessary. Do you think it makes sense to talk about good versus bad bacteria? And if so, what does good mean to you? Exactly,

June Round 3:55

it's such a good question. Nick, I guess I can't help but think of good versus bad, because a lot of our studies have identified bacteria that are beneficial, but I think in reality, it's definitely more of a spectrum. Good bugs can go bad, for sure. There can be organisms in your body that might be providing you a benefit, and then, if they're provided an opportunity, let's say they get out of the gut and into the systemic part of your body, they could cause a problem. So I think, or I think what you're hinting at is absolutely right, and that's not, there's not always good bugs and always bad bugs.

Nick Jikomes 4:37

So some of the good ones can become bad. And you know, my understanding is that this often means, you know, they have to sort of be in the right place. They have to be contained in the right area. And if they get out of where they're supposed to be, quote, unquote, then, as you said, they can become bad.

June Round 4:54

That's right, yeah, definitely. They need to be contained. Most of our microbiome lives in the intestine. In. So certainly, if those microbes get out, let's say they get in your liver or in your blood, they're, they're going to cause problems. Although, you know, most of them are highly anaerobic, so they, you know, can't survive in highly oxygenated areas. So most of them will, will rapidly die. But yes, if they get out of the out of the compartment, they can do some bad things. Yeah,

Nick Jikomes 5:23

and, you know, I've had, I've had microbiome people on before, and we've talked about various aspects of it. So my understanding is basically, right, we've got our immune system. You've got microbes in your gut and elsewhere, and the immune system is sort of, there's sort of a delicate balance there. On the one hand, you don't want to destroy some of these microbes, but the other hand, you want to contain them, keep them at bay, prevent them from going where they're not supposed to be. Can you give us just a general, basic sense for some of the communication that happens between the immune system and the microbiome? Sure,

June Round 5:55

definitely. I'll focus, I guess, on the things that my lab studies, because I know that stuff best. So we're really interested in antibodies. So most people are familiar with what antibodies are, but they're molecules that B cells produce, and you make a ton of them in your gut. You, the average human makes about two grams a day of an antibody called IgA, and these antibodies are one of the primary ways in which we contain our microbiome. So these antibodies are very specific for microbes. You know, there's lots of different parts of your immune system. Some of your immune system is very general and just recognizes, you know, cell wall, components of bacteria. But there's another part of your immune system which is very specific, and this is the part that antibodies are part of. So these antibodies are highly specific for the microbes in your gut, and they help to control them. And they don't just they do keep them contained in their area like we were just talking about, but they also control the types of molecules that they let those bacteria Express. Bacteria or fungi are viruses. I should, I should point out so they don't let, they don't let organisms Express molecules that are harmful to the host. So if there is a harmful toxin or adhesion or something that makes that organism, you know, invasive to the host. Antibodies will target it, and that bacteria will down regulate expression of it. So it's not about always getting rid of the bacteria. It's kind of about controlling their function, their behavior,

Nick Jikomes 7:38

I see. So, so it sounds like we IgA, this antibody we produce. We produce quite a lot of it. And if I'm hearing you correctly, you know, normally, when I sort of naively think about antibodies, you sort of mass produce them when you get sick, and they sort of just cover the entire outside portion of a bug, and then that's sort of a step towards destroying that bug. But it sounds like these IGA antibodies. They can actually be used not to sort of destroy or completely suffocate these microbes, but they actually just control, sort of, there's sort of a molecular communication there, and it controls what the pathogens are actually making molecularly. Yeah,

June Round 8:16

that's a great interpretation of it. And most people think like you Nick where they think about the mass production of antibodies, and they're in our blood, and their whole function is to tag a microbe for destruction, and IGA does do that in the gut. It just IGA is different in the sense from other antibodies in the blood, because it doesn't mount. There's no inflammatory response associated with IgA, its sole purpose is to target those organisms, and it does get rid of, you know, basically it groups the organisms that it wants to get rid of together, and then you will essentially poop it out. So there is some eradication that happens. But ultimately those bacteria, because of that response, will down regulate those those molecules. And,

Nick Jikomes 9:05

you know, before we get into some of the specifics around some of the work that you've done, some of your recent studies, so when we say that there's good bacteria, and you know, with the caveat that good bacteria could become bad, and things are a spectrum like, what are some of the major things that we know good bacteria generally do. Is it that they are providing key nutrients that we can't really produce otherwise or absorb otherwise? Is it they're sort of merely taking up space to box out pathogens like, what are some of the good things that tend to come from these gut microbes? Well,

June Round 9:37

I think you named, you know, some of the top two that people think about is, first of all, they take up a ton of space that kind of excludes any pathogenic bacteria. This is actually like a really important function of the microbiota, because they have evolved to live with us peacefully, whereas pathogens haven't. But by them taking up the space. Yes, that prevents us from getting sick, and C difficile is probably one of the best examples. So if you undergo antibiotic treatment, you kill a lot of those commensal microbes, and then C Diff has an opportunity to bloom, and this causes a lot of people problems. Another major benefit of bacteria is indeed, metabolism. So they do, you know, we can't process a lot of the fibers that we eat, like cellulose in plants. Our microbes help us extract energy and things that we might not normally extract. They can also, they also produce molecules that help absorption of certain things like lipids and sugars, they can also prevent absorption of things that perhaps are not good for us. So we still don't understand fully their metabolic capabilities, but we know that they're really important for metabolism. And then, of course, one of the major things, and that's what we study in my lab, is that they're really important in teaching your immune system about what to fight off and how to fight it off. So we in our lab, we use germ free mice, which maybe you've had previous guests talk about, but these are mice that have no microbiome of their own. And if you infect these animals with any sort of pathogen, they basically just die because, and it's largely because their immune system hasn't been taught how to fight off that pathogen. So, so it's like really important for our immune system maturation,

Nick Jikomes 11:39

yes, and the immune system has to be trained across development in order to function properly and effectively at getting rid of pathogens. You're saying, if you create animals that don't have a microbiome, basically there's no bacteria living inside of them, or other microbes, their immune systems just don't learn how to how to function

June Round 11:58

properly. That's right, yeah. So if you compare their immune system to that of a normal animal with a normal microbiota, they're missing a lot of immune cell populations, or the immune system populations that are there are very naive, or they're, you know, reduced in number. So that's it's a really important thing our microbiota does is to teach our immune system. And

Nick Jikomes 12:21

when you say germ free animals, how are you making these? Is this like a genetic thing? Or do you have to give them lifelong, you know, antibiotic treatment for birth,

June Round 12:30

so the way the original so we don't antibiotic treat these germ free animals. They basically live in these little bubbles. And you have to be very careful about the food you feed them. And we just have to keep them in the bubbles and only give them, you know, sterile food. The way the original germ free animal was created was that you had to do a C section of a pregnant mouse mother, and then those babies, they're like beads on a string. So you basically plump them in, like a plop them in a little sterile solution, and then you place them in this bubble, and then you take them out of their sack, and someone had to hand feed the first germ free mice ever made, because there was no mothers in the Oh, wow.

Nick Jikomes 13:20

So, so a couple of things here, like this is just sort of a lineage that's been going forever like this, since you made it, since people made it.

June Round 13:28

Yes. So now there are facilities around the country that maintain these animals germ free. And anytime you want to read or you can re derive any animal germ free, and you just have to take it through this process, but now they're now you can use the germ free moms that are currently in the bubbles as surrogate mothers. Yeah,

Nick Jikomes 13:47

yeah. And, you know, I don't necessarily know if this is your area, and I don't think we'll go into this too much, but, but I want to ask, because it's interesting. So you said, you know, when these mice were created, a C section is done. The little developing mice were taken out. One thing that's kind of implied there is that the microbiome they would have had would have come from the birth process. It would have been seeded by the mother, to a large extent. Can you talk a little bit about that? Is that basically how our microbiome of most animals get started? Yeah.

June Round 14:19

So at least in mammals, that is the case you acquire. You're fairly sterile when you were born. There's like, you know, contention as to whether there's microbes in the placenta and things like that. But you're basically sterile when you're born and you acquire your your first seating is really through the birthing process. So through the mom's vaginal canal is where you're really seated with your microbiome. Now, if C section babies often have a very different microbiome than a baby that's born via a vaginal birth, and then as you grow up, you acquire microbes, again, from your mother. Yeah, you'll get some from your, you know, father and siblings and then your environment, but really, that first seating is from that then initial birthing process.

Nick Jikomes 15:08

And do we know how, I mean, sounds like there's quite a big difference between babies born naturally passing through the vaginal canal versus those born by a C section. I was, I was a C section. Baby myself, Do we know anything about humans? How those two populations differ?

June Round 15:26

Yeah, there's, there's a lot of epidemiological studies done on this. Babies that are born via C section tend to develop more autoimmune disease. Later,

Nick Jikomes 15:39

interesting. I have an autoimmune condition.

June Round 15:43

I'm sorry to hear that. It's minor, and maybe later we can talk about some of the stuff we're doing with early life development, but that is one of the major things that is different with babies that are born via C section and yeah, vaginal birth is that they develop things like IBD, yeah, another disease that the tendency is, is that if you're born via C section, you have a higher chance of developing that later. So,

Nick Jikomes 16:13

and I guess if we, if we sort of put that together with what you said about the germ free mice, if germ free mice don't develop a very effective immune system because they completely are largely lack of microbiome. I think, you know, if you compare the C section babies to the natural birth babies, it would imply, at the very least, that their immune systems get trained up in a different way. And perhaps this is related, why you see these things with autoimmunity?

June Round 16:40

Yeah, that's right. I think, you know I said, I said, those microbes are really important in training your immune system to fend off a pathogen. But the microbes are also equally important in teaching your immune system when to not respond to things, including, like your own tissues, yeah, like, remember what autoimmune disease is, is when your immune system is inappropriately recognizing your own tissues. Yeah, so important in that,

Nick Jikomes 17:09

yeah. If I had to guess, I would guess that a natural birth results in a microbiome that's probably more dense and diverse in composition.

June Round 17:19

Yes and no. I don't know if the studies are clear on that. I think it's that the microbes are very different. So, yeah, when you're born via you know, a vaginal birth, there's a lot of lactobacillus that you're introduced to. There's a lot of, you know, Candida that you're introduced to. Whereas, if you're born via a cesarean birth, then you tend to have more of skin microbes. So I think you're not supposed to be exposed to those moment yet. Yeah,

Nick Jikomes 17:50

I've even heard, I've even heard that babies born by a C section tend to have microbiomes that start to resemble the skin microbiome of the doctor, whoever delivers the baby, that's

June Round 18:02

interesting. I've actually never heard that, but that's funny. That surprised me. I

Nick Jikomes 18:07

have not verified that, but I think I read that somewhere. Okay, so like, the composition of the microbiome, obviously, is very important for how the immune system gets trained up. It's natural to think how that would be related to things like autoimmune disorders or just your general ability to fight off pathogens. So the other thing I want to ask you for some background here is, you know, one of the things that seems like it's a fairly rock solid part of the literature that I hear over and over again is, you know, when we talk about nutrients that are good for your microbiome or that promote a healthy and diverse microbiome, the one that comes up the most is fiber. And you mentioned that fiber, things like cellulose, we don't digest them, but as people often say, they're food for the microbiome. What I want to I want to unpack that a little bit more. What do these microbes do with the fiber, and what are they producing that then turns out to be good for us, sure.

June Round 18:56

Um, so the mic, this is not, you know, I will disclose that this is not my area of great expertise. We don't study this a ton. But of course, it's one of the bigger things in the microbiome literature, is is diet. So the the fiber that there's lots of different types of fiber. So first, I'll say that not all fiber is created equally, and not all fiber is going to be metabolized by the microbes equally, and not all fiber is going to have a benefit. So there's, you know, there's been a couple studies that I've seen where the fiber inulin, which is one of the ones that a lot of people will take, actually is really bad for certain diseases. It's good for some but bad for others. Based off of you know, how the microbes metabolize it and how it influences your immune system. But I think you know, one of the best metabolites that studied because of fiber production, is short chain fatty acids. Yeah, you've heard of these before, but this, I mean, I. Everyone studies short chain fatty acids, and these just seem to be globally good for you, in that they induce an anti inflammatory response. They can also act as fuel for your intestinal epithelial cells, so your intestine is lined with these epithelium that's kind of one of the major cell types that creates a barrier between the microbiome and the host. And the short chain fatty acids are solely made by the microbiome, and they can be fuel for those intestinal epithelial cells and keep them, you know, keep that barrier tight. Yeah,

Nick Jikomes 20:36

yeah. Well, that's interesting. So, so these short chain fatty acids, maybe we'll talk about chain length later. But shorter, sort of smaller fatty acids. They can be used directly as fuel, sounds like. So if you've got microbiome, if you got microbes in the intestine, they can take that fiber, make these short chain fatty acids. It seems like it's a really good, efficient way to locally have energy for those cells. They probably don't need to spend as much of their, you know, their their time and energy making fuel, if you can have these microbes producing it locally, right there,

June Round 21:07

that's right, yeah,

Nick Jikomes 21:11

and so, and so. So what would be the difference between, you know, just at a high level? So when we talk about a short chain fatty acid being used for energy, as opposed to something like glucose, is there anything worth mentioning? There is like one of them better or preferred by our cells as a fuel source?

June Round 21:29

You know, glucose always seems to be the preferred fuel source for everybody, our cells and the microbes. So, you know, I don't think that I can intelligently comment on whether or not short chain fatty acids or glucose are preferred. I think it, you know, it all involves the environment, what the cell is doing, what the cell needs.

Nick Jikomes 21:54

And I guess one last question I have here is, so they produce the some of these microbes produce these short chain fatty acids, which can be used by cells for energy and perhaps for other things, is, are there other ways to get short chain fatty acids, or is this the only way

June Round 22:10

so our body doesn't produce them? It's, you know, the fermentation byproduct of fiber that produces them. The other way to get them is people do synthesize these, like chemical companies synthesize them. So for instance, in the lab, we can buy, because there's lots of different short chain fatty acids, there's butyrate, there's proprionate, and you can purchase these, and you can orally take them, and a lot of people will do that in their mouse studies to show that, oh, this short chain fatty acid is sufficient to have this effect. But,

Nick Jikomes 22:49

but other than that, other than these products, is this not a com Is this not really a component of natural sort of whole food diet?

June Round 22:57

Not that I'm aware of? No. So

Nick Jikomes 23:00

I know that there's, you know, the microbiome has been connected to, you know, all sorts of stuff. And we'll talk about some of that. Obviously, it's connected to, you know, gut issues that we can talk about, inflammatory bowel disease and things like this. But it's also been connected to obesity. And, you know, we're going to talk about one of your papers that that, that you shared with me that's really, really interesting here, but before we get to that in particular, what's sort of known, what's out there in the literature right now in terms of the connection between the gut microbiome and obesity.

June Round 23:31

So what is currently known is that a I guess, very on a very basic level, that the microbiome, when it is less diverse, if you will, is associated with increased obesity. So what does diversity mean? You know, we have these. We have these kind of like arguments in the lab about this, I think just on a very superficial level, if you are missing certain microbes, and we are still uncovering what these specific microbes are and what they do, you seem to be more prone to gaining weight. So your microbiome composition seems to be very important in how you gain or lose weight,

Nick Jikomes 24:19

and in in principle, like, what would be the ways we imagine that could happen? So off the top of my head, I could, I could imagine, well, maybe certain microbes are making certain key nutrients or producing metabolites that have to do with energy expenditure in our bodies, maybe regulating how much of the calories we're actually absorbing from the food that we put into our mouse, what's sort of the space of possibility there?

June Round 24:42

Yeah, so I think one of the first mechanisms ever discovered was really from Jeff Gordon's group, and this was when they basically took a microbiome from a obese mouse and transplanted it into a lean mouse, and that animal gained weight and. What they showed is that that microbiome was really good at extracting energy, so it was able to extract more energy from the food, and then it gave more energy to the host.

Nick Jikomes 25:11

I see, did those mice actually eat more? Was all that accounted for just by absorbing more

June Round 25:18

in the transplant? The animals did not eat more. It was more about, you know, them just having more nutrients and and extracting more energy. The obese animal used for the microbiome transplant, it was a leptin deficient animal, so it just constantly eats, you know, there's, there's no doubt, there's a component of, you know, diet in influencing the composition of your mic,

Nick Jikomes 25:43

but just just that microbiome change was accounting for a lot here. That's right, yeah, interesting. So tell us a little bit about this paper that you shared with me. Can you set that up for us in terms of what kind of questions you guys were asking, what the basic setup is sure

June Round 26:01

so during my so this was one of the first studies I embarked on when I started my own lab. So during my postdoc, I had been studying a bacteria that we had discovered was able to prevent inflammatory bowel disease in mice, and the mechanism by which it was doing that was inducing a T regulatory population, which is an anti inflammatory cell, and that's how it was able to suppress inflammatory bowel disease. And we identified a pathway within the cell that it was able to induce this T reg population. So it was basically inducing it by making a polysaccharide that bound to a toll like receptor on a T cell. So it and a toll like receptor is one of these receptors in innate immune cells that's able to recognize many components of bacteria. So they're somewhat skews. So

Nick Jikomes 26:59

these, yeah, so these are receptors are for, therefore, sort of recognizing what is and is not a pathogen or a human cell.

June Round 27:07

They are but they're very they're broad in scope, so they recognize pieces of bacterial cell walls or bacterial DNA, and they can do that whether it's a commensal or a pathogen. So they don't, they're not really great at differentiating between the two.

Nick Jikomes 27:24

I see, I see, they can just sort of see, like, this is our cell. This is human cell or not?

June Round 27:29

Yeah? Basically, yeah. So people are still trying to understand how these cells help distinguish between commensal and pathogen, but it made us really interested in that pathway with respect to because it seemed like this pathway was really important in inducing a healthy homeostatic intestine. So we made an animal. So I should preface this like I I did not get start my lab thinking I was going to study obesity. I would I thought we were gonna, you know, find a pathway that was involved in IBD. But, you know, you just follow the science. So we made this animal where we got rid of a signaling molecule that's downstream of toll like receptors. It's called Myd 88 and basically this is a signaling molecule downstream of most of toll like receptors. By getting rid of it, you're you're essentially disrupting the ability of whatever cell type we were looking at, a T cell at the time, but you're disrupting the ability of that T cell to signal through any of those toll like

Nick Jikomes 28:33

receptors. So does that mean basically, the immune system can recognize when it meets a non human cell through this toll like receptor, but it can't act on that because you're sort of blocking the information

June Round 28:44

flow. That's right, exactly. And I should say that we only knocked it out in the T cell, so the rest of the cells in the mouse's body were able to make that recognition. So they were still active. So one when we made that mouse, one of the major phenotypes of that mouse is that it had a significant reduction in the amount of IGA it produced in the gut. And you said we produced normally, a lot of it, a ton of it, right? But this mouse, when we knocked out this pathway, was not making as much. Then, if you let those animals grow up to old age. Most people do not let mice sit around in their in their facilities beyond eight weeks, because it's very expensive to keep mice. For some reason, my graduate student decided she was going to not cull any mice, and she was going to let them grow up to be like, over a year old. And these animals developed this spontaneous obesity. They were like, really fat. They were like, she always called them like, little

Nick Jikomes 29:45

pancakes. But late in life, did it develop this? Late in life?

June Round 29:49

Late in life, yes, it was not immediately. We didn't observe it in like, an eight week old

Nick Jikomes 29:56

animal I see so as the mice are growing up and going through adolescence. And things and becoming young adults, they basically they looked normal, macroscopically to the eye. That is

June Round 30:04

correct? Yes. So they did have this IGA deficiency at that early stage. But it wasn't until later in life that they developed the obesity. If you did put the animals on high fat diet, they were they developed the obesity quicker so you could start to observe it. But yeah, it seemed to be a spontaneous phenotype, which is very rare to see in animals. Actually, normally you have to push the obesity by giving them a lot of fat or eating their diet in some way. So this, this was a really striking phenotype to us, because we had knocked out this immune pathway, we thought it was going to be involved in gut homeostasis, but these animals were getting fat, so it made us think about the microbiota. I'm a microbiota lab, so of course, we thought about that. So we did transplant studies, where we took the microbiota that formed in these obese mice and we transplanted them into germ free wild type mice that did not have this knockout, and those animals got fatter

Nick Jikomes 31:10

same timing with the same developmental timing. No,

June Round 31:13

they actually gained weight faster than these other animals. Okay, so what I will say is, when you take that microbiota from the knockout animal and put it into a wild type animal over time, the immune system and that wild type animal will will kind of reshape that microbiota to be more of a healthy microbiota, if that makes sense.

Nick Jikomes 31:36

Yeah, yeah. And so in the genetically engineered mice that develop obesity in late age. Did you characterize, sort of how that's developing in terms of, are they expending less energy? Are they eating more? Or does it appear to be one of these things where they're just absorbing more from what they do eat?

June Round 31:56

Yeah, so we did all of that characterization, and the animals didn't eat more. So they were eating the same as the wild type animals. They were not expending more or less energy than wild type animals. The major difference seemed to be that they were not absorbing lipids as well. So there were more not absorbing them as well, not absorbing them as well, yes, so there was more left in the stool that would be excreted. Well, I'm sorry, the knockouts were absorbing more the wild. Okay, I

Nick Jikomes 32:28

was gonna say, I said that backwards, so that was so, yeah. So basically, they're pulling more fat out of the food and absorbing it to the body. Yes, yes, yes. Okay, and is that? So a couple questions here. So one, is it a specific type of fat? Are they? Are they absorbing saturated fatty acids, or is it just sort of everything?

June Round 32:51

So the ones that we really noticed a difference in were these long chain fatty acids. I mean, these are just like basic like once you once your lipases break down the fats that you eat, you get these long chain fatty acids. They bind to specific receptors on intestinal epithelial cells, and then they're taken up into the intestinal epithelium and then basically packaged into these chylomicrons and sent throughout the rest of the body for use. So those were the long chain fatty acids. Were the ones that we were noting were really different in our animal and is there,

Nick Jikomes 33:30

I'm asking from a place of ignorance here. So chain length is important for a variety of things when we start thinking about the different fats that animals consume and what they can be used for. So you're talking about long chain fatty acids here. These are the ones that are being absorbed more by these genetically altered mice earlier, when we were talking about fiber in the gut microbiome, that they were making short chain fatty acids. Is there any differences we should talk about here in terms of the short versus the long chain fatty acids that you think are relevant?

June Round 33:58

You know, other than their chain length, I mean one the long chain fatty acids I'm talking about are ones that come from the diet that have been acted on by the lipases that are excreted from your pancreas. So those, these are more dietary fats, and then our host enzymes make them into these long chain fatty acids. The other ones you know that we were talking about before, are products of the microbes, yeah? But at the end of the day, molecularly, it's, it's a difference in chain length. So I don't know that there's any anything to speak of beyond that, yeah,

Nick Jikomes 34:34

but I guess you know one of the questions so, so it's, I don't know this for a fact, but this is, this would be what I guess. So the short chain fatty acids are more readily burned as fuel. That kind of makes sense to me, that the shorter ones would be used as fuel more and then the longer ones are, they just more apt to be used for energy storage. And then maybe this is, yeah,

June Round 34:55

I see where you're going with this. Yeah. So short chain fatty acids can be absorbed. Charged more readily by an intestinal epithelial cell and used right then and there. Yeah, long chain fatty acids tend to be bind to receptors on the surface of the intestinal epithelial cell and then taken up and then delivered to the rest of the body. So I guess what you could say is short chain fatty acids are maybe used more locally, even though they delivered throughout the body as well, whereas the long chain fatty acids are packaged up and then sent to the rest of the body. So

Nick Jikomes 35:30

these long chain fatty acids, they're not just a repository for energy that can act as signaling molecules it sounds like and it just sounds and they just need to sort of be processed more before they can be used. Yes, you're That is correct. Okay, so, okay. So what comes next? You've got these genetically engineered mice. They get fat in late age. They've got this interesting immune phenotype that you've engineered into them. What comes next here?

June Round 36:01

So the next question to us is, well, there, I guess there's two, but you know, here we know it's a microbiota driven obesity. So one of our initial questions was, what microbes are driving this obese phenotype? So I think normally when you do these experiments, you're asked, you're looking at the obese mouse, and you're and you're asking questions about, well, what microbe is there that's making them obese? Because that's generally like, what pathogenesis people think about, like what microbes they're causing a disease. And we did do those study. We looked and there was nothing that really jumped out at us too much. The one thing we really noticed was different when we knock between the knockout and the wild type animal is that the knockout animal seemed to be missing a group of organisms within the clostridia. That was the biggest difference in them and the microbiota that we noted is really microbes missing in the knockout I

Nick Jikomes 37:02

see. So these animals don't have certain clostridia bacteria, that's correct. And what do we know about those bacteria? Like, what's our baseline knowledge? There? Are they doing something in particular that's important? So

June Round 37:15

at that point, we knew that some members of clostridia could induce Tregs that had been shown in the literature. But beyond that, we didn't know a ton. Because I should say this is like a huge class of microbes, okay, okay, and they're highly uncharacterized, I

Nick Jikomes 37:32

see. So there's all sorts of different species that are in this general group.

June Round 37:36

That's right. And when we had discovered it was this group, one was at 2019, we published that paper. So much more has been done regarding sequency and taxonomy of this group. A lot a lot of things have changed. But what's unique about these bacteria is that most of them are spore forming. So a spore a bacteria that can undergo sporulation, it's a way of protecting itself. So if, if it undergoes environmental stress, it can basically go into its spore form, and it can resist things like antibiotics. It can resist desiccation, which was, it was a nice way for us to be able to isolate these organisms, because we were able to take a healthy microbiota and extract all the spore forming organisms, which were mostly clostridia, and we could give them back to those obese mice, and we can make them lean again. So that was kind of the proof of principle experiment that we did to show like these are the organisms that are making these mice lean, helping them to stay lean, I see.

Nick Jikomes 38:41

So you've got this genetically engineered mouse. It's missing this key component in T cells of the immune system, and they get fat in late age, and they seem to be missing certain bacteria. But then you can give them the bacteria, and it reverses the obesity phenotype.

June Round 38:58

That's correct, yeah.

Nick Jikomes 39:00

How do you how do you give them, how do you give them the bacteria, and how is it a full reversal? How quickly does this happen? How dramatic is that reversal?

June Round 39:09

That's a good question. So we give the we give the bacteria via an oral gavage. So it would be the equivalent of a person like just taking a pill, yeah, yeah. It's like taking probiotics, that's right, yes, and we give it. We give it to the mice every other day. So it's not, you know, it's not a ton the reverse. The reversal is pretty dramatic. And actually, I shouldn't say the reversal. It is the prevention, because we, we basically start giving these clostridia to these animals before they develop, okay, because we knew, we knew that they would develop obesity later in life, yeah, so gave them the organism early in life. So we were asking if we could prevent the onset of obesity if we provided these organisms. So that's what we did. We still have to do that, the reversal experiments. We haven't done

Nick Jikomes 39:57

those. Yeah, yeah. Interesting. Okay, so. Genetically engineered mice. They're defective in their immune system this particular way. They don't have certain microbes that they would otherwise have. They develop obesity late in life, unless you give them these bacteria earlier in life, and then they don't develop obesity.

June Round 40:16

That's right, you're really good at this Nick

Nick Jikomes 40:18

Thank you. I'm just trying to make sure we're following so, so how do you interpret that so far? Is it just, and I may have missed this, were you giving them back just one species, or is it sort of like a bunch of different species in this family of bacteria? Yeah,

June Round 40:34

it was a it was a big group. It was probably 40 to 50 different types of organisms, all of them being spore formers, but all of them being part of clostridia.

Nick Jikomes 40:44

And then that, I assume, you characterize, sort of what was going on under the hood, the lipid absorb. The lipid absorption probably then just looks normal in these mice.

June Round 40:53

That's right, yeah, when you put in those clostridia, you resolve that increased absorption of those lipids. And

Nick Jikomes 41:00

so how do you so, you know, one thing people might think about here that I think immediately comes to mind is, you know, so many people have had experiences, or know of people who've had experiences where you know, even sometimes within the same family, or you know your friends, or whatever you know, you seem to be eating more or less the same diet. It's not obvious that one person's, like, completely gorging, you know, more than the other person, or even people that are, you know, really trying to lose weight, and they're cutting back, and they fail to do so, you know, one person's lean, one person's not lean or obese, but they seem to be eating comparable diets. This, you know, starts to kind of sound like that, where you could eat the you know, it's possible this. I mean, I think what this shows it's possible for two animals to eat the exact same diet and have dramatically different results in terms of body fat deposition, because the microbiome is regulating how much is being absorbed. That's

June Round 41:50

right. That is exactly right. And I think it's still not a very popular thing to say, because most people think it's, you know, energy out what you eat. If you expend the energy, you're going to be thinner. But what you just said is, right, we just showed two animals had the exact they ate the exact same they did the same movement, but one got obese and one didn't, and it was all based on the types of microbes they have. So to me, this, this is a really important finding, because this says the types of microbes you have are going to dictate your body composition, and this is going to dictate, you know, health.

Nick Jikomes 42:32

And you know, one thing that's interesting, unfortunate, you might say a little tricky, is these mice don't develop obesity till late in life. So it's not like, you know, you could see something happening earlier on. How do you start to think about like, you know, what that might mean for humans, and sort of detecting, you know, it's sort of like they go through their entire life and something you know is different about them under the hood, but they don't develop this phenotype till later in life. How do you start to think about that from from more of a human perspective? Sure.

June Round 43:05

So I think there's probably two things to say there. The first being is that we were able to induce these animals to become obese earlier in life, if we pushed it with a high fat diet,

Nick Jikomes 43:21

I see, so they more readily develop obesity is you most might say that's the phenotype, and it just, if you don't push it with a high fat diet, it takes a long time to set it longer I see, I see, so

June Round 43:31

diet was a really important component here, and we can talk more about why. Mechanistically, I think that is the case. The second thing to say, I just forgot, so maybe it'll come to me in a

Nick Jikomes 43:47

minute. Yeah, we'll come back to it. I wanted to ask you, so when you look under the hood and you compare the mice you guys made, the genetically engineered mice that are predisposed to obesity, basically, what else, if anything, is sort of wrong with them? Do they have fatty liver disease or the insulin resistant? What is sort of the physiological or metabolic health profile look like?

June Round 44:11

Great question. So it's not just obesity. These animals develop fatty liver they don't clear glucose as well. So they they they're starting to look like they're getting diabetes. So it's basically metabolic syndrome. It really is a metabolic syndrome. And I think we keep that terminology in our in our paper a lot, and this is, you know, something that's becoming a huge problem in western civilization.

Nick Jikomes 44:35

And the other thing that was interesting is, I think you have a result here where you took these genetically engineered mice that develop obesity, and as you said, you know, they're missing certain populations bacteria in the gut, they're developing metabolic syndrome, and then you just put them, you co housed them with other mice. What happened there?

June Round 44:59

Um. So those are interesting experiments. So this is very similar to a transfer, a microbiota transfer, so when you put mice into the same cage, they're coprophagic, so they essentially eat each other's poop. So that's, you know, essentially that's what a microbiota transfer is, is you are feeding mice. So by

Nick Jikomes 45:20

their nature, mice will automatically do a microbiome transfer. That's right.

June Round 45:25

So generally, if you put mice into the same cage, their microbiome starts to converge and look more like one another. It's not always the case, but for the most part, that's that happens. So when you put knockout and wild type mice together, what we saw was actually those, the animals, the knockout animals that were co housed with wild types. Those animals got, oh my gosh, they got fatter, so they took on the phenotype of whoever they were. Those mice that they were caged with. Those experiments are really nice, because you can start to follow what microbes are moving to what animal. And that was really one of the key experiments that helped us identify this clostridia population.

Nick Jikomes 46:14

And so when you give these animals high fat diets, can you say a little bit? So what does high fat mean exactly in terms of total fat, and is it important at all what the specific sort of fatty acid composition or the other composition of the food is?

June Round 46:30

So our high fat diet is a 45% high fat diet, which is actually low for what other people do in the field, a lot of people get 60% high fat diet. Most of the fat is coming from a palmitate in these diets, although not exclusively, and I think the source probably does, does matter, but that's just the diet that we

Nick Jikomes 46:53

is that a saturated fatty acid or unsaturated? Um,

June Round 46:58

I don't know. I think it's saturated. Okay?

Nick Jikomes 47:00

I'm with you, like, 80% sure it is okay. So, okay, so it's 45% fat. I don't know the numbers off the top of my head, but I believe, like, what would be a