 So, Tracey's an assistant professor up for associate professor in medicine in the endocrinology division. She's former chair and co-founder of the Stanford Hospital Diabetes Task Force. She has an active clinical research program in the areas of obesity, weight loss and the role of the adipocyte in modulating insulin resistance. I cite many of her studies and some of the various presentations I give and I am always inspired by her insights and contributions. Tracey, you get to close the session. Thanks. Okay, can you hear me? So, yeah, I would like to thank Christopher for inviting me to this illuminating conference, which was great last year and is already inspiring me this year. Is the volume okay? Okay, all right, so what I wanted to talk about today in 10 minutes is just a little snippet of what we're interested in related to the biological properties of adipose tissue that underlie insulin resistance. Okay, all right, so first of all, there is clearly an association between insulin resistance and body mass index or obesity. I think that's well established, but here's a nice graph from about 500 patients done mostly from Dr. Reven's work when I was working with him. So this is our, I'm not going to explain it in detail, but our measure of insulin resistance called the steady state plasma glucose, the higher the number, which is the glucose at the end of the steady state, the more insulin resistant the individual. And on this axis, you can see body mass index. These are all healthy non-diabetics. And as you can see, there's a linear association between increasing body mass index and increasing insulin resistance. However, you can see a tremendous amount of variability at any given BMI. For example, at a BMI of 30, you have some very insulin sensitive people down here and some very insulin resistant individuals up here. So what we're interested in is what explains the variability in these individuals who are similarly obese. This graph shows the distribution of SSPG or insulin resistance according to BMI subgroups in 500 normal glucose tolerant adults. In individuals who are a normal body mass index, this red bar represents those who have what we think is clinically significant insulin resistance. And you can see that a very small percentage, about 11% are insulin resistant in the normal body mass index range. And as your BMI goes up, by the time your BMI is over 35, about 75 or I think this is 85% are insulin resistant and none are insulin sensitive, represented by the orange bar. But in this group, between 25 and 35, there's a lot of variability. So people who are 30 to 35 BMI, about 60% are insulin resistant. And about 13% are insulin sensitive and some are in the middle. And in this group, only 40% are insulin resistant. So we're very interested in why some people are insulin resistant and others are not. And we've capitalized on this observation by studying individuals who are similarly obese but very resistant or very sensitive in comparing their adipose tissue. More evidence suggesting that the adipose tissue itself is related to insulin resistance in addition to these kind of correlative associations is the fact that weight loss, so decrease in body fat and mass can improve insulin sensitivity dramatically. So this is most dramatic in the setting of bariatric surgery. These are patients of Dr. Morton's and we've looked at these guys before and a year after surgery and you can see here just the decrease in body mass index from around 54 to an average of around 30. And here's their insulin resistance improving dramatically prior to surgery from an average of around 230 down to about 130 after losing 80 kilos or 80 pounds, sorry. So clearly they got more insulin sensitive. In fact, this isn't published yet, but they are more insulin sensitive than you would expect for their post-surgical BMI, the reason for which that happens is not clear. They also, people also improve their insulin resistance with just dietary weight loss of much more modest degree. These are individuals who did diet studies with us. They lost about four and a half kilos. Here's their weight before and their weight after. So they lost a little bit of weight and here's their insulin resistance response. These guys are likely the ones who didn't lose much on this side. But in general, there's also a reduction in insulin resistance of about 23% with dietary weight loss. Interestingly, if you remove body mass, body fat mass with liposuction, there is no change in insulin resistance. Here the term IMGU refers to insulin resistance. It means insulin mediated glucose uptake. This is a study by Sam Klein that was published a couple of years ago. He took eight obese normal glucose tolerant women with a BMI of 35. He performed a different test than the one that we do. He performed a euclycemic hyperinsulinic clamp to measure insulin resistance, or IMGU, before and 12 weeks after liposuction. These women had nine kilos of fat removed. And that's more than what I just showed you with dietary weight loss, which had improved insulin sensitivity. And we know from our data that our studies, if somebody loses nine kilos, they almost always improve their insulin sensitivity. And what he found was no significant differences in insulin mediated glucose uptake before and after liposuction, as evidenced by this bar graph here. In this setting, the RD refers to the insulin mediated glucose uptake. It's a different measure, so it's different units. But you can see there's essentially no change at all, with nine kilos of fat removed by liposuction. So what does this all mean? If you look back at some interesting experiments by Jerry Schulman a few years back, we can learn something from these mice. These are azip-fatless mice, so they have no subcutaneous fat. And if you look at this mouse, you can see that his abdomen is extremely distended. And the reason it's distended is because his liver is filled with fat. This mouse has hypertriglyceridemia, insulin resistance, glucose intolerance, a fatty liver, and fat in the skeletal muscle. They surgically implanted subcutaneous fat onto this mouse and found, you can see the size of the liver has gone down. Fat came out of the liver, came out of the skeletal muscle, and all the metabolic disturbances improved. So what we're seeing here is that the total absence of fat, subcutaneous fat, was causing essentially what we see associated with obesity, metabolic syndrome and ectopic fat. So with that background, we're trying to understand how obesity, just garden variety, obesity can lead to insulin resistance and all the metabolic perturbations. And I don't have time to go over all of these, but there are four leading hypotheses in this research community. One is that visceral fat is causing insulin resistance, so individuals who have relatively more visceral fat are more prone to insulin resistance. The second is inflammation, which we've touched on, perhaps mediated via the immune system. The third is impaired adipogenesis and fat storage. And the fourth is hypoxia. And it's very likely that these things are interrelated. I, for the sake of time, I'm going to focus on impaired adipogenesis and fat storage. So the hypothesis that we've been investigating is that perhaps impaired adipogenesis causes insulin resistance, just like the mouse I showed you. If you cannot, in the setting of caloric excess, ramp up your fat storage as needed, you may develop metabolic complications just like that fatless mouse. And these are human examples of something very similar. This girl on the left is a patient who has congenital lipodystrophy. She has no fat in her body. And the reason her belly's sticking out, just like the mouse, is because her liver's full of fat. She cannot store fat. And she has, interestingly, the same metabolic characteristics as that mouse. She has glucose intolerance, hypertriglyceridemia, insulin resistance, and fatty liver. So this is a little cartoon that describes what we believe is happening in the setting of caloric excess. So you have your fat cells here. And the fat cells in the setting of a caloric challenge can either get bigger or they can become more numerous. What our data shows, and other data as well from Peter Arner's group, is that the cells really can only get so big. And by the time your body mass index is 25, they're sort of maxed out. They can get a little bit bigger. Our morbidly obese patients have slightly larger fat cells, but it's not dramatically larger. And Peter Arner did this elegant work using carbon dating to show that, in fact, as people get more obese, they begin to make more fat cells. And so hyperplasia becomes important in expansion of the fat mass once you're above a normal body weight. So how does the body figure out whether the cells are getting bigger? What determines the maximum size? And what's the signal for hyperplasia? And these are all things that we don't quite understand. But there's another bit of data suggesting that once the cells get very large, they trigger maladaptive processes. They trigger inflammation. They attract, express signals that attract inflammatory cells. And I don't have a picture of this here, but there are these examples in mice showing these things called crown-like structures, which are essentially macrophages encircling a large necrotic fat cell and gobbling up the fat and debris. And we have seen those in our subjects as well. And once these cells become disturbed, you know, they're releasing fatty acids into the circulation, which are then going into the skeletal muscle and liver. So this is our example showing that in humans, the peak diameter of these big fat cells doesn't change a lot. These three curves show the peak diameter of mature cells. And the different color lines are individuals who have BMI of 27, 35, and 50. And you can see that there's not a large difference in the peak diameter as the individuals change their body mass index tremendously. A few years ago, in collaboration with Sam Cushman at the NIH, we showed that individuals who are insulin resistant in fact did not have much bigger fat cells. Over here, we looked at their fat cells and we compared very resistant to very sensitive individuals who were similarly obese. And we found that the peak diameter was not significantly different. But what we did find was that individuals had both small and fat cells. And you can see it on this curve. Every individual's got a bunch of these little cells, which are, they have a micron, you know, a diameter greater than 20 microns. And they are fat cells, but they're very small. And we found that the insulin resistant group had an increased ratio of small to fat cells. So they have a relative increase in the number of small cells. And in association with that, they had decreased expression of genes that were important for a dipocyte differentiation, which led us to pursue the hypothesis that impaired differentiation of adipose cells in the setting of obesity may underlie the development of insulin resistance by restricting the ability or the ease with which the subcutaneous fat can store the fat, which in turn may lead to the stress on the existing mature fat cells. So here's just a slide of what we're working on now. We're actually culturing the pre-adipocytes and looking at factors that determine how well they can differentiate. And Lee Fen Lu, a new addition to our lab has become very adept with this. And what is interesting here, this is another patient of Dr. Morton's, who has visceral and subcutaneous fat at day 14 of differentiation. And you can see here the subcutaneous fat has multiple lipid droplets inside the cells. So the blue is the nucleus, the green are the lipid droplets. And this is the visceral fat from the same person. It does not differentiate very well. Clearly, these two depots are very different. And with Ed Engelman, we're also looking at and finding differences in inflammation and immune subsets in these two depots. So the future directions for our group, we would love to collaborate with any number of the presenters here. We're interested in finding the trigger for adipogenesis and exploring that. Some triggers may be hypoxia or ER stress due to cells that have maxed out their size or inflammation. Again, in response to probably two large cells. And then what's defective in resistant versus sensitive subjects? Is this the problem, inflammation, or could it be a differential immune response, or perhaps a differential response to hypoxia? And what are the consequences of adipogenesis that mediate insulin resistance? Does it have to do with these cells getting very large because there wasn't a new crop of small cells to help store fat? Is it increased lipolysis or is it mediated through deposition of ectopic fat? So thank you for your attention. We'll have time for questions, I think, at the end. The preceding program is copyrighted by the Board of Trustees of the Leland Stanford Junior University. Please visit us at med.stanford.edu.