Review the role of genetics in the control of food intake and body-weight, the fate hormone-leptin, and the hypothalamic melanocortin pathway
Recently, there has been an increase in obesity due to changes in our lifestyle and in the types of food we eat. Although we are all exposed to these changes, not all of us are obese.
Watch as Dr Giles Yeo, from the Metabolic Research Labs at the University of Cambridge, discusses how differences in our genetic make-up cause us to respond differently to the same environment.
About the Presenter
Professor Giles Yeo joins us from the University of Cambridge. He is originally from San Francisco. Giles received his Bachelor's Degree in Molecular and Cell Biology from the University of California, Berkeley, before moving to complete his PhD in the lab of Professor Sydney Brenner at Cambridge University. He then joined Professor Stephen O'Rahilly at the Department of Clinical Biochemistry to work on the genetics of severe human obesity.
In 2007, Giles became the Director of the Core Genomics and Transcriptomics facilities, as well as a member of the University of Cambridge's Metabolic Research Labs.
In 2009, he became the Coordinator of the EC FP7 Consortium EUROCHIP, which focuses on studying the hypothalamic responses to gut hormones. His group is interested in studying the brain control of food intake and bodyweight, as well as the role that genetic modifiers, such as FTO, might play.
- The role of genetics in the control of food intake and body-weight
- Genome wide association studies and ‘common obesity’
- The fat hormone, leptin
- Fat mass and obesity related (FTO) plays a role in the genetic susceptibility to common obesity
- The hypothalamic melanocortin pathway
Good day, ladies and gentlemen, thank you for standing by and welcome to today's presentation: Are your genes to blame when your jeans don't fit? Your host today is Lucy Purser, Senior Events Coordinator with Abcam. I would now like to turn the conference over to Ms Purser.
LP: Thank you, Nathan. Hello and welcome to this webinar. Today's guest speaker is Professor Giles Yeo from the University of Cambridge. Giles is originally from San Francisco and he received his Bachelor's Degree in Molecular and Cell Biology from the University of California, Berkeley, before moving to complete his PhD in the lab of Professor Sydney Brenner at Cambridge University. After this, Giles joined Professor Stephen O'Rahilly at the Department of Clinical Biochemistry to work on the genetics of severe human obesity. In 2007, Giles became the Director of the Core Genomics/Transcriptomics facilities and a member of the University of Cambridge's Metabolic Research Labs. In 2009, he became the Coordinator of the EC FP7 Consortium EUROCHIP, which focuses on studying the hypothalamic responses to gut hormones. Giles's group is interested in studying the brain control of food intake and bodyweight, plus the role that genetic modifiers such as FTO might play.
Joining Giles today is Mandeep Sehmi, a member of Abcam's marketing team. Mandeep completed her Biology Degree at Aston University, followed by an MSc in Molecular Pathology and Toxicology at the University of Leicester. Following this, she completed her PhD at the MRC Toxicology Unit in Leicester. During this time she worked on B cell malignancies. Mandeep joined Abcam in 2011 and is the Marketing Coordinator for the Metabolism Portfolio.
As Nathan said, this is a quick reminder that questions for the question and answer section of the webinar can be submitted at any time during the presentation via the Q&A panel on the bottom right hand side of your screen. Also, when you log-off from the webinar you will be directed to a webpage where a copy of the presentation can be downloaded. I will now hand over to Giles who will start this webinar.
GY: Hello, thank you very much, Lucy. So, look, presentation overview; that was the introduction done, and let's go. So, like Lucy said, my name is Giles. She did promote me to professor, and I'm not professor yet, just in case people out there, but anyone looking to hire me as a professor, please use my email address to contact me. My name is Giles, once again, thank you for joining us and I'm here to talk to you guys about: Are your genes to blame when your jeans don't fit? I trained in genetics, and that's what I do, but I'm not interested in genetics within obesity as a purely nerdy thing to do. Which I am nerdy, and it is an interesting thing to do, but, largely, really as a tool; and as a tool to try and understand food intake. So just some numbers, I guess, to mull over and to actually put things into context before I start on the main body of the talk.
If we make an assumption of a 2,000 calorie a day diet, I don't think any of the guys out there are doing 2,000 calories a day, well, maybe some of the women, but that's a useful number to start with. We need roughly three-quarters of a million calories a year in order to survive. If we make another assumption while ageing from a youthful, exuberant, effervescent 20 years old to 50 years old, an average human being will gain about 15 kg in weight. Not everyone will gain the 15, some will gain 1, some will gain 30, but on average it is about 15 kg of weight that is gained over those 30 years, unfortunately.
We make another assumption, and people always ask me what is our caloric content, kind of like a Mars Bar. So, roughly speaking, if we assume some form of homogeneity, which is not necessarily true, I guess, but if one was homogenized, we are roughly 5,000 calories for every kilo of human body weight. It's a rough estimate. So if we take this 15 kg of excess body weight and see what's that in calories, that's 75,000 extra calories that we're actually carrying around? So we have over the 30 years gained this 75,000 extra calories. In order to do that, that's an intake and output imbalance of roughly 2,500 calories a year, or roughly a day's intake and a discrepancy of 0.34%. Looking at it in terms of calories, an excess of seven calories a day for 30 years is all that is needed to gain 15 kilograms of weight. That is actually quite an amazing number, I mean, what is seven calories, after all? Seven calories is absolutely next to nothing.
So I think there are two ways of looking at this: there's the glass half empty, which is, 'Oh my God, how come I'm not the size of a house?'. Then that is a very good question and if we consider that seven calories is something like two and a half Tic Tacs, I mean, it's a very good question. But that leads us to the glass half full way of looking at it, you know, why are we not in danger of exploding into a big red mess every time we sit down at the dinner table? Why are we not the size of a house? That is the interesting question to think about. How do we regulate our body weight, and we do regulate our body weight because otherwise we would not be able to keep to quite such a 0.34% over 30 years of our lives.
So we have known for a while now that we defend our body weight, so living creatures defend their body weight. Here is, for example, an old experiment, a schematic diagram representing the set point hypothesis experiment, which was done probably in the 40’s. Briefly, what this shows is if you put a rat in a relatively controlled environment for its whole life, it will achieve some form of trajectory of growth. If you underfeed a rat, they will lose weight, unsurprisingly, but if you put them back on a free choice type diet they will go back to a defended weight. If you overfeed a rat changing their type of diet, putting them on a western cafeteria diet, they will gain weight. But if you actually put them back on to a free choice diet, once again their body weight will trend back down to a so-called defended trajectory of weight. This is the so-called set point that all living creatures have predetermined, and you can read predetermination as a genetic determined set point.
Your body defends it by either altering food intake or altering energy expenditure, and when I mean defended I do not speak about a conscious executive decision to diet, which many of you may have done, or many of you know people who do, but I speak about a subconscious way of actually defending your body weight. So, for example, if you've spent a period of time overindulging yourself and when you come back to regular life suddenly you don't feel like eating so much at a specific meal. I don't feel like eating so much. What is that feeling? Why don't you suddenly feel like eating so much? Likewise, given the fact that I told you those number seven calories, 0.34% is all you need to gain that weight, it is nothing for your body to tweak down the efficiency of your liver, your skeletal muscle by 0.5% point, here or there.
Although we defend our body weight, we are in a problem situation. So this is data which I've downloaded from the US Centre for Disease Control, and this is data from 1985 mapping the prevalence of obesity in the United States, and these numbers are true now for most developed countries as well. We are assuming that obesity here is a BMI, a body mass index of over 30. What do we see here? The first thing we see in 1985, at any rate, is that most of the states are white, i.e. there are no data being collected and us being human beings, if there's no data being collected there's no problem to begin with. So I'm going to fast forward through time now, and what we begin to see is (a) the white states have disappeared, (b) now we're becoming to get to a situation where the colors are warm, and warm colors are bad, ladies and gentlemen, as you can see here by the prevalence data; and here we are in 2010. Guys, we've got a problem, and this is really only over the period of 25 years. What do we see now? From having no data, from having 10-15% levels of obesity, we now have a situation where all the states have at least 20-25% levels of obesity. In the Deep South, in Mississippi, in Louisiana we actually have a situation where over 30% of the population are obese. Once, again, like I said, this, although I have used the United States as an exemplar, this is true for in Europe, it's true in many of the up-and-coming developing countries as well in Asia and in the subcontinent of India. So we have a problem.
Now, if we actually map and graph that data from 1985 data and 2010 data, on the x-axis we have BMI and on the y-axis we have the frequency of BMI. What we see, is we see in 1985 the average or the mean or median BMI is roughly at around 22 to 23, and we can see it's a relatively narrow shape. What we have happened over the past 25 years, is a shift in the shape of the curve, a change in the shape of the curve, and it's clear we have become more obese as a species. Given that these changes have happened over such a compacted period of time - 25 years - it is entirely unlikely that these have happened. These have happened because of genetic changes, because this is a constant gene pool that has happened. Most of you, or the vast majority of you listening out there would have been alive throughout most, or, like myself, all of these changes that have occurred.
If we look at the question: Are your genes to blame when your jeans don't fit? From that prism, well, no, clearly not, because the changes that have occurred here are entirely down to environment. I'm using 'environment' as a catch-all phrase to represent socioeconomic status, your desire to exercise, what kind of job you do, etcetera, etcetera. Your environment, the environment we live in has caused this change. But if we have a closer look at the data, however, what we don't see is a shift in the entire 1985 histogram to the right. Such that it looks like the silhouette of the Golden Gate Bridge, that's not what we see. What we see is we see a shift, a change in shape of the curve, meaning that if we assume that all the 300 million Americans there are represented by a single spot there, so, therefore, the only way you change the shape of a curve is of each individual responds differently to the similar change in environment. So within the field of obesity we say that why have we become obese? We have become obese because we eat too much, because of the change of the environment that we live in; we don't exercise enough. How obese we've become, or how non-obese we've become within this environment, that is powerfully genetically determined.
So if we look at then the concept of genetic control of body weight, is there anything to it? Well, the first point we've just tackled, there are variable people have variable responses to the same environment. Point number two, there are some ethnic groups that are more likely to develop obesity than others, and I'm going to come back to you in the next slide or two with an extreme, but very informative example. There have always been some people predisposed to weight gain, and that is true, and then there are data from twin and adoption studies.
So what are twin and adoption studies? For the uninitiated amongst you, clearly there are identical twins and identical twins are, in effect, genetic clones. There are fraternal twins, or non-identical twins and those would then share as much genetic material as anyone's siblings out there would share, so 50% of genetic material that's actually out there. You could take any conceivable trait: hair color, eye color, nose size, the rate of toenail growth; or you can actually take height, or you could take weight. You could look at identical twins and say, 'Okay, well, within identical twins what are the variants there that is in terms of, for example, eye color?' and you'd say, 'Well, there's no difference in eye color, because it's 100% genetic'. Then you would compare that to fraternal twins in which you have 50% of genetic material, and from there you can actually work out the heritability of a specific trait. If you do it that way, what you see is you see that the heritability of fat mass is actually equivalent to that of height. No one would argue that height is genetic: tall parents, tall kids. But if we actually take that thought a little bit further, no one would also argue that, say 500 years ago, that we were all shorter as a human species. But why have we suddenly become taller as a human species over 500 years? Because of a change in environment, improved maternal in utero care, but that doesn't change the fact that if you are tall your kids are likely to be taller.
The same thing is true for obesity, except that the changes have happened over a far more compressed period of time. 25 years ago we were thinner as a species, but over the past 25 years, because of changes in environment, we have become obese. But that doesn't change the fact that if you are fat, obese, have a big bum, have a big tum, that your child is more likely to look like you, I fear, everyone looking in the mirror, and that to be the situation.
So just the example here of ethnicity, and can I just remind you guys, by the way, I'm throwing a lot of information out, that you can put down any questions you want to ask and I'll try my best to deal with them in the Q&A section on the bottom right hand corner. So in terms of dealing with an example of an ethnic group with the propensity for obesity, there are a group of people out there called the Pima Indians. Now, Pima Indians are not Indians like South Asian Indians; Indians in the Native-American-form, so indigenous peoples from the Americas. These specific groups, the Pimas, are hailed from these mountains in Central Mexico. They are agricultural peoples, they are still there, they still plough the land with animals, and they're all, as far as I can gather, stick thin, the ones that are living certainly in the central mountains of Mexico. Now, in the late-1800s during the Spanish-American War, I think - and people can correct if I'm wrong - the US Cavalry actually recruited a number of these Pimas as scouts; they were good at reading the land and things like that. So after the war finished, large groups of these Pima Indians recruited from Mexico settled in the area of Tex-Mex America now, so Arizona, New Mexico, Texas and actually stayed there. What has happened to the Pima Indians in the Tex-Mex area is that now in the twentieth and twenty-first centuries, they have become immensely obese with 50% of adult Pimas living in the Tex-Mex area having diabetes, 95% of these would then be morbidly obese, morbidly overweight. Compared to their genetically identical brethren and sisters, or as genetically identical as an ethnic group would be, of only 10% of diabetes living up in the mountains, and having no obesity problem at all.
So what is happening here? Well, the study of these peoples led to the so-called Thrifty Gene Theory, and for the Thrifty Gene Theory you really have to go back into evolution and think about things. Actually just say, 'Okay, well, what is the purpose?' when our purpose has to be to stay around long enough in order to reproduce, and a part of that is to actually eat enough food that is actually out there. What we have is that for most of evolution we have had the problem of too little food, as opposed to too much food. So we have been evolved to eat everything that is there whenever it is there, to prepare yourself for the famine that's going to come here. Our problem, and the problem with obesity today is we are all preparing for a famine that's never going to arrive. But even if looking at the Pimas, however, they have responded in a really quite extreme manner, which is not what we see today. I mean, we are fatter as a people, but not in such an extreme situation.
This is one of geographic isolation, so the vast majority of human kind, our so-called Plains Peoples, we live on continental big Plains and so that in the past if a famine had occurred, we would be able to move away from the famine. Whereas if you're geographically isolated, such as the Pimas on top of a mountain, you needed to come up with a different way of actually dealing with the situation, and the way they've dealt with it was to have a repertoire of gene changes which made them more thrifty. So, for example, for any calorie that I might take, and this is a number I've plucked out of the air, I might store half and burn half a calorie. Whereas a Pima might very well store three quarters of a calorie, and burn a quarter of that calorie. So they've become more thrifty for any given calorie that's actually given to us.
What are factors governing body size? Well, is it purely genetic? Unlikely to be. Is it purely environmental? It depends on the way you look at it, and clearly environment plays a major, major role. But it clearly is an interaction of your genetic susceptibility with the environment that actually governs body size. Now, there are multiple layers of complex psychological and social reasonings, but I'm neither a psychologist or a sociologist, but people of you are out there studying this, but I'm studying the physiological role that are actually governing body size. Once again, guys, lots of information - please don't hesitate to send your questions through the Q&A panel on the bottom right hand corner.
So I guess the first molecular handle we had on a molecule which controls body weight was the discovery of leptin. The discovery was made from this mouse here; this fat, fuzzy creature here on the right hand side, who you can clearly see weighs more than twice the weight of his wild-type litter mates on the left hand side. As it turns out, this mouse had a mutation in the gene called leptin, which is produced from fat and signals to the brain. From this initial opening where leptin was identified signaling from fat, it opened up a whole new field of biology studying the role of downstream leptin signaling. Such that, we now know, the leptin melanocortin pathway is one of the best defined pathways in the brain controlling food intake and body weight. This is what we have found out, that it is the brain that controls food intake and body weight. If you look here, the summary of the leptin melanocortin pathway, leptin is produced from fat, it signals to an area of the brain called the hypothalamus, particularly the arcuate nucleus. This up-regulates POMC or pro-opiomelanocortin, which is the process into melanocyte stimulating hormones, or MSHs, which signals the DMC-4 receptor causing a reduction in food intake. At every single stage of this pathway, if you genetically disrupt it you will get either an obese human being, as indicated by the fat red arrows pointing downwards; and/or if you genetically disrupt it in a mouse, indicated by the pink boxes, you end up with severe obesity in both man and mouse.
I will draw on just two examples here, because I realize that time is short. I've drawn two examples here with regards to that. The first is going back to leptin, if there are mutations in the leptin gene in mice causing obesity, are there mutations in the leptin gene in humans causing obesity? And there are, and here, for example, is what a leptin-deficient patient would look like, their phenotype is actually there. The interesting thing about them is that they are born of normal birth weight, but are hyperphagic after weaning; so hyperphagic, eating more, so as a pathogenic term. They also have a broad spectrum of neuroendocrine changes that are actually there. What happens when you replace leptin in a patient without leptin? Here on our left hand side we have one of those leptin-deficient patients, and this was worked on by my close colleagues, Professor O'Rahilly and Professor Farooqi. There is a three-year-old here weighing 42 kilograms without any leptin. After daily injections of leptin, this child has become a seven-year-old weighing 32 kilograms, and you wouldn't bat an eyelid looking at this child walking down the street, because they have replaced the leptin that is actually there. This is a fine example of leptin treatment being very useful in a situation when the patient has no leptin at all.
Now, leptin, however, as I mentioned, is a peripheral signal reflecting the body's peripheral nutritional status and signals to the brain. So are there any examples then, or what are some examples of molecules within the brain that when you take could cause obesity? Here we have a melanocortin-4 receptor, so this is further down the leptin melanocortin signaling pathway; and we see here that mutations in the melanocortin-4 receptor in mice cause obesity. What it does is it causes a dominant form of obesity, unlike leptin deficiency which is recessive, melanocortin-4 receptor is a dominant form of obesity where you only need one mutated form in order for it to cause obesity. To this moment, I'm sure my mum was very proud that we discovered mutations in the melanocortin-4 receptor, and were actually referred to in The Sun, although I didn't phone tap anyone to get my name in the paper!
We now have found multiple sequence variants in the melanocortin-4 receptor, causing obesity. Now, probably up to 300 different melanocortin-4 receptor mutations are actually causing obesity. The interesting thing is because there are so many different mutations in the melanocortin-4 receptor that are actually out there, we're able to look at the function of each of the receptors. For example, you're going to have specific receptors which have no activity, because of the type of mutations that happen, or you're going to have mutations which cause 50% levels of activity. The interesting thing is we are able to make a genotype-phenotype correlation from a tissue culture experiment indicating levels of activity. We're able to actually predict in an ad libitum buffet test meal; predict how much the patient is actually going to eat. On the right hand side we can see the information there, where if we compare the patients with leptin deficiency on the furthest left, and there on the furthest right with controls, and then treated leptin deficiency, we can see that if we predict whether or not a melanocortin-4 receptor mutation is inactive or partial, we're able to predict the amount of food eaten by that patient what they're actually going to eat. That is a very quick two examples that disruption of two components of the leptin melanocortin pathway results in severe obesity in humans and mice.
Now, in my last couple of slides, to finish off, however, I want to bring you back to the thought of genetics. Now, the syndromes which I've spoken to you about: leptin, melanocortin-4 and everything else within the leptin melanocortin pathway, are what we call monogenic syndromes. Meaning that a mutation in a specific gene causes the obesity, much like you might see in cystic fibrosis or muscular dystrophy, there is a pure genetic cause for the obesity. The problem is these are incredibly, incredibly rare, so, for example, the leptin-deficient patients, and they were first discovered in 1997 and my colleagues have been looking since then, and they have found a grand total of seven families in the world with leptin deficiency. So it's an incredibly rare syndrome, much like the MC-4 receptors, a little bit more common, but still incredibly rare. The vast majority of us, however, are just a few kilos heavier when we don't have monogenic syndromes of obesity, and that's not the reason for the obesity that's around. These reasons are more likely to be polygenic, i.e. we are more likely to have subtle variants in multiple genes, each causing a small difference.
An example of this, which was discovered in 2007, is FTO, such that if you are homozygous for the so-called risk allele in FTO, you are on average 3 kg heavier than if you were homozygous for the non-risk allele in FTO. So people say, 'But 3 kg, that is not a lot, why are you studying a gene in which there is only a 3 kg difference in body weight?', and that is true. But what is interesting is that 16% of the human species, of the human population are homozygous for these FTO risk alleles. If you count the heterozygous, so the carriers for it, 50% of the population have at least one copy of the risk allele, and are then on average one and a half kilos heavier. So we have 50 per cent of the human population whose body weight is influenced by FTO in some way, and so I have been studying it.
There's a lot of data in FTO out there that you guys can look up. Just one bit that we discovered a little while back was that specifically within the brain, although FTO is expressed everywhere, specifically within the brain and the hypothalamus we find that fasting reduces FTO, and a high-fat diet increases FTO expression. If we modulate FTO levels in rodents we are able to bi-directionally influence food intake.
But FTO is just one of many of the genes that are out there, there are now more than 50 of these polygenic obesity genes that are out there. Here is FTO, which still has the largest effect size of 3 kg. But there are a whole host of other genes that are actually there, and each having a subtle effect. But the interesting thing, on the right hand side on the histogram, if you then create an obesity risk score using all of the single nucleotide polymorphisms of the slips that are there, such that if you had two risk copies of FTO you had a score of two, and if you had one risk copy of FTO you had a risk score of one. If you add all of those up and you have a normal distribution, the more copies of slips of all these risk alleles you have, subtly, the higher your BMI.
The other interesting thing, as I mentioned earlier, the leptin melanocortin pathway implicated the brain in the control of food intake, but that was in severe and monogenic obesity. The interesting thing, however, is that from these slip studies that have occurred from these genome-wide association studies, the vast majority of these genes that have come up in polygenic obesity have also been highly expressed and enriched within the brain. So it appears to be - and we also have the data of FTO - within the brain being influenced by food intake. So I think obesity, and certainly the data is stating whether monogenic or polygenic appears to be a grave disease of some description. That there are going to be genetic influences within the brain either monogenic or polygenic that actually influence body weight. I'd like to end there, and this is where I work at the Metabolic Research Labs at the University of Cambridge. I'm now going to pass you over to Mandeep. Thank you very much, guys. I'll be back for questions. Questions - bottom right hand corner - Q&A.
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Abcam's scientific support are always here to assist you. For the US please contact our US technical team. For Asia-Pacific please contact our Hong Kong office. For the UK, Europe and the Middle-East please contact our UK technical team, and for Japan, our Japan technical team. Thank you for listening and I would like to hand you over to Giles to answer any further questions.
GY: Thank you, Mandeep. You guys have been busy on the Q&A session coming through. Let's see what we can do to answer some of your questions. If I pronounce some of your names wrong, please forgive me, I am clearly linguistically challenged. We've got a question here from Clint. I feel like a radio presenter, this is Radio 1! Clint, you ask: Leptin is constitutively secreted proportional to the size of fat stores, but is the secretion boosted postprandially? It is secreted proportional to fats, but not constitutively, so it's actually a pulsatile secretion and what does happen is that you actually follow a typical feeding/fasting routine. Leptin levels will actually drop in fasting and then rises after food intake. Now, if you actually go on a prolonged fast, before you even begin to drop your fat mass, leptin levels would then stay low. So that's the answer to your question, and it actually moves around with respect to the food intake. Not a great deal, not like insulin, but it does move around a lot.
Next, we have Tony with a related question: When can we expect the leptin pill? So that is an interesting question, given the fact that these patients that without leptin were then so magically, miraculously cured almost by giving leptin, how come they haven't been given to normal human beings who are fat? The answer is they were, actually, so you can understand that when they saw the data of that leptin treatment patient, that the drug companies who licensed leptin were wetting themselves, they were thinking, come on, this is the cure to obesity. But it isn't, so leptin has been around and, trust me, they gave leptin to everyone; they gave leptin to people who were fat, people who were thin, people who were thin and who used to be fat, people who were fat that used to be thin and nothing happened. It's an interesting question, why? Leptin, as it turns out, is not a hormone which lets you know you are too fat, because there's no evolutionary purpose for that. But leptin actually is there to let you know when you have too little fat, so it only functions as it disappears. Whereas for the vast majority of us, be you Kate Moss or a very large human being, you actually have a range of leptin levels that are actually there. But having an increased amount of leptin in normal state actually doesn't increase leptin's function at all. It only functions when you actually begin to have so little leptin, meaning that reflecting pseudo fat mass, that it actually works. So the interesting thing about those patients that you see is their brain actually thinks they're starving, because they don't have leptin their brains thinks there is absolutely no fat on them at all, so their response is a starvation response where they're looking for food, they're hypophagic. What leptin does is to actually prepare your brain for the starvation response, to save enough fuel so that you can actually look for food that is actually there.
So who else is here? Valerie is then asking a question about epigenetics and obesity, and that is an interesting question as a hot topic. I think there is very powerful evidence for epigenetics having a role to play in metabolic disease, particularly when it comes to diabetes, type II diabetes, insulin resistance. For those uninitiated amongst you, this is a situation where if you are actually in utero, so when your mum was pregnant, and the environment around her was very important to how you adapted to the environment when you came out, and you might understand how that is a very useful evolutionary concept. So, for example, if your mother, while having you, was in a situation where there was a famine, so she became pregnant and then there was no food, the harvest has failed, whatever. It would then be very, very advantageous if you knew that -you being the fetus - knew that and you were then programmed, in inverted commas, to respond to this difficult environment when you came out. So what then happens is you came out, you were prepared for a fast, for a famine environment. The problem, however, is if you are preparing yourself for a famine environment, you're being extra thrifty with things, you are changing the way your biochemistry works based on epigenetics. But then when you're born you come out into a time of plenty, because the famine has disappeared, then you are actually at greater risk of developing diabetes, because you're almost trying to be too efficient with the nutrients that are actually given upon you. One of the evidence for this having a role to play in obesity, less so, I mean, I think people are studying it, but the evidence is not solid of a key role that epigenetics might play in obesity. But, certainly, a role of epigenetics in metabolic diseases and other situations that are out there.
Steven, you asked a very interesting question regarding the role that gut flora has to play. Now, I have - I raise my hand, I am guilty, I have ignored the gut flora. Now, once again, to the uninitiated amongst you, a rather scary number, there are more bacteria in us than there are actually cells, they're just smaller and they're all in our gut. But there are actually more in terms of just sheer numbers, and they live in our gut and they have evolved with us. They play a critically important role in the way we metabolize, digest and move our food. So the gut flora play an incredibly important role and a lot of people - the technology is now out there to study, the population of gut flora within each of our guts, are they different between Eskimos and non-Eskimos, are they different in lean and obese people? What happens if you take too much antibiotics, does that mess up your metabolism? These are all very interesting questions, and it will play, no doubt, an important role in the control of our energy homeostasis systems.
Homer Yin, I think, asks two different questions. I think the first question that was asked was regarding about whether or not there is any gene screening for MC4R? There are, actually, but at the moment on a research basis, and I know that there are some companies in the States at the moment doing it on a customer basis for screening melanocortin-4 receptor mutations. But, certainly, in the UK the NHS does not screen it as a matter of fact. It's an interesting concept, because it is actually - I ran over it quite quickly - it's actually relatively frequent, so I would have thought that of people of a BMI above 30 and 35, we're probably looking at half to 1% of the population with pathogenic mutations in the MC4R. Now, it's nothing as severe as leptin deficiency, in a sense, for any number of different reasons, but it is definitely there are a lot of people out there that have not been identified with these changes in MC4R. But it's a relatively pure phenotype, so to speak, it is an energy homeostasis, it is an obesity phenotype, and there is debate out there about whether or not this is something that the NHS should do to actually start screening. Because I think you've got to watch this space.
Then the second question you asked is that has there been any effort to silence the gene that is involved in obesity? I think, I'm not sure I understand the question, there's not only one gene there are many different genes. But if you're asking about the concept of trying to silence a gene which is known to increase food intake as a way of controlling obesity, a form of gene therapy, I think it has a concept that's out there. I think technically it's difficult to deliver, and there are a couple of different reasons why, because you have to direct this silencing agent somewhere, but I guess you can use an antibody. But a large problem is that because it is the brain that controls food intake, largely, any targeting effects would necessarily have to be able to cross the blood/brain barrier and then specifically target molecules within the brain. People do try and do that, but when you're messing around with the brain there's always the issue of specificity versus effect. So I think - I don't know if I answered your question.
Now, what else do we have here? David, you asked an interesting question: What are the pros and cons of using non-vertebrate models for studying satiation and hunger pathways? Well, if we deal with the obvious pros first, is that invertebrates are easy to culture, so if you, for example, work on flies or work on C. elegans, the worms, you can have your entire experiment in the size of a filing cabinet. So, obviously, it's a lot less red space and there's a lot less red tape in terms of dealing with the Home Office. They don't care if you're working on worms, they just don't, okay? Or flies, who cares about flies? I don't want to get complaints from fly people out there. But that's the point, it is actually useful in that sense and I think you can ask certain specific questions about the pathways.
The cons, however, have to do with how we actually parcel energy homeostasis. If you look in mammals, so, say, a mouse, an invertebrate, there is actual fat, so energy is actually stored as fat in a specific place, and there are a lot of shared pathways. Within something like, for example, the fly you'd have to look at the fat body which has certain shared pathways, but not necessarily analogous, so that's a problem. I mean, down in the molecular level I think there are a lot of shared pathways, but on a physiological level of where the fat is, that becomes difficult. It even becomes more difficult when you actually deal with the worm, which don't have fat per se. It stores as lipids within the area, and how would you actually measure food intake very accurately within a worm? So, clearly, when you're studying food intake which is a systemic situation, it's easier to use mammals of all description in order to study it. However, the invertebrates are very useful because you can knock down a billion genes - not a billion, that's an exaggeration - you can knock down all their genes within flies and within C. elegans and ask very specific questions on a molecular level. So I think there is a space out there for invertebrates.
What other questions do we have? What about leptin resistance? That's an interesting question. So what is leptin resistance? Well, leptin resistance is the phenomenon in which if increases in leptin causes a decrease in food intake, how come if you're fat and you have lots of leptin you don't decrease food intake? So this goes back to the situation of what I was talking about, about whether leptin can be used as a drug, and leptin resistance just describes this phenomenon in which where leptin doesn't have an increase in function past a certain concentration level. That is resistance, if you want to call it, but it is because it's evolutionary, not designed to function in a pharmacological fashion, past a certain concentration level. So that is really the description of leptin resistance. It's interesting, because there are a lot of people out there that say, 'Well, if we can overcome this resistance' and let's use resistance in inverted commas, 'Would this be a real, an interesting target to use in order to target obesity?'. I think there is an argument out there for that, but people are still trying to overcome this resistance, which is actually quite difficult.
Ian: Is it understood how FTO is acting, and how the different alleles cause the additive phenotype? So my current research focuses on FTO. Do we know how FTO is acting? The short answer - do we know how the slips in FTO link to obesity? No. Do we know what FTO does? We're becoming to have a clearer idea. We now think and we now know that one of FTO's roles is as a nucleic acid modifier, specifically it modifies RNA. That's what it does, and we're trying to find out what that means, but the likelihood is that by modifying RNA it controls translation to some effect. How the different alleles cause the additive effect? We don't know is the answer, but we're currently in the process of trying to understand. So this is a cutting edge question or a cutting edge topic, and we know that it modifies RNA.
So we've got a question here from Tatiana. Thank you for your kind comments, I'm glad you - wherever you are calling from - stayed on to actually listen to this. Hello Tatiana. What do you think about stress-induced appetite suppression by MC4R, and what about comfort eating, it studies completely different pathways? So stress is not my speciality, I didn't realize - unless you typed the question wrong - I didn't realize that MC4R played a role in stress-induced appetite suppression. So I'm not sure about that, although stress does play a role in the flight. If you're stressed, say, for example, a lion was chasing you, you run, so adrenaline plays a role. There are different pathways that are there to actually get you going. I'm not sure the role of the MC4R necessarily plays in stress-induced appetite suppression, so I think it is a completely different pathway.
Comfort eating, ooh, that is interesting. I think you're asking a complex psychological question about why somebody might eat, and how you actually get the rewarding feeling from it, therefore feeling comfort? I don't know how to answer the question. I think I can answer the question about what the rewarding feeling is there for, first, so why is there a reward feeling? Why is there a concept of comfort eating to begin with? I think if you look at the control of food intake in two different ways, there is the homeostatic control, meaning the fuel gauge control: I have burnt 2,000 calories today, therefore, I need to eat 2,000 calories in order to survive. Why have the rewarding element? Well, because remember we talked about the evolution of eating, and eating as much as you can so that you would survive the famine. If you relied entirely on a fuel gauge, you'd eat 2,000 calories and survive the day, but if suddenly there were no calories tomorrow, the chances are you'd die. So you needed something on top of the fuel gauge to make sure you eat more.
Look into this as if you go to a three-course meal in a restaurant the chances are you have fulfilled your homeostatic requirements after your appetizer and your main, that's just the way it is. But, yet, when the waiter comes by with the dessert cart, or dessert trolley, 'Oh, there's chocolate cake' and you'll eat the chocolate cake. You'll eat the chocolate cake even though you're homeostatically full. But the 'ooh' factor, is what I call it - trademarked, patented - the 'ooh' factor is when you actually eat beyond your metabolic need. There is the chocolate cake, you eat it and why? Because it makes you feel good, and it makes you feel good so like sex it feels good so that you do it, otherwise you don't reproduce. Like food when you eat it it feels good so that you eat it.
So does this have any role in MC4R? Sorry, this is going a long way around. I think there are necessarily some overlapping pathways, but the hedonic pathways, the reward pathways are controlled in a different part of the brain that actually then projects to the hypothalamus.
So guys, listen, there are people frantically waving their hands at me saying that it's over time, it's over time, you're costing me a fortune! So, listen, I am really, really happy you guys stuck around to listen to me babble on, and anything else before I pass you back on to Lucy, otherwise thank you guys. So are your genes are to blame if your jeans don't fit? More than you think! Thanks guys.
LP: Thank you, Giles. So that's the end of our webinar and on behalf of Abcam I'd like to thank you for attending. For those whose questions weren't answered, we will contact you shortly with a response to your query. Just as a reminder, a PDF of this webinar will be available for download once you log-off; you will be redirected to a webpage. Also, if you have any further questions, please do not hesitate to contact our scientific support team on [email protected] We hope you found this webinar useful, and we look forward to welcoming you to another webinar in the future. Thank you again for attending, and good luck with your research!
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