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Posts Tagged ‘leptins’


Obesity

Larry H. Bernstein, MD, FCAP, Curator

Leaders in Pharmaceutical Intervention

2010 Douglas L. ColemanJeffrey M. Friedman

Shaw Laureates 2009 Life Science and Medicine

Douglas L. Coleman (6 October 1931 – 16 April 2014) was a scientist and professor at The Jackson Laboratory, in Bar Harbor, Maine. His work predicted that the ob gene encoded the hormoneleptin,[1] later co-discovered in 1994 by Jeffrey Friedman, Rudolph Leibel and their research teams at Rockefeller University.[2][3][4][5][6][7][8] This work has had a major role in our understanding of the mechanisms regulating body weight and that cause of humanobesity.[9]

Coleman was born in Stratford, Ontario. He obtained his BS degree from McMaster University in 1954 and his PhD in Biochemistry from the University of Wisconsin in 1958. He was elected a member of the US National Academy of Sciences in 1998. He won the Shaw Prize in 2009,[10] the Albert Lasker Award for Basic Medical Research in 2010, the 2012 BBVA Foundation Frontiers of Knowledge Award in the Biomedicine category and the 2013 King Faisal International Prize for Medicine[11] jointly with Jeffrey M. Friedman[9] for the discovery of leptin.

http://www.nytimes.com/2014/04/26/us/douglas-l-coleman-82-dies-found-a-genetic-cause-of-obesity.html

The Genetics of Obesity

Winner of the  2013 KFIP Prize for  Medicine

Professor Douglas Coleman was born on October 5, 1931, in Stratford, Ontario, Canada. He obtained a B.Sc. in Chemistry in 1954 from McMaster University in Hamilton, Ontario, then went to the University of Wisconsin in Madison, WI, U.S.A., where he obtained M.S. and Ph.D. degrees in Biochemistry in 1956 and 1958, respectively. He served as a Research Assistant at the University of Wisconsin from 1954-1957 and as E.I. Dupont de Nemours Fellow from 1957-1958. He joined the Jackson Laboratory in Bar Harbor, ME, where he spent his entire career rising from Associate Staff Scientist In 1958 to Senior Staff Scientist in 1968. He also served as Assistant Director for Research from 1969-1970 and Interim Director  from 1975-1976. Upon his retirement in 1991, he was appointed Senior Staff Scientist Emeritus at Jackson. He was also consultant to the National Health Institutes, serving on the Metabolism Study Section from 1972-1974 and was frequently consulted on various other special study sections involving genetic diabetes, obesity and nutrition. He also served as Visiting Professor at the University of Geneva (1979-1980).

Professor Coleman’s research interests focus on biochemical genetics, regulation of metabolism, obesity, diabetes and hormone action. He is best known for his studies on the obesity-diabetes syndrome. He discovered the db gene, one of the two genes responsible for the genetic events regulating appetite control. He carried out a series of fundamental experiments with parabiotic mice which demonstrated the hormone-hormone receptor axis of leptin and the leptin receptor long before their discovery. The discoveries of Coleman and Friedman represent one of the most important biological breakthroughs in recent decades.

Professor Coleman received several prestigious awards and honors, including the Claude Bernard Medal by the European Diabetes Foundation in 1977, the Distinguished Alumni Award in Science by McMaster University in 1999, the Gairdner International Award in 2005, the Shaw Prize for Life Sciences and Medicine in 2009 (jointly with Jeffrey M. Friedman), the Albert Lasker Basic Medical Research Award (jointly with Jeffrey M. Friedman) and the Outstanding Forest Stewardship Award (Maine Forest Service). He was elected to the National Academy of Sciences in 1991, and was awarded Honorary D.Sc. from Louisiana State University in 2005 and Honorary D.Sc. from McMaster University in 2006. He is a member of the American Association of Biological Chemists.

Professor Douglas Leonard Coleman was awarded the prize because the research findings by him and Professor Friedman led to the identification and characterization of the leptin pathway. This seminal discovery has had a major impact on our understanding of the biology of obesity, describing some of the key afferent pathways in body weight regulation active in man. Their fundamental discoveries have also helped in the recognition of more illuminating views of the endocrine system. Because of their major contribution to the field of the genetics of obesity they have been awarded King Faisal International Prize in Medicine for the year 2013.

Leaping for leptin: the 2010 Albert Lasker Basic Medical Research Award goes to Douglas Coleman and Jeffrey M. Friedman

Ushma S. Neill

J Clin Invest. 2010 Oct 1; 120(10): 3413–3418.
Published online 2010 Sep 21. doi:  10.1172/JCI45094

Douglas Coleman never intended to study diabetes or obesity. Jeffrey M. Friedman had childhood dreams of being a veterinarian. But together, the two scientists have opened the field of obesity research to molecular exploration. On September 21, the Albert and Mary Lasker Foundation announced that they will award Coleman and Friedman (Figure (Figure1)1) with the 2010 Albert Lasker Basic Medical Research Award in recognition of their contributions toward the discovery of leptin, a hormone that regulates appetite and body weight. This hormone provides a key means by which changes in nutritional state are sensed and in turn modulate the function of many other physiologic processes. The story of the discovery of the first molecular target of obesity is one of tenacity and determination.

Figure 1

Douglas Coleman (left) and Jeffrey M. Friedman (right) share the 2010 Albert Lasker Basic Medical Research Award for the discovery of leptin, a breakthrough that opened obesity research to molecular exploration.

From Canada to Maine

Douglas Coleman was raised in Ontario, Canada, the only child of English immigrant parents, who encouraged him to excel in school; he recalled, “Although my parents never had the luxury of completing high school, they always encouraged me to pursue a higher education, and in high school, I developed a keen interest in chemistry and biology.” Coleman pursued his interest in chemistry at McMaster University. It was there he met his future wife, Beverly Benallick, “the only girl to graduate in Chemistry in the Class of 1954.” During his time at McMaster University, Coleman began to focus on organic chemistry and had the fortune of working with, “a very dynamic professor, Sam Kirkwood, who not only taught me the rudiments of biochemistry, but also instilled an appreciation of the scientific method.” Kirkwood encouraged Coleman to continue his biochemistry studies at the University of Wisconsin, at which he received a PhD in 1958.

In those days, postdoctoral fellowships were rare, and graduates had two options: academia or industry. Coleman took a third option, as an associate staff scientist at what was then known as the Roscoe B. Jackson Memorial Laboratory in Bar Harbor, Maine. Coleman has noted, “My intention was to stay one or two years, expanding my skills in multiple fields, especially genetics and immunology. To my great pleasure, The Jackson Laboratory provided a rich environment, including world-class animal models of disease, interactive colleagues, and a backyard that included the stunning beauty of Acadia National Park.” The Coleman family put down roots, raising their three sons there as Coleman rose through the ranks to senior staff scientist and served terms as assistant director of research and interim director (Figure (Figure2).2). He noted, “Without a doubt, I was lucky in my choice of starting my career at The Jackson Laboratory. It was a wonderful place in which to work, and I never pursued another position.”

Figure 2

Coleman at the bench at The Jackson Laboratory in 1960.

Making magic from a mutant

His early work involved muscular dystrophy and the development of a new field, mammalian biochemical genetics, establishing that genes control enzyme turnover as well as structure. However, his focus changed when a colleague asked for his help characterizing a mutant (Figure (Figure3)3) that had spontaneously arisen at the labs. He recalled, “Initially, I had no intention of studying the diabetes/obesity syndrome, but in 1965, a spontaneous mouse mutation was discovered, and I began research that would consume much of my scientific thought for the better part of three decades.” The new mutant was polydipsic and polyuric as well as being massively obese and hyperphagic. His colleague, Katherine Hummel, was studying diabetes insipidus and asked if he could determine whether the new mutant had diabetes insipidus or mellitus. He reported back that it was diabetes mellitus: “Her initial response was that she was not interested, but I convinced her that with a little further work we could produce a solid manuscript announcing this potentially valuable mutant to the world.” This mouse owed its phenotype to two defective copies of a gene that researchers dubbed diabetes (db) (1).

Figure 3

Wild-type and obese mice.

When Coleman and his colleagues began characterizing the db/db mouse, they began to ponder whether some circulating factor might regulate the severity of diabetes: perhaps a factor in the normal mouse could inhibit the development of the obesity and diabetes found in the db/db mutant. Conversely, perhaps a circulating factor present in the db/db mouse might cause the diabetes-like syndrome in the normal mouse. If the hypothetical factor was carried through the blood, Coleman reasoned, they could test for its presence by linking the blood supplies of the various mouse strains — an experimental setup called parabiosis. Fortunately, others at The Jackson Laboratory were using parabiosis to assess whether any circulating factors were involved in anemic mutants, and they were able to show Coleman how to do it successfully.

When Coleman hooked the wild-type mice and the db/db mice together, rather than overeating, as the db/dbmice did, the wild-type mice stopped eating and died from starvation (Figure (Figure44 and ref. 2). His hypothesis was correct: the db/db mice indeed must have released a factor that inhibited the wild-type animals’ drive to eat, but the mutant animals could not respond to it.

Figure 4

Summary of parabiosis experiments performed by Coleman.

Coleman needed more proof of this mystery circulating factor regulating food intake. He turned to another overweight mouse that also had arisen by chance at The Jackson Laboratory, this one called “obese,” whose aberrant physiology arises from two defective copies of a different gene (ob) (3). Unfortunately, the ob/obmouse was on a different genetic background, and due to immune-mediated rejection, parabiosis could only be performed successfully on mice with the same strain background. Coleman described his need for resolve, “Since the obese and diabetic mutants were on different genetic backgrounds, it took years for me to be able to perform all of the desired pairings.”

Coleman persevered and finally got the strains to match so he could successfully hook them together in a parabiosis experiment. When joined to a db/db mouse, the ob/ob mouse stopped eating and starved to death, while the db/db mouse remained obese, just as the normal mice had in the previous experiment. In contrast, attaching wild-type mice to ob/ob animals did nothing to the wild-type mice and caused the ob/ob mice to limit their food consumption and gain less weight (Figure (Figure4).4). Coleman concluded that the ob/ob mice failed to produce a hormone that inhibits eating, while the db/db mice overproduced it but lack the receptor to transmit the hormonal signal (4).

Coleman faced some skepticism for his conclusion that obesity was not just about willpower and eating habits but also involved chemical and genetic factors. In this regard, he said, “When I published these findings, the long-standing dogma was that obesity was a behavioral problem (a lack of willpower) and not a physiological problem (a hormonal imbalance). I had to deal with this behavioral dogma most of my career.”

To validate his hypothesis, Coleman would need to identify the db and ob genes and protein products, a task that proved to be an insurmountable challenge at the time. He noted, “Definitive proof of my conclusions required isolating the satiety factor — a feat that resisted rigorous experimentation.” That is, until Jeffrey Friedman set his sights upon the task.

 After his third year of internal medicine residency at Albany Medical Center Hospital, Friedman  had no concrete plans for the following year, as he was not scheduled to begin a fellowship at the Brigham and Women’s Hospital in Boston until a year later. Friedman recalled, “I had no particular plans for the gap year, and John Balint, one of my professors, thought I might like research — why he thought I might have some particular aptitude, I can’t really tell. He said, ‘I have this friend at Rockefeller [Mary Jeanne Kreek], why don’t you go spend a year with her and see if you like research?’ I didn’t know what else I was going to do. My mother thought I should go spend the year as a ship’s doctor.”
A fat chance

Friedman was enraptured by what Kreek studied: how molecules control behavior. “That was 1981 and it was beginning to be evident that molecular biology was going to have a big impact, so instead of going to the Brigham for a fellowship, I abandoned medicine and decided to get a PhD with Jim Darnell [2002 Lasker award winner for his work in RNA processing and cytokine signaling], who was one of the leaders in molecular biology,” he noted. Friedman’s thesis was on the regulation of liver gene expression — how genes are turned on and off as liver regenerates. However, there was something he did on the side that was more impactful: Kreek had asked him to work with Bruce Schneider, another faculty member at Rockefeller University, to make an RIA for β-endorphin. However, Schneider’s primary interest was not in β-endorphin, but rather in cholecystokinin (CCK). In 1979, Rosalyn Yalow had published a paper in which she reported reduced levels of CCK in the brain of ob/ob mice and boldly claimed that CCK was the circulating factor that caused the ob/ob mice to be fat (5). Friedman recalled, “Well, Bruce had the exact opposite data, this was published in the JCI (6), and this started a battle with Yalow over who was correct. To address this, in 1982 Don Powell, Bruce, and I set out to clone the Cck gene so we could map it. We collaborated with Peter D’Eustachio at NYU, who showed that it was on chromosome 9 (7); ob is on 6, db is on 4. I still have Peter’s notebook entry from that time in which he wrote, ‘CCK does not map to chromosome 6, home ofob.’” So the question for Friedman became, if the circulating hormone is not CCK, then what is? When he started his own laboratory in 1986 at Rockefeller, he set out to find it, and as he recalls, “In a way what theob mouse represented to me was another instance where a molecule was controlling a behavior, the same as in Mary Jeanne’s lab.”

Do these genes make me look fat?

In the mid ’80s, positional cloning was not easy, but Friedman turned to the then-new techniques of physical gene mapping, complimented by conventional genetic mapping in mice. It had long been known that the obgene resided somewhere on mouse chromosome 6, but narrowing down the region was arduous, as the trait is recessive, necessitating the breeding of several generations. Friedman and his laboratory first determined which DNA markers were inherited along with the obese phenotype in over 1,600 mice crossbred from obese and nonobese strains. He remembers, “It was a mind numbing exercise you hoped someday would lead somewhere.” Since the genetic and physical maps are colinear, DNA markers that were linked to ob in genetic crosses could be used to clone the surrounding DNA. Using this approach, they eventually identified the portion of the genome in which all markers were always coinherited with ob among the progeny of the crosses. This region defined the chromosomal region in which the ob gene resided. As they had predicted when the crosses were set up, this region corresponded to an approximately 300,000–base pair region on chromosome 6. They then screened recombinant clones across this region for exon-intron boundaries, which indicate the presence of genes. One of the first three genes they isolated was expressed exclusively in adipose tissue, and the expression of the mutant gene was found to be 20 times greater in one of the ob/ob mutants than in controls. In a second mutant, the gene was not expressed at all, providing clear evidence that this gene encoded the ob gene. When they looked in the human genome, they found an ob homolog that was 84% identical with the mouse ob gene, establishing ob as a highly conserved, biologically important gene (8).

Once a fat-specific gene was found in the vicinity of ob, he remembered being almost numb with excitement as a set of confirmatory experiments unfolded. “I went in late on a Saturday night, and I found a radioactive probe for this gene, and I found a blot with RNA from fat tissue of normal and mutant mice. I hybridized the blot that evening and washed it at 1 in the morning. I couldn’t sleep, and I woke up at 5 or 6 and developed the blot. When I looked at the data, I immediately knew that we had cloned ob. When I saw it, I was in the darkroom, and I pulled up the film and looked at it under the light and got weak-kneed. I sort of fell backwards against the wall. This gene was in the right region of the chromosome, it was fat specific, and its expression was altered in two independent strains of ob mice. Before this, we didn’t know where ob would be expressed — and while fat was one of the tissues I considered, in principle the gene could have been expressed in any specialized cell type anywhere that had no obvious relationship to fat. But on the other hand, seeing a gene in the right region expressed exclusively in the fat . . . that gets your attention.” When he found out at 6 in the morning, he called his wife and said “we did it!,” and then, a few hours later he, called his former PhD advisor Jim Darnell: “I told him but I wasn’t sure he believed me.” That afternoon, he met some friends at Pete’s Tavern, “and we opened a bottle of champagne, and I told them, ‘I think this is going to be pretty big.’”

Next Friedman set his sights on actually identifying the product secreted by the ob gene and validating Coleman’s circulating hormone hypothesis. Together with Stephen Burley, his laboratory engineered E. colito fabricate the secreted protein, generated antibodies that would bind it, and showed that humans and rodents secrete it. In the last sentence of the 1995 Science paper describing these findings, Friedman “propose[d] that this 16-KD protein be called leptin, derived from the Greek root leptos, meaning thin” (9). The paper also showed that db/db mice made excess quantities of leptin, as predicted by Coleman, and its levels in plasma decreased in normal animals and obese humans after weight loss. He remembered, “It was an unbelievable time in the lab. The idea that there was this hormone that regulated body weight, and that we had found it, was just unimaginable. I’d wake up in the middle of the night just smiling.”

As for the name leptin, it has not only a Greek root, but a French one too. At a meeting, Friedman met Frenchman Roger Guillemin, who won a Nobel Prize for his work on peptide hormone production by the brain. A few weeks after the meeting, Friedman got a letter from him that he recalls saying, “I really liked what you had to say, but I have one quibble: you refer to these as obesity genes, but I think they are lean genes because the normal allele keeps you thin. But calling them lean genes sounds awkward. The nicest sounding root for thin is from Greek, so I propose you call ob and db ‘lepto-genes.’” So when it came time to name it, Friedman remembered Guillemin’s suggestion, and therein, the name leptin was coined.

Leptin’s legacy

Later in 1995, another group described the leptin receptor (10), and then subsequently, Friedman and another group showed that this leptin receptor is encoded by the db gene and has multiple forms, one of which is defective in Coleman’s originally described db/db mice (11, 12). Friedman also showed that the leptin receptor is especially abundant in the hypothalamus in which leptin can activate signal transduction and phosphorylation of the Stat3 transcription factor (13).

Over the years, numerous laboratories have studied leptin’s mechanism of action. Leptin acts on receptors expressed in groups of neurons in the hypothalamus, in which it inhibits appetite, in part, by counteracting the effects of neuropeptide Y, a potent feeding stimulant secreted by cells in the gut and in the hypothalamus, by thwarting the effects of anandamide, another potent feeding stimulant, and by promoting the synthesis of α-MSH (melanocyte stimulating hormone), an appetite suppressant (14). Leptin is produced in large amounts by white adipose tissue but can also be produced in lesser amounts by brown adipose tissue, syncytiotrophoblasts, ovaries, skeletal muscle, stomach, mammary epithelial cells, bone marrow, pituitary, and liver. Leptin’s actions are also not limited to regulating food intake, as it is has been shown to have roles in fertility, immunity, angiogenesis, and surfactant production. Friedman adds that the hormone, “has effects on many physiological systems, including the immune system where it modulates T cells, macrophages, and platelets. It now appears that leptin provides a key means by which nutritional state can regulate a host of other physiological systems.” While most of these actions are mediated by effects on the CNS, two of many key questions are, which of leptin’s effects on peripheral systems are direct, and which are indirect via the brain?

A magic bullet?

The first proof that leptin was important in humans came in 1997 when Stephen O’Rahilly and colleagues found two morbidly obese children who carried a mutation in the leptin gene (15). These researchers went on to show that leptin-replacement therapy could be useful in individuals with leptin mutations (16). Injection of leptin into these children led to rapid weight loss and markedly reduced food intake (Figure (Figure5).5). Leptin-replacement therapy also has potent effects in other clinical settings, including lipodystrophy, a disease state in which animals and humans have little white fat and develop severe diabetes, with profound insulin resistance and high plasma lipid levels. Because this syndrome is associated with low circulating levels of leptin, Shimomura and colleagues tested the effects of leptin-replacement therapy in mice and showed that it was highly effective (17); similar efficacy was later shown in humans (18). More recently, leptin treatment has shown a profound anti-diabetic effect in type 1 diabetic animals (19). Leptin replacement has also been shown to be of clinical benefit in other states of leptin deficiency, including hypothalamic amenorrhea (20).

Figure 5

Effects of r-metHuLeptin on the weight a child with congenital leptin deficiency.

Excited by leptin’s potential for the treatment of obesity, the biotech company Amgen paid $20 million to Rockefeller to license the hormone. With so much of the world’s population overweight or obese, a treatment or cure would be a major advance in public health and would likely be very lucrative. Amgen sponsored a large clinical trial, giving leptin to overweight adults, but while a subset of obese patients lost significant amounts of weight on leptin, the average magnitude of the effect was minimal, dampening hopes that leptin was the magic bullet in the obesity fight (21). After the trial, Amgen announced that they had suspended studies of the effects of leptin for the treatment of human obesity.

Friedman says he understands why the trials failed: “Even before leptin was tested in obese patients, we knew from animal studies that this hormone was not likely to be a panacea for every obese patient and that the response seen in ob/ob mice wasn’t going to be the typical case for obese humans. Leptin levels are elevated in obese humans, suggesting that obesity is often associated with leptin resistance and raising the possibility that increasing already high levels was going to be of arguable benefit.” The key to making leptin work may be in coaxing the brain to respond to leptin: some people are simply not sensitive enough or they develop resistance. Friedman predicts that through personalized medicine, doctors may at some point be able to identify which obese people will respond to leptin. In the meantime, there is some clinical evidence that leptin’s ability to reduce weight among obese patients can be restored by combining it with other agents (22).

The thrill of discovery

For all the social implications, potential profits, and medical possibilities, Friedman is circumspect but proud about the discovery of leptin, saying, “whether it finds its way into general usage as an antiobesity drug, the use of modern methods to identify and target the components of the leptin- signaling pathway will, I believe, form the basis for new pharmacological approaches to the treatment of obesity and other nutritional disorders.” Coleman agrees, stating that “with the discovery of leptin and the subsequent cloning of the leptin receptor, the field exploded. With these findings, two long-standing misconceptions were definitively laid to rest: obesity was not merely a behavioral problem but rather had a significant physiological component; and adipose tissue was not merely a fat-storage site but rather an important endocrine organ.”

Both Coleman and Friedman (Figure (Figure6)6) were overwhelmed and humbled by the news that they would receive the 2010 Lasker Award for Basic Medical Research. Coleman notes, “I have always viewed this award as one of the most esteemed of the several truly prestigious biomedical research awards, and it is with great pride and humility that I accept this prestigious prize. I was also especially delighted to learn that I would be sharing this award with Jeffrey Friedman, who always acknowledged my earlier contributions to our field.” Friedman added, “It is an honor to join a group of other winners who really are at the highest level of science. To be placed among them is just hard to fathom.”

Figure 6

Coleman and Friedman, together at The Jackson Laboratory, in 1995.

Coleman retired from his scientific career in 1991. He has said that at his retirement ceremony “someone commented that my career was characterized by the ability to use the simplest technique to answer the most complex biological questions.” Friedman, however, is still at the bench and active as ever in his hunt to determine exactly how leptin regulates food intake. Through their determination and persistence, the two have provided a molecular framework for understanding obesity, but they have different opinions about how much luck played into their findings. Coleman has noted that he favors the Louis Pasteur quote, “Luck favors the prepared mind.” But Friedman has a different perspective, stating “my story suggests that in many cases, the prepared mind is favored by chance.”

Acknowledgments

As Coleman was away and unavailable for comment during the preparation of this article, his quotations were taken from an autobiography he wrote when accepting the Shaw prize in 2009, from his acceptance remarks for the Lasker prize, and from a profile written by Luther Young posted on the Bangor Daily Newsin 2009 ( http://www.bangordailynews.com/story/Hancock/Scientists-work-at-Jackson-Lab-lauded,118612?print=1).

References
1. Hummel KP, Dickie MM, Coleman DL. Diabetes, a new mutation in the mouse. Science.1966;153(740):1127–1128. doi: 10.1126/science.153.3740.1127. [PubMed] [Cross Ref]
2. Coleman DL, Hummel KP. Effects of parabiosis of normal with genetically diabetic mice. Am J Physiol.1969;217(5):1298–1304. [PubMed]
3. Ingalls AM, Dickie MM, Snell GD. Obese, a new mutation in the house mouse. J Hered.1950;41(12):317–318. [PubMed]
4. Coleman DL. Effects of parabiosis of obese with diabetes and normal mice. Diabetologia. 1973;9(4):294–298. doi: 10.1007/BF01221857. [PubMed] [Cross Ref]
5. Straus E, Yalow RS. Gastrointestinal peptides in the brain. Fed Proc. 1979;38(9):2320–2324. [PubMed]
6. Schneider BS, Monahan JW, Hirsch J. Brain cholecystokinin and nutritional status in rats and mice. J Clin Invest. 1979;64(5):1348–1356. doi: 10.1172/JCI109591. [PMC free article] [PubMed] [Cross Ref]
7. Friedman JM, Schneider BS, Barton DE, Francke U. Level of expression and chromosome mapping of the mouse cholecystokinin gene: implications for murine models of genetic obesity. Genomics.1989;5(3):463–469. doi: 10.1016/0888-7543(89)90010-4. [PubMed] [Cross Ref]
8. Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM. Positional cloning of the mouse obese gene and its human homologue. Nature. 1994;372(6505):425–432. doi: 10.1038/372425a0. [PubMed][Cross Ref]
9. Halaas JL, et al. Weight-reducing effects of the plasma protein encoded by the obese gene. Science.1995;269(5223):543–546. doi: 10.1126/science.7624777. [PubMed] [Cross Ref]
10. Tartaglia LA, et al. Identification and expression cloning of a leptin receptor, OB-R. Cell.1995;83(7):1263–1271. doi: 10.1016/0092-8674(95)90151-5. [PubMed] [Cross Ref]
11. Chen H, et al. Evidence that the diabetes gene encodes the leptin receptor: identification of a mutation in the leptin receptor gene in db/db mice. Cell. 1996;84(3):491–495. doi: 10.1016/S0092-8674(00)81294-5.[PubMed] [Cross Ref]
12. Lee GH, et al. Abnormal splicing of the leptin receptor in diabetic mice. Nature. 1996;379(6566):632–635. doi: 10.1038/379632a0. [PubMed] [Cross Ref]
13. Vaisse C, Halaas JL, Horvath CM, Darnell JE, Jr, Stoffel M, Friedman JM. Leptin activation of Stat3 in the hypothalamus of wild-type and ob/ob mice but not db/db mice. Nat Genet. 1996;14(1):95–97. [PubMed]
14. Friedman JM, Halaas JL. Leptin and the regulation of body weight in mammals. Nature.1998;395(6704):763–770. doi: 10.1038/27376. [PubMed] [Cross Ref]
15. Montague CT, et al. Congenital leptin deficiency is associated with severe early-onset obesity in humans.Nature. 1997;387(6636):903–908. doi: 10.1038/43185. [PubMed] [Cross Ref]
16. Farooqi IS, et al. Beneficial effects of leptin on obesity, T cell hyporesponsiveness, and neuroendocrine/metabolic dysfunction of human congenital leptin deficiency. J Clin Invest.2002;110(8):1093–1103. [PMC free article] [PubMed]
17. Shimomura I, Hammer RE, Ikemoto S, Brown MS, Goldstein JL. Leptin reverses insulin resistance and diabetes mellitus in mice with congenital lipodystrophy. Nature. 1999;401(6748):73–76. doi: 10.1038/43448.[PubMed] [Cross Ref]
18. Oral EA, et al. Leptin-replacement therapy for lipodystrophy. N Engl J Med. 2002;346(8):570–578. doi: 10.1056/NEJMoa012437. [PubMed] [Cross Ref]
19. Wang MY, et al. Leptin therapy in insulin-deficient type I diabetes. Proc Natl Acad Sci U S A.2010;107(11):4813–4819. doi: 10.1073/pnas.0909422107. [PMC free article] [PubMed] [Cross Ref]
20. Welt CK, et al. Recombinant human leptin in women with hypothalamic amenorrhea. N Engl J Med.2004;351(10):987–997. doi: 10.1056/NEJMoa040388. [PubMed] [Cross Ref]
21. Heymsfield SB, et al. Recombinant leptin for weight loss in obese and lean adults: a randomized, controlled, dose-escalation trial. JAMA. 1999;282(16):1568–1575. doi: 10.1001/jama.282.16.1568.[PubMed] [Cross Ref]
22. Roth JD, et al. Leptin responsiveness restored by amylin agonism in diet-induced obesity: evidence from nonclinical and clinical studies. Proc Natl Acad Sci U S A. 2008;105(20):7257–7262. doi: 10.1073/pnas.0706473105. [PMC free article] [PubMed] [Cross Ref]
Autobiography of Jeffrey M Friedman

My laboratory identified leptin, a hormone that is produced by fat tissue. Leptin acts on the brain to modulate food intake and functions as an afferent signal in a feedback loop that regulates weight. My route to this hormone is filled with a number of chance events and turns of fate that were in no way predictable at the time that I started my career.I grew up in the suburbs of New York City in a village where children had enormous freedom. I recall from an early age riding my bicycle everywhere without my parents, or anyone else for that matter, knowing my whereabouts. My father was a radiologist and my mother was a teacher. No one in my family or community had pursued an academic career and at the time I was completely unaware of the possibility that one could make a career in science. In my family, the highest level of achievement was to become a doctor and, despite my earliest dreams of a career as a professional athlete (made unlikely by a notable lack of talent) and a later wish to become a veterinarian, I became a doctor.I was originally trained in internal medicine with some subspecialty training in gastroenterology. In medical school and as a medical resident, I participated in some modest research studies. The first piece of work I completed related to the effects of dietary salt on the regulation of blood pressure. After completing this project, I excitedly submitted a paper for publication. I remember one of the reviews verbatim: “This paper should not be published in the Journal of Clinical Investigation or anywhere else.” Fortunately, one of my mentors in medical school still thought I might have some aptitude for research. He suggested that I go to The Rockefeller University to work in a basic science research laboratory. I joined the laboratory of Dr Mary-Jeanne Kreek to study the effects of endorphins in the development of narcotic addiction.I was fascinated by the idea that endogenous molecules could alter behaviour and emotional state. At The Rockefeller University, I met another scientist, Bruce Schneider. Bruce was studying cholecystokinin (CCK), a peptide hormone that is secreted by intestinal cells. CCK aids digestion by stimulating the secretion of enzymes from the pancreas and bile from the gallbladder. CCK had also been found in neurons of the brain, although its function there was less clear. In the late 1970s, it was shown that injections of CCK reduce food intake. This finding appealed to me as another example of how a single molecule can change behavior. One other fact also piqued my interest: There were indications that the levels of CCK were decreased in a genetically obese ob/ob mouse. These mutant mice are massively obese as a consequence of a defect in a single gene. The mice eat excessively and weigh 3 to 5 times as much as normal mice. It was thus hypothesized that CCK functions as an endogenous appetite suppressant and that a deficiency of CCK caused the obesity evident in ob/ob mice. Fascinated by this possibility, I set out to establish the possible role of CCK in the pathogenesis of obesity in these animals. To do this I was going to need additional training in basic research, so I abandoned my plans to continue medical training in gastroenterology and instead entered the PhD program at The Rockefeller University.As a PhD student I worked in the laboratory of Jim Darnell, studying the regulation of gene expression in liver, and learning the basic tools of molecular biology. But I carried my interest in the ob/ob gene with me. At the end of my graduate studies, two colleagues and I successfully isolated the CCK gene from mouse. One of the first studies we performed after isolating the gene was to determine its chromosomal position. We found that the CCK gene was not on chromosome 6, where the ob mutation had been localized, which thus excluded defective CCK as the cause of the obesity. The question thus remained: What is the nature of the defective gene in ob/ob mice?

After receiving my PhD in 1986, I became an assistant professor at The Rockefeller University and set out to answer this question. The culmination of what proved to be an 8-year odyssey was the identification of the ob gene in 1994. We now know that the ob gene encodes the hormone leptin. The discovery of this hormone, a singular event in my life, was absolutely exhilarating. The realization that nature had happened upon such a simple and elegant solution for regulating weight was the closest thing I have ever had to a religious experience. Subsequent studies revealed that injections of leptin dramatically decrease the food intake of mice and other mammals. My current studies now focus on several questions, including the one that originally aroused my interest in this mutation: How is it that a single molecule – leptin – profoundly influences feeding behavior? An esteemed colleague of mine remarked recently that I had searched for the ob gene primarily so that I could approach the question I had started with. It is as yet unclear whether I will succeed in understanding how a single molecule can influence a complex behaviour.

  1. Coleman, DL (1978). “Obese and Diabetes: two mutant genes causing diabetes-obesity syndromes in mice”. Diabetologia 14: 141–148. doi:10.1007/bf00429772.
  2. Jump up^ Green ED, Maffei M, Braden VV, Proenca R, DeSilva U, Zhang Y, Chua SC Jr, Leibel RL, Weissenbach J, Friedman JM. (August 1995). “The human obese (OB) gene: RNA expression pattern and mapping on the physical, cytogenetic, and genetic maps of chromosome 7”.Genome Research 5 (1): 5–12. doi:10.1101/gr.5.1.5.PMID 8717050.
  3. Jump up^ Shell E (January 1, 2002). “Chapter 4: On the Cutting Edge”. The Hungry Gene: The Inside Story of the Obesity Industry. Atlantic Monthly Press. ISBN 978-1-4223-5243-4.
  4. Jump up^ Shell E (January 1, 2002). “Chapter 5: Hunger”. The Hungry Gene: The Inside Story of the Obesity Industry. Atlantic Monthly Press.ISBN 978-1-4223-5243-4.
  5. Jump up^ Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM (December 1994). “Positional cloning of the mouse obese gene and its human homologue”. Nature 372 (6505): 425–432.doi:10.1038/372425a0. PMID 7984236.
  6. Jump up^ Rosenbaum M (1998). “Leptin”. The Scientist Magazine.
  7. Jump up^ Okie S (February 11, 2005). “Chapter 2: Obese Twins and Thrifty Genes”. Fed Up!: Winning the War Against Childhood Obesity. Joseph Henry Press, an imprint of the National Academies Press. ISBN 978-0-309-09310-1.
  8. Jump up^ Zhang, Y; Proenca, P; Maffei, M; Barone, M; Leopold, L; Friedman, JM. (1994). “Positional cloning of the mouse obese gene and its human homologue”. Nature 372 (6505): 425–432.doi:10.1038/372425a0. PMID 7984236.
  9. ^ Jump up to:a b Friedman, Jeffrey (2014). “Douglas Coleman (1931–2014) Biochemist who revealed biology behind obesity”. Nature 509 (7502): 564. doi:10.1038/509564a. PMID 24870535.
  10. Jump up^ Shaw Prize 2009
  11. Jump up^ King Faisal Prize 2013 for Medicine

A Metabolic Master Switch Underlying Human Obesity

Researchers find pathway that controls metabolism by prompting fat cells to store or burn fat

Aug 21, 2015  http://www.technologynetworks.com/Metabolomics/news.aspx?ID=182195

Researchers find pathway that controls metabolism by prompting fat cells to store or burn fat.

Obesity is one of the biggest public health challenges of the 21st century. Affecting more than 500 million people worldwide, obesity costs at least $200 billion each year in the United States alone, and contributes to potentially fatal disorders such as cardiovascular disease, type 2 diabetes, and cancer.

But there may now be a new approach to prevent and even cure obesity, thanks to a study led by researchers at MIT and Harvard Medical School. By analyzing the cellular circuitry underlying the strongest genetic association with obesity, the researchers have unveiled a new pathway that controls human metabolism by prompting our adipocytes, or fat cells, to store fat or burn it away.

“Obesity has traditionally been seen as the result of an imbalance between the amount of food we eat and how much we exercise, but this view ignores the contribution of genetics to each individual’s metabolism,” says senior author Manolis Kellis, a professor of computer science and a member of MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) and of the Broad Institute.

New mechanism found

The strongest association with obesity resides in a gene region known as “FTO,” which has been the focus of intense scrutiny since its discovery in 2007. However, previous studies have failed to find a mechanism to explain how genetic differences in the region lead to obesity.

“Many studies attempted to link the FTO region with brain circuits that control appetite or propensity to exercise,” says first author Melina Claussnitzer, a visiting professor at CSAIL and instructor in medicine at Beth Israel Deaconess Medical Center and Harvard Medical School. “Our results indicate that the obesity-associated region acts primarily in adipocyte progenitor cells in a brain-independent way.”

To recognize the cell types where the obesity-associated region may act, the researchers used annotations of genomic control switches across more than 100 tissues and cell types. They found evidence of a major control switchboard in human adipocyte progenitor cells, suggesting that genetic differences may affect the functioning of human fat stores.

To study the effects of genetic differences in adipocytes, the researchers gathered adipose samples from healthy Europeans carrying either the risk or the non-risk version of the region. They found that the risk version activated a major control region in adipocyte progenitor cells, which turned on two distant genes, IRX3 and IRX5.

Control of thermogenesis

Follow-up experiments showed that IRX3 and IRX5 act as master controllers of a process known as thermogenesis, whereby adipocytes dissipate energy as heat, instead of storing it as fat. Thermogenesis can be triggered by exercise, diet, or exposure to cold, and occurs both in mitochondria-rich brown adipocytes that are developmentally related to muscle, and in beige adipocytes that are instead related to energy-storing white adipocytes.

“Early studies of thermogenesis focused primarily on brown fat, which plays a major role in mice, but is virtually nonexistent in human adults,” Claussnitzer says. “This new pathway controls thermogenesis in the more abundant white fat stores instead, and its genetic association with obesity indicates it affects global energy balance in humans.”

The researchers predicted that a genetic difference of only one nucleotide is responsible for the obesity association. In risk individuals, a thymine (T) is replaced by a cytosine (C) nucleobase, which disrupts repression of the control region and turns on IRX3 and IRX5. This then turns off thermogenesis, leading to lipid accumulation and ultimately obesity.

By editing a single nucleotide position using the CRISPR/Cas9 system — a technology that allows researchers to make precise changes to a DNA sequence — the researchers could switch between lean and obese signatures in human pre-adipocytes. Switching the C to a T in risk individuals turned off IRX3 and IRX5, restored thermogenesis to non-risk levels, and switched off lipid storage genes.

“Knowing the causal variant underlying the obesity association may allow somatic genome editing as a therapeutic avenue for individuals carrying the risk allele,” Kellis says. “But more importantly, the uncovered cellular circuits may allow us to dial a metabolic master switch for both risk and non-risk individuals, as a means to counter environmental, lifestyle, or genetic contributors to obesity.”

Success in human and mouse cells

The researchers showed that they could indeed manipulate this new pathway to reverse the signatures of obesity in both human cells and mice.

In primary adipose cells from either risk or non-risk individuals, altering the expression of either IRX3 or IRX5 switched between energy-storing white adipocyte functions and energy-burning beige adipocyte functions.

Similarly, repression of IRX3 in mouse adipocytes led to dramatic changes in whole-body energy balance, resulting in a reduction of body weight and all major fat stores, and complete resistance to a high-fat diet.

“By manipulating this new pathway, we could switch between energy storage and energy dissipation programs at both the cellular and the organismal level, providing new hope for a cure against obesity,” Kellis says.

The researchers are currently establishing collaborations in academia and industry to translate their findings into obesity therapeutics. They are also using their approach as a model to understand the circuitry of other disease-associated regions in the human genome.

Flipping a Genetic Switch on Obesity?

Illustration of a DNA switchWhen weight loss is the goal, the equation seems simple enough: consume fewer calories and burn more of them exercising. But for some people, losing and keeping off the weight is much more difficult for reasons that can include a genetic component. While there are rare genetic causes of extreme obesity, the strongest common genetic contributor discovered so far is a variant found in an intron of the FTO gene. Variations in this untranslated region of the gene have been tied to differences in body mass and a risk of obesity [1]. For the one in six people of European descent born with two copies of the risk variant, the consequence is carrying around an average of an extra 7 pounds [2].

Now, NIH-funded researchers reporting in The New England Journal of Medicine [3] have figured out how this gene influences body weight. The answer is not, as many had suspected, in regions of the brain that control appetite, but in the progenitor cells that produce white and beige fat. The researchers found that the risk variant is part of a larger genetic circuit that determines whether our bodies burn or store fat. This discovery may yield new approaches to intervene in obesity with treatments designed to change the way fat cells handle calories.

The team—led by Melina Claussnitzer of Beth Israel Deaconess Medical Center, Boston, and Manolis Kellis of the Massachusetts Institute of Technology (MIT), Cambridge—started with a basic question: where in the body does this variant act to influence weight? For the answer, the team turned to the NIH-funded Roadmap Epigenomics Project. There, they found comprehensive data on 127 human cell types and the occurrence of common chemical modifications that act like volume knobs to turn gene activity “up” or “down” based on changes in the way DNA is packaged. While the FTO gene is active in the human brain, the team couldn’t connect any differences there with obesity.

They began to wonder whether this obesity-risk variant affected FTO at all (and prior studies had suggested this [4]). Maybe it operated at a distance to change the expression of other protein-coding genes? Sure enough, further study in fat collected from patients showed that the obesity risk variant works in those progenitor cells to control the activity of two other genes, IRX3 andIRX5, both found quite a distance away.

The fat in people with the obesity risk variant and greater expression of IRX3 and IRX5 genes contains fewer beige cells than normal. Beige cells, which were discovered just three years ago [5], are produced sometimes by fat cell progenitors to burn rather than stockpile energy. This new evidence suggests that beige fat may play an unexpectedly important role in protecting against obesity.

Using a method they developed last year [6], the researchers traced the effects of the obesity risk variant to a single nucleotide change—a small typo in the DNA sequence that changes a “T” to a “C.” They then used the nifty CRISPR-Cas genome editing system (see Copy-Editing the Genome) to switch between this obesity risk variant and the protective variant in human cells. As the researchers did this, they saw fat cells turn energy-burning heat production off and back on again. In other words, the obesity signature in the cells could be turned on and off at the flip of this genetic switch!

They also showed in mice that the shift toward energy-burning beige cells led to weight loss. Animals engineered in a way that blocked Irx3 expression in adipose tissue became significantly thinner with no change in their eating or exercise habits. This new collection of evidence suggests that treatments designed to program fat cells to burn more energy (such as antagonists against the IRX3 or IRX5 proteins) might have similar benefits in people, and the researchers are working with collaborators in academia and industry to pursue this line of investigation.

This is a great example of how discoveries about genetic factors in common disease, uncovered by applying the genome-wide association study (GWAS) approach to large numbers of affected and unaffected individuals, are revealing critical and previously unknown pathways in human biology and medicine. This case also points out how our terminology may need attention, however; for the last several years, this genetic variant for obesity has been called “the FTO variant,” perhaps it should now be called “the IRX3/5 variant.”

Genes, of course, are only part of the story. It’s still important to eat healthy, limit your portions, and maintain a regular exercise program. Leading an active lifestyle both keeps weight down and improves the overall sense of well being.

References:

[1] FTO genotype is associated with phenotypic variability of body mass index.Yang J, Loos RJ, Powell JE, TM, Frayling TM, Hirschhorn JN, Goddard ME, Visscher PM, et al. Nature. 2012 Oct 11;490(7419):267-72.

[2] A common variant in the FTO gene is associated with body mass index and predisposes to childhood and adult obesity. Frayling TM, Timpson NJ, Weedon MN, Morris AD, Smith GD, Hattersley AT, McCarthy MI, et al. Science. 2007 May 11;316(5826):889-94.

[3] FTO Obesity Variant Circuitry and Adipocyte Browning in Humans. Claussnitzer M, Dankel SN, Kim KH, Quon G, Meuleman W, Haugen C, Glunk V, Sousa IS, Beaudry JL, Puviindran V, Abdennur NA, Liu J, Svensson PA, Hsu YH, Drucker DJ, Mellgren G, Hui CC, Hauner H, Kellis M. N Engl J Med. 2015 Aug 19. [Epub ahead of print]

[4] Obesity-associated variants within FTO form long-range functional connections with IRX3. Smemo S, Tena JJ, Kim KH, Hui CC, Gomez-Skarmeta JL, Nobrega MA, et al. Nature 2014 Mar 20; 507(7492):371-375.

[5] Beige adipocytes are a distinct type of themogenic fat cell in mouse and human. Wu J, Boström P, Sparks LM, Schrauwen P, Spiegelman BM. Cell 2012 Jul 20:150(2):366-376.

[6] Leveraging cross-species transcription factor binding site patterns: from diabetes risk loci to disease mechanisms. Claussnitzer M, Dankel SN, Klocke Mellgren G, Hauner H, Laumen H, et al. Cell. 2014 Jan 16;156(1-2):343-58.

Links:

Manolis Kellis (Massachusetts Institute of Technology, Cambridge)

What are overweight and obesity? (National Heart, Lung, and Blood Institute/NIH)

NIH Roadmap Epigenomics Project

NIH Support: National Human Genome Research Institute; National Institute of General Medical Sciences

MiR-93 Controls Adiposity via Inhibition of Sirt7 and Tbx3

CELL REPORTS · AUGUST 2015
Impact Factor: 8.36 · DOI: 10.1016/j.celrep.2015.08.006 

https://www.researchgate.net/publication/281394525_MiR-93_Controls_Adiposity_via_Inhibition_of_Sirt7_and_Tbx3

Conquering obesity has become a major socioeconomic challenge. Here, we show that reduced expression of the miR-25-93-106b cluster, or miR-93 alone, increases fat mass and, subsequently, insulin resistance. Mechanistically, we discovered an intricate interplay between enhanced adipocyte precursor turnover and increased adipogenesis. First, miR-93 controls Tbx3, thereby limiting self-renewal in early adipocyte precursors. Second, miR-93 inhibits the metabolic target Sirt7, which we identified as a major driver of in vivo adipogenesis via induction of differentiation and maturation of early adipocyte precursors. Using mouse parabiosis, obesity in mir-25-93-106b(-/-) mice could be rescued by restoring levels of circulating miRNA and subsequent inhibition of Tbx3 and Sirt7. Downregulation of miR-93 also occurred in obese ob/ob mice, and this phenocopy of mir-25-93-106b(-/-) was partially reversible with injection of miR-93 mimics. Our data establish miR-93 as a negative regulator of adipogenesis and a potential therapeutic option for obesity and the metabolic syndrome.

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