LASKER BASIC MEDICA L RESEARCH AWARD COMMENTARY A historical perspective on leptin Douglas L Coleman As the only child of a self-employed and largely that the db mutation is on chromosome 4 and, self-taught Canadian radio-and-refrigeration like the ob/ob mutant mouse, the db/db mouse repairman, I spent much of my childhood develops marked obesity and hyperphagia, but, investigating how things worked by taking unlike the ob/ob mutant, it develops severe, them apart. As I grew older, I developed a life-shortening diabetes2. Figure 1 illustrates keen interest in science, and, while I was an the striking obesity of the db/db mutant undergraduate at McMaster University, my mouse compared with a normal littermate at scientific interests converged on biology, geol- eight weeks of age. The db/db mouse is much ogy and chemistry. During this time, a very larger than the normal mouse (30 grams com- dynamic biochemistry professor encouraged pared with 20 grams), and the extra weight is me to attend graduate school at the University all adipose tissue. Because both ob/ob and db/ of Wisconsin and study biochemistry. Upon db mice become morbidly obese with similar Figure 1 An obese db/db mouse (right) next to a receiving my PhD from the University of speed, the db/db mutant shown in this figure normal mouse (left). Wisconsin in 1958, I knew that the prospects looks just like an ob/ob mouse; to the unaided of returning to employment in Canada were eye, the two mouse types are phenotypically poor, and I was offered a position at the Jackson identical2. the db/db mutant to a normal mouse3 (Fig. 2a). Laboratory in Bar Harbor, Maine. When I When I began to characterize this new After what seemed to be good wound healing accepted this position, my plan was to remain mutation, I wondered whether some circu- and a healthy-looking parabiotic pair, I was at the Jackson Laboratory for one or two years lating factor might control the obese pheno- surprised to see that the normal mouse died. to further my education in biology, especially type. For example, could a factor produced My immediate thought was that I was a pretty genetics and immunology. As things turned in a normal mouse prevent or remediate the poor surgeon, but repeated attempts con- out, however, the Laboratory provided a very metabolic abnormalities? Conversely, might a sistently yielded the same outcome: only the fertile environment—with excellent colleagues factor produced by the db/db mutant mouse normal mouse in the pair died. Encouraged and world-class mouse models of disease—and cause obesity in a normal mouse? If this hypo- by this stereotypic pattern, I initiated a more I spent my entire career in Bar Harbor. I never thetical factor were carried through the blood, detailed characterization of the normal part- dreamed that I would work on obesity and I reasoned, I could test for its presence by link- ners and found that, after about one week, diabetes or that my research would one day be ing the blood supplies of the various mouse their blood sugar concentrations had declined deemed important enough to be considered for strains. Fortunately, two of my colleagues at to starvation levels. Moreover, at necropsy, the a major scientific award. the Jackson Laboratory were using parabio- normal mice not only consistently lacked food In 1958, only one obese mutant mouse—the sis to characterize anemia mutant mice and in their stomachs and food remnants in their ob/ob mouse—was known1. It had been discov- were pleased to instruct me in this technique. intestines but also had no detectable glycogen ered in 1950 and characterized as a model for Parabiosis requires the surgical joining of two in their livers. In marked contrast, the diabetes mild diabetes, but it was not the subject of any mice by skin-to-skin anastomosis from the partners consistently retained elevated blood ongoing studies by other investigators at the shoulder to the pelvic girdle. Wound healing sugar concentrations, and their stomachs and Jackson Laboratory. The ob mutation is located and cross circulation is established in two to intestines were distended with food and food on chromosome 6, and the mouse is character- three days. To avoid a vigorous immune-medi- residues. This was my ‘Eureka’ moment! These ized by massive obesity, marked hyperphagia ated rejection, this technique requires that the results led me to conclude that the db/db mouse and mild transient diabetes. In 1965, a new mice be on the same genetic background, an produced a blood-borne satiety factor so pow- obesity mutant—the db/db mouse—was dis- issue that would delay some desired pairings erful that it could induce the normal partner to covered. I was asked to assist in characteriz- (see below). Most parabiosis experiments fail, starve to death, even in the face of the limited ing this new mutant mouse and, in particular, either because there is no factor or because the cross-circulation between parabiotic pairs. comparing it to the ob/ob mutant. We found factor exchanged is insufficient, owing to the Despite my excitement, my colleagues and lack of major blood vessels in the skin to medi- most of the scientific community remained ate the cross-circulation. largely unconvinced. Douglas L. Coleman is at the Jackson Laboratory, Because the ob/ob and db/db mutant mice At about the same time as these first para- Bar Harbor, Maine, USA. were on different genetic backgrounds, my first biosis studies, a new obese mutant mouse e-mail: [email protected] parabiosis experiment involved the joining of spontaneously emerged4. This mouse did not NATURE MEDICINE VOLUME 16 | NUMBER 10 | OCTOBER 2010 ix COMMENTARY a b c d Further studies with db/db mutant mice that were lesioned in the ventromedial nucleus or the arcuate nucleus of the hypothalamus (or both) suggested that the receptor for this satiety db/db +/++db/db ob/ob ob/ob /++/++/+ factor is found in these brain areas7. Additional support for the idea that a satiety factor acts on a receptor in the brain came from a study in which rats with lesions in the ventromedial Diabetes Diabetes Obese nucleus of the hypothalamus became hyper- ↑Body weight ↑Body weight ↓Food intake phagic and obese8. When lesioned rats were ↑Adipose tissue mass ↑Adipose tissue mass ↓Insulinemia Lean ↓Blood sugar parabiosed with normal rats, the normal rat Lean Obese Normal insulin ↓Food intake ↓Food intake Normal blood sugar lost weight and failed to grow but did not die. ↓Insulinemia ↓Adipose tissue mass ↓Fat pad size ↓Blood sugar ↓Insulinemia Lean Despite these clear results, many of my col- Death by starvation ↓Blood sugar No change leagues and many in the obesity field main- Death by starvation tained the dogma that obesity is entirely Figure 2 Summary of the parabiosis experiments. (a–d) Four different parabiotic combinations and the behavioral, not physiological. On the basis of main phenotypes observed in each mouse in the pair. these experiments, however, some investigators did accept a physiological basis as an underly- ing cause that contributes to obesity, and the have diabetes and therefore appeared identical to eat? Parabiosis of mutant mice of the same hunt for the satiety factor became a race. None to the ob/ob mutant, but, like the db/db mutant, weight would address this issue. These addi- of the early satiety factor candidates (cholecys- the mutation mapped to chromosome 4. This tional parabiosis experiments revealed that tokinin, somatostatin, pancreatic polypeptide new mutation arose in an unrelated strain, but the ob/ob and db/db mutant mice responded and others) stood up to rigorous experimen- when crossed into either the C57BL/Ks inbred similarly to the procedure regardless of inbred tation, and I continued my own attempts to background (in which the db/db mutation was background. After collateral circulation devel- identify the factor. In control parabiosis studies maintained) or the related C57BL/6 inbred oped, blood sugar concentration in the ob/ob using two normal mice (Fig. 2d), I had found background (in which the ob/ob mutation mutant mouse declined, eventually reaching that the pairs remained active and healthy for was maintained) it caused markedly different starvation levels. Survival time ranged from four months (until they were culled). But, at disease syndromes—leading me to wonder 20 to 30 days. At necropsy, it was clear that the necropsy, they did show one abnormality: the whether the inbred background could medi- adipose tissue mass in the ob/ob parabiont had fat pads were smaller in size than those iso- ate the severity of the disease. To answer this decreased and that neither food nor food resi- lated from unparabiosed normal mice. This question, I placed the diabetes mutation on the due could be found in the stomach or intestinal suggested to me that the factor might be a C57BL/6 background and the obese mutation tract of the ob/ob partner. By contrast, the db/ component of adipose tissue. Although the fac- on the C57BL/Ks background by five cycles of db mutant was gorged with food and gaining tor was produced by adipose tissue, my time- cross-intercross breeding, thereby producing weight. Consistent with the lack of food in the consuming attempts to isolate it proved futile, two new congenic lines5. I found that both the ob/ob partner, the food consumption of the as I concentrated my efforts on individual fatty ob/ob and the db/db mutations, when main- pair was decreased to about that typical of a acids or lipid extracts of adipose tissue.