Studies on the body composition, fat distribution and fat cell size and number of 'Ad', a new obese mutant mouse

Cold exposure suppresses serum adiponectin levels through sympathetic nerve activation in mice

OBJECTIVE

Several lines of evidence suggest important roles for adiponectin in glucose and lipid metabolism and atherosclerosis. However, the mechanisms regulating serum adiponectin levels and adiponectin production are still not completely understood. Our aim was to determine whether adiponectin synthesis is physiologically regulated by the sympathetic nervous system (SNS).

RESEARCH METHODS AND PROCEDURES

Mice were exposed to cold (4 degrees C) for 12 hours and for 24 hours with or without inhibition of noradrenaline synthesis or pan-beta adrenergic function, followed by measurement of serum adiponectin concentrations and levels of adiponectin and uncoupling protein (UCP) 1 expressions in various white adipose tissues (WATs).

RESULTS

Cold exposure significantly reduced serum adiponectin concentrations without changing body weights or WAT sizes in either subcutaneous or intra-abdominal fat tissues. The serum adiponectin reduction was associated with a decrease in adiponectin mRNA expression in subcutaneous, epididymal, and mesenteric fat tissues. In these adipose tissues, UCP1 expression was markedly enhanced, suggesting SNS activation in these tissues. Administration of alpha-methyl-p-tyrosine or a combination of SR59230A and propranolol reversed the cold-exposure-induced decreases in serum adiponectin concentrations and adiponectin mRNA expression in these tissues. In contrast, in retroperitoneal fat, the effects of cold exposure on adiponectin and UCP1 expressions were strikingly weak but were not reversed by SNS inhibitors.

DISCUSSION

SNS physiologically regulates serum adiponectin levels and adiponectin synthesis in WATs in vivo, although responsiveness to SNS stimulation differs markedly among WATs. Sympathetic activation might be involved in development of the metabolic syndrome by modulation of serum adiponectin concentrations.

Genes involved in animal models of obesity and anorexia

Pathological deviations in bodyweight is a major increasing health problem in industrialized societies. It is currently unclear what genetic mechanisms are involved in the long-term control of human body-weight and to what extent these genes are involved in pathological deviations of bodyweight control such as anorexia and obesity. Major support for the concept of genetic control of bodyweight has recently emerged from different animal models. A number of new genes have been found during recent years that, when mutated, have a negative effect on bodyweight in animals and sometimes also in man. Although available evidence points toward a multifactorial nature of weight disorders in most human subjects, the single genes isolated in animal models may become powerful tools to elucidate the genetics also in man. In addition, these genes may serve to promote the development of targeted small-drug pharmaceuticals aimed at novel biochemical pathways. Finally, the uncovering of several quantitative trait loci (QTL) influencing body mass, body fat or fat topography in the mouse and rat has now also made it possible to perform studies of polygenically caused obesity in rodents. The role of the Genome Project in developing a complete gene map will greatly facilitate transforming these OTLs to actual molecules involved in the biology of bodyweight.

Genetic modifiers of Leprfa associated with variability in insulin production and susceptibility to NIDDM

In an attempt to identify the genetic basis for susceptibility to non-insulin-dependent diabetes mellitus within the context of obesity, we generated 401 genetically obese Leprfa/Leprfa F2 WKY13M intercross rats that demonstrated wide variation in multiple phenotypic measures related to diabetes, including plasma glucose concentration, percentage of glycosylated hemoglobin, plasma insulin concentration, and pancreatic islet morphology. Using selective genotyping genome scanning approaches, we have identified three quantitative trait loci (QTLs) on Chr. 1 (LOD 7.1 for pancreatic morpholology), Chr. 12 (LOD 5.1 for body mass index and LOD 3.4 for plasma glucose concentration), and Chr. 16 (P < 0.001 for genotype effect on plasma glucose concentration). The obese F2 progeny demonstrated sexual dimorphism for these traits, with increased diabetes susceptibility in the males appearing at approximately 6 weeks of age, as sexual maturation occurred. For each of the QTLs, the linked phenotypes demonstrated sexual dimorphism (more severe affection in males). The QTL on Chr. 1 maps to a region vicinal to that previously linked to adiposity in studies of diabetes susceptibility in the nonobese Goto-Kakizaki rat, which is genetically closely related to the Wistar counterstrain we employed. Several candidate genes, including tubby (tub), multigenic obesity 1 (Mob1), adult obesity and diabetes (Ad), and insulin-like growth factor-2 (Igf2), map to murine regions homologous to the QTL region identified on rat Chr. 1.

An inherited mild middle-aged adiposity in wild mice

In a warfarin-resistant population of wild mice reared in the laboratory, a dominant gene for adiposity, Ad, was found to segregate. The onset of obesity is at 4--6 months, and adipose mice suffer from hyperinsulinaemia; the sexes differ in penetrance, males having greater penetrance then females. Linkage backcrosses show the gene to be situated on chromosome 7 with about 25% recombination with the closely linked warfarin-resistance genes War, and frizzy, fr. The finding of adipose in two other wild populations also carrying War is discussed as an ecological and physiological problem.