No abstract

The mitochondrial uncoupling protein (UCP) is usually expressed only in brown adipose tissue (BAT) and a key molecule for metabolic thermogenesis. The effects of a highly selective ␤ 3-adrenergic agonist, CL316,243 (CL), on UCP expression in skeletal muscle and adipose tissues were examined in mice. Daily injection of CL (0.1 mg/kg, sc) to obese yellow KK mice for two weeks caused a significant reduction of body weight, associated with a marked decrease of white fat pad weight and hypertrophy of the interscapular BAT with a sixfold increase in UCP content. Clear signals of UCP protein and mRNA were detected by Western and Northern blot analyses in inguinal, mesenteric and retroperitoneal white fat pads, and also in gastrocnemius and quadriceps muscles, whereas no signal in saline-treated mice. The presence of UCP mRNA in muscle tissues was also confirmed by reverse transcription-PCR analysis. Weaker UCP signals were also detected in control C57BL mice treated with CL, but only in inguinal and retroperitoneal fat pads. Immunohistochemical examinations revealed that UCP stains in the white fat pads were localized on multilocular cells quite similar to typical brown adipocyte, and those in the muscle tissues on myocytes. The mitochondrial localization of UCP in myocytes was confirmed by immunoelectron microscopy. In addition to UCP protein, UCP mRNA was also detected in myocytes by in situ hybridization analysis. Thus, chronic stimulation of the ␤ 3-adrenergic receptor induces ectopic expression of UCP in adipose tissues conventionally considered as white fat and even in skeletal muscle, which probably contributes to the potent anti-obesity effect of the ␤ 3-adrenergic agonist. ( J. Clin. Invest. 1996. 97:2898-2904.) Key words: brown adipose tissue • immunohistochemistry • obesity • yellow KK mice

The recently described variant of the human beta3-adrenergic receptor (AR) gene located mainly in visceral adipocytes is associated with earlier onset of NIDDM, abdominal obesity, insulin resistance, and an increased capacity to gain weight. We investigated whether lipolysis in human omental adipocytes induced by a potent and selective human beta3-AR agonist (L-755,507) was affected by the Trp64Arg mutation of the beta3-adrenoceptor, using 18 omental fat samples obtained during total hysterectomy. The Trp64Arg mutation was determined by polymerase chain reaction-restriction fragment length polymorphism analysis. Arg64 homozygous (n = 4) had a lower median effective concentration (EC50) and lower responsiveness compared with wild-type (n = 8) (EC50: -6.55 +/- 0.21 vs. -7.53 +/- 0.35 log mol/l, P = 0.007; responsiveness: 3.48 +/- 0.32 vs. 5.76 +/- 0.36 micromol x 10(5) cells(-1) x 90 min(-1), P = 0.014, respectively), although there was no difference in lipolysis induced by isoproterenol or CGP12177. Trp64Arg heterozygous (n = 6) also had a significantly lower EC50 and lower responsiveness (EC50: -6.18 +/- 0.09 log mol/l; responsiveness: 4.17 +/- 0.33 micromol x 10(5) cells(-1) x 90 min(-1)). We concluded that the Trp64Arg mutation of the beta3-AR gene is associated with lower lipolytic activities.

These present findings show that the Trp64Arg allele of the beta 3-adrenergic receptor gene may predict difficulty in losing body weight, lowering WHR, and improving glycemic control and insulin resistance in obese patients with type 2 diabetes.

Obesity is a complex phenotype resulting from the combined effects of genes, behavioural and lifestyle factors, and their interactions [1]. The associations between obesity and increased risk of morbidity and mortality are well documented [2]; however, distribution of body fat is also of importance [3]. A syndrome with a clustering of multiple risk factors for coronary atherosclerosis has been described and defined by Reaven [4] as syndrome X; by Kaplan [5] as the deadly quartet; and by Matsuzawa et al. [6] as visceral fat obesity, which is more strongly associated with metabolic and cardiovascular diseases than subcutaneous fat obesity [7,8]. From clinical and basic experiments, the imbalance of sex hormones [9], aging [10], excessive intake of sucrose [11] and lack of physical exercise [10] have been suggested to be major factors for visceral fat accumulation. However, it is not known whether a major gene exists which promotes visceral fat accumulation, although Bouchard et al. [12] demonstrated six times more variation between twin pairs than within twin pairs for an Diabetologia (1997) Summary We investigated whether the polymorphism of the b 3 -adrenergic receptor (b 3 -AR) gene, which is associated with insulin resistance in non-diabetic subjects and an earlier onset of non-insulin-dependent diabetes mellitus in Pima Indians, was associated with visceral fat obesity and features of the insulin resistance syndrome in Japanese premenopausal obese women. There was no difference between 131 obese women and 256 control subjects , n = 48) women than in women homozygous for the Trp 64 Trp (121 ± 46 cm 2 , n = 77) genotype (p < 0.01). This was also reflected by increased total body fat but not by increased body mass index. The association between the Trp 64 allele and visceral fat mass by multiple regression analysis, was independent of age, body mass index and total fat mass (p < 0.004). Moreover, homozygous carriers of the Arg 64 allele had higher systolic blood pressure, higher fasting and post-load glucose and insulin concentrations, higher cholesterol, and triglyceride and lower HDL-cholesterol concentrations than homozygous carriers of the Trp 64 allele. Some of these differences were also observed between heterozygous Trp 64 Arg and homozygous Trp 64 Trp genotypes (glucose tolerance, insulin and cholesterol concentration). We conclude that in obese women the b 3 -AR polymorphism may be used as a genetic marker for visceral fat obesity and the insulin resistance syndrome. [Diabetologia (1997) 40: 200-204]

No abstract

OBJECTIVE: To test the hypothesis that nicotine not only activates uncoupling protein1 (UCP1) in brown adipose tissue (BAT), but also induces UCP1 in white adipose tissue (WAT), which contributes to the mitigation of obesity in obese mice. DESIGN: Weights of the whole body, the gastrocnemius muscle, interscapular BAT and subcutaneous and retroperitoneal WAT, food intake and the mRNA and protein of UCP1 in these tissues were measured and immunohistochemistry using antiserum against UCP1 was also performed in obese yellow KK mice treated with nicotine for 6 months and control mice treated with physiological saline. RESULTS: Obese mice treated with nicotine for 6 months, compared with those injected with saline, weighed signi®cantly less (P`0.01) and had smaller subcutaneous and retroperitoneal WAT pads (P`0.01), while obese mice that received nicotine ate less (P`0.05) than those injected with saline. In mice treated with nicotine, the mRNA and protein of UCP1 was detected not only in BAT, but also in subcutaneous and retroperitoneal WATs. Immunohistochemically, the BAT of obese mice contained large lipid droplets and appeared rather WAT-like, but changed to typical brown adipocytes after nicotine treatment. The fat pads of nicotine-treated mice contained many multilocular cells that were positive for UCP1. CONCLUSION: Nicotine not only activates UCP1 in BAT, but also induces UCP1 in WAT and decreases food intake, which contributes to the mitigation of obesity.

1. The hypothesis that caffeine upregulates uncoupling protein (UCP)-1, UCP-2 and UCP-3 expression, which contribute to thermogenesis, was investigated in obese mice. 2. The mRNA levels of UCP-1, -2 and -3 in brown adipose tissue (BAT), UCP-2 in white adipose tissue (WAT), and UCP-2 and -3 in skeletal muscle were measured using real-time quantitative reverse transcription-polymerase chain reaction analysis in obese yellow KK mice 4 h after the subcutaneous administration of either 60 mg/kg caffeine or physiological saline. Plasma free fatty acids, adrenaline, noradrenaline and dopamine levels were also measured. 3. In caffeine-injected obese mice, UCP-1 mRNA levels were significantly increased by 1.5-fold in BAT, UCP-2 mRNA levels were increased by 1.8- and 2.5-fold in BAT and skeletal muscles, respectively, and UCP-3 mRNA levels were increased 1.7- and 3.4-fold in BAT and skeletal muscles, respectively, compared with control mice injected with physiological saline. There was no difference in UCP-2 mRNA levels in WAT between the two groups. 4. Plasma free fatty acids and adrenaline levels were significantly elevated in mice treated with caffeine compared with those injected with physiological saline. 5. It was concluded that caffeine upregulates the expression of UCP-1, UCP-2 and UCP-3 in BAT and UCP-2 and UCP-3 in skeletal muscles, which may contribute to thermogenesis in obese mice.