Role of Gs-alpha in central regulation of energy and glucose metabolism

我们通过将Gs-α外显子1周围有loxP重组位点的Gs-α开花等位基因杂合子的雌性小鼠与携带巢蛋白启动子-cre重组酶转基因的雄性小鼠交配，产生了中枢神经系统(MBGsKO)母体等位基因Gs-α表达中断的小鼠。通过正反交产生类似于父亲等位基因(PBGsKO)的Gs-α在中枢神经系统中表达缺失的小鼠。通过多种实验方法(体重和成分、器官重量、血清化学和激素、葡萄糖和胰岛素耐量试验、代谢率和摄食量测量)测定，pBGsKO小鼠的存活和总表型正常，对葡萄糖或能量代谢和血脂没有影响。相比之下，mBGsKO出现了严重的肥胖和糖尿病、严重的胰岛素抵抗和高甘油三酯血症。肥胖在5周后开始发展。对年轻小鼠的研究表明，胰岛素抵抗和葡萄糖耐受性在肥胖之前就开始发展，这表明对葡萄糖代谢的影响不依赖于肥胖。对mBGsKO小鼠的进一步研究表明，肥胖主要是能量消耗减少和与能量消耗相关的棕色脂肪组织基因表达减少的结果，如解偶联蛋白1(UCP1)，对食物摄入量没有主要影响。我们推测，mBGsKO小鼠可能存在黑素皮质素系统刺激交感神经系统活动和能量消耗的能力缺陷。为了验证这一假说，我们测量了黑素皮质素激动剂(MTII)的急性食物摄入量和能量消耗反应。PBGsKO小鼠与对照组相比差异无统计学意义，对MTII抑制mBGsKO小鼠摄食能力影响不大。然而，与对照组相比，mBGsKO小鼠MTII刺激能量消耗的能力显著降低。此外，MGsKO小鼠还削弱了饮食诱导的产热作用，并降低了心率和血压。总体而言，这些结果证实，中枢神经系统中的Gs-α通路是新陈代谢的关键调节器，小鼠(以及最有可能是奥尔布赖特遗传性骨病患者)中的母体Gs-α突变是由于Gs-α印记在中枢神经系统的一个或多个位置造成的。原位杂交研究表明Gs-α印记在下丘脑室旁核，这是一个已知的黑素皮质素作用和代谢调节的部位。我们目前正试图通过与具有更多限制性分布模式的cre转基因品系配对来确定这些位点。

We generated mice with disruption of Gs-alpha expression from the maternal allele in the central nervous system (mBGsKO) by mating females heterozygous for a Gs-alpha floxed allele with loxP recombination sites surrounding Gs-alpha exon 1 to males with a nestin promoter-cre recombinase transgene. Mice with similar loss of Gs-alpha expression in the central nervous system on the paternal allele (pBGsKO) were generated with reciprocal crosses. pBGsKO mice had normal survival and overall phenotype with no effect on glucose or energy metabolism or serum lipids as determined by multiple experimental approaches (body weight and composition, organ weights, serum chemistries and hormones, glucose and insulin tolerance tests, metabolic rate and food intake measurements). In contrast, mBGsKO developed severe obesity with diabetes, severe insulin resistance, and hypertriglyceridemia. The obesity began to develop after 5 weeks. Studies in younger mice indicate that the insulin resistance and glucose intolerance begin to develop prior to obesity, indicating an effect on glucose metabolism independent of obesity. Further studies in mBGsKO mice showed that the obesity was primarily the result of reduced energy expenditure and reduced expression of brown adipose tissue genes associated with energy dissipation, such as uncoupling protein 1 (UCP1), with no primary effect on food intake. We hypothesized that mBGsKO mice may be defective the ability of the melanocortin system to stimulate sympathetic nervous system activity and energy expenditure. To test this hypothesis, acute food intake and energy expenditure responses to a melanocortin agonist (MTII) were measured. There were no differences between pBGsKO mice and controls, and there was little effect on the ability of MTII to inhibit food intake in mBGsKO mice. However, the ability of MTII to stimulate energy expenditure was markedly reduced in mBGsKO mice as compared to controls. Moreover MGsKO mice have impaired diet-induced thermogenesis and reduced heart rate and blood pressure. Overall these results confirm that Gs-alpha pathways in the central nervous system are critical regulators of metabolism and that maternal Gs-alpha mutations in mice (and most likely Albright hereditary osteodystrophy patients) results from Gs-alpha imprinting in one or more site in the central nervous system. In situ hybridization studies suggest that Gs-alpha is imprinted in the paraventricular nucleus of the hypothalamus, a known site of melanocortin action and metabolic regulation. We are presently trying to define these sites through matings with cre transgenic lines with a more restrictive distribution pattern.