Role of Gs-alpha in regulation of skeletal muscle metabolism

我们用肌肉重链启动子-cre重组酶转基因小鼠与Gs-α外显子1周围有loxP重组位点的转基因小鼠反复配对，获得了骨骼肌Gs-α缺陷小鼠(MGsKO小鼠)。MGsKO小鼠存活正常，没有明显的生理表型。MGsKO小鼠生长正常，体重和成分正常，摄食量和能量消耗没有变化。这些结果表明，在正常的卡路里饮食中，肌肉中Gs-α的丢失似乎不会影响全身的能量代谢。对高脂肪饮食的研究也没有证据表明新陈代谢存在差异。对葡萄糖代谢的研究(基线血清化学、葡萄糖和胰岛素耐量试验、高胰岛素正常血糖钳夹试验，以及离体肌的葡萄糖摄取)表明，尽管MGsKO小鼠具有正常的胰岛素分泌和对注射胰岛素的低血糖反应，但这些小鼠仍存在葡萄糖耐受性。事实上，在分离肌肉中的研究表明，在存在最大胰岛素刺激的情况下，基础葡萄糖摄取量增加，葡萄糖摄取量没有变化，尽管MGsKO小鼠肌肉中胰岛素刺激后的基础葡萄糖摄取量增加较低。此外，AMP类似物AICAR对肌肉葡萄糖的摄取没有受到影响，这表明AMP激酶及其下游通路保持完整。MGsKO组骨骼肌明显萎缩，纤维横截面积减小。此外，根据肌球蛋白重链亚型和动力学特性，肌肉会从1型(白色，快抽动)纤维切换到2型(红色，慢抽动)纤维，即使肌肉的线粒体含量和氧化能力降低，以及已知的线粒体氧化转录诱导剂PGC-1pha的表达减少，也会切换到1型纤维。因此，在MGsKO小鼠中，纤维类型转换和预期的代谢特性变化之间存在分离。这些小鼠也被证明有助于研究肌钙蛋白在心肌中的作用，作为一种减少β-肾上腺素能信号的代偿机制。最近的研究表明，这种向2型肌肉的转变是渐进的，可能是肌肉质量减少的一种代偿机制，可能会模仿衰老和肌肉萎缩障碍的情况。

We generated mice with Gs-alpha deficiency in skeletal muscle (MGsKO mice) by repeated matings of muscle heavy chain promoter -cre recombinase transgenic mice with floxed Gs-alpha mice which have loxP recombination sites surrounding Gs-alpha exon 1. MGsKO mice have normal survival and no obvious physical phenotype. MGsKO mice had normal growth and body weight and composition and no changes in food intake and energy expenditure. These results show that loss of Gs-alpha in muscle does not appear to affect whole body energy metabolism on a regular calorie diet. Studies on high fat diet also show no evidence of differences in metabolism. Studies in glucose metabolism (baseline serum chemistries, glucose and insulin tolerance tests, hyperinsulinemic euglycemic clamp studies, and glucose uptake in isolated muscles) show that MGsKO mice are glucose intolerant despite the fact that the mice have normal insulin secretion and hypoglycemic response to administered insulin. In fact studies in isolated muscles show basal glucose uptake to be increased and with no change in glucose uptake in the presence of maximal insulin stimulation, although the increase from baseline with insulin was lower in muscles from MGsKO mice. In addition, muscle glucose uptake in response to the AMP analog AICAR was unaffected, indicating that AMP kinase and its downstream pathways remain intact. Skeletal muscles in MGsKO show significant atrophy with reduced fiber cross-sectional area. In addition, there is a switch in from type 1 (white, fast-twitch) to type 2 (red, slow-twitch) fibers based upon myosin heavy chain subtypes and kinetic properties even though the muscles have reduced mitochondrial content and oxidative capacity and reduced expression of PGC-1alpha, a known transcriptional inducer of mitochondrial oxifation and switch to type 1 fibers. Therefore in MGsKO mice there is a dissociation between the fiber type switch and the expected changes in metabolic properties. These mice have also proven useful to examine the role of troponin processing in cardiac muscle as a compensatory mechanism to reduced beta-adrenergic signaling. More recent studies have suggested that this switch to type 2 muscle is progressive and may be a compensatory mechanism for reduced muscle mass, and may mimic the situation seen in aging and muscle wasting disorders.