Martins Vitor F, Tahvilian Shahriar, Kang Ji H, Svensson Kristoffer, Hetrick Byron, Chick Wallace S, Schenk Simon, McCurdy Carrie E
Department of Orthopaedic Surgery, University of California, San Diego, La Jolla, CA, United States.
Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, CA, United States.
Front Physiol. 2018 Jun 27;9:789. doi: 10.3389/fphys.2018.00789. eCollection 2018.
The Phosphoinositide 3-kinase (PI3K) signaling pathway plays an important role in skeletal muscle insulin-stimulated glucose uptake. While whole-body and tissue specific knockout (KO) of individual or combinations of the regulatory subunits of PI3K (p85α, p55α, and p50α or p85β); increase insulin sensitivity, no study has examined whether increasing the expression of the individual regulatory subunits would inhibit insulin action . Therefore, the objective of this study was to determine whether skeletal muscle-specific overexpression of the p55α regulatory subunit of PI3K impairs skeletal muscle insulin sensitivity, or prevents its enhancement by caloric restriction. We developed a novel "floxed" mouse that, through the Cre-LoxP approach, allows for tamoxifen (TMX)-inducible and skeletal muscle-specific overexpression of the p55α subunit of PI3K (referred to as, 'p55α-mOX'). Beginning at 10 weeks of age, p55α-mOX mice and their floxed littermates (referred to as wildtype [WT]) either continued with free access to food ( AL), or were switched to a calorie restricted diet (CR; 60% of AL intake) for 20 days. We measured body composition, whole-body energy expenditure, oral glucose tolerance and skeletal muscle insulin sensitivity in isolated soleus and extensor digitorum longus muscles using the 2-deoxy-glucose (2DOG) uptake method. p55α mRNA and protein expression was increased ∼2 fold in muscle from p55α-mOX versus WT mice. There were no differences in energy expenditure, total activity, or food intake of AL-fed mice between genotypes. Body weight, fat and lean mass, tissue weights, and fasting glucose and insulin were comparable between p55α-mOX and WT mice on AL, and were decreased equally by CR. Interestingly, overexpression of p55α did not impair oral glucose tolerance or skeletal muscle insulin signaling or sensitivity, nor did it impact the ability of CR to enhance these parameters. Skeletal muscle-specific overexpression of p55α does not impact skeletal muscle insulin action, suggesting that p85α and/or p50α may be more important regulators of skeletal muscle insulin signaling and sensitivity.
磷酸肌醇3激酶（PI3K）信号通路在骨骼肌胰岛素刺激的葡萄糖摄取中起重要作用。虽然PI3K调节亚基（p85α、p55α和p50α或p85β）的单个或组合的全身及组织特异性敲除（KO）可提高胰岛素敏感性，但尚无研究探讨增加单个调节亚基的表达是否会抑制胰岛素作用。因此，本研究的目的是确定PI3K的p55α调节亚基的骨骼肌特异性过表达是否会损害骨骼肌胰岛素敏感性，或阻止热量限制对其的增强作用。我们开发了一种新型的“floxed”小鼠，通过Cre-LoxP方法，可实现他莫昔芬（TMX）诱导的PI3K的p55α亚基的骨骼肌特异性过表达（称为“p55α-mOX”）。从10周龄开始，p55α-mOX小鼠及其floxed同窝小鼠（称为野生型[WT]）要么继续自由进食（AL），要么改为热量限制饮食（CR；AL摄入量的60%），持续20天。我们使用2-脱氧葡萄糖（2DOG）摄取法测量了体成分、全身能量消耗、口服葡萄糖耐量以及分离的比目鱼肌和趾长伸肌中的骨骼肌胰岛素敏感性。与WT小鼠相比，p55α-mOX小鼠肌肉中的p55α mRNA和蛋白表达增加了约2倍。不同基因型的AL喂养小鼠在能量消耗、总活动量或食物摄入量方面没有差异。p55α-mOX小鼠和WT小鼠在AL喂养时的体重、脂肪和瘦体重、组织重量以及空腹血糖和胰岛素水平相当，并且CR均使其同等程度降低。有趣的是，p55α的过表达并未损害口服葡萄糖耐量或骨骼肌胰岛素信号传导及敏感性，也未影响CR增强这些参数的能力。p55α的骨骼肌特异性过表达不会影响骨骼肌胰岛素作用，这表明p85α和/或p50α可能是骨骼肌胰岛素信号传导和敏感性更重要的调节因子。
