Role of Gs-alpha in pancreatic islet cell growth and function

我们通过将大鼠胰岛素II启动子-cre重组酶转基因小鼠与在gs - α外显子1周围有loxP重组位点的floxed gs - α小鼠重复配对，产生了β细胞中gs - α缺乏的小鼠（betaGsKO小鼠）。在大多数与高血糖相关的情况下，BetaGsKO小鼠在生命的最初几周内存活率非常低，此外，产后生长也非常差。对成年小鼠的研究表明，尽管β agsko小鼠的胰岛素敏感性高于正常水平，但它们有严重的高血糖症和葡萄糖耐受不良。葡萄糖耐量受损是由于这些小鼠低胰岛素血症，胰岛胰岛素含量降低，葡萄糖刺激胰岛素释放。尽管胰岛结构得以维持，但betaGsKO小鼠的β细胞质量显著降低，β细胞增殖减少，β细胞凋亡增加。对年轻老鼠的研究表明，从出生开始，β细胞的增殖就减少了。虽然有研究表明，Gs-cAMP通过刺激胰岛素受体底物2 （Irs2）的表达来介导这些对β细胞生长、存活和胰岛素释放的影响，但我们没有观察到Irs2或Pdx1（一种由Irs2信号诱导的β细胞生长基因）的表达发生变化。相反，细胞周期蛋白D2的表达有特异性降低。最近，我们用Pdx1-cre制造了第二种具有β细胞gs - α缺陷的小鼠系。这些小鼠的整个内分泌和外分泌胰腺都缺乏gs。结果显示，这些小鼠也会患上严重的胰岛素缺乏性糖尿病。然而，这些小鼠或多或少都有正常的存活，胰岛中有更大比例的胰腺α细胞，没有证据表明这些细胞的增殖减少。此外，对α -细胞系的研究表明，gs - α导致这些细胞的增殖减少，这表明gs - α可能分别对α -细胞和β -细胞的增殖产生相反的影响。外分泌胰腺异常，导管增大，伴有大量嗜酸性细胞，可能导致胃肠道吸收不良。我们最近用胰高血糖素-cre转基因小鼠产生了仅限于α细胞的gs - α缺陷小鼠，以直接检查对α细胞的影响。在这些老鼠身上的初步结果显示，对体重没有明显的影响，但胰高血糖素水平、胰岛大小和质量都有所增加。对胰腺细胞质量的影响正在进行中。

We generated mice with Gs-alpha deficiency in beta cells (betaGsKO mice) by repeated matings of rat insulin II promoter-cre recombinase transgenic mice with floxed Gs-alpha mice which have loxP recombination sites surrounding Gs-alpha exon 1. BetaGsKO mice have very poor survival during the first several weeks of life in most cases associated with hyperglycemia and in addition had very poor postnatal growth. Studies in adult mice showed that betaGsKO mice had severe hyperglycemia and glucose intolerance despite having greater than normal insulin sensitivity. Impaired glucose tolerance was due to the fact that these mice were hypoinsulinemic, with reduced islet insulin content and glucose-stimulated insulin release. Although islet architecture was maintained, betaGsKO mice had significantly reduced beta cell mass with reduced beta cell proliferation and increased beta cell apoptosis. Studies on younger mice show that beta cell proliferation is reduced from birth. Although studies have suggested that Gs-cAMP mediates these effects on beta cell growth, survival, and insulin release by stimulating insulin receptor substrate 2 (Irs2) expression, we observed no change in expression of Irs2 or Pdx1, a beta cell growth gene which is induced by Irs2 signaling. Rather, there was a specific reduction in cyclin D2 expression. More recently we have made a second mouse line with beta-cell Gs-alpha deficiency using Pdx1-cre. These mice have Gs-deficiency throughout the endocrine and exocrine pancreas. Results show these mice to also develop severe insulin-deficient diabetes. However these mice have more or less normal survival and there is a greater proportion of pancreatic alpha-cells in the islets with no evidence for reduced proliferation of these cells. Moreover studies in an alpha-cell line showed evidence that Gs-alpha leads to reduced proliferation of these cells, indicating that Gs-alpha may have opposite effects on proliferation of alpha- and beta-cells, respectively. The exocrine pancreas was abnormal with enlarged ducts with large eosinophic cells, which may lead to GI malabsorption. We have most recently generated mice with Gs-alpha deficiency limited to alpha cells using a glucagon-cre transgenic mouse to examine the effects on alpha cells directly. Initial results in these mice show no obvious effects on body weight but there is an increase in glucagon levels and islet size and mass. Effects on pancreatic alpha-cell mass are underway.