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-alpha外显子1周围具有loxP重组位点的floxed Gs-alpha小鼠重复交配，产生了β细胞中Gs-alpha缺陷的小鼠（betaGsKO小鼠）。在大多数情况下，BetaGsKO小鼠在生命的前几周内的存活率非常差，与高血糖症相关，此外，出生后生长非常差。对成年小鼠的研究表明，尽管β GsKO小鼠具有高于正常的胰岛素敏感性，但其具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是低胰岛素血症，胰岛胰岛素含量减少和葡萄糖刺激的胰岛素释放。尽管胰岛结构得以维持，但betaGsKO小鼠的β细胞质量显著减少，β细胞增殖减少，β细胞凋亡增加。对年轻小鼠的研究表明，β细胞增殖从出生开始就减少了。尽管研究表明Gs-cAMP通过刺激胰岛素受体底物2（Irs 2）表达介导对β细胞生长、存活和胰岛素释放的这些作用，但我们观察到Irs 2或Pdx 1（一种由Irs 2信号诱导的β细胞生长基因）的表达没有变化。相反，细胞周期蛋白D2的表达有一个特定的减少。最近，我们使用Pdx 1-cre制备了第二个β细胞Gs-alpha缺陷小鼠系。这些小鼠在整个内分泌和外分泌胰腺中具有GS缺乏。结果显示，这些小鼠也会患上严重的胰岛素缺乏型糖尿病。然而，这些小鼠具有或多或少的正常存活，并且胰岛中存在更大比例的胰腺α细胞，没有证据表明这些细胞的增殖减少。此外，在α-细胞系中的研究表明，Gs-alpha导致这些细胞的增殖减少，这表明Gs-alpha可能分别对α-细胞和β-细胞的增殖具有相反的作用。胰腺外分泌异常，导管增大，并伴有大嗜酸性细胞，这可能导致GI吸收不良。我们最近产生的小鼠与Gs-alpha缺陷限于α细胞使用胰高血糖素-cre转基因小鼠直接检查对α细胞的影响。这些小鼠的初步结果显示对体重没有明显影响，但胰岛大小和质量增加，细胞结构正常，α和β细胞相对丰富。研究正在进行中，以了解这种现象。我们还分别研究了体内α和β细胞中激活Gs突变的影响。

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 islet size and mass, with a normal cellular architecture and relative abundance of alpha and beta cells. Studies are underway to understand this phenomenom. We are also examining the effects of activating Gs mutations in alpha and beta cells in vivo, respectively.