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

我们通过大鼠胰岛素II启动子-cre重组酶转基因小鼠与Gs-α外显子1周围有loxP重组位点的小鼠重复配对，产生了β细胞Gs-α缺陷小鼠(BetaGsKO小鼠)。BetaGsKO小鼠在出生后最初几周的存活率非常低，大多数情况下与高血糖有关，此外出生后生长也非常差。对成年小鼠的研究表明，尽管BetaGsKO小鼠的胰岛素敏感度高于正常水平，但仍有严重的高血糖和葡萄糖耐受性。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，葡萄糖刺激的胰岛素释放。尽管胰岛结构保持不变，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。对年龄较小的老鼠的研究表明，β细胞的增殖从出生起就会减弱。尽管研究表明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，但我们观察到IRS2或Pdx1的表达没有变化，IRS2或Pdx1是由Irs2信号诱导的β细胞生长基因。相反，细胞周期蛋白D2的表达有特异性的降低。最近，我们使用Pdx1-cre建立了第二个β细胞Gs-α缺乏症小鼠系。这些小鼠的内分泌和外分泌胰腺都有Gs缺乏。结果显示，这些小鼠还会患上严重的胰岛素缺乏性糖尿病。然而，这些小鼠或多或少有正常的存活，胰岛中有更大比例的胰腺阿尔法细胞，没有证据表明这些细胞的增殖减少。此外，在阿尔法细胞系中的研究表明，Gs-α导致这些细胞的增殖减少，这表明Gs-α可能对α细胞和β细胞的增殖分别具有相反的影响。胰腺外分泌异常，导管增大，嗜酸细胞增多，可能导致胃肠道吸收不良。我们最近用胰升糖素-cre转基因小鼠产生了仅限于阿尔法细胞的Gs-α缺乏症小鼠，以直接检查对阿尔法细胞的影响。在这些小鼠身上的初步结果显示，对体重没有明显的影响，但胰岛的大小和质量增加了，细胞结构正常，α和β细胞相对丰富。为了理解这一现象，研究正在进行中，包括细胞线性示踪以及总细胞和单细胞RNAseq实验。我们还在体内分别检测激活α细胞和β细胞中Gs突变的效果。

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, including cellular linear tracing and total and single cell RNAseq experiments. We are also examining the effects of activating Gs mutations in alpha and beta cells in vivo, respectively.