Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.
Diabetes. 2010 Sep;59(9):2188-97. doi: 10.2337/db09-0890. Epub 2010 Jun 14.
Cellular stress and proinflammatory cytokines induce phosphorylation of insulin receptor substrate (IRS) proteins at Ser sites that inhibit insulin and IGF-1 signaling. Here, we examined the role of Ser phosphorylation of IRS-2 in mediating the inhibitory effects of proinflammatory cytokines and cellular stress on beta-cell function.
Five potential inhibitory Ser sites located proximally to the P-Tyr binding domain of IRS-2 were mutated to Ala. These IRS-2 mutants, denoted IRS-2(5A), and their wild-type controls (IRS-2(WT)) were introduced into adenoviral constructs that were infected into Min6 cells or into cultured murine islets.
When expressed in cultured mouse islets, IRS-2(5A) was better than IRS-2(WT) in protecting beta-cells from apoptosis induced by a combination of IL-1beta, IFN-gamma, TNF-alpha, and Fas ligand. Cytokine-treated islets expressing IRS2(5A) secreted significantly more insulin in response to glucose than did islets expressing IRS-2(WT). This could be attributed to the higher transcription of Pdx1 in cytokine-treated islets that expressed IRS-2(5A). Accordingly, transplantation of 200 islets expressing IRS2(5A) into STZ-induced diabetic mice restored their ability to respond to a glucose load similar to naïve mice. In contrast, mice transplanted with islets expressing IRS2(WT) maintained sustained hyperglycemia 3 days after transplantation.
Elimination of a physiological negative feedback control mechanism along the insulin-signaling pathway that involves Ser/Thr phosphorylation of IRS-2 affords protection against the adverse effects of proinflammatory cytokines and improves beta-cell function under stress. Genetic approaches that promote IRS2(5A) expression in pancreatic beta-cells, therefore, could be considered a rational treatment against beta-cell failure after islet transplantation.
细胞应激和促炎细胞因子诱导胰岛素受体底物（IRS）蛋白丝氨酸（Ser）位点磷酸化，从而抑制胰岛素和 IGF-1 信号。在此，我们研究了 IRS-2 的 Ser 磷酸化在介导促炎细胞因子和细胞应激对β细胞功能的抑制作用中的作用。
将 IRS-2 中靠近 P-Tyr 结合域的 5 个潜在抑制性 Ser 位点突变为 Ala。这些 IRS-2 突变体（称为 IRS-2(5A)）及其野生型对照（IRS-2(WT)）被引入腺病毒构建体中，然后感染 Min6 细胞或培养的小鼠胰岛。
当在培养的小鼠胰岛中表达时，IRS-2(5A)比 IRS-2(WT)更能保护β细胞免受由 IL-1β、IFN-γ、TNF-α 和 Fas 配体组成的细胞因子诱导的凋亡。与表达 IRS-2(WT)的胰岛相比，用细胞因子处理表达 IRS2(5A)的胰岛分泌更多的胰岛素对葡萄糖作出反应。这可以归因于用细胞因子处理表达 IRS-2(5A)的胰岛中 Pdx1 的转录更高。相应地，将 200 个表达 IRS2(5A)的胰岛移植到 STZ 诱导的糖尿病小鼠中，恢复了它们对葡萄糖负荷的反应能力，与未处理的小鼠相似。相比之下，移植表达 IRS2(WT)的胰岛的小鼠在移植后 3 天仍保持持续高血糖。
消除胰岛素信号通路中涉及 IRS-2 的 Ser/Thr 磷酸化的生理负反馈控制机制可防止促炎细胞因子的不良影响，并在应激下改善β细胞功能。因此，促进胰腺β细胞中 IRS2(5A)表达的遗传方法可以被认为是胰岛移植后β细胞衰竭的合理治疗方法。
