Upregulation of the Mammalian Target of Rapamycin Complex 1 Pathway by Ras Homolog Enriched in Brain in Pancreatic β-Cells Leads to Increased β-Cell Mass and Prevention of Hyperglycemia

OBJECTIVE-Components of insulin/IGF-1 receptor-mediated signaling pathways in pancreatic beta-cells have been implicated in the development of diabetes, in part through the regulation of beta-cell mass. the protein Ras homolog in vivo. Studies in vitro have shown that, enriched in brain (Rheb) plays a key role as a positive upstream regulator of the mammalian target of rapamycin complex 1 (mTORC1) pathway in integrating inputs from nutrients and growth factors for cell growth. Our objective was to investigate the role of the mTORC1 pathway in the regulation of beta-cell mass in vivo. RESEARCH DESIGN AND METHODS-We generated transgenic mice that, overexpress Rheb in beta-cells. We examined the activation of the mTORC1 pathway and its effects on beta-cell mass, on glucose metabolism, and on protection against, hyperglycemia. RESULTS-Immunoblots of islet extracts revealed that the phosphorylation levels of ribosomal protein S6 and eukaryotic initiation factor 4E binding protein 1, downstream effectors for mTORC1, were upregulated in transgenic beta-cells. Immunostaining of the pancreatic sections with anti-phospho-S6 antibody confirmed upregulation of the mTORC1 pathway in beta-cells in vivo. The mice showed improved glucose tolerance with higher insulin secretion. This arose from increased beta-cell mass accompanied by increased cell size. The mice also exhibited resistance to hyperglycemia induced by streptozotocin and obesity. CONCLUSIONS-Activation of the mTORC1 pathway by Rheb led to increased beta-cell mass in this mouse model without producing obvious unfavorable effects, giving a potential approach for the treatment of beta-cell failure and diabetes. Diabetes 58:1321-1332, 2009