Pancreatic deletion of insulin receptor substrate 2 reduces beta and alpha cell mass and impairs glucose homeostasis in mice

Abstract

Aims/hypothesis Insulin signalling pathways regulate pancreatic beta cell function. Conditional gene targeting using the Cre/loxP system has demonstrated that mice lacking insulin receptor substrate 2 (IRS2) in the beta cell have reduced beta cell mass. However, these studies have been complicated by hypothalamic deletion when the RIPCre (B6.Cg-tg(Ins2-cre) 25Mgn/J) transgenic mouse (expressing Cre recombinase under the control of the rat insulin II promoter) is used to delete floxed alleles in insulin-expressing cells. These features have led to marked insulin resistance making the beta cellautonomous role of IRS2 difficult to determine. To establish the effect of deleting Irs2 only in the pancreas, we generated PIrs2KO mice in which Cre recombinase expression was driven by the promoter of the pancreatic and duodenal homeobox factor 1 (Pdx1, also known as Ipf1) gene. Materials and methodsIn vivo glucose homeostasis was examined in PIrs2KO mice using glucose tolerance and glucose-stimulated insulin secretion tests. Endocrine cell mass was determined by morphometric analysis. Islet function was examined in static cultures and by performing calcium imaging in Fluo3am-loaded beta cells. Islet gene expression was determined by RT-PCR. Results The PIrs2KO mice displayed glucose intolerance and impaired glucose-stimulated insulin secretion in vivo. Pancreatic insulin and glucagon content and beta and alpha cell mass were reduced. Glucose-stimulated insulin secretion and calcium mobilisation were attenuated in PIrs2KO islets. Expression of the Glut2 gene (also known as Slc2a2) was also reduced in PIrs2KO mice. Conclusions/interpretation These studies suggest that IRS2-dependent signalling in pancreatic islets is required not only for the maintenance of normal beta and alpha cell mass but is also involved in the regulation of insulin secretion.

The regulation of pre- and post-maturational plasticity of mammalian islet cell mass

“…Studies on these disruptions suggest that, similar to the observations on beta cell hyperplasia in insulin resistance, an increase in alpha cell proliferation and hormone production occurs in states of glucagon resistance. In addition, the contribution of hyperinsulinaemia to alpha cell hyperplasia is supported by observations that IRS2 KO mice exhibit reduced alpha cell mass and glucagon secretion [69], while in vitro insulin treatment of alpha TC1 cells leads to increased alpha cell proliferation by triggering mTOR [78].…”

“…Insulin/IGF-1 and glucagon signalling Genetically engineered knockout and transgenic mouse models and knockdown approaches targeting one or more proteins in the insulin/IGF-1 signalling pathway, including the insulin and IGF-1 receptors [66,67], IRS-1 and IRS-2 [68,69], Akt [70], phosphoinositide 3-kinase (PI3-kinase) [71] or FOXO1 [72], point to their significant roles in the regulation of islet biology. Several groups, including ours, have reported on the significance of insulin/IGF-1 signalling in the regulation of both beta and alpha cells [66,28].…”

Time-dependent effects of Prkce deletion on glucose homeostasis and hepatic lipid metabolism on dietary lipid oversupply in mice

“…Islet isolation and insulin secretion assays Islets were isolated as previously described [11]. After pancreatic digestion, islets were purified using a Ficoll-Paque (GE Healthcare, Chalfont St Giles, UK) gradient.…”

Differentially Expressed MicroRNA-483 Confers Distinct Functions in Pancreatic β- and α-Cells

“…However, activated insulin signaling is considered to induce ␣-cell proliferation based on the findings from ␣-cell-specific insulin receptor knock-out (␣IRKO) mice and pancreas-specific IRS2 knockout mice (20,21). A recent study also demonstrated that insulin stimulates ␣-cell proliferation through the IR/IRS2/AKT/ mTOR (mammalian target of rapamycin) signaling pathway (22).…”