Elimination of Negative Feedback Control Mechanisms Along the Insulin Signaling Pathway Improves β-Cell Function Under Stress

Abstract

OBJECTIVECellular 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 β-cell function.RESEARCH DESIGN AND METHODSFive 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-25A, and their wild-type controls (IRS-2WT) were introduced into adenoviral constructs that were infected into Min6 cells or into cultured murine islets.RESULTSWhen expressed in cultured mouse islets, IRS-25A was better than IRS-2WT in protecting β-cells from apoptosis induced by a combination of IL-1β, IFN-γ, TNF-α, and Fas ligand. Cytokine-treated islets expressing IRS25A secreted significantly more insulin in response to glucose than did islets expressing IRS-2WT. This could be attributed to the higher transcription of Pdx1 in cytokine-treated islets that expressed IRS-25A. Accordingly, transplantation of 200 islets expressing IRS25A 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 IRS2WT maintained sustained hyperglycemia 3 days after transplantation.CONCLUSIONSElimination 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 β-cell function under stress. Genetic approaches that promote IRS25A expression in pancreatic β-cells, therefore, could be considered a rational treatment against β-cell failure after islet transplantation.

Selective Serotonin Reuptake Inhibitors (SSRIs) Inhibit Insulin Secretion and Action in Pancreatic β Cells*

“…Isolation of Murine Islets-Murine islets were isolated as we described (32,33). In brief, digested pancreata were filtered through a 1000-m and 500-m sieves and islets Ͼ75 and Ͻ250 m were handpicked under a stereoscope.…”

“…Generation of Adenoviral Constructs Expressing Myc-tagged IRS-2-Adenoviral constructs were generated as we described (32) according to the protocol provided by AdEasy vector system (Quantum). Briefly, cDNA encoding Myc-IRS-2 was ligated into the shuttle plasmid pAdTrack-CMV, which contains a GFP cassette driven by an independent promoter that served as a tracing marker.…”

Prolonged insulin treatment sensitizes apoptosis pathways in pancreatic β cells

“…As shown in numerous studies by us and others (Gurevitch et al 2010, Tseng et al 2002, insulin mainly plays antiapoptotic roles and exerts its trophic effects on β-cells through an IRS-2-mediated signaling pathway. Still, growth factors, such as insulin, might also induce ROS production and proapoptotic signals under certain circumstances (Porras et al 2003, Bryson & White 2012, Graham et al 2012.…”

MicroRNA-30d Induces Insulin Transcription Factor MafA and Insulin Production by Targeting Mitogen-activated Protein 4 Kinase 4 (MAP4K4) in Pancreatic β-Cells

“…TNF-␣ has been shown to inhibit IRS2-mediated insulin signaling (28). To determine whether miR-30d is a general counterfactor of TNF-␣ action in the pathway of insulin signaling, miR-30d-overexpressed and TNF-␣-treated MIN6 cells were further characterized for IRS2 expression.…”