RyR2 and Calpain-10 Delineate a Novel Apoptosis Pathway in Pancreatic Islets

Kenichi Otani,Hong Wu,Stanley Misler,Honggang Ye,Yan Zhang,Zhiqiang Han,Kenneth S Polonsky,Yukio Horikawa,Graeme I Bell,James D Johnson

doi:10.1074/jbc.m401216200

Abstract

Cells are programmed to die when critical signaling and metabolic pathways are disrupted. Inhibiting the type 2 ryanodine receptor (RyR2) in human and mouse pancreatic beta-cells markedly increased apoptosis. This mode of programmed cell death was not associated with robust caspase-3 activation prompting a search for an alternative mechanism. Increased calpain activity and calpain gene expression suggested a role for a calpain-dependent death pathway. Using a combination of pharmacological and genetic approaches, we demonstrated that the calpain-10 isoform mediated ryanodine-induced apoptosis. Apoptosis induced by the fatty acid palmitate and by low glucose also required calpain-10. Ryanodine-induced calpain activation and apoptosis were reversed by glucagon-like peptide or short-term exposure to high glucose. Thus RyR2 activity seems to play an essential role in beta-cell survival in vitro by suppressing a death pathway mediated by calpain-10, a type 2 diabetes susceptibility gene with previously unknown function.

Highlights

Cells are programmed to die when critical signaling and metabolic pathways are disrupted
The present studies were undertaken to assess the role of ryanodine receptor Ca2ϩ channels (RyR) in the survival of pancreatic ␤-cells and to determine the mechanism by which these Ca2ϩ channels regulate apoptosis
Our findings indicate that inhibiting the RyR2 is associated with increased apoptosis, suggesting that maintenance of normal basal Ca2ϩ flux through this channel is essential for ␤-cell survival

Summary

Introduction

Cells are programmed to die when critical signaling and metabolic pathways are disrupted. Inhibiting the type 2 ryanodine receptor (RyR2) in human and mouse pancreatic ␤-cells markedly increased apoptosis. This mode of programmed cell death was not associated with robust caspase-3 activation prompting a search for an alternative mechanism. RyR2 activity seems to play an essential role in ␤-cell survival in vitro by suppressing a death pathway mediated by calpain-10, a type 2 diabetes susceptibility gene with previously unknown function. In the MIN6 ␤-cell line, RyR were shown to regulate ATP production [20] Because of their role in regulating intracellular Ca2ϩ and mitochondrial function, we focused on RyR as likely mediators of ␤-cell apoptosis. A plant alkaloid, is the most specific probe for all RyR subtypes, and its activity is lost in RyR-deficient cells [23, 24]

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Results

Conclusion