Bcl-2 and Bcl-x_L Suppress Glucose Signaling in Pancreatic β-Cells

Abstract

B-cell lymphoma 2 (Bcl-2) family proteins are established regulators of cell survival, but their involvement in the normal function of primary cells has only recently begun to receive attention. In this study, we demonstrate that chemical and genetic loss-of-function of antiapoptotic Bcl-2 and Bcl-x_L significantly augments glucose-dependent metabolic and Ca²⁺ signals in primary pancreatic β-cells. Antagonism of Bcl-2/Bcl-x_L by two distinct small-molecule compounds rapidly hyperpolarized β-cell mitochondria, increased cytosolic Ca²⁺, and stimulated insulin release via the ATP-dependent pathway in β-cell under substimulatory glucose conditions. Experiments with single and double Bax–Bak knockout β-cells established that this occurred independently of these proapoptotic binding partners. Pancreatic β-cells from Bcl-2^−/− mice responded to glucose with significantly increased NAD(P)H levels and cytosolic Ca²⁺ signals, as well as significantly augmented insulin secretion. Inducible deletion of Bcl-x_L in adult mouse β-cells also increased glucose-stimulated NAD(P)H and Ca²⁺ responses and resulted in an improvement of in vivo glucose tolerance in the conditional Bcl-x_L knockout animals. Our work suggests that prosurvival Bcl proteins normally dampen the β-cell response to glucose and thus reveals these core apoptosis proteins as integrators of cell death and physiology in pancreatic β-cells.