A glycerol shunt functions as a glucose excess security valve in pancreatic β-cells

Abstract

The recently identified glycerol-3-phosphate (Gro3P) phosphatase (G3PP) in mammalian cells, encoded by the PGP gene, was shown to regulate intermediary metabolism by hydrolyzing Gro3P and to control glucose-stimulated insulin secretion (GSIS) in {beta}-cells, in vitro. We now examined in inducible {beta}-cell specific G3PP-KO (BKO) mice, the role of G3PP in the control of insulin secretion in vivo, {beta}-cell function and glucotoxicity. BKO mice, compared to MCre controls, showed increased body weight, adiposity, fed insulinemia, GSIS, reduced plasma triglycerides and mildly altered glucose tolerance. Isolated BKO mouse islets at high (16.7 mM) but not low or intermediate glucose (3-8 mM) showed elevated GSIS, Gro3P, metabolites reflecting {beta}-cell activation, O2 consumption, ATP production and reduced glycerol release. BKO islets chronically exposed to elevated glucose showed increased apoptosis, reduced insulin content and expression of Pdx-1, MafA and Ins-2 genes. As G3PP channels glucose carbons towards glycerol formation and release, the results demonstrate that {beta}-cell are endowed with a "glycerol shunt" acting as a glucose excess security valve. We propose that the glycerol shunt plays a role in glucodetoxification, the prevention of insulin hypersecretion, acts as a defense against excess body weight gain and contributes to {beta}-cell mass preservation in the face of hyperglycemia.