Student McGill University, Montreal Diabetes Research Center Montreal, Quebec, Canada
Anfal Almass (McGill University, Montreal Diabetes Research Center)| Pegah Poursharifi (Montreal Diabetes Research Center)| Marie-Line Peyot (Montreal Diabetes Research Center)| Roxane Lussier (Montreal Diabetes Research Center)| Emily Levens (McGill University)| Julian Guida (McGill University)| Yves Mugabo (Montreal Diabetes Research Center)| Elite Possik (Montreal Diabetes Research Center)| Heidi Erb (Montreal Diabetes Research Center)| Erik Joly (Montreal Diabetes Research Center)| S.R.Murthy Madiraju (Montreal Diabetes Research Center)| Robert Sladek (McGill University, Montreal Diabetes Research Center)| Marc Prentki (Montreal Diabetes Research Center)
Objective: The recently identified enzyme in mammalian cells, glycerol-3-phosphate (Gro3P) phosphatase (G3PP), gene name Pgp, was proposed to regulate intermediary metabolism. G3PP was shown in in vitro studies to regulate metabolism and glucose stimulated insulin secretion (GSIS) in ß-cells. We now examined the in vivo role of G3PP in the control of insulin secretion and ß-cell glucotoxicity.
Methods: Glucose and insulin tolerance were studied in ß-cell specific G3PP-KO (BKO) mice. Body weight gain, fed glycemia and insulinemia were measured. Pancreatic islets were isolated for ex vivo GSIS and biochemical measurements.
Results: BKO mice show increased body weight gain, unaltered fed glycemia and insulinemia, and enhanced insulin secretion in response to glucose load in an intraperitoneal but not oral glucose tolerance test, reaching 21 and 14 mM glucose, respectively. Insulin sensitivity in vivo remains unchanged in the BKO mice. GSIS response ex vivo at 16 mM but not 8 mM glucose is higher in BKO mouse islets. BKO islets show reduced glucose-induced glycerol release and elevated O2 consumption and ATP production at high (16 mM) but not low (4 mM) glucose levels. Glucotoxicity at 30 mM glucose for 7 days led to increased apoptosis, reduced insulin content and expression of Pdx-1 and Ins-2 genes in BKO islets.
Conclusion: G3PP impacts insulin secretion in vivo and ex vivo only under conditions of high but not intermediate and low glucose levels. G3PP plays a role in preventing ß-cell glucotoxicity. These effect likely result from the capacity of G3PP to redirect the excess glucose carbons from intermediate metabolism to glycerol that exits ß-cells. We propose that G3PP acts as a glucose excess security valve to prevent excessive insulin secretion and ß-cell dysfunction when blood glucose reaches very high levels.