Abstract
PURPOSE: Group X (GX) and group V (GV) secretory phospholipase A(2) (sPLA(2)) potently release arachidonic acid (AA) from the plasma membrane of intact cells. We previously demonstrated that GX sPLA(2) negatively regulates glucose-stimulated insulin secretion (GSIS) by a prostaglandin E2 (PGE2)-dependent mechanism. In this study we investigated whether GV sPLA(2) similarly regulates GSIS. METHODS: GSIS and pancreatic islet-size were assessed in wild-type (WT) and GV sPLA(2)-knock out (GV KO) mice. GSIS was also assessed ex vivo in isolated islets and in vitro using MIN6 pancreatic beta cell lines with or without GV sPLA(2) overexpression or silencing. RESULTS: GSIS was significantly decreased in islets isolated from GV KO mice compared to WT mice and in MIN6 cells with siRNA-mediated GV sPLA(2) suppression. MIN6 cells overexpressing GV sPLA(2) (MIN6-GV) showed a significant increase in GSIS compared to control cells. Though the amount of AA released into the media by MIN6-GV cells was significantly higher, PGE2 production was not enhanced or cAMP content decreased compared to control MIN6 cells. Surprisingly, GV KO mice exhibited a significant increase in plasma insulin levels following i.p. injection of glucose compared to WT mice. This increase in GSIS in GV KO mice was associated with a significant increase in pancreatic islet size and number of proliferating cells in β-islets compared to WT mice. CONCLUSIONS: Deficiency of GV sPLA(2) results in diminished GSIS in isolated pancreatic beta-cells. However, the reduced GSIS in islets lacking GV sPLA(2) appears to be compensated by increased islet mass in GV KO mice.