Abstract 143: Group X Secretory Phospholipase A2 Regulates Insulin Secretion by Mouse Pancreatic Beta Cells

Abstract

Background: Group X secretory phospholipase A2 (GX sPLA2) potently releases arachidonic acid (AA) from the plasma membrane of intact cells. AA is a precursor of bioactive prostaglandins that are known to modulate insulin secretion by β-islet cells. C57BL/6 mice deficient in GX sPLA2 (GX KO) are protected from age-related defect in glucose tolerance. GX sPLA2 is expressed in mouse pancreatic islet cells. In this study we tested the hypothesis that GX sPLA2 regulates pancreatic insulin secretion. Methods and results: Glucose stimulated insulin secretion (GSIS) was measured in vivo in WT and GX KO mice and ex vivo using pancreatic islet cells isolated from WT and GX KO mice. To complement these studies, GSIS was also assessed in vitro using Min6 pancreatic beta cell lines with or without GX sPLA2 overexpression. GSIS was significantly increased in GX KO mice compared to WT mice, and in islet cells isolated from GX KO mice compared to WT mice. Consistent with this finding, Min6 cells overexpressing GX sPLA2 demonstrated significantly decreased GSIS compared to control cells. Expression of ABCA1 and ABCG1 mRNAs were significantly upregulated in islet cells from GX KO mice compared to WT mice, consistent with our previous report that GX sPLA2 negatively regulates LXR activity. However, there was no significant difference in cholesterol content between islets from WT and GX KO mice suggesting that altered LXR activity may not be the mechanism. Min6 cells overexpressing GX sPLA2 secrete significantly increased levels of PGE2- a known negative regulator of GSIS, in the medium compared to control cells. Treatment of these cells with NS398- an inhibitor of COX2 enzyme, abolished the decrease in GSIS shown by these cells. Conclusions: We conclude that GX sPLA2 plays a previously unrecognized role in negatively regulating pancreatic insulin secretion most likely by enhancing PGE2 production.