ER Stress-Induced β-Cell Apoptosis is Linked to Novel Select Lipid Signaling at the Transcriptional Level: Implications in T1D Developmen t

Abstract Type 1 diabetes (T1D) is a consequence of β-cell death. ER stress precedes T1D onset and prolonged ER stress in β-cells can lead to β-cell apoptosis. We reported that lipid signaling generated by the Ca 2+ -independent phospholipase A 2 β (iPLA 2 β), encoded by Pla2g6 , participates in ER stress-mediated β-cell apoptosis. β-Cell membranes are enriched in arachidonic acid containing glycerophospholipids and the iPLA 2 β catalyzes the hydrolysis of arachidonic acid in ER stressed β-cells. Metabolism of arachidonic acid leads to the generation of various proinflammatory lipids, raising the possibility that they contribute to ER stress and β-cell death leading to T1D. However, molecular mechanisms by which such β-cell-iPLA 2 β-derived lipid (iDL) signaling contributes to β-cell apoptosis are not understood. It is well known that ER stress-mediated β-cell apoptosis is associated with induction of transcription factors, NFκB and STAT1. We report here that both induce Pla2g6 and, unexpectedly, we find that iPLA 2 β, which lacks DNA-binding motifs, associates with NFkB , Stat1 , and Pla2g6 promoter regions. Consistently, p65-NFκB and pSTAT1 induction is reduced with select inhibition or knockdown of iPLA 2 β. Surprisingly, iPLA 2 β expression is also reduced by select inhibition of iPLA 2 β, raising the possibility of feedback regulation by iDLs. In support, we find that select iDLs, recognized to be proinflammatory, enhance association of iPLA 2 β with Pla2g6 , Nfkb , and Stat1 promoter regions leading to induction of all three gene products and β-cell apoptosis. Our findings reveal previously unrecognized transcriptional regulation by iDL signaling and, iPLA 2 β itself, that leads to gene products that promote β-cell apoptosis. Analogous findings in human islets validate this mechanism raising the possibility that targeting select lipid signaling can reduce ER stress in β-cells and ameliorate T1D development.