340-OR: Transcriptional Activation in Beta-Cells during ER Stress Linking iPLA₂beta with NFkB

ER stress in β-cells has been reported to precede T1D development and we reported that the Ca²⁺-independent phospholipase A₂β (iPLA₂β) participates in ER stress-mediated β-cell apoptosis. Recently, we found that reduction in iPLA₂β lowers T1D incidence. The iPLA₂β hydrolyzes β-cell membrane glycerophospholipids to release arachidonic acid, which can be metabolized to inflammatory eicosanoids. Herein, we used insulinoma cells, human islets, spontaneously diabetes-prone NOD mice, and CRISPR-modified β-cells to address processes linking iPLA₂β and ER stress. We find that cytokine-induced ER stress induces iPLA₂β-mediated eicosanoid production, in association with NFκB activation and β-cell apoptosis. Surprisingly, inhibition or decreased iPLA₂β expression also reduced NFκB activation at the transcriptional and protein levels. These observations were recapitulated in human and NOD.iPLA₂β^-/- islet β-cells and suggested potential regulatory links between iPLA₂β and NFκB. To assess this at the molecular level, ChIP analyses were performed using MIN6 cells and not unexpectedly, an association between the transcription factor NFκB and PLA2G6, gene that encodes iPLA₂β was observed. Intriguingly, ER stress also promoted association of iPLA₂β with NF κ B and PLA2G6. Whereas inhibition of iPLA₂β did not affect these associations, CRISPR-mediated reduction of iPLA₂β significantly reduced both interactions. These observations suggest that iPLA₂β protein itself, and not its lipid products, triggers transcriptional events to regulate its own production and that of apoptotic factors. Curiously, the iPLA₂β protein is not recognized to have a DNA binding motif, therefore, suggesting that non-lipid co-factors likely link iPLA₂β with target genes. Our findings identify a novel role for iPLA₂β in modulating transcriptional events that are triggered during the development of ER stress, leading to β-cell death and T1D onset.