Contribution of β-Cell- & Immune Cell-Derived Lipids to β-Cell Death and Diabetes

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Type 1 diabetes (T1D) is a consequence of autoimmune destruction of pancreatic islet β-cells and the underlying causes for this process are not completely understood. Yet to be defined are the roles of lipids generated in β-cells and immune cells in this process. Islet β-cells and immune cells express Ca2+- independent phospholipase A2β (iPLA2β), which hydrolyzes membrane phospholipids at the sn-2 position to generate lipids that can promote inflammatory responses. We hypothesize that iPLA2β-derived lipids (iDLs) provide critical signals linking immune cells, β-cells, and ER stress with β-cell death associated with autoimmune diabetes. In support, we find that (a) iPLA2β is induced by pro-inflammatory cytokines and cytokine-mediated ER stress and β-cell apoptosis are reversed by iPLA2β inhibition, (b) β-cells and immune cells in a spontaneous model of autoimmune diabetes (non-obese diabetic mice, NOD) express higher iPLA2β during the pre-diabetic phase, (c) administration of an iPLA2β-selective inhibitor (FKGK18) to NOD mice preserves β-cells mass and reduces diabetes incidence, insulitis, and autoimmunity, (d) pre-treatment of immunodeficient mice with FKGK18 reduces adoptive transfer of diabetes by T-cells, (e) overexpression of iPLA2β in β-cells accelerates and increases the incidence of diabetes in NOD, (f) reduction of iPLA2β in NOD mice mimics the protective effects seen with FKGK18 administration, (g) M1 inflammatory macrophage polarization is reduced with iPLA2β deficiency, and (h) there is feedback regulation between iPLA2β and ER stress, and between inflammation-related transcription factors and iPLA2β. Our hypothesis will be tested using whole animal (mouse models with altered iPLA2β expression on a NOD or immunodeficient-NOD background), mechanism-based in vitro, and translational (human T1D and autoantibody positive but not diabetic subjects) approaches through the following Aims: 1. Delineate the impact of iDLs generated by immune cells on autoimmune diabetes development. 2. Delineate the impact of iDLs generated by β-cells on autoimmune diabetes development. 3. Delineate the cellular mechanisms by which iDLs induce β-cell death in autoimmune diabetes. 4. Assess the contribution of iDLs to human T1D development. These Aims will encompass generation of islet and immune cell lipidome during autoimmune diabetes development; adoptive transfer protocols to distinguish importance of iDLs generated by immune cells and β-cells to diabetes development; co-culture assays to assess impact of iDLs on islet antigenicity; protein and message analyses to address link between ER stress, iDLs, and inflammation; ChIP and CRISPR/Cas9 analyses to examine transcriptional regulation of iPLA2β; and human subjects to asses the potential of iPLA2β as a biomarker of T1D susceptibility. Our long-term goal is to elucidate underlying mechanisms by which iPLA2β-derived lipid signals contribute to the pathogenesis of T1D, so that novel targets that might be candidates for drug intervention to counter T1D can be developed.