370-OR: Proinflammatory Stress Activates Neutral Sphingomyelinase 2 Based Generation of Ceramide-Enriched ß-Cell Exosomes

Data suggest that β cell exosomes, extracellular vesicles released by exocytosis of multivesicular endosomes (MVEs) , may act as paracrine effectors in islet health. However, mechanisms linking β cell stress to changes in exosomes and whether activation of these pathways can impact diabetes remain less explored. In other cells, the enzyme neutral spingomyelinase 2 (nSMase2) induces ceramide dependent MVE vesicle formation and release of ceramide-enriched exosomes. We hypothesized that β cell inflammatory stress engages ceramide-dependent exosomal formation pathways, and that ceramide-enriched exosomes could then impact surrounding β cells. To test this we treated INS-1 β cells with 24 hrs of 5 ng/mL of IL1β. nSMase 2 and ceramide expression were quantified with immunoblot and/or flow cytometry and exosomes were isolated using a tetraspanin bead-based pulldown. IL1β increased β cell nSMase2 expression and ceramide expression in concert. Direct nSMase2 activation with 24 hrs of 5-ng/mL Caffeic acid phenethyl ester (CAPE) also increased β cell ceramide staining. IL1β and CAPE treatments also yielded increased ceramide expression on β cell exosomes. Human islets exhibited similar increases in cellular nSMase2 and ceramide staining after 24-hr cytokine mix treatment (5ng/mL IL1β, 10ng/mL TNFα, and 100ng/mL IFNγ) . To test the potential for transfer of β cell exosomes to surrounding cells, we generated INS-1 cells with GFP tagged CD9 (exosome transmembrane protein) , which release GFP labeled exosomes. Flow cytometry staining in wild-type INS-1 cells after 24-hr transwell coculture with CD9-GFP cells showed that cocultured wild-type cells exhibited increased green fluorescence, suggesting transfer of CD9-GFP exosomes. Our findings suggest that nSMase2 activity may regulate β cell exosome subpopulations under conditions of inflammatory stress. Future work will interrogate impacts on exosome cargo and physiologic impacts of transfer on recipient cells.