Sphingosine-1-phosphate (S1P) as a check point for proinflammatory cytokine-induced inflammation and death in pancreatic beta-cells during T1DM development – in search for a novel beta-cell specific target to prevent and treat the disease

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Type 1 diabetes (T1DM) is a chronic autoimmune disease with a strong genetic background, leading to a gradual loss of pancreatic insulin-secreting beta-cells that control glucose homeostasis. Proinflammatory cytokines released by activated immune cells infiltrating pancreatic islets during T1DM development induce a stress response resulting in beta-cell death. Beta-cells are very susceptible to cytokine toxicity due to a weak antioxidative defense and predominance of proinflammatory over antiinflammatory cytokine signaling. The molecular mechanisms of inflammation remain poorly understood in beta-cells, disabling the generation of novel therapeutic approaches. Recently significant disturbances in serum and PBMCs sphingolipid profiles in individuals at risk of or lately diagnosed with T1DM were described. Studies using fingolimod, a sphingosine-1 phosphate (S1P) receptor 1 antagonist, documented diabetes prevention and reduced islet infiltration in animal models of autoimmune diabetes. However, evaluation of S1P contribution, particularly of beta-cell origin, to cytokine-induced inflammation in beta-cells is still missing. Our project aims to close this knowledge gap. We will study the role of beta-cell S1P metabolism in cytokine toxicity and inflammation, with a particular focus on human beta-cells. Our preliminary results show that S1P is predominantly generated by the proinflammatory sphingosine kinase 2 (SK2), of which a gene polymorphism has been identified in T1DM subjects and which generates S1P in certain cellular organelles. Our data demonstrate protection against cytokine-mediated toxicity by SK2 knockdown and a pro-apoptotic effect of SK2 overexpression, even without a parallel cytokine exposure. Moreover, our preliminary lipidomics results suggest substantial cytokine-mediated lipid rearrangements that can be linked to inflammation and are likely related to an aberrant S1P metabolism. We will use an array of modern molecular biology techniques and tools to investigate whether S1P acts as an inflammation check point in beta-cells exposed to cytokines. The effects of genetic manipulations of S1P metabolizing enzymes on cytokine-mediated beta-cell fate will be studied in rat and humanbeta-cells, primary islets and animal models. We aim to uncover novel S1P-dependent inflammation mechanisms induced by cytokines. Using a co-culture model of genetically modified human beta-cells with PBMCs from T1DM individuals we will explore a role of beta-cell derived S1P secreted within islets in the autoimmune-mediated beta-cell destruction under T1DM conditions. Finally, the abundance of S1P-metabolizing enzymes in parallel with inflammation and beta-cell identity markers will be analyzed in pancreatic tissue from nondiabetic and T1DM individuals. Our project aims to identify the most relevant S1P metabolizing enzyme associated with cytokine-mediated inflammation and beta-cell failure as a novel druggable target for beta-cell protection in T1DM.