Roles of Sphingolipid Metabolism in Pancreatic β Cell Dysfunction Induced by Lipotoxicity

Pancreatic β cells secrete insulin in order to maintain glucose homeostasis. However, various environmental stresses such as obesity have been shown to induce loss of secretory responsiveness in pancreatic β cells and pancreatic β cell apoptosis which can favor the development of type 2 diabetes (T2D). Indeed, elevated levels of free fatty acids (FFAs) have been shown to induce β cell apoptosis. Importantly, the chronic adverse effects of FFAs on β cell function and viability are potentiated in the presence of hyperglycaemia, a phenomenon that has been termed gluco-lipotoxicity. The molecular mechanisms underlying the pathogenesis of gluco-lipotoxicity in pancreatic β cells are not completely understood. Recent studies have shown that sphingolipid metabolism plays a key role in gluco-lipotoxicity induced apoptosis and loss of function of pancreatic β cells. The present review focuses on how the two main sphingolipid mediators, ceramides and sphingoid base-1-phosphates, regulate the deleterious effects of gluco-lipotoxicity on pancreatic β cells. The review highlights the role of a sphingolipid biostat on the dysregulation of β cell fate and function induced by gluco-lipotoxicity, offering the possibility of new therapeutic targets to prevent the onset of T2D

Targeting sphingolipid metabolism in the treatment of obesity/type 2 diabetes

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Ceramide synthase 4 and de novo production of ceramides with specific N-acyl chain lengths are involved in gluco-lipotoxicity-induced apoptosis of INS-1 β-cells.

International audiencePancreatic β-cell apoptosis induced by palmitate requires high glucose concentrations. Ceramides have been suggested to be important mediators of gluco-lipotoxicity-induced β-cell apoptosis. In INS-1 β-cells, 0.4 mM palmitate with 5 mM glucose increased the levels of dihydrosphingosine and dihydroceramides, two lipid intermediates in the de novo biosynthesis of ceramides, without inducing apoptosis. Increasing glucose concentrations to 30 mM amplified palmitate-induced accumulation of dihydrosphingosine and the formation of (dihydro)-ceramides. Of note, gluco-lipotoxicity specifically induced the formation of 18:0, 22:0 and 24:1 (dihydro)-ceramide molecular species, which was associated with the up-regulation of ceramide synthase 4 (CerS4) levels. Fumonisin-B1, a ceramide synthase inhibitor, partially blocked apoptosis induced by gluco-lipotoxicity. In contrast, apoptosis was potentiated in the presence of D,L-threo-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol, an inhibitor of glucosyl-ceramide synthase. Moreover, over-expression of CerS4 amplified ceramide production and apoptosis induced by palmitate with 30 mM glucose whereas down-regulation of CerS4 by siRNA reduced apoptosis. CerS4 also potentiates ceramide accumulation and apoptosis induced by another saturated fatty acid, stearate. Collectively, our results suggest that gluco-lipotoxicity induced β-cell apoptosis through a dual mechanism involving the de novo ceramide biosynthesis and the formation of ceramides with specific N-acyl chain lengths rather than an overall increase of ceramide content

Deciphering the Link Between Hyperhomocysteinemia and Ceramide Metabolism in Alzheimer-Type Neurodegeneration

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Ceramide Transporter CERT Is Involved in Muscle Insulin Signaling Defects Under Lipotoxic Conditions

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