2177-P: Role of De Novo Sphingolipid Metabolites in Oleate-Induced Pancreatic ß-Cell Proliferation in Rats

Fatty acids (FA) are major regulators of pancreatic β-cell function. In a rat model of nutrient excess we previously showed that FA potentiate glucose-induced β-cell proliferation. Sphingolipids, derived from the intracellular metabolism of FA, act as cellular mediators in the regulation of pancreatic β-cell function. However, the contribution of sphingolipid species to FA-induced β-cell proliferation is unknown.

Objective: To determine the role of de novo sphingolipid synthesis in FA-induced β-cell proliferation.

Methods: Isolated rat islets were exposed to oleate or palmitate (0.5 mM) in the presence of 16.7 mM glucose for 48h. Sphingosine kinase (SphK) 1 and 2 expression was measured by real-time PCR. Serine palmitoyl transferase (SPT), SphK, and the S1P₃ receptor were inhibited with Myriocin, SKI II and TY52156, respectively. β-cell proliferation was assessed in cryosections by immunohistochemical detection of insulin and the proliferation marker Ki67 or by flow cytometry by labeling for C-peptide and EdU incorporation. Wistar rats were infused for 72 hours with glucose and a lipid emulsion (CLI) to induce β-cell proliferation.

Results: The monounsaturated FA oleate, but not the saturated FA palmitate, increased β-cell proliferation. Blocking de novo sphingolipid synthesis by SPT inhibition decreased oleate-induced β-cell proliferation as did inhibition of SphK and S1P₃ receptor activation. Sphk1/2 mRNA levels in islets were not significantly changed following nutrient infusion in rats or FA exposure ex vivo.

Conclusion: β-cell proliferation in response to oleate requires de novo sphingolipid synthesis and S1P₃ signaling. Analyses are underway to assess the contribution of SphK products sphingosine-1-phosphate and dihydrosphinganine-1-phosphate in S1P₃-mediated β-cell proliferation.