Very Long-Chain Unsaturated Sphingolipids Mediate Oleate-Induced Rat β-Cell Proliferation

Fatty-acid (FA) signaling contributes to β-cell mass expansion in response to nutrient excess, but the underlying mechanisms are poorly understood. In the presence of elevated glucose, FA metabolism is shifted towards synthesis of complex lipids, including sphingolipids. Here we tested the hypothesis that sphingolipids are involved in the β-cell proliferative response to FA. Isolated rat islets were exposed to FA and 16.7 mM glucose for 48-72 h and the contribution of the de novo sphingolipid synthesis pathway was tested using the serine palmitoyltransferase inhibitor myriocin, the sphingosine kinase (SphK) inhibitor SKI II, or knockdown of SphK, fatty-acid-elongase-1 (ELOVL1) and acyl-CoA-binding protein (ACBP). Rats were infused with glucose and the lipid emulsion ClinOleic and received SKI II by gavage. B-cell proliferation was assessed by immunochemistry or flow cytometry. Sphingolipids were analyzed by LC-MS/MS. Amongst the FA tested, only oleate increased β-cell proliferation. Myriocin, SKI II, and SphK knockdown all decreased oleate-induced b-cell proliferation. Oleate exposure did not increase the total amount of sphingolipids but led to a specific rise in 24:1 species. Knockdown of ACBP or ELOVL1 inhibited oleate-induced β-cell proliferation. We conclude that unsaturated very long-chain sphingolipids produced from the available C24:1 acyl-CoA pool mediate oleate-induced β-cell proliferation in rats.