Expression of PPARα modifies fatty acid effects on insulin secretion in uncoupling protein-2 knockout mice

Aims/ hypothesis: In uncoupling protein-2 (UCP2) knockout ( KO) mice, protection of beta cells from fatty acid exposure is dependent upon transcriptional events mediated by peroxisome proliferator-activated receptor-alpha (PPAR alpha). Methods: PPAR alpha expression was reduced in isolated islets from UCP2KO and wild-type (WT) mice with siRNA for PPAR alpha (siPPAR alpha) overnight. Some islets were also cultured with oleic or palmitic acid, then glucose stimulated insulin secretion (GSIS) was measured. Expression of genes was examined by quantitative RT-PCR or immunoblotting. PPAR alpha activation was assessed by oligonucleotide consensus sequence binding. Results: siPPAR alpha treatment reduced PPAR alpha protein expression in KO and WT islets by > 85%. In siPPAR alpha-treated UCP2KO islets, PA but not OA treatment significantly decreased the insulin response to 16.5 mM glucose. In WT islets, siPPAR alpha treatment did not modify GSIS in PA and OA exposed groups. In WT islets, PA treatment significantly increased UCP2 mRNA and protein expression. Both PA and OA treatment significantly increased PPAR alpha expression in UCP2KO and WT islets but OA treatment augmented PPAR alpha protein expression only in UCP2KO islets ( p < 0.05). PA treatment induced carnitine palmitoyltransferase I, acyl CoA oxidase and malonyl CoA decarboxylase mRNA in UCP2KO islets. Conclusion: These data show that the negative effect of saturated fatty acid on GSIS is mediated by PPAR alpha/UCP2. Knockout of UCP2 protects beta-cells from PA exposure. However, in the absence of both UCP2 and PPAR alpha even a short exposure ( 24 h) to PA significantly impairs GSIS.