Lipoapoptosis plays an important role in the pathogenesis of type 2 diabetes. Peroxisome proliferator-activated receptor delta (PPARdelta), a vital regulator of glucose and lipid metabolism, may reduce fatty acid-induced pancreatic β cell lipotoxicity in diabetes. However, the detailed molecular mechanisms underlying this process are not fully understood. In this study, we investigated the effect of activation of PPARdelta on palmitate-induced β cell apoptosis, and we explored the potential mechanism of the antiapoptotic effect. The cell apoptosis was determined by DNA fragmentation analysis and Hoechst 33342 staining. The expressing of glucagon-like peptide-1 receptor (GLP-1R) in INS-1 cells was assessed by Western blotting, quantification of PCR, and was further confirmed by immunofluorescence staining. The potential of PPARdelta to interact with homologous PPRE in the GLP-1R gene was determined by Chromatin immunoprecipitation (ChIP). Our results showed that exposure of INS-1 cells to palmitate for 24 h caused a significant increase in cell apoptosis, which was inhibited by GW501516. PPARdelta exerted anti-apoptotic effects in pancreatic β cells via the PI3 K/PKB/FoxO1 signaling pathway. Moreover, PPARdelta upregulated the GLP-1R expression under lipotoxic conditions. The ChIP assay revealed a direct binding of PPARdelta to a noncanonical PPRE motif of the GLP-1R gene in INS-1 cells. Our study suggested that the anti-apoptotic action of PPARdelta may involve its transcriptional regulation of GLP-1R and PI3 K/PKB/FoxO1 signaling. GW501516 and possible other GW-based strategies may confer additional benefit beyond improved glycemic control.
Keywords: Apoptosis; GLP-1R; PPARdelta; Palmitate; Pancreatic β cells.