GLP-1 Receptor Activation Inhibits Palmitate-Induced Apoptosis via Ceramide in Human Cardiac Progenitor Cells.

Abstract

Increased apoptosis of cardiomyocytes and cardiac progenitor cells (CPCs) in response to saturated fatty acids (SFAs) can lead to myocardial damage and dysfunction. Ceramides mediate lipotoxicity-induced apoptosis. Glucagonlike peptide-1 receptor (GLP1R) agonists exert beneficial effects on cardiac cells in experimental models. To investigate the protective effects of GLP1R activation on SFA-mediated apoptotic death of human CPCs. Human CPCs were isolated from cardiac appendages of nondiabetic donors and then exposed to palmitate with or without pretreatment with the GLP1R agonist exendin-4. Ceramide accumulation was evaluated by immunofluorescence. Expression of key enzymes in de novo ceramide biosynthesis was studied by quantitative reverse-transcription polymerase chain reaction and immunoblotting. Apoptosis was evaluated by measuring release of oligonucleosomes, caspase-3 cleavage, caspase activity, and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling. Exposure of the CPCs to palmitate resulted in 2.3- and 1.9-fold higher expression of ceramide synthase 5 (CERS5) and ceramide desaturase-1, respectively (P < 0.05). This was associated with intracellular accumulation of ceramide and activation of c-Jun NH2-terminal protein kinase (JNK) signaling and apoptosis (P < 0.05). Both coincubation with fumonisin B1, a specific ceramide synthase inhibitor, and CERS5 knockdown prevented ceramide accumulation, JNK activation, and apoptosis in response to palmitate (P < 0.05). Exendin-4 also prevented the activation of the ceramide biosynthesis and JNK in response to palmitate, inhibiting apoptosis (P < 0.05). Excess palmitate results in activation of ceramide biosynthesis, JNK signaling, and apoptosis in human CPCs. GLP1R activation counteracts this lipotoxic damage via inhibition of ceramide generation, and this may represent a cardioprotective mechanism.