Exendin-4 attenuates high glucose-induced cardiomyocyte apoptosis via inhibition of endoplasmic reticulum stress and activation of SERCA2a

摘要

Hyperglycemia-induced cardiomyocyte apoptosis contributes to diabetic cardiomyopathy. Glucagon-like peptide-1 (Glp1) receptor (Glp1r) agonists improve cardiac function and survival in response to ischemia-reperfusion and myocardial infarction. The present studies assessed whether Glplr activation exerts direct cardioprotective effects in response to hyperglycemia. Treatment with the Glplr agonist Exendin-4 attenuated apoptosis in neonatal rat ventricular cardiomyocytes cultured in high (33 mM) glucose. This protective effect was mimicked by the cAMP inducer forskolin. The Exendin-4 protective effect was blocked by the Glplr antagonist Exendin(9-39) or the PKA antagonist H-89. Exendin-4 also protected cardiomyocytes from hydrogen peroxide (H_2O_2)-induced cell death. Cardiomyocyte protection by Exendin-4 was not due to reduced reactive oxygen species levels. Instead, Exendin-4 treatment reduced endoplasmic reticulum (ER) stress, demonstrated by decreased expression of glucose-regulated protein-78 (GRP78) and CCAT/enhancer-binding homologous protein (CHOP). Reduced ER stress was not due to activation of the unfolded protein response, indicating that Exendin-4 directly prevents ER stress. Exendin-4 treatment selectively protected cardiomyocytes from thapsigargin- but not tunica-mycin-induced death. This suggests that Exendin-4 attenuates thapsi-gargin-mediated inhibition of the sarco/endoplasmic reticulum Ca~(2+) ATPase-2a (SERCA2a). High glucose attenuates SERCA2a function by reducing SERCA2a mRNA and protein levels, but Exendin-4 treatment prevented this reduction. Exendin-4 treatment also enhanced phosphor-ylation of the SERCA2a regulator phospholamban (PLN), which would be expected to stimulate SERCA2a activity. In sum, Glplr activation attenuates high glucose-induced cardiomyocyte apoptosis in association with decreased ER stress and markers of enhanced SERCA2a activity. These findings identify a novel mechanism whereby Glp1-based therapies could be used as treatments for diabetic cardiomyopathy.