High-glucose-induced apoptosis, ROS production and pro-inflammatory response in cardiomyocytes is attenuated by metformin treatment via PP2A activation

Metformin has been shown to ameliorate diabetic cardiomyopathy. In the present research we investigated whether metformin would reduce cardiomyocyte apoptosis that was induced by high-glucose stimulationin vitrovia activation of PP2A. Primary human and rat cardiomyocytes were subject to high-glucose stimulation. Okadaic acid was used to inhibit PP2A activity. Cell viability and apoptosis was assessed using CCK-8 and by flow cytometry, respectively. Release of HMGB1, TNF alpha or IL-6 was analyzed by ELISA. Oxidative stress was evaluated by measuring cellular ROS and mitochondrial superoxide level. PP2A activity was evaluated by Serine/Threonine phosphatase assay system or analyzing Y307 phosphorylation level of PP2A catalytic domain (PP2Ac) by Western blot and the association between PP2Ac and alpha 4 by co-immunoprecipitation. Activation of the NF-kappa B signaling pathway was assessed by detecting Ser32 phosphorylation level of I kappa B alpha as well as nuclear entry of p65 protein by Western blot. Activation of the GSK3 beta/MCL1 signaling pathway was assessed by detecting Ser9 phosphorylation level of GSK3 beta and protein level of MCL1. We found Metformin pre-treatment attenuated human and rat cardiomyocytes apoptosis, HMGB1, TNF alpha and IL-6 release and ROS production that were induced by high-glucose stimulation, and these effects of metformin could be blocked by okadaic acid treatment. Metformin reduced the upregulation of PP2Ac pY307 and the PP2Ac-alpha 4 association, which was not affected by okadaic acid treatment. Metformin pre-treatment reduced NF-kappa B activation in human and rat cardiomyocytes apoptosis that was elicited by high-glucose stimulation, and this effect of metformin could be blocked by okadaic acid treatment. GSK3 beta/MCL1 is not part of metformin activating PP2A induced myocardial cell death inhibition. In conclusion, metformin reduced apoptosis, ROS production and inflammatory response in primary human and rat cardiomyocytesin vitroin a PP2A dependent manner.