Empagliflozin alleviates diabetic cardiomyopathy via inhibiting excessive autophagy and adverse remodeling in type 1 diabetic mice

Abstract

Abstract Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce cardiovascular mortality in patients with and without diabetes mellitus, but underlying mechanisms remain unclear. Autophagy is an important cardioprotective mechanism under acute stress conditions, but excessive autophagy can accelerate myocardial cell death leading to autosis. In this study we evaluated the role of empagliflozin (EMPA) against cardiac injury in streptozotocin (STZ)-induced diabetic mice, and assessed underlying mechanisms. EMPA (10 mg/kg/die)-treated diabetic male mice had a lower number of TUNEL-positive apoptotic cells (%TdT+ 4.9±2, p<0.05), lower percentage of SA-β-gal positive senescent cardiac area (%SA-β-gal 7.9±1, p<0.05), lower fibrotic area (%picrosirius red 0.15±0.06, p<0.05), lower autophagy (%green fluorescence 2.3±0.6, p<0.01), compared to diabetic mice (%TdT+ 4.9±2; %SA-β-gal 10±2; %picrosirius red fibrotic area 0.24±0.08; %green fluorescence autophagic area 3.98±0.5). Proteomics analysis of cardiac tissue showed downregulation of apoptosis, necrosis and 5' adenosine monophosphate-activated protein kinase (AMPK) pathways, along with upstream activation of vascular endothelial growth factor and sirtuins in the heart of EMPA+STZ treated mice compared to STZ mice. Since activation of sirtuins leads to modulation of cardiomyogenic transcription factors, we analyzed total expression of serum response factor (SRF), myocardin and myocardin-related transcription factor (MRTF), and DNA binding activity of SRF by electromobility shift assay. While EMPA only increased MRTF, EMPA (2.2±0.01, p<0.01) and EMPA+STZ (2.0±0.1, p<0.01) significantly increased SRF/SRE binding activity compared with STZ alone (0.5±0.01), which was paralleled by the increase in cardiac actin expression (4.06±0.1 vs 2.2±0.01, p<0.01). EMPA significantly reversed STZ-induced systolic cardiac dysfunction at echocardiography, and downregulation of pS368-connexin 43 active isoform (Table). In parallel in vitro experiments, EMPA inhibited excessive autophagy in high glucose-treated cardiomyocytes by inhibiting the autophagy inducer GSK3β, leading to reactivation of transcriptional complex for cardiomyocyte contractile genes. Our results indicate that EMPA plays a cardioprotective effect by inhibiting excessive autophagy through the mTOR/AMPK axis in the mouse model of STZ-induced type 1 diabetes. EMPA also promotes cardiac reverse remodeling by inhibiting fibrosis, activates cardiac Cx43 and the promyogenic transcriptional program through the sirtuins-SRF axis (Figure 1), in the context of diabetes. Funding Acknowledgement Type of funding sources: None.