Metformin Inhibits Endoplasmic Reticulum Stress & Attenuates Autophagy in Glucose Starved Microvascular Endothelial Cells

Metformin, the first choice of drug to treat diabetes, confers protection against cardiovascular disease (CVD) & also suppress tumor growth albeit at high concentrations. Since scientific evidence suggest a strong association between diabetes & CVD & more recently between concurrent diabetes & cancer, it is important to evaluate how the microvascular endothelial cells (MECs), which receive the initial impact of reduced oxygen & nutrient/glucose starvation (GS) during a myocardial infarction or in a tumor microenvironment, respond to metformin treatment. In the present study we investigated the effect of varying concentrations of metformin on GS induced endoplasmic reticulum (ER) stress & autophagy in MECs. Mouse Microvasuclar Endothelial Cells (MMECs) were subjected to GS for 24h in the presence & absence metformin (50μM & 2mM) & western blot analysis was performed to assess the induction of ER stress & autophagy. Immunofluorescence staining followed by confocal microscopy was also done to assess LC3B punctae staining in cells, indicating autophagy. ER stress activation & autophagic induction was observed in MMECs subjected to GS as evidenced by significant increase in the levels of ER stress markers (GRP78, ATF4 & CHOP) & autophagic markers (LC3A/B‐II), respectively. Accumulation of LC3B stained punctae in glucose‐starved cells also confirmed autophagic activation. Metformin treatment (2mM), independent of AMPK, significantly reversed GS induced ER stress & autophagy in MECs while lower concentrations had no effect. Our study demonstrates for the first time that metformin reverses GS induced ER stress & autophagy in the microvascular endothelium.