Interactions between sirtuin 1, miRNAs and metformin in prevention of hyperglycaemia-induced endothelial dysfunction

G Arunachalam1, R Upadhyay1, CR Triggle1,2, H Ding1,2. 1Department of Pharmacology, Weill Cornell Medical College in Qatar, Doha, Qatar, 2Medical Education, Weill Cornell Medical College in Qatar, Doha, Qatar

MicroRNAs (miRNAs) are a novel group of non-coding small RNAs that have been implicated to play a crucial role in the pathogenesis of diabetes-associated cardiovascular complications (1). We have shown that in mouse microvascular endothelial cells (MMECs) the presence of metformin protects against hyperglycaemia-induced downregulation of sirtuin 1, and enhanced endothelial cell senescence and apoptosis (2). The aim of the current study is to evaluate the molecular cross talk between sirtuin 1, metformin and miRNA expression in endothelial cells maintained in either normo- or hyperglycaemic conditions. MMECs were maintained in culture under either normoglycaemic (NG, 11mM glucose) or hyperglycaemic (HG, 40mM) conditions. Sirtuin 1-associated downstream signalling and miRNAs expression in the absence or presence of metformin were analysed by real-time PCR and western blotting. Data were given as Mean±SEM, analyses was performed using one-way analysis of variance (ANOVA) and p<0.05 used to indicate statistical significance. Exposure to HG induced expression of miR-34a/221/222, but suppressed miR-103/107 in MMECs. 50μM metformin restored expression of miR-34a, miR221, miR107 but not miR222 and miR-103. Specifically HG-exposure resulted in an increase of miR-34a expression (1.80±0.03 fold increase vs. NG) and this induction paralleled and correlated with altered expression of sirtuin 1 (2.41±0.2 fold decrease vs. NG), and decreased phosphorylation of eNOS (1.40±0.15 fold decrease vs. NG, phospho/total eNOS). Inhibition of miR-34a (anti-miR) significantly (p<0.05) increased the expression of sirtuin 1 (2.46±0.2 fold vs. HG alone) and attenuated changes in eNOS phosphorylation in HG-exposed MMECs. Conversely, treatment with metformin (50μM) also inhibited miR-34a expression and attenuated HG-induced impaired SIRT1 and eNOS signalling in MMECs. Metformin protects endothelial cells against glucose toxicity via maintaining sirtuin 1 protein levels directly or indirectly and selective modulation of the expression of miR-34a, 107 and 221 by metformin suggesting a novel mode of action for this oral hypoglycaemic drug.

(1) Small EM et al (2010). Circulation 121:022-1032.

(2) Arunachalam G et al (2014). Brit J Pharmacol 171:523-535.