Hyperglycemia-induced Ang II generation activates JAK2 in human failing myocytes

Background. The results of several studies indicate that strict glycemic control can prevent the onset and progression of diabetic complications. Other studies showed that Angiotensin (Ang)-II antagonism reduces cardiovascular morbidity and mortality in diabetic patients, thus suggesting an important role in the diabetic complications of the renin-angiotensin system (RAS). Studies in vascular smooth muscle cells showed that both HG and Ang II, enhance the generation of intracellular reactive oxygen species (ROS), able to stimulate growth-promoting kinases such as janus-activated kinase (JAK2) but no information are available regarding human cardiomyocytes. Aims and Methods. Aim of our study was to investigate whether hyperglicemia activates Ang-II generation and JAK2 signalling pathway in human myocytes. Therefore we investigated the effects of high glucose concentration (HG, 25 mM for 6 hours) on human myocytes (1x105 cell/ml) isolated from failing explanted hearts (n=4) and tentative donors (n=3) in the presence of Ang II antagonism. JAK2 phosphorylation was investigated by Western blot analysis. Results. HG enhanced JAK2 phosphorylation vs normal glucose (5.5 mM) only in failing myocytes (+107%, p<0.05) with no detectable effect in NF cells. JAK2 activation was mediated by myocyte production of Ang II as shown by the inhibitory effects of co-incubation with ACE inhibitor (ramipril, 100 nM) or AT1 antagonist (valsartan, 1 µM). The inhibition of NADPH oxidase (DPI, 100 µM) prevented HG induced JAK2 phosphorylation. Conclusions. In conclusion, hyperglycemia induced Ang II generation in human failing myocytes which in turn induces JAK2 phosphorylation via enhanced oxidative stress related with NADPH oxidase activation.