Mechanical stretch and angiotensin II activate Janus tyrosine kinase-2 in human podocytes

Abstract: Aim. In diabetes glomerular capillary hypertension induces an abnormal mechanical stretching of glomerular resident cells that contributes to glomerular injury. The signalling molecule Janus tyrosine kinase-2 (JAK2) has been recently implicated in the pathogenesis of diabetic nephropathy. The aim of this study was to assess in vitro the effect of mechanical stretch in podocytes and mesangial cells (MC), mimicking in vitro the hemodynamic insult of glomerular hypertension, on JAK2 expression/activation. Methods. MC and podocytes were exposed to mechanical stretching using a Stress Unit for short (5, 10, 30, 60 min) and long (12, 24, 72 hours) time periods. To investigate the potential role of angiotensina II as a mediator of stretch, in selected experiments, cells were exposed to exogenous angiotensin II (0.1 mM) and stretched in the presence/absence of candesartan (1 mM). Protein expression of both total and phosphorylated (activated) JAK2 was measured by immunoblotting. Results. Stretch did not affect JAK2 expression in either podocytes or MC, but induced a significant increase in the phosphorylated/activated form of JAK2 at 12-24 hours with a return to baseline by 72 hours in podocytes. Although exposure to angiotensina II induced a rapid JAK2 activation in podocytes, stretch-induced JAK2 activation was AT1-indipendent as it was not altered by the addition of candesartan. Conclusion. Mechanical stretch and angiotensin II induce JAK2 activation in podocytes.