ALTERED STATS RESPONSE TO JAK2 ACTIVATION IN FAILING AND NON FAILING HUMAN CARDIAC MYOCYTES

OBJECTIVE. A reversal of the intracellular signaling pathways downstream Ang II binding to AT1 receptor with depressed extracellular signal-regulated kinase (ERK)-1/2 activation and enhanced Janus-activated kinase (JAK)-2 phosphorylation was observed in human failing cardiomyocytes. This study was performed to investigate the response of different signal trasducers and activators of transcription (STATs) following Ang II induced JAK2 activation in isolated failing and non failing human ventricular myocytes. In particular the response of different STATs connected with pro-hypertrophic and cardio-protective pathways (STAT3) and with proinflammatory pathways (STAT2, STAT5) was investigated. DESIGN AND METHOD. Ventricular myocytes were isolated from patients undergoing cardiac transplantation for heart failure due to either idiopathic (DCM, n=6) and ischemic dilated cardiomyopathy (ICM, n=6). Control myocytes were also isolated from the hearts of six tentative donors excluded from donation for noncardiac reasons. Myocytes were isolated with the enzymatic digestion method and resuspended in basic buffer (105 cells/ml). STATs activation following Ang II (100 nmol/l) stimulation was investigated with specific antibodies in Western blot studies. RESULTS. In human non failing myocytes, Ang II induced activation of STAT3 only in the presence of high glucose (25 mmol/l). Ang II-induced STAT3 phosphorylation was prevented by JAK2 antagonism (AG490, 10 μmol/l) and AT1 antagonism (Valsartan, 1 μmol/l). Conversely ERK1/2 antagonism (PD98059, 30 μmol/l) enhanced STAT3 phosphorylation (+70%). No response of STAT2 and STAT5 was observed. When failing myocytes were studied, Ang II failed to induce STAT3 activation. Conversely STAT2 and STAT5 phosphorylation was found. STAT2 and STAT5 phosphorylation were strongly reduced by AT1 antagonism and by inhibitors of reactive oxygen species (ROS) generation (diphenyleneiodonium [DPI], tiron, rotenon and apocynin), but not by AT2 antagonism (PD123319, 1 μmol/l). CONCLUSIONS. The present study revels that JAK2 activation is followed by the STAT3 activation in human nonfailing myocytes and by STAT2 and STAT5 activation in failing myocytes. The different activation pathway may be of relevance due to the selective activity of STATs involved.