Role of p90 ribosomal S6 kinase-mediated prorenin-converting enzyme in ischemic and diabetic myocardium

Background: Epidemiological data strongly indicate that diabetes increases the incidence of heart failure. Although the benefit of angiotensin-converting Enzyme inhibitor (ACE-I) treatment during and after myocardial infarction has been found to be greater in diabetics than nondiabetics and activation of the renin-angiotensin system (Ras) has been implicated, the molecular basis of these actions remains unclear.

Methods and results: We generated transgenic mice with cardiac-specific overexpression of wild-type p90 ribosomal S6 kinase (WT-p90RSK-Tg) and a dominant-negative form of p90RSK (DN-p90RSK-Tg). Recovery of cardiac function after ischemia/reperfusion in WT-p90RSK-Tg isolated mouse hearts was significantly impaired. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed specific induction of prorenin-converting Enzyme (PRECE) in WT-p90RSK-Tg mice. mRNA induction of PRECE was confirmed with serial Angiotensinogen protein reduction after perfusion in WT-p90RSK-Tg mice, suggesting an increase of Angiotensinogen cleavage and subsequent Ras activation in WT-p90RSK-Tg mice. We investigated the role of the Ras in WT-p90RSK-Tg Animals after ischemia/reperfusion with the use of an ACE-I (captopril) and an angiotensin II type 1 receptor blocker (olmesartan). We did not observe any effect of these inhibitors in non-Tg littermate controls, thus corroborating Other reports in rodents. In contrast, both captopril and olmesartan significantly improved cardiac function and reduced infarct size in WT-p90RSK-Tg mice. At 8 months of age, WT-p90RSK-Tg mice developed cardiac dysfunction. p90RSK activity and PRECE mRNA were both increased by streptozotocin-induced hyperglycemia in non-Tg littermate controls, whereas DN-p90RSK-Tg Animals exposed to streptozotocin did not have PRECE induction.

Conclusions: This study demonstrates the critical role of p90RSK in hyperglycemia-mediated myocardial PRECE induction, which may explain the augmentation of the Ras in diabetic hearts and provide an alternative therapeutic approach to treat diabetic cardiomyopathy.