Abstract
Background / Aim: The upregulation of the renin-angiotensin system (RAS) represents a major pathological mechanism in diabetes. We have previously reported that hyperglycemia preferentially increases intracellular generation of angiotensin (Ang) II. However, circulating RAS is down regulated in diabetes implying the accelerated intracellular RAS mechanism as a major contributor to diabetic cardiomyopathy. In this study, we determined expression of RAS components and their effect on cardiac cells to give us a venue to intervene.
Methods: Diabetes was induced in Sprague-Dawley rats and C57/BL6J mice with injection of streptozotocin for 5 days and verified by sustained blood glucose levels >15 mmol/L. Control mice received buffered saline alone. One week after diabetes induction the mice hearts were removed and perfused by the Langendorff method. Myocytes were isolated with enzymatic dispersion and centrifugation. RAS proteins were determined by real-time PCR and Western analysis. These included angiotensinogen, renin, angiotensin converting enzyme, AT1, AT2, and ACE 2. Angiotensin II was purified by reverse-phase chromatography and quantified by competitive ELISA.
Results: Among cells obtained from diabetic hearts, expression of AGT (3.5+/− 0.8 fold), renin (2.4 +/− 0.4), and AT1 (2.6+/− 0.3) was significantly increased compared to cells from control hearts (p<0.05, ANOVA). No significant change in the gene expression of ACE (1.2+/− 0.4), ACE2 (0.97+/− 0.2), and AT2 (1.2+/− 0.2), was observed. Increased expression at the protein level for AGT (2.2 +/− 0.1), renin (1.9 +/− 0.08), and AT1 (2.3+/− 0.2) was also observed by Western analysis. No significant changes in the protein levels of AT2, ACE, and ACE2 were observed. AngII levels in cardiac myocytes were determined by quantitative ELISA, which demonstrated significantly enhanced levels of AngII (140+/− 10 fmol/mg protein) synthesis in diabetic mice compared to controls (20 +/− 10 fmol/mg protein).
Conclusions: This study suggests that local activation of the RAS in diabetes has a significant role in the development of cardiac dysfunction. Demonstration of renin expression in cardiac myocytes and enhanced expression in diabetic conditions represent a particularly significant finding. The latter suggests that locally produced, not circulating renin has a major role in cardiac Ang II generation and subsequent cardiomyopathy.
- Received May 27, 2010.
- Accepted May 27, 2010.
