Renin expression at sites of repair in the infarcted rat heart

Y. Sun, J. Zhang, J. Q. Zhang and K. T. Weber. Renin Expression at Sites of Repair in the Infarcted Rat Heart. Journal of Molecular and Cellular Cardiology (2001) 33, 995-1003. Angiotensin (Ang) II has autocrine and paracrine functions that contribute to structural cardiac remodeling by fibrous tissue following myocardial infarction (MI). The recruitment of angiotensin converting enzyme (ACE) and AngII receptors by inflammatory and fibroblast-like cells involved in tissue repair of the infarcted heart is now well established. On the other hand, the temporal and spatial response and cellular source of renin in infarcted hearts have not been fully elucidated. The relationship between renin synthesis and circulating renin activity have likewise not been addressed. The present study sought to assess the cellular source, spatial distribution and temporal response of renin expression and synthesis in the rat heart following anterior transmural MI, and to determine its relationship to circulating renin activity. At day 3 and weeks 1, 2, 3 and 4 following left coronary artery ligation, the localization and optical density of cardiac renin mRNA was detected by quantitative in situ hybridization; cardiac and circulating renin activity was measured by radioimmunoassay; cells expressing cardiac renin were detected by immunohistochemistry; and injury/repair was assessed by hematoxylin/eosin and collagen-specific picrosirius red staining. Unoperated rats served as normal controls. The authors found: (1) renin mRNA and activity were not detected in either normal control or non-infarcted myocardium, but were expressed at the site of infarction and other sites of repair involving visceral pericardium and endocardium of interventricular septum at all time points; (2) cells expressing renin at day 3 and weeks 1 and 2 were predominantly macrophages, while at weeks 3 and 4, they were primarily myofibroblasts; (3) renin activity in the infarcted myocardium rose progressively over the course of 4 weeks; and (4) circulating renin activity was significantly increased at day 3 and week 1, reached a peak at week 2, declined at week 3 and returned to normal levels at week 4. Thus, renin expression and activity appear at sites of repair in the infarcted rat heart on day 3 and rise progressively thereafter over 4 weeks, independent of circulating renin. Several types of cells are responsible for renin synthesis at these sites; primarily macrophages during the inflammatory phase of repair, and myofibroblasts during the subsequent fibrogenic phase. Cardiac renin production following MI contributes to local AngII generation that regulates tissue repair and structural remodeling following MI.