Altered Renal Expression of Angiotensin II Receptors, Renin Receptor, and ACE-2 Precede the Development of Renal Fibrosis in Aging Rats

Background: The susceptibility to fibrosis and progression of renal disease is mitigated by inhibition of the renin-angiotensin system (RAS). We hypothesized that activation of the intrarenal RAS predisposes to renal fibrosis in aging. Methods: Intrarenal expression of angiotensin II type 1 (AT(1)R), type 2 (AT(2)R), and (pro) renin receptors, ACE and ACE-2, as well as pro- and antioxidant enzymes were measured in 3-month-old (young), 14-month-old (middle-aged), and 24-month-old (old) male Sprague-Dawley rats. Results: Old rats manifested glomerulosclerosis and severe tubulointerstitial fibrosis with increased fibronectin and TGF-beta expression (7-fold). AT(1)R /AT(2)R ratios were increased in middle-aged (cortical 1.6-fold, medullary 5-fold) and old rats (cortical 2-fold, medullary 4-fold). Similarly, (pro) renin receptor expression was increased in middle-aged (cortical 2-fold, medullary 3-fold) and old (cortical 5-fold, medullary 3-fold) rats. Cortical ACE was increased (+35%) in old rats, whereas ACE-2 was decreased (-50%) in middle-aged and old rats. NADPH oxidase activity was increased (2-fold), whereas antioxidant capacity and expression of the mitochondrial enzyme manganese superoxide dismutase (cortical -40%, medullary -53%) and medullary endothelial nitric oxide synthase (-48%) were decreased in old rats. Conclusion: Age-related intrarenal activation of the RAS preceded the development of severe renal fibrosis, suggesting that it contributes to the increased susceptibility to renal injury observed in the elderly. Copyright (C) 2010 S. Karger AG, Basel