The susceptibility to fibrosis and progression of renal disease is mitigated by inhibition of the renin-angiotensin system (RAS). It is hypothesized that activation of the intrarenal RAS predisposes to renal fibrosis in aging. To test this scientists measured 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 in 3-month-old (young), 14-month-old (middle-aged), and 24-month-old (old) male Sprague-Dawley rats.

The study has shown that old rats manifested glomerulosclerosis and severe tubulointerstitial fibrosis with increased fibronectin and TGF-β 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.

Results allow to conclude that 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.