Abstract
Angiotensin II (Ang-II) and connective tissue growth factor (CTGF) are involved in various renal disorders that lead to end-stage renal disease. Here, we determined the role of Ang-II and CTGF in the progression of tubulointerstitial injury in the rat unilateral ureteral obstruction (UUO) model. Sprague-Dawley rats (n=16) were used; 10 rats underwent UUO, and 6 control rats underwent sham operation; and rats of both groups were sacrificed on days 7 or 14. Histomorphometric analysis was performed to quantitate tubulointerstitial injuries in the experimental group. Kidney sections were stained immunohistochemically for Ang-II, CTGF, transforming growth factor-β1 (TGF-β1), type III collagen and α-smooth muscle actin (α-SMA). Renal CTGF expression was studied using in situ hybridization and reverse transcriptase-polymerase chain reaction. Double staining for Ang-II with α-SMA and CTGF with α-SMA was performed to identify cells with enhanced expression of Ang-II and CTGF. Similar dual staining of Ang-II with type III collagen and CTGF with type III collagen was performed. The correlation between Ang-II and CTGF expression and tubulointerstitial injury was examined. In obstructed kidneys, there was a significant (p<0.001) increase in expression of Ang-II, CTGF, TGF-β1, type III collagen and α-SMA, compared with control kidneys. Tubular epithelial cells and interstitial cells were the main Ang-II- and CTGF-producing cells in the obstructed kidneys. A significantly (p<0.001) positive correlation was detected in obstructed kidneys between renal expression of CTGF and expression of TGF-β1 (r=0.91), type III collagen (r=0.87) or α-SMA (r=0.90). Similarly a significantly (p<0.001) positive correlation was found in obstructed kidneys between Ang-II expression and expression of TGF-β1 (r=0.88), type III collagen (r=0.79) and α-SMA (r=0.91). Finally, there were significantly positive correlations between CTGF /Ang-II expression and tubulointerstitial fibrosis in the obstructed kidneys (r=0.88, p<0.001). The results of our in vivo studies suggest that both Ang-II and CTGF, produced by intrarenal cells, coordinately regulate progression of renal tubulointerstitial injury, by facilitating increased accumulation of interstitial collagens in obstructed kidneys.
