The role of TGF-β signal protein Smad2/3 in tubulointerstitial fibrosis associated with unilateral ureteral obstruction in rats

AIM:To investigate the functional role of TGF-β₁ signal protein Smad2/3 in tubulointerstitial fibrosis associated with unilateral ureteral obstruction in rats. METHODS:The unilateral ureteral obstruction (UUO) model was induced by the ligation of left ureter. Rats were sacrificed at 1, 3, 7, 14, 21, and 28 days after UUO was initiated. TGFβ₁ protein, phosphorylated Smad2/3 and interstitial α-smooth muscle actin (α-SMA) expression were assayed by immunohistochemical staining. TGF-β1 mRNA in the obstructed kidney was analyzed with in situ hybridration. HE and Masson staining were used for histological and morphometric studies of the pathological change in obstructed kidney. RESULTS:The results showed that upregulation of TGF-β₁ in tubulointerstitium of both cortex and medulla at day 3 (a 3.1 fold increase vs control, P<0.05) when interstitial volume started to increase significantly. The highest expression of TGF-β1 was detected at day 7 (6.2 folds vs control, P<0.01). Phosphorylated Smad2/3, mainly detected in the nucleus of tubular cells, were also markedly upregulated at day 3 (a 3.5 fold increase vs control, P<0.05), and this was steadily increased by day 7 (7.8 folds vs control, P<0.01). The expression of interstitial α-SMA in both cortex and medulla was evident at day 3 (a 3.8 fold increase vs control, P<0.05) and peaked by day 7 (9.2 folds vs control, P<0.01). The deposit of extracellular matrix (ECM) and interstitial volume in renal cortex and medulla continued to increase until day 28 in obstructed kidney. CONCLUSION:These findings suggest that TGF-β₁ signal protein Smad2/3 may play an important role in tubulointerstitial fibrosis associated with unilateral ureteral obstruction in rats.