Role of bone morphogenetic protein 4 on the progression of renal interstitial fibrosis in mice model of unilateral ureteral obstruction

Objective To observe the effects of bone morphogenetic protein 4 (BMP4) on the progression of renal interstitial fibrosis in mice model of unilateral ureteral obstruction (UUO). Methods C57BL/6 mice were randomly divided into four groups: injection intra-abdominally with saline-sham-operated group (saline-sham, n=8), injection intra-abdominally with saline-UUO-operated group (saline-UUO, n=8), injection intra-abdominally with anti-BMP4-sham-operated group (anti-BMP4-sham, n=8), and injection intra-abdominally with anti-BMP4-UUO-operated group (anti-BMP4-UUO, n=8). Either saline or anti-BMP4 (200 μl/g of body weight per day) were injection intra-abdominally for 7 days after surgery. Mice were sacrificed at 7 day to evaluate the fibrosis by Masson staining. The expression of BMP4 in renal tissue of normal mice was assayed by immunofluorescence. Immunohistochemical staining was used to detect the expression of α-smooth muscle actin (α-SMA), collagen Ⅲ (COL-Ⅲ) and p-Smad3 in each group. Besides, the TNF-α mRNA and MCP-1 mRNA levels were also analyzed by fluorescent quantitative Real-time polymerase chain reaction in four groups. Results The expression of BMP4 was mainly distributed in the renal tubules of mice. The area of renal interstitial fibrosis in anti-BMP4-Sham group and saline-Sham group were (1.01±0.21)% and (0.81±0.19)%, respectively. There was no significant difference in the expression of collagen fibers in 2 Sham groups (t=0.983, P>0.05). A significantly reduced collagen deposition was observed in anti-BMP4-UUO group [(15.08±2.43)%] compared to the saline-UUO group [(21.23±3.19)%, t=3.651, P 0.05; t=0.896, P>0.05; t=0.753, P>0.05). the expression of α-SMA, COL-Ⅲ and p-Smad3 were significantly decreased in anti-BMP4-UUO group than in saline-UUO group [α-SMA: (9.11±1.03)% vs. (16.18±2.15)%, COL-Ⅲ: (7.08±0.83)% vs. (12.55±1.88)%, p-Smad3: (6.14±0.76)% vs. (11.66±1.91)%, t=2.991, P 0.05; t=0.715, P>0.05). The expression of TNF-α mRNA and MCP-1 mRNA were obviously decreased in anti-BMP4-UUO group than in saline-UUO group (t=3.117, P<0.01; t=3.762, P<0.01). Conclusion BMP4 contributes to renal interstitial fibrosis in obstructive nephropathy through activation Smad3 pathway, and inhibition of BMP4 may be a choice for preventing interstitial fibrosis. Key words: Bone morphogenetic protein 4; Ureteral obstruction, unilateral; Fibrosis, renal interstitium