Effect Of Spironolactone On Expression Of Bone Morphogenetic Protein-7(BMP-7) In Rats After Unilateral Ureteral Obstruction

Objective: Renal interstitial fibrosis is the excessive deposition of extra cellular matrix(ECM)which can be caused by kinds of reasons. Renal interstitial fibrosis is the common way to final renal failure. Renal interstitial fibrosis play more dangerous role than glomerulosclerosis in the kidney. We pay more and more attention to the onset and the progression as well as prevention and therapy. Studies show that all kind of growth factors and cytokines play an important role in the onset and progression of renal interstitial fibrosis. Transforming growth factor-beta-1(TGF-β1)are important factors inducing fibrosis. BMP-7 is another one of the transforming growth factor super family. It can protect kidney and prevent from renal tubule interstitial fibrosis. But the study of BMP-7 in kidney aspect is not very consummate internal. Transforming growth factor-beta 1(TGF-β1)are important factors inducing fibrosis. Both increasing synthesis and decreasing degradation of extra cellular matrix (ECM) are thought to be involved in ECM accumulation. ECM accumulation is one of the most important mechanisms of renal interstitial fibrosis.TGF-β1 promotes ECM accumulation through increasing components of ECM such as CollagenⅠ,II,III,IV and fibronectin. TGF-β1 also can decrease catabolism of ECM through increasing synthesis of TIMP-1 which is one of the most important enzymes of degrading ECM. So down regulating expression of TGF-β1and suppressing their action in the development of renal interstitial fibrosis is a effective method to inhibit fibrosis. In the renin-angiotensin-aldosterone system(RAAS), angiotensin II receptor blocker has protective action to kidney. Recently, several lines of experimental evidence demonstrate that aldosterone, independent of renin-angiotensin, reduces fibrosis of heart,liver and lungs. Recent evidence also implicates aldosterone as an important pathogenetic factor in progressive renal fibrosis. It is reported that aldosterone induced renal injury and fibrosis has inflammatory components involving macrophage infiltration and cytokine up-regulation in the hypertensive rat model and induced proteinuria and glomerulosclerosis in the subtotally nephrectomized rat model. Studies show that aldosterone induced renal dysfunction and up-regulation of TGF-β1 and ECM proteins mRNA in the pathogenesis of chronic CsA nephropathy. These findings also indicate that aldosterone receptor antagonist can attenuate renal damage and inflammation, it prevented the fall in renal function and TGF-β1, collagenⅠ, and fibronectin up-regulation, together with a reduction of tubulointerstitial fibrosis. Our studies aim to find one of the mechanism how aldosterone receptor antagonist protects kidney. Rat UUO models was used in our studies. We administer aldosterone antagonist spironolactone to UUO rats. To observe the expression of Bone Morphogenetic Protein-7 (BMP-7) in the obstructed rat kidney in unilateral ureteral obstruction (UUO) models and explore the relationship of BMP-7with renal tubulointerstitial lesion. Through HE stain, routine immunohistochemical, RT-PCR method, we researched the changes of expression of TGF-β1 and BMP-7proteins, mRNA. We hope our studies can make the actions of TGF-β1, BMP-7and aldosterone receptor antagonist clearer.Methods: 36 male SD rats weighing 180-200g were randomly divided into 3 groups: sham-operated group(A),UUO group(B), UUO with spironolactone treated group(C), (n=12). Each group was also randomly divided into 7, 14 groups in term of the days after surgery(n=6).Under pentobarbitale sodium anesthesia, the rats left ureter was ligated with 0 silk at two points and cut between the ligatures. Then the unilateral ureteral obstructive rat model was established. Sham-operated rats had their ureters manipulated but not ligated. Spironolactone began to administer 2 days before surgery. UUO and sham rats were received equal volume water by daily gastric gavage. All rats were allowed free access to food and water. Rats were killed after 7, 14days. In obstructed kidney, use HE stain to examine the area of pathological changes. The changes of expression of TGF-β1 and BMP-7 proteins were analyzed by routine immunohistochemical method. At the same time, BMP-7mRNA was detected by RT-PCR. The results were analyzed semi-quantitatively with the pathological image analysis system. The experimental data was demonstrated in mean±standard deviation. The analysis of variance test and the relation about data were used by SPSS 10.0, a statistic software.Results: In HE staining,There were different degrees of interstitial fibrosis, interstitial leukocyte infiltration, tubular dilation, and the relative area of renal tubule interstitium expansion in the obstructed kidneys of groups B7, B14 days after UUO. By routine immunohistochemical method, the expression of BMP-7 in UUO group was negative related to the relative volume of cortieal interstitium(P<0.05) . The results of RT-PCR showed, the expression of BMP-7 mRNA in groups B7, B14, was various and significantly lower than that in groups A7, A14 (P<0.05). In groupsC7, C14, the expression of BMP-7 mRNA was significantly highter than that in groups B7, B14 (P<0.05).Conclusion: In UUO rats, with the obstruction time prolonged the expression of BMP-7 in obstructed kidney decreased gradually and it was negative related to the degree of renal tubulointersititial lesion. Aldosterone receptor antagonist spironolactone significantly reduced tubular lesions, up-regulate BMP-7 and attenuated interstitial fibrosis, spironolactone has protective effect of kidney.