The Roles Of 1,25(OH)₂D₃ In Renal Tubulointerstitial Fibrosis Of Unilateral Ureteral Obstruction

Objective:Renal fibrosis conclude glomerulorsclerosis and renal interstitial fibrosis.Renal interstitial fibrosis is the common pathway of various cause induce injure of tubulointerstitial and develop to final renal failure.Most studies show that renal interstitial fibrosis correlate much better than glomerulorsclerosis with the degree and progression of renal impairment.Thus the mechanism of tubulointerstitial fibrosis has been drawing more and more attention,and how to prevent the advance of tubulointerstitial fibrosis has been a hot topic in the field of renal disease reseaches recently.Hepatocyte growth fator(HGF) and Bone morphogenetic protein-7(BMP-7) is the most improtent antifibrosis.HGF expressed in interstitial cell,endothelia and macrophage.It effect on target cell by endocrine ,autocrine and paracrine.While Bone morphogenetic protein-7(BMP-7) is a member of the transforming growth factorβ(TGF-β) superfamily. Not only it is important to the occurrence of the kidney,but also it can treat some kinds of renal diseases.Company with antifibrosis,TGF-β1 participate in every procedure of tubulointerstitial fibrosis and play an important role in the epithelial-Mesenchymal Transition (EMT). So inhibiting its effect in the process of renal interstitial fibrosis perhaps is a efficiency means to prevent and cure the fibrosis. 1,25-dihydroxyvitamin D3,the activate form of vitamin D,has widely biologic activity.In addition to possessing a regulatory effects on calciumm and phosphorus metabolism,it can protect renal function. But the certain mechanism were not found.This study is about renal interstitial fibrosis through UUO.Rat underwent unilateral ureteral obstruction is a mature model of tubulointerstitial fibrosis.So we chose this model to investigate the renoprotective effects of 1,25(OH)₂VitD₃.Methods:54 male Wistar rats were randomly divided into 3 groups:sham-operated group(A),UUO group(B),UUO with Irbesartan treated group(C)(n=18).Each group was also randomly divided into 3,7,14 groups in term of the days after surgery(n=6).Under Chloral Hydrate anesthesia(0.1ml/Kg body wt,i.p),the left ureter was ligated by 4.0 silk at two points and cut between the ligatures in order to prevent retrograde urinary tract infection.Sham-operated group had their ureters manipulated but not ligated.1,25(OH)₂D₃ (9ng/100g) began to administrate one day before surgery.UUO and sham groups were received equal volume peanut oil by daily gastric gavage. Rats were killed in the 3,7,14 day after surgery.Using routine immunohistochemical method to analyzed the change of BMP-7,HGF,TGF-β1 and their expression positions,using HE,Masson to calculate the area of pathological changes.The results were analyzed semi-quantitatively by the pathological image analysis system. All the data were analysed by SPSS 11.0 statistics software,P value<0.05 was considered to have statistical significance.Results:Compared with group A,the level of Ca,P in group B and group C have difference,but the difference had no statistical significance(P>0.05)There were different degrees of interstitial fibrosis,interstitial leukocyte infiltration,tubular dilation and the relative area of renal tubulointerstitium expantion in the obstructed kidneys of groups B3,B7,B14 days after UUO in light microscrope using the staining mathods of HE and Masson.The relative area of renal tubulointerstitium was significantly increased in the obstructed kidneys compared with that of group A(P<0.01).However, the relative area of renal tubulointerstitium of group C significantly decreased compared with that of group B(P<0.01).The results of immunohistochemical staining:BMP-7 chiefly expressed in the renal tubule and renal interstitial;the expression in medulla is more than the expression in cortex.And BMP-7 had almost no expression in glomerulus.BMP-7 were highly expressed in group A.While the level of BMP-7 in group B was significantly decreased than that of group A.In group C,the level of BMP-7 was higher than that of group B at the same timepoint(P<0.01). HGF mainly expressed in renal tubule and had a small quantity of expression in renal interstitial in group B.There was no expression in group A.In group B and group C,the level of HGF is increase in 3 days,7 days reach the peak,14 days decrese.The level of HGF in group C was increased than that in group B at the same timepoint(P<0.01).The expression of TGF-β1 was occasionally found in group A,and the expression was higher and higher along with the obstructed time.Group C had significant change compared with group B,the difference had no statistical significance(P<0.01).The result of correlation analysis was BMP-7 and HGF had the negative relation with TGF-β1.Conclusion:1,25-dihydroxyvitamin D3 can protect renal function and delay the progression of renal interstitial fibrosis, independing on regulatory effects of calciumm and phosphorus.Increasing the expression of BMP-7 and HGF, decreasing the expression of TGF-β1 probably are the probabe mechanism.