The Effect Of Bone Morphogenetic Protein7, Connective Tissue Growth Factor And Hepatocyte Growth Factor Cross-talk On The Tubulointerstitial Fibrosis

OBJECTIVE: Fibrosis is a common feature of progressive renal diseases regardless of the initiating insult. Emerging evidence has suggested that tubular epithelial-myofibroblast transdifferentiation (TEMT) may play an important role in the pathogenesis of renal fibrosis. There are many cytokines, growth factors that may be involved in these processes. Of them, transforming growth factor-β1 (TGF β1 ) is a key fibrogenic growth factor that regulates tubular epithelial-myofibroblast transdifferentiation. The connective tissue growth factor (CTGF), which is one of the candidate factors mediating downstream events of TGFβ1, may also induce these processes. Importantly, the recent discovery of bone morphogenetic protein-7 (BMP-7) may promote maintenance of epithelial phenotypein in vitro. We investigated the expression of CTGF in rats with renal tubulointerstitial fibrosis and the effects of hepatocyte growth factor (HGF) treatment on CTGF and BMP-7 protein production, and examined whether hepatocyte growth factor (HGF)exhibited the ability to block this phenotypic transition in vivo.METHODS: Rats were randomly assigned into unilateral ureteral obstruction (UUO), HGF treatment and sham-operated groups (SOR). Pig HGF protein was administrated by injections at 15ug/kg body wt every 12 h for 14 days after initial UUO and control rats were injected with the same volume of vehicle in an identical manner. The rats were killed at 3, 7,14 and 21 days after UUO or SOR, and in HGF treatment group at days 3, 7, and 14, respectively. The levels of serum creatinine and 24-hour urine protein were measured at each time point .At the same time, the degree of tubulointerstitial damage was scored. The protein expression of TGFpi, a -smooth muscle actin( a -SMA), and fibronection (FN) were detected by immunohistochemitry at each time point. The sites and levels of expression of BMP-7 and CTGF protein were examined by immunohistochemitry staining and Western blot. The levels of BMP-7 and CTGF mRNA were examined by real-time reverse transcription-polymerase chain reaction (RT-PCR).RESULTS: The level of serum creatinine was significantly higher in UUO group than SOR and HGF treatment groups at day 7 after UUO (p<0.05). There was no difference in the level of 24-hour urine protein among each group. From day 3 the number of a -SMA-positive interstitial cells increased and some tubular epithelial cells also expressed a -SMA at day 7 after UUO. Renal BMP-7 mRNA and BMP-7 protein levels progressively decreased during the progression of obstructive nephropathy. Compared with the UUO group, the levels of BMP-7 mRNA and protein were significantly increased in HGF treatment group (/?<0.05), whereas the levels of CTGFmRNA and protein in the HGF treatment group significantly decreased (p<0.05). The levels of TGFpi, a -SMA and FN in UUO group were increase remarkably compared with the SOR O<0.05)and HGF treatment groups(p<0.05) and consistently associated with interstitial fibrosis progressed. The renal tubulointerstitial expression of CTGF was found to be significantly associated with the relative volume ofinterstitium(r=0.997,jt?<0.001), expression of FN (r=0.966,p<0.001), expression of TGFpl (r=0.993,p<0.001) and the positive area of a -SMA (r=0.956,/)<0.001). The renal tubulointerstitial expression of BMP-7 was significantly correlated with expression of TGFpi (r=-0.764,/?<0.05),the relative volume of interstitium (r=-0.773,/?<0.05), expression of FN (r=-0.865,^<0.05),and the positive area of a -SMA (r=-0.895,/?=0.001).The a -SMA positive cells were correlated with the expression of TGFpi (r=0.961,p<0.001), expression of FN (r=0.994,/><0.001), and the relative volume of interstitiurn(r=0.967,/K0.001).CONCLUSION: Unilateral ureteral obstruction (UUO) is a well-characterized model of experimental renal disease culminating in tubulointerstitial fibrosis and tubular epithelial-myofibroblast transdifferentiation. The loss of BMP-7 and increase of CTGF correlated with the increased expression of a -SMA and the degree of interstitial lesions in obstructive nephropathy . This suggested that BMP-7 may block morphologic transformation of tubular epithelial cells, and CTGF may induce TEMT. HGF may suppress fibrosis, at least in part via down-regulating CTGF expression and up-regulating BMP-7 expression in the affected kidney, and exhibit a remarkable ability to block this epithelial to myofibroblast transition in vivo.From our results, HGF may be taken into consideration as a potential a therapeutic agent for the prevention and treatment of chronic renal diseases (CRD).