The Study On The Renal Fibrosis In Chronic Allograft Nephropathy

Clinical backgroundThe past two decades have seen considerable improvements in 1-year renal allograft survival rates to over 80 per cent for cadaveric and 90-95 per cent for living related donors. These commendable outcomes may be largely attributed to the introduction of more potent and selective immunosuppressants ,such as cyclosporin and tacrolimus, as well as to improvements in understanding of the immunology of transplantation, tissue typing, organ preservation and the management of acute rejection. However, despite reducing the frequency and severity of acute rejection episodes, cyclosporin and tacrolimus have had no effect on the development of chronic allograft dysfunction, and the half life of renal allografts has remained unchanged for over a decade. Approximately 50 percent of transplanted kidneys develop progressive dysfunction within a few months of transplantation, necessitating dialysis or retransplantation within a decade. Data from Leicester show that , despite a 1-year graft survival of about 85per cent, there is a gradual attrition of 4-5 per cent graft loss per year, leading to 5- and 10-year allograft survival rates of approximately 70 and 50 per cent respectively. The most common cause of this decline in allograft survival is chronic rejection, perhaps more accurately described aschronic allograft nephropathy (CAN). CAN remains the single most important cause of renal allograft failure after the first year following transplantation, accounting for some 50-80 per cent of graft losses after this time. The most important characteristic of CAN renal tissues is the fibrosis of renal allograft. So it is very important to explore the mechanisms of the renal allograft fibrosis and prevent the fibrosis progress of renal allograft to therapy CAN. ObjectiveTo study the histopathologic characteristics of renal allograft tissues with chronic allograft nephropathy (CAN) and the functions of the angiotensin ATi receptor, transforming growth factor- 3 i and collagen IV in the renal fibrosis course of CAN, and to analyze the mechanisms of renal fibrosis of CAN for presenting the direction and theoretic evidences to treat the disease of CAN. MethodsCollecting 19 samples of renal tissues with CAN proved by pathology from the renal resection. These patients lost their renal function within 11 years postoperatively, in which nine of them were male, and ten of them were female and their ages were during 20 to 55 years old, and eleven of them were treated with CsA , eight of them with FK506. The average survival time of allograft was 4.4 years. The controlled group was made up of ten cases of normal renal tissues, in which six of them were from the kidney resected because of trauma and four were normal renal tissues five centimeters far away from the renal carcinoma. All the 29 samples were made paraffin blocks, then were stained by HE, PASM, Masson methods. These samples were classifiedas three grades according to the Banff 97 pathologic diagnostic classification standard. Grade I: slight interstitial fibrosis and renal tubular atrophy with or without special alterations of chronic rejection. Grade II: midrange interstitial fibrosis and renal tubular atrophy with or without special alterations of chronic rejection.Grade III: severe interstitial fibrosis and renal tubular atrophy with or without special alterations of chronic rejection. Then all the samples were stained by ATiR, TGF-P i and Collagen IV with SABC method. The HPIAS-1000 high acuity color pathologic analysis and report system was used to analyze images, which were taken by light microscope enlarged 200 times. Each of samples took randomly 10 images of glomeruli and renal tubes, then these images were analyzed by image analysis system to assess the expressions of each factors. Calculated the stained area proportion in each glomerulus and renal tubes and the proportion represented the expression level of a factor in this tissue. The SPSS 10.0 software was used to analyze the data. The statistical methods to compare the three factors' expression level between the normal renal tissues and CAN renal tissues adopted Mann-Whitney Test, and the compares between different pathologic grades adopted Nemenyi Test. The Spearman method was used to analyze the relationship among the three factors. ResultsThe histopathology of CAN is characterized by intimal hyperplasia, glomerulosclerosis, tubular atrophy and interstitial fibrosis, associated with a mononuclear cellular infiltrate. This experiment showed that, in normal renal tissues, ATiR slightlyexpressed in the vascular smooth muscle cells and renal tubular epithelial cells; TGF- P i slightly expressed mainly in the plasm of renal tublar epithelial cells; Collagen IV mainly located in the glomerulus, renal tubular basement membrane, Bowman's capsule and mesangium area, partly in the interstitial area and negative in the renal tubular epithelial. ATiR expressed much more in the CAN renal tissues than that in the normal tissues, which mainly located in the glomerulus, renal tubular epithelial cell membrane, vascular smooth muscle cell, vascular surrounding and renal interstitium. The expression location of Collagen IV in the CAN was like that in the normal renal tissues, but the expression was more stronger. TGF- P i expressed evidently in CAN renal tissues ,most of wich located in the renal tubular epithelial cell palsm and membrane and partly in the Bowman's capsule. Statistical analyses showed that the expressions of ATiR-. TGF- P i and collage IV in the glomerulus, renal tubule and interstitium of CAN renal tissues were much more than those in the normal renal tissues (/><0.01) and their expressions have a trend to be correlated with the grades of CAN. There exists a positive correlation between ATiR and TGF- P i expression(r=0.843, p<0.01;r=0.836, /?<0.01),and between TGF- P 1 and Collage IV expression(r=0.943, P<0.01 and r=0.910, P<0.01) in the glomerulus and renal tuble. ConclusionsThe major histopathology of CAN is characterized by intimal hyperplasia, glomerulosclerosis, tubular atrophy and interstitial fibrosis, associated with mononuclear cellular infiltrate. The dominant underlying pathological process is an excessive accumulation ofextracellular matrix proteins leading to fibrosis. ECM includes the collagen proteins ( type I ,111 and IV) and non-collagenous matrix proteins(glycoproteins laminin, fibronectin and tenascin, and the proteoglycans, decorin and biglycan). Collagen IV is the principal collagenous component of the renal tissues, our study shows that Collagen IV expression have a trend to be correlated with the grades of CAN and the expression level of Collagen IV represent the fibrosis level of allograft, and prove that the accumulation of Collagen IV is an important factor in the fibrosis process of CAN. It indicates that we can inhibit the accumulation of Collagen IV to delay the fibrosis process of CAN. TGF- 3 is a potent profibrotic cytokine signaling molecule, which correlate with some chronic fibrotic disease of kidney and other organs. Our study show that TGF- P expression has a trend to be correlated with the grades of CAN and has a positive correlation with Collagen IV expression. It indicates that TGF- P can modulate the accumulation of collagen IV and play an important role in the fibrosis process of CAN. ATiR expression has a trend to be correlated with the grades of CAN and has a positive correlation with TGF- 3 i expression. It indicates that ATiR increases abnormally in CAN, which once bounds with AT II will increase the TGF- P i expression. Losartan is an antagonist against ATiR. Campistol JM[13] and el-Agroudy AE[14] used losartan to treat patients with CAN, which can reduce the TGF- 3 concentration in blood, associated with decompression and decreasing proteinuria. However large randomized studies are required to assess whether or not angiotensin-converting enzyme inhibitor and ATiR antagonist therapies can delay the fibrosis process of CAN and prolong allograft survival after kidney transplantation.