The Role And Pathogenesis Of Mast Cell Infiltration In Renal Interstitial Fibrosis Of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is one of the major causes of End-stage renal disease(ESRD).It has recently been demonstrated that the development of tubulointerstitial fibrosis is more closely correlated with a progressive decline in renal function compared to glomerularsclerosis and tubulointerstitial injury serves as an important mediator of chronic renal failure and predictor of outcome in patients with DKD,but the machanism is complicated. Research the pathogenesis of tubulointerstitial fibrosis,targeted blocking the cells and signaling pathways involved in tubulointerstitial fibrosis, slow down the DKD tubulointerstitial fibrosis and to prevent the progress of renal function has become a focus of current research.In a long-term,DKD is a non-inflammatory diseases. In recent years, more and more attention has been paid on the role of inflammatory cells and inflammatory factors in tubulointerstitial fibrosis of DKD.Mast cells(MCs) as an important inflammatory cells, which are rich source of cytokines, growth factors or chemokines,have been more and more concern. MCs are CD34+multipotent bone marrow derived cells that play a key role in inflammation and tissue fibrosis of many kinds of chronic renal disease. MCs have been proven to contain tryptase, chymase, TGF-β, renin,TNF-aand so on.Some present studies suggest that increased MCs and degranulation level were found at all stages of DKD which play important roles in the development of DKD in patients, especially in tubular interstitial injury. However,further work is necessary to research the pathogenesis and signaling pathways in tubulointerstitial fibrosis of DKD.Stem cell factor (SCF; c-kit ligand)/c-Kit is a major signaling pathway of regulating the migration and survival of mast cell precursors.SCF and c-Kit can express in tubular interstitial cells and tubular epithelial cells, and SCF enhance collagen synthesis and extracellular matrix accumulation,the role of SCF/c-Kit in the tubulointerstitial fibrosis of DKD should be studied further. ObjectiveTo investigate the effect of MCs in tubulointersitial firosis in DKD and the possible mechanism, the infiltration of MCs and the degree of fibrosis were analysed,and expression of MCs,FN(fibronectin), collagen I were analysed in normal control group, STZ-induced diabetic model and intervention of tranilast group in SD rats. The expression of SCF、c-Kit were also observed in the model. Furthermore,the role of MCs was proved to promote the tubulointerstitial fibrosis induced by SCF/c-Kit signaling pathway.Methods1. Fourteen type2diabetic patients with biopsy-proven diabetic nephropathy, who were hospitalised at the clinical unit of the nephrology centre of XiangYa Hospital from2010to2011, were recruited. And seven minimal change disease(MCD) cases were selected as control group,which nephridial tissue pathological changes were slight,the infiltration of Inflammatory cells and the tubulointerstitial fibrosis were not yet obviously observed in MCD. Toluidine blue Staining used to detect the infiltration of MCs, the distribution of C3aR highly expressing cells were found in the renal tissue of both MCD people and DKD patients by immunohistochemical staining.2.Sprague-Dawley rats were randomly divided into control(n=6), DN(n=8) low dose tranilast(200mg/kg/d) groups(n=8), and high dose tranilast(400mg/kg/d) groups(n=8).The DN model was induced by injection intraperitoneally with30mg/kg body weight STZ in0.1mol/L sodium citrate solution(pH4.5),after high calorie given for two months. The rats in the control group were injected with0.1mol/L sodium citrate solution.Diabetic model was considered to be successful when the blood glucose was≥16.7mmol/L and the urine glucose was+++～++++after72hours of the injection.Tranilast was administered daily after the model was built. Rats were sacrificed at day56after and24hours urine were collected to measured24-hour urine albumin excretion and blood were collected to determine renal function and serum albumin,then the kidneys were harvested and subjected to the studies. Renal lesions were detected by HE,Masson staining and the expression of FN,collagen I, SCFand c-Kit were detected by immunohistochemical staining and PCR respectively. Results:1.Infiltration of MCs in DKD patients were obviously increased than in MCD patients, the degree of increased MCs correlated significantly with the indices indicating tubular and interstitial injury and renal function.2. Extracellular matrix(ECM) deposition and tubulointerstitial fibrosis in DKD rats were observed,while the pathological changes were reduced in that of tranilast-treated group(P<0.05). The expressions of FN,collagen Ⅰ and SCF、c-Kit were increased in the tubulointerstitial fields of DKD rats compared with the control.After treatment with tranilast, these changes were relieved to a certein degree(P<0.05).3.Compared with control group, infiltration of MCs in DKD model rats were obviously increased,relative area of ECM were increased (P<0.05), the expressions of FN,collagen Ⅰ were increased in the tubulointerstitial fields. After treatment of tranilast, these changes were relieved to a certein degree(P<0.05), the degree infiltration of MCs were significantly positive correlated with the expressions of FN,collagen Ⅰ (P＜0.05).4.The expressions of SCF and c-Kit in tubular and interstitial tissue is slight.The increased expressions of SCF and c-Kit protein and mRNA can be downregulated by tranilat(P<0.05). The expressions of SCF and c-Kit were significantly positive correlated with the degree infiltration of MCs and the expressions of FN,collagen IConclusions1.MCs could promote renal tubulointerstitial fibrosis and thus contribute to DKD patients.2. The infiltration of MCs were significantly positive correlated with the expressions of FN,collagen I in DKD rats,indicating MCs involved in tubulointerstitial fibrosis of DKD.3. The expressions of SCF and c-Kit obviously increased in DKD renal tissue and tranilast could inhibit the expressions of SCF and c-Kit to reduce the infiltration of MCs and may have an positive effect in attenuating tubulointerstitial fibrosis of DKD.It is demonstrated that MCs mediated DKD tubulointerstitial fibrosis by SCF/c-Kit signaling pathway possibly.