Upregulation of connective tissue growth factor in a rat model of chronic allograft nephropathy

Connective Tissue Growth Factor and Renal Fibrosis

CCN2, also known as connective tissue growth factor (CTGF), is one of important members of the CCN family. Generally, CTGF expresses at low levels in normal adult kidney, while increases significantly in various kidney diseases, playing an important role in the development of glomerular and tubulointerstitial fibrosis in progressive kidney diseases. CTGF is involved in cell proliferation, migration, and differentiation and can promote the progression of fibrosis directly or act as a downstream factor of transforming growth factor β (TGF-β). CTGF also regulates the expression and activity of TGF-β and bone morphogenetic protein (BMP), thereby playing an important role in the process of kidney repair. In patients with chronic kidney disease, elevated plasma CTGF is an independent risk factor for progression to end-stage renal disease and is closely related to glomerular filtration rate. Therefore, CTGF may be a potential biological marker of kidney fibrosis, but more clinical studies are needed to confirm this view. This section briefly describes the role and molecular mechanisms of CTGF in renal fibrosis and also discusses the potential value of targeting CCN2 for the treatment of renal fibrosis.

Epithelial cells as active player in fibrosis: findings from an in vitro model

Kidney fibrosis, a scarring of the tubulo-interstitial space, is due to activation of interstitial myofibroblasts recruited locally or systemically with consecutive extracellular matrix deposition. Newly published clinical studies correlating acute kidney injury (AKI) to chronic kidney disease (CKD) challenge this pathological concept putting tubular epithelial cells into the spotlight. In this work we investigated the role of epithelial cells in fibrosis using a simple controlled in vitro system. An epithelial/mesenchymal 3D cell culture model composed of human proximal renal tubular cells and fibroblasts was challenged with toxic doses of Cisplatin, thus injuring epithelial cells. RT-PCR for classical fibrotic markers was performed on fibroblasts to assess their modulation toward an activated myofibroblast phenotype in presence or absence of that stimulus. Epithelial cell lesion triggered a phenotypical modulation of fibroblasts toward activated myofibroblasts as assessed by main fibrotic marker analysis. Uninjured 3D cell culture as well as fibroblasts alone treated with toxic stimulus in the absence of epithelial cells were used as control. Our results, with the caveats due to the limited, but highly controllable and reproducible in vitro approach, suggest that epithelial cells can control and regulate fibroblast phenotype. Therefore they emerge as relevant target cells for the development of new preventive anti-fibrotic therapeutic approaches.

Epithelial-mesenchymal crosstalk alteration in kidney fibrosis

The incidence of chronic kidney diseases (CKD) is constantly rising, reaching epidemic proportions in the western world and leading to an enormous threat, even to modern health-care systems, in industrialized countries. Therapies of CKD have greatly improved following the introduction of drugs targeting the renin-angiotensin system (RAAS) but even this refined pharmacological approach has failed to stop progression to end-stage renal disease (ESRD) in many individuals. In vitro historical data and recent new findings have suggested that progression of renal fibrosis might occur as a result of an altered tubulo-interstitial microenvironment and, more specifically, as a result of an altered epithelial-mesenchymal crosstalk. Here we the review biological findings that support the hypothesis of an altered cellular crosstalk in an injured local tubulo-interstitial microenvironment leading to renal disease progression. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

From acute injury to chronic disease: pathophysiological hypothesis of an epithelial/mesenchymal crosstalk alteration in CKD

Observational clinical studies link acute kidney injury to chronic kidney disease (CKD) progression. The pathophysiological mechanisms that underlie this process are currently unknown but recently published papers suggest that tubular epithelial cells and interstitial mesenchymal cells emerge as a single unit, and their integrity alteration as a whole might lead to renal fibrosis and CKD. The present article reviews the biological findings supporting the hypothesis of an altered epithelial/mesenchymal crosstalk in fibrosis development and progression toward CKD.

Rapamycin is less fibrogenic than Cyclosporin A as demonstrated in a rat model of chronic allograft nephropathy

BACKGROUND

Cyclosporin A (CsA) is associated with significant chronic nephrotoxicity, which typically manifests as renal fibrosis. In contrast, rapamycin (RAPA) has been shown to inhibit fibrosis. This study sought to determine the effect of CsA and RAPA on the expression of connective tissue growth factor (CTGF) and E-cadherin in a rat kidney model of chronic allograft nephropathy.

MATERIALS AND METHODS

Left renal grafts from male Fisher (F344, RT1(1v1)) rats were orthotopically transplanted into Lewis (LEW, RT1(1)) rats. After transplantation, all recipients were given CsA 10 mg/kg(-1) d(-1) for 10 d and divided into three groups (n = 9/group): (1) vehicle, administered orally; (2) CsA, 6 mg/kg(-1) d(-1); (3) RAPA, 0.8 mg/kg(-1) d(-1). At 4, 8, and 12 wk posttransplantation, the kidney allografts were harvested and serum creatinine levels were measured. Connective tissue growth factor expression was determined using real-time polymerase chain reaction and Western blot. Kidney allografts sections also underwent hematoxylin-eosin and Masson trichrome staining, in addition to CTGF and E-cadherin immunostaining.

RESULTS

The serum creatinine levels were increased at 8 and 12 wk posttransplantation and were significantly lower in the RAPA group (P < 0.05). The Banff score also showed a significant decrease at 4, 8, and 12 wk (P < 0.05). CTGF messenger ribonucleic acid and protein levels were significantly lower in the RAPA group (P < 0.05), whereas E-cadherin expression was higher in the RAPA group at 4, 8, and 12 wk (P < 0.05). Masson's trichrome staining showed a significant decrease in collagen deposition at 8 and 12 wk after RAPA treatment.

CONCLUSION

RAPA can ameliorate fibrogenesis in kidney allografts by inhibiting epithelial-mesenchymal transition process, whereas CsA did not have this effect.

Urinary connective tissue growth factor is a biomarker in a rat model of chronic nephropathy

AIM

This study sought to determine whether urinary connective tissue growth factor (CTGF) was a molecular marker for chronic allograft nephropathy (CAN).

METHODS

F344 rat renal grafts orthotopically transplanted into Lewis rats following the procedure of Kamada were harvested at 4,8,12, or 16 weeks. Morphological changes were studied using hematoxylin eosin (HE) and Masson trichrome stains. Serum creatinine (SCr) was measured. CAN grades were evaluated according to the Banff97 schema. Expressions of CTGF in the kidney and urine were determined using real-time polymerase chain reaction (PCR) Western blots, and competitive indirect enzyme-linked immunosorbent assay (ELISA). Spearman correlation analysis was used to compare urinary CTGF expression and CAN development.

RESULTS

SCr levels and Banff scores increased in a time-dependent manner. The expression of CTGF in the graft was markedly elevated compared with the control group. Urine CTGF increased by week 4, and maintained high levels up to week 16. The urinary levels correlated positively with the histological presence of CAN. Thus, urine CTGF concentrations reflected the course of CAN, especially at an early stage.

CONCLUSION

CTGF plays a significant role in the pathological changes of CAN after kidney transplantation. Urinary CTGF has the potential to be a biomarker for CAN.

Increased connective tissue growth factor expression in a rat model of chronic heart allograft rejection

BACKGROUND/PURPOSE

Chronic rejection limits the long-term success of cardiac transplantation and the underlying cause of the disease is unknown. Connective tissue growth factor (CTGF) is considered as a mitogenic and chemotactic factor for fibroblasts, and is associated with cell proliferation and collagen synthesis. We evaluated the expression of CTGF in a rat model of heart allograft chronic rejection.

METHODS

Intra-abdominal heterotopic heart transplantation was performed from 20 Wistar rats to 20 Sprague-Dawley (SD) rats that received cyclosporine, mycophenolate mofetil and methylprednisolone as immunosuppression. Ten heart allografts were explanted at 2 and 8 weeks postoperatively for analysis of morphologic changes. The hearts from 10 normal Wistar rats served as a control group. Coronary artery density, luminal loss of myocardial coronary arteries, and myocardial fibrosis were measured. The expression of CTGF was studied by immunohistochemistry. Correlation between CTGF expression and development of cardiac allograft vasculopathy (CAV) or fibrosis was studied.

RESULTS

Allografts harvested at 8 weeks postoperatively showed more coronary intimal proliferation, fibrosis and CTGF expression compared with the 2-week allografts (p < 0.05) and the controls (p < 0.01), but the coronary artery density was lower than in the control group (p < 0.05). However, the control group showed negligible CTGF expression. There were strong negative correlations between the gray value of CTGF protein expression and cardiac fibrosis and coronary intimal occlusion (r = -0.734, -0.713; p < 0.01), which demonstrated that CTGF protein expression was positively correlated with cardiac fibrosis and coronary intimal occlusion.

CONCLUSION

CTGF is expressed in cardiomyocytes in CAV. Increased expression of CTGF in cardiac allografts is associated with development of CAV and fibrosis formation.