Cyclosporine enhances the expression of TGF-beta in the juxtaglomerular cells of the rat kidney

Renal expression of transforming growth factor-beta inducible gene-h3 (beta ig-h3) in normal and diabetic rats

BACKGROUND

Transforming growth factor-beta (TGF-beta) has been implicated in the pathogenesis of a number of kidney diseases characterized by glomerulosclerosis and tubulointerstitial fibrosis. TGF-beta is secreted in a latent form requiring extracellular modification to become biologically active. TGF-beta inducible gene-h3 (beta ig-h3) is a recently identified TGF-beta-induced gene product. The present study sought to examine beta ig-h3 expression in normal and diabetic rats.

METHODS

Beta ig-h3, TGF-beta1 and alpha1 (IV) collagen gene expression were assessed by Northern blot analysis and in situ hybridization in 20 Sprague Dawley rats, randomly assigned to receive streptozotocin (diabetic, N = 11) or citrate buffer alone (control, N = 9) and sacrificed eight months later. The effect of exogenous TGF-beta1 on beta ig-h3 expression was also assessed in cultured proximal tubular cells.

RESULTS

In situ hybridization localized beta ig-h3 gene expression to the juxtaglomerular apparatus and the pars recta (S3 segment) of proximal tubules in both control and diabetic animals. Kidney TGF-beta 1, beta ig-h3 and alpha1 (IV) collagen mRNA from diabetic rats were increased two- to threefold compared with controls (P < 0.01). There was a significant correlation between TGF-beta1 and beta ig-h3 gene expression in kidneys from diabetic rats (r = 0.73, P = 0.01). In addition, beta ig-h3 mRNA increased in response to exogenous TGF-beta1 in a dose-dependent fashion in cultured proximal tubular cells.

CONCLUSION

These findings support the hypothesis that biologically active TGF-beta plays a pathogenetic role in diabetic kidney disease and suggest that beta ig-h3 may be a useful index of TGF-beta1 bioactivity in the kidney.

Gingival fibroblast response to cyclosporin A and transforming growth factor beta 1

This study investigates a potential role for TGF beta 1 in the pathogenesis of cyclosporin A-induced gingival overgrowth (CsA-OG). TGF beta 1 was localized immunohistochemically in the connective tissue of both normal gingiva and CsA-OG. Intense staining for TGF beta 1 was detected at the tips of the dermal papillae of the overgrown gingiva. In addition, fibroblasts derived from healthy gingiva and fibroblasts derived from CsA-OG were cultured both as monolayers or embedded in a 3D-collagen gel. Fibroblast activity was monitored in terms of protein and collagen production in the presence of (i) 1 ng/ml TGF beta 1, (ii) 500 ng/ml CsA, or (iii) 500 ng/ml CsA and 1 ng/ml TGF beta 1. In monolayer culture TGF beta 1 significantly increased protein and collagen production in all cell strains (p < 0.05); however, there was no difference in response between fibroblasts from overgrown and healthy tissue. The production of both protein and collagen was significantly lower in the presence of the combination of CsA and TGF beta 1 when compared with the maximal stimulation produced by TGF beta 1 alone. In gel, TGF beta 1 significantly elevated matrix production by all overgrown cell strains (p < 0.05) but had little or no effect on the normal cell strains. The combination of CsA and TGF beta 1 in gel cultures reduced protein and collagen production by overgrown cell strains compared with TGF beta 1 alone. It is concluded that the cellular activity of gingival fibroblasts is dependent on culture conditions and that fibroblasts derived from overgrown gingival tissue are more responsive to TGF beta 1 than normal gingival fibroblasts when cultured in type I collagen gel.

Mechanism of fibrosis in experimental tacrolimus nephrotoxicity

The clinical use of tacrolimus (FK506) is limited by nephrotoxicity. The pathogenesis of fibrosis in chronic FK506 nephrotoxicity remains unknown. Because transforming growth factor (TGF)-beta plays a key role in the fibrogenesis of many diseases, including cyclosporine nephrotoxicity, we studied a salt-depleted rat model of chronic FK506 nephropathy in which clinically relevant FK506 blood levels are obtained and which shows similarities to the lesions described in patients receiving FK506. Pair-fed rats were treated with either FK506 (1 mg/kg/day s.c.) or an equivalent dose of vehicle and were killed at 7 or 28 days. Characteristic histologic changes of tubular injury, interstitial fibrosis, and arteriolopathy developed in FK506-treated rats at 28 days and were accompanied by worsening kidney function, decreased concentrating ability, and enzymuria. FK506-treated kidneys had a progressive increase in the expression of TGF-beta1 and matrix proteins (biglycan, tenascin, fibronectin, and type I collagen). This effect seems to be specific because the expression of type IV collagen, a basement membrane collagen, was not affected. Matrix deposition was present mostly in the tubulointerstitium and vessels in accordance with the FK506 chronic lesion. The expression of plasminogen activator inhibitor-1, a protease inhibitor influenced by TGF-beta, followed TGF-beta1 and matrix proteins, suggesting that the fibrosis of chronic FK506 nephropathy likely involves the dual action of TGF-beta1 on matrix deposition and degradation. Since both peripheral and tissue renin expression were elevated with FK506, the renin-angiotensin system may play a role in the pathogenesis of this condition.

Angiotensin II blockade decreases TGF-beta1 and matrix proteins in cyclosporine nephropathy

Angiotensin II (Ang II) is implicated in fibrosis but the precise mechanism of this effect remains unclear. In a model of chronic cyclosporine (CsA) nephropathy, we previously showed that TGF-beta1 plays a role in CsA-induced tubulointerstitial fibrosis and arteriolopathy by stimulating extracellular matrix (ECM) protein synthesis and inhibiting ECM degradation through increasing the synthesis of plasminogen activator inhibitor (PAI)-1. We hypothesized that Ang II contributes to fibrosis by inducing TGF-beta1. Salt-depleted rats were given placebo, CsA alone, CsA + nilvadipine, CsA + hydralazine/hydrochlorthiazide, CsA + losartan (AT1 receptor antagonist) or CsA + enalapril (Ang converting enzyme inhibitor) and were sacrificed at 7 and 28 days. All treated groups achieved similar blood pressures and glomerular filtration rates. The lesion of chronic CsA nephropathy was ameliorated by concomitant therapy with losartan or enalapril at 28 days, a phenomenon not observed in the other treatment groups. Similarly, Ang II blockade resulted in decreased expression of TGF-beta1 and PAI-1 by Northern and ELISA. Similarly, the expression of ECM proteins directly influenced by TGF-beta decreased with Ang II blockade. These results suggest that CsA-induced fibrosis in this model is independent of renal hemodynamics and is mediated, at least partly, through Ang II induction of TGF-beta1 expression.

Sodium depletion enhances fibrosis and the expression of TGF-beta1 and matrix proteins in experimental chronic cyclosporine nephropathy

The major limitation to the clinical use of cyclosporine (CsA) is renal toxicity. In the past, the lack of an animal model of chronic CsA nephropathy has hampered the study of its pathogenesis. Rats given CsA and placed on a low sodium diet (LSD) develop a histology similar to human lesions of chronic CsA nephropathy, a phenomenon not observed in animals on a normal sodium diet (NSD). We have previously shown that transforming growth factor-beta1 (TGF-beta1) is involved in the CsA-induced renal fibrosis in rats on a LSD. We hypothesized that sodium depletion is critical to the increase in TGF-beta1 expression, which, in turn, results in excessive matrix accumulation. Pair-fed rats were placed on a NSD or LSD, treated with CsA or vehicle, and killed at 7 or 28 days (N = 4 to 6 in each group). All rats achieved similar blood pressure control, and all CsA-treated rats achieved similar CsA blood levels. However, while CsA did not affect creatinine clearance in rats on a NSD, it lowered creatinine clearance in rats on a LSD (P < 0.01). Cyclosporine-induced tubulointerstitial fibrosis and arteriolopathy was observed at 28 days only in the rats on a LSD (P < 0.05). In addition, peripheral renin activity was increased only in the rats on a LSD (P < 0.01), while it remained normal in the rats on a NSD. In addition, CsA-treated rats on a LSD developed a progressive increase in the mRNA expression of TGF-beta1 and the matrix proteins biglycan and type I collagen at 7 and 28 days. Most of the changes were seen at 28 days (P < 0.001 for TGF-beta1, P < 0.01 for biglycan and type I collagen). On the other hand, CsA treatment in rats on a NSD did not affect the mRNA expression of TGF-beta1 and matrix proteins. Most of the changes in the immunofluorescence deposition of the glycoproteins tenascin and fibronectin EDA+ were in the tubulointerstitium and vessels of the kidneys of rats on a LSD and were mostly significant at 28 days, in accordance with the characteristic histology of chronic CsA nephropathy. The mRNA expression of plasminogen activator inhibitor-1, a protease inhibitor involved in matrix degradation and stimulated by TGF-beta1, was observed only in kidneys of rats on a LSD (P < 0.01). Since sodium depletion elevates peripheral renin activity, our experiments suggest a role for the renin-angiotensin system in the expression of TGF-beta1 and matrix proteins in CsA-induced renal fibrosis of rats on a LSD.

Drug nephrotoxicity: an overview

Drug-induced nephrotoxicity is common in clinical practice and should be sought out by clinicians seeking to understand the causes of renal disease and renal syndromes in particular patients. Insights into the pathophysiology of drug-induced disorders should provide clues to disease mechanisms which ultimately might lead to better treatments and more rational prevention of all renal diseases.

Increased renal tubular expression of transforming growth factor beta in human allografts correlates with cyclosporine toxicity

Cyclosporine A (CsA) is a potent immunosuppressive drug that inhibits the transcription of several proinflammatory cytokines including interleukin-2. In contrast, CsA stimulates transcription of the pleuripotent cytokine, transforming growth factor-beta (TGF beta). Since the effect of CsA in transplant recipients is unpredictable, we examined whether tissue levels of TGF beta protein in renal allografts correlate with in vivo CsA responsiveness. Intra-allograft TGF beta protein content was assessed in renal biopsies by immunohistochemical means using the mouse anti-TGF beta monoclonal antibody (Mab), 1D11. We studied 68 specimens: 21 with acute CsA toxicity (ACT), 11 with acute tubular necrosis (ATN) and 36 with acute cellular rejection (ACR). Intensity of TGF beta immunostaining was evaluated in a blinded fashion using a scale from 0 to 3+. In biopsies with histological evidence of CsA toxicity, 77% demonstrated intense (2 to 3+) TGF beta immunostaining. TGF beta protein was detected in both proximal and distal tubules but was either absent or present in low levels within glomeruli and interstitium. In contrast, only one of the 11 biopsies with ATN had minimal staining (1+) for TGF beta. The remaining 10 biopsies with ATN were negative for TGF beta immunostaining. In biopsies with ACR, the levels of renal TGF beta were more variable with 36% showing intense (2 to 3+) staining and 64% having minimal or no (0 to 1+) tubular TGF beta. Within the first 18 months post-transplantation, patients with intense TGF beta staining and ACR underwent an average of 4.1 +/- 1.8 allograft biopsies and suffered 33% graft losses. During the same period of time, the patients with ACR and absent or low (0 to 1+) TGF beta levels underwent only 2.1 +/- 1.2 biopsies, maintained better late renal function and suffered 4% graft losses. In conclusion, we demonstrate that TGF beta protein levels in renal allografts correlate with CsA effect and differentiate ACT from ATN. In CsA treated patients who develop ACR, TGF beta levels predict the subsequent clinical course and graft function. Therefore, evaluating tissue levels of TGF beta may offer unique diagnostic and prognostic benefits in the care of patients receiving CsA based immunosuppression.

Growth factor transcripts in rat renal transplants

Locally produced cytokines and growth factors may mediate tissue remodelling processes, as observed in renal transplants exposed to ischemia or acute rejection episodes. The present study was designed to investigate mRNA transcript levels of platelet-derived growth factor (PDGF)-receptor beta, PDGF-A, PDGF-B, fibroblast growth factor-1, and transforming growth factor beta 1 in normal rat kidneys, in kidneys following contralateral nephrectomy and in renal transplants with acute or chronic rejection. Platelet-derived growth factor-receptor beta mRNA levels increased significantly in syngeneic and allogeneic transplants in the first week after transplantation and in allogeneic transplants with chronic rejection. Immunohistochemistry showed induction of PDGF-receptor beta protein expression on vascular wall cells in such grafts. Platelet-derived growth factor-A chain mRNA levels increased in day 3 allografts and in syngeneic LEW grafts, while PDGF-B chain mRNA levels showed no significant changes with transplantation. Fibroblast growth factor-1 mRNA levels were detectable in normal kidneys, tended to decrease with acute rejection, and increased significantly in chronic rejection. Transforming growth factor-beta 1 transcripts increased in acute and chronic rejection; immunohistochemistry showed predominantly glomerular localization of the transforming growth factor-beta 1 protein. We conclude that transplantation and rejection are associated with changes in the intragraft mRNA levels for several growth factors; chronic rejection is characterized by an increase in fibroblast growth factor-1 and transforming growth factor-beta 1 transcript levels.

Synergistic effects of cyclosporine and rapamycin in a chronic nephrotoxicity model

Rapamycin (RAPA) acts synergistically with cyclosporine (CsA) to achieve powerful immunosuppression in several animal models of organ transplantation and autoimmune disease. If these drugs are to be used together, they should not enhance toxicity. Thus, we examined the effects of combining CsA and RAPA on renal structure and function in a rat model of chronic CSA nephropathy. Rats were given placebo, CSA (2, 4, and 8 mg/kg), RAPA (0.01 and 0.1 mg/kg), or CsA+RAPA for 28 days while on a low-salt diet. RAPA at a subtherapeutic dose of 0.1 mg/kg worsened glucose metabolism and potentiated chronic nephrotoxicity induced by CsA at 8 mg/kg in terms of both renal function and structural injury. Since hyperglycemia is known to accelerate fibrotic processes, the impairment of glucose metabolism may play a role in tubulointerstitial fibrosis (plasma glucose vs. tubulointerstitial fibrosis, r=0.72, n=18, P<0.001). RAPA had to be given at a dose 10-fold lower (0.01 mg/kg) and CsA at a dose 4-fold lower (2 mg/kg) than the dose required for complete immunosuppression to minimize nephrotoxicity. Although the CsA+RAPA combination acts synergistically on immunosuppression, the combination at the subtherapeutic dose of each drug may be synergistically nephrotoxic, perhaps due to hyperglycemia. Clinical combinations of CsA and RAPA must be tested carefully for chronic nephrotoxicity.