Expression of transforming growth factor-β–inducible gene-h3 in normal and cyclosporine-treated rat kidney

Abstract

Up-regulation of transforming growth factor-β (TGF-β) is known to play an important role in the tubulointerstitial injury of chronic cyclosporin A (CsA) nephropathy, but the expression of the TGF-β–inducible gene-h3 (βig-h3) is undetermined. In this study we examined βig-h3 expression and its relationship to tubulointerstitial injury in a rat model of chronic CsA nephropathy. Sprague-Dawley rats kept on a low-salt diet (0.05% sodium) were treated daily for 4 weeks with subcutaneous injections of vehicle (olive oil, 1 mL/kg) or CsA (15 mg/kg). The expression of βig-h3 messenger RNA (mRNA) and protein was evaluated with the use of in situ hybridization, immunohistochemical methods, and immunoblotting. We also compared renal function, histologic findings (tubulointerstitial fibrosis), and expression of TGF-β1 among treatment groups. In vehicle-treated kidney, βig-h3 mRNA and protein were constitutively expressed in the outer medulla and cortex, which was confined to the terminal portion of afferent arterioles, the S3 segment of the proximal tubules, and distal convoluted tubules. CsA treatment significantly up-regulated βig-h3 expression in the interstitium, especially in expanded and fibrotic areas. Quantitative analysis revealed that CsA induced a significant (twofold) increase in βig-h3 mRNA and protein, and this increase was correlated with up-regulation of TGF-β1 expression ( r = .943, P < .001) and the tubulointerstitial fibrosis score ( r = .746, P = .05). Our observations indicate that an increase in βig-h3 expression, along with TGF-β1 up-regulation, is closely associated with tubulointerstitial fibrosis in a rat model of chronic CsA nephropathy.