Treatment with anti-TGF-β antibody ameliorates chronic progressive nephritis by inhibiting Smad/TGF-β signaling

Background. Although short-term treatment with antitransforming growth factor-beta (TGF-beta) antibody (alphaT) has been shown to prevent early glomerular lesions, its long-term effects and molecular mechanisms, including intracellular signaling, remain poorly understood. We examined whether a T treatment induces prevention of renal insufficiency and fibrosis, and affects the TGF-beta/Smad signaling pathway in rats with chronic progressive anti-thymocyte serum (ATS) nephritis induced by repeated ATS injections on days 0 and 7. Methods. Nephritic and non-nephritic rats were treated with either a T or control immunoglobulin (Ig) G twice weekly for 4 weeks from days 7 to 35 (each group, N = 21). Renal lesions and cortical expression of TGF-beta1, TGF-beta2, TGF-beta3, type II TGF-beta receptor (TbetaRII), Smads, type I collagen, and plasminogen activator inhibitor-1 were examined by immunohistochemistry, Western blot, and/or real-time reverse transcription polymerase chain reaction (RT-PCR). The binding of Smad3 in renal cortical cell nuclei to the Smad-binding element (SBE) was investigated by the electrophoretic mobility shift assay. Results. Nephritic rats developed heavy proteinuria, renal insufficiency, and increased extracellular matrix deposition resulting in renal fibrosis. Cortical expression levels of TGF-beta1, TGF-beta2, TbetaRII, and Smad2, but not TGF-beta3, Smad3, and Smad4 were increased. Expression and preferential localization of phosphorylated Smad2/3 in the glomerular and tubular cell nuclei, and Smad3-SBE complex-forming activity were also increased. Four-week alphaT treatment resulted in marked amelioration of chronic progressive ATS nephritis at 8 weeks. Conclusion. In chronic progressive ATS nephritis, the TGF-beta/Smad signaling was up-regulated. TGF-beta blockade by alphaT suppressed the progression of renal scarring, at least in part, via inhibition of activated TGF-beta/Smad signaling.