Cell proliferation, matrix production, and Smad-mediated intracellular TGF-β signaling in glomerulonephritis

我们研究了抗胸腺细胞血清（ATS）肾炎大鼠肾小球中smad介导的细胞内TGF-β信号通路的变化，在抗胸腺细胞血清（ATS）肾炎中，肾小球中TGF-β1表达和基质沉积出现一过性升高，结果如下：ATS肾病肾小球中Smad2蛋白水平明显降低，而Smad3和Smad4蛋白水平无明显变化。肾小球中Smad2 mRNA的表达未见明显变化，提示Smad2蛋白的表达减少不是由于基因表达减少，而是由于Smad2蛋白的降解受到调控。3 .内源性Smad2蛋白在ATS肾病肾小球中的降解显著增加。外源性重组Smad2在ATS肾炎大鼠肾小球提取物中泛素化升高。Smad2的E3泛素连接酶Smurf2的表达在ATS肾病肾小球中升高。ATS肾小球中Smad3阳性的肾小球核数增加，提示Smad3介导的TGF-β信号通路在ATS肾小球中起作用。这些数据表明，Smurf2介导的Smad2泛素依赖性降解增强导致Smad2的降低参与了ATS肾病肾小球中Smad2介导的TGF-β信号的调控。Smad2选择性降解的增加可能导致smad3介导的TGF-β信号在ATS肾病肾小球中相对占优势。

We investigated the changes of Smad-mediated intracellular TGF-β signaling in glomeruli of rats with anti-thymocyte serum (ATS) nephritis, in which glomeruli show transient increase of TGF-β1 expression and matrix deposition, and found the following results.1. Smad2 protein decreased markedly in ATS nephritic glomeruli, while no significant changes were noted in the levels of Smad3 and Smad4 proteins.2. No significant changes were noted in glomerular expression of Smad2 mRNA, suggesting that the decrease of Smad2 protein was not due to decreased gene expression, but to regulated degradation of Smad2 protein.3. Degradation of endogenous Smad2 protein increased remarkably in ATS nephritic glomeruli.4. Ubiquitination of exogenous recombinant Smad2 increased in the glomerular extracts obtained from rats with ATS nephritis.5. Expression of Smurf2, an E3 ubiquitin ligase for Smad2, increased in ATS nephritic glomeruli.6. The number of glomerular nuclei positive for Smad3 increased in ATS nephritic glomeruli, suggesting that Smad3-mediated TGF-β signaling worked in ATS nephritic glomeruli.These data suggest that the decrease of Smad2 resulted from enhanced ubiquitin-dependent degradation of Smad2 mediated by Smurf2 is involved in the regulation of Smad2-mediated TGF-β signaling in ATS nephritic glomeruli. Increase of the selective degradation of Smad2 may cause relative predominance of Smad3-mediated TGF-β signaling in ATS nephritic glomeruli.