localization and changes of expressions of Smad2, Smad3, Smad4, and Smad7 proteins in the 5/6 subtotally nephrectomized rat kidney

Objective To investigate the localization of Smad2, Smad3, Smad4, and Smad7 proteins and their expression changes in the 5/6 subtotally nephrectomized rat kidney. Methods The rat model of chronic renal failure was established by performing 5/6 subtotally nephrectomy (SNx) and rats in the control group underwent sham-operation. The rats were sacrificed at 4, 8, and 12 week after operation. The sites and levels of expressions of Smad2, Smad3, Smad4, and Smad7 proteins were examined by immunohistochemical staining. Renal fibrosis was assessed by measuring tissue hydroxyproline. Results Immunohistochemical staining indicated that Smad2, Smad3, and Smad4 proteins were mainly expressed in glomeruli and renal tubular cells, while Smad protein 7 was expressed in glomeruli, but rarely in proximal renal tubular cells. Expressions of Smad2, Smad3, and Smad4 proteins in glomeruli were significantly increased during 4-12 weeks after 5/6 nephrectomy, but the expression level of Smad protein 7 was significantly decreased, but accompanied increase of hydroxyproline content in the renal tissues. Conclusion These results indicate that TGF-β/Smad signaling is involved in the progress of chronic glomerulosclerosis. The high level expressions of Smad2, Smad3, and Smad4 proteins and the down-regulation of Smad7 protein may be the major cause of the glomerulosclerosis in this model.