TGF-beta 1/Smads signaling stimulates renal interstitial fibrosis in experimental AAN

Abstract

Aristolochic acid nephropathy (AAN) is regarded as a kind of rapidly progressive renal fibrosis caused by the ingestion of herbal remedies containing aristolochic acids (AA). A mouse model of AAN was used to assess the patterns of renal injury and TGF-β1/Smads signaling pathway during the evolution of tubulointerstitial damage and to relate them to the development of fibrosis. A total of 28 mice were randomly assigned to four groups. Three groups were given aristolochic acid I (AAI) at different doses consecutively by gavage for 30 days, while the control group received only phosphate-buffered saline (PBS). Immunohistochemistry and semi-quantitative reverse transcriptase (RT-PCR) detection of the increased expression of fibroblast marker vimentin and de novo expression of α-smooth muscle actin (α-SMA) with the loss of epithelial maker cytokeratin 18 (CK18) can be utilized to assess AAI-induced tubular necrosis and extensive cortical interstitial fibrosis in a dose-dependent manner. Transforming growth factor-β1 (TGF-β1) has been widely recognized as a key fibrogenic cytokine. In our study, TGF-β1 in the group at dose of 12 mg/kg/ day AAI increased 109.9% compared to control. Smad2 mRNA level in the group at dose of 4.2 mg/kg/day AAI increased 106.4%, and declined 12% in the group at dose of 12 mg/kg/day AAI; Smad4 expression was down-regulated in experimental groups, which declined 13% in the group at dose of 4.2 mg/kg/day AAI. Smad7 mRNA level was down-regulated by AAI in dose-dependence. Collectively, the involvement in interstitial fibrosis progression of active TGF-β is highly suggested, via the Smads intracellular signaling pathway. These results may be attributed to the dosage of drug and the treatment of renal interstitial fibrosis.

Keywords::

• Aristolochic acid I
• renal tubular epithelial cells
• renal tubulointerstitial fibrosis
• mouse
• TGF-β1

Acknowledgments

This work was supported by grants from National Natural Science Foundation of China (30771625, 30471306), and funded by Academic Human Resources Development in Institutions of Higher Learning Under the Jurisdiction of Beijing Municipality (PHR2009-07135), Beijing Municipal Natural Science Foundation (6092004), Beijing Municipal Education Commission (KM20051002002).

Decleration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.