Iguratimod Inhibits Renal Interstitial Fibrosis in Lupus Nephritis

Abstract Background: Renal interstitial fibrosis (RIF) is one of the main poor prognostic factors of lupus nephritis (LN). Here, we tested whether iguratimod could inhibit RIF in LN. Methods: MRL/lpr mice, an animal model of lupus, were treated with iguratimod or vehicle solution. Pathological changes of kidney was evaluated blindly by the same pathologist. Renal type I collagen (COL-I), IgG, E-cadherin, fibroblast-specific protein 1 (FSP-1) were detected by immunofluorescence, immunohistochemical staining or quantitative real-time PCR. After treated with transforming growth factor β1 (TGF-β1) and iguratimod, E-cadherin, fibronectin, Smad2/3, p38 MAPK, p-Smad2/3 and p-p38 MAPK in HK2 cells were measured by western blotting, quantitative real-time PCR or immunofluorescence. Results: In MRL/lpr mice, iguratimod eased the renal interstitial deposition of collagen fibers, further confirmed by decreased expression of COL-I after iguratimod treatment. Moreover, upstream pathological processes of RIF, including IgG deposition along the tubular basement membrane, infiltration of inflammatory cells into renal interstitium and tubular injury, were also prevented effectively by iguratimod treatment. Furthermore, iguratimod suppressed the expression of FSP-1 and raised the expression of E-cadherin in renal tubular epithelial cells, suggesting that iguratimod reversed the process of tubular epithelial-to-mesenchymal transition (EMT). In HK2 cells induced by TGF-β1, co-treatment with iguratimod not only reversed cellular morphologic change, but also prevented down-regulation of E-cadherin and up-regulation of fibronectin. Finally, iguratimod blocked TGF-β1-induced phosphorylation of Smad2/3 and p38 MAPK in HK2 cells. Conclusions: Our results suggest that iguratimod shows an inhibitory effect on the progress of RIF in vivo and in vitro, so iguratimod may be a potential drug for the treatment of RIF in LN.