Nr4a1 promotes renal interstitial fibrosis by regulating the p38 MAPK phosphorylation

Abstract

Abstract Background Renal interstitial fibrosis (RIF) is a common pathological change in kidney diseases progressing into end-stage renal disease and involves multiple cell types, but the key targets and regulatory mechanisms have not been fully elucidated. Nuclear receptor subfamily 4 group A member 1(Nr4a1) belongs to a subfamily of nuclear receptors, and in this study, we found a regulatory effect of Nr4a1 on p38 MAPK phosphorylation in renal tubular epithelial cells with renal interstitial fibrosis. Methods Firstly, we collected human renal fibrosis specimens and used unilateral ureteral obstruction (UUO) mice and transforming growth factor (TGF)-β1-stimulated human renal proximal tubular epithelial cells (HK-2) as in vivo and in vitro models to detect the expression of Nr4a1. Subsequently, using Nr4a1-specific agonist Cytosporone B (Csn-B) in vivo and in vitro and Nr4a1 small interfering RNA in vitro, we observed renal pathological changes by HE and Masson staining, and immunohistochemical staining and western blot were performed to detect the expression of fibronectin (Fn) and collagen-I (Col-I), as well as p38 MAPK phosphorylation level. Results The results showed that firstly Nr4a1 expression was upregulated in human fibrosis and UUO mice kidney, and positively correlated with the degree of interstitial kidney injury and fibrotic protein expression. Csn-B aggravated UUO-caused renal interstitial fibrosis and activated p38 MAPK phosphorylation. In vitro it also showed that Nr4a1 expression increased under TGF-β1 stimulation, and transfection with Nr4a1 small interfering RNA reduced the expression of TGF-β1-stimulated Fn、Col-I and p38 MAPK phosphorylation levels. Similary, Csn-B induced Fn、Col-I expression and p38 MAPK phosphorylation in HK-2 cells. Further, p38 MAPK inhibitor SB203580 reversed the Csn-B-induced Fn and Col-I expression. In addition, immunofluorescence and western blot suggested that Csn-B induced increased Nr4a1 expression in the cytoplasm. Conclusion The above results indicated that Nr4a1 could exert pro-fibrotic effect by regulating p38 MAPK phosphorylation in renal interstitial fibrosis.