Nr4a1 promotes renal interstitial fibrosis by regulating the p38 MAPK phosphorylation

by Selleckchem | Oct 05 2023

Background: Renal interstitial fibrosis (RIF) is a common pathway to end-stage renal disease regardless of the initial etiology. Currently, the molecular mechanisms for RIF remains not fully elucidated. Nuclear receptor subfamily 4 group A member 1(Nr4a1), a member of the NR4A subfamily of nuclear receptors, is a ligand-activated transcription factor. The role of Nr4a1 in RIF remains largely unknown.

Methods: In this study, we determined the role and action mechanism of Nr4a1 in RIF. We used unilateral ureteral obstruction (UUO) mice and transforming growth factor (TGF)-β1-treated human renal proximal tubular epithelial cells (HK-2 cells) as in vivo and in vitro models of RIF. A specific Nr4a1 agonist Cytosporone B (Csn-B) was applied to activate Nr4a1 both in vivo and in vitro, and Nr4a1 small interfering RNA was applied in vitro. Renal pathological changes were evaluated by hematoxylin and eosin and Masson staining, and the expression of fibrotic proteins including fibronectin (Fn) and collagen-I (Col-I), and phosphorylated p38 MAPK was measure by immunohistochemical staining and western blot analysis.

Results: The results showed that Nr4a1 was upregulated in UUO mouse kidneys, and was positively correlated with the degree of interstitial kidney injury and the levels of fibrotic proteins. Csn-B treatment aggravated UUO-induced renal interstitial fibrosis, and induced p38 MAPK phosphorylation. In vitro, TGF-β induced Nr4a1 expression, and Nr4a1 downregulation prevented TGF-β1-induced expression of Fn and Col-I and the activation of p38 MAPK. Csn-B induced fibrotic proteins expression and p38 MAPK phosphorylation, and moreover Csn-B induced fibrotic proteins expression was abrogated by treatment with p38 MAPK inhibitor SB203580. We provided further evidence that Csn-B treatment promoted cytoplasmic accumulation of Nr4a1.

Conclusion: The findings in the present study indicate that Nr4a1 promotes renal fibrosis potentially through activating p38 MAPK kinase.

Comments:

Summary: This study investigated the role and mechanism of action of a transcription factor called Nuclear receptor subfamily 4 group A member 1 (Nr4a1) in renal interstitial fibrosis (RIF), which is a common pathway to end-stage renal disease. The researchers used mouse models of RIF (unilateral ureteral obstruction or UUO) and human renal proximal tubular epithelial cells (HK-2 cells) treated with transforming growth factor (TGF)-β1 to simulate RIF in vivo and in vitro, respectively.

The results showed that Nr4a1 expression was upregulated in the kidneys of UUO mice and correlated with the severity of interstitial kidney injury and levels of fibrotic proteins. The researchers used a specific Nr4a1 agonist called Cytosporone B (Csn-B) to activate Nr4a1 both in vivo and in vitro. They found that Csn-B treatment aggravated renal interstitial fibrosis in UUO mice and induced phosphorylation of p38 MAPK, a signaling protein involved in fibrosis.

In the in vitro experiments, TGF-β1 treatment induced Nr4a1 expression, and downregulation of Nr4a1 prevented TGF-β1-induced expression of fibronectin (Fn) and collagen-I (Col-I), two fibrotic proteins, as well as the activation of p38 MAPK. Csn-B treatment also induced the expression of fibrotic proteins and p38 MAPK phosphorylation. Importantly, the researchers demonstrated that the induction of fibrotic proteins by Csn-B could be blocked by treatment with an inhibitor of p38 MAPK (SB203580), suggesting that p38 MAPK activation is involved in Nr4a1-mediated renal fibrosis.

Furthermore, the researchers observed that Csn-B treatment led to the cytoplasmic accumulation of Nr4a1, which may contribute to its fibrotic effects.

In conclusion, this study suggests that Nr4a1 promotes renal fibrosis potentially through the activation of p38 MAPK. These findings contribute to the understanding of the molecular mechanisms underlying renal interstitial fibrosis and provide insights into the potential therapeutic targets for the treatment of kidney diseases associated with fibrosis.