Reactivation of NR4A1 Restrains Chondrocyte Inflammation and Ameliorates Osteoarthritis in Rats

Abstract

Osteoarthritis (OA) is the most prevalent joint disease and uncontrolled inflammation is now recognized to play vital roles in OA development. Targeting the endogenous counterpart of inflammation may develop new therapeutic approaches in resolving inflammation persistence and treating inflammatory disease including OA. The orphan nuclear receptor 4A1 (NR4A1) is a key negative regulator of inflammatory responses but its role in osteoarthritis remains unclear. In the present study, we found that the NR4A1 expression was elevated in human osteoarthritis cartilage and in vitro OA model, which could be blocked by NF-κB signal inhibitor JSH23. The overexpression of NR4A1 inhibited, whereas knockdown of NR4A1 enhanced IL-1β induced COX-2, iNOS, MMP3, MMP9 and MMP13 expression, and luciferase reporter activity of NF-κB response element. Though NR4A1 was upregulated in inflammatory stimulation and creates a negative feedback loop, persistent inflammatory stimulation inhibited NR4A1 expression and activation. The expression of NR4A1 declined rapidly after an initial peak in conditions of chronic IL-1β stimulation, which could be partially restored by HDACs inhibitor SAHA. The phosphorylation of NR4A1 was increased in human osteoarthritis cartilage, and p38 inhibitor SB203580, JNK inhibitor SP600125 and ERK inhibitor FR180204 could significantly inhibited IL-1β induced NR4A1 phosphorylation. Reactivation of NR4A1 by its agonist cytosporone B could inhibit IL-1β induced chondrocyte inflammation and expression of COX-2, iNOS, MMP3, MMP9, and MMP13. In rat OA model, intra-articular injection of cytosporone B protected cartilage damage and ameliorated osteoarthritis. Thus, our study demonstrated that the NR4A1 is a key endogenous inhibitor of chondrocyte inflammation, which was relatively inactivated under chronic inflammatory stimulation through HDACs mediated transcriptional suppression and MAKP dependent phosphorylation in osteoarthritis. NR4A1 agonist cytosporone B could reactivate and restore the inhibitory regulatory ability of NR4A1, prevent excessive inflammation, and ameliorates osteoarthritis.

A systematic dissection of human primary osteoblasts in vivo at single-cell resolution

“…Further, if the existence of cluster O3 is due to the osteoarthritis, specific markers NR4A1 and NR4A2, would have important roles in osteoarthritis pathogenesis. While previous studies have reported NR4A1 [ 80 ] and NR4A2 [ 81 ] to be regulators of inflammatory responses in chondrocytes, no study has proposed the relationship between osteoarthritis and NR4A1 produced by osteoblasts. In addition, scRNA-seq studies in both normal mouse osteoblasts in vivo performed by Tikhonova et al [ 17 ] and transcriptional profiles of mouse osteoblasts in vitro [ 76 ] showed the presence of NR4A1 in normal osteoblasts.…”

Targeting NR4A Nuclear Receptors to Control Stromal Cell Inflammation, Metabolism, Angiogenesis, and Tumorigenesis

“…NR4A1–NR4A3 expression is elevated in synovial tissue MSC and fibroblast-like stromal cells (FLSs), macrophage, endothelium, cartilage, and PGE2-stimulated chondrocytes from patients with RA, psoriatic arthritis, or osteoarthritis, making NR4A receptors attractive targets in rheumatic and skin diseases (McMorrow and Murphy, 2011 ; Marzaioli et al, 2012 ; Shi et al, 2017 ; Xiong et al, 2020 ). Stromal cell hyperplasia and development of a “tumor-like pannus” are characteristics of chronic inflammatory diseases including RA and psoriatic arthritis (Bottini and Firestein, 2013 ).…”

The role of nuclear receptor 4A1 (NR4A1) in drug‐induced gingival overgrowth

“…7 NR4A1 expression levels were also found to be elevated in the joint tissues of patients with knee osteoarthritis, and a dysfunction due to phosphorylation was shown to contribute to the exacerbation of inflammation. 35 On the other hand, the expression levels of NR4A1 were decreased in the intestines of patients with ulcerative colitis and Crohn's disease, which is characterized by fibrosis in the colon, and the transcriptional activity of NR4A1 was decreased by SNPs in H3K27. 36 While the expression pattern of NR4A1 varies under different disease conditions, the loss-of-function of NR4A1 is commonly involved in their pathogenesis.…”