The pro-inflammatory effect of NR4A3 in osteoarthritis.

NR4A3 is a member of nuclear receptor subfamily 4, which is an important regulator of cellular function and inflammation. In this study, high expression of NR4A3 in human osteoarthritis (OA) cartilage was firstly observed. To explore the relationship between NR4A3 and OA, we used a lentivirus overexpression system to simulate its high expression and study its role in OA. Additionally, siRNA-mediated knockdown of NR4A3 was used to confirm the findings of overexpression experiments. The results showed the stimulatory effect of IL-1ß on cartilage matrix-degrading enzyme expression such as MMP-3, 9, INOS and COX-2 was enhanced in NR4A3-overexpressed chondrocytes and decreased in NR4A3-knockdown chondrocytes at both mRNA and protein levels, while IL-1ß-induced chondrocyte-specific gene (collagen 2 and SOX-9) degradation was only regulated by NR4A3 at protein level. Furthermore, overexpression of NR4A3 would also enhance EBSS-induced chondrocytes apoptosis, while knockdown of NR4A3 decreased apoptotic level after EBSS treatment. A pathway study indicated that IL-1ß-induced NF-κB activation was enhanced by NR4A3 overexpression and reduced by NR4A3 knockdown. We suggest that NR4A3 plays a pro-inflammatory role in the development of OA, and we also speculate that NR4A3 mainly regulates cartilage matrix-degrading gene expression under inflammatory conditions via the NF-κB pathway.

Tectorigenin inhibits RANKL-induced osteoclastogenesis via suppression of NF-κB signalling and decreases bone loss in ovariectomized C57BL/6.

Metabolism of bone is regulated by the balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. Activation of osteoclasts could lead to osteoporosis. Thus, inhibiting the activity of osteoclasts becomes an available strategy for the treatment of osteoporosis. Tectorigenin is an extract of Belamcanda chinensis In the present study, the anti-osteoclastogenesis effects of tectorigenin were investigated in vitro and in vivo. The results showed preventive and therapeutic effects of tectorigenin at concentrations of 0, 10, 40, and 80 µmol/L in the maturation and activation of osteoclasts. A signalling study also indicated that tectorigenin treatment reduces activation of NF-κB signalling in osteoclastogenesis. Animal experiment demonstrated that tectorigenin treatment (1-10 mg/kg, abdominal injection every 3 days) significantly inhibits bone loss in ovariectomized C57BL/6. Our data suggest that tectorigenin is a potential pharmacological choice for osteoporosis.

Reactivation of NR4A1 Restrains Chondrocyte Inflammation and Ameliorates Osteoarthritis in Rats.

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-1ß 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-1ß 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-1ß induced NR4A1 phosphorylation. Reactivation of NR4A1 by its agonist cytosporone B could inhibit IL-1ß 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.

Polygalacic acid inhibits MMPs expression and osteoarthritis via Wnt/ß-catenin and MAPK signal pathways suppression.

Osteoarthritis (OA) is a chronic degenerative joint disease that has been shown to be closely related to the over expression of matrix metalloproteinases (MMPs). Polygalacic acid is a triterpene isolated from the root of Polygala tenuifolia Willd. In the present study, the anti-inflammatory effect of polygalacic acid in OA was investigated as well as its in vitro and in vivo mechanism. In vitro, rat chondrocytes were induced with interleukin-1beta (IL-1ß) and treated with different concentrations of polygalacic acid; real-time PCR and Western blotting were performed to evaluate the expressions of MMP-3, MMP-9, MMP-13, and COX-2. In addition, the MAPK and Wnt/ß-catenin signaling pathways were analyzed via Western blotting and immunofluorescence staining. In vivo, a rat OA model was treated with polygalacic acid. Gross morphological and histological assessments were performed to evaluate the resulting cartilage damage. Polygalacic acid significantly reduced the expression of MMPs and COX-2, which could be induced by IL-1ß in rat chondrocytes. Furthermore, polygalacic acid treatment prevented the degeneration of cartilage in the rat OA model. To investigate the underlying mechanism, we found that polygalacic acid suppressed both the IL-1ß-induced activation of Wnt/ß-catenin and the mitogen-activated protein kinase (MAPK) signal pathway in chondrocytes. These results suggest that polygalacic acid may have a therapeutic effect in OA treatment.