Nuclear receptor 4A1 inhibits chondrocyte inflammation and cartilage degeneration in osteoarthritis by inhibiting NF-κB signal pathway.

OBJECTIVE

The objective of this study is to explore the mechanism of nuclear receptor subfamily 4 group A member 1 (NR4A1) inhibiting the inflammatory response and cartilage degeneration of osteoarthritis (OA) chondrocytes by inhibiting the nuclear factor κB (NF-κB).

METHODS

A total of 45 Sprague-Dawley (SD) rats were randomly divided into three groups (n = 15 in each group): the blank control group (BCG), OA model group (OAG), and NR4A1 overexpression group (OE-NR4A1). The rat model of knee OA was established by medial meniscectomy. A total of 1 week after the operation, the rat model of NR4A1 overexpression was established by injecting NR4A1 overexpression lentivirus into the articular cavity of rats; 5 weeks after the establishment of the model, the rats were killed, and the morphological changes of knee cartilage were observed by hematoxylin and eosin (HE) staining under light microscope. The expression of NR4A1 and NF-κB protein in cartilage tissue was detected by western blot, and the relative expression of NR4A1 and NF-κB mRNA in cartilage tissue was detected by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). The levels of interleukin (IL)-6, IL-8 and tumor necrosis factor (TNF)-α in the supernatant of chondrocytes were detected by ELISA, and the apoptosis of chondrocytes was detected by TUNEL staining.

RESULTS

The relative expression of NR4A1 mRNA and protein in knee cartilage of rats in OE-NR4A1 were raised compared with those of OAG and BCG (P < 0.05). The relative expression of NF-κB mRNA and protein expression in knee joint cartilage in OE-NR4A1 were reduced compared with those of OAG and BCG, while their expression in the OE-NR4A1 (200 μL) and OE-NR4A1 (300 μL) groups were lower than in the OE-NR4A1 (100 μL) group(P < 0.05). The knee cartilage Mankin's score and knee joint diameter in the OAG were raised compared with those in the BCG (P < 0.05), while those in the OE-NR4A1 were reduced compared with the OAG (P < 0.05), but higher than in the BCG; these measures in the OE-NR4A1 (200 μL) and OE-NR4A1 (300 μL) groups were lower than in the OE-NR4A1 (100 μL) group (P < 0.05). The levels of IL-6, TNF-α, and IL-1β in knee synovial fluid of rats in OE-NR4A1 were reduced compared with those in the OAG (P < 0.05), but raised compared with those in the BCG; and these in the OE-NR4A1 (200 μL) and OE-NR4A1 (300 μL) groups were lower than in the OE-NR4A1 (100 μL) group (P < 0.05). The scorch rate of chondrocytes in the OE-NR4A1 was reduced compared with that in the OAG and higher than that of the BCG, and this measure in the OE-NR4A1 (200 μL) and OE-NR4A1 (300 μL) groups was lower than in the OE-NR4A1 (100 μL) group (P < 0.05).

CONCLUSIONS

R4A1 can improve the level of intraarticular inflammatory factors by inhibiting the NF-κB signal pathway, thereby reducing intraarticular inflammation and cartilage degeneration, and it plays a protective role in OA.