Tetrahydropalmatine Alleviates Osteoarthritis-Associated Pain and Inflammation by Suppressing...

Osteoarthritis (OA)-associated pain, driven by M1 macrophage polarization and inflammation, lacks effective therapies. Tetrahydropalmatine (THP), known for its anti-inflammatory and analgesic properties, was evaluated for its effects on OA-induced pain and macrophage polarization. A destabilization of the medial meniscus (DMM)-induced OA mouse model and lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages were used. Behavioral tests, histology, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), reverse transcription-quantitative polymerase chain reaction (RT-qPCR), Western blotting (WB), and immunohistochemistry (IHC) were used to assess pain, inflammation, and the expression of lysine demethylase 4A (KDM4A), murine double minute 2 (MDM2), and hypoxia-inducible factor-1α (HIF-1α). THP treatment alleviated OA-induced pain and cartilage damage and reduced CD86 expression, and reduced the expression of pro-inflammatory factors tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), and key signaling molecules (KDM4A, MDM2, and HIF-1α). Mechanistically, KDM4A directly bound to the MDM2 promoter and activated its transcription via H3K9me3 demethylation, whereas MDM2 enhanced HIF-1α signaling to promote M1 polarization. Overexpression of KDM4A reversed the inhibitory effects of THP on MDM2/HIF-1α signaling and inflammation. These findings indicate that THP mitigates OA-associated pain and inflammation by blocking KDM4A-mediated MDM2 transcription and suppressing HIF-1α-dependent M1 macrophage polarization, highlighting the KDM4A-MDM2-HIF-1α axis as a potential therapeutic target.