APOA4 Protects Chondrocytes and Modulates Wnt Signaling in Osteoarthritis

Background: Osteoarthritis (OA) pathogenesis involves dysregulated extracellular matrix (ECM) remodeling and inflammation. Apolipoprotein A4 (APOA4), while known for lipid metabolism, has an uncharacterized role in OA. Methods: Clinical samples including infrapatellar fat pad (IFP) (n=3), synovial fluid (n=11), and serum (n=11) from patients with and without OA were analyzed via immunohistochemistry (IHC) and ELISA. In vitro, human chondrocytes (C28/I2) were treated with recombinant APOA4 (5 nM), siRNA knockdown (si-APOA4), or overexpression (OE-APOA4). Functional assays (qPCR, RNA-seq, CCK-8, colony formation) and inflammatory modeling (IL-1β ± APOA4) assessed chondrocyte responses. Wnt pathway involvement was probed via Wnt3a rescue. Results: APOA4 expression was significantly elevated in OA IFP tissues, synovial fluid, and serum vs. controls (p < 0.05). APOA4 treatment upregulated the level of anabolic markers (COL2, p=0.0006; ACAN p=0.0055) and downregulated catabolic factors (MMP3, p=0.0249; MMP13, p=0.0214), while enhancing chondrocyte proliferation. OE-APOA4 mimicked these effects, whereas si-APOA4 reversed them. APOA4 attenuated IL-1β-induced inflammation, preserving COL2/ACAN and suppressing MMPs. RNA-seq implicated Wnt/β-catenin suppression (NES = − 1.314; p = 0.008) as a key mechanism. Wnt3a treatment partially reversed APOA4’s chondroprotective effects. Conclusion: APOA4 mitigates OA progression by promoting ECM anabolism, inhibiting inflammation, and suppressing Wnt/β-catenin signaling. It represents a novel therapeutic target for OA. Keywords: osteoarthritis, APOA4, chondrocyte, Wnt/β-catenin, RNA-seq, qPCR