APOA4 Protects Chondrocytes and Modulates Wnt Signaling in Osteoarthritis

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.

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.

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.

APOA4 mitigates OA progression by promoting ECM anabolism, inhibiting inflammation, and suppressing Wnt/β-catenin signaling. It represents a novel therapeutic target for OA.