Upregulation of ACSL1 in synovial macrophages promotes lipid peroxidation via the IκB/NF-κB pathway to accelerate osteoarthritis

Background: Osteoarthritis (OA) is a globally prevalent degenerative joint disease, characterized by cartilage degradation and synovial inflammation. Increasing evidence suggests that macrophages in the synovium play a pivotal role in OA pathogenesis. Energy metabolism reprogramming has emerged as a key regulator of macrophage activation in inflammatory diseases. Long-chain fatty acid-CoA ligase 1 (ACSL1), an enzyme critical for lipid metabolism, has been implicated in various diseases. However, the specific mechanism by which ACSL1 regulates macrophage polarization and contributes to OA progression remains unclear. Methods: In this study, we examined ACSL1 expression in the hyperplastic synovium of patients with knee OA and in a mouse model of OA induced by destabilization of the medial meniscus (DMM). We isolated bone marrow-derived macrophages (BMDMs) from C57 mice and transfected them with ACSL1 knockdown plasmids to assess the impact of ACSL1 on macrophage polarization and inflammatory cytokine release. We also investigated the effect of ACSL1 knockdown on cartilage degradation using BMDM supernatant in cartilage explant cultures. Intra-articular injection of AAV-shACSL1 was performed to evaluate its effect on OA progression in a trauma-induced mouse model. The expression of ACSL1, inflammatory cytokines (IL-1, IL-6, TNF-α), and lipopolysaccharide (LPS)-induced macrophage polarization markers (M1 and M2 markers) was assessed using qRT-PCR, Western blotting, and ELISA. Lipid peroxidation and the activation of the IκB/NF-κB signaling pathway were examined to elucidate the mechanism by which ACSL1 regulates inflammation. Results: We observed increased ACSL1 expression in both the hyperplastic synovium of OA patients and the synovium of DMM-induced OA mice. Knockdown of ACSL1 in macrophages inhibited M1 polarization and reduced the release of key inflammatory cytokines, including IL-1, IL-6, and TNF-α. Furthermore, supernatants from ACSL1-knockdown BMDMs mitigated cartilage degradation in explant cultures. Intra-articular injection of AAV-shACSL1 reduced OA progression in a mouse model of trauma-induced OA. Mechanistically, ACSL1 knockdown alleviated LPS-induced inflammation by inhibiting lipid peroxidation and reducing the activation of the IκB/NF-κB pathway, a major regulator of inflammatory responses in macrophages. Conclusions: ACSL1 plays a crucial role in regulating the inflammatory state of synovial macrophages in OA. By modulating macrophage polarization and lipid peroxidation, ACSL1 contributes to the progression of OA. Targeting ACSL1 could provide a novel therapeutic strategy for the prevention and treatment of OA. The translational potential of this article: This study highlights the pivotal role of ACSL1 in regulating macrophage-mediated inflammation in OA. Targeting ACSL1 expression or its associated pathways could offer a new approach for modulating synovial macrophage activation and preventing cartilage degradation. These findings suggest that ACSL1 may serve as a potential therapeutic target for both the prevention and treatment of OA, particularly through strategies aimed at controlling lipid metabolism and inflammatory responses in the synovium.