Retinoic Acid-Loaded Cartilage Organoids Attenuate Chondrocyte Senescence in Osteoarthritis.

BACKGROUND: Osteoarthritis (OA) is a debilitating degenerative joint disease characterized by chondrocyte senescence and cartilage degradation. Despite extensive research, effective therapeutic strategies targeting the underlying mechanisms of chondrocyte senescence remain limited. METHODS: We employed an integrated multi-omics approach combining weighted gene co-expression network analysis (WGCNA) and machine learning algorithms with the SenMayo gene set to identify key senescence-associated genes in OA. Single-cell RNA sequencing was used to characterize distinct chondrocyte subpopulations. Computational screening, molecular docking, and dynamics simulations identified potential therapeutic compounds. We engineered a triphasic gelatin methacryloyl/hyaluronic acid methacryloyl (GelMA/HAMA) cartilage organoid system for controlled delivery of retinoic acid (RA) and evaluated its efficacy in vitro and in a rat destabilization of the medial meniscus (DMM) model of OA. RESULTS: Our bioinformatic analysis identified ANGPT1, MMP1, EGF, and IGF1 as critical senescence-associated genes in OA, forming the basis for a robust clinical prediction model (area under the curve [AUC] = 0.931). Single-cell analysis revealed dysregulated TGF-β1 signaling as central to senescence-mediated cartilage degeneration. In vitro, RA attenuated chondrocyte senescence by activating the TGFβ/Smad pathway, reducing apoptotic markers, and restoring extracellular matrix components. The biomimetic cartilage organoid system facilitated spatiotemporally controlled release of RA within the joint environment. When implanted in the rat OA model, these RA-loaded organoids significantly reduced cartilage degeneration as evidenced by improved Osteoarthritis Research Society International (OARSI) scores, enhanced tissue architecture, and increased cartilage thickness. CONCLUSION: Our findings establish RA delivered via biomimetic cartilage organoids as a promising therapeutic strategy that addresses the cellular mechanisms underlying OA progression. This approach may represent a paradigm shift from symptom management to disease modification by targeting chondrocyte senescence and promoting cartilage regeneration, offering new avenues for developing effective treatments for OA.