Study of Retinoic Acid-Induced Osteoarthritis: Integrating RNA-Sequencing, Network Pharmacology, Molecular Docking, and Experimental Validation.

Osteoarthritis (OA) is a debilitating joint disorder characterized by cartilage degradation and disruption of chondrocyte homeostasis. Although retinoic acid (RA) has been used in OA models, its precise targets are not clear. A translational framework was employed, integrating RNA-sequencing results, network pharmacology prediction, computational ligand-receptor molecular docking, and biological experimental validation, to systematically elucidate RA's disease-modifying targets in OA pathogenesis. RNA-sequencing of RA-treated chondrocytes revealed 656 differentially expressed genes (DEGs). Protein-protein interaction (PPI) network analysis and functional enrichment [Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG)] highlighted key pathways, including extracellular matrix (ECM) reorganization and PI3K-Akt-mediated mechanotransduction and others. Network pharmacology analysis identified 42 shared targets between RA and OA. PPI analysis and functional enrichment (GO/KEGG) highlighted pathways including the renin-angiotensin system and the neuroactive ligand-receptor interaction, among others. Molecular docking ranked candidate targets by binding affinity of RA in descending order as MAPK14 (p38α), PTGER3 (PGE2 receptor), CA2 (CA2), and others. Five intersecting targets CA2, ACE, PTGS1 (COX-1), PGR, and EDNRA (ETAR) were identified by integrating RNA-sequencing (RNA-seq) results and network pharmacology predictions. These interactions were experimentally validated via western blot, RT-qPCR and immunofluorescence. RA increased the expression of MMP13, CA2 and ACE, and decreased the expression of COL2A1 in chondrocytes. siRNA-mediated knockdown of both CA2 (human CA2 homolog) and ACE (human ACE homolog) inhibit cartilage degradation through downregulating MMP13 and upregulating COL2A1. This study not only elucidates potential molecular mechanisms by which RA modulates chondrocyte catabolism but also offers a valuable reference for the development of novel OA therapeutics.