THBS2 Marks Disease-Associated Chondrocyte States in Knee Osteoarthritis Cartilage: An Integrative Transcriptomic and...

Background/Objectives: Knee osteoarthritis (KOA) is a major cause of disability, yet the molecular links between extracellular matrix (ECM) remodeling, focal adhesion signaling, and pathological chondrocyte state transitions remain incompletely defined. We aimed to identify focal adhesion-related molecules associated with KOA and characterize their genetic, tissue-level, and single-cell features. Methods: Global Burden of Disease (GBD) 2021 data were used only to provide epidemiologic context for KOA-related disability-adjusted life years (DALYs). Bulk transcriptomic datasets (GSE114007 and GSE169077) were analyzed for differential expression, pathway enrichment, and focal adhesion-related genes. Two-sample Mendelian randomization (MR) integrating blood-derived cis-eQTL summary statistics from eQTLGen with KOA GWAS data was used for exploratory genetic prioritization; these eQTLs were not used as a surrogate measure of cartilage THBS2 expression. THBS2 was further evaluated by expression validation, gene set enrichment, immune-related ssGSEA signature analysis, single-cell RNA sequencing (GSE255460), Slingshot pseudotime analysis, and CellChat. Results: As epidemiologic context, global KOA related DALYs increased from 5.17 million in 1990 to 12.12 million in 2021. Bulk analysis identified 1584 differentially expressed genes (DEGs) and 32 focal adhesion-related candidates. Blood-derived cis-eQTL-based MR showed that genetically instrumented higher THBS2 expression was associated with lower KOA risk (OR = 0.718, 95% CI:0.570-0.905, p = 0.00497), whereas bulk transcriptomic analyses showed higher tissue-level THBS2 expression in KOA cartilage; this bulk difference may reflect both cell-composition changes and cell-intrinsic regulation. Single-cell analysis localized THBS2 mainly to fibrochondrocytes and osteogenic chondrocytes; At the pooled-cell level, THBS2-detectable cells were more frequent in OA than control cartilage (19.45% vs. 1.44%). Pooled CellChat analysis suggested differences in several communication pathways, including higher COLLAGEN, FN1, MIF, LAMININ, and SPP1 pathway scores but a lower THBS pathway score in OA. Conclusions: THBS2 is a genetically prioritized, disease-associated matricellular molecule linked to ECM remodeling and selected disease-associated chondrocyte states in KOA. The CellChat findings describe parallel, broader communication remodeling in the cartilage microenvironment.