Single-cell transcriptomics reveals chondrocyte state transitions and ECM remodeling in osteoarthritic knee cartilage

BackgroundOsteoarthritis cartilage contains heterogeneous chondrocyte states, but molecular programs linked to state transitions within human cartilage remain incompletely resolved using public single-cell data. MethodsA retrospective reanalysis was conducted of a public human knee cartilage single-cell RNA sequencing dataset (GSE255460) including 8 osteoarthritis donors and 3 non-osteoarthritis donors (19 samples). Cells underwent sample-wise quality control and doublet removal, followed by batch-corrected clustering, chondrocyte subclustering with marker-based annotation, and trajectory inference using Slingshot. Regulatory chondrocytes were prioritized for osteoarthritis versus control differential expression, with downstream Gene Ontology/KEGG enrichment (Benjamini-Hochberg false discovery rate <0.05) and protein-protein interaction network hub screening. ResultsAfter quality control, 27,036 cells were retained. Chondrocytes formed multiple transcriptional states with branching-like continuous relationships, and regulatory chondrocytes localized near the main manifold and adjacent to multiple inferred branches, consistent with a transition-adjacent state. In regulatory chondrocytes, osteoarthritis versus control differential expression was enriched for collagen-containing extracellular matrix and extracellular matrix organization, endoplasmic reticulum lumen-associated secretory/proteostasis processes, cell-matrix adhesion (including focal adhesion), and transforming growth factor beta/SMAD-related signaling. Protein-protein interaction analysis of regulatory-chondrocyte differential genes identified five high-connectivity hub genes: COL5A1, COL5A2, COL6A1, COL1A2, and COL3A1. ConclusionThis public-dataset reanalysis supports a transition-adjacent regulatory chondrocyte program in osteoarthritis characterized by coordinated extracellular matrix remodeling with concurrent secretory/proteostasis and adhesion-transforming growth factor beta signatures, nominating collagen-network hubs as candidates for downstream validation.