A Systems-Level Transcriptomic Framework Identifies Shared Cellular Hubs in Osteoarthritis and Alzheimer's Disease

Osteoarthritis (OA) and Alzheimer's disease (AD) are prevalent age-associated disorders that frequently co-occur, yet the molecular basis of their comorbidity remains incompletely understood. To explore potential shared cellular programs, we performed an integrative analysis of publicly available bulk and single-cell transcriptomic datasets derived from human OA cartilage and AD cortex. Cross-disease comparison identified 60 overlapping differentially expressed genes, including 18 consistently up-regulated genes, which we defined as a shared up-regulated gene set (SUGS). Functional enrichment analyses indicated convergence on extracellular matrix remodeling, inflammatory signaling, metabolic stress responses, and immune regulation. Single-cell analysis of OA cartilage revealed expansion of a fibrochondrocyte subpopulation enriched for SUGS activity and extracellular-matrix-associated ligands. In AD cortex, a disease-associated oligodendrocyte subcluster displayed elevated SUGS activity and stress-response gene expression and occupied a prominent-receiver-like position within inferred neuronal-glial communication networks. Ligand-receptor analysis performed independently within each tissue identified collagen-related signaling in OA and neurexin-associated signaling in AD as dominant intratissue pathways. Because the OA and AD datasets are cross-sectional and were derived from independent cohorts and distinct tissues, these analyses do not establish direct inter-organ communication, temporal sequence, or causal directionality. In addition, CellChat-based ligand-receptor inference was performed independently within each tissue and does not itself infer cross-organ communication. The identification of sender-like and receiver-like cellular hubs should therefore be interpreted as a hypothesis-generating, systems-level conceptual framework that may help organize future experimental studies investigating potential links between joint inflammation and neurodegeneration in aging.