Senescence-associated gene pathways are differentially expressed in equine aging-related osteoarthritis.

Objective: Osteoarthritis (OA) is a aging-associated degenerative joint disease. The objective was to determine relative senescence gene expression in joints and leukocytes of OA horses toward considering senotherapeutics to manage OA. Methods: To define local (joint) and systemic (peripheral blood mononuclear cells [PBMCs]) senescence burden, synovial fluid cell single-cell RNA sequencing and PBMC mRNA sequencing datasets (n = 65 samples) were examined. Differential analyses were conducted using limma to compare OA versus control. A custom 3,043-gene senescence set curated from published metadata was applied to differential analyses to investigate senescence-specific pathways. Senescence genes were divided into 8 categories; scores were calculated with fast gene set enrichment analysis with P value computed via permutation and log2 fold change ranks. Results: Synovial fluid single-cell RNA sequencing data revealed cell type-specific heterogeneity in senescence gene expression. Fast gene set enrichment analysis pathway analysis confirmed enrichment/upregulation in inflammatory and stress-induced senescence in dendritic, cycling, CD8 T, and gamma delta T cells. Senescence-associated secretory phenotype pathways were predominantly represented in cycling cells. Senescence genes aryl hydrocarbon receptor (AHR), IL-1 receptor antagonist (IL1RN), heme oxygenase 1 (HMOX1), plasminogen activator, urokinase receptor (PLAUR), and tissue inhibitor of metalloproteinase 1 (TIMP1) were upregulated in multiple synovial fluid cell types. In contrast, genes in most senescence categories were downregulated in PBMCs. Conclusions: Senescence pathways were differentially expressed in aged horses with OA, with upregulation of senescence genes in the joint and downregulation in PBMCs. Clinical Relevance: Therapeutic strategies targeting senescent cells may be a disease-modifying strategy to treat equine OA.