Differential Gene Expression in Synovium Between Male and Female Knee Osteoarthritis

Background and Objectives: Sex differences are well recognized in the epidemiology and clinical manifestations of knee osteoarthritis (OA), with women exhibiting a higher prevalence and greater disease severity than men. Although synovial inflammation is increasingly recognized as a key contributor to OA pathology, the molecular mechanisms underlying sex-related differences in OA synovium remain incompletely understood. Materials and Methods: Synovial tissues were obtained from patients with knee OA undergoing total knee arthroplasty. RNA sequencing (RNA-seq) was initially performed using synovial samples from five female and five male patients to identify differentially expressed genes (DEGs) associated with sex. Candidate genes identified by RNA-seq were subsequently validated by quantitative PCR (qPCR) using an independent cohort consisting of 78 female and 27 male patients. Multivariable analyses adjusted for age, body mass index (BMI), and Kellgren-Lawrence (KL) grade were performed to evaluate the independent association between gene expression and sex. Results: RNA-seq analysis identified 12 female-upregulated genes and 13 male-upregulated genes. Several Y chromosome-related genes showed marked male-specific expression and were excluded from downstream validation analyses. qPCR validation demonstrated significantly higher expression of CAPN6, COL6A6, EGFL6, LAMP3, and MMD in female synovial tissues. After adjustment for age, BMI, and KL grade, EGFL6 (β = 0.829, p = 0.004), LAMP3 (β = 0.596, p = 0.029), and MMD (β = 0.698, p = 0.014) remained significantly associated with female sex. In contrast, DAW1 became significantly associated with male sex after multivariable adjustment (β = 0.753, p = 0.009). Conclusions: Distinct sex-related synovial gene expression profiles were identified in knee OA. In particular, EGFL6, LAMP3, and MMD were independently associated with female sex, suggesting potential sex-related pathology in OA synovium. These findings provide new insight into the molecular basis of sex differences in OA and may contribute to the development of sex-specific therapeutic strategies.