Expression characteristics of miR-502-5p/p53/NF-κB signaling pathway in patients with different degrees of knee osteoarthritis: a cross-sectional observational study with methodological limitations.

BACKGROUND AND OBJECTIVE: Knee osteoarthritis (KOA) is a prevalent degenerative joint disease affecting millions worldwide. Recent evidence has demonstrated the crucial role of non-coding RNAs, including microRNAs, in the pathogenesis of musculoskeletal disorders. While previous studies have demonstrated that microRNA-502-5p (miR-502-5p) can protect chondrocytes through p53/NF-κB pathway modulation, its role in human synovial tissue remains unclear. This study aimed to investigate the expression patterns and correlations of the miR-502-5p/p53/NF-κB signaling pathway in KOA synovial tissue across different disease severities. METHODS: This cross-sectional observational study enrolled 80 KOA patients undergoing knee arthroscopy from March 2019 to October 2019, stratified by Kellgren-Lawrence (KL) grades (20 patients per grade). Due to ethical constraints, true healthy control synovial tissue could not be obtained; therefore, synovial samples from 6 KL grade I patients with minimal pathology served as reference controls. Clinical assessments included Visual Analog Scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. Synovial tissue samples were collected from standardized locations in the suprapatellar pouch during surgery and processed within 2 h. Histopathological analysis was performed using hematoxylin and eosin (HE) staining with Mankin's scoring system. Expression of miR-502-5p and p53/NF-κB pathway components was analyzed using immunofluorescence double-labeling (primary antibodies: anti-p53 1:200, anti-NF-κB p65 1:100, with appropriate negative and isotype controls) and quantitative real-time PCR (qRT-PCR) with U6 as internal control. Sample size for molecular analyses (n = 6 per group) limits statistical power. RESULTS: (1) Clinical scores (VAS, WOMAC) and pathological scores (synovial Mankin's score, cartilage injury score) showed progressive increases with KL grade advancement (all P < 0.01 after Bonferroni correction). Strong positive correlations were observed between clinical symptoms and tissue pathology (r = 0.69-0.87, P < 0.001), though causality cannot be inferred. (2) Immunofluorescence analysis revealed p53 protein expression decreased progressively from reference to severe synovitis (P < 0.05), while TRAF2, NF-κB, IL-1β, TNF-α, and MMP-13 showed opposite trends (all P < 0.05). (3) qRT-PCR demonstrated miR-502-5p mRNA expression increased 2.5-fold in mild, 4.2-fold in moderate, and 3.8-fold in severe synovitis compared to reference tissue (P < 0.001). However, these findings represent associations only and do not establish causal relationships. CONCLUSION: Our findings reveal an association between miR-502-5p upregulation and KOA severity in synovial tissue, contrasting with its reported protective role in chondrocytes. While we observed correlations between miR-502-5p expression, p53 suppression, and NF-κB activation, causal relationships remain unestablished due to lack of functional validation. These results suggest tissue-specific expression patterns that warrant further mechanistic investigation before therapeutic implications can be determined.