Epigallocatechin-3-gallate attenuates PAR-2–mediated inflammatory signaling and preserves markers of mitochondrial integrity in osteoarthritic chondrocytes

Epigallocatechin-3-gallate (EGCG), the principal catechin of green tea, exhibits broad anti-inflammatory properties; however, its effect on protease-activated receptor-2 (PAR-2)-mediated signaling in osteoarthritis (OA) has not been investigated. Here, we report that EGCG (5-10 µM) dose-dependently suppresses PAR-2 expression at both mRNA and protein levels in lipopolysaccharide (LPS)-stimulated human chondrocytes derived from bone marrow mesenchymal stem cells. This upstream inhibition attenuated ERK1/2 phosphorylation (pERK/total ERK ratio reduced below basal levels at 10 µM) and produced concordant suppression of three functionally linked effector arms: (i) pro-inflammatory cytokines (TNF-α, IL-1β, MCP-1), with near-maximal inhibition at 10 µM and a saturation plateau at 20 µM; (ii) the SOX4-ADAMTS-5 catabolic axis (81.9% and 66.2% protein reduction, respectively); and (iii) RANK/RANKL surface expression. EGCG also restored mitochondrial membrane potential and biomass to near-homeostatic levels. Crucially, small interfering RNA (siRNA)-mediated PAR-2 silencing reduced LPS-induced TNF-α by ~38% and substantially blunted EGCG's incremental efficacy, supporting PAR-2 as a predominant, though not exclusive, mediator of EGCG's anti-inflammatory action. The effective concentrations employed are physiologically attainable through dietary green tea consumption, as documented by a comprehensive survey of EGCG content across 36 commercial varieties. These findings support PAR-2 as a candidate upstream target of EGCG in OA chondrocytes and suggest a mechanistic model involving PAR-2 → ERK1/2 → TNF-α/SOX4/ADAMTS-5, through which a dietary polyphenol exerts coordinated anti-inflammatory and anti-catabolic effects, while preserving structural and thermodynamic markers of mitochondrial integrity.