Comparison of the effects of oxidative and inflammatory stresses on rat chondrocyte senescence.

Osteoarthritis (OA) is an age-related degenerative joint disease that causes progressive cartilage loss. Chondrocyte senescence is a fundamental mechanism that contributes to the imbalance of matrix homeostasis in OA by inducing senescence-associated secretory phenotype (SASP). Although OA chondrocytes are mainly exposed to oxidative and inflammatory stresses, the role of these individual stresses in chondrocyte senescence remains unclear. In this study, we compared the effects of these stresses on the senescence of rat chondrocytes. Rat chondrocytes were treated with HO and a combination of IL-1β and TNF-α (IL/TNF) to compare their in vitro effect on senescent phenotypes. For in vivo evaluation, HO and IL/TNF were injected into rat knee joints for 4 weeks. The in vitro results showed that HO treatment increased reactive oxygen species, γ-H2AX, and p21 levels, stopped cell proliferation, and decreased glycosaminoglycan (GAG)-producing ability. In contrast, IL/TNF increased the expression of p16 and SASP factors, resulting in increased GAG degradation. Intraarticular injections of HO did not cause any changes in senescent markers; however, IL/TNF injections reduced safranin O staining and increased the proportion of p16- and SASP factor-positive chondrocytes. Our results indicate that oxidative and inflammatory stresses have significantly different effects on the senescence of rat chondrocytes.