Haem oxygenase-1 counteracts the effects of interleukin-1β on inflammatory and senescence markers in cartilage–subchondral bone explants from osteoarthritic patients

IL (interleukin)-1β plays an important role in cartilage extracellular matrix degradation and bone resorption in OA (osteoarthritis) through the induction of degradative enzymes and pro-inflammatory mediators. In the present study, we have determined the consequences of HO-1 (haem oxygenase-1) induction on markers of inflammation and senescence in the functional unit cartilage–subchondral bone stimulated with IL-1β. Cartilage–subchondral bone specimens were obtained from the knees of osteoarthritic patients. Treatment with the HO-1 inducer CoPP (cobalt protoporphyrin IX) counteracted the stimulatory effects of IL-1β on IL-6, nitrite, PGE₂ (prostaglandin E₂), TGF (transforming growth factor) β₂, TGFβ₃ and osteocalcin. Immunohistochemical analyses indicated that CoPP treatment of explants down-regulated iNOS (inducible nitric oxide synthase), COX-2 (cyclooxygenase-2) and mPGES-1 (microsomal prostaglandin E synthase-1) induced by IL-1β. In contrast, the expression of HMGB1 (high-mobility group box 1) was not significantly modified. In addition, CoPP decreased the expression of iNOS and mPGES-1 in cells isolated from the explants and stimulated with IL-1β, which was counteracted by an siRNA (small interfering RNA) specific for human HO-1. In isolated primary chondrocytes, we determined senescence-associated β-galactosidase activity and the expression of senescence markers by real-time PCR. We have found that HO-1 induction could regulate senescence markers in the presence of IL-1β and significantly affected telomerase expression, as well as β-galactosidase activity and hTERT (human telomerase reverse transcriptase) and p21 expression in chondrocytes. The findings of the present study support the view that HO-1 induction results in the down-regulation of inflammatory and senescence responses in OA articular tissues.