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

IL (interleukin)-1 beta plays an important role in cartilage extracellular matrix degradation and bone resorption in OA (osteoarthritis) through the induction of degradative enzymes and proinflammatory 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-1 beta. 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-1 beta on IL-6, nitrite, PGE(2) (prostaglandin E-2), TGF (transforming growth factor) beta(2), TGF beta(3) 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-1 beta. In contrast, the expression of HMGB I (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-1 beta, which was counteracted by an siRNA (small interfering RNA) specific for human HO-I. In isolated primary chondrocytes, we determined senescence-associated beta-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-1 beta and significantly affected telomerase expression, as well as beta-galactosidase activity and hTERT (human telomerase reverse transcriptase) and p2I 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.