Activation of osteoarthritic synoviocytes by pro-inflammatory cytokines results in the release of biochemical mediators such as MMPs and high mobility group box 1 (HMGB1). Extracellular HMGB1 can play an important role in joint diseases as a mediator of synovitis. We have shown previously that haem oxygenase-1 (HO-1) exerts protective effects during inflammatory responses. In this study, we have examined whether HO-1 induction would be an effective strategy to control MMP and HMGB1 production in osteoarthritic synoviocytes.
Osteoarthritic synoviocytes were obtained by digestion with collagenase and cultured until third passage. HO-1 was induced by cobalt protoporphyrin IX (CoPP). Lentiviral HO-1 vector (LV-HO-1) was also used for HO-1 overexpression. HO-1 gene silencing was achieved by using a specific small interfering RNA. Gene expression was analysed by quantitative PCR and protein expression by western blot, ELISA and IF. MMP activity was studied by fluorometric procedures.
Induction of HO-1 by CoPP in the presence of IL-1beta decreased the expression of MMP-1 and -3, and MMP activity. IL-1beta stimulation of synoviocytes increased HMGB1 expression, its translocation into the cytoplasm and secretion. HO-1 induction exerted inhibitory effects on these processes. The consequences of HO-1 induction were counteracted by HO-1 gene silencing, whereas transfection with LV-HO-1 confirmed the effects of pharmacological HO-1 induction.
We have provided direct evidence that HO-1 down-regulates MMP-1, -3 and HMGB1 in osteoarthritic synoviocytes. HO-1 may be a potential strategy to control inflammatory and degradative processes in the progression of OA.