Catabolic factors induce the expression of HIF-1α protein in human articular cartilage. (a)Hypoxia-inducible factor 1α (HIF-1α) protein was accelerated by IL-1β or H2O2in cultured chondrocytes under hypoxic conditions. (b)Under hypoxic conditions, the inhibitors of PI3K and p38 mitogen-activated protein kinase (MAPK) reduced protein levels of IL-1β-induced HIF-1α expression. Cobalt chloride (CoCl2), chemical inducer of HIF-1, was used for the positive control. *P < 0.05, **P < 0.01 compared with the control. LY294002: phosphatidylinositol 3-kinase inhibitor; SB203580: p38 mitogen-activated protein kinase inhibitor; PD98059: extracellular signal-regulated kinase inhibitor.