Apoptosis induction in HIF-1α-deficient chondrocytes. IL-1β was used for apoptosis induction under hypoxic or normoxic conditions in chondrocytes lacking hypoxia-inducible factor 1α (HIF-1α), treated with oligonucleotide, and cultured without oligonucleotide, and also not exposed to the oligonucleotide or HIF-1α antisense nucleotides. IL-1β-induced apoptosis was significantly increased in HIF-1α-deficient chondrocytes compared with chondrocytes treated with scrambled oligonucleotide under both normoxic and hypoxic culture conditions. Statistical differences were calculated using data from four independent experiments. **P < 0.01, control oligonucleotide group vs HIF-1α-antisense group.