Effect of HIF-1α on ATP production and glycolysis in human articular cartilage. (a)Hypoxia-inducible factor 1α (HIF-1α) depletion by antisense oligonucleotide was assessed by RT-PCR and western blotting analyses. HIF-1α mRNA and protein expressions were reduced in antisense HIF-1α-treated chondrocyte populations. Scrambled oligonucleotide was used as control oligonucleotide. Representative data from four independent experiments are shown. (b)In hypoxia, HIF-1α-deficient chondrocytes showed a significant decrease of free ATP in comparison with control oligonucleotide-treated chondrocytes. Statistical differences were calculated using data from four independent experiments. (c, d) The levels of lactate (c) and glucose transporter-1 (Glu-1) (d) were increased in the scrambled ODN-treated chondrocytes under hypoxic culture conditions compared with normoxic culture condition. In HIF-1α-deficient chondrocytes, both glycolytic activities were reduced under hypoxic conditions. Statistical differences were calculated using data from four independent experiments. aP < 0.01, control oligonucleotide hypoxia vs HIF-1α-deficient hypoxia; *P < 0.05, **P < 0.01.