The nucleus pulposus is an aggrecan-rich, avascular tissue that permits the 
intervertebral disk to resist compressive loads. In the disk, nucleus pulposus 
cells express hypoxia-inducible factor (HIF)-1alpha, a transcription factor that 
responds to oxygen tension and regulates glycolysis. The goal of the present 
study was to examine the importance of HIF-1alpha in rat nucleus pulposus cells 
and to probe the function of this transcription factor in terms of regulating 
aggrecan gene expression. We found that HIF-1alpha protein levels and mRNA 
stability were similar at 20 and 2% O(2); there was a small, but significant 
increase in HIF-1alpha transactivation domain activity in hypoxia. With respect 
to HIF-1alpha target genes GAPDH, GLUT-1, and GLUT-3, mRNA and protein levels 
were independent of the oxygen tension. Other than a modest increase in 
6-phosphofructo-2-kinase/fructose-2,6-biphosphatase reporter activity, the 
oxemic state did not change GAPDH, GLUT-1, and GLUT-3 promoter activities. 
Treatment of cells with 2-deoxyglucose (2-DG), a glycolytic inhibitor, resulted 
in a significant suppression in ATP synthesis in normoxia, whereas treatment 
with mitochondrial inhibitors did not affect ATP production and cell viability. 
However, measurement of the rate of fatty acid oxidation indicated that these 
cells contained functioning mitochondria. Finally, we showed that when 
HIF-1alpha was suppressed, irrespective of the oxemic state, there was a partial 
loss of aggrecan expression and promoter activity. Moreover, when cells were 
treated with 2-DG, there was inhibition in aggrecan promoter activity. Results 
of this study indicate that oxygen-independent stabilization of HIF-1alpha in 
nucleus pulposus cells is a metabolic adaptation that drives glycolysis and 
aggrecan expression.