Expression of glucose transporters GLUT-1, GLUT-3, GLUT-9 and HIF-1alpha in normal and degenerate human intervertebral disc.

The glucose transporters GLUT-1 and GLUT-3 are targets of the hypoxia-inducible transcription factor HIF-1alpha and it has been shown that nucleus pulposus (NP) cells in rat intervertebral discs (IVD) express both HIF-1alpha and GLUT-1. However, there is limited data on the expression of HIF-1alpha and GLUTs in human IVD. The aim here was to (1) determine whether, like articular chondrocytes, human IVD cells express GLUT-1, 3 and 9 and whether there was any co-expression with HIF-1alpha; and (2) to localise expression of the GLUT isoforms in the disc and identify any changes during degeneration. Real-time PCR was used to identify expression of GLUT1, 3, 9 and HIF-1alpha mRNAs and immunohistochemistry was used to analyse protein expression and localisation of GLUTs in normal and degenerate IVD biopsies. Results confirmed HIF-1alpha, GLUT1, 3 and 9 mRNA expression in NP and AF and co-expression of each GLUT isoform with HIF-1alpha in the NP, but not the AF. Immunohistochemistry demonstrated regional differences in GLUT expression, with the highest expression being in the NP. GLUT expression also changed as degeneration progressed. This study demonstrates that NP and AF cells have different GLUT expression profiles that suggest regional differences in the metabolic nature of the human IVD and that this environment changes during degeneration.