INTRODUCTION: The nucleus pulposus (NP) is an aggrecan‐rich, avascular tissue. Aggrecan is major extracellular matrix which permits the intervertebral disc(IVD) to withstand compressive loads. Hypoxia‐inducible factor (HIF‐1¥á) and glucose transporter‐1 (GLUT‐1) appear to be excellent marker for avascular tissue such as cartilage and IVD. GLUT‐1 expression is also stimulated in a variety of cells under hypoxic condition, a response that is mediated by the transcription factor HIF‐1¥á. Therefore, the goal of the study is to examine the importance of stabilization of HIF‐1‐¥á in human IVD under hypoxic condition.
METHODS: IVD from lumbar spine with disc degeneration were harvested and cultured. To induce hypoxic environment, IVD cells were treated with various dose of deferoxamine mesylate(DFO) and cultured for 1, 3days. Proliferation was assessed by alamarblue assay. Reverse transcription‐polymerase chain reaction (RT‐PCR) for the expression of HIF‐1¥á, aggrecan and GLUT‐1 was performed. Newly synthesized proteoglycan was measured by incorporation of [35S] sulfate.
RESULTS: The expressions of HIF‐1¥á and GLUT‐1 are confined only to NP and transitional zone not annulus fibrosus and endplate, which support that HIF‐1¥á and GLUT‐1 are a phenotypical signature of NP. The results demonstrated increase expression of aggrecan and GLUT‐1 mRNA in response to DFO dose‐dependently. NP cell cultures with DFO showed increase in newly proteoglycan synthesis compared to control.
DISCUSSION: Chemically induced hypoxic condition by DFO rendered increase in aggrecan and GLUT‐1 mRNA expression which also provided phenotypical stabilization under the hypoxic condition. With given dose of DFO there was increase in newly synthesized proteoglycan content, which signifies the role of hypoxia in matrix metabolism of avascular IVD tissue. In conclusion, controlled hypoxic condition provided suitable environment for IVD cell metabolism in terms of matrix synthesis and phenotypical stability.