Abstract: Objective To investigate the effect of hypoxia on the proliferation of nucleus pulposus-derived mesenchymal stem cell (NPMSC) in vitro and explore its possible mechanism．Methods NPMSC was isolated from nucleus pulposus of Sprague-Dawley rats. Cellular morphology was observed and expression of CD11b, CD45, CD73, CD90 and CD105 was detected using flow cytometry. The third generation NPMSC was cultured under normoxia (20% O2) and hypoxia (2% O2) for 14 days. Cell viability was determined by the annexin-V-FITC/propidium iodide doublestaining assay and cell proliferation was measured by MTT assay. The expression of hypoxia-inducible factor-1α(HIF-1α), glucose transporter 1(GLUT-1), vascular endothelial growth factor (VEGF), silent information regulator protein 1(SIRT1) and silent information regulator protein 6 (SIRT6) at the mRNA level were examined by semi-quantitative reverse transcription polymerase chain reaction(RT-qPCR)．Results NPMSC could form sunflower-like colonies and the third passage NPMSC became homogeneous and exhibited spindle-like morphology. Meanwhile, high expression levels of stem cell-related positive antigen molecules and low expression levels of negative antigen molecules. Hypoxia promoted proliferation of NPMSC and promoted gene expression of HIF-1α, GLUT-1, VEGF, SIRT1 and SIRT6 significantly(P＜0.05). Conclusions Hypoxia had a significant impact on the proliferation of NPMSC, and the SIRT1 and SIRT6 mediated HIF-1α pathway might be involved in the mechanism．

Key words: nucleus pulposus mesenchymal stem cells, hypoxia, proliferation, HIF-1α, silent information regulator protein