Effects of cyclic tensile stress on biological function and degeneration of nucleus pulposus cells / 中华骨科杂志

ABSTRACT

Objective:To investigate the effects of cyclic tensile stress on the function and degeneration of nucleus pulposus cells.Methods:The human primary nucleus pulposus cells were isolated and cultured. The cyclic tensile stress (100 000 μ?, 10% tensile strain, 0.1 Hz, 8 640 cycles) was loaded on the cells for 24 h. The proliferation of the cells was examined by MTT method. The cell cycle and apoptosis were detected through flow cytometry. Gene expression profile chip was used to detect the differentially expressed genes between the tensile stress group and control group. The function of these gene was analyzed by bioinformatics. The expression of inflammatory related factors, TGF-β, matrix degrading enzymes and extracellular matrix molecules were examined by qRT-PCR.Results:The cyclic tensile stress significantly promoted proliferation and cell cycle of nucleus pulposus cells. The cell percentage of S phase ( t=5.336, P<0.05) and G2/M phase ( t=7.288, P<0.01) was significantly different between the tensile stress group and control group. The cyclic tensile stress inhibited apoptosis of nucleus pulposus cells (8.56%±0.48% vs 10.63%±0.32%, t=4.474, P<0.05). A total of 866 differentially expressed genes were detected. Gene ontology analysis showed the roles of these genes in cells including focal adhesion, extractable matrix, membrane raft, condensed chrome kinetochore, cytoskeleton, etc. The cyclic tensile stress significantly affected the mRNA expression of inflammatory related factors, TGF-β genes, matrix proteinase and extracellular matrix molecules. Compared with the control group, the mRNA expression of inflammatory related factors IL15 ( t=5.379, P<0.05), IGF1 ( t=5.454, P<0.05) and IGFBP7 ( t=13.57, P<0.01) were significantly decreased in the tensile stress group; The mRNA expression of TGF-β genes TGFB1 ( t=6.931, P<0.05), TGFB2 ( t= 15.56, P<0.01) and TGFB3 ( t=7.744, P<0.05) were significantly increased in the tensile stress group; The mRNA expression of matrix proteinase ADAMTS3 ( t=5.241, P<0.05) and MMP19 ( t=24.72, P<0.01) were significantly decreased, and TIMP3 ( t=8.472, P<0.01) increased in the tensile stress group; The mRNA expression of extracellular matrix molecules COL2A1 ( t=5.871, P<0.05), FLRT2 ( t=5.216, P<0.05) and FN1 ( t=4.289, P<0.05) were significantly increased. Conclusion:The cyclic tensile stress promoted cell cycle and proliferation and inhibited apoptosis of nucleus pulposus cells. The cyclic tensile stress may affect the function and degeneration of nucleus pulposus cells by regulating the expression of inflammatory related factors, TGF-β, matrix degradation enzymes and ECM molecules.