Effects of Mechanical Vibration on Proliferation and Differentiation of Neural Stem Cells

Neural stem cells have been studied to promote neurogenesis in regenerative therapy. The control of differentiation of neural stem cells to nerve cells and the increase of the number of nerve cells are needed. For the purpose of them, it is important to investigate not only chemical factors but also mechanical factors such as hydrostatic pressure in brain and mechanical vibration in walking. In this study, sinusoidal inertia force was applied to cultured neural stem cells and the effects of mechanical vibration on the cells were investigated. After the cells were cultured in culture plates for one day and adhered on the cultured plane, vibrating group of the culture plates was set on an aluminum plate attached to an exciter and cultured under sinusoidal excitation for 24 hours a day during 26 days. The amplitude of the acceleration on the culture plate was set to 0.25 G and the frequency was set to 25 Hz. The time evolution of cell density was obtained by counting the number of cells at every 3 or 4 days. The expression of Akt, phosphorylated Akt (p-Akt), MAPK, and phosphorylated MAPK (p-MAPK) was detected by western blotting analysis at 7 days of culture to understand the mechanism of cell proliferation. Akt and MAPK are part of signaling pathways in relation to cell proliferation. The phosphorylation of Akt suppresses apoptosis and the phosphorylation of MAPK activates cell division. The gene expression of MAP-2, NFH, GFAP, and nestin was detected by real-time RT-PCR analysis at 7 days of culture to obtain a ratio of differentiation of neural stem cells to nerve or glia cells. MAP-2 and NFH are nerve cell markers, GFAP is a glia cell marker, and nestin is a stem cell marker. The results obtained are as follows. The cell density of the vibrating group was three times higher than that of the non-vibrating group at 26 days of culture. p-Akt was enhanced by the mechanical vibration while p-MAPK was not. There is no significant difference of the gene expression level of MAP-2, NFH, GFAP, and nestin between the vibrating and non-vibrating groups. These results suggest that the mechanical vibration promotes the proliferation of neural stem cells and its cause is likely the suppression of apoptosis but not the activation of cell division, and that the mechanical vibration at the experimental condition does not affect the differentiation of neural stem cells to nerve or glia cells.