The Frequency Magnetic Field Inhibits The Migration Of U251 Cells By Inhibiting The Activity Of MMP-9

Electromagnetic field (EMF) is a physical field generated by the charged object. Electric changes and magnetic field generates and changes together to form a unified field. The electromagnetic wave is formed through the spatial propagation of the changed EMF. The electromagnetic waves can be arranged according to the wavelength or frequency of electromagnetic waves; and such spectrum is named the electromagnetic spectrum. From low to high frequencies there are: radio waves, infrared, visible light, ultraviolet, X-rays and y-rays. Recent years, with the wide application of different frequency electromagnetic waves, the global village has been in an increasingly complicated magnetic field circle. More and more attention has been taken on the health issues that magnetic field of the environment can lead to. The physiological effects of the EMF are dependent on both strength and length of the exposure. Strong EMF are considered to have a significant biological effect, however, no convincing data has showed the harmful effect of low level electromagnetic fields so far. The exposure limit of 50 Hz EMF is 0.5mT as indicated by International Commission on Non-Ionizing Radiation Protection (ICNIRP) in 2004. Though, there were some studies showed that EMF below 0.5mT could also cause certain biological effects.0.4mT weak EMF alone was capable of inducing the aggregation of epidermal growth factor receptor in vitro, while even lower intensity 0.2mT 50Hz EMF could cause actin cytoskeleton reorganization in human amnion fibroblast cells. Those biological effects are related to cell skeleton reorganization, which plays important role during cell migration and tumor metastasis. Especially the destruction of the actin bundles and focal adhesion of tumor cell is related to highly metastatic tumors. Therefore, our study focused on exploring the effect of 0.2mT and 0.4mT 50Hz EMF on tumor cell migration and the corresponding molecular mechanisms.In our experiments, we used both wound healing and Transwell chamber methods to detect the effect of 50Hz EMF on the migration of astrocytoma cells (U251). Our results revealed that the 50Hz EMF could inhibit the migration of U251 cells, and the inhibition effect was both time and intensity dependent.24 hours’ irradiation at 0.2mT significantly inhibited the migration of U251 cells. While 0.4mT EMF had stronger inhibition effect on cell migration than 0.2mT EMF when exposed at the same time 12 hours.We also detected the effect of magnetic fields on the expression of cell migration related proteins, such as ADAM 17, ERK and MMP-9. We found that 0.2mT magnetic field irradiation for lhour could significantly inhibit the activity of ADAM17 and increase the phosphorylation of ERK. Because the two processes had opposite effects on cell migration, there is no significant inhibitory effect on cell migration at 0.2mT magnetic field irradiation for lh. But 0.2mT magnetic field irradiation for longer hours had no effect on the activity of ADAM 17 and the phosphorylation of ERK. Even after application of PMA, which activated intracellular PKC (protein kinase C) pathway, the magnetic field still had a significant inhibition on cell migration which was time and doses dependent. The AD AM17 expression level and phosphorylation level of ERK were also not changed after long-term exposure. Those results indicated that the magnetic field inhibition effect on the U251 cell migration is not dependent on phosphorylation pathways within the cells. But with the PMA enlarging intracellular signaling,12 hours irradiation of 0.2mT magnetic field significantly inhibited the emission of intracellular MMP-9 while 0.4mT magnetic field had a stronger inhibition, which was the same inhibitory trend with the inhibitory trend of migration.Based on our results, we concluded that long irradiation time of 50Hz EMF could inhibit cell migration mediated by inhibiting the expression of MMP-9 in the cells.