| Extremely-low frequency electromagnetic fields (ELF-EMF) generally refers to EMF with frequency ranging from 0 to 300 Hz. Particularly, the magnetic fields (MF) with a frequency of 50/60 Hz is also called power frequency MF emitted from household appliances and power transmission lines, existing profusely in the public and occupational environments. Since Wertheimer and Leeper reported a risk of childhood leukemia correlated to electrical wiring configurations in houses in 1979, the possible biological effects of ELF-EMF on human health have become a public concern. After that, a number of studies have reported that ELF-EMF exposure could increase the risk to develop certain diseases such as cancers, nervous system diseases, infertility, and so on. However, up to now, the biological mechanism underlying the effects of ELF-EMF is still unclear.Mitochondria, as the energy factories of cell, can not only generate reactive oxygen species (ROS) but also balance ion concentration. Thus, it is likely for mitochondria to be a target of external stimuli. Our previous study found that MF exposure could induce cytochrome c (Cyt-c) releasing into cytoplasm followed mitochondrial permeability transition (MPT), while cell apoptosis was not affected. Mitochondria have two membranes, the inner membrane and the outer membrane. Physically, the inner membrane is highly impermeable to almost any molecules even protons. When mitochondrial permeability transition pores (mPTP) open in certain conditions, the permeability of inner membrane suddenly increases to solutes with a mass less than 1500 Da. This process might induce swelling of mitochondrial matrix and lead to a series of biological effects.Recent research showed that numerous cellular molecules could mediate mPTP opening, such as Bcl-2 family, GSK-3β, ROS,and so on. Up to now, ROS is a relatively definite target for ELF-MF. So, the mechanism of MPT induced by MF exposure was firstly explored in the thesis. Results indicated that MF exposure significantly increased ROS production and changed GSK-3β (Ser9) phosphorylation state, but not affecting Bcl-2 or Bax. Additionally, pretreatment with ROS scavenger (NAC) or GSK-3β inhibitor (SB216763)effectively inhibited MF-induced MPT, and NAC pretreatment prevented GSK-3β (Ser9) phosphorylation and dephosphorylation. The results suggested that MF-induced MPT was mediated through the ROS/GSK-3β signaling pathway.On the other hand, FL cells did not undergo apoptosis despite induction of MPT and release of Cyt-c after MF exposure. It was presumed that MF exposure might change the state of cells and further affect cellular response for other stimuli. Therefore, the possible combined effects of MF and staurosporine (STS) were investigated. The results demonstrated that MF exposure attenuated early apoptosis induced by staurosporine with time and intensity windows. Pretreatment with MPT inhibitors abrogated this anti-apoptotic effect, indicating that MPT might play an important role in this process. It was reported that mitochondrial ROS is usually released into cytoplasm through mPTP and subsequently activates certain signaling pathways when MPT occurs. We found here, MF exposure could enhance mitochondrial ROS releasing into cytoplasm through mPTP and activate Akt. PI3K/Akt inhibitor prevented MF-induced anti-apoptotic effect. Taken together, these results indicated that mitochondrial ROS releasing through mPTP and subsequent Akt activation were necessary for the anti-apoptotic effect of MF.In summary, this master dissertation uncovered the role of ROS/GSK-3(3 signaling pathway in MF-induced MPT and the role of MF-induced MPT against apoptotic effect caused by STS. |
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