The Effects Of Electromagnetic Fields Exposure On DNA Damage And Cellular Functionsin Neurogenic Cells

The nervous system is sensitive to different environmental stimulus, and has been considered as a target system of environmental electromagnetic fields (EMF) exposure (e.g., mobile phone radiation). Based on limited epidemiological studies, the International Agency for Research on Cancer (IARC) classified extremely low frequency magnetic fields (ELF-MF) and radiofrequency EMF (RF-EMF), two common environmental EMF, as possible carcinogens to human, however, these declarations are lack of laboratory evidence. A large number of in vitro studies have been conducted to investigate EMF exposure induced biological effects, including cellular functions, e.g., cell proliferation/apoptosis, cell cycle progression and cell differentiation, genotoxicity, gene/protein expression and secretion of cytokine, in neurogenic cells, but the results are mostly inconsistent or controversial, and the mechanisms of EMF induced biological effects are unclear. Two major reasons may account for this situation. Firstly, the cellular response to EMF exposure might be different, but most of previous studies were conducted only in one cell model from nervous system. Secondly, different EMF exposure systems and exposure parameters used in previous studies gave rise to the incomparability of results. Thus, it is critical to adopt standardized EMF expose systems and systematically investigate EMF induced biological effects, e.g., genotoxicity and abnormal cellular functions, in different neurogenic cells.In the present study, we proposed a systematic research to evaluate the effects of EMF exposure on DNA damage and cellular functions in both neurogenic tumor cell lines (U251, A172 and SH-SY5Y) and primary cultured neruogenic cells from rats, including microglia cells, astrocytes and cortical neurons. The cells were exposed to 50 Hz MF or 1800 MHz RF-EMF in the internationally recognized ELF-EMF or RF-EMF exposure system respectively. To evaluate the effects of EMF exposure on DNA damage, we firstly examined the yH2AX foci formation in six different types of neurogenic cells after 50 Hz MF or 1800 MHz RF-EMF exposure. Since the neurogenic tumor cells are proliferative, we assessed the effects of 50 Hz MF or 1800 MHz RF-EMF exposure on cell cycle progression, cell proliferation and cell viability in U251, A172 and SH-SY5Y cells. To determine if EMF exposure can affect the cellular functions in primary cultured neurogenic cells, we investigated the effects of 50 Hz MF or 1800 MHz RF-EMF on cytokines secretion of primary cultured rat astrocytes, phagocytic activity and cytokines secretion of primary cultured rat microglia cells, and morphological development of axon and dendrites and the synapse density in primary cultured rat cortical neurons.The results showed that exposure to 50 Hz MF at 1.0 mT or 2.0 mT for 1 h,6 h, or 24 h did not induce significant changes of yH2AX foci formation in six different types of cells from nervous system. Exposure to 2.0 mT of 50 Hz MF for 24 h did not affect cell cycle progression, cell proliferation and cell viability in U251, A172 and SH-SY5Y cells. Furthermore, exposure to 2.0 mT of 50 Hz MF for 24 h did not significantly influence secretion of TNF-a, IL-6 and IL-1β in primary cultured rat astrocytes. The exposure did not significant activate phagocytic activity and secretion of cytokines TNF-a, IL-6 and IL-1β in primary cultured rat microglia cells. For primary cultured rat cortical neurons, the exposure did not change the length of axon and number of axon branches, the length and number of dendrites and their branches, and the density of excitatory and inhibitory synapses.As to RF-EMF, we found that exposure to 1800 MHz RF-EMF at a special absorption rate (SAR) of 4.0 W/kg for 1 h,6 h, or 24 h did not result in changes of yH2AX foci formation in these six types of neurogenic cells. Exposure to 1800 MHz RF-EMF at a SAR of 4.0 W/kg for 24 h did not affect cell cycle progression, cell proliferation and cell viability in U251, A172 and SH-SY5Y cells. The exposure did not influence secretion of TNF-a, IL-6 and IL-1β in primary cultured rat astrocytes either. Interestingly, exposure to RF-EMF at a SAR of 4.0 W/kg for 24 h significantly decreased phagocytic activity of primary cultured rat microglia cells, but not affected secretion of TNF-a, IL-6 and IL-1β in the cells. In addition, exposure to RF-EMF significantly decreased the length of primary dendrites, while the exposure did not influence other index of morphological development of axon and dendrites, and the synapse density in primary cultured rat cortical neurons.In conclusion, the present study showed that exposure to 50 Hz MF or 1800 MHz RF-EMF was unlikely to elicit a genotoxic effect in six different types of cells from nervous system under the current experimental conditions, and the exposure did not result in abnormal cellular behaviors in three neurogenic tumor cell lines. Exposure to 50 Hz MF or 1800 MHz RF-EMF did not affect secretion of TNF-α, IL-6 and IL-1β in primary cultured rat astrocytes and microglia cells. Exposure to 1800 MHz RF-EMF significantly inhibited phagocytic activity of primary cultured rat microglia cells and decreased primary dendrite length of primary cultured rat cortical neurons, while these primary cultured cells did not respond to 50 Hz MF exposure.To the best of our knowledge, this study for the first time reports that exposure to 1800 MHz RF-EMF but not 50 Hz MF significantly decreases microglial phagocytosis and influences neuronal morphology during the early stages of development. Our data suggest the responses of primary cultured neurogenic cells to EMF exposure may be frequency-dependent.