The Effects Of Electromagnetic Field Exposure On Embryonic Lens Development And Lens Epithelial Cells

Debate on the adverse health effects of power-frequency (50/60 Hz) electric and magnetic fields (EMF) was triggered by an epidemiological study in 1979. With the increase of occupational exposure to power-frequency magnetic fields and general exposure to sources such as electric power lines or electric appliances, more attention has been paid to the related biological effects, both in vitro and in vivo.Concern has been expressed about the possible adverse effects of exposure to power-frequency EMF on the development of the embryo and foetus. A number of epidemiological studies have reported pregnancy outcomes from exposure to power-frequency EMF, including spontaneous abortion, lowered birth weight, select central nervous system defects, cardiac and respiratory system defects, increased risk of clubfoot, altered sex ratio, etc. Some studies do not support the positive association. Because the results of epidemiological studies are inconclusive, further experimental or mechanistic studies have been recommended.The lens is a polarized tissue derived from one cell type, with epithelial (precursor) cells covering the anterior hemisphere and terminally differentiated lens fiber cells occupying the posterior surface and the interior. This specificity and remarkable transparency make it vulnerable to damage by radiation and be the focus of many research programs. With the increase of occupational and general exposure to power-frequency magnetic fields, we wanted to detect the biological effects of power-frequency EMF on lens development which had not been investigated by systematic studies. The growing public concerns about the possible health effects of exposure to radio frequency (RF) fields from mobile telephones have arisen in many countries because of the increased use of mobile telecommunication devices. This in turn has led to an increase in epidemiological and experimental investigations. However, the results from epidemiological or basic experimental studies are conflicting. Some have indicated an increased risk, but most studies have shown no effects.The lens epithelial cell is a single layer of cuboidal cells at the anterior surface of the lens which retains a proliferative capacity throughout its lifespan and is important for maintaining metabolic homeostasis and transparency. Damage to lens epithelial cells (LECs) has been found to be associated with cataractogenesis. In our research group, exposure of human LECs to 1.8 GHz RF has been found to result in repairable DNA damage and increased heat shock protein (HSP)70 protein expression, and we have also pointed out the effect of 2.45 GHz RF exposure on rabbit LECs.HSPs are one family of stress-activated proteins that participate in the protein folding, repair, and degeneration which characterize the cellular responses to various types of stresses, such as changes in pH, heavy metal, and sudden temperature increases. The main function of these adenosine triphosphate (ATP)-dependent proteins is to chaperone and assist in protein folding. They also participate in the activation of glucocorticoid receptors, polymerization of actin, and transfer of proteins to lysosomes. HSPs help to prevent apoptosis after a shocking stimulus, providing time for the repair mechanisms to act.Mitogen-activated protein kinases (MAPKs) mediate the response of cells to a wide variety of physiological and stress-related stimuli, including ultraviolet light, heat shock, ischemia, and oxygen free radicals, for example. Studies have provided evidence that the induction of the MAPK pathway plays significant roles in the activation of specific HSPs. It has been proposed that activation of c-Jun N-terminal kinases (JNKs) and p38 MAP kinases contributes to cell death, whereas activation of extracellular signal-regulated kinases (ERKs) contributes to protection against cell injury in multiple organs.In the present study, we investigated whether 1.8 GHz RF exposure of human LECs activates HSP90, HSP70, and HSP27 in vitro. Subsequently, to gain insight into the cell signaling pathway in human LECs following 1.8 GHz magnetic fields exposure, we studied the behavior of the MAPKs family.Part I The Effect of power-frequency magnetic fields exposure on mouse embryoniclens developmentObjectiveThere are no reports in the literature investigating the biological effect of power-frequency (50/60 Hz) magnetic fields on embryonic lens development. We investigated whether power-frequency magnetic fields act as an environmental insult and induce changes in morphology or protein and/or transcription factor mRNA expression levels in developing mouse embryonic lenses.MethodsThree groups of pregnant mice were exposed to magnetic fields (60 Hz) of varying intensities (0.0, 1.5 and 4.5 mT) for 3 hours per day from Gestation Day (GD) 0 to 18. The embryonic lenses were enucleated on GD 18, the transparence of lenses and the ultrastructure of lens epithelial cells (LECs) were observed. The remaining lenses were examined for quantity of water soluble protein (WSP) and water insoluble protein (WIP), ratio of WIP to total protein, and mRNA expression levels of four major developmentally regulated DNA-binding transcription factors- Pax6, Prox1, Sox1, and c-maf.ResultsThe lenses in three groups were shown transparent and the LECs from experimental groups were in normal ultrastructure as control. No significant differences were found among three groups in quantity of WSP, WIP, ratio of WIP to total protein, and mRNA expression levels of Pax6, Prox1, Sox1, and c-maf. We preserved one pregnant mouse per group, fed the neonatal mice until 2 weeks of age, and then found the lenses transparent.ConclusionsOur results did not detect any effects on the development of embryonic lenses in mice exposed to power-frequency magnetic fields. Part II The Effects of 1.8 GHz Radiofrequency Field Exposure on the Expression of HSP and Phosphorylation of MAPKs in Human Lens Epithelial CellsObjectiveTo investigate the expression of heat shock protein (HSP) and the activation of mitogen-activated protein kinases (MAPKs) of human lens epithelial cells (LECs) after exposure to the 1.8GHz radiofrequency field (RF) of a global system for mobile communications (GSM).MethodsImmediately after 2 hour exposure to RF at a specific absorption rate (SAR) 1, 2, 3, 4 W/kg, the expression of HSP27, HSP70 and HSP90 was evaluated by Western-blot. Based on the results of HSP expression, the activation of MAPKs was detected after exposure to RF at SAR 2,3,4 W/kg for 0,5,15,30,60,120 minutes by Western-blot.ResultsHSP27 and HSP70 protein expression but not HSP90 increased significantly after exposure at a SAR of 2, 3, 4 W/kg for 2 hours (P<0.05), and there were no significant differences in HSP27 and HSP70 expression among cells exposed at SAR 2, 3, 4 W/kg (P>0.05). The results show that ERK1/2 was markedly activated as early as 5 min after RF exposure, peaked at 30 min and lasted up to 2 h after exposure at SAR 2, 3, 4 W/kg. Phosphorylation of JNK1/2 was detected at 2 hours after exposure at SAR 2, 3, 4 W/kg. P38 MAPK was not activated.ConclusionsThe results suggest that non-thermal exposure of RF for wireless communications can induce increased HSP27 and HSP70 protein expression, and the activation of ERK1/2 and JNK1/2 in human LECs.