IMPACT OF ELECTROMAGNETIC FIELDS EMITTED BY NUCLEAR MAGNETIC RESONANCE DEVICES ON HIPPOCAMPAL NEURAL STEM CELLS

Experimental evidence suggests that electromagnetic fields (EMFs) markedly affect the biology of different cell types, including stem cells. Our previous studies showed that extremely low-frequency (50 Hz) EMFs promote proliferation of rodent neural stem cells (NSCs) and their neuronal differentiation both in vitro and in vivo via epigenetic mechanisms leading to pro-neuronal gene expression (Piacentini et al., 2008; Cuccurazzu et al., 2010; Podda et al., 2014; Leone et al., 2014). The present study was aimed at determining the effects of in vitro exposure to EMFs emitted by nuclear magnetic resonance (NMR) devices on NSCs with the final goal to identify novel stimuli affecting the neurogenic process and, more importantly, to evaluate potential risks for the health of exposed hospital workers. First, we measured exposure to EMFs of staff working in NMR units to subsequently stimulate in vitro cultures of NSCs through an experimental device reproducing the same sequence of stimuli experienced by workers. NSCs isolated from the hippocampi of newborn mice were subjected to 6 or 72 h EMF stimulation. The expression of genes involved in NSC proliferation (Hes1 and TLX) and their fate determination (Mash1, NeuroD1) was assessed by Real Time RT-qPCR. At the protein level, Western immunoblot analysis assessed the expression of Hes1, as a marker of stemness and NSC proliferation, doublecortin (DCX) and NeuroD1 as markers of commitment to the neuronal lineage. Methyl-CpG-binding domain protein 1 (MBD1) expression at mRNA and protein levels was also quantified as index of DNA methylation. In differentiating NSCs exposed to EMFs for 6 h the levels of Hes1 and TLX mRNAs were significantly higher than those observed in sham-exposed control cells, suggesting that EMFs promoted the persistence of proliferation status. Accordingly, 6-h exposure to EMFs prevented the up-regulation of the determination gene Mash1 whose mRNA levels were comparable to those observed in proliferative condition even after 72 h exposure to EMFs. The pattern of NeuroD1 expression was seemingly inhibited by EMF exposure at both 6 and 72 h. Furthermore, Western blot analysis revealed decreased expression of DCX in differentiating NSCs following 72 h of exposure. With regard to possible mechanism underlying EMF-induced modulation of gene expression, we found that MBD1 mRNA levels were significantly increased after 6 h exposure to EMFs thus suggesting the involvement of DNA methylation as epigenetic modification leading to the repression of neuronal determination genes. Collectively, our findings suggest that EMF stimulation protocols reproducing EMFs emitted by NMR devices promote NSC proliferation while inhibiting their differentiation towards the neuronal phenotype