Fifty-Hertz Magnetic Field Affects the Epigenetic Modulation of the miR-34b/c in Neuronal Cells

Abstract

The exposure to extremely low-frequency magnetic fields (ELF-MFs) has been associated to increased risk of neurodegenerative diseases, although the underlying molecular mechanisms are still undefined. Since epigenetic modulation has been recently encountered among the key events leading to neuronal degeneration, we here aimed at assessing if the control of gene expression mediated by miRNAs, namely miRs-34, has any roles in driving neuronal cell response to 50-Hz (1 mT) magnetic field in vitro. We demonstrate that ELF-MFs drive an early reduction of the expression level of miR-34b and miR-34c in SH-SY5Y human neuroblastoma cells, as well as in mouse primary cortical neurons, by affecting the transcription of the common pri-miR-34. This modulation is not p53 dependent, but attributable to the hyper-methylation of the CpG island mapping within the miR-34b/c promoter. Incubation with N-acetyl-l-cysteine or glutathione ethyl-ester fails to restore miR-34b/c expression, suggesting that miRs-34 are not responsive to ELF-MF-induced oxidative stress. By contrast, we show that miRs-34 control reactive oxygen species production and affect mitochondrial oxidative stress triggered by ELF-MFs, likely by modulating mitochondria-related miR-34 targets identified by in silico analysis. We finally demonstrate that ELF-MFs alter the expression of the α-synuclein, which is specifically stimulated upon ELF-MFs exposure via both direct miR-34 targeting and oxidative stress. Altogether, our data highlight the potential of the ELF-MFs to tune redox homeostasis and epigenetic control of gene expression in vitro and shed light on the possible mechanism(s) producing detrimental effects and predisposing neurons to degeneration.

50‐Hz MF does not affect global DNA methylation of SH‐SY5Y cells treated with the neurotoxin MPP+

“…SH‐SY5Y neuroblastoma cells can be differentiated toward a dopaminergic phenotype when administered with RA‐PMA, as previously characterized [Benassi et al, ; Consales et al, ]. As shown in Figure , all the sequences analyzed in differentiated SH‐SY5Y cells showed a strong statistically significant difference in the 5‐mC percentage compared to the proliferating counterpart.…”

“…The extent of global DNA methylation and its possible changes do not necessarily overlap with DNA methylation changes occurring at gene‐specific promoters [Sharma et al, ; Öner et al, ]. Indeed, we recently reported that ELF‐MFs (applied to both proliferating and differentiated SH‐SY5Y under the same experimental conditions used in this study) trigger hypermethylation of the miR‐34b/c promoter [Consales et al, ].…”

“…At 60–70% confluence, cells were subcultured and differentiated into a dopaminergic phenotype with 5 µM RA for the first 3 days, followed by 80 nM PMA for 3 more days in reduced serum condition (5%). The dose of 5 µM RA was selected in the range between 1 and 10 µM, as it allowed a detectable expression of dopamine transporter and tyrosine hydroxylase without severely affecting cell viability [Benassi et al, ; Consales et al, ].…”

“…The ELF‐MF exposure system consisted of two pairs of square coils (two coils for each sub‐system, arranged coaxially in Helmholtz configuration), as previously characterized and detailed [Benassi et al, ; Consales et al, ]. Briefly, the coils were connected to a Variac (40NC; Ing.…”

Extremely low frequency magnetic field induces human neuronal differentiation through NMDA receptor activation

“…Furthermore, these effects appear under exposure to much weaker magnetic fields, on the level of several milliTeslas (mT) which present no cytotoxic or genotoxic effects (Boorman et al 1997;Pettenati et al 2018). There is already growing concern about the effects of exposure to ELF MFs as epidemiological (Davanipour et al 2007;Zhou et al 2012) and experimental (Consales et al 2012(Consales et al , 2018 findings point to possible associations with neurodegenerative diseases. However, efforts are being made to identify useful effects under controlled exposure conditions.…”