To investigate whether a 50 Hz magnetic field alters epigenetic processes, especially expression of miRNA 34b and 34c, in human neuroblastoma cells and mouse primary cortical cells in vitro.
Extremely low frequency magnetic fields have been associated with the onset of neurodegenerative diseases (see also "info text about neurodegenerative diseases" in the EMF-Portal).
MicroRNAs (miRNA) are small, non-coding RNA molecules, which play a critical role in gene regulation. To examine whether these miRNAs induce molecular changes, mimicking molecules were partially added to the cells (miR-34b/c mimic molecules).
Human neuroblastoma cells were examined during proliferation and in a post-mitotic stage.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
continuous for 4-72 hours
|
|
|
Exposure 2:
50 Hz
Exposure duration:
continuous for 4-72 hours
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | continuous for 4-72 hours |
| Additional info | human neuroblastoma cells |
| Exposure source | |
|---|---|
| Chamber | exposure/sham exposure in 60 mm petri dishes |
| Setup | exposure system consisted of two pairs of square coils (two coils for each sub-system, arranged coaxially in Helmholtz configuration); two systems were used for exposure and sham exposure at the same time, thus allowing blind experimental conditions; current was 3.4 A for the desired magnetic flux density; homogeneity of the magnetic field was 95%; temperature was controlled and kept constant at 37°C ± 0.2°C |
| Sham exposure | A sham exposure was conducted. |
| Additional info | a coil double wire configuration was used for sham exposure implementation, which allows to obtain a null MF by using currents flowing in opposite directions; background magnetic field of the incubator was 0.3 µT |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | measured | - | - |
| Chamber | exposure/sham exposure in 24 well plates |
|---|---|
| Setup | same as exposure 1 |
| Sham exposure | A sham exposure was conducted. |
| Additional info | same as exposure 1 |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | - | - | - |
The expression of the miRNAs miR-34b/c was significantly decreased in exposed proliferating and post-mitotic neuroblastoma cells as well as in primary cortical neurons compared to sham exposed cells. Additionally, the expression level of btg4 was significantly reduced in exposed neuroblastoma cells compared to the corresponding sham exposure, but not in primary cortical neurons. The observed miRNA changes did not depend on p53, because no significant alterations of the p53 expression level which correlated with the miRNA changes were found. However, the DNA methylation level was significantly increased within the miR-34b/c promoter of exposed neuroblastoma cells compared to sham exposed ones.
The levels of superoxide and hydrogen peroxide were significantly decreased in exposed neuroblastoma cells with the miR mimics of 34b/c compared to exposed cells without the miR mimics. Furthermore, the mitochondrial integrity was significantly reduced in 24 and 72 hours exposed neuroblastoma cells when compared to sham exposed ones. This effect was partially reverted by the administration of the miR-34b mimic molecule.
Magnetic field exposure of neuroblastoma for 48 hours cells significantly up-regulated gene and protein expression of α-Synuclein compared to sham exposed cells which was also confirmed by microscopy. Addition of the miR-34c mimic molecule led to a significant decrease in the mRNA expression of α-Synuclein in magnetic field exposed neuroblastoma cells and to a significant increase in sham exposed neuroblastoma cells (compared to exposed/sham exposed cells without miR-34c mimic).
The authors conclude that the exposure to 50 Hz magnetic fields could promote epigenetic and biochemical alterations in neuroblastoma cells and in primary mouse cortical neurons suggesting a pathogenic role of those fields in the onset of neuron degeneration.
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