The effects of exposure of human keratinocytes to a 50 Hz magnetic field on cell proliferation and the underlying molecular mechanisms of action should be investigated.
Previous studies indicated that magnetic field exposure can increase keratinocyte proliferation (Vianale et al. 2008, Patruno et al. 2010) and can have positive effects on wound healing (Stiller et al. 1992, Matic et al. 2009).
Cells were divided into two groups: exposure and control group. Cells were exposed or not exposed for 30 minutes, 1 h, 3 h or 24 hours. All results were obtained from at least three independent experiments.
mTOR (mechanistic target of rapamycin) is an important key enzyme for growth, proliferation and survival of cells, which is involved in several signal pathways.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
continuous for up to 24 hours
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | continuous for up to 24 hours |
| Exposure source | |
|---|---|
| Chamber | culture plates in incubator |
| Setup | a 160-turn solenoid coil (22 cm length, 6 cm radius, copper wire diameter of 1.25x10-5 cm, current flow of 1.2 A) generated the MF in the incubator; culture plates were placed at the center of the solenoid with 98% uniformity; cells were incubated at 37°C in a humidified atmosphere and 5% CO2; max. temperature difference in cell cultures between exposure and control group was 0.1°C |
| Additional info | an identical incubator was used for the control group |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | effective value | measured | - | - |
Cell proliferation was significantly increased and the cell cycle distribution was significantly altered after 1 h and 24 hours of exposure compared to the control group. Addition of ERK, phosphoinositide 3-kinase or JNK inhibitors led to a significantly decreased cell proliferation in both, exposure and control group, compared to respective cell cultures without inhibitors. When cells exposed for 1 h were treated with rapamycin, they showed a significantly decreased proliferation compared to non-treated exposed cells. However, cells in the control group did not react to rapamycin.
In the microarrays, a total of 153 genes were significantly differently expressed in exposed cells compared to the control group. Pathway analysis showed an association with growth and proliferation processes for the majority of the identified genes. Key enzyme genes were selected and except for mTOR and RPS6, overexpression could be confirmed for all via RT-PCR.
However, protein expression of phosphorylated mTOR was significantly increased after 1h and 3 h of exposure compared to the control group and exposed cells with addition of rapamycin or inhibitors of ERK and phosphoinositide 3-kinase showed a significantly reduced mTOR protein expression compared to exposed cells without these additives. Moreover, exposure led to significantly increased protein expression rates of ERK, JNK and protein kinase B and to a significantly reduced expression of p38 MAPK compared to the control group.
The authors conclude that exposure of human keratinocytes to a 50 Hz magnetic field might increase cell proliferation. The molecular targets of the magnetic field seem to be the protein kinase B and ERK signaling pathways, which activate mTOR.
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