Objective To explore the effects of direct current electric fields on directional migration and arrangement of dermal fibroblasts in neonatal BALB/c mice and the related mechanisms.
Methods Twelve neonatal BALB/c mice were divided into 4 batches. The skin on the back of 3 neonatal mice in each batch was obtained to culture fibroblasts. Fibroblasts of the second passage were inoculated in 27 square cover slips with the concentration of 5×10
4 cells per mL. (1) Experiment 1. Six square cover slips inoculated with fibroblasts of the second passage were divided into electric field group (EF) and sham electric field group (SEF), with 3 cover slips in each group. The cover slips were put in live cell imaging workstation. The cells in group EF was treated with electric power with EF intensity of 200 mV/mm, while simulating process without actual power was given to SEF group (the same below) for 6 h. Cell proliferation rate was subsequently counted. (2) Experiment 2. Six cover slips were divided and underwent the same processes as in experiment 1. Cell movement locus within EF hour (EFH) 6, direction change of cell migration at EFH 0 (immediately), 1, 2, 3, 4, 5, and 6 which was denoted as cos(α), cell migration velocity within EFH 6, direction change of long axis of cell within EFH 6, and direction change of cell arrangement at EFH 0, 1, 2, 3, 4, 5, and 6 which was denoted as polarity value cos[2(θ-90)] were observed under live cell imaging workstation. After EFH 6, the morphological changes in microtubules and microfilaments were observed with immunofluorescent staining. (3) Experiment 3. Six cover slips were divided into cytochalasin D group (treated with 1 μmol/L cytochalasin D for 10 min) and colchicine group (treated with 5 μmol/L colchicine for 10 min), with 3 cover slips in each group. The morphological changes in microfilaments and microtubules were observed with the same method as in experiment 2. (4) Experiment 4. Nine cover slips were divided into control group (no reagent was added), cytochalasin D group and colchicine group (added with the same reagents as in experiment 3), with 3 cover slips in each group. Cells in the 3 groups were exposed to an EF of 200 mV/mm for 6 h. Cell movement locus within EFH 6, cell migration velocity within EFH 6, cell polarity values at EFH 0, 3, and 6, and morphological changes of cells at EFH 0 and 6 were observed. Data were processed with independent samples
t-test, one-way analysis of variance, and LSD test.
Results (1) There was no statistically significant difference in cell proliferation rate in group EF and group SEF (
t=-0.24,
P﹥0.05). (2) Within EFH 6, cells in group EF migrated towards the anode of EF, while cells in group SEF moved randomly. At EFH 0, the values of cos(α) of cells in the 2 groups were both 0. The absolute value of cos(α) of cells in group EF (-0.57±0.06) was significantly higher than that in group SEF (0.13±0.09,
t=6.68,
P<0.01) at EFH 1, and it was still higher than that in group SEF from EFH 2 to 6 (with
t values from 5.33 to 6.83,
P values below 0.01). Within EFH 6, migration velocity of cells in group EF was (0.308±0.019) μm/min, which was significantly higher than that in group SEF [(0.228±0.021) μm/min,
t=-2.76,
P<0.01]. Within EFH 6, long axis of cells in group EF was perpendicular to the direction of EF, while arrangement of cells in group SEF was irregular. Cell polarity values in group EF were significantly higher than that in group SEF from EFH 2 to 6 (with
t values from -7.52 to -0.90,
P values below 0.01). At EFH 6, the morphology of microfilaments and microtubules of cells in EF group was similar to that in SEF group. (3) The fluorescent intensity of microfilaments of cells in cytochalasin D group became weakened, and the filamentary structure became fuzzy. The microtubules of cells in colchicine group became fuzzy with low fluorescent intensity. (4) Within EFH 6, cells in control group migrated towards the anode of EF, while cells in cytochalasin D group and colchicine group moved randomly. Within EFH 6, there was statistically significant difference in migration velocity of cells in the 3 groups (
F=6.36,
P<0.01). Migration velocity of cells in cytochalasin D group and colchicine group was significantly slower than that in control group (
P<0.05 or
P<0.01). At EFH 0, 3, and 6, cell polarity values in the 3 groups were close (with
F values from 0.99 to 1.51,
P values above 0.05). At EFH 0, cells in control group were spindle; cells in cytochalasin D group were polygonal or in irregular shapes; cells in colchicine group were serrated circle or oval. At EFH 6, no morphological change was observed in cells in control group; cells in cytochalasin D group were spindle with split ends on both ends; cells in colchicine group were serrated oval.
Conclusions The physiologic strength of exogenous direct current EF can induce directional migration and alignment of dermal fibroblasts in neonatal BALB/c mice. Microfilaments and microtubules are necessary skeleton structure for cell directional migration induced by EF, while they are not necessary for cell directional arrangement induced by EF.
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