Effects of sinusoidal electromagnetic fields at different exposure times on osteoblastic activity and the underlying signal transduction mechanisms / 中华老年医学杂志

ABSTRACT

Objective To investigate the signal transduction mechanisms of time-dependent effects of 50 Hz 1.8 mT sinusoidal electromagnetic fields(SEMFs)on osteoblastic activity.Methods Newborn rat calvarial osteoblasts(ROBs) were treated with 50 Hz 1.8mT SEMFs for 30,60,90,120,and 150 min,respectively.Intracellular alkaline phosphatase (ALP) activity was assayed,and protein expression of Runt-related transcription factor 2 (Runx2),Smad1/5/8 and mitogen-activated protein kinases(MAPKs)were examined by Western blot.The Dual-Luciferase Reporter Assay System was used to measure the activity of the Wnt pathway.Immunofluorescence staining and laser confocal microscopy were applied to examine the nuclear translocation of Smad1/5/8 and β-catenin.Changes in ALP activity were determined after inhibiting p38 MAPK using a specific inhibitor.Results ALP activity of ROBs increased after 30,60,90,120 and 150 min of SEMFs treatment,compared with the control group(51.41±5.21,59.47±4.02,67.56[4.68,63.69±3.92,and 58.16±3.61 vs.45.53± 3.24),and reached the highest value at 90 min and then started to decline.Protein expression of Runx-2,p-Smad1/5/8,p-p38 and β-catenin increased after SEMFs treatment,and reached the highest value at 90 min and then gradually returned to baseline levels.The values for Wnt pathway activity for the control group and with SEMFs treatment at 30,60,90,120 and 150 min were 0.49± 0.06,0.52 ± 0.09,0.75±0.05,0.77 ± 0.42,0.58 ± 0.08 and 0.42 ± 0.09,respectively.Wnt pathway activity,the nuclear translocation of β-catenin and Smad1/5/8 reached the highest level at 90 min.Values of ALP activity in the control group and the SEMFs group were 44.60±3.84 and 71.54±7.34,respectively,before specifically inhibiting p38 MAPK,and were 52.08±0.83 and 52.15±10.77,respectively,after p38 MAPK inhibition,indicating that ALP activity could not be increased with inhibition.Conclusions 50 Hz 1.8 mT SEMFs increase osteoblastic activity by activating the BMP-2/Smad1/5/8,Wnt/β-catenin and p38 MAPK signal pathways.The optimal duration of treatment is 90 min per day.