Pulsed electromagnetic fields affect phenotype and connexin 43 protein expression in MLO-Y4 osteocyte-like cells and ROS 17/2.8 osteoblast-like cells.
Osteocytes, the predominant cells in bone, are postulated to be responsible for sensing mechanical and electrical stimuli, transducing signals via gap junctions. Osteocytes respond to induced shear by increasing connexin 43 (Cx43) levels, suggesting that they might be sensitive to physical stimuli like low-frequency electromagnetic fields (EMF). Immature osteoblasts exhibit decreased intercellular communication in response to EMF but no change in Cx43. Here, we examined long term effects of pulsed EMF (PEMF) on MLO-Y4 osteocyte-like cells and ROS 17/2.8 osteoblast-like cells. In MLO-Y4 cell cultures, PEMF for 8 h/day for one, two or four days increased alkaline phosphatase activity but had no effect on cell number or osteocalcin. Transforming growth factor beta-1 (TGF-beta 1) and prostaglandin E(2) were increased, and NO(2-) was altered. PEMFs effect on TGF-beta1 was via a prostaglandin-dependent mechanism involving Cox-1 but not Cox-2. In ROS 17/2.8 cells, PEMF for 24, 48 or 72 h did not affect cell number, osteocalcin mRNA or osteocalcin protein. PEMF reduced Cx43 protein in both cells. Longer exposures decreased Cx43 mRNA. This indicates that cells in the osteoblast lineage, including well-differentiated osteoblast-like ROS 17/2.8 cells and terminally differentiated osteocyte-like MLO-Y4 cells, respond to PEMF with changes in local factor production and reduced Cx43, suggesting decreased gap junctional signaling.
Lohmann
C H
CH
Department of Orthopaedics, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
Schwartz
Z
Z
Liu
Y
Y
Li
Z
Z
Simon
B J
BJ
Sylvia
V L
VL
Dean
D D
DD
Bonewald
L F
LF
Donahue
H J
HJ
Boyan
B D
BD
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism*; D051545:Cyclooxygenase 1; D015232:Dinoprostone / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004599:Electric Stimulation Therapy; D004574:Electromagnetic Fields; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D008822:Mice, Transgenic; D009573:Nitrites / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D010011:Osteocytes / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D010641:Phenotype; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D053773:Transforming Growth Factor beta1; D014407:Tumor Cells, Cultured
D018031:Connexin 43; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D008565:Membrane Proteins; D009573:Nitrites; D012333:RNA, Messenger; C508961:Tgfb1 protein, mouse; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D051545:Cyclooxygenase 1; D011451:Prostaglandin-Endoperoxide Synthases; C496512:Ptgs1 protein, mouse; D000469:Alkaline Phosphatase; D015232:Dinoprostone