Up-regulation of bone morphogenetic proteins in cultured murine bone cells with use of specific electric fields.
BACKGROUND
Capacitively coupled electric stimulation has been successfully used in the treatment of bone nonunions and to effect spinal fusions. However, the pathway of biologic events whereby this is accomplished has not been fully elucidated. To determine whether bone morphogenetic proteins (BMPs) could be involved, the effect of electrical stimulation on BMP gene expression was investigated.


METHODS
Postconfluent cultures of MC3T3-E1 bone cells were exposed to a series of capacitively coupled signals in which the duration, amplitude, frequency, and duty cycle were sequentially and systematically varied. The cellular response was measured by quantifying the mRNA levels of BMP-2 through BMP-8, as well as the BMP antagonists gremlin and noggin, with use of reverse transcription followed by real-time quantitative polymerase chain reaction. BMP-2 protein was measured by enzyme-linked immunosorbent assay, and alkaline phosphatase activity was measured by a specific colorimetric assay.


RESULTS
The results showed that BMP-2 through BMP-8, gremlin, and noggin were all normally expressed by MC3T3-E1 cells, and could be significantly up-regulated by specific and selective capacitively coupled electric fields (p < 0.05). However, mRNA expression for BMP-2, 4, 5, 6, and 7 was consistently up-regulated several times higher than that for BMP-3 and BMP-8, gremlin, and noggin under identical conditions. Concomitantly, BMP-2 protein production and alkaline phosphatase activity were both significantly increased in the same electrically stimulated cultures (p = 0.001 and p < 0.01, respectively).


CONCLUSIONS
These data clearly show that our optimal capacitively coupled signal (60 kHz, 20 mV/cm at a 50% duty cycle for twenty-four hours) can specifically, selectively, and simultaneously up-regulate the expression of a number of osteoinductive BMPs; other BMPs and antagonists are only moderately affected.
Wang
Zhenyu
Z
McKay Laboratory of Orthopaedic Surgery Research, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
Clark
Charles C
CC
Brighton
Carl T
CT
D016475:3T3 Cells; D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D018929:Cell Culture Techniques; D016207:Cytokines; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D000099176:Noggin Protein
D019485:Bone Morphogenetic Proteins; D002352:Carrier Proteins; D016207:Cytokines; D036341:Intercellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D000099176:Noggin Protein; C113178:Grem1 protein, mouse