Effects of BMP-2 and pulsed electromagnetic field (PEMF) on rat primary osteoblastic cell proliferation and gene expression.

Bone morphogenetic proteins (BMPs) strongly promote osteoblast differentiation. Pulsed electromagnetic fields (PEMFs) promote fracture healing in non-union fractures. In this study, we hypothesized that a combined BMP-2 and PEMF stimulation would augment bone formation to a greater degree than treatment with either single stimulus. BMP-2 maximally increased the proliferative activity of rat primary osteoblastic cells at 25 ng/ml concentration. Real-time reverse transcription-polymerase chain reaction (RT-PCR) showed that BMP-2 stimulated mRNA levels of alkaline phosphatase (ALP), alpha(1) (I) procollagen, and osteocalcin (OC) in the differentiation phase and only OC mRNA expression in the mineralization phase after 24-h treatment. Both BMP-2 and PEMF (Spinal-Stim) increased cell proliferation, which was additive when both agents were combined. PEMF alone or together with BMP-2 increased only ALP mRNA expression and only during the differentiation phase 24 h after one 4-h treatment. This effect was additive when both agents were combined. Continuous daily 4-h treatment with PEMF alone or together with BMP-2 increased expression of all three osteoblast marker genes during the differentiation phase and increased the mineralized matrix. This effect was additive when both agents were combined, suggesting that the two interventions may be working on different cellular pathways. Thus, a combined effect of BMP-2 and PEMF in vitro could be considered as groundwork for in vivo bone development that may support skeletal therapy.