Bone Morphogenetic Protein-2 Signaling in the Osteogenic Differentiation of Human Bone Marrow Mesenchymal Stem Cells Induced by Pulsed Electromagnetic Fields

Abstract

Pulsed electromagnetic fields (PEMFs) are clinically used with beneficial effects in the treatment of bone fracture healing. This is due to PEMF ability to favor the osteogenic differentiation of mesenchymal stem cells (MSCs). Previous studies suggest that PEMFs enhance the osteogenic activity of bone morphogenetic protein-2 (BMP2) which is used in various therapeutic interventions. This study investigated the molecular events associated to the synergistic activity of PEMFs and BMP2 on osteogenic differentiation. To this aim, human MSCs (hMSCs) were exposed to PEMFs (75 Hz, 1.5 mT) in combination with BMP2, upon detection of the minimal dose able to induce differentiation. Changes in the expression of BMP signaling pathway genes including receptors and ligands, as well as in the phosphorylation of BMP downstream signaling proteins, such as SMAD1/5/8 and MAPK, were analyzed. Results showed the synergistic activity of PEMFs and BMP2 on osteogenic differentiation transcription factors and markers. The PEMF effects were associated to the increase in BMP2, BMP6, and BMP type I receptor gene expression, as well as SMAD1/5/8 and p38 MAPK activation. These results increase knowledge concerning the molecular events involved in PEMF stimulation showing that PEMFs favor hMSCs osteogenic differentiation by the modulation of BMP signaling components.

Pulsed Electromagnetic Field Stimulation in Osteogenesis and Chondrogenesis: Signaling Pathways and Therapeutic Implications

“…Several studies demonstrated that PEMFs stimulation significantly increases the pro-osteogenic activity of members of the TGF-β gene family, including BMP-2 and -4. Recently, in human bone marrow MSCs (hBM-MSCs), Martini et al confirmed the combined osteogenic activity of PEMFs and BMP-2 [ 55 , 56 , 66 ], in the presence of low doses of BMP-2. Furthermore, the authors showed that the PEMFs effects were associated to increased gene expression of several BMP signaling components including BMP-2, BMP-6, BMP type I receptor, and to the activation of SMAD1/5/8, the main player in the canonical BMP signaling pathway [ 66 ].…”

“…Recently, in human bone marrow MSCs (hBM-MSCs), Martini et al confirmed the combined osteogenic activity of PEMFs and BMP-2 [ 55 , 56 , 66 ], in the presence of low doses of BMP-2. Furthermore, the authors showed that the PEMFs effects were associated to increased gene expression of several BMP signaling components including BMP-2, BMP-6, BMP type I receptor, and to the activation of SMAD1/5/8, the main player in the canonical BMP signaling pathway [ 66 ]. Synergistic effects on osteogenic differentiation of periodontal ligament stem cells (hPDLSCs) have been also observed following combined treatment of PEMFs and BMP-9, another component of the BMP family [ 63 ].…”

“…The MAPK signaling pathway includes a class of protein kinases which, through a cascade reaction, activates transcription factors and regulates gene expression and differentiation [ 53 , 72 ]. Several studies have shown the involvement of the MEK/ERK cascade in the osteogenic differentiation induced by PEMFs in human MSCs [ 57 , 66 ]. In hADMSC, Poh et al reported increased levels of phosphorylated Akt, p70 S6 kinase, S6 ribosomal protein, and ERK1/2 shortly after PEMF exposure, suggesting that a combination of ERK and Akt activation in response to extremely low frequency pulsed electromagnetic fields (ELF-PEMFs) promoted hADMSC growth and survival [ 57 ].…”

“…In hADMSC, Poh et al reported increased levels of phosphorylated Akt, p70 S6 kinase, S6 ribosomal protein, and ERK1/2 shortly after PEMF exposure, suggesting that a combination of ERK and Akt activation in response to extremely low frequency pulsed electromagnetic fields (ELF-PEMFs) promoted hADMSC growth and survival [ 57 ]. On the other side, the activation of p38 MAPK, largely investigated for its role in the modulation of the osteogenic master gene Runx2 [ 72 ], has been recently reported during the differentiation of hBM-MSCs induced by PEMFs [ 66 ].…”

“…First of all, it appears especially relevant the observation that PEMFs modulate BMP signaling and increase the osteogenic effects of low BMP-2 doses [ 66 ]. In fact, as BMP-2 treatment is currently approved for bone therapy, these results support the idea that the combined use of PEMFs and BMP-2 may be useful in orthopedic treatments, with the potential advantage of limiting BMP-2 clinical side effects, probably related to the high BMP-2 doses used, as well as of lowering BMP-2 therapy costs.…”