Pulsed electromagnetic fields accelerate proliferation and osteogenic gene expression in human bone marrow mesenchymal stem cells during osteogenic differentiation

Osteogenesis is a complex series of events involving the differentiation of mesenchymal stem cells to generate new bone. In this study, we examined the effect of pulsed electromagnetic fields (PEMFs) on cell proliferation, alkaline phosphatase (ALP) activity, mineralization of the extracellular matrix, and gene expression in bone marrow mesenchymal stem cells (BMMSCs) during osteogenic differentiation. Exposure of BMMSCs to PEMFs increased cell proliferation by 29.6% compared to untreated cells at day 1 of differentiation. Semi‐quantitative RT‐PCR indicated that PEMFs significantly altered temporal expression of osteogenesis‐related genes, including a 2.7‐fold increase in expression of the key osteogenesis regulatory gene cbfa1, compared to untreated controls. In addition, exposure to PEMFs significantly increased ALP expression during the early stages of osteogenesis and substantially enhanced mineralization near the midpoint of osteogenesis. These results suggest that PEMFs enhance early cell proliferation in BMMSC‐mediated osteogenesis, and accelerate the osteogenesis. Bioelectromagnetics 31:209–219, 2010. © 2009 Wiley‐Liss, Inc.     

Bone loss induced by Runx2 Over‐expression in mice is blunted by osteoblastic over‐expression of TIMP‐1

The Runx2 gene is essential for osteoblast differentiation and function. In vivo over‐expression of Runx2 in osteoblasts increases bone resorption, and blocks terminal osteoblast differentiation. Several lines of evidence suggest that osteoblastic matrix metalloproteinases (MMPs) could contribute to the increased bone resorption observed in mice over‐expressing Runx2 (Runx2 mice). The goal of our study was to use a transgenic approach to find out whether the inhibition of osteoblastic MMPs can reduce the bone loss induced by the over‐expression of Runx2. We analyzed the effect of the in vivo over‐expression of the TIMP‐1 in osteoblasts on the severe osteopenic phenotype in Runx2 mice. Females with the different genotypes (WT, Runx2, TIMP‐1 and TIMP‐1/Runx2) were analyzed for bone density, architecture, osteoblastic and osteoclastic activity and gene expression using qPCR. TIMP‐1 over‐expression reduces the bone loss in adult Runx2 mice. The prevention of the bone loss in TIMP‐1/Runx2 mice was due to a combination of reduced bone resorption and sustained bone formation. We present evidence that the ability of osteoblastic cells to induce osteoclastic differentiation is lower in TIMP‐1/Runx2 mice than in Runx2 mice, probably due to a reduction in the expression of RANK‐L and of the Runx2 transgene. Osteoblast primary cells from TIMP‐1/Runx2 mice, but not from Runx2 mice, were able to differentiate into fully mature osteoblasts producing high osteocalcin levels. In conclusion, our findings suggest that osteoblastic MMPs can affect osteoblast differentiation. Our work also indicates that osteoblastic MMPs are partly responsible for the bone loss observed in Runx2 transgenic mice. J. Cell. Physiol. 222:219–229, 2010. © 2009 Wiley‐Liss, Inc.