Comparative In Vitro Osteogenic Capacities of Bone Marrow- and Periosteal-Derived Progenitor Cells

Fracture repair complications occur in 5-10% of cases, despite bone's regenerative capacity. Bone marrow-derived (BM) stem cells have been extensively investigated for orthopedic applications but, given the critical role that periosteum plays in fracture repair, periosteal-derived (PO) cells offer a promising alternative cell source. This study compared the in vitro osteogenic capacities of equine BM and PO cells. Passage 3 cells from each source were maintained in osteogenic medium for up to 10 days. Osteogenesis was assessed by Runx2, Osterix, and alkaline phosphatase (ALP) mRNA up-regulation, induction of ALP activity, and matrix mineralization. Comparisons were made by paired <i>t</i> tests, repeated measures one-way or two-way ANOVAs, as indicated. BM cells proved superior to PO cells in osteogenesis assays. BM cells significantly up-regulated Runx2, Osterix, and ALP mRNAs, ALP activity, and secreted a mineralized matrix by day 10. PO cells did not. BMP-2 expression increased significantly in BM cells in osteogenic medium, whereas BMP-2 expression in PO cells was unchanged. Exogenous BMP-2 did not restore osteogenesis in periosteal cells, indicating that ex vivo expansion affects periosteal osteogenic capacity beyond BMP-2 downregulation. Clinical applications of PO cells will require the identification and exogenous provision of requisite stimulatory factors and substrates.