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

## TL;DR

This study compares bone-forming abilities of cells from the periosteum and bone marrow, finding that bone marrow cells perform better in laboratory conditions.

## Contribution

The study reveals that periosteal-derived cells lose osteogenic potential in vitro, unlike bone marrow-derived cells.

## Key findings

- Bone marrow-derived cells showed robust osteogenesis, while periosteal-derived cells did not.
- BMP-2 stimulation failed to restore osteogenic capacity in periosteal cells.
- Ex vivo expansion negatively affects periosteal cell osteogenic potential.

## Abstract

Cartilage- and bone-forming cells from the periosteum are responsible for increasing bone width during skeletal growth, and fracture repair is also primarily orchestrated by these cells. These activities make periosteal cells excellent candidates for cell-based strategies to improve fracture outcomes. With this in mind, we compared the in vitro osteogenic (bone-forming) capacity of adult equine periosteal cells with that of bone marrow-derived stem cells. Against expectations, periosteum-derived cells exhibited little or no osteogenic activity while bone marrow-derived cells demonstrated robust osteogenesis. Further, the administration of the osteo-stimulatory growth factor BMP-2 was not sufficient to restore the in vitro bone-forming capacity of periosteal cells. Collectively, these outcomes demonstrate that isolation of periosteal cells from native tissue and/or in in vitro expansion of these cells have profound negative effects on their osteogenic capacity, an effect not seen in bone marrow-derived progenitors. Until appropriate phenotype-sparing isolation protocols are developed for periosteal cell isolation, bone marrow-derived cells should be preferred for cell-based strategies to facilitate bone repair.

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 t 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.