Comparative In Vivo and In Vitro Osteogenic Activities of Foal and Adult Equine Periosteal Cells

Introduction: Periosteum is vital for skeletal growth and bone repair by callus formation. Fracture repair occurs more rapidly in young patients than in older patients. This study assessed differences between foal and adult periosteal cells and addressed the hypothesis that foal periosteal cells exhibit greater proliferative and osteogenic capacities than adult periosteal cells.

Materials and Methods: Periosteum from proximal tibias of five foals and five adult horses were collected for RNA isolation or periosteal cell isolation. Cells were expanded through two passages then transferred to osteogenic medium ±BMP-2 for up to 15 days. Transcriptional profiles of foal and adult periosteum were assessed by RNA sequence. Osteogenic status of periosteal tissues and cultures was assessed by osteogenic gene expression, ALP activity and matrix mineralization. Statistical comparisons were made by t-tests or ANOVA (p < 0.05).

Results: Around 3460 periosteal genes were differentially expressed. “Cell cycle,” “matrix,” and “osteogenic” gene expression was significantly higher in foal periosteum. Cell yields and primary culture proliferation was significantly higher in foals, but proliferation was similar in subsequent passages. Osterix and BMP-2 expression fell dramatically during periosteal cell culture. Osteogenic gene expression was similar, and ALP activity and matrix mineralization were negligible in both age groups. BMP-2 supplementation was required to stimulate osteogenesis in both groups.

Discussion/Conclusion: Profound differences between foal and adult periosteal cells in vivo were not sustained after isolation. Neither group exhibited significant osteogenesis in vitro without exogenous BMP-2. Extrinsic stimuli are required for sustained periosteal cell osteogenesis.

Acknowledgment: This project was funded by a USDA Hatch Research award.