Differential BMP Expression and Activities Impact the Osteogenic Capacities of Equine Bone Marrow and Adipose Stem Cells

Introduction: In equine practice, stem cell therapies primarily utilize cells from bone marrow (BM) and adipose tissue (ADI). Although adipose-derived stem cells are easily accessible, the biological activities and responses of ADI cells are less robust than those of BM cells. We addressed the hypothesis that poor osteogenic capacity of ADI cells is a result of inadequate endogenous BMP ligand expression and/or induction.

Materials and Methods: Bone marrow and adipose collections from four horses were approved by our institutional IACUC. Bone marrow aspirates and adipose cells were seeded at low density and expanded through two passages. P3 cells were transferred to control or osteogenic cultures for up to 10 days. BMP ligand and osteogenic gene expression was assessed by QPCR. Alkaline phosphatase (ALP) activity was measured by an enzymatic assay. Mineralized matrix formation was monitored by Alizarin Red staining.

Results: Under basal conditions, both BMP-2 and -4 expression was consistently four to seven times higher in BM cells than in ADI cells. BMP-2 and -4 expressions increased by over 100-fold by day 10 in BM osteogenic cultures. In contrast, there was little change in expression of either BMP in ADI cell cultures. Exogenous BMP-2 significantly increased Runx2, Osterix and ALP expression in osteogenic ADI cultures.

Discussion/Conclusion: These findings suggest that differential osteogenic capacities of BM and ADI cells derive from differential intrinsic BMP activities. Exogenous BMP stimulation will likely be necessary if ADI cells are used to support bone repair.

Acknowledgement: This research was supported by USDA Hatch Research funds and The Companion Animal Research Fund.