Canine Mesenchymal Stem Cell-Mediated Bone Regeneration is Enhanced in the Presence of Sub-Therapeutic Concentrations of Rhbmp-2 in a Murine Critical-Sized Calvarial Defect

Introduction: Canine mesenchymal stem cells (cMSCs) require supplementation with BMP-2 to consistently undergo osteogenesis in vitro. Interestingly, murine calvarial defects treated with canine adipose MSCs exhibited markedly reduced healing when compared with defects treated with human MSCs. We hypothesized that healing of calvarial defects in vivo would be enhanced by supplementation with a sub-therapeutic concentration of BMP-2.

Materials and Methods: Unilateral calvarial defects (4 mm diameter) were created in 60 days Nu/J mice (n = 5 mice/group). Defects were treated with 2 × 10⁶ canine marrow MSCs, 6 µg/mL rhBMP-2, or a combination of MSCs and BMP-2. A negative control group (n = 4) did not receive treatment. At 4 weeks, mice were terminated and quantitatively assessed for healing with radiography. Healing indices (HI) were generated for each defect (0 = no healing, 1 = complete healing). Micro-CT images were obtained to further assess the healing response. Healing indices were evaluated using one-way ANOVA with Dunnett’s multiple comparisons post-test.

Results: HI were negative control (0.18 + 0.11), MSCs (0.23 + 0.17), BMP-2 (0.16 + 0.09), and MSCs + BMP-2 (0.49 + 0.15). Treatment of calvarial defects with MSCs + BMP-2 resulted in a significantly higher healing index (p = 0.009). Micro-CT imaging confirmed these results.

Discussion/Conclusion: Canine MSCs supplemented with sub-therapeutic BMP-2 are capable of inducing bone regeneration in vivo. These results represent a substantial advancement for the field of canine MSC bone regeneration and will serve as a foundation for future canine bone healing efforts.

Acknowledgement: There was no proprietary interest. Funding provided by CST*R and the Bone and Joint Fund, Texas A and M Foundation.

No conflict of interest has been declared by the author(s).