R. Tevlin1,2, A. Mc Ardle1,2, E. Seo2, K. Senarath-Yapa1,2, C. Duldulao1, T. Wearda1,2, O. Marecic1,2, E. R. Zielins1, D. Atashroo1, M. S. Hu1, G. G. Walmsley1,2, S. Li1, Z. Maan1, D. C. Wan1, C. K. Chan2, G. C. Gurtner1, M. T. Longaker1 1Stanford University,Division Of Plastic Surgery,Palo Alto, CA, USA 2Stanford University,Institute For Stem Cell Biology And Regenerative Medicine,Palo Alto, CA, USA
Introduction:
Diabetes mellitus results in a decline in the regenerative capacity of bone and is associated with increased incidence of malunion, non-union and delayed union of fractures. Our previous studies have illustrated that this phenotype of impaired fracture healing is preserved in a mouse model of diabetes and that reduced angiogenesis occurs in the diabetic fracture callus. As osteogenesis and angiogenesis are intrinsically linked, we hypothesize that exposure to a healthy, wild-type (Wt) circulation will ameliorate the impairment of fracture healing in diabetic (Db) mice and that this effect may arise from improved systemic response to the ischemic injury of a fracture.
Methods:
Parabiosis was surgically established between Db and Wt mice, and experimental chimeric controls were created consisting of homogenous Wt/Wt pairs and Db/Db pairs. The creation of a chimeric circulation between Db and Wt mice allowed for evaluation of the role of the skeletal niche in promoting a diabetic phenotype during normal homeostasis and in response to injury. Four weeks post parabiosis, after confirmation of chimeric circulation, a stabilized midshaft femoral fracture was created in one mouse of each chimeric pair. Fracture healing was assessed by weekly radiography and femoral mechanical strength testing was performed at 4 weeks post injury. Protein immunoblot of the circulating serum was performed prior to harvest at 4 weeks post fracture to delineate the effect of parabiosis on the systemic angiogenic response, quantifying angiokines known to be of importance in response to fracture healing
Results:
Diabetes is associated with impaired fracture healing. Heterogenous parabiosis (Db/Wt) accelerates both the development of the diabetic callus as seen radiographically and increases resistance to failure upon mechanical strength testing. Furthermore, exposure of the injured Db mouse to a healthy Wt circulation results in a significant increase in systemic angiokines, such as stromal derived factor-1, matrix metalloproteinases and serpin F1, in response to fracture injury in comparison to Db/Db control chimeric pairs (p<0.05).
Conclusion:
Skeletal regeneration is intrinsically linked to angiogenesis, a process known to be dysfunctional in the presence of diabetes. Following exposure to a healthy wild-type circulation, we note improvement in indices of fracture healing in a mouse model of diabetes, with concomitant significant systemic upregulation of angiokines, known to play an instrumental role in fracture healing.