T. Boyko1,2, O. Marecic1, M. Lopez1, C. Chan1, M. T. Longaker1, G. P. Yang1 1Stanford University School Of Medicine,Surgery,Stanford, CALIFORNIA, USA 2University At Buffalo,Surgery,Buffalo, NY, USA
Introduction: Millions of people fracture their bones yearly, 5% of which fail to heal properly. Risk factors for this include old age, osteoporosis and diabetes. Failure of bony fusion also complicates thousands of orthopedic, spinal and maxillofacial surgeries including joint replacements, spinal fusion and dental implants resulting in significant morbidity and increased costs. Skeletal progenitor cells have recently been described. They give rise to three main tissues of the skeletal system: bone, cartilage and stroma, and are responsible for bone healing. We have previously shown that the extracellular matrix protein Del1 acts to promote proliferation and prevents apoptosis of the subpopulation of mouse skeletal progenitor cells involved in fracture healing – theBone Cartilage Stroma Progenitor cells (BCSPs). Del1 knockout mice heal fractures with less bone, and the healed bone is weaker than that of wild type control fractures. We hypothesized that addition of exogenous Del1 protein could promote proliferation of human skeletal stem cell (HSSC).
Methods: Femur heads of three patients undergoing hip replacement surgery, age 70, 71 and 75, were obtained. Following mechanical and enzymatic digestion, HSSCs were isolated via FACS, using previously identified cell surface markers. HSCCs were plated in vitro with or without the addition of human Del1 protein. Proliferation was measured daily over 5 days.
Results: The addition of exogenous human Del1 protein to cultured HSSCs led to increased proliferation rates compared to untreated HSSCs. Cell numbers reached statistical significance on the third day of treatment (p<0.05) and remained statistically significant over the remaining days cells were counted in all three human samples.
Conclusion: Del1 knockout mice do not have a significant phenotype without injury. Following fracture, knockout mice are able to heal, but with significantly less bone. We have shown that the underlying mechanism consists of Del1 acting as a pro-proliferative and anti-apoptotic factor for mouse skeletal progenitor cells. In this study, we demonstrate that exogenous human Del1 can promote proliferation of human skeletal progenitor cells. This suggests that Del1 has the potential for therapeutic use to reduce morbidity from failure of bone fracture healing or inadequate bone fixation of an implant.