Sutures Possess Strong Regenerative Capacity for Calvarial Bone Injury

Abstract

Repair of calvarial bony defects remains challenging for craniofacial surgeons. Injury experiments on animal calvarial bones are widely used to study healing mechanisms and test tissue engineering approaches. Previously, we identified Gli1+ cells within the calvarial sutures as stem cells supporting calvarial bone turnover and injury repair. In this study, we tested the regenerative capacity of the suture region compared with other areas of calvarial bone. Injuries were made to mouse sagittal sutures or other areas of the calvarial bone at varying distances from the suture. Samples were collected at different time points after injury for evaluation. MicroCT and histological analyses were conducted. EdU incorporation analysis was performed to assay cell proliferation. Gli1-CreERT2;Tdtomatoflox mice were used to trace the fate of Gli1+ stem cells after injury. Calvarial sutures possess much stronger regeneration capability than the nonsuture bony areas of the calvaria. The healing rate of the calvarial bone is inversely proportional to the distance between the suture and injury site: injuries closer to the suture heal faster. After complete removal of the sagittal suture, regeneration and restoration of normal organization occur within 6 weeks. Gli1+ cells within the suture mesenchyme are the cellular source for injury repair and bone regeneration. These results demonstrate that calvarial bone healing is not an evenly distributed event on the calvarial surface. Sutures contain stem cells and are the origin of calvarial bone tissue regeneration. Therefore, current practice in calvarial surgery needs to be reevaluated and modified. These findings also necessitate the design of new approaches for repairing calvarial bony defects.