Distribution of Bone Marrow-Derived Cells in the Fracture Callus during Plate Fixation in a Green Fluorescent Protein-Chimeric Mouse Model

Abstract

Abstract:To clarify the distribution of bone-marrow-derived cells in fractures treated by plate fixation, fracture models were created using the green fluorescent protein (GFP) chimeric mouse. We observed 2 types of fracture healing processes with different types of callus formation and cellular events by using Mouse Fix™, a device allowing plate fixation on the mouse femur, and differences in the distribution of bone-marrow-derived cells between the 2 types. The GFP chimeric mice were created by bone marrow transplantation. Fractures were created on the left femurs of mice and stabilized with either rigid (Group R) or flexible (Group F) plates to prepare undecalcified fresh-frozen sections. In Group F, a large external callus and a large intramedullary callus were formed mostly by endochondral ossification. The cells that made up the intramedullary callus and callus in the fracture gap were GFP positive, but most cells of the external callus were not. In Group R, bone union was achieved mostly without external callus formation, bone apposition occurred directly in the gap, and a small intramedullary callus was formed. As observed in Group F, this group had GFP-positive cells in the callus within the fracture gap and in the intramedullary calluses. The results of this study provided direct evidence of the distribution of bone-marrow-derived cells in the callus of fractures treated by plate fixation under different stability conditions.

NOTCH signaling in skeletal progenitors is critical for fracture repair

“…Periosteal progenitors give rise solely to skeletal cells specifically localized within the developing external callus (39,40). Alternatively, reporter-tagged BM/ BMSC transplantations have demonstrated that BMSCs localize to the fracture gap and may contribute to intramedullary or internal callus formation (13,14). Based on these and other findings, we speculate that skeletal progenitors derived from the periosteum and BM/endosteum contribute differently to bone healing.…”

“…Current dogma suggests that various skeletal progenitors are recruited to the fracture site during bone repair, with at least 2 likely participants being BMSCs and PSCs (36,37). Fracture callus development is known to occur at 3 specific loci: the medullary canal, the area between fractured cortices, and the extramedullary space, including the subperiosteal layer and surrounding soft tissues (13,14). However, the precise identity of cells contributing to callus development and their relative contribution are not well defined.…”

“…It is difficult to distinguish the precise role of various skeletal progenitors during fracture repair, partly due to the complex nature of the fracture-healing process, but also due to the lack of specific progenitor markers. Thus far, studies assessing the contribution of progenitor sources to bone healing have largely relied on transplantation approaches (13,14,(38)(39)(40)(41). In vivo lineage analyses using transplanted live bone grafts have demonstrated that the periosteum supports endochondral ossification, while BM/endosteum supports intramembranous ossification during bone repair (40).…”

“…The administration of BMSCs has shown promise in treating patients with fracture nonunions in some settings (7)(8)(9)(10)(11)(12). Interestingly, recent studies using reporter-tagged BMSCs have demonstrated that transplanted BMSCs specifically localize within the fracture gap and intramedullary or internal calluses rather than within the external callus tissues mostly derived from the periosteum and surrounding soft tissue, suggesting a localized and specific role for BMSCs in fracture repair (13,14). While the importance of BMSC-associated osteogenesis during development has been established, the functional role and importance of BMSCs in fracture healing remain to be determined.…”

Bone Marrow-Engrafted Cells after Mice Umbilical Cord Blood Transplantation Differentiate into Osteoblastic Cells in Response to Fracture and Placement of Titanium Screws

“…recently, we also reported that bone marrow cells differentiate into osteoblastic cells in response to fractures that are rigidly fixed using a mouse plate fixation device [24]. therefore, the reconstitution of mesenchymal cells may be important for not only the acceleration of hsc engraftment, but also several healing processes after Ucb transplantation.…”