Periosteal Progenitor Cell Fate in Segmental Cortical Bone Graft Transplantations: Implications for Functional Tissue Engineering

Abstract

A murine segmental femoral bone graft model was used to show the essential role of donor periosteal progenitor cells in bone graft healing. Transplantation of live bone graft harvested from Rosa 26A mice showed that ∼70% of osteogenesis on the graft was attributed to the expansion and differentiation of donor periosteal progenitor cells. Furthermore, engraftment of BMP-2-producing bone marrow stromal cells on nonvital allografts showed marked increases in cortical graft incorporation and neovascularization, suggesting that gene-enhanced, tissue engineered functional periosteum may improve allograft incorporation and repair.Introduction: The loss of cellular activity in a structural bone allograft markedly reduces its healing potential compared with a live autograft. To further understand the cellular mechanisms for structural bone graft healing and repair and to devise a therapeutic strategy aimed at enhancing the performance of allograft, we established a segmental femoral structural bone graft model in mice that permits qualitative and quantitative analyses of graft healing and neovascularization. Materials and Methods: Using this segmental femoral bone graft model, we transplanted live isografts harvested from Rosa 26A mice that constitutively express ␤-galactosidase into their wildtype control mice. In an attempt to emulate the osteogenic and angiogenic properties of periosteum, we applied a cell-based, adenovirus-mediated gene therapy approach to engraft BMP-2-producing bone marrow stromal cells onto devitalized allografts. Results: X-gal staining for donor cells allowed monitoring the progression of periosteal progenitor cell fate and showed that 70% of osteogenesis was attributed to cellular proliferation and differentiation of donor progenitor cells on the surface of the live bone graft. Quantitative CT analyses showed a 3-fold increase in new bone callus formation and a 6.8-fold increase in neovascularization for BMP-2/stromal cell-treated allograft compared with control acellular allografts. Histologic analyses showed the key features of autograft healing in the BMP-2/stromal cell-treated allografts, including the formation of a mineralized bone callus completely bridging the segmental defects, abundant neovascularization, and extensive resorption of bone graft. Conclusions:The marked improvement of healing in these cellularized allografts suggests a clinical strategy for engineering a functional periosteum to improve the osteogenic and angiogenic properties of processed allografts.

A Perspective: Engineering Periosteum for Structural Bone Graft Healing

“…By comparing live isograft healing with devitalized allograft, devitalized isograft, or periosteum-free isograft, we demonstrated live periosteum is essential for bone graft healing and remodeling. Removal of periosteum from a live bone graft resulted in a 73% decrease in new bone and cartilage formation on the graft and a 10-fold decrease in neovascularization as measured by histomorphometry and micro-CT [102]. The absence of periosteum also resulted in 75% reduction of osteoclast numbers on bone graft, which correlated with the poor remodeling activity of the devitalized bone allograft or isograft.…”

“…By transplanting live bone graft derived from LacZ reporter mice (R26A) that constitutively express b-galactosidase (b-gal) in nearly all cells, we marked the early periosteal progenitors and followed the fate of these cells during the process of graft healing [102]. We found b-gal-positive cells largely localized to the region directly overlying the graft (Fig.…”

“…The marking of the dynamic progression of donor periosteal reparative callus formation suggested live bone iso-or autograft healing was initiated and driven by pluripotent local mesenchymal stem cells [102]. The initiation of graft repair required activation, differentiation, and expansion of residing periosteal stem/progenitor cells.…”

Regenerative medicine in orthopaedic surgery

“…To the end of developing a tissue engineered structural allograft that achieves these outcomes, stem cell and gene therapy approaches have been developed. [40][41][42] Radiological and biomechanical outcome measures in a murine femur model have also been developed and have demonstrated the efficacy of these tissue engineered allografts. 43 …”

Development of Poly(Ethylene Glycol) Hydrogels for Salivary Gland Tissue Engineering Applications

“…31,42 Critical to this approach was the localization and temporal release of MSCs provided by the PEG hydrogel, 43 as MSCs seeded directly on an allograft have little effect on healing. [107][108][109] In previous studies, transplantation of primary SMG cells into irradiated glands was performed using intraglandular *5-10 mL injections. 10,12,13 We speculate that in situ polymerization of a hydrogel to surround damaged salivary glands may provide a direct means of delivering SMG cells for regeneration.…”