Periosteal Mesenchymal Progenitor Dysfunction and Extraskeletally-Derived Fibrosis Contribute to Atrophic Fracture Nonunion

Wang, Luqiang; Tower, Robert J.; Chandra, Abhishek; Yao, Lutian; Tong, Wei; Xiong, Zekang; Tang, Kai; Zhang, Yejia; Liu, X Sherry; Boerckel, Joel D.; Guo, Xiaodong; Ahn, Jaimo; Qin, Ling

doi:10.1002/jbmr.3626

Cited by 36 publications

(80 citation statements)

References 41 publications

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“…Gli1+ cells contributed to more chondrocytes than osteoblasts in a similar fracture model (8). Gli1+ cells also formed fibrous tissue in fractures that failed to heal due to radiation exposure, while αSMA+ cells did not (39). The contribution of Gli1+ cells in the fibrous layer of the periosteum, or from non-periosteal sources could explain these observations.…”

Section: Discussionmentioning

confidence: 92%

“…Interestingly, they report the absence of αSMA+ LRCs, however many antibodies to αSMA stain perivascular cells in larger blood vessels, but do not detect αSMA+ cells in the cambium layer of the periosteum. The αSMA+ cells in the cambium layer appear to be the cell subset involved in fracture healing (20,39). Label-retention may be a useful tool to enrich for periosteal stem cells in ex vivo assays, although more robust assays for testing self-renewal such as serial transplantation are required.…”

Section: Discussionmentioning

confidence: 99%

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Heterogeneity of murine periosteum progenitors involved in fracture healing

Matthews

Novak

Sbrana

et al. 2020

Preprint

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The periosteum is the major source of cells involved in fracture healing. We sought to characterize differences in progenitor cell populations between periosteum and other bone compartments, and identify periosteal cells involved in fracture healing. The periosteum is highly enriched for progenitor cells, including Sca1+ cells, CFU-F and label-retaining cells. Lineage tracing with αSMACreER identifies periosteal cells that contribute to >80% of osteoblasts and ~40% of chondrocytes following fracture.A subset of αSMA+ cells are quiescent long-term injury-responsive progenitors. Ablation of αSMA+ cells impairs fracture callus formation. In addition, committed osteoblast-lineage cells contributed around 10% of osteoblasts, but no chondrocytes in fracture calluses. Most periosteal progenitors, particularly those that form osteoblasts, can be targeted by αSMACreER. We have demonstrated that the periosteum is highly enriched for skeletal stem and progenitor cells and there is heterogeneity in the populations of cells that contribute to mature lineages during periosteal fracture healing.

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Section: Discussionmentioning

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Heterogeneity of murine periosteum progenitors involved in fracture healing

Matthews

Novak

Sbrana

et al. 2020

Preprint

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“…Quantification Immunofluorescence sections of 4 dpf limbs were imaged on an Axio Observer Z1 (Zeiss) at the 5x, 10x, and 25x objectives. To determine the number of positively EdU-stained periosteal cells, 4 regions of interest were outlined per mouse 1-3 mm from the fracture on the periosteal cortical bone (28) . Images were manually scored as either positive or negative, averaged together from each of the 4 regions and reported as percent positively stained per total number of periosteal cells in ImageJ (NIH).…”

Section: Imaging and Histomorphometric Analysismentioning

confidence: 99%

“…To elucidate if inducible YAP/TAZ deletion regulated periosteal osteoprogenitor differentiation, we isolated activated periosteal progenitor cells at 4 dpf ( Fig. 7G) (28,29) . Following culture for 21 days in osteogenic media, inducible, Osterix-conditional YAP/TAZ deletion reduced mineral deposition stained with Alizarin Red (Fig.…”

Section: Inducible Osterix-conditional Yap/taz Deletion Reduced Periomentioning

confidence: 99%

YAP and TAZ promote periosteal osteoblast precursor expansion and differentiation for fracture repair

Kegelman

Nijsure

Moharrer

et al. 2020

Preprint

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In response to bone fracture, periosteal progenitor cells proliferate, expand, and differentiate to form cartilage and bone in the fracture callus. These cellular functions require the coordinated activation of multiple transcriptional programs, and the transcriptional regulators Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) regulate osteochondroprogenitor activation during endochondral bone development.However, recent observations raise important distinctions between the signaling mechanisms used to control bone morphogenesis and repair. Here, we tested the hypothesis that YAP and TAZ regulate osteochondroprogenitor activation during endochondral bone fracture healing. Constitutive YAP and/or TAZ deletion from Osterixexpressing cells impaired both cartilage callus formation and subsequent mineralization. However, this could be explained either by direct defects in osteochondroprogenitor differentiation after fracture, or by developmental deficiencies in the progenitor cell pool prior to fracture. Consistent with the second possibility, we found that developmental YAP/TAZ deletion produced long bones with impaired periosteal thickness and cellularity. Therefore, to remove the contributions of developmental history, we next generated adult onset-inducible knockout mice (using Osx1-Cre tetOff ) in which YAP and TAZ were deleted prior to fracture, but after normal development. Adult onset-induced YAP/TAZ deletion had no effect on cartilaginous callus formation, but impaired bone formation at 14 days post-fracture (dpf). Earlier, at 4 dpf, adult onset-induced YAP/TAZ deletion impaired the proliferation and expansion of osteoblast precursor cells located in the shoulder of the callus. Further, activated periosteal cells isolated from this region at 4 dpf exhibited impaired osteogenic differentiation in vitro upon YAP/TAZ deletion. Finally, confirming the effects on osteoblast function in vivo, adult onset-induced YAP/TAZ deletion impaired bone formation in the callus shoulder at 7 dpf, prior to the initiation of endochondral ossification. Together, these data show that YAP and TAZ promote the expansion and differentiation of periosteal osteoblast precursors to accelerate bone fracture healing.

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“…While many early studies created these models of atrophic nonunion in rabbits [30][31][32], more recent work has migrated towards rat [33][34][35][36][37] and mouse [13] models. Specifically, a recent study by Wang, L., et al [38] demonstrated a nonsurgical atrophic nonunion fracture model using radiation to induce periosteal damage.…”

Section: Discussionmentioning

confidence: 99%

Ablation of Proliferating Osteoblast Lineage Cells After Fracture Leads to Atrophic Nonunion in a Mouse Model

Hixon

Sykes

Yoneda

et al. 2020

Preprint

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Nonunion is defined as the permanent failure of a fractured bone to heal, often necessitating surgical intervention. Atrophic nonunions are a subtype that are particularly difficult to treat. Animal models of atrophic nonunion are available; however, these require surgical or radiation induced trauma to disrupt periosteal healing. While these approaches can result in nonunion, such invasive methods are not representative of many clinical nonunions where osseous regeneration has been arrested by a “failure of biology”. We hypothesized that arresting osteoblast cell proliferation after fracture would lead to atrophic nonunion in mice. Using mice that express a thymidine kinase (tk) ‘suicide gene’ driven by the 3.6Col1a1 promoter (Col1-tk), proliferating osteoblast lineage cells can be ablated upon exposure to the nucleoside analog ganciclovir (GCV). Wild-type (WT; control) and Col1-tk littermates were subjected to a full femur fracture and intramedullary fixation at 12 weeks old. Post injury, mice were dosed with GCV twice daily for 2 or 4 weeks. Histologically, we confirmed abundant tk+ expression in fracture callus, and diminished periosteal cell proliferation in Col1-tk mice at 3 weeks post fracture. Moreover, Col1-tk mice had less osteoclast activity, mineralized callus, and vasculature at the fracture site compared to WT mice. Additional mice were monitored for 12 weeks with in vivo radiographs and microCT scans, which revealed delayed bone bridging and reduced callus size in Col1-tk mice. Following sacrifice, ex vivo microCT and histology demonstrated failed union with residual bone fragments and fibrous tissue in Col1-tk mice. Biomechanical testing demonstrated an inability to recover torsional strength in Col1-tk mice compared to WT. Our data indicates that suppression of proliferating osteoblast-lineage cells for either 2 or 4 weeks after fracture blunts the formation and remodeling of a mineralized callus leading to a functional nonunion. We propose this as a new murine model of atrophic nonunion.

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Periosteal Mesenchymal Progenitor Dysfunction and Extraskeletally-Derived Fibrosis Contribute to Atrophic Fracture Nonunion

Cited by 36 publications

References 41 publications

Heterogeneity of murine periosteum progenitors involved in fracture healing

Heterogeneity of murine periosteum progenitors involved in fracture healing

YAP and TAZ promote periosteal osteoblast precursor expansion and differentiation for fracture repair

Ablation of Proliferating Osteoblast Lineage Cells After Fracture Leads to Atrophic Nonunion in a Mouse Model

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