title: The ameloblastin extracellular matrix molecule enhances bone fracture resistance and promotes rapid bone fracture healing.
abstract: The extracellular matrix (ECM) provides structural support, cell migration anchorage, cell differentiation cues, and fine-tuned cell proliferation signals during all stages of bone fracture healing, including cartilaginous callus formation, callus remodeling, and bony bridging of the fracture gap. In the present study we have defined the role of the extracellular matrix protein ameloblastin (AMBN) in fracture resistance and fracture healing of mouse long bones. To this end, long bones from WT and AMBN(Δ5-6) truncation model mice were subjected to biomechanical analysis, fracture healing assays, and stem cell colony formation comparisons. The effect of exogenous AMBN addition to fracture sites was also determined. Our data indicate that lack of a functional AMBN in the bone matrix resulted in 31% decreased femur bone mass and 40% reduced energy to failure. On a cellular level, AMBN function inhibition diminished the proliferative capacity of fracture repair callus cells, as evidenced by a 58% reduction in PCNA and a 40% reduction in Cyclin D1 gene expression, as well as PCNA immunohistochemistry. In terms of fracture healing, AMBN truncation was associated with an enhanced and prolonged chondrogenic phase, resulting in delayed mineralized tissue gene expression and delayed ossification of the fracture repair callus. Underscoring a role of AMBN in fracture healing, there was a 6.9-fold increase in AMBN expression at the fracture site one week after fracture, and distinct AMBN immunolabeling in the fracture gap. Finally, application of exogenous AMBN protein to bone fracture sites accelerated callus formation and bone fracture healing (33% increase in bone volume and 19% increase in bone mineral density), validating the findings of our AMBN loss of function studies. Together, these data demonstrate the functional importance of the AMBN extracellular matrix protein in bone fracture prevention and rapid fracture healing.
authors.affiliation: University of Illinois College of Dentistry, Brodie Laboratory for Craniofacial Genetics, Department of Oral Biology, United States; University of Illinois College of Dentistry, Brodie Laboratory for Craniofacial Genetics, Department of Orthodontics, United States.
authors.forename: Xuanyu
authors.initials: X
authors.lastname: Lu
authors.affiliation: Department of Prosthodontics, University of Shanxi, Shanxi, China.
authors.forename: Wenjin
authors.initials: W
authors.lastname: Li
authors.affiliation: Craniofacial Developmental Biology and Regeneration Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, United States.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fukumoto
authors.affiliation: Craniofacial Developmental Biology and Regeneration Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, United States.
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Yamada
authors.affiliation: University of Illinois College of Dentistry, Brodie Laboratory for Craniofacial Genetics, Department of Orthodontics, United States.
authors.forename: Carla A
authors.initials: CA
authors.lastname: Evans
authors.affiliation: University of Illinois College of Dentistry, Brodie Laboratory for Craniofacial Genetics, Department of Oral Biology, United States; Texas A&M Baylor College of Dentistry, Department of Periodontics, United States. Electronic address: diekwisch@bcd.tamhsc.edu.
authors.forename: Tom
authors.initials: T
authors.lastname: Diekwisch
authors.affiliation: University of Illinois College of Dentistry, Brodie Laboratory for Craniofacial Genetics, Department of Oral Biology, United States; University of Illinois College of Dentistry, Brodie Laboratory for Craniofacial Genetics, Department of Orthodontics, United States. Electronic address: luan@uic.edu.
authors.forename: Xianghong
authors.initials: X
authors.lastname: Luan
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002146:Bony Callus / Q000166:cytology; D002454:Cell Differentiation; D003746:Dental Enamel Proteins / Q000235:genetics* / Q000378:metabolism*; D004195:Disease Models, Animal; D005260:Female; D005269:Femur / Q000293:injuries* / Q000473:pathology; D017102:Fracture Healing; D050723:Fractures, Bone / Q000235:genetics / Q000517:prevention & control*; D008297:Male; D051379:Mice; D009154:Mutation
chemical_list: C490890:Ambn protein, mouse; D003746:Dental Enamel Proteins
keywords: Ameloblastin; Bone fracture; Fracture healing; Mesenchymal stem cells; Proliferation