title: Fracture healing via periosteal callus formation requires macrophages for both initiation and progression of early endochondral ossification.
abstract: The distribution, phenotype, and requirement of macrophages for fracture-associated inflammation and/or early anabolic progression during endochondral callus formation were investigated. A murine femoral fracture model [internally fixed using a flexible plate (MouseFix)] was used to facilitate reproducible fracture reduction. IHC demonstrated that inflammatory macrophages (F4/80(+)Mac-2(+)) were localized with initiating chondrification centers and persisted within granulation tissue at the expanding soft callus front. They were also associated with key events during soft-to-hard callus transition. Resident macrophages (F4/80(+)Mac-2(neg)), including osteal macrophages, predominated in the maturing hard callus. Macrophage Fas-induced apoptosis transgenic mice were used to induce macrophage depletion in vivo in the femoral fracture model. Callus formation was completely abolished when macrophage depletion was initiated at the time of surgery and was significantly reduced when depletion was delayed to coincide with initiation of early anabolic phase. Treatment initiating 5 days after fracture with the pro-macrophage cytokine colony stimulating factor-1 significantly enhanced soft callus formation. The data support that inflammatory macrophages were required for initiation of fracture repair, whereas both inflammatory and resident macrophages promoted anabolic mechanisms during endochondral callus formation. Overall, macrophages make substantive and prolonged contributions to fracture healing and can be targeted as a therapeutic approach for enhancing repair mechanisms. Thus, macrophages represent a viable target for the development of pro-anabolic fracture treatments with a potentially broad therapeutic window.
authors.affiliation: Bone and Immunology Laboratory, Mater Research Institute-UQ, Translational Research Institute, The University of Queensland, Woolloongabba, Queensland, Australia; UQ-Centre for Clinical Research, Faculty of Health Sciences, The University of Queensland, Herston, Queensland, Australia.
authors.forename: Liza J
authors.initials: LJ
authors.lastname: Raggatt
authors.affiliation: Trauma Service, Royal Brisbane and Women's Hospital, Herston, Queensland, Australia; School of Medicine, Faculty of Health Sciences, The University of Queensland, Herston, Queensland, Australia.
authors.forename: Martin E
authors.initials: ME
authors.lastname: Wullschleger
authors.affiliation: UQ-Centre for Clinical Research, Faculty of Health Sciences, The University of Queensland, Herston, Queensland, Australia.
authors.forename: Kylie A
authors.initials: KA
authors.lastname: Alexander
authors.affiliation: UQ-Centre for Clinical Research, Faculty of Health Sciences, The University of Queensland, Herston, Queensland, Australia.
authors.forename: Andy C K
authors.initials: AC
authors.lastname: Wu
authors.affiliation: Bone and Immunology Laboratory, Mater Research Institute-UQ, Translational Research Institute, The University of Queensland, Woolloongabba, Queensland, Australia.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Millard
authors.affiliation: Bone and Immunology Laboratory, Mater Research Institute-UQ, Translational Research Institute, The University of Queensland, Woolloongabba, Queensland, Australia; UQ-Centre for Clinical Research, Faculty of Health Sciences, The University of Queensland, Herston, Queensland, Australia.
authors.forename: Simranpreet
authors.initials: S
authors.lastname: Kaur
authors.affiliation: Bone and Immunology Laboratory, Mater Research Institute-UQ, Translational Research Institute, The University of Queensland, Woolloongabba, Queensland, Australia.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Maugham
authors.affiliation: Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Queensland, Australia.
authors.forename: Laura S
authors.initials: LS
authors.lastname: Gregory
authors.affiliation: Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Queensland, Australia.
authors.forename: Roland
authors.initials: R
authors.lastname: Steck
authors.affiliation: Bone and Immunology Laboratory, Mater Research Institute-UQ, Translational Research Institute, The University of Queensland, Woolloongabba, Queensland, Australia; UQ-Centre for Clinical Research, Faculty of Health Sciences, The University of Queensland, Herston, Queensland, Australia. Electronic address: allison.pettit@mater.uq.edu.au.
authors.forename: Allison R
authors.initials: AR
authors.lastname: Pettit
mesh_terms: D000818:Animals; D017209:Apoptosis; D002454:Cell Differentiation; D049109:Cell Proliferation; D016207:Cytokines / Q000378:metabolism; D018450:Disease Progression; D005264:Femoral Fractures / Q000503:physiopathology*; D005434:Flow Cytometry; D005592:Fracture Fixation; D017102:Fracture Healing; D007150:Immunohistochemistry; D007249:Inflammation; D016268:Internal Fixators; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009000:Monocytes / Q000166:cytology; D010012:Osteogenesis / Q000502:physiology*; D010521:Periosteum / Q000378:metabolism*; D010641:Phenotype
chemical_list: D016207:Cytokines; D016173:Macrophage Colony-Stimulating Factor