title: Hypoxia and Reactive Oxygen Species Homeostasis in Mesenchymal Progenitor Cells Define a Molecular Mechanism for Fracture Nonunion.
abstract: Fracture nonunion is a major complication of bone fracture regeneration and repair. The molecular mechanisms that result in fracture nonunion appearance are not fully determined. We hypothesized that fracture nonunion results from the failure of hypoxia and hematoma, the primary signals in response to bone injury, to trigger Bmp2 expression by mesenchymal progenitor cells (MSCs). Using a model of nonstabilized fracture healing in transgenic 5'Bmp2BAC mice we determined that Bmp2 expression appears in close association with hypoxic tissue and hematoma during the early phases of fracture healing. In addition, BMP2 expression is induced when human periosteum explants are exposed to hypoxia ex vivo. Transient interference of hypoxia signaling in vivo with PX-12, a thioredoxin inhibitor, results in reduced Bmp2 expression, impaired fracture callus formation and atrophic-like nonunion by a HIF-1α independent mechanism. In isolated human periosteum-derived MSCs, BMP2 expression could be induced with the addition of platelets concentrate lysate but not with hypoxia treatment, confirming HIF-1α-independent BMP2 expression. Interestingly, in isolated human periosteum-derived mesenchymal progenitor cells, inhibition of BMP2 expression by PX-12 is accomplished only under hypoxic conditions seemingly through dis-regulation of reactive oxygen species (ROS) levels. In conclusion, we provide evidence of a molecular mechanism of hypoxia-dependent BMP2 expression in MSCs where interference with ROS homeostasis specifies fracture nonunion-like appearance in vivo through inhibition of Bmp2 expression. Stem Cells 2016;34:2342-2353.
authors.affiliation: Cell Therapy Area.
authors.forename: Emma
authors.initials: E
authors.lastname: Muinos-López
authors.affiliation: Department of Orthopaedic Surgery and Traumatology.
authors.forename: Purificación
authors.initials: P
authors.lastname: Ripalda-Cemboráin
authors.affiliation: Cell Therapy Area.
authors.forename: Tania
authors.initials: T
authors.lastname: López-Martínez
authors.affiliation: Department of Orthopaedic Surgery and Traumatology.
authors.forename: Ana B
authors.initials: AB
authors.lastname: González-Gil
authors.affiliation: Department of Orthopaedic Surgery and Traumatology.
authors.forename: José M
authors.initials: JM
authors.lastname: Lamo-Espinosa
authors.affiliation: Department of Orthopaedic Surgery and Traumatology.
authors.forename: Andrés
authors.initials: A
authors.lastname: Valentí
authors.affiliation: Department of Molecular Physiology and Biophysics, Center for Human Genetics Research, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Mortlock
authors.affiliation: Department of Orthopaedic Surgery and Traumatology.
authors.forename: Juan R
authors.initials: JR
authors.lastname: Valentí
authors.affiliation: Cell Therapy Area.|Department of Hematology, Clínica Universidad De Navarra, Pamplona, Spain.
authors.forename: Felipe
authors.initials: F
authors.lastname: Prósper
authors.affiliation: Cell Therapy Area. fgranero@unav.es.|Department of Orthopaedic Surgery and Traumatology. fgranero@unav.es.
authors.forename: Froilán
authors.initials: F
authors.lastname: Granero-Moltó
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects; D002469:Cell Separation; D004220:Disulfides / Q000494:pharmacology; D017102:Fracture Healing / Q000187:drug effects; D005599:Fractures, Ununited / Q000378:metabolism* / Q000473:pathology*; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D010012:Osteogenesis / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects; D010521:Periosteum / Q000473:pathology; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D055396:Bone Morphogenetic Protein 2; D004220:Disulfides; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007093:Imidazoles; D017382:Reactive Oxygen Species; C412893:1-methylpropyl-2-imidazolyl disulfide
keywords: BMP2; Fracture nonunion; Hypoxia; Mesenchymal progenitor cells; Reactive oxygen species