title: Early Characterization of Blast-related Heterotopic Ossification in a Rat Model.
abstract: BACKGROUND
  Heterotopic ossification (HO) affects the majority of combat-related lower extremity wounds involving severe fracture and amputation. Defining the timing of early osteogenic-related genes may help identify candidate prophylactic agents and guide the timing of prophylactic therapy after blast and other combat-related extremity injuries.
  
  
  OBJECTIVE
  Using a recently developed animal model of combat-related HO, we sought to determine (1) the timing of early chondrogenesis, cartilage formation, and radiographic ectopic bone development; and (2) the early cartilage and bone-related gene and protein patterns in traumatized soft tissue.
  
  
  METHODS
  We used an established rat HO model consisting of blast exposure, controlled femur fracture, crush injury, and transfemoral amputation through the zone of injury. Postoperatively, rats were euthanized on Days 3 to 28. We assessed evidence of early ectopic bone formation by micro-CT and histology and performed proteomic and gene expression analysis.
  
  
  RESULTS
  All rats showed radiographic evidence of HO within 28 days. Key chondrogenic (collagen type I alpha 1 [COL1α1], p = 0.016) and osteogenic-related genes (Runt-related transcription factor 2 [RUNX-2], p = 0.029; osteoclacin [OCN], p = 0.032; phosphate-regulating neutral endopeptidase, X-linked [PHEX], p = 0.0290, and POU domain class 5 transcription factor [POU5F], p = 0.016) and proteins (Noggin [NOG], p = 0.04, OCN, p = 0.02, RUNX- 2, p = 0.04, and substance P-1 [SP-1], p = 0.01) in the injured soft tissue, normalized to the contralateral limb and/or sham-treated naïve rats, increased on Days 3 to 14 postinjury. By 14 days, foci of hypertrophic chondrocytes, hyaline cartilage, and woven bone were present in the soft tissue surrounding the amputation site.
  
  
  CONCLUSIONS
  We found that genes that regulate early chondrogenic and osteogenic signaling and bone development (COL1α1, RUNX-2, OCN, PHEX, and POU5F1) are induced early during the tissue reparative/healing phase in a rat model simulating a combat-related extremity injury.
  
  
  CONCLUSIONS
  The ability to correlate molecular events with histologic and morphologic changes will assist researchers and clinicians to understand HO and hence formulate therapeutic interventions.
authors.affiliation: Regenerative Medicine Department, Naval Medical Research Center, 503 Robert Grant Avenue, Silver Spring, MD, 20910, USA.
authors.forename: Ammar T
authors.initials: AT
authors.lastname: Qureshi
authors.forename: Erica K
authors.initials: EK
authors.lastname: Crump
authors.forename: Gabriel J
authors.initials: GJ
authors.lastname: Pavey
authors.forename: Donald N
authors.initials: DN
authors.lastname: Hope
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Forsberg
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Davis
mesh_terms: D000671:Amputation, Surgical; D000818:Animals; D001753:Blast Injuries / Q000150:complications*; D020219:Chondrogenesis / Q000235:genetics; D004195:Disease Models, Animal; D005264:Femoral Fractures / Q000150:complications*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D005819:Genetic Markers; D008297:Male; D009999:Ossification, Heterotopic / Q000000981:diagnostic imaging / Q000209:etiology* / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D010012:Osteogenesis / Q000235:genetics; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D013997:Time Factors; D055114:X-Ray Microtomography
chemical_list: D005819:Genetic Markers