title: BRONJ-related jaw bone is associated with increased Dlx-5 and suppressed osteopontin-implication in the site-specific alteration of angiogenesis and bone turnover by bisphosphonates.
abstract: OBJECTIVE
  Site-specific suppression of bone remodelling has been implicated in bisphosphonate-(BP)-related osteonecrosis of the jaws (BRONJ). Due to the origin of jaw bone from cranial neural crest, osseous differentiation is regulated specifically by the antagonizing BMP-2-downstream-transcription factors Msx-1 and Dlx-5. Osteopontin has been implicated in bone remodelling and angiogenesis. The osteoblast and osteoclast progenitor proliferation mediating Msx-1 has been demonstrated to be suppressed in BRONJ. In vitro BPs were shown to increase Dlx-5 and to suppress osteopontin expression. This study targeted Dlx-5 and osteopontin in BRONJ-related and BP-exposed jaw bone compared with healthy jaw bone samples at protein- and messenger RNA (mRNA) level, since increased Dlx-5 and suppressed osteopontin might account for impaired bone turnover in BRONJ.
  
  
  METHODS
  Fifteen BRONJ-exposed, 15 BP-exposed and 20 healthy jaw bone samples were processed for real-time reverse transcription polymerase chain reaction (RT-PCR) and for immunohistochemistry. Targeting Dlx-5, osteopontin and glyceraldehyde 3-phosphate dehydrogenase mRNA was extracted, quantified by the LabChip-method, followed by quantitative RT-PCR. For immunohistochemistry, an autostaining-based alkaline phosphatase antialkaline phosphatase (APAPP) staining kit was used. Semiquantitative assessment was performed measuring the ratio of stained cells/total number of cells (labelling index, Bonferroni adjustment).
  
  
  RESULTS
  The labelling index was significant decreased for osteopontin (p < 0.017) and significantly increased for Dlx-5 (p < 0.021) in BRONJ samples. In BRONJ specimens, a significant fivefold decrease in gene expression for osteopontin (p < 0.015) and a significant eightfold increase in Dlx-5 expression (p < 0.012) were found.
  
  
  CONCLUSIONS
  BRONJ-related suppression of bone turnover is consistent with increased Dlx-5 expression and with suppression of osteopontin. The BP-related impaired BMP-2-Msx-1-Dlx-5 axis might explain the jaw bone specific alteration by BP.
  
  
  CONCLUSIONS
  The findings of this study help to explain the restriction of RONJ to craniofacial bones. BRONJ might serve as a model of disease elucidating the specific signal transduction of neural crest cell-derived bone structures in health and disease.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Friedrich-Alexander-University of Erlangen, Glueckstrasse 11, 91054, Erlangen, Germany, Falk.Wehrhan@uk-erlangen.de.
authors.forename: Falk
authors.initials: F
authors.lastname: Wehrhan
authors.forename: Kerstin
authors.initials: K
authors.lastname: Amann
authors.forename: Patrick
authors.initials: P
authors.lastname: Möbius
authors.forename: Manuel
authors.initials: M
authors.lastname: Weber
authors.forename: Raimund
authors.initials: R
authors.lastname: Preidl
authors.forename: Jutta
authors.initials: J
authors.lastname: Ries
authors.forename: Phillip
authors.initials: P
authors.lastname: Stockmann
mesh_terms: D059266:Bisphosphonate-Associated Osteonecrosis of the Jaw / Q000378:metabolism*; D050071:Bone Density Conservation Agents / Q000494:pharmacology*; D016723:Bone Remodeling / Q000187:drug effects*; D002454:Cell Differentiation / Q000187:drug effects; D018398:Homeodomain Proteins / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D053495:Osteopontin / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D050071:Bone Density Conservation Agents; C100596:DLX5 protein, human; D018398:Homeodomain Proteins; D014157:Transcription Factors; D053495:Osteopontin