title: Ossification process involving the human thoracic ligamentum flavum: role of transcription factors.
abstract: BACKGROUND
  Ossification of the ligamentum flavum (OLF) of the spine is associated with serious neurologic compromise, but the pathomechanism of this process remains unclear. The objective of this study was to investigate the pathomechanism of the ossification process, including the roles of various transcriptional factors in the ossification of human thoracic ligamentum flavum.
  
  
  METHODS
  Sections of the thoracic ligamentum flavum were obtained from 31 patients with OLF who underwent posterior thoracic decompression, and from six control patients free of OLF. Cultured ligamentum flavum cells (n = 6, each) were examined with real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis for Sry-type high-mobility group box 9 (Sox9), runt-related transcription factor 2 (Runx2), muscle segment homeobox 2 (Msx2), Osterix, distal-less homeobox 5 (Dlx5), and AP-1. The harvested sections were examined with hematoxylin-eosin, the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) method, and immunohistochemistry for the transcriptional factors.
  
  
  RESULTS
  Compared with the control, the OLF showed disorganization of the elastic fiber bundles and abundant hypertrophic chondrocytes in the ossification front. TUNEL-positive chondrocytes were found near the ossified plaques. The mRNA expression levels of Sox9, Runx2, Msx2, and AP-1 in cultured cells from the ligamentum flavum of OLF patients were significantly different from those of the control. OLF samples were strongly immunoreactive to Sox9, Runx2, and Msx2 at proliferating chondrocytes in the fibrocartilage area. Hypertrophic chondrocytes were positive for Runx2, Osterix, Dlx5, and AP-1.
  
  
  CONCLUSIONS
  The ossification process in OLF seems to involve chondrocyte differentiation under the unique expression of transcriptional factors. Accumulation of hypertrophic chondrocytes was evident around the calcified area at the ossification front, and we suggest that the differentiation of these cells seems to be concerned with the ossification process.
authors.affiliation: Department of Orthopaedics and Rehabilitation Medicine, Faculty of Medical Sciences, Fukui University, Eiheiji, Fukui 910-1193, Japan.
authors.forename: Kenzo
authors.initials: K
authors.lastname: Uchida
authors.forename: Takafumi
authors.initials: T
authors.lastname: Yayama
authors.forename: Hong-Xin
authors.initials: HX
authors.lastname: Cai
authors.forename: Hideaki
authors.initials: H
authors.lastname: Nakajima
authors.forename: Daisuke
authors.initials: D
authors.lastname: Sugita
authors.forename: Alexander Rodríguez
authors.initials: AR
authors.lastname: Guerrero
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Ai
authors.initials: A
authors.lastname: Yoshida
authors.forename: Ke-Bing
authors.initials: KB
authors.lastname: Chen
authors.forename: Hisatoshi
authors.initials: H
authors.lastname: Baba
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002478:Cells, Cultured; D019902:Chondrocytes / Q000737:chemistry / Q000473:pathology / Q000502:physiology; D005260:Female; D006801:Humans; D017843:Ligamentum Flavum / Q000737:chemistry / Q000473:pathology* / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009999:Ossification, Heterotopic / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D013904:Thoracic Vertebrae / Q000737:chemistry / Q000473:pathology* / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
chemical_list: D014157:Transcription Factors