Open Access Research article

Ossification process involving the human thoracic ligamentum flavum: role of transcription factors

Kenzo Uchida1, Takafumi Yayama1*, Hong-Xin Cai12, Hideaki Nakajima1, Daisuke Sugita1, Alexander Rodríguez Guerrero13, Shigeru Kobayashi1, Ai Yoshida1, Ke-Bing Chen14 and Hisatoshi Baba1

Author affiliations

1 Department of Orthopaedics and Rehabilitation Medicine, Faculty of Medical Sciences, Fukui University, Eiheiji, Fukui 910-1193, Japan

2 Department of Orthopedic Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310016, People's Republic of China

3 Servicio de Neurocirugia, Hospital Nacional Rosales, Universidad de El Salvador, San Salvador 106-8000, El Salvador

4 Department of Spinal Surgery, The First Affiliated Hospital, Sun Yat-Sen University School of Medicine, Guangzhou 510080, People's Republic of China

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Citation and License

Arthritis Research & Therapy 2011, 13:R144  doi:10.1186/ar3458

Published: 13 September 2011

Abstract

Introduction

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.