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

Abstract

IntroductionOssification 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.MethodsSections 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.ResultsCompared 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.ConclusionsThe 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.

Clinical characteristics and surgical outcome of thoracic myelopathy caused by ossification of the ligamentum flavum: a retrospective analysis of 85 cases

“…25,34,37 Although it has been 90 years since the first description of OLF, very little is known about the pathophysiology of OLF. Currently, several studies have described the possible roles of mechanical/traumatic, 14 [50][51][52][53] in the development and progression of OLF.…”

Indian Hedgehog Signaling Promotes Chondrocyte Differentiation in Enchondral Ossification in Human Cervical Ossification of the Posterior Longitudinal Ligament

“…In our previous study using reverse-transcriptase polymersae chain reaction, we have demonstrated that cultured cells derived from ossifi ed spinal ligament express high levels of Sox9 and Runx2. 15 Sox9 is known to promote chondrocyte differentiation, and Runx2 promotes the differentiation of premature chondrocytes to hypertrophic chondrocytes. 16 Considering these results, we hypothesize that overexpression of Sox9 and Runx2 is due to differences in genetic background.…”

Recombinant human bone morphogenetic protein-2–induced ossification of the ligamentum flavum in rats and the associated global modification of histone H3

“…25 In this study, these transcription-activating histone modifications and transcription factors localized to the same area. Therefore, we hypothesize that histone modifications (H3K18ac, H3K9ac, H3K4me3, and H3K36me3) create a favorable microenvironment for transcription factors (osterix and Runx2) to access osteogenic genes during ossification.…”