Human retinoic X receptor beta: complete genomic sequence and mutation search for ossification of posterior longitudinal ligament of the spine

Genetics of Diffuse Idiopathic Skeletal Hyperostosis and Ossification of the Spinal Ligaments

PURPOSE OF REVIEW

The study aims to provide updated information on the genetic factors associated with the diagnoses 'Diffuse Idiopathic Skeletal Hyperostosis' (DISH), 'Ossification of the Posterior Longitudinal Ligament' (OPLL), and in patients with spinal ligament ossification.

RECENT FINDINGS

Recent studies have advanced our knowledge of genetic factors associated with DISH, OPLL, and other spinal ossification (ossification of the anterior longitudinal ligament [OALL] and the yellow ligament [OYL]). Several case studies of individuals afflicted with monogenic disorders, such as X-linked hypophosphatemia (XLH), demonstrate the strong association of fibroblast growth factor 23-related hypophosphatemia with OPLL, suggesting that pathogenic variants in PHEX, ENPP1, and DMP1 are associated with FGF23-phosphate wasting phenotype and strong genetic factors placing patients at risk for OPLL. Moreover, emerging evidence demonstrates that heterozygous and compound heterozygous ENPP1 pathogenic variants inducing 'Autosomal Recessive Hypophosphatemic Rickets Type 2' (ARHR2) also place patients at risk for DISH and OPLL, possibly due to the loss of inhibitory plasma pyrophosphate (PPi) which suppresses ectopic calcification and enthesis mineralization. Our findings emphasize the importance of genetic and plasma biomarker screening in the clinical evaluation of DISH and OPLL patients, with plasma PPi constituting an important new biomarker for the identification of DISH and OPLL patients whose disease course may be responsive to ENPP1 enzyme therapy, now in clinical trials for rare calcification disorders.

Evidence for a genetic contribution to the ossification of spinal ligaments in Ossification of Posterior Longitudinal Ligament and Diffuse idiopathic skeletal hyperostosis: A narrative review

Diffuse Idiopathic Skeletal Hyperostosis (DISH) and Ossification of the Posterior Longitudinal Ligament (OPLL) are common disorders characterized by the ossification of spinal ligaments. The cause for this ossification is currently unknown but a genetic contribution has been hypothesized. Over the last decade, many studies on the genetics of ectopic calcification disorders have been performed, mainly on OPLL. Most of these studies were based on linkage analysis and case control association studies. Animal models have provided some clues but so far, the involvement of the identified genes has not been confirmed in human cases. In the last few years, many common variants in several genes have been associated with OPLL. However, these associations have not been at definitive levels of significance and evidence of functional significance is generally modest. The current evidence suggests a multifactorial aetiopathogenesis for DISH and OPLL with a subset of cases showing a stronger genetic component.

Ecdysone signal pathway participates in shell formation in pearl oysters Pinctada fucata martensii

Ecdysone exists in arthropods, Mollusca and other invertebrates and plays vital roles in exoskeleton formation of Ecdysozoa. However, little is known about its functions in bivalve species. Herein, we identified ecdysone from the serum of pearl oyster Pinctada fucata martensii and obtained the coding sequence of ecdysone receptor (PmEcR) and homologue of its heterodimer protein retinoid X receptor (PmRXR). The deduced amino acid sequences of PmEcR and PmRXR contained a DNA-binding and ligand-binding domain and were very similar to the orthologs of other species. Moreover, PmEcR and PmRXR were located in the nuclei and cytoplasm of HEK-293T cells. PmEcR and PmRXR were highly expressed in early embryos and biomineralized mantle tissue. Moreover, the serum concentration of ecdysone significantly increased at 2, 4, 6, and 8 h post-shell notching. The expression of PmEcR in the mantle tissue was significantly induced at the corresponding time points, while that of PmRXR was significantly induced at 6 h. Ecdysone stimulation remarkably induced the expression of growth factors (BMP2 and BMP7), transcription factors (PmRunt and AP-1), and shell matrix protein genes (chitinase, lysine-rich matrix protein (KRMP), TYR2, and PmCOLVI), which indicated that ecdysone signaling plays important roles in shell repair. However, yeast two-hybrid assay and bimolecular fluorescence complementation showed that PmEcR and PmRXR did not form dimers, suggesting the different molecular interactions of EcR in bivalves. These findings provide insights into the function of ecdysone and its regulation pathway in bivalve species.

Retinoid X Receptor: Cellular and Biochemical Roles of Nuclear Receptor with a Focus on Neuropathological Involvement

Retinoid X receptors (RXRs) present a subgroup of the nuclear receptor superfamily with particularly high evolutionary conservation of ligand binding domain. The receptor exists in α, β, and γ isotypes that form homo-/heterodimeric complexes with other permissive and non-permissive receptors. While research has identified the biochemical roles of several nuclear receptor family members, the roles of RXRs in various neurological disorders remain relatively under-investigated. RXR acts as ligand-regulated transcription factor, modulating the expression of genes that plays a critical role in mediating several developmental, metabolic, and biochemical processes. Cumulative evidence indicates that abnormal RXR signalling affects neuronal stress and neuroinflammatory networks in several neuropathological conditions. Protective effects of targeting RXRs through pharmacological ligands have been established in various cell and animal models of neuronal injury including Alzheimer disease, Parkinson disease, glaucoma, multiple sclerosis, and stroke. This review summarises the existing knowledge about the roles of RXR, its interacting partners, and ligands in CNS disorders. Future research will determine the importance of structural and functional heterogeneity amongst various RXR isotypes as well as elucidate functional links between RXR homo- or heterodimers and specific physiological conditions to increase drug targeting efficiency in pathological conditions.

Degenerative cervical myelopathy - update and future directions

Degenerative cervical myelopathy (DCM) is the leading cause of spinal cord dysfunction in adults worldwide. DCM encompasses various acquired (age-related) and congenital pathologies related to degeneration of the cervical spinal column, including hypertrophy and/or calcification of the ligaments, intervertebral discs and osseous tissues. These pathologies narrow the spinal canal, leading to chronic spinal cord compression and disability. Owing to the ageing population, rates of DCM are increasing. Expeditious diagnosis and treatment of DCM are needed to avoid permanent disability. Over the past 10 years, advances in basic science and in translational and clinical research have improved our understanding of the pathophysiology of DCM and helped delineate evidence-based practices for diagnosis and treatment. Surgical decompression is recommended for moderate and severe DCM; the best strategy for mild myelopathy remains unclear. Next-generation quantitative microstructural MRI and neurophysiological recordings promise to enable quantification of spinal cord tissue damage and help predict clinical outcomes. Here, we provide a comprehensive, evidence-based review of DCM, including its definition, epidemiology, pathophysiology, clinical presentation, diagnosis and differential diagnosis, and non-operative and operative management. With this Review, we aim to equip physicians across broad disciplines with the knowledge necessary to make a timely diagnosis of DCM, recognize the clinical features that influence management and identify when urgent surgical intervention is warranted.

Whole-genome sequencing reveals novel genes in ossification of the posterior longitudinal ligament of the thoracic spine in the Chinese population

BACKGROUND

Ossification of the posterior longitudinal ligament (OPLL) of the spine is a complex, multifactorial disease. Although several genes that are linked to cervical OPLL susceptibility have been reported, specific genetic studies regarding thoracic OPLL are lacking. Whole-genome sequencing has been considered as an efficient strategy to search for disease-causing genes.

METHODS

We analysed whole-genome sequences in a cohort of 25 unrelated patients with thoracic OPLL. Bioinformatics analysis and various algorithms were used to predict deleterious variants. Sanger sequencing was used to confirm the variants.

RESULTS

Four deleterious mutations in three genes (c.2716C>T (p.Arg906Cys) in collagen type VI α6 (COL6A6); c.1946G>C (p.Gly649Ala) in collagen type IX α1 (COL9A1); and c.301T>C (p.Ser101Pro) and c.171A>G (p.Ile57Met) in toll-like receptor 1 (TLR1)) were successfully identified. All the variants were confirmed by Sanger sequencing.

CONCLUSION

The novel deleterious mutations of the three genes may contribute to the development of thoracic OPLL.

The Pathogenesis of Ossification of the Posterior Longitudinal Ligament

Ossification of the posterior longitudinal ligament (OPLL) is a multi-factorial disease involving an ectopic bone formation of spinal ligaments. It affects 0.8-3.0% aging Asian and 0.1-1.7% aging European Caucasian. The ossified ligament compresses nerve roots in the spinal cord and causes serious neurological problems such as myelopathy and radiculopathy. Research in understanding pathogenesis of OPLL over the past several decades have revealed many genetic and non-genetic factors contributing to the development and progress of OPLL. The characterizations of aberrant signaling of bone morphogenetic protein (BMP) and mitogen-activated protein kinases (MAPK), and the pathological phenotypes of OPLL-derived mesenchymal stem cells (MSCs) have provided new insights on the molecular mechanisms underlying OPLL. This paper reviews the recent progress in understanding the pathophysiology of OPLL and proposes future research directions on OPLL.

Genetics Underlying an Individualized Approach to Adult Spinal Disorders

Adult spinal disorders are a significant cause of morbidity across the world and carry significant health and economic burdens. Genetic predispositions are increasingly considered for these conditions and are becoming understood. Advances in molecular technologies since the mid-1990s have made possible genetic characterizations of these diseases in many populations, and recent findings have provided insight into the underlying pathophysiologic mechanisms. These studies have made clear the genetic heterogeneity producing clinical phenotypes and suggest that individualized treatments are possible in the future. We review the genetics and heritability of cervical spondylotic myelopathy and ossification of the posterior longitudinal ligament and perform a systematic review of the genetics of adult lumbar degenerative scoliotic deformity, highlighting recent discoveries and the potential for personalized future therapeutics for these patients.

Uniaxial cyclic stretch promotes osteogenic differentiation and synthesis of BMP2 in the C3H10T1/2 cells with BMP2 gene variant of rs2273073 (T/G)

Ossification of the posterior longitudinal ligament of the cervical spine (OPLL) is characterized by the replacement of ligament tissues with ectopic bone formation, and this result is strongly affected by genetic and local factors. Two single nucleotide polymorphisms (SNPs) of rs2273073 (T/G) and rs235768 (A/T) of bone morphogenetic protein 2 (BMP2) gene which are associated with OPLL have been reported in our previous report. In this study, we confirmed the connection in 18 case samples analysis of BMP2 gene in OPLL patients; additionally, it was also shown from the OPLL patients with ligament tissues that enchondral ossification and expression of BMP2 were significantly higher compared with the non-OPLL patients by histological examination, immunohistochemistry and Western blotting analysis. To investigate the underlying mechanism, we studied the effect of SNPs in cell model. The C3H10T1/2 cells with different BMP2 gene variants were constructed and then subjected to uniaxial cyclic stretch (0.5 Hz, 10% stretch). In the presence of mechanical stress, the expression of BMP2 protein in C3H10T1/2 cells transfected by BMP2 (rs2273073 (T/G)) and BMP2 (rs2273073 (T/G), rs235768 (A/T)) were significantly higher than the corresponding static groups (P<0.05). In conclusion, these results suggested that BMP2 gene variant of rs2273073 (T/G) could not only increase cell susceptibility to bone transformation similar to pre-OPLL change, but also increase the sensibility to mechanical stress which might play an important role during the progression of OPLL.

Genetics of ossification of the posterior longitudinal ligament of the spine: a mini review

Ossification of the posterior longitudinal ligament of the spine (OPLL) is a common disease in aging populations and sometimes results in serious neurological problems due to compression of the spinal cord and nerve roots. OPLL is a multi-factorial (polygenic) disease controlled by genetic and environmental factors. Studies searching for the genetic component of OPLL, using linkage and association analyses, are in progress and several susceptibility genes have been reported. This paper reviews the recent progress in the genetic study of OPLL and comments on its future task.

Genetics and heritability of cervical spondylotic myelopathy and ossification of the posterior longitudinal ligament: results of a systematic review

STUDY DESIGN

Systematic review.

OBJECTIVE

To answer the following 3 clinical questions: (1) What is the evidence supporting a heritable predisposition for cervical spondylotic myelopathy (CSM) and ossification of the posterior longitudinal ligament (OPLL)? (2) What specific genetic polymorphisms have been associated with CSM and OPLL? (3) What is the evidence supporting a genetic basis for predicting postoperative outcomes for patients with CSM and OPLL?

SUMMARY OF BACKGROUND DATA

OPLL and CSM are thought to be multifactorial conditions resulting from a combination of environmental and genetic factors.

METHODS

A systematic review of the English language literature was undertaken for articles published between 1980 and November 7, 2012. The strength of evidence was determined by 2 independent reviewers using the Grading of Recommendation Assessment, Development and Evaluation (GRADE) criteria for studies addressing the first question of heritability and using the criteria set forth by the HuGENet Working Group in the Venice Interim Guidelines to address the last 2 questions of genetic association.

RESULTS

Of the 118 citations identified through the initial literature search, a total of 23 articles remained after application of inclusion/exclusion criteria. The 3 family association studies related to question 1 supported the principle of an inherited predisposition to CSM and OPLL; however, the strength of evidence supporting these findings was low. Within the 19 case-control studies related to question 2, 2 single nucleotide polymorphisms (COL6A1/Intron 32(-29) and COL11A2/Intron 6(-4)) were observed at higher frequencies in OPLL cases than in controls in more than 1 study and may be associated with its development. There was insufficient evidence to support an association between CSM and any specific single nucleotide polymorphism or haplotype or to support the association of specific gene alleles with postoperative CSM outcomes.

CONCLUSION

Existing family studies provide support for the principle of an inherited predisposition to CSM and OPLL. Multiple studies support the association of 2 collagen gene related single nucleotide polymorphisms with OPLL; however, there is insufficient evidence to support the association between CSM and any genetic polymorphism or to support a genetic predictor of surgical outcome. SUMMARY STATEMENTS: STATEMENT 1: Existing family studies provide support for the principle of an inherited predisposition to CSM and OPLL. STATEMENT 2: Two SNPs related to the collagen 6A1 gene (COL6A1/Intron 32(-29)) and the collagen 11A2 gene (COL11A2/Intron 6(-4)) have been associated with OPLL in multiple studies and may be associated with its development. STATEMENT 3: No statement can be made from the literature regarding the association of specific SNPs or haplotypes with CSM. STATEMENT 4: No statement can be made from the literature regarding genetic predictors of surgical outcome in the context of OPLL or CSM.

A genome-wide sib-pair linkage analysis of ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament of the spine (OPLL) is a common musculoskeletal disease among people after middle age. The OPLL presents with serious neurological abnormalities due to compression of the spinal cord and nerve roots. The OPLL is caused by genetic and environment factors; however, its etiology and pathogenesis still remain to be elucidated. To determine the susceptibility loci for OPLL, we performed a genome-wide linkage study using 214 affected sib-pairs of Japanese. In stratification analyses for definite cervical OPLL, we found loci with suggestive linkage on 1p21, 2p22-2p24, 7q22, 16q24 and 20p12. Fine mapping using additional markers detected the highest non-parametric linkage score (3.43, P = 0.00027) at D20S894 on chromosome 20p12 in a subgroup that had no complication of diabetes mellitus. Our result would shed a new light on genetic aspects of OPLL.

The genetics of ossification of the posterior longitudinal ligament

OBJECT

Ossification of the posterior longitudinal ligament (OPLL) is a pathological process of ectopic calcification with a preponderance for the cervical spine. Epidemiological and familial studies have both indicated predisposition; however, the genetic inheritance pattern and responsible genes for OPLL are still uncertain. The aim of this study was to evaluate and summarize the current understanding of the genetics underlying OPLL.

METHODS

The authors reviewed epidemiological and genetic studies surrounding OPLL, with a particular focus on inheritance patterns and potential genes responsible for OPLL, using a PubMed database literature search.

RESULTS

Despite an unclear inheritance pattern, there appears to be a strong familial link in patients with OPLL. Examination of these patterns using linkage analysis has shown multiple candidate genes that could be responsible for the inheritance of OPLL. Genes for collagen, nucleotide pyrophosphatase, transforming growth factors, and the vitamin D receptor have all been implicated. Additionally, multiple cytokines and growth factors, including bone morphogenetic proteins as well as other proteins and interleukins involved in bone development, have been shown to be abnormally expressed in patients with OPLL. In addition, multiple mechanical and metabolic factors such as hyperinsulinemia and obesity have been shown to be linked to OPLL.

CONCLUSIONS

Ossification of the posterior longitudinal ligament has a complex inheritance pattern. It does not appear that OPLL follows a simple, single-gene Mendelian inheritance pattern. Development of OPLL is more likely multifactorial in nature and develops in patients with a genetic predisposition from a variety of different mutations in various genes on various chromosomes. Additionally, environmental factors and interaction by other pathological disease processes, such as obesity and diabetes mellitus, may play a role in the development of OPLL in susceptible individuals.

Upregulated expression of connexin43 in spinal ligament fibroblasts derived from patients presenting ossification of the posterior longitudinal ligament

STUDY DESIGN

A case-control study was conducted.

OBJECTIVE

To investigate different expressions of connexin43 (Cx43) between spinal ligament fibroblasts from patients with ossification of the posterior longitudinal ligament (OPLL) and non-OPLL patients and demonstrate knockdown of Cx43 protein expression by RNA interference inhibiting expression of osteoblast-specific genes in OPLL cells.

SUMMARY OF BACKGROUND DATA

The OPLL is characterized by ectopic bone formation in spinal ligaments. Some evidence indicates that ligament fibroblasts from OPLL patients have osteogenic characteristics. However, the relevant cellular signaling pathways remain unclear.

METHODS

Twenty patients presenting with OPLL and 18 non-OPLL patients underwent anterior decompression between January 2008 and June 2009. Specimens of the posterior longitudinal ligament were collected intraoperatively. Tissue fragment cell culture was performed. Inverted phase contrast microscopy and hematoxylin-eosin staining were used to observe cell morphology. The mouse antivimentin antibody was used to identify the cultured cells via immunocytochemistry and immunofluorescence. The messenger RNA expression of osteoblast-specific genes of osteocalcin (OCN), alkaline phosphatase (ALP), and type I collagen (COL I) were detected in OPLL and non-OPLL cells by semiquantitative reverse transcription-polymerase chain reaction. The protein expression of Cx43 was detected via Western blotting. And then, after 72 hours, when RNA interference against Cx43 was performed in OPLL cells, expression of the indexes mentioned earlier was compared again between the transfection group and the nontransfection group.

RESULTS

Cultivated cells were observed 7 to 10 days after cell culture. Hematoxylin-eosin staining showed fusiform and multiangular star morphologies, large and elliptical cell nuclei, and ill-defined cell appearances. Immunocytochemistry and immunofluorescence exhibited positive results of vimentin staining. The messenger RNA expressions of OCN, ALP, and COL I and protein expressions of Cx43 from OPLL fibroblasts were greater than those from non-OPLL cells, and the difference was significant. Furthermore, knockdown of Cx43 protein expression inhibited the messenger RNA expressions of OCN, ALP, and COL I remarkably in the transfection group compared with the nontransfection group, 72 hours after RNA interference targeting Cx43 was performed in OPLL cells.

CONCLUSION

Tissue fragment culture of the cervical posterior longitudinal ligament provided a successful fibroblast culture, showing good adherence and subculture. The cultured fibroblasts from OPLL patients exhibited osteogenic characteristics, in which Cx43 played an important role.

The retinoid X receptors and their ligands

This chapter presents an overview of the current status of studies on the structural and molecular biology of the retinoid X receptor subtypes α, β, and γ (RXRs, NR2B1-3), their nuclear and cytoplasmic functions, post-transcriptional processing, and recently reported ligands. Points of interest are the different changes in the ligand-binding pocket induced by variously shaped agonists, the communication of the ligand-bound pocket with the coactivator binding surface and the heterodimerization interface, and recently identified ligands that are natural products, those that function as environmental toxins or drugs that had been originally designed to interact with other targets, as well as those that were deliberately designed as RXR-selective transcriptional agonists, synergists, or antagonists. Of these synthetic ligands, the general trend in design appears to be away from fully aromatic rigid structures to those containing partial elements of the flexible tetraene side chain of 9-cis-retinoic acid. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Genetic differences in the osteogenic differentiation potency according to the classification of ossification of the posterior longitudinal ligament of the cervical spine

STUDY DESIGN

We categorized the four types of ossification of the posterior longitudinal ligament (OPLL) of the cervical spine into two groups. We biochemically investigated the genetic differences in the osteogenic differentiation potency between the two groups.

OBJECTIVE

To investigate the genetic differences in the osteogenic differentiation potency according to the OPLL classification.

SUMMARY OF BACKGROUND DATA

Clinical studies on OPLL have revealed that the risk of progression of the ossification area is greatest for continuous and mixed type OPLL. However, until now, these four types of OPLL have been studied as a single condition.

METHODS

We categorized the four types of OPLL into the OPLL continuous (continuous or mixed type) and OPLL segmental groups (segmental or circumscribed type). Paraspinal ligaments were aseptically obtained from OPLL patients during surgery. The fibroblast-like cells that migrated from the explants were used for experiments. The cells were placed in a 60-mm culture dishes for total ribonucleic acid preparation and 12 well microplates for alkaline phosphatase (ALP) activity staining. After cultures reached confluence, the cells were cultured in osteogenic medium. The messenger ribonucleic acid expression of bone morphogenetic protein-2 (BMP-2), osterix, tumor necrosis factor-α-stimulated gene-6, and ALP was analyzed by quantitative real time-polymerase chain reaction. Osteogenic differentiation of fibroblast-like cells was determined by histochemically detecting ALP production.

RESULTS

After osteogenic induction, BMP-2 expression increased in the OPLL continuous and segmental groups. Osterix expression increased in the OPLL continuous group only. Tumor necrosis factor-α-stimulated gene-6 expression was suppressed in the OPLL continuous and segmental groups. ALP expression as well as ALP activity staining was higher in the OPLL continuous group than in the OPLL segmental group. CONCLUSION.: The study revealed genetic differences in the osteogenic differentiation potency between the OPLL continuous and segmental groups. We propose to distinguish OPLL continuous group from segmental group in biochemical studies on OPLL.

Ossification of the posterior longitudinal ligament: a review

Ossification of the posterior longitudinal ligament (OPLL) is most commonly found in men, the elderly, and Asian patients. There are many diseases associated with OPLL, such as diffuse idiopathic skeletal hyperostosis, ankylosing spondylitis, and other spondyloarthropathies. Several factors have been reported to be associated with OPLL formation and progression, including genetic, hormonal, environmental, and lifestyle factors. However, the pathogenesis of OPLL is still unclear. Most symptomatic patients with OPLL present with neurological deficits such as myelopathy, radiculopathy, and/or bowel and bladder symptoms. There are some reports of asymptomatic OPLL. Both static and dynamic factors are related to the development of myelopathy. Plain radiography, CT, and MR imaging are used to evaluate OPLL extension and the area of spinal cord compression. Management of OPLL continues to be controversial. Each surgical technique has some advantages and disadvantages, and the choice of operation should be made case by case, depending on the patient's condition, level of pathology, type of OPLL, and the surgeon's experience. In this paper, the authors attempt to review the incidence, pathology, pathogenesis, natural history, clinical presentation, classification, radiological evaluation, and management of OPLL.

A functional RNAi screen for Runx2-regulated genes associated with ectopic bone formation in human spinal ligaments

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic ossification in the spinal ligaments, which enlarges with time and compresses the spinal cord, resulting in serious neurological symptoms. We previously reported that Runx2 expression was enhanced in spinal ligament cells from OPLL patients (OPLL cells). To clarify genes regulated by Runx2, Runx2 expression was first enhanced by culturing primary OPLL cells in osteogenic medium (OS induction) and then inhibited by siRNAs targeted to Runx2. DNA microarray demonstrated that in addition to chondrogenic factors such as connective tissue growth factor and cartilage oligomeric matrix protein, angiopoietin-1 was also significantly increased by OS induction and decreased by siRNAs for Runx2 in OPLL cells, suggesting that these genes are regulated by Runx2. However, these changes were not observed in non-OPLL control cells (from cervical spondylotic myelopathy patients). Furthermore, Runx2 was not decreased by siRNAs for angiopoietin-1. OS induction and RNAi inhibition of angiopoietin-1 expression was also observed in osteoblasts. Both siRNAs for Runx2 and angiopoietin-1 completely inhibited aggrecan-1 expression. These results suggest that angiopoietin-1 is downstream of Runx2 in both OPLL primary cells and osteoblasts. Angiopoietin-1 may play an important role in ectopic ossification.

Symptomatic ossification of the ligamentum flavum at the lumbar spine: a retrospective study

STUDY DESIGN

A retrospective study on 9 patients treated for ossification of the ligamentum flavum (OLF) at the lumbar spine.

OBJECTIVE

To evaluate the clinical and radiologic findings as well as the postoperative results of the patients.

SUMMARY OF BACKGROUND DATA

Ossification of ligamentum flavum (OLF) in the lumbar region causing neurologic impairment is a rare pathologic entity described mainly in Japanese literature. The present study represents the largest surgical series of European patients with OLF at the lumbar spine.

METHODS

A retrospective study of 9 consecutive patients was conducted between 2000 and 2005. The clinical status was evaluated according to the Japanese Orthopedic Association scale. Potential associated disorders were also recorded. Diagnosis in each case was established using computed tomography and magnetic resonance imaging. Whole-spine magnetic resonance imaging was routinely used in order to reveal possible coexisting spinal lesions. Pathologic confirmation was available in all cases.

RESULTS

Radicular pain was the most common presenting symptom. Myotomal weakness was found in most of the cases. A majority of our patients had lesions located at the L3-L5 levels. Thoracic OLF was recorded as a spinal coexisting ossified lesion. Surgery led to neurologic improvement with a statistically significant increase in the Japanese Orthopedic Association score (P = 0.007). The median recovery rate was 91.60% +/- 43.85%.

CONCLUSION

It is possible that OLF is underreported in the Greek population. Surgical treatment is important in order to improve functional outcomes.

COL6A1 polymorphisms associated with ossification of the ligamentum flavum and ossification of the posterior longitudinal ligament

STUDY DESIGN

A case-control association study was conducted to investigate the genetic etiology for ossification of the ligamentum flavum (OLF) and ossification of the posterior longitudinal ligament of the spine (OPLL).

OBJECTIVE

To determine whether COL6A1 polymorphisms are associated with susceptibility to OLF and OPLL in Chinese Han population.

SUMMARY OF BACKGROUND DATA

The COL6A1 has been identified as a susceptibility gene for OPLL in Japanese. The susceptibility gene for OPLL may be different among various populations, so we investigated whether COL6A1 polymorphisms are also associated with OPLL in Chinese Han population. OLF and OPLL are similar in epidemiology, etiology, and pathology, and common coexist. Hereditary factors may be implicated in OLF and COL6A1 may be a potential susceptibility gene for OLF, so we investigated the relations between COL6A1 polymorphisms and OLF.

METHODS

Four known single nucleotide polymorphisms (SNPs) of COL6A1 were genotyped among 338 Chinese Han subjects by high throughput GenomeLab SNPstream genotyping system. Allele frequency and genotype distribution of each polymorphism were compared using a contingency chi2 test between 183 cases (90 OPLL, 61 OLF, and 32 OPLL coexisting with OLF) and 155 controls.

RESULTS

Among 4 studied SNPs, allele frequency of promoter (-572T) SNP demonstrated the most significant difference not only between OPLL cases and controls (P = 2.65E-4), but also between OLF cases and controls (P =7.38E-4). Moreover, the overall frequency of haplotypes constructed from promoter (-572), intron 32 (-29), and intron 33 (+20) SNPs showed significant difference not only between the patients with OPLL and controls, but also between the patients with OLF and controls (P = 5.86E-3, P = 1.5E-8, respectively).

CONCLUSION

This is the first report on SNPs of COL6A1 in OLF that suggests polymorphisms may be a risk factor for OLF. Our findings indicate that COL6A1 may be a common susceptibility gene for OLF and OPLL in Chinese Han population.

Hormones and growth factors in the pathogenesis of spinal ligament ossification

Ossification of the spinal ligaments (OSL) is a pathologic condition that causes ectopic bone formation and subsequently results in various degrees of neurological deficit, but the etiology of OSL remains almost unknown. Some systemic hormones, such as 1,25-dihydroxyvitamin D, parathyroid hormone (PTH), insulin and leptin, and local growth factors, such as transforming growth factor-beta (TGF-beta), and bone morphogenetic protein (BMP), have been studied and are thought to be involved in the initiation and development of OSL. This review article summarizes these studies, delineates the possible mechanisms, and puts forward doubts and new questions. The related findings from studies of genes and target cells in the ligament of OSL are also discussed. Although these findings may be helpful in understanding the pathogenesis of OSL, much more research needs to be conducted in order to investigate the nature of OSL.

Comparative analysis of serum proteomes to discover biomarkers for ossification of the posterior longitudinal ligament

STUDY DESIGN

Serum proteomes from normal subjects and the patients with ossification of the posterior longitudinal ligament (OPLL) were analyzed by using proteomics.

OBJECTIVES

To identify novel serologic biomarkers for diagnosing OPLL.

SUMMARY OF BACKGROUND DATA

OPLL can compress the spinal cord, and special planning is required for surgeries that are done from the front of the cervical spine. However, the definitive serologic biomarkers for OPLL are still unclear.

METHODS

The 2-dimensional electrophoresis patterns of sera from OPLL patients and normal subjects were compared. The differentially expressed spots were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and electrospray ionization quadruple time-of-flight mass spectrometry.

RESULTS

Nine spots that were differentially expressed in the sera of OPLL patients were found and were identified. PRO2675, human serum albumin in a complex with myristic acid and tri-iodobenzoic acid, an unknown protein, chain B of the crystal structure of deoxy-human hemoglobin beta6, pro-apolipoprotein, ALB protein, retinol binding protein and chain A of human serum albumin mutant R218h complexed with thyroxine (3,3',5,5', tetraiodo-L-thyronine), were up-regulated in the sera of OPLL patients, whereas alpha1-microglobulin/bikunin precursor was down-regulated.

CONCLUSIONS

These proteins could be used as diagnostic biomarkers of OPLL.

International Union of Pharmacology. LXIII. Retinoid X receptors

The physiological effects of retinoic acids (RAs) are mediated by members of two families of nuclear receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), which are encoded by three distinct human genes, RXRalpha, RXRbeta, and RXRgamma. RARs bind both all-trans- and 9-cis-RA, whereas only the 9-cis-RA stereoisomer binds to RXRs. As RXR/RAR heterodimers, these receptors control the transcription of RA target genes through binding to RA-response elements. This review is focused on the structure, mode of action, ligands, expression, and pharmacology of RXRs. Given their role as common partners to many other members of the nuclear receptor superfamily, these receptors have been the subject of intense scrutiny. Moreover, and despite numerous studies since their initial discovery, RXRs remain enigmatic nuclear receptors, and there is still no consensus regarding their role. Indeed, multiple questions about the actual biological role of RXRs and the existence of an endogenous ligand have still to be answered.

Pathophysiological role of endothelin in ectopic ossification of human spinal ligaments induced by mechanical stress

Ossification of the posterior longitudinal ligament (OPLL) of the spine is characterized by progressive ectopic bone formation in the spinal ligament. To identify the genes related to ossification affected by mechanical stress during OPLL, analyses using cDNA microarray were carried out using cultured human spinal ligament cells that had been subjected to uniaxial cyclic stretching. Samples were obtained from a total of 14 patients: seven cervical or thoracic OPLL patients and seven control patients. Spinal ligament cells derived from tissues of OPLL (OPLL cells) and control (non-OPLL cells) patients were subjected to uniaxial sinusoidal cyclic stretching (0.5 Hz, 20% stretch) for various time periods (0-9 hours). cDNA microarrays revealed that ranges of distribution of both up- and downregulated genes evoked by cyclic stretching were significantly wider in OPLL cells than in non-OPLL cells. Increases in the mRNA expression of endothelin-1 (ET-1) as well as various marker genes related to ossification were also observed. mRNA expression of ET-1 and alkaline phosphatase was increased by mechanical stress in a time-dependent manner, while addition of ET-1 to static cultures of OPLL cells increased mRNA expression of alkaline phosphatase in a dose-dependent manner. During 9 hours of cyclic stretching, ET-1 release increased to about sixfold the amount observed in nonstretched cells. In non-OPLL cells, neither cyclic stretching nor ET-1 induced any increase in alkaline phosphatase expression. These results suggest that mechanical stress promotes the progression of ossification in OPLL cells through autocrine and/or paracrine mechanisms of ET-1.

How does the ossification area of the posterior longitudinal ligament progress after cervical laminoplasty?

STUDY DESIGN

Retrospective case series.

OBJECTIVE

To investigate the progression pattern of ossification of the posterior longitudinal ligament (OPLL) after cervical laminoplasty.

SUMMARY OF BACKGROUND DATA

OPLL is a progressive disease, and an increased area of ossification affects the surgical results after laminoplasty. However, it is uncertain how the ossification area progresses with time after surgery.

METHODS

Fifty-five patients who were available for serial radiographs of more than 5 years were included. The extent of ossification in the longitudinal axis was assessed using computer software. The associations between the progression of OPLL and the clinical and radiologic data were analyzed.

RESULTS

Forty-one patients had OPLL progression. The patients were divided into three groups according to the pattern of progression. Group 1 consisted of patients 40 to 49 years of age with continuous or mixed type, showing slow progression at the beginning, then fast. Group 2 consisted of patients older than 50 years with continuous or mixed type, showing rapid progression at the beginning and then slow. The patients in Group 3 had segmental type with no or slight progression.

CONCLUSIONS

We speculated that the progression of OPLL decreases as the patient ages. These findings will be important for the management of patients with OPLL after surgery.

Ossification of the Posterior Longitudinal Ligament: An Update on Its Biology, Epidemiology, and Natural History

SIGNIFICANT PROGRESS HAS been achieved in basic research during the past decade on the pathogenesis of ossification of the posterior longitudinal ligament (OPLL), a multifactorial disease in which complex genetic and environmental factors interact. A review of the literature was conducted to update recent findings on the biology, epidemiology, natural history, and related diseases of OPLL. Gene analysis studies found specific polymorphisms that may be associated with OPLL in several collagen genes, which encode for extracellular matrix proteins. Polymorphisms in the nucleotide pyrophosphate gene, which is involved in regulation of calcification in chondrocytes, may also be associated with OPLL. However, the results of the gene analysis studies have not always been consistent. Involvement of many growth factors and cytokines, including bone morphogenic proteins and transforming growth factor-β, has been demonstrated in various histochemical and cytochemical analyses. Several transcription factors involved in cellular differentiation may also have a role. Recent epidemiological studies reaffirmed an earlier finding that diabetes mellitus is a distinct risk factor for OPLL. The long-term follow-up studies of OPLL patients are disclosing the natural history, as well as the frequency and rate of progression, of OPLL after surgical intervention. Further knowledge on the factors responsible for progression of OPLL may predict its behavior in each patient, and treatment may be tailored accordingly. The coexistence of OPLL with other diseases of ectopic ossification of the spine, such as ossification of the ligamentum flavum and diffuse idiopathic skeletal hyperostosis, is not uncommon. Scientific breakthrough in those diseases may, in turn, give insights into the pathogenesis of OPLL.

Spinal stenosis due to ossified lumbar lesions

OBJECT

Spinal stenosis due to lumbar ossified lesions is a rare pathological entity. The authors retrospectively evaluated the clinical features and surgical results associated with cases involving lumbar ossified lesion-induced stenosis.

METHODS

Data obtained in 20 surgically treated patients with lumbar hyperostotic spinal stenosis were included. To evaluate the background of the disease, body mass index and general complications were assessed. Whole-spine radiological examination was conducted. The presence of ossification of the posterior longitudinal ligament or ossification of the ligamentum flavum was evaluated. Surgical results were classified according to the Japanese Orthopaedic Association (JOA) scale. In the patients in whom neurological deterioration was observed during follow up, the causes of deterioration were reviewed. Seven patients (35%) were obese and six patients (30%) suffered diabetes mellitus. Twelve patients harbored coexisting cervical and/or thoracic ossified lesions. The overall mean JOA score improved from 10.2 to a peak of 22.5; at last follow-up examination the mean JOA score was 20.9. In female and older patients with a long history of preoperative symptoms, a low preoperative JOA score, and other spinal lesions, recovery tended to be poorer. Recovery was poor in one patient, and neurological deterioration due to coexisting ossified spinal lesions occurred in another patient during the follow-up period.

CONCLUSIONS

Because coexisting ossified lesions were frequently seen, whole-spine analysis is recommended. Early diagnosis and appropriate treatment are important to achieve a better surgical outcome.

Appropriateness of internal digital phantoms for monitoring the stability of the UBIS 5000 quantitative ultrasound device in clinical trials

In bone status assessment, proper quality assurance/quality control is crucial since changes due to disease or therapeutic treatment are very small, in the order of 2-5%. Unlike for dual X-ray absorptiometry, quality control procedures have not been extensively developed and validated for quantitative ultrasound technology, limiting its use in longitudinal monitoring. While the challenge of developing an ideal anthropometric phantom is still open, some manufacturers use the concept of the internal digital phantom mimicking human characteristics to check the stability of their device. The objective of the study was to develop a sensitive model of quality control suitable for the correction of QUS patient data. In order to achieve this goal, we simulated a longitudinal device lifetime with both correct and malfunctioning behaviors. Then, we verified the efficiency of digital phantoms in detecting those changes and subsequently established the in vitro/in vivo relationship. This is the first time that an attempt to validate an internal digital phantom has made, and that this type of validation approach is used. The digital phantom (DP) was designed to mimic normal bone (BUAP2) and osteoporotic bone (BUAP1) properties. The DP was studied using the UBIS 5000 ultrasound device (DMS, France). Diverse malfunctions of the UBIS-5000 were simulated. Several series of measurements were performed on both BUAP1 and 2 and on 12 volunteers at each grade of malfunction. The effect of each simulated malfunction on in vivo and in vitro results was presented graphically by plotting the average BUA values against the percentage change from baseline. The change from baseline in BUA was modeled using linear regression, and the in vivo/in vitro ratio was obtained from the model. All experimentations influenced the measure of BUAP1 and 2 as well as the measure of our 12 volunteers. However, the degree of significance varied as a function of the severity of the malfunction, and the results also differed substantially in magnitude between in vivo and in vitro. Indeed, the DP was about 10 times more sensitive to variations of the transfer function than was the in vivo measurement, which is very reassuring. The sensitivity of the digital phantoms was reliable in the determination of simulated malfunctions of the UBIS-5000. The digital phantoms provided an accurate evaluation of the acoustic performance of the scanner, including the fidelity of transducers. In light of these results, the QC approach of the UBIS-5000 will be extremely simple to implement compared with other devices. Indeed, since the digital phantom was automatically measured during every patient measurement, the QC approach could be built on an individual level basis rather than on an average basis.

High body mass index after age 20 and diabetes mellitus are independent risk factors for ossification of the posterior longitudinal ligament of the spine in Japanese subjects: a case-control study in multiple hospitals

STUDY DESIGN

A sex- and age-matched case-control study was carried out.

OBJECTIVES

To facilitate early prediction, prevention, and treatment of ossification of the posterior longitudinal ligament of the spine, the authors analyzed histories of past illness, past body mass indexes, and body pliableness by nature, adjusted for other factors considered to be risk factors.

SUMMARY OF BACKGROUND DATA

The cause of ossification of the posterior longitudinal ligament of the spine has not yet been elucidated in detail, although many possible causative factors have been suggested, including gender, diabetes mellitus, trauma, hormonal imbalance, and dietary habits.

METHODS

A self-administered questionnaire was obtained from 69 patients with ossification of the posterior longitudinal ligament of the spine and 138 sex- and age-matched control participants who were free of spinal disease, randomly selected from participants in a health checkup in a town. After univariate analysis, a stepwise method was applied to select significant factors in multivariate analysis.

RESULTS

A multivariate analysis revealed that the following three indicators were independent potent risk factors for ossification of the posterior longitudinal ligament of the spine: history of diabetes mellitus, history of lumbago, and maximum body mass index before manifestation > or =25, after adjustment for other possible lifestyle risk factors.

CONCLUSION

Excessive weight gain between 20 and 40 years of age, diabetes mellitus, and lumbago were found to be independent risk factors for ossification of the posterior longitudinal ligament of the spine. Follow-up studies, including the addition of hospital-based control participants and analysis of genetic polymorphisms, will be needed in the future.

Sequence variations in the collagen IX and XI genes are associated with degenerative lumbar spinal stenosis

BACKGROUND

Degenerative lumbar spinal stenosis (LSS) is usually caused by disc herniation or degeneration. Several genetic factors have been implicated in disc disease. Tryptophan alleles in COL9A2 and COL9A3 have been shown to be associated with lumbar disc disease in the Finnish population, and polymorphisms in the vitamin D receptor gene (VDR) (FokI and TaqI), the matrix metalloproteinase-3 gene (MMP-3) and an aggrecan gene (AGC1) VNTR have been reported to be associated with disc degeneration. In addition, an IVS6-4 a>t polymorphism in COL11A2 has been found in connection with stenosis caused by ossification of the posterior longitudinal ligament in the Japanese population.

OBJECTIVE

To study the role of genetic factors in LSS.

METHODS

29 Finnish probands were analysed for mutations in the genes coding for intervertebral disc matrix proteins, COL1A1, COL1A2, COL2A1, COL9A1, COL9A2, COL9A3, COL11A1, COL11A2, and AGC1. VDR and MMP-3 polymorphisms were also analysed. Sequence variations were tested in 56 Finnish controls.

RESULTS

Several disease associated alleles were identified. A splice site mutation in COL9A2 leading to a premature translation termination codon and the generation of a truncated protein was identified in one proband, another had the Trp2 allele, and four others the Trp3 allele. The frequency of the COL11A2 IVS6(-4) t allele was 93.1% in the probands and 72.3% in controls (p = 0.0016). The differences in genotype frequencies for this site were less significant (p = 0.0043).

CONCLUSIONS

Genetic factors have an important role in the pathogenesis of LSS.

Uniaxial cyclic stretch induces osteogenic differentiation and synthesis of bone morphogenetic proteins of spinal ligament cells derived from patients with ossification of the posterior longitudinal ligaments

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic bone formation in the spinal ligaments. Mechanical stress, which acts on the posterior ligaments, is thought to be an important factor in the progression of OPLL. To elucidate this mechanism, we investigated the effects of in vitro sinusoidal cyclic stretch (120% peak to peak, at 1 Hz) on cultured spinal ligament cells derived from OPLL and non-OPLL patients. The mRNA expressions of alkaline phosphatase (ALP), osteopontin, bone morphogenetic protein (BMP)-2, BMP-4, and BMP receptors as well as ALP activity in cell layers and production of BMPs into the conditioned medium were significantly increased by cyclic stretch in OPLL cells, whereas no change was observed in non-OPLL cells. A stretch-activated Ca(2+) channel blocker, Gd(3+), the voltage-dependent L-type Ca(2+) channel blockers diltiazem and nifedipine, and Ca(2+)-free medium suppressed stretch-induced ALP activity, which suggests a role of Ca(2+) influx in the signal transduction of mechanical stress to the osteogenic response of OPLL cells. Our study provides first evidences that mechanical stress plays a key role in the progression of OPLL through the induction of osteogenic differentiation in spinal ligament cells and the promotion of the autocrine/paracrine mechanism of BMPs in this lesion.

High serum levels of menatetrenone in male patients with ossification of the posterior longitudinal ligament

STUDY DESIGN

This work was performed to investigate the role of vitamin K (VK) in the pathogenesis of ossification of posterior longitudinal ligament (OPLL), by analyzing the biochemical markers of the blood samples of OPLL patients and responses of ligament cells derived from OPLL lesion to VK2.

OBJECTIVES

The pathogenesis of OPLL, classified as a form of diffuse idiopathic skeletal hyperostosis, is still unclear. In this study, we investigated the role of menaquinone (VK2) in patients with OPLL (OPLL patients) and the effects of VK2 on ligament cells isolated from OPLL lesion.

METHODS

Serum levels of intact osteocalcin, glu-osteocalcin, MK-4, -7 (VK2 variants) and other minerals in spot blood samples were measured in 24 OPLL patients and in 24 age-matched control patients (non-OPLL patients). The cultured cells isolated from an OPLL patient were treated with MK-4. Alkaline phosphatase (Al-p) activity and osteocalcin release were measured after 2 weeks of culture.

RESULTS

In the clinical study, the serum MK-4 in male OPLL patients was significantly higher than that in male non-OPLL patients. However, among female patients, the difference was not significant. Although the serum osteocalcin in females was significantly higher than that in males, there was no significant difference between the OPLL and non-OPLL groups. In in vitro study, MK-4 did not increase Al-p activity in the ligament cells isolated from nonossified region of OPLL patient. Osteoblastic activity of the cultured cells was not stimulated by MK-4.

CONCLUSION

From these results and previous reports, we propose the possibility of the impediment in VK2 metabolism in OPLL patients. The results also implicate the gender tendency in OPLL, because the difference of serum level of MK-4 in OPLL patients was significant only in male.

Role of prostaglandin I2 in the gene expression induced by mechanical stress in spinal ligament cells derived from patients with ossification of the posterior longitudinal ligament

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic bone formation in the spinal ligaments, and mechanical stress has been suggested to play an important role in the progression of OPLL. To identify the genes that participate in OPLL, the differential display reverse transcription-polymerase chain reaction (RT-PCR) method was used. A 283-base pair cDNA fragment corresponding to prostaglandin I2 (PGI2) synthase was highly expressed in OPLL cells compared with non-OPLL cells. To examine the effect of mechanical stress on the expression of PGI2 synthase, cells were subjected to uniaxial cyclic stretch (0.5 Hz, 20% stretch), and PGI2 synthase mRNA expression was assessed by quantitative RT-PCR. Cyclic stretch induced an increase in PGI2 synthase in OPLL cells in a time-dependent manner, whereas no change was observed in non-OPLL cells. Cyclic stretch for 9 h also induced a 2.86x increase in PGI2 production. Beraprost (a stable PGI2 analog) and dibutyryl cAMP (a membrane-permeable cAMP analog) increased the mRNA expression of alkaline phosphatase (ALP) as a marker for osteogenic differentiation up to 240 and 200%, respectively, in OPLL cells, whereas no change was observed in non-OPLL cells. The increases in ALP mRNA induced by beraprost and cyclic stretch were both inhibited by SQ22536, a potent adenylate cyclase inhibitor. These data suggest that the increase in PGI2 synthase induced by mechanical stress plays a key role in the progression of OPLL, at least in part through the induction of osteogenic differentiation in spinal ligament cells via the PGI2/cAMP system.

Linkage disequilibrium between HLA-DPB1 alleles and retinoid X receptor beta haplotypes

The human retinoid X receptor beta (RXRB) gene maps to the major histocompatibility complex (MHC) region, between KE4 and COL11A2, approximately 130-kb centromeric to HLA-DPB1. We have recently reported a new polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to detect the G to T single nucleotide polymorphism (SNP) located seven nucleotides after the tenth exon of the RXRB gene, or 3'end+7 position according to existing nomenclature. We also reported strong linkage disequilibrium between the HLA-DPB1*0401 and RXRB+7*T alleles. In the present study, we describe two PCR-RFLP methods to detect additional SNPs in the RXRB gene, T to A, at exon10+378 and A to T at 3'end+140. This new methodology permitted the unambiguous assignment of three distinct SNPs at RXRB exon10+378, 3'end+7 and 3'end+140 to form an "RXRB haplotype." The data generated from this study were used to determine linkage disequilibrium between several MHC markers and the RXRB alleles and haplotypes. Family studies revealed significant linkage disequilibrium between the RXRB alleles and a number of HLA-DPB1 alleles.

Possible roles of CTGF/Hcs24 in the initiation and development of ossification of the posterior longitudinal ligament

STUDY DESIGN

A biochemical and histochemical study investigating the role of CTGF/Hcs24 in the ossification of the posterior longitudinal ligament (OPLL) was conducted.

OBJECTIVE

To clarify the involvement of CTGF/Hcs24 in ectopic bone formation in OPLL through endochondral ossification using human tissue.

SUMMARY OF BACKGROUND DATA

Previous studies have shown that various cytokines are involved in the occurrence or development of ectopic bone formation in OPLL. Recently, the authors cloned an mRNA predominantly expressed in chondrocytes by differential display PCR and found that its gene, hcs24, is identical to that of connective tissue growth factor. It has been shown that CTGF/Hcs24 plays a major role in endochondral ossification.

METHODS

Ossified ligament tissues were taken from seven male OPLL patients during surgery. Immunohistochemical staining was performed using an antibody specific for CTGF/Hcs24. Spinal ligament cells were isolated from five OPLL patients as well as five non-OPLL patients. The cells were incubated with recombinant human CTGF/Hcs24 or TGFbeta. The expression of ALP was analyzed by RT-PCR. For the effects of TGFbeta, the expression of CTGF/Hcs24 mRNA was analyzed.

RESULTS

Immunohistochemical staining showed that chondrocytes in the transitional region from nonossified to ossified ligament were stained with an antibody against CTGF/Hcs24. It was found that CTGF/Hcs24 enhanced the expression ALP mRNA in OPLL cells, whereas the expression remained unchanged in non-OPLL cells. The expression of CTGF/Hcs24 mRNA in OPLL and non-OPLL cell lines was increased by TGFbeta, and there was no significant difference between the two groups. However, TGFbeta and CTGF/Hcs24 enhanced the expression of ALP mRNA only in OPLL cells.

CONCLUSIONS

According to the study results, CTGF/Hcs24 may not only be an important factor in the development of endochondral ossification in OPLL, but may also be responsible for initiating osteogenesis in spinal ligament cells.

Polymorphism of the human retinoid X receptor beta and linkage disequilibrium with HLA-DPB1

The human retinoid X receptor beta (RXRB) gene is localized in the major histocompatibility complex (MHC) region between DPB1 and RING2. The RXRB gene sequence reported by different investigators suggests that the gene may be polymorphic. In this study, we confirmed one polymorphism by sequencing genomic DNA from four Caucasian individuals. We also developed a restriction fragment length polymorphism (RFLP) analysis to detect this specific polymorphism. Linkage analysis studies between RXRB alleles and a number of HLA markers showed significant linkage disequilibrium between RXRB*T and HLA-DPB1*0401.

Functional impact of human collagen alpha2(XI) gene polymorphism in pathogenesis of ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament (OPLL) of the spine is the leading cause of myelopathy in Japan. In earlier studies, we provided genetic linkage and allelic association evidence of distinct differences in the human collagen alpha2(XI) gene (COL11A2) that might constitute inherited predisposition to OPLL. In the present study, a strong allelic association with non-OPLL (p = 0.0003) was observed with an intron 6 polymorphism [intron 6 (-4A)], in which the intron 6 (-4A) allele is more frequently observed in non-OPLL subjects than in OPLL patients. In addition, a newly identified polymorphism in exon 6 [exon 6 (+28A)] was in linkage disequilibrium with the intron 6 (-4A). The functional impact of the polymorphisms was analyzed by comparing the differences in messenger RNA (mRNA) splicing by reverse-transcription polymerase chain reaction (RT-PCR) analysis in cultured cells from the interspinous ligament and an in vitro exon trapping study. The intron 6 (-4A) allele resulted in skipping exon 6 and retaining exon 7, while the exon 6 (+28A) allele was not associated with alteration in mRNA splicing. Similar mRNA species were observed in undifferentiated osteoblast (Ob) cells and in cells from posterior longitudinal ligament of non-OPLL subjects. The region containing exons 6-8 is an acidic subdomain presumably exposed to the surface that could interact with molecules of the extracellular matrix. Accordingly, retaining exon 7 together with removal of exon 6 observed in intron 6 (-4A) could play a protective role in the ectopic ossification process because the same pattern was observed in undifferentiated Ob cells and nonossified posterior longitudinal ligament cells.