Ossification of the posterior longitudinal ligament (OPLL) is a condition comprising ectopic bone formation from spinal ligaments. This disease is a leading cause of myelopathy in the Asian population. However, the molecular mechanism underlying OPLL and efficient preventive interventions remain unclear. Here, we performed single-cell RNA sequencing and revealed that type I interferon (IFN) signaling was activated in the ossified ligament of patients with OPLL. We also observed that IFN-β stimulation promoted the osteogenic differentiation of preosteoblasts in vitro and activated the ossification-related gene SPP1, thereby confirming the single-cell RNA sequencing findings. Further, blocking the IFN-α/β subunit 1 receptor (IFNAR1) using an anti-IFNAR1 neutralizing antibody markedly suppressed osteogenic differentiation. Together, these results demonstrated that the type I IFN signaling pathway facilitated ligament ossification, and the blockade of this signaling might provide a foundation for the prevention of OPLL.
Humans ; Signal Transduction ; Interferon Type I/metabolism* ; Ossification of Posterior Longitudinal Ligament/genetics* ; Gene Expression Profiling ; Single-Cell Analysis ; Osteogenesis/genetics* ; Receptor, Interferon alpha-beta/metabolism* ; Male ; Female ; Cell Differentiation ; Middle Aged

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.
Aging ; Genetic Association Studies ; Genetics* ; Longitudinal Ligaments* ; Ossification of Posterior Longitudinal Ligament ; Spinal Cord ; Spine*

BACKGROUNDOssification of the posterior longitudinal ligament (OPLL) is characterized by the replacement of ligamentous tissue with new ectopic bone formation, and has a strong genetic background. Because of the abnormal bone metabolic features and the strong genetic component, osteoporosis is a related disorder with OPLL. Three polymorphisms on chromosome 20p12 were identified associated with the risk of osteoporosis and osteoporotic fracture. The rs996544 (C/T) "TT" and rs965291 (G/A) "AA" genotypes conferred higher risks for vertebral and hip fractures. The osteoporosis haplotype is defined by two polymorphisms, rs1116867 (A) and D35548 (T). However, it remains unknown whether these three polymorphisms predispose to an increased frequency and severity of OPLL in Han Chinese patients.

METHODSA total of 420 OPLL patients and 506 age- and sex-matched controls were studied. Three single nucleotide polymorphisms (SNPs), rs996544 (C/T), rs965291 (G/A) and rs1116867 (A/G), were analyzed by direct sequencing. Associations between these SNPs with the occurrence and extent of OPLL were statistically evaluated.

RESULTSThere was no significant association between the rs996544 (C/T) polymorphism and the prevalence of OPLL. The rs1116867 (A/G) polymorphism "AG" genotype was associated with the occurrence of OPLL. The rs1116867 (A/G) polymorphism "G" allele was associated with the occurrence of OPLL, but not with the extent of OPLL. The rs965291 (G/A) polymorphism in female patients was statistically different between cases and controls (P < 0.05). The rs965291 (G/A) polymorphism "A" allele was associated with the occurrence of OPLL in female patients. For the rs965291 (G/A) polymorphism, patients with the "A" allele (genotype, "AG" or "AA") showed a significantly greater number of ossified cervical vertebrae than those without the "A" allele (genotype, "GG", P < 0.05), particularly in female patients.

CONCLUSIONSThe rs1116867 (A/G) and rs965291 (G/A) polymorphisms on chromosome 20p12 are associated with the occurrence and the extent of OPLL, at least in Han Chinese subjects. Our data should advance our understanding of the molecular etiology of OPLL and may guide approaches to prevent the onset of OPLL.

Adult ; Aged ; Bone Morphogenetic Protein 2 ; genetics ; China ; ethnology ; Chromosomes, Human, Pair 20 ; Female ; Genetic Linkage ; Genotype ; Humans ; Male ; Middle Aged ; Ossification of Posterior Longitudinal Ligament ; genetics ; Polymorphism, Single Nucleotide

BACKGROUNDSeveral candidate genes of ossification of the posterior longitudinal ligament (OPLL) susceptibility have been identified, but their polymorphisms account for only a small percent of the total variance. Bone morphogenetic protein-4 (BMP4) is a potent ectopic ossification inducing factor. BMP4 protein and mRNA are present in cells from OPLL patients, but not non-OPLL controls. A single nucleotide polymorphism of 6007C>T(rs17563) of BMP4 has been reported to affect bone density in postmenopausal women. Thus, BMP4 may function in OPLL development. Appropriately, the relationship between BMP4 polymorphisms and OPLL was investigated.

METHODSA case-control association study investigated the genetic etiology in 179 OPLL patients and 298 non-OPLL controls. Extent of OPLL was analyzed by radiologic examinations. Whether single nucleotide polymorphism (SNP) of -5826G>A(rs1957860) 5' of the transcription start site and 6007C>T(rs17563) in exon 4 of the BMP4 gene were statistically associated with genetic susceptibility to OPLL in Chinese Han subjects was assessed.

RESULTSA significant statistical difference in genotype of 6007C>T polymorphism between male OPLL patients and male controls was evident, and the frequency of "TT" genotype in male OPLL patients was significantly higher than in male controls (P = 0.039). The frequency of the "T" allele was also significantly higher in male OPLL subjects than in male controls (P = 0.014, OR = 1.57). A significant difference was also observed between the 6007C>T polymorphism and the number of ossified cervical vertebrae in OPLL patients, while no statistical difference was apparent between the -5826G>A polymorphism and OPLL occurrence.

CONCLUSIONSThe T allele in the 6007C>T polymorphism may be a risk factor for male Han Chinese with ossification of the posterior longitudinal ligament in the cervical spine. Chinese Han male patients with CT and TT 6007C>T genotypes have a genetic susceptibility to OPLL and more extensive OPLL in the cervical spine.

Alleles ; Asian Continental Ancestry Group ; genetics ; Bone Morphogenetic Protein 4 ; genetics ; Female ; Genetic Predisposition to Disease ; genetics ; Genotype ; Humans ; Male ; Middle Aged ; Ossification of Posterior Longitudinal Ligament ; genetics ; Polymorphism, Single Nucleotide ; genetics

BACKGROUNDOssification of the posterior longitudinal ligament (OPLL) has a strong genetic background. Previous studies have shown that bone morphogenetic protein-2 (BMP2) and BMP2 mRNA are expressed in ossifying matrix and chondrocytes adjacent to cartilaginous areas of OPLL tissues and mesenchymal cells with fibroblastic features in the immediate vicinity of the cartilaginous areas. It is suggested that BMP2 plays different roles in the different stages of development of OPLL. However, it remains unknown which factors induce ligament cells to produce BMP2.

METHODSOPLL patients (n = 192) and non-OPLL controls (n = 304) were studied. Radiographs of the cervical spine were analyzed for extent of OPLL. We investigated whether single nucleotide polymorphisms of exons 3 (-726) T/C and 3 (-583) A/G in the BMP2 gene are statistically associated with genetic susceptibility to OPLL in Chinese Han subjects.

RESULTSThere was no statistical difference between the occurrence of exons 3 (-726) T/C and 3 (-583) A/G and the occurrence of OPLL in the cervical spine. However, there was a significant association between occurrence of exon 3 (-726) T/C polymorphism and occurrence of OPLL in males of cases and controls in the cervical spine. In addition, no significant association was found between the exons 3 (-726) T/C and 3 (-583) A/G with number of ossified cervical vertebrae in OPLL patients.

CONCLUSIONSExon 3 (-583) A/G polymorphism in BMP2 gene is not associated with the occurrence and the extent of OPLL in the cervical spine. Chinese Han male patients with TC and CC genotypes in exon 3 (-726) T/C have genetic susceptibility to OPLL but not to more extensive OPLL in the cervical spine.

Asian Continental Ancestry Group ; genetics ; Bone Morphogenetic Protein 2 ; genetics ; China ; Exons ; Female ; Genetic Predisposition to Disease ; genetics ; Humans ; Male ; Middle Aged ; Neck ; Ossification of Posterior Longitudinal Ligament ; genetics ; Polymorphism, Genetic