Aggravation of Ossified Ligamentum Flavum Lesion Is Associated With the Degree of Obesity

Interleukin-17A Promotes Proliferation and Osteogenic Differentiation of Human Ligamentum Flavum Cells Through Regulation of β-Catenin Signaling

STUDY DESIGN

A basic experimental study.

OBJECTIVE

To elucidate the role and mechanism of interleukin (IL)-17A in thoracic ossification of the ligamentum flavum (TOLF).

SUMMARY OF BACKGROUND DATA

TOLF is characterized by the replacement of the thoracic ligamentum flavum with ossified tissue and is one of the leading causes of thoracic spinal stenosis. IL-17A is an important member of the IL-17 family that has received widespread attention for its key contributions to the regulation of bone metabolism and heterotopic ossification. However, it is unclear whether IL-17A is involved in TOLF.

MATERIALS AND METHODS

Cell counting kit-8 assay and 5-ethynyl-2'-deoxyuridine staining were performed to assess the proliferation of ligamentum flavum cells (LFCs). Alkaline phosphatase activity assay, Alizarin red staining, and protein level expression of osteogenic-related genes were used to evaluate the osteogenic differentiation potential of LFCs. The effect of IL-17A on the proliferation and osteogenic differentiation of LFCs was further assessed after silencing β-catenin by transfection with small interfering RNA. In addition, the possible source of IL-17A was further demonstrated by coculture assays of T helper 17 (Th17) cells with LFCs. Student t test was used for comparisons between groups, and the one-way analysis of variance, followed by the Tukey post hoc test, was used for comparison of more than two groups.

RESULTS

IL-17A was elevated in TOLF tissue compared with normal ligamentum flavum. IL-17A stimulation promoted the proliferation and osteogenic differentiation of LFCs derived from patients with TOLF. We found that IL-17A promoted the proliferation and osteogenic differentiation of LFCs by regulating the β-catenin signaling. Coculture of Th17 cells with LFCs enhanced β-catenin signaling-mediated proliferation and osteogenic differentiation of LFCs. However, these effects were markedly attenuated after the neutralization of IL-17A.

CONCLUSIONS

This is the first work we are aware of to highlight the importance of IL-17A in TOLF. IL-17A secreted by Th17 cells in the ligamentum flavum may be involved in the ossification of the microenvironment by regulating β-catenin signaling to promote the proliferation and osteogenic differentiation of LFCs.

Lumbar ossification of the ligamentum flavum reflects a strong ossification tendency of the entire spinal ligament

Patients with ossification of the ligamentum flavum (OLF) in the lumbar spine may be at high risk of developing concomitant ossification of the entire spinal ligament, but the etiology remains unclear. We investigated the propensity for spinal ligament ossification in asymptomatic subjects with lumbar OLF using the data of 595 Japanese individuals receiving medical check-ups, including computed tomography (CT) scanning. The severity of OLF (total number of intervertebral segments with OLF) of the entire spine on CT was quantified using an OLF index. Subjects with OLF were grouped according to this index: localized OLF (n = 138), intermediate OLF (n = 70), and extensive OLF (n = 31). The proportion of subjects with lumbar OLF increased with increasing OLF index (localized 13.7%, intermediate 41.4%, and extensive 70.9%). Multiple regression analysis found that lumbar OLF index was associated with thoracic OLF index, and co-existence of ossification of the posterior longitudinal ligament (OPLL) of the thoracic and lumbar spine. This study showed that subjects with more multilevel lumbar OLF were more likely to develop multilevel thoracic OLF and to have coexisting OPLL. Patients with lumbar OLF may be a distinctive subgroup with a strong tendency to ossification of the entire spinal ligament.

Strong relationship between dyslipidemia and the ectopic ossification of the spinal ligaments

Obesity and metabolic disturbances are prevalent in ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF); however, the involvement of dyslipidemia (DL) in OPLL/OLF remains uncertain. We investigated the association between dyslipidemia and OPLL/OLF using a dataset of 458 individuals receiving health screening tests, including computed tomography. Subjects were grouped according to the presence or location of OPLL/OLF: controls (no OPLL/OLF, n = 230), OLF (n = 167), cervical OPLL (n = 28), and thoracic OPLL (n = 33). They were also grouped according to the presence of dyslipidemia (DL[+], n = 215; DL[-], n = 243). The proportion of dyslipidemia in the OLF and OPLL groups was 1.6-2.2 times higher than that in the control group. The proportion of OLF and OPLL in the DL(+) group was significantly higher than that in the DL(-) group (OLF, 43% vs. 29%; cervical OPLL, 14.4% vs. 3.2%; thoracic OPLL, 11.1% vs. 3.7%). Multivariate logistic regression analysis showed an association between all ossification types and dyslipidemia. This study demonstrated an association of dyslipidemia with OPLL/OLF; further investigation on the causal relationship between dyslipidemia and ectopic spinal ligament ossification is warranted to develop a therapeutic intervention for OPLL/OLF.

Significance of body mass index on thoracic ossification of the ligamentum flavum in Chinese population

PURPOSE

To investigate the risk factors for thoracic ossification of the ligamentum flavum (TOLF), especially the relationship between BMI and TOLF.

METHODS

A total of 856 individuals consisting of 326 controls without ossification of spinal ligaments and 530 TOLF inpatients who underwent thoracic spine decompression surgery at our hospital between January 2013 and September 2020 were included. All subjects were classified into 4 grades: Grade 0) control; Grade 1) single-segment TOLF; Grade 2) multi-segment TOLF; and Grade 3) TOLF combined thoracic ossification of the posterior longitudinal ligament (T-OPLL). Logistic regression analysis was performed to identify the risk factors for TOLF. The TOLF index was calculated to assess the severity of TOLF, and its relationship with BMI was investigated by correlation analysis.

RESULTS

Overall, TOLF patients are most numerous in the 50-59 age group. Age and gender were considered as independent risk factors for Grades 1 and 2. BMI was identified as an independent risk factor for TOLF. Furthermore, BMI was significantly higher in Grade 1 (26.1 VS 24.5 kg/m², P = 0.0001), Grade 2 (28.2 VS 24.5 kg/m², P < 0.0001), and Grade 3 (29.1 VS 24.5 kg/m², P < 0.0001) than Grade 0. Notably, in TOLF patients without combined T-OPLL, BMI was positively correlated with TOLF index, while BMI was negatively correlated with age in younger individuals.

CONCLUSION

BMI is a crucial risk factor for TOLF. It highlights the necessity of close follow-up of asymptomatic TOLF patients with high BMI to detect and treat their TOLF progression promptly.

High Systemic Immune-Inflammation Index and Body Mass Index Are Independent Risk Factors of the Thoracic Ossification of the Ligamentum Flavum

Background

Inflammation has been considered to play an important role in the pathogenesis of the thoracic ossification of the ligamentum flavum (OLF). However, the inflammation-related risk factors of thoracic OLF have not been fully investigated to date.

Methods

A total of 95 patients (48 in the OLF group and 47 in the control group) were included in this retrospective study to explore the independent risk factors of thoracic OLF. The following demographic and clinical variables were compared between the two groups: gender, age, body mass index (BMI), coexistence of hypertension or diabetes, and inflammation-related variables. Multivariate logistic regression analysis was utilized to determine the independent risk factors.

Results

High systemic immune-inflammation index (SII) (≥621) (odds ratio [OR] = 12.16, 95% confidence interval [CI] = 2.95–50.17, p < 0.01) and BMI (≥25 kg/m²) (OR = 9.17, 95%CI = 3.22–26.08, p < 0.01) were independent risk factors of thoracic OLF. SII (R = 0.38, p < 0.01) and BMI (R = 0.46, p < 0.01) were positively associated with OLF score.

Conclusion

High SII and BMI were the independent risk factors of thoracic OLF. Multicenter prospective studies with a large population should be conducted in the future to verify our findings.

High Body Mass Index Is Associated with an Increased Risk of the Onset and Severity of Ossification of Spinal Ligaments

Background

Ossification of the posterior longitudinal ligament (OPLL) and that of ligamentum flavum (OLF) are the main types of the ossification of spinal ligaments (OSL) that cause the thoracic myelopathy. Although several studies have investigated the relationship of body mass index (BMI) with the onset or severity of OSL, it remains unverified due to the contradictory results of existing evidence. A systematic review and meta-analysis were performed in this work to determine the relationship of BMI with the onset and severity of OSL.

Methods

PubMed, EMBASE, Web of Science, and Cochrane Library were comprehensively searched online for relevant studies focusing on the relationship of BMI with the onset or severity of the OSL. The difference in BMI of OSL (or severe OSL group) and non-OSL (or nonsevere OSL group) groups was evaluated using the mean difference (MD) with a corresponding 95% confidence interval (CI).

Results

Fifteen studies were included in this systematic review and meta-analysis. The BMI of the OSL group was significantly higher than that of the non-OSL group (MD = 1.70 kg/m², 95% CI = 1.02–2.39 kg/m², and P < 0.01). Similar results were observed in the subgroup analysis of female (P < 0.01), OPLL (P < 0.01), and OLF (P < 0.01) populations. Three studies reported a significant association of BMI with the ossification index of OSL and the standardized regression coefficient ranging from 0.11 to 0.43 (P < 0.05). Moreover, a significantly higher BMI was observed in the severe OSL group compared with that in the nonsevere OSL group (MD = 3.09, 95% CI, 0.22–5.97 kg/m², and P = 0.04).

Conclusion

The significant association of high BMI with the onset and severity of OSL may provide new evidence and insights into the mechanism research and management of OSL.

Case Report: Multilevel Ossification of the Ligamentum Flavum in a Patient With Spinal Osteoblastoma

Introduction

Spinal osteoblastomas are primary benign bone tumors most commonly presenting as diffuse back pain in young adults. Rarely, spinal osteoblastoma is associated with ossification of the ligamentum flavum (OLF), a form of ectopic bone formation, which can present with myelopathy. This report highlights a unique case of a patient with spinal osteoblastoma, associated OLF, and thoracic myelopathy.

Case Description

The patient presented with subtle myelopathy consisting of mid-thoracic back pain, paresthesias, and gait instability. Imaging findings were suggestive of spinal osteoblastoma with multifocal OLF. The patient was consented for thoracic decompression and stabilization at the T6-10 levels. Histopathology confirmed osteoblastoma with associated OLF. At follow up, the patient’s neurological symptoms had completely resolved.

Conclusion

This case describes management for a rare presentation of osteoblastoma with associated OLF and myelopathy. Surgeons should be wary of disproportionate neurological compromise when spinal osteoblastoma is associated with OLF. Further study is required to elucidate the pathogenesis of this condition.

Association between obesity and ossification of spinal ligaments in 622 asymptomatic subjects: a cross-sectional study

INTRODUCTION

Previous studies on patients with symptoms of spinal ligament ossification, including ossification of the posterior longitudinal ligament (OPLL) and ligamentum flavum (OLF), have not clarified whether obesity is a cause or consequence of these diseases and were limited by selection bias. Thus, we investigated the association between obesity and the prevalence of spinal ligament ossification in randomly selected asymptomatic subjects.

MATERIALS AND METHODS

Between April 2020 and March 2021, 622 asymptomatic Japanese subjects who underwent computed tomography of neck to pelvis for medical check-up purposes were included. All subjects were divided into the following three groups: normal weight (body mass index [BMI] < 25 kg/m²), obese I (25 ≤ BMI < 30 kg/m²), and obese II (BMI ≥ 30 kg/m²). The relationship between factors affecting the presence of each spinal ligament ossification was evaluated using multivariate logistic regression analysis.

RESULTS

The proportion of subjects with thoracic OPLL was significantly higher in the obese II group than in the other two groups (vs. normal weight, P < 0.001; vs. obese I, P < 0.001). BMI was associated with the prevalence of OLF, cervical OPLL, thoracic OPLL, and ossification of the anterior longitudinal ligament (OALL). BMI was most significantly associated with the prevalence of thoracic OPLL (β, 0.28; 95% confidence interval, 0.17-0.39).

CONCLUSION

BMI was associated with the prevalence of OALL, cervical OPLL, thoracic OPLL, and OLF in asymptomatic subjects, suggesting that obesity is associated with the development of heterotopic ossification of the spinal ligaments.

Deciphering Obesity-Related Gene Clusters Unearths SOCS3 Immune Infiltrates and 5mC/m6A Modifiers in Ossification of Ligamentum Flavum Pathogenesis

BACKGROUND

Ossification of ligamentum flavum (OLF) is an insidious and debilitating heterotopic ossifying disease with etiological heterogeneity and undefined pathogenesis. Obese individuals predispose to OLF, whereas the underlying connections between obesity phenotype and OLF pathomechanism are not fully understood. Therefore, this study aims to explore distinct obesity-related genes and their functional signatures in OLF.

METHODS

The transcriptome sequencing data related to OLF were downloaded from the GSE106253 in the Gene Expression Omnibus (GEO) database. The obesity-related differentially expressed genes (ORDEGs) in OLF were screened, and functional and pathway enrichment analysis were applied for these genes. Furthermore, protein-protein interactions (PPI), module analysis, transcription factor enrichment analysis (TFEA), and experiment validation were used to identify hub ORDEGs. The immune infiltration landscape in OLF was depicted, and correlation analysis between core gene SOCS3 and OLF-related infiltrating immune cells (OIICs) as well as 5mC/m6A modifiers in OLF was constructed.

RESULTS

Ninety-nine ORDEGs were preliminarily identified, and functional annotations showed these genes were mainly involved in metabolism, inflammation, and immune-related biological functions and pathways. Integrative bioinformatic algorithms determined a crucial gene cluster associated with inflammatory/immune responses, such as TNF signaling pathway, JAK-STAT signaling pathway, and regulation of interferon-gamma-mediated signaling. Eight hub ORDEGs were validated, including 6 down-regulated genes (SOCS3, PPARG, ICAM-1, CCL2, MYC, and NT5E) and 2 up-regulated genes (PTGS2 and VEGFA). Furthermore, 14 differential OIICs were identified by ssGSEA and xCell, and SOCS3 was overlapped to be the core gene, which was associated with multiple immune infiltrates (dendritic cells, macrophage, and T cells) and six m6A modifiers as well as four 5mC regulators in OLF. Reduced SOCS3 and FTO expression and up-regulated DNMT1 level in OLF were validated by Western blotting.

CONCLUSION

This study deciphered immune/inflammatory signatures of obesity-related gene clusters for the first time, and defined SOCS3 as one core gene. The crosstalk between 5mC/m6A methylation may be a key mediator of SOCS3 expression and immune infiltration. These findings will provide more insights into molecular mechanisms and therapeutic targets of obesity-related OLF.