Relationship between bone density and bone metabolism in adolescent idiopathic scoliosis

Pattern of bone marrow lipid composition measures along the vertebral column: A descriptive study of adolescents with idiopathic scoliosis

BACKGROUND

There is evidence that the extent of vertebral bone marrow adiposity increases caudally along the vertebral column in children and adolescents. However, no studies have examined the lipid composition of bone marrow along the vertebral column, which may uniquely influence bone acquisition and metabolism during growth independent of the amount of bone marrow adipose tissue. The goal of this study was to characterize the pattern of lipid composition index measures from the thoracic to lumbar spine (T11-L4) among a sample of adolescents with idiopathic scoliosis (AIS) undergoing routine orthopedic surgical care for scoliosis correction.

METHODS

Adolescents between 14 and 18 years of age, with a confirmed diagnosis of AIS, and undergoing routine posterior spinal fusion surgery at our institution were initially included for this descriptive study. The surgery yielded transpedicular vertebral body marrow samples from T11 through L4; 11 participants had bone marrow samples from T11 through L2 and 4 of the 11 participants had marrow samples from T11 through L4. Lipid composition index measures, including the saturated, monounsaturated, and polyunsaturated index, were measured using a targeted lipidomics technique. Linear regression equation for the slope (m) and Pearson correlation coefficient (r) was computed to assess the pattern of lipid composition index measures along the vertebral column from T11 to L2 (n = 11) and extended analysis to L4. Exploratory analyses were performed to examine the association between the pattern of lipid composition measures (individual slopes) and physical characteristics for T11-L2.

RESULTS

For T11-L2, the slope of the saturated index was near 0 (r = 0.08; P = 0.92), whereas the slopes of the unsaturated indices were approximately opposite of one another: the monounsaturated index exhibited a -0.55 change (r = 0.58; P = 0.42) per vertebra and the polyunsaturated index exhibited a 0.52 change (r = 0.72; P = 0.28) per vertebra in the caudal direction from T11-L2. For T11-L4, there were modest changes in slope for the saturated (m = 0.12; r = 0.30; P = 0.57) and monounsaturated (m = -0.68; r = 0.74; P = 0.09) indices, while the polyunsaturated index slope remained similar (m = 0.56; r = 0.89; P = 0.02). Age, sex, height, body mass, and BMI were not associated with the pattern of any of the lipid composition index measures.

CONCLUSIONS

Study findings in this small sample of individuals with AIS suggest that the bone marrow saturated index may be relatively stable across T11-L4, while the monounsaturated index may decrease by 0.55-0.68% per vertebra and the polyunsaturated index may increase by 0.52-0.56% per vertebra in the caudal direction.

Test-Retest Reliability and Correlates of Vertebral Bone Marrow Lipid Composition by Lipidomics Among Children With Varying Degrees of Bone Fragility

The reliability of lipidomics, an approach to identify the presence and interactions of lipids, to analyze the bone marrow lipid composition among pediatric populations with bone fragility is unknown. The objective of this study was to assess the test–retest reliability, standard error of measurement (SEM), and the minimal detectable change (MDC) of vertebral bone marrow lipid composition determined by targeted lipidomics among children with varying degrees of bone fragility undergoing routine orthopedic surgery. Children aged 10 to 19 years, with a confirmed diagnosis of adolescent idiopathic scoliosis (n = 13) or neuromuscular scoliosis and cerebral palsy (n = 3), undergoing posterior spinal fusion surgery at our institution were included in this study. Transpedicular vertebral body bone marrow samples were taken from thoracic vertebrae (T11, 12) or lumbar vertebrae (L1 to L4). Lipid composition was assessed via targeted lipidomics and all samples were analyzed in the same batch. Lipid composition measures were examined as the saturated, monounsaturated, and polyunsaturated index and as individual fatty acids. Relative and absolute test–retest reliability was assessed using the intraclass correlation coefficient (ICC), SEM, and MDC. Associations between demographics and index measures were explored. The ICC, SEM, and MDC were 0.81 (95% CI, 0.55–0.93), 1.6%, and 4.3%, respectively, for the saturated index, 0.66 (95% CI, 0.25–0.87), 3.5%, and 9.7%, respectively, for the monounsaturated index, and 0.60 (95% CI, 0.17–0.84), 3.6%, and 9.9%, respectively, for the polyunsaturated index. For the individual fatty acids, the ICC showed a considerable range from 0.04 (22:2n‐6) to 0.97 (18:3n‐3). Age was positively correlated with the saturated index (r² = 0.36; p = 0.014) and negatively correlated with the polyunsaturated index (r² = 0.26; p = 0.043); there was no difference in index measures by sex (p > 0.58). The test–retest reliability was moderate‐to‐good for index measures and poor to excellent for individual fatty acids; this information can be used to power research studies and identify measures for clinical or research monitoring. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Long noncoding RNA lncAIS downregulation in mesenchymal stem cells is implicated in the pathogenesis of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a complex, three dimensional deformity of the spine that commonly occurs in pubescent girls. Abnormal osteogenic differentiation of mesenchymal stem cells (MSCs) is implicated in the pathogenesis of AIS. However, the biological roles of long noncoding RNAs (lncRNAs) in the regulation of osteogenic differentiation of MSCs are unknown. Through microarray analyses of bone marrow (BM) MSCs from healthy donors and AIS patients, we identified 1483 differentially expressed lncRNAs in AIS BM-MSCs. We defined a novel lncAIS (gene symbol: ENST00000453347) is dramatically downregulated in AIS BM-MSCs. In normal BM-MSCs, lncAIS interacts with NF90 to promote HOXD8 mRNA stability that enhances RUNX2 transcription in BM-MSCs, leading to osteogenic differentiation of normal BM-MSCs. By contrast, lncAIS downregualtion in AIS BM-MSCs cannot recruit NF90 and abrogates HOXD8 mRNA stability, which impedes RUNX2 transcription for osteogenic differentiation. Thereby lncAIS downregualtion in BM-MSCs suppresses osteogenic differentiation that is implicated in the pathogenesis of AIS.

Differential miRNAs profile and bioinformatics analyses in bone marrow mesenchymal stem cells from adolescent idiopathic scoliosis patients

BACKGROUND CONTEXT

Coexistence of abnormal skeletal growth and reduced bone mineral density in the context of adolescent idiopathic scoliosis (AIS) suggests disturbed bone metabolism existing in such patients. Our previous study suggested increased proliferation ability and decreased osteogenic differentiation ability of bone marrow mesenchymal stem cells (BM-MSCs) of AIS.

PURPOSE

To explore the differential miRNA expression profile, Go (gene ontology) terms and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways in BM-MSCs of AIS and non-AIS controls were conducted using microarray approach and bioinformatics analyses.

STUDY DESIGN

miRNA microarray approach and bioinformatics analysis.

METHODS

The differentially expressed miRNAs (DEMs) of BM-MSCs from AIS patients compared with those from healthy individuals were analyzed using a microarray analysis. Comprehensive bioinformatics analyses were then used to enrich datasets for gene ontology and pathway. Based on the interaction network analysis of DEMs contained in significant pathways, 12 potential crucial miRNAs were selected for validation by RT-PCR.

RESULTS

The study identified 54 previously unrecognized DEMs (12 upregulated, 42 downregulated) in BM-MSCs from AIS patients. These miRNAs are involved in multiple biological processes, including small GTPase-mediated signal transduction, DNA-dependent transcription, cytokinesis, cell adhesion, transmembrane transport, response to hypoxia, etc. Pathway analysis of these new identified miRNAs revealed dysregulated MAPK signaling pathway, PI3K-Akt signaling pathway, calcium signaling pathway, Notch signaling pathway, and ubiquitin-mediated proteolysis pathway, all of which have been reported to play important role in regulating the osteogenic or adipogenic differentiation of MSCs. Furthermore, interaction networks analysis indicated that seven most significant central miRNAs, including miR-17-5p, miR-106a-5p, miR-106b-5p, miR-16-5p, miR-93-5p, miR-15a-5p, and miR-181b-5p may play essential roles in AIS pathogenesis and accompanied osteopenia.

CONCLUSION

The current study reports the differential miRNAs expression profiles of BM-MSCs from AIS patients and related pathways for the first time. The identification of these candidate miRNAs provides a deep insight into the pathogenesis of AIS and the accompanying generalized osteopenia.

Can posterior implant removal prevent device-related vertebral osteopenia after posterior fusion in adolescent idiopathic scoliosis? A mean 29-year follow-up study

PURPOSE

To determine whether posterior implant removal prevents stress-shielding-induced vertebral osteopenia within the posterior fusion area in surgically treated patients with adolescent idiopathic scoliosis (AIS).

METHODS

Eighteen patients with major thoracic AIS (mean age, 43.3 years; range, 32-56 years; mean follow-up, 28.8 years, range, 20-39 years) who underwent posterior spinal fusion (PSF) alone between 1973 and 1994 were included. Participants were divided into implant removal (group R, n = 10, mean interval until implant removal, 50 months) and implant non-removal groups (group NR, n = 8). Bone mineral density was evaluated using the Hounsfield units (HU) of the computed tomography image of the full spine. The HU values of the UIV-1 (one level below the uppermost instrumented vertebra), apex, LIV+1 (one level above the lowermost instrumented vertebra), and LIV-1 (one level below the lowermost instrumented vertebra; as a standard value) were obtained. Stress-shielding-induced osteopenia was assessed as the UIV-1/LIV-1, apex/LIV-1, and LIV+1/LIV-1 HU ratios (× 100).

RESULTS

Overall (median, 25th-75th percentile), the apex (144.7, 108.6-176.0) and LIV+1 (159.4, 129.7-172.3) demonstrated lower HU values than LIV-1 (180.3, 149.2-200.2) (both comparisons, p < .05). Comparison of groups R and NR showed no significant differences in the scoliosis correction rate, bone mineral density of the proximal femur, the HU absolute values of all investigated vertebrae, or in the HU ratios of the investigated vertebrae to LIV-1.

CONCLUSION

Instrumented PSF causes stress-shielding-induced osteopenia of the vertebral body within the fusion area in adulthood, which cannot be prevented by posterior implant removal, probably due to firm fusion mass formation. These slides can be retrieved under Electronic Supplementary Material.

The 17β-estradiol induced upregulation of the adhesion G-protein coupled receptor (ADGRG7) is modulated by ESRα and SP1 complex

The physiological role and the regulation of ADGRG7 are not yet elucidated. The functional involvement of this receptor was linked with different physiological process such as reduced body weight, gastrointestinal function and recently, a gene variant in ADGRG7 was observed in patients with adolescent idiopathic scoliosis. Here, we identify the ADGRG7 as an estrogen-responsive gene under the regulation of estrogen receptor ERα in scoliotic osteoblasts and other cells lines. We found that ADGRG7 expression was upregulated in response to estrogen (E2) in adolescent idiopathic scoliosis (AIS) cells. ADGRG7 promoter studies indicate the presence of an ERα response half site in close vicinity of a specificity protein 1 (SP1) binding site. Mutation of the SP1 site completely abrogated the response to E2, indicating its essential requirement. ChIP confirmed the binding of SP1 and ERα to the ADGRG7 promoter. Our results identify the ADGRG7 gene as an estrogen-responsive gene under the control of ERα and SP1 tethered actions, suggesting a possible role of estrogens in the regulation of ADGRG7 This article has an associated First Person interview with the first author of the paper.

Sexual Dimorphism and the Origins of Human Spinal Health

Recent observations indicate that the cross-sectional area (CSA) of vertebral bodies is on average 10% smaller in healthy newborn girls than in newborn boys, a striking difference that increases during infancy and puberty and is greatest by the time of sexual and skeletal maturity. The smaller CSA of female vertebrae is associated with greater spinal flexibility and could represent the human adaptation to fetal load in bipedal posture. Unfortunately, it also imparts a mechanical disadvantage that increases stress within the vertebrae for all physical activities. This review summarizes the potential endocrine, genetic, and environmental determinants of vertebral cross-sectional growth and current knowledge of the association between the small female vertebrae and greater risk for a broad array of spinal conditions across the lifespan.

Vertebral cross-sectional area: an orphan phenotype with potential implications for female spinal health

A high priority in imaging-based research is the identification of the structural basis that confers greater risk for spinal disorders. New evidence indicates that factors related to sex influence the fetal development of the axial skeleton. Girls are born with smaller vertebral cross-sectional area compared to boys-a sexual dimorphism that is present throughout life and independent of body size. The smaller female vertebra is associated with greater flexibility of the spine that could represent the human adaptation to fetal load. It also likely contributes to the higher prevalence of spinal deformities, such as exaggerated lordosis and progressive scoliosis in adolescent girls when compared to boys, and to the greater susceptibility for spinal osteoporosis and vertebral fractures in elderly women than men.

Small vertebral cross-sectional area and tall intervertebral disc in adolescent idiopathic scoliosis

BACKGROUND

When compared to boys, girls have smaller vertebral cross-sectional area, which conveys a greater spinal flexibility, and a higher prevalence of adolescent idiopathic scoliosis.

OBJECTIVE

To test the hypothesis that small vertebral cross-sectional area and tall intervertebral disc height are structural characteristics of patients with adolescent idiopathic scoliosis.

MATERIALS AND METHODS

Using multiplanar imaging techniques, measures of vertebral cross-sectional area, vertebral height and intervertebral disc height in the lumbar spine were obtained in 35 pairs of girls and 11 pairs of boys with and without adolescent idiopathic scoliosis of the thoracic spine matched for age, height and weight.

RESULTS

Compared to adolescents without spinal deformity, girls and boys with adolescent idiopathic scoliosis had, on average, 9.8% (6.68 ± 0.81 vs. 7.40 ± 0.99 cm(2); P = 0.0007) and 13.9% (8.22 ± 0.84 vs. 9.55 ± 1.61 cm(2); P = 0.009) smaller vertebral cross-sectional dimensions, respectively. Additionally, patients with adolescent idiopathic scoliosis had significantly greater values for intervertebral disc heights (9.06 ± 0.85 vs. 7.31 ± 0.62 mm and 9.09 ± 0.87 vs. 7.61 ± 1.00 mm for girls and boys respectively; both P ≤ 0.011). Multiple regression analysis indicated that the presence of scoliosis was negatively associated with vertebral cross-sectional area and positively with intervertebral disc height, independent of sex, age and body mass index.

CONCLUSION

We provide new evidence that girls and boys with adolescent idiopathic scoliosis have significantly smaller vertebral cross-sectional area and taller intervertebral disc heights - two major structural determinants that influence trunk flexibility. With appropriate validation, these findings may have implications for the identification of children at the highest risk for developing scoliosis.

Planning the Surgical Correction of Spinal Deformities: Toward the Identification of the Biomechanical Principles by Means of Numerical Simulation

In decades of technical developments after the first surgical corrections of spinal deformities, the set of devices, techniques, and tools available to the surgeons has widened dramatically. Nevertheless, the rate of complications due to mechanical failure of the fixation or the instrumentation remains rather high. Indeed, basic and clinical research about the principles of deformity correction and the optimal surgical strategies (i.e., the choice of the fusion length, the most appropriate instrumentation, and the degree of tolerable correction) did not progress as much as the implantable devices and the surgical techniques. In this work, a software approach for the biomechanical simulation of the correction of patient-specific spinal deformities aimed to the identification of its biomechanical principles is presented. The method is based on three-dimensional reconstructions of the spinal anatomy obtained from biplanar radiographic images. A user-friendly graphical user interface allows for the planning of the desired deformity correction and to simulate the implantation of pedicle screws. Robust meshing of the instrumented spine is provided by using consolidated computational geometry and meshing libraries. Based on a finite element simulation, the program is able to predict the loads and stresses acting in the instrumentation as well as those in the biological tissues. A simple test case (reduction of a low-grade spondylolisthesis at L3–L4) was simulated as a proof of concept, and showed plausible results. Despite the numerous limitations of this approach which will be addressed in future implementations, the preliminary outcome is promising and encourages a wide effort toward its refinement.