Immunolocalization of thrombospondin in the human and sand rat intervertebral disc

Exosomes Immunity Strategy: A Novel Approach for Ameliorating Intervertebral Disc Degeneration

Low back pain (LBP), which is one of the most severe medical and social problems globally, has affected nearly 80% of the population worldwide, and intervertebral disc degeneration (IDD) is a common musculoskeletal disorder that happens to be the primary trigger of LBP. The pathology of IDD is based on the impaired homeostasis of catabolism and anabolism in the extracellular matrix (ECM), uncontrolled activation of immunologic cascades, dysfunction, and loss of nucleus pulposus (NP) cells in addition to dynamic cellular and biochemical alterations in the microenvironment of intervertebral disc (IVD). Currently, the main therapeutic approach regarding IDD is surgical intervention, but it could not considerably cure IDD. Exosomes, extracellular vesicles with a diameter of 30–150 nm, are secreted by various kinds of cell types like stem cells, tumor cells, immune cells, and endothelial cells; the lipid bilayer of the exosomes protects them from ribonuclease degradation and helps improve their biological efficiency in recipient cells. Increasing lines of evidence have reported the promising applications of exosomes in immunological diseases, and regarded exosomes as a potential therapeutic source for IDD. This review focuses on clarifying novel therapies based on exosomes derived from different cell sources and the essential roles of exosomes in regulating IDD, especially the immunologic strategy.

A population-based study identifies an association of THBS2 with intervertebral disc degeneration

OBJECTIVE

To clarify the genetic mechanisms underlying intervertebral disc degeneration (IDD), we examined the associations between single-nucleotide polymorphisms (SNPs) and indicated as coefficient of interaction term (IDD) in a general population in Japan.

METHODS

This was a cross-sectional study. In 1,605 participants, C2-3 to L5/S1 in the total spine magnetic resonance imaging (MRI) were evaluated using the Pfirrmann's scoring system. Disc scores of 4 and 5 were defined as IDD. Eight SNPs in eight genes associated with IDD were examined at each disc level, considering the non-genetic risk factors of age, sex, and body mass index (BMI).

RESULTS

The highest odds ratio was found for rs9406328 in the THBS2 gene at disc level T12-L1 (OR 1.27, 95%CI 1.05 to 1.53), and this association was strengthened after adjustment for age using logistic regression (OR 1.37, 95%CI 1.12 to 1.67). Among participants aged <50 years and 50-59, the average IDD score in those with 2 risk alleles of rs9406328 was markedly higher than in those with 0 or 1 risk allele, and the difference is much wider than the elderly participants. It indicates the genetic effect of rs9406328 is stronger in the younger age groups. Finally, multiple linear regression analyses of the association between rs9406328 and IDD, adjusted for age, sex, and BMI at each disc level, showed a statistical interaction between age and the number of risk alleles at C7-T1, T3-4 and T4-T5 as well as T12-L1.

CONCLUSION

CONCLUSION: The association between rs9406328 in THBS2 and IDD was replicated. The contributions of genetic and environmental factors to IDD differed by disc level.

Bioinformatics analysis reveals different gene expression patterns in the annulus fibrosis and nucleus pulpous during intervertebral disc degeneration

Degeneration of the intervertebral disc (IVD), which consists of the annulus fibrosus (AF) and nucleus pulposus (NP), is a multifactorial physiological process associated with lower back pain. Despite decades of research, the knowledge of the underlying molecular mechanisms of IVD degeneration (IDD) has remained limited. The present study aimed to reveal the differential gene expression patterns in AF and NP during the process of IDD and to identify key biomarkers contributing to these differences. The microarray dataset GSE70362 containing 24 AF and 24 NP samples was retrieved from the Gene Expression Omnibus database. Of these, 8 healthy samples were discarded. GeneSpring11.5 software was employed to identify differentially expressed genes (DEGs). Metascape online tools were used to perform enrichment analyses. Finally, the DEGs were mapped with the Search Tool for the Retrieval of Interacting Genes, and a protein-protein interaction (PPI) network was constructed in Cytoscape software. A total of 87 DEGs were identified. Gene ontology enrichment revealed that these DEGs were mainly involved in the inflammatory response, the extracellular matrix and RNA polymerase II transcription factor activity. Pathway enrichment revealed that the DEGs were mainly involved in the transforming growth factor (TGF-β) and estrogen signaling pathways. Matrix metalloproteinase (MMP)1 and interleukin (IL)6 were included in the genes enriched in rheumatoid arthritis, whereas bone morphogenetic protein (BMP)2 and thrombospondin 1 (THBS1) were among the genes enriched in the TGF-β signaling pathway. In the PPI network, IL6 was identified as the central gene. In conclusion, as MMP1 has been demonstrated degrade collagen III at higher rates compared with other types of collagen (which is at a higher quantity in AF than NP), collagen types may be in different distribution patterns, which may contribute to the upregulation of MMP1 in AF. Differences in the expression of BMP2, ESR1 and THBS1 may explain for the pathological differences between AF and NP. IL6 may have a key role in different degeneration processes in AF and NP.

Human notochordal cell transcriptome unveils potential regulators of cell function in the developing intervertebral disc

The adult nucleus pulposus originates from the embryonic notochord, but loss of notochordal cells with skeletal maturity in humans is thought to contribute to the onset of intervertebral disc degeneration. Thus, defining the phenotype of human embryonic/fetal notochordal cells is essential for understanding their roles and for development of novel therapies. However, a detailed transcriptomic profiling of human notochordal cells has never been achieved. In this study, the notochord-specific marker CD24 was used to specifically label and isolate (using FACS) notochordal cells from human embryonic and fetal spines (7.5–14 weeks post-conception). Microarray analysis and qPCR validation identified CD24, STMN2, RTN1, PRPH, CXCL12, IGF1, MAP1B, ISL1, CLDN1 and THBS2 as notochord-specific markers. Expression of these markers was confirmed in nucleus pulposus cells from aged and degenerate discs. Ingenuity pathway analysis revealed molecules involved in inhibition of vascularisation (WISP2, Noggin and EDN2) and inflammation (IL1-RN) to be master regulators of notochordal genes. Importantly, this study has, for the first time, defined the human notochordal cell transcriptome and suggests inhibition of inflammation and vascularisation may be key roles for notochordal cells during intervertebral disc development. The molecules and pathways identified in this study have potential for use in developing strategies to retard/prevent disc degeneration, or regenerate tissue.

The chondrodystrophic dog: A clinically relevant intermediate-sized animal model for the study of intervertebral disc-associated spinal pain

Low back pain (LBP) is the leading cause of disability worldwide, with an estimated 80% of the American population suffering from a painful back condition at some point during their lives. The most common cause of LBP is intervertebral disc (IVD) degeneration (IVDD), a condition that can be difficult to treat, either surgically or medically, with current available therapies. Thus, understanding the pathological mechanisms of IVDD and developing novel treatments are critical for improving outcome and quality of life in people living with LBP. While experimental animal models provide valuable mechanistic insight, each model has limitations that complicate translation to the clinical setting. This review focuses on the chondrodystrophic canine clinical model of IVDD as a promising model to assess IVD-associated spinal pain and translational therapeutic strategies for LBP. The canine IVD, while smaller in size than human, goat, ovine, and bovine IVDs, is larger than most other small animal IVDD models and undergoes maturational changes similar to those of the human IVD. Furthermore, both dogs and humans develop painful IVDD as a spontaneous process, resulting in similar characteristic pathologies and clinical signs. Future exploration of the canine model as a model of IVD-associated spinal pain and biological treatments using the canine clinical model will further demonstrate its translational capabilities with the added ethical benefit of treating an existing veterinary patient population with IVDD.

Identification of critical genes in nucleus pulposus cells isolated from degenerated intervertebral discs using bioinformatics analysis

Intervertebral disc (IVD) degeneration is a pathological process, which may lead to lower back pain. The present study aimed to investigate the pathogenesis of IVD degeneration. GSE42611 was downloaded from Gene Expression Omnibus, including 4 nucleus pulposus samples isolated from degenerated IVDs and 4 nucleus pulposus samples separated from normal IVDs. The differentially expressed genes (DEGs) between the degenerated and normal samples were screened using the limma package in R. Functional and pathway enrichment analyses were conducted separately for the upregulated and downregulated genes, using Database for Annotation, Visualization and Integrated Discovery software. In addition, protein-protein interaction (PPI) networks were constructed using the Search Tool for the Retrieval of Interacting Genes database and Cytoscape software. Finally, module analyses were conducted for the PPI networks using the MCODE plug-in in Cytoscape. A total of 558 DEGs were identified in the degenerated nucleus pulposus cells: 253 upregulated and 305 downregulated. Pathway enrichment analysis revealed that downregulated thrombospondin 1 (THBS1) was enriched in extracellular matrix-receptor interaction. Interleukin (IL)-6 in the PPI network for the upregulated genes and vascular endothelial growth factor A (VEGFA) in the PPI network for the downregulated genes had higher degrees. Additionally, four modules (µM1, µM2, µM3 and µM4) were identified from the PPI network for the upregulated genes. Four modules (dM1, dM2, dM3 and dM4) were identified from the PPI network for the downregulated genes. In the dM2 module, collagen genes and integrin subunit α4 (ITGA4) may interact with each other. Additionally, functional enrichment indicated that collagen genes were enriched in extracellular matrix organization. In conclusion, IL-6, VEGFA, THBS1, ITGA4 and collagen genes may contribute to the progression of IVD degeneration. These results suggested that the manipulation of these genes and their products may have potential as a novel therapeutic strategy for the treatment of patients with IVD.

Targeting the annulus fibrosus of the intervertebral disc: Col1a2-Cre(ER)T mice show specific activity of Cre recombinase in the outer annulus fibrosus

Degeneration of the intervertebral disc (IVD) is a major underlying contributor to back pain-the single leading cause of disability worldwide. However, we possess a limited understanding of the etiology underlying IVD degeneration. To date, there are a limited number of mouse models that have been used to target proteins in specific compartments of the IVD to explore their functions in disc development, homeostasis and disease. Furthermore, the majority of reports exploring the composition and function of the outer encapsulating annulus fibrosus (AF) of the IVD have considered it as one tissue, without considering the numerous structural and functional differences existing between the inner and outer AF. In addition, no mouse models have yet been reported that enable specific targeting of genes within the outer AF. In the current report, we discuss these issues and demonstrate the localized activity of Cre recombinase in the IVD of Col1a2-Cre(ER)T;ROSA26mTmG mice possessing a tamoxifen-dependent Cre recombinase driven by a Cola2 promoter and distal enhancer and the mTmG fluorescent reporter. Following tamoxifen injection of 3-week-old Col1a2-Cre(ER)T;ROSA26mTmG mice, we show Cre activity specifically in the outer AF of the IVD, as indicated by expression of the GFP reporter. Thus, Col1a2-Cre(ER)T;ROSA26mTmG mice may prove to be a valuable tool in delineating the function of proteins in this unique compartment of the IVD, and in further exploring the compositional differences between the inner and outer AF in disc homeostasis, aging and disease.

Fibrotic-like changes in degenerate human intervertebral discs revealed by quantitative proteomic analysis

OBJECTIVE

Intervertebral disc degeneration (IDD) can lead to symptomatic conditions including sciatica and back pain. The purpose of this study is to understand the extracellular matrix (ECM) changes in disc biology through comparative proteomic analysis of degenerated and non-degenerated human intervertebral disc (IVD) tissues of different ages.

DESIGN

Seven non-degenerated (11-46 years of age) and seven degenerated (16-53 years of age) annulus fibrosus (AF) and nucleus pulposus (NP) samples were used. Proteins were extracted using guanidine hydrochloride, separated from large proteoglycans (PGs) by caesium chloride (CsCl) density gradient ultracentrifugation, and identified using liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS). For quantitative comparison, proteins were labeled with iTRAQ reagents. Collagen fibrils in the NP were assessed using scanning electron microscopy (SEM).

RESULTS

In the AF, quantitative analysis revealed increased levels of HTRA1, COMP and CILP in degeneration when compared with samples from older individuals. Fibronectin showed increment with age and degeneration. In the NP, more CILP and CILP2 were present in degenerated samples of younger individuals. Reduced protein solubility was observed in degenerated and older non-degenerated samples correlated with an accumulation of type I collagen in the insoluble fibers. Characterization of collagen fibrils in the NP revealed smaller mean fibril diameters and decreased porosity in the degenerated samples.

CONCLUSIONS

Our study identified distinct matrix changes associated with aging and degeneration in the intervertebral discs (IVDs). The nature of the ECM changes, together with observed decreased in solubility and changes in fibril diameter is consistent with a fibrotic-like environment.

Hypoxia promotes nucleus pulposus phenotype in 3D scaffolds in vitro and in vivo: laboratory investigation

OBJECT

The role of oxygen in disc metabolism remains a matter of debate. Whether the effect of hypoxic priming on the nucleus pulposus phenotype can be maintained in vivo is not clear. The goal of the present study was to test the hypothesis that priming in a low oxygen tension in vitro could promote a nucleus pulposus phenotype in vivo.

METHODS

Bovine nucleus pulposus cells were seeded in 3D scaffolds and subjected to varying oxygen tensions (2% and 20%) for 3 weeks. The constructs were then implanted subcutaneously for 8 weeks. Changes in the extracellular matrix were evaluated using quantitative real-time reverse transcriptase polymerase chain reaction, glycosaminoglycan (GAG) assay, DNA assay, collagen quantification, and histological and immunohistological analyses.

RESULTS

Hypoxia resulted in greater production of sulfated glycosaminoglycan and higher levels of gene expression for collagen Type II, aggrecan, and SOX-9. Furthermore, after hypoxic priming, the subcutaneously implanted constructs maintained the nucleus pulposus phenotype, which was indicated by a significantly higher amount of glycosaminoglycan and collagen Type II.

CONCLUSIONS

Hypoxia enhanced the nucleus pulposus phenotype under experimental conditions both in vitro and in vivo. When used in combination with appropriate scaffold material, nucleus pulposus cells could be regenerated for tissue-engineering applications.

A novel catechol-O-methyltransferase variant associated with human disc degeneration

BACKGROUND

Disc degeneration and its associated low back pain are a major health care concern causing disability with a prominent role in this country's medical, social and economic structure. Low back pain is devastating and influences the quality of life for millions. Low back pain lifetime prevalence approximates 80% with an estimated direct cost burden of $86 billion per year. Back pain patients incur higher costs, greater health care utilization, and greater work loss than patients without back pain.

METHODS

Research was performed following approval of our Institutional Review Board. DNA was isolated, processed and amplified using routine techniques. Amplified DNA was hybridized to Affymetrix Genome-Wide Human SNP Arrays. Quality control and genotyping analysis were performed using Affymetrix Genotyping Console. The Birdseed v2 algorithm was used for genotyping analysis. 2589 SNPs were selected a priori to enter statistical analysis using lotistic regression in SAS.

RESULTS

Our objective was to search for novel single nucleotide polymorphisms (SNPs) associated with disc degeneration. Four SNPs were found to have a significant relationship to disc degeneration; three are novel. Rs165656, a new SNP found to be associated with disc degeneration, was in catechol-O-methyltransferase (COMT), a gene with well-recognized pain involvement, especially in female subjects (p=0.01). Analysis confirmed the previously association between COMT SNP rs4633 and disc degeneration. We also report two novel disc degeneration-related SNPs (rs2095019 and rs470859) located in intergenic regions upstream to thrombospondin 2.

CONCLUSIONS

Findings contribute to the challenging field of disc degeneration and pain, and are important in light of the high clinical relevance of low back pain and the need for improved understanding of its fundamental basis.

Progression of lumbar spinal stenosis is influenced by polymorphism of thrombospondin 2 gene in the Korean population

PURPOSE

The aim of this study is to determine the contribution of thrombospondin 2 (THBS2) polymorphisms to the development and progression of lumbar spinal stenosis (LSS) in the Korean population.

METHODS

We studied 148 symptomatic patients with radiographically proven LSS and 157 volunteers with no history of back problems from our institution. Magnetic resonance images were obtained for all the patients and controls. Quantitative image evaluation for LSS was performed to evaluate the severity of LSS. All patients and controls were genotyped for THBS2 allele variations using a polymerase chain reaction-based technique.

RESULTS

We found no causal single nucleotide polymorphism (SNPs) in THBS2 that were significantly associated with LSS. Two SNPs (rs6422747, rs6422748) were over-represented in controls [P = 0.042, odds ratio [OR] = 0.55 and P = 0.042, OR = 0.55, respectively]. Haplotype analysis showed that the ''AGAGACG'' haplotype (HAP4) and ''AAGGACG'' haplotype (HAP5) were over-represented in severe LSS patients (P = 0.0147, OR = 2.02 and P = 0.0137, OR = 2.48, respectively). In addition, the ''AAAGGGG'' haplotype (HAP1) was over-represented in controls (P = 0.0068, OR = 0.30).

CONCLUSIONS

Although no SNPs in THBS2 were associated with LSS, haplotypes (HAP4 and HAP5) were significantly associated with progression of LSS in the Korean population, whereas another haplotype (HAP1) may play a protective role against LSS development.

Connective tissue growth factor expression in human intervertebral disc: implications for angiogenesis in intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is strongly associated with chronic low back pain, one of the most common causes of morbidity in the West. While normal healthy IVD is avascular, angiogenesis is a constant feature of IVD degeneration and has been shown to be associated with in-growth of nerves. Connective tissue growth factor (CTGF) plays a pivotal role in angiogenesis. To investigate the expression of CTGF in both normal and degenerated IVD, 21 IVDs were obtained from patients at surgery or postmortem examination and grouped according to the severity of histological degeneration. The immunohistochemical expression of CTGF was correlated with the degree of degeneration. CD31 immunohistochemistry was used to correlate IVD degeneration with vasculature. Our results showed that CTGF is expressed in non-degenerated and degenerated human IVDs and increased expression of CTGF is associated with degenerated discs, particularly within areas of neovascularization. We suggest that CTGF may play a role in angiogenesis in the human degenerated IVD.

Disruption of the thrombospondin-2 gene alters the lamellar morphology but does not permit vascularization of the adult mouse lumbar disc

Introduction

The biological basis for the avascular state of the intervertebral disc is not well understood. Previous work has suggested that the presence of thrombospondin-1 (TSP-1), a matricellular protein, in the outer annulus reflects a role for this protein in conferring an avascular status to the disc. In the present study we have examined thrombospondin-2 (TSP-2), a matricellular protein with recognized anti-angiogenic activity in vivo and in vitro.

Methods

We examined both the location and expression of TSP-2 in the human disc, and its location in the disc and bordering soft tissues of 5-month-old normal wild-type (WT) mice and of mice with a targeted disruption of the TSP-2 gene. Immunohistochemistry and quantitative histology were utilized in this study.

Results

TSP-2 was found to be present in some, but not all, annulus cells of the human annulus and the mouse annulus. Although there was no difference in the number of disc cells in the annulus of TSP-2-null mice compared with that of WT animals, polarized light microscopy revealed a more irregular lamellar collagen structure in null mouse discs compared with WT mouse discs. Additionally, vascular beds at the margins of discs of TSP-2-null mice were substantially more irregular than those of WT animals. Counts of platelet endothelial cell adhesion molecule-1-positive blood vessels in the tissue margin bordering the ventral annulus showed a significantly larger vascular bed in the tissue bordering the disc of TSP-2-null mice compared with that of WT mice (P = 0.0002). There was, however, no vascular ingrowth into discs of the TSP-2-null mice.

Conclusion

These data confirm a role for TSP-2 in the morphology of the disc and suggest the presence of other inhibitors of angiogenesis in the disc. We have shown that although an increase in vasculature was present in the TSP-2-null tissue in the margin of the disc, vascular ingrowth into the body of the disc did not occur. Our results point to the need for future research to understand the transition from the well-vascularized status of the fetal and young discs to the avascular state of the adult human disc or the small mammalian disc.

A functional polymorphism in THBS2 that affects alternative splicing and MMP binding is associated with lumbar-disc herniation

Lumbar-disc herniation (LDH), one of the most common musculoskeletal diseases, has strong genetic determinants. Recently, several genes that encode extracellular matrix (ECM) proteins in the intervertebral disc have been reported to associate with LDH. Thrombospondins (THBSs) 1 and 2 are good candidates for the LDH susceptibility gene: They are intervertebral disc ECM proteins that regulate the effective levels of matrix metalloproteinases (MMPs) 2 and 9, which are key effectors of ECM remodeling. Here, we report that THBS2 is associated with LDH in Japanese populations. An intronic SNP in THBS2 (IVS10-8C --> T; rs9406328) showed significant association (p = 0.0000028) with LDH in two independent Japanese populations. This SNP, located in a polypyrimidine tract upstream of the 3' splice site of intron 10, exerts allelic differences on exon 11 skipping rates in vivo, with the susceptibility allele showing increased skipping. Skipping of exon 11 results in decreased THBS2 interaction with MMP2 and MMP9. Further, a missense SNP in MMP9 (Q279R; rs17576) is also strongly associated with LDH in the Japanese population (p = 0.00049) and shows a combinatorial effect with THBS2 (odds ratio 3.03, 95% confidence interval 1.58-5.77). Thus, a splicing-affecting SNP in THBS2 and a missense SNP in MMP9 are associated with susceptibility to LDH. Our data indicate that regulation of intervertebral disc ECM metabolism by the THBS2-MMP system plays an essential role in the etiology and pathogenesis of LDH.