The relationship between disc degeneration, low back pain, and human pain genetics

Pure platelet-rich plasma promotes semaphorin-3A expression: a novel insight to ameliorate intervertebral disk degeneration in vitro

INTRODUCTION

Intervertebral disk degeneration (IVDD) can be effectively treated using platelet-rich plasma (PRP). While the exact process is fully understood, it is believed that using pure PRP (P-PRP) without leukocytes is a better option for preventing IVDD. Semaphorin-3A (Sema3A), an inhibitor of angiogenesis and innervation, is essential for preserving IVDD's homeostasis. Whether PRP prevents IVDD by modifying Sema3A has yet to receive much research. This work aims to clarify how P-PRP affects Sema3A when IVDD develops in vitro.

METHODS

Nucleus pulposus cells (NPCs) isolated from 8-week-old male Sprague-Dawley rats were exposed to 10 ng/ml IL-1β and then treated with P-PRP or leukocyte platelet-rich plasma (L-PRP) in vitro, followed by measuring cell proliferation, apoptosis and microstructures, inflammatory gene and Sema3A expression, as well as anabolic and catabolic protein expression by immunostaining, quantitative real-time polymerase chain reaction (qPCR), western blot, and enzyme-linked immunosorbent assay (ELISA).

RESULTS

In comparison with L-PRP, P-PRP had a higher concentration of growth factors but a lower concentration of inflammatory substances. P-PRP increased the proliferation of NPCs, while IL-1 relieved the amount of apoptosis due to its intervention. Anabolic genes, aggrecan, and collagen II had higher expression levels. MMP-3 and ADAMTS-4, two catabolic or inflammatory genes, showed lower expression levels. Sema3A activity was enhanced after P-PRP injection, whereas CD31 and NF200 expression levels were suppressed.

CONCLUSIONS

P-PRP enhanced the performance of NPCs in IVDD by modifying the NF-κB signaling pathway and encouraging Sema3A expression, which may offer new therapy options for IVDD.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

The findings provide a new therapeutic target for the treatment of IVDD and show a novel light on the probable mechanism of PRP and the function of Sema3A in the progression of IVDD.

Predictive Classification System for Low Back Pain Based on Unsupervised Clustering

STUDY DESIGN

Retrospective study.

OBJECTIVE

Lumbar magnetic resonance imaging (MRI) findings are believed to be associated with low back pain (LBP). This study sought to develop a new predictive classification system for low back pain.

METHOD

Normal subjects with repeated lumbar MRI scans were retrospectively enrolled. A new classification system, based on the radiological features on MRI, was developed using an unsupervised clustering method.

RESULTS

One hundred and fifty-nine subjects were included. Three distinguishable clusters were identified with unsupervised clustering that were significantly correlated with LBP (P = .017). The incidence of LBP was highest in cluster 3 (57.14%), nearly twice the incidence in cluster 1 (30.11%). There were obvious differences in the sagittal parameters among the 3 clusters. Cluster 3 had the smallest intervertebral height. Based on follow-up findings, 27% of subjects changed clusters. More subjects changed from cluster 1 to clusters 2 or 3 (14.5%) than changed from cluster 2 or cluster 3 to cluster 1 (5%). Participation in sport was more frequent in subjects who changed from cluster 3 to cluster 1.

CONCLUSION

Using an unsupervised clustering method, we developed a new classification system comprising 3 clusters, which were significantly correlated with LBP. The prediction of LBP is independent of age and better than that based on individual sagittal parameters derived from MRI. A change in cluster during follow-up may partially predict lumbar degeneration. This study provides a new system for the prediction of LBP that should be useful for its diagnosis and treatment.

Shikonin protects against lipopolysaccharide-induced inflammation and apoptosis in human nucleus pulposus cells through the nuclear factor-kappa B pathway

OBJECTIVE

To investigate the protective effect and mechanism of shikonin on human intervertebral disk degeneration.

METHODS

Human primary nucleus pulposus (NP) cells cultured in vitro were used for the experiments. The effects of different concentrations of shikonin (1, 2, 4, 8, and 16 µM) on the activity of lipopolysaccharide (LPS)-induced NP cells were determined using the CCK-8 assay, and the appropriate drug concentration was determined. The experiment was divided into the control, LPS, and LPS + shikonin groups. ELISA and Western blot were used to detect the expression of the inflammatory factors tumor necrosis factor (TNF)-α and interleukin (IL)-1β. NP cell apoptosis was measured using Western blot and caspase 3 activity. Western blot and immunofluorescence assays were used to detect the protein expression of p-P65 and P65 and the nuclear translocation of P65.

RESULTS

The CCK-8 assay showed that shikonin had no cytotoxic effect on NP cells and increased the activity of LPS-induced NP cells, especially at a concentration of 4 μM. Shikonin reversed the expression of the inflammatory cytokines TNF-α and IL-1β and apoptosis-related molecules Bax, Bcl-2, and cleaved caspase 3 in LPS-induced NP cells. In addition, shikonin significantly decreased apoptosis and caspase-3 activity in LPS-induced NP cells. Furthermore, shikonin treatment significantly inhibited the expression of p-P65 and nuclear translocation of P65, and nuclear factor-kappa B (NF-κB) pathway inhibitor Pyrrolidinedithiocarbamate ammonium (PDTC) significantly enhanced the anti-inflammatory and antiapoptotic effects of shikonin in LPS-induced NP cells.

CONCLUSION

Shikonin significantly inhibited the inflammatory response and apoptosis of human primary NP cells, possibly through the NF-κB pathway.

Atorvastatin inhibited TNF-α induced matrix degradation in rat nucleus pulposus cells by suppressing NLRP3 inflammasome activity and inducing autophagy through NF-κB signaling

Intervertebral disc degeneration (IDD) is one of the main causes of lower back pain (LBP). It results from an imbalance between the degradation and synthesis of extracellular matrix (ECM) components in nucleus pulposus (NP) cells. Atorvastatin, an HMG-CoA reductase inhibitor, plays a vital role in many diseases, such as cardiovascular disease and osteoarthritis. However, the effect of atorvastatin on IDD is unclear. Herein, we demonstrated that atorvastatin affects matrix degradation induced by TNF-α and demonstrated the mechanism by which TNF-α modulates matrix metabolism in rat NP cells. Real-time PCR, western blotting and immunofluorescence staining were performed to detect the mRNA and protein expression of related genes. mRFP-GFP-LC3 adenovirus plasmid transfection and transmission electron microscopy (TEM) were used to detect cell autophagy. NLRP3 inhibitor and lentiviral vectors containing shRNA-NLRP3 were used to show the effect of NLRP3 on autophagic flux and the NF-κB signaling pathway. The results revealed that atorvastatin might suppress matrix degradation induced by TNF-α by suppressing NLRP3 inflammasome activity and inducing autophagic flux. Moreover, atorvastatin suppressed NF-κB signaling induced by TNF-α. NF-κB signaling inhibition suppressed NLRP3 inflammasome activity, and NLRP3 inhibition suppressed NF-κB signaling activation induced by TNF-α. NLRP3 inhibition or NLRP3 knockdown induced autophagic flux in the presence of TNF-α. Overall, the present study demonstrated that atorvastatin might suppress matrix degradation induced by TNF-α and further revealed the crosstalk among NLRP3 inflammasome activity, autophagy and NF-κB signaling.

M2a Macrophage-Secreted CHI3L1 Promotes Extracellular Matrix Metabolic Imbalances via Activation of IL-13Rα2/MAPK Pathway in Rat Intervertebral Disc Degeneration

The accumulation of macrophages in degenerated discs is a common phenomenon. However, the roles and mechanisms of M2a macrophages in intervertebral disc degeneration (IDD) have not been illuminated. This study investigated the expression of the M2a macrophage marker (CD206) in human and rat intervertebral disc tissues by immunohistochemistry. To explore the roles of M2a macrophages in IDD, nucleus pulposus (NP) cells were co-cultured with M2a macrophages in vitro. To clarify whether the CHI3L1 protein mediates the effect of M2a macrophages on NP cells, siRNA was used to knock down CHI3L1 transcription. To elucidate the underlying mechanisms, NP cells were incubated with recombinant CHI3L1 proteins, then subjected to western blotting analysis of the IL-13Rα2 receptor and MAPK pathway. CD206-positive cells were detected in degenerated human and rat intervertebral disc tissues. Notably, M2a macrophages promoted the expression of catabolism genes (MMP-3 and MMP-9) and suppressed the expression of anabolism genes (aggrecan and collagen II) in NP cells. These effects were abrogated by CHI3L1 knockdown in M2a macrophages. Exposure to recombinant CHI3L1 promoted an extracellular matrix metabolic imbalance in NP cells via the IL-13Rα2 receptor, along with activation of the ERK and JNK MAPK signaling pathways. This study elucidated the roles of M2a macrophages in IDD and identified potential mechanisms for these effects.

ACTG1 regulates intervertebral disc degeneration via the NF-κB-p65 and Akt pathways

ACTG1 is a member of the actin family but is not a muscle actin gene. The ACTG1 mutation leads to hearing loss in humans, and the knockdown of ACTG1 suppresses the proliferation and migration of tumor cells; however, its role in intervertebral disc degeneration (IDD) is yet unclear. Bioinformatics methods revealed that ACTG1 might be a hub gene in IDD. Furthermore, the expression ACTG1 in severely degenerated nucleus pulposus (NP) tissues (Pfirrmann grade IV and V) was low as compared to that in mildly degenerated samples (Pfirrmann grade II and III). Moreover, the ACTG1 level was negatively correlated with human disc degeneration grades. The low expression of ACTG1 is also found in degenerated NP tissues in the rat. To further explore the function of ACTG1 in IDD, the gene expression was depleted in human NP cells via siRNA transfection. The ablation of ACTG1 increased MMP3 expression but decreased the level of collagen II. Excessive apoptosis was observed in ACTG1 knockdown groups, indicating that the absence of ACTG1 exacerbated IDD. GO function and pathway enrichment analysis for differentially expressed genes (DEGs) of two microarray datasets (GSE56081 and GSE42611) indicated that inflammatory response plays a crucial role in IDD. Interestingly, in the protein-protein interaction (PPI) network, ACTG1 is connected to the proteins of inflammation-related pathways. Furthermore, ACTG1 knockdown upregulated P-P65 level but suppressed P-Akt expression. These data collectively demonstrated that ACTG1 regulated the development of IDD through the NF-κB-p65 and Akt pathways, and ACTG1 may be a novel marker and therapeutic target of IDD in the future.

No evidence of a correlation between lumbar spinal subtypes and intervertebral disc degeneration among asymptomatic middle-aged and aged patients

The aim of the present study was to identify whether lumbar spinal subtypes (LSS) were associated with lumbar disc degeneration (LDD) among asymptomatic middle-aged and aged subjects. A cohort of 158 asymptomatic Chinese adults aged >40 years was recruited and 97 volunteers that met the inclusion criteria with complete information available were selected for inclusion. According to spinal morphology, volunteers were divided into four subtypes based on the classification of Roussouly. After baseline information was collected and spinopelvic parameters were measured, the data were compared among the four groups. According to the Pfirrmann classification, the degree of LDD was evaluated at each level on the MRI. For grades I-V, LDD at each level was effectively compared. Each of the four LSS from I to IV according to Roussouly classification from types I to IV were comprised of 25 (25.8%), 19 (19.6%), 38 (39.2%) and 15 (15.5%) of volunteers, respectively. Lumbar lordosis, sacral slope and pelvic incidence were significantly different among the four sub-types (P<0.001 for each), but no difference in pelvic tilt was observed (P=0.21). From types I to IV LSS, the proportion of disc degeneration was found to be 44, 52, 50 and 48%, respectively, which exhibited no statistically significant difference among LSS. No correlation between LSS and intervertebral disc degeneration was obtained among the asymptomatic middle-aged and aged subjects. The present study provides a reference for spinal surgery and indicated that additional risk factors should be assessed in the asymptomatic population of this age group, particularly in terms of differentially expressed genes.

Spine Explorer: a deep learning based fully automated program for efficient and reliable quantifications of the vertebrae and discs on sagittal lumbar spine MR images

BACKGROUND CONTEXT

Although quantitative measurements improve the assessment of disc degeneration, acquirement of quantitative measurements relies on manual segmentation on lumbar magnetic resonance images (MRIs), which may introduce subjective bias. To date, only a few semiautomatic systems have been developed to quantify important components on MRIs.

PURPOSE

To develop a deep learning based program (Spine Explorer) for automated segmentation and quantification of the vertebrae and intervertebral discs on lumbar spine MRIs.

STUDY DESIGN

Cross-sectional study.

PATIENT SAMPLE

The study was extended on the Hangzhou Lumbar Spine Study, a population-based study of mainland Chinese with focuses on lumbar degenerative changes. From this population-based database, 50 sets lumbar MRIs were randomly selected as training dataset, and another 50 as test dataset.

OUTCOME MEASURES

Regions of vertebrae and discs were manually segmented on T2W sagittal MRIs to train a convolutional neural network for automated segmentation. Intersection-over-union was calculated to evaluate segmentation performance. Computational definitions were proposed to acquire quantitative morphometric and signal measurements for lumbar vertebrae and discs. MRIs in the test dataset were automatically measured with Spine Explorer and manually with ImageJ.

METHODS

Intraclass correlation coefficient (ICC) were calculated to examine inter-software agreements. Correlations between disc measurements and Pfirrmann score as well as age were examined to assess measurement validity.

RESULTS

The trained Spine Explorer automatically segments and measures a lumbar MRI in half a second, with mean Intersection-over-union of 94.7% and 92.6% for the vertebra and disc, respectively. For both vertebra and disc measurements acquired with Spine Explorer and ImageJ, the agreements were excellent (ICC=0.81~1.00). Disc measurements significantly correlated to Pfirrmann score, and greater age was associated with greater anterior disc bulging area (r=0.35~0.44) and fewer signal measurements (r=-0.62~-0.77) as automatically acquired with Spine Explorer.

CONCLUSIONS

Spine Explorer is an efficient, accurate, and reliable tool to acquire comprehensive quantitative measurements for lumbar vertebra and disc. Implication of such deep learning based program can facilitate clinical studies of the lumbar spine.

Mechanobiology of annulus fibrosus and nucleus pulposus cells in intervertebral discs

Low back pain (LBP) is a chronic condition that can affect up to 80% of the global population. It is the number one cause of disability worldwide and has enormous socioeconomic consequences. One of the main causes of this condition is intervertebral disc (IVD) degeneration. IVD degenerative processes and inflammation associated with it has been the subject of many studies in both tissue and cell level. It is believed that the phenotype of the resident cells within the IVD directly affects homeostasis of the tissue. At the same time, IVDs located between vertebral bodies of spine are under various mechanical loading conditions in vivo. Therefore, investigating how mechanical loading can affect the behaviour of IVD cells has been a subject of many research articles. In this review paper, following a brief explanation of the anatomy of the IVD and its resident cells, we compiled mechanobiological studies of IVD cells (specifically, annulus fibrosus and nucleus pulposus cells) and synthesized and discussed the key findings of the field.

Impact of NF-κB pathway on the apoptosis-inflammation-autophagy crosstalk in human degenerative nucleus pulposus cells

The NF-κB pathway has been reported to play a very important role in the process of intervertebral disc degeneration (IVDD). Our results demonstrated that knockdown of NF-κB with P65-siRNA can significantly decrease cell apoptosis and the expression of pro-inflammation factors TNF-α and IL-1β in LPS-induced nucleus pulposus cells (NPCs). However, the molecular mechanism of NF-κB pathway exerting anti-inflammation and anti-apoptosis function remains unclear. Some researchers reported that inhibiting NF-κB pathway can attenuate the catabolic effect by promoting autophagy during inflammatory conditions in rat nucleus pulposus cells. Therefore, we hypothesized that in human NPCs, inhibiting NF-κB pathway may also promote autophagy. Our results indicated that after knockdown of NF-κB, the autophagy was significantly increased and the expression of p-AKT and p-mTOR protein markedly decreased, but the level of autophagy was inhibited after treatment with AKT activator SC79, suggesting the involvement of AKT/mTOR-mediated autophagy was under autophagy activation. However, both LPS-induced NPCs apoptosis and expression of pro-inflammation factors were further increased by pretreatment with the autophagy inhibitor chloroquine (CQ). These suggested that inhibiting NF-κB pathway can promote autophagy and decrease apoptosis and inflammation response in LPS-induced NPCs. Meanwhile, autophagy triggered by NF-κB inhibition plays a protective role against apoptosis and inflammation.

Paraoxonase 1 Was Negatively Associated With Intervertebral Disc Degeneration

STUDY DESIGN

An in vivo and in vitro study of the correlation between Paraoxonase 1 (PON1) and intervertebral disc degeneration (IVDD).

OBJECTIVE

The aim of this study is to clarify the expression and role of PON1 on the process of IVDD.

SUMMARY OF BACKGROUND DATA

IVDD is responsible for most of the spinal degenerative diseases. Inflammation and oxidative stress can deteriorate the living environment of nucleus pulposus (NP) cells, leading to IVDD. PON1 is an enzyme reported to have anti-inflammatory and anti-oxidative effects. There is no study about the correlation of PON1 expression with IVDD.

METHODS

Immunohistochemical (IHC), hematoxylin and eosin (H&E) staining, and Western blot examined the expression of PON1 in 88 human disc samples (male: female 43: 45) and rat models (n = 5 each group). The level of PON1 is measured in the tumor necrosis factor (TNF)-α and oxidative stress (H2O2)-induced degenerative NP cell models using Western blot and reverse transcription-polymerase chain reaction (RT-qPCR). The TNF-α, interleukin (IL)-1β, Mito superoxide (SOX), aggrecan, and collagen II are detected in nucleus pulposus (NP) cells transfected with si-RNA of PON1 using Enzyme-Linked Immunosorbent Assay (ELISA), mitoSOX staining Western blot, and RT-qPCR.

RESULTS

The expression of PON1 is significantly suppressed in human and rat degenerative intervertebral discs. The level of PON1 is significantly decreased in TNF-α and oxidative stress (H2O2)-induced degenerative NP cell models. ELISA results show that the level of TNF-α and IL-1β obviously increased; Mito SOX staining indicates that the Mito SOX fluorescence significantly increased, and the expression of aggrecan and collagen reduced in NP cells transfected with si-RNA of PON1.

CONCLUSION

Our study indicates that low PON1 expression is predictive of severe IVDD; PON1 plays an important role of keeping the homeostatic balance of intervertebral discs, and therapeutic approach regarding PON1 may be helpful to alleviate IVDD in the future.

LEVEL OF EVIDENCE

N/A.

Extracellular matrix composition of connective tissues: a systematic review and meta-analysis

The function of connective tissues depends on the physical and biochemical properties of their extracellular matrix (ECM), which are in turn dictated by ECM protein composition. With the primary objective of obtaining quantitative estimates for absolute and relative amounts of ECM proteins, we performed a systematic review of papers reporting protein composition of human connective tissues. Articles were included in meta-analysis if they contained absolute or relative quantification of proteins found in the ECM of human bone, adipose tissue, tendon, ligament, cartilage and skeletal muscle. We generated absolute quantitative estimates for collagen in articular cartilage, intervertebral disk (IVD), skeletal muscle, tendon, and adipose tissue. In addition, sulfated glycosaminoglycans were quantified in articular cartilage, tendon and skeletal muscle; total proteoglycans in IVD and articular cartilage, fibronectin in tendon, ligament and articular cartilage, and elastin in tendon and IVD cartilage. We identified significant increases in collagen content in the annulus fibrosus of degenerating IVD and osteoarthritic articular cartilage, and in elastin content in degenerating disc. In contrast, collagen content was decreased in the scoliotic IVD. Finally, we built quantitative whole-tissue component breakdowns. Quantitative estimates improve our understanding of composition of human connective tissues, providing insights into their function in physiology and pathology.

Autophagy protects nucleus pulposus cells from cyclic mechanical tension‑induced apoptosis

Intervertebral disc (IVD) degeneration (IDD) is considered to be a primary cause of lower back pain. Mechanical stress is one of the most important factors affecting IDD. It has been demonstrated that apoptosis is important in the decrease of functional IVD cells, and that mechanical stress influences disc cell apoptosis. Autophagy, an adaptive response of the cells to survival when faced with different conditions of stress, has been documented in IDD. Apoptosis and autophagy share the same stimuli and regulatory proteins, but have different threshold responses. Recently, cyclic mechanical tension (CMT) has been shown to influence IVD cell apoptosis and autophagy. However, the conversion and coordination between apoptosis and autophagy induced by CMT remains to be fully elucidated. In the present study, it was found that CMT with 20% elongation generated by the Flexercell Tension system induced the apoptosis of nucleus pulposus (NP) cells in a time‑dependent manner. When the cells were stretched for >6 h, autophagy was increased, and showed a tendency to decrease with the duration of CMT. The autophagic activity of NP cells was partially decreased by 3‑MA and was not significantly regulated by rapamycin. CMT‑induced apoptosis was partially enhanced by the decreased autophagic activity induced by 3‑MA. In addition, the level of reactive oxygen species (ROS) in NP cells induced by CMT was significantly upregulated by 3‑MA. These results suggested that abnormal mechanical stress enhanced disc cell apoptosis and consequently accelerated the process of IDD. Autophagy helps to protect against CMT‑induced apoptosis in disc cells and ROS may be important in this process. These findings are beneficial for further understanding the mechanism of disc cell apoptosis and autophagy.

Unexpectedly decreased plasma cytokines in patients with chronic back pain

Introduction

Chronic back pain is one of the most important socioeconomic problems that affects the global population. Elevated levels of inflammatory mediators, such as cytokines, have been correlated with pain, but their role in chronic back pain remains unclear. The effectiveness of anti-inflammatory drugs seems to be limited for chronic back pain. The authors wanted to investigate the levels of inflammatory mediators in long-term medically treated patients with persistent chronic back pain.

Methods

Cytokine plasma levels of patients with chronic back pain (n=23), compared to pain-free healthy controls (n=30), were investigated by immunoassay. Patients with chronic back pain were exposed to long-term conservative medical therapy with physiotherapy and anti-inflammatories, also combined with antidepressants and/or muscle-relaxants.

Results

The patients with chronic back pain expressed lower levels of the chemokines MCP1, CCL5, and CXCL6 compared to pain-free healthy controls. Significantly lower concentrations of the anti-inflammatory cytokines, interleukin (IL)-4 and granulocyte-colony stimulating factor were also found. Interestingly, levels of proinflammatory cytokines (IL-2, IL-6, IL-1β, tumor necrosis factor alpha), IL-10, granulocyte-macrophage colony-stimulating factor, and stromal cell-derived factor 1 alpha showed no significant differences between both groups.

Conclusion

This decrease of inflammatory mediators in medically treated patients with chronic back pain is of unclear origin and might be either a long-term side effect of medical therapy or related to chronic pain. Further longitudinal research is necessary to elucidate the underlying cause of these findings.

Honokiol alleviates the degeneration of intervertebral disc via suppressing the activation of TXNIP-NLRP3 inflammasome signal pathway

Intervertebral disc degeneration (IVDD) is a multifactorial disease and responsible for many spine related disorders, causes disability in the workforce and heavy social costs all over the world. Honokiol, a low molecular weight natural product, could penetrate into and distribute in IVDs to achieve therapeutic effect in a rat tail model. Therefore, the present study was undertaken to examine the antiinflammatory, antioxidation and IVD-protective effect of honokiol using nucleus pulposus cells and investigate its mechanisms to provide a new basis for future clinical treatment of IVDD. In the current study, we demonstrated that honokiol inhibits the H₂O₂-induced apoptosis (caspase-9, caspase-3, and bax), levels of oxidative stress mediators (ROS, MDA), expression of inflammatory mediators (Interleukin-6, COX-2, and iNOS), major matrix degrading proteases (MMP-3, MMP-13, ADAMTS5, and ADAMTS4) associated with nucleus pulposus degradation. Furthermore, we found nucleus pulposus protective ability of honokiol by up-regulating extra cellular matrix anabolic factors like type II collagen (Col II) and SOX9 in nucleus pulposus. We also found that honokiol suppressed the phosphorylation of NF-kB and JNK, and activation of TXNIP-NLRP3 inflammasome in H₂O₂-stimulated nucleus pulposus cells, thereby inhibiting the activation of downstream inflammatory mediators such as Interleukin-1β. Furthermore, honokiol showed a cartilage protective effect in the progression of IVDD in a rat model induced by puncture. Thus, our results demonstrate that honokiol inhibited the H₂O₂ induced apoptosis, oxidative stress, and inflammatory responses through the depression of TXNIP/NLRP3/caspase-1/ Interleukin - 1β signaling axis and the activation of NF-kB and JNK. Honokiol possess nucleus pulposus protective properties and may be of value in suppressing the pathogenesis of IVDD.

Leptin regulates disc cartilage endplate degeneration and ossification through activation of the MAPK-ERK signalling pathway in vivo and in vitro

Recent findings demonstrate that leptin plays a significant role in chondrocyte and osteoblast differentiation. However, the mechanisms by which leptin acts on cartilage endplate (CEP) cells to give rise to calcification are still unclear. The aim of this study was to evaluate the effects of leptin that induced mineralization of CEP cells in vitro and in vivo. We constructed a rat model of lumbar disc degeneration and determined that leptin was highly expressed in the presence of CEP calcification. Rat CEP cells treated with or without leptin were used for in vitro analysis using RT‐PCR and Western blotting to examine the expression of osteocalcin (OCN) and runt‐related transcription factor 2 (Runx2). Both OCN and Runx2 expression levels were significantly increased in a dose‐ and time‐dependent manner. Leptin activated ERK1/2 and STAT3 phosphorylation in a time‐dependent manner. Inhibition of phosphorylated ERK1/2 using targeted siRNA suppressed leptin‐induced OCN and Runx2 expression and blocked the formation of mineralized nodules in CEP cells. We further demonstrated that exogenous leptin induced matrix mineralization of CEP cells in vivo. We suggest that leptin promotes the osteoblastic differentiation of CEP cells via the MAPK/ERK signal transduction pathway and may be used to investigate the mechanisms of disc degeneration.

ADAMTS5 Deficiency Protects Mice From Chronic Tobacco Smoking-induced Intervertebral Disc Degeneration

STUDY DESIGN

ADAMTS5-deficient and wild type (WT) mice were chronically exposed to tobacco smoke to investigate effects on intervertebral disc degeneration (IDD).

OBJECTIVE

The aim of this study was to demonstrate a role for ADAMTS5 in mediating tobacco smoking-induced IDD.

SUMMARY OF BACKGROUND DATA

We previously demonstrated that chronic tobacco smoking causes IDD in mice because, in part, of proteolytic destruction of disc aggrecan. However, it was unknown which matrix proteinase(s) drive these detrimental effects.

METHODS

Three-month-old WT (C57BL/6) and ADAMTS5 mice were chronically exposed to tobacco smoke (four cigarettes/day, 5 day/week for 6 months). ADAMTS-mediated cleavage of disc aggrecan was analyzed by Western blot. Disc total glycosaminoglycan (GAG) content was assessed by dimethyl methylene blue assay and safranin O/fast green histology. Vertebral osteoporosity was measured by microcomputed tomography. Human nucleus pulposus (hNP) cell cultures were also exposed directly to tobacco smoke extract (TSE), a condensate containing the water-soluble compounds inhaled by smokers, to measure ADAMTS5 expression and ADAMTS-mediated cleavage of aggrecan. Activation of nuclear factor (NF)-κB, a family of transcription factors essential for modulating the cellular response to stress, was measured by immunofluorescence assay.

RESULTS

Genetic depletion of ADAMTS5 prevented vertebral bone loss, substantially reduced loss of disc GAG content, and completely obviated ADAMTS-mediated proteolysis of disc aggrecan within its interglobular domain (IGD) in mice following exposure to tobacco smoke. hNP cell cultures exposed to TSE also resulted in upregulation of ADAMTS5 protein expression and a concomitant increase in ADAMTS-mediated cleavage within aggrecan IGD. Activation of NF-κB, known to be required for ADAMTS5 gene expression, was observed in both TSE-treated hNP cell cultures and disc tissue of tobacco smoke-exposed mice.

CONCLUSION

The findings demonstrate that ADAMTS5 is the primary aggrecanase mediating smoking-induced disc aggrecanolysis and IDD. Mouse models of chronic tobacco smoking are important and useful for probing the mechanisms of disc aggrecan catabolism and IDD.

LEVEL OF EVIDENCE

N/A.

Methylation of microRNA-129-5P modulates nucleus pulposus cell autophagy by targeting Beclin-1 in intervertebral disc degeneration

MicroRNAs play an important role in the etiology and progression of many diseases, including intervertebral disc degeneration (IVDD). The miRNA miR-129-5P regulates autophagy in various cancers, but its role in human nucleus pulposus (NP) cells is unclear. The present study investigated whether miR-129-5p regulates the expression of Beclin-1 which is known to induce autophagy in NP cells by evaluating their levels in normal and degenerative disc tissues and human NP cells transfected with miR-129-5P mimic or inhibitor by quantitative real-time (qRT-)PCR, western blotting, flow cytometry, and immunofluorescence analysis. A bioinformatics analysis was used to predict the relationship between miR-129-5P and Beclin-1, which was confirmed by the dual luciferase assay. DNA methylation status was assessed by methylation-specific PCR, and the effect of demethylation on miR-129-5P level and autophagy was examined by qRT-PCR, western blotting, and flow cytometry. We found that miR-129-5P expression was downregulated while that of Beclin-1 and LC3-II was upregulated in degenerative disc NP cells. Meanwhile, autophagy was reduced in human NP cells transfected with miR-129-5P mimic, whereas the opposite result was observed upon treatment with miR-129-5P inhibitor. Bioinformatics analysis and the luciferase reporter assay revealed that Beclin-1 is a target of and is inhibited by miR-129-5P. We also found that CpG islands in the miR-129-5P promoter region were hypermethylated in degenerative as compared to normal disc tissue. Thus, miR-129-5P blocks NP cell autophagy by directly inhibiting Beclin-1, a process that is dependent on miR-129-5P promoter methylation.

Intermittent Cyclic Mechanical Tension Promotes Degeneration of Endplate Cartilage via the Nuclear Factor-κB Signaling Pathway: an in Vivo Study

OBJECTIVE

To establish a rabbit model for investigating the effects of intermittent cyclic mechanical tension (ICMT) on promoting degeneration of endplate cartilage.

METHODS

Forty New Zealand white rabbits were subjected to surgery and randomly divided into three equal groups as follows: control group (no treatment, n = 10), sham group (animals underwent a sham operation but were not subjected to mechanical tensile strain, n = 15) and loaded group (discs were subjected to 1.5 MPa external tensile loading by using an external loading device during the animals' daily activity, n = 15). Mechanical tensile strain was applied for 8 h/d. The animals were examined radiologically after 8 weeks treatment and then killed for removal of endplate cartilage tissue samples from their spines. Histological staining was performed to examine the morphology of endplate cartilage tissue. Multiple strategies were employed to examine degeneration of endplate cartilage and nuclear factor (NF)-κB signaling pathway activation.

RESULTS

After ICMT loading for 56 days, radiology revealed ossification, hyperosteogeny and stenosis in the intervertebral spaces. Examination of hematoxylin and eosin staining of sections of endplate cartilage showed significant damage as the load duration increased in the ICMT loading group. Expression of aggrecan (ACAN), type II collagen (COL-2A), SRY-related high mobility group-box gene 9 (SOX9) was down-regulated (FACAN = 21.515, P < 0.01; FCOL-2A = 6.670, P = 0.05; FSOX9 = 7.888, P < 0.05), whereas that of matrix metallopeptidase 13 (MMP13) was up-regulated (FMMP13 = 14.120, P < 0.01) after ICMT. Western blot and immunofluorescence revealed that expression of protein was consistent with gene expression results. Additionally, ICMT loading can lead to NF-κB signaling pathway activation as well as degeneration of endplate cartilage.

CONCLUSION

These experiments indicate that ICMT contributes to the activation of NF-κB signaling pathway in vivo and that the NF-κB signaling pathway further up-regulates MMP13, leading to degeneration of endplate cartilage.

ISSLS PRIZE IN BIOENGINEERING SCIENCE 2017: Automation of reading of radiological features from magnetic resonance images (MRIs) of the lumbar spine without human intervention is comparable with an expert radiologist

STUDY DESIGN

Investigation of the automation of radiological features from magnetic resonance images (MRIs) of the lumbar spine.

OBJECTIVE

To automate the process of grading lumbar intervertebral discs and vertebral bodies from MRIs. MR imaging is the most common imaging technique used in investigating low back pain (LBP). Various features of degradation, based on MRIs, are commonly recorded and graded, e.g., Modic change and Pfirrmann grading of intervertebral discs. Consistent scoring and grading is important for developing robust clinical systems and research. Automation facilitates this consistency and reduces the time of radiological analysis considerably and hence the expense.

METHODS

12,018 intervertebral discs, from 2009 patients, were graded by a radiologist and were then used to train: (1) a system to detect and label vertebrae and discs in a given scan, and (2) a convolutional neural network (CNN) model that predicts several radiological gradings. The performance of the model, in terms of class average accuracy, was compared with the intra-observer class average accuracy of the radiologist.

RESULTS

The detection system achieved 95.6% accuracy in terms of disc detection and labeling. The model is able to produce predictions of multiple pathological gradings that consistently matched those of the radiologist. The model identifies 'Evidence Hotspots' that are the voxels that most contribute to the degradation scores.

CONCLUSIONS

Automation of radiological grading is now on par with human performance. The system can be beneficial in aiding clinical diagnoses in terms of objectivity of gradings and the speed of analysis. It can also draw the attention of a radiologist to regions of degradation. This objectivity and speed is an important stepping stone in the investigation of the relationship between MRIs and clinical diagnoses of back pain in large cohorts.

LEVEL OF EVIDENCE

Level 3.

The Paracrine Effect of Degenerated Disc Cells on Healthy Human Nucleus Pulposus Cells Is Mediated by MAPK and NF-κB Pathways and Can Be Reduced by TGF-β1

Inflammation is thought to have a major role in the pathogenesis of disc degeneration. Studies have shown that nucleus pulposus cells (NPCs) respond to one or two specific cytokines by regulating cell proliferation or matrix synthesis. However, the effects of a cocktail of factors secreted by degenerated disc cells on transplanted exogenous healthy NPCs remain unknown. Concentrations of multiple cytokines in degenerated disc tissue-conditioned medium (dCM) were measured using enzyme-linked immunosorbent assay (ELISA). 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay and Ki67 immunofluorescence staining were used to evaluate the proliferation of cells in dCM. The function of exogenous NPCs cultured in dCM was evaluated by examining catabolic markers (ADAMTS-4, ADAMTS-5, MMP-1, MMP-3, and MMP-13), anabolic markers (TIMP-1, TIMP-2, and TIMP-3), and the extracellular matrix protein-aggrecan (ACAN) and collagen II (COL2)-expression with real time polymerase chain reaction (RT-PCR). Mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) pathway activation was observed using Western blotting. Finally, we examined the role of transforming growth factor (TGF)-β1 in reducing dCM-mediated exogenous NPC dysfunction. Levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-1α, IL-2, IL-4, IL-6, IL-8, IL-10, IL-17, interferon-γ (IFN-γ), and prostaglandin E2 (PGE2) were higher and TGF-β1 levels were lower in dCM compared with the control medium. Treatment with dCM increased the proliferation of healthy NPCs. NPCs exhibited significantly higher expression of ADAMTS-4, ADAMTS-5, MMP-1, MMP-3, and MMP-13 and decreased TIMP-2, ACAN, and COL2 expression in the dCM group in a dose- and time-dependent manner. Treatment with dCM moderately increased TIMP-1 expression and had no effect on TIMP-3 mRNA levels. The MAPK and NF-κB pathways were implicated in dCM-mediated responses of healthy NPCs. TGF-β1 partially reversed the dCM-mediated NPC dysfunction. Increased levels of inflammatory factors and decreased TGF-β1 levels in dCM suggest an inflammatory environment in degenerated disc tissue. The catabolic effect of dCM on human healthy NPCs is mediated by MAPK and NF-κB pathways and can be reduced by TGF-β1.

Cut-Off Value for Pain Sensitivity Questionnaire in Predicting Surgical Success in Patients with Lumbar Disc Herniation

Various factors related to predict surgical success were studied; however, a standard cut-off point for the Pain Sensitivity Questionnaire (PSQ) measure has not yet been established for a favorable surgical outcome for lumbar disc herniation (LDH). This study was to find the optimal cut-off point on the PSQ to distinguish surgical success in patients with LDH. A total of 154 patients with LDH consecutively referred to our clinic were enrolled into this prospective study between February 2011 and January 2014. All participants completed the PSQ. Patients completed the Oswestry Disability Index (ODI) score before surgery, and at 2 years after surgery. Surgical success was defined as a 13-point improvement from the baseline ODI scores. The cut-off value for PSQ was determined by the receiver-operating characteristic curve (ROC). The mean age of patients was 49.3±9.6 years, and there were 80 women. The mean time for follow-up assessment was 31±5 months (range 24–35). Post-surgical success was 79.9% (n = 123) at 2 years follow up. The mean score for the total PSQ, PSQ-minor, and PSQ-moderate were 6.0 (SD = 1.6), 5.4 (SD = 1.9) and 6.5 (SD = 1.7), respectively. Total PSQ score was also significantly correlated with the total scores of the ODI. The optimal total PSQ cut-off point was determined as > 5.2 to predict surgical success in LDH patients, with 80.0% sensitivity and 75.6% specificity (AUC-0.814, 95% CI 0.703–0.926). This study showed that the PSQ could be considered a parameter for predicting surgical success in patients with LDH, and can be useful in clinical practice.

A novel technique for the contrast-enhanced microCT imaging of murine intervertebral discs

Disc degeneration is one of the leading factors that contribute to low back pain. Thus, the further understanding of the mechanisms contributing to degeneration of the intervertebral disc degeneration is critical for the development of therapies and strategies for treating low back pain. Rodent models are attractive for conducting mechanistic studies particularly because of the availability of genetically modified animals. However, current imaging technologies such as magnetic resonance imaging, do not have the ability to resolve spatial features at the tens- to single- micrometer scale. We propose here a contrast-enhanced microCT technique to conduct high-resolution imaging of the rodent intervertebral discs at 10µm spatial resolution. Based on the iodinated-hydrophilic contrast agent Ioversol, we are able to conduct high resolution imaging on rat and mouse intervertebral discs. Leveraging the hydrophilic characteristic of the contrast agent, we are able to discriminate the annulus fibrosus from the water-rich nucleus pulposus. Moreover, this technique allows for the quantitative measurement of disc morphologies and volumes, and we demonstrate the versatility of this technique on cultured live intervertebral discs. Coupled with our semi-automated segmentation technique, we are able to quantify the intervertebral disc volumes with a high degree of reproducibility. The contrast-enhanced microCT images were qualitatively and quantitatively indistinguishable from the traditional histological assessment of the same sample. Furthermore, stereological measures compared well between histology and microCT images. Taken together, the results reveal that rat and mouse intervertebral discs can be imaged longitudinally in vitro at high resolutions, with no adverse effects on viability and features of the intervertebral disc.

Determination of the Optimal Cutoff Values for Pain Sensitivity Questionnaire Scores and the Oswestry Disability Index for Favorable Surgical Outcomes in Subjects With Lumbar Spinal Stenosis

STUDY DESIGN

Retrospective analysis of prospectively collected data (NCT02134821).

OBJECTIVE

The aim of this study was to elucidate the cutoff values for significant predictors for favorable outcomes after lumbar spine surgery in patients with lumbar spinal stenosis (LSS).

SUMMARY OF BACKGROUND DATA

Various factors are associated with the surgical outcomes for patients with LSS. However, we did not know the odds ratio and/or cutoff values of a predictive factor for a favorable surgical outcome for LSS.

METHODS

A total of 157 patients who underwent spine surgery due to LSS between June 2012 and April 2013 were included in this study. The patients were dichotomized into 2 groups on the basis of an Oswestry Disability Index (ODI) score of 22 or less (favorable outcome group) or more than 22 (unfavorable outcome group) at 12 months after surgery. Regarding favorable outcomes, the odds ratio for each preoperative variable including demographic data, preoperative symptom severity, and pain sensitivity questionnaire (PSQ) score was calculated using univariate and multivariate logistic regression analyses. For the significant variables for surgical outcome, receiver operating characteristic (ROC) curve was plotted with calculation of the area under the ROC curve.

RESULTS

Multivariate analysis revealed that the ODI and total PSQ scores were significantly associated with a greater likelihood of an unfavorable surgical outcome [odds ratio (95% confidence interval) of ODI, 1.289 (1.028-1.616); odds ratio (95% confidence interval) of total PSQ, 1.060 (1.009-1.113)]. ROC analysis revealed area under the ROC curves for the total PSQ and ODI scores of 0.638 (P = 0.005) and 0.692 (P < 0.001), respectively.

CONCLUSION

Preoperative disability and pain sensitivity can be predictors of the functional level achieved after spine surgery in patients with LSS, and the ideal cutoff values for the total PSQ and ODI scores were 6.6 and 45.0, respectively.

Alternative Splicing of G Protein-Coupled Receptors: Relevance to Pain Management

Drugs that target G protein-coupled receptors (GPCRs) represent the primary treatment strategy for patients with acute and chronic pain; however, there is substantial individual variability in both the efficacy and adverse effects associated with these drugs. Variability in drug responses is due, in part, to individuals' diversity in alternative splicing of pain-relevant GPCRs. G protein-coupled receptor alternative splice variants often exhibit distinct tissue distribution patterns, drug-binding properties, and signaling characteristics that may impact disease pathology as well as the extent and direction of analgesic effects. We review the importance of GPCRs and their known splice variants to the management of pain.

The high-throughput phenotyping of the viscoelastic behavior of whole mouse intervertebral discs using a novel method of dynamic mechanical testing

Intervertebral disc (IVD) degeneration is highly correlated with lower back pain, and thus understanding the mechanisms of IVD degeneration is critical for the treatment of this disease. Utilizing mouse models to probe the mechanisms of degeneration is especially attractive due to the ease of manipulating mouse models and the availability of transgenics. Yet characterizing the mechanical behavior of mice IVDs remain challenging due to their minute size (approximately 540 μm in height and 1080 μm(2) in cross sectional area). We have thus developed a simple method to dynamically characterize the mechanical properties of intact mouse IVDs. The IVDs were dissected with the endplates intact, and dynamically compressed in the axial direction at 1% and 5% peak strains at 1 Hz. Utilizing this novel approach, we examined the effects of in vitro ribosylation and trypsin digestion for 24 or 72 h on the viscoelastic behavior of the whole murine IVD. Trypsin treatment resulted in a decrease of proteoglycans and loss of disc height, while ribosylation had no effect on structure or proteoglycan composition. The 72 h ribosylation group exhibited a stiffening of the disc, and both treatments significantly reduced viscous behavior of the IVDs, with the effects being more pronounced at 5% strain. Here we demonstrate a novel high-throughput method to mechanically characterize murine IVDs and detect strain-dependent differences in the elastic and the viscous behavior of the treated IVDs due to ribose and trypsin treatments.

Progranulin knockout accelerates intervertebral disc degeneration in aging mice

Intervertebral disc (IVD) degeneration is a common degenerative disease, yet much is unknown about the mechanisms during its pathogenesis. Herein we investigated whether progranulin (PGRN), a chondroprotective growth factor, is associated with IVD degeneration. PGRN was detectable in both human and murine IVD. The levels of PGRN were upregulated in murine IVD tissue during aging process. Loss of PGRN resulted in an early onset of degenerative changes in the IVD tissue and altered expressions of the degeneration-associated molecules in the mouse IVD tissue. Moreover, PGRN knockout mice exhibited accelerated IVD matrix degeneration, abnormal bone formation and exaggerated bone resorption in vertebra with aging. The acceleration of IVD degeneration observed in PGRN null mice was probably due to the enhanced activation of NF-κB signaling and β-catenin signaling. Taken together, PGRN may play a critical role in homeostasis of IVD, and may serve as a potential molecular target for prevention and treatment of disc degenerative diseases.

Effects of nuclear factor kappa B signaling pathway in human intervertebral disc degeneration

STUDY DESIGN

IL-1β (interleukin-1β) can activate human nucleus pulposus cells with or without nuclear factor kappa B (NF-κB) inhibition. We undertook a descriptive and mechanistic investigation of catabolic effects of NF-κB signaling pathway in intervertebral disc degenerative changes.

OBJECTIVE

To clarify the mediatory role of NF-κB signaling pathway in human intervertebral disc degeneration (IDD).

SUMMARY OF BACKGROUND DATA

IDD is a major cause of lower back pain, but the molecular mechanism behind this process is poorly understood. NF-κB is a family of transcription factors that play a central role in mediating cellular response to damage, stress, and inflammation. Growing evidence implicates chronic activation of NF-κB in many degenerative diseases, but its role in IDD has not been adequately explored.

METHODS

Human nucleus pulposus cells in monolayer culture were exposed to IL-1β, which increases matrix-degrading enzyme activity in the nucleus pulposus, with or without NF-κB inhibition by BAY11-7082; ribonucleic acid was isolated for real-time polymerase chain reaction analysis of gene expression, Western blot analysis was performed to detect the changes of protein expression.

RESULTS

NF-κB specific inhibitor BAY11-7082 significantly inhibited IL-1β-induced NF-κB activation. IL-1β-dependent gene upregulation of matrix metalloproteinase (MMP)-3, MMP-9, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4, and ADAMTS-5 was significantly reduced by NF-κB inhibition. The decreased gene expression of aggrecan and type II collagen, induced by IL-1β was also reversed by BAY11-7082. NF-κB inhibition reversed the IL-1β-induced changes of protein expression of MMP-3, MMP-9, MMP-13, ADAMTS-4, ADAMTS-5, aggrecan, and type II collagen.

CONCLUSION

These findings demonstrate that the NF-κB signaling pathway is a key mediator of IDD and represents a therapeutic target for mitigating disc degenerative diseases.

LEVEL OF EVIDENCE

N/A.

Effects of secreted factors in culture medium of annulus fibrosus cells on microvascular endothelial cells: elucidating the possible pathomechanisms of matrix degradation and nerve in-growth in disc degeneration

OBJECTIVE

To test whether the interaction between annulus fibrosus cells (AFCs) and endothelial cells (ECs) disrupts matrix homeostasis and stimulates production of innervation mediators.

METHODS

Human microvascular ECs were cultured in the conditioned media of AF cell culture derived from degenerated human surgical specimen. Matrix-metalloproteinases (MMPs) and platelet-derived growth factor (PDGF) of ECs of this culture were analyzed by qRT-PCR, Western, and immunofluorescence. Vascular endothelial growth factor (VEGF), Interleukin-8 (IL-8), and nerve growth factor (NGF) in the media of this cell culture were assayed by ELISA. To determine the effects of ECs on AFCs, qRT-PCR was performed to determine mRNA levels of collagen I, II and aggrecan in AFCs cultured in EC conditioned media.

RESULTS

Compared to ECs cultured in naïve media, ECs exposed to AFC conditioned media expressed higher mRNA and protein levels of key biomarkers of invasive EC phenotype, MMP-2 (2×), MMP-13 (4×), and PDGF-B (1.5-2×), and NGF (24.9 ± 15.2 pg/mL vs 0 in naïve media). Treatment of AF cells with EC culture conditioned media decreased collagen type II expression two fold. Considerable quantities of pro-angiogenic factors IL-8 (396.7 ± 302.0 pg/mL) and VEGF (756.2 ± 375.9 pg/mL) were also detected in the conditioned media of untreated AF cell culture.

DISCUSSION

AFCs from degenerated discs secreted factors which stimulated EC production of factors known to induce matrix degradation, angiogenesis, and innervation. IL-8 and VEGF maybe the secreted factors from AFCs which mediate a pro-angiogenic stimulus often implicated in the development of disc degeneration.

Both expression of cytokines and posterior annulus fibrosus rupture are essential for pain behavior changes induced by degenerative intervertebral disc: An experimental study in rats

The aim of this study was to analyze the relationship between intervertebral disc degeneration and low back pain (LBP). Rat L4/5 disc degeneration model was established by annular puncture using a 0.4 mm needle anteriorly or posteriorly. In both anterior and posterior puncture models, magnetic resonance imaging (MRI) and histological analyses revealed marked disc degeneration 2 weeks after puncture. Cytokine expression was up-regulated in different level in nucleus pulposus (NP) from 3 days after puncture. Pain behavioral tests indicated that the anterior disc puncture did not induce pain behavior changes, whereas the posterior disc puncture resulted in mechanical allodynia from 1 day to 21 days after injury. Besides, cytokine expression was significantly increased in dorsal root ganglion (DRG) at 1 and 2 weeks after posterior puncture, but not after the anterior puncture. These findings indicate the NP of the degenerative disc expresses different levels of inflammatory cytokines, and posterior disc puncture produced mechanical allodynia. The expression phase of cytokines in the NP was accordance with mechanical hyperalgesia in the posterior disc puncture model. Both expression of cytokines and posterior annulus fibrosus (AF) rupture in degenerative intervertebral disc are essential for pain behavior changes.

Role of cytokines in intervertebral disc degeneration: pain and disc content

Degeneration of the intervertebral discs (IVDs) is a major contributor to back, neck and radicular pain. IVD degeneration is characterized by increases in levels of the proinflammatory cytokines TNF, IL-1α, IL-1β, IL-6 and IL-17 secreted by the IVD cells; these cytokines promote extracellular matrix degradation, chemokine production and changes in IVD cell phenotype. The resulting imbalance in catabolic and anabolic responses leads to the degeneration of IVD tissues, as well as disc herniation and radicular pain. The release of chemokines from degenerating discs promotes the infiltration and activation of immune cells, further amplifying the inflammatory cascade. Leukocyte migration into the IVD is accompanied by the appearance of microvasculature tissue and nerve fibres. Furthermore, neurogenic factors, generated by both disc and immune cells, induce expression of pain-associated cation channels in the dorsal root ganglion. Depolarization of these ion channels is likely to promote discogenic and radicular pain, and reinforce the cytokine-mediated degenerative cascade. Taken together, an enhanced understanding of the contribution of cytokines and immune cells to these catabolic, angiogenic and nociceptive processes could provide new targets for the treatment of symptomatic disc disease. In this Review, the role of key inflammatory cytokines during each of the individual phases of degenerative disc disease, as well as the outcomes of major clinical studies aimed at blocking cytokine function, are discussed.

Genomics of pain in osteoarthritis

Osteoarthritis (OA) accounts for the majority of the disease burden for musculoskeletal disorders and is one of the leading causes of disability worldwide. This disability is the result not of the cartilage loss that defines OA radiographically, but of the chronic pain whose presence defines symptomatic OA. It is becoming clear that many genes, each with a small effect size, contribute to the risk of developing OA. However, the genetics of OA pain are only just starting to be explored. This review will describe the first genes to have been identified in genomic studies of OA pain, as well as the possible dual roles of genes previously identified in genomic studies of OA in the context of pain. Difficulties associated with attempting to characterise the genetics of OA pain will be discussed and promising future avenues of research into genetic and epigenetic factors affecting OA pain described.

Ex vivo porcine model to measure pH dependence of chemical exchange saturation transfer effect of glycosaminoglycan in the intervertebral disc

PURPOSE

Studies have linked low pH and loss of glycosaminoglycan (GAG) in the intervertebral discs (IVDs) of patients with discogenic back pain. The purpose of this study is to determine whether the chemical exchange saturation transfer (CEST) effect of GAG (gagCEST) is pH dependent and whether it can be used to detect pH changes in IVD specimens. Iopromide, a Food and Drug Administration approved agent for CT/X-Ray, was also evaluated as a pH-sensitive CEST probe to explore the agents' potential to measure IVD pH.

METHODS

The pH dependency of the CEST effect of chondroitin sulfate (containing GAG) and Iopromide phantoms was investigated at 7 T. Z-spectra from porcine IVD specimens were acquired before and after manipulating the pH with sodium lactate. Iopromide was injected into the specimens and the calibration curve was used to determine the pH status.

RESULTS

Chondroitin sulfate showed a non-linear dependence of gagCEST effect with pH and gagCEST signal differences were detected in the specimens. The CEST effect of Iopromide resulted in a sigmoidal relation with pH and was used to measure pH.

CONCLUSION

gagCEST is sensitive to pH and enables investigation of the IVD pH status. Iopromide CEST is independent of the local GAG concentration and has the potential for measuring pH in the IVD.

Dynamic and static overloading induce early degenerative processes in caprine lumbar intervertebral discs

Mechanical overloading of the spine is associated with low back pain and intervertebral disc (IVD) degeneration. How excessive loading elicits degenerative changes in the IVD is poorly understood. Comprehensive knowledge of the interaction between mechanical loading, cell responses and changes in the extracellular matrix of the disc is needed in order to successfully intervene in this process. The purpose of the current study was to investigate whether dynamic and static overloading affect caprine lumbar discs differently and what mechanisms lead to mechanically induced IVD degeneration. Lumbar caprine IVDs (n = 175) were cultured 7, 14 and 21 days under simulated-physiological loading (control), high dynamic or high static loading. Axial deformation and stiffness were continuously measured. Cell viability, cell density, and gene expression were assessed in the nucleus, inner- and outer annulus. The extracellular matrix (ECM) was analyzed for water, glycosaminoglycan and collagen content. IVD height loss and changes in axial deformation were gradual with dynamic and acute with static overloading. Dynamic overloading caused cell death in all IVD regions, whereas static overloading mostly affected the outer annulus. IVDs expression of catabolic and inflammation-related genes was up-regulated directly, whereas loss of water and glycosaminoglycan were significant only after 21 days. Static and dynamic overloading both induced pathological changes to caprine lumbar IVDs within 21 days. The mechanism by which they inflict biomechanical, cellular, and extracellular changes to the nucleus and annulus differed. The described cascades provide leads for the development of new pharmacological and rehabilitative therapies to halt the progression of DDD.

Annulus fibrosus cells can induce mineralization: an in vitro study

BACKGROUND CONTEXT

There is still no consensus as to whether the calcification observed in degenerate intervertebral discs (IVDs) is a cause or a consequence of disc degeneration.

PURPOSE

To investigate the mineralization potential of healthy (independent of other associated changes) annulus fibrosus (AF) cells under controlled in vitro conditions.

STUDY DESIGN/SETTING

In vitro study to investigate the mineralization potential of the AF cells.

METHODS

Annulus fibrosus cells, isolated from bovine IVDs, were grown in monolayer. The effect of cell density, culture time, age of cell source, and passage on the percentage of AF cells with alkaline phosphatase activity (ALPa) was evaluated. Gene expression of mineralization-associated markers was determined. Cells were immunostained for Type I, II, and X collagens. To study mineralization potential, AF cells and AF cells that were sorted into two populations, high (top 5% ± 1%) or low (bottom 5% ± 1%) ALPa expressors, were grown in the presence of β-glycerophosphate for 2 weeks.

RESULTS

The percentage of AF cells that express ALPa changes with time in culture and seeding density for primary immature and mature cell sources but not for passaged cells. Gene expression of ALP, matrix metallopeptidase-13 (MMP-13), osteopontin, and runt-related transcription factor 2 was upregulated by Day 7. Under mineralization-inducing conditions, high ALPa expressors and unsorted AF cells formed von Kossa-positive nodules, composed of hydroxyapatite as determined by electron diffraction analysis. Low ALPa expressors had significantly fewer von Kossa-positive nodules (p<.01) compared with high ALPa expressors. Cells showed colocalization of Type I collagen and ALPa. No Type II collagen was detected suggesting that these were AF cells and not chondrocytes.

CONCLUSIONS

Annulus fibrosus cells have mineralizing capability and form hydroxyapatite crystalline deposits when cultured under appropriate conditions. This system could be used to investigate mineralization mechanisms in the AF during pathological calcification and at the AF-bone interface in disc degeneration.

Global identification of genes related to nutrient deficiency in intervertebral disc cells in an experimental nutrient deprivation model

Background

Intervertebral disc degeneration is a significant cause of degenerative spinal diseases. Nucleus pulposus (NP) cells reportedly fail to survive in large degenerated discs with limited nutrient availability. Therefore, understanding the regulatory mechanism of the molecular response of NP cells to nutrient deprivation may reveal a new strategy to treat disc degeneration. This study aimed to identify genes related to nutrient deprivation in NP cells on a global scale in an experimental nutrient deprivation model.

Methodology/Principal Findings

Rat NP cells were subjected to serum starvation. Global gene expression was profiled by microarray analysis. Confirmation of the selected genes was obtained by real-time polymerase chain reaction array analysis. Western blotting was used to confirm the expression of selected genes. Functional interactions between p21^Cip1 and caspase 3 were examined. Finally, flow cytometric analyses of NP cells were performed. Microarray analysis revealed 2922 differentially expressed probe sets with ≥1.5-fold changes in expression. Serum starvation of NP cells significantly affected the expression of several genes involved in DNA damage checkpoints of the cell cycle, including Atm, Brca1, Cdc25, Gadd45, Hus1, Ppm1D, Rad 9, Tp53, and Cyclin D1. Both p27^Kip1 and p53 protein expression was upregulated in serum-starved cells. p21^Cip1 expression remained in NP cells transfected with short interfering RNA targeting caspase 3 (caspase 3 siRNA). Both G1 arrest and apoptosis induced by serum starvation were inhibited in cells transfected with caspase 3 siRNA.

Conclusions/Significance

Nutrient deprivation in NP cells results in the activation of a signaling response including DNA damage checkpoint genes regulating the cell cycle. These results provide novel possibilities to improve the success of intervertebral disc regenerative techniques.

New hypothesis of chronic back pain: low pH promotes nerve ingrowth into damaged intervertebral disks

The pathogenesis of low back pain is still elusive. Here, we proposed a new hypothesis that low pH is a possible cause of the development and progression of low back pain. We propose that low pH promotes the production of the inflammatory mediators and the depletion of proteoglycan in the damaged intervertebral disk. The inflammation response, evoked by the dorsal root ganglia, changes the delicate nutrient balance in the nucleus, resulting in a vicious cycle and leading to choronic back pain. Our hypothesis may explain many of the available clinical and experimental data on low back pain, thus it may help elucidate the pathogenesis of low back pain and improve clinical management.

ISSLS prize winner: inhibition of NF-κB activity ameliorates age-associated disc degeneration in a mouse model of accelerated aging

STUDY DESIGN

NF-κB activity was pharmacologically and genetically blocked in an accelerated aging mouse model to mitigate age-related disc degenerative changes.

OBJECTIVE

To study the mediatory role of NF-κB-signaling pathway in age-dependent intervertebral disc degeneration.

SUMMARY OF BACKGROUND DATA

Aging is a major contributor to intervertebral disc degeneration (IDD), but the molecular mechanism behind this process is poorly understood. NF-κB is a family of transcription factors that play a central role in mediating cellular response to damage, stress, and inflammation. Growing evidence implicates chronic NF-κB activation as a culprit in many aging-related diseases, but its role in aging-related IDD has not been adequately explored. We studied the effects of NF-κB inhibition on IDD, using a DNA repair-deficient mouse model of accelerated aging (Ercc1 mice) previously been reported to exhibit age-related IDD.

METHODS

Systemic inhibition of NF-κB activation was achieved either genetically by deletion of 1 allele of the NF-κB subunit p65 (Ercc1p65 mice) or pharmacologically by chronic intraperitoneal administration of the Nemo Binding Domain (8K-NBD) peptide to block the formation of the upstream activator of NF-κB, IκB Inducible Kinase (IKK), in Ercc1 mice. Disc cellularity, total proteoglycan content and proteoglycan synthesis of treated mice, and untreated controls were assessed. RESULTS.: Decreased disc matrix proteoglycan content, a hallmark feature of IDD, and elevated disc NF-κB activity were observed in discs of progeroid Ercc1 mice and naturally aged wild-type mice compared with young wild-type mice. Systemic inhibition of NF-κB by the 8K-NBD peptide in Ercc1 mice increased disc proteoglycan synthesis and ameriolated loss of disc cellularity and matrix proteoglycan. These results were confirmed genetically by using the p65 haploinsufficient Ercc1p65 mice.

CONCLUSION

These findings demonstrate that the IKK/NF-κB signaling pathway is a key mediator of age-dependent IDD and represents a therapeutic target for mitigating disc degenerative diseases associated with aging.

Spine degeneration in a murine model of chronic human tobacco smokers

OBJECTIVE

To investigate the mechanisms by which chronic tobacco smoking promotes intervertebral disc degeneration (IDD) and vertebral degeneration in mice.

METHODS

Three month old C57BL/6 mice were exposed to tobacco smoke by direct inhalation (4 cigarettes/day, 5 days/week for 6 months) to model long-term smoking in humans. Total disc proteoglycan (PG) content [1,9-dimethylmethylene blue (DMMB) assay], aggrecan proteolysis (immunobloting analysis), and cellular senescence (p16INK4a immunohistochemistry) were analyzed. PG and collagen syntheses ((35)S-sulfate and (3)H-proline incorporation, respectively) were measured using disc organotypic culture. Vertebral osteoporosity was measured by micro-computed tomography.

RESULTS

Disc PG content of smoke-exposed mice was 63% of unexposed control, while new PG and collagen syntheses were 59% and 41% of those of untreated mice, respectively. Exposure to tobacco smoke dramatically increased metalloproteinase-mediated proteolysis of disc aggrecan within its interglobular domain (IGD). Cellular senescence was elevated two-fold in discs of smoke-exposed mice. Smoke exposure increased vertebral endplate porosity, which closely correlates with IDD in humans.

CONCLUSIONS

These findings further support tobacco smoke as a contributor to spinal degeneration. Furthermore, the data provide a novel mechanistic insight, indicating that smoking-induced IDD is a result of both reduced PG synthesis and increased degradation of a key disc extracellular matrix protein, aggrecan. Cleavage of aggrecan IGD is extremely detrimental as this results in the loss of the entire glycosaminoglycan-attachment region of aggrecan, which is vital for attracting water necessary to counteract compressive forces. Our results suggest identification and inhibition of specific metalloproteinases responsible for smoke-induced aggrecanolysis as a potential therapeutic strategy to treat IDD.

Characterization of the annulus fibrosus-vertebral body interface: identification of new structural features

Current surgical treatments for degenerative intervertebral disc disease do not restore full normal spinal movement. Tissue engineering a functional disc replacement may be one way to circumvent this limitation, but will require an integration of the different tissues making up the disc for this approach to be successful. Hence, an in-depth characterization of the native tissue interfaces, including annulus insertion into bone is necessary, as knowledge of this interface is limited. The objective of this study was to characterize the annulus fibrosus-vertebral bone (AF-VB) interface in immature (6-9 months old) and mature (18-24 months old) bovine discs, as well as to define these structures for normal adult human (22 and 45 years old) discs. Histological assessment showed that collagen fibers in the inner annulus, which are predominantly type II collagen, all appear to insert into the mineralized endplate zone. In contrast, some of the collagen fibers of the outer annulus, predominantly type I collagen, insert into this endplate, while other fibers curve laterally, at an ∼ 90° angle, to the outer aspect of the bone, and merge with the periosteum. This is seen in both human and bovine discs. Where the AF inserts into the calcified zone of the AF-VB interface, it passes through a chondroid region, rich in type II collagen and proteoglycans. Annulus cells (elongated cells that are not surrounded by proteoglycans) are present at this interface. This cartilage zone is evident in both human and bovine discs. Type X collagen and alkaline phosphatase are localized to the interface region. Age-associated differences in bovine spines are observed when examining the interface thickness and the matrix composition of the cartilaginous endplate, as well as the thickness of the mineralized endplate. These findings will assist with the design of the AF-VB interface in the tissue engineered disc.

Low back pain in the United States: incidence and risk factors for presentation in the emergency setting

BACKGROUND CONTEXT

Low back pain is prevalent in the United States. At the present time, no large longitudinal study is available characterizing the incidence of this condition in the US population or identifying potential risk factors for its development.

PURPOSE

To characterize the incidence of acute low back pain requiring medical evaluation in the emergency department and establish risk factors for its development.

STUDY DESIGN

Cross-sectional study.

PATIENT SAMPLE

United States population estimates.

OUTCOME MEASURES

Incidence rate ratios were calculated to determine the influence of age, sex, and race on the development of low back pain requiring emergent medical evaluation.

METHODS

The National Electronic Injury Surveillance System was queried for all cases of low back pain presenting to emergency departments between 2004 and 2008. Incidence rate ratios were then calculated with respect to age, sex, and race. The chi-square statistic was used to identify statistically significant differences in the incidence of low back pain requiring emergent medical evaluation between subgroups.

RESULTS

An estimated 2.06 million episodes of low back pain occurred among a population at risk of over 1.48 billion person-years for an incidence rate of 1.39 per 1,000 person-years in the United States. Low back pain accounted for 3.15% of all emergency visits. Injuries sustained at home (65%) accounted for most patients presenting with low back pain. Low back pain demonstrates a bimodal distribution with peaks between 25 and 29 years of age (2.58/1,000 person-years) and 95 to 99 years of age (1.47/1,000) without differentiation by underlying etiology. When compared with females, males showed no significant differences in the rates of low back pain. However, when analyzed by 5-year age group, males aged 10 to 49 years and females aged 65 to 94 years had increased risk of low back pain than their opposite sex counterparts. When compared with Asian race, patients of black and white race were found to have significantly higher rates of low back pain. Older patients were found to be at a greater risk of hospital admission for low back pain.

CONCLUSION

Age, sex, and race are significant risk factors for the development of low back pain necessitating treatment in an emergency department.