Behavioral signs of axial low back pain and motor impairment correlate with the severity of intervertebral disc degeneration in a mouse model

Hypertrophic Ligamentum Flavum in Lumbar Spine Stenosis Is Associated With the Increased Expression of Secreted Protein Acidic and Rich in Cysteine

STUDY DESIGN

Basic research.

OBJECTIVES

Secreted protein acidic and rich in cysteine (SPARC) is a critical pro-fibrotic mediator. This study aims to characterize the role of SPARC in hypertrophic ligamentum flavum (LF) and fibrosis.

METHODS

Hypertrophic LF samples were obtained from 8 patients with L4/5 lumbar spinal stenosis (LSS) during the decompressive laminectomy. Non-hypertrophic LF from age- and sex-matched 8 patients with L4/5 lumbar disc herniation was selected as control. An in vitro model of fibrosis in human LF cells was established by interleukin 6 (IL-6) to assess SPARC expression.

RESULTS

Hypertrophic LF samples had higher fibrosis scores than control samples by Masson's trichrome staining (3.6 vs. 1.3, P < .001). Hypertrophic LF samples had significantly more positive staining for collagen and SPARC. Collagen III (Col3), α smooth muscle actin (α-SMA), and SPARC mRNA expression levels were significantly higher in hypertrophic LF samples than in control samples by qPCR. SPARC expression and fibrotic and inflammatory makers (collagen I, Col3, IL-6, interleukin 1β) were significantly upregulated in IL-6 stimulation of normal LF in vitro.

CONCLUSION

SPARC was detected in human LF and significantly upregulated in the clinical samples of hypertrophic LF compared to their normal counterparts. We also demonstrated an increased level of SPARC in an in vitro fibrosis model of LF. Thus, SPARC could be a crucial biomarker for the pathogenesis of hypertrophic LF and a therapeutic target for LSS.

Roles of organokines in intervertebral disc homeostasis and degeneration

The intervertebral disc is not isolated from other tissues. Recently, abundant research has linked intervertebral disc homeostasis and degeneration to various systemic diseases, including obesity, metabolic syndrome, and diabetes. Organokines are a group of diverse factors named for the tissue of origin, including adipokines, osteokines, myokines, cardiokines, gastrointestinal hormones, and hepatokines. Through endocrine, paracrine, and autocrine mechanisms, organokines modulate energy homeostasis, oxidative stress, and metabolic balance in various tissues to mediate cross-organ communication. These molecules are involved in the regulation of cellular behavior, inflammation, and matrix metabolism under physiological and pathological conditions. In this review, we aimed to summarize the impact of organokines on disc homeostasis and degeneration and the underlying signaling mechanism. We focused on the regulatory mechanisms of organokines to provide a basis for the development of early diagnostic and therapeutic strategies for disc degeneration.

Pain behavior and phenotype in a modified anterior lumbar disc puncture mouse model

Background

An experimental study was performed to improve the anterior approach model of intervertebral disc degeneration (IVDD).

Objective

The aims of this study were to investigate the anterior approach model of IVDD for the cause of death, phenotypes, and underlying mechanisms of low back pain in mice.

Method

In this study, we conducted an anterior puncture procedure on a cohort of 300 C57BL/6J mice that were 8 weeks old. Our investigation focused on exploring the causes of death in the study population (n = 300) and assessing the time-course changes in various parameters, including radiographical, histological, immunofluorescence, and immunohistochemistry analyses (n = 10). Additionally, we conducted behavioral assessments on a subset of the animals (n = 30).

Results

Transverse vertebral artery rupture is a major factor in surgical death. Radiographical analyses showed that the hydration of the nucleus pulposus began to decrease at 2 weeks after puncture and obviously disappeared over 4 weeks. 3D-CT showed that disc height was significantly decreased at 4 weeks. Osteophyte at the anterior vertebral rims was observed at 2 weeks after the puncture. As the time course increased, histological analyses showed progressive disruption of the destruction of the extracellular matrix and increased secretion of inflammatory cytokines and apoptosis. Behavioral signs of low back pain were increased between the puncture and sham groups at 4 weeks.

Conclusion

The improvement of anterior intervertebral disc approach model in mice will be useful to investigate underlying mechanisms and potential therapeutic strategies for behavior and phenotypes. Furthermore, the application of vibrational pre-treatment can be used to increase the sensitivity of axial back pain in the model, thereby providing researchers with a reliable method for measuring this critical phenotype.

Hypoxia-treated adipose mesenchymal stem cell-derived exosomes attenuate lumbar facet joint osteoarthritis

BACKGROUND

Lumbar facet joint osteoarthritis (LFJ OA) is a common disease, and there is still a lack of effective disease-modifying therapies. Our aim was to determine the therapeutic effect of hypoxia-treated adipose mesenchymal stem cell (ADSC)-derived exosomes (Hypo-ADSC-Exos) on the protective effect against LFJ OA.

METHODS

The protective effect of Hypo-ADSC-Exos against LFJ OA was examined in lumbar spinal instability (LSI)-induced LFJ OA models. Spinal pain behavioural assessments and CGRP (Calcitonin Gene-Related Peptide positive) immunofluorescence were evaluated. Cartilage degradation and subchondral bone remodelling were assessed by histological methods, immunohistochemistry, synchrotron radiation-Fourier transform infrared spectroscopy (SR-FTIR), and 3D X-ray microscope scanning.

RESULTS

Hypoxia enhanced the protective effect of ADSC-Exos on LFJ OA. Specifically, tail vein injection of Hypo-ADSC-Exos protected articular cartilage from degradation, as demonstrated by lower FJ OA scores of articular cartilage and less proteoglycan loss in lumbar facet joint (LFJ) cartilage than in the ADSC-Exo group, and these parameters were significantly improved compared to those in the PBS group. In addition, the levels and distribution of collagen and proteoglycan in LFJ cartilage were increased in the Hypo-ADSC-Exo group compared to the ADSC-Exo or PBS group by SR-FTIR. Furthermore, Hypo-ADSC-Exos normalized uncoupled bone remodelling and aberrant H-type vessel formation in subchondral bone and effectively reduced symptomatic spinal pain caused by LFJ OA in mice compared with those in the ADSC-Exo or PBS group.

CONCLUSIONS

Our results show that hypoxia is an effective method to improve the therapeutic effect of ADSC-Exos on ameliorating spinal pain and LFJ OA progression.

Stiffness and axial pain are associated with the progression of calcification in a mouse model of diffuse idiopathic skeletal hyperostosis

BACKGROUND

Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by progressive calcification of spinal tissues; however, the impact of calcification on pain and function is poorly understood. This study examined the association between progressive ectopic spine calcification in mice lacking equilibrative nucleoside transporter 1 (ENT1^-/-), a preclinical model of DISH, and behavioral indicators of pain.

METHODS

A longitudinal study design was used to assess radiating pain, axial discomfort, and physical function in wild-type and ENT1^-/- mice at 2, 4, and 6 months. At endpoint, spinal cords were isolated for immunohistochemical analysis of astrocytes (GFAP), microglia (IBA1), and nociceptive innervation (CGRP).

RESULTS

Increased spine calcification in ENT1^-/- mice was associated with reductions in flexmaze exploration, vertical activity in an open field, and self-supporting behavior in tail suspension, suggesting flexion-induced discomfort or stiffness. Grip force during the axial stretch was also reduced in ENT1^-/- mice at 6 months of age. Increased CGRP immunoreactivity was detected in the spinal cords of female and male ENT1^-/- mice compared to wild-type. GFAP- and IBA1-immunoreactivity were increased in female ENT1^-/- mice compared to wild-type, suggesting an increase in nociceptive innervation.

CONCLUSION

These data suggest that ENT1^-/- mice experience axial discomfort and/or stiffness and importantly that these features are detected during the early stages of spine calcification.

Constructing intervertebral disc degeneration animal model: A review of current models

Low back pain is one of the top disorders that leads to disability and affects disability-adjusted life years (DALY) globally. Intervertebral disc degeneration (IDD) and subsequent discogenic pain composed major causes of low back pain. Recent studies have identified several important risk factors contributing to IDD's development, such as inflammation, mechanical imbalance, and aging. Based on these etiology findings, three categories of animal models for inducing IDD are developed: the damage-induced model, the mechanical model, and the spontaneous model. These models are essential measures in studying the natural history of IDD and finding the possible therapeutic target against IDD. In this review, we will discuss the technical details of these models, the duration between model establishment, the occurrence of observable degeneration, and the potential in different study ranges. In promoting future research for IDD, each animal model should examine its concordance with natural IDD pathogenesis in humans. We hope this review can enhance the understanding and proper use of multiple animal models, which may attract more attention to this disease and contribute to translation research.

Loss of lumbar disc height with age and its impact on pain and sensitivity associated behaviors in mice

PURPOSE

Aging is a risk factor for several debilitating conditions including those related to chronic back pain and intervertebral disc degeneration, both of which have no cure. Mouse models are useful tools for studying disc degeneration and chronic back pain in a tightly controlled and clinically relevant aging environment. Moreover, mice offer the advantage of carrying out longitudinal studies to understand the etiology and progression of disc pathology induced by genetic or surgical strategies. Previously, age-related behavioral trends of discomfort and enhanced nociception in mice were reported; however, whether these measures are mediated by structural and pathological changes in the disc is unknown.

METHODS

The goal of the present observational study was to identify behavioral correlates of age-related degenerative changes in the disc. Towards this, we collected radiographs from 150 mice (77 females) between three and 23 months of age and measured the disc height index for each level of lumbar disc. Behavioral measures were collected on several of these mice which included rearing and distance travelled in an open field test; time spent in rearing, reaching, immobile, and self-suspended in the tail suspension test; bilateral hind paw licking in response to cold allodynia using acetone; and unilateral hind paw licking in response to heat hyperalgesia using capsaicin.

RESULTS

Results show that the lower lumbar discs lose height with age and these changes are independent of body composition measures including body weight, bone mineral density, fat mass, lean weight mass, percent fat mass, and percent lean mass. Disc height positively correlates with rearing and mobility in the open field test, immobility in the tail suspension test, and thermal hyperalgesia. Disc height negatively correlates with cold allodynia and rearing in the tail suspension test. Furthermore, mediation analysis shows that the lumbosacral disc significantly mediates the effect of age on rearing in the open field test, but not cold allodynia, suggesting this behavior is a useful measure of age-related axial discomfort due to disc degeneration.

CONCLUSION

In summary, the findings from the current study show that disc height are associated with measures of axial discomfort and nociception in mice.

Estrogen receptor β/substance P signaling in spinal cord mediates antinociceptive effect in a mouse model of discogenic low back pain

Introduction

Discogenic low back pain (DLBP) is the most commonly described form of back pain. Our previous studies indicated that estrogen-dependent DLBP mechanism was mediated by estrogen receptors (ERs) in the intervertebral disc (IVD) tissue, and the IVD degeneration degree is accompanied by downregulation of ERs, particularly ERβ. However, the neuropathological mechanisms underlying ERs modulation of DLBP are still not well understood. In this study, we investigated the antinociceptive effects of selective ERβ agonists on DLBP-related behavior by regulating substance P in spinal cord and dorsal root ganglia.

Methods

Two weeks after ovariectomies, 18-week-old female mice were randomly separated into four groups: control group; DLBP sham surgery plus vehicle group; DLBP plus vehicle group; DLBP plus ERβ-specific agonist diarylpropionitrile (DPN) group. Behavioral data was collected including behavioral measures of axial back pain (grip force and tail suspension tests) and radiating hypersensitivity (mechanical sensitivity and cold sensitivity test). Dual label scanning confocal immunofluorescence microscopy was used to observe spatial colocalization of ERβ and substance P in spinal cord. Substance P changes in spinal cord and dorsal root ganglia were measured by immunohistochemistry and real-time PCR.

Results

ERβ activation could improve both axial and radiating behavioral disorders of DLBP. DPN facilitated the decrease of the amount of time in immobility 1 week after agonist administration. At the time point of 3 weeks, DPN group spent significantly less time in immobility than the vehicle group. In the grip strength tests, starting from postoperative week 1-week 3, DPN injection DLBP mice showed more resistance to stretch than the vehicle injection DLBP mice. Significant differences of cold withdrawal latency time were observed between the DLBP plus DPN injection and DLBP vehicle injection groups at 2- and 3-week injection time point. DPN significantly reversed the paw withdrawal threshold of DLBP mice at the time point of 1, 2, and 3 weeks. Substance P colocalized with ERβ in spinal dorsal horn, mainly in laminae I and II, a connection site of pain transmission. Substance P levels in dorsal horn and dorsal root ganglia of DLBP group were distinctly increased compared with that of control and DLBP sham group. DPN therapy could decrease substance P content in the dorsal horn and the dorsal root ganglia of DLBP mice compared with that of vehicle-treated DLBP mice.

Discussion

Activation of ERβ is antinociceptive in the DLBP model by controlling substance P in spinal cord and dorsal root ganglia, which might provide a therapeutic target to manage DLBP in the clinic.

Controversies in spine research: Organ culture versus in vivo models for studies of the intervertebral disc

Intervertebral disc degeneration is a common cause of low back pain, the leading cause of disability worldwide. Appropriate preclinical models for intervertebral disc research are essential to achieving a better understanding of underlying pathophysiology and for the development, evaluation, and translation of more effective treatments. To this end, in vivo animal and ex vivo organ culture models are both widely used by spine researchers; however, the relative strengths and weaknesses of these two approaches are a source of ongoing controversy. In this article, members from the Spine and Preclinical Models Sections of the Orthopedic Research Society, including experts in both basic and translational spine research, present contrasting arguments in support of in vivo animal models versus ex vivo organ culture models for studies of the disc, supported by a comprehensive review of the relevant literature. The objective is to provide a deeper understanding of the respective advantages and limitations of these approaches, and advance the field toward a consensus with respect to appropriate model selection and implementation. We conclude that complementary use of several model types and leveraging the unique advantages of each is likely to result in the highest impact research in most instances.

Intervertebral disc degeneration and how it leads to low back pain

The purpose of this review was to evaluate data generated by animal models of intervertebral disc (IVD) degeneration published in the last decade and show how this has made invaluable contributions to the identification of molecular events occurring in and contributing to pain generation. IVD degeneration and associated spinal pain is a complex multifactorial process, its complexity poses difficulties in the selection of the most appropriate therapeutic target to focus on of many potential candidates in the formulation of strategies to alleviate pain perception and to effect disc repair and regeneration and the prevention of associated neuropathic and nociceptive pain. Nerve ingrowth and increased numbers of nociceptors and mechanoreceptors in the degenerate IVD are mechanically stimulated in the biomechanically incompetent abnormally loaded degenerate IVD leading to increased generation of low back pain. Maintenance of a healthy IVD is, thus, an important preventative measure that warrants further investigation to preclude the generation of low back pain. Recent studies with growth and differentiation factor 6 in IVD puncture and multi-level IVD degeneration models and a rat xenograft radiculopathy pain model have shown it has considerable potential in the prevention of further deterioration in degenerate IVDs, has regenerative properties that promote recovery of normal IVD architectural functional organization and inhibits the generation of inflammatory mediators that lead to disc degeneration and the generation of low back pain. Human clinical trials are warranted and eagerly anticipated with this compound to assess its efficacy in the treatment of IVD degeneration and the prevention of the generation of low back pain.

In vivo Mouse Intervertebral Disc Degeneration Models and Their Utility as Translational Models of Clinical Discogenic Back Pain: A Comparative Review

Low back pain is a leading cause of disability worldwide and studies have demonstrated intervertebral disc (IVD) degeneration as a major risk factor. While many in vitro models have been developed and used to study IVD pathophysiology and therapeutic strategies, the etiology of IVD degeneration is a complex multifactorial process involving crosstalk of nearby tissues and systemic effects. Thus, the use of appropriate in vivo models is necessary to fully understand the associated molecular, structural, and functional changes and how they relate to pain. Mouse models have been widely adopted due to accessibility and ease of genetic manipulation compared to other animal models. Despite their small size, mice lumbar discs demonstrate significant similarities to the human IVD in terms of geometry, structure, and mechanical properties. While several different mouse models of IVD degeneration exist, greater standardization of the methods for inducing degeneration and the development of a consistent set of output measurements could allow mouse models to become a stronger tool for clinical translation. This article reviews current mouse models of IVD degeneration in the context of clinical translation and highlights a critical set of output measurements for studying disease pathology or screening regenerative therapies with an emphasis on pain phenotyping. First, we summarized and categorized these models into genetic, age-related, and mechanically induced. Then, the outcome parameters assessed in these models are compared including, molecular, cellular, functional/structural, and pain assessments for both evoked and spontaneous pain. These comparisons highlight a set of potential key parameters that can be used to validate the model and inform its utility to screen potential therapies for IVD degeneration and their translation to the human condition. As treatment of symptomatic pain is important, this review provides an emphasis on critical pain-like behavior assessments in mice and explores current behavioral assessments relevant to discogenic back pain. Overall, the specific research question was determined to be essential to identify the relevant model with histological staining, imaging, extracellular matrix composition, mechanics, and pain as critical parameters for assessing degeneration and regenerative strategies.

Recent Advances in Managing Spinal Intervertebral Discs Degeneration

Low back pain (LBP) represents a frequent and debilitating condition affecting a large part of the global population and posing a worldwide health and economic burden. The major cause of LBP is intervertebral disc degeneration (IDD), a complex disease that can further aggravate and give rise to severe spine problems. As most of the current treatments for IDD either only alleviate the associated symptoms or expose patients to the risk of intraoperative and postoperative complications, there is a pressing need to develop better therapeutic strategies. In this respect, the present paper first describes the pathogenesis and etiology of IDD to set the framework for what has to be combated to restore the normal state of intervertebral discs (IVDs), then further elaborates on the recent advances in managing IDD. Specifically, there are reviewed bioactive compounds and growth factors that have shown promising potential against underlying factors of IDD, cell-based therapies for IVD regeneration, biomimetic artificial IVDs, and several other emerging IDD therapeutic options (e.g., exosomes, RNA approaches, and artificial intelligence).

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.

Voluntary running attenuates behavioural signs of low back pain: dimorphic regulation of intervertebral disc inflammation in male and female SPARC-null mice

OBJECTIVE

To examine the effect of running exercise on behavioral measures of pain and intervertebral disc (IVD) inflammation in the SPARC-null mouse model.

METHODS

Male and female 8-month old SPARC-null and age-matched control mice received a home cage running wheel or a control, fixed wheel for 6 months. Behavioral assays were performed to assess axial discomfort (grip test) and radiating leg pain (von Frey, acetone tests) and voluntary running was confirmed. Expression of inflammatory mediators (TNF-α, IL-1β, IL-2, IL-10, CCL5, CXCL1, CXCL5, RANKL, M-CSF, and VEGF) in IVDs was determined. Additional inflammatory (IL-1β, IL-1Ra, CXCR1, CXCR2) and macrophage phenotypic markers (ITGAM, CD80, CD86, CD206, Arg1) in IVDs were investigated by qPCR.

RESULTS

Voluntary running attenuated behavioral measures of pain in male and female SPARC-null mice. Increases in mediators including IL-1β, CXCL1 and CXCL5 were observed in SPARC-null compared to control IVDs. After 6 months of running, increases in M-CSF and VEGF were observed in male SPARC-null IVDs. In females, pro-inflammatory mediators, including CXCL1 and CXCL5 were downregulated by running in SPARC-null mice. qPCR analysis further confirmed the anti-inflammatory effect of running in female IVDs with increased IL-1Ra mRNA. Running induced upregulation of the macrophage marker ITGAM mRNA in males.

CONCLUSIONS

Voluntary running reversed behavioral signs of pain in male and female mice and reduced inflammatory mediators in females, but not males. Thus, the therapeutic mechanism of action may be sex-specific.

Exercise attenuates low back pain and alters epigenetic regulation in intervertebral discs in a mouse model

BACKGROUND CONTEXT

Chronic low back pain (LBP) is a multifactorial disorder with complex underlying mechanisms, including associations with intervertebral disc (IVD) degeneration in some individuals. It has been demonstrated that epigenetic processes are involved in the pathology of IVD degeneration. Epigenetics refers to several mechanisms, including DNA methylation, that have the ability to change gene expression without inducing any change in the underlying DNA sequence. DNA methylation can alter the entire state of a tissue for an extended period of time and thus could potentially be harnessed for long-term pain relief. Lifestyle factors, such as physical activity, have a strong influence on epigenetic regulation. Exercise is a commonly prescribed treatment for chronic LBP, and sex-specific epigenetic adaptations in response to endurance exercise have been reported. However, whether exercise interventions that attenuate LBP are associated with epigenetic alterations in degenerating IVDs has not been evaluated.

PURPOSE

We hypothesize that the therapeutic efficacy of physical activity is mediated, at least in part, at the epigenetic level. The purpose of this study was to use the SPARC-null mouse model of LBP associated with IVD degeneration to clarify (1) if IVD degeneration is associated with altered expression of epigenetic regulatory genes in the IVDs, (2) if epigenetic regulatory machinery is sensitive to therapeutic environmental intervention, and (3) if there are sex-specific differences in (1) and/or (2).

STUDY DESIGN

Eight-month-old male and female SPARC-null and age-matched control (WT) mice (n=108) were assigned to exercise (n=56) or sedentary (n=52) groups. Deletion of SPARC is associated with progressive IVD degeneration and behavioral signs of LBP. The exercise group received a circular plastic home cage running wheel on which they could run freely. The sedentary group received an identical wheel secured in place to prevent rotation. After 6 months, the results obtained in each group were compared.

METHODS

After 6 months of exercise, LBP-related behavioral indices were determined, and global DNA methylation (5-methylcytosine) and epigenetic regulatory gene mRNA expression in IVDs were assessed. This project was supported by the Canadian Institutes for Health Research. The authors have no conflicts of interest.

RESULTS

Lumbar IVDs from WT sedentary and SPARC-null sedentary mice had similar levels of global DNA methylation (%5-mC) and comparable mRNA expression of epigenetic regulatory genes (Dnmt1,3a,b, Mecp2, Mbd2a,b, Tet1-3) in both sexes. Exercise attenuated LBP-related behaviors, decreased global DNA methylation in both WT (p<.05) and SPARC-null mice (p<.01) and reduced mRNA expression of Mecp2 in SPARC-null mice (p<.05). Sex-specific effects of exercise on expression of mRNA were also observed.

CONCLUSIONS

Exercise alleviates LBP in a mouse model. This may be mediated, in part, by changes in the epigenetic regulatory machinery in degenerating IVDs. Epigenetic alterations due to a lifestyle change could have a long-lasting therapeutic impact by changing tissue homeostasis in IVDs.

CLINICAL SIGNIFICANCE

This study confirmed the therapeutic benefits of exercise on LBP and suggests that exercise results in sex-specific alterations in epigenetic regulation in IVDs. Elucidating the effects of exercise on epigenetic regulation may enable the discovery of novel gene targets or new strategies to improve the treatment of chronic LBP.

Effect of voluntary running activity on mRNA expression of extracellular matrix genes in a mouse model of intervertebral disc degeneration

INTRODUCTION

Low back pain (LBP), a leading cause of global disability, is often associated with intervertebral disc degeneration (IDD). Exercise therapy is recommended for chronic LBP management and affects many tissues and organ systems. However, the ability of exercise to repair the extracellular matrix (ECM) in degenerating discs is unclear. The aims of the study were to examine mRNA expression of ECM structural components (collagen I, II, X, aggrecan) and regulators of matrix turnover (matrix metalloproteinases (MMP)-3, - 9, - 13, ADAMTS-4, - 5, TIMP1-4, CCN2) between age-matched (a) wild-type and secreted protein acidic and rich in cysteine (SPARC)-null, (b) sedentary and active, and (c) male and female mice.

METHODS

At 8 months of age, male and female SPARC-null and wild-type control mice received a home cage running wheel or a control, fixed wheel for 6 months. Deletion of the SPARC gene results in progressive IDD beginning at 2 to 4 months of age. Increased activity was confirmed, and qPCR was performed on excised lumbar discs.

RESULTS

Male SPARC-null mice expressed less aggrecan mRNA than wild-type controls. After 6 months of running, collagen, MMP3, and MMP13 expression was increased in male and MMP3 was increased in female SPARC-null mice. Sex differences were observed in wild-type mice and in response to IDD and long-term running.

CONCLUSIONS

Voluntary running results in changes in mRNA consistent with increased ECM turnover and disc regeneration. Improved disc ECM might contribute to the beneficial effects of exercise on LBP and may create an intradiscal environment hospitable to regenerative therapies. Sex-specific differences should be considered in the development of disc-targeting therapies.

Establishment of a Rabbit Intervertebral Disc Degeneration Model by Percutaneous Posterolateral Puncturing of Lumbar Discs Under Local Anesthesia

OBJECTIVE

An anterior approach is applied to establish the majority of rabbit intervertebral disc degeneration (IDD) models in current studies. However, for research on disc repair via biomaterial implantation and tissue engineering, this traditional model establishment method has many shortcomings, such as the risk of general anesthesia, unnecessary tissue damage, and the influence of scar formation on the visual field for secondary implantation surgery. The aim of this study was to report a modified method of establishing an IDD model by applying percutaneous posterolateral puncturing for rabbit lumbar disc surgery under local anesthesia.

METHODS

We built a rabbit model of IDD by percutaneous posterolateral annulus fibrosus puncturing (AFP) (with or without nucleus pulposus aspiration [NPA]) under local anesthesia. Then, we analyzed the outcome after 12 weeks via magnetic resonance images, disc height changes, and disc histologic grades determined from morphologic observation and histologic analyses (hematoxylin and eosin and safranin-O staining and type II collagen expression analysis).

RESULTS

The IDD model was successfully built based on both AFP and AFP/NPA, as demonstrated by the results of magnetic resonance imaging index, morphologic, and histologic analyses. Both methods can successfully produce an IDD model after 12 weeks. However, we found that the addition of NPA significantly enhanced the modeling results.

CONCLUSIONS

Our results show that percutaneous posterolateral AFP/NPA of rabbit lumbar discs under local anesthesia is a minimally invasive, safe and reproducible method of establishing an IDD model. The posterolateral surgical approach is especially suitable for disc regeneration studies that require secondary biomaterial implantation via an anterior approach after the IDD model is established.

Disc degeneration spreads: long-term behavioural, histologic and radiologic consequences of a single-level disc injury in active and sedentary mice

STUDY DESIGN

A multi-cohort, case-control rodent study.

PURPOSE

Investigate the long-term behavioural, histologic and radiologic consequences on the complete lumbar spine of L4/5 intervertebral disc (IVD) injury in mice and determine if increased physical activity mitigates the observed changes.

METHODS

Cohorts of 2-month-old CD1 female mice underwent a single ventral puncture of the L4/5 IVD. 0.5-, 3- or 12-months after injury, general health (body weight and locomotor capacity), behavioural signs of axial discomfort (tail suspension, grip strength and FlexMaze assays) and radiating pain (von Frey and acetone tests) were assessed. Experimental groups with free access to an activity wheel in their home cages were including in the 12-month cohort. Lumbar disc status was determined using colorimetric staining and radiologic (X-ray and T2-MRI) analysis. Innervation was measured by immunoreactivity for PGP9.5 and calcitonin gene-related peptide.

RESULTS

No changes in general health or persistent signs of axial discomfort were observed up to one year post-injury. In contrast, signs of radiating pain developed in injured mice at 3 months post-injury, persisted up to 12 months and were reversed by long-term physical activity. At 12-months post-injury, degeneration was observed in non-injured lumbar discs. Secondary degenerating IVDs were similar to the injured discs by X-ray (narrowing) and T2-MRI (internal disc disruption) but did not show abnormal innervation. Increased physical activity had no impact on mechanically injured IVDs, but attenuated disc narrowing at other lumbar levels.

CONCLUSIONS

Mechanical injury of L4/5-IVDs induces delayed radiating pain and degeneration of adjacent discs; increased physical activity positively mitigated both.

Compression stress induces nucleus pulposus cell autophagy by inhibition of the PI3K/AKT/mTOR pathway and activation of the JNK pathway

Purpose: Reactive oxygen species (ROS) are related to compression stress-induced nucleus pulposus (NP) cell autophagy, but the specific mechanism is unknown in compression stress-induced intervertebral disc degeneration (IVDD). Here, we discuss the specific molecular mechanism and explore whether ROS scavengers could be employed as specific drugs to inhibit compression stress-induced IVDD.Methods: Rat NP cells were exposed to 1.0 MPa compression and pretreatment with the ROS scavenger N-acetylcysteine (NAC) or the JNK-selective inhibitor SP600125 not. Intracellular ROS production was monitored by confocal microscopy. Autophagy was detected by observing the NP cell ultrastructural features using TEM and examining autophagic vacuoles by flow cytometry. The levels of autophagy-associated molecules, the JNK pathway and the PI3K/AKT/mTOR pathway were analyzed by western blotting.Results: Compression-mediated autophagy in rat NP cells was implicated in ROS generation. The ROS scavenger NAC could protect compression-induced NP cell injures by inhibiting ROS production. And SP600125, a JNK inhibitor, attenuated compression-induced NP cell autophagy. Additionally, this is the first report showing that compression induces autophagy in rat NP cells by impeding the compression-induced ROS dependent PI3K/AKT/mTOR pathway and the ROS independent activation of JNK pathway. And the involvement of JNK pathway was in different mechanism of action that when inhibited leaded to increased cell death, increased generation of ROS but decreased autophagy.Conclusions: These results show a new regulatory mechanism involving ROS-mediated autophagy in rat NP cells, which may provide ideas for drug development to improve compression stress-induced IVDD and help avoid eventual surgical treatment of IVD herniation.

Diet-induced obesity leads to behavioral indicators of pain preceding structural joint damage in wild-type mice

Introduction

Obesity is one of the largest modifiable risk factors for the development of musculoskeletal diseases, including intervertebral disc (IVD) degeneration and back pain. Despite the clinical association, no studies have directly assessed whether diet-induced obesity accelerates IVD degeneration, back pain, or investigated the biological mediators underlying this association. In this study, we examine the effects of chronic consumption of a high-fat or high-fat/high-sugar (western) diet on the IVD, knee joint, and pain-associated outcomes.

Methods

Male C57BL/6N mice were randomized into one of three diet groups (chow control; high-fat; high-fat, high-sugar western diet) at 10 weeks of age and remained on the diet for 12, 24, or 40 weeks. At endpoint, animals were assessed for behavioral indicators of pain, joint tissues were collected for histological and molecular analysis, serum was collected to assess for markers of systemic inflammation, and IBA-1, GFAP, and CGRP were measured in spinal cords by immunohistochemistry.

Results

Animals fed obesogenic (high-fat or western) diets showed behavioral indicators of pain beginning at 12 weeks and persisting up to 40 weeks of diet consumption. Histological indicators of moderate joint degeneration were detected in the IVD and knee following 40 weeks on the experimental diets. Mice fed the obesogenic diets showed synovitis, increased intradiscal expression of inflammatory cytokines and circulating levels of MCP-1 compared to control. Linear regression modeling demonstrated that age and diet were both significant predictors of most pain-related behavioral outcomes, but not histopathological joint degeneration. Synovitis was associated with alterations in spontaneous activity.

Conclusion

Diet-induced obesity accelerates IVD degeneration and knee OA in mice; however, pain-related behaviors precede and are independent of histopathological structural damage. These findings contribute to understanding the source of obesity-related back pain and the contribution of structural IVD degeneration.

The Effect and Possible Mechanism of Intradiscal Injection of Simvastatin in the Treatment of Discogenic Pain in Rats

To study the effect of intradiscal injection of simvastatin on discogenic pain in rats and its possible mechanism, 30 adult female rats were used in this experiment. Twenty rats were randomly divided into sham operation group (Control group), intervertebral disk degeneration group (DDD group), intervertebral disk degeneration + hydrogel group (DDD + GEL group), and intervertebral disk degeneration + simvastatin group (DDD + SIM group). The mechanical pain threshold and cold sensation in rats were measured. The contents of NF-kappa B1, RelA, GAP43, SP, CGRP, TRPM 8, IL-1β, and TNF-α in the intervertebral disk (IVD), the corresponding contents of dorsal root ganglion (DRG) and plantar skin GAP43 and TRPM 8 were quantitatively detected by PCR. The corresponding IVDs were stained to detect their degeneration. There was no significant difference in the mechanical pain threshold between the groups at each time point. From the first day to the 8th week after surgery, the cold-sensing response of the DDD group was significantly higher than that of the Control group (P < 0.05). At 7 and 8 weeks postoperatively, the cold-sensing response of the DDD + SIM group was significantly lower than that of the DDD + GEL group (P < 0.05). The levels of NF-κB1, RelA, GAP43, SP, CGRP, TRPM8, IL-1β, and TNF-α in the IVD of DDD + SIM group were significantly lower than those in DDD group (P < 0.05). The content of GAP43 and TRPM8 in rat plantar skin decreased significantly and TRPM8 in DRG decreased significantly (P < 0.05).

Mechanical Consequence of Induced Intervertebral Disc Degeneration in the SPARC-Null Mouse

Intervertebral disc (IVD) degeneration is associated with low back pain (LBP) and accompanied by mechanical changes to the spine. Secreted protein acidic and rich in cysteine (SPARC) is a protein that contributes to the functioning and maintenance of the extracellular matrix. SPARC-null mice display accelerated IVD degeneration and pain-associated behaviors. This study examined if SPARC-null mice also display altered spine mechanics as compared to wild-type (WT) mice. Lumbar spines from SPARC-null (n = 36) and WT (n = 18) mice aged 14-25 months were subjected to cyclic axial tension and compression to determine neutral zone (NZ) length and stiffness. Three separate mechanical tests were completed for each spine to determine the effect of the number of IVDs tested in series (one versus two versus three IVDs). SPARC-null spine NZs were both stiffer (p < 0.001) and smaller in length (p < 0.001) than WT spines. There was an effect of the number of IVDs tested in series for NZ length but not NZ stiffness when collapsed across condition (SPARC-null and WT). Correlation analysis revealed a weak negative correlation (r = -0.24) between age and NZ length in SPARC-null mice and a weak positive correlation (r = 0.30) between age and NZ stiffness in WT mice. In conclusion, SPARC-null mice had stiffer and smaller NZs than WT mice, regardless of the number of IVDs in series being tested. The increased stiffness of these IVDs likely influences mobility at these spinal joints thereby potentially contributing to low back pain.

Painful intervertebral disc degeneration and inflammation: from laboratory evidence to clinical interventions

Low back pain (LBP), as a leading cause of disability, is a common musculoskeletal disorder that results in major social and economic burdens. Recent research has identified inflammation and related signaling pathways as important factors in the onset and progression of disc degeneration, a significant contributor to LBP. Inflammatory mediators also play an indispensable role in discogenic LBP. The suppression of LBP is a primary goal of clinical practice but has not received enough attention in disc research studies. Here, an overview of the advances in inflammation-related pain in disc degeneration is provided, with a discussion on the role of inflammation in IVD degeneration and pain induction. Puncture models, mechanical models, and spontaneous models as the main animal models to study painful disc degeneration are discussed, and the underlying signaling pathways are summarized. Furthermore, potential drug candidates, either under laboratory investigation or undergoing clinical trials, to suppress discogenic LBP by eliminating inflammation are explored. We hope to attract more research interest to address inflammation and pain in IDD and contribute to promoting more translational research.

Targeted therapy for intervertebral disc degeneration: inhibiting apoptosis is a promising treatment strategy

Intervertebral disc (IVD) degeneration (IDD) is a multifactorial pathological process associated with low back pain (LBP). The pathogenesis is complicated, and the main pathological changes are IVD cell apoptosis and extracellular matrix (ECM) degradation. Apoptotic cell loss leads to ECM degradation, which plays an essential role in IDD pathogenesis. Apoptosis regulation may be a potential attractive therapeutic strategy for IDD. Previous studies have shown that IVD cell apoptosis is mainly induced by the death receptor pathway, mitochondrial pathway, and endoplasmic reticulum stress (ERS) pathway. This article mainly summarizes the factors that induce IDD and apoptosis, the relationship between the three apoptotic pathways and IDD, and potential therapeutic strategies. Preliminary animal and cell experiments show that targeting apoptotic pathway genes or drug inhibition can effectively inhibit IVD cell apoptosis and slow IDD progression. Targeted apoptotic pathway inhibition may be an effective strategy to alleviate IDD at the gene level. This manuscript provides new insights and ideas for IDD therapy.

Animal models of regenerative medicine for biological treatment approaches of degenerative disc diseases

Degenerative disc disease (DDD) is a painful, chronic and progressive disease, which is characterized by inflammation, structural and biological deterioration of the intervertebral disc (IVD) tissues. DDD is specified as cell-, age-, and genetic-dependent degenerative process that can be accelerated by environmental factors. It is one of the major causes of chronic back pain and disability affecting millions of people globally. Current treatment options, such as physical rehabilitation, pain management, and surgical intervention, can provide only temporary pain relief. Different animal models have been used to study the process of IVD degeneration and develop therapeutic options that may restore the structure and function of degenerative discs. Several research works have depicted considerable progress in understanding the biological basis of disc degeneration and the therapeutic potentials of cell transplantation, gene therapy, applications of supporting biomaterials and bioactive factors, or a combination thereof. Since animal models play increasingly significant roles in treatment approaches of DDD, we conducted an electronic database search on Medline through June 2020 to identify, compare, and discuss publications regarding biological therapeutic approaches of DDD that based on intradiscal treatment strategies. We provide an up-to-date overview of biological treatment strategies in animal models including mouse, rat, rabbit, porcine, bovine, ovine, caprine, canine, and primate models. Although no animal model could profoundly reproduce the clinical conditions in humans; animal models have played important roles in specifying our knowledge about the pathophysiology of DDD. They are crucial for developing new therapy approaches for clinical applications.

Analysis of key genes and pathways associated with the pathogenesis of intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration (IDD) is widely known as the main contributor to low back pain which has a negative socioeconomic impact worldwide. However, the underlying mechanism remains unclear. This study aims to analyze the dataset GSE23130 using bioinformatics methods to identify the pivotal genes and pathways associated with IDD.

MATERIAL/METHODS

The gene expression data of GSE23130 was downloaded, and differentially expressed genes (DEGs) were extracted from 8 samples and 15 controls. GO and KEGG pathway enrichment analyses were performed. Also, protein-protein interaction (PPI) network was constructed and visualized, followed by identification of hub genes and key module.

RESULTS

A total of 30 downregulated and 79 upregulated genes were identified. The DEGs were mainly enriched in the regulation of protein catabolic process, extracellular matrix organization, collagen fibril organization, and extracellular structure organization. Meanwhile, we found that most DEGs were primarily enriched in the PI3K-Akt signaling pathway. The top 10 hub genes were FN1, COL1A2, SPARC, COL3A1, CTGF, LUM, TIMP1, THBS2, COL5A2, and TGFB1.

CONCLUSIONS

In summary, key candidate genes and pathways were identified by using integrated bioinformatics analysis, which may provide insights into the underlying mechanisms and offer potential target genes for the treatment of IDD.

Long-term histological analysis of innervation and macrophage infiltration in a mouse model of intervertebral disc injury-induced low back pain

Low back pain (LBP) is a leading cause of global disability. Multiple anatomical, cellular, and molecular factors are implicated in LBP, including the degeneration of lumbar intervertebral discs (IVDs). We previously described a mouse model that displays behavioral symptoms of chronic LBP. Here, we investigated the development of pathological innervation and macrophage infiltration into injured IVDs following a puncture injury in mice over 12 months. 2-month old CD1 female mice underwent a single puncture of the ventral L4/5 IVD using a 30G needle, and were sacrificed 4 days and 0.5-, 3-, 6- and 12-months post-injury. Severity of disc degeneration was assessed using colorimetric staining. IVD innervation was measured by PGP9.5-immunoreactivity (-ir) and calcitonin gene-related peptide-ir (CGRP-ir). Macrophage accumulation into IVDs was detected by F4/80-ir. Mechanical IVD injury resulted in severe degeneration and increased PGP9.5-ir nerve fiber density starting at 4 days that persisted for up to 12 months and dorsal herniations began to occur at 3 months. CGRP-ir was also upregulated in injured IVDs, with the largest increase at 12 months after injury. Infiltration of F4/80-ir macrophages was observed in injured IVDs by day 4 both dorsally and ventrally, with the latter diminishing in the later stage. Persistent LBP is a complex disease with multiple underlying pathologies. By highlighting pathological changes in IVD innervation and inflammation, our study suggests that strategies targeting these mechanisms might be useful therapeutically.

Optimization of a rat lumbar IVD degeneration model for low back pain

INTRODUCTION

Intervertebral disc (IVD) degeneration is often associated with low back pain and radiating leg pain. The purpose of this study is to develop a reproducible and standardized preclinical model of painful lumbar IVD degeneration by evaluation of structural and behavioral changes in response to IVD injury with increasing needle sizes. This model can be used to develop new therapies for IVD degeneration.

METHODS

Forty-five female Sprague Dawley rats underwent anterior lumbar disc needle puncture at levels L4-5 and L5-6 under fluoroscopic guidance. Animals were randomly assigned to four different experimental groups: needle sizes of 18 Gauge (G), 21G, 23G, and sham control. To monitor the progression of IVD degeneration and pain, the following methods were employed: μMRI, qRT-PCR, histology, and biobehavioral analysis.

RESULTS

T1- and T2-weighted μMRI analysis showed a correlation between the degree of IVD degeneration and needle diameter, with the most severe degeneration in the 18G group. mRNA expression of markers for IVD degeneration markers were dysregulated in the 18G and 21G groups, while pro-nociceptive markers were increased in the 18G group only. Hematoxylin and Eosin (H&E) and Alcian Blue/Picrosirius Red staining confirmed the most pronounced IVD degeneration in the 18G group. Randall-Selitto and von Frey tests showed increased hindpaw sensitivity in the 18G group.

CONCLUSION

Our findings demonstrate that anterior disc injury with an 18G needle creates severe IVD degeneration and mechanical hypersensitivity, while the 21G needle results in moderate degeneration with no increased pain sensitivity. Therefore, needle sizes should be selected depending on the desired phenotype for the pre-clinical model.

Significance of the Association between Disc Degeneration Changes on Imaging and Low Back Pain: A Review Article

Low back pain (LBP) is a major health issue resulting in a huge economic burden on the community. It not only increases the medical costs directly, but also raises the disability and loss of productivity in the general population. Symptoms include local pain over the spinal area, pain radiating to the lower leg, stiffness, and muscle tension. LBP is strongly linked with intervertebral disc degeneration that is further associated with the disruption of the complex anatomy of nucleus pulposus, annulus fibrosus, and adjacent supporting structures of the spine. Change in the shape and intensity of nucleus pulposus, decreased disc height, disc herniation, vertebral endplate changes, presence of osteophyte, and posterior high intensity zones are degenerative changes found in imaging studies. Every feature is considered while grading the severity score. Modic changes, DEBIT (disc extension beyond interspace) score, and Pfirrmann criteria are some of the scoring criteria used for evaluating disc degeneration severity. Moreover, the total number and contiguous pattern of affected discs play a crucial role in symptom generation of back pain. Many studies have reported asymptomatic patients. Thus, the correlation between degeneration severity found in imaging study and symptom severity of LBP remain unclear. This review discusses and summarizes the available literature on the significance of the association between the severity of degenerative changes found in imaging study with the presence and intensity of LBP.

The search for translational pain outcomes to refine analgesic development: Where did we come from and where are we going?

Pain measures traditionally used in rodents record mere reflexes evoked by sensory stimuli; the results thus may not fully reflect the human pain phenotype. Alterations in physical and emotional functioning, pain-depressed behaviors and facial pain expressions were recently proposed as additional pain outcomes to provide a more accurate measure of clinical pain in rodents, and hence to potentially enhance analgesic drug development. We aimed to review how preclinical pain assessment has evolved since the development of the tail flick test in 1941, with a particular focus on a critical analysis of some nonstandard pain outcomes, and a consideration of how sex differences may affect the performance of these pain surrogates. We tracked original research articles in Medline for the following periods: 1973-1977, 1983-1987, 1993-1997, 2003-2007, and 2014-2018. We identified 606 research articles about alternative surrogate pain measures, 473 of which were published between 2014 and 2018. This indicates that preclinical pain assessment is moving toward the use of these measures, which may soon become standard procedures in preclinical pain laboratories.

Autologous fibroblasts induce fibrosis of the nucleus pulposus to maintain the stability of degenerative intervertebral discs

Lumbar degenerative disc diseases cause low back pain (LBP). The maintenance of the height and stability of the intervertebral disc (IVD) space is an effective treatment for LBP. The following study evaluated the effects of fibroblast injection on intervertebral disc degeneration (IDD) in a preclinical setting. Compared with the IDD group, the fibroblast treatment group demonstrated effective maintenance of IVD height, reduced endplate degeneration, and improved nuclear magnetic resonance signals and overall histological structure. In doing so, fibrotic IVDs maintained the stability and biomechanics of the vertebra. This finding is in agreement with clinical findings that human nucleus pulposus (NP) fibrosis is essential for the maintenance of IVD height and mechanical properties in patients following percutaneous endoscopic lumbar discectomy (PELD). Mechanistically, we demonstrated that injected fibroblasts not only proliferated but also induced NP cells to adopt a fibrotic phenotype via the secretion of TGF-β. Finally, to better mimic human conditions, the efficacy of autologous fibroblast injection in the treatment of IDD was further examined in a nonhuman primate cynomolgus monkey model due to their capacity for upright posture. We showed that the injection of fibroblasts could maintain the IVD height and rescue IVD signals in cynomolgus monkeys. Taken together, the results of our study reveal that autologous fibroblast injection can enhance the natural process of fibrosis during acute and subacute stages of stress-induced IDD. Fibrotic IVDs can maintain the stability, biological activity, and mechanical properties of the intervertebral space, thus providing a new direction for the treatment of intervertebral space-derived lumbar degenerative diseases.

Sensory innervation in porous endplates by Netrin-1 from osteoclasts mediates PGE2-induced spinal hypersensitivity in mice

Spinal pain is a major clinical problem, however, its origins and underlying mechanisms remain unclear. Here we report that in mice, osteoclasts induce sensory innervation in the porous endplates which contributes to spinal hypersensitivity in mice. Sensory innervation of the porous areas of sclerotic endplates in mice was confirmed. Lumbar spine instability (LSI), or aging, induces spinal hypersensitivity in mice. In these conditions, we show that there are elevated levels of PGE2 which activate sensory nerves, leading to sodium influx through Na_v 1.8 channels. We show that knockout of PGE2 receptor 4 in sensory nerves significantly reduces spinal hypersensitivity. Inhibition of osteoclast formation by knockout Rankl in the osteocytes significantly inhibits LSI-induced porosity of endplates, sensory innervation, and spinal hypersensitivity. Knockout of Netrin-1 in osteoclasts abrogates sensory innervation into porous endplates and spinal hypersensitivity. These findings suggest that osteoclast-initiated porosity of endplates and sensory innervation are potential therapeutic targets for spinal pain.

Spinal pain is a major clinical problem. Here the authors show that osteoclasts create porous area of endplates of the vertebrae and sensory innervation of porous endplates by Netrin-1 release from osteoclasts mediates PGE2-induced spinal hypersensitivity in mice.

A step-by-step protocol for isolation of murine nucleus pulposus cells

The intervertebral disc (IVD) is composed of three separate tissues with distinct origins and properties. Elucidating changes occurring in these tissues in response to injury or age is paramount to identify new therapies to better manage disc and spine degenerative conditions, including low back pain. Despite their small size and different mechanical load pattern compared to higher species, the use of mouse models represents a cost-effective and powerful approach to better understand the formation, maintenance, and degeneration of the IVD. However, the isolation of the different compartments of the IVD is complicated by their diminutive size. Here, we describe a simple, step-by-step protocol for the isolation of the nucleus pulposus (NP) tissues that can then be processed for further analyses. Analysis from mouse NP tissues shows sufficient quantities of RNAs, purity of the NP fraction, and overall RNA quality for gene expression studies, and reveals no increase in expression of disc degeneration markers, including TNFa, IL1b, and Mmp1 up to 15 months of age in C57BL6 wildtype mice.

Aging of mouse intervertebral disc and association with back pain

With the increased burden of low back pain (LBP) in our globally aging population there is a need to develop preclinical models of LBP that capture clinically relevant features of physiological aging, degeneration, and disability. Here we assess the validity of using a mouse model system for age-related LBP by characterizing aging mice for features of intervertebral disc (IVD) degeneration, molecular markers of peripheral sensitization, and behavioral signs of pain. Compared to three-month-old and one-year-old mice, two-year-old mice show features typical of IVD degeneration including loss of disc height, bulging, innervation and vascularization in the caudal lumbar IVDs. Aging is also associated with the loss of whole-body bone mineral density in both male and female mice, but not associated with percent lean mass or body fat. Additionally, two-year-old mice have an accumulation of TRPA1 channels and sodium channels NaV1.8 and NaV1.9 in the L4 and L5 lumbar dorsal root ganglia consistent with changes in nociceptive signaling. Lastly, the effect of age, sex, and weight on mobility, axial stretching and radiating pain measures was assessed in male and female mice ranging from two months to two years in a general linear model. The model revealed that regardless of sex or weight, increased age was a predictor of greater reluctance to perform axial stretching and sensitivity to cold, but not heat in mice.

Diverse Role of Biological Plasticity in Low Back Pain and Its Impact on Sensorimotor Control of the Spine

Pain is complex. It is no longer acceptable to consider pain solely as a peripheral phenomenon involving activation of nociceptive neurons. The contemporary understanding of pain involves consideration of different underlying pain mechanisms and an increasing awareness of plasticity in all of the biological systems. Of note, recent advances in technology and understanding have highlighted the critical importance of neuroimmune interactions, both in the peripheral and central nervous systems, and the interaction between the nervous system and body tissues in the development and maintenance of pain, including low back pain (LBP). Further, the biology of many tissues changes when challenged by pain and injury, as reported in a growing body of literature on the biology of muscle, fat, and connective tissue. These advances in understanding of the complexity of LBP have implications for our understanding of pain and its interaction with the motor system, and may change how we consider motor control in the rehabilitation of LBP. This commentary provides a state-of-the-art overview of plasticity of biology in LBP. The paper is divided into 4 parts that address (1) biology of pain mechanisms, (2) neuroimmune interaction in the central nervous system, (3) neuroimmune interaction in the periphery, and (4) brain and peripheral tissue interaction. Each section considers the implications for clinical management of LBP. J Orthop Sports Phys Ther 2019;49(6):389-401. doi:10.2519/jospt.2019.8716.

Interleukin-8 as a therapeutic target for chronic low back pain: Upregulation in human cerebrospinal fluid and pre-clinical validation with chronic reparixin in the SPARC-null mouse model

Background

Low back pain (LBP) is the leading global cause of disability and is associated with intervertebral disc degeneration (DD) in some individuals. However, many adults have DD without LBP. Understanding why DD is painful in some and not others may unmask novel therapies for chronic LBP. The objectives of this study were to a) identify factors in human cerebrospinal fluid (CSF) associated with chronic LBP and b) examine their therapeutic utility in a proof-of-concept pre-clinical study.

Methods

Pain-free human subjects without DD, pain-free human subjects with DD, and patients with chronic LBP linked to DD were recruited and lumbar MRIs, pain and disability levels were obtained. CSF was collected and analyzed by multiplex cytokine assay. Interleukin-8 (IL-8) expression was confirmed by ELISA in CSF and in intervertebral discs.

The SPARC-null mouse model of progressive, age-dependent DD and chronic LBP was used for pre-clinical validation. Male SPARC-null and control mice received systemic Reparixin, a CXCR1/2 (receptors for IL-8 and murine analogues) inhibitor, for 8 weeks. Behavioral signs of axial discomfort and radiating pain were assessed. Following completion of the study, discs were excised and cultured, and conditioned media was evaluated with a protein array.

Findings

IL-8 was elevated in CSF of chronic LBP patients with DD compared to pain-free subjects with or without DD. Chronic inhibition with reparixin alleviated low back pain behaviors and attenuated disc inflammation in SPARC-null mice.

Interpretation

These studies suggest that the IL-8 signaling pathway is a viable therapy for chronic LBP.

Fund

Supported by NIH, MMF, CIHR and FRQS.

ISSLS Prize in Basic science 2019: Physical activity attenuates fibrotic alterations to the multifidus muscle associated with intervertebral disc degeneration

PURPOSE

Chronic low back pain causes structural remodelling and inflammation in the multifidus muscle. Collagen expression is increased in the multifidus of humans with lumbar disc degeneration. However, the extent and mechanisms underlying the increased fibrotic activity in the multifidus are unknown. Physical activity reduces local inflammation that precedes multifidus fibrosis during intervertebral disc degeneration (IDD), but its effect on amelioration of fibrosis is unknown. This study aimed to assess the development of fibrosis and its underlying genetic network during IDD and the impact of physical activity.

METHODS

Wild-type and SPARC-null mice were either sedentary or housed with a running wheel, to allow voluntary physical activity. At 12 months of age, IDD was assessed with MRI, and multifidus muscle samples were harvested from L2 to L6. In SPARC-null mice, the L1/2 and L3/4 discs had low and high levels of IDD, respectively. Thus, multifidus samples from L2 and L4 were allocated to low- and high-IDD groups compared to assess the effects of IDD and physical activity on connective tissue and fibrotic genes.

RESULTS

High IDD was associated with greater connective tissue thickness and dysregulation of collagen-III, fibronectin, CTGF, substance P, TIMP1 and TIMP2 in the multifidus muscle. Physical activity attenuated the IDD-dependent increased connective tissue thickness and reduced the expression of collagen-I, fibronectin, CTGF, substance P, MMP2 and TIMP2 in SPARC-null animals and wild-type mice. Collagen-III and TIMP1 were only reduced in wild-type animals.

CONCLUSIONS

These data reveal the fibrotic networks that promote fibrosis in the multifidus muscle during chronic IDD. Furthermore, physical activity is shown to reduce fibrosis and regulate the fibrotic gene network. These slides can be retrieved under Electronic Supplementary Material.

A Comparison of Two Ovine Lumbar Intervertebral Disc Injury Models for the Evaluation and Development of Novel Regenerative Therapies

STUDY DESIGN

Large animal research.

OBJECTIVE

Lumbar discectomy is the most commonly performed spinal surgical procedure. We investigated 2 large animal models of lumbar discectomy in order to study the regenerative capacity of mesenchymal stem cells following disc injury.

METHODS

Twelve adult ewes underwent baseline 3-T magnetic resonance imaging (MRI) followed by lumbar intervertebral disc injury by either drill bit (n = 6) or annulotomy and partial nucleotomy (APN) (n = 6). Necropsies were performed 6 months later. Lumbar spines underwent 3-T and 9.4-T MRI prior to histological, morphological and biochemical analysis.

RESULTS

Drill bit-injured (DBI) and APN-injured discs demonstrated increased Pfirrmann grades relative to uninjured controls (P < .005), with no difference between the 2 models. Disc height index loss was greater in the APN group compared with the DBI group (P < .005). Gross morphology injury scores were higher in APN than DBI discs (P < .05) and both were higher than controls (P < .005). Proteoglycan was reduced in the discs of both injury models relative to controls (P < .005), but lower in the APN group (P < .05). Total collagen of the APN group disc regions was higher than DBI and control discs (P < .05). Histology revealed more matrix degeneration, vascular infiltration, and granulation in the APN model.

CONCLUSION

Although both models produced disc degeneration, the APN model better replicated the pathobiology of human discs postdiscectomy. We therefore concluded that the APN model was a more appropriate model for the investigation of the regenerative capacity of mesenchymal stem cells administered postdiscectomy.

Efficacy of administered mesenchymal stem cells in the initiation and co-ordination of repair processes by resident disc cells in an ovine (Ovis aries) large destabilizing lesion model of experimental disc degeneration

BACKGROUND

Forty percent of low back pain cases are due to intervertebral disc degeneration (IVDD), with mesenchymal stem cells (MSCs) a reported treatment. We utilized an ovine IVDD model and intradiscal heterologous MSCs to determine therapeutic efficacy at different stages of IVDD.

METHODOLOGY

Three nonoperated control (NOC) sheep were used for MSC isolation. In 36 sheep, 6 × 20 mm annular lesions were made at three spinal levels using customized blades/scalpel handles, and IVDD was allowed to develop for 4 weeks in the Early (EA) and late Acute (LA) groups, or 12 weeks in the chronic (EST) group. Lesion IVDs received injections of 10 × 106 MSCs or PBS, and after 8 (EA), 22 (LA) or 14 (EST) weeks recuperation the sheep were sacrificed. Longitudinal lateral radiographs were used to determine disc heights. IVD glycosaminoglycan (GAG) and hydroxyproline contents were quantified using established methods. An Instron materials testing machine and customized jigs analyzed IVD (range of motion, neutral zone [NZ] and stiffness) in flexion/extension, lateral bending and axial rotation. qRTPCR gene profiles of key anabolic and catabolic matrix molecules were undertaken. Toluidine blue and hematoxylin and eosin stained IVD sections were histopathologically scoring by two blinded observers.

RESULTS

IVDD significantly reduced disc heights. MSC treatment restored 95% to 100% of disc height, maximally improved NZ and stiffness in flexion/extension and lateral bending in the EST group, restoring GAG levels. With IVDD qRTPCR demonstrated elevated catabolic gene expression (MMP2/3/9/13, ADAMTS4/5) in the PBS IVDs and expession normalization in MSC-treated IVDs. Histopathology degeneracy scores were close to levels of NOC IVDs in MSC IVDs but IVDD developed in PBS injected IVDs.

DISCUSSION

Administered MSCs produced recovery in degenerate IVDs, restored disc height, composition, biomechanical properties, down regulated MMPs and fibrosis, strongly supporting the efficacy of MSCs for disc repair.

Implication of microglia activation and CSF-1/CSF-1Rpathway in lumbar disc degeneration-related back pain

Back pain is common and costly. Although lumbar disc degeneration has long been regarded as a major contributor to back pain, how disc degeneration leads to back pain remains unclear. Recent studies observed microglia activation in the spinal cord after disc degeneration, suggesting activated microglia may be involved in discogenic back pain. To determine whether microglia activation participates in disc degeneration-induced back pain, we used a modified disc puncture-induced degeneration-related back pain mouse model to examine the changes in spinal microglia and investigate the potential link between microglia activation and discogenic back pain. In this study, 46 CX3CR1^GFP/+ male mice were used in experimental and sham groups. A modified posterolateral retroperitoneal approach was used to expose the L3/L4 disc to induce the needle puncture in the experimental group. Behavioral tests, including grip force and physical function, were used to measure back pain at pre- and postsurgery. The L3 dorsal root ganglions and lumbar spinal cord were obtained at postoperative weeks 1 to 4 followed by immunofluorescence with different antibodies. Micrographs were obtained by confocal microscopy, and morphometric measurements of microglia were analyzed using Imaris. The punctured disc underwent progressive degeneration and mice with disc degeneration showed impaired grip force and physical function. Compared to the control mice, the number of microglia in the lumbar spinal cord was significantly increased in the disc-punctured animals. Moreover, accumulated microglia exhibited larger soma size and lesser ramification in the disc-injured mice. Immunofluorescence demonstrated colony-stimulating factor 1, a cytokine that promotes microglia repopulation, was significantly increased in L3 dorsal root ganglions, whereas its receptor colony-stimulating factor 1 receptor was upregulated on microglia in the disc-injured mice. In summary, lumbar disc puncture caused progressive disc degeneration which induced microglia activation and back pain in mice. Increased colony-stimulating factor 1/colony-stimulating factor 1 receptor signaling is involved in the disc degeneration-induced microglia activation and back pain.

Dysregulation of the Inflammatory Mediators in the Multifidus Muscle After Spontaneous Intervertebral Disc Degeneration SPARC-null Mice is Ameliorated by Physical Activity

STUDY DESIGN

A longitudinal case-control animal model.

OBJECTIVE

The aim of this study was to investigate the inflammatory pathways active in the multifidus muscle after spontaneous intervertebral disc degeneration (IDD), and whether these IDD-related muscle changes can be ameliorated by exercise.

SUMMARY OF BACKGROUND DATA

A pro-inflammatory response is present in the multifidus muscle after an intervertebral disc lesion and has been proposed to drive the structural alterations present during low back pain. However, it is not known whether spontaneous IDD produces an inflammatory response. Furthermore, exercise/physical activity produces a strong anti-inflammatory response, but its effectiveness in ameliorating inflammation in the multifidus is unknown. We assessed the inflammatory profile of the multifidus and the effectiveness of physical activity as a treatment using an animal model of spontaneous model of IDD.

METHODS

Wild-type and SPARC null mice that were sedentary or housed with a running wheel were used in this study. Multifidus muscle segments were harvested from L2-L6 from the mice at 9 months of age after they had undergone a magnetic resonance imaging (MRI) scan to determine levels with IDD. The inflammatory profile of the multifidus was examined using quantitative polymerase chain reaction (PCR) assays.

RESULTS

Spontaneous IDD in the SPARC-null mice caused a dysregulation of interleukin (IL)-1β, IL6, transforming growth factor-beta (TGFβ1), and adiponectin expression. More specifically, the proximity and degree of IDD was related to levels of IL-1β expression. Physical activity reduced the pro-inflammatory response to IDD in the multifidus. IL-1β, tumor necrosis factor (TNF), IL-10, adiponectin, and leptin levels were lower in the physically active group.

CONCLUSION

These results reveal that spontaneous IDD causes dysregulation of the inflammatory pathways active in the multifidus muscle. These alterations were related to the severity of IDD and were prevented by physical activity.

LEVEL OF EVIDENCE

N/A.

Age-related spontaneous lumbar intervertebral disc degeneration in a mouse model

The pathogenesis of intervertebral disc degeneration is unclear, but it is a major cause of several spinal diseases. Animal models have historically provided an appropriate benchmark for understanding the human spine. However, there is little information about when intervertebral disc degeneration begins in the mouse or regarding the relationship between magnetic resonance imaging and histological findings. The aim for this study was to obtain information about age-related spontaneous intervertebral disc degeneration in the mouse lumbar spine using magnetic resonance imaging and a histological score regarding when the intervertebral disc degeneration started and how rapidly it progressed, as well as how our histological score detected the degeneration. The magnetic resonance imaging index yielded a moderate correlation with our Age-related model score. The Pfirrmann grade and magnetic resonance imaging index had moderate correlations with age. However, our Age-related model score had a high correlation with age. Intervertebral disc level was not a significant variable for the severity of disc degeneration. Both Pfirrmann grade and the Age-related model score were higher in the ≥14-month-old group than in the 6-month-old group. The present results indicated that mild but significant intervertebral disc degeneration occurred in 14-month-old mice, and the degree of degeneration progressed slowly, reaching a moderate to severe condition for 22-month-old mice. At least a 14-month follow-up is mandatory for evaluating spontaneous age-related mouse intervertebral disc degeneration. The histological classification score can precisely detect the gradual progression of age-related spontaneous intervertebral disc degeneration in the mouse lumbar spine, and is appropriate for evaluating it. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:224-232, 2018.

Animal models for disc degeneration-an update

Intervertebral disc degeneration is considered a major cause of back pain that places a heavy burden on society, both because of its effect on the physiology of individuals and its consequences on the world economy. During the past few decades, research findings in the pre-clinical setting have led to a significant increase in the understanding of intervertebral disc degeneration, although many aspects of the disease remain unclear. The goal of this review is to summarize existing animal models for disc degeneration studies and the difficulties that are associated with the use of such models. A firm understanding of the cellular and molecular events that ensue as a result of injuries, as well as environmental factors, could be instrumental in the development of targeted therapies for the treatment of intervertebral disc degeneration.

Chronic Osteoporotic Pain in Mice: Cutaneous and Deep Musculoskeletal Pain Are Partially Independent of Bone Resorption and Differentially Sensitive to Pharmacological Interventions

Although the pathological changes in osteoporotic bones are well established, the characterization of the osteoporotic pain and its appropriate treatment are not fully elucidated. We investigated the behavioral signs of cutaneous and deep musculoskeletal pain and physical function; time-dependent changes in bone mineral density (BMD) and the emergence of the behavioral phenotype; and the effects of pharmacological interventions having different mechanisms of action (chronic intraperitoneal administration of pamidronate [0.25 mg/kg, 5x/week for 5 weeks] versus acute treatment with intraperitoneal morphine [10 mg/kg] and pregabalin [100 mg/kg]) in a mouse model of ovariectomized or sham-operated mice 6 months following surgery. We observed reduced BMD associated with weight gain, referred cutaneous hypersensitivity, and deep musculoskeletal pain that persisted for 6 months. Chronic bisphosphonate treatment, 6 months after ovariectomy, reversed bone loss and hypersensitivity to cold, but other behavioral indices of osteoporotic pain were unchanged. While the efficacy of acute morphine on cutaneous pain was weak, pregabalin was highly effective; deep musculoskeletal pain was intractable. In conclusion, the reversal of bone loss alone is insufficient to manage pain in chronic osteoporosis. Additional treatments, both pharmacological and nonpharmacological, should be implemented to improve quality of life for osteoporosis patients.

Whole-body vibration induces pain and lumbar spinal inflammation responses in the rat that vary with the vibration profile

Whole-body vibration (WBV) is linked epidemiologically to neck and back pain in humans, and to forepaw mechanical allodynia and cervical neuroinflammation in a rodent model of WBV, but the response of the low back and lumbar spine to WBV is unknown. A rat model of WBV was used to determine the effect of different WBV exposures on hind paw behavioral sensitivity and neuroinflammation in the lumbar spinal cord. Rats were exposed to 30 min of WBV at either 8 or 15 Hz on days 0 and 7, with the lumbar spinal cord assayed using immunohistochemistry at day 14. Behavioral sensitivity was measured using mechanical stimulation of the hind paws to determine the onset, persistence, and/or recovery of allodynia. Both WBV exposures induce mechanical allodynia 1 day following WBV, but only the 8 Hz WBV induces a sustained decrease in the withdrawal threshold through day 14. Similarly, increased activation of microglia, macrophages, and astrocytes in the superficial dorsal horn of the lumbar spinal cord is only evident after the painful 8 Hz WBV. Moreover, extracellular signal-regulated kinase (ERK)-phosphorylation is most robust in neurons and astrocytes of the dorsal horn, with the most ERK phosphorylation occurring in the 8 Hz group. These findings indicate that a WBV exposure that induces persistent pain also induces a host of neuroimmune cellular activation responses that are also sustained. This work indicates there is an injury-dependent response that is based on the vibration parameters, providing a potentially useful platform for studying mechanisms of painful spinal injuries. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1439-1446, 2016.