Repeated exposure to high-frequency low-amplitude vibration induces degeneration of murine intervertebral discs and knee joints

Structural changes of the multifidus in animal models of intervertebral disk degeneration: a systematic review

Study design

Low back pain (LBP) is a widespread clinical symptom affecting nearly all age groups and is a leading cause of disability worldwide. Degenerative changes in the spine and paraspinal tissues primarily contribute to the etiology of LBP.

Objectives

We conducted this systematic review of animal models of paraspinal muscle (PSM) degeneration secondary to degenerative intervertebral disc (IVD), providing a comprehensive evaluation of PSM structural changes observed in these models at both macroscopic and microscopic levels.

Methods

PubMed, EMBASE, Web of Science, Cochrane Library, and MEDLINE Ovid databases were searched through November 2023. Literature was sequentially screened based on titles, abstracts, inclusion of animal models and full texts. A manual search of reference lists from all eligible studies was also performed to identify any eligible article. Two independent reviewers screened the articles according to inclusion and exclusion criteria. The risk of bias was assessed using the Systematic Review Centre for Laboratory Animal Experimentation's Risk of Bias tool.

Results

A total of nine studies were included in the final analysis after a comprehensive screening process. The included studies were assessed for various aspects of the multifidus muscle. Given the limited number of studies and the substantial heterogeneity among them, a quantitative meta-analysis was deemed inappropriate.

Conclusions

This systematic review shows a comprehensive analysis of structural changes in the multifidus muscle in animal models of IVD degeneration and offers crucial insights for developing improved rodent models of IVD degeneration and assessing a battery of approaches for multifidus degeneration.

Establishment of intervertebral disc degeneration models; A review of the currently used models

One of the frequent causes of low back pain is intervertebral disc degeneration (IDD), which is followed by discogenic pain. Some significant risk factors that have been linked to the onset and progression of IDD include age, mechanical imbalance, changes in nutrition and inflammation. According to recent studies, five types of animal models are established for producing IDD: the spontaneous models, the puncture models, the biomechanical models, the chemical models and the hybrid models. These models are crucial in studying and understanding IDD's natural history and identifying potential treatment targets for IDD. In our study, we'll talk about the technical aspects of these models, the time between model establishment and the apparition of observable degradation, and their potential in various research. Each animal model should be compared to the human natural IDD pathogenesis to guide future research efforts in this area. By improving knowledge and appropriate application of various animal models, we seek to raise awareness of this illness and further translational research.

Pannexin 3 deletion in mice results in knee osteoarthritis and intervertebral disc degeneration after forced treadmill running

Pannexin 3 (Panx3) is a glycoprotein that forms mechanosensitive channels expressed in chondrocytes and annulus fibrosus cells of the intervertebral disc (IVD). Evidence suggests Panx3 plays contrasting roles in traumatic versus aging osteoarthritis (OA) and intervertebral disc degeneration (IDD). However, whether its deletion influences the response of joint tissue to forced use is unknown. The purpose of this study was to determine if Panx3 deletion in mice causes increased knee joint OA and IDD after forced treadmill running. Male and female wildtype (WT) and Panx3 knockout (KO) mice were randomized to either a no-exercise group (sedentary; SED) or daily forced treadmill running (forced exercise; FEX) from 24 to 30 weeks of age. Knee cartilage and IVD histopathology were evaluated by histology, while tibial secondary ossification centers were analyzed using microcomputed tomography (µCT). Both male and female Panx3 KO mice developed larger superficial defects of the tibial cartilage after forced treadmill running compared with SED WT mice. Additionally, Panx3 KO mice developed reduced bone volume, and female PANX3 KO mice had lengthening of the lateral tubercle at the intercondylar eminence. In the lower lumbar spine, both male and female Panx3 KO mice developed histopathological features of IDD after running compared to SED WT mice. These findings suggest that the combination of deleting Panx3 and forced treadmill running induces OA and causes histopathological changes associated with the degeneration of the IVDs in mice.

Role of Galectin-3 in intervertebral disc degeneration: an experimental study

BACKGROUND

This study investigated the role of Galectin-3 in the degeneration of intervertebral disc cartilage.

METHODS

The patients who underwent lumbar spine surgery due to degenerative disc disease were recruited and divided into Modic I, Modic II, and Modic III; groups. HE staining was used to detect the pathological changes in endplates. The changes of Galectin-3, MMP3, Aggrecan, CCL3, and Col II were detected by immunohistochemistry, RT-PCR, and Western blot. MTT and flow cytometry were used to detect cartilage endplate cell proliferation, cell cycle, and apoptosis.

RESULTS

With the progression of degeneration (from Modic I to III), the chondrocytes and density of the cartilage endplate of the intervertebral disc decreased, and the collagen arrangement of the cartilage endplate of the intervertebral disc was broken and calcified. Meanwhile, the expressions of Aggrecan, Col II, Galectin-3, Aggrecan, and CCL3 gradually decreased. After treatment with Galectin-3 inhibitor GB1107, the proliferation of rat cartilage end plate cells was significantly reduced (P < 0.05). GB1107 (25 µmol/L) also significantly promoted the apoptosis of cartilage endplate cells (P < 0.05). Moreover, the percentage of cartilage endplate cells in the G1 phase was significantly higher, while that in the G2 and S phases was significantly lower (P < 0.05). Additionally, the mRNA and protein expression levels of MMP3, CCL3, and Aggrecan in rat cartilage end plate cells were lower than those in the control group.

CONCLUSIONS

Galectin-3 decreases with the progression of the cartilage endplate degeneration of the intervertebral disc. Galectin-3 may affect intervertebral disc degeneration by regulating the degradation of the extracellular matrix.

Comparative histopathological analysis of age-associated intervertebral disc degeneration in CD-1 and C57BL/6 mice: Anatomical and sex-based differences

Background

Intervertebral disc (IVD) degeneration is a major contributor to back pain and disability. The cause of IVD degeneration is multifactorial, with no disease-modifying treatments. Mouse models are commonly used to study IVD degeneration; however, the effects of anatomical location, strain, and sex on the progression of age-associated degeneration are poorly understood.

Methods

A longitudinal study was conducted to characterize age-, anatomical-, and sex-specific differences in IVD degeneration in two commonly used strains of mice, C57BL/6 and CD-1. Histopathological evaluation of the cervical, thoracic, lumbar, and caudal regions of mice at 6, 12, 20, and 24 months of age was conducted by two blinded observers at each IVD for the nucleus pulposus (NP), annulus fibrosus (AF), and the NP/AF boundary compartments, enabling analysis of scores by tissue compartment, summed scores for each IVD, or averaged scores for each anatomical region.

Results

C57BL/6 mice displayed mild IVD degeneration until 24 months of age; at this point, the lumbar spine demonstrated the most degeneration compared to other regions. Degeneration was detected earlier in the CD-1 mice (20 months of age) in both the thoracic and lumbar spine. In CD-1 mice, moderate to severe degeneration was noted in the cervical spine at all time points assessed. In both strains, age-associated IVD degeneration in the thoracic and lumbar spine was associated with increased histopathological scores in all IVD compartments. In both strains, minimal degeneration was detected in caudal IVDs out to 24 months of age. Both C57BL/6 and CD-1 mice displayed sex-specific differences in the presentation and progression of age-associated IVD degeneration.

Conclusions

These results showed that the progression and severity of age-associated degeneration in mouse models is associated with marked differences based on anatomical region, sex, and strain. This information provides a fundamental baseline characterization for users of mouse models to enable effective and appropriate experimental design, interpretation, and comparison between studies.

Pathogenesis and therapeutic implications of matrix metalloproteinases in intervertebral disc degeneration: A comprehensive review

Intervertebral disc (IVD) degeneration (IDD) is a common disorder that affects the spine and is a major cause of lower back pain (LBP). The extracellular matrix (ECM) is the structural foundation of the biomechanical properties of IVD, and its degradation is the main pathological characteristic of IDD. Matrix metalloproteinases (MMPs) are a group of endopeptidases that play an important role in the degradation and remodeling of the ECM. Several recent studies have shown that the expression and activity of many MMP subgroups are significantly upregulated in degenerated IVD tissue. This upregulation of MMPs results in an imbalance of ECM anabolism and catabolism, leading to the degradation of the ECM and the development of IDD. Therefore, the regulation of MMP expression is a potential therapeutic target for the treatment of IDD. Recent research has focused on identifying the mechanisms by which MMPs cause ECM degradation and promote IDD, as well as on developing therapies that target MMPs. In summary, MMP dysregulation is a crucial factor in the development of IDD, and a deeper understanding of the mechanisms involved is needed to develop effective biological therapies that target MMPs to treat IDD.

Oestrogen and Vibration Improve Intervertebral Disc Cell Viability and Decrease Catabolism in Bovine Organ Cultures

Postmenopausal women are at an increased risk for intervertebral disc degeneration, possibly due to the decrease in oestrogen levels. Low-magnitude, high-frequency vibration (LMHFV) is applied as a therapeutic approach for postmenopausal osteoporosis; however, less is known regarding possible effects on the intervertebral disc (IVD) and whether these may be oestrogen-dependent. The present study investigated the effect of 17β-oestradiol (E2) and LMHFV in an IVD organ culture model. Bovine IVDs (n = 6 IVDs/group) were treated with either (i) E2, (ii) LMHFV or (iii) the combination of E2 + LMHFV for 2 or 14 days. Minor changes in gene expression, cellularity and matrix metabolism were observed after E2 treatment, except for a significant increase in matrix metalloproteinase (MMP)-3 and interleukin (IL)-6 production. Interestingly, LMHFV alone induced cell loss and increased IL-6 production compared to the control. The combination of E2 + LMHFV induced a protective effect against cell loss and decreased IL-6 production compared to the LMHFV group. This indicates possible benefits of oestrogen therapy for the IVDs of postmenopausal women undergoing LMHFV exercises.

Long-term whole-body vibration induces degeneration of intervertebral disc and facet joint in a bipedal mouse model

Background: Whole body vibration (WBV) has been used to treat various musculoskeletal diseases in recent years. However, there is limited knowledge about its effects on the lumbar segments in upright posture mice. This study was performed to investigate the effects of axial Whole body vibration on the intervertebral disc (IVD) and facet joint (FJ) in a novel bipedal mouse model.

Methods: Six-week-old male mice were divided into control, bipedal, and bipedal + vibration groups. Taking advantage of the hydrophobia of mice, mice in the bipedal and bipedal + vibration groups were placed in a limited water container and were thus built standing posture for a long time. The standing posture was conducted twice a day for a total of 6 hours per day, 7 days per week. Whole body vibration was conducted during the first stage of bipedal building for 30 min per day (45 Hz with peak acceleration at 0.3 g). The mice of the control group were placed in a water-free container. At the 10th-week after experimentation, intervertebral disc and facet joint were examined by micro-computed tomography (micro-CT), histologic staining, and immunohistochemistry (IHC), and gene expression was quantified using real-time polymerase chain reaction. Further, a finite element (FE) model was built based on the micro-CT, and dynamic Whole body vibration was loaded on the spine model at 10, 20, and 45 Hz.

Results: Following 10 weeks of model building, intervertebral disc showed histological markers of degeneration, such as disorders of annulus fibrosus and increased cell death. Catabolism genes’ expression, such as Mmp13, and Adamts 4/5, were enhanced in the bipedal groups, and Whole body vibration promoted these catabolism genes’ expression. Examination of the facet joint after 10 weeks of bipedal with/without Whole body vibration loading revealed rough surface and hypertrophic changes at the facet joint cartilage resembling osteoarthritis. Moreover, immunohistochemistry results demonstrated that the protein level of hypertrophic markers (Mmp13 and Collagen X) were increased by long-durationstanding posture, and Whole body vibration also accelerated the degenerative changes of facet joint induced by bipedal postures. No changes in the anabolism of intervertebral disc and facet joint were observed in the present study. Furthermore, finite element analysis revealed that a larger frequency of Whole body vibration loading conditions induced higher Von Mises stresses on intervertebral disc, contact force, and displacement on facet joint.

Conclusion: The present study revealed significant damage effects of Whole body vibration on intervertebral disc and facet joint in a bipedal mouse model. These findings suggested the need for further studies of the effects of Whole body vibration on lumbar segments of humans.

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.

Increase in serum nerve growth factor but not intervertebral disc degeneration following whole-body vibration in rats

BACKGROUND

Low back pain is a leading cause of disability and is frequently associated with whole-body vibration exposure in industrial workers and military personnel. While the pathophysiological mechanisms by which whole-body vibration causes low back pain have been studied in vivo, there is little data to inform low back pain diagnosis. Using a rat model of repetitive whole-body vibration followed by recovery, our objective was to determine the effects of vibration frequency on hind paw withdrawal threshold, circulating nerve growth factor concentration, and intervertebral disc degeneration.

METHODS

Male Sprague-Dawley rats were vibrated for 30 min at an 8 Hz or 11 Hz frequency every other day for two weeks and then recovered (no vibration) for one week. Von Frey was used to determine hind paw mechanical sensitivity every two days. Serum nerve growth factor concentration was determined every four days. At the three-week endpoint, intervertebral discs were graded histologically for degeneration.

FINDINGS

The nerve growth factor concentration increased threefold in the 8 Hz group and twofold in the 11 Hz group. The nerve growth factor concentration did not return to baseline by the end of the one-week recovery period for the 8 Hz group. Nerve growth factor serum concentration did not coincide with intervertebral disc degeneration, as no differences in degeneration were observed among groups. Mechanical sensitivity generally decreased over time for all groups, suggesting a habituation (desensitization) effect.

INTERPRETATION

This study demonstrates the potential of nerve growth factor as a diagnostic biomarker for low back pain due to whole-body vibration.

Neoepitope fragments as biomarkers for different phenotypes of intervertebral disc degeneration

Background

During the intervertebral disc (IVD) degeneration process, initial degenerative events occur at the extracellular matrix level, with the appearance of neoepitope peptides formed by the cleavage of aggrecan and collagen. This study aims to elucidate the spatial and temporal alterations of aggrecan and collagen neoepitope level during IVD degeneration.

Methods

Bovine caudal IVDs were cultured under four different conditions to mimic different degenerative situations. Samples cultured after 1- or 8-days were collected for analysis. Human IVD samples were obtained from patients diagnosed with lumbar disc herniation (LDH) or adolescent idiopathic scoliosis (AIS). After immunohistochemical (IHC) staining of Aggrecanase Cleaved C-terminus Aggrecan Neoepitope (NB100), MMP Cleaved C-terminus Aggrecan Neoepitope (MMPCC), Collagen Type 1α1 1/4 fragment (C1α1) and Collagenase Cleaved Type I and II Collagen Neoepitope (C1,2C), staining optical density (OD)/area in extracellular matrix (OECM) and pericellular zone (OPCZ) were analyzed. Conditioned media of the bovine IVD was collected to measure protein level of inflammatory cytokines and C1,2C.

Results

For the bovine IVD sections, the aggrecan MMPCC neoepitope was accumulated in nucleus pulposus (NP) and cartilage endplate (EP) regions following mechanical overload in the one strike model after long-term culture; as for the TNF-α induced degeneration, the OECM and OPCZ of collagen C1,2C neoepitope was significantly increased in the outer AF region after long-term culture; moreover, the C1,2C was only detected in conditioned medium from TNF-α injection + Degenerative loading group after 8 days of culture. LDH patients showed higher MMPCC OECM in NP and higher C1,2C OECM in AF region compared with AIS patients.

Conclusions

In summary, aggrecan and collagen neoepitope profiles showed degeneration induction trigger- and region-specific differences in the IVD organ culture models. Different IVD degeneration types are correlated with specific neoepitope expression profiles. These neoepitopes may be helpful as biomarkers of ECM degradation in early IVD degeneration and indicators of different degeneration phenotypes.

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.

The Long-Term Residual Effects of Low-Magnitude Mechanical Stimulation on Murine Femoral Mechanics

As an alternative to drug treatments, low-magnitude mechanical stimulation (LMMS) may improve skeletal health without potential side effects from drugs. LMMS has been shown to increase bone health short term in both animal and clinical studies. Long-term changes to the mechanical properties of bone from LMMS are currently unknown, so the objective of this research was to establish the methodology and preliminary results for investigating the long-term effects of whole body vibration therapy on the elastic and viscoelastic properties of bone. In this study, 10-week-old female BALB/cByJ mice were given LMMS (15 min/day, 5 days/week, 0.3 g, 90 Hz) for 8 weeks; SHAM did not receive LMMS. Two sets of groups remained on study for an additional 8 or 16 weeks post-LMMS (N = 17). Micro-CT and fluorochrome histomorphology of these femurs were studied and results were published by Bodnyk et al. (2020, "The Long-Term Residual Effects of Low-Magnitude Mechanical Stimulation Therapy on Skeletal Health," J. Biol. Eng., 14, Article No. 9.). Femoral quasi-static bending stiffness trended 4.2% increase in stiffness after 8 weeks of LMMS and 1.3% increase 8 weeks post-LMMS compared to SHAM. Damping, tan delta, and loss stiffness significantly increased by 17.6%, 16.3%, and 16.6%, respectively, at 8 weeks LMMS compared to SHAM. Finite element models of applied LMMS signal showed decreased stress in the mid-diaphyseal region at both 8-week LMMS and 8-week post-LMMS compared to SHAM. Residual mechanical changes in bone during and post-LMMS indicate that LMMS could be used to increase long-term mechanical integrity of bone.

Low-Frequency Vibration Promotes Tumor Necrosis Factor-α Production to Increase Cartilage Degeneration in Knee Osteoarthritis

OBJECTIVE

Low-frequency vibration accelerates cartilage degeneration in knee osteoarthritis (KOA) rat model. In this article, we investigated whether whole-body vibration (WBV) increases cartilage degeneration by regulating tumor necrosis factor-α (TNF-α) in KOA.

DESIGN

Proteomics analysis was used to filter candidate protein from synovial fluid (SF) in KOA people after WBV. Enzyme-linked immunosorbent assay (ELISA) was used to estimate changes in TNF-α levels in SF. The C57 mice and TNF-α knock-out mice were sacrificed for the KOA model and WBV intervention. The cartilage was tested by ELISA, histology, terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL), immunohistochemistry, and reverse transcriptase polymerase chain reaction. Luciferase activity test in vitro study was conducted to confirm the relationship between TNF-α and the candidate protein.

RESULTS

Differentially expressed proteins were enriched in the glycolytic process, glucose catabolic, and regulation of interleukin-8 (IL-8) secretion processes. Phosphoglycerate kinase, triosephosphate isomerase 1, T cell immunoglobulin- and mucin-domain-containing molecules 2, fumarylacetoacetate hydrolase (FAH), and TNF were the hub node. TNF-α expression increased in SF after WBV (P < 0.05). The cartilage was more degenerated in the TNF-α^-/- mice group compared to controls. A significant change was observed in collagen II and FAH (P < 0.05). TNF-α expression improved in C57 mice (P < 0.05). Apoptosis of chondrocytes was inhibited in TNF-α^-/- mice by the TUNEL test. Luciferase activity significantly increased in TNF-α + FAH-Luc cells (P < 0.05).

CONCLUSION

A novel mechanism underlying WBV-triggered cartilage degeneration was found in KOA that demonstrated the critical regulatory function of TNF-α and FAH during WBV.

A finite element model of the human lower thorax to pelvis spinal segment: Validation and modal analysis

BACKGROUND

Several finite element (FE) models have been developed to study the effects of vibration on human lumbar spine. However, the authors know of no published results so far that have proposed computed tomography-based FE models of whole lumbar spine including the pelvis to conduct dynamic analysis.

OBJECTIVE

To create and validate a three-dimensional ligamentous FE model of the human lower thorax to pelvis spinal segment (T12-Pelvis) and provide a detailed simulation environment to investigate the dynamic characteristics of the lumbar spine under whole body vibration (WBV).

METHODS

The T12-Pelvis model was generated based on volume reconstruction from computed tomography scans and validated against the published experimental data. FE modal analysis was implemented to predict dynamic characteristics associated with the first-order vertical resonant frequency and vibration mode of the model with upper body mass of 40 kg under WBV.

RESULTS

It was found that the current FE model was validated and corresponded closely with the published data. The obtained results from the modal analysis indicated that the first-order vertical resonant frequency of the T12-Pelvis model was 6.702 Hz, and the lumbar spine mainly performed vertical motion with a small anteroposterior motion. It was also found that shifting the upper body mass centroid onwards or rearwards from the normal upright sitting posture reduced the vertical resonant frequency.

CONCLUSIONS

These findings may be helpful to better understand vibration response of the human spine, and provide important information to minimize injury and discomfort for these WBV-exposed occupational groups.

Development of a standardized histopathology scoring system using machine learning algorithms for intervertebral disc degeneration in the mouse model-An ORS spine section initiative

Mice have been increasingly used as preclinical model to elucidate mechanisms and test therapeutics for treating intervertebral disc degeneration (IDD). Several intervertebral disc (IVD) histological scoring systems have been proposed, but none exists that reliably quantitate mouse disc pathologies. Here, we report a new robust quantitative mouse IVD histopathological scoring system developed by building consensus from the spine community analyses of previous scoring systems and features noted on different mouse models of IDD. The new scoring system analyzes 14 key histopathological features from nucleus pulposus (NP), annulus fibrosus (AF), endplate (EP), and AF/NP/EP interface regions. Each feature is categorized and scored; hence, the weight for quantifying the disc histopathology is equally distributed and not driven by only a few features. We tested the new histopathological scoring criteria using images of lumbar and coccygeal discs from different IDD models of both sexes, including genetic, needle-punctured, static compressive models, and natural aging mice spanning neonatal to old age stages. Moreover, disc sections from common histological preparation techniques and stains including H&E, SafraninO/Fast green, and FAST were analyzed to enable better cross-study comparisons. Fleiss's multi-rater agreement test shows significant agreement by both experienced and novice multiple raters for all 14 features on several mouse models and sections prepared using various histological techniques. The sensitivity and specificity of the new scoring system was validated using artificial intelligence and supervised and unsupervised machine learning algorithms, including artificial neural networks, k-means clustering, and principal component analysis. Finally, we applied the new scoring system on established disc degeneration models and demonstrated high sensitivity and specificity of histopathological scoring changes. Overall, the new histopathological scoring system offers the ability to quantify histological changes in mouse models of disc degeneration and regeneration with high sensitivity and specificity.

Deleterious effects of whole-body vibration on the spine: A review of in vivo, ex vivo, and in vitro models

Occupational exposure to whole-body vibration is associated with the development of musculoskeletal, neurological, and other ailments. Low back pain and other spine disorders are prevalent among those exposed to whole-body vibration in occupational and military settings. Although standards for limiting exposure to whole-body vibration have been in place for decades, there is a lack of understanding of whole-body vibration-associated risks among safety and healthcare professionals. Consequently, disorders associated with whole-body vibration exposure remain prevalent in the workforce and military. The relationship between whole-body vibration and low back pain in humans has been established largely through cohort studies, for which vibration inputs that lead to symptoms are rarely, if ever, quantified. This gap in knowledge highlights the need for the development of relevant in vivo, ex vivo, and in vitro models to study such pathologies. The parameters of vibrational stimuli (eg, frequency and direction) play critical roles in such pathologies, but the specific cause-and-effect relationships between whole-body vibration and spinal pathologies remain mostly unknown. This paper provides a summary of whole-body vibration parameters; reviews in vivo, ex vivo, and in vitro models for spinal pathologies resulting from whole-body vibration; and offers suggestions to address the gaps in translating injury biomechanics data to inform clinical practice.

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.

Protocol for parallel proteomic and metabolomic analysis of mouse intervertebral disc tissues

The comprehensiveness of data collected by "omics" modalities has demonstrated the ability to drastically transform our understanding of the molecular mechanisms of chronic, complex diseases such as musculoskeletal pathologies, how biomarkers are identified, and how therapeutic targets are developed. Standardization of protocols will enable comparisons between findings reported by multiple research groups and move the application of these technologies forward. Herein, we describe a protocol for parallel proteomic and metabolomic analysis of mouse intervertebral disc (IVD) tissues, building from the combined expertise of our collaborative team. This protocol covers dissection of murine IVD tissues, sample isolation, and data analysis for both proteomics and metabolomics applications. The protocol presented below was optimized to maximize the utility of a mouse model for "omics" applications, accounting for the challenges associated with the small starting quantity of sample due to small tissue size as well as the extracellular matrix-rich nature of the tissue.

Effect of whole body vibration on HIF-2α expression in SD rats with early knee osteoarthritis

INTRODUCTION

To investigate the effect of different frequencies of whole body vibration (WBV) on articular cartilage of early knee osteoarthritis (OA) rats and determine whether WBV would influence the pathway of hypoxia-inducible factor-2α (HIF-2α) regulation-related genes after 8 weeks of treatment.

MATERIALS AND METHODS

Forty 8-week-old OA rats were divided into five groups: sham control (SC); high frequency 60 Hz (HV₁); high frequency 40 Hz (HV₂); middle frequency 20 Hz (MV) and low frequency 10 Hz (LV). WBV (0.3 g) treatment was given 40 min/day and 5 days/week. After 8 weeks, rats were killed and knees were harvested. OA grading score: Osteoarthritis Research Society International (OARSI), and the expression of related genes: interleukin-1β (IL-1β), HIF-2α, matrix metalloproteinases-13 (MMP-13), and collagen type II alpha 1 (COL2A1), at both mRNA and protein levels were analyzed.

RESULTS

After 8 weeks of WBV, our data showed that lower frequency (10 Hz) was more effective than the higher ones, yet they all suggested that WBV alleviates the erosion of knee articular cartilage in early OA. The expression of IL-1β, HIF-2α and MMP-13 decreased with frequency and reached the lowest level at 10 Hz, the expression of COL2A1 increased with frequency and reached the highest level at 10 Hz.

CONCLUSIONS

This study demonstrates that WBV could alleviate the degeneration of knee joints in an early OA rat model. WBV regulates related gene expression at both mRNA and protein levels. HIF-2α could be a therapeutic target. The effect of WBV is frequency dependent; the lower frequency shows better effects.

Pain After Whole-Body Vibration Exposure Is Frequency Dependent and Independent of the Resonant Frequency: Lessons From an In Vivo Rat Model

Occupational whole-body vibration (WBV) increases the risk of developing low back and neck pain; yet, there has also been an increased use of therapeutic WBV in recent years. Although the resonant frequency (fr) of the spine decreases as the exposure acceleration increases, effects of varying the vibration profile, including peak-to-peak displacement (sptp), root-mean-squared acceleration (arms), and frequency (f), on pain onset are not known. An established in vivo rat model of WBV was used to characterize the resonance of the spine using sinusoidal sweeps. The relationship between arms and fr was defined and implemented to assess behavioral sensitivity-a proxy for pain. Five groups were subjected to a single 30-min exposure, each with a different vibration profile, and a sham group underwent only anesthesia exposure. The behavioral sensitivity was assessed at baseline and for 7 days following WBV-exposure. Only WBV at 8 Hz induced behavioral sensitivity, and the higher arms exposure at 8 Hz led to a more robust pain response. These results suggest that the development of pain is frequency-dependent, but further research into the mechanisms leading to pain is warranted to fully understand which WBV profiles may be detrimental or beneficial.

Differential Effect of Long-Term Systemic Exposure of TNFα on Health of the Annulus Fibrosus and Nucleus Pulposus of the Intervertebral Disc

The inflammatory cytokine tumor necrosis factor alpha (TNFα) is considered to play a key role in the pathogenesis of intervertebral disc disease. To evaluate the importance of this cytokine we examined the inflammatory environment and spinal phenotype of 9-month-old human TNFα overexpressing transgenic (hTNFα-TG) mice. The mice evidenced increased circulating levels of interleukin-1β (IL-1β), IL-2, keratinocyte chemoattractant/human growth-regulated oncogene (KC/GRO), and monocyte chemoattractant protein-1 (MCP-1) along with thinning of the cortical and trabecular vertebral bone. Surprisingly, although the nucleus pulposus (NP) of these mice was intact and healthy, the caudal annulus fibrosus (AF) evidenced robust cell death and immune cell infiltration. Despite these differences, there were no obvious alterations in the collagen or aggrecan content in the NP and AF. However, there was a reduction in cartilage oligomeric matrix protein (COMP), suggesting destabilization of the AF matrix. Microarray analysis of the NP from hTNFα-TG mice cells revealed minimal changes in global gene expression. These findings lend support to the notion that NP tissue is isolated from systemic inflammation. In contrast, the severe AF phenotype suggests that systemic inflammation interferes with AF health, predisposing discs to herniation as opposed to directly causing NP degeneration. © 2020 American Society for Bone and Mineral Research.

Pathomechanism of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the main contributor to low back pain, which is a leading cause of disability worldwide. Although substantial progress has been made in elucidating the molecular mechanisms of IDD, fundamental and long-lasting treatments for IDD are still lacking. With increased understanding of the complex pathomechanism of IDD, alternative strategies for treating IDD can be discovered. A brief overview of the prevalence and epidemiologic risk factors of IDD is provided in this review, followed by the descriptions of anatomic, cellular, and molecular structure of the intervertebral disc as well as the molecular pathophysiology of IDD. Finally, the recent findings of intervertebral disc progenitors are reviewed and the future perspectives are discussed.

Transcriptional profiling of the murine intervertebral disc and age-associated changes in the nucleus pulposus

Purpose/Aim: The intervertebral disc (IVD) is composed of cell types whose subtle phenotypic differences allow for the formation of distinct tissues. The role of the nucleus pulposus (NP) in the initiation and progression of IVD degeneration is well established; however, the genes and pathways associated with NP degeneration are poorly characterized.Materials and Methods: Using a genetic strategy for IVD lineage-specific fluorescent reporter expression to isolate cells, gene expression and bioinformatic analysis was conducted on the murine NP at 2.5, 6, and 21 months-of-age and the annulus fibrosus (AF) at 2.5 and 6 months-of-age. A subset of differentially regulated genes was validated by qRT-PCR.Results: Transcriptome analysis identified distinct profiles of NP and AF gene expression that were remarkably consistent at 2.5 and 6 months-of-age. Prg4, Cilp, Ibsp and Comp were increased >50-fold in the AF relative to NP. The most highly enriched NP genes included Dsc3 and Cdh6, members of the cadherin superfamily, and microRNAs mir218-1 and mir490. Changes in the NP between 2.5 and 6 months-of-age were associated with up-regulation of molecular functions linked to laminin and Bmp receptor binding (including up-regulation of Bmp5 & 7), with the most up-regulated genes being Mir703, Shh, and Sfrp5. NP degeneration was associated with molecular functions linked to alpha-actinin binding (including up-regulation of Ttn & Myot) and cytoskeletal protein binding, with the overall most up-regulated genes being Rnu3a, Snora2b and Mir669h.Conclusions: This study provided insight into the phenotypes of NP and AF cells, and identified candidate pathways that may regulate degeneration.

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.

Vibration of osteoblastic cells using a novel motion-control platform does not acutely alter cytosolic calcium, but desensitizes subsequent responses to extracellular ATP

Low-magnitude high-frequency mechanical vibration induces biological responses in many tissues. Like many cell types, osteoblasts respond rapidly to certain forms of mechanostimulation, such as fluid shear, with transient elevation in the concentration of cytosolic free calcium ([Ca²⁺ ]_i ). However, it is not known whether vibration of osteoblastic cells also induces acute elevation in [Ca²⁺ ]_i . To address this question, we built a platform for vibrating live cells that is compatible with microscopy and microspectrofluorometry, enabling us to observe immediate responses of cells to low-magnitude high-frequency vibrations. The horizontal vibration system was mounted on an inverted microscope, and its mechanical performance was evaluated using optical tracking and accelerometry. The platform was driven by a sinusoidal signal at 20-500 Hz, producing peak accelerations from 0.1 to 1 g. Accelerometer-derived displacements matched those observed optically within 10%. We then used this system to investigate the effect of acceleration on [Ca²⁺ ]_i in rodent osteoblastic cells. Cells were loaded with fura-2, and [Ca²⁺ ]_i was monitored using microspectrofluorometry and fluorescence ratio imaging. No acute changes in [Ca²⁺ ]_i or cell morphology were detected in response to vibration over the range of frequencies and accelerations studied. However, vibration did attenuate Ca²⁺ transients generated subsequently by extracellular ATP, which activates P2 purinoceptors and has been implicated in mechanical signaling in bone. In summary, we developed and validated a motion-control system capable of precisely delivering vibrations to live cells during real-time microscopy. Vibration did not elicit acute elevation of [Ca²⁺ ]_i , but did desensitize responses to later stimulation with ATP.

A New Understanding of the Role of IL-1 in Age-Related Intervertebral Disc Degeneration in a Murine Model

Increased cytokine expression, in particular interleukin-1β (IL-1β), is considered a hallmark of intervertebral disc degeneration. However, the causative relationship between IL-1 and age-dependent degeneration has not been established. To investigate the role of IL-1 in driving age-related disc degeneration, we studied the spine phenotype of global IL-1α/β double knockout (IL-1KO) mice at 12 and 20 months. Multiplex ELISA analysis of blood revealed significant reductions in the concentrations of IFN-γ, IL-5, IL-15, TNF-α, IP-10, and a trend of reduced concentrations of IL-10, macrophage inflammatory protein 1α (MIP-1α), keratinocyte chemoattractant/human growth-regulated oncogene (KC/GRO), and IL-6. However, the circulating level of MIP-2, a neutrophil chemoattractant, was increased in the IL-1KO. The alterations in systemic cytokine levels coincided with altered bone morphology-IL-1KO mice exhibited significantly thicker caudal cortical bone at 12 and 20 months. Despite these systemic inflammatory and bony changes, IL-1 deletion only minimally affected disc health. Both wild-type (WT) and IL-1KO mice showed age-dependent disc degeneration. Unexpectedly, rather than protecting the animals from degeneration, the aging phenotype was more pronounced in IL-1KO animals: knockout mice evidenced significantly more degenerative changes in the annulus fibrosis (AF) together with alterations in collagen type and maturity. At 20 months, there were no changes in nucleus pulposus (NP) extracellular matrix composition or cellular marker expression; however, the IL-1KO NP cells occupied a smaller proportion of the NP compartment that those of WT controls. Taken together, these results show that IL-1 deletion altered the systemic inflammatory environment and vertebral bone morphology. However, instead of protecting discs from age-related disc degeneration, global IL-1 deletion amplified the degenerative phenotype. © 2019 American Society for Bone and Mineral Research.

Creep experimental study on the lumbar intervertebral disk under vibration compression load

The intervertebral disk cushions the load generated by human activity and absorbs energy to keep the spine moving steadily. Vibration condition is one of the important causes of disk degeneration. Creep experiments using the sheep lumbar intervertebral disk were carried out under vibration compression. Regularities of the strain of the disk with time were obtained and compared with those of static load. The influence of vibration frequency and time on the creep properties of the intervertebral disk was analyzed. An intervertebral disk three-parameter solid creep constitutive model considering vibration factors was established and the parameters in the model were identified. The results show that the strain of the lumbar intervertebral disk exhibits an exponential relationship with time and is unrelated to static compression or vibration load. Under the same vibration amplitude, the creep increases with vibration frequency and the relationship between them is nonlinear. The vibration frequency has a significant effect on the strain. The creep rate decreases gradually with time and is obviously influenced by vibration frequency at low vibration amplitudes. The creep prediction results obtained using the constitutive model with the time-varying material parameters are in good agreement with the experimental results. The two elastic moduli in the model decrease with time and the viscosity coefficient increases with time.

Transgenic mice overexpressing human TNF-α experience early onset spontaneous intervertebral disc herniation in the absence of overt degeneration

There is a well-established link between cytokine expression and the progression of intervertebral disc degeneration. Among these cytokines, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) are the most commonly studied. To investigate whether systemic hTNF-α overexpression affects intervertebral disc health, we studied the spine phenotype of Tg197 mice, a widely used hTNF-α transgenic line. These mice were studied at 12–16 weeks of age using comprehensive histochemical and immunohistological analysis of the spinal motion segment. Micro-CT analysis was performed to quantify vertebral trabecular bone architecture. The Tg197 mice evidenced spontaneous annular tears and herniation with increased vascularity in subchondral bone and significant immune cell infiltration. The full-thickness annular tear without nucleus pulposus (NP) extrusion resulted in neutrophil, macrophage, and mast cell infiltration into the disc, whereas the disc with full-thickness tear and pronounced NP herniation showed additional presence of CD4+ and CD8+ T cells. While the observed defects involved failure of the annular, endplate, and vertebral junction, there were no obvious alterations in the collagen or aggrecan content in the NP and annulus fibrosus or the maturity of collagen fibers in Tg197 mice. Despite elevated systemic inflammation and pronounced loss of trabecular bone in the vertebrae, intact Tg197 discs were healthy and showed an increase in NP cell number. The NP cells in intact discs preserved expression of phenotypic markers: CAIII, Glut1, and Krt19. In conclusion, elevated systemic TNF-α increases the susceptibility of mice to spontaneous disc herniation and possibly radiculopathy, without adversely affecting intact intervertebral disc health.

Osteoarthritis and intervertebral disc degeneration: Quite different, quite similar

Intervertebral disc degeneration describes the vicious cycle of the deterioration of intervertebral discs and can eventually result in degenerative disc disease (DDD), which is accompanied by low-back pain, the musculoskeletal disorder with the largest socioeconomic impact world-wide. In more severe stages, intervertebral disc degeneration is accompanied by loss of joint space, subchondral sclerosis, and osteophytes, similar to osteoarthritis (OA) in the articular joint. Inspired by this resemblance, we investigated the analogy between human intervertebral discs and articular joints. Although embryonic origin and anatomy suggest substantial differences between the two types of joint, some features of cell physiology and extracellular matrix in the nucleus pulposus and articular cartilage share numerous parallels. Moreover, there are great similarities in the response to mechanical loading and the matrix-degrading factors involved in the cascade of degeneration in both tissues. This suggests that the local environment of the cell is more important to its behavior than embryonic origin. Nevertheless, OA is widely regarded as a true disease, while intervertebral disc degeneration is often regarded as a radiological finding and DDD is undervalued as a cause of chronic low-back pain by clinicians, patients and society. Emphasizing the similarities rather than the differences between the two diseases may create more awareness in the clinic, improve diagnostics in DDD, and provide cross-fertilization of clinicians and scientists involved in both intervertebral disc degeneration and OA.

A novel mouse model of intervertebral disc degeneration shows altered cell fate and matrix homeostasis

Intervertebral disc degeneration and associated low back and neck pain is a ubiquitous health condition that affects millions of people world-wide, and causes high incidence of disability and enormous medical/societal costs. However, lack of appropriate small animal models with spontaneous disease onset has impeded our ability to understand the pathogenetic mechanisms that characterize and drive the degenerative process. We report, for the first time, early onset spontaneous disc degeneration in SM/J mice known for their poor regenerative capacities compared to "super-healer" LG/J mice. In SM/J mice, degenerative process was marked by decreased nucleus pulposus (NP) cellularity and changes in matrix composition at P7, 4, and 8 weeks with increased severity by 17 weeks. Distinctions between NP and annulus fibrosus (AF) or endplate cartilage were lost, and NP and AF of SM/J mice showed higher histological grades. There was increased NP cell death in SM/J mice with decreased phenotypic marker expression. Polarized microscopy and FTIR spectroscopy demonstrated replacement of glycosaminoglycan-rich NP matrix with collagenous fibrous tissue. The levels of ARGxx were increased in, indicating higher aggrecan turnover. Furthermore, an aberrant expression of collagen X and MMP13 was observed in the NP of SM/J mice, along with elevated expression of Col10a1, Ctgf, and Runx2, markers of chondrocyte hypertrophy. Likewise, expression of Enpp1 as well as Alpl was higher, suggesting NP cells of SM/J mice promote dystrophic mineralization. There was also a decrease in several pathways necessary for NP cell survival and function including Wnt and VEGF signaling. Importantly, SM/J discs were stiffer, had decreased height, and poor vertebral bone quality, suggesting compromised motion segment mechanical functionality. Taken together, our results clearly demonstrate that SM/J mouse strain recapitulates many salient features of human disc degeneration, and serves as a novel small animal model.

A Mouse Intervertebral Disc Degeneration Model by Surgically Induced Instability

STUDY DESIGN

An experimental study to develop a mouse model of lumbar intervertebral disc degeneration (IDD).

OBJECTIVE

The aim of this study was to develop a mouse lumbar IDD model using surgically induced instability and to compare the findings of this model to those in human IDD.

SUMMARY OF BACKGROUND DATA

Previously, various kinds of inducers have been used to reproduce IDD in experimental animals; however, there is yet no standard mouse lumbar IDD model without direct injury to intervertebral disc.

METHODS

A total number of 59 C57BL/6J male mice at 8 weeks old were used. Instability of lumbar spine was induced by surgical resection of posterior elements, including facet joints, supra- and interspinous ligaments. We then analyzed time course changes in radiographical (n = 17) and histological analyses (n = 42), and compared these findings with those in human IDD.

RESULTS

Radiographical analyses showed that the disc height began to decrease in the first 2 weeks after the surgery, and the decrease continued throughout 12 weeks. Bone spurs at the vertebral rims were observed in the late stage of 8 and 12 weeks after the surgery. Histological analyses showed that the disorder of the anterior anulus fibrosus (AF) was initially obvious, followed by posterior shift and degeneration of the nucleus pulposus (NP). Proteoglycan detected in inner layer of AF and periphery of NP was decreased after 8 weeks. Immunohistochemistry displayed the increase of type I and X collagen, and matrix metalloproteinase 13 in the anterior AF.

CONCLUSION

Surgical resection of posterior elements of mouse lumbar spine resulted in reproducible IDD. Because the present procedure does not employ direct injury to intervertebral disc and the radiological and histological findings are compatible with those in human IDD, it may contribute to further understanding of the native pathophysiology of IDD in future.

LEVEL OF EVIDENCE

N/A.

Low-intensity vibration increases cartilage thickness in obese mice

Obesity is associated with an elevated risk of osteoarthritis (OA). We examined here whether high fat diet administered in young mice, compromised the attainment of articular cartilage thickness. Further, we sought to determine if low-intensity vibration (LIV) could protect the retention of articular cartilage in a mouse model of diet-induced obesity. Five-week-old, male, C57BL/6 mice were separated into three groups (n = 10): Regular diet (RD), High fat diet (HF), and HF + LIV (HFv; 90 Hz, 0.2g, 30 min/d, 5 d/w) administered for 6 weeks. Additionally, an extended HF diet study was run for 6 months (LIV at 15 m/d). Articular cartilage and subchondral bone morphology, and sulfated GAG content were quantified using contrast agent enhanced μCT and histology. Gene expression within femoral condyles was quantified using real-time polymerase chain reaction. Contrary to our hypothesis, HF cartilage thickness was not statistically different from RD. However, LIV increased cartilage thickness compared to HF, and the elevated thickness was maintained when diet and LIV were extended into adulthood. RT-PCR analysis showed a reduction of aggrecan expression with high fat diet, while application of LIV reduced the expression of degradative MMP-13. Further, long-term HF diet resulted in subchondral bone thickening, compared to RD, providing early evidence of OA pathology-LIV suppressed the thickening, such that levels were not significantly different from RD. These data suggest that dynamic loading, via LIV, protected the retention of cartilage thickness, potentially resulting in joint surfaces better suited to endure the risks of elevated loading that parallel obesity. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:751-759, 2018.

Non-invasive Loading Model of Murine Osteoarthritis

Osteoarthritis is the commonest degenerative joint disease, leading to joint pain and disability. The mouse has been the primary animal used for research, due to its size, relatively short lifespan, and the availability of genetically modified animals. Importantly, they show pathogenesis similar to osteoarthritis in humans. Mechanical loading is a major risk factor for osteoarthritis, and various mouse models have been developed to study the role and effects of mechanics on health and disease in various joints. This review describes the main mouse models used to non-invasively apply mechanical loads on joints. Most of the mouse models of osteoarthritis target the knee, including repetitive loading and joint injury such as ligament rupture, but a few studies have also characterised models for elbow, temporomandibular joint, and whole-body vibration spinal loading. These models are a great opportunity to dissect the influences of various types of mechanical input on joint health and disease.

Do Occupational Risks for Low Back Pain Differ From Risks for Specific Lumbar Disc Diseases?: Results of the German Lumbar Spine Study (EPILIFT)

STUDY DESIGN

A multicenter, population based, case-control study.

OBJECTIVE

The aim of the present analysis is to clarify potential differences in the "occupational risk profiles" of structural lumbar disc diseases on the one hand, and low back pain (LBP) on the other hand.

SUMMARY OF BACKGROUND DATA

Physical workplace factors seem to play an important etiological role.

METHODS

We recruited 901 patients with structural lumbar disc diseases (disc herniation or severe disc space narrowing) and 233 control subjects with "low-back-pain." Both groups were compared with 422 "low-back pain free" control subjects. Case history, pain data, neurological deficits, and movement restrictions were documented. LBP was recorded by the Nordic questionnaire on musculoskeletal symptoms. All magnetic resonance imaging, computed tomography, and X-rays were inspected by an independent study radiologist. The calculation of cumulative physical workload was based on a computer-assisted interview and a biomechanical analysis by 3-D-dynamic simulation tool. Occupational exposures were documented for the whole working life.

RESULTS

We found a positive dose-response relationship between cumulative lumbar load and LBP among men, but not among women. Physical occupational risks for structural lumbar disc diseases [odds ratio (OR) 3.7; 95% confidence interval (95% CI) 2.3-6.0] are higher than for LBP (OR 1.9; 95% CI 1.0-3.5).

CONCLUSION

Our finding points to potentially different etiological pathways in the heterogeneous disease group of LBP. Results suggest that not all of the structural disc damage arising from physical workload leads to LBP.

LEVEL OF EVIDENCE

4.

Mechanical signals protect stem cell lineage selection, preserving the bone and muscle phenotypes in obesity

The incidence of obesity is rapidly rising, increasing morbidity and mortality rates worldwide. Associated comorbidities include type 2 diabetes, heart disease, fatty liver disease, and cancer. The impact of excess fat on musculoskeletal health is still unclear, although it is associated with increased fracture risk and a decline in muscular function. The complexity of obesity makes understanding the etiology of bone and muscle abnormalities difficult. Exercise is an effective and commonly prescribed nonpharmacological treatment option, but it can be difficult or unsafe for the frail, elderly, and morbidly obese. Exercise alternatives, such as low-intensity vibration (LIV), have potential for improving musculoskeletal health, particularly in conditions with excess fat. LIV has been shown to influence bone marrow mesenchymal stem cell differentiation toward higher-order tissues (i.e., bone) and away from fat. While the exact mechanisms are not fully understood, recent studies utilizing LIV both at the bench and in the clinic have demonstrated some efficacy. Here, we discuss the current literature investigating the effects of obesity on bone, muscle, and bone marrow and how exercise and LIV can be used as effective treatments for combating the negative effects in the presence of excess fat.

MiR-210 facilitates ECM degradation by suppressing autophagy via silencing of ATG7 in human degenerated NP cells

Intervertebral disc degeneration (IDD) is thought to be the most common cause of low back pain. Dysregulation of microRNAs (miRNAs) is involved in the development of IDD. The aim of this study was to explore the influence of miR-210 on type II collagen (Col II) and aggrecan expression and possible mechanisms in human degenerated nucleus pulposus (NP) cells. Our results showed that miR-210 levels were significantly increased in degenerated NP tissues compared with healthy controls, and positively correlated with disc degeneration grade. By gain-of-function and loss-of-function studies in human degenerated NP cells, miR-210 was shown to inhibit autophagy and then upregulate MMP-3 and MMP-13 expression, leading to increased degradation of Col II and aggrecan. Autophagy-related gene 7 (ATG7) was identified as a direct target of miR-210. Knockdown of ATG7 by small interfering RNA (siRNA) abrogated the effects of miR-210 inhibitor on MMP-3, MMP-13, Col II and aggrecan expression. Taken together, these results suggest that miR-210 inhibits autophagy via silencing of ATG7, leading to increased Col II and aggrecan degradation in human degenerated NP cells.

Different doses of strontium ranelate and mechanical vibration modulate distinct responses in the articular cartilage of ovariectomized rats

OBJECTIVE

To investigate the effects of different strontium ranelate (SrR) doses alone or in combination with low-intensity and high-frequency mechanical vibration (MV) on articular cartilage in ovariectomized rats.

DESIGN

Fifty 6-month-old female Wistar rats underwent ovariectomy (OVX) and after 3 months were divided into: control group (Control); SrR 300 mg/kg/day (SrR300); SrR 625 mg/kg/day (SrR625); MV; SrR 625 mg/kg/day plus MV (SrR625 + MV). The vehicle and the SrR were administered by gavage 7 days/week and vibration (0.6 g/60 Hz) was performed for 20 min/day, 5 days/week. Bone mineral density (BMD) and body composition were evaluated by densitometry. Changes in cartilage were assessed 90 days after treatment by histomorphometry; immunohistochemistry analysis evaluating cell death (caspase-3), tumor necrosis factor-α (TNF-α), metalloproteinase 9 (MMP-9) and type II collagen; Osteoarthritis Research Society International (OARSI) grading system and glycosaminoglycans (GAGs) analyses.

RESULTS

SrR-treated groups exhibited a lower OARSI grade, a smaller number of chondrocyte clusters, increased levels of chondroitin sulfate (CS) and decreased expression of caspase-3. Additionally, compared to all the groups, SrR300 exhibited increased levels of hyaluronic acid (HA). Vibration applied alone or in combination accelerated cartilage degradation, as demonstrated by increased OARSI grade, reduced number of chondrocytes, increased number of clusters, elevated expression of type II collagen and cell death, and was accompanied by decreased amounts of CS and HA; however, MV alone was able to reduce MMP-9.

CONCLUSIONS

SrR and vibration modulate distinct responses in cartilage. Combined treatment accelerates degeneration. In contrast, SrR treatment at 300 mg/kg/day attenuates osteoarthritis (OA) progression, improving cartilage matrix quality and preserving cell viability in ovariectomized rats.

Whole-body vibration of mice induces articular cartilage degeneration with minimal changes in subchondral bone

OBJECTIVE

Low-amplitude, high-frequency whole-body vibration (WBV) has been adopted for the treatment of musculoskeletal diseases including osteoarthritis (OA); however, there is limited knowledge of the direct effects of vibration on joint tissues. Our recent studies revealed striking damage to the knee joint following exposure of mice to WBV. The current study examined the effects of WBV on specific compartments of the murine tibiofemoral joint over 8 weeks, including microarchitecture of the tibia, to understand the mechanisms associated with WBV-induced joint damage.

DESIGN

Ten-week-old male CD-1 mice were exposed to WBV (45 Hz, 0.3 g peak acceleration; 30 min/day, 5 days/week) for 4 weeks, 8 weeks, or 4 weeks WBV followed by 4 weeks recovery. The knee joint was evaluated histologically for tissue damage. Architecture of the subchondral bone plate, subchondral trabecular bone, primary and secondary spongiosa of the tibia was assessed using micro-CT.

RESULTS

Meniscal tears and focal articular cartilage damage were induced by WBV; the extent of damage increased between 4 and 8-week exposures to WBV. WBV did not alter the subchondral bone plate, or trabecular bone of the tibial spongiosa; however, a transient increase was detected in the subchondral trabecular bone volume and density.

CONCLUSIONS

The lack of WBV-induced changes in the underlying subchondral bone suggests that damage to the articular cartilage may be secondary to the meniscal injury we detected. Our findings underscore the need for further studies to assess the safety of WBV in the human population to avoid long-term joint damage.

Whole-body vibration of mice induces progressive degeneration of intervertebral discs associated with increased expression of Il-1β and multiple matrix degrading enzymes

OBJECTIVE

Whole-body vibration (WBV) is a popular fitness trend based on claims of increased muscle mass, weight loss and reduced joint pain. Following its original implementation as a treatment to increase bone mass in patients with osteoporosis, WBV has been incorporated into clinical practice for musculoskeletal disorders, including back pain. However, our recent studies revealed damaging effects of WBV on joint health in a murine model. In this report, we examined potential mechanisms underlying disc degeneration following exposure of mice to WBV.

METHODS

Ten-week-old male mice were exposed to WBV (45 Hz, 0.3 g peak acceleration, 30 min/day, 5 days/week) for 4 weeks, 8 weeks, or 4 weeks WBV followed by 4 weeks recovery. Micro-computed tomography (micro-CT), histological, and gene expression analyses were used to assess the effects of WBV on spinal tissues.

RESULTS

Exposure of mice to 4 or 8 weeks of WBV did not alter total body composition or induce significant changes in vertebral bone density. On the other hand, WBV-induced intervertebral disc (IVD) degeneration, associated with decreased disc height and degenerative changes in the annulus fibrosus (AF) that did not recover within 4 weeks after cessation of WBV. Gene expression analysis showed that WBV for 8 weeks induced expression of Mmp3, Mmp13, and Adamts5 in IVD tissues, changes preceded by increased expression of Il-1β.

CONCLUSIONS

Progressive IVD degeneration induced by WBV was associated with increased expression of Il-1β within the IVD that preceded Mmp and Adamts gene induction. Moreover, WBV-induced IVD degeneration is not reversed following cessation of vibration.

Using mouse models to investigate the pathophysiology, treatment, and prevention of post-traumatic osteoarthritis

Post-traumatic osteoarthritis (PTOA) is defined by its development after joint injury. Factors contributing to the risk of PTOA occurring, the rate of progression, and degree of associated disability in any individual, remain incompletely understood. What constitutes an "OA-inducing injury" is not defined. In line with advances in the traumatic brain injury field, we propose the scope of PTOA-inducing injuries be expanded to include not only those causing immediate structural damage and instability (Type I), but also those without initial instability/damage from moderate (Type II) or minor (Type III) loading severity. A review of the literature revealed this full spectrum of potential PTOA subtypes can be modeled in mice, with 27 Type I, 6 Type II, and 4 Type III models identified. Despite limitations due to cartilage anatomy, joint size, and bio-fluid availability, mice offer advantages as preclinical models to study PTOA, particularly genetically modified strains. Histopathology was the most common disease outcome, cartilage more frequently studied than bone or synovium, and meniscus and ligaments rarely evaluated. Other methods used to examine PTOA included gene expression, protein analysis, and imaging. Despite the major issues reported by patients being pain and biomechanical dysfunction, these were the least commonly measured outcomes in mouse models. Informative correlations of simultaneously measured disease outcomes in individual animals, was rarely done in any mouse PTOA model. This review has identified knowledge gaps that need to be addressed to increase understanding and improve prevention and management of PTOA. Preclinical mouse models play a critical role in these endeavors. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:424-439, 2017.

C57BL/6 mice are resistant to joint degeneration induced by whole-body vibration

OBJECTIVE

Whole-body vibration (WBV) platforms are commercially available devices that are used clinically to treat numerous musculoskeletal conditions based on their reported ability to increase bone mineral density and muscle strength. Despite widespread use, there is an alarming lack of understanding of the direct effects of WBV on joint health. Previous work by our lab demonstrated that repeated exposure to WBV using protocols that model those used clinically, induces intervertebral disc (IVD) degeneration and osteoarthritis-like damage in the knee of skeletally mature, male mice of a single outbred strain (CD-1). The present study examined whether exposure to WBV induces similar deleterious effects in a genetically different strain of mouse (C57BL/6).

DESIGN

Male 10-week-old C57BL/6 mice were exposed to vertical sinusoidal WBV for 30 min/day, 5 days/week, for 4 or 8 weeks using previously reported protocols (45 Hz, 0.3 g peak acceleration). Following WBV, joint tissues were examined using histological analysis and gene expression was quantified using real-time PCR (qPCR).

RESULTS

Our analyses show a lack of WBV-induced degeneration in either the knee or IVDs of C57BL/6 mice exposed to WBV for 4 or 8 weeks, in direct contrast to the WBV-induced damage previously reported by our lab in CD-1 mice.

CONCLUSIONS

Together with previous studies from our group, the present study demonstrates that the effects of WBV on joint tissues vary in a strain-specific manner. These findings highlight the need to examine genetic or physiological differences that may underlie susceptibility to the deleterious effects of WBV on joint tissues.

Nuclear receptors regulate lipid metabolism and oxidative stress markers in chondrocytes

Abstract

Joint homeostasis failure can result in osteoarthritis (OA). Currently, there are no treatments to alter disease progression in OA, but targeting early changes in cellular behavior has great potential. Recent data show that nuclear receptors contribute to the pathogenesis of OA and could be viable therapeutic targets, but their molecular mechanisms in cartilage are incompletely understood. This study examines global changes in gene expression after treatment with agonists for four nuclear receptor implicated in OA (LXR, PPARδ, PPARγ, and RXR). Murine articular chondrocytes were treated with agonists for LXR, PPARδ, PPARγ, or RXR and underwent microarray, qPCR, and cellular lipid analyses to evaluate changes in gene expression and lipid profile. Immunohistochemistry was conducted to compare two differentially expressed targets (Txnip, Gsta4) in control and cartilage-specific PPARδ knockout mice subjected to surgical destabilization of the medial meniscus (DMM). Nuclear receptor agonists induced different gene expression profiles with many responses affecting lipid metabolism. LXR activation downregulated gene expression of proteases involved in OA, whereas RXR agonism decreased expression of ECM components and increased expression of Mmp13. Functional assays indicate increases in cell triglyceride accumulation after PPARγ, LXR, and RXR agonism but a decrease after PPARδ agonism. PPARδ and RXR downregulate the antioxidant Gsta4, and PPARδ upregulates Txnip. Wild-type, but not PPARδ-deficient mice, display increased staining for Txnip after DMM. Collectively, these data demonstrate that nuclear receptor activation in chondrocytes primarily affects lipid metabolism. In the case of PPARδ, this change might lead to increased oxidative stress, possibly contributing to OA-associated changes.

Key message

Nuclear receptors regulate metabolic genes in chondrocytes.

Nuclear receptors affect triglyceride levels.

PPARδ mediates regulation of oxidative stress markers.

Nuclear receptors are promising therapeutic targets for osteoarthritis.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-016-1501-5) contains supplementary material, which is available to authorized users.

Tumor necrosis factor-α: a key contributor to intervertebral disc degeneration

Intervertebral disc (IVD) degeneration (IDD) is the most common cause leading to low back pain (LBP), which is a highly prevalent, costly, and crippling condition worldwide. Current treatments for IDD are limited to treat the symptoms and do not target the pathophysiology. Tumor necrosis factor-α (TNF-α) is one of the most potent pro-inflammatory cytokines and signals through its receptors TNFR1 and TNFR2. TNF-α is highly expressed in degenerative IVD tissues, and it is deeply involved in multiple pathological processes of disc degeneration, including matrix destruction, inflammatory responses, apoptosis, autophagy, and cell proliferation. Importantly, anti-TNF-α therapy has shown promise for mitigating disc degeneration and relieving LBP. In this review, following a brief description of TNF-α signal transduction, we mainly focus on the expression pattern and roles of TNF-α in IDD, and summarize the emerging progress regarding its inhibition as a promising biological therapeutic approach to disc degeneration and associated LBP. A better understanding will help to develop novel TNF-α-centered therapeutic interventions for degenerative disc disease.

Vibratory stimulation enhances thyroid epithelial cell function

The tissues of the body are routinely subjected to various forms of mechanical vibration, the frequency, amplitude, and duration of which can contribute both positively and negatively to human health. The vocal cords, which are in close proximity to the thyroid, may also supply the thyroid with important mechanical signals that modulate hormone production via mechanical vibrations from phonation. In order to explore the possibility that vibrational stimulation from vocalization can enhance thyroid epithelial cell function, FRTL-5 rat thyroid cells were subjected to either chemical stimulation with thyroid stimulating hormone (TSH), mechanical stimulation with physiological vibrations, or a combination of the two, all in a well-characterized, torsional rheometer-bioreactor. The FRTL-5 cells responded to mechanical stimulation with significantly (p<0.05) increased metabolic activity, significantly (p<0.05) increased ROS production, and increased gene expression of thyroglobulin and sodium-iodide symporter compared to un-stimulated controls, and showed an equivalent or greater response than TSH only stimulated cells. Furthermore, the combination of TSH and oscillatory motion produced a greater response than mechanical or chemical stimulation alone. Taken together, these results suggest that mechanical vibrations could provide stimulatory cues that help maintain thyroid function.

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Thyroid epithelial cells responded to mechanical vibrations similar to those from vocalization.

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This response was equivalent or greater compared to chemical stimulation.

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The combination of mechanical and chemical stimulation was synergistic.

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It may be possible to influence thyroid function with mechanical vibrations.

ISSLS Prize Winner: Vibration Really Does Disrupt the Disc: A Microanatomical Investigation

STUDY DESIGN

Microstructural investigation of vibration-induced disruption of the flexed lumbar disc.

OBJECTIVE

The aim of the study was to explore micro-level structural damage in motion segments subjected to vibration at subcritical peak loads.

SUMMARY OF BACKGROUND DATA

Epidemiological evidence suggests that cumulative whole body vibration may damage the disc and thus play an important role in low back pain. In vitro investigations have produced herniations via cyclic loading (and cyclic with added vibrations as an exacerbating exposure), but offered only limited microstructural analysis.

METHODS

Twenty-nine healthy mature ovine lumbar motion segments flexed 7° and subjected to vibration loading (1300 ± 500 N) in a sinusoidal waveform at 5 Hz to simulate moderately severe physiologic exposure. Discs were tested either in the range of 20,000 to 48,000 cycles (medium dose) or 70,000 to 120,000 cycles (high dose). Damaged discs were analyzed microstructurally.

RESULTS

There was no large drop in displacement over the duration of both vibration doses indicating an absence of catastrophic failure in all tests. The tested discs experienced internal damage that included delamination and disruption to the inner and mid-annular layers as well as diffuse tracking of nucleus material, and involved both the posterior and anterior regions. Less frequent tearing between the inner disc and endplate was also observed. Annular distortions also progressed into a more severe form of damage, which included intralamellar tearing and buckling and obvious strain distortion around the bridging elements within the annular wall.

CONCLUSION

Vibration loading causes delamination and disruption of the inner and mid-annular layers and limited diffuse tracking of nucleus material. These subtle levels of disruption could play a significant role in initiating the degenerative cascade via micro-level disruption leading to cell death and altered nutrient pathways.

LEVEL OF EVIDENCE

5.

Whole-body vibration improves the anti-inflammatory status in elderly subjects through toll-like receptor 2 and 4 signaling pathways

Regular physical exercise has anti-inflammatory effects in elderly subjects. Yet, the inflammatory responses after whole body vibration (WBV) training, a popular exercise paradigm for the elderly, remain to be elucidated. This study assessed the effects of WBV training on the inflammatory response associated with toll-like receptors (TLRs) signaling pathways. Twenty-eight subjects were randomized to a training group (TG) or a control group (CG). TG followed an 8-week WBV training program. Blood samples were obtained before and after the training period in both groups. Peripheral blood mononuclear cells were isolated, and mRNA and protein levels of makers involved in the TLR2/TLR4 myeloid differentiation primary response gen 88 (MyD88) and TIR domain-containing adaptor inducing interferon (TRIF)-dependent pathways were analyzed. Plasma TNFα and C-reactive protein levels were also assessed. The WBV program reduced protein expression of TLR2, TLR4, MyD88, p65, TRIF and heat shock protein (HSP) 60, while HSP70 content increased. IL-10 mRNA level and protein concentration were upregulated, and TNFα protein content decreased, after WBV training. Plasma concentration of C-reactive protein and TNFα decreased in the TG. The current data suggest WBV may improve the anti-inflammatory status of elderly subjects through an attenuation of MyD88- and TRIF-dependent TLRs signaling pathways.