Decreased physical function and increased pain sensitivity in mice deficient for type IX collagen

The progression of neurovascular features and chemokine signatures of the intervertebral disc with degeneration

Inflammatory cytokine production and de novo neurovascularization have been identified in painful, degenerated intervertebral discs (IVDs). However, the temporal trajectories of these key pathoanatomical features, including the cascade of inflammatory chemokines and neo- vessel and neurite infiltration, and their associations with IVD degeneration, remain relatively unknown. Investigating this process in the caudal mouse IVD enables the opportunity to study the tissue-specific response without confounding inflammatory signaling from neighboring structures. Thus this study aims to define the progression of chemokine production and neurovascular invasion during the IVD degeneration initiated by injury in the caudal spine 3-month-old C57BL6/J mice. Forty-nine IVD-secreted chemokines and matrix metalloproteinases (MMPs) was measured using multiplex ELISA, and the intradiscal infiltrating vessels (endomucin) and nerves (protein-gene-product 9.5) was quantified in the tissue volume using immunohistochemistry. Injury provoked the increase secretion of IL6, CCL2, CCL12, CCL17, CCL20, CCL21, CCL22, CXCL2 and MMP2 proteins. The centrality and structure of inflammatory networks in IVDs evolved over the 12 post-injury weeks, highlighting distinct responses between the acute and chronic phases. Neurites propagated rapidly within 2-weeks post-injury and remained relatively constant until 12-weeks. Vascular vessel length was observed to peak at 4-weeks post-injury and it regressed by 12-weeks. These findings identified the temporal flux of inflammatory chemokines and pain-associated pathoanatomy in a model of IVD degeneration using the mouse caudal spine.

A mouse model of chronic primary pain that integrates clinically relevant genetic vulnerability, stress, and minor injury

Chronic primary pain conditions (CPPCs) affect over 100 million Americans, predominantly women. They remain ineffectively treated, in large part because of a lack of valid animal models with translational relevance. Here, we characterized a CPPC mouse model that integrated clinically relevant genetic (catechol-O-methyltransferase; COMT knockdown) and environmental (stress and injury) factors. Compared with wild-type mice, Comt+/- mice undergoing repeated swim stress and molar extraction surgery intervention exhibited pronounced multisite body pain and depressive-like behavior lasting >3 months. Comt+/- mice undergoing the intervention also exhibited enhanced activity of primary afferent nociceptors innervating hindpaw and low back sites and increased plasma concentrations of norepinephrine and pro-inflammatory cytokines interleukin-6 (IL-6) and IL-17A. The pain and depressive-like behavior were of greater magnitude and longer duration (≥12 months) in females versus males. Furthermore, increases in anxiety-like behavior and IL-6 were female-specific. The effect of COMT genotype × stress interactions on pain, IL-6, and IL-17A was validated in a cohort of 549 patients with CPPCs, demonstrating clinical relevance. Last, we assessed the predictive validity of the model for analgesic screening and found that it successfully predicted the lack of efficacy of minocycline and the CB2 agonist GW842166X, which were effective in spared nerve injury and complete Freund's adjuvant models, respectively, but failed in clinical trials. Yet, pain in the CPPC model was alleviated by the beta-3 adrenergic antagonist SR59230A. Thus, the CPPC mouse model reliably recapitulates clinically and biologically relevant features of CPPCs and may be implemented to test underlying mechanisms and find new therapeutics.

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.

Impacts of aging on murine cartilage biomechanics and chondrocyte in situ calcium signaling

Aging is the most prominent risk factor for osteoarthritis onset, but the etiology of aging-associated cartilage degeneration is not fully understood. Recent studies by Guilak and colleagues have highlighted the crucial roles of cell-matrix interactions in cartilage homeostasis and disease. This study thus quantified aging-associated changes in cartilage biomechanics and chondrocyte intracellular calcium signaling, [Ca2+]i, activities in wild-type mice at 3, 12 and 22 months of age. In aged mice, articular cartilage exhibits reduced staining of sulfated glycosaminoglycans (sGAGs), indicating decreased aggrecan content. On cartilage surface, collagen fibrils undergo significant thickening while retaining their transverse isotropic architecture, and exhibit signs of fibril crimping in the 22-month group. These compositional and structural changes contribute to a significant decrease in cartilage modulus at 22 months of age (0.55 ± 0.25 MPa, mean ± 95 % CI, n = 8) relative to those at 3 and 12 months (1.82 ± 0.48 MPa and 1.45 ± 0.46 MPa, respectively, n ≥ 8). Despite the decreases in sGAG content and tissue modulus, chondrocytes do not exhibit significantly demoted [Ca2+]i activities in situ, in both physiological (isotonic) and osmotically instigated (hypo- and hypertonic) conditions. At 12 months of age, there exists a sub-population of chondrocytes with hyper-active [Ca2+]i responses under hypotonic stimuli, possibly indicating a phenotypic shift of chondrocytes during aging. Together, these results yield new insights into aging-associated biomechanical and mechanobiological changes of murine cartilage, providing a benchmark for elucidating the molecular mechanisms of age-related changes in cell-matrix interactions.

Rodent models of knee osteoarthritis for pain research

Osteoarthritis (OA) is a chronic degenerative joint disease and a leading cause of disability worldwide. Pain is the main symptom, yet no current treatment can halt disease progression or effectively provide symptomatic relief. Numerous animal models have been described for studying OA and some for the associated OA pain. This review aims to update on current models used for studying OA pain, focusing on mice and rats. These models include surgical, chemical, mechanical, and spontaneous OA models. The impact of sex and age will also be addressed in the context of OA modelling. Although no single animal model has been shown ideal for studying OA pain, increased efforts to phenotype OA will likely impact the choice of models for pre-clinical and basic research studies.

In vivo methodologies to assist preclinical development of topical fixed-dose combinations for pain management

The combination in a fixed dose of two or more active pharmaceutical ingredients in the same pharmaceutical dosage form is an approach that has been used successfully in the treatment of several pathologies, including pain. In the preclinical development of a topical fixed-dose combination product with analgesic and anti-inflammatory activities for pain management, the main objective is to establish the nature of the interaction between the different active pharmaceutical ingredients while obtaining data on the medicinal product safety and efficacy. Despite the improvement of in vitro assays, animal models remain a fundamental strategy to characterise the interaction, efficacy and safety of active pharmaceutical ingredients at the physiological level, which cannot be reached by in vitro assays. Thus, the main goal of this review is to systematise the available animal models to evaluate the efficacy and safety of a new fixed-dose combination product for topical administration indicated for pain management. Particular emphasis is given to animal models that are accepted for regulatory purposes.

Mouse Models of Osteoarthritis: A Summary of Models and Outcomes Assessment

Osteoarthritis (OA) is a multidimensional health problem and a common chronic disease. It has a substantial impact onpatient quality of life and is a common cause of pain and mobility issues in older adults. The functional limitations, lack of curative treatments, and cost to society all demonstrate the need for translational and clinical research. The use of OA models in mice is important for achieving a better understanding of the disease. Models with clinical relevance are needed to achieve 2 main goals: to assess the impact of the OA disease (pain and function) and to study the efficacy of potential treatments. However, few OA models include practical strategies for functional assessment of the mice. OA signs in mice incorporate complex interrelations between pain and dysfunction. The current review provides a comprehensive compilation of mousemodels of OA and animal evaluations that include static and dynamic clinical assessment of the mice, merging evaluationof pain and function by using automatic and noninvasive techniques. These new techniques allow simultaneous recordingof spontaneous activity from thousands of home cages and also monitor environment conditions. Technologies such as videographyand computational approaches can also be used to improve pain assessment in rodents but these new tools must first be validated experimentally. An example of a new tool is the digital ventilated cage, which is an automated home-cage monitor that records spontaneous activity in the cages.

Posttraumatic Osteoarthritis Damage in Mice: From Histological and Micro-Computed Tomodensitometric Changes to Gait Disturbance

OBJECTIVES

Osteoarthritis is a painful joint disease responsible for walking impairment. Its quantitative assessment by gait analysis in mice may be a relevant and noninvasive strategy to assess the disease severity. In this study, we aimed to determine the severity of osteoarthritis at the tissular and gait levels in unilateral and bilateral posttraumatic murine osteoarthritis.

METHODS

Twenty-four C57BL/6 male mice were randomly assigned to 3 groups (n = 8/group): controls, unilateral surgery, and bilateral surgery. Posttraumatic osteoarthritis was induced unilaterally or bilaterally by destabilization of the medial meniscus. Gait analysis was performed weekly with the CatWalkTM XT system until the 16th week after surgery. After animal sacrifices, histological and micro-computed tomographic assessment was performed.

RESULTS

Operated knees showed a significant increase in the histological score compared with controls (P < 0.001). Calcified anterior medial meniscal bone volume was higher on the ipsilateral side after unilateral destabilization of the medial meniscus (P < 0.001) and on both sides after bilateral intervention (P < 0.01). One week after surgery, the mice mean speed decreased significantly in both operated groups (P < 0.001 and P < 0.05). In the unilateral group, a significant increase in the contralateral hind print area appeared from week 4 to week 16.

CONCLUSIONS

While bilateral destabilization of the medial meniscus induced no detectable gait modification except 1 week after surgery, unilateral model was responsible for a gait disturbance on the contralateral side. Further studies are needed to better define the place of the CatWalkTM in the evaluation of mouse models of osteoarthritis.

Chronic subacromial impingement leads to supraspinatus muscle functional and morphological changes: Evaluation in a murine model

Muscle atrophy and fatty infiltration have been directly correlated with higher rates of incomplete or failed healing following surgical repair of the rotator cuff. The purpose of this study was to evaluate clinically relevant functional and morphological changes in the supraspinatus muscle at various time points in this model of rotator cuff tendinopathy. Subacromial impingement was induced in 47, male C57BL/6 mice (total 94 limbs) by implantation of a metal clip in the subacromial space. Specimens were evaluated at 4, 6, and 12 weeks postoperatively. Gait analysis was used to measure various kinematic parameters. Supraspinatus muscle wet weight, histology, and quantitative reverse-transcription polymerase chain reaction analysis of genes related to muscle atrophy and adipogenesis were performed to characterize the structural, cellular, and molecular changes. Muscle atrophy and fatty infiltration was evident beginning at 6 weeks, with progression out to 12 weeks. Gait analysis identified significant functional changes in many aspects of gait and abnormal stance tracing as early as 4 weeks, verifying alterations in upper extremity function. We have demonstrated that clinically relevant changes to the supraspinatus muscle are seen starting 6 weeks after induction of subacromial impingement. Furthermore, the gait analysis provides key functional outcome measurements that may be useful for future evaluation of new therapeutic strategies.

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.

Primary Osteoarthritis Early Joint Degeneration Induced by Endoplasmic Reticulum Stress Is Mitigated by Resveratrol

Increasing numbers of people are living with osteoarthritis (OA) due to aging and obesity, creating an urgent need for effective treatment and preventions. Two top risk factors for OA, age and obesity, are associated with endoplasmic reticulum (ER) stress. The I-ERS mouse, an ER stress-driven model of primary OA, was developed to study the role of ER stress in primary OA susceptibility. The I-ERS mouse has the unique ability to induce ER stress in healthy adult articular chondrocytes and cartilage, driving joint degeneration that mimics early primary OA. In this study, ER stress-induced damage occurred gradually and stimulated joint degeneration with OA characteristics including increased matrix metalloproteinase activity, inflammation, senescence, chondrocyte death, decreased proteoglycans, autophagy block, and gait dysfunction. Consistent with human OA, intense exercise hastened and increased the level of ER stress-induced joint damage. Notably, loss of a critical ER stress response protein (CHOP) largely ameliorated ER stress-stimulated OA outcomes including preserving proteoglycan content, reducing inflammation, and relieving autophagy block. Resveratrol diminished ER stress-induced joint degeneration by decreasing CHOP, TNFα, IL-1β, MMP-13, pS6, number of TUNEL-positive chondrocytes, and senescence marker p16 INK4a. The finding, that a dietary supplement can prevent ER stressed-induced joint degeneration in mice, provides a preclinical foundation to potentially develop a prevention strategy for those at high risk to develop OA.

Intra-articular collagenase in the spinal facet joint induces pain, DRG neuron dysregulation and increased MMP-1 absent evidence of joint destruction

Degeneration is a hallmark of painful joint disease and is mediated by many proteases that degrade joint tissues, including collagenases. We hypothesized that purified bacterial collagenase would initiate nociceptive cascades in the joint by degrading the capsular ligament's matrix and activating innervating pain fibers. Intra-articular collagenase in the rat facet joint was investigated for its effects on behavioral sensitivity, joint degeneration, and nociceptive pathways in the peripheral and central nervous systems. In parallel, a co-culture collagen gel model of the ligament was used to evaluate effects of collagenase on microscale changes to the collagen fibers and embedded neurons. Collagenase induced sensitivity within one day, lasting for 3 weeks (p < 0.001) but did not alter ligament structure, cartilage health, or chondrocyte homeostasis. Yet, nociceptive mediators were increased in the periphery (substance P, pERK, and MMP-1; p ≤ 0.039) and spinal cord (substance P and MMP-1; p ≤ 0.041). The collagen loss (p = 0.008) induced by exposing co-cultures to collagenase was accompanied by altered neuronal activity (p = 0.002) and elevated neuronal MMP-1 (p < 0.001), suggesting microscale collagen degradation mediates sensitivity in vivo. The induction of sustained sensitivity and nociception without joint damage may explain the clinical disconnect in which symptomatic joint pain patients present without radiographic evidence of joint destruction.

Males and females exhibit distinct relationships between intervertebral disc degeneration and pain in a rat model

Back pain is linked to intervertebral disc (IVD) degeneration, but clinical studies show the relationship is complex. This study assessed whether males and females have distinct relationships between IVD degeneration and pain using an in vivo rat model. Forty-eight male and female Sprague-Dawley rats had lumbar IVD puncture or sham surgery. Six weeks after surgery, IVDs were evaluated by radiologic IVD height, histological grading, and biomechanical testing. Pain was assessed by von Frey assay and dorsal root ganglia (DRG) expression of Calca and Tac1 genes. Network analysis visualized which measures of IVD degeneration most related to pain by sex. In both females and males, annular puncture induced structural IVD degeneration, but functional biomechanical properties were similar to sham. Females and males had distinct differences in mechanical allodynia and DRG gene expression, even though sex differences in IVD measurements were limited. Network analysis also differed by sex, with more associations between annular puncture injury and pain in the male network. Sex differences exist in the interactions between IVD degeneration and pain. Limited correlation between measures of pain and IVD degeneration highlights the need to evaluate pain or nociception in IVD degeneration models to better understand nervous system involvement in discogenic pain.

Factors affecting the reliability of behavioral assessments for rodent osteoarthritis models

The translational value of osteoarthritis (OA) models is often debated because numerous studies have shown that animal models frequently fail to predict the efficacy of therapies in humans. In part, this failing may be due to the paucity of preclinical studies that include behavioral assessments in their metrics. Behavioral assessments of animal OA models can provide valuable data on the pain and disability associated with disease-sequelae of significant clinical relevance. Clinical definitions of efficacy for OA therapeutics often center on their palliative effects. Thus, the widespread inclusion of behaviors indicative of pain and disability in preclinical animal studies may contribute to greater success identifying clinically relevant interventions. Unfortunately, studies that include behavioral assays still frequently encounter pitfalls in assay selection, protocol consistency, and data/methods transparency. Targeted selection of behavioral assays, with consideration of the array of clinical OA phenotypes and the limitations of individual behavioral assays, is necessary to identify clinically relevant outcomes in OA animal models appropriately. Furthermore, to facilitate accurate comparisons across research groups and studies, it is necessary to improve the transparency of methods. Finally, establishing agreed-upon and clear definitions of behavioral data will reduce the convolution of data both within and between studies. Improvement in these areas is critical to the continued benefit of preclinical animal studies as translationally relevant data in OA research. As such, this review highlights the current state of behavioral analyses in preclinical OA models.

Correlation network analysis shows divergent effects of a long-term, high-fat diet and exercise on early stage osteoarthritis phenotypes in mice

BACKGROUND

Obesity increases knee osteoarthritis (OA) risk through metabolic, inflammatory, and biomechanical factors, but how these systemic and local mediators interact to drive OA pathology is not well understood. We tested the effect of voluntary running exercise after chronic diet-induced obesity on knee OA-related cartilage and bone pathology in mice. We then used a correlation-based network analysis to identify systemic and local factors associated with early-stage knee OA phenotypes among the different diet and exercise groups.

METHODS

Male C57BL/6J mice were fed a defined control (10% kcal fat) or high fat (HF) (60% kcal fat) diet from 6 to 37 weeks of age. At 25 weeks, one-half of the mice from each diet group were housed in cages with running wheels for the remainder of the study. Histology, micro computed tomography, and magnetic resonance imaging were used to evaluate changes in joint tissue structure and OA pathology. These local variables were then compared to systemic metabolic (body mass, body fat, and glucose tolerance), inflammatory (serum adipokines and inflammatory mediators), and functional (mechanical tactile sensitivity and grip strength) outcomes using a correlation-based network analysis. Diet and exercise effects were evaluated by two-way analysis of variance.

RESULTS

An HF diet increased the infrapatellar fat pad size and posterior joint osteophytes, and wheel running primarily altered the subchondral cortical and trabecular bone. Neither HF diet nor exercise altered average knee cartilage OA scores compared to control groups. However, the coefficient of variation was ≥25% for many outcomes, and some mice in both diet groups developed moderate OA (≥33% maximum score). This supported using correlation-based network analyses to identify systemic and local factors associated with early-stage knee OA phenotypes. In wheel-running cohorts, an HF diet reduced the network size compared to the control diet group despite similar running distances, suggesting that diet-induced obesity dampens the effects of exercise on systemic and local OA-related factors. Each of the 4 diet and activity groups showed mostly unique networks of local and systemic factors correlated with early-stage knee OA.

CONCLUSION

Despite minimal group-level effects of chronic diet-induced obesity and voluntary wheel running on knee OA pathology under the current test durations, diet and exercise substantially altered the relationships among systemic and local variables associated with early-stage knee OA. These results suggest that distinct pre-OA phenotypes may exist prior to the development of disease.

Altered rodent gait characteristics after ~35 days in orbit aboard the International Space Station

The long-term adaptations to microgravity and other spaceflight challenges within the confines of a spacecraft, and readaptations to weight-bearing upon reaching a destination, are unclear. While post-flight gait change in astronauts have been well documented and reflect multi-system deficits, no data from rodents have been collected. Thus, the purpose of this study was to evaluate gait changes in response to spaceflight. A prospective collection of gait data was collected on 3 groups of mice: those who spent~35 days in orbit (FLIGHT) aboard the International Space Station (ISS); a ground-based control with the same habitat conditions as ISS (Ground Control; GC); and a vivarium control with typical rodent housing conditions (VIV). Pre-flight and post-flight gait measurements were conducted utilizing an optimized and portable gait analysis system (DigiGait, Mouse Specifics, Inc). The total data acquisition time for gait patterns of FLIGHT and control mice was 1.5-5 min/mouse, allowing all 20 mice per group to be assessed in less than an hour. Patterns of longitudinal gait changes were observed in the hind limbs and the forelimbs of the FLIGHT mice after ~35 days in orbit; few differences were observed in gait characteristics within the GC and VIV controls from the initial to the final gait assessment, and between groups. For FLIGHT mice, 12 out of 18 of the evaluated gait characteristics in the hind limbs were significantly changed, including: stride width variability; stride length and variance; stride, swing, and stance duration; paw angle and area at peak stance; and step angle, among others. Gait characteristics that decreased included stride frequency, and others. Moreover, numerous forelimb gait characteristics in the FLIGHT mice were changed at post-flight measures relative to pre-flight. This rapid DigiGait gait measurement tool and customized spaceflight protocol is useful for providing preliminary insight into how spaceflight could affect multiple systems in rodents in which deficits are reflected by altered gait characteristics.

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.

Pros and cons of mouse models for studying osteoarthritis

Osteoarthritis (OA) is one of the most common chronic conditions in the world today. It results in breakdown of cartilage in joints and causes the patient to experience intense pain and even disability. The pathophysiology of OA is not fully understood; therefore, there is currently no cure for OA. Many researchers are investigating the pathophysiology of the disease and attempting to develop methods to alleviate the symptoms or cure the OA entirely using animal models. Most studies on OA use animal models; this is necessary as the disease develops very slowly in humans and presents differently in each patient. This makes it difficult to effectively study the progression of osteoarthritis. Animal models can be spontaneous, in which OA naturally occurs in the animal. Genetic modifications can be used to make the mice more susceptible to developing OA. Osteoarthritis can also be induced via surgery, chemical injections, or non-invasive trauma. This review aims to describe animal models of inducing osteoarthritis with a focus on the models used on mice and their advantages and disadvantages that each model presents.

Models of Disease

Osteochondral (OC) lesions are a major cause of chronic musculoskeletal pain and functional disability, which reduces the quality of life of the patients and entails high costs to the society. Currently, there are no effective treatments, so in vitro and in vivo disease models are critically important to obtain knowledge about the causes and to develop effective treatments for OC injuries. In vitro models are essential to clarify the causes of the disease and the subsequent design of the first barrier to test potential therapeutics. On the other hand, in vivo models are anatomically more similar to humans allowing to reproduce the pattern and progression of the lesion in a controlled scene and offering the opportunity to study the symptoms and responses to new treatments. Moreover, in vivo models are the most suitable preclinical model, being a fundamental and a mandatory step to ensure the successful transfer to clinical trials. Both in vitro and in vitro models have a number of advantages and limitation, and the choice of the most appropriate model for each study depends on many factors, such as the purpose of the study, handling or the ease to obtain, and cost, among others. In this chapter, we present the main in vitro and in vivo OC disease models that have been used over the years in the study of origin, progress, and treatment approaches of OC defects.

Interleukin-17 Can Induce Osteoarthritis in Rabbit Knee Joints Similar to Hulth's Method

Interleukin-17 (IL-17) is closely related to osteoarthritis (OA), but animal studies that employ IL-17 to induce OA are currently lacking. Therefore, this study evaluated the effect of IL-17 in the rabbit knee joint. The right knees served as the control group. The left knees were divided randomly into 4 groups: a Hulth group and 3 IL-17 groups (1-ng, 10-ng, and 50-ng groups). OA was induced in the Hulth group using Hulth's method. The IL-17 groups were injected with 1, 10, or 50 ng of IL-17 as indicated. Specimens were collected at 72 h, 1 week, 3 weeks, 6 weeks, and 12 weeks after surgery or the last injection. Subsequently, the following experiments were conducted: X-ray analysis, histological evaluation, and polymerase chain reaction (PCR) analysis of the mRNA expression levels of cartilage degeneration-related markers. At 12 weeks, like the Hulth group, the 10-ng and 50-ng IL-17 groups displayed typical manifestations of OA. The X-ray results, histological scores, and mRNA expression levels showed statistically significant differences between the control group and the 10-ng and 50-ng IL-17 groups. In sum, injecting 10 ng of IL-17 into the rabbit knee joint can induce OA similar to OA induced by Hulth's method.

Automated Gait Analysis Through Hues and Areas (AGATHA): A Method to Characterize the Spatiotemporal Pattern of Rat Gait

While rodent gait analysis can quantify the behavioral consequences of disease, significant methodological differences exist between analysis platforms and little validation has been performed to understand or mitigate these sources of variance. By providing the algorithms used to quantify gait, open-source gait analysis software can be validated and used to explore methodological differences. Our group is introducing, for the first time, a fully-automated, open-source method for the characterization of rodent spatiotemporal gait patterns, termed Automated Gait Analysis Through Hues and Areas (AGATHA). This study describes how AGATHA identifies gait events, validates AGATHA relative to manual digitization methods, and utilizes AGATHA to detect gait compensations in orthopaedic and spinal cord injury models. To validate AGATHA against manual digitization, results from videos of rodent gait, recorded at 1000 frames per second (fps), were compared. To assess one common source of variance (the effects of video frame rate), these 1000 fps videos were re-sampled to mimic several lower fps and compared again. While spatial variables were indistinguishable between AGATHA and manual digitization, low video frame rates resulted in temporal errors for both methods. At frame rates over 125 fps, AGATHA achieved a comparable accuracy and precision to manual digitization for all gait variables. Moreover, AGATHA detected unique gait changes in each injury model. These data demonstrate AGATHA is an accurate and precise platform for the analysis of rodent spatiotemporal gait patterns.

Gait analysis methods for rodent models of arthritic disorders: reviews and recommendations

Gait analysis is a useful tool to understand behavioral changes in preclinical arthritis models. While observational scoring and spatiotemporal gait parameters are the most widely performed gait analyses in rodents, commercially available systems can now provide quantitative assessments of spatiotemporal patterns. However, inconsistencies remain between testing platforms, and laboratories often select different gait pattern descriptors to report in the literature. Rodent gait can also be described through kinetic and kinematic analyses, but systems to analyze rodent kinetics and kinematics are typically custom made and often require sensitive, custom equipment. While the use of rodent gait analysis rapidly expands, it is important to remember that, while rodent gait analysis is a relatively modern behavioral assay, the study of quadrupedal gait is not new. Nearly all gait parameters are correlated, and a collection of gait parameters is needed to understand a compensatory gait pattern used by the animal. As such, a change in a single gait parameter is unlikely to tell the full biomechanical story; and to effectively use gait analysis, one must consider how multiple different parameters contribute to an altered gait pattern. The goal of this article is to review rodent gait analysis techniques and provide recommendations on how to use these technologies in rodent arthritis models, including discussions on the strengths and limitations of observational scoring, spatiotemporal, kinetic, and kinematic measures. Recognizing rodent gait analysis is an evolving tool, we also provide technical recommendations we hope will improve the utility of these analyses in the future.

Mouse model of rare TOR1A variant found in sporadic focal dystonia impairs domains affected in DYT1 dystonia patients and animal models

Rare de novo mutations in genes associated with inherited Mendelian disorders are potential contributors to sporadic disease. DYT1 dystonia is an autosomal dominant, early-onset, generalized dystonia associated with an in-frame, trinucleotide deletion (n. delGAG, p. ΔE 302/303) in the Tor1a gene. Here we examine the significance of a rare missense variant in the Tor1a gene (c. 613T>A, p. F205I), previously identified in a patient with sporadic late-onset focal dystonia, by modeling it in mice. Homozygous F205I mice have motor impairment, reduced steady-state levels of TorsinA, altered corticostriatal synaptic plasticity, and prominent brain imaging abnormalities in areas associated with motor function. Thus, the F205I variant causes abnormalities in domains affected in people and/or mouse models with the DYT1 Tor1a mutation (ΔE). Our findings establish the pathological significance of the F205I Tor1a variant and provide a model with both etiological and phenotypic relevance to further investigate dystonia mechanisms.

CD146+ mesenchymal stem cells display greater therapeutic potential than CD146- cells for treating collagen-induced arthritis in mice

Background

The characteristics and therapeutic potential of subtypes of mesenchymal stem cells (MSCs) are largely unknown. In this study, CD146⁺ and CD146^– MSCs were separated from human umbilical cords, and their effects on regulatory T cells (Tregs), Th17 cells, chondrogenesis, and osteogenesis were investigated.

Methods

Flow cytometry was used to quantify IL-6 and TGF-β1 expressed on CD146⁺ and CD146^– MSCs. The therapeutic potential of both subpopulations was determined by measuring the clinical score and joint histology after intra-articular (IA) transfer of the cells into mice with collagen-induced arthritis (CIA).

Results

Compared with CD146^– MSCs, CD146⁺ MSCs expressed less IL-6 and had a significantly greater effect on chondrogenesis. After T lymphocyte activation, Th17 cells were activated when exposed to CD146^– cells but not when exposed to CD146⁺ cells both in vitro and in vivo. IA injection of CD146⁺ MSCs attenuated the progression of CIA. Immunohistochemistry showed that only HLA-A⁺ CD146⁺ cells were detected in the cartilage of CIA mice. These cells may help preserve proteoglycan expression.

Conclusions

This study suggests that CD146⁺ cells have greater potency than CD146^– cells for cartilage protection and can suppress Th17 cell activation. These data suggest a potential therapeutic application for CD146⁺ cells in treating inflammatory arthritis.

Animal models of osteoarthritis: classification, update, and measurement of outcomes

Osteoarthritis (OA) is one of the most commonly occurring forms of arthritis in the world today. It is a debilitating chronic illness causing pain and immense discomfort to the affected individual. Significant research is currently ongoing to understand its pathophysiology and develop successful treatment regimens based on this knowledge. Animal models have played a key role in achieving this goal. Animal models currently used to study osteoarthritis can be classified based on the etiology under investigation, primary osteoarthritis, and post-traumatic osteoarthritis, to better clarify the relationship between these models and the pathogenesis of the disease. Non-invasive animal models have shown significant promise in understanding early osteoarthritic changes. Imaging modalities play a pivotal role in understanding the pathogenesis of OA and the correlation with pain. These imaging studies would also allow in vivo surveillance of the disease as a function of time in the animal model. This review summarizes the current understanding of the disease pathogenesis, invasive and non-invasive animal models, imaging modalities, and pain assessment techniques in the animals.

Ground reaction forces are more sensitive gait measures than temporal parameters in rodents following rotator cuff injury

Gait analysis is a quantitative, non-invasive technique that can be used to investigate functional changes in animal models of musculoskeletal disease. Changes in ground reaction forces following injury have been observed that coincide with differences in tissue mechanical and histological properties during healing. However, measurement of these kinetic gait parameters can be laborious compared to the simpler and less time-consuming analysis of temporal gait parameters alone. We compared the sensitivity of temporal and kinetic gait parameters in detecting functional changes following rotator cuff injury in rats. Although these parameters were strongly correlated, temporal measures were unable to detect greater than 50% of the functional gait differences between injured and uninjured animals identified simultaneously by ground reaction forces. Regression analysis was used to predict ground reaction forces from temporal parameters. This model improved the ability of temporal parameters to identify known functional changes, but only when these differences were large in magnitude (i.e., between injured vs. uninjured animals, but not between different post-operative treatments). The results of this study suggest that ground reaction forces are more sensitive measures of limb/joint function than temporal parameters following rotator cuff injury in rats. Therefore, although gait analysis systems without force plates are typically efficient and easy to use, they may be most appropriate for use when major functional changes are expected.

Spatiotemporal gait compensations following medial collateral ligament and medial meniscus injury in the rat: correlating gait patterns to joint damage

Introduction

After transection of the medial collateral ligament and medial meniscus (MCLT + MMT) in the rat, focal cartilage lesions develop over 4–6 weeks; however, sham surgery (MCLT alone) does not result in cartilage damage over a similar period. Thus, comparison of MCLT + MMT with the MCLT sham group offers an opportunity to investigate behavioral modifications related to focal cartilage and meniscus damage in the rat.

Methods

MCLT or MCLT + MMT surgery was performed in the right knees of male Lewis rats, with spatiotemporal gait patterns and hind limb sensitivity assessed at 1, 2, 4, and 6 weeks postsurgery (n = 8 rats per group per time point, n = 64 total). After the animals were euthanized, Histology was performed to assess joint damage.

Results

MCLT + MMT animals had unilateral gait compensations at early time points, but by week 6 bilateral gait compensations had developed in both the MCLT sham and MCLT + MMT groups. Conversely, heightened tactile sensitivity was detected in both MCLT sham and MCLT + MMT animals at week 1, but only the MCLT + MMT animals maintained heightened sensitivity to week 6. Cartilage lesions were found in the MCLT + MMT group but not in the MCLT sham group. Correlations could be identified between joint damage and gait changes in MCLT + MMT animals; however, the same gait changes were found with MCLT sham animals despite a lack of joint damage.

Conclusions

Combined, our data highlight a common conundrum in osteoarthritis (OA) research: Some behavioral changes correlate to cartilage damage in the OA group, but the same changes can be identified in non-OA controls. Of the behavioral changes detected, allodynia was maintained in MCLT + MMT animals but not in the MCLT sham group. However, the correlation between cartilage damage and hind limb sensitivity is relatively weak (R = −0.4498), and the range of sensitivity measures overlaps between groups. The factors driving gait abnormalities in MCLT and MCLT + MMT animals also remain uncertain. The gait modifications are similar between groups and do not appear until weeks after surgery, despite cartilage damage being focused in the MCLT + MMT group. Combined, our data highlight the need to evaluate the links between noncartilage changes and behavioral changes following joint injury in the rat.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0791-2) contains supplementary material, which is available to authorized users.

Gait analysis methods for rodent models of osteoarthritis

Patients with osteoarthritis (OA) primarily seek treatment due to pain and disability, yet the primary endpoints for rodent OA models tend to be histological measures of joint destruction. The discrepancy between clinical and preclinical evaluations is problematic, given that radiographic evidence of OA in humans does not always correlate to the severity of patient-reported symptoms. Recent advances in behavioral analyses have provided new methods to evaluate disease sequelae in rodents. Of particular relevance to rodent OA models are methods to assess rodent gait. While obvious differences exist between quadrupedal and bipedal gait sequences, the gait abnormalities seen in humans and in rodent OA models reflect similar compensatory behaviors that protect an injured limb from loading. The purpose of this review is to describe these compensations and current methods used to assess rodent gait characteristics, while detailing important considerations for the selection of gait analysis methods in rodent OA models.

Novel insights into the function and dynamics of extracellular matrix in liver fibrosis

Emerging evidence suggests that altered components and posttranslational modifications of proteins in the extracellular matrix (ECM) may both initiate and drive disease progression. The ECM is a complex grid consisting of multiple proteins, most of which play a vital role in containing the essential information needed for maintenance of a sophisticated structure anchoring the cells and sustaining normal function of tissues. Therefore, the matrix itself may be considered as a paracrine/endocrine entity, with more complex functions than previously appreciated. The aims of this review are to 1) explore key structural and functional components of the ECM as exemplified by monogenetic disorders leading to severe pathologies, 2) discuss selected pathological posttranslational modifications of ECM proteins resulting in altered functional (signaling) properties from the original structural proteins, and 3) discuss how these findings support the novel concept that an increasing number of components of the ECM harbor signaling functions that can modulate fibrotic liver disease. The ECM entails functions in addition to anchoring cells and modulating their migratory behavior. Key ECM components and their posttranslational modifications often harbor multiple domains with different signaling potential, in particular when modified during inflammation or wound healing. This signaling by the ECM should be considered a paracrine/endocrine function, as it affects cell phenotype, function, fate, and finally tissue homeostasis. These properties should be exploited to establish novel biochemical markers and antifibrotic treatment strategies for liver fibrosis as well as other fibrotic diseases.

Subchondral bone in osteoarthritis: insight into risk factors and microstructural changes

Osteoarthritis (OA) is a major cause of disability in the adult population. As a progressive degenerative joint disorder, OA is characterized by cartilage damage, changes in the subchondral bone, osteophyte formation, muscle weakness, and inflammation of the synovium tissue and tendon. Although OA has long been viewed as a primary disorder of articular cartilage, subchondral bone is attracting increasing attention. It is commonly reported to play a vital role in the pathogenesis of OA. Subchondral bone sclerosis, together with progressive cartilage degradation, is widely considered as a hallmark of OA. Despite the increase in bone volume fraction, subchondral bone is hypomineralized, due to abnormal bone remodeling. Some histopathological changes in the subchondral bone have also been detected, including microdamage, bone marrow edema-like lesions and bone cysts. This review summarizes basic features of the osteochondral junction, which comprises subchondral bone and articular cartilage. Importantly, we discuss risk factors influencing subchondral bone integrity. We also focus on the microarchitectural and histopathological changes of subchondral bone in OA, and provide an overview of their potential contribution to the progression of OA. A hypothetical model for the pathogenesis of OA is proposed.

Modifications of gait as predictors of natural osteoarthritis progression in STR/Ort mice

Objective

Osteoarthritis (OA) is a common chronic disease for which disease-modifying therapies are not currently available. Studies to seek new targets for slowing the progress of OA rely on mouse models, but these do not allow for longitudinal monitoring of disease development. This study was undertaken to determine whether gait can be used to measure disease severity in the STR/Ort mouse model of spontaneous OA and whether gait changes are related to OA joint pain.

Methods

Gait was monitored using a treadmill-based video system. Correlations between OA severity and gait at 3 treadmill speeds were assessed in STR/Ort mice. Gait and pain behaviors of STR/Ort mice and control CBA mice were analyzed longitudinally, with monthly assessments.

Results

The best speed to identify paw area changes associated with OA severity in STR/Ort mice was found to be 17 cm · seconds⁻¹. Paw area was modified with age in CBA and STR/Ort mice, but this began earlier in STR/Ort mice and correlated with the onset of OA at 20 weeks of age. In addition, task noncompliance appeared at 20 weeks. Surprisingly, STR/Ort mice did not show any signs of pain with OA development, even when treated with the opioid antagonist naloxone, but did exhibit normal pain behaviors in response to complete Freund's adjuvant–induced arthritis.

Conclusion

The present results identify an animal model in which OA severity and OA pain can be studied in isolation from one another. The findings suggest that paw area and treadmill noncompliance may be useful tools to longitudinally monitor nonpainful OA development in STR/Ort mice. This will help in providing a noninvasive means of assessing new therapies to slow the progression of OA.

A comparison of DigiGait™ and TreadScan™ imaging systems: assessment of pain using gait analysis in murine monoarthritis

Purpose

Carrageenan-induced arthritis is a painful acute arthritis model that is simple to induce, with peak pain and inflammation occurring at about 3 hours. This arthritis model can be evaluated using semiquantitative evoked or non-evoked pain scoring systems. These measures are subjective and are often time- and labor-intensive. It would be beneficial to utilize quantitative, nonsubjective evaluations of pain with rapid assessment tools. We sought to compare the DigiGait™ and TreadScan™ systems and to validate the two gait analysis platforms for detection of carrageenan-induced monoarthritis pain and analgesic response through changes in gait behavior.

Methods

Non-arthritic mice and carrageenan-induced arthritic mice with and without analgesia were examined. A painful arthritic knee was produced by injection of 3% carrageenan into the knee joint of adult mice. Analgesic-treated mice were injected subcutaneously with 0.015 mg/mL (0.5 mg/kg) buprenorphine. Five-second videos were captured on the DigiGait™ or TreadScan™ system and, after calculating gait parameters, were compared using student’s unpaired t-test.

Results

We found the DigiGait™ system consistently measured significantly longer stride measures (swing time, stance time, and stride time) than did TreadScan™. Both systems’ measures of variability were equal. Reproducibility was inconsistent on both systems. While both systems detected alterations in some gait measures after carrageenan injection, none of the alterations were seen with both systems. Only the TreadScan™ detected normalization of gait measures after analgesia, but the system could not detect normalization across all measures that altered due to arthritis pain. Time spent on analysis was dependent on operator experience.

Conclusion

Neither the DigiGait™ nor TreadScan™ system was useful for measuring changes in pain behaviors or analgesic responses in acute inflammatory monoarthritic mice.

Enhancement of neuromuscular dynamics and strength behavior using extremely low magnitude mechanical signals in mice

Exercise in general, and mechanical signals in particular, help ameliorate the neuromuscular symptoms of aging and possibly other neurodegenerative disorders by enhancing muscle function. To better understand the salutary mechanisms of such physical stimuli, we evaluated the potential for low intensity mechanical signals to promote enhanced muscle dynamics. The effects of daily brief periods of low intensity vibration (LIV) on neuromuscular functions and behavioral correlates were assessed in mice. Physiological analysis revealed that LIV increased isometric force production in semitendinosus skeletal muscle. This effect was evident in both young and old mice. Isometric force recordings also showed that LIV reduced the fatiguing effects of intensive synaptic muscle stimulation. Furthermore, LIV increased evoked neurotransmitter release at neuromuscular synapses but had no effect on spontaneous end plate potential amplitude or frequency. In behavioral studies, LIV increased mouse grip strength and potentiated initial motor activity in a novel environment. These results provide evidence for the efficacy of LIV in producing changes in the neuromuscular system that translate into performance gains at a behavioral scale.

A pilot trial of intravenous pamidronate for chronic low back pain

Intravenous (i.v.) bisphosphonates relieve pain in conditions such as Paget's disease of bone, metastatic bone disease, and multiple myeloma. Based on positive findings from a prior case series, we conducted a randomized placebo-controlled study to assess the analgesic effect of i.v. pamidronate in subjects with chronic low back pain (CLBP) and evidence of degenerative disease of the spine. Four groups of 11 subjects (7 active, 4 placebo) were enrolled at escalating dose levels of 30, 60, 90, and 180 mg pamidronate (the latter administered as two 90 mg infusions). Primary outcomes were safety and change from baseline in average daily pain scores, recorded at 1, 2, 3, and 6 months postinfusion using electronic diaries. Secondary outcomes included responder rate, daily worst pain, and pain-related interference with daily function. There were no pamidronate-related serious adverse events or other significant safety findings. A statistically significant overall treatment difference in pain scores was observed, with clinically meaningful effects persisting for 6 months in the 180 mg pamidronate group. Least squares mean changes in daily average pain score were -1.39 (SE=0.43) for placebo, and -1.53 (0.71), -1.26 (0.81), -1.42 (0.65), and -4.13 (0.65) for pamidronate 30, 60, 90, and 180 mg, respectively (P=0.012 for pamidronate 180 mg vs placebo). The proportion of responders, changes in worst pain, and pain interference with daily function were also significantly improved for pamidronate 180 mg compared with placebo. In conclusion, i.v. pamidronate, administered as two 90 mg infusions, decreased pain intensity for 6 months in subjects with CLBP.

Pain, motor and gait assessment of murine osteoarthritis in a cruciate ligament transection model

OBJECTIVE

The major complaint of Osteoarthritis (OA) patients is pain. However, due to the nature of clinical studies and the limitation of animal studies, few studies have linked function impairment and behavioral changes in OA animal models to cartilage loss and histopathology. Our objective was to study surrogate markers of functional impairment in relation to cartilage loss and pathological changes in a post-traumatic mouse model of OA.

METHOD

We performed a battery of functional analyses in a mouse model of OA generated by cruciate ligament transection (CLT). The changes in functional analyses were linked to histological changes graded by OARSI standards, histological grading of synovitis, and volumetric changes of the articular cartilage and osteophytes quantified by phase contrast micro-computed tomography (μCT).

RESULTS

OA generated by CLT led to decreased time on rotarod, delayed response on hotplate analysis, and altered gait starting from 4 weeks after surgery. Activity in open field analysis did not change at 4, 8, or 12 weeks after CLT. The magnitude of behavioral changes was directly correlated with higher OARSI histological scores of OA, synovitis in the knee joints, cartilage volume loss, and osteophyte formation.

CONCLUSION

Our findings link functional analyses to histological grading, synovitis, comprehensive three-dimensional assessment of cartilage volume and osteophyte formation. This serves as a reference for a mouse model in predicting outcomes of OA treatment.

Changes in midbrain pain receptor expression, gait and behavioral sensitivity in a rat model of radiculopathy

Intervertebral disc herniation may contribute to inflammatory processes that associate with radicular pain and motor deficits. Molecular changes at the affected dorsal root ganglion (DRG), spinal cord, and even midbrain, have been documented in rat models of radiculopathy or nerve injury. The objective of this study was to evaluate gait and the expression of key pain receptors in the midbrain in a rodent model of radiculopathy. Radiculopathy was induced by harvesting tail nucleus pulposus (NP) and placing upon the right L5 DRG in rats (NP-treated, n=12). Tail NP was discarded in sham-operated animals (n=12). Mechanical allodynia, weight-bearing, and gait were evaluated in all animals over time. At 1 and 4 weeks after surgery, astrocyte and microglial activation was tested in DRG sections. Midbrain sections were similarly evaluated for immunoreactivity to serotonin (5HT_2B), mu-opioid (µ-OR), and metabotropic glutamate (mGluR4 and 5) receptor antibodies. NP-treated animals placed less weight on the affected limb 1 week after surgery and experienced mechanical hypersensitivity over the duration of the study. Astroctye activation was observed at DRGs only at 4 weeks after surgery. Findings for pain receptors in the midbrain of NP-treated rats included an increased expression of 5HT_2B at 1, but not 4 weeks; increased expression of µ-OR and mGluR5 at 1 and 4 weeks (periaqueductal gray region only); and no changes in expression of mGluR4 at any point in this study. These observations provide support for the hypothesis that the midbrain responds to DRG injury with a transient change in receptors regulating pain responses.

Chondrogenesis, chondrocyte differentiation, and articular cartilage metabolism in health and osteoarthritis

Chondrogenesis occurs as a result of mesenchymal cell condensation and chondroprogenitor cell differentiation. Following chondrogenesis, the chondrocytes remain as resting cells to form the articular cartilage or undergo proliferation, terminal differentiation to chondrocyte hypertrophy, and apoptosis in a process termed endochondral ossification, whereby the hypertrophic cartilage is replaced by bone. Human adult articular cartilage is a complex tissue of matrix proteins that varies from superficial to deep layers and from loaded to unloaded zones. A major challenge to efforts to repair cartilage by stem cell-based and other tissue-engineering strategies is the inability of the resident chondrocytes to lay down a new matrix with the same properties as it had when it was formed during development. Thus, understanding and comparing the mechanisms of cartilage remodeling during development, osteoarthritis (OA), and aging may lead to more effective strategies for preventing cartilage damage and promoting repair. The pivotal proteinase that marks OA progression is matrix metalloproteinase 13 (MMP-13), the major type II collagen-degrading collagenase, which is regulated by both stress and inflammatory signals. We and other investigators have found that there are common mediators of these processes in human OA cartilage. We also observe temporal and spatial expression of these mediators in early through late stages of OA in mouse models and are analyzing the consequences of knockout or transgenic overexpression of critical genes. Since the chondrocytes in adult human cartilage are normally quiescent and maintain the matrix in a low turnover state, understanding how they undergo phenotypic modulation and promote matrix destruction and abnormal repair in OA may to lead to identification of critical targets for therapy to block cartilage damage and promote effective cartilage repair.

Initial application of EPIC-μCT to assess mouse articular cartilage morphology and composition: effects of aging and treadmill running

OBJECTIVE

The current study was undertaken to adapt Equilibrium Partitioning of an Ionic Contrast agent via microcomputed tomography (EPIC-μCT) to mouse articular cartilage (AC), which presents a particular challenge because it is thin (30 μm) and has a small volume (0.2-0.4 mm(3)), meaning there is only approximately 2-4 μg of chondroitin sulfate (CS) glycosaminoglycan per joint surface cartilage.

DESIGN

Using 6 μm isotropic voxels and the negatively charged contrast agent ioxaglate (Hexabrix), we optimized contrast agent concentration and incubation time, assessed two methods of tissue preservation (formalin fixation and freezing), examined the effect of ex vivo chondroitinase ABC digestion on X-ray attenuation, assessed accuracy and precision, compared young and skeletally mature cartilage, and determined patterns of degradation in a murine cartilage damage model induced by treadmill running.

RESULTS

The optimal concentration of the contrast agent was 15%, formalin fixation was preferred to freezing, and 2 h of incubation was needed to reach contrast agent equilibrium with formalin-fixed specimens. There was good agreement with histologic measurements of cartilage thickness, although μCT over-estimated thickness by 13% (5 μm) in 6-week-old mice. Enzymatic release of 0.8 μg of chondrotin sulfate (about 40% of the total) increased X-ray attenuation by 17%. There was a 15% increase in X-ray attenuation in 14-week-old mice compared to 6-week-old mice (P < 0.001) and this corresponded to 65% decrease in CS content at 14 weeks. The older mice also had reductions of 33% in cartilage thickness and 44% in cartilage volume (P < 0.001). Treadmill running induced a 16% decrease in cartilage thickness (P = 0.012) and a 12% increase in X-ray attenuation (P = 0.006) in 14-week-old mice.

CONCLUSION

This technique enables non-destructive visualization and quantification of murine femoral AC in three dimensions with anatomic specificity and should prove to be a useful new tool in studying degeneration of cartilage in mouse models.

Immunodominant liver-specific expression suppresses transgene-directed immune responses in murine pompe disease

Pompe disease can be treated effectively, if immune tolerance to enzyme replacement therapy (ERT) with acid α-glucosidase (GAA) is present. An adeno-associated viral (AAV) vector carrying a liver-specific regulatory cassette to drive GAA expression (AAV-LSPhGAA) established immune tolerance in GAA knockout (KO) mice, whereas ubiquitous expression with AAV-CBhGAA provoked immune responses. Therefore, we investigated the hypothesis that immune tolerance induced by hepatic-restricted expression was dominant. AAV-LSPhGAA and AAV-CBhGAA were administered singly or in combination to groups of adult GAA-KO mice, and AAV-LSPhGAA induced immune tolerance even in combination with AAV-CBhGAA. The dual vector approach to GAA expression improved biochemical correction of GAA deficiency and glycogen accumulations at 18 weeks, and improved motor function testing including wire-hang and grip-strength testing. The greatest efficacy was demonstrated by dual vector administration, when both vectors were pseudotyped as AAV8. T cells from mice injected with AAV-LSPhGAA failed to proliferate at all after an immune challenge with GAA and adjuvant, whereas mock-treated GAA-KO mice mounted vigorous T cell proliferation. Unlike AAV-LSPhGAA, AAV-CBhGAA induced selective cytokine and chemokine expression in liver and spleen after the immune challenge. AAV-CBhGAA transduced dendritic cells and expressed high-level GAA, whereas AAV-LSPhGAA failed to express GAA in dendritic cells. The level of transduction in liver was much higher after dual AAV8 vector administration at 18 weeks, in comparison with either vector alone. Dual vector administration failed to provoke antibody formation in response to GAA expression with AAV-CBhGAA; however, hepatic-restricted expression from dual vector expression did not prevent antibody formation after a strong immune challenge with GAA and adjuvant. The relevance of immune tolerance to gene therapy in Pompe disease indicates that hepatic expression might best be combined with nonhepatic expression, achieving the benefits of ubiquitous expression in addition to evading deleterious immune responses.

Kinematic and dynamic gait compensations resulting from knee instability in a rat model of osteoarthritis

Introduction

Osteoarthritis (OA) results in pain and disability; however, preclinical OA models often focus on joint-level changes. Gait analysis is one method used to evaluate both preclinical OA models and OA patients. The objective of this study is to describe spatiotemporal and ground reaction force changes in a rat medial meniscus transection (MMT) model of knee OA and to compare these gait measures with assays of weight bearing and tactile allodynia.

Methods

Sixteen rats were used in the study. The medial collateral ligament (MCL) was transected in twelve Lewis rats (male, 200 to 250 g); in six rats, the medial meniscus was transected, and the remaining six rats served as sham controls. The remaining four rats served as naïve controls. Gait, weight-bearing as measured by an incapacitance meter, and tactile allodynia were assessed on postoperative days 9 to 24. On day 28, knee joints were collected for histology. Cytokine concentrations in the serum were assessed with a 10-plex cytokine panel.

Results

Weight bearing was not affected by sham or MMT surgery; however, the MMT group had decreased mechanical paw-withdrawal thresholds in the operated limb relative to the contralateral limb (P = 0.017). The gait of the MMT group became increasingly asymmetric from postoperative days 9 to 24 (P = 0.020); moreover, MMT animals tended to spend more time on their contralateral limb than their operated limb while walking (P < 0.1). Ground reaction forces confirmed temporal shifts in symmetry and stance time, as the MMT group had lower vertical and propulsive ground reaction forces in their operated limb relative to the contralateral limb, naïve, and sham controls (P < 0.05). Levels of interleukin 6 in the MMT group tended to be higher than naïve controls (P = 0.072). Histology confirmed increased cartilage damage in the MMT group, consistent with OA initiation. Post hoc analysis revealed that gait symmetry, stance time imbalance, peak propulsive force, and serum interleukin 6 concentrations had significant correlations to the severity of cartilage lesion formation.

Conclusion

These data indicate significant gait compensations were present in the MMT group relative to medial collateral ligament (MCL) injury (sham) alone and naïve controls. Moreover, these data suggest that gait compensations are likely driven by meniscal instability and/or cartilage damage, and not by MCL injury alone.

Lumbar intervertebral disc degeneration associated with axial and radiating low back pain in ageing SPARC-null mice

Chronic low back pain (LBP) is a complex, multifactorial disorder with unclear underlying mechanisms. In humans and rodents, decreased expression of secreted protein acidic rich in cysteine (SPARC) is associated with intervertebral disc (IVD) degeneration and signs of LBP. The current study investigates the hypothesis that IVD degeneration is a risk factor for chronic LBP. SPARC-null and age-matched control mice ranging from 6 to 78 weeks of age were evaluated in this study. X-ray and histologic analysis revealed reduced IVD height, increased wedging, and signs of degeneration (bulging and herniation). Cutaneous sensitivity to cold, heat, and mechanical stimuli were used as measures of referred (low back and tail) and radiating pain (hind paw). Region specificity was assessed by measuring icilin- and capsaicin-evoked behaviour after subcutaneous injection into the hind paw or upper lip. Axial discomfort was measured by the tail suspension and grip force assays. Motor impairment was determined by the accelerating rotarod. Physical function was evaluated by voluntary activity after axial strain or during ambulation with forced lateral flexion. SPARC-null mice developed (1) region-specific, age-dependent hypersensitivity to cold, icilin, and capsaicin (hind paw only), (2) axial discomfort, (3) motor impairment, and (4) reduced physical function. Morphine (6 mg/kg, i.p.) reduced cutaneous sensitivity and alleviated axial discomfort in SPARC-null mice. Ageing SPARC-null mice mirror many aspects of the complex and challenging nature of LBP in humans and incorporate both anatomic and functional components of the disease. The current study supports the hypothesis that IVD degeneration is a risk factor for chronic LBP.

Kinematic and dynamic gait compensations in a rat model of lumbar radiculopathy and the effects of tumor necrosis factor-alpha antagonism

Introduction

Tumor necrosis factor-α (TNFα) has received significant attention as a mediator of lumbar radiculopathy, with interest in TNF antagonism to treat radiculopathy. Prior studies have demonstrated that TNF antagonists can attenuate heightened nociception resulting from lumbar radiculopathy in the preclinical model. Less is known about the potential impact of TNF antagonism on gait compensations, despite being of clinical relevance. In this study, we expand on previous descriptions of gait compensations resulting from lumbar radiculopathy in the rat and describe the ability of local TNF antagonism to prevent the development of gait compensations, altered weight bearing, and heightened nociception.

Methods

Eighteen male Sprague-Dawley rats were investigated for mechanical sensitivity, weight-bearing, and gait pre- and post-operatively. For surgery, tail nucleus pulposus (NP) tissue was collected and the right L5 dorsal root ganglion (DRG) was exposed (Day 0). In sham animals, NP tissue was discarded (n = 6); for experimental animals, autologous NP was placed on the DRG with or without 20 μg of soluble TNF receptor type II (sTNFRII, n = 6 per group). Spatiotemporal gait characteristics (open arena) and mechanical sensitivity (von Frey filaments) were assessed on post-operative Day 5; gait dynamics (force plate arena) and weight-bearing (incapacitance meter) were assessed on post-operative Day 6.

Results

High-speed gait characterization revealed animals with NP alone had a 5% decrease in stance time on their affected limbs on Day 5 (P ≤0.032). Ground reaction force analysis on Day 6 aligned with temporal changes observed on Day 5, with vertical impulse reduced in the affected limb of animals with NP alone (area under the vertical force-time curve, P <0.02). Concordant with gait, animals with NP alone also had some evidence of affected limb mechanical allodynia on Day 5 (P = 0.08) and reduced weight-bearing on the affected limb on Day 6 (P <0.05). Delivery of sTNFRII at the time of NP placement ameliorated signs of mechanical hypersensitivity, imbalanced weight distribution, and gait compensations (P <0.1).

Conclusions

Our data indicate gait characterization has value for describing early limb dysfunctions in pre-clinical models of lumbar radiculopathy. Furthermore, TNF antagonism prevented the development of gait compensations subsequent to lumbar radiculopathy in our model.

Intraarticular injection of hyaluronan prevents cartilage erosion, periarticular fibrosis and mechanical allodynia and normalizes stance time in murine knee osteoarthritis

Introduction

Intraarticular hyaluronan (HA) is used clinically for symptomatic relief in patients with knee osteoarthritis (OA); however, the mechanism of action is unclear. In this study, we examined the effects of a single injection of HA on joint tissue pathology, mechanical allodynia and gait changes (measured by stride times) in a murine model of OA.

Methods

OA was induced in the right knee joint (stifle) of 12-week-old male C57BL/6 mice by transforming growth factor β1 (TGFβ1) injection and treadmill running for 14 days. Gait parameters were quantified by using TreadScan, mechanical allodynia was evaluated with von Frey filaments, and joint pathology was evaluated by scoring of macroscopic images for both cartilage erosion and periarticular fibrosis. HA or saline control was injected 1 day after TGFβ1 injection but before the start of treadmill running.

Results

OA development in this model was accompanied by significant (P < 0.01) enhancement of the stance and propulsion times of affected legs. HA injection (but not saline injection) blocked all gait changes and also protected joints from femoral cartilage erosion as well as tibial and femoral tissue fibrosis. Both HA injection and saline injection attenuated acute allodynia, but the HA effect was more pronounced and prolonged than the saline injection.

Conclusions

We conclude that videographic gait analysis is an objective, sensitive and reproducible means of monitoring joint pathology in experimental murine OA, since stance time appears to correlate directly with OA severity. A single injection of HA prevents acute and prolonged gait changes and ameliorates the cartilage erosion and periarticular fibrosis normally seen in this model. We speculate that the capacity of HA to prevent cartilage erosion results from its normalization of joint biomechanics and its inhibitory effects on periarticular cells, which are involved in tissue hyperplasia and fibrosis. This effect of exogenous HA appears to mimic the protective effects of ablation of Adamts5 (a disintegrin and metalloproteinase with thrombospondin motifs 5) on experimental murine OA, and we speculate that a common mechanism is involved.

Neurophenotyping genetically modified mice for social behavior

Sociability in mice is a multidimensional adaptive and functional response. Due to its complexity, it is important that researchers use well-defined behavioral assays that are easily replicated with clearly defined ethograms. In the Mouse Behavioral and Neuroendocrine Analysis Core Facility at Duke University, we have developed a broad series of tests that examine different components of neonatal and adult social behaviors that include sociability, sexual behavior, aggressive and territorial responses, and maternal behaviors. While the purpose of this chapter is not to provide an exhaustive description of all mouse social tests available, we provide investigators with a description of basic procedures and considerations necessary to develop a successful social behavior testing program within their laboratories.

Inhibition of osteoclasts prevents cartilage loss and pain in a rat model of degenerative joint disease

OBJECTIVE

To investigate the relationship between efficacy of a bisphosphonate, pain and extent of joint damage in the monosodium iodoacetate (MIA) model of painful degenerative joint disease.

METHODS

Zoledronate treatment was initiated prior to and at various times following model induction, including late time points representing advanced disease. Radiographic and histological structural parameters were correlated with pain as measured by weight bearing.

RESULTS

Intraarticular (IA) MIA resulted in a progressive loss of bone mineral density (BMD) and chondrocytes, thinning of cartilage, loss of proteoglycan, resorption of calcified cartilage and subchondral bone, as well as pain. This was completely prevented by pre-emptive chronic zoledronate treatment with joint sections being histologically indistinguishable from saline-injected controls. When initiation of treatment was delayed efficacy was reduced. In animals with advanced joint degeneration, treatment partially restored BMD and had a significant, but limited, effect on pain. We confirmed these radiographic and behavioral findings in the medial meniscal tear model. To understand the mechanism-of-action of zoledronate we investigated an early time point 4 days post-model induction when chondrocytes were histologically viable, with minor loss of proteoglycan and generalized synovitis. Osteoclast-mediated resorption of the calcified cartilage was observed and was prevented by two doses of zoledronate.

CONCLUSION

Subchondral bone remodeling plays an important role in nociception and the pathobiology of the MIA model with osteoclasts being implicated in both bone and cartilage resorption. Inhibition of osteoclastic activity when initiated early leads to improved efficacy.

Evaluating intra-articular drug delivery for the treatment of osteoarthritis in a rat model

Osteoarthritis (OA) is a degenerative joint disease that can result in joint pain, loss of joint function, and deleterious effects on activity levels and lifestyle habits. Current therapies for OA are largely aimed at symptomatic relief and may have limited effects on the underlying cascade of joint degradation. Local drug delivery strategies may provide for the development of more successful OA treatment outcomes that have potential to reduce local joint inflammation, reduce joint destruction, offer pain relief, and restore patient activity levels and joint function. As increasing interest turns toward intra-articular drug delivery routes, parallel interest has emerged in evaluating drug biodistribution, safety, and efficacy in preclinical models. Rodent models provide major advantages for the development of drug delivery strategies, chiefly because of lower cost, successful replication of human OA-like characteristics, rapid disease development, and small joint volumes that enable use of lower total drug amounts during protocol development. These models, however, also offer the potential to investigate the therapeutic effects of local drug therapy on animal behavior, including pain sensitivity thresholds and locomotion characteristics. Herein, we describe a translational paradigm for the evaluation of an intra-articular drug delivery strategy in a rat OA model. This model, a rat interleukin-1beta overexpression model, offers the ability to evaluate anti-interleukin-1 therapeutics for drug biodistribution, activity, and safety as well as the therapeutic relief of disease symptoms. Once the action against interleukin-1 is confirmed in vivo, the newly developed anti-inflammatory drug can be evaluated for evidence of disease-modifying effects in more complex preclinical models.