A longitudinal study on an autoimmune murine model of ankylosing spondylitis

Intermittent administration of PTH for the treatment of inflammatory bone loss does not enhance entheseal pathological new bone formation

OBJECTIVE

To investigate the effect of intermittent parathyroid hormone (iPTH) administration on pathological new bone formation during treatment of ankylosing spondylitis-related osteoporosis.

METHODS

Animal models with pathological bone formation caused by hypothetical AS pathogenesis received treatment with iPTH. We determined the effects of iPTH on bone loss and the formation of pathological new bone with micro-computed tomography (micro-CT) and histological examination. In addition, the tamoxifen-inducible conditional knockout mice (CAGGCre-ERTM; PTHflox/flox, PTH-/-) was established to delete PTH and investigate the effect of endogenous PTH on pathological new bone formation.

RESULTS

iPTH treatment significantly improved trabecular bone mass in the modified collagen-induced arthritis (m-CIA) model and unbalanced mechanical loading models. Meanwhile, iPTH treatment did not enhance pathological new bone formation in all types of animal models. Endogenous PTH deficiency had no effects on pathological new bone formation in unbalanced mechanical loading models.

CONCLUSION

Experimental animal models of AS treated with iPTH show improvement in trabecular bone density, but not entheseal pathological bone formation，indicating it may be a potential treatment for inflammatory bone loss does in AS.

An update of murine models and their methodologies in immune-mediated joint damage and pain research

Murine models have played an indispensable role in the understanding of rheumatic and musculoskeletal disorders (RMD), elucidating the genetic, endocrine and biomechanical pathways involved in joint pathology and associated pain. To date, the available models in RMD can be classified as induced or spontaneous, both incorporating transgenic alternatives that improve specific insights. It is worth noting that the selection of the most appropriate model together with the evaluation of their specific characteristics and technical capabilities are crucial when designing the experiments. Furthermore, it is also imperative to consistently adhere to the ethical standards concerning animal experimentation. Recognizing the inherent limitation that any model can entirely encapsulates the complexity of the pathophysiology of these conditions, the aim of this review is to provide an updated overview on the methodology of current murine models in major arthropathies and their immune-mediated pathways, addressing to basic, translational and pharmacological research in joint damage and pain.

Advances in experimental models of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by persistent articular inflammation and joint damage. RA was first described over 200 years ago; however, its etiology and pathophysiology remain insufficiently understood. The current treatment of RA is mainly empirical or based on the current understanding of etiology with limited efficacy and/or substantial side effects. Thus, the development of safer and more potent therapeutics, validated and optimized in experimental models, is urgently required. To improve the transition from bench to bedside, researchers must carefully select the appropriate experimental models as well as draw the right conclusions. Here, we summarize the establishment, pathological features, potential mechanisms, advantages, and limitations of the currently available RA models. The aim of the review is to help researchers better understand available RA models; discuss future trends in RA model development, which can help highlight new translational and human-based avenues in RA research.

CXCL12/CXCR4-Rac1-mediated migration of osteogenic precursor cells contributes to pathological new bone formation in ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized by inflammatory back pain and spinal ankylosis due to pathological new bone formation. Here, we identified CXCL12 as a critical contributor to pathological new bone formation through recruitment of osteogenic precursor cells (OPCs). CXCL12 was found highly expressed in the regions that would potentially develop pathological new bone. OPCs were recruited to the regions where CXCL12 was up-regulated. Inhibition of CXCL12/CXCR4 axis with AMD3100 or conditional knockout of CXCR4 attenuated OPCs migration and subsequent pathological new bone formation in animal models of AS. By contrast, a genetically engineered animal model with CXCL12 overexpression developed a joint ankylosis phenotype. Furthermore, Rac1 was found essential for OPCs migration and pathological new bone formation. These findings ravel the novel role of CXCL12 in AS and indicate a potential strategy for targeting the CXCL12/CXCR4-Rac1 axis to prevent progression of axial skeleton ankylosis.

Moxibustion attenuates inflammation and alleviates axial spondyloarthritis in mice: Possible role of APOE in the inhibition of the Wnt pathway

Background and aim

Moxibustion is widely used in China and other East Asian countries to manage the symptom of ankylosing spondylitis (AS). This study investigated the effects of moxibustion intervention on protein expression through proteomics analysis in AS mice.

Experimental procedure

Proteoglycan-induced spondylitis (PGISp) was established in Balb/c mice. PGISp mice were intervened with daily moxibustion at ST36, BL23, and DU4 for four weeks. Various biochemical (including pro-inflammatory cytokines and bone metabolism indexes) and histopathological parameters were determined. The effects of moxibustion on protein changes in AS mice were analyzed using data-independent acquisition-mass spectrometry (DIA-MS). The target proteins were then confirmed by Western blot analysis.

Results

Moxibustion significantly decreased pro-inflammatory cytokine expression including IL-1β, TNF-α, IL-17, and IL-6, reduced the mRNA expression of RANKL, RANK, ALP, and OCN, and improved the histopathological examination in AS mice. DIA-MS proteomic technique has identified 25 candidate proteins involved in the mechanisms of moxibustion for AS mice, most of which are mainly associated with the regulation of Wnt/β-catenin. Integrated pathway analysis revealed that glycine, serine and threonine metabolism together with lipid metabolism were the most important canonical pathways involved in the anti-AS effect of moxibustion. In line with the multi-omic data, the levels of BPGM, APOC₂, APOE, and GPD1 modified in the AS mice, intervened with moxibustion as confirmed by Western blot. In particular, APOE may play a key role in linking the lipid metabolism and the Wnt/β-catenin pathway of new bone formation.

Conclusion

In conclusion, moxibustion may reduce pro-inflammatory cytokines and improve bone erosion for AS mice. The regulation of APOE by moxibustion may have a potential inhibitory effect on the Wnt/β-catenin pathway in AS mice. However, due to the lack of silencing or overexpression of key molecules of the signal pathway, whether the beneficial and positive effect of moxibustion involved in the regulation of Wnt/β-catenin signaling pathway by APOE or other aspects, needed to be explored in further study.

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Moxibustion reduced the levels of pro-inflammatory cytokine.

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Moxibustion alleviated bone erosion and prohibited the new bone formation.

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Moxibustion inhibited Wnt signaling pathway by APOE.

A Potential New Mouse Model of Axial Spondyloarthritis Involving the Complement System

Many mouse models of rheumatoid arthritis have been identified, but only a limited number are present for axial spondyloarthritis (AxSpA). Collagen Ab-induced arthritis (CAIA) is one of the most widely used mouse models of arthritis, and it is complement-dependent. We found that mice developing CAIA also developed spinal lesions similar to those found in AxSpA. To induce CAIA, mice were injected intraperitoneally at day 0 with anti-collagen Abs, followed by LPS injection at day 3. CAIA mice demonstrated a significant kyphosis through the spine, as well as hypertrophic cartilage and osseous damage of the intravertebral joints. Immunohistochemical staining of the kyphotic area revealed increased complement C3 deposition and macrophage infiltration, with localization to the intravertebral joint margins. Near Infrared (NIR) in vivo imaging showed that anti-collagen Abs conjugated with IRDye^® 800CW not only localized to cartilage surface in the joints but also to the spine in arthritic mice. We report here a novel preclinical mouse model in which, associated with the induction of CAIA, mice also exhibited salient features of AxSpA; this new experimental model of AxSpA may allow investigators to shed light on the local causal mechanisms of AxSpA bone and soft tissue changes as well as treatment.

A new and spontaneous animal model for ankylosing spondylitis is found in cynomolgus monkeys

BACKGROUND

Ankylosing spondylitis is a progressive, disabling joint disease that affects millions worldwide. Given its unclear etiology, studies of ankylosing spondylitis relied heavily on drug-induced or transgenic rodent models which retain only partial clinical features. There is obviously a lack of a useful disease model to conduct comprehensive mechanistic studies.

METHODS

We followed a group of cynomolgus monkeys having joint lesions reported of spinal stiffness for 2 years by conducting hematological testing, radiographic examination, family aggregation analysis, pathological analysis, and genetic testing.

RESULTS

The results confirmed that these diseased animals suffered from spontaneous ankylosing spondylitis with clinical features recapitulating human ankylosing spondylitis disease progression, manifested by pathological changes and biochemical indicators similar to that of ankylosing spondylitis patients.

CONCLUSION

The study offers a promising non-human primate model for spontaneous ankylosing spondylitis which may serve as an excellent substitute for its pre-clinical research.

Targeting chondrocytes for arresting bony fusion in ankylosing spondylitis

Bony fusion caused by pathological new bone formation manifests the clinical feature of ankylosing spondylitis (AS). However, the underlying mechanism remains elusive. Here we discovered spontaneous kyphosis, arthritis and bony fusion in mature CD4-Cre;Ptpn11^f/f mice, which present the pathophysiological features of AS. A population of CD4-Cre-expressing proliferating chondrocytes was SHP2 deficient, which could differentiate into pre-hypertrophic and hypertrophic chondrocytes. Functionally, SHP2 deficiency in chondrocytes impeded the fusion of epiphyseal plate and promoted chondrogenesis in joint cavity and enthesis. Mechanistically, aberrant chondrocytes promoted ectopic new bone formation through BMP6/pSmad1/5 signaling. It is worth emphasizing that such pathological thickness of growth plates was evident in adolescent humans with enthesitis-related arthritis, which could progress to AS in adulthood. Targeting dysfunctional chondrogenesis with Smo inhibitor sonidegib significantly alleviated the AS-like bone disease in mice. These findings suggest that blockade of chondrogenesis by sonidegib would be a drug repurposing strategy for AS treatment.

Current treatments cannot significantly alleviate the radiographic progression in ankylosing spondylitis (AS), which results in joints stiffness and bony fusion of AS. Smo inhibitor sonidegib retards the pathological new bone formation in AS through targeting dysfunctional chondrogenesis.

Inflammatory Foot Involvement in Spondyloarthritis: From Tarsitis to Ankylosing Tarsitis

Spondyloarthritis (SpA) is a group that includes a wide spectrum of clinically similar diseases manifested by oligoarticular arthritis and axial or peripheral ankylosis. Although axial SpA is predominant in Caucasians and adult-onset patients, juvenile-onset and Latin American patients are characterized by severe peripheral arthritis and particularly foot involvement. The peripheral involvement of SpA can vary from tarsal arthritis to the most severe form named ankylosing tarsitis (AT). Although the cause and etiopathogenesis of axSpA are often studied, the specific characteristics of pSpA are unknown. Several animal models of SpA develop initial tarsitis and foot ankylosis as the main signs, emphasizing the role of foot inflammation in the overall SpA spectrum. In this review, we attempt to highlight the clinical characteristics of foot involvement in SpA and update the knowledge regarding its pathogenesis, focusing on animal models and the role of mechanical forces in inflammation.

Testing if Micro-CT Is Capable of Quantitating the Extent of Proteoglycan-Aggrecan Induced Axial Spondyloarthritis in Mice

Objective

Injections of proteoglycan aggrecan (PGA) have been reported to induce axial spondyloarthritis (ax-SpA) in BALB/c mice. It is considered to be a model for radiographic ax-SpA. However, evaluation of the extent of axial disease by histopathological assessment of every intervertebral space is labor-intensive. The objective of our paper is to test the feasibility of Micro Computed Tomography (Micro-CT) in rapidly enumerating the number of intervertebral spaces affected in each mouse.

Methods

Arthritis was induced in BALB/c mice by intraperitoneal injections of PGA. Involvement of several spinal segments, and selected sacroiliac and hip joints were evaluated by histopathology. The involvement of all intervertebral spaces, sacroiliac and hip joints was evaluated by Micro-CT.

Results

BALB/c mice injected with PGA developed histopathology of SpA-like axial lesions, including spondylitis, sacroiliac joint arthritis and hip joint arthritis. Micro-CT allowed us to clearly enumerate the number of lesions in each mouse.

Conclusion

Micro-CT allows quantitative assessment of the extent of axial involvement in PGA-induced mouse spondylitis. This can be a useful tool in assessing therapeutic interventions.

Proper animal experimental designs for preclinical research of biomaterials for intervertebral disc regeneration

Low back pain is a vital musculoskeletal disease that impairs life quality, leads to disability and imposes heavy economic burden on the society, while it is greatly attributed to intervertebral disc degeneration (IDD). However, the existing treatments, such as medicines, chiropractic adjustments and surgery, cannot achieve ideal disc regeneration. Therefore, advanced bioactive therapies are implemented, including stem cells delivery, bioreagents administration, and implantation of biomaterials etc. Among these researches, few reported unsatisfying regenerative outcomes. However, these advanced therapies have barely achieved successful clinical translation. The main reason for the inconsistency between satisfying preclinical results and poor clinical translation may largely rely on the animal models that cannot actually simulate the human disc degeneration. The inappropriate animal model also leads to difficulties in comparing the efficacies among biomaterials in different reaches. Therefore, animal models that better simulate the clinical charateristics of human IDD should be acknowledged. In addition, in vivo regenerative outcomes should be carefully evaluated to obtain robust results. Nevertheless, many researches neglect certain critical characteristics, such as adhesive properties for biomaterials blocking annulus fibrosus defects and hyperalgesia that is closely related to the clinical manifestations, e.g., low back pain. Herein, in this review, we summarized the animal models established for IDD, and highlighted the proper models and parameters that may result in acknowledged IDD models. Then, we discussed the existing biomaterials for disc regeneration and the characteristics that should be considered for regenerating different parts of discs. Finally, well-established assays and parameters for in vivo disc regeneration are explored.

Inflammation in the intervertebral disc herniation

Up until fairly recently, it was thought that sciatic pain in the lumbar herniated disc was caused by compression on the nerve root. However, the lumbar herniated disc shows mixed pictures which are difficult to explain by simple mechanical compromise. In recent years various immunology, immunohistochemistry and molecular biology studies have shown that the herniated tissue is not an inert material, but rather it Is biologically very active with the capability of expressing a series of inflammatory mediators: cytokines such as interleukin-1, interleukin-6, interleuquin-8 and tumor necrosis factor being the ones which stand out. The inflammation is not only induced by the chemical irritation of the bioactive substances released by the nucleus pulposus but also by an autoimmune response against itself. Thus, in addition to the mechanical factor, the biomechanical mediation plays an important role in the pathophysiology of sciatic pain and of radiculopathy. Through a review of a wide range of literature, we researched the cellular molecular mediators involved in this inflammatory process around the lumbar herniated disc and its involvement in sciatic pain.

Aberrant upregulation of CaSR promotes pathological new bone formation in ankylosing spondylitis

Pathological new bone formation is a typical pathological feature in ankylosing spondylitis (AS), and the underlying molecular mechanism remains elusive. Previous studies have shown that the calcium‐sensing receptor (CaSR) is critical for osteogenic differentiation while also being highly involved in many inflammatory diseases. However, whether it plays a role in pathological new bone formation of AS has not been reported. Here, we report the first piece of evidence that expression of CaSR is aberrantly upregulated in entheseal tissues collected from AS patients and animal models with different hypothetical types of pathogenesis. Systemic inhibition of CaSR reduced the incidence of pathological new bone formation and the severity of the ankylosing phenotype in animal models. Activation of PLCγ signalling by CaSR promoted bone formation both in vitro and in vivo. In addition, various inflammatory cytokines induced upregulation of CaSR through NF‐κB/p65 and JAK/Stat3 pathways in osteoblasts. These novel findings suggest that inflammation‐induced aberrant upregulation of CaSR and activation of CaSR‐PLCγ signalling in osteoblasts act as mediators of inflammation, affecting pathological new bone formation in AS.

Punicalagin Exerts Protective Effects against Ankylosing Spondylitis by Regulating NF-κB-TH17/JAK2/STAT3 Signaling and Oxidative Stress

Background

Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized by sacroiliitis and spinal rigidity of the axial joints. The role of oxidative stress and increased proinflammatory cytokines is well documented in AS pathogenesis. Punicalagin (2,3-hexahydroxydiphenoyl-gallagyl-D-glucose), an ellagitannin widely present in pomegranates, is found to exhibit potent anti-inflammatory, antiproliferative, and antioxidative effects. The present study was undertaken to investigate the effects of punicalagin in a rodent model of AS.

Methods

BALB/c mice induced spondylitis were sacrificed 24 h after the last injection of proteoglycan extract. Histological scoring was done to assess the degree of the disease. The expression of JAK2/STAT3 proteins and proteins of the nuclear factor-κB (NF-κB) pathway was determined by immunoblotting. Serum levels of inflammatory mediators—TNF-α, IL-1β, IL-6, IL-17A, and IL-23—were assessed. Levels of lipid peroxidation and reactive oxygen species (ROS) were quantified. Antioxidant status as a measure of activities of antioxidant enzymes—catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD)—was determined.

Results

Punicalagin effectively improved antioxidant status and decreased lipid peroxidation, ROS production, and serum levels of inflammatory mediators. NF-κB pathway and JAK2/STAT3 signaling were significantly (p < 0.05) downregulated. Punicalagin effectively regulated the production of cytokines by the Th17 cells and the IL-17A/IL-23 axis.

Conclusion

The observations suggest that punicalagin exerts a protective role in AS via reducing oxidative stress and regulating NF-κB/TH17/JAK2/STAT3 signal. Punicalagin thus could be explored further as a potent candidate compound in the treatment of AS.

Effect of tumor necrosis factor inhibition on spinal inflammation and spinal ankylosis in SKG mice

To prevent spinal progression in ankylosing spondylitis, initiating TNF-inhibitor treatment as early as possible is suggested. However, the outcomes are inconsistent in previous clinical studies. Here, we investigated the effect of TNF inhibition alone on spinal progression when used during arthritis development in a murine model. We injected 8-week-old SKG mice with curdlan (curdlan group). We injected adalimumab at 3 and 9 weeks after the first curdlan injection (ADA group). The clinical scores of peripheral arthritis decreased in the ADA group at 3 weeks after first adalimumab injection. Using positron emission tomography–magnetic resonance imaging and histologic examination, spinal inflammation was observed in the curdlan group, and was significantly deceased in the ADA group. However, spinal osteoblast activities by imaging using OsteoSense 680 EX and bone metabolism-related cytokines such as receptor activator of nuclear factor-kappa B ligand, osteoprotegerin, Dickkopf-1, and sclerostin levels except IL-17A level were not different between the two groups. We conclude that treating TNF inhibitor alone reduced peripheral arthritis score and spinal inflammation in curdlan-injected SKG mice but did not decrease the spinal osteoblast activity, suggesting little effect on spinal ankylosis.

Anti-TNF-α therapy alters the gut microbiota in proteoglycan-induced ankylosing spondylitis in mice

Ankylosing spondylitis is a chronic, progressive disease, and its treatment is relevant to the gut microbiota. Anti-tumor necrosis factor-alpha (anti-TNF-α) therapy alters the gut microbiota in many diseases, including inflammatory bowel disease. However, little is known about the effect of TNF-α blocker treatment on the gut microbiota in ankylosing spondylitis. Herein, the effect of a TNF-α blocker on the gut microbiota in proteoglycan-induced arthritis was investigated. Proteoglycan-induced mice were treated with an rhTNFR:Fc solution of etanercept (5 µg/g) for 4 weeks. rhTNFR:Fc treatment attenuated the arthritis incidence and severity of arthritis in the proteoglycan-induced mice and decreased inflammation in the ankle joints and ameliorated ileal tissue destruction. Moreover, high gut permeability occurred, and zonula occludens-1 and occludin protein levels were reduced in proteoglycan-induced mice. These levels were significantly restored by the administration of rhTNFR:Fc. The serum TNF-α and IL-17 levels were also decreased. In addition, flora analysis via 16S rDNA high-throughput sequencing revealed that rhTNFR:Fc treatment restored the gut microbiota composition to a composition similar to that in control mice. In conclusion, anti-TNF-α therapy attenuated proteoglycan-induced arthritis progression and modulated the gut microbiota and intestinal barrier function. These results provide new insights for anti-TNF-α therapy strategies via regulating the gut microbiota in ankylosing spondylitis.

Regulatory role of capsaicin-sensitive peptidergic sensory nerves in the proteoglycan-induced autoimmune arthritis model of the mouse

Objective

The regulatory role of capsaicin-sensitive peptidergic sensory nerves has been shown in acute inflammation, but little is known about their involvement in T/B-cell driven autoimmune arthritis. This study integratively characterized the function of these nerve endings in the proteoglycan-induced chronic arthritis (PGIA), a translational model of rheumatoid arthritis.

Methods

Peptidergic afferents were defunctionalized by resiniferatoxin (RTX) pretreatment in BALB/c mice, PGIA was induced by repeated antigen challenges. Hind paw volume, arthritis severity, grasping ability and the mechanonociceptive threshold were monitored during the 17-week experiment. Myeloperoxidase activity, vascular leakage and bone turnover were evaluated by in vivo optical imaging. Bone morphology was assessed using micro-CT, the intertarsal small joints were processed for histopathological analysis.

Results

Following desensitization of the capsaicin-sensitive afferents, ankle edema, arthritis severity and mechanical hyperalgesia were markedly diminished. Myeloperoxidase activity was lower in the early, but increased in the late phase, whilst plasma leakage and bone turnover were not altered. Desensitized mice displayed similar bone spurs and erosions, but increased trabecular thickness of the tibia and bony ankylosis of the spine. Intertarsal cartilage thickness was not altered in the model, but desensitization increased this parameter in both the non-arthritic and arthritic groups.

Conclusion

This is the first integrative in vivo functional and morphological characterization of the PGIA mouse model, wherein peptidergic afferents have an important regulatory function. Their overall effect is proinflammatory by increasing acute inflammation, immune cell activity and pain. Meanwhile, their activation decreases spinal ankylosis, arthritis-induced altered trabecularity, and cartilage thickness in small joints.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1364-5) contains supplementary material, which is available to authorized users.

Changes in bone mineral density and bone metabolic indexes in ankylosing spondylitis mouse model complicated with osteoporosis

Changes in bone mineral density and bone metabolic indexes in a model of ankylosing spondylitis (AS) mice complicated with osteoporosis (OP) were investigated. BLAB/c mice were used as the subjects. AS was induced using proteoglycan, and OP was induced using tail suspension method. The mice were randomly divided into four groups: AS group, OP group, AS + OP group and negative control group. Changes in bone mineral density, bone strength, serum calcium (Ca), phosphorus, alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRACP), in mice of each group were detected and compared. There were statistically significant differences in bone mineral density and bone strength among groups. Compared with the negative control group, bone mineral density and bone strength in the AS, the OP and the AS + OP groups were significantly decreased, and the lowest bone mineral density and bone strength were found in the AS + OP group (P<0.05). There were no significant differences in bone mineral density and bone strength between the AS group and the OP group. Significant differences in serum Ca, ALP and TRACP but not in serum phosphorus were found among groups. Compared with the control group, serum levels of Ca and TRACP in the AS, the OP and the AS + OP groups were significantly increased, while levels of ALP were obviously decreased (P<0.05). Bone destruction in AS mice complicated with osteoarthritis was more serious than that in mice with simple AS.

Inflammation Intensity-Dependent Expression of Osteoinductive Wnt Proteins Is Critical for Ectopic New Bone Formation in Ankylosing Spondylitis

OBJECTIVE

To investigate the molecular mechanism underlying inflammation-related ectopic new bone formation in ankylosing spondylitis (AS).

METHODS

Spinal tissues and sera were collected from patients with AS and healthy volunteers and examined for the expression of Wnt proteins. An in vitro cell culture system mimicking the local inflammatory microenvironment of bone-forming sites was established to study the relationship between inflammation and Wnt expression, the regulatory mechanism of inflammation-induced Wnt expression, and the role of Wnt signaling in new bone formation. Modified collagen-induced arthritis (CIA) and proteoglycan-induced spondylitis (PGIS) animal models were used to confirm the key findings in vivo.

RESULTS

The levels of osteoinductive Wnt proteins were increased in sera and spinal ligament tissues from patients with AS. Constitutive low-intensity tumor necrosis factor (TNF) stimulation, but not short-term or high-intensity TNF stimulation, induced persistent expression of osteoinductive Wnt proteins and subsequent bone formation through NF-κB (p65) and JNK/activator protein 1 (c-Jun) signaling pathways. Furthermore, inhibition of either the Wnt/β-catenin or Wnt/protein kinase Cδ (PKCδ) pathway significantly suppressed new bone formation. The increased expression of Wnt proteins was confirmed in both the modified CIA and PGIS models. A kyphotic and ankylosing phenotype of the spine was seen during long-term observation in the modified CIA model. Inhibition of either the Wnt/β-catenin or Wnt/PKCδ signaling pathway significantly reduced the incidence and severity of this phenotype.

CONCLUSION

Inflammation intensity-dependent expression of osteoinductive Wnt proteins is a key link between inflammation and ectopic new bone formation in AS. Activation of both the canonical Wnt/β-catenin and noncanonical Wnt/PKCδ pathways is required for inflammation-induced new bone formation.

The Protective Effect of Chrysanthemum indicum Extract against Ankylosing Spondylitis in Mouse Models

In traditional Chinese and Korean homeopathic medicine, Chrysanthemum indicum Linné (Asteraceae) is a time-honored herb, prescribed for the resolution of symptoms associated with inflammatory and hypertensive conditions as well as those affecting the lungs and its associated structures. The goal of this work is to investigate the defensive role of Chrysanthemum indicum extract in fighting ankylosing spondylitis (AS) using mouse models, through which the manifestation and extent of the disease progression were measured with quantitative analysis of the intervertebral joints. Markers of inflammation as well as oxidative stress were also analysed. Western blot was used to quantify the levels of Nuclear Factor-κB (NF-κB) p65, Dickkopf-1 (DKK-1), and sclerostin (SOST). Consequently, the findings of this experiment demonstrated that AS in mice that were given Chrysanthemum indicum extract had lower level of TNF-α, IL-1β, and IL-6 (P < 0.05) and increased level of catalase (CAT), glutathione peroxidase (GSH-PX), and superoxide dismutase (SOD) (P < 0.05). The results also revealed that Chrysanthemum indicum supplemented with diet contributed to a decrease in Nuclear Factor-κB (NF-κB) p65 protein expression (P < 0.05) and higher levels of DKK-1 and SOST proteins (P < 0.05). Therefore, we concluded that the beneficial role of Chrysanthemum indicum in AS is manifested through downregulating oxidative stress, inhibiting inflammatory mediators and NF-κB, and increasing DKK-1 and SOST levels.

Pathobiology of Modic changes

PURPOSE

Low back pain (LBP) is the most disabling condition worldwide. Although LBP relates to different spinal pathologies, vertebral bone marrow lesions visualized as Modic changes on MRI have a high specificity for discogenic LBP. This review summarizes the pathobiology of Modic changes and suggests a disease model.

METHODS

Non-systematic literature review.

RESULTS

Chemical and mechanical stimulation of nociceptors adjacent to damaged endplates are likely a source of pain. Modic changes are adjacent to a degenerated intervertebral disc and have three generally interconvertible types suggesting that the different Modic change types represent different stages of the same pathological process, which is characterized by inflammation, high bone turnover, and fibrosis. A disease model is suggested where disc/endplate damage and the persistence of an inflammatory stimulus (i.e., occult discitis or autoimmune response against disc material) create predisposing conditions. The risk to develop Modic changes likely depends on the inflammatory potential of the disc and the capacity of the bone marrow to respond to it. Bone marrow lesions in osteoarthritic knee joints share many characteristics with Modic changes adjacent to degenerated discs and suggest that damage-associated molecular patterns and marrow fat metabolism are important pathogenetic factors. There is no consensus on the ideal therapy. Non-surgical treatment approaches including intradiscal steroid injections, anti-TNF-α antibody, antibiotics, and bisphosphonates have some demonstrated efficacy in mostly non-replicated clinical studies in reducing Modic changes in the short term, but with unknown long-term benefits. New diagnostic tools and animal models are required to improve painful Modic change identification and classification, and to clarify the pathogenesis.

CONCLUSION

Modic changes are likely to be more than just a coincidental imaging finding in LBP patients and rather represent an underlying pathology that should be a target for therapy.

Inhibition of Complement Retards Ankylosing Spondylitis Progression

Ankylosing spondylitis (AS) is a chronic axial spondyloarthritis (SpA) resulting in back pain and progressive spinal ankyloses. Currently, there are no effective therapeutics targeting AS largely due to elusive pathogenesis mechanisms, even as potential candidates such as HLA-B27 autoantigen have been identified. Herein, we employed a proteoglycan (PG)-induced AS mouse model together with clinical specimens, and found that the complement system was substantially activated in the spinal bone marrow, accompanied by a remarkable proportion alteration of neutrophils and macrophage in bone marrow and spleen, and by the significant increase of TGF-β1 in serum. The combined treatment with a bacteria-derived complement inhibitor Efb-C (C-terminal of extracellular fibrinogen-binding protein of Staphylococcus aureus) remarkably retarded the progression of mouse AS by reducing osteoblast differentiation. Furthermore, we demonstrated that two important modulators involved in AS disease, TGF-β1 and RANKL, were elevated upon in vitro complement attack in osteoblast and/or osteoclast cells. These findings further unravel that complement activation is closely related with the pathogenesis of AS, and suggest that complement inhibition may hold great potential for AS therapy.

Inflammation-driven bone formation in a mouse model of ankylosing spondylitis: sequential not parallel processes

Background

Ankylosing spondylitis (AS) is an immune-mediated arthritis particularly targeting the spine and pelvis and is characterised by inflammation, osteoproliferation and frequently ankylosis. Current treatments that predominately target inflammatory pathways have disappointing efficacy in slowing disease progression. Thus, a better understanding of the causal association and pathological progression from inflammation to bone formation, particularly whether inflammation directly initiates osteoproliferation, is required.

Methods

The proteoglycan-induced spondylitis (PGISp) mouse model of AS was used to histopathologically map the progressive axial disease events, assess molecular changes during disease progression and define disease progression using unbiased clustering of semi-quantitative histology. PGISp mice were followed over a 24-week time course. Spinal disease was assessed using a novel semi-quantitative histological scoring system that independently evaluated the breadth of pathological features associated with PGISp axial disease, including inflammation, joint destruction and excessive tissue formation (osteoproliferation). Matrix components were identified using immunohistochemistry.

Results

Disease initiated with inflammation at the periphery of the intervertebral disc (IVD) adjacent to the longitudinal ligament, reminiscent of enthesitis, and was associated with upregulated tumor necrosis factor and metalloproteinases. After a lag phase, established inflammation was temporospatially associated with destruction of IVDs, cartilage and bone. At later time points, advanced disease was characterised by substantially reduced inflammation, excessive tissue formation and ectopic chondrocyte expansion. These distinct features differentiated affected mice into early, intermediate and advanced disease stages. Excessive tissue formation was observed in vertebral joints only if the IVD was destroyed as a consequence of the early inflammation. Ectopic excessive tissue was predominantly chondroidal with chondrocyte-like cells embedded within collagen type II- and X-rich matrix. This corresponded with upregulation of mRNA for cartilage markers Col2a1, sox9 and Comp. Osteophytes, though infrequent, were more prevalent in later disease.

Conclusions

The inflammation-driven IVD destruction was shown to be a prerequisite for axial disease progression to osteoproliferation in the PGISp mouse. Osteoproliferation led to vertebral body deformity and fusion but was never seen concurrent with persistent inflammation, suggesting a sequential process. The findings support that early intervention with anti-inflammatory therapies will be needed to limit destructive processes and consequently prevent progression of AS.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0805-0) contains supplementary material, which is available to authorized users.

Treatment of a mouse model of ankylosing spondylitis with exogenous sclerostin has no effect on disease progression

Background

No treatment to date is available which specifically targets bone formation in ankylosing spondylitis (AS). Several recent studies have shown that sclerostin (SOST), a Wnt inhibitor specific to osteocytes and chondrocytes, is down-regulated in AS patients. This suggests Wnt signalling may be upregulated, and application of exogenous recombinant SOST (rSOST) may inhibit Wnt signalling and slow pathological bone formation.

Methods

The proteoglycan-induced spondylitis (PGISp) mouse model in which we have previously demonstrated downregulated SOST expression, was used for this study. Mice were injected with 2.5ug rSOST/day for a period of 8 weeks following induction of disease. Axial skeleton disease development was assessed by histology and skeletal changes examined using DEXA.

Results

rSOST treatment had no effect on peripheral or axial disease development, bone density or disease severity. Injected rSOST was stable over 8 h and residual levels were evident 24 h after injection, resulting in a cumulative increase in SOST serum levels over the treatment time course. Immunohistochemical examination of SOST levels within the joints in non-rSOST treated PGISp mice showed a significant decrease in the percentage of positive osteocytes in the unaffected joints compared to the affected joints, while no difference was seen in rSOST treated mice. This suggests that rSOST treatment increases the number of SOST-positive osteocytes in unaffected joints but not affected joints, despite having no impact on the number of joints affected by disease.

Conclusions

Although not disease-modifying, rSOST treatment did appear to regulate SOST levels in the joints suggesting biological activity. Further dose response studies are required and SOST may require modifications to improve its bone targeting ability in order to affect tissue formation to a meaningful level in this model.

The genetic basis of ankylosing spondylitis: new insights into disease pathogenesis

Ankylosing spondylitis (AS) is a complex disease involving multiple risk factors, both genetic and environmental. AS patients are predominantly young men, and the disease is characterized by inflammation and ankylosis, mainly at the cartilage–bone interface and enthesis. HLA-B27 has been known to be the major AS-susceptibility gene for more than 40 years. Despite advances made in the past few years, progress in the search for non-human leukocyte antigen susceptibility genes has been hampered by the heterogeneity of the disease. Compared to other complex diseases, such as inflammatory bowel disease (IBD), fewer susceptibility loci have been identified in AS. Furthermore, non-major histocompatibility-complex susceptibility loci discovered, such as ERAP1 and IL23R, are likely contributors to joint inflammation. Identification and confirmation of functional variants remains a significant challenge of investigations involving genome-wide association studies (GWAS). It remains unclear why none of the AS-susceptibility genes identified in GWAS appear to be directly involved in the ankylosing process. Numerous reviews have recently been published on the genetics of AS. Therefore, aside from a brief summary of what AS GWAS has successfully achieved thus far, this review will focus on directions that could address unanswered questions raised by GWAS.

Excessive bone formation in a mouse model of ankylosing spondylitis is associated with decreases in Wnt pathway inhibitors

Introduction

Ankylosing spondylitis (AS) is unique in its pathology where inflammation commences at the entheses before progressing to an osteoproliferative phenotype generating excessive bone formation that can result in joint fusion. The underlying mechanisms of this progression are poorly understood. Recent work has suggested that changes in Wnt signalling, a key bone regulatory pathway, may contribute to joint ankylosis in AS. Using the proteoglycan-induced spondylitis (PGISp) mouse model which displays spondylitis and eventual joint fusion following an initial inflammatory stimulus, we have characterised the structural and molecular changes that underlie disease progression.

Methods

PGISp mice were characterised 12 weeks after initiation of inflammation using histology, immunohistochemistry (IHC) and expression profiling.

Results

Inflammation initiated at the periphery of the intervertebral discs progressing to disc destruction followed by massively excessive cartilage and bone matrix formation, as demonstrated by toluidine blue staining and IHC for collagen type I and osteocalcin, leading to syndesmophyte formation. Expression levels of DKK1 and SOST, Wnt signalling inhibitors highly expressed in joints, were reduced by 49% and 63% respectively in the spine PGISp compared with control mice (P < 0.05) with SOST inhibition confirmed by IHC. Microarray profiling showed genes involved in inflammation and immune-regulation were altered. Further, a number of genes specifically involved in bone regulation including other members of the Wnt pathway were also dysregulated.

Conclusions

This study implicates the Wnt pathway as a likely mediator of the mechanism by which inflammation induces bony ankylosis in spondyloarthritis, raising the potential that therapies targeting this pathway may be effective in preventing this process.

Interferon-γ regulates discordant mechanisms of uveitis versus joint and axial disease in a murine model resembling spondylarthritis

OBJECTIVE

The spondylarthritides (such as ankylosing spondylitis) are multisystem inflammatory diseases that frequently result in uveitis. Despite the common co-occurrence of uveitis with arthritis, there has been no explanation for the susceptibility of the eye to inflammation. Using an innovative intravital videomicroscopic approach, we discovered the coexistence of uveitis with axial and peripheral joint inflammation in mice immunized with cartilage proteoglycan (PG). The aim of this study was to elucidate the characteristics of uveitis and test the impact of interferon-γ (IFNγ) deficiency on the eye versus the joint and spine.

METHODS

Female T cell receptor (TCR)-transgenic mice or IFNγ-knockout mice crossed to TCR-transgenic mice were immunized with PG. Uveitis was assessed by intravital videomicroscopy and histology. The clinical and histopathologic severity of arthritis and spondylitis were evaluated. The bone remodeling process within the spine was assessed by whole-body near-infrared imaging. Immunoblotting and immunofluorescence staining were used to examine the expression of PG and ADAMTS-5 and to examine the cellular composition of eyes with uveitis.

RESULTS

PG neoepitopes along with the aggrecanase ADAMTS-5 were present in the eye, as they were the joint. Anterior uveitis developed in response to PG immunization. The cellular infiltrate consisted mainly of neutrophils and eosinophils. Unexpectedly, IFNγ deficiency markedly exacerbated uveitis while ameliorating joint and spine disease, indicating divergent mechanisms that drive diseases in the eye versus the joints and spine.

CONCLUSION

This study provides the first detailed description of a murine disease model in which uveitis coincides with arthritis and spondylitis. Our observations provide a great opportunity for understanding the pathogenesis of a relatively common but poorly understood disease.

Visualizing arthritic inflammation and therapeutic response by fluorine-19 magnetic resonance imaging (19F MRI)

Background

Non-invasive imaging of inflammation to measure the progression of autoimmune diseases, such as rheumatoid arthritis (RA), and to monitor responses to therapy is critically needed. V-Sense, a perfluorocarbon (PFC) contrast agent that preferentially labels inflammatory cells, which are then recruited out of systemic circulation to sites of inflammation, enables detection by ¹⁹F MRI. With no ¹⁹F background in the host, detection is highly-specific and can act as a proxy biomarker of the degree of inflammation present.

Methods

Collagen-induced arthritis in rats, a model with many similarities to human RA, was used to study the ability of the PFC contrast agent to reveal the accumulation of inflammation over time using ¹⁹F MRI. Disease progression in the rat hind limbs was monitored by caliper measurements and ¹⁹F MRI on days 15, 22 and 29, including the height of clinically symptomatic disease. Naïve rats served as controls. The capacity of the PFC contrast agent and ¹⁹F MRI to assess the effectiveness of therapy was studied in a cohort of rats administered oral prednisolone on days 14 to 28.

Results

Quantification of ¹⁹F signal measured by MRI in affected limbs was linearly correlated with disease severity. In animals with progressive disease, increases in ¹⁹F signal reflected the ongoing recruitment of inflammatory cells to the site, while no increase in ¹⁹F signal was observed in animals receiving treatment which resulted in clinical resolution of disease.

Conclusion

These results indicate that ¹⁹F MRI may be used to quantitatively and qualitatively evaluate longitudinal responses to a therapeutic regimen, while additionally revealing the recruitment of monocytic cells involved in the inflammatory process to the anatomical site. This study may support the use of ¹⁹F MRI to clinically quantify and monitor the severity of inflammation, and to assess the effectiveness of treatments in RA and other diseases with an inflammatory component.

Mapping pathogenesis of arthritis through small animal models

Animal models have been used for a number of decades to study arthritis and have contributed greatly to unravelling mechanisms of pathogenesis and validating new targets for treatment. All animal models have sets of limitations and over the years there has been natural refinement of existing models as well as creation of new ones. The success of genetic modification in mice has fuelled an exponential increase in the use of murine models for arthritis research and has significantly increased our understanding of disease processes. This review focuses on those rodent models of RA and OA that have current utility and are widely used by the research community. We highlight the subtle but important differences in existing models by positioning them on a pathogenesis map whereby model selection is determined by the specific aspect of disease to be studied. We discuss the evolving challenges in in vivo arthritis studies and our perceived gaps for future new model development. The document includes technical and cost implications of performing the described models, and the ethical considerations of such approaches.

Neutralization of IL-17 ameliorates uveitis but damages photoreceptors in a murine model of spondyloarthritis

Introduction

Uveitis, or intraocular inflammatory disease, is a frequent extra-articular manifestation of several forms of arthritis. Despite the frequent co-occurrence of uveitis and arthritis, little is understood of the eye's predisposition to this disease. We recently described a previously unreported uveitis in a murine model of spondyloarthropathy triggered by autoimmunity to aggrecan, a prominent proteoglycan (PG) macromolecule in cartilage. In contrast to the joint and spine, wherein interferon-gamma (IFNγ) deficiency reduced disease, IFNγ deficiency worsened uveitis. Given the regulatory role of IFNγ on the Th17 response and the current focus of anti-interleukin-17 therapeutics in patients with uveitis and spondyloarthritis, we sought to determine the extent to which interleukin (IL)-17 mediates uveitis in the absence of IFNγ.

Methods

Antigen specific T cell cytokine production was measured in splenocyte cultures using multiplex-ELISA. Transgenic (Tg) mice expressing the T cell receptor (TCR) recognizing the dominant arthritogenic epitope in the G1 domain of PG (TCR-Tg), also lacking IFNγ, were immunized with PG. Mice were then systemically administered an anti-IL-17 neutralizing antibody. The onset and severity of peripheral arthritis was evaluated by clinical scoring criteria and histology. Uveitis was assessed using intravital videomicroscopy, which visualizes leukocyte trafficking within the vasculature and tissue of the iris, and by histology.

Results

TCR-Tg splenocytes stimulated in vitro with recombinant G1 peptide demonstrated exacerbated production of cytokines, such as macrophage inflammatory protein (MIP)-1α, MIP-1β, IL-1β, and most notably IL-17A as a consequence of IFNγ deficiency. In vivo, IL-17 inhibition prevented the component of PG-induced arthritis that occurs independently of IFNγ. Blockade of IL-17 ameliorated the ongoing leukocyte trafficking responses within the iris vasculature and tissue, which coincided with reduced infiltration of leukocytes within the anterior and posterior eye segments. However, the anti-IL-17 treatment resulted in unanticipated photoreceptor toxicity.

Conclusions

These data support a protective, regulatory role for IFNγ in suppression of IL-17-mediated intraocular disease and to a lesser extent, joint disease. The unanticipated photoreceptor toxicity raises some caution regarding the use of anti-IL-17 therapeutics until the mechanism of this potential effect is determined.

Assessment of radiographic progression in the spines of patients with ankylosing spondylitis treated with adalimumab for up to 2 years

Introduction

Ankylosing spondylitis (AS) is a chronic rheumatic disease associated with spinal inflammation that subsequently leads to progression of structural damage and loss of function. The fully human anti-tumor necrosis factor (anti-TNF) antibody adalimumab reduces the signs and symptoms and improves overall quality of life in patients with active AS; these benefits have been maintained through 2 years of treatment. Our objective was to compare the progression of structural damage in the spine in patients with AS treated with adalimumab for up to 2 years versus patients who had not received TNF antagonist therapy.

Methods

Radiographs from patients with AS who received adalimumab 40 mg every other week subcutaneously were pooled from the Adalimumab Trial Evaluating Long-Term Efficacy and Safety for Ankylosing Spondylitis (ATLAS) study and a Canadian AS study (M03-606). Radiographic progression from baseline to 2 years in the spine of adalimumab-treated patients from these two studies (adalimumab cohort, n = 307) was compared with an historic anti-TNF-naïve cohort (Outcome in AS International Study [OASIS], n = 169) using the modified Stoke AS Spine Score (mSASSS) method.

Results

mSASSS results were not significantly different between the adalimumab cohort and the OASIS cohort, based on baseline and 2-year radiographs. Mean changes in mSASSS from baseline to 2 years were 0.9 for the OASIS cohort and 0.8 for the adalimumab cohort (P = 0.771), indicating similar radiographic progression in both groups. When results for patients in the OASIS cohort who met the baseline disease activity criteria for the ATLAS and Canadian studies (OASIS-Eligible cohort) were analyzed, there was no significant difference in mean change in mSASSS from baseline to 2 years between OASIS-Eligible patients and adalimumab-treated patients; the mean changes in mSASSS were 0.9 for the OASIS-Eligible cohort and 0.8 for the adalimumab cohort (P = 0.744).

Conclusions

Two years of treatment with adalimumab did not slow radiographic progression in patients with AS, as assessed by the mSASSS scoring system, when compared with radiographic data from patients naïve to TNF antagonist therapy.

Trial registration

Canadian study (M03-606) ClinicalTrials.gov identifier: NCT00195819; ATLAS study (M03-607) ClinicalTrials.gov identifier: NCT00085644.

BALB/c mice genetically susceptible to proteoglycan-induced arthritis and spondylitis show colony-dependent differences in disease penetrance

Introduction

The major histocompatibility complex (H-2d) and non-major histocompatibility complex genetic backgrounds make the BALB/c strain highly susceptible to inflammatory arthritis and spondylitis. Although different BALB/c colonies develop proteoglycan-induced arthritis and proteoglycan-induced spondylitis in response to immunization with human cartilage proteoglycan, they show significant differences in disease penetrance despite being maintained by the same vendor at either the same or a different location.

Methods

BALB/c female mice (24 to 26 weeks old after 4 weeks of acclimatization) were immunized with a suboptimal dose of cartilage proteoglycan to explore even minute differences among 11 subcolonies purchased from five different vendors. In vitro-measured T-cell responses, and serum cytokines and (auto)antibodies were correlated with arthritis (and spondylitis) phenotypic scores. cDNA microarrays were also performed using spleen cells of naïve and immunized BALB/cJ and BALB/cByJ mice (both colonies from The Jackson Laboratory, Bar Harbor, ME, USA), which represent the two major BALB/c sublines.

Results

The 11 BALB/c colonies could be separated into high (n = 3), average (n = 6), and low (n = 2) responder groups based upon their arthritis scores. While the clinical phenotypes showed significant differences, only a few immune parameters correlated with clinical or histopathological abnormalities, and seemingly none of them affected differences found in altered clinical phenotypes (onset time, severity or incidence of arthritis, or severity and progression of spondylitis). Affymetrix assay (Affymetrix, Santa Clara, CA, USA) explored 77 differentially expressed genes (at a significant level, P < 0.05) between The Jackson Laboratory's BALB/cJ (original) and BALB/cByJ (transferred from the National Institutes of Health, Bethesda, MD, USA). Fourteen of the 77 differentially expressed genes had unknown function; 24 of 77 genes showed over twofold differences, and only 8 genes were induced by immunization, some in both colonies.

Conclusions

Using different subcolonies of the BALB/c strain, we can detect significant differences in arthritis phenotypes, single-nucleotide polymorphisms (SNPs), and a large number of differentially expressed genes, even in non-immunized animals. A number of the known genes (and SNPs) are associated with immune responses and/or arthritis in this genetically arthritis-prone murine strain, and a number of genes of as-yet-unknown function may affect or modify clinical phenotypes of arthritis and/or spondylitis.

[Contribution of animal models to the study and treatment of systemic autoimmune disease]

Animal models of autoimmune diseases, either spontaneous or induced, have been very useful tools to investigate the mechanisms involved in the pathogenesis of human autoimmune diseases as well as in the design of new therapeutic strategies for their treatment. The development of biotechnology and molecular biology resulted in the production of transgenic animals overexpressing or lacking a given protein. As a result of this technology, a great number of animal models of human diseases have been developed in recent years. A further evolution in transgenic methodology allows the selective control of gene expression in a particular organ or tissue at desired time points during embryonic or postnatal development. In the present article the authors discuss the advantages and inconveniences of animal models and describe the most frequently employed models in the study of 4 rheumatologic syndromes with an autoimmune origin: rheumatoid arthritis, systemic lupus erythematosus, scleroderma, and spondiloarthritis.

Animal models of spondyloarthritis

Animal models are available for the study of several different aspects of spondyloarthritis. The models include naturally occurring spontaneous disorders in primates and rodents, spontaneous disorders in transgenic or gene-deleted rodents and induced disorders in rodents. Areas of investigation to which these models contribute include the role HLA-B27, processes of spinal and peripheral joint inflammation and calcification, immune responses to candidate antigens and the role of TNF.

Radiographic progression of ankylosing spondylitis after up to two years of treatment with etanercept

OBJECTIVE

To investigate the effect of etanercept therapy on radiographic progression in patients with ankylosing spondylitis (AS).

METHODS

Patients with AS who had previously participated in a 24-week randomized, double-blind, placebo-controlled trial of etanercept therapy were enrolled in a 72-week open-label extension. Radiographs of the cervical and lumbar spine from patients who received etanercept (25 mg twice weekly) for up to 96 weeks were compared with radiographs from patients in a large prevalence cohort (Outcome Assessments in Ankylosing Spondylitis International Study [OASIS]) who had not been treated with anti-tumor necrosis factor alpha (anti-TNFalpha) agents. Radiographs obtained at 2 time points up to 96 weeks apart from patients in both study populations were digitized and read by 2 independent readers who were blinded with regard to patient group and sequence. The primary end point was the 96-week change in the modified Stoke AS Spine Score (mSASSS).

RESULTS

A total of 257 patients treated with etanercept were compared with 175 unselected patients from the OASIS study. There was no significant difference in the change in the mSASSS from baseline among patients who received etanercept (mean +/- SD 0.91 +/- 2.45) versus those from the OASIS group (0.95 +/- 3.18).

CONCLUSION

Unlike other inflammatory rheumatic diseases such as rheumatoid arthritis and psoriatic arthritis, structural progression in AS seems to be independent of TNF, despite the fact that TNF is responsible for the signs and symptoms due to inflammation in this disease.

The intimate relationship between gut and joint in spondyloarthropathies

PURPOSE OF REVIEW

The aim of this article is to highlight recent progress in the combined joint and gut disease in spondyloarthropathies.

RECENT FINDINGS

A set of genes has been identified that are differentially expressed in the colon of spondyloarthropathy and Crohn's disease patients. Reduction of human leukocyte antigen B27 (HLA B27) misfolding by additional beta2-microglobulin in HLA B27 transgenic rats unexpectedly increased disease severity, with more similarities to spondyloarthropathies. By contrast, colitis disappeared.

SUMMARY

Human genomic studies combined with animal model research provide new clues concerning the common pathogenesis of spondyloarthropathy and Crohn's disease, further substantiating the unique relationship between gut and joint inflammation.

Ankylosing spondylitis

Ankylosing spondylitis is a common inflammatory rheumatic disease that affects the axial skeleton, causing characteristic inflammatory back pain, which can lead to structural and functional impairments and a decrease in quality of life. New imaging techniques and therapies have substantially changed the management of this disease in the past decade. Whether inhibition of radiographic progression and structural damage can be reached with available drugs is as yet unclear. Furthermore, treatment with non-steroidal anti-inflammatory agents and physiotherapy remains an important approach to long-term management of patients with ankylosing spondylitis. The new treatment options with tumour necrosis factor blockers seems a breakthrough for patients refractory to conventional treatment.

Animal models of spondyloarthritis

PURPOSE OF REVIEW

The aim of this article is to review new insights into spondyloarthritis obtained in animal models during the last year.

RECENT FINDINGS

HLA-B27 misfolding has been demonstrated in HLA-B27/human beta2-microglobulin transgenic rats. HLA-B27 misfolding is associated with a typical unfolded protein stress response and with an interferon-response signature. Prebiotic treatment of these rats reduced colitis and arthritis. Proteoglycan-induced spondylitis is distinct from proteoglycan-induced arthritis. Specific susceptibility loci for proteoglycan-induced spondylitis have been demonstrated. Bone morphogenetic proteins are important in new cartilage and bone formation in ankylosing enthesitis. Psoriasis and psoriatic arthritis-like disease develops in conditional double JunB/c-Jun knockout mice.

SUMMARY

Insights into the molecular signaling pathways driving HLA-B27 associated spondylitis, autoimmune spondylitis, ankylosing enthesitis and psoriasis, resulting from animal models, identify new and specific therapeutic targets in spondyloarthritis.

Experimental spondyloarthropathies: Animal models of ankylosing spondylitis

Spondyloarthropathies (SpAs), including ankylosing spondylitis, are chronic inflammatory diseases of the axial skeleton. Genomic scans of SpA families revealed the overwhelming complexity of the disease, which appears to be under the control of over 20 chromosome loci, including the major SpA gene HLA-B27 within class I of the major histocompatibility complex (MHC). Animal models confirmed the primary role of MHC in SpA susceptibility and supported the hypothesis that certain enterobacterial infections can trigger SpA. Immunization of mice with proteoglycan aggrecan also can provoke SpA, thus providing the opportunity to study genetic and clinical details of the disease initiation.

Can unresolved infection precipitate autoimmune disease?

Autoimmune diseases are frequently postulated to arise as post-infectious phenomena. Here we survey the evidence supporting these theories, with particular emphasis on Crohn's disease and ankylosing spondylitis. Direct proof that infection establishes persistent autoimmunity remains lacking, although it may provoke a prolonged inflammatory response when occurring on a susceptible immunological background. The argument of infective causality is by no means trivial, since it carries important consequences for the safety of vaccine development.

Immunohistochemical analysis of hip arthritis in ankylosing spondylitis: Evaluation of the bone–cartilage interface and subchondral bone marrow

OBJECTIVE

Previous histopathologic and magnetic resonance imaging studies suggest that the subchondral bone marrow might be the primary site of inflammation in patients with ankylosing spondylitis (AS) and that this might be reflected by inflammation found in hip joints. The aim of this study was to conduct an immunohistologic assessment of the bone-cartilage interface and subchondral bone marrow in AS patients with hip arthritis.

METHODS

We collected femoral heads from patients with AS, osteoarthritis (OA), and rheumatoid arthritis (RA) who were undergoing hip replacement. The subchondral bone marrow and bone-cartilage interface were assessed immunohistochemically by evaluating infiltrating T cells, microvessel density, and osteoclasts. Areas of the femoral head surface with and without cartilage were assessed separately.

RESULTS

At sites with surface cartilage, we found subchondral infiltration of CD3+ T cell aggregates at significantly higher numbers in AS patients as compared with OA patients, but not RA patients. At sites of complete cartilage destruction, the frequency of CD3+ T cell aggregates was significantly reduced as compared with sites with cartilage on the surface in AS patients, but not in RA patients. Similar differences were found for CD4+ and CD8+ T cells. Only at sites with surface cartilage, but not those without, angiogenesis and osteoclastic foci in the subchondral bone marrow in AS patients were significantly increased as compared with RA patients and with OA patients.

CONCLUSION

These findings suggest that the subchondral bone marrow and bone-cartilage interface are primary sites of inflammation in AS and that cartilage might be necessary for the induction of inflammation.

[Enthesis as a target element in spondylarthritides]

Enthesis is a structure frequently involved in spondyloarthritides. According to a recent hypothesis, it may play a key role in the pathogenesis of these entities. The present review discusses the most important aspects of current knowledge of enthesis, such as its anatomy and the extracellular matrix components present within it. Clinical evaluation and the new imaging techniques (magnetic resonance imaging and ultrasound) that complement its evaluation will be briefly described. Immunohistological studies as well as animal models developed with enthesis molecules underline the importance of enthesis in the pathogenesis of spondyloarthritides. Finally, the latest research assessing the T cell response to enthesis components in patients with ankylosing spondylitis will be reviewed.

Two Major Interacting Chromosome Loci Control Disease Susceptibility in Murine Model of Spondyloarthropathy

Autoimmune spondylitis was induced in BALB/c mice and their MHC-matched (BALB/c x DBA/2)F1 and F2 hybrids by systemic immunization with cartilage/intervertebral disk proteoglycan (PG). As in human ankylosing spondylitis, the MHC was the major permissive genetic locus in murine PG-induced spondylitis (PGIS). Two major non-MHC chromosome loci with highly significant linkage were found on chromosomes 2 (Pgis2) and 18 (Pgis1) accounting for 40% of the entire F2 trait variance. The dominant spondylitis-susceptibility allele for Pgis2 locus is derived from the BALB/c strain, whereas the Pgis1 recessive allele was present in the disease-resistant DBA/2 strain. The Pgis1 locus significantly affected the disease-controlling Pgis2 locus, inducing as high incidence of spondylitis in F2 hybrids as was found in the spondylitis-susceptible parent BALB/c strain. Additional disease-controlling loci with suggestive linkage were mapped to the chromosomes 12, 15, and 19. Severity of spondylitis in F2 mice positively correlated with serum levels of amyloid A, IL-6, and Pg-specific Abs, and showed negative correlation with Ag-induced T cell proliferation, IFN-gamma, IL-4, and TNF-alpha production. A major locus controlling serum IL-6 was found on chromosome 14 near osteoclast differentiation factor Tnfsf11. Locus on chromosome 11 near the Stat3 and Stat5 genes controlled serum level of the Ig IgG2a isotype. The two major genetic loci Pgis1 and Pgis2 of murine spondylitis were homologous to chromosome regions in human genome, which control ankylosing spondylitis in human patients. Thus, this animal model of experimentally induced spondylitis might facilitate the identification of spondylitis-susceptibility genes in humans.