Genetic control of experimental spondylarthropathy

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.

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.

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.

Proteoglycan-induced arthritis and recombinant human proteoglycan aggrecan G1 domain-induced arthritis in BALB/c mice resembling two subtypes of rheumatoid arthritis

OBJECTIVE

To develop a simplified and relatively inexpensive version of cartilage proteoglycan-induced arthritis (PGIA), an autoimmunity model of rheumatoid arthritis (RA), and to evaluate the extent to which this new model replicates the disease parameters of PGIA and RA.

METHODS

Recombinant human G1 domain of human cartilage PG containing "arthritogenic" T cell epitopes was generated in a mammalian expression system and used for immunization of BALB/c mice. The development and progression of arthritis in recombinant human PG G1-immunized mice (designated recombinant human PG G1-induced arthritis [GIA]) was monitored, and disease parameters were compared with those in the parent PGIA model.

RESULTS

GIA strongly resembled PGIA, although the clinical symptoms and immune responses in mice with GIA were more uniform than in those with PGIA. Mice with GIA showed evidence of stronger Th1 and Th17 polarization than those with PGIA, and anti-mouse PG autoantibodies were produced in different isotype ratios in the 2 models. Rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies were detected in both models; however, serum levels of IgG-RF and anti-CCP antibodies were different in GIA and PGIA, and both parameters correlated better with disease severity in GIA than in PGIA.

CONCLUSION

GIA is a novel model of seropositive RA that exhibits all of the characteristics of PGIA. Although the clinical phenotypes are similar, GIA and PGIA are characterized by different autoantibody profiles, and the 2 models may represent 2 subtypes of seropositive RA, in which more than 1 type of autoantibody can be used to monitor disease severity and response to treatment.

The genetic background of ankylosing spondylitis

It has long been known that the major histocompatibility complex (MHC) is essentially involved in genetic susceptibility to ankylosing spondylitis (AS). The HLA-B27 antigen has been accounted for 20 to 50% of the total genetic risk for this disease. However, susceptibility to AS cannot be fully explained by associations with the MHC. Recent studies including linkage analyses as well as candidate gene and, most recently, genome-wide association studies indicate significant associations of the interleukin-1 gene cluster, interleukin-23 receptor and ARTS1 genes as well as other possible loci with AS. In the murine model of proteoglycan-induced spondylitis, two susceptibility loci termed Pgis1 and Pgis2 were identified. Thus, AS is not a single-gene disease and the involvement of multiple non-MHC genes may account for the individual as well as geographical differences seen in AS.

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.

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.

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.

Expression of extracellular matrix molecules typical of articular cartilage in the human scapholunate interosseous ligament

The scapholunate interosseous ligament (SLIL) connects the scaphoid and lunate bones and plays a crucial role in carpal kinematics. Its rupture leads to carpal instability and impairment of radiocarpal joint function. As the ligament is one of the first structures affected in rheumatoid arthritis, we conducted an immunohistochemical study of cadaveric tissue to determine whether it contains known autoantigens for rheumatoid arthritis. We immunolabelled the ligament from one hand in 12 cadavers with monoclonal antibodies directed against a wide range of extracellular matrix (ECM) molecules associated with both fibrous and cartilaginous tissues. The labelling profile has also enabled us to comment on how the molecular composition of the ligament relates to its mechanical function. All regions of the ligament labelled for types I, III and VI collagens, chondroitin 4 and 6 sulphates, keratan sulphate, dermatan sulphate, versican, tenascin and cartilage oligomeric matrix protein (COMP). However, both entheses labelled strongly for type II collagen, aggrecan and link protein and were distinctly fibrocartilaginous. In some regions, the ligament attached to bone via a region of hyaline cartilage that was continuous with articular cartilage. Labelling for cartilage molecules in the midsubstance was most evident dorsally. We conclude that the SLIL has an ECM which is typical of other highly fibrocartilaginous ligaments that experience both tensile load and shear. The presence of aggrecan, link protein, COMP and type II collagen could explain why the ligament may be a target for autoantigenic destruction in some forms of rheumatoid arthritis.