Progressive ankylosis in mice. An animal model of spondylarthropathy. I. Clinical and radiographic findings

Immunoproteasome in animal models of Duchenne muscular dystrophy

Increased proteasome activity has been implicated in the atrophy and deterioration associated with dystrophic muscles of Duchenne muscular dystrophy (DMD). While proteasome inhibitors show promise in the attenuation of muscle degeneration, proteasome inhibition-induced toxicity was a major drawback of this therapeutic strategy. Inhibitors that selectively target the proteasome subtype that is responsible for the loss in muscle mass and quality would reduce side effects and be less toxic. This study examined proteasome activity and subtype populations, along with muscle function, morphology and damage in wild-type (WT) mice and two murine models of DMD, dystrophin-deficient (MDX) and dystrophin- and utrophin-double-knockout (DKO) mice. We found that immunoproteasome content was increased in dystrophic muscles while the total proteasome content was unchanged among the three genotypes of mice. Proteasome proteolytic activity was elevated in dystrophic muscles, especially in DKO mice. These mice also exhibited more severe muscle atrophy than either WT or MDX mice. Muscle damage and regeneration, characterized by the activity of muscle creatine kinase in the blood and the percentage of central nuclei were equally increased in dystrophic mice. Accordingly, the overall muscle function was similarly reduced in both dystrophic mice compared with WT. These data demonstrated that there was transformation of standard proteasomes to immunoproteasomes in dystrophic muscles. In addition, DKO that showed greatest increase in proteasome activities also demonstrated more severe atrophy compared with MDX and WT. These results suggest a putative role for the immunoproteasome in muscle deterioration associated with DMD and provide a potential target for therapeutic intervention.

Aberrant axial mineralization precedes spinal ankylosis: a molecular imaging study in ank/ank mice

INTRODUCTION

The diagnosis of ankylosing spondylitis is made from a combination of clinical features and the presence of radiographic evidence that may be detected only after many years of inflammatory back pain. It is not uncommon to have a diagnosis confirmed 5 to 10 years after the initial onset of symptoms. Development of a more-sensitive molecular imaging technology to detect structural changes in the joints would lead to earlier diagnosis and quantitative tracking of ankylosis progression. Progressive ankylosis (ank/ank) mice have a loss of function in the Ank gene, which codes for a regulator of PPi transport. In this study, we used these ank/ank mutant mice to assess a noninvasive, quantitative measure of joint ankylosis with near-infrared (NIR) molecular imaging in vivo.

METHODS

Three age groups (8, 12, and 18 weeks) of ank/ank (15 mice) and wild-type littermates (12 +/+ mice) were assessed histologically and radiographically. Before imaging, OsteoSense 750 (bisphosphonate pamidronate) was injected i.v. Whole-body images were analyzed by using the multispectral Maestro imaging system.

RESULTS

OsteoSense 750 signals in the paw joints were higher in ank/ank mice in all three age groups compared with controls. In the spine, significantly higher OsteoSense 750 signals were detected early, in 8-week-old ank/ank mice compared with controls, although minimal radiographic differences were noted at this time point. The molecular imaging changes in the ank/ank spine (8 weeks) were supported by histologic changes, including calcium apatite crystals at the edge of the vertebral bodies and new syndesmophyte formation.

CONCLUSIONS

Changes in joint pathology of ank/ank mice, as evaluated by histologic and radiographic means, are qualitative, but only semiquantitative. In contrast, molecular imaging provides a quantitative assessment. Ankylosis in ank/ank mice developed simultaneously in distal and axial joints, contrary to the previous notion that it is a centripetal process. NIR imaging might be feasible for early disease diagnosis and for monitoring disease progression in ankylosing spondylitis.

Pain behavior measures to quantitate joint pain and response to neurotoxin treatment in murine models of arthritis

OBJECTIVE

To evaluate the validity of newly developed pain behavior measures in two murine models of inflammatory arthritis and to determine the ability of these measures to evaluate the analgesic effectiveness of intra-articular (IA) botulinum toxin type A (BoNT/A) for treatment of arthritis pain.

DESIGN

Acute inflammatory arthritis was produced in adult female mice by IA injection of carrageenan and chronic inflammatory arthritis by IA injection of CFA. The presence of arthritis was confirmed by the presence of swelling and erythema. A menu of pain behavior measures was devised for quantitating pain in these models including tenderness, and spontaneous nocturnal wheel running. Toxicity due to neurotoxin was measured as gross limb weakness and impaired functional ability during wheel running.

RESULTS

Tenderness measures and spontaneous nocturnal wheel-running are valid measures of arthritis pain and are sensitive to the effects of analgesia. Narcotic analgesics are effective, but in fully analgesic doses impair wheel-running. IA BoNT/A is an effective analgesic for chronic arthritis pain, but not for acute arthritis pain. High doses can produce local limb muscle weakness, which impairs wheel-running function. Doses of botulinum toxin that are not toxic retain their analgesic function.

CONCLUSIONS

Tenderness and spontaneous pain behavior measures are valid and sensitive for the measurement of pain and analgesia in murine models of inflammatory arthritis. Effective narcotic analgesia produces a decline in function in mice similar to that seen in humans. IA neurotoxin is a promising therapy for chronic inflammatory arthritis but may not be effective for acute arthritis pain.

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.

Renal calcium stones: insights from the control of bone mineralization

Extracellular pyrophosphate (PPi) plays a central role in the control of normal bone mineralization since it antagonizes inorganic phosphate in the promotion of hydroxyapatite deposition. Studies using knock-out mice have established the functional importance of PPi generation via nucleotide pyrophosphatase phosphodiesterases (NPP) and of PPi transmembrane transport by the progressive ankylosis (ANK) protein. Tissue non-specific alkaline phosphatase activity counteracts this by hydrolysis of PPi to inorganic phosphate. The molecular nature and transport function of ANK are reviewed. A close parallel is drawn between the controlled mineralization of bone and the prevention of abnormal calcium crystal deposition within the kidney, especially when concentrated urine is produced. Pyrophosphate is present in urine, and ANK is expressed in the cortical collecting duct where PPi transport to both the tubular lumen and the renal interstitium may occur. Pyrophosphate may also be generated here by nucleoside triphosphate diphosphohydrolases (NTPD2 and 3) together with NPP1. Alkaline phosphatase activity is restricted to the proximal nephron, remote from these sites of PPi generation, transport and function. The physiological importance of PPi generation and transport in preventing idiopathic calcium renal stone disease and nephrocalcinosis now needs to be established.

Spondyloarthropathy: an independent risk factor for kidney stones

PURPOSE

To better stratify risk and to verify previous prevalence reports, we conducted a retrospective cohort study comparing the lifetime incidence of nephrolithiasis in patients with spondyloarthropathies (SpA) and rheumatoid arthritis (RA).

PATIENTS AND METHODS

Patients with SpA or rheumatoid factor-positive RA were identified from the rheumatology clinics of two Veterans Affairs hospitals and the University of Minnesota. Among them, 168 were confirmed to meet the American College of Rheumatology criteria and gave informed consent to participation. They were sent a survey regarding their rheumatologic diagnosis, coexistent conditions, medications, and history of kidney stones. Of the total, 143 patients responded and met the criteria for analysis. Rheumatoid arthritis patients were age and sex matched with SpA patients as controls.

RESULTS

Populations were similar in all categories except that RA patients were more likely to have used prednisone (P < 0.001), bisphosphonates (P < 0.001), and calcium supplementation (P = 0.03). Kidney stones were reported by 23 (29.11%) of the 79 SpA patients compared with 8 (12.5%) of the 64 RA patients (chi (2) = 5.75; P = 0.025). Subgroup analysis of self-reporting stone history in 85 patients was found to be reliable on imaging review (sensitivity 82%; specificity 100%).

CONCLUSIONS

Self-reporting of kidney stones by patients is a reliable measure. Despite adjusting for medication use and matching two similar arthritic populations, patients with SpA had a higher incidence of kidney stones than those with RA. This finding suggests that SpA is an independent risk factor for nephrolithiasis. Future studies will evaluate urinary risk factors and polymorphisms in the ANKH gene that may predispose to stone formation in this high-risk group.

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.

Progressive arthropathy in mice with a targeted disruption of the Mop3/Bmal-1 locus

Disruption of the murine Mop3 (also known as Bmal1 or Arntl) locus results in a loss of behavioral and molecular circadian rhythms. Although Mop3 null mice do not display anomalies in early development, they do display reduced activity as they age. In an effort to explain this decreased activity, we characterized the physiological and anatomical changes that occurred with age. We observed that Mop3 null mice display an increased mortality after 26 weeks of age and a phenotype best described as a progressive noninflammatory arthropathy. Although little pathology is observed prior to 11 weeks of age, by 35 weeks of age essentially all Mop3 null animals develop joint ankylosis due to flowing ossification of ligaments and tendons and almost complete immobilization of weight-bearing and nonweight-bearing joints. This pathology appears to explain the decreased activity of Mop3 null mice and suggests that MOP3 is an inhibitor of ligament and tendon ossification.

A longitudinal study on an autoimmune murine model of ankylosing spondylitis

BACKGROUND

Proteoglycan aggrecan (PG)-induced arthritis (PGIA) is the only systemic autoimmune murine model which affects the axial skeleton, but no studies have been performed characterising the progression of spine involvement.

OBJECTIVES

To follow pathological events in experimental spondylitis, and underline its clinical, radiographic, and histological similarities to human ankylosing spondylitis (AS); and to determine whether the spondyloarthropathy is a shared phenomenon with PGIA, or an "independent" disease.

METHODS

Arthritis/spondylitis susceptible BALB/c and resistant DBA/2 mice, and their F1 and F2 hybrids were immunised with cartilage PG, and radiographic and histological studies were performed before onset and weekly during the progression of spondylitis.

RESULTS

About 70% of the PG immunised BALB/c mice develop spondyloarthropathy (proteoglycan-induced spondylitis (PGISp), and the progression of the disease is very similar to human AS. It begins with inflammation in the sacroiliac joints and with enthesitis, and then progresses upwards, affecting multiple intervertebral disks. In F2 hybrids of arthritis/spondylitis susceptible BALB/c and resistant DBA/2 mice the incidence of arthritis was 43.5%, whereas the incidence of spondylitis was >60%. Some arthritic F2 hybrid mice had no spondylitis, whereas others developed spondylitis in the absence of peripheral arthritis.

CONCLUSIONS

The PGISp model provides a valuable tool for studying autoimmune reactions in spondylitis, and identifying genetic loci associated with spondyloarthropathy.

Investigation of the role of ANKH in ankylosing spondylitis

OBJECTIVE

The ank/ank mouse develops a phenotype similar to ankylosing spondylitis (AS) in humans. ANKH, the human homolog of the mutated gene in the ank/ank mouse, has been implicated in familial autosomal-dominant chondrocalcinosis and autosomal-dominant craniometaphyseal dysplasia. This study was undertaken to investigate the role of ANKH in susceptibility to and clinical manifestations of AS.

METHODS

Sequence variants were identified by genomic sequencing of the 12 ANKH exons and their flanking splice sites in 48 AS patients; variants were then screened in 233 patients and 478 controls. Linkage to the ANKH locus was assessed in 185 affected-sibling-pair families.

RESULTS

Five single-nucleotide polymorphisms were identified within the coding region and flanking splice sites. No association between either susceptibility to AS or its clinical manifestations and these novel polymorphisms, or between disease susceptibility and 3 known promoter variants, was seen. No linkage between the ANKH locus and AS was observed. Multipoint exclusion mapping rejected the hypothesis of a locus of a magnitude lambda>/=1.4 (logarithm of odds score <-2) (equivalent to a genetic contribution of >10% to the AS sibling recurrence risk ratio) within this area contributing to AS.

CONCLUSION

These findings indicate that ANKH is not significantly involved in susceptibility to or clinical manifestations of AS.

Polypeptide growth factors and phorbol ester induce progressive ankylosis (ank) gene expression in murine and human fibroblasts

Polypeptide growth factors promote cellular proliferation by binding to specific plasma membrane-anchored receptors. This interaction triggers the phosphorylation of signal transducing molecules and the transcriptional activation of numerous genes. We have used a differential display approach to identify fibroblast growth factor (FGF)-1-inducible genes in murine NIH 3T3 fibroblasts. Here we report that one of these genes encodes ank, a type IIIa transmembrane protein reported to function in cells as an inorganic pyrophosphate transporter. FGF-1 induction of ank mRNA expression is first detectable at 2 h after growth factor addition and is dependent on de novo RNA and protein synthesis. Ank gene expression is also upregulated after treating quiescent fibroblasts with several other mitogenic agents (e.g., calf serum or platelet-derived growth factor-BB) or the tumor promoter phorbol 12-myristate 13-acetate. Furthermore, in comparison to parental NIH 3T3 cells, oncogene-transformed NIH 3T3 cells constitutively express elevated levels of ank mRNA. FGF-1 also increases ank gene expression in non-immortalized human embryonic lung fibroblasts. Finally, the murine and human ank genes are expressed in vivo in a tissue-specific manner, with highest levels of mRNA expression found in brain, heart, and skeletal muscle. These results indicate that ank is a growth factor-regulated delayed-early response gene in mammalian cells, and we propose that increased ank expression during cell cycle progression may be necessary to maintain proper intracellular pyrophosphate levels during conditions of high cellular metabolic activity.

The ank gene story

The underlying molecular defect resulting in the abnormal calcification observed in ank/ank mice has been identified. The responsible nonsense mutation affects the protein product of ank, resulting in diminished production of extracellular inorganic pyrophosphate, an important inhibitor of nucleation and of the growth of apatite crystals. The ank gene product is one of several cell membrane proteins, including ectonucleoside triphosphate pyrophosphohydrolase enzymes and alkaline phosphatase, that regulate extracellular inorganic pyrophosphate levels and thereby regulate mineralization.

Phosphocitrate prevents disease progression in murine progressive ankylosis

OBJECTIVE

Mice with progressive ankylosis, a spontaneous arthropathy, were treated with phosphocitrate (PC) in vivo to determine the effect of PC on disease progression.

METHODS

Two groups of mice with progressive ankylosis (matched for age, weight, and sex) were treated parenterally for 6 weeks with either PC or saline vehicle.

RESULTS

Clinically, histologically, and microradiographically, there were significant differences in disease progression and severity in the PC-treated and the saline-treated mice.

CONCLUSION

PC appears to inhibit disease progression in murine progressive ankylosis.

Transient inhibition of murine progressive ankylosis by indomethacin

Murine progressive ankylosis (MPA) is an heritable disorder which produces acute arthritis and ankylosis of peripheral and axial joints similar to ankylosing spondylitis. Because indomethacin inhibits heterotopic bone formation in vivo, we studied its effects on MPA. Indomethacin was administered for 6 weeks beginning at weaning to litters from heterozygote breeder pairs. Progression curves for peripheral, spinal and thoracic joint ankylosis in treated and untreated ank/ank animals wer compared. There was no delay in ankylosis of peripheral or spinal joint ankylosis in MPA animals treated with indomethacin. interestingly, transient delay of thoracic ankylosis occurred in indomethacin treated MPA animals.

Calcergy in murine progressive ankylosis

Murine progressive ankylosis (MPA) is characterized by periarticular ossification and joint ankylosis. We studied calcergy and calciphylaxis in MPA. Calcergy represents a chemical attraction between heavy metal salts and apatite followed by hydroxyapatite deposition around collagen. Mice were injected subcutaneously with FeCl2, PbAcetate, and saline, and sacrificed at intervals between 5 minutes and 14 days. Section of skin and subcutaneous tissues were stained with Von Kossa's stain. No mice developed calcifylaxis. PbAcetate produced calcergy in all mice. MPA mice exhibited calcergy qualitatively and quantitatively the same as normal mice suggesting abnormal calcergy is not responsible for joint ankylosis in MPA.

Spontaneous rheumatoid-like arthritis in a line of mice sensitive to collagen-induced arthritis

Twenty-eight percent of 13-month-old male mice of the high antibody responder line of Biozzi's selection I (HI) spontaneously developed a long-lasting inflammatory arthritis. This disease was clinically and histologically similar to human rheumatoid arthritis. The synovium of joints and some tendons was hypertrophied, with thickening of the synovial cell layer and infiltration by polymorphonuclear and mononuclear leukocytes. In some cases, synovial pannus formation led to destructive damage of articular cartilage and bone. Rheumatoid factor and antinuclear, anti-DNA, and anti-type II collagen (CII) antibodies were often found in the sera of both arthritic mice and clinically normal littermates. The presence of CII autoantibodies in this line of mice suggests that a potentially harmful anti-CII T cell autoimmunity can also develop spontaneously and lead to joint damage. Moreover, HI mice are also susceptible to collagen-induced arthritis, while a closely related mouse line (HII) is resistant to both diseases. These data support the hypothesis that collagen-induced arthritis is pathogenetically related both to this spontaneous arthritis and to rheumatoid arthritis.

Intervertebral disk mineralization in progressive ankylosis mice

The objective of this study was to quantitate the increasing mineral content of the intervertebral disk of progressive ankylosis mice and to identify changes in serum and bone mineral levels that might occur concurrent with the rapid mineralization of the disk. Serum calcium (8.43 +/- 1.01 mg/dl vs. 7.48 +/- 2.07) and phosphorus (6.66 +/- 1.32 mg/dl vs. 5.53 +/- 2.19) levels were within normal limits. Ankylosing mice had a 5.2% decrease in water content, a 24% increase in calcium content and a 29% decrease in phosphorus content of the intervertebral disks. The magnitude of these changes increased with age. There was no significant difference in mineral or water content of the vertebral bodies. The mineral levels per gram of tissue were much greater in ankylosing disks than in the vertebral bodies. No correlation was identified between ankylosing disks and serum or bone mineral levels.

Dysfunction of HLA-B27

Every HLA antigen, as defined by the WHO-HLA Nomenclature, is unique. The major function of these molecules is to present antigen-peptides to the T-cell receptor, thereby contributing to the immunological defence mechanism. This function is regulated for each MHC antigen by its unique structure, with the peptide-binding pockets of the three-dimensional groove of the corresponding molecules playing the critical role. However, HLA-B27 is special by virtue of its disease association(s). Various aspects which might provide an explanation for--or at least a clue to an understanding of the specific role of--B27 in its disease associations are reviewed. Since it appears that there are no published experimental data which would support either of the alternative hypothetical possibilities, the bulk of current theories must therefore be purely speculative. The only lead to a better understanding of the function of B27 in disease associations is the postinfectious reactive arthritis. If it is the B27 molecule itself which is involved, further in vivo work on B27 transgenic animals might help solve this problem with its numerous unknown factors.