Animal models of systemic sclerosis

Co-existence of Marfan syndrome and systemic sclerosis: A case report and a hypothesis suggesting a common link

FBN1 gene encodes for the connective tissue protein fibrillin-1 which can also regulate the profibrotic cytokine transforming growth factor (TGF)-ß1. Mutations in the FBN1 gene cause Marfan syndrome (MFS), a genetic condition with defective connective tissues. FBN1 haplotypes and single nucleotide polymorphisms have also been reported to be associated with systemic sclerosis (SSc), a connective tissue disease characterized by fibrosis of multiple organs. Furthermore, the duplication of the Fbn1 gene causes a SSc-like disease in the TsK1 mouse model. To the best of our knowledge, there are no reports of MFS and SSc co-existing in a patient. Here, we describe a 46-year-old woman who presented with cardiac failure. She had a family history of MFS. Physical examination revealed marfanoid habitus and scleroderma features. Echocardiography demonstrated dilated cardiomyopathy with aortic root dilatation, aortic regurgitation and mitral regurgitation. Cardiac magnetic resonance imaging was consistent with dilated cardiomyopathy, mid-wall fibrosis at basal septal wall and dilated aortic root. Extractable nuclear antigen panel detected anti-Scl 70. She fulfilled Ghent criteria for MFS and satisfied American College of Rheumatology/ European League Against Rheumatism classification criteria for SSc. Although we do not have the FBN1 sequence in our patient, the co-existence of MFS and SSc in this patient raises the possibility of co-existence of distinct mutations in the FBN1 gene that could affect TGF-β signaling differently, resulting in divergent pathologic consequences - loss of structural integrity in MFS versus increased extracellular matrix deposition in SSc, and different clinical manifestations.

Collagen content in skin and internal organs of the tight skin mouse: an animal model of scleroderma

The Tight Skin mouse is a genetically induced animal model of tissue fibrosis caused by a large in-frame mutation in the gene encoding fibrillin-1 (Fbn-1). We examined the influence of gender on the collagen content of tissues in C57BL/6J wild type (+/+) and mutant Tight Skin (Tsk/+) mice employing hydroxyproline assays. Tissue sections were stained with Masson's trichrome to identify collagen in situ. Adult Tsk/+ mice skin contains ~15% more collagen, on average, than skin from +/+ mice of the same gender. The heart of Tsk/+ males had significantly more collagen than that of +/+ males. No significant gender differences were found in lungs and kidney collagen content. Overall, the collagen content of Tsk/+ males and +/+ males was higher than that of their Tsk/+ and +/+ female counterparts, respectively. Our data confirm increased deposition of collagen in skin and hearts of Tsk/+ mice; however, the effects of the Tsk mutation on collagen content are both tissue specific and gender specific. These results indicate that comparative studies of collagen content between normal and Tsk/+ mice skin and internal organs must take into account gender differences caused by expression of the androgen receptor.

Effect of mast cell chymase inhibitor on the development of scleroderma in tight-skin mice

1 Although the pathogenesis of scleroderma is not fully understood, activation of connective-tissue-type mast cells (CTMCs) has been implicated in various fibrotic diseases. 2 Our previous study showed that the number of CTMCs was markedly increased during fibrous proliferation in the skin of a scleroderma model, namely tight-skin (Tsk) mice. Because mast cells express numerous bioactive factors, such as cytokines, growth factors, proteases, and others, it is crucial to identify the primary factors that may be involved in the pathogenesis of scleroderma. Our previous study also showed that a CTMC-specific protease, chymase-4, was selectively upregulated in accordance with the development of skin fibrosis in Tsk mice. 3 To further elucidate the role of chymase secreted from CTMCs, we evaluated the therapeutic effects of a synthetic chymase-specific inhibitor, SUN-C8257, on the development of skin fibrosis in Tsk mice. SUN-C8257 (50 mg kg-1 day-1) was administered via intraperitoneal injection in 13-week-old Tsk mice for a period of 2 weeks. 4 Treatment with SUN-C8257 significantly reduced chymase activity by 43% and the chymase-4 mRNA level by 47%, and also decreased the thickness of the subcutaneous fibrous layer of Tsk mice by 42% compared with that of Tsk mice injected with vehicle. 5 Furthermore, immunohistochemical analysis revealed that transforming growth factor (TGF)-beta1 staining in the fibrous layer of Tsk skin was markedly reduced by the treatment with SUN-C8257. This chymase inhibitor may prevent the chymase-dependent pathway that activates the latent TGF-beta1 in fibrous tissue, and may exhibit beneficial effects that inhibit the development of fibrosis. 6 In conclusion, our results strongly support the assumption that CTMC-derived chymase may play a key role in the pathogenesis of scleroderma.

Animal models in scleroderma

Scleroderma or systemic sclerosis is an insidious connective tissue disease with no known cure. A hallmark feature of scleroderma is the excess synthesis and deposition of collagen resulting in a fibrotic state. In scleroderma, fibrosis is not confined only to the skin but impacts internal organs as well. In an effort to better understand the pathophysiology of this disease, researchers have developed a variety of animal models that display features of the human condition. This paper focuses on mouse models of scleroderma and summarizes work conducted with these experimental paradigms that is focused on understanding the cellular and molecular events associated with the onset and maintenance of fibrosis.

Hepatocyte growth factor both prevents and ameliorates the symptoms of dermal sclerosis in a mouse model of scleroderma

Systemic sclerosis (SSc) is a connective tissue disorder with an unknown etiology. There are currently no effective therapies for SSc. (In this study, working with a bleomycin(BLM)-induced scleroderma model mice, we performed two transfections of human hepatocyte growth factor (HGF) cDNA into the skeletal muscle and showed that this treatment not only helped to prevent the dermal sclerosis simultaneously injected BLM but also improved the symptoms of dermal sclerosis induced by BLM 4 weeks previously.) RT-PCR, ELISA and an immunohistochemical analysis revealed that both mRNA and protein of human HGF as well as murine HGF were enhanced in the skin, lung, muscle and the serum after two transfections of human HGF cDNA. These analyses also revealed that this treatment significantly reduced both the expression of the TGF-beta1 mRNA and the production of TGF-beta1 on macrophage-like cells that infiltrated the dermis and the fibroblastic cells in BLM-induced scleroderma. Furthermore, HGF-gene transfection both prevented and ameliorated the symptoms of not only dermal sclerosis but also of lung fibrosis induced by a subcutaneous BLM injection. These results indicated that gene therapy by the transfection of the human HGF cDNA may thus be a useful therapy for SSc and lung fibrosis involved with SSc.

Animal models for scleroderma: an update

Scleroderma is a progressive debilitating fibrosing disease that may involve multiple organs. The pathogenesis of this disease remains unclear. Animal models for scleroderma are valuable for studying the pathogenesis of this complex disorder and for testing potential treatments for human scleroderma. There are several animal models available that exhibit important features of scleroderma, each with an emphasis on different aspects of the disease (tissue fibrosis, inflammation, vascular injury, or immunologic changes). These models can be separated into several categories in which fibrosis is induced by external agents (vinyl chloride, bleomycin), by breeding of mutant strain combinations (integrin alpha 1 null mouse, MRL/lpr gamma R-/- mouse), and by transplantation of disparate immune cells (sclerodermatous graft versus host disease). In addition, there are spontaneous mutations (UCD 200 chicken, tight skin mouse) in which fibrosis occurs. The tight skin mouse has been reviewed recently. This review discusses the other animal models and some interventions in each.

Abnormalities in fibrillin 1-containing microfibrils in dermal fibroblast cultures from patients with systemic sclerosis (scleroderma)

OBJECTIVE

To determine if there are abnormalities in fibrillin 1-containing microfibrils in the extracellular matrix (ECM) of primary dermal fibroblasts explanted from patients with systemic sclerosis (SSc).

METHODS

Explanted fibroblasts from unaffected skin of 12 SSc patients were used to examine fibrillin 1-containing microfibrils by immunofluorescence (IF) using a monoclonal antibody (mAb) to fibrillin 1. Metabolic labeling of the fibroblast cultures was used to study the synthesis, secretion, and processing of fibrillin 1, as well as to observe microfibril formation and stability. Microfibrils elaborated by the SSc cells were analyzed by electron microscopy for ultrastructural abnormalities, and the results were confirmed by immunoblotting.

RESULTS

Control and SSc fibroblasts displayed a prominent meshwork of fibrillin 1-containing microfibrils when visualized by IF using a fibrillin 1 mAb. Paradoxically, metabolic studies indicated a paucity of fibrillin 1 in the ECM in the majority of the SSc fibroblast strains. Subsequent rotary-shadowed electron microscopy revealed reduced amounts of and ultrastructural abnormalities in the microfibrils elaborated by all strains of SSc cells. Immunoblots confirmed the lack of the high molecular weight form of fibrillin 1 in the SSc fibroblasts of Choctaw American Indians. Finally, in vitro studies indicated that the amount of fibrillin 1 in the ECM of SSc cells diminished at a faster rate than the amount of fibrillin 1 in the ECM of control cells with time.

CONCLUSION

Although SSc fibroblasts assemble microfibrils, these microfibrils are unstable, suggesting that an inherent defect of fibrillin 1-containing microfibrils may play a role in the pathogenesis of SSc.

Differential expression of nitric oxide by dermal microvascular endothelial cells from patients with scleroderma

Vascular abnormalities in scleroderma are fundamental to the pathogenesis of this disease. The objective of this study was to characterize dermal microvascular endothelial cells (DMEC) isolated from scleroderma patients with respect to growth and expression of the constitutive form of endothelial nitric oxide synthase (eNOS). DMEC from patients with both systemic sclerosis (SSc) and localized scleroderma (Loc Scl) contained small intact microvascular structures in contrast to single cell isolations obtained from control skin. Immunoaffinity selection on anti-PECAM-1 beads yielded pure populations of DMEC expressing normal markers. While the morphology and initial growth of SSc DMEC closely paralleled control cells, the growth of SSc DMEC decreased with time in culture (doubling time of 3 days vs. 5 days). Expression of ecNOS mRNA was reduced in both Loc Scl and SSc as shown by semi-quantitative RT-PCR (p < 0.001). Western blots showed variable but generally lower ecNOS protein levels and decreased levels of nitrogen oxides in media were found from both SSc and Loc Scl relative to control cells. The results indicate an intrinsic defect in the mechanism of nitric oxide production in DMEC isolated from scleroderma patients and suggest its possible involvement in the pathophysiology of scleroderma.

Development of the tight-skin phenotype in immune-deficient mice

OBJECTIVE

To determine if cutaneous thickening, a major phenotypic feature of the tight-skin (Tsk) mutation, could develop in an immune-deficient mouse.

METHODS

Experimental crosses among different strains of mice were conducted to create mice that were genetically Tsk/+, and that were also homozgyous for a mutation at the Prkdc(scid) locus and thus lacked mature T and B lymphocytes. Skin samples prepared from experimental and control genotypic groups of mice were evaluated for skin thickness.

RESULTS

The data showed that the Tsk/+ mice developed the Tsk phenotype in the absence of a functional immune system.

CONCLUSION

Mature T and B cells are not required for the development of the cutaneous thickening in mice carrying the Tsk mutation.

Isoform-selective upregulation of mast cell chymase in the development of skin fibrosis in scleroderma model mice

The involvement of connective-tissue-type mast cells and chymase, a protease unique to their secretory granules, has been implicated in fibrotic diseases. To elucidate the role of chymase in fibroproliferative inflammation, in this study we examined the enzymatic activity and mRNA expression of chymase in the sclerotic skin of tight-skin mice; syngeneic Pallid mice served as the control. Dorsal skin specimens from mice aged 5, 10, and 20 wk were evaluated by morphometric and biochemical analyses. At ages 10 and 20 wk, the hydroxyproline concentration in tight-skin dermis was higher than that in Pallid. At any age, the subcutaneous fibrous layer was thicker in tight-skin than in Pallid. In accordance with these fibrous changes, both connective-tissue-type mast cell counts and chymase activity were higher in tight-skin skin than in Pallid skin up to 20 wk of age. Age-matched (10-wk-old) tight-skin and Pallid were quantified for their mRNA of connective-tissue-type mast-cell-specific chymase, mouse mast cell protease-4, by the competitive reverse transcriptase polymerase chain reaction technique, which revealed its higher level in tight-skin than Pallid. In contrast, the mRNA level of mouse mast cell protease-5, the chymase isoform of undifferentiated mast cells, in tight-skin skin was only a tenth that of mouse mast cell protease-4 and no different from the mouse mast cell protease-5 mRNA level of Pallid mice. An in situ hybridization study confirmed the higher expression of mouse mast cell protease-4 by connective-tissue-type mast cells in tight-skin skin than Pallid skin. These results strongly support the contention that the connective-tissue-type mast cell chymase plays a crucial role in fibroproliferative remodeling of the skin.

Association of functional microsatellites in the human type I collagen alpha2 chain (COL1A2) gene with systemic sclerosis

Systemic sclerosis (SSc) or scleroderma is a generalized disorder of connective tissue. The etiology is poorly understood; however, both genetic and environmental factors have been implicated. To investigate the disease-susceptible gene for SSc, we examined the association of the disease with a gene (COL1A2) for type I collagen, which accumulates excessively in the affected organs. The COL1A2 gene containing a specific combination of the two dinucleotide repeats, repeat-haplotype, is involved in the regulation of gene expression. Homozygotes for a 5'-(CA)13CGCACA(CG)6(CA)8 -(GT)12 -3' were found with significantly higher frequency (P = 0.029, relative risk, RR > 6.93) in SSc patients than in controls, and association was prominent (P = 0.0042, RR > 32.0) in the male patients positive for SSc-specific antinuclear antibodies (ANAs). This repeat-haplotype showed the highest stimulative activity for the transcription of the COL1A2 promoter among the reporter gene constructs tested. The results indicate that a portion of the patients having a specific dinucleotide repeat-haplotype homozygously and expressing the ANAs have a significantly higher risk for SSc than those individuals with other combinations of the repeat-haplotypes.

T cells infiltrating the skin of Tsk2 scleroderma-like mice exhibit T cell receptor bias

The T cell repertoire expressed by Tsk2 mice, a novel experimental model of systemic sclerosis, was examined to determine whether cells infiltrating the areas of involved skin exhibit a T cell receptor (TCR) bias. Reverse transcription-polymerase chain reactions (RT-PCR) were conducted using RNA extracted from lymph nodes and skin from TSk2 mice and from normal mice, with an oligonucleotide primer library specific for the variable region of the TCR (beta) chain. RT-PCR signals were observed in all lymph node cell (LNC) samples from both Tsk2 mice and control mice, with eighteen of the twenty-one Vbeta types present. In contrast, cDNA extracted from areas of involved skin from Tsk2 mice exhibited a restricted pattern, with positive Vbeta signals corresponding to eight T cell subtypes (Vbeta1, 6, 8.1, 8.2, 10, 11, 16, and 18). Band strength analysis revealed that three Vbeta subtypes dominated within this restricted pattern (Vbeta8.1, 11, and 18). Moreover, this pattern of Vbeta bias was consistent among the four skin samples from different Tsk2 mice. These data suggest that a restricted T cell population participates in the inflammatory cell infiltrate of Tsk2 skin.

Immune ablation and hematopoietic stem cell rescue for severe autoimmune diseases (SADS)

In addition to our center (Northwestern University, Chicago), several institutions in the United States (Fred Hutchinson Cancer Center, University of California at Los Angeles, and Medical College of Wisconsin) and Europe are activating protocols to transplant patients with SADS. In this age of cost-effectiveness, it will be difficult to arrange third-party reimbursement for a hematopoietic stem cell transplant that may lead to medical charges of between $100,000 and $200,000. However, the cost of standard medical care for patients with SADS is not trivial. Dialysis for an SLE patient with renal failure costs $40,000 per year, while the medical resources required to care for a patient with progressive multiple sclerosis may exceed $35,000 per year. Unique BMT regimen-related toxicities may occur, including intracranial hemorrhage in the SLE or rheumatoid arthritis patient who has vasculitis; acute neurologic decompensation in patients with multiple sclerosis, especially if the conditioning regimen contains neurotoxic agents that cross a compromised blood-brain barrier; respiratory failure in patients with myasthenia gravis; and increased renal or pulmonary toxicity in patients with scleroderma and parenchymal fibrosis. Scleroderma-associated gastrointestinal dysmotility and bacterial overgrowth may also lead to greater fungal and bacterial infections [76]. BMT is currently considered appropriate therapy for patients with chronic-phase Chronic myelogenous leukemia (CML) and indolent lymphomas who otherwise have a relatively long life expectancy of 5 and 10 years, respectively. The roughly similar long survival but greater functional impairment of patients with SADS may justify consideration of immune ablation and hematopoietic stem cell rescue.

A tandem duplication within the fibrillin 1 gene is associated with the mouse tight skin mutation

Mice carrying the Tight skin (Tsk) mutation have thickened skin and visceral fibrosis resulting from an accumulation of extracellular matrix molecules. These and other connective tissue abnormalities have made Tskl + mice models for scleroderma, hereditary emphysema, and myocardial hypertrophy. Previously we localized Tsk to mouse chromosome 2 in a region syntenic with human chromosome 15. The microfibrillar glycoprotein gene, fibrillin 1 (FBN1), on human chromosome 15q, provided a candidate for the Tsk mutation. We now demonstrate that the Tsk chromosome harbors a 30- to 40-kb genomic duplication within the Fbn1 gene that results in a larger than normal in-frame Fbn1 transcript. These findings provide hypotheses to explain some of the phenotypic characteristics of Tskl + mice and the lethality of Tsk/Tsk embryos.

The tight skin 2 mouse. An animal model of scleroderma displaying cutaneous fibrosis and mononuclear cell infiltration

OBJECTIVE

To describe the histopathologic and biochemical characteristics of skin from the Tsk2/+ mouse, a mutation with phenotypic features resembling those of systemic sclerosis (SSc), and to report the initial genetic mapping of the Tsk2 locus.

METHODS

Histologic examination was performed and collagen content and type I collagen messenger RNA (mRNA) levels were determined in skin biopsy specimens from Tsk2/+ mice and normal mice. An intersubspecific backcross was conducted as a first step toward identifying the position of the Tsk2 locus on mouse chromosome 1.

RESULTS

Histologic examination of Tsk2/+ mouse skin revealed marked accumulation of collagen and infiltration with mononuclear cells in the dermis and adipose tissue. Biochemical studies of Tsk2/+ mouse skin showed increased collagen content and elevated steady-state levels of alpha 1 (I) procollagen mRNA. Tsk2 was mapped to a 15.3-centimorgan interval on mouse chromosome 1.

CONCLUSION

Tsk2 is a novel mutation which displays histopathologic and biochemical abnormalities similar to those present in the skin of patients with SSc, including increased collagen content and expression of type I collagen genes. This mutation has been mapped to a 15.3-cM region on mouse chromosome 1. Further study of this novel mutation will allow the identification of previously undescribed mechanisms involved in the regulation of normal and pathologic collagen gene expression.