Genetic and immunologic features associated with scleroderma-like syndrome of TSK mice

B cells in systemic sclerosis: from pathophysiology to treatment

Systemic sclerosis is a debilitating autoimmune disease with unknown pathogenesis. The clinical phenotype of fibrosis is preceded by vascular and immunologic aberrations. Adaptive immunity has been extensively studied in patients with the disease and B cells appear to be dysregulated. This is evident in peripheral blood B cell subsets, with activated effector B cells and impaired B regulatory function. In addition, B cells infiltrate target organs and tissues of patients with the disease, such as the skin and the lung, indicating a probable role in the pathogenesis. Impaired B cell homeostasis explains the rationale behind B cell therapeutic targeting. Indeed, several studies in recent years have shown that depletion of B cells appears to be a promising treatment alongside current established therapeutic choices, such as mycophenolate. In this review, B cell aberrations in animal models and human patients with systemic sclerosis will be presented. Moreover, we will also summarize current existing data regarding therapeutic targeting of the B cells in systemic sclerosis.

Use of biologics and other novel therapies for the treatment of systemic sclerosis

INTRODUCTION

Systemic sclerosis (SSc) is a systemic autoimmune disease characterized by vasculopathy, inflammation and fibrosis. These three main disease-determining pathways are the target of the currently available treatments used to possibly modify the progression of disease-related manifestations, although this synergy has not been fully applied on SSc joint, skin or lung involvement yet. Areas covered: we describe the current status of SSc treatment/therapy performing a literature search in MEDLINE/Pubmed and Thomson Reuter's Web of Science for articles published until March 2016. Moreover, ongoing registered clinical trials (RCTs) on SSc were searched through clinicaltrials.gov website. Expert commentary: presently, promising drugs are under evaluation to target the different pathogenic pathways of systemic sclerosis: Tocilizumab and Abatacept for skin and lung fibrosis; Riociguat and Selexipag are approved for pulmonary arterial hypertension but promising anti-fibrotic effects are now being studied. Finally, several anti-fibrotic molecules are currently involved in RCTs, such as Nintedanib, IVA-337, Terguride.

Recent advances in the genetics of systemic sclerosis: toward biological and clinical significance

Significant advances have been made in understanding the genetic basis of systemic sclerosis (SSc) in recent years. Genomewide association and other large-scale genetic studies have identified 30 largely immunity-related genes which are significantly associated with SSc. We review these studies, along with genomewide expression studies, proteomic studies, genetic mouse models, and insights from rare sclerodermatous diseases. Collectively, these studies have begun to identify pathways that are relevant to SSc pathogenesis. The findings presented in this review illustrate how both genetic and genomic aberrations play important roles in the development of SSc. However, despite these recent discoveries, there remain major gaps between current knowledge of SSc, a unified understanding of pathogenesis, and effective treatment. To this aim, we address the important issue of SSc heterogeneity and discuss how future research needs to address this in order to develop a clearer understanding of this devastating and complex disease.

B-cell depletion therapy in systemic sclerosis: experimental rationale and update on clinical evidence

Systemic sclerosis (SSc) is a systemic rheumatic disease with poor prognosis since therapeutic options are limited. Recent evidence from animal models suggests that B-cells may be actively involved in the fibrotic process. B-cells from tight skin mice, an animal model of scleroderma, display a “hyperresponsive” phenotype; treatment with rituximab (RTX) significantly attenuates skin fibrosis in this animal model. In humans, B-cell infiltration is a prominent finding in most lung biopsies obtained from patients with SSc-associated interstitial lung disease. Several open label studies have assessed the clinical efficacy of RTX in SSc. In most patients skin fibrosis improved; lung function either improved or remained stable. Definite conclusions regarding the clinical efficacy of RTX in SSc cannot be drawn but further exploration with a multicenter, randomized study is warranted.

Is there a role for B-cell depletion as therapy for scleroderma? A case report and review of the literature

OBJECTIVES

Rituximab (RTX) has been successfully used in the treatment of several rheumatic diseases with an acceptable safety profile. We present herein a patient with systemic sclerosis (SSc) who exhibited significant improvement of his lung function and skin fibrosis following RTX administration, and review the literature regarding the role of B-cells in SSc and the potential efficacy of RTX in its treatment.

METHODS

We performed an internet search using the keywords systemic sclerosis, scleroderma, rituximab, B-cells, fibrosis, interstitial lung disease (ILD), and therapy.

RESULTS

Our patient, a 40-year old man with severe SSc-associated ILD, received 4 courses of RTX. The patient's lung function improved; forced vital capacity and diffusing capacity of carbon monoxide reached values of 35% and 33%, respectively, compared with 30% and 14% of pretreatment values. Skin thickening assessed clinically and histologically improved as well. Several lines of evidence suggest that B-cells may have a pathogenic role in SSc. B-cells from tight skin mice--an animal model of SSc--exhibit chronic hyperactivity; likewise, B-cells from patients with SSc overexpress CD19 and are chronically activated. Furthermore, studies have revealed that B-cell genes were specifically transcribed in SSc skin and that B-cell infiltration was a prominent feature of SSc-associated ILD. The potential clinical efficacy of RTX in SSc has been explored in a limited number of patients with encouraging results. Preliminary data suggest that RTX may favorably affect skin as well as lung disease in SSc.

CONCLUSIONS

Several basic research data underscore the potential pathogenic role of B-cells in SSc and clinical evidence suggests that RTX might be a therapeutic option in SSc. Large-scale multicenter studies are needed to evaluate the potential clinical efficacy of RTX in SSc.

Polymorphisms of the TGF-β1 Promoter in Tight Skin (TSK) Mice

TGF-beta1 plays a major role in fibrotic diseases including scleroderma. Human fibroblasts from sclerotic lesions display an increased sensitivity to TGF-beta1. Similarly, fibroblasts from TSK mice which develop a scleroderma-like syndrome are hyperresponsive to TGF-beta. The aim of the present study was to investigate whether the TGF-beta hypersensitivity demonstrated by TSK/+ fibroblasts is associated with polymorphisms of the TGF-beta1 promoter. Sequence analysis revealed one polymorphism (a G --> T at -1133 bp) unique to the TSK/+ mouse. Transfection of fibroblasts with a 1.8 kb fragment of the TGF-beta1 promoter containing the -1133 polymorphism exhibited increased basal TGF-beta1 promoter activity which was enhanced upon incubation with TGF-beta1. This may be related to the loss of a negative regulatory site in the TSK/+ TGF-beta1 promoter.

Elevated expression of isopeptide bond cross-links contributes to fibrosis in scleroderma and the healing wounds of tight skin mice

Scleroderma is a chronic disease characterized by excessive tissue fibrosis. Recent studies indicate that cultured dermal fibroblasts isolated from patients produce excessive amounts of collagen and other extracellular matrix components. In this study, we investigated the mechanism(s) of abnormal extracellular matrix accumulation in the scleroderma biopsies and the healing wounds of Tsk1/+ mice. Full-thickness excisional wounds were made in Tsk1/+ and wild-type mice and were subsequently harvested at days 7, 10, and 14 postinjury. The levels of pro-fibrotic cytokine, transforming growth factor were elevated in the wounds of Tsk1/+ mice. Interestingly, the levels of matrix metalloproteinase were significantly reduced in the granulation tissue of Tsk1/+ mice in comparison with wild-type. Furthermore, immunohistochemical analysis of the wounds indicated that the levels of gamma-glutamyl-epsilon-lysine cross-links were elevated in the granulation tissue of Tsk1/+ mice as well as the fibrotic lesions of scleroderma specimens. Collectively, these findings indicate that elevated collagen synthesis and decreased matrix metalloproteinase levels, in combination with increased isopeptide bond cross-links, contribute to abnormal collagen synthesis and assembly in granulation tissue of Tsk1/+ mice and the fibrotic lesions of scleroderma patients.

Molecular aspects of regulation of collagen gene expression in fibrosis

Fibrosis, the hyper-accumulation of scar tissue, is characterized by the overproduction and deposition of type I and III collagen by fibroblasts and is the one of the main pathologic outcomes of the autoimmune disorder scleroderma. While the causes of fibrosis in scleroderma are unknown, cytokines such as TGF-beta, IL-4 and IL-13, play a crucial role in the stimulation of collagen production have been implicated in the disease process. In fibroblasts stimulation of collagen production by these cytokines is dependent on the Smad and STAT6 signaling pathways induced by TGF-beta and IL-4, IL-13 respectively. Furthermore, mounting evidence suggest cytokine crosstalk is relevant in the sclerotic process. Our laboratory demonstrated an increase in TGF-beta1 gene transcription from fibroblasts stimulated with IL-4. In addition, TSK/+ mice lacking the IL-4alpha receptor show impaired transcription of the TGF-beta1 gene and did not display fibrosis. Likewise, it appears that STAT6 plays a role in fibroblast TGF-beta1 transcription after IL-4 or IL-13 stimulation. These findings suggest that an epistatic interaction between IL-4 and TGF-beta may exist which is crucial for pathologic sclerotic activity.

Scleroderma-like remodeling induced by type V collagen

Recently, we discovered that New Zealand rabbits immunized with human type V collagen plus Freund's adjuvant present fibrosis and vasculitis of organs usually affected by systemic sclerosis. In this way, we studied the fibrillogenesis process to identify possible factors involved in altered remodeling observed in this scleroderma-like model. Additionally, we have done a very preliminary comparison with human skins obtained from scleroderma patients (n=3). Female New Zealand rabbits (n=10) were immunized subcutaneously with two doses of 1 mg collagen V (COL V) plus complete Freund's adjuvant for a 30-day interval, followed by two additional intramuscular booster immunizations in incomplete Freund's adjuvant for a 15-day interval. Animals from control group (n=10), were only inoculated with complete and incomplete Freund's adjuvant given at same conditions of COL V. Histological analysis of skins from animals and patients were done by Masson's trichrome staining, and immunofluorescence method to detect collagen fibers and interactions of types I, III and V collagen in the remodeling process. The analysis of animal skins showed collagen fibril deposits in the dermis after 7 days of sensibilization and an increase in these deposits after 75 and 120 days, respectively. Skin thickness and atrophy of sebaceous and sweat glands were progressively more intense in late sacrificed animals and correlated with increased amount of collagen deposition. Surprisingly, type V collagen was overexpressed both in animals and patients, forming dense and atypical collagen fibers in the dermis. We suggest that this anomalous expression of morphologically different type V collagen could justify the remodeling observed in scleroderma plaque.

Analysis of the tight skin (Tsk1/+) mouse as a model for testing antifibrotic agents

The tight skin 1 (B6.CgFbn1(Tsk)+/+Pldn(pa)/J, henceforth referred to as Tsk1/+) mouse was first described as a spontaneously occurring mutant that resulted in hyperplasia of the subcutaneous loose connective tissue, and has subsequently been proposed to be a model of the human fibrotic disorder scleroderma. We have investigated the Tsk1/+ mouse as a model system for testing the efficacy of antifibrotic agents against skin fibrosis. We find that the tightness of the skin at the scruff of the neck leads to a measurably thicker skin pinch, but we suggest that this is due to hyperplasia of the subdermal loose connective tissue, which results in increased tethering of the skin to the underlying muscle layers. In contrast to previously published data, we do not find a significant difference in the dermal thickness or collagen content of the Tsk1/+ mouse skin compared with wild-type controls. In addition, expression profiling of Tsk1/+ mouse skin indicated that there are very few changes in gene expression, and that there is no evidence for upregulation of the transforming growth factor beta signaling axis. Therefore, we conclude that this model is not suitable for testing the effect of antifibrotic agents on the dermis, and that changes potentially related to scleroderma may be confined to subdermal connective tissue.

B Lymphocyte signaling established by the CD19/CD22 loop regulates autoimmunity in the tight-skin mouse

Systemic sclerosis (SSc) is characterized by fibrosis and autoimmmunity. Peripheral blood B cells from SSc patients specifically overexpress CD19, a critical cell-surface signal transduction molecule in B cells. CD19 deficiency in B cells also attenuates skin fibrosis in the tight-skin (TSK/+) mouse, a genetic model for SSc. Herein we analyzed two transgenic mouse lines that overexpress CD19. Remarkably, 20% increase of CD19 expression in mice spontaneously induced SSc-specific anti-DNA topoisomerase I (topo I) antibody (Ab) production, which was further augmented by 200% overexpression. In TSK/+ mice overexpressing CD19, skin thickness did not increase, although anti-topo I Ab levels were significantly augmented, indicating that abnormal CD19 signaling influences autoimmunity in TSK/+ mice and also that anti-topo I Ab does not have a pathogenic role. The molecular mechanisms for abnormal CD19 signaling were further assessed. B-cell antigen receptor crosslinking induced exaggerated calcium responses and augmented activation of extracellular signal-regulated kinase in TSK/+ B cells. CD22 function was specifically impaired in TSK/+ B cells. Consistently, CD19, a major target of CD22-negative regulation, was hyperphosphorylated in TSK/+ B cells. These findings indicate that reduced inhibitory signal provided by CD22 results in abnormal activation of signaling pathways including CD19 in TSK/+ mice and also suggest that this disrupted B cell signaling contribute to specific autoantibody production.

Mercuric chloride induces a strong immune activation, but does not accelerate the development of dermal fibrosis in tight skin 1 mice

In susceptible mice, mercuric chloride induces a systemic autoimmune disease characterized by increased serum levels of immunoglobulin (Ig) G1 and IgE, production of anti-nucleolar autoantibodies (ANolA) and formation of renal IgG deposits. We have previously hypothesized that mercury confers more adverse immunological effects on those mouse strains, which are genetically prone to develop spontaneous autoimmune diseases than on normal strains. In this study, we tested our hypothesis in tight skin 1 (Tsk1/+) mice, a murine model for human scleroderma. As a support for our hypothesis, we observed that in Tsk1/+ mice, B cells were spontaneously hyperactive and that treatment with mercury induced a strong immune/autoimmune response in these mice, but not in their non-Tsk (+/+) littermates. This response was characterized by the formation of high numbers of splenic IgG1, IgG2b and IgG3 antibody-secreting cells, increased serum levels of IgE, production of IgG1 antibodies against single-stranded DNA (ssDNA), trinitrophenol (TNP) as well as thyroglobulin and the development of renal IgG1 deposits. Neither Tsk1/+ mice nor F1 hybrid crosses between this strain, and mercury susceptible B10.S (H-2(s)) were able to produce IgG1-ANolA in response to mercury. Moreover, mercury-induced immune activation in Tsk1/+ was not able to potentiate the progression of skin fibrosis in this strain. Thus, exposure to mercury accelerates the immune dysregulation, but not the development of skin fibrosis in Tsk1/+ mice.

Murine animal models of systemic sclerosis

Animal models of systemic connective tissue diseases have provided valuable insights into the causative mechanisms and the pathogenesis of these diseases, and have provided the means to test potentially useful therapeutic interventions. Although numerous animal models for systemic sclerosis (SSc) have been described, the most extensively studied are murine. One advantage of murine animal models is the large body of genetic information available for the mouse that is not available for other species. No animal model described to date reproduces precisely all manifestations of SSc. However, all animal models display tissue fibrotic changes similar to those present in SSc. The prudent interpretation of the results obtained from the study of animal models has provided substantial and valuable information about the pathogenesis of the human disease.

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.