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

Artificial keloid skin models: understanding the pathophysiological mechanisms and application in therapeutic studies

Keloid is a type of scar formed by the overexpression of extracellular matrix substances from fibroblasts following inflammation after trauma. The existing keloid treatment methods include drug injection, surgical intervention, light exposure, cryotherapy, etc. However, these methods have limitations such as recurrence, low treatment efficacy, and side effects. Consequently, studies are being conducted on the treatment of keloids from the perspective of inflammatory mechanisms. In this study, keloid models are created to understand inflammatory mechanisms and explore treatment methods to address them. While previous studies have used animal models with gene mutations, chemical treatments, and keloid tissue transplantation, there are limitations in fully reproducing the characteristics of keloids unique to humans, and ethical issues related to animal welfare pose additional challenges. Consequently, studies are underway to create in vitro artificial skin models to simulate keloid disease and apply them to the development of treatments for skin diseases. In particular, herein, scaffold technologies that implement three-dimensional (3D) full-thickness keloid models are introduced to enhance mechanical properties as well as biological properties of tissues, such as cell proliferation, differentiation, and cellular interactions. It is anticipated that applying these technologies to the production of artificial skin for keloid simulation could contribute to the development of inflammatory keloid treatment techniques in the future.

Deficiency of inhibitory TLR4 homolog RP105 exacerbates fibrosis

Activation of TLR4 by its cognate damage-associated molecular patterns (DAMPs) elicits potent profibrotic effects and myofibroblast activation in systemic sclerosis (SSc), while genetic targeting of TLR4 or its DAMPs in mice accelerates fibrosis resolution. To prevent aberrant DAMP/TLR4 activity, a variety of negative regulators evolved to dampen the magnitude and duration of the signaling. These include radioprotective 105 kDa (RP105), a transmembrane TLR4 homolog that competitively inhibits DAMP recognition of TLR4, blocking TLR4 signaling in immune cells. The role of RP105 in TLR4-dependent fibrotic responses in SSc is unknown. Using unbiased transcriptome analysis of skin biopsies, we found that levels of both TLR4 and its adaptor protein MD2 were elevated in SSc skin and significantly correlated with each other. Expression of RP105 was negatively associated with myofibroblast differentiation in SSc. Importantly, RP105-TLR4 association was reduced, whereas TLR4-TLR4 showed strong association in fibroblasts from patients with SSc, as evidenced by PLA assays. Moreover, RP105 adaptor MD1 expression was significantly reduced in SSc skin biopsies and explanted SSc skin fibroblasts. Exogenous RP105-MD1 abrogated, while loss of RP105 exaggerated, fibrotic cellular responses. Importantly, ablation of RP105 in mice was associated with augmented TLR4 signaling and aggravated skin fibrosis in complementary disease models. Thus, we believe RP105-MD1 to be a novel cell-intrinsic negative regulator of TLR4-MD2-driven sustained fibroblast activation, representing a critical regulatory network governing the fibrotic process. Impaired RP105 function in SSc might contribute to persistence of progression of the disease.

Mouse Models of Skin Fibrosis

Systemic sclerosis (SSc) is a rare systemic autoimmune disease associated with a high mortality. The first histopathological hallmarks are vasculopathy and inflammation, followed by fibrosis of the skin and internal organs. The molecular and cellular mechanisms are incompletely understood. Rodent models provide important insights into the pathogenesis of SSc and are a mainstay for the development of novel targeted therapies. Here we describe the mechanistic insights of inducible and genetic models, and also discuss in detail the limitations and pitfalls of the most frequently used SSc mouse models. We also describe protocols for running the established bleomycin-induced scleroderma skin fibrosis model.

Engineering Advanced In Vitro Models of Systemic Sclerosis for Drug Discovery and Development

Systemic sclerosis (SSc) is a complex multisystem disease with the highest case-specific mortality among all autoimmune rheumatic diseases, yet without any available curative therapy. Therefore, the development of novel therapeutic antifibrotic strategies that effectively decrease skin and organ fibrosis is needed. Existing animal models are cost-intensive, laborious and do not recapitulate the full spectrum of the disease and thus commonly fail to predict human efficacy. Advanced in vitro models, which closely mimic critical aspects of the pathology, have emerged as valuable platforms to investigate novel pharmaceutical therapies for the treatment of SSc. This review focuses on recent advancements in the development of SSc in vitro models, sheds light onto biological (e.g., growth factors, cytokines, coculture systems), biochemical (e.g., hypoxia, reactive oxygen species) and biophysical (e.g., stiffness, topography, dimensionality) cues that have been utilized for the in vitro recapitulation of the SSc microenvironment, and highlights future perspectives for effective drug discovery and validation.

Cardiac phenotype in mouse models of systemic autoimmunity

Patients suffering from systemic autoimmune diseases are at significant risk of cardiovascular complications. This can be due to systemically increased levels of inflammation leading to accelerated atherosclerosis, or due to direct damage to the tissues and cells of the heart. Cardiac complications include an increased risk of myocardial infarction, myocarditis and dilated cardiomyopathy, valve disease, endothelial dysfunction, excessive fibrosis, and bona fide autoimmune-mediated tissue damage by autoantibodies or auto-reactive cells. There is, however, still a considerable need to better understand how to diagnose and treat cardiac complications in autoimmune patients. A range of inducible and spontaneous mouse models of systemic autoimmune diseases is available for mechanistic and therapeutic studies. For this Review, we systematically collated information on the cardiac phenotype in the most common inducible, spontaneous and engineered mouse models of systemic lupus erythematosus, rheumatoid arthritis and systemic sclerosis. We also highlight selected lesser-known models of interest to provide researchers with a decision framework to choose the most suitable model for their study of heart involvement in systemic autoimmunity.

Mesenchymal Stem Cells in Systemic Sclerosis: Allogenic or Autologous Approaches for Therapeutic Use?

Systemic sclerosis (SSc) is a rare autoimmune disease, which is potentially lethal. The physiopathology of the disease is still incompletely elucidated although the role of fibroblasts, endothelial cells (ECs), immune cells. and the environment (i.e., oxidative stress) has been demonstrated. This is an intractable disease with an urgent need to provide better therapeutic options to patients. Mesenchymal stem cells (MSCs) represent a promising therapeutic approach thanks to the number of trophic and pleiotropic properties they exert. Among these, MSCs display anti-fibrotic, angiogenic, and immunomodulatory capacities that might be of interest in the treatment of SSc by acting on different processes that are dysregulated in the disease. In the recent years, the therapeutic effectiveness of MSCs has been demonstrated in different preclinical animal models and is being investigated in phase I clinical trials. Both allogenic and autologous transplantation of MSCs isolated from bone marrow or adipose tissue is being evaluated. The rationale for using allogenic MSCs in SSc, as well as in other autoimmune diseases, is based on the possibility that autologous MSCs might be altered in these diseases. In SSc, reports from the literature are controversial. Nevertheless, the role of the oxidative environment and of the crosstalk with neighboring cells (fibroblasts and ECs) on the functional properties of MSCs has been reported. Here, we review the preclinical and clinical data reporting the interest of MSC-based treatment in SSc and question the use of autologous or allogeneic MSCs in perspective of clinical applications.

Targeting of cadherin-11 decreases skin fibrosis in the tight skin-1 mouse model

Objective

Systemic sclerosis (SSc) is an autoimmune disease clinically manifesting as progressive fibrosis of the skin and internal organs. Cadherin-11 (CDH11) expression is increased in fibrotic skin and lung tissue. Targeting CDH11 may be an effective approach to treating fibrosis. We hypothesize that targeting CDH11 will decrease fibrosis in the tight skin-1 (Tsk-1) mouse model.

Methods

CDH11 expression was determined in the Tsk-1 mouse model using quantitative real time PCR and immunofluorescence (IF). Inhibitory anti- CDH11 monoclonal antibodies were tested in Tsk-1 mice for their ability to decrease hypodermal fibrosis.

Results

Expression of CDH11 was increased in fibrotic skin from Tsk-1 mice compared to pallid controls. IF staining demonstrated that CDH11 expression localized to fibroblasts within the hypodermis of fibrotic skin. Treatment with inhibitory anti-CDH11 monoclonal antibodies decreased hypodermal thickness and fibrotic mediators in Tsk-1 mice compared to control antibodies.

Conclusions

These data demonstrate an important role for CDH11 in the development of skin fibrosis in Tsk-1 mice. These data add to the growing evidence for the important role of CDH11 in tissue fibrosis and fibrotic disease such as systemic sclerosis.

Identification of Optimal Mouse Models of Systemic Sclerosis by Interspecies Comparative Genomics

OBJECTIVE

Understanding the pathogenesis of systemic sclerosis (SSc) is confounded by considerable disease heterogeneity. Animal models of SSc that recapitulate distinct subsets of disease at the molecular level have not been delineated. We applied interspecies comparative analysis of genomic data from multiple mouse models of SSc and patients with SSc to determine which animal models best reflect the SSc intrinsic molecular subsets.

METHODS

Gene expression measured in skin from mice with sclerodermatous graft-versus-host disease (GVHD), bleomycin-induced fibrosis, Tsk1/+ or Tsk2/+ mice was mapped to human orthologs and compared to SSc skin biopsy-derived gene expression. Transforming growth factor β (TGFβ) activation was assessed using a responsive signature in mice, and tumor necrosis factor receptor superfamily member 12A (TNFRSF12A) expression was measured in SSc patient and mouse skin.

RESULTS

Gene expression in skin from mice with sclerodermatous GVHD and bleomycin-induced fibrosis corresponded to that in SSc patients in the inflammatory molecular subset. In contrast, Tsk2/+ mice showed gene expression corresponding to the fibroproliferative SSc subset. Enrichment of a TGFβ-responsive signature was observed in both Tsk2/+ mice and mice with bleomycin-induced skin fibrosis. Expression of TNFRSF12A (the TWEAK receptor/fibroblast growth factor-inducible 14) was elevated in skin from patients with fibroproliferative SSc and the skin of Tsk2/+ mice.

CONCLUSION

This study reveals similarities in cutaneous gene expression between distinct mouse models of SSc and specific molecular subsets of the disease. Different pathways underlie the intrinsic subsets including TGFβ, interleukin-13 (IL-13), and IL-4. We identify a novel target, Tnfrsf12a, with elevated expression in skin from patients with fibroproliferative SSc and Tsk2/+ mice. These findings will inform mechanistic and translational preclinical studies in SSc.

Updates on animal models of systemic sclerosis

Systemic sclerosis (SSc) is a connective tissue disease of unknown etiology that is characterized by fibrosis of the skin and several internal organs, vasculopathy, inflammation and autoimmunity. Animal models have improved our understanding of the pathogenesis of SSc. Many inducible and genetic animal models of SSc have been developed and characterized in the last years. All of these models have different strengths and limitations and mimic different aspects of the pathogenesis of SSc. The purpose of this review is to summarize the characteristics of the various animal models of SSc and to provide an outline of how to use these models to study certain aspects in the pathogenesis of SSc and to test the effects of potential therapeutic approaches.

An IRF5 Decoy Peptide Reduces Myocardial Inflammation and Fibrosis and Improves Endothelial Cell Function in Tight-Skin Mice

Interferon regulatory factor 5 (IRF5) has been called a "master switch" for its ability to determine whether cells mount proinflammatory or anti-inflammatory responses. Accordingly, IRF5 should be an attractive target for therapeutic drug development. Here we report on the development of a novel decoy peptide inhibitor of IRF5 that decreases myocardial inflammation and improves vascular endothelial cell (EC) function in tight-skin (Tsk/+) mice. Biolayer interferometry studies showed the Kd of IRF5D for recombinant IRF5 to be 3.72 ± 0.74x10-6M. Increasing concentrations of IRF5D (0-100 μg/mL, 24h) had no significant effect on EC proliferation or apoptosis. Treatment of Tsk/+ mice with IRF5D (1mg/kg/d subcutaneously, 21d) reduced IRF5 and ICAM-1 expression and monocyte/macrophage and neutrophil counts in Tsk/+ hearts compared to expression in hearts from PBS-treated Tsk/+ mice (p<0.05). EC-dependent vasodilatation of facialis arteries isolated from PBS-treated Tsk/+ mice was reduced (~15%). IRF5D treatments (1mg/kg/d, 21d) improved vasodilatation in arteries isolated from Tsk/+ mice nearly 3-fold (~45%, p<0.05), representing nearly 83% of the vasodilatation in arteries isolated from C57Bl/6J mice (~55%). IRF5D (50μg/mL, 24h) reduced nuclear translocation of IRF5 in myocytes cultured on both Tsk/+ cardiac matrix and C57Bl/6J cardiac matrix (p<0.05). These data suggest that IRF5 plays a causal role in inflammation, fibrosis and impaired vascular EC function in Tsk/+ mice and that treatment with IRF5D effectively counters IRF5-dependent mechanisms of inflammation and fibrosis in the myocardium in these mice.

Keloids: Animal models and pathologic equivalents to study tissue fibrosis

Animal models are crucial for the study of fibrosis. Keloids represent a unique type of fibrotic scarring that occurs only in humans, thus presenting a challenge for those studying the pathogenesis of this disease and its therapeutic options. Here, several animal models of fibrosis currently in use are described, emphasizing recent progress and highlighting encouraging challenges.

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.

Differences between Mice and Humans in Regulation and the Molecular Network of Collagen, Type III, Alpha-1 at the Gene Expression Level: Obstacles that Translational Research Must Overcome

Collagen, type III, alpha-1 (COL3A1) is essential for normal collagen I fibrillogenesis in many organs. There are differences in phenotypes of mutations in the COL3A1 gene in humans and mutations in mice. In order to investigate whether the regulation and gene network of COL3A1 is the same in healthy populations of mice and humans, we compared the quantitative trait loci (QTL) that regulate the expression level of COL3A1 and the gene network of COL3A1 pathways between humans and mice using whole genome expression profiles. Our results showed that, for the regulation of expression of Col3a1 in mice, an eQTL on chromosome (Chr) 12 regulates the expression of Col3a1. However, expression of genes in the syntenic region on human Chr 7 has no association with the expression level of COL3A1. For the gene network comparison, we identified 44 top genes whose expression levels are strongly associated with that of Col3a1 in mice. We next identified 41 genes strongly associated with the expression level of COL3A1 in humans. There are a few but significant differences in the COL3A1 gene network between humans and mice. Several genes showed opposite association with expression of COL3A1. These genes are known to play important roles in development and function of the extracellular matrix of the lung. Difference in the molecular pathway of key genes in the COL3A1 gene network in humans and mice suggest caution should be used in extrapolating results from models of human lung diseases in mice to clinical lung diseases in humans. These differences may influence the efficacy of drugs in humans whose development employed mouse models.

Tight Skin 2 Mice Exhibit Delayed Wound Healing Caused by Increased Elastic Fibers in Fibrotic Skin

Rationale: The Tight Skin 2 (Tsk2) mouse model of systemic sclerosis (SSc) has many features of human disease, including tight skin, excessive collagen deposition, alterations in the extracellular matrix (ECM), increased elastic fibers, and occurrence of antinuclear antibodies with age. A tight skin phenotype is observed by 2 weeks of age, but measurable skin fibrosis is only apparent at 10 weeks. We completed a series of wound healing experiments to determine how fibrosis affects wound healing in Tsk2/+ mice compared with their wild-type (WT) littermates. Method: We performed these experiments by introducing four 4 mm biopsy punched wounds on the back of each mouse, ventral of the midline, and observed wound healing over 10 days. Tsk2/+ mice showed significantly delayed wound healing and increased wound size compared with the WT littermates at both 5 and 10 weeks of age. We explored the potential sources of this response by wounding Tsk2/+ mice that were genetically deficient either for the NLRP3 inflammasome (a known fibrosis mediator), or for elastic fibers in the skin, using a fibulin-5 knockout. Conclusion: We found that the loss of elastic fibers restores normal wound healing in the Tsk2/+ mouse and that the loss of the NLRP3 inflammasome had no effect. We conclude that elastic fiber dysregulation is the primary cause of delayed wound healing in the Tsk2/+ mouse and therapies that promote collagen deposition in the tissue matrix in the absence of elastin deposition might be beneficial in promoting wound healing in SSc and other diseases.

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.

Fibrillin assemblies: extracellular determinants of tissue formation and fibrosis

The extracellular matrix (ECM) plays a key role in tissue formation, homeostasis and repair, mutations in ECM components have catastrophic consequences for organ function and therefore, for the fitness and survival of the organism. Collagen, fibrillin and elastin polymers represent the architectural scaffolds that impart specific mechanic properties to tissues and organs. Fibrillin assemblies (microfibrils) have the additional function of distributing, concentrating and modulating local transforming growth factor (TGF)-β and bone morphogenetic protein (BMP) signals that regulate a plethora of cellular activities, including ECM formation and remodeling. Fibrillins also contain binding sites for integrin receptors, which induce adaptive responses to changes in the extracellular microenvironment by reorganizing the cytoskeleton, controlling gene expression, and releasing and activating matrix-bound latent TGF-β complexes. Genetic evidence has indicated that fibrillin-1 and fibrillin-2 contribute differently to the organization and structural properties of non-collagenous architectural scaffolds, which in turn translate into discrete regulatory outcomes of locally released TGF-β and BMP signals. Additionally, the study of congenital dysfunctions of fibrillin-1 has yielded insights into the pathogenesis of acquired connective tissue disorders of the connective tissue, such as scleroderma. On the one hand, mutations that affect the structure or expression of fibrillin-1 perturb microfibril biogenesis, stimulate improper latent TGF-β activation, and give rise to the pleiotropic manifestations in Marfan syndrome (MFS). On the other hand, mutations located around the integrin-binding site of fibrillin-1 perturb cell matrix interactions, architectural matrix assembly and extracellular distribution of latent TGF-β complexes, and lead to the highly restricted fibrotic phenotype of Stiff Skin syndrome. Understanding the molecular similarities and differences between congenital and acquired forms of skin fibrosis may therefore provide new therapeutic tools to mitigate or even prevent disease progression in scleroderma and perhaps other fibrotic conditions.

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.

In perspective: murine models of scleroderma

An understanding of the complex pathogenesis of systemic sclerosis (SSc) has been slow to emerge, due in large part to the lack of an animal model recapitulating the three cardinal attributes of SSc: autoimmunity, vasculopathy, and fibrosis. Experimental manipulations in inbred murine strains can lead to conditions that mimic SSc fibrosis. Furthermore, genetic engineering has enabled the creation of novel murine strains that spontaneously develop fibrosis or are protected from fibrosis development. Studies of these mice shed light on the cell types, cell interactions, molecules, and pathways that contribute to SSc manifestations. High-throughput discovery technologies such as DNA microarrays in animal models can identify novel genes and regulatory networks that are important for disease manifestations and that may be targets for therapy. In this brief review, we highlight recent progress in the field and attempt to place the strengths and limitations of popular SSc murine models in perspective.

Understanding systemic sclerosis through gene expression profiling

PURPOSE OF REVIEW

Genomic analysis has rapidly become commonplace in the study and treatment of complex disease. Several recent studies of gene expression profiling in systemic sclerosis have demonstrated its value in diagnosis and illustrate the potential for this technique in prognostication, as well as the elucidation of the underlying pathogenesis.

RECENT FINDINGS

Skin biopsies from patients with systemic sclerosis show robust changes in gene profile that precede clinically detectable involvement. Current results suggest that clinically indistinguishable subgroups may be identified with different pathogenesis and outcome. Expression profiling studies of animal models of systemic sclerosis and explanted fibroblasts have helped to reveal the utility and deficiencies of these surrogates in the study of systemic sclerosis.

SUMMARY

Gene profiling is likely to provide valuable prognostic information in systemic sclerosis patients. Recent advances in sample collection and standardization of analysis mean that longitudinal collection of samples for gene profiling, even in small numbers of patients from different clinical centers, will contribute enormously to our understanding of the disease.

Fibrosis in systemic sclerosis

This article reviews current understanding of the pathophysiology of fibrosis in systemic sclerosis. It highlights recent discoveries, insights, and emerging research, and potential opportunities for the development of targeted antifibrotic therapies.

Marfan-like skeletal phenotype in the tight skin (Tsk) mouse

Tight skin (Tsk) is an autosomal dominant mutation located on mouse chromosome 2 and is associated with an intragenic duplication of the fibrillin 1 (Fbn1) gene. Mutant mice (Tsk/+) display a tightness of skin in the interscapular region, lung emphysema, myocardial hypertrophy, skeletal overgrowth, and kyphosis. It is hypothesized in this study that in Tsk mice the mutation in Fbn1 alters bone cell metabolism. A detailed study of the Tsk skeletal phenotype revealed that Tsk mice have significantly longer femurs and axial skeleton as well as vertebral abnormalities. Cortical and trabecular bone volumes were significantly decreased in Tsk femurs from 2- and 4-month-old mice (13% and 39%, respectively) as well as trabecular thickness, number, connectivity, and surface area. These skeletal differences were also associated with a reduction in bone mineral density in mutant mice. Expression of the osteoblast-specific genes Col1a1, BSP and OC was examined in marrow stromal cell cultures at various time points. A decrease in the rate of maturation of the Tsk cells was indicated by a delay in the appearance of OC expression. These initial experiments demonstrated a significant role of the fibrillin 1 protein in the extracellular matrix of bone cells.

Systemic sclerosis: a prototypic multisystem fibrotic disorder

A unique feature of systemic sclerosis (SSc) that distinguishes it from other fibrotic disorders is that autoimmunity and vasculopathy characteristically precede fibrosis. Moreover, fibrosis in SSc is not restricted to a single organ, but rather affects many organs and accounts for much of the morbidity and mortality associated with this disease. Although immunomodulatory drugs have been used extensively in the treatment of SSc, no therapy to date has been able to reverse or slow the progression of tissue fibrosis or substantially modify the natural progression of the disease. In this Review, we highlight recent studies that shed light on the cellular and molecular mechanisms underlying the fibrotic process in SSc and that identify cellular processes and intra- and extracellular proteins as potential novel targets for therapy in this prototypic multisystemic fibrotic disease.

Postnatal induction of transforming growth factor beta signaling in fibroblasts of mice recapitulates clinical, histologic, and biochemical features of scleroderma

OBJECTIVE

Increased signaling by transforming growth factor beta (TGFbeta) has been implicated in systemic sclerosis (SSc; scleroderma), a complex disorder of connective tissues characterized by excessive accumulation of collagen and other extracellular matrix components in systemic organs. To directly assess the effect of sustained TGFbeta signaling in SSc, we established a novel mouse model in which the TGFbeta signaling pathway is activated in fibroblasts postnatally.

METHODS

The mice we used (termed TBR1(CA); Cre-ER mice) harbor both the DNA for an inducible constitutively active TGFbeta receptor I (TGFbetaRI) mutation, which has been targeted to the ROSA locus, and a Cre-ER transgene that is driven by a fibroblast-specific promoter. Administration of 4-hydroxytamoxifen 2 weeks after birth activates the expression of constitutively active TGFbetaRI.

RESULTS

These mice recapitulated clinical, histologic, and biochemical features of human SSc, showing pronounced and generalized fibrosis of the dermis, thinner epidermis, loss of hair follicles, and fibrotic thickening of small blood vessel walls in the lung and kidney. Primary skin fibroblasts from these mice showed elevated expression of downstream TGFbeta targets, reproducing the hallmark biochemical phenotype of explanted SSc dermal fibroblasts. The mouse fibroblasts also showed elevated basal expression of the TGFbeta-regulated promoters plasminogen activator inhibitor 1 and 3TP, increased Smad2/3 phosphorylation, and enhanced myofibroblast differentiation.

CONCLUSION

Constitutive activation of TGFbeta signaling in fibroblastic cells of mice after birth caused a marked fibrotic phenotype characteristic of SSc. These mice should be excellent models with which to test therapies aimed at correcting excessive TGFbeta signaling in human scleroderma.

Insulin-like growth factor binding protein 5 induces skin fibrosis: A novel murine model for dermal fibrosis

OBJECTIVE

To determine the role of insulin-like growth factor binding protein 5 (IGFBP-5) in the development of skin fibrosis in vivo, by examining the effect of overexpression of IGFBP-5 in mouse skin.

METHODS

Wild-type C57BL/6J mice were injected subcutaneously with replication-deficient serotype 5 adenovirus expressing human IGFBP-3 (Ad3), IGFBP-5 (Ad5), or no complementary DNA (cAd). Mice were killed 3, 8, or 22 days postinjection. The dermal thickness and dermal collagen bundle thickness in skin sections were measured. The deposition of collagen in the extracellular matrix (ECM) was quantified using the Sircol assay. Expression of proliferating cell nuclear antigen (PCNA) and fibronectin, as determined by immunohistochemical analysis, was used to evaluate fibroblast activation, and vimentin and alpha-smooth muscle actin (alpha-SMA) were used to evaluate the fibroblast phenotype.

RESULTS

Adenovirally expressed IGFBP was detected in dermal fibroblasts, endothelial cells, epithelial cells, and muscle bundles in Ad3- and Ad5-injected mice. Increased collagen deposition, denser dermal connective tissue, and increased collagen bundle thickness were observed in IGFBP-5-overexpressing mice. Dermal thickness and collagen bundle thickness were significantly increased in Ad5-injected mice compared with cAd- and Ad3-injected mice. Treatment with Ad5 resulted in a dose-dependent increase in dermal and collagen bundle thickness. Increased deposition of collagen and fibronectin, increased numbers of PCNA-positive fibroblasts, as well as increased numbers of vimentin- and alpha-SMA-double-positive fibroblasts were detected in the dermis of IGFBP-5-overexpressing mouse skin.

CONCLUSION

IGFBP-5 is a key mediator of fibrosis. IGFBP-5 mediates its profibrotic effects through fibroblast activation, increased ECM deposition, and myofibroblastic transformation of dermal fibroblasts. Overexpression of IGFBP-5 provides a novel model for studying the pathogenesis of skin fibrosis in systemic sclerosis.

B-lymphocyte depletion reduces skin fibrosis and autoimmunity in the tight-skin mouse model for systemic sclerosis

Systemic sclerosis (scleroderma) is an autoimmune disease characterized by excessive extracellular matrix deposition in the skin. A direct role for B lymphocytes in disease development or progression has remained controversial, although autoantibody production is a feature of this disease. To address this issue, skin sclerosis and autoimmunity were assessed in tight-skin mice, a genetic model of human systemic sclerosis, after circulating and tissue B-cell depletion using an anti-mouse CD20 monoclonal antibody before (day 3 after birth) and after disease development (day 56). CD20 monoclonal antibody treatment (10 to 20 microg) depleted the majority (85 to 99%) of circulating and tissue B cells in newborn and adult tight-skin mice by days 56 and 112, respectively. B-cell depletion in newborn tight-skin mice significantly suppressed (approximately 43%) the development of skin fibrosis, autoantibody production, and hypergammaglobulinemia. B-cell depletion also restored a more normal balance between Th1 and Th2 cytokine mRNA expression in the skin. By contrast, B-cell depletion did not affect skin fibrosis, hypergammaglobulinemia, and autoantibody levels in adult mice with established disease. Thereby, B-cell depletion during disease onset suppressed skin fibrosis, indicating that B cells contribute to the initiation of systemic sclerosis pathogenesis in tight-skin mice but are not required for disease maintenance.

Hammerhead ribozyme-mediated silencing of the mutant fibrillin-1 of tight skin mouse: insight into the functional role of mutant fibrillin-1

The tight skin (Tsk/+) mouse is a model for fibrotic disorders. The genetic defect in the Tsk/+ is an in-frame duplication between exons 17 and 40 of the fibrillin-1 gene which gives rise to a large transcript and protein. Mice homozygous for the mutation die in utero, whereas heterozygotes survive and spontaneously develop connective tissue disease. In this study, we generated hammerhead ribozymes directed against the mutant fibrillin-1 transcript. A partially mispairing ribozyme was the most effective vehicle to cleave the mutant transcript without undesired cleavage of wild type transcripts, as shown by cell-free RNA cleavage and cleavage in cell lines harboring the ribozyme, by RT-PCR, Northern and Western Blotting. Global gene expression profiling using oligonucleotide microarrays showed the expected reduction in fibrillin-1 mRNA, and down-regulation of several gene cohorts in ribozyme harboring TskR1 cells compared to Tsk/+ cells. Two of the functional clusters included genes regulating extracellular matrix such as connective tissue growth factor, serpine-1 (plasminogen activator inhibitor-1) and TIMP-1 and TIMP-3, and those involved in cytoskeletal organization and myofibroblast formation including calponins and transgelin. Ribozyme-mediated inhibition was confirmed by Western Blot and functional analysis using cell-reporter systems and remodeling of three dimensional collagen gels. Our results underline the therapeutic potential of hammerhead ribozymes in dominant negative defects and suggest that changes in microfibril architecture brought about by fibrillin-1 mutation lead to a complex disease phenotype.