Transgenic analysis of scleroderma: understanding key pathogenic events in vivo

Animal Models of Systemic Sclerosis: Using Nailfold Capillaroscopy as a Potential Tool to Evaluate Microcirculation and Microangiopathy: A Narrative Review

Systemic sclerosis (SSc) is an autoimmune disease with three pathogenic hallmarks, i.e., inflammation, vasculopathy, and fibrosis. A wide plethora of animal models have been developed to address the complex pathophysiology and for the development of possible anti-fibrotic treatments. However, no current model comprises all three pathological mechanisms of the disease. To highlight the lack of a complete model, a review of some of the most widely used animal models for SSc was performed. In addition, to date, no model has accomplished the recreation of primary or secondary Raynaud’s phenomenon, a key feature in SSc. In humans, nailfold capillaroscopy (NFC) has been used to evaluate secondary Raynaud’s phenomenon and microvasculature changes in SSc. Being a non-invasive technique, it is widely used both in clinical studies and as a tool for clinical evaluation. Because of this, its potential use in animal models has been neglected. We evaluated NFC in guinea pigs to investigate the possibility of applying this technique to study microcirculation in the nailfold of animal models and in the future, development of an animal model for Raynaud’s phenomenon. The applications are not only to elucidate the pathophysiological mechanisms of vasculopathy but can also be used in the development of novel treatment options.

Collagen triple helix repeat containing-1 exerts antifibrotic effects on human skin fibroblast and bleomycin-induced dermal fibrosis models

Background

Systemic scleroderma (SSc) is an acquired disorder characterized by excessive deposition of extracellular matrix in the skin and internal organs. So far, the molecular mechanisms underpinning the pathogenesis of SSc have remained unknown. Collagen triple helix repeat containing-1 (CTHRC1) has been indicated to be a cell type-specific inhibitor of transforming growth factor-β (TGF-β), which could have the potential for extensive clinical application owing to its ability to reduce collagen deposition. Our previous studies showed that CTHRC1 inhibited TGF-β1-induced collagen type I synthesis in keloid fibroblasts. In our present research, we attempted to probe the role of CTHRC1 in dermal fibrosis in bleomycin (BLM)-treated mice.

Methods

CTHRC1 and TGF-β1 expression was detected in dermal tissues from patients with SSc and BLM-treated mice by immunohistochemistry. A 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay was used to assess TGF-β1-induced proliferation of human dermal fibroblasts. Collagen expression and fibroblast synthesis were evaluated by quantitative real-time polymerase chain reaction and the 3H-proline incorporation. Masson’s trichrome staining and western blotting were carried out to analyze the deposits and protein levels of type I collagen, respectively.

Results

Compared with those in normal tissues, the levels of CTHRC1 and TGF-β1 were elevated in dermal tissues from patients with SSc and in skin tissues from BLM-treated mice, respectively. Furthermore, recombinant CTHRC1 was found to inhibit TGF-β1-stimulated collagen deposition by fibroblasts. Finally, the in vivo experiments showed that CTHRC1 alleviated BLM-induced dermal fibrotic changes.

Conclusions

CTHRC1 can inhibit human dermal fibroblast collagen deposition and can also exert protective effects against BLM-induced dermal fibrosis in mice. This research provides an indication that CTHRC1 may be a promising treatment choice for dermal fibrosis in SSc patients.

The IL-4/IL-13 axis in skin fibrosis and scarring: mechanistic concepts and therapeutic targets

Skin fibrosis, characterized by excessive fibroblast proliferation and extracellular matrix deposition in the dermis, is the histopathologic hallmark of dermatologic diseases such as systemic sclerosis, hypertrophic scars, and keloids. Effective anti-scarring therapeutics remain an unmet need, underscoring the complex pathophysiologic mechanisms of skin fibrosis. The Th2 cytokines interleukin (IL)-4 and IL-13 have been implicated as key mediators in the pathogenesis of fibroproliferative disorders. The goal of this article is to summarize the current understanding of the role of the IL-4/IL-13 axis in wound healing and skin fibrosis. We conducted a literature search to identify research studies investigating the roles of IL-4 and IL-13 in fibrotic skin diseases. While transforming growth factor-beta has long been regarded as the main driver of fibrotic processes, research into the cellular and molecular biology of wound healing has revealed other pathways that promote scar tissue formation. IL-4 and IL-13 are important mediators of skin fibrosis, supported by evidence from in vitro data, animal models of fibrosis, and clinical studies. Overactive signaling of the IL-4/IL-13 axis contributes to the initiation and perpetuation of fibrotic skin diseases. Further insights into the IL-4/IL-13 axis may reveal potential targets for the development of novel therapies that prevent or treat fibrotic skin diseases.

Fibroblast-Derived MMP-14 Regulates Collagen Homeostasis in Adult Skin

Proteolytic activities in the extracellular matrix by the matrix metalloproteinase (MMP)-14 have been implicated in the remodeling of collagenous proteins during development. To analyze the function of fibroblast-derived MMP-14 in adult skin homeostasis, we generated mice with inducible deletion of MMP-14 in the dermal fibroblast (MMP-14^Sf–/–). These mice are smaller and display a fibrosis-like phenotype in the skin. The skin of these mice showed increased stiffness and tensile strength but no altered collagen cross-links. In vivo, we measured a significantly increased amount of collagen type I accumulated in the skin of MMP-14^Sf–/– mice without an increase in collagen fibril diameters. However, bleomycin-induced fibrosis in skin proceeded in a comparable manner in MMP-14^Sf+/+ and MMP-14^Sf–/– mice, but resolution over time was impaired in MMP-14^Sf–/– mice. Increased accumulation of collagen type I was detected in MMP-14^Sf–/– fibroblasts in culture without significant enhancement of collagen de novo synthesis. This points to a degradative but not synthetic phenotype. In support of this, MMP-14^Sf–/– fibroblasts lost their ability to process fibrillar collagen type I and to activate proMMP-2. Taken together, these data indicate that MMP-14 expression in fibroblasts plays a crucial role in collagen remodeling in adult skin and largely contributes to dermal homeostasis underlying its pathogenic role in fibrotic skin disease.

Transforming growth factor-β1 in plaque morphea

Introduction

Morphea (localized scleroderma) is a rare cutaneous disease characterized by skin fibrosis of unknown pathogenesis. Transforming growth factor-β (TGF-β) is a potent profibrotic factor. The role of TGF-β in morphea remains unclear.

Aim

The goal of this study was to estimate the expression level of TGF-β1 in skin and peripheral blood mononuclear cells as well as the plasma levels of TGF-β1 in plaque morphea (MEP).

Material and methods

The study involved 20 MEP patients. Three control groups were involved: 1 – plasma: 36 healthy volunteers; 2 – PBMC: 47 healthy volunteers; 3 – skin biopsies: 13 samples collected during mastectomy (breast cancer was not skin involved). The analysis of TGF-β1 plasma levels was performed with the use an adequate ELISA kit, while real-time polymerase chain reaction was employed for the expression of TGF-β1 in peripheral blood mononuclear cells (PBMC) and skin.

Results

In our study we have not detected differences in TGF-β 1 expression in PBMC, skin, nor in plasma levels of TGF-β1 between MEP patients and healthy controls, regardless of disease activity and its duration.

Conclusions

The results of our study contradict the claim of the substantial role of TGF-β1 in the most common morphea subtype – MEP.

Treatment of dermal fibroblasts with GPI-anchored human TIMP-1 protein moderates processes linked to scar formation

Tissue inhibitors of metalloproteinases exhibit diverse physiological/biological functions including moderation of the proteolytic processing of growth factors and turnover of extracellular matrix. These various biological activities are linked in part to the stoichiometry of tissue inhibitor of metalloprotein/matrix metalloprotein (TIMP/MMP)/surface protein interactions. TIMP-1, a secreted protein, can be detected on the cell surface only through its interaction with surface-bound proteins. Proteins anchored by glycosylphosphatidylinositol (GPI), when purified and added to cells or tissues, are efficiently incorporated into their surface membranes. A GPI anchor was fused to TIMP-1 to focus defined concentrations of the inhibitory protein independently on the surface of primary dermal fibroblast cells. Exogenously added recombinant TIMP-1-GPI effectively inserted into the cell membrane of fibroblasts blocked the secretion of MMPs and markedly altered the stoichiometry of MMP association with the cell surface. TIMP-1-GPI treatment resulted in inhibition of fibroblast-reduced proliferation, and transiently reduced expression of fibrosis-associated genes. These effects were dose dependent. Treated cells also showed a more proapoptotic phenotype based on apoptotic assays and western blot analysis for apoptosis-associated protein expression. GPI-anchored TIMP-1 may represent a more effective version of the protein for use in therapeutic approaches to help control fibrosis and scar formation.

TGF-β in progression of liver disease

Transforming growth factor-β (TGF-β) is a central regulator in chronic liver disease contributing to all stages of disease progression from initial liver injury through inflammation and fibrosis to cirrhosis and hepatocellular carcinoma. Liver-damage-induced levels of active TGF-β enhance hepatocyte destruction and mediate hepatic stellate cell and fibroblast activation resulting in a wound-healing response, including myofibroblast generation and extracellular matrix deposition. Being recognised as a major profibrogenic cytokine, the targeting of the TGF-β signalling pathway has been explored with respect to the inhibition of liver disease progression. Whereas interference with TGF-β signalling in various short-term animal models has provided promising results, liver disease progression in humans is a process of decades with different phases in which TGF-β or its targeting might have both beneficial and adverse outcomes. Based on recent literature, we summarise the cell-type-directed double-edged role of TGF-β in various liver disease stages. We emphasise that, in order to achieve therapeutic effects, we need to target TGF-β signalling in the right cell type at the right time.

Surface morphology and mechanical properties of fibroblasts from scleroderma patients

Overproduction of extracellular matrix components by fibroblasts plays a key role in the pathogenesis of scleroderma. To investigate whether these functional alterations are accompanied by changes in the mechanical properties and morphology of fibroblast, atomic force microscopy was applied to dermal fibroblasts derived either from scleroderma patients or from healthy donors. No significant morphological differences could be observed among the different cell strains showing long cytoskeleton fibres similar in length and irregularly distributed protrusions on the cell surface. In contrast, significant differences in cellular stiffness of dermal fibroblasts derived from scleroderma lesions were detected. Compared to fibroblasts from healthy donors, diseased cells were characterized by a reduced elastic constant both when the global and local mechanical properties were probed. The altered stiffness of scleroderma fibroblasts may be important in the pathogenesis of the disease as it could lead to the abnormal response of fibroblasts to mechanical stimuli.

Fibrillin-1 staining anomalies are associated with increased staining for TGF-beta and elastic fibre degradation; new clues to the pathogenesis of emphysema

We recently demonstrated aberrant staining of fibrillin-1 in lung tissue specimens with emphysematous lesions. In this study, we have extended this observation by an elaborate analysis of the elastic fibre. Using domain-specific antibodies to fibrillin-1, and to other elastin fibre-associated molecules, lung tissue derived from patients without obvious clinical emphysema, but harbouring various degrees of microscopical emphysematous lesions, was analysed. In addition, the fibrillin-regulated growth factor TGF-beta was studied. Electron microscopy and biochemical analysis of desmosine (a marker for elastin) were also performed. Results were compared with lung tissue derived from patients with clinical emphysema. Domain-specific antibodies recognizing the C-terminal, N-terminal, and middle part of fibrillin-1 showed aberrant staining patterns associated with increasing degrees of microscopical emphysema. Staining for elastin, emilin-1, and fibulin-2 was, however, not aberrant. TGF-beta staining was markedly increased. On the electron microscopic, but not light microscopical, level, initial elastic fibre degradation was noticed in specimens with microscopical emphysema. Lung specimens from patients with clinical emphysema also displayed fragmented fibrillin-1 staining and, in addition, displayed extensive degradation of the elastic fibre. The results suggest that fibrillin-1 anomalies and TGF-beta overexpression are associated with initial events occurring during the emphysematous process. Based on these and other data, a mechanism for emphysematogenesis is proposed.

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.

Role of endogenous endothelin in endothelial dysfunction in murine model of systemic sclerosis: tight skin mice 1

Systemic sclerosis (SSc) is a systemic inflammatory disorder, resulting in severe vascular dysfunction. The endothelin (ET) system has vasoconstrictor and profibrotic properties and has been shown to be activated in SSc. ET antagonists are currently used in SSc-related pulmonary arterial hypertension, but the endothelial impact of ET antagonists remains less known in SSc. We thus assessed the effects of the dual ET(A)-ET(B) antagonist, bosentan, on endothelial dysfunction in a murine model of SSc, the heterozygous tight-skin mice 1 (TSK1(+)). Six-week-old TSK1(+) were either untreated or treated for 6 weeks with bosentan (100 mg/kg/day), and compared with controls. Endothelial function was evaluated in isolated mesenteric resistance arteries, using a small vessel myograph. TSK1(+) displayed endothelial dysfunction, as shown by a decreased response of mesenteric arteries to acetylcholine, especially in the presence of L-nitro-arginine methyl ester (L-NAME), corresponding to NO-independent, prostaglandin-mediated relaxation. The NO-independent relaxation was partially restored in bosentan-treated TSK1(+), and this was abolished by a cyclo-oxygenase inhibitor. Therefore, the murine model of SSc, TSK1(+) exhibits severe endothelial dysfunction of peripheral resistance arteries. The ET antagonist bosentan prevents endothelial alterations, suggesting a major role of ET in the adverse vascular effects of SSc.

Human skin culture as an ex vivo model for assessing the fibrotic effects of insulin-like growth factor binding proteins

Systemic sclerosis (SSc) is a connective tissue disease of unknown etiology. A hallmark of SSc is fibrosis of the skin and internal organs. We recently demonstrated increased expression of IGFBP-3 and IGFBP-5 in primary cultures of fibroblasts from the skin of patients with SSc. In vitro, IGFBP-3 and IGFBP-5 induced a fibrotic phenotype and IGFBP-5 triggered dermal fibrosis in mice. To assess the ability of IGFBPs to trigger fibrosis, we used an ex vivo human skin organ culture model. Our findings demonstrate that IGFBP-3 and IGFBP-5, but not IGFBP-4, increase dermal and collagen bundle thickness in human skin explants, resulting in substantial dermal fibrosis and thickening. These fibrotic effects were sustained for at least two weeks. Our findings demonstrate that human skin ex vivo is an appropriate model to assess the effects of fibrosis-inducing factors such as IGFBPs, and for evaluating the efficacy of inhibitors/therapies to halt the progression of fibrosis and potentially reverse it.

Mechanical tension and integrin alpha 2 beta 1 regulate fibroblast functions

The extracellular matrix (ECM) environment in connective tissues provides fibroblasts with a structural scaffold and modulates cell shape, but it also profoundly influences the fibroblast phenotype. Here we studied fibroblasts cultured in a three-dimensional network of native collagen, which was either mechanically stressed or relaxed. Mechanical load induces fibroblasts that synthesize abundant ECM and a characteristic array of cytokines/chemokines. This phenotype is reminiscent of late granulation tissue or scleroderma fibroblasts. By contrast, relaxed fibroblasts are characterized by induction of proteases and a subset of cytokines that does not overlap with that of mechanically stimulated cells. Thus, the biochemical composition and physical nature of the ECM exert powerful control over the phenotypes of fibroblasts, ranging from "synthetic" to "inflammatory" phenotypes. Interactions between fibroblasts and collagen fibrils are mostly mediated by a subset of beta 1 integrin receptors. Fibroblasts utilize alpha 1 beta 1, alpha 2 beta 1, and alpha 11 beta 1 integrins for establishing collagen contacts and transducing signals. In vitro assays and mouse genetics have demonstrated individual tasks served by each receptor, but also functional redundancy. Unraveling the integrated functions of fibroblasts, collagen integrin receptors, collagen fibrils, and mechanical tension will be important to understand the molecular mechanisms underlying tissue repair and fibrosis.

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.

Cutaneous gene expression by DNA microarray in murine sclerodermatous graft-versus-host disease, a model for human scleroderma

The molecular mechanisms governing skin fibrosis in murine sclerodermatous graft-versus-host disease (Scl GVHD) are not known. We used Affymetrix DNA microarrays representing >14,000 mouse genes to characterize global gene expression in skin during development of Scl GVHD in lethally irradiated BALB/c (H-2d) mice transplanted with B10.D2 (H-2d) bone marrow and spleen cells. These mice develop skin thickening, whereas control mice transplanted with syngeneic BALB/c (H-2d) bone marrow and spleen cells do not develop disease. We found consistent differences between mice with Scl GVHD and controls in cytokine messenger RNAs (mRNAs) for both Th1-like (IFN-gamma) and Th2-like (IL-6, Il-10, and IL-13) inflammatory patterns. mRNAs for chemokines CCL2, CCL5, CCL17, IFN-gamma inducible chemokines (CXCL9/Mig, CXCL10/IP-10, and CXCL11/I-TAC), and for growth factors such as platelet-derived growth factor-c, connective tissue growth factor, fibroblast growth factor 1, epidermal growth factor, nerve growth factor-beta, vascular endothelial growth factor (VEGF)-alpha, and VEGF-beta were elevated, similar to human scleroderma. mRNAs for cell adhesion molecules, such as L-selectin (selectin lymphocyte), P-selectin (selectin platelet), E-selectin (selectin endothelium), and vascular cell adhesion molecule 1, were also upregulated. In separate experiments, we confirmed the increased synthesis of IFN-gamma and IL-2, unchanged IL-10, and absence of tumor necrosis factor-alpha, and IL-4 proteins by flow cytometry of isolated skin T cells. These constellations of immunologic changes provide a "fingerprint" for fibrosing autoimmune disease. They are useful to understand the pathogenesis of Scl GVHD, to identify markers for early diagnosis of disease, and to devise more effective strategies for intervention in early scleroderma and Scl GVHD.

[Current pathophysiological aspects of systemic sclerosis]

Systemic scleroderma is characterized by a chronic inflammatory process of unknown etiology resulting in an increased deposition of connective tissue proteins in the involved organs. Involvement of the vascular system and the resulting fibrosis lead to atrophy and malfunction of the involved internal organs and the skin. Due to the development of new therapeutic concepts in particular with regard to the vascular involvement, the interaction between the vascular system and the connective tissue moves increasingly into focus. This review describes the major advancemades during recent years for the understanding of the pathophysiology of systemic scleroderma.

Contribution of activin receptor–like kinase 5 (transforming growth factor β receptor type I) signaling to the fibrotic phenotype of scleroderma fibroblasts

OBJECTIVE

To use a specific transforming growth factor beta receptor type I (TGFbetaRI; activin receptor-like kinase 5 [ALK-5]) kinase inhibitor (SD208) to determine the role of activation of the TGFbetaRI kinase (ALK-5) in maintaining the profibrotic phenotype of dermal fibroblasts in systemic sclerosis (SSc).

METHODS

The effect of SD208 on the expression of key biochemical markers of the fibrotic phenotype was compared in fibroblasts cultured from clinically involved (lesional) and clinically uninvolved skin of patients with diffuse cutaneous SSc (dcSSc) and in fibroblasts from healthy controls matched for age, sex, and anatomic site. Protein expression was compared together with the ability of fibroblasts to adhere to the extracellular matrix and to remodel and contract a free-floating fibroblast-populated type I collagen lattice.

RESULTS

Inhibiting TGFbetaRI kinase reduced the expression of a cohort of fibrotic markers by dermal fibroblasts from patients with dcSSc, including type I collagen and beta1 integrin. Moreover, inhibition also attenuated the elevated adhesive and contractile abilities of dcSSc fibroblasts.

CONCLUSION

Our data suggest that some of the key profibrotic features of lesional SSc fibroblasts are dependent upon ALK-5 activity. Thus, TGFbetaRI kinase-mediated signaling may contribute to dermal fibrosis in dcSSc.

Scleroderma: from cell and molecular mechanisms to disease models

Scleroderma [also known as systemic sclerosis (SSc)] is a complex autoimmune disease characterised by pathological remodelling of connective tissues. Although the earliest and most frequent manifestations include blood vessel and immunological abnormalities, the systemic and progressive pathology suggests that fundamental interactions between microvascular damage and inflammation are mechanistically linked to obliterative tissue fibrosis. This review will focus on how model systems have provided clues to these relationships and will discuss new data from the study of novel animal disease models. These reveal how vascular damage and leukocyte accumulation generate the molecular cues that control the profiles of soluble mediators, which regulate the aberrant behaviour of mesenchymal cells within connective tissues, and how the dysregulated expression of these components and their differentiation contribute to the persistent fibrogenic response.

Classification of systemic sclerosis. Visions and reality

Systemic sclerosis, scleroderma (SSc) is a disabling condition that shortens life expectancy. Disease heterogeneity and difficulties separating SSc from SSc-like conditions make classification an important issue. Limited cutaneous and diffuse cutaneous SSc, with different severity and survival, have been recognized for several years as distinct subsets. Some authors have suggested an intermediate cutaneous form with intermediate survival. This issue remains unsettled, however. The technique of capillaroscopy is helpful as an adjunct diagnostic tool to separate idiopathic Raynaud's phenomenon from SSc. Digitized video-capillaroscopy is developing as a powerful new method to assess individual capillaries over time. Using the simpler techniques of video-capillaroscopy, different patterns have been described and named 'early', 'active', 'late' and 'slow'. The value of nailfold video-capillaroscopy to distinguish different subsets or provide prognostic information for use in daily practice remains to be assessed. The features of CREST (calcinosis, Raynaud's, oesophagus dysmotility, sclerodactyly, telangiectasias) are not confined to single subsets of SSc. There is no convincing evidence of any advantage for distinguishing the limited, intermediate and diffuse forms of SSc rather than only the limited and diffuse forms.

Activation of Key Profibrotic Mechanisms in Transgenic Fibroblasts Expressing Kinase-deficient Type II Transforming Growth Factor-β Receptor (TβRIIΔk)

We have generated transgenic mice expressing a kinase-deficient type II transforming growth factor-beta (TGFbeta) receptor selectively on fibroblasts (TbetaRIIDeltak-fib). These mice develop dermal and pulmonary fibrosis. In the present study we explore activation of TGFbeta signaling pathways in this strain and examine the profibrotic properties of explanted transgenic fibroblasts including myofibroblast differentiation and abnormal metalloproteinase production. Gene expression profiles of littermate wild type or transgenic fibroblasts were compared using high-density gene arrays and validated by Taqman reverse transcriptase-PCR, Northern and Western blotting. Using a specific inhibitor (SD-208) we demonstrate that the abnormal phenotype of these cells is dependent upon TbetaRI kinase (ALK5) activity, and that transgenic fibroblasts show enhanced expression and activation of TGFbeta together with increased levels of wild type TbetaRII. Moreover, we confirm that transgene expression is itself regulated by TGFbeta and that expression at low levels facilitates signaling, whereas high level expression is inhibitory. For a subset of TGFbeta responsive genes basal up-regulation is normalized or suppressed by exogenous recombinant TGFbeta1 at time points coincident with increased transgene expression. These findings explain the profound refractoriness of TbetaRIIDeltak-fib fibroblasts to exogenous TGFbeta1, despite their activated phenotype. Thus, transgenic fibroblasts recapitulate many hallmark biochemical properties of fibrotic cells, including high level CTGF (CCN2) expression and type I collagen overproduction, altered MMP production, and myofibroblast differentiation. These cells also show an enhanced ability to contract collagen gel matrices. Our study demonstrates that altered high affinity TGFbeta receptor function may lead to ligand-dependent activation of downstream signaling, and provides further evidence of a pivotal role for sustained TGFbeta overactivity in fibrosis.