Scleroderma, fibroblasts, signaling, and excessive extracellular matrix

Assessment of skin fibrosis in a murine model of systemic sclerosis with multifunctional optical coherence tomography

Significance

Systemic sclerosis (SSc) is a chronic idiopathic disease that causes immune dysregulation, vasculopathy, and organ fibrosis that affects more than 3 million people in the US alone. The modified Rodnan skin score (mRSS) is the current gold standard for diagnosing and staging skin fibrosis in SSc. However, mRSS is subjective, requires extensive training, and has high observer variability.

Aim

We aim to provide a quantitative method for the assessment of fibrosis.

Approach

We utilized optical coherence tomography (OCT), its extensions, optical coherence elastography (OCE), and OCT angiography (OCTA) to evaluate SSc-like fibrosis and therapy response in a mouse model.

Results

We showed stiffness differences between fibrotic and normal mouse skin by week 4 ( p = 0.02 ) during the longitudinal study. In the treatment response study, OCE recorded higher elastic wave velocity in untreated fibrotic skin ( p = 0.04 ). Treated fibrotic skin stiffness was between normal and fibrotic levels. OCTA indicated significantly dilated microvasculature in fibrotic skin versus control ( p ≪ 0.01 ), with more dilation in the treatment group ( p ≪ 0.01 ) than in normal skin.

Conclusions

Our results indicate that OCT and its extensions effectively analyze dermal fibrosis. OCE revealed increased stiffness in fibrotic skin, OCTA showed vessel dilation, and OCT noted morphological changes in fibrosis tissue.

scPanel: a tool for automatic identification of sparse gene panels for generalizable patient classification using scRNA-seq datasets

Single-cell RNA sequencing (scRNA-seq) technologies can generate transcriptomic profiles at a single-cell resolution in large patient cohorts, facilitating discovery of gene and cellular biomarkers for disease. Yet, when the number of biomarker genes is large, the translation to clinical applications is challenging due to prohibitive sequencing costs. Here, we introduce scPanel, a computational framework designed to bridge the gap between biomarker discovery and clinical application by identifying a sparse gene panel for patient classification from the cell population(s) most responsive to perturbations (e.g. diseases/drugs). scPanel incorporates a data-driven way to automatically determine a minimal number of informative biomarker genes. Patient-level classification is achieved by aggregating the prediction probabilities of cells associated with a patient using the area under the curve score. Application of scPanel to scleroderma, colorectal cancer, and COVID-19 datasets resulted in high patient classification accuracy using only a small number of genes (<20), automatically selected from the entire transcriptome. In the COVID-19 case study, we demonstrated cross-dataset generalizability in predicting disease state in an external patient cohort. scPanel outperforms other state-of-the-art gene selection methods for patient classification and can be used to identify parsimonious sets of reliable biomarker candidates for clinical translation.

Could Gas6/TAM Axis Provide Valuable Insights into the Pathogenesis of Systemic Sclerosis?

Systemic sclerosis (SSc) is a connective tissue disorder characterized by microvascular injury, extracellular matrix deposition, autoimmunity, inflammation, and fibrosis. The clinical complexity and high heterogeneity of the disease make the discovery of potential therapeutic targets difficult. However, the recent progress in the comprehension of its pathogenesis is encouraging. Growth Arrest-Specific 6 (Gas6) and Tyro3, Axl, and MerTK (TAM) receptors are involved in multiple biological processes, including modulation of the immune response, phagocytosis, apoptosis, fibrosis, inflammation, cancer development, and autoimmune disorders. In the present manuscript, we review the current evidence regarding SSc pathogenesis and the role of the Gas6/TAM system in several human diseases, suggesting its likely contribution in SSc and highlighting areas where further research is necessary to fully comprehend the role of TAM receptors in this condition. Indeed, understanding the involvement of TAM receptors in SSc, which is currently unknown, could provide valuable insights for novel potential therapeutic targets.

Delivery technologies for therapeutic targeting of fibronectin in autoimmunity and fibrosis applications

Fibronectin (FN) is a critical component of the extracellular matrix (ECM) contributing to various physiological processes, including tissue repair and immune response regulation. FN regulates various cellular functions such as adhesion, proliferation, migration, differentiation, and cytokine release. Alterations in FN expression, deposition, and molecular structure can profoundly impact its interaction with other ECM proteins, growth factors, cells, and associated signaling pathways, thus influencing the progress of diseases such as fibrosis and autoimmune disorders. Therefore, developing therapeutics that directly target FN or its interaction with cells and other ECM components can be an intriguing approach to address autoimmune and fibrosis pathogenesis.

Fibroblast activation protein: Pivoting cancer/chemotherapeutic insight towards heart failure

An important mechanism for cancer progression is degradation of the extracellular matrix (ECM) which is accompanied by the emergence and proliferation of an activated fibroblast, termed the cancer associated fibroblast (CAF). More specifically, an enzyme pathway identified to be amplified with local cancer progression and proliferation of the CAF, is fibroblast activation protein (FAP). The development and progression of heart failure (HF) irrespective of the etiology is associated with left ventricular (LV) remodeling and changes in ECM structure and function. As with cancer, HF progression is associated with a change in LV myocardial fibroblast growth and function, and expresses a protein signature not dissimilar to the CAF. The overall goal of this review is to put forward the postulate that scientific discoveries regarding FAP in cancer as well as the development of specific chemotherapeutics could be pivoted to target the emergence of FAP in the activated fibroblast subtype and thus hold translationally relevant diagnostic and therapeutic targets in HF.

Release of TGF-β3 from Surface-Modified PCL Fiber Mats Triggers a Dose-Dependent Chondrogenic Differentiation of Human Mesenchymal Stromal Cells

The design of implants for tissue transitions remains a major scientific challenge. This is due to gradients in characteristics that need to be restored. The rotator cuff in the shoulder, with its direct osteo-tendinous junction (enthesis), is a prime example of such a transition. Our approach towards an optimized implant for entheses is based on electrospun fiber mats of poly(ε-caprolactone) (PCL) as biodegradable scaffold material, loaded with biologically active factors. Chitosan/tripolyphosphate (CS/TPP) nanoparticles were used to load transforming growth factor-β₃ (TGF-β₃) with increasing loading concentrations for the regeneration of the cartilage zone within direct entheses. Release experiments were performed, and the concentration of TGF-β₃ in the release medium was determined by ELISA. Chondrogenic differentiation of human mesenchymal stromal cells (MSCs) was analyzed in the presence of released TGF-β₃. The amount of released TGF-β₃ increased with the use of higher loading concentrations. This correlated with larger cell pellets and an increase in chondrogenic marker genes (SOX9, COL2A1, COMP). These data were further supported by an increase in the glycosaminoglycan (GAG)-to-DNA ratio of the cell pellets. The results demonstrate an increase in the total release of TGF-β₃ by loading higher concentrations to the implant, which led to the desired biological effect.

Lung-kidney interactions and their role in chronic kidney disease-associated pulmonary diseases

Chronic illnesses rarely present in a vacuum, devoid of other complications, and chronic kidney disease is hardly an exception. Comorbidities associated with chronic kidney disease lead to faster disease progression, expedited dialysis dependency, and a higher mortality rate. Although chronic kidney disease is most commonly accompanied by cardiovascular diseases and diabetes, there is clear cross talk between the lungs and kidneys pH balance, phosphate metabolism, and immune system regulation. Our present understanding of the exact underlying mechanisms that contribute to chronic kidney disease-related pulmonary disease is poor. This review summarizes the current research on kidney-pulmonary interorgan cross talk in the context of chronic kidney disease, highlighting various acute and chronic pulmonary diseases that lead to further complications in patient care. Treatment options for patients presenting with chronic kidney disease and lung disease are explored by assessing activated molecular pathways and the body's compensatory response mechanisms following homeostatic imbalance. Understanding the link between the lungs and kidneys will potentially improve health outcomes for patients and guide healthcare professionals to better understand how and when to treat each of the pulmonary comorbidities that can present with chronic kidney disease.

Fibroblast growth factor receptor 3 activates a network of profibrotic signaling pathways to promote fibrosis in systemic sclerosis

Aberrant activation of fibroblasts with progressive deposition of extracellular matrix is a key feature of systemic sclerosis (SSc), a prototypical idiopathic fibrotic disease. Here, we demonstrate that the profibrotic cytokine transforming growth factor β selectively up-regulates fibroblast growth factor receptor 3 (FGFR3) and its ligand FGF9 to promote fibroblast activation and tissue fibrosis, leading to a prominent FGFR3 signature in the SSc skin. Transcriptome profiling, in silico analysis and functional experiments revealed that FGFR3 induces multiple profibrotic pathways including endothelin, interleukin-4, and connective tissue growth factor signaling mediated by transcription factor CREB (cAMP response element-binding protein). Inhibition of FGFR3 signaling by fibroblast-specific knockout of FGFR3 or FGF9 or pharmacological inhibition of FGFR3 blocked fibroblast activation and attenuated experimental skin fibrosis in mice. These findings characterize FGFR3 as an upstream regulator of a network of profibrotic mediators in SSc and as a potential target for the treatment of fibrosis.

Collagen Structure-Function Mapping Informs Applications for Regenerative Medicine

Type I collagen, the predominant protein of vertebrates, assembles into fibrils that orchestrate the form and function of bone, tendon, skin, and other tissues. Collagen plays roles in hemostasis, wound healing, angiogenesis, and biomineralization, and its dysfunction contributes to fibrosis, atherosclerosis, cancer metastasis, and brittle bone disease. To elucidate the type I collagen structure-function relationship, we constructed a type I collagen fibril interactome, including its functional sites and disease-associated mutations. When projected onto an X-ray diffraction model of the native collagen microfibril, data revealed a matrix interaction domain that assumes structural roles including collagen assembly, crosslinking, proteoglycan (PG) binding, and mineralization, and the cell interaction domain supporting dynamic aspects of collagen biology such as hemostasis, tissue remodeling, and cell adhesion. Our type III collagen interactome corroborates this model. We propose that in quiescent tissues, the fibril projects a structural face; however, tissue injury releases blood into the collagenous stroma, triggering exposure of the fibrils' cell and ligand binding sites crucial for tissue remodeling and regeneration. Applications of our research include discovery of anti-fibrotic antibodies and elucidating their interactions with collagen, and using insights from our angiogenesis studies and collagen structure-function model to inform the design of super-angiogenic collagens and collagen mimetics.

Integrated, multicohort analysis of systemic sclerosis identifies robust transcriptional signature of disease severity

Systemic sclerosis (SSc) is a rare autoimmune disease with the highest case-fatality rate of all connective tissue diseases. Current efforts to determine patient response to a given treatment using the modified Rodnan skin score (mRSS) are complicated by interclinician variability, confounding, and the time required between sequential mRSS measurements to observe meaningful change. There is an unmet critical need for an objective metric of SSc disease severity. Here, we performed an integrated, multicohort analysis of SSc transcriptome data across 7 datasets from 6 centers composed of 515 samples. Using 158 skin samples from SSc patients and healthy controls recruited at 2 centers as a discovery cohort, we identified a 415-gene expression signature specific for SSc, and validated its ability to distinguish SSc patients from healthy controls in an additional 357 skin samples from 5 independent cohorts. Next, we defined the SSc skin severity score (4S). In every SSc cohort of skin biopsy samples analyzed in our study, 4S correlated significantly with mRSS, allowing objective quantification of SSc disease severity. Using transcriptome data from the largest longitudinal trial of SSc patients to date, we showed that 4S allowed us to objectively monitor individual SSc patients over time, as (a) the change in 4S of a patient is significantly correlated with change in the mRSS, and (b) the change in 4S at 12 months of treatment could predict the change in mRSS at 24 months. Our results suggest that 4S could be used to distinguish treatment responders from nonresponders prior to mRSS change. Our results demonstrate the potential clinical utility of a novel robust molecular signature and a computational approach to SSc disease severity quantification.

Type I IFNs Regulate Inflammation, Vasculopathy, and Fibrosis in Chronic Cutaneous Graft-versus-Host Disease

Type I IFNs play a critical role in the immune response to viral infection and may also drive autoimmunity through modulation of monocyte maturation and promotion of autoreactive lymphocyte survival. Recent demonstrations of type I IFN gene signatures in autoimmune diseases, including scleroderma, led us to investigate the pathological role of IFNs in a preclinical model of sclerodermatous graft-versus-host disease. Using a neutralizing Ab against the type I IFN receptor IFNAR1, we observed a marked reduction in dermal inflammation, vasculopathy, and fibrosis compared with that seen in the presence of intact IFNAR1 signaling. The ameliorative effects of IFNAR1 blockade were restricted to the skin and were highly associated with inhibition of chronic vascular injury responses and not due to the inhibition of the T or B cell alloresponse. Inhibition of IFNAR1 normalized the overexpression of IFN-inducible genes in graft-versus-host disease skin and markedly reduced dermal IFN-α levels. Depletion of plasmacytoid dendritic cells, a major cellular source of type I IFNs, did not reduce the severity of fibrosis or type I IFN gene signature in the skin. Taken together, these studies demonstrate an important role for type I IFN in skin fibrosis, and they provide a rationale for IFNAR1 inhibition in scleroderma.

Sildenafil attenuates the fibrotic phenotype of skin fibroblasts in patients with systemic sclerosis

Systemic sclerosis (SSc) is a multi-organ fibrotic disease that affects the skin and various internal organs. Therapeutic strategies for tissue fibrosis have not been established; however, aberrantly activated fibroblasts in affected lesions are key targets for modulating fibrosis. Recently, increased intracellular cyclic GMP (cGMP) levels were demonstrated to improve fibrosis levels in various diseases. The purpose of this study was to assess the anti-fibrotic properties of cGMP in cultured fibroblasts from patients with SSc. The phosphodiesterase (PDE) 5 inhibitor sildenafil increased the intracellular cGMP levels in skin fibroblasts in a dose-dependent manner. Sildenafil treatment also significantly decreased the expression of several pro-fibrotic factors that were upregulated by TGF-β1 treatment in SSc skin fibroblasts. These inhibitory effects occurred via non-canonical TGF-β signaling. Our findings revealed that sildenafil might be a novel strategy to treat tissue fibrosis and vasculopathy in SSc.

Vasculopathy in scleroderma

Systemic sclerosis (SSc) is a multisystem connective tissue disorder featured by vascular injury and fibrosis of the skin and various internal organs with autoimmune background. Although the pathogenesis of SSc still remains elusive, it is generally accepted that initial vascular injury due to autoimmunity and/or environmental factors causes structural and functional abnormalities of vasculature which eventually result in the constitutive activation of fibroblasts in various organs. Structural alterations consist of destructive vasculopathy (loss of small vessels) and proliferative obliterative vasculopathy (occlusion of arterioles and small arteries with fibro-proliferative change) caused by impaired compensatory vasculogenesis and angiogenesis. Impaired function of SSc vasculature includes the altered expression of cell adhesion molecules predominantly inducing Th2 and Th17 cell infiltration, endothelial dysfunction primarily due to the low availability of nitric oxide, the activated endothelial-to-mesenchymal transition leading to fibro-proliferative vascular change and tissue fibrosis, and the impaired coagulation/fibrinolysis system promoting the formation of intravascular fibrin deposits. Recent new insights into the therapeutic mechanisms of intravenous cyclophosphamide pulse and bosentan and the establishment of a new SSc animal model (Klf5 (+/-);Fli1 (+/-) mice) provide us useful clues to further understand the development of vascular alterations characteristic of SSc. This article overviewed the present understanding of the pathogenesis of SSc vasculopathy.

Cytokines in the immunopathology of systemic sclerosis

Cytokines and growth factors are key regulators of immune activation, vascular alteration and excessive production of extracellular matrix which are hallmark events in the pathogenesis of systemic sclerosis (SSc). They modulate cell-cell and cell-matrix interactions. In particular, cytokines play a central role in the immunopathogenesis of SSc on the basis of molecular pathways which are complex and not completely understood. The majority of cytokines that may be involved in SSc pathogenesis have effect upon or are derived from cells of the immune system, including both the innate and adaptive compartments. Novel therapies that block key mediators that drive the fibrotic response are being developed and appear as potential therapeutic tools in the treatment of SSc, highlighting the importance for an effective therapy targeted towards the molecular and cellular pathways. This article reviews cytokine biology in that context, with particular emphasis on immunopathology of the disease, therapeutic targeting and the way that current or emerging treatments for SSc might impact on cytokine biology.

Attenuation of fibrosis with selective inhibition of c-Abl by siRNA in systemic sclerosis dermal fibroblasts

Cellular abelson (c-Abl), a non-receptor tyrosine kinase, is an important molecule in the pathogenesis of systemic sclerosis. There have been reports of beneficial effects of pharmacological tyrosine kinase inhibitors, such as imatinib mesylate, on fibrosis. However, these inhibitors affect multiple tyrosine kinases including c-Abl, c-kit, and platelet-derived growth factor receptor. The effects of selective inhibition of c-Abl using small interfering RNA (siRNA) on dermal fibrosis have not yet been explored. The aim of this study is to evaluate whether specific inhibition of c-Abl by siRNA can influence the transforming growth factor-β1 (TGF-β1)-induced fibrotic responses. Dermal fibroblasts from systemic sclerosis patients and healthy controls were transfected with c-Abl siRNA. The expression levels of collagen type I, fibronectin, connective tissue growth factor (CTGF), and α-smooth muscle actin (α-SMA) were measured at both the mRNA and protein levels in the absence or presence of TGF-β1 pro-fibrotic cytokine. In healthy dermal fibroblasts, the expression of collagen type 1, fibronectin, α-SMA, and CTGF mRNAs and proteins that were upregulated after stimulation with TGF-β1 was markedly decreased by c-Abl siRNA. Silencing of c-Abl via siRNA efficiently reduced the basal synthesis of collagen type I, fibronectin, α-SMA, and CTGF mRNAs and proteins in systemic sclerosis fibroblasts, but it had no effect on the baseline expression of these genes and proteins in healthy dermal fibroblasts. In conclusion, specific c-Abl gene silencing using siRNA effectively reduced fibrosis-related gene expression. Inhibition of c-Abl by siRNA may be a potential therapeutic approach for fibrotic diseases such as systemic sclerosis.

Comparative proteomic analysis of extracellular matrix proteins secreted by hypertrophic scar with normal skin fibroblasts

The formation of hypertrophic scars (HSs) is a fibroproliferative disorder of abnormal wound healing. HSs usually characterize excessive proliferation of fibroblasts, abnormal deposition of extracellular matrix (ECM) during wound healing, associated with cosmetic, functional, and psychological problems. Owing to the role of ECM proteins in scar formation, we comparatively analyzed matrix proteins secreted by normal skin fibroblasts (NSFs) and HS fibroblasts (HSFs). The acetone-extracted secreted proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and identified by mass spectrometry (MS). Based on Go annotation of MS data, the profiling of ECM proteins was established and scar-related proteins have been screened out. The functions of several ECM proteins identified by MS have been discussed, such as collagens I, VI, XII, fibronectin, decorin, lumican, and protein procollagen C endopeptidase enhancer 1 (PCPE-1). Among them, the MS result of PCPE-1 was supported by Western blotting that PCPE-1 from HSFs were significantly upregulated than that from NSFs. It is suggested that PCPE-1 could be a potential target for scar treatment. The exploration of scar related proteins may provide new perspectives on understanding the mechanism of scar formation and open a new way to scar treatment and prevention.

Serum levels of tenascin-C in collagen diseases

Tenascins are a family of large multimetric extracellular matrix (ECM) proteins. Among them, large molecular weight variant tenascin-C is known to be specifically expressed in pathological conditions. However, no link between tenascin-C and collagen diseases has been established. The aim of our study was to determine the serum tenascin-C levels in patients with various collagen diseases, and to evaluate the possibility that serum levels of tenascin-C can be a useful marker for collagen diseases, correlating with the pathogenesis. Serum tenascin-C levels of 33 patients with scleroderma (SSc), 10 patients with scleroderma spectrum disorder (SSD), 15 patients with localized scleroderma (LSc), 12 patients with dermatomyositis (DM), 10 patients with systemic lupus erythematosus (SLE) and 15 healthy controls were measured with specific enzyme-linked immunosorbent assays. Serum tenascin-C levels were significantly elevated in patients with SSc, SSD and LSc than in healthy controls. Significantly higher total skin thickness score or higher incidence of pitting scars/ulcers and diffuse pigmentation were observed in SSc patients with elevated tenascin-C levels than in those with normal levels. Our study suggests that serum tenascin-C levels are increased in fibrotic conditions, and that tenascin-C contributes to the pathogenesis of vascular damage as well as fibrosis in SSc patients. Clarifying the role of tenascin-C in the pathogenesis of collagen diseases may lead to a new therapeutic approach.

Angiotensin II induces skin fibrosis: a novel mouse model of dermal fibrosis

Introduction

Systemic sclerosis (SSc) is an autoimmune inflammatory disorder of unknown etiology characterized by fibrosis of the skin and internal organs. Ang II (angiotensin II), a vasoconstrictive peptide, is a well-known inducer of kidney, heart, and liver fibrosis. The goal of this study was to investigate the profibrotic potential of Ang II in the mouse skin.

Methods

Ang II was administered by subcutaneous osmotic mini pumps to C57BL/6 male mice. Collagen-content measurements were performed with Gomori Trichrome staining and hydroxyproline assay. The mRNA expression level of collagens, TGF-β1, TGF-β2, TGF-β3, CTGF, αSMA, CD3, Emr1, CD45/B220, MCP1, and FSP1 were quantified with real-time polymerase chain reaction (PCR). Immunostaining was performed for markers of inflammation and fibrosis, including, phospho-Smad2, αSMA, CD3, Mac3, CD45/B220, and CD163B. Fibrocytes were identified by double staining with CD45/FSP1 and CD45/PH4. Endothelial cells undergoing endothelial-to-mesenchymal transition (EndoMT) were identified by double staining with VE-cadherin/FSP1.

Results

Ang II-infused mice develop prominent dermal fibrosis in the area proximal to the pump, as shown by increased collagen and CTGF mRNA levels, increased hydroxyproline content, and more tightly packed collagen fibers. In addition, elevated mRNA levels of TGF-β2 and TGF-β3 along with increased expression of pSmad2 were observed in the skin of Ang II-treated mice. Dermal fibrosis was accompanied by an increased number of infiltrating fibrocytes, and an increased number of αSMA-positive cells, as well as CD163B⁺ macrophages in the upper dermis. This correlated with significantly increased mRNA levels of αSMA, Emr1, and MCP1. Infiltration of CD3-, CD45/B220-, and Mac3-positive cells was observed mainly in the hypodermis. Furthermore, an increased number of double-positive VE-cadherin/FSP1 cells were detected in the hypodermis only.

Conclusions

This work demonstrates that Ang II induces both inflammation and fibrosis in the skin via MCP1 upregulation and accumulation of activated fibroblasts. Additionally, our data suggest that populations of these fibroblasts originate from circulating blood cells. Ang II infusion via osmotic minipumps could serve as a useful mouse model of skin fibrosis to gain new insights into pathogenic mechanisms and to test new antifibrotic therapies.

A lipocalin-derived Peptide modulating fibroblasts and extracellular matrix proteins

Lipocalin family members have been implicated in development, regeneration, and pathological processes, but their roles are unclear. Interestingly, these proteins are found abundant in the venom of the Lonomia obliqua caterpillar. Lipocalins are β-barrel proteins, which have three conserved motifs in their amino acid sequence. One of these motifs was shown to be a sequence signature involved in cell modulation. The aim of this study is to investigate the effects of a synthetic peptide comprising the lipocalin sequence motif in fibroblasts. This peptide suppressed caspase 3 activity and upregulated Bcl-2 and Ki-67, but did not interfere with GPCR calcium mobilization. Fibroblast responses also involved increased expression of proinflammatory mediators. Increase of extracellular matrix proteins, such as collagen, fibronectin, and tenascin, was observed. Increase in collagen content was also observed in vivo. Results indicate that modulation effects displayed by lipocalins through this sequence motif involve cell survival, extracellular matrix remodeling, and cytokine signaling. Such effects can be related to the lipocalin roles in disease, development, and tissue repair.

Understanding fibrosis in systemic sclerosis: shifting paradigms, emerging opportunities

Fibrosis in multiple organs is a prominent pathological finding and distinguishing hallmark of systemic sclerosis (SSc). Findings during the past 5 years have contributed to a more complete understanding of the complex cellular and molecular underpinning of fibrosis in SSc. Fibroblasts, the principal effector cells, are activated in the profibrotic cellular milieu by cytokines and growth factors, developmental pathways, endothelin 1 and thrombin. Innate immune signaling via Toll-like receptors, matrix-generated biomechanical stress signaling via integrins, hypoxia and oxidative stress seem to be implicated in perpetuating the process. Beyond chronic fibroblast activation, fibrosis represents a failure to terminate tissue repair, coupled with an expanded population of mesenchymal cells originating from bone marrow and transdifferentiation of epithelial cells, endothelial cells and pericytes. In addition, studies have identified intrinsic alterations in SSc fibroblasts resulting from epigenetic changes, as well as altered microRNA expression that might underlie the cell-autonomous, persistent activation phenotype of these cells. Precise characterization of the deregulated extracellular and intracellular signaling pathways, mediators and cellular differentiation programs that contribute to fibrosis in SSc will facilitate the development of selective, targeted therapeutic strategies. Effective antifibrotic therapy will ultimately involve novel compounds and repurposing of drugs that are already approved for other indications.

Plasma and cellular fibronectin: distinct and independent functions during tissue repair

Fibronectin (FN) is a ubiquitous extracellular matrix (ECM) glycoprotein that plays vital roles during tissue repair. The plasma form of FN circulates in the blood, and upon tissue injury, is incorporated into fibrin clots to exert effects on platelet function and to mediate hemostasis. Cellular FN is then synthesized and assembled by cells as they migrate into the clot to reconstitute damaged tissue. The assembly of FN into a complex three-dimensional matrix during physiological repair plays a key role not only as a structural scaffold, but also as a regulator of cell function during this stage of tissue repair. FN fibrillogenesis is a complex, stepwise process that is strictly regulated by a multitude of factors. During fibrosis, there is excessive deposition of ECM, of which FN is one of the major components. Aberrant FN-matrix assembly is a major contributing factor to the switch from normal tissue repair to misregulated fibrosis. Understanding the mechanisms involved in FN assembly and how these interplay with cellular, fibrotic and immune responses may reveal targets for the future development of therapies to regulate aberrant tissue-repair processes.

Cell-extracellular matrix interactions in normal and diseased skin

Mammalian skin comprises a multi-layered epithelium, the epidermis, and an underlying connective tissue, the dermis. The epidermal extracellular matrix is a basement membrane, whereas the dermal ECM comprises fibrillar collagens and associated proteins. There is considerable heterogeneity in ECM composition within both epidermis and dermis. The functional significance of this extends beyond cell adhesion to a range of cell autonomous and nonautonomous processes, including control of epidermal stem cell fate. In skin, cell-ECM interactions influence normal homeostasis, aging, wound healing, and disease. Disturbed integrin and ECM signaling contributes to both tumor formation and fibrosis. Strategies for manipulating cell-ECM interactions to repair skin defects and intervene in a variety of skin diseases hold promise for the future.

Fibrosis in systemic sclerosis: emerging concepts and implications for targeted therapy

Systemic sclerosis (SSc) is a complex and incompletely understood disease associated with fibrosis in multiple organs. Recent findings identify transforming growth factor-ß (TGF-ß), Wnt ligands, toll-like receptor-mediated signaling, hypoxia, type I interferon, type 2 immune responses and mechanical stress as extracellular cues that modulate fibroblast function and differentiation, and as potential targets for therapy. Moreover, fibrillin-1 has a major role in storing and regulating the bioavailability of TGF-ß and other cytokines, and fibrillin-1 mutations are implicated in a congenital form of scleroderma called stiff skin syndrome. Fibrosis is due not only to the activation of tissue-resident fibroblasts and their transdifferentiation into myofibroblasts, but also the differentiation of bone marrow-derived fibrocytes, and transition of endothelial and epithelial cells, pericytes and adipocytes into activated mesenchymal cells. These responses are modulated by signaling mediators and microRNAs that amplify or inhibit TGF-ß and Wnt signaling. Gain-of-function and loss-of-function abnormalities of these mediators may account for the characteristic activated phenotype of SSc fibroblasts. The nuclear orphan receptor PPAR-γ plays a particularly important role in limiting the duration and intensity of fibroblast activation and differentiation, and impaired PPAR-γ expression or function in SSc may underlie the uncontrolled progression of fibrosis. Identifying the perturbations in signaling pathways, mediators and differentiation programs that are responsible for SSc tissue damage allows their selective targeting. This in turn opens the door for therapies utilizing novel compounds, or drug repurposing by innovative uses of already-approved drugs. In view of the heterogeneous clinical presentation and unpredictable course of SSc, as well as its complex pathogenesis, only robust clinical trials incorporating the judicious application of biomarkers will be able to clarify the clinical utility of these innovative approaches.

Characterization of monocyte/macrophage subsets in the skin and peripheral blood derived from patients with systemic sclerosis

Introduction

Recent accumulating evidence indicates a crucial involvement of macrophage lineage in the pathogenesis of systemic sclerosis (SSc). To analyze the assembly of the monocyte/macrophage population, we evaluated the expression of CD163 and CD204 and various activated macrophage markers, in the inflammatory cells of the skin and in the peripheral blood mononuclear cells (PBMCs) derived from patients with SSc.

Methods

Skin biopsy specimens from 6 healthy controls and 10 SSc patients (7 limited cutaneous SSc and 3 diffuse cutaneous SSc) were analyzed by immunohistochemistry using monoclonal antibody against CD68 (pan-macrophage marker), CD163 and CD204. Surface and/or intracellular protein expression of CD14 (marker for monocyte lineage), CD163 and CD204 was analysed by flow cytometry in PBMCs from 16 healthy controls and 41 SSc patients (26 limited cutaneous SSc and 15 diffuse cutaneous SSc). Statistical analysis was carried out using Mann-Whitney U test for comparison of means.

Results

In the skin from SSc patients, the number of CD163⁺ cells or CD204⁺ cells between the collagen fibers was significantly larger than that in healthy controls. Flow cytometry showed that the population of CD14⁺ cells was significantly greater in PBMCs from SSc patients than that in healthy controls. Further analysis of CD14⁺ cells in SSc patients revealed higher expression of CD163 and the presence of two unique peaks in the CD204 histogram. Additionally, we found that the CD163⁺ cells belong to CD14^brightCD204⁺ population.

Conclusions

This is the first report indicating CD163⁺ or CD204⁺ activated macrophages may be one of the potential fibrogenic regulators in the SSc skin. Furthermore, this study suggests a portion of PBMCs in SSc patients abnormally differentiates into CD14^brightCD163⁺CD204⁺ subset. The subset specific to SSc may play an important role in the pathogenesis of this disease, as the source of CD163⁺ or CD204⁺ macrophages in the skin.

Transcriptional regulation of matrix metalloproteinase-1 and collagen 1A2 explains the anti-fibrotic effect exerted by proteasome inhibition in human dermal fibroblasts

Introduction

Extracellular matrix (ECM) turnover is controlled by the synthetic rate of matrix proteins, including type I collagen, and their enzymatic degradation by matrix metalloproteinases (MMPs). Fibrosis is characterized by an unbalanced accumulation of ECM leading to organ dysfunction as observed in systemic sclerosis. We previously reported that proteasome inhibition (PI) in vitro decreases type I collagen and enhances MMP-1 production by human fibroblasts, thus favoring an antifibrotic fibroblast phenotype. These effects were dominant over the pro-fibrotic phenotype induced by transforming growth factor (TGF)-β. Here we investigate the molecular events responsible for the anti-fibrotic phenotype induced in fibroblasts by the proteasome inhibitor bortezomib.

Methods

The steady-state mRNA levels of COL1A1, COL1A2, TIMP-1, MMP-1, and MMP-2 were assessed by quantitative PCR in human dermal fibroblasts cultured in the presence of TGF-β, bortezomib, or both. Transient fibroblast transfection was performed with wild-type and mutated COL1A1 and MMP-1 promoters. Chromatin immunoprecipitation, electrophoretic mobility shift assay (EMSA), and DNA pull-down assays were used to assess the binding of c-Jun, SP1, AP2, and Smad2 transcription factors. Immunoblotting and immunofluorescent microscopy were performed for identifying phosphorylated transcription factors and their cellular localization.

Results

Bortezomib decreased the steady-state mRNA levels of COL1A1 and COL1A2, and abrogated SP1 binding to the promoter of COL1A2 in both untreated and TGF-β-activated fibroblasts. Reduced COL1A2 expression was not due to altered TGF-β-induced Smad2 phosphorylation, nuclear translocation, or binding to the COL1A2 promoter. In contrast to collagen, bortezomib specifically increased the steady-state mRNA levels of MMP-1 and enhanced the binding of c-Jun to the promoter of MMP-1. Furthermore, disruption of the proximal AP-1-binding site in the promoter of MMP-1 severely impaired MMP-1 transcription in response to bortezomib.

Conclusions

By altering the binding of at least two transcription factors, c-Jun and SP1, proteasome inhibition results in increased production of MMP-1 and decreased synthesis of type I collagen in human dermal fibroblasts. Thus, the antifibrotic phenotype observed in fibroblasts submitted to proteasome inhibition results from profound modifications in the binding of key transcription factors. This provides a novel rationale for assessing the potential of drugs targeting the proteasome for their anti-fibrotic properties.

A review of the foreign-body response to subcutaneously-implanted devices: the role of macrophages and cytokines in biofouling and fibrosis

The biological response to implanted biomaterials in mammals is a complex series of events that involves many biochemical pathways. Shortly after implantation, fibrinogen and other proteins bind to the device surface, a process known as biofouling. Macrophages then bind to receptors on the proteins, join into multinucleated giant cells, and release transforming growth factor beta and other inflammatory cytokines. In response to these signals, quiescent fibroblasts are transformed into myofibroblasts, which synthesize procollagen via activation of Smad mediators. The procollagen becomes crosslinked after secretion into the extracellular space. Mature crosslinked collagen and other extracellular matrix proteins gradually contribute to formation of a hypocellular dense fibrous capsule that becomes impermeable or hypopermeable to many compounds. Porous substrates and angiogenic growth factors can stimulate formation of microvessels, which to some extent can maintain analyte delivery to implanted sensors. However, stimulation by vascular endothelial growth factor alone may lead to formation of leaky, thin-walled, immature vessels. Other growth factors are most probably needed to act upon these immature structures to create more robust vessels.During implantation of foreign bodies, the foreign-body response is difficult to overcome, and thousands of biomaterials have been tested. Biomimicry (i.e., creating membranes whose chemical structure mimics natural cellular compounds) may diminish the response, but as of this writing, it has not been possible to create a stealth material that circumvents the ability of the mammalian surveillance systems to distinguish foreign from self.

Recent advances on pathogenesis and therapies in systemic sclerosis

Systemic sclerosis (SSc) is a systemic autoimmune disease characterized by extensive fibrotic changes in various organs, including skin and lung. Although the etiology of SSc remains unknown, three major abnormalities, abnormal humoral immunity, microvasculature, and fibroblast dysfunctions are considered to play important roles. Significant progress has been made in understanding the pathogenesis on SSc, and has been also providing clues to the treatment for this disease. This review summarizes recent advances on the pathogenesis and new therapeutic strategy for SSc.

Molecular pathways as novel therapeutic targets in systemic sclerosis

PURPOSE OF REVIEW

Systemic sclerosis is a complex disease characterized by immune/inflammatory, vascular and fibrotic processes. To date, no treatment has proven effective in modifying the course of the disease. Recent studies have begun to yield insights into the nature and interrelationship among these processes, and their cellular and molecular components.

RECENT FINDINGS

Novel intracellular molecular pathways have been characterized that positively or negatively regulate fibroblast responses contributing to the process of fibrosis. These include signaling mediators that specify and amplify transforming growth factor-beta responses, or inhibit collagen stimulation and block these responses in vitro and in animal models. Various gain of function or loss of function abnormalities in these mediators have been identified in systemic sclerosis, and may account for the characteristic activated phenotype of systemic sclerosis fibroblasts.

SUMMARY

The identification of novel signaling pathways and mediators that are altered in systemic sclerosis and contribute to tissue damage allows their selective targeting. This in turn opens the door for novel therapeutic strategies utilizing novel compounds, or innovative ways of using already-approved drugs. In light of the complex pathogenesis of systemic sclerosis, however, only carefully designed clinical trials with appropriate biomarkers and outcome measures will be able to clarify the clinical utility of these innovative approaches.

How does endothelial cell injury start? The role of endothelin in systemic sclerosis

A considerable amount of research time has been invested in studies aimed at elucidating pathogenic processes in systemic sclerosis (SSc). Despite this, major challenges for biomedical science remain, such as identification of the key factors that determine susceptibility to SSc, and elucidation of the precise nature of the initiating event that causes endothelial cell injury and ultimately brings about the biological cascade(s) that lead to the pathologic vascular changes. Involved factors are likely to include genetic perturbations, environmental cues, tissue injury, infection and hypoxia/oxidative stress. As important as determining the initiating events are the identification and characterization of key factors that are functionally important in driving vascular disease progression, because these factors are potential targets for therapeutic intervention. This article reviews the role of endothelin as an example of a pleiotropic mediator with effects on various aspects of SSc pathogenesis, such as inflammation, vasculopathy and tissue remodelling.

In vitro models of TGF-β-induced fibrosis suitable for high-throughput screening of antifibrotic agents

Progressive fibrosis is a cause of progressive organ dysfunction. Lack of quantitative in vitro models of fibrosis accounts, at least partially, for the slow progress in developing effective antifibrotic drugs. Here, we report two complementary in vitro models of fibrosis suitable for high-throughput screening. We found that, in mesangial cells and renal fibroblasts grown in eight-well chamber slides, transforming growth factor-β1 (TGF-β1) disrupted the cell monolayer and induced cell migration into nodules in a dose-, time- and Smad3-dependent manner. The nodules contained increased interstitial collagens and showed an increased collagen I:IV ratio. Nodules are likely a biological consequence of TGF-β1-induced matrix overexpression since they were mimicked by addition of collagen I to the cell culture medium. TGF-β1-induced nodule formation was inhibited by vacuum ionized gas treatment of the plate surface. This blockage was further enhanced by precoating plates with matrix proteins but was prevented, at least in part, by poly-l-lysine (PLL). We have established two cell-based models of TGF-β-induced fibrogenesis, using mesangial cells or fibroblasts cultured in matrix protein or PLL-coated 96-well plates, on which TGF-β1-induced two-dimensional matrix accumulation, three-dimensional nodule formation, and monolayer disruption can be quantitated either spectrophotometrically or by using a colony counter, respectively. As a proof of principle, chemical inhibitors of Alk5 and the antifibrotic compound tranilast were shown to have inhibitory activities in both assays.

Trichostatin A blocks TGF-beta-induced collagen gene expression in skin fibroblasts: involvement of Sp1

Transforming growth factor- beta (TGF-beta) stimulates Type I collagen synthesis by fibroblasts and is implicated in tissue fibrosis. Here, we demonstrate that histone deacetylase inhibitor Trichostatin A (TSA) suppresses the TGF-beta-induced Type I collagen synthesis but not induced PAI-1 synthesis suggesting the influence of TSA is gene specific. Results further reveal that there is no significant alteration in Smad activation and function in presence of TSA suggesting suppression of TGF-beta-induced collagen synthesis is not due to impaired Smad signaling. TGF-beta induces the levels of Sp1, an essential transcription factor of Smad-dependent stimulation of collagen synthesis. However, in presence of TSA, TGF-beta fails to induce Sp1 levels, its interaction with Smad complex and Sp1 binding site in COL1A2 promoter. Furthermore, overexpressed Sp1 reverses the TSA-mediated inhibition of TGF-beta-induced collagen gene expression. Collectively, these results suggest that TSA-mediated suppression of Smad-dependent TGF-beta-induced collagen synthesis is due to suppression of Sp1 activity in skin fibroblasts.

Increased levels of transforming growth factor beta receptor type I and up-regulation of matrix gene program: A model of scleroderma

OBJECTIVE

Previously published studies have demonstrated that a majority of systemic sclerosis (SSc) fibroblasts exhibit elevated levels of transforming growth factor beta type I receptor (TGFbetaRI). An experimental model that recapitulates this condition was established in control dermal fibroblasts by titrating the dose of adenovirus vector expressing TGFbetaRI (AdTGFbetaRI). The present study was undertaken to determine the functional consequences of increased levels of TGFbetaRI in SSc.

METHODS

Gene array analysis of control dermal fibroblasts transduced with AdTGFbetaRI was performed using GeneChip expression arrays. Gene validation was done by Northern blot, quantitative reverse transcriptase-polymerase chain reaction, and Western blot techniques. TGFbeta blockade was performed using soluble TGFbeta receptor. TGFbetaRI kinase/activin receptor-like kinase 5 was inhibited with pharmacologic inhibitors. TGFbetaRI and TGFbetaRII protein levels and collagen production were examined by Western blotting in primary dermal fibroblasts from 9 SSc patients and 9 healthy adults. Endogenous TGFbetaRI levels were suppressed in control and SSc fibroblasts using specific small interfering RNA (siRNA).

RESULTS

Global gene analysis indicated that a 2-fold increase in TGFbetaRI levels in control fibroblasts resulted in profibrotic changes that closely resembled the phenotype of SSc fibroblasts. A total of 125 genes were up-regulated, including COL1A1, COL1A2, and connective tissue growth factor, and 206 genes were down-regulated. Elevated production of collagen in cells transduced with AdTGFbetaRI was dependent on the autocrine TGFbeta, but not TGFbetaRI kinase activity. Eight of the 9 SSc strains exhibited increased levels of TGFbetaRI protein, which correlated with increased collagen synthesis. Treatment of SSc and matched control fibroblasts with siRNA that normalizes TGFbetaRI levels reverted collagen protein production in SSc fibroblasts to the levels observed in control fibroblasts.

CONCLUSION

Our findings demonstrate that aberrantly expressed TGFbetaRI may drive an autocrine loop involved in the up-regulation of collagen and other matrix-related genes in SSc fibroblasts.

Intracellular TGF-beta receptor blockade abrogates Smad-dependent fibroblast activation in vitro and in vivo

Fibrosis, the hallmark of scleroderma, is characterized by excessive synthesis of collagen and extracellular matrix proteins and accumulation of myofibroblasts. Transforming growth factor-beta (TGF-beta), a potent inducer of collagen synthesis, cytokine production, and myofibroblast transdifferentiation, is implicated in fibrosis. Profibrotic TGF-beta responses are induced primarily via the type I activin-like receptor kinase 5 (ALK5) TGF-beta receptor coupled to Smad signal transducers. Here, we investigated the effect of blocking ALK5 function with SM305, a novel small-molecule kinase inhibitor, on fibrotic TGF-beta responses. In normal dermal fibroblasts, SM305 abrogated the ligand-induced phosphorylation, nuclear import, and DNA-binding activity of Smad2/3 and Smad4, and inhibited Smad2/3-dependent transcriptional responses. Furthermore, SM305 blocked TGF-beta-induced extracellular matrix gene expression, cytokine production, and myofibroblast transdifferentiation. In unstimulated scleroderma fibroblasts, SM305 caused a variable and modest reduction in type I collagen levels, and failed to abrogate constitutive nuclear accumulation of Smad2/3, or alter the proportion of smooth muscle actin stress fiber-positive fibroblasts. In vivo, SM305 prevented TGF-beta-induced Smad2/3 phosphorylation type I collagen (COL1)A2 promoter activation in dermal fibroblasts. Taken together, these results indicate that SM305 inhibits intracellular TGF-beta signaling through selective interference with ALK5-mediated Smad activation, resulting in marked suppression of profibrotic responses induced by TGF-beta in vivo and in vitro.

Monocyte chemoattractant protein 1 released from glycosaminoglycans mediates its profibrotic effects in systemic sclerosis via the release of interleukin-4 from T cells

OBJECTIVE

Monocyte chemoattractant protein 1 (MCP-1; CCL2) has been implicated in the pathogenesis of fibrotic diseases and is up-regulated in patients with systemic sclerosis (SSc). The aim of the present study was to examine the mechanisms by which MCP-1 mediates its profibrotic effects in the setting of SSc.

METHODS

The expression of receptors for MCP-1 on dermal fibroblasts was analyzed by real-time polymerase chain reaction and fluorescence-activated cell sorting. The ability of extracellular matrix proteins to bind and release MCP-1 was quantified by enzyme-linked immunosorbent assay. Th0 cells were isolated using a magnetic-activated cell sorting system and were stimulated twice in the presence of MCP-1. The synthesis of collagen was measured using the Sircol collagen assay kit.

RESULTS

The glycosaminoglycan chondroitin sulfate, but not fibronectin or collagens, bound and released MCP-1 in a time-dependent manner. MCP-1 that was released from chondroitin sulfate induced the differentiation of interleukin-4 (IL-4)-producing T cells in a dose-dependent manner. In turn, dermal fibroblasts from patients with SSc expressed IL-4 receptor, and stimulation with IL-4 significantly increased the production of collagen in dermal fibroblasts. In contrast, CCR2a and CCR2b, as well as D6 and US28 (other potential receptors of MCP-1), were not detectable in SSc and normal fibroblasts, and their expression was not induced by platelet-derived growth factor, IL-1beta, or IL-4. In addition, MCP-1 had no direct effects on collagen production by fibroblasts.

CONCLUSION

MCP-1 has no direct effects on dermal fibroblasts but contributes to fibrosis in patients with SSc by inducing the differentiation of IL-4-producing T cells. Because MCP-1 has both proinflammatory and profibrotic effects, pharmacologic targeting of MCP-1 could be a promising therapeutic approach in SSc.

Avian models with spontaneous autoimmune diseases

Autoimmune diseases in human patients only become clinically manifest when the disease process has developed to a stage where functional compensation by the afflicted organ or system is not possible anymore. In order to understand the initial etiologic and pathogenic events that are generally not yet accessible in humans, appropriate animal models are required. In this respect, spontaneously developing models--albeit rare--reflect the situation in humans much more closely than experimentally induced models, including knockout and transgenic mice. The present chapter describes three spontaneous chicken models for human autoimmune diseases, the Obese strain (OS) with a Hashimoto-like autoimmune thyroiditis, the University of California at Davis lines 200 and 206 (UCD-200 and -206) with a scleroderma-like disease, and the amelanotic Smyth line with a vitiligo-like syndrome (SLV). Special emphasis is given to the new opportunities to unravel the genetic basis of these diseases in view of the recently completed sequencing of the chicken genome.