Association of markers for TGFbeta3, TGFbeta2 and TIMP1 with systemic sclerosis

Transforming growth factor-β receptors: versatile mechanisms of ligand activation

Transforming growth factor-β (TGF-β) signaling is initiated by activation of transmembrane TGF-β receptors (TGFBR), which deploys Smad2/3 transcription factors to control cellular responses. Failure or dysregulation in the TGF-β signaling pathways leads to pathological conditions. TGF-β signaling is regulated at different levels along the pathways and begins with the liberation of TGF-β ligand from its latent form. The mechanisms of TGFBR activation display selectivity to cell types, agonists, and TGF-β isoforms, enabling precise control of TGF-β signals. In addition, the cell surface compartments used to release active TGF-β are surprisingly vibrant, using thrombospondins, integrins, matrix metalloproteinases and reactive oxygen species. The scope of TGFBR activation is further unfolded with the discovery of TGFBR activation initiated by other signaling pathways. The unique combination of mechanisms works in series to trigger TGFBR activation, which can be explored as therapeutic targets. This comprehensive review provides valuable insights into the diverse mechanisms underpinning TGFBR activation, shedding light on potential avenues for therapeutic exploration.

Hub genes, diagnostic model, and predicted drugs in systemic sclerosis by integrated bioinformatics analysis

Background: Systemic sclerosis (scleroderma; SSc), a rare and heterogeneous connective tissue disease, remains unclear in terms of its underlying causative genes and effective therapeutic approaches. The purpose of the present study was to identify hub genes, diagnostic markers and explore potential small-molecule drugs of SSc. Methods: The cohorts of data used in this study were downloaded from the Gene Expression Complex (GEO) database. Integrated bioinformatic tools were utilized for exploration, including Weighted Gene Co-Expression Network Analysis (WGCNA), least absolute shrinkage and selection operator (LASSO) regression, gene set enrichment analysis (GSEA), Connectivity Map (CMap) analysis, molecular docking, and pharmacokinetic/toxicity properties exploration. Results: Seven hub genes (THY1, SULF1, PRSS23, COL5A2, NNMT, SLCO2B1, and TIMP1) were obtained in the merged gene expression profiles of GSE45485 and GSE76885. GSEA results have shown that they are associated with autoimmune diseases, microorganism infections, inflammatory related pathways, immune responses, and fibrosis process. Among them, THY1 and SULF1 were identified as diagnostic markers and validated in skin samples from GSE32413, GSE95065, GSE58095 and GSE125362. Finally, ten small-molecule drugs with potential therapeutic effects were identified, mainly including phosphodiesterase (PDE) inhibitors (BRL-50481, dipyridamole), TGF-β receptor inhibitor (SB-525334), and so on. Conclusion: This study provides new sights into a deeper understanding the molecular mechanisms in the pathogenesis of SSc. More importantly, the results may offer promising clues for further experimental studies and novel treatment strategies.

Investigational drugs for the treatment of scleroderma: what's new?

INTRODUCTION

Systemic sclerosis (SSc) is an orphan, chronic, autoimmune, fibrotic disease with unknown etiology characterized by progressive fibrosis of the skin and internal organs. SSc has the highest mortality, the deadliest among the connective tissue diseases, despite the introduction of new treatment options in the past decades.

AREAS COVERED

The aim of the current systematic review was to investigate new targeted therapy and their impact on disease progression, mainly focusing on phase I and II clinical trials within the past three years.

EXPERT OPINION

Despite recent groundbreaking advancements in understanding SSc pathophysiology, early diagnosis and early introduction of effective targeted treatments within the optimal window of opportunity to prevent irreversible disease damage still represents a significant clinical challenge. Ongoing significant research for new molecular and epigenetics pathways is of fundamental importance to offer new perspectives on disease phenotype and for the development of personalized treatment strategies.

Safety and Efficacy of B-Cell Depletion with Rituximab for the Treatment of Systemic Sclerosis-associated Pulmonary Arterial Hypertension: A Multicenter, Double-Blind, Randomized, Placebo-controlled Trial

Rationale: Systemic sclerosis (SSc)-pulmonary arterial hypertension (PAH) is one of the most prevalent and deadly forms of PAH. B cells may contribute to SSc pathogenesis. Objectives: We investigated the safety and efficacy of B-cell depletion for SSc-PAH. Methods: In an NIH-sponsored, multicenter, double-blinded, randomized, placebo-controlled, proof-of-concept trial, 57 patients with SSc-PAH on stable-dose standard medical therapy received two infusions of 1,000 mg rituximab or placebo administered 2 weeks apart. The primary outcome measure was the change in 6-minute-walk distance (6MWD) at 24 weeks. Secondary endpoints included safety and invasive hemodynamics. We applied a machine learning approach to predict drug responsiveness. Measurements and Main Results: We randomized 57 subjects from 2010 to 2018. In the primary analysis, using data through Week 24, the adjusted mean change in 6MWD at 24 weeks favored the treatment arm but did not reach statistical significance (23.6 ± 11.1 m vs. 0.5 ± 9.7 m; P = 0.12). Although a negative study, when data through Week 48 were also considered, the estimated change in 6MWD at Week 24 was 25.5 ± 8.8 m for rituximab and 0.4 ± 7.4 m for placebo (P = 0.03). Rituximab treatment appeared to be safe and well tolerated. Low levels of RF (rheumatoid factor), IL-12, and IL-17 were sensitive and specific as favorable predictors of a rituximab response as measured by an improved 6MWD (receiver operating characteristic area under the curve, 0.88-0.95). Conclusions: B-cell depletion therapy is a potentially effective and safe adjuvant treatment for SSc-PAH. Future studies in these patients can confirm whether the identified biomarkers predict rituximab responsiveness. Clinical trial registered with www.clinicaltrails.gov (NCT01086540).

Foxf2 and Smad6 co-regulation of collagen 5A2 transcription is involved in the pathogenesis of intrauterine adhesion

The replacement of normal endometrial epithelium by fibrotic tissue is the pathological feature of intrauterine adhesion (IUA), which is caused by trauma to the basal layer of the endometrium. COL5A2 is a molecular subtype of collagen V that regulates collagen production in fibrotic tissue. Here, we investigated the roles of Foxf2 and Smad6 in regulating the transcription of COL5A2 and their involvement in the pathogenesis of IUA. Small interference‐mediated Foxf2 (si‐Foxf2) silencing and pcDNA3.1‐mediated Smad6 (pcDNA3.1‐Smad6) up‐regulation were performed in a TGF‐β1‐induced human endometrial stromal cell line (HESC) fibrosis model. Assessment of collagen expression by Western blotting, immunofluorescence and qRT‐PCR showed that COL5A2, COL1A1 and FN were significantly down‐regulated in response to si‐Foxf2 and pcDNA3.1‐Smad6. Transfection of lentivirus vector‐Foxf2 (LV‐Foxf2) and pcDNA3.1‐Smad6 into HESCs and qRT‐PCR showed that Foxf2 promoted COL5A2 expression and Smad6 inhibited Foxf2‐induced COL5A2 expression. Co‐immunoprecipitation, chromatin immunoprecipitation and dual‐luciferase reporter assays to detect the interaction between Foxf2 and Smad6 and their role in COL5A2 transcription showed that Foxf2 interacted with Smad6 and bond the same promoter region of COL5A2. In a rat IUA model, injection of ADV2‐Foxf2‐1810 and ADV4‐Smad6 into the uterine wall showed that Foxf2 down‐regulation and Smad6 up‐regulation decreased fibrosis and the expression of COL5A2 and COL1A1, as detected by haematoxylin/eosin, Masson trichrome staining and immunohistochemistry. Taken together, these results suggested that Foxf2 interacted with Smad6 and co‐regulated COL5A2 transcription in the pathogenesis of IUA, whereas they played opposite roles in fibrosis.

Insulin-like growth factor (IGF)-II- mediated fibrosis in pathogenic lung conditions

Type 2 insulin-like growth factor (IGF-II) levels are increased in fibrosing lung diseases such as idiopathic pulmonary fibrosis (IPF) and scleroderma/systemic sclerosis-associated pulmonary fibrosis (SSc). Our goal was to investigate the contribution of IGF receptors to IGF-II-mediated fibrosis in these diseases and identify other potential mechanisms key to the fibrotic process. Cognate receptor gene and protein expression were analyzed with qRT-PCR and immunoblot in primary fibroblasts derived from lung tissues of normal donors (NL) and patients with IPF or SSc. Compared to NL, steady-state receptor gene expression was decreased in SSc but not in IPF. IGF-II stimulation differentially decreased receptor mRNA and protein levels in NL, IPF, and SSc fibroblasts. Neutralizing antibody, siRNA, and receptor inhibition targeting endogenous IGF-II and its primary receptors, type 1 IGF receptor (IGF1R), IGF2R, and insulin receptor (IR) resulted in loss of the IGF-II response. IGF-II tipped the TIMP:MMP balance, promoting a fibrotic environment both intracellularly and extracellularly. Differentiation of fibroblasts into myofibroblasts by IGF-II was blocked with a TGFβ1 receptor inhibitor. IGF-II also increased TGFβ2 and TGFβ3 expression, with subsequent activation of canonical SMAD2/3 signaling. Therefore, IGF-II promoted fibrosis through IGF1R, IR, and IGF1R/IR, differentiated fibroblasts into myofibroblasts, decreased protease production and extracellular matrix degradation, and stimulated expression of two TGFβ isoforms, suggesting that IGF-II exerts pro-fibrotic effects via multiple mechanisms.

Sarcoidosis and Systemic Sclerosis: Strange Bedfellows

Coexistence of systemic sclerosis and sarcoidosis is rare. Both have predominant lung manifestations, each with distinctive features on computed tomography (CT) of the chest. We present herein a 52-year-old male with limited systemic sclerosis manifested primarily by sclerodactyly and subsequently by shortness of breath. A series of CT scans of the chest were reviewed. Initial CT chest one year prior to sclerodactyly onset revealed bilateral hilar and right paratracheal, prevascular, and subcarinal adenopathy. Five-year follow-up demonstrated thin-walled cysts, mediastinal lymphadenopathy, and nonspecific nodules. Due to progression of dyspnea, follow-up CT chest after one year again demonstrated multiple cysts with peripheral nodularity and subpleural nodules, but no longer with hilar or mediastinal adenopathy. Diagnostic open lung biopsy was significant for noncaseating granulomas suggestive of sarcoidosis. This is the first known case of a patient with systemic sclerosis diagnosed with sarcoidosis through lung biopsy without radiographic evidence of hilar or mediastinal lymphadenopathy at the time of biopsy. A review of cases of concomitant sarcoidosis and systemic sclerosis is discussed, including the pathophysiology of each disease with shared pathways leading to the development of both conditions in one patient.

[Therapeutic effect of enhancer of Zeste homolog 2 inhibitor GSK343 on periodontitis by regulating macrophage differentiation]

OBJECTIVE

To explore the therapeutic effect of enhancer of Zeste homolog 2 (EZH2) inhibitor GSK343 on periodontitis by regulating microphage differentiation.

METHODS

Macrophage RAW264.7 cells were divided into the blank (A group), control (B group), lipopolysaccharide (LPS) stimulation (C group), and LPS+GSK343 (D group) groups. Phenotype transformations was determined through Western blot analysis and enzyme-linked immunosorbent assay by detecting the differentiation of phenotypic biological markers, including tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS), interleukin-10 (IL-10), and Arginase-1 (Arg-1). Metergasis was identified by performing a phagocytosis test on Escherichia coli (E. coli).

RESULTS

Macrophage RAW264.7 cells produced classical phenotypic biomarkers (M1) TNF-α and iNOS under LPS stimulation. The expression levels of IL-10 and Arg-1 increased after adding GSK343 into the culture medium. GSK343 also induced the conversion of M1 macrophages into M2 macrophages. Macrophage RAW264.7 cells exerted a phagocytic effect on E. coli, and this effect was enhanced after adding LPS into the culture medium. GSK343 regulated the macrophage RAW264.7 phagocytosis of E. coli.

CONCLUSIONS

GSK343 possibly participates in the regulation of macrophage differentiation and, consequently, in the latent treatment of periodontitis.

Genomic and genetic studies of systemic sclerosis: A systematic review

Systemic sclerosis is an autoimmune rheumatic disease characterised by fibrosis, vasculopathy and inflammation. The exact aetiology of SSc remains unknown but evidences show that various genetic factors may be involved. This review aimed to assess HLA alleles/non-HLA polymorphisms, microsatellites and chromosomal abnormalities that have thus far been associated with SSc. PubMed, Embase and Scopus databases were searched up to July 29, 2015 using a combination of search-terms. Articles retrieved were evaluated based on set exclusion and inclusion criteria. A total of 150 publications passed the filters. HLA and non-HLA studies showed that particular alleles in the HLA-DRB1, HLA-DQB1, HLA-DQA1, HLA-DPB1 genes and variants in STAT4, IRF5 and CD247 are frequently associated with SSc. Non-HLA genes analysis was performed using the PANTHER and STRING₁₀ databases. PANTHER classification revealed that inflammation mediated by chemokine and cytokine, interleukin and integrin signalling pathways are among the common extracted pathways associated with SSc. STRING₁₀ analysis showed that NFKB1, CSF3R, STAT4, IFNG, PRL and ILs are the main "hubs" of interaction network of the non-HLA genes associated with SSc. This study gathers data of valid genetic factors associated with SSc and discusses the possible interactions of implicated molecules.

Challenges and opportunities in treating inflammation associated with pulmonary hypertension

INTRODUCTION

Inflammatory cells are present in the lungs from patients with many, if not all, forms of severe pulmonary hypertension.

AREAS COVERED

Historically the first inflammatory cell identified in the pulmonary vascular lesions was the mast cell. T and B lymphocytes, as well as macrophages, are present in and around the pulmonary arterioles and many patients have elevated blood levels of interleukin 1 and 6; some patients show elevated levels of leukotriene B4. An overlap between collagen-vascular disease-associated pulmonary arterial hypertension (PAH) and idiopathic PAH exists, yet only a few studies have been designed that evaluate the effect of anti-inflammatory treatments. Here we review the pertinent data that connect PAH and inflammation/autoimmune dysregulation and evaluate experimental models of severe PAH with an emphasis on the Sugen/athymic rat model of severe PAH. Expert commentary: We postulate that there are several inflammatory phenotypes and predict that there will be several anti-inflammatory treatment strategies for severe PAH.

Transforming growth factor beta (TGF-β) isoforms in wound healing and fibrosis

Scar formation, with persistent alteration of the normal tissue structure, is an undesirable and significant result of both wound healing and fibrosing disorders. There are few strategies to prevent or to treat scarring. The transforming growth factor beta (TGF-β) superfamily is an important mediator of tissue repair. Each TGF-β isoform may exert a different effect on wound healing, which may be context-dependent. In particular, TGF-β1 may mediate fibrosis in adults' wounds, while TGF-β3 may promote scarless healing in the fetus and reduced scarring in adults. Thus, TGF-β3 may offer a scar-reducing therapy for acute and chronic wounds and fibrosing disorders.

Association of TIMP-1 +372 SNP with digital ulcer manifestation in female systemic sclerosis patients

A candidate gene for TIMP-1 gene located on the X-chromosome (rs4898) was selected for a control case study to investigate a possible association of this SNP with the susceptibility to systemic sclerosis and its digit ulcer manifestation. A total of 461 individuals of Italian Caucasian origin (228 SSc patients and 233 healthy control subjects) were genotyped for TIMP-1 +372 T/C single nucleotide polymorphism rs4898. Subgroups were analyzed according to the presence or absence of digital ulcers. The CC genotype and C allele frequencies were significantly lower in female SSc patients than in controls (OR 0.53, CI 0.29-0.96, p=0.03 and OR 0.72, CI 0.53-0.98 p=0.04, respectively). CC genotypes frequency was lower also in female patients with ulcers than those without ulcers (OR 0.37, CI 0.14-1.00, p=0.03). Furthermore, CC genotype and C allele frequencies were lower also in female patients with ulcers in comparison to female healthy control subjects (OR 0.27, CI 0.10-0.70, p=0.004; OR 0.60, CI 0.40-0.89, p=0.01, respectively). The TIMP-1 rs4898 polymorphism may play a protective role in the susceptibility to SSC in females, and in particular to digital ulcer formation.

Genetic susceptibility to systemic sclerosis from clinical aspect to genetic factor analyses

BACKGROUND

Systemic sclerosis is a rare autoimmune disease mainly characterized by vascular alteration and fibrosis involving skin but also visceral organs such as lungs, digestive tract, and heart. This disease leads to high morbidity and mortality. Its pathogenesis remains unclear, but recent attention has focus on genetic factors.

OBJECTIVE

We first recall the main manifestations associated with systemic sclerosis and leading to its diagnosis and prognosis. Then we propose an overview on human genetics studies, as a number of genetic loci have been identified that appear to be associated with the disease.

METHODS

Articles concerning association studies with candidate genes encoding for extracellular matrix proteins, cytokines, growth factors, chemokines, and proteins involved in vascular tone and immune regulations are presented and discussed.

RESULTS/CONCLUSION

Systemic sclerosis is a multigenic complex disorder. Genetic associations are observed in distinct phenotypes such as the diffuse cutaneous form or the limited form, or in association with specific autoantibody pattern. Promising candidate genes are those involved in pathways that lead to the vascular damage and fibrosis. A better knowledge of crucial mediators involved in systemic sclerosis could in the future provide new therapeutic strategies to control the disease.

Combined analysis of monocyte and lymphocyte messenger RNA expression with serum protein profiles in patients with scleroderma

OBJECTIVE

We attempted to elucidate possible pathogenetic mechanisms in scleroderma by analysis of gene expression patterns of purified monocytes and lymphocytes, as well as protein profiles of cytokines and growth factors.

METHODS

Expression analysis was performed on messenger RNA (mRNA) from cells that had been purified with magnetic beads. Plasma samples from the same patients were used for multiplex cytokine analysis. Potential sources of proteins were also examined by in situ hybridization of skin specimens.

RESULTS

A total of 1,800 genes from monocytes and 863 genes from CD4+ T cells were differentially expressed in scleroderma patients. As observed by other investigators using unfractionated peripheral blood cells from patients with autoimmune connective tissue diseases, the cell type-specific analyses of our scleroderma samples showed expression of genes suggesting the presence of interferon-alpha (IFNalpha), despite the apparent absence of this cytokine in plasma. IFNalpha RNA was, however, expressed at enhanced levels in vascular and perivascular cells in scleroderma skin samples. While levels of interleukin-1alpha (IL-1alpha) and IL-16 were among 10 proteins found to be significantly elevated in scleroderma patients, none of the large panel of plasma cytokines we analyzed correlated with the expression levels of putative IFN response genes.

CONCLUSION

The pattern of up-regulation of mRNA in both the monocytes and CD4 lymphocytes of scleroderma patients, together with the detection of IFNalpha RNA in the microvasculature, suggests that leukocytes respond to this cytokine locally in the vessels. Detection of high levels of IL-1alpha and IL-16 in plasma and the independence of these protein levels from the IFN signature, implicates an independent contribution of other cytokines to immune activation and/or inflammation in scleroderma.

Implication de l'interleukine 13 et de son récepteur dans la sclérodermie systémique

PURPOSE

Interleukin 13 is an immunoregulatory cytokine predominantly secreted by activated Th2 cells. It has similar functions with interleukin 4 and they share a common receptor. However, unlike interleukin 4, l'interleukin 13 does not appear to be important in the initial differentiation of CD4 T into Th2-type cells, but rather appears to be necessary in the effector phase of inflammation and fibrosis. This cytokine has been involved in recent works in allergic inflammation and in some fibrotic diseases leading to a scientific interest to analysis the role of interleukin 13 in systemic sclerosis (scleroderma).

MAIN POINTS

Systemic sclerosis is an autoimmune disease characterized by vascular alteration and skin and visceral fibrosis. A genetic background associated with susceptibility is supposed. Knowing the profibrogenic properties of interleukin 13, we asked if polymorphisms located in interleukin 13 and interleukin 13 receptor genes could be associated with systemic sclerosis. We observed significant associations between IL13 and IL13RA2 gene polymorphisms and the disease, particularly the cutaneous diffuse form of the disease.

PERSPECTIVES AND PROJECTS

Results concerning the involvement of interleukin 13 pathway in systemic sclerosis need to be confirmed on another larger population. Functional studies will be done to explain the effect of these associations. We feel that IL13/IL13R pathway is interesting as immunomodulation with the interleukin 13 receptor inhibitor is possible in therapy.

Analysis of TIMP-1 gene polymorphisms in Italian sclerodermic patients

Systemic sclerosis (SSc) is an autoimmune disease characterized by skin and internal organs fibrosis due to an extracellular matrix (ECM) accumulation of type I collagen. The turnover of the ECM is dependent on the balance between matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs). The disruption of this balance is involved in SSc because higher serum TIMP-1 levels have been demonstrated in SSc patients than in controls. On this basis, we analyzed three polymorphisms: -19A>G, +261C>T, and +372T>C of the TIMP-1 gene in SSc patients (67 females, eight males) and controls (29 females, nine males). The C allele of the +372T>C single nucleotide polymorphism (SNP) was observed at a higher frequency in male patients than in healthy individuals (P=0.02), while no differences were observed in the female subjects. Our findings suggest that the +372T>C polymorphism of the TIMP-1 gene is associated with SSc in male individuals. No association with the clinical characteristics of SSc Italian patients and TIMP-1 gene polymorphisms was observed. Thus, the role of TIMP-1 gene in predisposition to SSc remains controversial.

Clinical outcomes of bosentan in pulmonary arterial hypertension do not correlate with levels of TIMPs

BACKGROUND

Matrix metalloproteinases (MMP) and their inhibitors, tissue inhibitors of metalloproteinases (TIMP), are involved in tissue inflammation and fibrotic processes. Treatment with bosentan has been shown to improve the clinical outcome of patients with pulmonary arterial hypertension (PAH) with and without association with systemic sclerosis (SSc), and also to modulate the serum levels of matrix metalloproteases-9. We measured TIMP-1 and TIMP-2 in the serum of patients with SSc with and without PAH treated with long-term bosentan compared with healthy donors (HD).

MATERIALS AND METHODS

Serum samples from HD (n = 16) and patients with SSc (n = 35), including patients with SSc without PAH (n = 23) and patients with PAH (n = 12), were analyzed using enzyme-linked immunosorbent assays (ELISAs) for total TIMP-1 and TIMP-2.

RESULTS

Both mean TIMP-1 and TIMP-2 levels were significantly increased in patients with SSc compared with HD, but no differences were observed between patients with SSc with and without PAH. In the eight bosentan-treated patients, TIMP-1 and TIMP-2 levels did not change during 1 year of treatment, while bosentan increased the 6-min walking distance by 136 meters after 1 year, as well as clinical outcomes.

CONCLUSIONS

Increased levels of TIMP-1 and TIMP-2 in patients with SSc compared with HD suggest that the inhibition of proteolysis allows the accumulation of ECM proteins. As bosentan does not stimulate TIMPs, it appears to favour proteolytic imbalance and to increase the turnover of ECM proteins.

Transforming Growth Factor-β Gene Polymorphisms in Sarcoidosis Patients With and Without Fibrosis

STUDY OBJECTIVES

Pulmonary fibrosis develops in approximately 25% of patients with chronic sarcoidosis. Transforming growth factor (TGF)-beta1 plays a central role in fibrosis, and accruing reports address the implication of TGF-beta2 and TGF-beta3 in this process. We determined whether single-nucleotide polymorphisms (SNPs) in the TGF-beta1, TGF-beta2, and TGF-beta3 genes might contribute to pulmonary fibrosis in sarcoidosis patients.

SETTING

A hospital in the Netherlands.

DESIGN

Five SNPs per TGF-beta gene were investigated.

PATIENTS AND CONTROL SUBJECTS

Patients with either acute/self-remitting sarcoidosis (n = 50) and Löfgren syndrome (n = 46) or chronic disease with fibrosis (n = 24) and without fibrosis (n = 34) were assessed over a 4-year follow-up period. The control subjects included 315 individuals.

MEASUREMENTS AND RESULTS

Polymorphism frequencies were not discordant between the patients and control subjects. The TGF-beta3 4875 A allele was significantly higher in fibrotic patients (carrier frequency, 0.29) than in patients with acute/self-remitting (0.06) and chronic (0.03) sarcoidosis combined (corrected p = 0.01; odds ratio [OR], 7.9). The TGF-beta3 17369 C allele carrier frequency was significantly higher in fibrotic patients (0.29) compared to acute/self-remitting (0.08) and chronic (0.06) patients combined (corrected p = 0.05; OR, 5.1). Although not significant after correction, the TGF-beta3 15101 G allele carrier frequency was lower in fibrotic patients (0.79) compared to acute/self-remitting (0.94) and chronic (1.00) patients combined (p = 0.02; corrected p = 0.1; OR, 0.15). The TGF-beta2 59941 G allele was more abundant in fibrotic patients (carrier frequency, 0.62) compared to patients with acute/self-remitting (0.41) and chronic sarcoidosis combined (0.28) [p = 0.04; corrected p = 0.2; OR, 2.9]. TGF-beta1 gene polymorphisms were not associated with fibrosis.

CONCLUSIONS

This study is the first to suggest the implication of genetic variation of TGF-beta3 in the predilection for pulmonary fibrosis developing in sarcoidosis patients.

Facteurs de prédisposition génétiques à la fibrose au cours de la sclérodermie systémique

PURPOSE

Physiopathology of systemic sclerosis includes autoimmunity factors, endothelial lesions and abnormal fibrotic process which characterizes this disease in the field of systemic autoimmune disorders. Genetic factors of susceptibility are showed by possibility of familial forms of the disease, Choctaw American Indians homogenous population with high disease prevalence of systemic sclerosis and experimental animal models.

KEY POINTS

We propose a review of the articles published to date in the literature concerning genetical analysis of genes coding for factors potentially involved in the fibrotic process of systemic sclerosis. This includes cytokines (TNF-alpha, interleukin-1, chemokines), growth factors (TGF-beta), extracellular matrix proteins (collagen, fibrillin, fibronectine) and agents acting on vascular tone (angiotensin-converting enzyme and NO synthase).

PERSPECTIVES

Identification of genetic factors involved in the susceptibility to fibrosis of systemic sclerosis would lead to a better understanding of physiopathological mechanisms of this disease and to therapeutic targets using immunomodulation with drugs, such as already performed in rheumatoid arthritis.

Genetics and proteomics in scleroderma

The pathogenesis of systemic sclerosis (SSc; scleroderma) is still enigmatic. Genetic, familial, and twin studies suggest that SSc occurs in genetically susceptible individuals. Recent high-throughput technologies, including gene expression profiling and proteomics, have accelerated the rate of information acquired on possible mechanisms involved in SSc pathogenesis. The potential of the data obtained lies in their use for identifying new disease markers, monitoring disease activity, and developing tailored therapies. The result is an era of unprecedented advance that will benefit SSc and many other diseases.

Systemic sclerosis: the susceptible host (genetics and environment)

It is becoming evident that several genetic factors participate in modulating susceptibility to SSc and its clinical manifestations. Some genes that specifically affect ECM metabolism and vascular function may be unique to SSc and scleroderma-related disorders; others, such as those genes involved in regulating immune tolerance, are likely shared with other autoimmune diseases. The effect of genetic variations (or polymorphisms) that are found in most of these genes taken individually will likely have only a small or modest effect on disease risk; only a few genetic variations are expected to be highly penetrant. Moreover, genetic studies in SSc have to deal with the additional issues of heterogeneous phenotypes, low disease prevalence in the general population, and an even greater paucity of multiplex families that makes traditional linkage studies difficult, if not impossible. Alternative approaches include allelic association studies, but conventional case-controls designs may be subject to selection bias and will require large sample sizes if the genes that are under investigation confer only modest (OR = 1.5-2.0) disease risk (Fig. 2). The simultaneous examination of several genes that are biologically relevant to a specific disease process to attain higher aggregate ORs, is one approach that was used in several reports that were cited in this review. The use of family-based controls, such as in the transmission-disequilibrium test (based on assessment of the transmitted or nontransmitted alleles that are associated with disease from heterozygous parents to affected offspring), would provide more robustness to spurious associations from population stratification, but is actually less powerful and efficient than case-control designs. Furthermore, for many late adult-onset diseases the effort required to obtain samples from living parents are for a variety of reasons not trivial. The success of these allelic association-based approaches depends on the identification of likely candidate disease genes (or at least markers in disequilibrium with disease genes), careful definition/ascertainment of disease phenotypes to minimize genetic heterogeneity, and for case-control designs, strategies to account for population stratification or admixture. The identification of candidate genes will be aided by rapid progress in the Human Genome Project and other genome efforts that will eventually identify all human genetic variations. Although this will lead to better understanding of the genes that might be involved in complex diseases, much work is required to understand the basic biology of how disease genotypes become clinical phenotypes. This is especially daunting in complex diseases, such as SSc, where the phenotype (including disease susceptibility and clinical presentation) is influenced by dynamic interactions between genetic variations and environment. Multi-center collaborative efforts with research paradigms that integrate genetic and environmental factors (including sociodemographic variables) will be required to elucidate the contribution of environment and genetics in the pathogenesis of SSc.

Pulmonary hypertension in systemic sclerosis

Pulmonary arterial hypertension occurs in up to 15% of patients who have systemic sclerosis (SSc) and has a high mortality. It can develop as an isolated complication or secondary to pulmonary fibrosis. There have been significant advances in assessment and therapy for this complication. Patients should be screened regularly by Doppler-echocardiography and pulmonary function tests. Right heart catheterization provides important diagnostic and prognostic information. Drawing from experience with treating primary pulmonary hypertension, treatment in the context of SSc is now possible. Patients should receive oral anticoagulation and oxygen supplementation. Calcium channel blockers are rarely effective, but parenteral prostacyclin analogs improve functional capacity and pulmonary hemodynamics. The oral endothelin-receptor blocker, bosentan, was shown to be an effective therapy for established symptomatic pulmonary hypertension in SSc. The next major challenge is to improve diagnosis and treatment of early stage or presymptomatic pulmonary hypertension with the goal of preventing this important cause of premature SSc-related mortality.

Fibrosis in scleroderma

The pathogenesis of fibrosis in scleroderma involves a complex set of interactions between the fibroblast and its surroundings. Multiple fibrotic pathways are activated for reasons that are not completely clear, but involve immune activation, microvascular damage, and fibroblast transformation into the myofibroblast. Differential proliferation and apoptosis preserve the myofibroblast phenotype rather that leading to a selective depletion of activated fibroblasts after an acute injury has healed. Disproportionate fibroblast activity could result from a combination of possible cellular and matrix defects that include fibrillin protein abnormalities, autoantibody formation, type II immune response, excessive endothelial reaction to injury, and excessive fibroblast response to TGF-beta. Development of therapies that are targeted to correcting these abnormalities will eventually lead to effective treatment for the fibrotic complications of scleroderma.

Transforming growth factor beta induces fibroblast fibrillin-1 matrix formation

OBJECTIVE

Fibrillin, an extracellular matrix protein implicated in dermal fibrosis, is increased in the reticular dermis of systemic sclerosis (SSc) skin. We undertook this study to investigate the hypothesis that transforming growth factor beta (TGFbeta) or other cytokines regulate fibrillin matrix formation by normal and SSc fibroblasts. We further investigated the mechanism of TGFbeta-induced fibrillin fibrillogenesis and its relationship to myofibroblasts.

METHODS

Fibrillin and fibronectin matrix deposition and alpha-smooth muscle actin expression by fibroblast cultures from normal and SSc skin treated with TGFbeta or other cytokines were analyzed by immunofluorescence. Supernatant and extracellular matrix from normal and SSc fibroblasts treated with or without TGFbeta were evaluated by Western blot and Northern blot for fibrillin protein and messenger RNA (mRNA) expression, respectively.

RESULTS

Immunofluorescence demonstrated increased fibrillin matrix formation by normal and scleroderma fibroblasts after TGFbeta treatment. Other cytokines, including tumor necrosis factor alpha, interleukin-1beta (IL-1beta), IL-4, granulocyte-macrophage colony-stimulating factor, and platelet-derived growth factor, did not affect fibrillin fibrillogenesis. Fibrillin matrix formed in proximity to myofibroblasts and independently of up-regulation of fibronectin matrix or cell number. Western blot analysis of extracellular matrix confirmed increased fibrillin after TGFbeta stimulation of normal or scleroderma fibroblasts. However, TGFbeta did not alter the expression of either soluble fibrillin protein or fibrillin mRNA.

CONCLUSION

Our data show that TGFbeta induces fibrillin protein incorporation into the extracellular matrix without affecting fibrillin gene expression or protein synthesis, suggesting that fibrillin matrix assembly is regulated extracellularly. TGFbeta might increase fibrillin matrix by activating myofibroblasts. Such TGFbeta-mediated effects could account for the increased fibrillin matrix observed in SSc skin.

Ligand-dependent genetic recombination in fibroblasts : a potentially powerful technique for investigating gene function in fibrosis

Strategies for conditional induction of transgene expression in mice are likely to be valuable for testing the role of candidate genes in disease pathogenesis. We have developed a system for lineage-specific, ligand-dependent, induction of sustained transgene expression in fibroblastic cells in mice using a chimeric gene encoding the Cre-ER(T) fusion protein, under the control of a fibroblast-specific regulatory sequence from the pro alpha 2(I)collagen gene. Cre-ER(T) operates as a tamoxifen-dependent DNA recombinase to excise fragments flanked by specific LoxP consensus sequences. To test efficiency and ligand dependency of this strategy, Cre-ER(T)-expressing mice were backcrossed with heterozygous ROSA26-LacZ reporter mice, in which a floxed-STOP cassette has been introduced upstream of a bacterial beta-galactosidase (LacZ) reporter gene at a ubiquitously expressed locus. Constitutive or tamoxifen-induced LacZ expression was examined in embryonic, neonatal, and adult compound-transgenic mice. When pregnant ROSA26-LacZ females received a single dose of tamoxifen, high-level expression of LacZ in the skin was demonstrable from 24 hours after injection in double-transgenic embryos harboring both the Cre-ER(T) transgene and the target ROSA26-LacZ allele. High-level expression of LacZ was also induced postnatally by tamoxifen specifically in dermal and visceral fibroblasts. By allowing efficient embryonic or postnatal modification of alleles that have been targeted to incorporate LoxP sites, or to switch on transgenes cloned downstream of the floxed-STOP cassette, this system will allow fibroblast-specific genetic perturbations to be induced at predetermined embryonic or postnatal time points. This should greatly assist in in vivo functional studies of candidate genes in fibrotic diseases such as systemic sclerosis.

The genetics of systemic sclerosis

The etiopathogenesis of systemic sclerosis (SSc) is unclear. With no definitive evidence supporting an environmental cause, recent attention has focused on genetic factors. Familial clustering and ethnic influences have been demonstrated. Human leukocyte antigen (HLA) associations exist but are more related to the presence of particular autoantibodies rather than to the disease. In addition, no single major histocompatibility complex (MHC) allele predisposes to SSc in all ethnic groups. The role of microchimerism in SSc is a novel yet unproven hypothesis that may be related to intergenerational HLA compatibility. Recent studies investigating polymorphisms in genes coding for extracellular matrix proteins and cell-signaling molecules implicate non-MHC areas in SSc pathogenesis. The data reviewed suggest that SSc is a multigenic complex disorder.

Apoptosis and myofibroblasts in the pathogenesis of systemic sclerosis

Tissue fibrosis is the result of a complex series of events focusing on regulation of fibroblast proliferation, synthesis of extracellular matrix, and apoptosis. Transforming growth factor-beta is important for the stimulation of the fibrotic response by promoting the production of extracellular matrix proteins, by promoting the differentiation of the myofibroblast cell morphology, and by protecting these cells against apoptotic stimuli. Other cytokines such as interleukin-1 may have stimulatory and counter-regulatory effects on fibrosis. The effects of these signaling molecules depend on cellular environment and are organ specific. Furthermore, intercellular interactions and cell-matrix interactions can stimulate or inhibit the apoptotic pathway. Through selective inhibition of apoptosis in myofibroblasts, fibrosis can become dysregulated and lead to diseases such as systemic sclerosis.

Genetic epidemiology: systemic sclerosis

Systemic sclerosis (SSc) is a multisystem connective tissue disease characterised phenotypically by fibrosis and ischaemic atrophy. Its aetiology is most likely multifactorial. A genetic predisposition to the condition is suggested by reports of familial SSc (a positive family history is the strongest risk factor yet identified), by animal models, and by disease-association studies, in which researchers have examined a wide variety of genes including those involved in fibrosis, in vascular function and structure, and in autoimmunity - the relative rarity of SSc has precluded linkage studies, except in the Choctaw Indians. Recent advances in genetic methodologies should further our understanding of this complex disease process.

Transforming growth factor-beta and connective tissue growth factor: key cytokines in scleroderma pathogenesis

Evidence for a role for members of the transforming growth factor beta (TGF-beta) family of cytokines in the pathogensis of systemic sclerosis and other fibrotic conditions is provided from studies of TGF-beta protein and gene expression in lesional biopsy specimens, from altered responses of explanted fibroblasts to TGF-beta stimulation which are associated with increased receptor expression on these cells and from genetic data linking TGF-beta gene loci to the disease. Of the many effects of TGF-beta on fibroblast properties induction of the connective tissue growth factor/Cyr61/NOV (CCN) family members, connective tissue growth factor (CTGF) may be particularly relevant to fibrosis. Moreover, systemic sclerosis (SSc) fibroblasts demonstrate constitutive over expression of CTGF that promotes migration, proliferation and matrix production. Studies of mechanisms regulating constitutive expression of CTGF by SSc fibroblasts are currently being undertaken and indicate that a TGF-beta responsive element in the CTGF promoter is involved, although this appears to function independent of the Smad proteins, suggesting that other TGF-beta-regulated pathways may be involved. TGF-neutralizing strategies have now been shown to abrogate many animal models of fibrosis, and will soon reach the clinical arena for SSc. These agents will further clarify the role of this ligand in initiating or sustaining fibrosis and offer the exciting possibility of targeted therapy for this disease.