Fibroblast expression of the coactivator p300 governs the intensity of profibrotic response to transforming growth factor beta

Taraxerone exerts antipulmonary fibrosis effect through Smad signaling pathway and antioxidant stress response in a Sirtuin1-dependent manner

Idiopathic pulmonary fibrosis treatments are limited, often with severe side effects, highlighting the need for novel options. Taraxerone has diverse biomedical properties, but its mechanism remains unclear. This study investigates taraxerone's impact and the mechanisms involved in bleomycin-induced pulmonary fibrosis in mice. After establishing a pulmonary fibrosis mouse model, taraxerone was intraperitoneally injected continuously for 14-28 days. The in vivo antifibrotic and antioxidative stress effects of taraxerone were assessed. In vitro, the influence of taraxerone on transforming growth factor-β1-induced myofibroblast transformation and oxidative stress was investigated. Subsequently, quantitative polymerase chain reaction screened the histone deacetylase and Sirtuin family, and taraxerone's effects on SIRT1 were assessed. After SIRT1 siRNA treatment, changes in myofibroblast transformation and antioxidant capacity in response to taraxerone were observed. Acetylation and phosphorylation levels of Smad3 were evaluated. We also examined the binding levels of SIRT1 with Pho-Smad3 and Smad3, as well as the nuclear localization of Smad2/3. EX527 confirmed SIRT1's in vivo action in response to taraxerone. In vitro experiments suggested that taraxerone inhibited myofibroblast differentiation by activating SIRT1 and reducing oxidative stress. We also observed a new interaction between SIRT1 and the Smad complex. Taraxerone activates SIRT1, enabling it to bind directly to Smad3. This leads to reduced Smad complex phosphorylation and limited nuclear translocation. As a result, the transcription of fibrotic factors is reduced. In vivo validation confirms taraxerone's SIRT1-mediated antifibrotic effectiveness. This suggests that targeting SIRT1-mediated inhibition of myofibroblast differentiation could be a key strategy in taraxerone-based therapy for pulmonary fibrosis.

Recombinant Human HAPLN1 Mitigates Pulmonary Emphysema by Increasing TGF-β Receptor I and Sirtuins Levels in Human Alveolar Epithelial Cells

Chronic obstructive pulmonary disease (COPD) will be the third leading cause of death worldwide by 2030. One of its components, emphysema, has been defined as a lung disease that irreversibly damages the lungs' alveoli. Treatment is currently unavailable for emphysema symptoms and complete cure of the disease. Hyaluronan (HA) and proteoglycan link protein 1 (HAPLN1), an HA-binding protein linking HA in the extracellular matrix to stabilize the proteoglycan structure, forms a bulky hydrogel-like aggregate. Studies on the biological role of the full-length HAPLN1, a simple structure-stabilizing protein, are limited. Here, we demonstrated for the first time that treating human alveolar epithelial type 2 cells with recombinant human HAPLN1 (rhHAPLN1) increased TGF-β receptor 1 (TGF-β RI) protein levels, but not TGF-β RII, in a CD44-dependent manner with concurrent enhancement of the phosphorylated Smad3 (p-Smad3), but not p-Smad2, upon TGF-β1 stimulation. Furthermore, rhHAPLN1 significantly increased sirtuins levels (i.e., SIRT1/2/6) without TGF-β1 and inhibited acetylated p300 levels that were increased by TGF-β1. rhHAPLN1 is crucial in regulating cellular senescence, including p53, p21, and p16, and inflammation markers such as p-NF-κB and Nrf2. Both senile emphysema mouse model induced via intraperitoneal rhHAPLN1 injections and porcine pancreatic elastase (PPE)-induced COPD mouse model generated via rhHAPLN1-containing aerosols inhalations showed a significantly potent efficacy in reducing alveolar spaces enlargement. Preclinical trials are underway to investigate the effects of inhaled rhHAPLN1-containing aerosols on several COPD animal models.

PPARδ Agonist GW501516 Suppresses the TGF-β-Induced Profibrotic Response of Human Bronchial Fibroblasts from Asthmatic Patients

The airway wall remodeling observed in asthma is associated with subepithelial fibrosis and enhanced activation of human bronchial fibroblasts (HBFs) in the fibroblast to myofibroblast transition (FMT), induced mainly by transforming growth factor-β (TGF-β). The relationships between asthma severity, obesity, and hyperlipidemia suggest the involvement of peroxisome proliferator-activated receptors (PPARs) in the remodeling of asthmatic bronchi. In this study, we investigated the effect of PPARδ ligands (GW501516 as an agonist, and GSK0660 as an antagonist) on the FMT potential of HBFs derived from asthmatic patients cultured in vitro. This report shows, for the first time, the inhibitory effect of a PPARδ agonist on the number of myofibroblasts and the expression of myofibroblast-related markers-α-smooth muscle actin, collagen 1, tenascin C, and connexin 43-in asthma-related TGF-β-treated HBF populations. We suggest that actin cytoskeleton reorganization and Smad2 transcriptional activity altered by GW501516 lead to the attenuation of the FMT in HBF populations derived from asthmatics. In conclusion, our data demonstrate that a PPARδ agonist stimulates antifibrotic effects in an in vitro model of bronchial subepithelial fibrosis. This suggests its potential role in the development of a possible novel therapeutic approach for the treatment of subepithelial fibrosis during asthma.

Deficiency of inhibitory TLR4 homolog RP105 exacerbates fibrosis

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

Field-based rational design of p300 histone acetyltransferase inhibitor and systematic evaluation as an anti-fibrotic agent

(E)-3-(3-(4-((3-Carbamoylbenzyl)oxy)-3-iodo-5-methoxyphenyl) acryloyl)benzamide (A6) was found to be a potent p300 inhibitor (IC50 = 870 nM) showing a similar binding mode to that of acetyl-CoA, a p300 substrate, and effective anti-fibrotic activity in both TGF-β1-stimulated lung fibroblast cells and bleomycin-induced in vivo lung fibrosis mice.

Cellular and molecular mechanisms in fibrosis

The activation of fibroblasts is required for physiological tissue remodelling such as wound healing. However, when the regulatory mechanisms are disrupted and fibroblasts remain persistently activated, the progressive deposition of extracellular matrix proteins leads to tissue fibrosis, which results in dysfunction or even loss of function of the affected organ. Although fibrosis has been recognized as a major cause of morbidity and mortality in modern societies, there are only few treatment options available that directly disrupt the release of extracellular matrix from fibroblasts. Intensive research in recent years, however, identified several pathways as core fibrotic mechanisms that are shared across different fibrotic diseases and organs. We discuss herein selection of those core pathways, especially downstream of the profibrotic TGF-β pathway, which are druggable and which may be transferable from bench to bedside.

Transient receptor potential vanilloid-3 (TRPV3) channel induces dermal fibrosis via the TRPV3/TSLP/Smad2/3 pathways in dermal fibroblasts

BACKGROUND

Excessive wound healing can lead to hypertrophic scars, which are not only a cosmetic issue but could also be itchy or painful. Previously, we reported that, in comparison with normal tissue, thymic stromal lymphopoietin (TSLP) expression was increased in skin burn scars when the activation of transient receptor potential vanilloid-3 (TRPV3) of keratinocytes was increased. However, the functional role of TRPV3 in dermal fibrosis remains unclear.

OBJECTIVE

We aimed to determine whether TRPV3 affects the collagen production of human primary dermal fibroblasts (HPDFs) and to investigate the mechanism involved.

METHOD

Human primary dermal fibroblasts were cultured and transformed into myofibroblasts using TSLP and carvacrol. Expression levels of α-SMA, fibronectin, and COL1A1 were determined using qPCR, western blotting, and immunofluorescence staining. Ca²⁺ influx was measured using a calcium-sensitive fluorescent dye, Fura3-AM. Nuclear factor of activated T-cells (NFAT) and phosphorylated-Smad2/3 were determined by western blotting. Silencing of TRPV3 with TRPV3-specific small interference RNA was evaluated using qPCR and western blotting.

RESULTS

The expression levels of α-SMA, fibronectin, COL1A1, and TSLP were significantly increased in carvacrol-treated HPDFs. The expression levels of α-SMA, fibronectin, and COL1A1 were significantly increased by TSLP. The expression levels of TSLP and COL1A1 were significantly blocked by TRPV3 silencing in HPDFs. Regulation of Ca²⁺ influx and the expression levels of NFAT and p-Smad2/3 were significantly increased in carvacrol-treated HPDFs. ECM productions induced via the TRPV3/TSLP/Smad2/3 pathways.

CONCLUSIONS

The activation of the TRPV3 channels regulates dermal fibrosis by reducing extracellular matrix production via the TRPV3/TSLP/Smad2/3 pathways in dermal fibroblasts.

Epigenetic Control of Scleroderma: Current Knowledge and Future Perspectives

PURPOSE OF REVIEW

Epigenetics has been implicated in the pathogenesis of systemic sclerosis (SSc). In this review, the involvement of the three epigenetic mechanisms in SSc development and progression-DNA methylation, histone modifications, and non-coding RNAs-will be discussed.

RECENT FINDINGS

Alteration in epigenetics was observed in immune cells, dermal fibroblasts, and endothelial cells derived from SSc patients. Genes that are affected include those involved in immune cell function and differentiation, TGFβ and Wnt pathways, extracellular matrix accumulation, transcription factors, and angiogenesis. All the studies remain in the pre-clinical stage. Extensive research provides evidence that epigenetic alterations are critical for SSc pathogenesis. Future epigenomic studies will undoubtedly continue to broaden our understanding of disease pathogenesis and clinical heterogeneity. They will also provide the scientific basis for repurposing epigenetic-modifying agents for SSc patients.

Epigenetic modulation as a therapy in systemic sclerosis

SSc is an autoimmune idiopathic disease in which there is an inflammatory component driving fibrosis. The chief cell involved is the myofibroblast, which when activated secretes copious amounts of extracellular matrix that forms deposits, leading to stiffness and fibrosis. The fibrosis is most prevalent in the skin and lungs. In recent years epigenetic modifications have been uncovered that positively and negatively regulate the genesis of the myofibroblasts and that can be activated and regulated by a variety of cytokines and hormones. The epigenetic contribution to these cells and to SSc is only now really coming to light, and this opens up a new therapeutic target for the disease for which many epigenetic drugs, such as miRNA replacements, are beginning to be developed. This review will examine the epigenetic regulators in the disease and possible targeting of these.

Epigenetics of scleroderma: Integrating genetic, ethnic, age, and environmental effects

Scleroderma or systemic sclerosis is thought to result from the interplay between environmental or non-genetic factors in a genetically susceptible individual. Epigenetic modifications are influenced by genetic variation and environmental exposures, and change with chronological age and between populations. Despite progress in identifying genetic, epigenetic, and environmental risk factors, the underlying mechanism of systemic sclerosis remains unclear. Since epigenetics provides the regulatory mechanism linking genetic and non-genetic factors to gene expression, understanding the role of epigenetic regulation in systemic sclerosis will elucidate how these factors interact to cause systemic sclerosis. Among the cell types under tight epigenetic control and susceptible to epigenetic dysregulation, immune cells are critically involved in early pathogenic events in the progression of fibrosis and systemic sclerosis. This review starts by summarizing the changes in DNA methylation, histone modification, and non-coding RNAs associated with systemic sclerosis. It then discusses the role of genetic, ethnic, age, and environmental effects on epigenetic regulation, with a focus on immune system dysregulation. Given the potential of epigenome editing technologies for cell reprogramming and as a therapeutic approach for durable gene regulation, this review concludes with a prospect on epigenetic editing. Although epigenomics in systemic sclerosis is in its infancy, future studies will help elucidate the regulatory mechanisms underpinning systemic sclerosis and inform the design of targeted epigenetic therapies to control its dysregulation.

p300 Acetyltransferase Is a Cytoplasm-to-Nucleus Shuttle for SMAD2/3 and TAZ Nuclear Transport in Transforming Growth Factor β-Stimulated Hepatic Stellate Cells

Nuclear translocation of mothers against decapentaplegic homolog 2/3 (SMAD2/3), core transcription factors of transforming growth factor β (TGF-β) signaling, is critical for hepatic stellate cell (HSC) differentiation into metastasis-promoting myofibroblasts. SMAD2/3 have multiple coactivators, including WW domain-containing transcription regulator protein 1 (WWTR1 or TAZ) and p300 acetyltransferase. In the nucleus, TAZ binds to SMAD2/3 to prevent SMAD2/3 nuclear export. However, how TAZ and SMAD2/3 enter the nucleus remains poorly understood because neither contains a nuclear localization signal (NLS), an amino acid sequence tagging proteins for nuclear transport. p300 is an NLS-containing large scaffold protein, so we hypothesized that SMAD2/3 and TAZ may undergo nuclear import through complexing with p300. Coimmunoprecipitation, immunofluorescence, and nuclear fractionation assays revealed that TGF-β1 promoted binding of SMAD2/3 and TAZ to p300 and that p300 inactivation disrupted TGF-β1-mediated SMAD2/3 and TAZ nuclear accumulation. Deleting the p300 NLS blocked TGF-β1-induced SMAD2/3 and TAZ nuclear transport. Consistently, p300 inactivation suppressed TGF-β1-mediated HSC activation and transcription of genes encoding tumor-promoting factors, such as connective tissue growth factor, Tenascin C, Periostin, platelet-derived growth factor C, and fibroblast growth factor 2, as revealed by microarray analysis. Chromatin immunoprecipitation-real-time quantitative PCR showed that canonical p300-mediated acetylation of histones also facilitated transcription in response to TGF-β1 stimulation. Interestingly, although both TGF-β1-mediated and stiffness-mediated HSC activation require p300, comparison of gene expression data sets revealed that transcriptional targets of TGF-β1 were distinct from those of stiffness-p300 mechanosignaling. Lastly, in tumor/HSC coinjection and intrasplenic tumor injection models, targeting p300 of activated-HSC/myofibroblasts by C646, short hairpin RNA, or cre-mediated gene disruption reduced tumor and liver metastatic growth in mice. Conclusion: p300 facilitates TGF-β1-stimulated HSC activation by both noncanonical (cytoplasm-to-nucleus shuttle for SMAD2/3 and TAZ) and canonical (histone acetylation) mechanisms. p300 is an attractive target for inhibiting HSC activation and the prometastatic liver microenvironment.

P300 Acetyltransferase Mediates Stiffness-Induced Activation of Hepatic Stellate Cells Into Tumor-Promoting Myofibroblasts

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) contribute to desmoplasia and stiffness of liver metastases by differentiating into matrix-producing myofibroblasts. We investigated whether stiffness due to the presence of tumors increases activation of HSCs into myofibroblasts and their tumor-promoting effects, as well as the role of E1A binding protein p300, a histone acetyltransferase that regulates transcription, in these processes.

METHODS

HSCs were isolated from liver tissues of patients, mice in which the p300 gene was flanked by 2 loxP sites (p300F/F mice), and p300+/+ mice (controls). The HSCs were placed on polyacrylamide gels with precisely defined stiffness, and their activation (differentiation into myofibroblasts) was assessed by immunofluorescence and immunoblot analyses for alpha-smooth muscle actin. In HSCs from mice, the p300 gene was disrupted by cre recombinase. In human HSCs, levels of p300 were knocked down with small hairpin RNAs or a mutant form of p300 that is not phosphorylated by AKT (p300S1834A) was overexpressed. Human HSCs were also cultured with inhibitors of p300 (C646), PI3K signaling to AKT (LY294002), or RHOA (C3 transferase) and effects on stiffness-induced activation were measured. RNA sequencing and chromatin immunoprecipitation-quantitative polymerase chain reaction were used to identify HSC genes that changed expression levels in response to stiffness. We measured effects of HSC-conditioned media on proliferation of HT29 colon cancer cells and growth of tumors following subcutaneous injection of these cells into mice. MC38 colon cancer cells were injected into portal veins of p300F/Fcre and control mice, and liver metastases were measured. p300F/Fcre and control mice were given intraperitoneal injections of CCl₄ to induce liver fibrosis. Liver tissues were collected and analyzed by immunofluorescence, immunoblot, and histology.

RESULTS

Substrate stiffness was sufficient to activate HSCs, leading to nuclear accumulation of p300. Disrupting p300 level or activity blocked stiffness-induced activation of HSCs. In HSCs, substrate stiffness activated AKT signaling via RHOA to induce phosphorylation of p300 at serine 1834; this caused p300 to translocate to the nucleus, where it up-regulated transcription of genes that increase activation of HSCs and metastasis, including CXCL12. MC38 cells, injected into portal veins, formed fewer metastases in livers of p300F/Fcre mice than control mice. Expression of p300 was increased in livers of mice following injection of CCl4; HSC activation and collagen deposition were reduced in livers of p300F/Fcre mice compared with control mice.

CONCLUSIONS

In studies of mice, we found liver stiffness to activate HSC differentiation into myofibroblasts, which required nuclear accumulation of p300. p300 increases HSC expression of genes that promote metastasis.

Epigenetic Regulation of Myofibroblast Phenotypes in Fibrosis

Purpose of Review

Myofibroblasts are the fundamental drivers of fibrosing disorders; there is great value in better defining epigenetic networks involved in myofibroblast behavior. Complex epigenetic paradigms, which are likely organ and/or disease specific, direct pathologic myofibroblast phenotypes. In this review, we highlight epigenetic regulators and the mechanisms through which they shape myofibroblast phenotype in fibrotic diseases of different organs.

Recent Findings

Hundreds of genes and their expression contribute to the myofibroblast transcriptional regime influencing myofibroblast phenotype. An increasingly large number of epigenetic modifications have been identified in the regulation of these signaling pathways driving myofibroblast activation and disease progression. Drugs that inhibit or reverse profibrotic epigenetic modifications have shown promise in vitro and in vivo; however, no current epigenetic therapies have been approved to treat fibrosis. Newly described epigenetic mechanisms will be mentioned, along with potential therapeutic targets and innovative strategies to further understand myofibroblast-directed fibrosis.

Summary

Epigenetic regulators that direct myofibroblast behavior and differentiation into pathologic myofibroblast phenotypes in fibrotic disorders comprise both overlapping and organ-specific epigenetic mechanisms.

Protective effect of α-lipoic acid against radiation-induced fibrosis in mice

Radiation-induced fibrosis (RIF) is one of the most common late complications of radiation therapy. We found that α-lipoic acid (α-LA) effectively prevents RIF. In RIF a mouse model, leg contracture assay was used to test the in vivo efficacy of α-LA. α-LA suppressed the expression of pro-fibrotic genes after irradiation, both in vivo and in vitro, and inhibited the up-regulation of TGF-β1-mediated p300/CBP activity. Thus, α-LA prevents radiation-induced fibrosis (RIF) by inhibiting the transcriptional activity of NF-κB through inhibition of histone acetyltransferase activity. α-LA is a new therapeutic methods that can be used in the prevention-treatment of RIF.

Thrombin Induces CCL2 Expression in Human Lung Fibroblasts via p300 Mediated Histone Acetylation and NF-KappaB Activation

Thrombin has been shown to play a key role in lung diseases such as pulmonary fibrosis via the induction of fibrotic cytokine- chemokine (CC motif) ligand-2 (CCL2) expression. We previously reported that transcription factor nuclear factor-κB (NF-κB) is responsible for thrombin-induced CCL2 expression in human lung fibroblasts (HLFs). Here, we extended our study to investigate the epigenetic regulation mechanism for thrombin-induced CCL2 expression in HLFs. HLFs were cultured in F-12 medium. CCL2 protein and mRNA levels were detected by ELISA and quantitative real-time PCR, respectively. Histone, histone acetyltransferases, and NF-κB binding to CCL2 promoter were detected by ChIP assay. NF-κB activation was detected by Western blotting. We revealed that increased binding of histone acetyltransferase p300 and acetylated histone H3 and H4 to CCL2 promoter are responsible for thrombin induced CCL2 expression in HLF cells. In addition, p300 inhibition attenuates both thrombin induced-CCL2 expression and histone H3 and H4 acetylation in HLFs, suggesting that p300 is involved in thrombin-induced CCL2 expression via hyperacetylating histone H3 and H4. Our data further showed that p300 also regulates CCL2 expression via interaction with NF-κB p65, as depletion of p300 inhibits both NF-κB p65 activation and its binding to CCL2 promoter. The findings strongly suggest that epigenetic dysregulation and the interaction between histone acetyltransferase and transcription factor may be responsible for thrombin induced-CCL2 expression in HLFs. Increased understanding of the epigenetic mechanisms of CCL2 regulation may provide opportunities for identifying novel molecular targets for therapeutic purposes. J. Cell. Biochem. 118: 4012-4019, 2017. © 2017 Wiley Periodicals, Inc.

The histone demethylase Jumonji domain-containing protein 3 (JMJD3) regulates fibroblast activation in systemic sclerosis

Objectives

Systemic sclerosis (SSc) fibroblasts remain activated even in the absence of exogenous stimuli. Epigenetic alterations are thought to play a role for this endogenous activation. Trimethylation of histone H3 on lysine 27 (H3K27me3) is regulated by Jumonji domain-containing protein 3 (JMJD3) and ubiquitously transcribed tetratricopeptide repeat on chromosome X (UTX) in a therapeutically targetable manner. The aim of this study was to explore H3K27me3 demethylases as potential targets for the treatment of fibrosis.

Methods

JMJD3 was inactivated by small interfering RNA-mediated knockdown and by pharmacological inhibition with GSKJ4. The effects of targeted inactivation of JMJD3 were analysed in cultured fibroblasts and in the murine models of bleomycin-induced and topoisomerase-I (topoI)-induced fibrosis. H3K27me3 at the FRA2 promoter was analysed by ChIP.

Results

The expression of JMJD3, but not of UTX, was increased in fibroblasts in SSc skin and in experimental fibrosis in a transforming growth factor beta (TGFβ)-dependent manner. Inactivation of JMJD3 reversed the activated fibroblast phenotype in SSc fibroblasts and prevented the activation of healthy dermal fibroblasts by TGFβ. Pharmacological inhibition of JMJD3 ameliorated bleomycin-induced and topoI-induced fibrosis in well-tolerated doses. JMJD3 regulated fibroblast activation in a FRA2-dependent manner: Inactivation of JMJD3 reduced the expression of FRA2 by inducing accumulation of H3K27me3 at the FRA2 promoter. Moreover, the antifibrotic effects of JMJD3 inhibition were reduced on knockdown of FRA2.

Conclusion

We present first evidence for a deregulation of JMJD3 in SSc. JMJD3 modulates fibroblast activation by regulating the levels of H3K27me3 at the promoter of FRA2. Targeted inhibition of JMJD3 limits the aberrant activation of SSc fibroblasts and exerts antifibrotic effects in two murine models.

Inhibition of β-Catenin Signaling in the Skin Rescues Cutaneous Adipogenesis in Systemic Sclerosis: A Randomized, Double-Blind, Placebo-Controlled Trial of C-82

Several studies have suggested that Wnts might contribute to skin fibrosis in systemic sclerosis (SSc) by affecting the differentiation of pluripotent dermal cells. We tested C-82, a therapeutic that inhibits canonical Wnt signaling by blocking the interaction of the protein CBP with β-Catenin and inhibiting Wnt-activated genes. We used a trial design formulating C-82 for topical application and conducting a placebo-controlled, double-blinded clinical trial in which patients with diffuse cutaneous SSc were treated with C-82 or placebo on opposite forearms. C-82- compared with placebo-treated forearms did not show any clinical effect. Skin biopsies performed before and after treatment showed a very weak trend toward improvement in the C-82-treated skin of biomarkers of local skin disease, THBS1 and COMP. However, on microarray analysis C-82 treatment strongly up-regulated two clusters of genes that correlate negatively with the severity of SSc skin disease. These clusters are highly associated with metabolism and one gene, PLIN2, expressed only by sebocytes and subcutaneous fat cells. These changes in gene expression strongly support a role for Wnts in differentiation of pluripotent cells into profibrotic fibroblasts and the potential for C-82 with longer treatment to promote fat regeneration in SSc skin.

Unfolding the pathogenesis of scleroderma through genomics and epigenomics

With unknown etiology, scleroderma (SSc) is a multifaceted disease characterized by immune activation, vascular complications, and excessive fibrosis in internal organs. Genetic studies, including candidate gene association studies, genome-wide association studies, and whole-exome sequencing have supported the notion that while genetic susceptibility to SSc appears to be modest, SSc patients are genetically predisposed to this disease. The strongest genetic association for SSc lies within the MHC region, with loci in HLA-DRB1, HLA-DQB1, HLA-DPB1, and HLA-DOA1 being the most replicated. The non-HLA genes associated with SSc are involved in various functions, with the most robust associations including genes for B and T cell activation and innate immunity. Other pathways include genes involved in extracellular matrix deposition, cytokines, and autophagy. Among these genes, IRF5, STAT4, and CD247 were replicated most frequently while SNPs rs35677470 in DNASE1L3, rs5029939 in TNFAIP3, and rs7574685 in STAT4 have the strongest associations with SSc. In addition to genetic predisposition, it became clear that environmental factors and epigenetic influences also contribute to the development of SSc. Epigenetics, which refers to studies that focus on heritable phenotypes resulting from changes in chromatin structure without affecting the DNA sequence, is one of the most rapidly expanding fields in biomedical research. Indeed extensive epigenetic changes have been described in SSc. Alteration in enzymes and mediators involved in DNA methylation and histone modification, as well as dysregulated non-coding RNA levels all contribute to fibrosis, immune dysregulation, and impaired angiogenesis in this disease. Genes that are affected by epigenetic dysregulation include ones involved in autoimmunity, T cell function and regulation, TGFβ pathway, Wnt pathway, extracellular matrix, and transcription factors governing fibrosis and angiogenesis. In this review, we provide a comprehensive overview of the current findings of SSc genetic susceptibility, followed by an extensive description and a systematic review of epigenetic research that has been carried out to date in SSc. We also summarize the therapeutic potential of drugs that affect epigenetic mechanisms, and outline the future prospective of genomics and epigenomics research in SSc.

Epigenetic factors as drivers of fibrosis in systemic sclerosis

Prolonged activation of fibroblasts is a central hallmark of fibrosing disorders such as systemic sclerosis (SSc). Fibroblasts are the key effector cells. They differentiate into an activated myofibroblast phenotype. In contrast to normal wound healing with transient activation, myofibroblasts persist in fibrosing disorders. Current hypothesis suggests that profibrotic cytokines might trigger epigenetic changes which contribute to the persistently activated fibroblast phenotype. In the last years, several epigenetic alterations have been described in SSc and have been linked to different pathogenic aspects of the disease, in particular to aberrant fibroblast activation and tissue fibrosis, but also to vascular manifestations and inflammation. The focus of this review is the current knowledge on epigenetic changes in fibroblast activation in SSc.

Epigenetics in Reactive and Reparative Cardiac Fibrogenesis: The Promise of Epigenetic Therapy

Epigenetic changes play a pivotal role in the development of a wide spectrum of human diseases including cardiovascular diseases, cancer, diabetes, and intellectual disabilities. Cardiac fibrogenesis is a common pathophysiological process seen during chronic and stress-induced accelerated cardiac aging. While adequate production of extracellular matrix (ECM) proteins is necessary for post-injury wound healing, excessive synthesis and accumulation of extracellular matrix protein in the stressed or injured hearts causes decreased or loss of lusitropy that leads to cardiac failure. This self-perpetuating deposition of collagen and other matrix proteins eventually alter cellular homeostasis; impair tissue elasticity and leads to multi-organ failure, as seen during pathogenesis of cardiovascular diseases, chronic kidney diseases, cirrhosis, idiopathic pulmonary fibrosis, and scleroderma. In the last 25 years, multiple studies have investigated the molecular basis of organ fibrosis and highlighted its multi-factorial genetic, epigenetic, and environmental regulation. In this minireview, we focus on five major epigenetic regulators and discuss their central role in cardiac fibrogenesis. Additionally, we compare and contrast the epigenetic regulation of hypertension-induced reactive fibrogenesis and myocardial infarction-induced reparative or replacement cardiac fibrogenesis. As microRNAs-one of the major epigenetic regulators-circulate in plasma, we also advocate their potential diagnostic role in cardiac fibrosis. Lastly, we discuss the evolution of novel epigenetic-regulating drugs and predict their clinical role in the suppression of pathological cardiac remodeling, cardiac aging, and heart failure. J. Cell. Physiol. 232: 1941-1956, 2017. © 2016 Wiley Periodicals, Inc.

From genetics to epigenetics: new insights into keloid scarring

Keloid scarring is a dermal fibroproliferative response characterized by excessive and progressive deposition of collagen; aetiology and molecular pathology underlying keloid formation and progression remain unclear. Genetic predisposition is important in the pathogenic processes of keloid formation, however, environmental factors and epigenetic mechanisms may also play pivotal roles. Epigenetic modification is a recent area of investigation in understanding the molecular pathogenesis of keloid scarring and there is increasing evidence that epigenetic changes may play a role in induction and persistent activation of fibroblasts in keloid scars. Here we have reviewed three epigenetic mechanisms: DNA methylation, histone modification and the role of non-coding RNAs. We also review the evidence that these mechanisms may play a role in keloid formation - in future, it may be possible that epigenetic markers may be used instead of prognostic or diagnostic markers here. However, there is a significant amount of work required to increase our current understanding of the role of epigenetic modification in keloid disease.

Epigenetic regulation of cardiac fibrosis

Fibrosis is defined as excess deposition of extracellular matrix (ECM), resulting in tissue scarring and organ dysfunction. In the heart, fibrosis may be reparative, replacing areas of myocyte loss with a structural scar following infarction, or reactive, which is triggered in the absence of cell death and involves interstitial ECM deposition in response to long-lasting stress. Interstitial fibrosis can increase the passive stiffness of the myocardium, resulting in impaired relaxation and diastolic dysfunction. Additionally, fibrosis can lead to disruption of electrical conduction in the heart, causing arrhythmias, and can limit myocyte oxygen availability and thus exacerbate myocardial ischemia. Here, we review recent studies that have illustrated key roles for epigenetic events in the control of pro-fibrotic gene expression, and highlight the potential of small molecules that target epigenetic regulators as a means of treating fibrotic cardiac diseases.

Epigenetic switch drives the conversion of fibroblasts into proinvasive cancer-associated fibroblasts

Carcinoma-associated fibroblasts (CAF) mediate the onset of a proinvasive tumour microenvironment. The proinflammatory cytokine LIF reprograms fibroblasts into a proinvasive phenotype, which promotes extracellular matrix remodelling and collective invasion of cancer cells. Here we unveil that exposure to LIF initiates an epigenetic switch leading to the constitutive activation of JAK1/STAT3 signalling, which results in sustained proinvasive activity of CAF. Mechanistically, p300-histone acetyltransferase acetylates STAT3, which, in turn, upregulates and activates the DNMT3b DNA methyltransferase. DNMT3b methylates CpG sites of the SHP-1 phosphatase promoter, which abrogates SHP-1 expression, and results in constitutive phosphorylation of JAK1. Sustained JAK1/STAT3 signalling is maintained by DNA methyltransferase DNMT1. Consistently, in human lung and head and neck carcinomas, STAT3 acetylation and phosphorylation are inversely correlated with SHP-1 expression. Combined inhibition of DNMT activities and JAK signalling, in vitro and in vivo, results in long-term reversion of CAF-associated proinvasive activity and restoration of the wild-type fibroblast phenotype.

Carcinoma-associated fibroblasts are key components of solid tumours and associated with poor clinical outcome. Here the authors show that the cytokine LIF initiates an epigenetic switch which results in the sustained invasive activity of the tumour cells.

FAT-free p300 is good for scar-free tissue repair

Fibrosis, the deadly pathological manifestation of an abnormal tissue remodeling in any organ due to excessive collagen deposition, is associated with a wide variety of organ failure-related human diseases. Chronic stress or repeated injury in a particular organ induces abnormal molecular signals that lead to super-activation of matrix protein producing fibroblasts, excessive matrix proteins accumulation, loss of physiological tissue architecture or elasticity, and ultimately leading to organ failure. There is no effective therapy for fibrosis. Factor acetyltransferase p300 (FATp300), a major epigenetic regulator that acetylates specific lysines in histones and transcription factors, is essential for elevated collagen synthesis and the levels of FATp300 are significantly elevated in different fibrotic tissues. Pharmacological inhibition of FAT activity of p300 is associated with decreased collagen synthesis by fibroblasts in tissues and amelioration of organ fibrosis. Therefore, FAT-free p300 is superior for physiological tissue repair and must be exploited as a viable therapeutic target against multi-organ fibrosis.

The Histone Deacetylase Sirtuin 1 Is Reduced in Systemic Sclerosis and Abrogates Fibrotic Responses by Targeting Transforming Growth Factor β Signaling

OBJECTIVE

Persistent fibroblast activation underlies skin fibrosis in systemic sclerosis (SSc), but the transcriptional and epigenetic mechanisms controlling this process are not well understood. In view of the potent influence of acetylation status governing tissue fibrosis, we undertook this study to investigate the expression of the antiaging deacetylase enzyme sirtuin 1 (SIRT1) in SSc and its effects on fibrotic responses in vitro and in vivo.

METHODS

Tissue expression of SIRTs was interrogated from publicly available genome-wide expression data sets and by immunohistochemistry. The effects of SIRT1 on modulating fibrotic responses, as well as the underlying mechanisms, were examined in human and mouse fibroblasts in culture and in an experimental fibrosis model in the mouse.

RESULTS

Analysis of transcriptome data revealed a selective reduction of SIRT1 messenger RNA (mRNA) levels in SSc skin biopsy samples as well as a negative correlation of SIRT1 mRNA with the skin score. Cellular SIRT1 levels were suppressed in normal fibroblasts exposed to hypoxia or platelet-derived growth factor and were constitutively down-regulated in SSc fibroblasts. Activation of SIRT1 attenuated fibrotic responses in skin fibroblasts and skin organ cultures, while genetic or pharmacologic inhibition of SIRT1 had profibrotic effects. The antifibrotic effects of SIRT1 were due in part to decreased expression and function of the acetyltransferase p300. In mice, experimentally induced skin fibrosis was accompanied by reduced SIRT1 expression in lesional tissue fibroblasts, and both fibrosis and loss of SIRT1 in these mice were mitigated by treatment with a SIRT1 activator.

CONCLUSION

SIRT1 has antifibrotic effects, and its reduced tissue expression in patients with SSc might have a direct causal role in progression of fibrosis. Pharmacologic modulation of SIRT1 in these patients therefore might represent a potential treatment strategy.

Causes and consequences of epigenetic regulation in wound healing

Wound healing is a complex and systematic tissue level response to mechanical and chemical injuries that may cause the release of growth factors, cytokines, and chemokines by damaged tissues. For the complex features of these restorative processes, it is a crucial challenge to identify the relevant cell types and biochemical pathways that are involved in wound healing. Epigenetic mechanisms, such as DNA methylation, histone modification, and noncoding regulatory RNA editing, play important roles in many biological processes, including cell proliferation, migration and differentiation, signal pathway activation or inhibition, and cell senescence. Epigenetic regulations can coordinately control a considerable subset of known repair genes and thus serve as master regulators of wound healing. An abundance of evidence has also shown that epigenetic modifications participate in the short- and long-term control of crucial gene expression and cell signal transduction that are involved in the healing process. These data provide a foundation for probable epigenetic-based therapeutic strategies that are aimed at stimulating tissue regeneration. This review describes the epigenetic alterations in different cellular types at injury sites, induced signals, and resulting tissue repair. With the increased interest in the epigenetics of wound and repair processes, this field will soon begin to flourish.

Theobromine increases NAD⁺/Sirt-1 activity and protects the kidney under diabetic conditions

Reduction in sirtuin 1 (Sirt-1) is associated with extracellular matrix (ECM) accumulation in the diabetic kidney. Theobromine may reduce kidney ECM accumulation in diabetic rats. In the current study, we aimed to unravel, under diabetic conditions, the mechanism of kidney ECM accumulation induced by a reduction in Sirt-1 and the effect of theobromine in these events. In vitro, we used immortalized human mesangial cells (iHMCs) exposed to high glucose (HG; 30 mM), with or without small interfering RNA for NOX4 and Sirt-1. In vivo, spontaneously hypertensive rats (SHR) were rendered diabetic by means of streptozotocin and studied after 12 wk. The effects of treatment with theobromine were investigated under both conditions. HG leads to a decrease in Sirt-1 activity and NAD(+) levels in iHMCs. Sirt-1 activity could be reestablished by treatment with NAD(+), silencing NOX4, and poly (ADP-ribose) polymerase-1 (PARP-1) blockade, or with theobromine. HG also leads to a low AMP/ATP ratio, acetylation of SMAD3, and increased collagen IV, which is prevented by theobromine. Sirt-1 or AMPK blockade abolished these effects of theobromine. In diabetic SHR, theobromine prevented increases in albuminuria and kidney collagen IV, reduced AMPK, elevated NADPH oxidase activity and PARP-1, and reduced NAD(+) levels and Sirt-1 activity. These results suggest that in diabetes mellitus, Sirt-1 activity is reduced by PARP-1 activation and NAD(+) depletion due to low AMPK, which increases NOX4 expression, leading to ECM accumulation mediated by transforming growth factor (TGF)-β1 signaling. It is suggested that Sirt-1 activation by theobromine may have therapeutic potential for diabetic nephropathy.

Pathophysiology of systemic sclerosis: state of the art in 2014

Major work has been done in order to improve the understanding of systemic sclerosis (SSc) pathogenesis. A number of new experimental models have been set up, that should help to understand the disease pathogenesis and test new therapeutic targets. Reactive oxygen species represent a hallmark of the pathogenesis of SSc, both at the fibroblast and at the endothelial cell levels. Although a large number of genetic studies have been conducted, it is still difficult to identify a genetic background specific to SSc, and the major progress in this setting is probably the identification of an interferon signature. Besides endothelial cells and fibroblasts, major development has been made in the understanding of the role of B cells and autoantibodies in the pathogenesis of SSc. Plasmacytoid dendritic cells seem to play a major role in the pathogenesis of SSc through the secretion of CXCL4, although these data will need to be confirmed in the near future.

The role of genetics and epigenetics in the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is a complex autoimmune disease of unclear aetiology. A multitude of genetic studies, ranging from candidate-gene studies to genome-wide association studies, have identified a large number of genetic susceptibility factors for SSc and its clinical phenotypes, but the contribution of these factors to disease susceptibility is only modest. However, in an endeavour to explore how the environment might affect genetic susceptibility, epigenetic research into SSc is rapidly expanding. Orchestrated by environmental factors, epigenetic modifications can drive genetically predisposed individuals to develop autoimmunity, and are thought to represent the crossroads between the environment and genetics in SSc. Therefore, in addition to providing a comprehensive description of the current understanding of genetic susceptibility underlying SSc, this Review describes the involvement of epigenetic phenomena, including DNA methylation patterns, histone modifications and microRNAs, in SSc.

Epigenetics in radiation-induced fibrosis

Radiotherapy is a major cancer treatment option but dose-limiting side effects such as late-onset fibrosis in the irradiated tissue severely impair quality of life in cancer survivors. Efforts to explain radiation-induced fibrosis, for example, by genetic variation remained largely inconclusive. Recently published molecular analyses on radiation response and fibrogenesis showed a prominent role of epigenetic gene regulation. This review summarizes the current knowledge on epigenetic modifications in fibrotic disease and radiation response, and it points out the important role for epigenetic mechanisms such as DNA methylation, microRNAs and histone modifications in the development of this disease. The synopsis illustrates the complexity of radiation-induced fibrosis and reveals the need for investigations to further unravel its molecular mechanisms. Importantly, epigenetic changes are long-term determinants of gene expression and can therefore support those mechanisms that induce and perpetuate fibrogenesis even in the absence of the initial damaging stimulus. Future work must comprise the interconnection of acute radiation response and long-lasting epigenetic effects in order to assess their role in late-onset radiation fibrosis. An improved understanding of the underlying biology is fundamental to better comprehend the origin of this disease and to improve both preventive and therapeutic strategies.

Molecular basis of organ fibrosis: potential therapeutic approaches

Fibrosis, a non-physiological wound healing in multiple organs, is associated with end-stage pathological symptoms of a wide variety of vascular injury and inflammation related diseases. In response to chemical, immunological and physical insults, the body's defense system and matrix synthetic machinery respond to healing the wound and maintain tissue homeostasis. However, uncontrolled wound healing leads to scarring or fibrosis, a pathological condition characterized by excessive synthesis and accumulation of extracellular matrix proteins, loss of tissue homeostasis and organ failure. Understanding the actual cause of pathological wound healing and identification of igniter(s) of fibrogenesis would be helpful to design novel therapeutic approaches to control pathological wound healing and to prevent fibrosis related morbidity and mortality. In this article, we review the significance of a few key cytokines (TGF-β, IFN-γ, IL-10) transcriptional activators (Sp1, Egr-1, Smad3), repressors (Smad7, Fli-1, PPAR-γ, p53, Klotho) and epigenetic modulators (acetyltransferase, methyltransferases, deacetylases, microRNAs) involved in major matrix protein collagen synthesis under pathological stage of wound healing, and the potentiality of these regulators as therapeutic targets for fibrosis treatment. The significance of endothelial to mesenchymal transition (EndMT) and senescence, two newly emerged fields in fibrosis research, has also been discussed.

Assessment of Brd4 inhibition in idiopathic pulmonary fibrosis lung fibroblasts and in vivo models of lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease of high unmet medical need. Although bromodomain (Brd) and extra terminal domain isoforms have recently been implicated in mediating inflammatory and oncologic indications, their roles in lung fibrosis have not been comprehensively assessed. We investigated the role of Brd on the profibrotic responses of lung fibroblasts (LFs) in patients with rapidly progressing IPF and a mouse bleomycin model of lung fibrosis. The enhanced migration, proliferation, and IL-6 release observed in LFs from patients with rapidly progressing IPF are attenuated by pharmacologic inhibition of Brd4. These changes are accompanied by enhanced histone H4 lysine5 acetylation and association of Brd4 with genes involved in the profibrotic responses in IPF LFs as demonstrated using chromatin immunoprecipitation and quantitative PCR. Oral administration of 200 mg/kg per day Brd4 inhibitor JQ1 in a therapeutic dosing regimen substantially attenuated lung fibrosis induced by bleomycin in C57BL/6 mice. In conclusion, this study shows that the Brd4 inhibitor JQ1, administered in a therapeutic dosage, is capable of inhibiting the profibrotic effects of IPF LFs and attenuates bleomycin-induced lung fibrosis in mice. These results suggest that Brd4 inhibitors may represent a novel therapy for the treatment of rapidly progressing IPF.

p300 is elevated in systemic sclerosis and its expression is positively regulated by TGF-β: epigenetic feed-forward amplification of fibrosis

Fibrosis, the hallmark of systemic sclerosis (SSc), is characterized by persistent fibroblast activation triggered by transforming growth factor-β (TGF-β). Since the acetyltransferase p300 plays a key role in fibrosis and its availability governs the intensity of fibrotic responses, we investigated p300 expression in SSc and the molecular basis of its regulation. We found that expression of p300 was markedly elevated in SSc skin biopsies, and was induced by TGF-β in explanted normal skin fibroblasts. Stimulation of p300 by TGF-β was independent of Smads, and involved the early-immediate transcription factor Egr-1, a key regulator of profibrotic TGF-β signaling. Indeed, Egr-1 was both sufficient and necessary for p300 regulation in vitro and in vivo. Increased p300 accumulation in TGF-β-treated fibroblasts was associated with histone hyperacetylation, whereas p300 depletion, or selective pharmacological blockade of its acetyltransferase activity, attenuated TGF-β-induced responses. Moreover, TGF-β enhanced both p300 recruitment and in vivo histone H4 acetylation at the COL1A2 locus. These findings implicate p300-mediated histone acetylation as a fundamental epigenetic mechanism in fibrogenesis, and place Egr-1 upstream in TGF-β-driven stimulation of p300 gene expression. The results establish a firm link between fibrosis with aberrant p300 expression and epigenetic activity to our knowledge previously unreported. Targeted disruption of p300-mediated histone acetylation might therefore represent a viable anti-fibrotic strategy.

Egr-1: new conductor for the tissue repair orchestra directs harmony (regeneration) or cacophony (fibrosis)

Fibroblasts and myofibroblasts are the key effector cells executing physiological tissue repair leading to regeneration on the one hand, and pathological fibrogenesis leading to chronic fibrosing conditions on the other. Recent studies identify the multifunctional transcription factor early growth response-1(Egr-1) as an important mediator of fibroblast activation triggered by diverse stimuli. Egr-1 has potent stimulatory effects on fibrotic gene expression, and aberrant Egr-1 expression or function is associated with animal models of fibrosis and human fibrotic disorders, including emphysema, pulmonary fibrosis, pulmonary hypertension and systemic sclerosis. Pharmacological suppression or genetic targeting of Egr-1 blocks fibrotic responses in vitro and ameliorates experimental fibrosis in the skin and lung. In contrast, Egr-1 appears to act as a negative regulator of hepatic fibrosis in mouse models, suggesting a context-dependent role in fibrosis. The Egr-1-binding protein Nab2 is an endogenous inhibitor of Egr-1-mediated signalling and abrogates the stimulation of fibrotic responses induced by transforming growth factor-β (TGFβ). Moreover, mice deficient in Nab2 show excessive collagen accumulation in the skin. These observations highlight a previously unsuspected fundamental physiological function for the Egr-1-Nab2 signalling axis in regulating fibrogenesis, and suggest that Egr-1 may be a potential novel therapeutic target in human diseases complicated by fibrosis. This review summarizes recent advances in understanding the regulation and complex functional role of Egr-1 and its related proteins and inhibitors in pathological fibrosis.

Mitochondrial reactive oxygen species regulate transforming growth factor-β signaling

TGF-β signaling is required for normal tissue repair; however, excessive TGF-β signaling can lead to robust profibrotic gene expression in fibroblasts, resulting in tissue fibrosis. TGF-β binds to cell-surface receptors, resulting in the phosphorylation of the Smad family of transcription factors to initiate gene expression. TGF-β also initiates Smad-independent pathways, which augment gene expression. Here, we report that mitochondrial reactive oxygen species (ROS) generated at complex III are required for TGF-β-induced gene expression in primary normal human lung fibroblasts. TGF-β-induced ROS could be detected in both the mitochondrial matrix and cytosol. Mitochondrially targeted antioxidants markedly attenuated TGF-β-induced gene expression without affecting Smad phosphorylation or nuclear translocation. Genetically disrupting mitochondrial complex III-generated ROS production attenuated TGF-β-induced profibrotic gene expression. Furthermore, inhibiting mitochondrial ROS generation attenuated NOX4 (NADPH oxidase 4) expression, which is required for TGF-β induced myofibroblast differentiation. Lung fibroblasts from patients with pulmonary fibrosis generated more mitochondrial ROS than normal human lung fibroblasts, and mitochondrially targeted antioxidants attenuated profibrotic gene expression in both normal and fibrotic lung fibroblasts. Collectively, our results indicate that mitochondrial ROS are essential for normal TGF-β-mediated gene expression and that targeting mitochondrial ROS might be beneficial in diseases associated with excessive fibrosis.

Fibroblast autophagy in fibrotic disorders

Fibrotic disorders are multistage progressive processes that often arise from different causes and are commonly associated with chronic inflammation. Excessive deposition of extracellular matrix is the hallmark of many fibrotic diseases. This may be due to an excess of fibroblast recruitment and activation, as well as to their differentiation in myofibroblasts. These events may be triggered by cytokines, chemokines and growth factors released by lymphocytes or macrophages. The excessive production of extracellular matrix is apparently due to alterations of metabolic pathways in activated fibroblasts. It has been suggested that a defective autophagy, an important subcellular pathway with multiple homeostatic roles, also recognized as a key component of both innate and acquired immunity, could play a role. In this review we illustrate recent insights in the field, suggesting the possible implication of the immune system in orchestrating the fibrotic response via the modulation of autophagic pathways.

Toll-like receptor 4 signaling augments transforming growth factor-β responses: a novel mechanism for maintaining and amplifying fibrosis in scleroderma

Because recent studies implicate Toll-like receptors (TLRs) in the pathogenesis of fibrosis, we sought to investigate the in vitro and in vivo role and mechanism of TLR4-mediated fibroblast responses in fibrogenesis. We found that TLR4 was constitutively expressed, and accumulation of endogenous TLR4 ligands significantly elevated, in lesional skin and lung tissues from patients with scleroderma. Activation of TLR4 signaling in explanted fibroblasts resulted in enhanced collagen synthesis and increased expression of multiple genes involved in tissue remodeling and extracellular matrix homeostasis. Moreover, TLR4 dramatically enhanced the sensitivity of fibroblasts to the stimulatory effect of transforming growth factor-β1. These profibrotic responses were abrogated by both genetic and pharmacological disruption of TLR4 signaling in vitro, and skin fibrosis induced by bleomycin in vivo was attenuated in mice harboring a mutated TLR4. Activation of TLR4 in fibroblasts augmented the intensity of canonical Smad signaling, and was accompanied by suppression of anti-fibrotic microRNA expression. Together, these results suggest a novel model to account for persistent fibrogenesis in scleroderma, in which activation of fibroblast TLR4 signaling, triggered by damage-associated endogenous TLR4 ligands, results in augmented transforming growth factor-β1 sensitivity with increased matrix production and progressive connective tissue remodeling. Under these conditions, fibroblast TLR4 serves as the switch for converting self-limited tissue repair into intractable fibrosis.

BET bromodomain proteins mediate downstream signaling events following growth factor stimulation in human lung fibroblasts and are involved in bleomycin-induced pulmonary fibrosis

Epigenetic alterations, such as histone acetylation, regulate the signaling outcomes and phenotypic responses of fibroblasts after growth factor stimulation. The bromodomain and extra-terminal domain-containing proteins (Brd) bind to acetylated histone residues, resulting in recruitment of components of the transcriptional machinery and subsequent gene transcription. Given the central importance of fibroblasts in tissue fibrosis, this study sought to determine the role of Brd proteins in human lung fibroblasts (LFs) after growth factor stimulation and in the murine bleomycin model of lung fibrosis. Using small interfering RNA against human Brd2 and Brd4 and pharmacologic Brd inhibitors, this study found that Brd2 and Brd4 are essential in mediating the phenotypic responses of LFs downstream of multiple growth factor pathways. Growth factor stimulation of LFs causes increased histone acetylation, association of Brd4 with growth factor-responsive genes, and enhanced transcription of these genes that could be attenuated with pharmacologic Brd inhibitors. Of note, lung fibrosis induced after intratracheal bleomycin challenge in mice could be prevented by pretreatment of animals with pharmacologic inhibitors of Brd proteins. This study is the first demonstration of a role for Brd2 and Brd4 proteins in mediating the responses of LFs after growth factor stimulation and in driving the induction of lung fibrosis in mice in response to bleomycin challenge.

AMP-activated protein kinase inhibits TGF-β-induced fibrogenic responses of hepatic stellate cells by targeting transcriptional coactivator p300

Liver fibrosis is a common consequence of various chronic liver injuries, including virus infection and ethanol. Activated hepatic stellate cells (HSCs) contribute to liver fibrosis through the accumulation of extracellular matrix proteins, including type I alpha collagen (COL1A). The activation of adenosine monophosphate-activated protein kinase (AMPK) modulates HSCs activation, but its underlying mechanism remains unclear. Here, we report that AMPK inhibits transforming growth factor (TGF)-β-induced fibrogenic property of HSCs by regulating transcriptional coactivator p300. We treated human (LX-2) and rat (CFSC-2G) HSC lines with TGF-β to induce fibrogenic activation of HSCs. Pharmacological activation of AMPK by treatment with 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR), metformin, or adiponectin lowered TGF-β-induced expression of COL1A and myofibroblast marker alpha-smooth muscle actin (α-SMA). Transient transduction of constitutively active AMPKα (caAMPKα) was sufficient to attenuate COL1A and α-SMA expression, whereas an AMPK inhibitor considerably abrogated the inhibitory effect of AICAR on fibrogenic gene expression. Although AMPK significantly suppressed Smad-dependent transcription, it did not affect TGF-β-stimulated phosphorylation, nuclear localization, or DNA-binding activity of Smad2/3. AICAR rather attenuated TGF-β-induced Smad3 interaction with transcriptional coactivator p300 accompanying with reduction of Smad3 acetylation. Moreover, AICAR induced not only physical interaction between AMPK and p300 but also proteasomal degradation of p300 protein. Our data provide substantial evidence that AMPK could be a novel therapeutic target for treatment of liver fibrosis, by demonstrating the underlying mechanism of AMPK-induced antifibrotic function in HSCs.

Histone deacetylase inhibitor m-carboxycinnamic acid bis-hydroxamide attenuates plasminogen activator inhibitor-1 expression in human pleural mesothelial cells

Plasminogen activator inhibitor-1 (PAI-1), primarily up-regulated by transforming growth factor (TGF)-β, is essential in the development of fibrosis. Histone deacetylase (HDAC) was shown to modulate gene expression and fibrogenesis in various tissues. However, the implications of HDAC in terms of PAI-1 expression and pleural fibrosis remain unclear. In this study, we examined the effects of m-carboxycinnamic acid bis-hydroxamide (CBHA), a hybrid-polar HDAC inhibitor, on the TGF-β1-induced expression of PAI-1 in a human pleural mesothelial cell line (MeT-5A). MeT-5A cells were treated with TGF-β1 in the presence or absence of CBHA. We assayed the expression and stability of PAI-1 mRNA and protein, PAI-1 promoter activity, the activation of Smad signaling, the protein-protein interactions of Smads with transcriptional cofactors Sp1 and coactivator p300, and the expression of the mRNA-stabilizing protein nucleolin. The results indicate that CBHA significantly inhibited TGF-β1-induced PAI-1 mRNA and protein expression, and attenuated PAI-1 promoter activity in MeT-5A cells. CBHA abrogated TGF-β1-induced Smad4 nuclear translocation, but not Smad2/3 activation. Furthermore, the association of Smad4 with p300, but not with Sp1, was disrupted by CBHA. Alternatively, CBHA suppressed TGF-β1-induced nucleolin expression, and thereby destabilized PAI-1 mRNA and decreased PAI-1 protein concentrations. These findings suggest that the inhibition of HDAC activity by CBHA may attenuate PAI-1 expression through the modulation of cellular signaling at multiple levels. Given the down-regulating effect of CBHA on PAI-1 expression, HDAC inhibitors should be tested further in animal models as potential therapeutic agents for pleural fibrosis.

Animal models of cutaneous and hepatic fibrosis

Fibrosis occurs as a part of normal wound healing. However, excessive or dysregulated fibrosis can lead to severe organ dysfunction and is a feature of a variety of diseases. Due to its insidious onset, fibrosis tends to go undetected in its early stages. This is in part why these diseases remain so poorly understood. Animal models have provided a means to examine these early stages and to isolate and understand the effect of perturbations in signaling pathways, chemokines, and cytokines. Here, we summarize recent progress in the understanding of the molecular pathogenesis of fibrosis, both its initiation and its maintenance phases, from animal models of fibrosis in the skin and liver. Due to these organs' properties, modeling fibrosis in them poses unique challenges. Elegant solutions have therefore been developed for modeling fibrosis in each, and now, great potential for animal models to contribute to our understanding appears scientifically imminent.

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.

Mithramycin reduces expression of fibro-proliferative mRNAs in human gingival fibroblasts

Fibrosis is characterized by loss of normal structure and function of a tissue or organ resulting from excessive fibroblast proliferation and extracellular matrix production. Currently, there is no efficient treatment for fibrosis. Herein, we test effects of the drug mithramycin, which targets the Sp1 family of transcription factors, on mRNA expression by human gingival fibroblasts. Mithramycin reduced expression of connective tissue growth factor and type I collagen mRNAs. Microarray profiling revealed that mithramycin selectively blocked expression of cell proliferation and transforming growth factor-beta (TGF-β) signalling clusters. These microarray data were validated using real-time polymerase chain reaction and western blot analyses. Mithramycin suppressed expression of key profibrotic TGF-β signalling mediators, Smad3 and p300, as well as cell proliferation. Taken together, these data suggest that the Sp1 family of transcription factors may contribute to expression of fibrogenic genes in human gingival fibroblasts; drugs targeting the Sp1 family may be beneficial in treatment of fibro-proliferative diseases.

Early growth response transcription factors: key mediators of fibrosis and novel targets for anti-fibrotic therapy

Fibrosis is a deregulated and ultimately defective form of tissue repair that underlies a large number of chronic human diseases, as well as obesity and aging. The pathogenesis of fibrosis involves multiple cell types and extracellular signals, of which transforming growth factor-ß (TGF-ß) is pre-eminent. The prevalence of fibrosis is rising worldwide, and to date no agents has shown clinical efficacy in the attenuating or reversing the process. Recent studies implicate the immediate-early response transcription factor Egr-1 in the pathogenesis of fibrosis. Egr-1 couples acute changes in the cellular environment to sustained alterations in gene expression, and mediates a broad spectrum of biological responses to injury and stress. In contrast to other ligand-activated transcription factors such as NF-κB, c-jun and Smad2/3 that undergo post-translational modification such as phosphorylation and nuclear translocation, Egr-1 activity is regulated via its biosynthesis. Aberrant Egr-1 expression or activity is implicated in cancer, inflammation, atherosclerosis, and ischemic injury and recent studies now indicate an important role for Egr-1 in TGF-ß-dependent profibrotic responses. Fibrosis in various animal models and human diseases such as scleroderma (SSc) and idiopathic pulmonary fibrosis (IPF) is accompanied by aberrant Egr-1 expression. Moreover Egr-1 appears to be required for physiologic and pathological connective tissue remodeling, and Egr-1-null mice are protected from fibrosis. As a novel profibrotic mediator, Egr-1 thus appears to be a promising potential target for the development of anti-fibrotic therapies.