Microarray profiling reveals suppressed interferon stimulated gene program in fibroblasts from scleroderma-associated interstitial lung disease.

BACKGROUND: Interstitial lung disease is a major cause of morbidity and mortality in systemic sclerosis (SSc), with insufficiently effective treatment options. Progression of pulmonary fibrosis involves expanding populations of fibroblasts, and the accumulation of extracellular matrix proteins. Characterisation of SSc lung fibroblast gene expression profiles underlying the fibrotic cell phenotype could enable a better understanding of the processes leading to the progressive build-up of scar tissue in the lungs. In this study we evaluate the transcriptomes of fibroblasts isolated from SSc lung biopsies at the time of diagnosis, compared with those from control lungs. METHODS: We used Affymetrix oligonucleotide microarrays to compare the gene expression profile of pulmonary fibroblasts cultured from 8 patients with pulmonary fibrosis associated with SSc (SSc-ILD), with those from control lung tissue peripheral to resected cancer (n=10). Fibroblast cultures from 3 patients with idiopathic pulmonary fibrosis (IPF) were included as a further comparison. Genes differentially expressed were identified using two separate analysis programs following a set of pre-determined criteria: only genes significant in both analyses were considered. Microarray expression data was verified by qRT-PCR and/or western blot analysis. RESULTS: A total of 843 genes were identified as differentially expressed in pulmonary fibroblasts from SSc-ILD and/or IPF compared to control lung, with a large overlap in the expression profiles of both diseases. We observed increased expression of a TGF-ß response signature including fibrosis associated genes and myofibroblast markers, with marked heterogeneity across samples. Strongly suppressed expression of interferon stimulated genes, including antiviral, chemokine, and MHC class 1 genes, was uniformly observed in fibrotic fibroblasts. This expression profile includes key regulators and mediators of the interferon response, such as STAT1, and CXCL10, and was also independent of disease group. CONCLUSIONS: This study identified a strongly suppressed interferon-stimulated gene program in fibroblasts from fibrotic lung. The data suggests that the repressed expression of interferon-stimulated genes may underpin critical aspects of the profibrotic fibroblast phenotype, identifying an area in pulmonary fibrosis that requires further investigation.

Inhibition of focal adhesion kinase prevents experimental lung fibrosis and myofibroblast formation.

OBJECTIVE: Enhanced adhesive signaling, including activation of focal adhesion kinase (FAK), is a hallmark of fibroblasts from lung fibrosis patients, and FAK has therefore been hypothesized to be a key mediator of this disease. This study was undertaken to characterize the contribution of FAK to the development of pulmonary fibrosis both in vivo and in vitro. METHODS: FAK expression and activity were analyzed in lung tissue samples from lung fibrosis patients by immunohistochemistry. Mice orally treated with the FAK inhibitor PF-562,271, or with small interfering RNA (siRNA)-mediated silencing of FAK were exposed to intratracheally instilled bleomycin to induce lung fibrosis, and lungs were harvested for histologic and biochemical analysis. Using endothelin 1 (ET-1) as a stimulus, cell adhesion and contraction, as well as profibrotic gene expression, were studied in fibroblasts isolated from wild-type and FAK-deficient mouse embryos. ET-1-mediated FAK activation and gene expression were studied in primary mouse lung fibroblasts, as well as in wild-type and ß1 integrin-deficient mouse fibroblasts. RESULTS: FAK expression and activity were up-regulated in fibroblast foci and remodeled vessels from lung fibrosis patients. Pharmacologic or siRNA-mediated targeting of FAK resulted in marked abrogation of bleomycin-induced lung fibrosis in mice. Loss of FAK impaired the acquisition of a profibrotic phenotype in response to ET-1. Profibrotic gene expression leading to myofibroblast differentiation required cell adhesion, and was driven by JNK activation through ß1 integrin/FAK signaling. CONCLUSION: These results implicate FAK as a central mediator of fibrogenesis, and highlight this kinase as a potential therapeutic target in fibrotic diseases.

Endothelin-1 stimulates colon cancer adjacent fibroblasts.

Endothelin-1 (ET-1) is produced by and stimulates colorectal cancer cells. Fibroblasts produce tumour stroma required for cancer development. We investigated whether ET-1 stimulated processes involved in tumour stroma production by colonic fibroblasts. Primary human fibroblasts, isolated from normal tissues adjacent to colon cancers, were cultured with or without ET-1 and its antagonists. Cellular proliferation, migration and contraction were measured. Expression of enzymes involved in tumour stroma development and alterations in gene transcription were determined by Western blotting and genome microarrays. ET-1 stimulated proliferation, contraction and migration (p < 0.01 v control) and the expression of matrix degrading enzymes TIMP-1 and MMP-2, but not MMP-3. ET-1 upregulated genes for profibrotic growth factors and receptors, signalling molecules, actin modulators and extracellular matrix components. ET-1 stimulated colonic fibroblast cellular processes in vitro that are involved in developing tumour stroma. Upregulated genes were consistent with these processes. By acting as a strong stimulus for tumour stroma creation, ET-1 is proposed as a target for adjuvant cancer therapy.

Focal adhesion kinase and reactive oxygen species contribute to the persistent fibrotic phenotype of lesional scleroderma fibroblasts.

OBJECTIVE: Fibrotic diseases such as SSc (systemic sclerosis, scleroderma) are characterized by the abnormal presence of the myofibroblast, a specialized type of fibroblast that overexpresses the highly contractile protein α-smooth muscle actin. Myofibroblasts display excessive adhesive properties and hence exert a potent mechanical force. We aim to identify the precise contribution of adhesive signalling, which requires integrin-mediated activation of focal adhesion kinase (FAK)/src, to fibrogenic gene expression in normal and fibrotic SSc fibroblasts. METHODS: We subject either FAK wild-type and knockout fibroblasts or normal and SSc fibroblasts treated with FAK/src inhibitors to real-time polymerase chain, western blot, cell migration and collagen gel contraction analyses. RESULTS: FAK operates downstream of both integrin ß1 and reactive oxygen species (ROS) to promote the expression of genes involved in matrix production and remodelling, including CCN2, α-smooth muscle actin and type I collagen. Blocking either FAK/src with PP2 or ROS with N-acetyl cysteine alleviates the elevated contractile and migratory capability of lesional SSc dermal fibroblasts. CONCLUSIONS: Excessive adhesive signalling is intimately involved with the fibrotic phenotype of lesional SSc fibroblasts; blocking adhesive signalling or ROS generation may be beneficial in controlling the fibrosis observed in SSc.

Gut fibrosis with altered colonic contractility in a mouse model of scleroderma.

OBJECTIVE: Gastrointestinal involvement occurs in up to 90% of patients with SSc. Animal models of SSc mimic some of the pathophysiological disease processes of SSc. The transgenic (TG) mouse strain TßRIIΔk-fib is characterized by ligand-dependent up-regulation of TGF-ß signalling and has been shown to develop skin fibrosis, lung fibrosis and diminished aortic ring contractility and adventitial fibrosis. We investigated if similar changes are observed in the gut tissue in this mouse model. METHODS: Colonic tissue was examined using histology and immunohistochemistry analyses. Tissue architecture was examined by haematoxylin and eosin (H&E), picrosirius red and immunohistochemical markers for α-smooth muscle actin (α-SMA), phospho-Smad 2/3 (pSmad2/3), Ki-67, protein gene product 9.5 and S-100. Fibrosis was quantified using the NIS Elements BR 2.30 system and by Sircol assay. Colonic strip contractile responses to potassium chloride (KCl) and carbachol were assessed in isolated organ baths. Confirmatory gut fibroblast and intestinal tissue biochemical assays, including cellular signalling mechanisms, were performed. RESULTS: H&E staining and staining for α-SMA, Ki-67, pSmad2/3 or neural tissue staining showed no differences between TG and wild-type (WT) mice gut tissue. There was increased collagen deposition in the gut of TG mice. Quantitative PCR results of TG gut fibroblasts showed evidence of up-regulated collagen and CTGF transcription, and non-canonical TGF-ß signalling pathways were also up-regulated. The organ bath studies showed diminished colonic strip contractility in TG mice compared with WT control mice to KCl and carbachol. CONCLUSION: We have shown that this TG mouse model, previously shown to develop skin and lung, develops colonic fibrosis with associated effects on colonic tissue contractility. This may offer further insight in pathological processes leading to the development of gut fibrosis.

CCN2 is required for bleomycin-induced skin fibrosis in mice.

OBJECTIVE: No therapy for fibrotic disease is available. The proadhesive matricellular protein connective tissue growth factor CCN2 is a marker of fibrotic cells; however, the specific role of CCN2 in connective tissue biology in general and in fibrogenesis in particular is unclear. The aim of this study was to assess whether adult mice bearing a smooth muscle cell/fibroblast-specific deletion of CCN2 are resistant to bleomycin-induced skin scleroderma. METHODS: Cutaneous fibrosis was induced in mice by subcutaneous injection of bleomycin. Untreated control groups were injected with phosphate buffered saline. Mice bearing a fibroblast/smooth muscle cell-specific deletion of CCN2 were investigated for changes in dermal thickness, collagen content, and the number of α-smooth muscle actin (α-SMA)-positive cells. Dermal fibroblasts were isolated to assess whether the induction of collagen and α-SMA messenger RNA in response to transforming growth factor ß (TGFß) was impaired. RESULTS: The loss of CCN2 resulted in resistance to bleomycin-induced skin fibrosis. In response to bleomycin, wild-type mice possessed, but CCN2-deficient mice lacked, abundant α-SMA-expressing myofibroblasts within fibrotic lesions. Fibroblast responses to TGFß, a potent inducer of myofibroblast differentiation, were not affected. Collectively, these results indicate that CCN2 is essential for bleomycin-induced skin fibrosis, likely due to a defect in myofibroblast recruitment. CONCLUSION: These data indicate that therapeutic strategies that involve blocking CCN2 in vivo may be of benefit in combating fibrotic skin disease.

GSK-3beta in mouse fibroblasts controls wound healing and fibrosis through an endothelin-1-dependent mechanism.

Glycogen synthase kinase-3 (GSK-3) is a widely expressed and highly conserved serine/threonine protein kinase encoded by 2 genes, GSK3A and GSK3B. GSK-3 is thought to be involved in tissue repair and fibrogenesis, but its role in these processes is currently unknown. To investigate the function of GSK-3beta in fibroblasts, we generated mice harboring a fibroblast-specific deletion of Gsk3b and evaluated their wound-healing and fibrogenic responses. We have shown that Gsk3b-conditional-KO mice (Gsk3b-CKO mice) exhibited accelerated wound closure, increased fibrogenesis, and excessive scarring compared with control mice. In addition, Gsk3b-CKO mice showed elevated collagen production, decreased cell apoptosis, elevated levels of profibrotic alpha-SMA, and increased myofibroblast formation during wound healing. In cultured Gsk3b-CKO fibroblasts, adhesion, spreading, migration, and contraction were enhanced. Both Gsk3b-CKO mice and fibroblasts showed elevated expression and production of endothelin-1 (ET-1) compared with control mice and cells. Antagonizing ET-1 reversed the phenotype of Gsk3b-CKO fibroblasts and mice. Thus, GSK-3beta appears to control the progression of wound healing and fibrosis by modulating ET-1 levels. These results suggest that targeting the GSK-3beta pathway or ET-1 may be of benefit in controlling tissue repair and fibrogenic responses in vivo.

Endothelin-1 in peripheral arterial disease: a potential role in muscle damage.

The evidence for the role of endothelin-1 (ET-1) in endothelial dysfunction and atherosclerosis has been growing since its discovery. However most studies have focussed on cardiac disease and its role in peripheral arterial disease (PAD) is less clear. In addition to its role in the development and progression of atherosclerotic lesions in lower limb arteries, there is evidence that ET-1 adversely affects microvessels within the muscle and the viability of the ischemic muscle itself. This review summarises some of these findings which underscore the potential use of ET antagonists as an adjunct in the treatment of PAD.

Selective expression of connective tissue growth factor in fibroblasts in vivo promotes systemic tissue fibrosis.

OBJECTIVE: Connective tissue growth factor (CTGF) is a cysteine-rich secreted matricellular protein involved in wound healing and tissue repair. Enhanced and prolonged expression of CTGF has been associated with tissue fibrosis in humans. However, questions remain as to whether CTGF expression alone is sufficient to drive fibrosis. This study was undertaken to investigate whether CTGF alone is sufficient to cause fibrosis in intact animals and whether its effects are mediated through activation of transforming growth factor beta (TGFbeta) signaling or through distinct signal transduction pathways. METHODS: We generated mice overexpressing CTGF in fibroblasts under the control of the fibroblast-specific collagen alpha2(I) promoter enhancer. Tissues such as skin, lung, and kidney were harvested for histologic analysis. Mouse embryonic fibroblasts were prepared from embryos (14.5 days postcoitum) for biochemical analysis. RESULTS: Mice overexpressing CTGF in fibroblasts were susceptible to accelerated tissue fibrosis affecting the skin, lung, kidney, and vasculature, most notably the small arteries. We identified a marked expansion of the myofibroblast cell population in the dermis. RNA analysis of transgenic dermal fibroblasts revealed elevated expression of key matrix genes, consistent with a fibrogenic response. CTGF induced phosphorylation of p38, ERK-1/2, JNK, and Akt, but not Smad3, in transgenic mouse fibroblasts compared with wild-type mouse fibroblasts. Transfection experiments showed significantly increased basal activity of the CTGF and serum response element promoters, and enhanced induction of the CTGF promoter in the presence of TGFbeta. CONCLUSION: These results demonstrate that selective expression of CTGF in fibroblasts alone causes tissue fibrosis in vivo through specific signaling pathways, integrating cues from the extracellular matrix into signal transduction pathways to orchestrate pivotal biologic responses relevant to tissue repair and fibrosis.

Regulation and function of connective tissue growth factor/CCN2 in tissue repair, scarring and fibrosis.

Connective tissue growth factor (CTGF, CCN2) is a secreted protein with major roles in angiogenesis, chondrogenesis, osteogenesis, tissue repair, cancer and fibrosis. It is a member of the CCN family of immediate-early gene products which are characterised by four discrete protein modules in which reside growth factor binding domains, functional motifs for integrin recognition, heparin and proteoglycan binding, and dimerization motifs. A primary function of CTGF is to modulate and coordinate signaling responses involving cell surface proteoglycans, key components of the extracellular matrix, and growth factors. Integration of these molecular cues regulates growth factor and receptor interactions, cell motility and mesenchymal cell activation and differentiation in tissue remodelling. Abnormal amplification of CTGF dependent signals results in a failure to terminate tissue repair, leading pathological scarring in conditions such as fibrosis and cancer.

Verteporfin inhibits the persistent fibrotic phenotype of lesional scleroderma dermal fibroblasts.

Fibrosis is perpetuated by an autocrine, pro-adhesive signaling loop maintained by the synthetic and contractile abilities of myofibroblasts and the stiff, highly-crosslinked extracellular matrix. Transcriptional complexes that are exquisitely responsive to mechanotransduction include the co-activator YAP1, which regulates the expression of members of the CCN family of matricellular proteins such as CCN2 and CCN1. Although selective YAP1 inhibitors exist, the effect of these inhibitors on profibrotic gene expression in fibroblasts is largely unknown, and is the subject of our current study. Herein, we use genome-wide expression profiling, real-time polymerase chain reaction and Western blot analyses, cell migration and collagen gel contraction assays to assess the ability of a selective YAP inhibitor verteporfin (VP) to block fibrogenic activities in dermal fibroblasts from healthy individual human controls and those from isolated from fibrotic lesions of patients with diffuse cutaneous systemic sclerosis (dcSSc). In control fibroblasts, VP selectively reduced expression of fibrogenic genes and also blocked the ability of TGFbeta to induce actin stress fibers in dermal fibroblasts. VP also reduced the persistent profibrotic phenotype of dermal fibroblasts cultured from fibrotic lesions of patients with dcSSc. Our results are consistent with the notion that, in the future, YAP1 inhibitors may represent a novel, valuable method of treating fibrosis as seen in dcSSc.

A polymorphism in the CTGF promoter region associated with systemic sclerosis.

BACKGROUND: Systemic sclerosis (scleroderma) is a life-threatening autoimmune disease that is characterized by the presence of specific autoantibodies and fibrosis of the skin and major internal organs. METHODS: We genotyped a polymorphism (G-945C) in the promoter of the connective-tissue growth factor (CTGF) gene in 1000 subjects in two groups: group 1, consisting of 200 patients with systemic sclerosis and 188 control subjects; and group 2, consisting of 300 patients with systemic sclerosis and 312 control subjects. The combined groups represented an estimated 10% of patients with systemic sclerosis in the United Kingdom. We tested the effect of the polymorphism on the transcription of CTGF. RESULTS: The GG genotype was significantly more common in patients with systemic sclerosis than in control subjects in both groups, with an odds ratio for the combined group of 2.2 (95% confidence interval [CI], 1.5 to 3.2; P<0.001 for trend). Analysis of the combined group of patients with systemic sclerosis showed a significant association between homozygosity for the G allele and the presence of anti-topoisomerase I antibodies (odds ratio, 3.3; 95% CI, 2.0 to 5.6; P<0.001) and fibrosing alveolitis (odds ratio, 3.1; 95% CI, 1.9 to 5.0; P<0.001). We observed that the substitution of cytosine for guanine created a binding site of the transcriptional regulators Sp1 and Sp3. The C allele has high affinity for Sp3 and is associated with severely reduced transcriptional activity. A chromatin immunoprecipitation assay showed a marked shift in the ratio of Sp1 to Sp3 binding at this region, demonstrating functional relevance in vivo. CONCLUSIONS: The G-945C substitution represses CTGF transcription, and the -945G allele is significantly associated with susceptibility to systemic sclerosis.

Modulation of collagen type I, fibronectin and dermal fibroblast function and activity, in systemic sclerosis by the antioxidant epigallocatechin-3-gallate.

OBJECTIVES: SSc is characterized by the overproduction of extracellular matrix (ECM) proteins, such as collagen and fibronectin, by activated fibroblasts, as well as oxidative stress. This study investigates the anti-fibrotic potential of the antioxidant epigallocatechin-3-gallate (EGCG) on activated dermal fibroblasts from SSc patients. METHODS: Dermal fibroblasts from a cell line (AG), healthy individuals (CON) and SSc patients were treated with EGCG, TGF-ß, PDGF-BB or other antioxidants [antioxidants superoxide dismutase (SOD), catalase, N-acetyl-L-cysteine (NAC) and diphenyleneiodonium (DPI)]. Collagen type I, fibronectin, connective tissue growth factor (CTGF), α-smooth muscle actin and mitogen-activated protein (MAP) kinases were measured by ELISA and western blot. Fibroblast contractile forces were measured by collagen gel contraction. Reactive oxygen species (ROS) were assessed by dichlorofluorescein assay and nuclear factor κ beta (NF-κB) activity by DNA binding assay. RESULTS: EGCG (1-100 µM) dose-dependently decreased collagen type I secretion in culture medium after 24 h in AG fibroblasts. Collagen type I protein expression in cell lysates was also significantly reduced by 40% in EGCG-treated cells (40 µM). Furthermore, EGCG also down-regulated TGF-ß-induced collagen type I, fibronectin and CTGF. Similarly, in CON fibroblasts EGCG decreased basal and stimulated collagen type I, fibronectin and CTGF after 24 h, while in SSc the effects of the antioxidant were apparent after 48 h. Fibroblast-mediated contraction of collagen gels was inhibited by EGCG as early as 1 h in AG fibroblasts, and in the CON and SSc fibroblasts. Additionally, EGCG also inhibited TGF-ß-stimulated gel contraction similar to other antioxidants DPI and NAC, but not SOD or catalase. EGCG suppressed TGF-ß-induced ROS production in all fibroblasts. Furthermore, EGCG inhibited TGF-ß or PDGF-BB-induced phospho-extracellular signal-regulated kinase (ERK)1/2 MAP kinase and NF-κB activity in SSc fibroblasts. CONCLUSION: The results suggest that the antioxidant, EGCG, can reduce ECM production, the fibrotic marker CTGF and inhibit contraction of dermal fibroblasts from SSc patients. Furthermore, EGCG was able to suppress intracellular ROS, ERK1/2 kinase signalling and NF-κB activity. Taken together, EGCG may be a possible candidate for therapeutic treatment aimed at reducing both oxidant stress and the fibrotic effects associated with SSc.

Rosiglitazone alleviates the persistent fibrotic phenotype of lesional skin scleroderma fibroblasts.

OBJECTIVE: The transcription factor peroxisome proliferator-activated receptor (PPAR)-gamma plays an important role in controlling cell differentiation. The aim of the present study was to examine whether PPAR-gamma expression was reduced in skin scleroderma fibroblasts and whether PPAR-gamma agonists could suppress the persistent fibrotic phenotype of skin scleroderma fibroblasts. METHODS: Dermal fibroblasts were isolated from site-, age- and sex-matched healthy individuals and lesional areas of individuals with dcSSc. Western blot and collagen gel contraction analyses were used to detect protein expression in the presence or absence of the PPAR-gamma agonist rosiglitazone. RESULTS: PPAR-gamma expression was reduced in dcSSc fibroblasts. The PPAR-gamma agonist rosiglitazone alleviated the persistent fibrotic phenotype of dcSSc fibroblasts. CONCLUSION: Rosiglitazone may alleviate the extent of fibrosis in dcSSc.

Constitutive ALK5-independent c-Jun N-terminal kinase activation contributes to endothelin-1 overexpression in pulmonary fibrosis: evidence of an autocrine endothelin loop operating through the endothelin A and B receptors.

The signal transduction mechanisms generating pathological fibrosis are almost wholly unknown. Endothelin-1 (ET-1), which is up-regulated during tissue repair and fibrosis, induces lung fibroblasts to produce and contract extracellular matrix. Lung fibroblasts isolated from scleroderma patients with chronic pulmonary fibrosis produce elevated levels of ET-1, which contribute to the persistent fibrotic phenotype of these cells. Transforming growth factor beta (TGF-beta) induces fibroblasts to produce and contract matrix. In this report, we show that TGF-beta induces ET-1 in normal and fibrotic lung fibroblasts in a Smad-independent ALK5/c-Jun N-terminal kinase (JNK)/Ap-1-dependent fashion. ET-1 induces JNK through TAK1. Fibrotic lung fibroblasts display constitutive JNK activation, which was reduced by the dual ETA/ETB receptor inhibitor, bosentan, providing evidence of an autocrine endothelin loop. Thus, ET-1 and TGF-beta are likely to cooperate in the pathogenesis of pulmonary fibrosis. As elevated JNK activation in fibrotic lung fibroblasts contributes to the persistence of the myofibroblast phenotype in pulmonary fibrosis by promoting an autocrine ET-1 loop, targeting the ETA and ETB receptors or constitutive JNK activation by fibrotic lung fibroblasts is likely to be of benefit in combating chronic pulmonary fibrosis.

CCN1 expression by fibroblasts is required for bleomycin-induced skin fibrosis.

The microenvironment contributes to the excessive connective tissue deposition that characterizes fibrosis. Members of the CCN family of matricellular proteins are secreted by fibroblasts into the fibrotic microenvironment; however, the role of endogenous CCN1 in skin fibrosis is unknown. Mice harboring a fibroblast-specific deletion for CCN1 were used to assess if CCN1 contributes to dermal homeostasis, wound healing, and skin fibrosis. Mice with a fibroblast-specific CCN1 deletion showed progressive skin thinning and reduced accumulation of type I collagen; however, the overall mechanical property of skin (Young's modulus) was not significantly reduced. Real time-polymerase chain reaction analysis revealed that CCN1-deficient skin displayed reduced expression of mRNAs encoding enzymes that promote collagen stability (including prolyl-4-hydroxylase and PLOD2), although expression of COL1A1 mRNA was unaltered. CCN1-deficent skin showed reduced hydroxyproline levels. Electron microscopy revealed that collagen fibers were disorganized in CCN1-deficient skin. CCN1-deficient mice were resistant to bleomycin-induced skin fibrosis, as visualized by reduced collagen accumulation and skin thickness suggesting that deposition/accumulation of collagen is impaired in the absence of CCN1. Conversely, CCN1-deficient mice showed unaltered wound closure kinetics, suggesting de novo collagen production in response to injury did not require CCN1. In response to either wounding or bleomycin, induction of α-smooth muscle actin-positive myofibroblasts was unaffected by loss of CCN1. CCN1 protein was overexpressed by dermal fibroblasts isolated from lesional (i.e., fibrotic) areas of patients with early onset diffuse scleroderma. Thus, CCN1 expression by fibroblasts, being essential for skin fibrosis, is a viable anti-fibrotic target.

Fibroblast adhesion results in the induction of a matrix remodeling gene expression program.

Fibrosis is believed to occur through the failure to terminate the normal tissue remodeling program. Tissue repair intimately involves the ability of fibroblasts to attach to extracellular matrix (ECM), resulting in cell migration and ECM contraction. Elevated, activated adhesive signaling is a key phenotypic hallmark of fibrotic cells. The precise contribution of adhesion to tissue remodeling and repair and fibrotic responses in fibroblasts is unclear, but involves focal adhesion kinase (FAK). FAK signals downstream of integrin-mediates attachment of fibroblasts to extracellular matrix. In this report, we show that FAK is required for the expression of a cohort of mRNAs encoding ECM and matrix remodeling genes including CCN2, alpha-smooth muscle actin (SMA) and type I collagen. Adhesion of fibroblasts to fibronectin, a component of the provisional matrix deposited in the initial phases of tissue repair, also resulted in the induction of CCN2, alpha-SMA and type I collagen mRNAs. Endothelin-1 (ET-1), a key inducer of pro-fibrotic gene expression, was also induced upon fibroblast attachment to ECM, and antagonism of the ET-1 receptors significantly reduced the ability of adhesion to induce expression of CCN2, alpha-SMA and type I collagen mRNAs. These results suggest that adhesion of fibroblasts to matrix during the initial phases of tissue remodeling and repair may actively contribute to the tissue repair program through the induction of pro-fibrotic gene expression.

Endogenous endothelin-1 signaling contributes to type I collagen and CCN2 overexpression in fibrotic fibroblasts.

Fibrosis is excessive scarring caused by the accumulation of extracellular matrix proteins and is a common end pathway in many chronic diseases. Endothelin-1 is a possible contributor to the persistent fibrotic phenotype of fibroblasts isolated from fibrotic lesions. In this report we used a specific dual endothelin A/B receptor antagonist, bosentan, to determine the role of endogenous endothelin signaling in maintaining the profibrotic phenotype of lung fibroblasts from scleroderma patients. Bosentan treatment of lung fibroblasts cultured from normal individuals and individuals with scleroderma was assessed using Affymetrix genome-wide expression profiling, real-time polymerase chain reaction and Western blot analysis and revealed that approximately one-third of the transcripts elevated greater than two-fold in fibrotic fibroblasts were reduced by Bosentan treatment. Genes whose overexpression in fibrotic fibroblasts that were dependent on endogenous endothelin signaling included the matrix or matrix-associated genes type I collagen, fibronectin and CCN2. The elevated adhesive property of fibrotic fibroblasts was also reduced by endothelin receptor antagonism. Basal expression of collagen, fibronectin and CCN2 and adhesion to matrix was not affected. Thus endogenous endothelin signaling contributes to the fibrotic phenotype of fibrotic fibroblasts, suggesting that antagonizing endothelin receptors may be of benefit in combating fibrotic disease.

Effect of nitric oxide and peroxynitrite on type I collagen synthesis in normal and scleroderma dermal fibroblasts.

Nitric oxide ((.-)NO) is an important physiological signaling molecule and potent vasodilator. Recently, we have shown abnormal (.-)NO metabolism in the plasma of patients with systemic sclerosis (SSc), a disease that features excessive collagen overproduction as well as vascular dysfunction. The current study investigates the effects of (.-)NO and peroxynitrite (ONOO(-)) on secretion of type I collagen by SSc dermal fibroblasts, compared with those from normal dermal fibroblasts (CON) and a dermal fibroblast cell line (AG). Dermal fibroblasts were incubated with (.-)NO donors (SNP, DETA-NONOate) with or without the antioxidant ascorbic acid, or ONOO(-) for 24-72 h. In CON and AG fibroblasts, type I collagen was dose dependently decreased by SNP or DETA-NONOate. However, (.-)NO had no effect in SSc fibroblasts. Furthermore, the inhibition of collagen synthesis by (.-)NO was reversed by ascorbic acid and was not affected by 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanyl cyclase, or 8-bromoguanosine cyclic 3',5'-monophosphate, a cGMP agonist. SNP also showed a significant up-regulation of matrix metalloproteinase-1 (MMP-1) protein and activity levels, an essential collagenase involved in collagen degradation, in the AG fibroblasts. Additionally, (.-)NO-treated fibroblasts had lower prolyl hydroxylase activity, an enzyme important in the post-translational processing of collagen, while there was no effect on total protein levels. There were no significant effects on type I collagen levels when dermal fibroblasts were treated with ONOO(-). Taken together, ()NO inhibits collagen secretion in normal dermal fibroblasts but regulation is lost in SSc fibroblasts, while ONOO(-) itself is ineffective. (.-)NO inhibition of collagen was by cGMP-independent regulatory mechanisms and in part may be due to up-regulation of MMP-1 and/or inhibition of prolyl hydroxylase. These differences may contribute to the observed pathology of SSc.

CCN2 (connective tissue growth factor) promotes fibroblast adhesion to fibronectin.

In vivo, CCN2 (connective tissue growth factor) promotes angiogenesis, osteogenesis, tissue repair, and fibrosis, through largely unknown mechanisms. In vitro, CCN2 promotes cell adhesion in a variety of systems via integrins and heparin sulfate proteoglycans (HSPGs). However, the physiological relevance of CCN2-mediated cell adhesion is unknown. Here, we find that HSPGs and the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase cascade are required for adult human dermal fibroblasts to adhere to CCN2. Endogenous CCN2 directly binds fibronectin and the fibronectin receptors integrins alpha4 beta1 and alpha5 and syndecan 4. Using Ccn2-/- mouse embryonic fibroblasts, we show that loss of endogenous CCN2 results in impaired spreading on fibronectin, delayed alpha-smooth muscle actin stress fiber formation, and reduced ERK and focal adhesion kinase phosphorylation. These results suggest that a physiological role of CCN2 is to potentiate the ability of fibroblasts to spread on fibronectin, which may be important in modulating fibroblast adhesion to the provisional matrix during tissue development and wound healing. These results are consistent with the notion that a principal function of CCN2 is to modulate receptor/ligand interactions in vivo.