ABSTRACT: The factors responsible for maintaining persistent organ fibrosis in systemic sclerosis (SSc) are not known but emerging evidence implicates toll-like receptors (TLRs) in the pathogenesis of SSc. Here we show the expression, mechanism of action and pathogenic role of endogenous TLR activators in skin from patients with SSc, skin fibroblasts, and in mouse models of organ fibrosis. Levels of tenascin-C are elevated in SSc skin biopsy samples, and serum and SSc fibroblasts, and in fibrotic skin tissues from mice. Exogenous tenascin-C stimulates collagen gene expression and myofibroblast transformation via TLR4 signalling. Mice lacking tenascin-C show attenuation of skin and lung fibrosis, and accelerated fibrosis resolution. These results identify tenascin-C as an endogenous danger signal that is upregulated in SSc and drives TLR4-dependent fibroblast activation, and by its persistence impedes fibrosis resolution. Disrupting this fibrosis amplification loop might be a viable strategy for the treatment of SSc.
Project description:Systemic sclerosis (SSc) is a poorly understood heterogeneous condition with progressive multi-organ fibrosis. Recent genetic and genomic evidence suggest a pathogenic role for dysregulated innate immunity and toll-like receptor (TLR) activity in SSc. Levels of both TLR4, as well as certain endogenous TLR ligands, are elevated in skin and lung tissues from patients with SSc and correlate with clinical disease parameters. Conversely, genetic targeting of TLR4 or its endogenous "damage-associated" ligands ameliorates progressive tissue fibrosis. Targeting TLR4 signaling therefore represents a pharmacological strategy to prevent intractable fibrosis. We examined the effect of TAK242, a small molecule TLR4 inhibitor, in preclinical fibrosis models and in SSc fibroblasts. TAK242 treatment prevented, promoted regression of, bleomycin-induced dermal and pulmonary fibrosis, and reduced the expression of several pro-fibrotic mediators. Furthermore, TAK242 ameliorated peritoneal fibrosis and reduced spontaneous hypodermal thickness in TSK/+ mice. Importantly, TAK242 abrogated collagen synthesis and myofibroblasts differentiation in explanted constitutively active SSc fibroblast. Altogether, these findings identify TAK242 as an anti-fibrotic agent in preclinical models of organ fibrosis. TAK242 might potentially represent a novel strategy for the treatment of SSc and other fibrotic diseases.
Project description:Persistent fibrosis in multiple organs is the hallmark of systemic sclerosis (SSc). Recent genetic and genomic studies implicate TLRs and their damage-associated molecular pattern (DAMP) endogenous ligands in fibrosis. To test the hypothesis that TLR4 and its coreceptor myeloid differentiation 2 (MD2) drive fibrosis persistence, we measured MD2/TLR4 signaling in tissues from patients with fibrotic SSc, and we examined the impact of MD2 targeting using a potentially novel small molecule. Levels of MD2 and TLR4, and a TLR4-responsive gene signature, were enhanced in SSc skin biopsies. We developed a small molecule that selectively blocks MD2, which is uniquely required for TLR4 signaling. Targeting MD2/TLR4 abrogated inducible and constitutive myofibroblast transformation and matrix remodeling in fibroblast monolayers, as well as in 3-D scleroderma skin equivalents and human skin explants. Moreover, the selective TLR4 inhibitor prevented organ fibrosis in several preclinical disease models and mouse strains, and it reversed preexisting fibrosis. Fibroblast-specific deletion of TLR4 in mice afforded substantial protection from skin and lung fibrosis. By comparing experimentally generated fibroblast TLR4 gene signatures with SSc skin biopsy gene expression datasets, we identified a subset of SSc patients displaying an activated TLR4 signature. Together, results from these human and mouse studies implicate MD2/TLR4-dependent fibroblast activation as a key driver of persistent organ fibrosis. The results suggest that SSc patients with high TLR4 activity might show optimal therapeutic response to selective inhibitors of MD2/TLR4 complex formation.
Project description:The Insulin-like growth factor (IGF) system plays an important role in variety cellular biological functions; we previously reported levels of IGF binding proteins (IGFBP) -3 and -5 are increased in dermal and pulmonary fibrosis associated with the prototypic fibrosing disease systemic sclerosis (SSc), induce extracellular matrix (ECM) production, and promote fibrosis. We sought to examine the effects of another member of the family, IGFBP-4, on ECM production and fibrosis using cell-based, ex vivo organ culture and in vivo mouse lung fibrosis models. IGFBP-4 mRNA levels were significantly decreased in pulmonary fibroblasts of patients with SSc. ECM components were significantly reduced by endogenous and exogenous IGFBP-4. IGFBP-4 also blocked TGF?-induced ECM production, and inhibited ECM production ex vivo in human lung and skin in organ culture. In vivo, IGFBP-4 reduced bleomycin-induced collagen production and histologic evidence of fibrosis. Silencing IGFBP-4 expression to mimic levels observed in SSc lung fibroblasts resulted in increased ECM production. IGFBP-4 reduced mRNA and protein levels of the chemokine receptor CXCR4 and the pro-fibrotic factor CTGF. Further, CTGF silencing potentiated the anti-fibrotic effects of IGFBP-4. Reduced IGFBP-4 levels in SSc lung fibroblasts may contribute to the fibrotic phenotype via loss of IGFBP-4 anti-fibrotic activity.
Project description:Skin fibrosis in systemic sclerosis (SSc) is accompanied by attrition of dermal white adipose tissue (dWAT) and reduced levels of circulating adiponectin. Since adiponectin has potent regulatory effects on fibroblasts, we sought to assess adiponectin signaling in SSc skin biopsies, and evaluate fibrosis in mice with adiponectin gain- and loss-of-function mutations. Furthermore, we investigated the effects and mechanism of action of agonist peptides targeting adiponectin receptors in vitro and in vivo. We found that adiponectin pathway activity was significantly reduced in a subset of SSc skin biopsies. Mice lacking adiponectin mounted an exaggerated dermal fibrotic response, while transgenic mice with constitutively elevated adiponectin showed selective dWAT expansion and protection from skin and peritoneal fibrosis. Adiponectin receptor agonists abrogated ex vivo fibrotic responses in explanted normal and SSc fibroblasts and in 3D human skin equivalents, in part by attenuating focal adhesion complex assembly, and prevented and reversed experimentally-induced organ fibrosis in mice. These results implicate aberrant adiponectin pathway activity in skin fibrosis, identifying a novel function for this pleiotropic adipokine in regulation of tissue remodeling. Restoring adiponectin signaling in SSc patients therefore might represent an innovative pharmacological strategy for intractable organ fibrosis.
Project description:Constitutive fibroblast activation is responsible for organ fibrosis in fibrotic disorders including systemic sclerosis (SSc), but the underlying mechanisms are not fully understood, and effective therapies are lacking. We investigated the expression of the mitochondrial deacetylase sirtuin 3 (SIRT3) and its modulation by hexafluoro, a novel fluorinated synthetic honokiol analogue, in the context of fibrosis. We find that augmenting cellular SIRT3 by forced expression in normal lung and skin fibroblasts, or by hexafluoro treatment, blocked intracellular TGF-ß signaling and fibrotic responses, and mitigated the activated phenotype of SSc fibroblasts. Moreover, hexafluoro attenuated mitochondrial and cytosolic reactive oxygen species (ROS) accumulation in TGF-?-treated fibroblasts. Remarkably, we found that the expression of SIRT3 was significantly reduced in SSc skin biopsies and explanted fibroblasts, and was suppressed by TGF-? treatment in normal fibroblasts. Moreover, tissue levels of acetylated MnSOD, a sensitive marker of reduced SIRT3 activity, were dramatically enhanced in lesional skin and lung biopsies from SSc patients. Mice treated with hexafluoro showed substantial attenuation of bleomycin-induced fibrosis in the lung and skin. Our findings reveal a cell-autonomous function for SIRT3 in modulating fibrotic responses, and demonstrate the ability of a novel pharmacological SIRT3 agonist to attenuate fibrosis in vitro and in vivo. In light of the impaired expression and activity of SIRT3 associated with organ fibrosis in SSc, pharmacological approaches for augmenting SIRT3 might have therapeutic potential.
Project description:Systemic sclerosis (SSc) is a multi-organ fibrotic disease with few treatment options. Activated fibroblasts are the key effector cells in SSc responsible for the excessive production of collagen and the development of fibrosis. Platelet-derived growth factor (PDGF), a potent mitogen for cells of mesenchymal origin, has been implicated in the activation of SSc fibroblasts. Our aim was to examine the therapeutic potential of crenolanib, an inhibitor of PDGF receptor signaling, in cultured fibroblasts and in angiotensin II-induced skin and heart fibrosis. Crenolanib effectively inhibited proliferation and migration of SSc and healthy control fibroblasts and attenuated basal and transforming growth factor-?-induced expression of CCN2/CTGF and periostin. In contrast to healthy control fibroblasts, SSc fibroblasts proliferated in response to PDGFAA, whereas a combination of PDGFAA and CCN2 was required to elicit a similar response in healthy control fibroblasts. PDGF receptor ? mRNA correlated with CCN2 and other fibrotic markers in the skin of SSc patients. In mice challenged with angiotensin II, PDGF receptor ?-positive cells were increased in the skin and heart. These PDGF receptor ?-positive cells co-localized with PDGF receptor ?, procollagen, and periostin. Treatment with crenolanib attenuated the skin and heart fibrosis. Our data indicate that inhibition of PDGF signaling presents an attractive therapeutic approach for SSc.
Project description:The mechanisms underlying persistent fibroblast activation and myofibroblast phenoconversion in underlying multi-organ fibrosis in systemic sclerosis (SSc) remain incompletely understood, hindering effective therapies to slow or reverse the process. Cyclin-dependent kinase 5 (CDK5) is a pleiotropic member of the CDK family originally identified in neuronal cells. In contrast to other CDKs, CDK5 activity depends on its CDK5R1 subunit p35. Here we demonstrate that expression of p35 and CDK5 activity are induced by TGF-ß in fibroblasts and adipocytic cell types. Levels of p35 are markedly elevated in both SSc skin biopsies and explanted SSc fibroblasts, as well as in fibrotic skin in mice. Ectopic p35 and CDK5 suppressed adipogenic markers while stimulating collagen production and myofibroblast markers, whereas RNAi-mediated CDK5 knockdown abrogated TGF-? fibrotic responses in a Smad-independent manner. Pharmacological inhibitors of CDK5 likewise prevented and reversed TGF-? responses in fibroblast monolayers and in ex vivo human skin organ cultures, ameliorated collagen overproduction in SSc fibroblasts, and prevented and reversed skin fibrosis in two distinct mouse models of SSc. Together, these results reveal a previously unrecognized key function for p35/CDK5 as a mediator of mesenchymal cell fibrotic responses. The results suggest a potential pathogenic role for elevated p35 expression and CDK5 activity in SSc, and raise the possibility that their selective pharmacological targeting might represent a novel treatment approach in fibrosis.
Project description:The crucial role of innate immunity in the pathogenesis of systemic sclerosis (SSc) is well established, and in the past few years the hypothesis that Toll-like receptor 4 (TLR4) activation induced by endogenous ligands is involved in fibrogenesis has been supported by several studies on skin, liver, and kidney fibrosis. These findings suggest that TLR4 activation can enhance transforming growth factor beta (TGF-?) signaling, providing a potential mechanism for TLR4/Myeloid differentiation factor 88 (MyD88)-dependent fibrosis.The expression of TLR4, CD14 and MD2 genes was analyzed by real-time polymerase chain reaction from skin biopsies of 24 patients with diffuse cutaneous SSc. In order to investigate the effects of the chronic skin exposure to endotoxin (Lipopolysaccharide (LPS)) in vivo we examined the expression of inflammation, TGF-? signaling and cellular markers genes by nanostring. We also identified cellular subsets by immunohistochemistry and flow cytometry.We found that TLR4 and its co-receptors, MD2 and CD14, are over-expressed in lesional skin from patients with diffuse cutaneous SSc, and correlate significantly with progressive or regressive skin disease as assessed by the Delta Modified Rodnan Skin Score. In vivo, a model of chronic dermal LPS exposure showed overexpression of proinflammatory chemokines, recruitment and activation of macrophages, and upregulation of TGF-? signature genes.We delineated the role of MyD88 as necessary for the induction not only for the early phase of inflammation, but also for pro-fibrotic gene expression via activation of macrophages. Chronic LPS exposure might be a model of early stage of SSc when inflammation and macrophage activation are important pathological features of the disease, supporting a role for innate immune activation in SSc skin fibrosis.
Project description: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.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.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.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.
Project description:: Systemic sclerosis (SSc) is a complex multi-system autoimmune disease characterized by immune dysregulation, vasculopathy, and organ fibrosis. Skin fibrosis causes high morbidity and impaired quality of life in affected individuals. Animal models do not fully recapitulate the human disease. Thus, there is a critical need to identify ex vivo models for the dermal fibrosis characteristic of SSc. We identified genes regulated by the pro-fibrotic factor TGF? in human skin maintained in organ culture. The molecular signature of human skin overlapped with that which was identified in SSc patient biopsies, suggesting that this model recapitulates the dermal fibrosis characteristic of the human disease. We further characterized the regulation and functional impact of a previously unreported gene in the setting of dermal fibrosis, COL22A1, and show that silencing COL22A1 significantly reduced TGF?-induced ACTA2 expression. COL22A1 expression was significantly increased in dermal fibroblasts from patients with SSc. In summary, we identified the molecular fingerprint of TGF? in human skin and demonstrated that COL22A1 is associated with the pathogenesis of fibrosis in SSc as an early response gene that may have important implications for fibroblast activation. Further, this model will provide a critical tool with direct relevance to human disease to facilitate the assessment of potential therapies for fibrosis.