CXCR3A promotes the secretion of the antifibrotic decoy receptor sIL-13Rα2 by pulmonary fibroblasts.

CXC chemokine receptor 3 (CXCR3) A and its IFN-inducible ligands CXCL9 and CXCL10 regulate vascular remodeling and fibroblast motility. IL-13 is a profibrotic cytokine implicated in the pathogenesis of inflammatory and fibroproliferative conditions. Previous work from our laboratory has shown that CXCR3A is negatively regulated by IL-13 and is necessary for the basal regulation of the IL-13 receptor subunit IL-13Rα2. This study investigates the regulation of fibroblast phenotype, function, and downstream IL-13 signaling by CXCR3A in vitro. CXCR3A was overexpressed via transient transfection. CXCR3A-/- lung fibroblasts were isolated for functional analysis. Additionally, the contribution of CXCR3A to tissue remodeling following acute lung injury was assessed in vivo with wild-type (WT) and CXCR3-/- mice challenged with IL-13. CXCR3 and IL-13Rα2 displayed a reciprocal relationship after stimulation with either IL-13 or CXCR3 ligands. CXCR3A reduced expression of fibroblast activation makers, soluble collagen production, and proliferation. CXCR3A enhanced the basal expression of pERK1/2 while inducing IL-13-mediated downregulation of NF-κB-p65. CXCR3A-/- pulmonary fibroblasts were increasingly proliferative and displayed reduced contractility and α-smooth muscle actin expression. IL-13 challenge regulated expression of the CXCR3 ligands and soluble IL-13Rα2 levels in lungs and bronchoalveolar lavage fluid (BALF) of WT mice; this response was absent in CXCR3-/- mice. Alveolar macrophage accumulation and expression of genes involved in lung remodeling was increased in CXCR3-/- mice. We conclude that CXCR3A is a central antifibrotic factor in pulmonary fibroblasts, limiting fibroblast activation and reducing extracellular matrix (ECM) production. Therefore, targeting of CXCR3A may be a novel approach to regulating fibroblast activity in lung fibrosis and remodeling.

Novel differences in gene expression and functional capabilities of myofibroblast populations in idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF), a chronic progressive interstitial pneumonia, is characterized by excessive fibroproliferation. Key effector cells in IPF are myofibroblasts that are recruited from three potential sources: resident fibroblasts, fibrocytes, and epithelial cells. We hypothesized that IPF myofibroblasts from different sources display unique gene expression differences and distinct functional characteristics. Primary human pulmonary fibroblasts (normal and IPF), fibrocytes, and epithelial cells were activated using the profibrotic factors TGF-ß and TNF-α. The resulting myofibroblasts were characterized using cell proliferation, soluble collagen, and contractility assays, ELISA, and human fibrosis PCR arrays. Genes of significance in human whole lung were validated by immunohistochemistry on human lung sections. Fibroblast-derived myofibroblasts exhibited the greatest increase in expression of profibrotic genes and genes involved in extracellular matrix remodeling and signal transduction. Functional studies demonstrated that myofibroblasts derived from fibrocytes expressed mostly soluble collagen and chemokine (C-C) motif ligand (CCL) 18 but were the least proliferative of the myofibroblast progeny. Activated IPF fibroblasts displayed the highest levels of contractility and CCL2 production. This study identified novel differences in gene expression and functional characteristics of different myofibroblast populations. Further investigation into the myofibroblast phenotype may lead to potential therapeutic targets in future IPF research.

CXCL9 Regulates TGF-ß1-Induced Epithelial to Mesenchymal Transition in Human Alveolar Epithelial Cells.

Epithelial to mesenchymal cell transition (EMT), whereby fully differentiated epithelial cells transition to a mesenchymal phenotype, has been implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF). CXCR3 and its ligands are recognized to play a protective role in pulmonary fibrosis. In this study, we investigated the presence and extent of EMT and CXCR3 expression in human IPF surgical lung biopsies and assessed whether CXCR3 and its ligand CXCL9 modulate EMT in alveolar epithelial cells. Coexpression of the epithelial marker thyroid transcription factor-1 and the mesenchymal marker α-smooth muscle actin and CXCR3 expression was examined by immunohistochemical staining of IPF surgical lung biopsies. Epithelial and mesenchymal marker expression was examined by quantitative real-time PCR, Western blotting, and immunofluorescence in human alveolar epithelial (A549) cells treated with TGF-ß1 and CXCL9, with Smad2, Smad3, and Smad7 expression and cellular localization examined by Western blotting. We found that significantly more cells were undergoing EMT in fibrotic versus normal areas of lung in IPF surgical lung biopsy samples. CXCR3 was expressed by type II pneumocytes and fibroblasts in fibrotic areas in close proximity to cells undergoing EMT. In vitro, CXCL9 abrogated TGF-ß1-induced EMT. A decrease in TGF-ß1-induced phosphorylation of Smad2 and Smad3 occurred with CXCL9 treatment. This was associated with increased shuttling of Smad7 from the nucleus to the cytoplasm where it inhibits Smad phosphorylation. This suggests a role for EMT in the pathogenesis of IPF and provides a novel mechanism for the inhibitory effects of CXCL9 on TGF-ß1-induced EMT.

Modulation of pulmonary fibrosis by IL-13Rα2.

Pulmonary fibrosis is a progressive and fatal disease that involves the remodeling of the distal airspace and the lung parenchyma, which results in compromised gas exchange. The median survival time once diagnosed is less than three years. Interleukin (IL)-13 has been shown to play a role in a number of inflammatory and fibrotic diseases. IL-13 modulates its effector functions via a complex receptor system that includes the IL-4 receptor (R) α, IL-13Rα1, and the IL-13Rα2. IL-13Rα1 binds IL-13 with low affinity, yet, when it forms a complex with IL-4α, it binds with much higher affinity, inducing the effector functions of IL-13. IL-13Rα2 binds IL-13 with high affinity but has a short cytoplasmic tail and has been shown to act as a nonsignaling decoy receptor. Transfection of fibroblasts and epithelial cells with IL-13Rα2 inhibited the IL-13 induction of soluble collagen, TGF-ß, and CCL17. Adenoviral overexpression of IL-13Rα2 in the lung reduced bleomycin-induced fibrosis. Our work shows that overexpression of IL-13Rα2 inhibits the IL-13 induction of fibrotic markers in vitro and inhibits bleomycin-induced pulmonary fibrosis. In summary our study highlights the antifibrotic nature of IL-13Ra2.

CXCR3 Requirement for the Interleukin-13-Mediated Up-Regulation of Interleukin-13Rα2 in Pulmonary Fibroblasts.

Idiopathic pulmonary fibrosis (IPF) is a progressive disease characterized by fibrosis and abnormal vascularity. IL-13, a profibrotic cytokine that plays a role in IPF, functions through the Jak/STAT pathway after binding to the IL-13 receptor α1 (IL-13Rα1)/IL-4Rα complex. IL-13 also binds to IL-13Rα2, which has been thought to function as a nonsignaling decoy receptor, although possible signaling roles of this receptor have been proposed. CXCR3 and its IFN-inducible ligands-CXCL9, CXCL10, and CXCL11-have been implicated in vascular remodeling and fibroblast motility during the development of IPF. In this study, CXCR3 expression was demonstrated in cultured pulmonary fibroblasts from wild-type BALB/c mice and was found to be necessary for the IL-13-mediated gene and protein up-regulation of IL-13Rα2. In fibroblasts from CXCR3-deficient mice, STAT6 activation was prolonged. This study is the first to demonstrate the expression of CXCR3 in fibroblasts and its association with the expression of IL-13Rα2. Taken together, the results from this study point strongly to a requirement for CXCR3 for IL-13-mediated IL-13Rα2 gene expression. Understanding the function of CXCR3 in IL-13-mediated lung injury may lead to novel approaches to combat the development of pulmonary fibrosis, whether by limiting the effects of IL-13 or by manipulation of angiostatic pathways. The elucidation of the complex relationship between these antifibrotic receptors and manipulation of the CXCR3-mediated regulation of IL-13Rα2 may represent a novel therapeutic modality in cases of acute lung injury or chronic inflammation that may progress to fibrosis.

Connective tissue growth factor is increased in pseudoexfoliation glaucoma.

PURPOSE: Pseudoexfoliation (PXF) syndrome is a generalized disorder of the extracellular matrix (ECM) involving the trabecular meshwork (TM), associated with raised intraocular pressure, glaucoma, and cataract. The purposes of this study were to quantify aqueous humor connective tissue growth factor (CTGF) in PXF glaucoma, to determine the effect of CTGF on ECM production in TM cells, and to identify intracellular CTGF signaling pathways. METHODS: Aqueous humor samples were obtained from patients undergoing routine cataract surgery or trabeculectomy. CTGF levels were quantified by ELISA. The effect of CTGF on fibrillin-1 expression in TM cells was investigated by real-time PCR. Western immunoblot analysis was used to investigate CTGF signaling. c-Jun/AP-1 activation was measured in CHO cells by ELISA after stimulation with CTGF. RESULTS: PXF with glaucoma had the highest aqueous humor level of CTGF (n = 18; 5.15 ± 0.79 ng/mL [SEM]; P < 0.01) compared with PXF without glaucoma (n = 15; 2.76 ± 0.64 ng/mL), primary open-angle glaucoma (POAG; n = 20; 3.05 ± 0.40 ng/mL), and the control (n = 21; 2.60 ± 0.29 ng/mL). In vitro exposure of TM cells to CTGF resulted in a 50% upregulation of fibrillin-1, which was partially blocked with the MEK (mitogen-activated protein extracellular kinase) inhibitor PD098059. Western blot analysis demonstrated increased phosphorylation of p42/44 MAPK, p38 MAPK, and the JNK pathways in response to CTGF. c-Jun/AP-1 activity was significantly increased in response to CTGF treatment. CONCLUSIONS: Increased levels of CTGF in the aqueous humor of PXF patients likely has pathologic significance through increased production of fibrillin-1 by TM cells through activation of p42/44 MAPK, p38 MAPK, and JNK pathways.

Chordin-like 1, a bone morphogenetic protein-4 antagonist, is upregulated by hypoxia in human retinal pericytes and plays a role in regulating angiogenesis.

PURPOSE: Pericytes play a specialized role in regulating angiogenesis and vascular function by providing vascular stability and controlling endothelial cell proliferation. Disorders in pericyte function and pericyte-endothelial interaction have been observed in several disease states including tumor angiogenesis and diabetic microangiopathy. In ischemic retinal disease, hypoxia is a potent driver of retinal angiogenesis. This study investigated the effects of hypoxia on retinal pericyte gene expression, and demonstrates a role in angiogenesis regulation for the hypoxia driven gene, chordin-like 1 (CHL-1). METHODS: In the current studies, we investigated hypoxia-induced gene expression in human retinal pericytes and found that expression of CHL-1, a member of the bone morphogenetic protein (BMP) superfamily, is upregulated by hypoxia. We investigated regulation of CHL-1 expression and the ability of CHL-1 to antagonize the antiangiogenic properties of BMP-4 using a human cell-based angiogenesis assay. RESULTS: We report that hypoxia induced hypoxia inducible factor-1alpha-driven expression of CHL-1. Both CHL-1 and BMP-4 were secreted from human retinal pericytes. We found that CHL-1 complexes with BMP-4 to antagonize the antiangiogenic effects of BMP-4, and that BMP-4 and vascular endothelial growth factor (VEGF) co-regulate angiogenesis. CONCLUSIONS: We propose that hypoxia-induced upregulation of CHL-1 alters the homeostatic balance between BMP-4 and VEGF to synergize with VEGF in driving retinal angiogenesis.

The role of gremlin, a BMP antagonist, and epithelial-to-mesenchymal transition in proliferative vitreoretinopathy.

PURPOSE: Proliferative vitreoretinopathy (PVR), a major reason for failure of retinal detachment surgery, is characterized by the formation of scarlike tissue that contains transdifferentiated retinal pigment epithelial (RPE) cells. The scar tissue occurs in response to growth factors such as transforming growth factor (TGF)-beta and epidermal growth factor (EGF). The authors postulate that transdifferentiation of RPE cells may arise via epithelial-to-mesenchymal transition (EMT). Bone morphogenetic proteins (BMPs) are expressed in the retina and have an antiproliferative role. Gremlin is expressed in the outer retina and is a BMP antagonist. The study was conducted to establish a model of PVR by inducing EMT in the human RPE cell line ARPE-19, using TGF-beta and EGF and to establish the contribution of gremlin to EMT. METHODS: ARPE-19 cells were cultured and stimulated with TGF-beta1, EGF, and gremlin. The expression of alpha-smooth muscle actin (alpha-SMA), vimentin, and zona occludens (ZO)-1 were examined via PCR, Western blot analysis, and immunofluorescence. Zymography was performed for matrix metalloproteinase (MMP) activity. Scratch assays were performed to assess migration. RESULTS: A model of EMT was established in the ARPE-19 cell line. The characteristics of EMT include gain of alpha-SMA, loss of ZO-1, upregulation of MMP activity and enhanced migration. Gremlin plays an important role in this process, contributing to the gain of alpha-SMA, loss of ZO-1, and upregulation of MMP activity. CONCLUSIONS: EMT occurs in vitro in the ARPE-19 cell line in response to the growth factors TGF-beta1 and EGF. EMT is also induced by Gremlin.

Transcription factor NFIC undergoes N-glycosylation during early mammary gland involution.

Expression of a 74-kDa nuclear factor I (NFI) protein is triggered in early involution in the mouse mammary gland, and its expression correlates with enhanced occupation of a twin (NFI) binding element in the clusterin promoter, a gene whose transcription is induced at this time (Furlong, E. E., Keon, N. K., Thornton, F. D., Rein, T., and Martin, F. (1996) J. Biol. Chem. 271, 29688-29697). We now identify this 74-kDa NFI as an NFIC isoform based on its interaction in Western analysis with two NFIC-specific antibodies. A transition from the expression of a 49-kDa NFIC in lactation to the expression of the 74-kDa NFIC in early involution is demonstrated. We show that the 74-kDa NFIC binds specifically to concanavalin A (ConA) and that this binding can be reversed by the specific ConA ligands, methyl alpha-D-mannopyranoside and methyl alpha-D-glucopyranoside. In addition, its apparent molecular size was reduced to approximately 63 kDa by treatment with the peptide N-glycosidase. The 49-kDa lactation-associated NFIC did not bind ConA nor was it affected by peptide N-glycosidase. Tunicamycin, a specific inhibitor of N-glycosylation, blocked formation of the 74-kDa NFI in involuting mouse mammary gland in vivo when delivered from implanted Elvax depot pellets. Finally, the production of the ConA binding activity could be reiterated in "mammospheres" formed from primary mouse mammary epithelial cells associated with a laminin-rich extracellular matrix. Synthesis of the 74-kDa NFIC was also inhibited in this setting by tunicamycin. Thus, involution triggers the production of an NFIC isoform that is post-translationally modified by N-glycosylation. We further show, by using quantitative competitive reverse transcriptase-PCR, that there is increased expression of the major mouse mammary NFIC mRNA transcript, mNFIC2, in early involution, suggesting that the involution-associated change in NFIC expression also has a transcriptional contribution.