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Pulmonary arterial hypertension (PAH) has a multifactorial pathobiology. Vasoconstriction, remodeling of the pulmonary vessel wall, and thrombosis contribute to increased pulmonary vascular resistance in PAH. The process of pulmonary vascular remodeling involves all layers of the vessel wall and is complicated by cellular heterogeneity within each compartment of the pulmonary arterial wall. Indeed, each cell type (endothelial, smooth muscle, and fibroblast), as well as inflammatory cells and platelets, may play a significant role in PAH. Pulmonary vasoconstriction is believed to be an early component of the pulmonary hypertensive process. Excessive vasoconstriction has been related to abnormal function or expression of potassium channels and to endothelial dysfunction. Endothelial dysfunction leads to chronically impaired production of vasodilators such as nitric oxide and prostacyclin along with overexpression of vasoconstrictors such as endothelin (ET)-1. Many of these abnormalities not only elevate vascular tone and promote vascular remodeling but also represent logical pharmacological targets. Recent genetic and pathophysiologic studies have emphasized the relevance of several mediators in this condition, including prostacyclin, nitric oxide, ET-1, angiopoietin-1, serotonin, cytokines, chemokines, and members of the transforming-growth-factor-beta superfamily. Disordered proteolysis of the extracellular matrix is also evident in PAH. Future studies are required to find which if any of these abnormalities initiates PAH and which ones are best targeted to cure the disease.

Idiopathic pulmonary fibrosis (IPF) is characterized by distorted lung architecture and loss of respiratory function. Enhanced (myo)fibroblast activation, ECM deposition, and alveolar epithelial type II (ATII) cell dysfunction contribute to IPF pathogenesis. However, the molecular pathways linking ATII cell dysfunction with the development of fibrosis are poorly understood. Here, we demonstrate, in a mouse model of pulmonary fibrosis, increased proliferation and altered expression of components of the WNT/β-catenin signaling pathway in ATII cells. Further analysis revealed that expression of WNT1-inducible signaling protein-1 (WISP1), which is encoded by a WNT target gene, was increased in ATII cells in both a mouse model of pulmonary fibrosis and patients with IPF. Treatment of mouse primary ATII cells with recombinant WISP1 led to increased proliferation and epithelial-mesenchymal transition (EMT), while treatment of mouse and human lung fibroblasts with recombinant WISP1 enhanced deposition of ECM components. In the mouse model of pulmonary fibrosis, neutralizing mAbs specific for WISP1 reduced the expression of genes characteristic of fibrosis and reversed the expression of genes associated with EMT. More importantly, these changes in gene expression were associated with marked attenuation of lung fibrosis, including decreased collagen deposition and improved lung function and survival. Our study thus identifies WISP1 as a key regulator of ATII cell hyperplasia and plasticity as well as a potential therapeutic target for attenuation of pulmonary fibrosis.

The role of endogenous inducers of inflammation is poorly understood. To produce the proinflammatory master cytokine interleukin (IL)-1␤, macrophages need double stimulation with ligands to both Toll-like receptors (TLRs) for IL-1␤ gene transcription and nucleotide-binding oligomerization domain-like receptors for activation of the inflammasome. It is particularly intriguing to define how this complex regulation is mediated in the absence of an infectious trigger. Biglycan, a ubiquitous leucine-rich repeat proteoglycan of the extracellular matrix, interacts with TLR2/4 on macrophages. The objective of this study was to define the role of biglycan in the synthesis and activation of IL-1␤. Here we show that in macrophages, soluble biglycan induces the NLRP3/ASC inflammasome, activating caspase-1 and releasing mature IL-1␤ without the need for additional costimulatory factors. This is brought about by the interaction of biglycan with TLR2/4 and purinergic P2X 4 /P2X 7 receptors, which induces receptor cooperativity. Furthermore, reactive oxygen species formation is involved in biglycan-mediated activation of the inflammasome. By signaling through TLR2/4, biglycan stimulates the expression of NLRP3 and pro-IL-1␤ mRNA. Both in a model of non-infectious inflammatory renal injury (unilateral ureteral obstruction) and in lipopolysaccharide-induced sepsis, biglycan-deficient mice displayed lower levels of active caspase-1 and mature IL-1␤ in the kidney, lung, and circulation. Our results provide evidence for direct activation of the NLRP3 inflammasome by biglycan and describe a fundamental paradigm of how tissue stress or injury is monitored by innate immune receptors detecting the release of the extracellular matrix components and turning such a signal into a robust inflammatory response. IL-1␤2 is a proinflammatory master cytokine produced by macrophages in response to inflammatory stimuli, such as LPS. The activity of IL-1␤ is regulated sequentially by synthesis of the 31-kDa precursor pro-IL-1␤, intracellular proteolytic conversion into active IL-1␤ (17 kDa) by the cysteine protease caspase-1, also known as IL-1-converting enzyme (1, 2), and by secretion of IL-1␤ (3). The synthesis of pro-IL-1␤ is initiated by Toll-like receptor (TLR) agonists, whereas ATP stimulates cleavage and maturation of IL-1␤ (4, 5). Activation of caspase-1 requires the assembly and activity of a cytosolic multiprotein complex known as the inflammasome, consisting of nucleotide-binding oligomerization-like receptor family members (NLRs; NLRPs (NLR family, pyrin domain-containing 3), NAIP (NLR family, apoptosis inhibitory protein), and NLRC4 (NLR family caspase recruitment domain-containing 4)) (6), generating functional caspase-1 p20 and p10 subunits (1,7,8). TLRs and NLRs contain leucine-rich repeats (LRRs), which are used as ligand-sensing motifs (9, 10). NLRP3, the best characterized member of NLRs, recruits caspase-1 to the inflammasome via the adapter molecule ASC (apoptosis-associated specklike protein containing caspase activation and r...

Rationale: Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and usually lethal fibrotic lung disease characterized by profound changes in epithelial cell phenotype and fibroblast proliferation. Objectives: To determine changes in expression and role of microRNAs in IPF. Methods: RNA from 10 control and 10 IPF tissues was hybridized on Agilent microRNA microarrays and results were confirmed by quantitative real-time polymerase chain reaction and in situ hybridization. SMAD3 binding to the let-7d promoter was confirmed by chromatin immunoprecipitation, electrophoretic mobility shift assay, luciferase assays, and reduced expression of let-7d in response to transforming growth factor-b. HMGA2, a let-7d target, was localized by immunohistochemistry. In mice, let-7d was inhibited by intratracheal administration of a let-7d antagomir and its effects were determined by immunohistochemistry, immunofluorescence, quantitative real-time polymerase chain reaction, and morphometry. Measurements and Main Results: Eighteen microRNAs including let-7d were significantly decreased in IPF. Transforming growth factor-b down-regulated let-7d expression, and SMAD3 binding to the let-7d promoter was demonstrated. Inhibition of let-7d caused increases in mesenchymal markers N-cadherin-2, vimentin, and a-smooth muscle actin (ACTA2) as well as HMGA2 in multiple epithelial cell lines. let-7d was significantly reduced in IPF lungs and the number of epithelial cells expressing let-7d correlated with pulmonary functions. HMGA2 was increased in alveolar epithelial cells of IPF lungs. let-7d inhibition in vivo caused alveolar septal thickening and increases in collagen, ACTA2, and S100A4 expression in SFTPC (pulmonary-associated surfactant protein C) expressing alveolar epithelial cells. Conclusions: Our results indicate a role for microRNAs in IPF. The downregulation of let-7d in IPF and the profibrotic effects of this downregulation in vitro and in vivo suggest a key regulatory role for this microRNA in preventing lung fibrosis. Clinical trial registered with www.clinicaltrials.gov (NCT 00258544).

BackgroundIdiopathic pulmonary fibrosis (IPF) is a fatal lung disease, characterized by distorted lung architecture and loss of respiratory function. Alveolar epithelial cell injury and hyperplasia, enhanced extracellular matrix deposition, and (myo)fibroblast activation are features of IPF. Wnt/β-catenin signaling has been shown to determine epithelial cell fate during development. As aberrant reactivation of developmental signaling pathways has been suggested to contribute to IPF pathogenesis, we hypothesized that Wnt/β-catenin signaling is activated in epithelial cells in IPF. Thus, we quantified and localized the expression and activity of the Wnt/β-catenin pathway in IPF.Methodology/Principal FindingsThe expression of Wnt1, 3a, 7b, and 10b, the Wnt receptors Fzd1-4, Lrp5-6, as well as the intracellular signal transducers Gsk-3β, β-catenin, Tcf1, 3, 4, and Lef1 was analyzed in IPF and transplant donor lungs by quantitative real-time (q)RT-PCR. Wnt1, 7b and 10b, Fzd2 and 3, β-catenin, and Lef1 expression was significantly increased in IPF. Immunohistochemical analysis localized Wnt1, Wnt3a, β-catenin, and Gsk-3β expression largely to alveolar and bronchial epithelium. This was confirmed by qRT-PCR of primary alveolar epithelial type II (ATII) cells, demonstrating a significant increase of Wnt signaling in ATII cells derived from IPF patients. In addition, Western blot analysis of phospho-Gsk-3β, phospho-Lrp6, and β-catenin, and qRT-PCR of the Wnt target genes cyclin D1, Mmp 7, or Fibronectin 1 demonstrated increased functional Wnt/β-catenin signaling in IPF compared with controls. Functional in vitro studies further revealed that Wnt ligands induced lung epithelial cell proliferation and (myo)fibroblast activation and collagen synthesis.Conclusions/SignificanceOur study demonstrates that the Wnt/β-catenin pathway is expressed and operative in adult lung epithelium. Increased Wnt/β-catenin signaling may be involved in epithelial cell injury and hyperplasia, as well as impaired epithelial-mesenchymal cross-talk in IPF. Thus, modification of Wnt signaling may represent a therapeutic option in IPF.

The pulmonary extracellular matrix (ECM) determines the tissue architecture of the lung, and provides mechanical stability and elastic recoil, which are essential for physiological lung function. Biochemical and biomechanical signals initiated by the ECM direct cellular function and differentiation, and thus play a decisive role in lung development, tissue remodelling processes and maintenance of adult homeostasis. Recent proteomic studies have demonstrated that at least 150 different ECM proteins, glycosaminoglycans and modifying enzymes are expressed in the lung, and these assemble into intricate composite biomaterials. These highly insoluble assemblies of interacting ECM proteins and their glycan modifications can act as a solid phase-binding interface for hundreds of secreted proteins, which creates an information-rich signalling template for cell function and differentiation. Dynamic changes within the ECM that occur upon injury or with ageing are associated with several chronic lung diseases. In this review, we summarise the available data about the structure and function of the pulmonary ECM, and highlight changes that occur in idiopathic pulmonary fibrosis (IPF), pulmonary arterial hypertension (PAH), chronic obstructive pulmonary disease (COPD), asthma and lung cancer. We discuss potential mechanisms of ECM remodelling and modification, which we believe are relevant for future diagnosis and treatment of chronic lung disease.

Pulmonary arterial hypertension (PAH) is a rare disorder that may be hereditable (HPAH), idiopathic (IPAH), or associated with either drug-toxin exposures or other medical conditions. Familial cases have long been recognised and are usually due to mutations in Bone Morphogenetic Protein Receptor type 2 gene (BMPR2), or, much less commonly, 2 other members of the transforming growth factor-beta superfamily, Activin-like Kinase-Type I (ALK1) and Endoglin (ENG), which are associated with hereditary hemorrhagic telangiectasia. In addition, approximately 20% of patients with IPAH carry mutations in BMPR2. We provide a summary of BMPR2 mutations associated with IPAH/HPAH, most of which are unique to each family and are presumed to result in loss of function. We review the finding of missense variants and variants of unknown significance in BMPR2 in IPAH/HPAH, fenfluramine exposure, and PAH associated with congenital heart disease. Clinical testing for BMPR2 mutations is available and may be offered to HPAH and IPAH patients but should be preceded by genetic counselling, since lifetime penetrance is only 10%–20%, and there are currently no known effective preventative measures. Identification of a familial mutation can be valuable in reproductive planning and identifying family members who are not mutation carriers and thus will not require lifelong surveillance. With advances in genomic technology and with international collaborative efforts, genome-wide association studies will be conducted to identify additional genes for HPAH, genetic modifiers for BMPR2 penetrance, and genetic susceptibility to IPAH. In addition, collaborative studies of BMPR2 mutation carriers should enable identification of environmental modifiers, biomarkers for disease development and progression, and surrogate markers for efficacy end points in clinical drug development, thereby providing an invaluable resource for trials of PAH prevention.