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Progressive fibrosing interstitial lung disease (PF-ILD) has been redefined as a new clinical syndrome that shares similar genetics, pathophysiology, and natural history to idiopathic pulmonary fibrosis (IPF). IPF is the most common form of idiopathic interstitial pneumonias, which is progressive in nature and is associated with significant mortality. Therapies targeting an inflammatory and/or immune response have not been consistently effective or well tolerated in patients with IPF. The two antifibrotic drugs approved for IPF treatment, nintedanib and pirfenidone, have been shown to reduce lung function decline in PF-ILD. Novel uses of antifibrotic therapy are emerging due to a paucity of evidence-based treatments for multiple ILD subtypes. In this review, we describe the current body of knowledge on antifibrotic therapy and immunomodulators in PF-ILD, drawing from experience in IPF where appropriate., Author(s): Charlisa D. Gibson [sup.1], Matthias C. Kugler [sup.1], Himanshu Deshwal [sup.1], John S. Munger [sup.1], Rany Condos [sup.1] Author Affiliations: (1) grid.137628.9, 0000 0004 1936 8753, Division of Pulmonary [...]

Injury-initiated epithelial to mesenchymal transition (EMT) depends on contextual signals from the extracellular matrix, suggesting a role for integrin signaling. Primary epithelial cells deficient in their prominent laminin receptor, alpha3beta1, were found to have a markedly blunted EMT response to TGF-beta1. A mechanism for this defect was explored in alpha3-null cells reconstituted with wild-type (wt) alpha3 or point mutants unable to engage laminin 5 (G163A) or epithelial cadherin (E-cadherin; H245A). After TGF-beta1 stimulation, wt epithelial cells but not cells expressing the H245A mutant internalize complexes of E-cadherin and TGF-beta1 receptors, generate phospho-Smad2 (p-Smad2)-pY654-beta-catenin complexes, and up-regulate mesenchymal target genes. Although Smad2 phosphorylation is normal, p-Smad2-pY654-beta-catenin complexes do not form in the absence of alpha3 or when alpha3beta1 is mainly engaged on laminin 5 or E-cadherin in adherens junctions, leading to attenuated EMT. These findings demonstrate that alpha3beta1 coordinates cross talk between beta-catenin and Smad signaling pathways as a function of extracellular contact cues and thereby regulates responses to TGF-beta1 activation.

The integrin alpha3beta1 mediates cellular adhesion to the matrix ligand laminin-5. A second integrin ligand, the urokinase receptor (uPAR), associates with alpha3beta1 via a surface loop within the alpha3 beta-propeller (residues 242-246) but outside the laminin binding region, suggesting that uPAR-integrin interactions could signal differently from matrix engagement. To explore this, alpha3-/- epithelial cells were reconstituted with wild-type (wt) alpha3 or alpha3 with Ala mutations within the uPAR-interacting loop (H245A or R244A). Wt or mutant-bearing cells showed comparable expression and adhesion to laminin-5. Cells expressing wt alpha3 and uPAR dissociated in culture, with increased Src activity, up-regulation of SLUG, and down-regulation of E-cadherin and gamma-catenin. Src kinase inhibition or expression of Src 1-251 restored the epithelial phenotype. The H245A and R244A mutants were unaffected by coexpression of uPAR. We conclude that alpha3beta1 regulates both cell-cell contact and matrix adhesion, but through distinct protein interaction sites within its beta-propeller. These studies reveal an integrin- and Src-dependent pathway for SLUG expression and mesenchymal transition.

Normal lung development critically depends on HH (Hedgehog) and PDGF (platelet-derived growth factor) signaling, which coordinate mesenchymal differentiation and proliferation. PDGF signaling is required for postnatal alveolar septum formation by myofibroblasts. Recently, we demonstrated a requirement for HH in postnatal lung development involving alveolar myofibroblast differentiation. Given shared features of HH signaling and PDGF signaling and their impact on this key cell type, we sought to clarify their relationship during murine postnatal lung development. Timed experiments revealed that HH inhibition phenocopies the key lung myofibroblast phenotypes of Pdgfa (platelet-derived growth factor subunit A) and Pdgfra (platelet-derived growth factor receptor alpha) knockouts during secondary alveolar septation. Using a dual signaling reporter, Gli1lZ;PdgfraEGFP, we show that HH and PDGF pathway intermediates are concurrently expressed during alveolar septal myofibroblast accumulation, suggesting pathway convergence in the generation of lung myofibroblasts. Consistent with this hypothesis, HH inhibition reduces Pdgfra expression and diminishes the number of Pdgfra-positive and Pdgfra-lineage cells in postnatal lungs. Bulk RNA sequencing data of Pdgfra-expressing cells from Postnatal Day 8 (P8) lungs show that HH inhibition alters the expression not only of well-established HH targets but also of several putative PDGF target genes. This, together with the presence of Gli-binding sites in PDGF target genes, suggests HH input into PDGF signaling. We identified these HH/PDGF targets in several postnatal lung mesenchymal cell populations, including myofibroblasts, using single-cell transcriptomic analysis. Collectively, our data indicate that HH signaling and PDGF signaling intersect to support myofibroblast/fibroblast function during secondary alveolar septum formation. Moreover, they provide a molecular foundation relevant to perinatal lung diseases associated with impaired alveolarization. [ABSTRACT FROM AUTHOR]

Injury-initiated epithelial to mesenchymal transition (EMT) depends on contextual signals from the extracellular matrix, suggesting a role for integrin signaling. Primary epithelial cells deficient in their prominent laminin receptor, [alpha]3[beta]1, were found to have a markedly blunted EMT response to TGF-[beta]1. A mechanism for this defect was explored in [alpha]3-null cells reconstituted with wild-type (wt) [alpha]3 or point mutants unable to engage laminin 5 (G163A) or epithelial cadherin (E-cadherin; H245A). After TGF-[beta]1 stimulation, wt epithelial cells but not cells expressing the H245A mutant internalize complexes of E-cadherin and TGF-[beta]1 receptors, generate phospho-Smad2 (p-Smad2)-pY654-[beta]-catenin complexes, and upregulate mesenchymal target genes. Although Smad2 phosphorylation is normal, p-Smad2--pY654--[beta]-catenin complexes do not form in the absence of [alpha]3 or when [alpha]3[beta]1 is mainly engaged on laminin 5 or E-cadherin in adherens junctions, leading to attenuated EMT. These findings demonstrate that [alpha]3[beta]1 coordinates cross talk between [beta]-catenin and Smad signaling pathways as a function of extracellular contact cues and thereby regulates responses to TGF-[beta]1 activation.

Pulmonary fibrosis, in particular idiopathic pulmonary fibrosis (IPF), results from aberrant wound healing and scarification. One population of fibroblasts involved in the fibrotic process is thought to originate from lung epithelial cells via epithelial-mesenchymal transition (EMT). Indeed, alveolar epithelial cells (AECs) undergo EMT in vivo during experimental fibrosis and ex vivo in response to TGF-[beta]1. As the ECM critically regulates AEC responses to TGF-[beta]1, we explored the role of the prominent epithelial integrin [alpha]3[beta]1 in experimental fibrosis by generating mice with lung epithelial cell--specific loss of [alpha]3 integrin expression. These mice had a normal acute response to bleomycin injury, but they exhibited markedly decreased accumulation of lung myofibroblasts and type I collagen and did not progress to fibrosis. Signaling through [beta]-catenin has been implicated in EMT; we found that in primary AECs, [alpha]3 integrin was required for [beta]-catenin phosphorylation at tyrosine residue 654 (Y654), formation of the pY654-[beta]-catenin/pSmad2 complex, and initiation of EMT, both in vitro and in vivo during the fibrotic phase following bleomycin injury. Finally, analysis of lung tissue from IPF patients revealed the presence of pY654-[beta]-catenin/pSmad2 complexes and showed accumulation of pY654-[beta]-catenin in myofibroblasts. These findings demonstrate epithelial integrin--dependent profibrotic crosstalk between [beta]-catenin and Smad signaling and support the hypothesis that EMT is an important contributor to pathologic fibrosis., Introduction Progressive fibrosis of the lung, especially that of idiopathic pulmonary fibrosis (IPF), is thought to be a consequence of aberrant wound healing resulting in progressive scarification (1), (2). Fibroblast [...]

Urokinase-type plasminogen activator receptors (uPARs), up-regulated during tumor progression, associate with [beta]1 integrins, localizing urokinase to sites of cell attachment. Binding of uPAR to the [beta]-propeller of [alpha]3[beta]1 empowers vitronectin adhesion by this integrin. How uPAR modifies other [beta]1 integrins remains unknown. Using recombinant proteins, we found uPAR directly binds [alpha]5[beta]1 and rather than blocking, renders fibronectin (Fn) binding by [alpha]5[beta]1 Arg-Gly-Asp (RGD) resistant. This resulted from RGD-independent binding of [alpha]5[beta]1-uPAR to Fn type III repeats 12-15 in addition to type III repeats 9-11 bound by [alpha]5[beta]1. Suppression of endogenous uPAR by small interfering RNA in tumor cells promoted weaker, RGD-sensitive Fn adhesion and altered overall [alpha]5[beta]1 conformation. A [beta]1 peptide (res 224NLDSPEGGF232) that models near the known [alpha]-chain uPAR-binding region, or a [beta]1-chain Ser227Ala point mutation, abrogated effects of uPAR on [alpha]5[beta]1. Direct binding and regulation of [alpha]5[beta]1 by uPAR implies a modified 'bent' integrin conformation can function in an alternative activation state with this and possibly other cis-acting membrane ligands.

Injury-initiated epithelial to mesenchymal transition (EMT) depends on contextual signals from the extracellular matrix, suggesting a role for integrin signaling. Primary epithelial cells deficient in their prominent laminin receptor, α3β1, were found to have a markedly blunted EMT response to TGF-β1. A mechanism for this defect was explored in α3-null cells reconstituted with wild-type (wt) α3 or point mutants unable to engage laminin 5 (G163A) or epithelial cadherin (E-cadherin; H245A). After TGF-β1 stimulation, wt epithelial cells but not cells expressing the H245A mutant internalize complexes of E-cadherin and TGF-β1 receptors, generate phospho-Smad2 (p-Smad2)-pY654-β-catenin complexes, and upregulate mesenchymal target genes. Although Smad2 phosphorylation is normal, p-Smad2-pY654-β-catenin complexes do not form in the absence of α3 or when α3β1 is mainly engaged on laminin 5 or E-cadherin in adherens junctions, leading to attenuated EMT. These findings demonstrate that α3β1 coordinates cross talk between β-catenin and Smad signaling pathways as a function of extracellular contact cues and thereby regulates responses to TGF-β1 activation. [ABSTRACT FROM AUTHOR]

The integrin α3β1 mediates cellular adhesion to the matrix ligand laminin-5. A second integrin ligand, the urokinase receptor (uPAR), associates with &alpha3β1 via a surface loop within the α3 β-propeller (residues 242-246) but outside the laminin binding region, suggesting that uPAR-integrin interactions could signal differently from matrix engagement. To explore this, α3[sup-/-] epithelial cells were reconstituted with wild-type (wt) α3 or α3 with Ala mutations within the uPAR-interacting loop (H245A or R244A). Wt or mutant-bearing cells showed comparable expression and adhesion to laminin-5. Cells expressing wt α3 and uPAR dissociated in culture, with increased Src activity, up-regulation of SLUG, and down-regulation of E-cadherin and γ-catenin. Src kinase inhibition or expression of Src 1-251 restored the epithelial phenotype. The H245A and R244A mutants were unaffected by coexpression of uPAR. We conclude that α3β1 regulates both cell-cell contact and matrix adhesion, but through distinct protein interaction sites within its β-propeller. These studies reveal an integrin- and Src-dependent pathway for SLUG expression and mesenchymal transition. [ABSTRACT FROM AUTHOR]

Up-regulation of urokinase receptors is common during tumor progression and thought to promote invasion and metastasis. Urokinase receptors bind urokinase and a set of β1 integrins, but it remains unclear to what degree urokinase receptor/ integrin binding is important to β1 integrin signaling. Using site-directed mutagenesis, single amino acid mutants of the urokinase receptor were identified that fail to associate with either α3β1 (D262A) or α5β1 (H249A) but associate normally with urokinase. To study the effects of these mutations on β1 integrin function, endogenous urokinase receptors were first stably silenced in tumor cell lines HT1080 and H1299, and then wild type or mutant receptors were expressed. Knockdown of urokinase receptors resulted in markedly reduced fibronectin and α5β1-dependent ERK activation and metalloproteinase MMP-9 expression. Re-expression of wild type or D262A mutant receptors but not the α5β1 binding-deficient H249A mutant reconstituted fibronectin responses. Because urokinase receptor·α5β1 complexes bind in the fibronectin heparin-binding domain (Type III 12–14) whereas α5β1 primarily binds in the RGD-containing domain (Type III 7–10), signaling pathways leading to ERK and MMP-9 responses were dissected. Binding to III 7–10 led to Src/focal adhesion kinase activation, whereas binding to III 7–14 caused Rac 1 activation. Tumor cells engaging fibronectin required both Type III 7–10- and 12–14-initiated signals to activate ERK and up-regulate MMP-9. Thus urokinase receptor binding to α5β1 is required for maximal responses to fibronectin and tumor cell invasion, and this operates through an enhanced Src/Rac/ERK signaling pathway. [ABSTRACT FROM AUTHOR]

Urokinase-type plasminogen activator receptors (uPARs), up-regulated during tumor progression, associate with β1 integrins, localizing urokinase to sites of cell attachment. Binding of uPAR to the β-propeller of α3β1 empowers vitronectin adhesion by this integrin. How uPAR modifies other β1 integrins remains unknown. Using recombinant proteins, we found uPAR directly binds α5β1 and rather than blocking, renders fibronectin (Fn) binding by α5β1 Arg-Gly-Asp (RGD) resistant. This resulted from RGD-independent binding of α5β1-uPAR to Fn type III repeats 12-15 in addition to type III repeats 9-11 bound by α5β1. Suppression of endogenous uPAR by small interfering RNA in tumor cells promoted weaker, RGD-sensitive Fn adhesion and altered overall α5β1 conformation. A β1 peptide (res 224NLDSPEGGF232) that models near the known α-chain uPAR-binding region, or a β1-chain Ser227Ala point mutation, abrogated effects of uPAR on α5β1. Direct binding and regulation of α5β1 by uPAR implies a modified "bent" integrin conformation can function in an alternative activation state with this and possibly other cis-acting membrane ligands. [ABSTRACT FROM AUTHOR]

Background: Risk of early-stage lung adenocarcinoma (LUAD) recurrence after surgical resection is significant, and post-recurrence median survival is approximately two years. Currently there are no commercially available biomarkers that predict recurrence. Here, we investigated whether microbial and host genomic signatures in the lung can predict recurrence., Methods: In 91 early-stage (Stage IA/IB) LUAD-patients with extensive follow-up, we used 16s rRNA gene sequencing and host RNA-sequencing to map the microbial and host transcriptomic landscape in tumor and adjacent unaffected lung samples., Results: 23 out of 91 subjects had tumor recurrence over 5-year period. In tumor samples, LUAD recurrence was associated with enrichment with Dialister, Prevotella, while in unaffected lung, recurrence was associated with enrichment with Sphyngomonas and Alloiococcus. The strengths of the associations between microbial and host genomic signatures with LUAD recurrence were greater in adjacent unaffected lung samples than in the primary tumor. Among microbial-host features in the unaffected lung samples associated with recurrence, enrichment with Stenotrophomonas geniculata and Chryseobacterium were positively correlated with upregulation of IL-2, IL-3, IL-17, EGFR, HIF-1 signaling pathways among the host transcriptome. In tumor samples, enrichment with Veillonellaceae Dialister, Ruminococcacea, Haemophilus Influenza, and Neisseria were positively correlated with upregulation of IL-1, IL-6, IL17, IFN, and Tryptophan metabolism pathways., Conclusions: Overall, modeling suggested that a combined microbial/transcriptome approach using unaffected lung samples had the best biomarker performance (AUC=0.83)., Impact: This study suggests that LUAD recurrence is associated with distinct pathophysiological mechanisms of microbial-host interactions in the unaffected lung rather than those present in the resected tumor.

Rationale: Acute cellular rejection (ACR) after lung transplant is a leading risk factor for chronic lung allograft dysfunction. Prior studies have demonstrated dynamic microbial changes occurring within the allograft and gut that influence local adaptive and innate immune responses. However, the lung microbiome's overall impact on ACR risk remains poorly understood. Objectives: To evaluate whether temporal changes in microbial signatures were associated with the development of ACR. Methods: We performed cross-sectional and longitudinal analyses (joint modeling of longitudinal and time-to-event data and trajectory comparisons) of 16S rRNA gene sequencing results derived from lung transplant recipient lower airway samples collected at multiple time points. Measurements and Main Results: Among 103 lung transplant recipients, 25 (24.3%) developed ACR. In comparing samples acquired 1 month after transplant, subjects who never developed ACR demonstrated lower airway enrichment with several oral commensals (e.g., Prevotella and Veillonella spp.) than those with current or future (beyond 1 mo) ACR. However, a subgroup analysis of those who developed ACR beyond 1 month revealed delayed enrichment with oral commensals occurring at the time of ACR diagnosis compared with baseline, when enrichment with more traditionally pathogenic taxa was present. In longitudinal models, dynamic changes in α-diversity (characterized by an initial decrease and a subsequent increase) and in the taxonomic trajectories of numerous oral commensals were more commonly observed in subjects with ACR. Conclusions: Dynamic changes in the lower airway microbiota are associated with the development of ACR, supporting its potential role as a useful biomarker or in ACR pathogenesis.

Normal lung development critically depends on HH (Hedgehog) and PDGF (platelet-derived growth factor) signaling, which coordinate mesenchymal differentiation and proliferation. PDGF signaling is required for postnatal alveolar septum formation by myofibroblasts. Recently, we demonstrated a requirement for HH in postnatal lung development involving alveolar myofibroblast differentiation. Given shared features of HH signaling and PDGF signaling and their impact on this key cell type, we sought to clarify their relationship during murine postnatal lung development. Timed experiments revealed that HH inhibition phenocopies the key lung myofibroblast phenotypes of Pdgfa (platelet-derived growth factor subunit A) and Pdgfra (platelet-derived growth factor receptor alpha) knockouts during secondary alveolar septation. Using a dual signaling reporter, Gli1 lZ ;Pdgfra EGFP , we show that HH and PDGF pathway intermediates are concurrently expressed during alveolar septal myofibroblast accumulation, suggesting pathway convergence in the generation of lung myofibroblasts. Consistent with this hypothesis, HH inhibition reduces Pdgfra expression and diminishes the number of Pdgfra-positive and Pdgfra -lineage cells in postnatal lungs. Bulk RNA sequencing data of Pdgfra-expressing cells from Postnatal Day 8 (P8) lungs show that HH inhibition alters the expression not only of well-established HH targets but also of several putative PDGF target genes. This, together with the presence of Gli-binding sites in PDGF target genes, suggests HH input into PDGF signaling. We identified these HH/PDGF targets in several postnatal lung mesenchymal cell populations, including myofibroblasts, using single-cell transcriptomic analysis. Collectively, our data indicate that HH signaling and PDGF signaling intersect to support myofibroblast/fibroblast function during secondary alveolar septum formation. Moreover, they provide a molecular foundation relevant to perinatal lung diseases associated with impaired alveolarization.

Up-regulation of urokinase receptors is common during tumor progression and thought to promote invasion and metastasis. Urokinase receptors bind urokinase and a set of beta1 integrins, but it remains unclear to what degree urokinase receptor/integrin binding is important to beta1 integrin signaling. Using site-directed mutagenesis, single amino acid mutants of the urokinase receptor were identified that fail to associate with either alpha3beta1 (D262A) or alpha5beta1 (H249A) but associate normally with urokinase. To study the effects of these mutations on beta1 integrin function, endogenous urokinase receptors were first stably silenced in tumor cell lines HT1080 and H1299, and then wild type or mutant receptors were expressed. Knockdown of urokinase receptors resulted in markedly reduced fibronectin and alpha5beta1-dependent ERK activation and metalloproteinase MMP-9 expression. Re-expression of wild type or D262A mutant receptors but not the alpha5beta1 binding-deficient H249A mutant reconstituted fibronectin responses. Because urokinase receptor.alpha5beta1 complexes bind in the fibronectin heparin-binding domain (Type III 12-14) whereas alpha5beta1 primarily binds in the RGD-containing domain (Type III 7-10), signaling pathways leading to ERK and MMP-9 responses were dissected. Binding to III 7-10 led to Src/focal adhesion kinase activation, whereas binding to III 7-14 caused Rac 1 activation. Tumor cells engaging fibronectin required both Type III 7-10- and 12-14-initiated signals to activate ERK and up-regulate MMP-9. Thus urokinase receptor binding to alpha5beta1 is required for maximal responses to fibronectin and tumor cell invasion, and this operates through an enhanced Src/Rac/ERK signaling pathway.

Urokinase receptors (uPAR) were initially thought to function simply as a mechanism to concentrate the urokinase/plasmin system toward the cell surface. However, extensive evidence has accumulated that this glycolipid-anchored receptor also functions in both the adhesive and signaling pathways of many migratory cells. Mechanisms by which uPAR exercises these functions involve complexing with other membrane proteins for signal transduction. One set of functional partners for uPAR on the cell surface are integrins. Recent studies point to important structural features of uPAR:integrin interactions, indicating uPAR to be a cis-acting integrin ligand. In vivo data reveal altered integrin function and cell migration when uPAR:integrin interactions are impaired. Together these observations support the idea that uPAR:integrin interactions may be a focal point of intervention in pathobiology where integrin function is crucial, such as tumor metastasis.