Francis X. McCormack

Pulmonary fibrosis is a progressive, terminal disease with high morbidity. Existing therapeutics slow disease progression but do not reverse fibrotic lung remodeling, accentuating the importance of identifying cellular mechanisms that underlie lung fibrosis. Recent literature suggests that alveolar type 2 (AT2) progenitors undergo transition to stressed Krt8 ^high cells following lung injury. Accumulation of stressed Krt8 ^high cells is a hallmark of acute and chronic lung diseases, particularly pulmonary fibrosis. Whether Krt8 ^high cells actively participate in the fibrotic process or are simply an epiphenomenon of lung injury remains unclear. We previously described a genetic model in which deletion of the lung transcription factor Nkx2-1 in the AT2 progenitor lineage induces AT2 progenitors to transition to the Krt8 ^high cell state. Here, we use this tractable genetic model to directly test the pathogenic influence of Krt8 ^high cells. We show that Nkx2-1 ^-/- Krt8 ^high cells accumulate in a Krt7 ^high /Krt19 ^high /Krt17 ^neg alveolar-basal intermediate cell state (ABI). Following induction of fibrotic lung injury with inhaled silica, ABI enter a unique inflammatory state (iABI) that drives fibrotic remodeling via coordination of a fibrotic signaling niche containing inflammatory alveolar fibroblasts (iAF) and pulmonary osteoclast-like cells (POLC). Computational analysis predicts that iABI elaborate pro-inflammatory signals which increase matrix deposition by iAF and induce differentiation of interstitial macrophages to a profibrotic POLC variant. Niche mapping demonstrates that iABI, iAF, and POLCs interact within newly formed fibrotic niches in the lung alveolus in mice with pre-existing accumulation of ABI. These data provide direct evidence that ABI accumulation in fibrotic lung disease is pathogenic.

Rationale: Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) is characterised by diffuse bronchial hyperplasia of pulmonary neuroendocrine cells, which are situated within the walls of bronchi and bronchioles. Presenting symptoms are nonspecific and the clinical course varies, making diagnosis challenging. We sought to describe the clinical characteristics of patients with DIPNECH in a large multinational case series to guide and inform future care and research. Methods: Data were collated from 18 international centres. Information collected included disease presentation, pulmonary function testing, histopathology, radiological patterns and outcomes. The relationship between clinical features, radiology and symptoms were explored in parametric and nonparametric group-wise analyses, univariate linear regressions, and multivariate binomial logistic regression. Results: The mean± sd age of the 258 patients in this study was 63.3±10.6 years and 93.4% were female. Diffuse pulmonary nodules (98.8%) and mosaic attenuation (59.1%) were the most common radiological findings and 29.5% had obstructive spirometry with a mean± sd forced expiratory volume in 1 s (FEV ₁ ) % pred of 69.0±23.7%. There was a significant association between the number of nodules and a reduction in FEV ₁ % pred (p<0.001), while the presence of bronchial wall thickening on imaging was most closely associated with cough (OR 4.97, p=0.001) dyspnoea (OR 3.14, p=0.003) and bronchodilator responsiveness (OR 3.09, p=0.013). Approximately half of patients treated with inhaled beta agonist and corticosteroids (46.3%) or somatostatin analogue (54.1%) reported improvement in symptoms. Conclusions: The presence of radiological bronchial wall thickening is associated with the presence of symptoms, while mosaic attenuation is correlated with airflow obstruction; hence, the presence of these radiological findings has the potential to guide possible treatment decisions.

Talc pleurodesis is highly effective for preventing recurrence of pneumothorax and pleural effusion, but it can be complicated by dissemination, acute lung injury, lead exposure, and foreign body–induced chronic inflammation and pain. Our objective is to develop a safe, biodegradable, contaminant-free particle for pleurodesis. We used mouse models of pneumothorax and malignant pleural effusion to compare the efficacy and safety of pleurodesis with talc and hydroxyapatite microspheres (HAM). Intrapleural instillation of microspheres induced pleural adhesions, fibrosis, and symphysis as effectively as talc and resulted in more durable protection from experimental pneumothorax. HAM and talc both induced an osteoclastogenic, inflammatory, and fibrotic response in pleural lavage cells. Intrapleural HAM was resorbed by osteoclast action over 3 months, whereas talc was not cleared. Deletion of the osteoclast effector, CTSK, diminished pleural adhesion formation and fibrosis by HAM, and inhibition of osteoclastogenesis with anti-RANKL antibody delayed HAM clearance. We found no difference in activity level, feeding behavior, or lung compliance between particles, but talc induced more persistent pleural inflammation. We conclude that HAM resulted in an osteoclastogenic and fibrogenic pleural response that induced pleurodesis that was more durable than talc with a superior safety profile due in part to osteoclast-mediated particle clearance.

Idiopathic pulmonary fibrosis (IPF) is a fatal fibrotic lung disease characterized by impaired fibroblast clearance and excessive extracellular matrix (ECM) protein production. Wilms tumor 1 (WT1), a transcription factor, is selectively upregulated in IPF fibroblasts. However, the mechanisms by which WT1 contributes to fibroblast accumulation and ECM production remain unknown. Here, we investigated the heterogeneity of WT1-expressing mesenchymal cells using single-nucleus RNA-Seq of distal lung tissues from patients with IPF and control donors. WT1 was selectively upregulated in a subset of IPF fibroblasts that coexpressed several prosurvival and ECM genes. The results of both loss-of-function and gain-of-function studies were consistent with a role for WT1 as a positive regulator of prosurvival genes to impair apoptotic clearance and promote ECM production. Fibroblast-specific overexpression of WT1 augmented fibroproliferation, myofibroblast accumulation, and ECM production during bleomycin-induced pulmonary fibrosis in young and aged mice. Together, these findings suggest that targeting WT1 is a promising strategy for attenuating fibroblast expansion and ECM production during fibrogenesis.

Considering Patient Perspective Through Visual Representatives: Telemedicine Gives Voice to Rare Interstitial Lung Disease Patients - Thoracic Research and Practice

Lymphangioleiomyomatosis (LAM) is a cystic lung disease that primarily affects women. LAM is caused by the invasion of metastatic smooth muscle-like cells into the lung parenchyma, leading to abnormal cell proliferation, lung remodeling and progressive respiratory failure. LAM cells have TSC gene mutations, which occur sporadically or in people with Tuberous Sclerosis Complex. Although it is known that hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1) due to TSC2 gene mutations contributes to aberrant cell growth in LAM lung, tumor origin and invasive mechanism remain unclear. To determine molecular drivers responsible for aberrant LAM cell growth, we performed integrative single-cell transcriptomic analysis and predicted that STAT1 interacts with Pre-B cell leukemia transcription factor (PBX1) to regulate LAM cell survival. Here, we show activation of STAT1 and STAT3 proteins in TSC2- deficient LAM models. Fludarabine, a potent STAT1 inhibitor, induced the death of TSC2- deficient cells, increased caspase-3 cleavage, and phosphorylation of necroptosis marker RIP1. Fludarabine treatment impeded lung colonization of TSC2-deficient cells and uterine tumor progression, associated with reduced percentage of PCNA-positive cells in vivo. Interestingly, IFN-γ treatment increased STAT1 phosphorylation and PD-L1 expression, indicating that STAT1 aids TSC2-deficient tumor cells in evading immune surveillance in LAM. Our findings indicate that STAT1 signaling is critical for LAM cell survival and could be targeted to treat LAM and other mTORC1 hyperactive tumors.

Rationale: Approximately 80% of patients with non-familial pulmonary arterial hypertension (PAH) lack identifiable pathogenic genetic variants. While most genetic studies of PAH have focused on predicted loss-of-function variants, recent approaches have identified ultra-rare missense variants associated with the disease. FOXF1 encodes a highly conserved transcription factor, essential for angiogenesis and vasculogenesis in human and mouse lungs. Objectives: We identified a rare FOXF1 missense coding variant in two unrelated probands with PAH. FOXF1 is an evolutionarily conserved transcription factor required for lung vascular development and vascular integrity. Our aims were to determine the frequency of FOXF1 variants in larger PAH cohorts compared to the general population, study FOXF1 expression in explanted lung tissue from PAH patients versus control (failed-donor) lungs, and define potential downstream targets linked to PAH development. Methods: Three independent, international, multicenter cohorts were analyzed to evaluate the frequency of FOXF1 rare variants. Various composite prediction models assessed the deleteriousness of individual variants. Bulk RNA sequencing datasets from human explanted lung tissues were compared to failed-donor controls to determine FOXF1 expression. Bioinformatic tools identified putative FOXF1 binding targets, which were orthogonally validated using mouse ChIP-seq datasets. Measurements and Main Results: Seven novel or ultra-rare missense coding variants were identified across three patient cohorts in different regions of the FOXF1 gene, including the DNA binding domain. FOXF1 expression was dysregulated in PAH lungs, correlating with disease severity. Histological analysis showed heterogeneous FOXF1 expression, with the lowest levels in phenotypically abnormal endothelial cells within complex vascular lesions in PAH samples. A hybrid bioinformatic approach identified FOXF1 downstream targets potentially involved in PAH pathogenesis, including BMPR2 . Conclusions: Large genomic and transcriptomic datasets suggest that decreased FOXF1 expression or predicted dysfunction is associated with PAH.

The pathophysiology of silicosis is poorly understood, limiting development of therapies for those who have been exposed to the respirable particle. We explored mechanisms of silica-induced pulmonary fibrosis in human lung samples collected from patients with occupational exposure to silica and in a longitudinal mouse model of silicosis using multiple modalities including whole-lung single-cell RNA sequencing and histological, biochemical, and physiologic assessments. In addition to pulmonary inflammation and fibrosis, intratracheal silica challenge induced osteoclast-like differentiation of alveolar macrophages and recruited monocytes, driven by induction of the osteoclastogenic cytokine, receptor activator of nuclear factor κΒ ligand (RANKL) in pulmonary lymphocytes, and alveolar type II cells. Anti-RANKL monoclonal antibody treatment suppressed silica-induced osteoclast-like differentiation in the lung and attenuated pulmonary fibrosis. We conclude that silica induces differentiation of pulmonary osteoclast-like cells leading to progressive lung injury, likely due to sustained elaboration of bone-resorbing proteases and hydrochloric acid. Interrupting osteoclast-like differentiation may therefore constitute a promising avenue for moderating lung damage in silicosis.