Idiopathic Pulmonary Fibrosis (IPF) is an incurable disease with extensive molecular, cellular, and organ level dysfunction. A major gap in IPF research is the lack of understanding of how short-term cellular behavior causes long-term tissue remodeling. By optimizing lung slices from explanted human lungs, we discovered foci of migratory non-canonical alveolar type 2 (AT2) cells in regions of established lung fibrosis and found that these cells are trapped in states of cellular transition that are driven by persistent developmental repair programs. Consistent with these biophysical behaviors, pharmacological activation of β-catenin reproduced persistent migration, whereas YAP activation restrained it. We conclude that imbalanced developmental programs drive AT2 cell motility and lesion heterogeneity, providing a mechanistic link between short-term cellular dynamics and slowly progressive fibrosis of IPF.

RATIONALE:IPF is an irreversible and progressive type of lung fibrosis that is pathologically characterized as spatially heterogeneous. Despite the identified dominant risk factor for IPF as the gain-of-function MUC5B promoter variant, little is understood for how MUC5B drives lung fibrosis. OBJECTIVES:We used spatial transcriptomics from idiopathic pulmonary fibrosis (IPF) and unaffected control lung tissue to further understand the pathogenesis of MUC5B-driven lung fibrosis. METHODS:We captured 43 fields of view in 15 IPF and 13 controls with and without the MUC5B promoter variant using the CosMx® platform and identified 19 cell types via semi-supervised clustering. MEASUREMENTS AND MAIN RESULTS:MUC5B was ectopically expressed in AT2 cells in controls with the risk variant. We observed a decreased proportion of AT2 cells in controls and an increased proportion of aberrant basaloid cells in IPF associated with the MUC5B risk variant. We identified co-localized expression of MUC5B in respiratory bronchioles with 13 genes including the endoplasmic reticulum (ER) stress marker XBP1 and distal secretory markers SCGB3A1 and SCGB1A1. Experimentally, we demonstrated a direct relationship between MUC5B expression and ER stress in bronchiolar epithelia in vitro and validated the co-expression of MUC5B and XBP1 in the IPF lung. CONCLUSIONS:Based on our results, we conclude that MUC5B injures alveolar and bronchiolar epithelia that results in loss of AT2 cells and an increase in aberrant basaloid cells which initiates ER stress and a secretory phenotype in the terminal respiratory bronchiole, establishing a persistently injured distal airspace.

Connexin 43 mediated gap junction signaling between ABCG2 hi endothelial progenitor cells and alveolar epithelium governs epithelial differentiation and injury response. Here, we identify a previously unrecognized endothelial - epithelial communication axis that regulates AT2-to-AT1 transition during fibrotic repair. Disruption of ABCG2 hi derived endothelial Cx43 impairs canonical regeneration but activates an alternative basal cell driven repair program. These findings reveal intercellular communication as a key determinant of lung repair trajectory.

Introduction: Idiopathic giant bullous emphysema, or vanishing lung syndrome (VLS), is a rare diagnosis characterized by bilateral, upper lobe predominant emphysema which coalesce into giant bullae occupying more than one third of the hemithorax. In patients under 50, it is frequently associated with inhalational marijuana use or alpha-1 antitrypsin deficiency. This case describes a young male with negligible smoking history, no genetic predisposition, and frequent air travel who presented with dyspnea and chest pain diagnosed with VLS complicated by a secondary spontaneous pneumothorax. Case: A 25-year-old male with bullous lung disease and previous intermittent marijuana use presented with three days of chest pain and dyspnea and was found to have a large left sided pneumothorax. A chest tube was placed with post-procedure imaging demonstrating partial re-expansion of the left lung and bilateral bullous disease (Figure 1A). He had no family history of liver or lung disease nor personal history of prematurity. He endorsed light social marijuana use 2 years prior and intermittent tobacco use 4 years prior. He flew twice monthly between Michigan (sea-level) and Denver (5,000 feet). He underwent a VATS bullectomy and mechanical pleurodesis on the left followed by the same on the right two months later. Pathology results were consistent with emphysematous changes with bullae (Figure 1B). Both post-operative courses were uncomplicated and the patient is doing well without need for supplemental oxygen. A cystic fibrosis panel, folliculin gene sequencing, alpha-1 antitrypsin level, HIV, and urine toxicology were all unremarkable. Discussion: Marijuana-associated VLS is typically described in a long-standing, current marijuana smoker (1). This case describes a young patient with minimal, former marijuana use, suggesting another etiology of bullae enlargement. Air travel emerges as a potential mechanism of barotrauma, supported by a previous study demonstrating transient pulmonary cyst enlargement during air travel (2). This patient's frequent exposure to changes in altitude emerges as a potential mechanism of barotrauma leading to VLS analogous to the dynamics of marijuana inhalation previously described (3). References 1.Velez Oquendo G, Balaji N, Ignatowicz A, Qutob H. Vanishing Lung Syndrome in a Young Male With Chronic Marijuana Use: A Case Report. Cureus. 2023 Dec 28;15(12):e51223. doi: 10.7759/cureus.51223. 2.Hu X, Cowl CT, Baqir M, Ryu JH. Air travel and pneumothorax. Chest. 2014 Apr;145(4):688-694. doi: 10.1378/chest.13-2363. 3.Wu TC, Tashkin DP, Djahed B, Rose JE. Pulmonary hazards of smoking marijuana as compared with tobacco. N Engl J Med. 1988 Feb 11;318(6):347-51. Doi: 10.1056/NEJM198802113180603

The gain-of-function MUC5B promoter variant is the dominant risk factor for the development of idiopathic pulmonary fibrosis (IPF). However, its impact on protein expression in both nonfibrotic control and IPF lung specimens has not been well characterized. Utilizing laser capture microdissection coupled to mass spectrometry, we investigated the proteomic profiles of airway and alveolar epithelium in nonfibrotic controls (n = 12) and IPF specimens (n = 12), stratified by the MUC5B promoter variant. Through qualitative and quantitative analyses, as well as pathway analysis and immunohistological validation, we have identified a distinct MUC5B-associated protein profile. Notably, the nonfibrotic control alveoli exhibited substantial MUC5B-associated protein changes, with an increase in IL-3 signaling. Additionally, we found that epithelial cells overlying IPF fibroblastic foci clustered closely to alveolar epithelia and expressed proteins associated with cellular stress pathways. In conclusion, our findings suggest that the MUC5B promoter variant leads to protein changes in alveolar and airway epithelium that appear to be associated with initiation and progression of lung fibrosis.

Military deployment to Southwest Asia and Afghanistan is linked to complex hazardous airborne exposures, but ascertaining the contributions of specific environmental toxicants in causing or contributing to deployment-related distal lung diseases (DDLD) remains challenging. We applied a quantitative microscopy for particulate matter (QM-PM) technique to measure the in situ burden of pigmented and birefringent lung particulates in 24 veterans with DDLD, 10 smokers with respiratory bronchiolitis (RB), and 10 healthy controls. Veterans were more likely to be male (88%) and were significantly younger than RB and healthy controls (mean age 41 vs. 47 vs. 53 years, respectively). Adjusting for age, the anthracotic pigment fraction in lung tissue from DDLD was similar to RB (1.69% vs. 1.37%, P = 0.72), and was significantly greater than healthy controls (0.52%, P = 0.02). Pigment fraction in veterans was significantly associated with higher reported burn pit smoke exposure (P = 0.02), but not sandstorms or diesel exhaust. Birefringent dust density, indicating retained silica/silicates, was significantly increased in RB (28.89/mm2, P < 0.01) compared to DDLD and healthy control groups (8.93 and 9.44/mm2). Findings suggest that lung deposition of anthracotic dust from burn pit smoke exposure in previously deployed post-9/11 military veterans may be important in the pathogenesis of DDLD.

Rationale: Post-9/11 military deployment to Southwest Asia and Afghanistan is associated with exposure to complex inhalational hazards. Characterizing in situ lung dust may demonstrate causal associations with deployment-related respiratory diseases, but conventional advanced microscopy techniques have various technical limitations. We developed a novel, automated, quantitative microscopy technique (QM-PM) to characterize in situ particulate matter and analyzed retained particulates in lung biopsies from post-9/11 deployed military veterans. Methods: We obtained lung tissue from deployed veterans (n=24) with biopsy-proven deployment-related distal lung disease (DDLD, with bronchiolitis, emphysema, lymphocytic interstitial inflammation); from control subjects with smoking-related respiratory bronchiolitis (RB) (n=10); and from healthy controls (n=10). Using QM-PM (Figure 1), we measured the pigment fraction (percentage of lung tissue containing anthracotic pigment) and birefringent dust density for silica/silicates (birefringent particles/mm2 of tissue). We used a mixed model in R.v.4.2.3 with a random intercept for each subject to account for multiple lobe samples, and Tukey adjustment for multiple comparisons. We adjusted all models for age at biopsy due to differences among groups. Adjustment for smoking was precluded by missing smoking data in healthy controls. Among veterans with DDLD, we calculated individual weighted respiratory hazards scores for five deployment exposures (combat blasts, mortar fire, sandstorms, burn pit combustion products, and diesel exhaust) based on reported duration and frequency/intensity of exposure, and examined their relationship with pigment fraction and birefringent dust density. Results: Deployed veterans with DDLD were 41±7 years old at lung biopsy, 88% male, and 38% current/former smokers. Their lung tissue samples had significantly greater pigment fraction than healthy controls (1.65% vs 0.48%, P=0.03), but were similar to RB controls (1.33%, P=0.72). Birefringent dust density in veterans was similar to healthy controls (9.14/mm2 vs 9.66/mm2, P=0.98), and both were significantly less than subjects with RB (29.56/mm2, P=0.0009 and P=0.01). In deployed veterans, pigment fraction increased with higher respiratory hazards scores, largely driven by exposure to diesel exhaust (P=0.02), burn pit combustion products (P=0.03), and sandstorms (P=0.08). There were no significant relationships between birefringent dust density and weighted respiratory hazards scores. Conclusion: We found an increased burden of pigmented lung particulates, but not silica/silicates, associated with exposure to several airborne hazards in veterans with DDLD compared to healthy controls. Our findings implicate deployment exposure to dust from sources such as burn pits and diesel exhaust in distal lung injury. This study provides further validation for use of QM-PM in characterizing particulate exposures in occupational cohorts.

Sarcoidosis is a multisystem inflammatory disease of unknown etiology. Growing evidence indicates that occupational exposure to respirable crystalline silica (RCS) is associated with an increased incidence of sarcoidosis. Yet a diagnosis of sarcoidosis rarely prompts investigation to identify preventable exposures. We sought to elucidate features that identify this important clinical syndrome of silicosarcoidosis. We assembled a multinational case series of workers with sarcoidosis who also reported occupational RCS exposure. We characterized clinical and histopathologic findings using a standardized instrument. We also assessed lung specimens using a novel quantitative microscopy technique to measure birefringent dust density in silicosarcoidosis cases and compared them to control groups. We identified 35 silicosarcoidosis cases (97% male, mean age 48 years) from the United States, Israel, and Taiwan who reported 21 ± 9 years of RCS exposure. On histology scoring, 25/29 (86%) had granulomas and 17/18 (94%) with evaluable lung tissue had lymphocytic inflammation and/or lymphoid aggregates. Common lung interstitial findings included silicotic nodules (39%), mixed-dust macules/nodules (44%), and birefringent dust (50%). Quantitative birefringent dust density was significantly greater (p < 0.001) in silicosarcoidosis cases compared with healthy controls (147 ± 179 vs. 12 ± 9 particles/mm2) but lower than in coal miners with silica-related progressive massive fibrosis (623 ± 777). We found significant differences in the frequency of histologic abnormalities in large versus small biopsy specimens, with fewer findings of RCS exposure in smaller tissue samples. The use of the term silicosarcoidosis should enhance recognition of this significant exposure-related granulomatous lung disease and will help guide clinical management that addresses exposure prevention in combination with appropriate pharmacologic treatment.

Abstract Pulmonary veno‐occlusive disease (PVOD) is a rare form of pulmonary vascular disease that is difficult to distinguish clinically from pulmonary arterial hypertension (PAH). Multiple genes have been implicated in disease pathogenesis in PAH and PVOD and the diseases are thought to be genetically distinct. In this report we present a case of first‐degree relatives with pathological evidence of PVOD and PAH. The index patient was diagnosed with PAH at age 42, was treated with escalating pulmonary vasodilator therapy, but eventually succumbed to her disease. On autopsy, her pathology was consistent with PAH. Her son was diagnosed with PAH at age 16, did well on pulmonary vasodilator therapy for over 10 years, but ultimately developed refractory right ventricular failure and received a heart and lung transplantation. Pathology of his explanted lung was consistent with PVOD, and genetic testing was negative for recognized variants that cause PAH or PVOD.

CONTEXT.—The pathology of coal workers' pneumoconiosis (CWP) and its most severe form-progressive massive fibrosis (PMF)-in US coal miners has changed in recent years. Severe disease is occurring in younger miners and has been linked to an increase in silica dust exposure.OBJECTIVE.—To update the description of the pathologic features of CWP in contemporary miners compared to historical miners.DESIGN.—This study is a retrospective expert classification of lung tissue from 85 historical and contemporary coal miners with PMF. Significant pathologic features were scored by using a standardized instrument with consensus achieved for major findings, including newly defined categories of PMF as coal-type, mixed-type, and silica-type.RESULTS.—Pathologic features associated with silica dust exposure, including silica-type PMF, mineral dust alveolar proteinosis (MDAP), and immature (early stage) silicotic nodules were increased in contemporary miners. Detailed descriptions of the pathology of contemporary CWP with illustrative figures are provided.CONCLUSIONS.—Silica-related pathologies are more common in contemporary miners. Severe forms of CWP can be detected by subtyping PMF lesions (if present) or by identification of mature and immature silicotic nodules, coal mine dust-related alveolar proteinosis, and severe inflammation in coal miners' lungs. Silica-type PMF cases showed significantly higher levels of MDAP than either mixed- or coal-type PMF (P < .001). High profusion of birefringent silica/silicate particles was observed more frequently in cases with immature (early stage) silicotic nodules (P = .04). Severe inflammation was also significantly increased in contemporary miners (P = .03). Our findings underscore the urgent need to revise current exposure limits and monitoring of respirable crystalline silica in US coal mines.

Granulomatous-lymphocytic interstitial lung disease (GLILD) is a lymphoproliferative and granulomatous pulmonary manifestation of primary immune deficiency diseases, notably common variable immunodeficiency (CVID), and is an important contributor of excess morbidity. As with all forms of ILD, the significance of utilizing a multidisciplinary team discussion to enhance diagnostic and treatment confidence of GLILD cannot be overstated. In this review, key clinical, radiological, and pathological features are integrated into a diagnostic algorithm to facilitate a consensus diagnosis. As the evidence for diagnosing and managing patients with GLILD is limited, the viewpoints discussed here are not meant to resolve current controversies. Instead, this review aims to provide a practical framework for diagnosing and evaluating suspected cases and emphasizes the importance of a multidisciplinary approach when caring for GLILD patients.

Dendriform pulmonary ossification (DPO) is a rare condition characterized by mature bone formation in the lung. DPO has been linked to various conditions, but little is known about the link between DPO and hazardous airborne exposures. We queried research databases of military personnel evaluated for deployment-related respiratory diseases at two occupational pulmonary medicine clinics (Colorado, USA) for diagnoses of DPO, and summarized demographics, Gulf War military deployment history, medical history, and pulmonary function testing. Chest imaging was independently reviewed and scored by a thoracic radiologist, and all cases had undergone lung tissue biopsy. We identified five male combat veterans with DPO, median age 49 years [range: 32-64]. All had deployed to Southwest Asia or Afghanistan during the First or Second Gulf War, and all reported frequent, intense exposure to diesel exhaust, burn pit emissions, and sandstorms. Lung physiology was abnormal in all cases. The most prevalent chest imaging and histopathology findings were airway-centric injury, inflammation, and retained particulate matter, suggesting substantial hazardous exposure during military deployment. This case series of a rare lung disease from the only two contemporary Colorado clinics serving previously deployed veterans highlights a potential link between airborne hazards and lung injury leading to DPO. A high index of clinical suspicion combined with a detailed occupational history may reveal additional exposure-related associations with DPO. Access to large medical databases of military veterans with linkage to exposure histories may further elucidate risk factors for lung injury with ossification, paving the way for targeted prevention.

CONTEXT.— Current approaches for characterizing retained lung dust using pathologists' qualitative assessment or scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) have limitations. OBJECTIVE.— To explore polarized light microscopy coupled with image-processing software, termed quantitative microscopy-particulate matter (QM-PM), as a tool to characterize in situ dust in lung tissue of US coal miners with progressive massive fibrosis. DESIGN.— We developed a standardized protocol using microscopy images to characterize the in situ burden of birefringent crystalline silica/silicate particles (mineral density) and carbonaceous particles (pigment fraction). Mineral density and pigment fraction were compared with pathologists' qualitative assessments and SEM/EDS analyses. Particle features were compared between historical (born before 1930) and contemporary coal miners, who likely had different exposures following changes in mining technology. RESULTS.— Lung tissue samples from 85 coal miners (62 historical and 23 contemporary) and 10 healthy controls were analyzed using QM-PM. Mineral density and pigment fraction measurements with QM-PM were comparable to consensus pathologists' scoring and SEM/EDS analyses. Contemporary miners had greater mineral density than historical miners (186 456 versus 63 727/mm3; P = .02) and controls (4542/mm3), consistent with higher amounts of silica/silicate dust. Contemporary and historical miners had similar particle sizes (median area, 1.00 versus 1.14 μm2; P = .46) and birefringence under polarized light (median grayscale brightness: 80.9 versus 87.6; P = .29). CONCLUSIONS.— QM-PM reliably characterizes in situ silica/silicate and carbonaceous particles in a reproducible, automated, accessible, and time/cost/labor-efficient manner, and shows promise as a tool for understanding occupational lung pathology and targeting exposure controls.

Context.— Overexposure to respirable coal mine dust can cause severe lung disease including progressive massive fibrosis (PMF). Field emission scanning electron microscopy with energy dispersive x-ray spectroscopy (FESEM-EDS) has been used for in situ lung dust particle analysis for evaluation of disease etiology. Automating such work can reduce time, costs, and user bias. Objective.— To develop and test an automated FESEM-EDS method for in situ analysis of inorganic particles in coal miner lung tissue. Design.— We programmed an automated FESEM-EDS procedure to collect particle size and elemental data, using lung tissue from 10 underground coal miners with PMF and 4 control cases. A statistical clustering approach was used to establish classification criteria based on particle chemistry. Data were correlated to PMF/non-PMF areas of the tissue, using corresponding brightfield microscopy images. Results for each miner case were compared with a separate corresponding analysis of particles recovered following tissue digestion. Results.— In situ analysis of miner tissues showed higher particle number densities than controls and densities were generally higher in PMF than non-PMF areas. Particle counts were typically dominated by aluminum silicates with varying percentages of silica. Compared to digestion results for the miner tissues, in situ results indicated lower density of particles (number per tissue volume), larger size, and a lower ratio of silica to total silicates—probably due to frequent particle clustering in situ. Conclusions.— Automated FESEM-EDS analysis of lung dust is feasible in situ and could be applied to a larger set of mineral dust–exposed lung tissues to investigate specific histologic features of PMF and other dust-related occupational diseases.