Proximal and Distal Bronchioles Contribute to the Pathogenesis of Non-Cystic Fibrosis Bronchiectasis.

Rationale: Non-cystic fibrosis bronchiectasis (NCFB) may originate in bronchiolar regions of the lung. Accordingly, there is a need to characterize the morphology and molecular characteristics of NCFB bronchioles. Objectives: Test the hypothesis that NCFB exhibits a major component of bronchiolar disease manifest by mucus plugging and ectasia. Methods: Morphologic criteria and region-specific epithelial gene expression, measured histologically and by RNA in situ hybridization and immunohistochemistry, identified proximal and distal bronchioles in excised NCFB lungs. RNA in situ hybridization and immunohistochemistry assessed bronchiolar mucus accumulation and mucin gene expression. CRISPR-Cas9-mediated IL-1R1 knockout in human bronchial epithelial cultures tested IL-1α and IL-1ß contributions to mucin production. Spatial transcriptional profiling characterized NCFB distal bronchiolar gene expression. Measurements and Main Results: Bronchiolar perimeters and lumen areas per section area were increased in proximal, but not distal, bronchioles in NCFB versus control lungs, suggesting proximal bronchiolectasis. In NCFB, mucus plugging was observed in ectatic proximal bronchioles and associated nonectatic distal bronchioles in sections with disease. MUC5AC and MUC5B mucins were upregulated in NCFB proximal bronchioles, whereas MUC5B was selectively upregulated in distal bronchioles. Bronchiolar mucus plugs were populated by IL-1ß-expressing macrophages. NCFB sterile sputum supernatants induced human bronchial epithelial MUC5B and MUC5AC expression that was >80% blocked by IL-1R1 ablation. Spatial transcriptional profiling identified upregulation of genes associated with secretory cells, hypoxia, interleukin pathways, and IL-1ß-producing macrophages in mucus plugs and downregulation of epithelial ciliogenesis genes. Conclusions: NCFB exhibits distinctive proximal and distal bronchiolar disease. Both bronchiolar regions exhibit bronchiolar secretory cell features and mucus plugging but differ in mucin gene regulation and ectasia.

Bronchiole adenoma/pulmonary ciliated mucinous nodular papillary tumor: Case series and literature review.

OBJECTIVE: To analyze the clinical-pathological characteristics of 3 cases of bronchiolar adenoma/pulmonary ciliary mucinous nodular papillary tumors, and to improve the understanding of bronchiolar adenoma (BA)/ciliated muconodular papillary tumors (CMPT) (bronchiolar adenoma/ciliated muconodular papillary tumor). METHODS: Retrospective analysis was done on the clinical information, diagnosis, and treatment of 3 instances of BA/CMPT at the Second People's Hospital of Weifang City. By scanning the CNKI, Wanfang, VIP database, and Pubmed database using the English key words "bronchiolar adenoma, ciliated muconodular papillary tumor," respectively patients with comprehensive clinical data were gathered, and studies from January 2002 to August 2021 that were relevant to the patients were examined. RESULTS: A total of 35 articles and 71 instances were found, including 3 cases in our hospital, for a total of 74 cases. There were 31 males and 43 females among them, ranging in age from 18 to 84 years (average 63 years), and 15 cases had a smoking history. The majority of them were discovered by physical examination and had no clinical symptoms. The majority of the imaging revealed solid nodules with variable forms, with some ground-glass nodules displaying vacuole and bronchial inflation signs. BA/CMPT are generally gray-white, gray-brown solid nodules with obvious boundaries but no envelope with a maximum dimension of 4 to 45 mm (average 10.6 mm) on gross examination. Acinar, papillary, and lepidic formations can be seen under the microscope at high magnification; the majority of these structures are made up of tripartite epithelial components, including basal cells, mucous cells, ciliated columnar cells, and alveolar epithelial cells, demonstrating a variety of combinations. An important basis for diagnosis in immunohistochemistry is the continuous positive basal cell layer that is shown by p63, p40, and CK5/6. BRAF and epidermal growth factor receptor are the genes that are most frequently mutated. All of the patients showed no signs of metastasis or recurrence during follow-up period. CONCLUSION: BA/CMPT is a rare benign tumor of lung epithelium. Because imaging and intraoperative cryosection diagnosis are easy to be misdiagnosed as malignant, it is necessary to further improve understanding and improve immunohistochemistry and genetic examination.

Analysis of Airway Thickening and Serum Cytokines in COPD Patients with Frequent Exacerbations: A Heart of the Matter.

Background: Differences in lung function for Chronic Obstructive Pulmonary Disease (COPD) cause bias in the findings when identifying frequent exacerbator phenotype-related causes. The aim of this study was to determine whether computed tomographic (CT) biomarkers and circulating inflammatory biomarkers were associated with the COPD frequent exacerbator phenotype after eliminating the differences in lung function between a frequent exacerbator (FE) group and a non-frequent exacerbator (NFE) group. Methods: A total of 212 patients with stable COPD were divided into a FE group (n=106) and a NFE group (n=106) according to their exacerbation history. These patients were assessed by spirometry, quantitative CT measurements and blood sample measurements during their stable phase. Univariate and multivariate logistic regression were used to assess the association between airway thickening or serum cytokines and the COPD frequent exacerbator phenotype. Receiver operating characteristic (ROC) curves were calculated for Pi10, WA%, IL-1ß and IL-4 to identify frequent exacerbators. Results: Compared with NFE group, FE group had a greater inner perimeter wall thickness of a 10 mm diameter bronchiole (Pi10), a greater airway wall area percentage (WA%) and higher concentrations of IL-1ß and IL-4 (p<0.001). After adjusting for sex, age, BMI, FEV1%pred and smoking pack-years, Pi10, WA%, IL-ß and IL-4 were independently associated with a frequent exacerbator phenotype (p<0.001). Additionally, there was an increase in the odds ratio of the frequent exacerbator phenotype with increasing Pi10, WA%, IL-4, and IL-1ß (p for trend <0.001). The ROC curve demonstrated that IL-1ß had a significantly larger calculated area under the curve (p < 0.05) than Pi10, WA% and IL-4. Conclusion: Pi10, WA%, IL-4, and IL-1ß were independently associated with the frequent exacerbator phenotype among patients with stable COPD, suggesting that chronic airway and systemic inflammation contribute to the frequent exacerbator phenotype. Trial Registration: This trial was registered in Chinese Clinical Trial Registry (https://www.chictr.org.cn). Its registration number is ChiCTR2000038700, and date of registration is September 29, 2020.

Activation of the Complement and Coagulation Systems in the Small Airways in Asthma.

BACKGROUND: Several studies have shown the importance of the complement and coagulation systems in the pathogenesis of asthma. OBJECTIVES: We explored whether we could detect differentially abundant complement and coagulation proteins in the samples obtained from the small airway lining fluid by collection of exhaled particles in patients with asthma and whether these proteins are associated with small airway dysfunction and asthma control. METHOD: Exhaled particles were obtained from 20 subjects with asthma and 10 healthy controls (HC) with the PExA method and analysed with the SOMAscan proteomics platform. Lung function was assessed by nitrogen multiple breath washout test and spirometry. RESULTS: 53 proteins associated with the complement and coagulation systems were included in the analysis. Nine of those proteins were differentially abundant in subjects with asthma as compared to HC, and C3 was significantly higher in inadequately controlled asthma as compared to well-controlled asthma. Several proteins were associated with physiological tests assessing small airways. CONCLUSIONS: The study highlights the role of the local activation of the complement and coagulation systems in the small airway lining fluid in asthma and their association with both asthma control and small airway dysfunction. The findings highlight the potential of complement factors as biomarkers to identify different sub-groups among patients with asthma that could potentially benefit from a therapeutic approach targeting the complement system.

Computational fluid-particle dynamics modeling of ultrafine to coarse particles deposition in the human respiratory system, down to the terminal bronchiole.

BACKGROUND AND OBJECTIVES: Suspended respirable airborne particles are associated with human health risks and especially particles within the range of ultrafine (< 0.1 µm) or fine (< 2.5 µm) have a high possibility of penetrating the lung region, which is concerned to be closely related to the bronchial or alveoli tissue dosimetry. Nature complex structure of the respiratory system requires much effort to explore and comprehend the flow and the inhaled particle dynamics for precise health risk assessment. Therefore, this study applied the computational fluid-particle dynamics (CFPD) method to elucidate the deposition characteristics of ultrafine-to-coarse particles in the human respiratory tract from nostrils to the 16th generation of terminal bronchi. METHODS: The realistic bronchi up to the 8th generation are precisely and perfectly generated from computed tomography (CT) images, and an artificial model compensates for the 9th-16th bronchioles. Herein, the steady airflow is simulated at constant breathing flow rates of 7.5, 15, and 30 L/min, reproducing human resting-intense activity. Then, trajectories of the particle size ranging from 0.002 - 10 µm are tracked using a discrete phase model. RESULTS: Here, we report reliable results of airflow patterns and particle deposition efficiency in the human respiratory system validated against experimental data. The individual-related focal point of ultrafine and fine particles deposition rates was actualized at the 8th generation; whilst the hot-spot of the deposited coarse particles was found in the 6th generation. Lobar deposition characterizes the dominance of coarse particles deposited in the right lower lobe, whereas the left upper-lower and right lower lobes simultaneously occupy high deposition rates for ultrafine particles. Finally, the results indicate a higher deposition in the right lung compared to its counterpart. CONCLUSIONS: From the results, the developed realistic human respiratory system down to the terminal bronchiole in this study, in coupling with the CFPD method, delivers the accurate prediction of a wide range of particles in terms of particle dosimetry and visualization of site-specific in the consecutive respiratory system. In addition, the series of CFPD analyses and their results are to offer in-depth information on particle behavior in human bronchioles, which may benefit health risk assessment or drug delivery studies.

An update in club cell biology and its potential relevance to chronic obstructive pulmonary disease.

Club cells are found in human small airways where they play an important role in immune defense, xenobiotic metabolism, and repair after injury. Over the past few years, data from single-cell RNA sequencing (scRNA-seq) studies has generated new insights into club cell heterogeneity and function. In this review, we integrate findings from scRNA-seq experiments with earlier in vitro, in vivo, and microscopy studies and highlight the many ways club cells contribute to airway homeostasis. We then discuss evidence for loss of club cells or club cell products in the airways of patients with chronic obstructive pulmonary disease (COPD) and discuss potential mechanisms through which this might occur.

Clinicopathological features and genomic analysis of bronchiolar adenoma.

BACKGROUND: Bronchiolar adenoma (BA) is a rare tumor of the bronchioles with a double-layer structure, including the basal cell layer and the superficial cell layer, and it has a good prognosis. However, the concept of a putative variant of BA has been proposed in the recent literature. METHODS: Data on 17 cases of BA were collected from our center. The clinical data, morphology, immunophenotype, and molecular changes were retrospectively analyzed. We also collected the molecular changes in BA reported in the previous literature and summarized the putative driver mutations of BA. RESULTS: Out of 17 BAs, 13 were classic cases with a double-layer structure, including 9 proximal-type and 4 distal-type BAs. Of note, we also identified 3 cases that lacked a continuous basal cell layer, including 2 cases of mixed-type BA with monolayered lesions (basal cells were undetected in some areas) and 1 case of a monolayered BA-like lesion (basal cells were completely undetected). The immunohistochemical findings of monolayer cell lesions were closer to those of minimally invasive adenocarcinoma. We also found one case in which BA transformed into invasive adenocarcinoma accompanied by mutations in the TP53, JAK2, NF1 and RB1 genes. Combined with the previous literature, the most common putative driver gene mutations in 62 BA lesions were EGFR (25/62; 41%) and BRAF (21/62; 34.4%). CONCLUSION: Typical BA has a double-layer cell structure; however, there is also a putative variant of BA, which has a monolayer cell structure and lacks the basal cell layer. Transformation from BA into invasive adenocarcinoma is unusual but can occur.

A Unique Cellular Organization of Human Distal Airways and Its Disarray in Chronic Obstructive Pulmonary Disease.

Rationale: Remodeling and loss of distal conducting airways, including preterminal and terminal bronchioles (pre-TBs/TBs), underlie progressive airflow limitation in chronic obstructive pulmonary disease (COPD). The cellular basis of these structural changes remains unknown. Objectives: To identify biological changes in pre-TBs/TBs in COPD at single-cell resolution and determine their cellular origin. Methods: We established a novel method of distal airway dissection and performed single-cell transcriptomic profiling of 111,412 cells isolated from different airway regions of 12 healthy lung donors and pre-TBs of 5 patients with COPD. Imaging CyTOF and immunofluorescence analysis of pre-TBs/TBs from 24 healthy lung donors and 11 subjects with COPD were performed to characterize cellular phenotypes at a tissue level. Region-specific differentiation of basal cells isolated from proximal and distal airways was studied using an air-liquid interface model. Measurements and Main Results: The atlas of cellular heterogeneity along the proximal-distal axis of the human lung was assembled and identified region-specific cellular states, including SCGB3A2+ SFTPB+ terminal airway-enriched secretory cells (TASCs) unique to distal airways. TASCs were lost in COPD pre-TBs/TBs, paralleled by loss of region-specific endothelial capillary cells, increased frequency of CD8+ T cells normally enriched in proximal airways, and augmented IFN-γ signaling. Basal cells residing in pre-TBs/TBs were identified as a cellular origin of TASCs. Regeneration of TASCs by these progenitors was suppressed by IFN-γ. Conclusions: Altered maintenance of the unique cellular organization of pre-TBs/TBs, including loss of the region-specific epithelial differentiation in these bronchioles, represents the cellular manifestation and likely the cellular basis of distal airway remodeling in COPD.

Mucin distribution in bronchiolar adenoma/ciliated muconodular papillary tumor reveals organoid differentiation simulating the normal lung.

Bronchiolar adenoma/ciliated muconodular papillary tumor is a lung neoplasm exhibiting various degrees of proximal and distal bronchiolar differentiation. Here, we evaluated distribution of MUC5AC and MUC5B in bronchiolar adenoma/ciliated muconodular papillary tumor for comparison with that seen in normal respiratory tract. In normal respiratory tract, MUC5AC was mainly distributed in large bronchi, while MUC5B was distributed in bronchi, bronchioles, and submucosal glands. In bronchiolar adenoma/ciliated muconodular papillary tumor, MUC5AC was primarily distributed in luminal cells of large airspaces, and MUC5B was distributed in luminal cells of small airspaces and mucinous glands, in addition to large airspaces, regardless of distal or proximal differentiation. In particular, MUC5B was distributed in non-mucinous club and ciliated cells in both the normal respiratory tract and bronchiolar adenoma/ciliated muconodular papillary tumor. These results indicate that MUC5AC and MUC5B distribution in bronchiolar adenoma/ciliated muconodular papillary tumor is similar to that seen in normal respiratory tract, suggestive of organoid differentiation simulating the normal lung.

Human distal airways contain a multipotent secretory cell that can regenerate alveoli.

The human lung differs substantially from its mouse counterpart, resulting in a distinct distal airway architecture affected by disease pathology in chronic obstructive pulmonary disease. In humans, the distal branches of the airway interweave with the alveolar gas-exchange niche, forming an anatomical structure known as the respiratory bronchioles. Owing to the lack of a counterpart in mouse, the cellular and molecular mechanisms that govern respiratory bronchioles in the human lung remain uncharacterized. Here we show that human respiratory bronchioles contain a unique secretory cell population that is distinct from cells in larger proximal airways. Organoid modelling reveals that these respiratory airway secretory (RAS) cells act as unidirectional progenitors for alveolar type 2 cells, which are essential for maintaining and regenerating the alveolar niche. RAS cell lineage differentiation into alveolar type 2 cells is regulated by Notch and Wnt signalling. In chronic obstructive pulmonary disease, RAS cells are altered transcriptionally, corresponding to abnormal alveolar type 2 cell states, which are associated with smoking exposure in both humans and ferrets. These data identify a distinct progenitor in a region of the human lung that is not found in mouse that has a critical role in maintaining the gas-exchange compartment and is altered in chronic lung disease.

Adipose triglyceride lipase-mediated lipid catabolism is essential for bronchiolar regeneration.

The lung airways are constantly exposed to inhaled toxic substances, resulting in cellular damage that is repaired by local expansion of resident bronchiolar epithelial club cells. Disturbed bronchiolar epithelial damage repair lies at the core of many prevalent lung diseases, including chronic obstructive pulmonary disease, asthma, pulmonary fibrosis, and lung cancer. However, it is still not known how bronchiolar club cell energy metabolism contributes to this process. Here, we show that adipose triglyceride lipase (ATGL), the rate-limiting enzyme for intracellular lipolysis, is critical for normal club cell function in mice. Deletion of the gene encoding ATGL, Pnpla2 (also known as Atgl), induced substantial triglyceride accumulation, decreased mitochondrial numbers, and decreased mitochondrial respiration in club cells. This defect manifested as bronchiolar epithelial thickening and increased airway resistance under baseline conditions. After naphthalene­induced epithelial denudation, a regenerative defect was apparent. Mechanistically, dysfunctional PPARα lipid-signaling underlies this phenotype because (a) ATGL was needed for PPARα lipid-signaling in regenerating bronchioles and (b) administration of the specific PPARα agonist WY14643 restored normal bronchiolar club cell ultrastructure and regenerative potential. Our data emphasize the importance of the cellular energy metabolism for lung epithelial regeneration and highlight the significance of ATGL-mediated lipid catabolism for lung health.