BACKGROUND: Mucus plugs form in acute asthma and persist in chronic disease. Although eosinophils are implicated in mechanisms of mucus pathology, many mechanistic details about mucus plug formation and persistence in asthma are unknown. METHODS: Using histology and spatial, single-cell proteomics, we characterized mucus-plugged airways from nontransplantable donor lungs of 14 patients with asthma (9 with fatal asthma and 5 with nonfatal asthma) and individuals acting as controls (10 with chronic obstructive pulmonary disease and 14 free of lung disease). Additionally, we used an airway epithelial cell–eosinophil (AEC-eosinophil) coculture model to explore how AEC mucus affects eosinophil degranulation. RESULTS: Asthma mucus plugs were tethered to airways showing infiltration with innate lymphoid type 2 cells and hyperplasia of smooth muscle cells and MUC5AC-expressing goblet cells. Asthma mucus plugs were infiltrated with immune cells that were mostly dual positive for eosinophil peroxidase (EPX) and neutrophil elastase, suggesting that neutrophils internalize EPX from degranulating eosinophils. Indeed, eosinophils exposed to mucus from IL-13–activated AECs underwent CD11b- and glycan-dependent cytolytic degranulation. Dual-positive granulocytes varied in frequency in mucus plugs. Whereas paucigranulocytic plugs were MUC5AC rich, granulocytic plugs had a mix of MUC5AC, MUC5B, and extracellular DNA traps. Paucigranulocytic plugs occurred more frequently in (acute) fatal asthma and granulocytic plugs predominated in (chronic) nonfatal asthma. CONCLUSION: Together, our data suggest that mucin-rich mucus plugs in fatal asthma form because of acute goblet cell degranulation in remodeled airways and that granulocytic mucus plugs in chronic asthma persist because of a sustaining niche characterized by epithelial cell–mucin-granulocyte cross-talk. FUNDING: NIH grants HL080414, HL107202, and AI077439.

The extracellular matrix (ECM) supports lung tissue architecture and physiology by providing mechanical stability and elastic recoil. Over the last several decades, it has become increasingly clear that the stiffness of the ECM governs many cellular processes, including cell-phenotype and functions during development, healing, and disease. Of all the lung ECM proteins, collagen-I is the most abundant and provides tensile strength. In many fibrotic lung diseases, the expression of collagen is increased which affects the stiffness of the surrounding environment. The goal of this study was to assess the effect on fibroblast morphology, cell death, and inflammation when exposed to 2D and 3D low (0.4 mg/mL) versus high (2.0 mg/mL) collagen-I-matrix environments that model the mechanics of the breathing lung. This study demonstrates that human fetal lung fibroblasts (HFL1), grown in a 3D collagen type-I environment compared to a 2D one, do not form cells with a myofibroblast morphology, express less F-actin stress fibers, exhibit less cell death, and significantly produce less pro-inflammatory IL-6 and IL-8 cytokines. Exposure to mechanical strain to mimic breathing (0.2 Hz) led to the loss of HFL1 fibroblast dendritic extensions as well as F-actin stress fibers within the cell cytoskeleton, but did not influence cytokine production or cell death. This dynamic assay gives researchers the ability to consider the assessment of the mechanodynamic nature of the lung ECM environment in disease-relevant models and the potential of mechano-pharmacology to identify therapeutic targets for treatment.

Asthma is characterized by persistent airway epithelial dysfunction and remodelling of the reticular basement membrane (RBM). In healthy airways, the RBM is primarily composed of the extracellular matrix (ECM) proteins laminin and collagen-IV, but in remodelled asthmatic airways, the RBM has increased deposition of collagen-I, -III and fibronectin. Here, we systematically compared the effects of collagen-I, -III, -IV, fibronectin, laminin, and bovine serum albumin (BSA) control on bronchial epithelial cells (BECs) from six healthy controls and seven individuals with asthma. Epithelial attachment, spreading and barrier function were assessed in real time over 72 h using electrical cell–substrate impedance sensing. Cell culture supernatants were analyzed for release of epithelial cytokines, thymic stromal lymphopoietin (TSLP), interleukin (IL)-6, IL-8, and IL-11 using ELISA. BECs from both control and asthma donors had faster cell attachment, spreading, and barrier formation on collagen-I, -III, -IV, and fibronectin compared to laminin and BSA. BECs from both control and asthma donors cultured on collagen -I and -III produced more TSLP, but had no effect on IL-6, IL-8, and IL-11 expression. In summary, remodelling of the RBM in asthma may promote epithelial barrier formation whilst simultaneously enhancing epithelial-derived Th2 inflammation through increased TSLP release.