Pulmonary Regional Differences Highlight Profibrotic Airway Epithelial Cell Signaling in Obese Asthma
Mccravy, MS; Yang, Z; Mcquade, V; Mummy, D; Kim, H; Womble, JT; Driehuys, B; Ingram, JL; Que, LG
Published in: American Journal of Respiratory and Critical Care Medicine
Rationale: Obesity increases the severity of asthma and modifies airway pathobiology, contributing to lack of responsiveness to standard asthma therapies. The mechanisms driving altered lung function and airway remodeling in obese asthma are poorly understood. We hypothesized that in asthma with comorbid obesity, pulmonary ventilation defects identified using 129Xe magnetic resonance gas exchange imaging (129XeMRI) involve specific regional airway cellular changes that promote profibrotic signaling. Methods: Asthma (n=23) and non-asthma (n=7) participants with obesity underwent supine computed tomography (CT) and 129XeMRI, methacholine challenge, blood collection, spirometry, impulse oscillometry, and bronchoscopy. Chest CT scans were analyzed with the VIDA software package to delineate segmental boundaries and registered to the XeMRI images, with bronchopulmonary segments broadly delineated based on ventilation defects. Bronchoalveolar lavage (BAL), brushings, and endobronchial biopsies were performed at two identified segments in each participant: one with a reversible defect and one with an irreversible defect. In samples from each segment per participant, single-cell ribonucleic acid sequencing (scRNASeq) was performed on cells collected from brushings, total and differential cell counts were determined in BAL fluid, and fibroblasts and airway epithelial cells were cultured from biopsies and brushings, respectively. Airway epithelial cells at air-liquid interface were incubated with 20 ng/mL leptin, 50 ng/mL interleukin-13 (IL-13) or a combination of mediators. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to determine relative gene expression of periostin (POSTN). Results: In asthma participants, the percentage difference in total BAL fluid cells between the two bronchopulmonary sampling sites was positively associated with airway resistance at 5 Hz (R5) (p=0.02) and inversely associated with the provocative concentration of methacholine resulting in a 20% fall in forced expiratory volume in 1 second (MchPC20) (p=0.049). Also, the percent difference in leptin-, but not IL-13-, induced POSTN expression in airway epithelial cells between the two sites was positively associated with serum eosinophil counts in participants (p=0.038). Analysis of scRNASeq data in brushings at the two sites indicates shifts in two populations of cells corresponding to an epithelial and a lymphoid cell type between early and late onset asthma participants. Conclusions: Pulmonary regional differences in gas exchange in obese asthma may be attributed to metabolic hormone-induced profibrotic signaling by airway epithelial cells, which contributes to airway fibrosis, resistance and reactivity.
