Thelin, W. R. | bioRxiv Science

bioRxiv2019

Disulfide disruption reverses mucus dysfunction in allergic airway disease

Airway mucus is essential for healthy lung defense1, but excessive mucus in asthma obstructs airflow, leading to severe and potentially fatal outcomes2-5. Current asthma therapies reduce allergic inflammation and relax airway smooth muscle, but treatments are often inadequate due to their minimal effects on mucus obstruction6,7. The lack of efficacious mucus-targeted treatments stems from a poor understanding of healthy mucus function and pathological mucus dysfunction at a molecular level. The chief macromolecules in mucus, polymeric mucins, are massive glycoproteins whose sizes and biophysical properties are dictated in part by covalent disulfide bonds that link mucin molecules into assemblies of 10 or more subunits8. Once secreted, mucin glycopolymers can aggregate to form plugs that block airflow. Here we show that reducing mucin disulfide bonds depolymerizes mucus in human asthma and reverses pathological effects of mucus hypersecretion in a mouse allergic asthma model. In mice challenged with a fungal allergen, inhaled mucolytic treatment acutely loosened mucus mesh, enhanced mucociliary clearance (MCC), and abolished airway hyperreactivity (AHR) to the bronchoprovocative agent methacholine. AHR reversal was directly related to reduced mucus plugging. Furthermore, protection in mucolytic treated mice was identical to prevention observed in mice lacking Muc5ac, the polymeric mucin required for allergic AHR in murine models9. These findings establish grounds for developing novel fast-acting agents to treat mucus hypersecretion in asthma10,11. Efficacious mucolytic therapies could be used to directly improve airflow, help resolve inflammation, and enhance the effects of inhaled treatments for asthma and other respiratory conditions11,12.

physiology↗

bioRxiv2018

Sorting Nexin 27 (SNX27): A Novel Regulator of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Trafficking

The underlying defect in cystic fibrosis is mutation of the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel expressed at the apical surface of lung epithelia. In addition to its export and maintenance at the cell surface, CFTR regulation involves repeated cycles of transport through the endosomal trafficking system, including endocytosis and recycling. Many of the known disease mutations cause CFTR intracellular trafficking defects that result in failure of ion channel delivery to the apical plasma membrane. Corrective maneuvers directed at improving transport to the plasma membrane are thwarted by rapid internalization and degradation of the mutant CFTR proteins. The molecular mechanisms involved in these processes are not completely understood but may involve protein-protein interactions with the C-terminal type I PDZ-binding motif of CFTR. Using a proteomic approach, we identify sorting nexin 27 (SNX27) as a novel CFTR binding partner in human airway epithelial Calu-3 cells. SNX27 and CFTR interact directly, with the SNX27 PDZ domain being both necessary and sufficient for this interaction. SNX27 co-localizes with internalized CFTR at sub-apical endosomal sites in polarized Calu-3 cells, and either knockdown of the endogenous SNX27, or over-expression of a dominant-negative SNX27 mutant, resulted in significant decreases in cell surface CFTR levels. CFTR internalization was not affected by SNX27 knockdown, but defects were observed in the recycling arm of CFTR trafficking through the endosomal system. Furthermore, knockdown of SNX27 in Calu-3 cells resulted in significant decreases in CFTR protein levels, consistent with degradation of the internalized pool. These data identify SNX27 as a physiologically significant regulator of CFTR trafficking and homeostasis in epithelial cells.

cell biology↗