Function and Regulation of Airway Mucin Glycosylation

The lungs are exposed to billions of potentially harmful particles daily. Robust defense is crucial, but protection must cause minimal physiologic disruption. Accordingly, a thin and easily transported layer of mucus lines the airways in health. In asthma, mucus aggregates on airway surfaces and obstructs airflow, but this is not effectively treated with existing therapies. We seek to close this gap by building a better mechanistic understanding of how mucus function and dysfunction are mediated by the chief macromolecules in airway mucus--MUC5AC and MUC5B. Their importance is well-recognized through studies in humans and animal models. MUC5B is required for mucociliary clearance, host defense, and survival in both species. Muc5ac is dispensable in healthy mice, but in human asthma and in mouse models, it causes airway obstruction. Both mucins also have host defense and pathogenic roles in non-respiratory tissues. Accordingly, despite clear significance, there is a need to find treatments that prevent mucus dysfunction while also preserving defense. To investigate this, we are focusing on the defining characteristic of mucins – heavy O-glycosylation – and how MUC5AC and MUC5B glycosylation is carried out in the Golgi apparatus. Mucin glycosylation terminates when sugars such as fucose (Fuc) are attached. This terminal fucosylation process in mucins is mediated by the enzyme fucosyltransferase 2 (FUT2), which catalyzes transfer of Fuc to galactose (Gal) acceptors forming Fuc(α1-2)Gal bonds. FUT2 absence is protective in people with asthma and in mouse models where its deficiency protects against mucus plugging and obstruction. Fucosylation increases mucus viscoelasticity, transport, and aggregation, and it is associated with excessive mucus viscoelasticity, and asthma severity. Accordingly, a mechanistic understanding of how FUT2 mediates mucin fucosylation will reveal novel strategies that could be used to target mucus dysfunction in asthma. We hypothesize that trans Golgi- localized FUT2-dependent mucin fucosylation mediates allergic airway mucus dysfunction. We will test this in three Specific Aims that 1) test the hypothesis that mucin α1,2-fucosylation requires FUT2 localization and activity within trans Golgi compartments; 2) test the hypothesis that conserved catalytic sites and non-catalytic regions in FUT2 are required for mucin α1,2-fucosylation; and 3) test the hypothesis that Golgi specific FUT2- dependent α1,2-fucosylation mechanisms mediate mucociliary dysfunction and mucus obstruction. Our focused investigations could reveal ways to target the important, but currently untreatable, problem of mucus hypersecretion while also helping resolve unanswered basic science questions. Project Number: 1R01HL179623-01 | Fiscal Year: 2025 | NIH Institute/Center: National Heart Lung and Blood Institute (NHLBI) | Principal Investigator: Christopher Evans | Institution: UNIVERSITY OF COLORADO DENVER, Aurora, CO | Award Amount: $702,308 | Activity Code: R01 | Study Section: Pulmonary Injury, Repair, and Remodeling Study Section (PIRR)[PIRR] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R01HL17962301