MUC5B and MUC5AC function in combination to regulate mucociliary transport on human airway epithelium.

Muco-obstructive lung diseases are characterized by impaired airway clearance and altered mucin composition. MUC5B and MUC5AC are the primary gel-forming mucins in airway mucus, yet how their relative abundance influences the physical and functional properties of mucus remains poorly understood. Here, we investigated how compositional variations in MUC5B and MUC5AC within mucus impact mucociliary transport. Mucus enriched in either MUC5B or MUC5AC was generated using human airway epithelial models depleted for each mucin via CRISPR/Cas9-targeted knockout. Defined mixtures of these mucins were generated at physiologically relevant ratios, for assessment of their microrheological properties and mucociliary transport behavior in differentiated primary human airway epithelial tissue cultures. We found that increasing MUC5AC content reduced network pore size and increased microviscosity, concomitant with reduced mucociliary transport, demonstrating that mucin composition alters the biophysical and functional properties of the mucus barrier. In normal airway tissue cultures with MUC5B-predominant mucus, overlay of MUC5AC on the apical surface impaired mucociliary transport, whereas MUC5B had minimal effect. Conversely, MUC5B supplementation uniquely improved mucociliary transport in IL-13 stimulated cultures exhibiting mucostasis, whereas additional MUC5AC did not alter transport. Together, these findings demonstrate that the ratio of MUC5B to MUC5AC can shape mucus organization at the microscale, which in turn governs mucociliary transport at the tissue scale.