Visualization of hypersecreted mucus in the hydrated state in an HDM-induced allergic airway inflammation model using the NanoSuit method.

BACKGROUND

Airway mucus hypersecretion has become a focus for treatment in asthma. Yet, its spatial distribution in the hydrated state at the electron microscopic level in the airways remains poorly understood. Our goal was to investigate mucus distribution under near-physiological conditions using field-emission scanning electron microscopy (FE-SEM) in conjunction with the NanoSuit method, which enables well-preserved hydrated images, and immunoelectron microscopy.

METHODS

Wild-type C57BL/6 mice were sensitized with house dust mite (HDM) extract, and mucin expression, ciliary beating frequency (CBF), and cilia-driven flow were compared with those of control mice. We then assessed mucus distribution under near-physiological conditions with FE-SEM and the NanoSuit method and examined the interplay between mucus and cilia in the murine trachea using immunoelectron microscopy.

RESULTS

HDM-challenged mice showed increased MUC5AC, MUC5B, and MUC4 mRNA levels, reduced CBF, impaired cilia-driven flow, and abnormal flow direction, indicating disrupted mucociliary clearance. Using FE-SEM with the NanoSuit method, airway mucus in HDM mice was observed as droplet-like, non-uniform layers that differed from those in control mice. Immunoelectron microscopy revealed that mucus, coated with MUC5AC and MUC5B, covered the cilia, disrupting their arrangement in HDM-challenged mice.

CONCLUSIONS

Using FE-SEM with the NanoSuit method, we directly visualized spatial distribution of hydrated airway mucus at the electron microscopic level under near-physiological conditions. These findings provide new structural insights into mucus organization in an allergic airway inflammation model.