Novel Bioengineered Biomaterials and Tissue Culture Models to Understand Mucus Clearance Dysfunction in Asthma

Abstract

Airway mucus acts as a protective barrier and vehicle of clearance for inhaled pathogens, providing the lungs with a robust defense mechanism called mucociliary clearance. Airway mucus is composed of two gel-forming mucins, MUC5B and MUC5AC that form a hydrogel that maintains functional clearance in health. However, in asthma, mucus is produced with abnormal properties that result in impaired mucociliary clearance contributing to mucus accumulation and airway obstruction. Recent evidence from clinical studies revealed that mucus obtained from individuals with asthma possesses altered mucin composition as a function of disease severity with a significant shift from MUC5B to MUC5AC as the predominant mucin. However, how these changes alter the functional properties of mucus is not yet fully understood. The overall objective of this dissertation is to understand how an imbalance in the ratio of MUC5B and MUC5AC contributes to abnormal function of mucus in asthma. The central hypothesis is that relative increases in MUC5AC enhances viscoelasticity of the mucus gel, which contributes to the functional defects of mucus. To study this, we engineered two novel approaches: (i) mucin-based biomaterials with tunable mucin composition and (ii) genetically engineered in-vitro systems with targeted knock-out (KO) of each gel-forming mucin. In our first approach, we systematically varied the mucin composition of mucin-based biomaterials and found that a rise in MUC5AC, as observed in asthma, results in increased viscoelasticity, reduced transportability, and impaired barrier function against influenza A virus. Using our second approach, we found that MUC5AC gels produced from MUC5B-KO cultures resulted in impaired mucus clearance, whereas MUC5B gels produced from MUC5AC-KO cultures lacked spatial coordination. Together, these studies suggest that elevated levels of MUC5AC contribute to enhanced viscoelastic properties, while being the key driver of impaired mucociliary clearance in asthma. This work also offers new insight into the contribution of each gel-forming mucin on the dynamic control of mucus transport and flow alignment. This work was motivated by providing a path towards developing new therapeutic targets aimed at normalizing mucus function and improving airway patency in asthma.