Supramolecular Assembly of Mucins Instructs Health and Disease

Entangled polymeric networks are found throughout biology. Mucus is one such entangled polymer network, consisting of large, heavily glycosylated, polymeric proteins called mucins. Muco-obstructive pulmonary diseases are often characterized and studied as an increase in mucus concentration that causes accumulation, infection, and inflammation within the lung. While the effect of the bulk properties of mucus are well-studied, the effect of microstructure is unknown. Recently, two different structures have been reported to form within airway mucus: aggregates of mucus, termed flakes, that primarily form in individuals with cystic fibrosis (CF) and large bundles of highly aligned mucins that are secreted out of the glands in the upper airways. With our collaborators, we established flakes as a biomarker for CF progression reflected by a progressive increase in insoluble mucin concentrations, and an abundance of flakes in samples isolated from preschool- and school-aged children. Yet, it remains unclear how these architectures form, how CF pathophysiology influences their formation, composition, and properties, when they become disruptive to mucus clearance, and how to dissolve them to restore healthy lung function. It is difficult to isolate these structures in large quantities, and variability in volume and size distribution further complicates studying and characterizing the role of these structures in lung function. In this dissertation, I work to understand how mucus forms structures such as flakes and strands. In Chapter 2, I carefully characterize clinical samples to determine universal attributes within their structure and the supramolecular interactions that enable the formation of mucins to come together. I determine that flakes form when DNA is secreted into the airway layer to crosslink the mucin network into a rigid and immovable and insoluble aggregate. In Chapter 3, I utilize a similar philosophy and characterize submucosal gland mucus from both donor patients and trachea from pigs. I characterize the insoluble component of gland mucus in pig tracheas and determine that the degree of stimulation affects submucosal gland mucus microstructure. I replicate this process by flowing cell culture mucus through a capillary at high flow rates to reconstruct submucosal gland strands.