Buffer drains and mucus is transported upward in a tilted mucus clearance assay

• Published in: American journal of physiology. Lung cellular and molecular physiology Vol. 315; no. 5; pp. L910 - L918
• Main Authors: Carpenter, Jerome, Lynch, Suzanne E, Cribb, Jeremy A, Kylstra, Schuyler, Hill, David B, Superfine, Richard
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.11.2018
• Subjects: Cells, Cultured; Cilia - physiology; Drainage - methods; Epithelial Cells - physiology; Humans; Innovative Methodology; Mucociliary Clearance - physiology; Respiratory Mucosa - physiology; Rheology - methods; organ on a chip; drainage; mucociliary clearance; tilting microscope; mucus clearance assay
• ISSN: 1040-0605; 1522-1504
• DOI: 10.1152/ajplung.00274.2018

Mucociliary clearance (MCC) plays an essential role in maintaining airway sterility and health. Conversely, mucociliary dysfunction is implicated across many airway obstructive diseases. Understanding the necessary requirements for successful MCC is imperative to establish the pathology of disease, as well as to develop therapeutic strategies. Although postural, that is, gravitational, drainage is used clinically to aid mucus clearance, it is ignored in both animal and cell culture models of MCC. In this study, we develop a novel mucus clearance assay that enables the first particle image velocimetry of human bronchial epithelial cell cultures tilted relative to the gravitational field. This tilting system makes it possible to observe drainage of the airway surface liquid and, thus, reveals the effect gravity has on mucociliary clearance. First, we use this assay to demonstrate that beating cilia alone cannot transport buffer upward against gravity. Next, we show the same cilia successfully transporting mucus upward. These results indicate that the biophysical and biochemical properties of mucus enable vertical clearance and that current assay systems are not equipped to determine which properties are required for physiologically relevant vertical mucociliary clearance.