View Abstract

A7621 - Mucus Strands Initiate Ciliary Transport of Particles in Large Airways
Author Block: A. J. Fischer1, C. Shanrock1, A. Chaly1, M. Abou Alaiwa2, M. Welsh2; 1Pediatrics, University of Iowa, Iowa City, IA, United States, 2Internal Medicine, University of Iowa, Iowa City, IA, United States.
Background: Mucociliary transport defends the lungs from inhaled pathogens. We previously observed heterogeneous clearance of tantalum (Ta) microdisks from pig airways, including particles with delayed initiation of transport and others that abruptly stopped moving. We predicted that airway mucus regulates these starting and stopping events. Recent work indicates that submucosal glands and surface goblet cells secrete distinct forms of mucus, including large Muc5B strands in the central airways. We hypothesized that long mucus strands emerging from submucosal glands are required to transport large particles in the trachea.
Methods: We measured the transport of Ta spheres in wild type pig tracheas submerged in Krebs-Ringers buffer under control conditions or in the presence of either 1 mM dithiothreitol (DTT) or tris-(2-carboxyethyl)phosphine (TCEP). These reducing agents break disulfide bonds that hold together mucins. To visualize the interaction of mucus strands with Ta spheres, we examined tracheas by confocal microscopy using 40 nm fluorescent spheres to label the mucus strands.
Results: Ta spheres rolled in a direction opposite of ciliary beating and remained in position several minutes prior to initiating forward movement. In the presence of DTT or TCEP, Ta spheres were less likely to initiate movement when compared to control
conditions. In the presence of either reducing agent, significantly fewer Ta spheres moved, and there were longer lag periods prior to movement. Addition of methacholine significantly increased particle transport compared to baseline, but it was ineffective in the presence of either DTT or TCEP. Using confocal microscopy, we examined the interaction of Ta spheres with mucus. In the absence of reducing agent, mucus strands attached to spheres, stopped them from rolling, and initiated their transport. DTT and TCEP treatment caused mucus to appear as small fragments, which coated the spheres but did not promote their transport.
Conclusions: Reducing agents break mucus strands into small fragments. These fragments retain the ability to bind foreign particles. However, large intact mucus strands are required to initiate the transport of large particles in the trachea. Thus, intact mucus strands may play an important role in mucociliary transport.