Neuroepithelial Bodies as Mechanotransducers in the Intrapulmonary Airway Epithelium

Abstract

In rodent lungs, a major part of the myelinated vagal airway afferents selectively contacts pulmonary neuroepithelial bodies (NEBs). Because most myelinated vagal airway afferents concern physiologically characterized mechanoreceptors, the present study aimed at unraveling the potential involvement of NEB cells in transducing mechanosensory information from the airways to the central nervous system. Physiological studies were performed using confocal Ca(2+) imaging of airway epithelium in murine lung slices. Mechanical stimulation by short-term application of a mild hypoosmotic solution (230 mosmol) resulted in a selective, fast, reversible, and reproducible Ca(2+) rise in NEB cells. Other airway epithelial cells could only be activated using more severe hypoosmotic stimuli (< 200 mosmol). NEB cells selectively expressed the Ca(2+)-permeable osmo- and mechanosensitive transient receptor potential canonical channel 5 (TRPC5) in their apical membranes, whereas immunoreactivity for TRP vanilloid-4 and TRP melastatin-3 was abundant in virtually all other airway epithelial cells. Hypoosmotic activation of NEB cells was prevented by GsMTx-4, an inhibitor of mechanosensitive ion channels, and by SKF96365, an inhibitor of TRPC channels. Short application of gadolinium, reported to activate TRPC5 channels, evoked a transient Ca(2+) rise in NEB cells. Osmomechanical activation of NEB cells gave rise to a typical delayed activation of Clara-like cells due to the release of ATP from NEB cells. Because ATP may activate the NEB-associated P2X(2/3) ATP receptor expressing myelinated vagal afferents, the current observations strongly suggest that pulmonary NEB cells are fully equipped to initiate mechanosensory signal transduction to the central nervous system via a purinergic signaling pathway.

Morphologic Characterization of Nerves in Whole-Mount Airway Biopsies

“…Accordingly, it is probable that at least a proportion of these cells are innervated by vagal afferents (42). Although the formation of cytoneural junctions is generally regarded as unlikely, the close association of fibers with epithelial cells is strongly suggestive of the presence of afferent signaling (43). The chemical mediator for signaling between PNECs and vagal afferents is not known but may be ATP (43)(44)(45), which would be consistent with recent clinical studies of cough (46).…”

Functional expression of the multimodal extracellular calcium-sensing receptor in pulmonary neuroendocrine cells

“…In this way, we were able to demonstrate that ATP released from activated NEB cells typically gives rise to a delayed activation of Clara-like cells (De Proost et al, 2009;Lembrechts et al, 2012). In the present study, activation of CaSR expressed on NEB cells resulted in a delayed [Ca 2+ ] i rise in Clara-like cells, indicating that CaSR activation in NEB cells leads to [Ca 2+ ] i mediated exocytosis.…”

“…When local stimuli activate the release of secretory products from NEB cells, sensory nerve fibers in synaptic contact are believed to depolarize, triggering action potentials that can reach the CNS. The best characterized mechanism so far is the [Ca 2+ ] i -mediated release of ATP from activated NEB cells (De Proost et al, 2009;Lembrechts et al, 2012) influencing the P2X 2/3 ATP receptors expressed on the terminals of a population of vagal afferents that contacts pulmonary NEBs in rodents (Brouns et al, 2009a).…”

“…Today, extensive evidence implicates both NEBs in several species, and NEB-related cell models in hypoxia sensing (Cutz et al, 2003;Cutz and Jackson, 1999;Kemp et al, 2003). The involvement of NEBs in postnatal mechanosensing has recently regained interest (Lembrechts et al, 2011;Lembrechts et al, 2012). Postnatally, the close association of NEB cells with afferent nerve terminals argues for a function as a sensory receptor (Adriaensen et al, 2006), although the exact stimuli and molecular transduction mechanisms that are involved in their activation remain a matter of debate.…”

Plasticity in the lung: making and breaking cell identity

“…PNECs of the bronchiolar epithelium are also thought to serve as niche cells for naphthalene-resistant variant club cells (Guha et al, 2012;Hong et al, 2001). Several studies have suggested that PNECs perform many other functions including oxygen sensing, mechanotransduction, immune cell recruitment, and chemosensing (Branchfield et al, 2016;Lembrechts et al, 2012;Pan et al, 2002). Some of these functions are presumably mediated in part through their connections with nerve fibers.…”