Neurochemical pattern of the complex innervation of neuroepithelial bodies in mouse lungs

Abstract

As best characterized for rats, it is clear that pulmonary neuroepithelial bodies (NEBs) are contacted by a plethora of nerve fiber populations, suggesting that they represent an extensive group of multifunctional intraepithelial airway receptors. Because of the importance of genetically modified mice for functional studies, and the current lack of data, the main aim of the present study was to achieve a detailed analysis of the origin and neurochemical properties of nerve terminals associated with NEBs in mouse lungs. Antibodies against known selective markers for sensory and motor nerve terminals in rat lungs were used on lungs from control and vagotomized mice of two different strains, i.e., Swiss and C57-Bl6. NEB cells were visualized by antibodies against either the general neuroendocrine marker protein gene-product 9.5 (PGP9.5) or calcitonin gene-related peptide (CGRP). Thorough immunohistochemical examination of NEB cells showed that some of these NEB cells also exhibit calbindin D-28 k (CB) and vesicular acetylcholine transporter (VAChT) immunoreactivity (IR). Mouse pulmonary NEBs were found to receive intraepithelial nerve terminals of at least two different populations of myelinated vagal afferents: (1) Immunoreactive (ir) for vesicular glutamate transporters (VGLUTs) and CB; (2) expressing P2X(2) and P2X(3) ATP receptors. CGRP IR was seen in varicose vagal nerve fibers and in delicate non-vagal fibers, both in close proximity to NEBs. VAChT immunostaining showed very weak IR in the NEB-related intraepithelial vagal sensory nerve terminals. nNOS- or VIP-ir nerve terminals could be observed at the base of pulmonary NEBs. While a single NEB can be contacted by multiple nerve fiber populations, it was clear that none of the so far characterized nerve fiber populations contacts all pulmonary NEBs. The present study revealed that mouse lungs harbor several populations of nerve terminals that may selectively contact NEBs. Although at present the physiological significance of the innervation pattern of NEBs remains enigmatic, it is likely that NEBs are receptor-effector end-organs that may host complex and/or multiple functional properties in normal airways. The neurochemical information on the innervation of NEBs in mouse lungs gathered in the present study will be essential for the interpretation of upcoming functional data and for the study of transgenic mice.

Perspectives of purinergic signaling in stem cell differentiation and tissue regeneration

“…Furthermore, ATP regulates diverse processes involved in host defense such as anion transport, ciliary function and mucin expression and is also suggested to function in wound repair [126][127][128]. ATP-mediated P2 purinergic receptor activation promotes bronchial epithelial migration and epithelial repair.…”

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

“…In various other cell types (e.g. smooth muscle cells, breast cancer cells, ventricular cardiomyocytes) CaSR activation has been reported to mediate Ca 2+ entry through TRPC-encoded receptor-operated and store-operated channels (Chow et al, 2011;El Hiani et al, 2009;Sun et al, 2010 (Brouns et al, 2009a;Brouns et al, 2012;De Proost et al, 2009), and well-organized intercellular communication could be essential for normal physiology. Apart from its role in interactions between synaptic NEB cells and nerves (Sorokin and Hoyt, 1989), paracrine signaling between ATP-releasing NEB cells and P2Y 2 ATP-receptor-expressing Clara-like cells has been described after depolarization (De Proost et al, 2009) and specific stimulation of NEB cells .…”

“…Mouse NEBs express CGRP (Brouns et al, 2009a;Uddman et al, 1985), a neuropeptide encoded by the calcitonin gene via tissuespecific RNA processing (Rosenfeld et al, 1983); calcitonin was also reported to be expressed in mouse NEBs (Luts et al, 1991). As a secretory product of thyroid C-cells, calcitonin is well known as an important mediator in thyroid and parathyroid control of [Ca 2+ ] o homeostasis (Freichel et al, 1996;Garrett et al, 1995), in which the CaSR is the key [Ca 2+ ] o sensor (Chang and Shoback, 2004;Riccardi and Kemp, 2012).…”

“…2A-F). Combined immunostaining for CaSR and P2X 3 or CB, which are each markers for a different subpopulation of intraepithelial vagal sensory nerve terminals that arborize between NEB cells (Brouns et al, 2009a), demonstrated the exclusive expression of the CaSR in NEB cells, whereas the P2X 3 -and CB-immunoreactive nerve terminals in NEBs were negative ( Fig. 2G-K).…”

“…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).…”