Abstract
The nose is a complex organ that filters and warms breathing airflow. The nasal epithelium is the first barrier between the host and the external environment and is covered by a mucus gel that is poorly documented. Mucins are large, heavily O-glycosylated polymeric molecules secreted in the nose lumen by specialized cells, and they are responsible for the biochemical properties of the mucus gel. The mucus traps particles and clears them, and it also bathes microbiota, host molecules, and receptors that are all essential for odor perception in the olfactory epithelium. We used histology and immunohistochemistry to study the expression of the two main airway polymeric mucins, Muc5ac and Muc5b, in wild-type, green fluorescent protein-reporter Muc5b, and in genetically Muc5b-deficient mice. We report that Muc5ac is produced by goblet cells at the cell surface in the respiratory epithelium but is not expressed in the olfactory epithelium, whereas Muc5b is secreted by Bowman’s glands situated in the lamina propria beneath the olfactory epithelium and also by goblet cells in the distal part of the respiratory epithelium. We also observed that Muc5b-deficient mice exhibited depletion of Bowman’s glands. Using lectins, we found that terminally O-glycosylated chains of Muc5b were sialylated but not fucosylated, whereas Muc5ac was fucosylated but not sialylated. Specific localization and specific terminal glycosylation of the two mucins suggest different functions of the mucins.
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Acknowledgements
We thank J. Bara for the gift of the 45M1 antibody, M.H. Gevaert (Service Commun-Morphologie Cellulaire, Université de Lille) for the slides, J. Devassine and Y. Lepage from the EOPS animal facility (Université de Lille) for mouse colony management and S. Plet and M. Magnien (LIRIC) for genotyping and dissection and the Bio-imaging Center (plate-forme de microscopie photonique, Université Lille) for Carl Zeiss Axio Scan. Z1 scanner.
Funding
S.-E. A. is the recipient of a “Université de Lille” fellowship. C.P. was the recipient of a “Université Lille 2” fellowship.
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Suppl. Fig. 1
Immunohistochemical analysis of Muc5b and Muc5ac in nose coronal sections of the proximal (T1) nasal airway of WT mice. Serial sections were stained with antibodies against Muc5b (green) and Muc5ac (red). Higher magnification images taken from the boxed areas in the OE and RE are shown. Arrows indicate BGs. Lu: lumen. Scale bar = 50 μm. (TIFF 3366 kb)
Suppl. Fig. 2
Immunohistochemical analysis of Muc5b and Muc5ac in nose coronal sections of the proximal (T3) nasal airway of WT mice. Serial sections were stained with antibodies against Muc5b and Muc5ac. Higher magnification images of the OE and RE are shown. Muc5b staining was observed in BGs (arrows) and BGs ducts in the OE. Goblet cells of the RE produced both Muc5b and Muc5ac, with a higher number of goblet cells producing Muc5ac. Lu: lumen. Scale bar = 50 μm. (TIFF 3802 kb)
Suppl. Fig. 3
Multilabel immunohistochemical analysis of Muc5b with MAA or UEA-1 lectin in the OE and RE of coronal section T3 of the nasal airway from Muc5b–/– mice and with MAA and UEA-1 lectins in the OE and RE of coronal section T2 of the nasal airway from Muc5b-GFP reporter and WT mice. a. BGs underlying the OE are not visible (depleted) and are not stained with either the Muc5b antibody or MAA. Mucous cells of the RE were stained by UEA-1 and very faintly by MAA. Lu: lumen. Scale bar = 50 μm. b. High magnification images of the OE and RE are shown. MAA lectin binding was observed in BGs (arrows) underlying the OE and in Bowman’s gland ducts (d). Mucous cells of the RE are recognized by UEA-1 lectin. Lu: lumen. Scale bar = 50 μm. (TIFF 3603 kb)
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Amini, SE., Gouyer, V., Portal, C. et al. Muc5b is mainly expressed and sialylated in the nasal olfactory epithelium whereas Muc5ac is exclusively expressed and fucosylated in the nasal respiratory epithelium. Histochem Cell Biol 152, 167–174 (2019). https://doi.org/10.1007/s00418-019-01785-5
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DOI: https://doi.org/10.1007/s00418-019-01785-5