Cigarette Smoke-Induced Cell Death Causes Persistent Olfactory Dysfunction in Aged Mice

Abstract

Introduction: Exposure to cigarette smoke is a cause of olfactory dysfunction. We previously reported that in young mice, cigarette smoke damaged olfactory progenitors and decreased mature olfactory receptor neurons (ORNs), then, mature ORNs gradually recovered after smoking cessation. However, in aged populations, the target cells in ORNs by cigarette smoke, the underlying molecular mechanisms by which cigarette smoke impairs the regenerative ORNs, and the degree of ORN regeneration after smoking cessation remain unclear.Objectives: To explore the effects of cigarette smoke on the ORN cell system using an aged mouse model of smoking, and to investigate the extent to which smoke-induced damage to ORNs recovers following cessation of exposure to cigarette smoke in aged mice.Methods: We intranasally administered a cigarette smoke solution (CSS) to 16-month-old male mice over 24 days, then examined ORN existence, cell survival, changes of inflammatory cytokines in the olfactory epithelium (OE), and olfaction using histological analyses, gene analyses and olfactory habituation/dishabituation tests.Results: CSS administration reduced the number of mature ORNs in the OE and induced olfactory dysfunction. These changes coincided with an increase in the number of apoptotic cells and Tumor necrosis factor (TNF) expression and a decrease in Il6 expression. Notably, the reduction in mature ORNs did not recover even on day 28 after cessation of treatment with CSS, resulting in persistent olfactory dysfunction.Conclusion: In aged mice, by increasing ORN death, CSS exposure could eventually overwhelm the regenerative capacity of the OE, resulting in continued reduction in the number of mature ORNs and olfactory dysfunction.

Dose-Dependent Effects of Insulin-Like Growth Factor 1 in the Aged Olfactory Epithelium

“…Considering that the reduction in mature ORN numbers is associated with olfactory impairment in the aged population ( Ueha et al, 2018b ), IGF-1 administered at an appropriate dose could prevent aging-induced negative effects on ORNs. However, because our results were only obtained from mouse studies, care should be taken regarding IGF-1 application for the treatment of human olfactory impairment.…”

“…The septal nasal mucosa was harvested and prepared for histological analyses as described previously ( Ueha et al, 2014 , 2016a , b , 2018a , b ). In brief, all samples were cut at the level of the anterior end of the olfactory bulb.…”

“…GAP43 and OMP are expressed by immature ORNs and mature ORNs, respectively. Ki-67 is a marker for cell proliferation and expressed in all active stages of the cell cycle, and Ki-67-positive cells are particularly detected in the basal layer ( Ueha et al, 2018a , b ). Caspases are crucial mediators of programmed cell death (apoptosis) and Cas3 is a well-defined activated death protease ( Porter and Janicke, 1999 ).…”

Effects of Cigarette Smoke on the Nasal Respiratory and Olfactory Mucosa in Allergic Rhinitis Mice

“…The Ki67 protein is a cellular marker of proliferation strictly associated with cell proliferation (Duchrow et al, 1995), and Ki67-positive cells are detected throughout the depth of the nasal mucosa. Especially in the OE, such cells are observed mainly in the basal layer (Ueha et al, 2016a(Ueha et al, , 2018b. OMP is exclusively expressed in mature ORNs (Buiakova et al, 1996).…”

“…As previously described (Ueha et al, 2014(Ueha et al, , 2016a(Ueha et al, , 2018bNishijima et al, 2016), all samples were cut at the level of the incisive papilla of the hard palate in coronal sections for examinations of the RM (Nishijima et al, 2016), and were cut from the level of the anterior end of the olfactory bulb to the 1-mm anterior level for examinations of the OE (Ueha et al, 2014(Ueha et al, , 2016a(Ueha et al, , 2018b. Four-micrometer thick paraffin sections were deparaffinized in xylene and rehydrated in ethanol before hematoxylin and eosin staining for evaluation of whole tissue structure, Sirius red staining for eosinophils, periodic acid-Schiff and Alcian blue (PAS/AB) staining for goblet cells, and immunostaining.…”