Apoptosis and the insulin-like growth factor family in the developing olfactory epithelium

Endoplasmic reticulum stress associated with lead (Pb)-induced olfactory epithelium toxicity in an olfactory dark basal cell line

Lead (Pb) can damage organs and also have undesirable effects on neural development. To explore the effects of Pb on olfactory cells, we investigated Pb-induced cell toxicity in the DBC1.2 olfactory cell line, with a focus on endoplasmic reticulum (ER) stress, apoptosis, and necroptosis. Representative markers of ER stress, apoptosis, and necroptosis were analyzed by quantitative PCR. The mRNA expression levels of GRP94, GRP78, spliced XBP1, PERK, and ATF6 increased significantly after Pb exposure in a dose-dependent manner. The expression of Caspase 3 and Caspase 12 did not increase after Pb exposure, which suggested that apoptosis-induced cell death was not activated after Pb exposure. However, the mRNA of RIPK3 and MLKL showed increases in expression, which indicated that necroptosis-induced cell death was activated after Pb exposure. These results indicate that Pb exposure induced dose-dependent cytotoxicity through ER stress and necroptosis pathways in DBC1.2 cells, whereas the apoptosis pathway was not significantly stimulated. HEPES buffer showed a partial protective effect in terms of ER stress, apoptosis, and necroptosis. In summary, the necroptosis pathway plays a crucial rule in Pb exposure-induced cytotoxicity in olfactory cells.

Bilateral Olfactory Mucosa Damage Induces the Disappearance of Olfactory Glomerulus and Reduces the Expression of Extrasynaptic α5GABAARs in the Hippocampus in Early Postnatal Sprague Dawley Rats

Chloroform-induced olfactory mucosal degeneration has been reported in adult rats following gavage. We used fixed-point chloroform infusions on different postnatal days (PNDs) to investigate the effects of early olfactory bilateral deprivation on the main olfactory bulbs in Sprague Dawley rats. The experimental groups included rats infused with chloroform (5 μl) or saline (sham, 5 μl) on PNDs 3 and 8, and rats not receiving infusions (control) (n = 6 in all groups). Rats receiving chloroform on PND 3 showed significant hypoevolutism when compared to those in other groups (P < 0.05). There was a complete disappearance and a significant reduction in the size of olfactory glomeruli in the PND 3 and 8 groups, respectively, when compared to the respective sham groups. Rats receiving chloroform on PND 3 had significant memory impairment (P < 0.01) and increased levels of learned helplessness (P < 0.05), as measured using the Morris water maze and tail suspension tests, respectively. GABA_A receptor alpha5 subunit (α5GABA_AR) expression in hippocampal neurons was significantly lower in rats receiving chloroform on PND 3 than in rats in other groups (P < 0.01), as measured using immunohistochemistry and polymerase chain reaction. There was thus a critical period for the preservation of regenerative ability in olfactory receptor neurons, during which damage and olfactory deprivation led to altered rhinencephalon structure and disappearance of olfactory glomeruli, which induced hypoevolutism. Olfactory deprivation after the critical period had no significant effect on olfactory receptor neuron regeneration, leading to reduced developmental and behavioral effects in Sprague Dawley rats.

Insulin but not leptin protects olfactory mucosa from apoptosis

The mammalian olfactory mucosa (OM) is continually renewed throughout life. Owing to their position in the nasal cavity, OM cells are exposed to multiple insults, including high levels of odourants that can induce their death. OM regeneration is therefore essential to maintain olfactory function, and requires the tight control of both cell death and proliferation. Apoptosis has been implicated in OM cell death. Olfaction is one of the senses involved in food intake and depends on individual nutritional status. We have previously reported the influence of hormones related to nutritional status on odour perception and have shown that the OM is a target of insulin and leptin, two hormones known for their anti-apoptotic properties. In the present study, we investigated the potential anti-apoptotic effect of these metabolic hormones on OM cells. Both Odora cells (an olfactive cell line) and OM cells treated with etoposide, a p53 activity inducer, exhibited mitochondrial-dependent apoptosis that was inhibited by the pan-caspase inhibitor zVAD-fmk. Insulin, but not leptin, impaired this apoptotic effect. Insulin addition to the culture medium reduced p53 phosphorylation, caspase-3 and caspase-9 cleavage, and caspase-3 enzymatic activity induced by etoposide. The apoptotic wave observed in the OM after interruption of the neuronal connections between the OM and the olfactory bulb by bulbectomy was impaired by intranasal insulin treatment. These findings suggest that insulin may be involved in OM cellular dynamics, through endocrine and/or paracrine-autocrine effects of circulating or local insulin, respectively.

Site-specific population dynamics and variable olfactory marker protein expression in the postnatal canine olfactory epithelium

The main olfactory epithelium is a pseudostratified columnar epithelium that displays neurogenesis over the course of a lifetime. New olfactory neurons arise basally and are transferred to the middle third of the epithelium during maturation. It is generally believed that this pattern is present throughout the olfactory area. In the present study, we show that the postnatal canine olfactory epithelium is composed of two distinct types of epithelium, designated A and B, which not only differ in olfactory neuron morphology, marker expression and basal cell proliferation but also display a patchy distribution and preferential localization within the nasal cavity. Type A epithelium, abundant in the caudal part of the olfactory area, contains well-differentiated olfactory neurons positive for olfactory marker protein but low numbers of immature neurons and proliferating basal cells, as visualized by TrkB/Human Natural Killer-1 (HNK-1) glyco-epitope and Ki-67 immunostaining, respectively. In contrast, type B epithelium is mainly found in the rostral part and contains smaller and elongated neurons that display increased levels of TrkB/Human Natural Killer-1 (HNK-1) glyco-epitope immunoreactivity and a higher number of Ki-67-positive basal cells but lower and variable levels of olfactory marker protein. The vomeronasal organ displays a uniform distribution of molecular markers and proliferating basal cells. The observation that olfactory marker protein in type A and B epithelium is preferentially localized to the nucleus and cytoplasm, respectively, implies correlation between subcellular localization and olfactory neuron maturation and may indicate distinct functional roles of olfactory marker protein. Whether the site-specific population dynamics in the postnatal canine olfactory epithelium revealed in the present study are modulated by physiological parameters, such as airflow, has to be clarified in future studies.