Olfactory neuron-specific expression of NeuroD in mouse and human nasal mucosa

MRI tractography reveals the human olfactory nerve map connecting the olfactory epithelium and olfactory bulb

The olfactory nerve map describes the topographical neural connections between the olfactory epithelium in the nasal cavity and the olfactory bulb. Previous studies have constructed the olfactory nerve maps of rodents using histological analyses or transgenic animal models to investigate olfactory nerve pathways. However, the human olfactory nerve map remains unknown. Here, we demonstrate that high-field magnetic resonance imaging and diffusion tensor tractography can be used to visualize olfactory sensory neurons while maintaining their three-dimensional structures. This technique allowed us to evaluate the olfactory sensory neuron projections from the nasal cavities to the olfactory bulbs and visualize the olfactory nerve maps of humans, marmosets and mice. The olfactory nerve maps revealed that the dorsal-ventral and medial-lateral axes were preserved between the olfactory epithelium and olfactory bulb in all three species. Further development of this technique might allow it to be used clinically to facilitate the diagnosis of olfactory dysfunction.

Combined high-field MRI and DTI analyses in post-mortem mouse, marmoset, and human samples provide insight into the neural connections between nasal cavities and olfactory bulbs.

Transcriptional regulatory network during development in the olfactory epithelium

Regeneration, a process of reconstitution of the entire tissue, occurs throughout life in the olfactory epithelium (OE). Regeneration of OE consists of several stages: proliferation of progenitors, cell fate determination between neuronal and non-neuronal lineages, their differentiation and maturation. How the differentiated cell types that comprise the OE are regenerated, is one of the central questions in olfactory developmental neurobiology. The past decade has witnessed considerable progress regarding the regulation of transcription factors (TFs) involved in the remarkable regenerative potential of OE. Here, we review current state of knowledge of the transcriptional regulatory networks that are powerful modulators of the acquisition and maintenance of developmental stages during regeneration in the OE. Advance in our understanding of regeneration will not only shed light on the basic principles of adult plasticity of cell identity, but may also lead to new approaches for using stem cells and reprogramming after injury or degenerative neurological diseases.

Olfaction in neurologic and neurodegenerative diseases: a literature review

Introduction Loss of smell is involved in various neurologic and neurodegenerative diseases, such as Parkinson disease and Alzheimer disease. However, the olfactory test is usually neglected by physicians at large.

Objective The aim of this study was to review the current literature about the relationship between olfactory dysfunction and neurologic and neurodegenerative diseases.

Data Synthesis Twenty-seven studies were selected for analysis, and the olfactory system, olfaction, and the association between the olfactory dysfunction and dementias were reviewed. Furthermore, is described an up to date in olfaction.

Conclusion Otolaryngologist should remember the importance of olfaction evaluation in daily practice. Furthermore, neurologists and physicians in general should include olfactory tests in the screening of those at higher risk of dementia.

Profiling of olfactory receptor gene expression in whole human olfactory mucosa

Olfactory perception is mediated by a large array of olfactory receptor genes. The human genome contains 851 olfactory receptor gene loci. More than 50% of the loci are annotated as nonfunctional due to frame-disrupting mutations. Furthermore haplotypic missense alleles can be nonfunctional resulting from substitution of key amino acids governing protein folding or interactions with signal transduction components. Beyond their role in odor recognition, functional olfactory receptors are also required for a proper targeting of olfactory neuron axons to their corresponding glomeruli in the olfactory bulb. Therefore, we anticipate that profiling of olfactory receptor gene expression in whole human olfactory mucosa and analysis in the human population of their expression should provide an opportunity to select the frequently expressed and potentially functional olfactory receptors in view of a systematic deorphanization. To address this issue, we designed a TaqMan Low Density Array (Applied Biosystems), containing probes for 356 predicted human olfactory receptor loci to investigate their expression in whole human olfactory mucosa tissues from 26 individuals (13 women, 13 men; aged from 39 to 81 years, with an average of 67±11 years for women and 63±12 years for men). Total RNA isolation, DNase treatment, RNA integrity evaluation and reverse transcription were performed for these 26 samples. Then 384 targeted genes (including endogenous control genes and reference genes specifically expressed in olfactory epithelium for normalization purpose) were analyzed using the same real-time reverse transcription PCR platform. On average, the expression of 273 human olfactory receptor genes was observed in the 26 selected whole human olfactory mucosa analyzed, of which 90 were expressed in all 26 individuals. Most of the olfactory receptors deorphanized to date on the basis of sensitivity to known odorant molecules, which are described in the literature, were found in the expressed olfactory receptors gene set.

Comparison of two nasal cell collection methods in determining cyclic adenosine monophosphate levels and its association with olfaction: A feasibility study

Cyclic adenosine monophosphate (cAMP) is a second messenger that may be associated with olfactory function. No known studies have compared existing collection methods for determining nasal cAMP levels. This is a prospective study comparing the comfort and reliability of the nasal curette and cytobrush. A secondary outcome collected for feasibility testing was characterizing the association between cAMP and olfactory function. We enrolled 19 normal olfaction and 10 olfactory dysfunction subjects. Olfaction was measured by the University of Pennsylvania Smell Identification Test. Two samples were obtained from each nasal cavity at the initial visit and at 1 week follow-up. Comfort was measured by a visual analog scale (VAS). cAMP levels were determined by an enzyme immunoassay. For the curette and cytobrush, mean VAS scores were 0.3 and 0.7 cm (p = 0.48). Intraclass correlation coefficients were 0.81 (curette) and 0.65 (cytobrush) for the initial visit and 0.64 and 0.54 between the initial and follow-up visit. Using the curette, mean cAMP was 537 and 480 fmol/(mg/mL) for the normal and dysfunction cohorts (p = 0.18). Using the cytobrush, cAMP was 505 and 477, respectively (p = 0.65). The curette and cytobrush are both comfortable and reliable collection methods for determining nasal cAMP levels.

Conductive olfactory losses in chronic rhinosinusitis? A computational fluid dynamics study of 29 patients

BACKGROUND

Besides sensorineural factors, conductive impediments likely contribute to olfactory losses in chronic rhinosinusitis (CRS) patients, yet no conclusive evidence exists. We aimed to examine possible conductive factors using computational fluid dynamics (CFD) models.

METHODS

A total of 29 CRS patients were assessed via odorant detection thresholds (ODTs), rhinomanometry (nasal resistance [NR]), acoustic rhinometry (minimum-cross-sectional area [MCA]) and computed tomography (CT) staging. CFD simulations of nasal airflow and odorant absorption to olfactory region were carried out based on individual CTs. Biopsies of olfactory epithelium (OE) were collected, cryosectioned, stained, and scored for erosion.

RESULTS

Significant correlations to ODTs were found for 3 variables: odor absorption in the olfactory region (r = -0.60, p < 0.01), MCA (r = -0.40, p < 0.05), and CT staging (r = 0.42, p < 0.05). However, significant findings were limited to ODTs of the highly soluble l-carvone. Multiple regression analysis revealed that these variables combined, with the addition of NR, can account for 65% of the total variance in ODTs. CT staging correlated significantly with OE erosion (r = 0.77, p < 0.01) and can replace the latter in the regression with comparable outcomes. Partial correlations suggest the contributions of both conductive and sensorineural variables are more prominent if adjusted for the effects of the other. Olfactory loss and inflammatory factors have strong bilateral involvement, whereas conductive factors are independent between sides. As validation, CFD-simulated NRs significantly correlated with rhinomanometrically assessed NRs (r = 0.60, p < 0.01).

CONCLUSION

Both conductive and sensorineural mechanisms can contribute to olfactory losses in CRS. CFD modeling provides critical guidance in understanding the role of conductive impediments in olfactory dysfunction in CRS.

Assessing the efficacy of endoscopic office olfactory biopsy sites to produce neural progenitor cell cultures for the study of neuropsychiatric disorders

BACKGROUND

The olfactory region is capable of continuous neurogenesis. Situated on the cribriform plate and segments of the superior septum and both superior and middle turbinates, it is accessible through office-based biopsy and can be used to generate neural progenitor cells to study molecular abnormalities associated with neuropsychiatric disorders. The purpose of the study was to evaluate the efficacy of the endoscopic office olfactory biopsy from middle turbinate and superior-posterior septum to produce the neural progenitor cells.

METHODS

Endoscopic office-based biopsy samples were collected and cultured neuronal cells derived from olfactory neuroepithelium (CNON) were established from 40 healthy individuals and 40 schizophrenia patients. All patients underwent biopsies of both the middle turbinate and the superior-posterior septum. Specific culture conditions promoted the growth of neural progenitor cells from these biopsy sites. CNON cultures were established from such outgrowing neuronal cells. The study was institutional review board (IRB)-approved and informed consent was obtained.

RESULTS

Cultures were successfully developed from 98.8% of participants. No complications were observed. The single, unsuccessful specimen failed to grow any cell types due to tissue mishandling. Overall, we have observed no significant difference in the effectiveness of biopsy from middle turbinate and superior-posterior septum to produce neural progenitor cells.

CONCLUSION

The middle turbinate biopsies contain viable neural progenitor cells capable of generating neuronal cell cultures. Thus technically more simple biopsy of the middle turbinate can be used to propagate neural progenitor cells.

Concha bullosa surgery and the distribution of human olfactory neuroepithelium

In bullous middle turbinate surgery, controversy exists over which side of the bullous middle turbinate should be removed, as the distribution of human olfactory neuroepithelium is unclear. This study evaluated whether the middle turbinate tissue of patients undergoing endoscopic concha bullosa surgery contains functional olfactory epithelium. This prospective clinical study was conducted in tertiary referable center. It detected 70 conchae bullosa in 48 patients with sinonasal symptoms, who underwent paranasal computed tomography (CT) that showed pneumatization of the middle concha. All samples were obtained under general anesthesia. Three samples were obtained from each bullous middle turbinate: one each from the anterior, medial, and lateral portions. The mucosa from each sample was stained with olfactory marker protein (OMP). In total, 210 middle turbinate samples were taken from 48 patients during endoscopic surgery for conchae bullosa. The patients were 22 females and 26 males. Of the 70 conchae bullosa, OMP-stained nerve tissue was found in the lateral, anterior and medial aspects of 57 (81.4 %), 42 (60.0 %) and 23 (32.8 %) of the bullous middle turbinates, respectively. OMP-stained nerve tissue was found in 122 (58.1 %) of the 210 bullous middle turbinate tissue samples. OMP-stained nerve tissue was found on the lateral surface of the bullous middle turbinate more often than the medial surface. Therefore, during the concha bullosa surgery, OMP-stained nerve tissue found at least in the medial part of concha, suggested that the opening of the medial part of middle concha.

Progenitor cell capacity of NeuroD1-expressing globose basal cells in the mouse olfactory epithelium

The basic helix-loop-helix transcription factor NeuroD1 is expressed in embryonic and adult mouse olfactory epithelium (OE), as well as during epithelial regeneration, suggesting that it plays an important role in olfactory neurogenesis. We characterized NEUROD1-expressing progenitors, determined their progeny in the adult OE, and identified a subtle phenotype in ΔNeuroD1-knockout mice. All olfactory sensory neurons (OSNs) derive from a NeuroD1-expressing progenitor as shown by recombination-mediated lineage tracing, as do other sensory receptors of the nose, including vomeronasal, nasal septal, and Grunenberg ganglion neurons. NEUROD1-expressing cells are found among the globose basal cell population: they are actively proliferating and frequently coexpress Neurog1, but not the transit amplifying cell marker MASH1, nor the neuronal marker NCAM. As a consequence, NEUROD1-expressing globose basal cells are best classified as immediate neuronal precursors. In adolescent ΔNeuroD1-LacZ knock-in null mice the OE displays subtle abnormalities, as compared to wildtype and heterozygous littermates. In some areas of the OE, mature neurons are absent, or sparse, although those same areas retain immature OSNs and LacZ-expressing progenitors, albeit both of these populations are smaller than expected. Our results support the conclusion that most, if not all, nasal chemosensory neurons derive from NeuroD1-expressing globose basal cells of the immediate neuronal precursor variety. Moreover, elimination of NeuroD1 by gene knockout, while it does not disrupt initial OSN differentiation, does compromise the integrity of parts of the olfactory epithelium by altering proliferation, neuronal differentiation, or neuronal survival there.

The human olfactory mucosa

Studies of the tissues of the human olfactory mucosa have been performed to investigate olfactory dysfunction and, more recently, olfactory mucosa has attracted a novel interest of investigators because it can be used as an early marker of neurodegenerative conditions of the brain and as a source of multipotent neural stem cells, with applications in regenerative medicine. The olfactory mucosa is readily available to the otolaryngologist, but the harvesting of this tissue must be safe, effective, and reliable, obtaining as little tissue as necessary, while avoiding unnecessary harm to the remaining olfactory tissue and function. The purpose of this review is to summarize the results of the most important studies and knowledge with regard to the human olfactory mucosa and its applications, emphasizing the issue of the distribution of the olfactory mucosa in the nasal cavities.

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.

Human olfactory epithelial cells generated in vitro express diverse neuronal characteristics

The olfactory epithelium constitutes the sole source of regenerating neural cells that can be obtained from a living human. As such, primary cultures derived from human olfactory epithelial biopsies can be utilized to study neurobiological characteristics of individuals under different conditions and disease states. Here, using such human cultures, we report in vitro generation of cells that exhibit a complex neuronal phenotype, encompassing receptors and signaling pathways pertinent to both olfaction and other aspects of CNS function. Using in situ hybridization, we demonstrate for the first time the native expression of olfactory receptors in cultured cells derived from human olfactory epithelial tissue. We further establish the presence and function of olfactory transduction molecules in these cells using immunocytochemistry, calcium imaging and molecular methods. Western blot analysis revealed the expression of neurotransmitter receptors for dopamine (D2R), 5-HT (5HT2C) and NMDA subtypes 1 and 2A/2B. Stimulation with dopamine or 5-HT enhanced receptor G protein activation in a subtype specific manner, based on 35S-guanosine triphosphate incorporation assay. Functional characteristics of the cultured cells are demonstrated through enhanced tyrosine phosphorylation of NMDAR 2A/2B and recruitment of signaling partners in response to NMDA stimulation. The array of neuronal characteristics observed here establishes that proliferating cells derived from the human olfactory epithelium differentiate in vitro to express functional and molecular attributes of mature olfactory neurons. These cultured neural cells exhibit neurotransmitter pathways important in a number of neuropsychiatric disorders. Their ready availability from living humans thus provides a new tool to link functional and molecular features of neural cells with clinical characteristics of individual living patients.

Expressing exogenous functional odorant receptors in cultured olfactory sensory neurons

BACKGROUND

Olfactory discrimination depends on the large numbers of odorant receptor genes and differential ligand-receptor signaling among neurons expressing different receptors. In this study, we describe an in vitro system that enables the expression of exogenous odorant receptors in cultured olfactory sensory neurons. Olfactory sensory neurons in the culture express characteristic signaling molecules and, therefore, provide a system to study receptor function within its intrinsic cellular environment.

RESULTS

We demonstrate that cultured olfactory sensory neurons express endogenous odorant receptors. Lentiviral vector-mediated gene transfer enables successful ectopic expression of odorant receptors. We show that the ectopically expressed mouse I7 is functional in the cultured olfactory sensory neurons. When two different odorant receptors are ectopically expressed simultaneously, both receptor proteins co-localized in the same olfactory sensory neurons up to 10 days in vitro.

CONCLUSION

This culture technique provided an efficient method to culture olfactory sensory neurons whose morphology, molecular characteristics and maturation progression resembled those observed in vivo. Using this system, regulation of odorant receptor expression and its ligand specificity can be studied in its intrinsic cellular environment.

Horizontal basal cells are multipotent progenitors in normal and injured adult olfactory epithelium

The mammalian olfactory neuroepithelium provides a unique system for understanding the regulation of neurogenesis by adult neural stem cells. Recently, mouse horizontal basal cells (HBCs) were identified as stem cells that regenerate olfactory receptor neurons (ORNs) and non-neuronal cell types only after extensive injury of the olfactory epithelium (OE). Here we report a broader spectrum of action for these cells. We show that even during normal neuronal turnover, HBCs actively generate neuronal and non-neuronal cells throughout adulthood. This occurs in a temporally controlled manner: an initial wave of HBC-derived neurogenesis was observed soon after birth, and a second wave of neurogenesis was observed at 4 months of age. Moreover, upon selective depletion of mature ORNs by olfactory bulbectomy, HBCs give rise to more neurons. Our findings demonstrate a crucial role for HBCs as multipotent progenitors in the adult OE, acting during normal neuronal turnover as well as in acute regeneration upon injury.