Expression Of Olfactory Marker Protein Research Articles

Network pharmacology and experimental validation reveal the mechanisms of sniffing essential oil of Acori Tatarinowii rhizoma in treating olfactory dysfunction

Ethnopharmacological relevanceAcorus tatarinowii Rhizoma, a traditional Chinese medicine known for open the orifices and transform phlegm, is used in the treatment of brain disorders. The essential oil of Acorus tatarinowii Rhizoma (EOAT) has demonstrated neuroprotective properties clinically. However, research into its effect on Olfactory Dysfunction (OD) remains limited. Aim of the studyThis study aimed to investigate the effects and mechanisms of sniffing EOAT on improving olfactory function in a 3-Methylindole (3-MI)-induced OD mouse model. Materials and methodsThe research involved intraperitoneal injection of 3-MI to induce OD in mice. The effects of EOAT treatment were assessed on olfactory function, olfactory bulb (OB) pathology, inflammatory factors, olfactory marker protein (OMP), microglial activation, and related pathway proteins and mRNA. ResultsBased on the GC-MS analysis results of EOAT and network pharmacology studies, we predicted 18 targets associated with the treatment of OD. SLC6A3, MAOB, DRD1, and PTGS2 were identified as the core targets of EOAT against OD. Molecular docking and KEGG enrichment results indicated that EOAT may exert anti-inflammatory effects by acting on the core target PTGS2, with its anti-inflammatory mechanism possibly related to the PI3K/Akt signaling pathway. Subsequent animal experiments confirmed that inhalation of EOAT significantly increased the body weight of OD model mice, shortened the foraging time, enhanced the expression of OMP in OB, reduced damage to the OB cells, and improved olfactory function. Meanwhile, EOAT significantly alleviated the inflammatory response in OB of OD model mice, inhibited the activation of microglial cells, and suppressed the expression of PI3K/Akt signaling pathway proteins and mRNA. ConclusionEOAT inhalation could improve olfactory function in 3-MI-induced OD model. The underlying mechanism may be related to the modulation of the PI3K/Akt signaling pathway.

Craniofacial and olfactory sensory changes after long-term unilateral nasal obstruction—an animal study using MMP-3-LUC transgenic rats

Nasal obstruction exerts considerable physiological effects on the respiratory system and craniofacial morphology during the developmental stage. This study used MMP-3-LUC transgenic rats for in vivo tracking of long-term expression in the rat nasal region after unilateral nasal obstruction. Skeletal changes of the craniofacial, nasal, and sinus regions were measured through micro-computed tomography examination and analysis with 3D image processing and calculation. Matrix metalloproteinase-3 and olfactory marker protein expression were also investigated through immunohistochemistry (IHC). Unilateral nasal obstruction significantly reduced the MMP-3 signal in the nasal region of MMP-3-LUC transgenic rats, which was mainly expressed in the respiratory epithelium. Long-term obstruction also caused morphological changes of the craniofacial hard tissue, such as nasal septal deviation, longer inter-jaw distance, and increased maxillary molar dental height. It also caused compensatory growth in olfactory nerve bundles and the olfactory epithelium, as confirmed by IHC. In our study, long-term unilateral nasal obstruction caused nasal septal deviation toward the unobstructed side, hyper divergent facial development including longer molar dental height, and reduced MMP-3 production. However, further investigation is necessary to explore the mechanism in depth.

Acetate-Mediated Odorant Receptor OR51E2 Activation Results in Calcitonin Secretion in Parafollicular C-Cells: A Novel Diagnostic Target of Human Medullary Thyroid Cancer.

Medullary thyroid cancer originates from parafollicular C-cells in the thyroid. Despite successful thyroidectomy, localizing remnant cancer cells in patients with elevated calcitonin and carcinoembryonic antigen levels remains a challenge. Extranasal odorant receptors are expressed in cells from non-olfactory tissues, including C-cells. This study evaluates the odorant receptor signals from parafollicular C-cells, specifically, the presence of olfactory marker protein, and further assesses the ability of the protein in localizing and treating medullary thyroid cancer. We used immunohistochemistry, immunofluorescent staining, Western blot, RNA sequencing, and real time-PCR to analyze the expression of odorant receptors in mice thyroids, thyroid cancer cell lines, and patient specimens. We used in vivo assays to analyze acetate binding, calcitonin secretion, and cAMP pathway. We also used positron emission tomography (PET) to assess C11-acetate uptake in medullary thyroid cancer patients. We investigated olfactory marker protein expression in C-cells in patients and found that it co-localizes with calcitonin in C-cells from both normal and cancer cell lines. Specifically, we found that OR51E2 and OR51E1 were expressed in thyroid cancer cell lines and human medullary thyroid cancer cells. Furthermore, we found that in the C-cells, the binding of acetate to OR51E2 activates its migration into the nucleus, subsequently resulting in calcitonin secretion via the cAMP pathway. Finally, we found that C11-acetate, a positron emission tomography radiotracer analog for acetate, binds competitively to OR51E2. We confirmed C11-acetate uptake in cancer cells and in human patients using PET. We demonstrated that acetate binds to OR51E2 in C-cells. Using C11-acetate PET, we identified recurrence sites in post-operative medullary thyroid cancer patients. Therefore, OR51E2 may be a novel diagnostic and therapeutic target for medullary thyroid cancer.

Glycoconjugate-Specific Developmental Changes in the Horse Vomeronasal Organ

The vomeronasal organ (VNO) is a tubular pheromone-sensing organ in which the lumen is covered with sensory and non-sensory epithelia. This study used immunohistochemistry and lectin histochemistry techniques to evaluate developmental changes, specifically of the glycoconjugate profile, in the horse VNO epithelium. Immunostaining analysis revealed PGP9.5 expression in some vomeronasal non-sensory epithelium (VNSE) cells and in the vomeronasal receptor cells of the vomeronasal sensory epithelium (VSE) in fetuses, young foals, and adult horses. Olfactory marker protein expression was exclusively localized in receptor cells of the VSE in fetuses, young foals, and adult horses and absent in VNSE. To identify the glycoconjugate type, lectin histochemistry was performed using 21 lectins. Semi-quantitative analysis revealed that the intensities of glycoconjugates labeled with WGA, DSL, LEL, and RCA₁₂₀ were significantly higher in adult horse VSE than those in foal VSE, whereas the intensities of glycoconjugates labeled with LCA and PSA were significantly lower in adult horse VSE. The intensities of glycoconjugates labeled with s-WGA, WGA, BSL-II, DSL, LEL, STL, ConA, LCA, PSA, DBA, SBA, SJA, RCA₁₂₀, jacalin, and ECL were significantly higher in adult horse VNSE than those in foal VNSE, whereas the intensity of glycoconjugates labeled with UEA-I was lower in adult horse VNSE. Histochemical analysis of each lectin revealed that various glycoconjugates in the VSE were present in the receptor, supporting, and basal cells of foals and adult horses. A similar pattern of lectin histochemistry was also observed in the VNSE of foals and adult horses. In conclusion, these results suggest that there is an increase in the level of N-acetylglucosamine (labeled by WGA, DSL, LEL) and galactose (labeled by RCA₁₂₀) in horse VSE during postnatal development, implying that they may influence the function of VNO in adult horses.

Olfactory marker protein regulation of glucagon secretion in hyperglycemia

The olfactory marker protein (OMP), which is also expressed in nonolfactory tissues, plays a role in regulating the kinetics and termination of olfactory transduction. Thus, we hypothesized that OMP may play a similar role in modulating the secretion of hormones involved in Ca2+ and cAMP signaling, such as glucagon. In the present study, we confirmed nonolfactory α-cell-specific OMP expression in human and mouse pancreatic islets as well as in the murine α-cell line αTC1.9. Glucagon and OMP expression increased under hyperglycemic conditions. Omp knockdown in hyperglycemic αTC1.9 cells using small-interfering RNA (siRNA) reduced the responses to glucagon release and the related signaling pathways compared with the si-negative control. The OMPlox/lox;GCGcre/w mice expressed basal glucagon levels similar to those in the wild-type OMPlox/lox mice but showed resistance against streptozotocin-induced hyperglycemia. The ectopic olfactory signaling events in pancreatic α-cells suggest that olfactory receptor pathways could be therapeutic targets for reducing excessive glucagon levels.

Experimental study of dopamine ameliorating the inflammatory damage of olfactory bulb in mice with allergic rhinitis

Objective: To investigate the effects of dopamine on olfactory function and inflammatory injury of olfactory bulb in mice with allergic rhinitis (AR). Methods: AR mouse model was established by using ovalbumin (OVA), and the mice were divided into two groups: olfactory dysfunction (OD) group and without OD group through buried food pellet test (BFPT). The OD mice were randomly divided into 2 groups, and OVA combined with dopamine (3, 6, 9 and 12 days, respectively) or OVA combined with an equal amount of PBS (the same treatment time) was administered nasally. The olfactory function of mice was evaluated by BFPT. The number of eosinophils and goblet cells in the nasal mucosa were detected by HE and PAS staining. Western blotting, immunohistochemistry or immunofluorescence were used to detect the expression of olfactory marker protein (OMP) in olfactory epithelium, the important rate-limiting enzyme tyrosine hydroxylase (TH) of dopamine, and the marker proteins glial fibrillary acidic protein (GFAP) and CD11b of glial cell in the olfactory bulb. TUNEL staining was used to detect the damage of the olfactory bulb. SPSS 26.0 software was used for statistical analysis. Results: AR mice with OD had AR pathological characteristics. Compared with AR mice without OD, the expression of OMP in olfactory epithelium of AR mice with OD was reduced (F=26.09, P<0.05), the expression of GFAP and CD11b in the olfactory bulb was increased (F value was 38.95 and 71.71, respectively, both P<0.05), and the expression of TH in the olfactory bulb was decreased (F=77.00, P<0.05). Nasal administration of dopamine could shorten the time of food globule detection in mice to a certain extent, down-regulate the expression of GFAP and CD11b in the olfactory bulb (F value was 6.55 and 46.11, respectively, both P<0.05), and reduce the number of apoptotic cells in the olfactory bulb (F=25.64, P<0.05). But dopamine had no significant effect on the number of eosinophils and goblet cells in nasal mucosa (F value was 36.26 and 19.38, respectively, both P>0.05), and had no significant effect on the expression of OMP in the olfactory epithelium (F=55.27, P>0.05). Conclusion: Dopamine can improve olfactory function in mice with AR to a certain extent, possibly because of inhibiting the activation of glial cells in olfactory bulb and reducing the apoptotic injury of olfactory bulb cells.

Morphological features of changes in peripheral olfactory structures in SARS-COV-2 coronavirus infection

Coronavirus infection caused by the SARS-CoV-2 virus is an extremely important and urgent problem of modern medicine. It spreads quickly, has a high probability of a severe course and a large number of critical complications in patients from the risk group. The presence of pathognomonic symptoms, one of which is the development of hypo– or anosmia, makes it possible to quickly differentiate coronavirus infection from other acute respiratory viral infections, that is, to isolate the patient on time and begin correct treatment, taking all possible risks into account. The aim is to identify the morphological features of olfactory structural elements in patients with coronavirus disease (COVID-19) for a better understanding of the mechanisms of olfactory disorders development in coronavirus infection. Materials and methods. The basis of the work is a retrospective analysis of autopsy material, namely the mucous membrane of the upper parts of the nasal cavity (olfactory epithelium) and olfactory bulbs of nine deceased (4 women and 5 men) aged from 53 to 79 years with a laboratory-confirmed diagnosis of COVID-19 and anosmia in anamnesis. We used standard hematoxylin and eosin staining and immunohistochemical reactions in accordance with the TermoScientific protocols (USA) with antibodies to neurospecific beta-III tubulin (clone TuJ-1) and RnDsystems protocols with antibodies to olfactory marker protein (OMP) and angiotensin converting enzyme (ACE-2). To compare the results, a control group of 9 deaths (3 women and 6 men) aged from 59 to 68 years with a laboratory-refuted diagnosis of COVID-19 was formed. The causes of death of these patients were complications of diabetes, coronary heart disease and cerebrovascular disorders of the ischemictype. Results. The average age of the deceased with a laboratory-confirmed diagnosis of COVID-19 and a history of anosmia and the control group was 64.67 ± 7.73 and 62.33 ± 6.48 years, respectively. The expression of olfactory marker protein (OMP) and neurospecific beta-III tubulin (clone TuJ-1) was partially positive (40.89 (25.00–52.00) and 42.44 (29.00–55.00) cells in the field of view at a magnification of 200×, respectively) in seven out of nine sections of the olfactory mucous membrane of deaths with a laboratory-confirmed diagnosis of COVID-19 and anosmia in anamnesis. The reaction with antibodies to angiotensin converting enzyme (ACE-2) was focally or subtotally absent (34.33 (14.00–49.00) cells in the field of view at 200× magnification). There was expression of these three markers in control sections of the olfactory mucosa of a deceased with a laboratory excluded diagnosis of COVID-19 and no symptoms of anosmia (Mann–Whitney test, P &lt; 0.05). In sections of olfactory bulbs of patients with COVID-19 weak (Mann–Whitney test, P &lt; 0.05) expression of receptors for angiotensin-converting enzyme (ACE-2) (26.78 (15.00–39.00) cells in field of view at a magnification of 200×) was revealed in contrast to control sections (100.56 (94.00–107.00) cells in the field of view at a magnification of 200×). Conclusions. The development of anosmia in SARS-CoV-2 coronavirus infection has specific features. This may be due to the primary destruction of cells expressing receptors for the angiotensin-converting enzyme (ACE-2-positive: sustentacular cells of the olfactory mucosa, neurons of the olfactory bulbs). Subsequent dysfunction of olfactory cells (OMP- and TuJ-1-positive) is also possible.

Histological and Immunohistochemical Characterization of Vomeronasal Organ Aging in Mice.

Simple SummaryChemical communication has been intensely studied and the importance of its role in animal life has been ascertained. Located in the nasal cavity, the vomeronasal organ is one of the main actors in charge of chemical reception. Alterations of this organ have proven to modify behavioral responses to semiochemical expositions. For all the other organs, a well-known origin of alteration is aging. The objective of this study was to analyze this effect on the vomeronasal organ condition and to determine the nature of these potential changes. This study demonstrates that this organ is significantly impacted by aging. In particular, old mice present strong signs of neuronal degeneration compared to adults.The vomeronasal organ (VNO) plays a crucial role in animal behavior since it is responsible for semiochemical detection and, thus, for intra- and interspecific chemical communication, through the vomeronasal sensory epithelium (VNSE), composed of bipolar sensory neurons. This study aimed to explore a well-recognized cause of neuronal degeneration, only rarely explored in this organ: aging. Murine VNOs were evaluated according to 3 age groups (3, 10, and 24 months) by histology to assess VNSE changes such as cellular degeneration or glycogen accumulation and by immunohistochemistry to explore nervous configuration, proliferation capability, and apoptosis with the expression of olfactory marker protein (OMP), Gαi2, Gαo, Ki-67, and cleaved caspase-3 proteins. These markers were quantified as percentages of positive signal in the VNSE and statistical analyses were performed. Cellular degeneration increased with age (p < 0.0001) as well as glycogen accumulation (p < 0.0001), Gαo expression (p < 0.0001), and the number of cleaved-caspase3 positive cells (p = 0.0425), while OMP and Gαi2 expressions decreased with age (p = 0.0436 and p < 0.0001, respectively). Ki67-positive cells were reduced, even if this difference was not statistically significant (p = 0.9105). Due to the crucial role of VNO in animal life, this study opens the door to interesting perspectives about chemical communication efficiency in aging animals.

The functional relevance of olfactory marker protein in the vertebrate olfactory system: a never-ending story.

Olfactory marker protein (OMP) was first described as a protein expressed in olfactory receptor neurons (ORNs) in the nasal cavity. In particular, OMP, a small cytoplasmic protein, marks mature ORNs and is also expressed in the neurons of other nasal chemosensory systems: the vomeronasal organ, the septal organ of Masera, and the Grueneberg ganglion. While its expression pattern was more easily established, OMP's function remained relatively vague. To date, most of the work to understand OMP's role has been done using mice lacking OMP. This mostly phenomenological work has shown that OMP is involved in sharpening the odorant response profile and in quickening odorant response kinetics of ORNs and that it contributes to targeting of ORN axons to the olfactory bulb to refine the glomerular response map. Increasing evidence shows that OMP acts at the early stages of olfactory transduction by modulating the kinetics of cAMP, the second messenger of olfactory transduction. However, how this occurs at a mechanistic level is not understood, and it might also not be the only mechanism underlying all the changes observed in mice lacking OMP. Recently, OMP has been detected outside the nose, including the brain and other organs. Although no obvious logic has become apparent regarding the underlying commonality between nasal and extranasal expression of OMP, a broader approach to diverse cellular systems might help unravel OMP's functions and mechanisms of action inside and outside the nose.

Immunocytochemical Localization of Olfactory-signaling Molecules in Human and Rat Spermatozoa.

Expression of olfactory receptors (ORs) in non-olfactory tissues has been widely reported over the last 20 years. Olfactory marker protein (OMP) is highly expressed in mature olfactory sensory neurons (mOSNs) of the olfactory epithelium. It is involved in the olfactory signal transduction pathway, which is mediated by well-conserved components, including ORs, olfactory G protein (Golf), and adenylyl cyclase 3 (AC3). OMP is widely expressed in non-olfactory tissues with an apparent preference for motile cells. We hypothesized that OMP is expressed in compartment-specific locations and co-localize with an OR, Golf, and AC3 in rat epididymal and human-ejaculated spermatozoa. We used immunocytochemistry to examine the expression patterns of OMP and OR6B2 (human OR, served as positive olfactory control) in experimentally induced modes of activation and determine whether there are any observable differences in proteins expression during the post-ejaculatory stages of spermatozoal functional maturation. We found that OMP was expressed in compartment-specific locations in human and rat spermatozoa. OMP was co-expressed with Golf and AC3 in rat spermatozoa and with OR6B2 in all three modes of activation (control, activated, and hyperactivated), and the mode of activation changed the co-expression pattern in acrosomal-reacted human spermatozoa. These observations suggest that OMP expression is a reliable indicator of OR-mediated chemoreception, may be used to identify ectopically expressed ORs, and could participate in second messenger signaling cascades that mediate fertility.

Reversal of Olfactory Disturbance in Allergic Rhinitis Related to OMP Suppression by Intranasal Budesonide Treatment.

PurposeWe evaluated the severity of olfactory disturbance (OD) in the murine model of allergic rhinitis (AR) and local allergic rhinitis (LAR) in mice. We also investigated the therapeutic effect of an intranasal steroid on OD.MethodsForty BALB/c mice were divided into 5 groups (n = 8 for each). The control group was sensitized intraperitoneally (i.p.) and challenged intranasally (i.n.) with saline. Mice in the AR group got i.p. and i.n. ovalbumin (OVA) administration for AR induction. The LAR group was challenged i.n. with 1% OVA for inducing local nasal allergic inflammation, without inducing the systemic allergy. The OD group got an i.p. methimazole administration (75 mg/kg) to induce total destruction of olfactory mucosa. Mice in the intranasal budesonide group received i.n. budesonide (12.8 μg per time, 30 minutes after the i.n. OVA challenge) while using OVA to cause systemic allergies. We conducted a buried-food pellet test to functionally assess the degree of OD in each group by measuring the time taken until finding hidden food. We evaluated the damage to olfactory epithelium using histopathologic evaluation and compared the degree of olfactory marker protein (OMP) expression in olfactory epithelium using immunofluorescent staining.ResultsMice of the AR (81.3 ± 19.8 seconds) and LAR groups (66.2 ± 12.7 seconds) spent significantly more time to detect the pellets than the control group (35.6 ± 12.2 seconds, P < 0.01). After treatment, the intranasal budesonide group exhibited significantly better results (35.8 ± 11.9 seconds) compared with the AR and LAR groups (P < 0.01). The AR and LAR groups showed considerable olfactory epithelial damage and suppression of OMP expression compared with the control group. In the intranasal budesonide group, the olfactory lesions and OMP expression had improved substantially.ConclusionsOD may be caused by olfactory epithelial damage and suppression of OMP expression in nasal allergic inflammation and could be reversed using an intranasal steroid.

Sequential Maturation of Olfactory Sensory Neurons in the Mature Olfactory Epithelium.

The formation of the olfactory nerve and olfactory bulb (OB) glomeruli begins embryonically in mice. However, the development of the olfactory system continues throughout life with the addition of new olfactory sensory neurons (OSNs) in the olfactory epithelium (OE). Much attention has been given to the perinatal innervation of the OB by OSN axons, but in the young adult the process of OSN maturation and axon targeting to the OB remains controversial. To address this gap in understanding, we used BrdU to label late-born OSNs in young adult mice at postnatal day 25 (P25-born OSNs) and timed their molecular maturation following basal cell division. We show that OSNs in young adults undergo a sequential molecular development with the expression of GAP 43 (growth-associated protein 43) > AC3 (adenylyl cyclase 3) > OMP (olfactory marker protein), consecutively, in a time frame of ∼8 d. To assess OSN axon development, we implemented an in vivo fate-mapping strategy to label P25-born OSNs with ZsGreen. Using sampling intervals of 24 h, we demonstrate the progressive extension of OSN axons in the OE, through the foramen of the cribriform plate, and onto the surface of the OB. OSN axons reached the OB and began to target and robustly innervate specific glomeruli ∼10 d following basal cell division, a time point at which OMP expression becomes evident. Our data demonstrate a sequential process of correlated axon extension and molecular maturation that is similar to that seen in the neonate, but on a slightly longer timescale and with regional differences in the OE.

Regulation of chitosan-mediated differentiation of human olfactory receptor neurons by insulin-like growth factor binding protein-2

Olfaction is normally taken for granted in our lives, not only assisting us to escape from dangers, but also increasing our quality of life. Although olfactory neuroepithelium (ON) can reconstitute its olfactory receptor neurons (ORNs) after injury, no adequate treatment for olfactory loss has yet emerged. The present study investigates the role of glycosaminoglycans (GAGs) in modulating olfactory neuronal homeostasis and elucidates the regulatory mechanism. This work isolates and cultures human olfactory neuroepithelial cells (HONCs) with various GAGs for 7 days, and find that chitosan promotes ORN maturation, expressing olfactory marker protein (OMP) and its functional components. Growth factor protein array, ELISA and western blot analysis reveal that insulin-like growth factor binding protein 2 (IGFBP2) shows a higher level in chitosan-treated HONCs than in controls. Biological activity of insulin-like growth factor-1 (IGF-1), IGF-2 and IGF-1 receptor (IGF1R) is further investigated. Experimental results indicate that IGF-1 and IGF-2 enhance the growth of immature ORNs, expressing βIII tubulin, but decrease mature ORNs. Instead, down-regulation of phosphorylated IGF1R lifts the OMP expression, and lowers the βIII tubulin expression, by incubation with the phosphorylated inhibitor of IGF1R, OSI-906. Finally, the effect of chitosan on ORN maturity is antagonized by concurrently adding IGFBP2 protease, matrix metallopeptidase-1. Overall, our data demonstrate that chitosan promotes ORN differentiation by raising the level of IGFBP2 to sequestrate the IGFs-IGF1R signaling. Statement of SignificanceOlfactory dysfunction serves as a crucial alarm in neurodegenerative diseases, and one of its causes is lacking of sufficient mature olfactory receptor neurons to detect odorants in the air. However, the clinical treatment for olfactory dysfunction is still controversial. Chitosan is the natural linear polysaccharide and exists in rat olfactory neuroepithelium. Previously, chitosan has been demonstrated to mediate the differentiation of olfactory receptor neurons in an in vitro rat model, but the mechanism is unknown. The study aims to evaluate the role and mechanism of chitosan in an in vitro human olfactory neurons model. Overall, these results reveal that chitosan is a potential agent for treating olfactory disorder by the maintenance of olfactory neural homeostasis. This is the first report to demonstrate that chitosan promotes differentiation of olfactory receptor neurons through increasing IGFBP2 to sequestrate the IGFs-IGF1R.

Microglial and astroglial reaction in the olfactory bulb of mice after Triton X-100 application

Gliosis including microgliosis and astrogliosis is a response to central nervous system inflammation. The purpose of this study was to evaluate whether olfactory bulbs are influenced by intranasal exposure to the detergent Triton X-100, a non-ionic surfactant. In this experiment, we measured olfactory function in mice based on the time needed to identify hidden pellets. Our results found that more time was needed to find the buried pellets by mice exposed to Triton X-100 compared with mice without Triton X-100 exposure, up to day 7. Histopathological examination revealed inflammatory cells in the olfactory mucosa and olfactory bulbs in mice treated with Triton X-100. Western blot analysis revealed significant downregulation of olfactory marker proteins in the olfactory mucosa and bulbs of mice after intranasal exposure to Triton X-100. In the olfactory bulbs of mice exposed to Triton X-100, microgliosis and astrogliosis were evident using immunohistochemistry. Cathepsin D was also upregulated in Iba-1-positive microglia/macrophages and GFAP-positive astrocytes in the olfactory bulbs of mice exposed to Triton X-100. In mice, Triton X-100 induced olfactory sensory neuron death in the nasal cavity and gliosis in olfactory bulbs with concurrent downregulation of olfactory marker protein expression, resulting in transient olfactory dysfunction.

Excessive Expression of Microglia/Macrophage and Proinflammatory Mediators in Olfactory Bulb and Olfactory Dysfunction After Stroke.

Olfactory dysfunction can be caused by stroke but the pathogenesis is still unclear. Previous studies have proved that olfactory dysfunction could be caused by microglia activation in the olfactory bulb and that middle cerebral artery occlusion (MCAO) may induce ipsilateral olfactory bulb microglia activation. This study aimed to explore the possible pathogenesis of ischemic stroke-induced olfactory dysfunction. We used a rat model of MCAO to simulate ischemic stroke. Olfactory function tests were performed using buried food test. The mRNA expression of olfactory marker protein (OMP), microglia/macrophage activation, and proinflammatory mediators were measured using reverse transcription-quantitative polymerase chain reaction. Following MCAO, rats had poorer olfactory performance. In the olfactory bulb of the rats, the mRNA expression of OMP decreased and the mRNA expression of microglia/macrophage activation and proinflammatory mediators increased. Ischemic stroke causes microglia/macrophage activation and promotes neuroinflammation in the olfactory bulb, causing olfactory dysfunction.

Olfactory Receptor OR51E1 Mediates GLP-1 Secretion in Human and Rodent Enteroendocrine L Cells.

Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), produced by intestinal enteroendocrine L cells, are important gut hormones that coordinate gastrointestinal physiology, metabolism, and appetite. We aimed to investigate the role of olfactory receptor (OR) OR51E1 in GLP-1 and PYY secretion. We analyzed the expression of olfactory marker protein (OMP), an indicator of OR-mediated events in nonolfactory systems, in human intestinal L cells. Furthermore, we analyzed OMP and OR51E1 expression in the L cell line NCI-H716. To investigate whether odorant-activated OR signaling stimulates GLP-1 and PYY secretion, we used nonanoic acid, a known OR51E1 ligand. Treatment with 100 μM nonanoic acid increased GLP-1 secretion by 2.32 ± 0.41-fold and PYY secretion by 1.44 ± 0.10-fold; however, this effect was attenuated on small interfering RNA-mediated OR51E1 knockdown. Oral administration of nonanoic acid to rats resulted in a 2.89 ± 0.53-fold increase in GLP-1 levels and reductions in blood glucose levels compared with the control group. Nonanoic acid stimulates GLP-1 and PYY secretion via OR51E1 signaling in L cells, thereby indicating a potential role of OR-mediated events in GLP-1 and PYY secretion; this could be translated into a therapeutic approach in treating diabetes.

Olfactory marker protein regulates prolactin secretion and production by modulating Ca2+ and TRH signaling in lactotrophs

Olfactory marker protein (OMP) is a marker of olfactory receptor-mediated chemoreception, even outside the olfactory system. Here, we report that OMP expression in the pituitary gland plays a role in basal and thyrotropin-releasing hormone (TRH)-induced prolactin (PRL) production and secretion. We found that OMP was expressed in human and rodent pituitary glands, especially in PRL-secreting lactotrophs. OMP knockdown in GH4 rat pituitary cells increased PRL production and secretion via extracellular signal-regulated kinase (ERK)1/2 signaling. Real-time PCR analysis and the Ca2+ influx assay revealed that OMP was critical for TRH-induced PRL secretion. OMP-knockout mice showed lower fertility than control mice, which was associated with increased basal PRL production via activation of ERK1/2 signaling and reduced TRH-induced PRL secretion. However, both in vitro and in vivo results indicated that OMP was only required for hormone production and secretion because ERK1/2 activation failed to stimulate cell proliferation. Additionally, patients with prolactinoma lacked OMP expression in tumor tissues with hyperactivated ERK1/2 signaling. These findings indicate that OMP plays a role in PRL production and secretion in lactotrophs through the modulation of Ca2+ and TRH signaling.

Olfactory Dysfunction in Autoimmune Central Nervous System Neuroinflammation.

Olfactory dysfunction is an early sign of neuroinflammation of the central nervous system (CNS). Microgliosis and astrogliosis are representative pathological changes that develop during neuroinflammation of CNS tissues. Autoimmune CNS inflammation, including human multiple sclerosis, is an occasional cause of olfactory disorders. We evaluated whether gliosis and olfactory dysfunction developed in animals with experimental autoimmune encephalomyelitis (EAE), a model of human multiple sclerosis. Neuroinflammatory lesions characterized by infiltration of inflammatory cells and microglial cell activation were occasionally found in the olfactory bulbs of EAE-affected rats. Microglial activation, visualized by immunohistochemical staining of ionized calcium binding protein (Iba)-1, and astrogliosis in the olfactory bulb were also evident in the olfactory bulb of EAE rats. Inflammatory cells were found along the olfactory nerves and in the olfactory submucosa. Western blot analysis of olfactory marker protein (OMP) levels showed that OMP expression was significantly downregulated in the olfactory mucosa of EAE rats. On the buried food test, EAE-affected mice required significantly more time to find a bait pellet. Collectively, the results suggest that the olfactory dysfunction of EAE is closely linked to downregulation of OMP and the development of inflammatory foci in the olfactory system in an animal model of human multiple sclerosis.

Intranasal application of glucocorticoid alleviates olfactory dysfunction in mice with allergic rhinitis.

The aim of the present study was to investigate the effect of glucocorticoid intervention on olfactory dysfunction in mice with allergic rhinitis (AR). An AR animal model was established by intraperitoneal injection and intranasal application of ovalbumin to mice. The olfactory function of the mice was evaluated using a buried food test, and morphological changes in the nasal mucosa were determined using hematoxylin and eosin staining. The expression of olfactory marker protein (OMP) in the olfactory mucosa was tested by immunohistochemistry, and was observed on days 7 and 14 after the application of glucocorticoid. The incidence rate of olfactory dysfunction in AR mice was 75.34%, and the olfactory epithelium became thinner in mice with AR compared to the control group. In addition, the expression of OMP in the olfactory epithelium was downregulated in mice with AR compared with the control group. Expression of OMP in the olfactory epithelium was upregulated in the budesonide group A and betamethasone group A compared with the medicine-free group, whereas the expression of OMP in the olfactory epithelium of budesonide group A or betamethasone group A was not significantly different from the control group. Moreover, the expression of OMP in the budesonide group B was similar to budesonide group A, and expression of OMP in betamethasone group B was similar to betamethasone group A. The expression of OMP in olfactory mucosa is downregulated in AR mice with olfactory dysfunction. Following the application of glucocorticoid, the expression of OMP in the olfactory mucosa in mice is upregulated. Moreover, intranasal local glucocorticoid has a low incidence of systemic adverse reactions, and is recommended for the treatment of olfactory dysfunction in AR.

Nasal Administration of Cholera Toxin as a Mucosal Adjuvant Damages the Olfactory System in Mice

Cholera toxin (CT) induces severe diarrhea in humans but acts as an adjuvant to enhance immune responses to vaccines when administered orally. Nasally administered CT also acts as an adjuvant, but CT and CT derivatives, including the B subunit of CT (CTB), are taken up from the olfactory epithelium and transported to the olfactory bulbs and therefore may be toxic to the central nervous system. To assess the toxicity, we investigated whether nasally administered CT or CT derivatives impair the olfactory system. In mice, nasal administration of CT, but not CTB or a non-toxic CT derivative, reduced the expression of olfactory marker protein (OMP) in the olfactory epithelium and olfactory bulbs and impaired odor responses, as determined with behavioral tests and optical imaging. Thus, nasally administered CT, like orally administered CT, is toxic and damages the olfactory system in mice. However, CTB and a non-toxic CT derivative, do not damage the olfactory system. The optical imaging we used here will be useful for assessing the safety of nasal vaccines and adjuvants during their development for human use and CT can be used as a positive control in this test.