Differential Expression of Mucins in Murine Olfactory Versus Respiratory Epithelium

Olfactory immunology: the missing piece in airway and CNS defence

The olfactory mucosa is a component of the nasal airway that mediates the sense of smell. Recent studies point to an important role for the olfactory mucosa as a barrier to both respiratory pathogens and to neuroinvasive pathogens that hijack the olfactory nerve and invade the CNS. In particular, the COVID-19 pandemic has demonstrated that the olfactory mucosa is an integral part of a heterogeneous nasal mucosal barrier critical to upper airway immunity. However, our insufficient knowledge of olfactory mucosal immunity hinders attempts to protect this tissue from infection and other diseases. This Review summarizes the state of olfactory immunology by highlighting the unique immunologically relevant anatomy of the olfactory mucosa, describing what is known of olfactory immune cells, and considering the impact of common infectious diseases and inflammatory disorders at this site. We will offer our perspective on the future of the field and the many unresolved questions pertaining to olfactory immunity.

Combining skin and olfactory α-synuclein seed amplification assays (SAA)-towards biomarker-driven phenotyping in synucleinopathies

Seed amplification assays (SAA) are becoming commonly used in synucleinopathies to detect α-synuclein aggregates. Studies in Parkinson's disease (PD) and isolated REM-sleep behavior disorder (iRBD) have shown a considerably lower sensitivity in the olfactory epithelium than in CSF or skin. To get an insight into α-synuclein (α-syn) distribution within the nervous system and reasons for low sensitivity, we compared SAA assessment of nasal brushings and skin biopsies in PD (n = 27) and iRBD patients (n = 18) and unaffected controls (n = 30). α-syn misfolding was overall found less commonly in the olfactory epithelium than in the skin, which could be partially explained by the nasal brushing matrix exerting an inhibitory effect on aggregation. Importantly, the α-syn distribution was not uniform: there was a higher deposition of misfolded α-syn across all sampled tissues in the iRBD cohort compared to PD (supporting the notion of RBD as a marker of a more malignant subtype of synucleinopathy) and in a subgroup of PD patients, misfolded α-syn was detectable only in the olfactory epithelium, suggestive of the recently proposed brain-first PD subtype. Assaying α-syn of diverse origins, such as olfactory (part of the central nervous system) and skin (peripheral nervous system), could increase diagnostic accuracy and allow better stratification of patients.

Impairment mechanism of nasal mucosa after radiotherapy for nasopharyngeal carcinoma

The nasal mucosa, which performs the crucial functions of filtering, humidifying and temperature regulation, is one of the most vulnerable areas of nasopharyngeal carcinoma (NPC) patients after radiotherapy (RT). Following RT, NPC patients experience a series of pathological changes in the nasal mucosa, ultimately leading to physiological dysfunction of the nasal epithelium. This article systematically reviews the clinical and pathological manifestations of RT-related nasal damage in NPC patients and summarizes the potential mechanism of damage to the human nasal epithelium by RT. Finally, we outline the current mechanistic models of nasal epithelial alterations after RT in NPC patients and provide additional information to extend the in-depth study on the impairment mechanisms of the nasal mucosa resulting from RT. We also describe the relationship between structural and functional alterations in the nasal mucosa after RT to help mitigate and treat this damage and provide insights informing future clinical and fundamental investigations.

Oxidative Chemical Stressors Alter the Physiological State of the Nasal Olfactory Mucosa of Atlantic Salmon

The olfactory organs of fish have vital functions for chemosensory and defence. Though there have been some ground-breaking discoveries of their involvement in immunity against pathogens in recent years, little is known about how they respond to non-infectious agents, such as exogenous oxidants, which fish encounter regularly. To this end, we employed Atlantic salmon (Salmo salar) as a model to study the molecular responses at the nasal olfactory mucosa of a teleost fish when challenged with oxidants. Microarray analysis was employed to unravel the transcriptional changes at the nasal olfactory mucosa following two types of in vivo exposure to peracetic acid (PAA), a highly potent oxidative agent commonly used in aquaculture: Trial 1: periodic and low dose (1 ppm, every 3 days over 45 days) to simulate a routine disinfection; and Trial 2: less frequent and high dose (10 ppm for 30 min, every 15 days, 3 times) to mimic a bath treatment. Furthermore, leukocytes from the olfactory organ were isolated and exposed to PAA, as well as to hydrogen peroxide (H₂O₂) and acetic acid (AA)—the two other components of PAA trade products—to perform targeted cellular and molecular response profiling. In the first trial, microarrays identified 32 differentially expressed genes (DEG) after a 45-day oxidant exposure. Erythrocyte-specific genes were overly represented and substantially upregulated following exogenous oxidant exposure. In Trial 2, in which a higher dose was administered, 62 DEGs were identified, over 80% of which were significantly upregulated after exposure. Genes involved in immune response, redox balance and stress, maintenance of cellular integrity and extracellular matrix were markedly affected by the oxidant. All chemical stimuli (i.e., PAA, H₂O₂, AA) significantly affected the proliferation of nasal leukocytes, with indications of recovery observed in PAA- and H₂O₂-exposed cells. The migration of nasal leukocytes was promoted by H₂O₂, but not much by PAA and AA. The three chemical oxidative stressors triggered oxidative stress in nasal leukocytes as indicated by an increase in the intracellular reactive oxygen species level. This resulted in the mobilisation of antioxidant defences in the nasal leukocytes as shown by the upregulation of crucial genes for this response network. Though qPCR revealed changes in the expression of selected cytokines and heat shock protein genes following in vitro challenge, the responses were stochastic. The results from the study advance our understanding of the role that the nasal olfactory mucosa plays in host defence, particularly towards oxidative chemical stressors.

Improved In Vitro Model for Intranasal Mucosal Drug Delivery: Primary Olfactory and Respiratory Epithelial Cells Compared with the Permanent Nasal Cell Line RPMI 2650

Background: The epithelial layer of the nasal mucosa is the first barrier for drug permeation during intranasal drug delivery. With increasing interest for intranasal pathways, adequate in vitro models are required. Here, porcine olfactory (OEPC) and respiratory (REPC) primary cells were characterised against the nasal tumour cell line RPMI 2650. Methods: Culture conditions for primary cells from porcine nasal mucosa were optimized and the cells characterised via light microscope, RT-PCR and immunofluorescence. Epithelial barrier function was analysed via transepithelial electrical resistance (TEER), and FITC-dextran was used as model substance for transepithelial permeation. Beating cilia necessary for mucociliary clearance were studied by immunoreactivity against acetylated tubulin. Results: OEPC and REPC barrier models differ in TEER, transepithelial permeation and MUC5AC levels. In contrast, RPMI 2650 displayed lower levels of MUC5AC, cilia markers and TEER, and higher FITC-dextran flux rates. Conclusion: To screen pharmaceutical formulations for intranasal delivery in vitro, translational mucosal models are needed. Here, a novel and comprehensive characterisation of OEPC and REPC against RPMI 2650 is presented. The established primary models display an appropriate model for nasal mucosa with secreted MUC5AC, beating cilia and a functional epithelial barrier, which is suitable for long-term evaluation of sustained release dosage forms.