Olfactory Mucosa Research Articles

α-Synuclein distribution in olfactory mucosa and skin nerves in Parkinson disease associated with an EIF4G1 gene mutation.

The EIF4G1 gene has been considered an autosomal dominant cause of Parkinson disease (PD), even if its role is still debated. The objective of this study was to describe the phenotype and α-synuclein distribution in peripheral tissues in 2 related PD patients (mother and daughter), who are carriers of the same variant in exon 10 of EIF4G1 (c.1216G>A, p.Gly406Arg). We used the Burghart Sniffin Sticks test for olfactory function. α-Synuclein distribution in the olfactory mucosa and skin samples was analyzed using RT-QuIC, double immunofluorescence, and immunohistochemical staining. Both patients presented with a mild motor syndrome associated with hyposmia as prominent traits; pathological α-synuclein deposits were found in the olfactory mucosa but not in the skin. The phenotype and the findings in peripheral tissues suggest that PARK18 could manifest as a "benign" form of PD associated with hyposmia, with a slow progression and sparse α-synuclein accumulation in the peripheral nervous system.

Intranasal iron administration induces iron deposition, immunoactivation, and cell-specific vulnerability in the olfactory bulb of C57BL/6 mice.

Iron is the most abundant transition metal in the brain and is essential for brain development and neuronal function; however, its abnormal accumulation is also implicated in various neurological disorders. The olfactory bulb (OB), an early target in neurodegenerative diseases, acts as a gateway for environmental toxins and contains diverse neuronal populations with distinct roles. This study explored the cell-specific vulnerability to iron in the OB using a mouse model of intranasal administration of ferric ammonium citrate (FAC). Olfactory function was assessed through olfactory discrimination tests, while iron levels in OB tissues, cerebrospinal fluid (CSF), and serum were quantified using inductively coupled plasma mass spectrometry (ICP-MS), immunohistochemical staining, and iron assays. Transcriptomic changes and immune responses were assessed using RNA sequencing and immune cell infiltration analysis. Results showed that intranasal FAC administration impaired olfactory function, accompanied by iron deposition in the olfactory mucosa and OB, as well as damage to olfactory sensory neurons. Notably, these effects occurred without elevations in CSF or serum iron levels. OB iron accumulation activated multiple immune cells, including microglia and astrocytes, but did not trigger ferroptosis. Spatial transcriptomic sequencing of healthy adult mouse OBs revealed significant cellular heterogeneity, with an abundance of neuroglia and neurons. Among neurons, GABAergic neurons were the most prevalent, followed by glutamatergic and dopaminergic neurons, while cholinergic and serotonergic neurons were sparsely distributed. Under iron-stressed conditions, oligodendrocytes, dopaminergic neurons, and glutamatergic neurons exhibited significant damage, while GABAergic neurons remained unaffected. These findings highlight the selective vulnerability of neuronal and glial populations to iron-induced stress, offering novel insights into the loss of specific cell types in the OB during iron dysregulation.

Intranasal Calcitriol Accelerates Improvement of Sinonasal Inflammation and Olfactory Impairment in Mice After Cessation of Chronic Cigarette-Smoke Exposure.

Smoking has been shown to be associated with circulating deficiencies in 25(OH)D3 and reduced sinonasal tissue levels of the active form of vitamin D, 1,25(OH)2D3. Given vitamin D's ability to reduce inflammation, we sought to examine if intranasal (IN) delivery of calcitriol [clinical analog of 1,25(OH)2D3] could reduce inflammation and improve disease severity in a murine model of chronic cigarette smoke-induced sinonasal inflammation (CS-SI). Mice were exposed to CS 5 h/day, 5 days/week for 9 months, and then began IN calcitriol three times per week for 4 weeks. Micro-CT was used to assess disease severity. Sinonasal tissues were collected for RNA-seq analysis. Olfactory function was assessed using a T-maze odorant avoidance sniff behavior test. Nasal lavage fluid (NALF) was used for cytology and cytokines analysis. Quantification of disease severity by micro-CT showed IN calcitriol reduced opacification by 18%, as compared to smoke cessation alone, in which only a 5% reduction was noted. H&E analysis of NAFL demonstrated heightened neutrophil infiltration and neutrophil-associated chemokines in CS-SI mice, which was reduced with IN calcitriol treatment. RNA-seq pathway analysis demonstrated that smoking was associated with odorant binding changes and that calcitriol treatment reduced neutrophil migration and inflammation. Lastly, IN calcitriol reversed olfactory loss caused in CS-SI. IN delivery of calcitriol accelerates inflammatory resolution in the nose and olfactory mucosa after prolonged CS exposure. Furthermore, treatment was associated with improved olfactory function in mice CS-SI, as such local delivery of calcitriol may serve as a novel treatment for modulating sinonasal inflammation.

Nose-to-brain delivery of lithium via a sprayable in situ-forming hydrogel composed of chelating starch nanoparticles.

While bipolar disorder patients can benefit from lithium therapy, high levels of lithium in the serum can induce undesirable systemic side effects. Intranasal (IN) lithium delivery offers a potential solution to this challenge given its potential to facilitate improved lithium transport to brain when delivered to the olfactory mucosa. Herein, a sprayable, in situ forming nanoparticle network hydrogel (NNH) based on Schiff base interactions between chelator-functionalized oxidized starch nanoparticles (SNPs) and carboxymethyl chitosan (CMCh) is reported that can be deployed within the nasal cavity to release ultra-small penetrative SNPs over time. Chelating functional groups including citrate, ethylenediaminetetraacetic acid, and pentetic acid are shown to bind a variety of cations including lithium, magnesium, and calcium, with chelation directly linked to enhancements in the gel mechanics even for monovalent lithium. The hydrogels show high in vitro cytocompatibility with mouse striatal neuron and human primary nasal cell lines. Effective IN delivery of lithium to the brain is demonstrated for the first time, with both solution-based and hydrogel-loaded lithium showing in vivo efficacy in an amphetamine-induced pre-clinical rat bipolar manic phase model; specifically, IN-delivered NNHs can maintain successful attenuation of locomotor activity for up to 6 h while all other tested treatments (drug-only IN or conventional intraperitoneal delivery) failed to retain attenuation for more than two hours at the same lithium dose. As such, in situ-gelling and ion-chelating NNHs represent a new material that can effectively enable metal ion management in biomedical applications.

Proteopathic seed amplification assays in easily accessible specimens for human synucleinopathies, tauopathies, and prionopathies: A scoping review.

A hallmark event in neurodegenerative diseases is represented by the misfolding, aggregation and accumulation of proteins, leading to cellular and network dysfunction preceding the development of clinical symptoms by years. Early diagnosis represents a crucial issue in the field of neuroscience as it offers the potential to utilize this therapeutic window in the future to manage disease-modifying therapy. Seed amplification assays, including Real-Time Quaking-Induced Conversion (RT-QuIC) and Protein Misfolding Cyclic Amplification (PMCA), have emerged in recent years as innovative techniques developed to detect minute amounts of amyloidogenic proteins. These techniques can utilize various biological fluids and tissues, with most evidence to date regarding their potential diagnostic use focusing on cerebrospinal fluid. In this scoping review, we aimed to investigate and discuss the available evidence regarding the diagnostic use of these assays on easily accessible biological fluids and tissues in patients affected by synucleinopathies, tauopathies or prion diseases. From a systematic search on two databases, Scopus and Pubmed, we identified 49 studies. Although most identified studies have used skin and olfactory mucosa as biological samples, there is preliminary evidence suggesting the potential implementation of these techniques using fluids as blood, saliva and tears. The results achieved so far, as well as methodological aspects and limitations to overcome, are discussed.

Transcriptomic and epigenomic profiling reveals altered responses to diesel emissions in Alzheimer's disease both in vitro and in population-based data.

Studies have correlated living close to major roads with Alzheimer's disease (AD) risk. However, the mechanisms responsible for this link remain unclear. We exposed olfactory mucosa (OM) cells of healthy individuals and AD patients to diesel emissions (DE). Cytotoxicity of exposure was assessed, mRNA, miRNA expression, and DNA methylation analyses were performed. The discovered altered pathways were validated using data from the human population-based Rotterdam Study. DE exposure resulted in an almost four-fold higher response in AD OM cells, indicating increased susceptibility to DE effects. Methylation analysis detected different DNA methylation patterns, revealing new exposure targets. Findings were validated by analyzing data from the Rotterdam Study cohort and demonstrated a key role of nuclear factor erythroid 2-related factor 2 signaling in responses to air pollutants. This study identifies air pollution exposure biomarkers and pinpoints key pathways activated by exposure. The data suggest that AD individuals may face heightened risks due to impaired cellular defenses. Healthy and AD olfactory cells respond differently to DE exposure. AD cells are highly susceptible to DE exposure. The NRF2 oxidative stress response is highly activated upon air pollution exposure. DE-exposed AD cells activate the unfolded protein response pathway. Key findings are also confirmed in a population-based study.

Convergent effects of synthetic glucocorticoid dexamethasone and amyloid beta in human olfactory neurosphere-derived cells.

Stressful life events and glucocorticoid (stress) hormones appear to increase the risk of Alzheimer's disease and hasten its progression, but the reasons for this remain unclear. One potential explanation is that when amyloid β (Aβ) pathology is accumulating in the preclinical disease stage, glucocorticoid receptor signalling during stressful events exacerbates cellular dysfunction caused by Aβ. Alternatively, Aβ may disrupt glucocorticoid receptor signalling. To explore these possibilities, we investigated whether the synthetic glucocorticoid dexamethasone and Aβ have overlapping effects on the cellular proteome and whether Aβ influences canonical glucocorticoid receptor function. Human olfactory neurosphere-derived (ONS) cells, collected from the olfactory mucosa of six adult donors, were treated with soluble Aβ40 or Aβ42 followed by dexamethasone. Proteins were quantified by mass spectrometry. After 32 h treatment, Aβ40 and Aβ42 both induced profound changes in innate immunity-related proteins. After 72 h, Aβ42 formed widespread aggregates and induced few proteomic changes, whereas Aβ40 remained soluble and altered expression of mitochondrial and innate immunity-related proteins. ONS cells revealed overlapping impacts of Aβ40 and dexamethasone, with 23 proteins altered by both treatments. For 16 proteins (including eight mitochondrial proteins) dexamethasone counteracted the effects of Aβ40. For example, caspase 4 and methylmalonate-semialdehyde dehydrogenase were increased by Aβ40 and decreased by dexamethasone. Consistent with this finding, Aβ40 increased, but dexamethasone decreased, ONS cell proliferation. For seven proteins, including superoxide dismutase [Mn] mitochondrial, dexamethasone exacerbated the effects of Aβ40. For some proteins, including complement C3, the effects of dexamethasone differed depending on whether Aβ40 was present or absent. Neither Aβ species influenced glucocorticoid receptor nuclear translocation. Overall, this study revealed that glucocorticoid receptor signalling modifies the intracellular effects of Aß40, counteracting some effects and exacerbating others. It suggests that cellular mechanisms through which glucocorticoid receptor signalling influences Alzheimer's disease risk/progression are complex and determined by the balance of beneficial and detrimental glucocorticoid effects.

Single-cell transcriptomic landscape deciphers olfactory neuroblastoma subtypes and intra-tumoral heterogeneity.

Olfactory neuroblastoma (ONB) is a rare malignancy known to originate from the olfactory epithelium. The complex tumor ecosystem of this pathology remains unclear. Here, we explored the cellular components within ten ONB tumors and one olfactory mucosa sample based on single-cell RNA profiles. We showed the intra-tumoral heterogeneity by identifying five unique expression programs among malignant epithelial cells. A distinct three-classification system (neural, basal, mesenchymal) for ONB was established according to the distinguished gene expression patterns. Biomarkers for categorizing bulk tumors into uncharacterized subtypes were elucidated. Different responses towards certain chemotherapy regimens could be cautiously inferred according to the molecular features representing the three tumor types, thus helping with precision chemotherapy. We also analyzed subclusters of the tumor microenvironment (TME) and the interactions among different cell types within the TME. The relative abundance of immunosuppressive tumor-associated macrophages suggests potential benefits of immunotherapies targeting macrophages.

Assessment of Single-Cycle M-Protein Mutated Vesicular Stomatitis Virus as a Safe and Immunogenic Mucosal Vaccine Platform for SARS-CoV-2 Immunogen Delivery.

The goal of the next-generation COVID-19 vaccine is to provide rapid respiratory tract protection with a single dose. Circulating antibodies do not protect the olfactory mucosa from viral infection, necessitating localized mucosal immunization. Live attenuated vesicular stomatitis virus (VSVMT)-based COVID-19 vaccines effectively stimulate mucosal immunity in animals, though safety concerns remain, particularly in immunocompromised populations. A viral vector capable of single-cycle replication may face less stringent regulatory requirements. A replication-defective VSVMT is developed with its G protein replaced by a SARS-CoV-2 spike protein (S) mutant, where residues K986 and V987 are substituted by prolines (S2P). This studies show that single-cycle VSVMT encoding Omicron subvariant S2P (VSVMT-S2P) is safe in both healthy and immunocompromised animals treated with cyclophosphamide (CP). Significant antibody and T-cell responses against the spike protein are observed in VSVMT-S2P vaccinated healthy animals. Intramuscular VSVMT-S2P administration induces neutralizing antibody responses comparable to those from replication-competent VSVMT-S. In immunocompromised animals, lower and delayed immune responses are observed. Thus, single-cycle M-protein mutated VSV offers a safe and effective platform for SARS-CoV-2 immunogen delivery. Remarkably, replication-competent VSVMT-S caused no pathogenicity and elicited potent mucosal immunity via intranasal administration, highlighting its potential as a mucosal COVID-19 vaccine.

Unveiling the potential of intranasal delivery of renin-angiotensin system drugs: Insights on the pharmacokinetics of irbesartan

The therapeutic interest of renin-angiotensin system (RAS) drugs for the treatment of neuroinflammation has been recently acknowledged. Nevertheless, most of them display limited passage across the blood–brain barrier (BBB). Therefore, this study investigated the potential of intranasal (IN) delivery of six RAS drugs to circumvent the BBB and attain the brain, envisioning its future use in central nervous system (CNS) neuroinflammatory diseases, such as Alzheimer’s disease (AD).Captopril, enalaprilat, irbesartan, lisinopril, losartan and valsartan were firstly screened based on their impact on the viability of nasal, lung, and neuronal cell lines and their apparent permeability (Papp) across porcine olfactory mucosa. Irbesartan, identified as the one with the best safety and permeability balance, was selected for pharmacokinetic characterization following single and multidose IN administration to CD-1 mice. The results were compared to those obtained by intravenous (IV) injection to assess direct nose-to-brain drug delivery. Olfactory toxicity and anxiety were also evaluated after multidose IN treatment.Irbesartan IN administration significantly enhanced brain targeting, with a 3-fold increase in the maximum concentration (Cmax) and a 2.5-fold increase in the area under the curve (AUCt) in the brain compared to IV route. The drug exhibited a tmax of 15 min post-IN administration and achieved a brain targeting efficiency of 239.56%, with a significant direct transport percentage of 58.26%. Multidose administration indicated no systemic or tissue accumulation, with accumulation ratio (Rac) values below 1.0, and no significant olfactory toxicity.Overall, the study highlights the potential of IN delivery of irbesartan as a promising strategy to improve brain targeting and therapeutic outcomes in CNS diseases such as AD, providing an effective approach to bypass BBB limitations.

Visualizing the human olfactory projection and ancillary structures in a 3D reconstruction

Visualizing in 3D the histological microanatomy of the human olfactory projection from the olfactory mucosa in the nasal cavity to the olfactory bulbs in the cranial cavity necessitates a workflow for handling a great many sections. Here, we assembled a 3D reconstruction of a 7.45 cm3en-bloc specimen extracted from an embalmed human cadaver. A series of 10 µm coronal sections was stained with quadruple fluorescence histology and scanned in four channels. A trained anatomist manually segmented six structures of interest in a subset of the sections to generate the ground truth. Six convolutional neural networks were then trained for automatic segmentation of these structures in 1234 sections. A high-performance computing solution was engineered to register the sections based on the fluorescence signal and segmented structures. The resulting 3D visualization offers several novel didactic opportunities of interactive exploration and virtual manipulation. By extrapolating manual counts of OSNs in a subset of sections to the calculated volume of the envelope of the entire olfactory epithelium, we computed a total of ~2.7 million OSNs in the specimen. Such empirically derived information helps assess the extent to which the organizational principles of the human olfactory projection may differ from those in mice.

Technique for Intranasal Administration of α-Synuclein Aggregates.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the presence of Lewy bodies, which are aggregates of α-synuclein (α-Syn). Recently, the disease was proposed to develop and progress through the prion-like propagation of α-Syn aggregates from the olfactory bulb (OB) or dorsal nucleus of the vagus nerve. Although the origin of α-Syn aggregates in the OB remains unclear, their propagation from the olfactory mucosa has been recently suggested. We previously showed that intranasal administration of α-Syn aggregates in a mouse model induced α-Syn pathology in the OB of mice. In this study, we present a method of intranasal administration of α-Syn aggregates that induced α-Syn pathology in the OB of mice. Intranasal administration of α-Syn aggregates is a very simple and straightforward method, and we believe it will be a useful tool in the research for elucidating the origin of α-Syn pathology in the OB and the pathway of α-Syn propagation through the olfactory system.

Olfactory Evoked Potential Monitoring: Technical Note and Challenges Faced.

Despite the sustained progress in the realm of intraoperative neurophysiologic monitoring of the nervous system, little progress has been achieved in monitoring the olfactory pathway. Loss of olfactory function due to retraction-induced physical damage during operations has ill-appreciated negative consequences for the patients and is often underreported. Improvements in this area of neuromonitoring require a revisit of the technical challenges. We aim to describe the method to construct flexible, bipolar silver ball electrodes to stimulate the olfactory mucosa during cranial neurosurgery and suggest ways to overcome the challenges in eliciting olfactory evoked potentials. We analyze the potential difficulties in routinely eliciting olfactory evoked potential in neurosurgical operations and summarize ways to overcome them. We also describe the construction of a simple electrical stimulator electrode for the olfactory mucosa, its application, and potential recording sites in an effort to detect the potential during cranial neurosurgery. We created flexible, insulated bipolar silver electrodes and placed them atraumatically on the olfactory mucosa under endoscopic guidance, bilaterally, in 22 patients. We obtained an optimal position in less than 10 minutes in most cases. We also summarize the challenges faced and potential paths to overcome them. Though electrical stimulation of the olfactory mucosa using custom-made silver electrodes is possible and takes little time to place them as part of an intraoperative neurophysiologic monitoring setup, detecting the minute potential remains elusive.

The Effect of Transplantation of Ensheathing Cells of the Olfactory Mucosa into the Hippocampal Area on the Restoration of Cognitive Abilities in Rats with Experimental Alzheimer's Disease.

Alzheimer's disease was induced in female Wistar rats by bilateral injection of β-amyloid fragment 1-42 into the hippocampal region. After 8 weeks, ensheathing cells of the olfactory mucosa were transplanted into the hippocampus at the same stereotactic coordinates. These cells survived for 8 weeks; large clusters of cells were observed on week 4. On weeks 3-5 after transplantation of ensheathing cells, experimental animals demonstrated a significant cognitive improvement (memory and spatial orientation). The obtained results create prerequisites for further studies of ensheathing cells as a potential cell product for personalized therapy of Alzheimer's disease.

Preparation, physicochemical characterization, ex vivo, and in vivo evaluations of asiatic acid-loaded solid lipid nanoparticles formulated with natural waxes for nose-to-brain delivery

Asiatic acid (AA) has neuroprotective potential for prevention and treatment of Alzheimer's disease. Natural waxes with various ratios of Tween 80 and Span 80 or soybean lecithin were formulated to obtain AA-loaded solid lipid nanoparticles (AA-SLN) to improve direct nose to brain transport. Optimal AA-SLN had particle size below 200 nm with uniform size distribution and zeta potential of nearly -30 mV indicating a low risk of particle aggregation. Formulation with rice bran wax, Tween 80, and soybean lecithin (AA-RwS100) showed the highest entrapment efficiency and yield of >98 % while in vitro AA release of AA-SLN was linearly up to 48 h For ex vivo permeation, confocal laser scanning microscopy (CLSM) and histopathological studies on porcine olfactory mucosa (OM) and respiratory mucosa (RM), AA-SLN showed significantly higher permeation across OM than RM (p < 0.05) up to 6 h and AA-RwS100 also showed the highest amount of drug permeated as confirmed by CLSM results. Although AA-SLN showed non-significantly lower permeation than AA solution (AA-SOL) (p > 0.05), no epithelial and mucosal structure damages were observed in OM treated with AA-RwS100 and RM treated with all AA-SLNs indicating safety for nasal administration while AA-SOL showed significant damage to both OM and RM. In addition, in vivo brain distribution study by fluorescence imaging using Rhodamine (R6g) showed higher brain distribution after intranasal administration of R6g-loaded solid lipid nanoparticles (R6g-SLN) than R6g solution (R6g-SOL) and intravenous administration of R6g-SLN, and R6g-RwS100 also showed the highest brain accumulation at 8 h post administration.

Equine Herpesvirus Type 1 ORF76 Encoding US9 as a Neurovirulence Factor in the Mouse Infection Model.

Equine herpesvirus type 1 (EHV-1) causes rhinopneumonitis, abortion, and neurological outbreaks (equine herpesvirus myeloencephalopathy, EHM) in horses. EHV-1 also causes lethal encephalitis in small laboratory animals such as mice and hamsters experimentally. EHV-1 ORF76 is a homolog of HSV-1 US9, which is a herpesvirus kinase. Starting with an EHV-1 bacterial artificial chromosome clone of neuropathogenic strain Ab4p (pAb4p BAC), we constructed an ORF76 deletion mutant (Ab4p∆ORF76) by replacing ORF76 with the rpsLneo gene. Deletion of ORF76 had no influence on replication, cell-to-cell spread in cultured cells, or replication in primary neuronal cells. In Western blots of EHV-1-infected cell lysates, an EHV-1 US9-specific polyclonal antibody detected multiple bands ranging from 35 to 42 kDa. In a CBA/N1 mouse infection model following intranasal inoculation, the parent and Ab4p∆ORF76 revertant caused the same histopathology in the brain and olfactory bulbs. The parent, Ab4p∆ORF76, and revertant mutant replicated similarly in the olfactory mucosa, although Ab4p∆ORF76 was not transported to the olfactory bulbs and was unable to infect the CNS. These results indicated that ORF76 (US9) plays an essential role in the anterograde spread of EHV-1.

Biofluid Markers and Tissue Biopsies Analyses for the Prodromal and Earliest Phase of Parkinson's Disease.

The recent development of new methods to detect misfolded α-synuclein (αSyn) aggregates in biofluids and tissue biopsies in the earliest Parkinson's disease (PD) phases is dramatically challenging the biological definition of PD. The αSyn seed amplification methods in cerebrospinal fluid (CSF) showed high sensitivity and specificity for early diagnosis of PD and Lewy bodies disorders. Several studies in isolated REM sleep behavior disorders and other at-risk populations also demonstrated a high prevalence of CSF αSyn positivity and its potential value in predicting the phenoconversion to clinically manifested diseases. Growing evidence exists for αSyn aggregates in olfactory mucosa, skin, and other tissues in subjects with PD or at-risk subjects. DOPA decarboxylase and numerous other candidates have been additionally proposed for either diagnostic or prognostic purposes in earliest PD phases. The newly described αSyn detection in blood, through its quantification in neuronally-derived exosome vesicles, represents a technical challenge that could open a new scenario for the biological diagnosis of PD. Despite this growing evidence in the field, most of method of αSyn detection and markers still need to be validated in ongoing longitudinal studies through an accurate assessment of different prodromal disease subtypes and scenarios before being definitively implemented in clinical settings.

Transduced Olfactory Mucosa Cells Expressing Nerve Growth Factor for the Therapy of Experimental Spinal Cord Cysts.

A new gene-cell construct expressing nerve growth factor (NGF) has been developed. After obtaining engineered adenovectors Ad5-RGD-CAG-NGF and Ad5-RGD-CAG-EGFP, transduction efficiency and transgene expression were studied and multiplicity of infection was determined. The efficacy of transduced human olfactory ensheathing cells expressing NGF in restoring motor activity in rats has been shown in a limited period of time. Improved rat hindlimb mobility and cyst size reduction after gene-cell construct transplantation were more likely due to the cellular component of the construct.

The Domestication of Wild Boar Could Result in a Relaxed Selection for Maintaining Olfactory Capacity.

Domesticated animals are artificially selected to exhibit desirable traits, however not all traits of domesticated animals are the result of deliberate selection. Loss of olfactory capacity in the domesticated pig (Sus scrofa domesticus) is one example. We used whole transcriptome analysis (RNA-Seq) to compare patterns of gene expression in the olfactory mucosa of the pig and two subspecies of wild boar (Sus scrofa), and investigate candidate genes that could be responsible for the loss of olfactory capacity. We identified hundreds of genes with reductions in transcript abundance in pig relative to wild boar as well as differences between the two subspecies of wild boar. These differences were detected mainly in genes involved in the formation and motility of villi, cilia and microtubules, functions associated with olfaction. In addition, differences were found in the abundances of transcripts of genes related to immune defenses, with the highest levels in continental wild boar subspecies. Overall, the loss of olfactory capacity in pigs appears to have been accompanied by reductions in the expression of candidate genes for olfaction. These changes could have resulted from unintentional selection for reduced olfactory capacity, relaxed selection for maintaining olfactory capacity, pleiotropic effects of genes under selection, or other non-selective processes. Our findings could be a cornerstone for future researches on wild boars, pigs, feral populations, and their evolutionary trajectories, aimed to provide tools to better calibrate species management as well as guidelines for breeders.

Distinct olfactory mucosal macrophage populations mediate neuronal maintenance and pathogen defense

The olfactory mucosa is important for both the sense of smell and as a mucosal immune barrier to the upper airway and brain. However, little is known about how the immune system mediates the conflicting goals of neuronal maintenance and inflammation in this tissue. A number of immune cell populations reside within the olfactory mucosa and yet we have little understanding of how these resident olfactory immune cells functionally interact with the chemosensory environment. Identifying these interactions will allow therapeutic manipulations that treat disorders such as post-viral olfactory dysfunction. Macrophages are the most prevalent immune cell type in the uninflamed olfactory mucosa and here, we identify two distinct tissue macrophage populations in murine olfactory mucosa. P2ry12hi macrophages are transcriptionally specialized for neuron interactions, closely associated with olfactory neuron cell bodies, long-term tissue residents, and functionally specialized to phagocytose cells and debris, including olfactory neurons. Conversely, MHC Class IIhi macrophages are transcriptionally dedicated to cytokine production and antigen presentation, localized primarily within the olfactory lamina propria, more rapidly replaced by blood monocytes, and rapidly produce chemokines in response to viral infection. We further show that these macrophage signatures are present in human olfactory biopsies, and P2ry12-like olfactory macrophages are reduced in patients with long-term smell loss following COVID-19. Together, these data show that two olfactory macrophage populations regulate neurons and initiate the immune response, contributing to our understanding of both olfactory immunity and tissue-resident macrophage biology.