Bitter and sweet taste receptors regulate human upper respiratory innate immunity

Bitter taste receptors as sensors of gut luminal contents

Taste is important in the selection of food and is orchestrated by a group of distinct receptors, the taste G protein-coupled receptors (GPCRs). Taste 1 receptors (Tas1rs in mice and TAS1Rs in humans; also known as T1Rs) detect sweet and umami tastes, and taste 2 receptors (Tas2rs in mice and TAS2Rs in humans; also known as T2Rs) detect bitterness. These receptors are also expressed in extraoral sites, including the gastrointestinal mucosa. Tas2rs/TAS2Rs have gained interest as potential targets to prevent or treat metabolic disorders. These bitter taste receptors are expressed in functionally distinct types of gastrointestinal mucosal cells, including enteroendocrine cells, which, upon stimulation, increase intracellular Ca2+ and release signalling molecules that regulate gut chemosensory processes critical for digestion and absorption of nutrients, for neutralization and expulsion of harmful substances, and for metabolic regulation. Expression of Tas2rs/TAS2Rs in gut mucosa is upregulated by high-fat diets, and intraluminal bitter 'tastants' affect gastrointestinal functions and ingestive behaviour through local and gut-brain axis signalling. Tas2rs/TAS2Rs are also found in Paneth and goblet cells, which release antimicrobial peptides and glycoproteins, and in tuft cells, which trigger type 2 immune response against parasites, thus providing a direct line of defence against pathogens. This Review will focus on gut Tas2r/TAS2R distribution, signalling and regulation in enteroendocrine cells, supporting their role as chemosensors of luminal content that serve distinct functions as regulators of body homeostasis and immune response.

Common Cold Coronavirus 229E Induces Higher Interferon Stimulating Gene Responses in Human Nasal Epithelial Cells from Patients with Chronic Rhinosinusitis with Polyposis

BACKGROUND

Viral infections have long been implicated in the development of chronic rhinosinusitis with nasal polyps (CRSwNP). Given widespread exposure to the common cold coronavirus 229E (HCoV229E), we sought to investigate how HCoV-229E is cleared and stimulates interferon pathways in air-liquid interface (ALI) cultures from patients with CRSwNP.

OBJECTIVE

The objective of this study was to identify whether viral clearance and ISG expression is different in ALI cultures from donors with CRSwNP compared with controls.

METHODS

Plaque assays were used to quantify infectious virus released by infected air-liquid interface (ALI) cultures derived from patients with CRSwNP compared to patients without CRS (controls). Additionally, mock and induced levels of Interferon Stimulated Genes (ISGs) mRNA following HCoV-229E infection were quantified by RT-qPCR.

RESULTS

Quantification of infectious virus by plaque assay reveals that CRSwNP ALI cultures were equally susceptible to HCoV-229E infection, and surprisingly viral titers dropped significantly faster than in the control ALI cultures. We further demonstrate that this accelerated viral clearance correlates with increased mRNA expression of at least 4 ISGs following viral infection in the CRSwNP ALIs compared to the control ALIs.

CONCLUSION

This study paradoxically demonstrates that ALI cultures from patients with CRSwNP are more efficient at clearing the common cold HCoV-229E virus compared to controls. We also demonstrate significantly increased ISG mRNA expression following HCoV-229E infection in CRSwNP. These findings call for further investigation into the effect of unimpaired interferon signaling on the type 2 inflammatory environment in patients with CRSwNP.

Bitter taste receptor T2R14-Gαi coupling mediates innate immune responses to microbial quorum sensing molecules in cystic fibrosis

Cystic fibrosis (CF) is an autosomal recessive disease characterized by microbial infection and progressive decline in lung function, leading to significant morbidity and mortality. The bitter taste receptor T2R14 is a chemosensory receptor that is significantly expressed in airways. Using a combination of cell-based assays and T2R14 knockdown in bronchial epithelial cells from CF and non-CF individuals, we observed that T2R14 plays a crucial role in the detection of bacterial and fungal signals and enhances host innate immune responses. Expression of Gαi protein is enhanced in CF bronchial epithelial cells and T2R14-Gαi specific signaling leads to increased calcium mobilization. Knockdown of T2R14 leads to reduced innate immune activation by bacterial strains deficient in quorum sensing. The results demonstrate that T2R14 helps protect against microbial infection and thus may play an important role in the innate immune defense of the CF airway epithelium.

Endotyping in Chronic Rhinosinusitis-An EAACI Task Force Report

Chronic rhinosinusitis (CRS) is a clinical syndrome defined by typical sinonasal symptoms persisting for at least 12 weeks. CRS is divided into two distinct phenotypes, CRS with nasal polyps (CRSwNP) and without (CRSsNP). The aim of the review is to provide an update on the current knowledge in CRS endotypes. The prevailing hypothesis regarding the pathogenesis of CRS suggests that dysfunctional interactions between the host and environmental stressors at the mucosal surface drive the diverse inflammatory mechanisms. Genetic and epigenetic variations in the mucosal immune system are believed to play a significant role in the pathomechanisms of CRS. Various environmental agents (such as microbes and irritants) have been implicated in CRS. In a healthy state, the sinonasal mucosa acts as a barrier, modulating environmental stimulation and mounting appropriate immune responses against pathogens with minimal tissue damage. Different endotypes may exist based on the specific mechanistic pathways driving the chronic tissue inflammation of CRS. There is a need to understand endotypes in order to better predict, diagnose, and treat CRS. This literature review provides an update on the role of the endotypes in CRS and the limitations of endotyping CRS in clinical practice. Understanding of the pathogenesis and optimal management of CRS has progressed significantly in the last decades; however, there still are several unmet needs in endotype research.

Tuft cells in the intestine, immunity and beyond

Tuft cells have gained substantial attention over the past 10 years due to numerous reports linking them with type 2 immunity and microorganism-sensing capacity in many mucosal tissues. This heightened interest is fuelled by their unique ability to produce an array of biological effector molecules, including IL-25, allergy-related eicosanoids, and the neurotransmitter acetylcholine, enabling downstream responses in diverse cell types. Operating through G protein-coupled receptor-mediated signalling pathways reminiscent of type II taste cells in oral taste buds, tuft cells emerge as chemosensory sentinels that integrate luminal conditions, eliciting appropriate responses in immune, epithelial and neuronal populations. How tuft cells promote tissue alterations and adaptation to the variety of stimuli at mucosal surfaces has been explored in multiple studies in the past few years. Since the initial recognition of the role of tuft cells, the discovery of diverse tuft cell effector functions and associated feedback loops have also revealed the complexity of tuft cell biology. Although earlier work largely focused on extraintestinal tissues, novel genetic tools and recent mechanistic studies on intestinal tuft cells established fundamental concepts of tuft cell activation and functions. This Review is an overview of intestinal tuft cells, providing insights into their development, signalling and interaction modules in immunity and other states.

Assessment of Gustatory Function in Patients of Chronic Rhinosinusitis: A Case Control Study

Gustation is affected in patients of Chronic rhinosinusitis (CRS) depending on severity of diseases. This study aimed to find the prevalence of gustatory dysfunction in patients with CRS. This case-control study included 61 patients with CRS and 61 healthy controls. Patients were subjected to non-contrast CT scan of the paranasal sinuses. Disease severity was assessed using the Lund Mackay Scoring. Gustatory assessment was done as per scoring of Mueller et al. Taste score of 9 or more was considered normal. The outcome measures were gustatory dysfunction and association with presence of polyps and CRS severity. P-value < 0.05 was considered statistically significant. Compared to controls, cases had significantly lower total taste scores (12 vs. 15, P < 0.001). Gustatory dysfunction was seen among 13 (21.3%) patients. It was significantly more among those with polyps than without [8(53.3%) vs. 5(10.9%), P < 0.05]. There was a significant negative correlation between the gustatory dysfunction scores and the severity of CRS (r=-0.664, P < 0.001). In conclusion, we report a prevalence of gustatory dysfunction in 21.3% cases of CRS which was negatively affected by the presence of nasal polyps and CRS severity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12070-024-04978-0.

Extragustatory bitter taste receptors in head and neck health and disease

Taste receptors, first described for their gustatory functions within the oral cavity and oropharynx, are now known to be expressed in many organ systems. Even intraoral taste receptors regulate non-sensory pathways, and recent literature has connected bitter taste receptors to various states of health and disease. These extragustatory pathways involve previously unexplored, clinically relevant roles for taste signaling in areas including susceptibility to infection, antibiotic efficacy, and cancer outcomes. Among other physicians, otolaryngologists who manage head and neck diseases should be aware of this growing body of evidence and its relevance to their fields. In this review, we describe the role of extragustatory taste receptors in head and neck health and disease, highlighting recent advances, clinical implications, and directions for future investigation. Additionally, this review will discuss known TAS2R polymorphisms and the associated implications for clinical prognosis.

Aspartame enhances the scavenging activity of mice to low-dose Escherichia coli infection via strengthening macrophage phagocytosis caused by sweet taste receptor activation

Aspartame is the most common artificial sweetener and a famous sweet-taste receptor agonist. Macrophages are essential in the antibacterial system to maintain the stability of the intestinal environment. Recently, the sweet taste receptor has been found in macrophages. However, the effects of aspartame on macrophage phagocytosis in the gastrointestinal tract are little known. The current study sought to assess the influence of aspartame intake on the scavenging activity of mice to low-dose Escherichia coli infection and related mechanisms. Firstly, no inflammatory response or pathological injury was observed in the intestines of mice after oral administration of aspartame (25-100 mg/kg, i.g.) for 2 weeks. Subsequently, aspartame intake was found to enhance the scavenging activity of mice to low-dose E. coli infection. Similarly, aspartame dose-dependent strengthened the ability of RAW264.7 cells to phagocytose GFP-E.coli J96. Further mechanism evaluation reflected that aspartame could enhance macrophage phagocytosis, migration, and rearrangement via PLCβ-2/Ca2+/PKCβ/Rho A/ROCK1 pathway caused by sweet taste receptor activation. In conclusion, the present study, for the first time, demonstrated that aspartame could enhance the scavenging activity of mice to low-dose E. coli infection via strengthening macrophage phagocytic function through activating sweet taste receptor. It is then suggested that aspartame may affect the antibacterial activity of human gastrointestinal macrophages, and further studies need to validate these effects.

The Remarkable Diversity of Vertebrate Bitter Taste Receptors: Recent Advances in Genomic and Functional Studies

Bitter taste perception is crucial for animal survival. By detecting potentially harmful substances, such as plant secondary metabolites, as bitter, animals can avoid ingesting toxic compounds. In vertebrates, this function is mediated by taste receptors type 2 (T2Rs), a family of G protein-coupled receptors (GPCRs) expressed on taste buds. Given their vital roles, T2Rs have undergone significant selective pressures throughout vertebrate evolution, leading to frequent gene duplications and deletions, functional changes, and intrapopulation differentiation across various lineages. Recent advancements in genomic and functional research have uncovered the repertoires and functions of bitter taste receptors in a wide range of vertebrate species, shedding light on their evolution in relation to dietary habits and other ecological factors. This review summarizes recent research on bitter taste receptors and explores the mechanisms driving the diversity of these receptors from the perspective of vertebrate ecology and evolution.

Hops bitter β-acids have antibacterial effects against sinonasal Staphylococcus aureus but also induce sinonasal cilia and mitochondrial dysfunction

BACKGROUND

Routine prescription of antibiotics to treat chronic rhinosinusitis (CRS) exacerbations may contribute to the propagation of antibiotic resistance. Hops bitter β-acids lupulone and colupulone possess potent antibacterial activities and, as T2R1, T2R14, and/or T2R40 agonists, may improve the impaired mucociliary clearance described in CRS patients. We investigated these molecules as alternative treatments to antibiotics in CRS management based on their antibacterial and T2Rs agonists properties.

METHODS

Human nasal primary cells (HNECs) and RPMI2650 cells cultures were used as study models. T2Rs expression in cell culture models and human nasal tissue was assessed using immunofluorescence, quantitative PCR, and Western blot. We performed calcium imaging and cilia beat frequency experiments to investigate T2Rs activation in study models in response to lupulone and colupulone stimulations. Finally, we studied hops β-acids cytotoxicity on cells using CellEvent, crystal violet, lactate dehydrogenase assays, immunofluorescence, and transepithelial electrical resistance assays.

RESULTS

We confirmed lupulone and colupulone potent antibacterial effect on CRS-relevant methicillin-resistant Staphylococcus aureus but found minimal impact on P. aeruginosa. We also report T2R1, T2R14 and T2R40 expression in HNECs and RPMI2650 cell cultures. Lupulone and colupulone induced an increase in cytosolic calcium that appeared dependent on T2Rs signaling. This response was accompanied by mitochondrial membrane depolarization, cellular energy stress, decreased cell proliferation, ciliostasis, and HNECs remodeling after a single exposure to lupulone at micromolar concentrations.

CONCLUSION

Our data suggest that hops β-acids may not be beneficial as treatments in CRS patients and instead contribute to the disease by impairing cell health and further deteriorating the MCC.

Pseudomonas aeruginosa metabolite 3-oxo-C12HSL induces apoptosis through T2R14 and the mitochondrial calcium uniporter

Head and neck squamous cell carcinomas (HNSCCs) arise in the mucosal lining of the upper aerodigestive tract. HNSCCs have high mortality rates and current treatments can be associated with severe morbidities. It is vital to discover effective, minimally invasive therapies that improve survival and quality of life. We previously discovered that bitter taste receptor 14 (T2R14), a GPCR, kills HNSCC cells when activated by bitter agonists. We are now investigating endogenous bitter ligands that exist in HNSCC tumor microenvironment (TME). The TME includes cells, signaling molecules, and microbes that can greatly influence treatment responses and overall prognosis in HNSCC. Pseudomonas aeruginosa is a gram-negative bacterium that colonizes/infects HNSCC patients. 3-oxo-C12SHL is a quorum-sensing N-acyl homoserine lactone (AHL) secreted by P. aeruginosa which is also a bitter compound. 3-oxo-C12HSL induces apoptosis but this has never been linked to T2R activation. We hypothesized that 3-oxo-C12HSL induces apoptosis in HNSCC via T2R14. We show that 3-oxo-C12HSL activates intracellular Ca 2+ responses in HNSCC cells. This is inhibited with T2R14 antagonization. 3-oxo-C12HSL may activate additional Ca 2+ channels as the Ca 2+ dynamics are independent from store-operated calcium entry (SOCE). 3-oxo-C12HSL inhibits cell viability, depolarizes mitochondria, and produces ROS. This induces apoptosis in HNSCC cells. In a comparative screen of quorum-sensing AHLs, 3-oxo-C12HSL was the only AHL that elicited both a Ca 2+ response and reduced cell viability. These results suggest that P. aeruginosa may play a significant role in modulating an anti-tumor TME through 3-oxo-C12HSL. Moreover, 3-oxo-C12HSL could be a novel, higher-affinity bitter therapeutic for HNSCC. Further research is warranted to elucidate the mechanisms of other endogenous T2R agonists present in the TME.

TAS2R38 Genotype Does Not Affect SARS-CoV-2 Infection in Primary Ciliary Dyskinesia

Several chronic respiratory diseases could be risk factors for acquiring SARS-CoV-2 infection: among them, Primary Ciliary Dyskinesia (PCD) is a rare (about 1:10.000) inherited ciliopathy (MIM 242650) characterized by recurrent upper and lower respiratory tract infections due to a dysfunction of the respiratory cilia. In this study, we aimed to investigate whether PCD subjects are more susceptible to infection by SARS-CoV-2 and whether some polymorphisms of the TAS2R38 bitter taste receptor correlate with an increased prevalence of SARS-CoV-2 infection and severity of symptoms. Patients answered several questions about possible SARS-CoV-2 infection, experienced symptoms, and vaccinations; in the case of infection, they also filled out a SNOT-22 questionnaire and ARTIQ. Forty PCD adult patients (mean age, 36.6 ± 16.7 years; 23 females, 17 males) participated in this study, out of which 30% had tested positive for COVID-19 during the last four years; most of them reported a mildly symptomatic disease. We found no differences in age or sex, but a statistically significant difference (p = 0.03) was observed in body mass index (BMI), which was higher in the COVID-acquired group (23.2 ± 3.3 vs. 20.1 ± 4.1 kg/m2). Genotyping for TAS2R38 polymorphisms showed a prevalence of 28.6% PAV/PAV, 48.6% PAV/AVI, and 22.8% AVI/AVI individuals in our cohort. In contrast to our hypothesis, we did not observe a protective role of the PAV allele towards SARS-CoV-2 infection. Conclusions: Our findings suggest that subjects with PCD may not be at increased risk of severe outcomes from COVID-19 and the TAS2R38 bitter taste receptor genotype does not affect SARS-CoV-2 infection.

Mechanisms and Functions of Sweet Reception in Oral and Extraoral Organs

The oral detection of sugars relies on two types of receptor systems. The first is the G-protein-coupled receptor TAS1R2/TAS1R3. When activated, this receptor triggers a downstream signaling cascade involving gustducin, phospholipase Cβ2 (PLCβ2), and transient receptor potential channel M5 (TRPM5). The second type of receptor is the glucose transporter. When glucose enters the cell via this transporter, it is metabolized to produce ATP. This ATP inhibits the opening of KATP channels, leading to cell depolarization. Beside these receptor systems, sweet-sensitive taste cells have mechanisms to regulate their sensitivity to sweet substances based on internal and external states of the body. Sweet taste receptors are not limited to the oral cavity; they are also present in extraoral organs such as the gastrointestinal tract, pancreas, and brain. These extraoral sweet receptors are involved in various functions, including glucose absorption, insulin release, sugar preference, and food intake, contributing to the maintenance of energy homeostasis. Additionally, sweet receptors may have unique roles in certain organs like the trachea and bone. This review summarizes past and recent studies on sweet receptor systems, exploring the molecular mechanisms and physiological functions of sweet (sugar) detection in both oral and extraoral organs.

Exendin-4 blockade of T1R2/T1R3 activation improves Pseudomonas aeruginosa-related pneumonia in an animal model of chemically induced diabetes

OBJECTIVE

Poorly controlled diabetes frequently exacerbates lung infection, thereby complicating treatment strategies. Recent studies have shown that exendin-4 exhibits not only hypoglycemic but also anti-inflammatory properties. This study aimed to explore the role of exendin-4 in lung infection with diabetes, as well as its association with NOD1/NF-κB and the T1R2/T1R3 sweet taste receptor.

METHODS

16HBE human bronchial epithelial cells cultured with 20 mM glucose were stimulated with lipopolysaccharide (LPS) isolated from Pseudomonas aeruginosa (PA). Furthermore, Sprague‒Dawley rats were fed a high-fat diet, followed by intraperitoneal injection of streptozotocin and intratracheal instillation of PA. The levels of TNF-α, IL-1β and IL-6 were evaluated using ELISAs and RT‒qPCR. The expression of T1R2, T1R3, NOD1 and NF-κB p65 was assayed using western blotting and immunofluorescence staining. Pathological changes in the lungs of the rats were observed using hematoxylin and eosin (H&E) staining.

RESULTS

At the same dose of LPS, the 20 mM glucose group produced more proinflammatory cytokines (TNF-α, IL-1β and IL-6) and had higher levels of T1R2, T1R3, NOD1 and NF-κB p65 than the normal control group (with 5.6 mM glucose). However, preintervention with exendin-4 significantly reduced the levels of the aforementioned proinflammatory cytokines and signaling molecules. Similarly, diabetic rats infected with PA exhibited increased levels of proinflammatory cytokines in their lungs and increased expression of T1R2, T1R3, NOD1 and NF-κB p65, and these effects were reversed by exendin-4.

CONCLUSIONS

Diabetic hyperglycemia can exacerbate inflammation during lung infection, promote the increase in NOD1/NF-κB, and promote T1R2/T1R3. Exendin-4 can ameliorate PA-related pneumonia with diabetes and overexpression of NOD1/NF-κB. Additionally, exendin-4 suppresses T1R2/T1R3, potentially through its hypoglycemic effect or through a direct mechanism. The correlation between heightened expression of T1R2/T1R3 and an intensified inflammatory response in lung infection with diabetes requires further investigation.

Akt activator SC79 stimulates antibacterial nitric oxide generation in human nasal epithelial cells in vitro

BACKGROUND

The role of Akt in nasal immunity is unstudied. Akt phosphorylates and activates endothelial nitric oxide synthase (eNOS) expressed in epithelial ciliated cells. Nitric oxide (NO) production by ciliated cells can have antibacterial and antiviral effects. Increasing nasal NO may be a useful antipathogen strategy in chronic rhinosinusitis (CRS). We previously showed that small-molecule Akt activator SC79 induces nasal cell NO production and suppresses IL-8 via the transcription factor Nrf-2. We hypothesized that SC79 NO production may additionally have antibacterial effects.

METHODS

NO production was measured using fluorescent dye DAF-FM. We tested effects of SC79 during co-culture of Pseudomonas aeruginosa with primary nasal epithelial cells, using CFU counting and live-dead staining to quantify bacterial killing. Pharmacology determined the mechanism of SC79-induced NO production and tested dependence on Akt.

RESULTS

SC79 induced dose-dependent, Akt-dependent NO production in nasal epithelial cells. The NO production required eNOS and Akt. The NO released into the airway surface liquid killed P. aeruginosa. No toxicity (LDH release) or inflammatory effects (IL8 transcription) were observed over 24 h.

CONCLUSIONS

Together, these data suggest multiple immune pathways are stimulated by SC79, with antipathogen effects. This in vitro pilot study suggests that a small-molecule Akt activator may have clinical utility in CRS or respiratory other infection settings, warranting future in vivo studies.

Tuft cell-derived acetylcholine promotes epithelial chloride secretion and intestinal helminth clearance

Epithelial cells secrete chloride to regulate water release at mucosal barriers, supporting both homeostatic hydration and the "weep" response that is critical for type 2 immune defense against parasitic worms (helminths). Epithelial tuft cells in the small intestine sense helminths and release cytokines and lipids to activate type 2 immune cells, but whether they regulate epithelial secretion is unknown. Here, we found that tuft cell activation rapidly induced epithelial chloride secretion in the small intestine. This response required tuft cell sensory functions and tuft cell-derived acetylcholine (ACh), which acted directly on neighboring epithelial cells to stimulate chloride secretion, independent of neurons. Maximal tuft cell-induced chloride secretion coincided with immune restriction of helminths, and clearance was delayed in mice lacking tuft cell-derived ACh, despite normal type 2 inflammation. Thus, we have uncovered an epithelium-intrinsic response unit that uses ACh to couple tuft cell sensing to the secretory defenses of neighboring epithelial cells.

G protein subunit Gγ13-mediated signaling pathway is critical to the inflammation resolution and functional recovery of severely injured lungs

Tuft cells are a group of rare epithelial cells that can detect pathogenic microbes and parasites. Many of these cells express signaling proteins initially found in taste buds. It is, however, not well understood how these taste signaling proteins contribute to the response to the invading pathogens or to the recovery of injured tissues. In this study, we conditionally nullified the signaling G protein subunit Gγ13 and found that the number of ectopic tuft cells in the injured lung was reduced following the infection of the influenza virus H1N1. Furthermore, the infected mutant mice exhibited significantly larger areas of lung injury, increased macrophage infiltration, severer pulmonary epithelial leakage, augmented pyroptosis and cell death, greater bodyweight loss, slower recovery, worsened fibrosis and increased fatality. Our data demonstrate that the Gγ13-mediated signal transduction pathway is critical to tuft cells-mediated inflammation resolution and functional repair of the damaged lungs.To our best knowledge, it is the first report indicating subtype-specific contributions of tuft cells to the resolution and recovery.

Potential of Bitter Medicinal Plants: A Review of Flavor Physiology

The function of the sense of taste is usually confined to the ability to perceive the flavor of food to assess and use the nutrients necessary for healthy survival and to discard those that may be harmful, toxic, or unpleasant. It is almost unanimously agreed that the perception of bitter taste prevents the consumption of toxins from plants, decaying foods, and drugs. Forty years ago, while practicing medicine in a rural area of the Colombian Amazon, I had an unexpected encounter with the Inga Indians. I faced the challenge of accepting that their traditional medicine was effective and that the medicinal plants they used had a real therapeutic effect. Wanting to follow a process of learning about medicinal plants on their terms, I found that, for them, the taste of plants is a primary and fundamental key to understanding their functioning. One of the most exciting results was discovering the therapeutic value of bitter plants. The present review aims to understand whether there is any scientific support for this hypothesis from the traditional world. Can the taste of plants explain their possible therapeutic benefit? In the last 20 years, we have made novel advances in the knowledge of the physiology of taste. Our purpose will be to explore these scientific advances to determine if the bitter taste of medicinal plants benefits human health.

Tas1R3 Dependent and Independent Recognition of Sugars in the Urethra and the Role of Tuft Cells in this Process

Increased sugar concentrations on mucosal surfaces display risk factors for infections. This study aims to clarify sugar monitoring in the urethra. Urethral tuft cells (UTC) are known sentinels monitoring the urethral lumen for potentially harmful substances and initiating protective mechanisms. Next-generation sequencing (NGS), RT-PCR, and immunohistochemistry show expression of the taste receptor Tas1R3 in murine UTC, a crucial component of the classical sweet detection pathway. Isolated UTC respond to various sugars with an increase of intracellular [Ca2+]. The Tas1R3 inhibitor gurmarin and Tas1R3 deletion reduces these responses. Utilizing mice lacking UTC, glibenclamide, a K+-ATP channel antagonist, and phlorizin, a SGLT1 inhibitor, reveal an additional Tas1R3 independent sweet detection pathway. Inhibition of both pathways abrogates the sugar responses. Rat cystometry shows that intraurethral application of sucrose and glucose increases detrusor muscle activity Tas1R3 dependently. Sugar monitoring in the urethra occurs via two distinct pathways. A Tas1R3 dependent pathway, exclusive to UTC, and a Tas1R3 independent sweet detection pathway, which can be found both in UTC and in other urethral epithelial cells.

Membrane-bound chemoreception of bitter bile acids and peptides is mediated by the same subset of bitter taste receptors

The vertebrate sense of taste allows rapid assessment of the nutritional quality and potential presence of harmful substances prior to ingestion. Among the five basic taste qualities, salty, sour, sweet, umami, and bitter, bitterness is associated with the presence of putative toxic substances and elicits rejection behaviors in a wide range of animals including humans. However, not all bitter substances are harmful, some are thought to be health-beneficial and nutritious. Among those compound classes that elicit a bitter taste although being non-toxic and partly even essential for humans are bitter peptides and L-amino acids. Using functional heterologous expression assays, we observed that the 5 dominant human bitter taste receptors responsive to bitter peptides and amino acids are activated by bile acids, which are notorious for their extreme bitterness. We further demonstrate that the cross-reactivity of bitter taste receptors for these two different compound classes is evolutionary conserved and can be traced back to the amphibian lineage. Moreover, we show that the cross-detection by some receptors relies on "structural mimicry" between the very bitter peptide L-Trp-Trp-Trp and bile acids, whereas other receptors exhibit a phylogenetic conservation of this trait. As some bile acid-sensitive bitter taste receptor genes fulfill dual-roles in gustatory and non-gustatory systems, we suggest that the phylogenetic conservation of the rather surprising cross-detection of the two substance classes could rely on a gene-sharing-like mechanism in which the non-gustatory function accounts for the bitter taste response to amino acids and peptides.

How effective is topical miconazole or amorolfine for mild to moderately severe onychomycosis in primary care: the Onycho Trial - a randomised double-blind placebo-controlled trial

OBJECTIVES

To evaluate the efficacy of topical miconazole or amorolfine compared to placebo for mild to moderately severe onychomycosis.

DESIGN

Randomised, double-blind, placebo-controlled trial, with computer-generated treatment allocation at a 1:1:1 ratio.

SETTING

Primary care, recruitment from February 2020 to August 2022.

PARTICIPANTS

193 patients with suspected mild to moderately severe onychomycosis were recruited via general practices and from the general public, 111 of whom met the study criteria. The mean age of participants was 51 (SD 13.1), 51% were female and onychomycosis was moderately severe (mean OSI 12.1 (SD 8.0)).

INTERVENTIONS

Once-daily miconazole 20 mg/g or once-weekly amorolfine 5% nail lacquer solution was compared with placebo (denatonium benzoate solution).

MAIN OUTCOME MEASURES

Complete, clinical and mycological cure at 6 months. Secondary outcomes were clinical improvement, symptom burden, quality of life, adverse effects, compliance, patient-perceived improvement and treatment acceptability.

RESULTS

Based on intention-to-treat analysis, none of the participants receiving miconazole or amorolfine reached complete cure compared with two in the placebo group (OR not estimable (n.e.), p=0.493 and OR n.e., p=0.240, respectively). There was no evidence of a significant difference between groups regarding clinical cure (OR n.e., p=0.493 and OR 0.47, 95% CI 0.04 to 5.45, p=0.615) while miconazole and amorolfine were less effective than placebo at reaching both mycological cure (OR 0.25, 95% CI 0.06 to 0.98, p=0.037 and OR 0.23, 95% CI 0.06 to 0.92, p=0.029, respectively) and clinical improvement (OR 0.26, 95% CI 0.08 to 0.91, p=0.028 and OR 0.25, 95% CI 0.07 to 0.85, p=0.021, respectively). There was no evidence of a significant difference in disease burden, quality of life, adverse reactions, compliance, patient-perceived improvement or treatment acceptability.

CONCLUSIONS

Topical miconazole and amorolfine were not effective in achieving a complete, clinical or mycological cure of mild to moderately severe onychomycosis, nor did they significantly alleviate the severity or symptom burden. These treatments should, therefore, not be advised as monotherapy to treat onychomycosis.

TRIAL REGISTRATION NUMBER

WHO ICTRP NL8193.

Comparison of SARS-CoV-2 variants of concern in primary human nasal cultures demonstrates Delta as most cytopathic and Omicron as fastest replicating

The SARS-CoV-2 pandemic was marked with emerging viral variants, some of which were designated as variants of concern (VOCs) due to selection and rapid circulation in the human population. Here, we elucidate functional features of each VOC linked to variations in replication rate. Patient-derived primary nasal cultures grown at air-liquid interface were used to model upper respiratory infection and compared to cell lines derived from human lung epithelia. All VOCs replicated to higher titers than the ancestral virus, suggesting a selection for replication efficiency. In primary nasal cultures, Omicron replicated to the highest titers at early time points, followed by Delta, paralleling comparative studies of population sampling. All SARS-CoV-2 viruses entered the cell primarily via a transmembrane serine protease 2 (TMPRSS2)-dependent pathway, and Omicron was more likely to use an endosomal route of entry. All VOCs activated and overcame dsRNA-induced cellular responses, including interferon (IFN) signaling, oligoadenylate ribonuclease L degradation, and protein kinase R activation. Among the VOCs, Omicron infection induced expression of the most IFN and IFN-stimulated genes. Infections in nasal cultures resulted in cellular damage, including a compromise of cell barrier integrity and loss of nasal cilia and ciliary beating function, especially during Delta infection. Overall, Omicron was optimized for replication in the upper respiratory tract and least favorable in the lower respiratory cell line, and Delta was the most cytopathic for both upper and lower respiratory cells. Our findings highlight the functional differences among VOCs at the cellular level and imply distinct mechanisms of pathogenesis in infected individuals.

IMPORTANCE

Comparative analysis of infections by SARS-CoV-2 ancestral virus and variants of concern, including Alpha, Beta, Delta, and Omicron, indicated that variants were selected for efficiency in replication. In infections of patient-derived primary nasal cultures grown at air-liquid interface to model upper respiratory infection, Omicron reached the highest titers at early time points, a finding that was confirmed by parallel population sampling studies. While all infections overcame dsRNA-mediated host responses, infections with Omicron induced the strongest interferon and interferon-stimulated gene response. In both primary nasal cultures and lower respiratory cell line, infections by Delta were most damaging to the cells as indicated by syncytia formation, loss of cell barrier integrity, and nasal ciliary function.

Decoding chronic rhinosinusitis: A metabolomics-based approach

BACKGROUND

Chronic rhinosinusitis (CRS) is a common and intractable disease in otorhinolaryngology, laying a heavy burden on healthcare systems. The worldwide researchers are making efforts to find solutions to this disease. Metabolomics has recently gained more and more traction, and might become a promising tool to unravel the complexity of CRS. This paper provides an overview of current studies on the metabolomics of various CRS subtypes.

METHODS

We conducted a comprehensive literature search in PubMed, Web of Science, EMBASE, Google Scholar, and Cochrane Library, up to May 25, 2023. Search strategies incorporated key terms such as "chronic rhinosinusitis" and "metabolomics" with relevant synonyms and MeSH terms. Titles and abstracts of 86 screened articles were assessed for relevance to CRS and metabolomics. Methodological robustness, data reliability, and relevance were considered for shortlisted articles.

RESULTS

After the refined process, a total of 26 articles were included in this study and sorted out by research themes, methodology and pivotal discoveries. These included studies identified the metabolic pathways and markers related to the pathophysiology in each subtype of CRS.

CONCLUSIONS

Metabolomics helps to shed light on the complexity of CRS. The mentioned findings highlight the importance of specific metabolic pathways and markers in understanding the pathophysiology of CRS. Despite that, challenges and future directions in metabolomics research for CRS would be worth being further explored.

The Bittersweet Symphony of COVID-19: Associations between TAS1Rs and TAS2R38 Genetic Variations and COVID-19 Symptoms

The innate immune system is crucial in fighting SARS-CoV-2 infection, which is responsible for coronavirus disease 2019 (COVID-19). Therefore, deepening our understanding of the underlying immune response mechanisms is fundamental for the development of novel therapeutic strategies. The role of extra-oral bitter (TAS2Rs) and sweet (TAS1Rs) taste receptors in immune response regulation has yet to be fully understood. However, a few studies have investigated the association between taste receptor genes and COVID-19 symptom severity, with controversial results. Therefore, this study aims to deepen the relationship between COVID-19 symptom presence/severity and TAS1R and TAS2R38 (TAS2Rs member) genetic variations in a cohort of 196 COVID-19 patients. Statistical analyses detected significant associations between rs307355 of the TAS1R3 gene and the following COVID-19-related symptoms: chest pain and shortness of breath. Specifically, homozygous C/C patients are exposed to an increased risk of manifesting severe forms of chest pain (OR 8.11, 95% CI 2.26-51.99) and shortness of breath (OR 4.83, 95% CI 1.71-17.32) in comparison with T/C carriers. Finally, no significant associations between the TAS2R38 haplotype and the presence/severity of COVID-19 symptoms were detected. This study, taking advantage of a clinically and genetically characterised cohort of COVID-19 patients, revealed TAS1R3 gene involvement in determining COVID-19 symptom severity independently of TAS2R38 activity, thus providing novel insights into the role of TAS1Rs in regulating the immune response to viral infections.

ACE2 and TAS2R38 receptor expression in pediatric and adult patients in the nasal and oral cavity

Objective

To investigate differences in angiotensin-converting-enzyme-2 (ACE2) and bitter taste receptor (TAS2R38) expression between patient age groups and comorbidities to characterize the pathophysiology of coronavirus 19(COVID-19) pandemic. ACE2 is the receptor implicated to facilitate SARS-CoV-2 infections and levels of expression may correlate to the severity of COVID-19 infection. TAS2R38 has many non-gustatory roles in disease, with some evidence of severe COVID-19 disease in certain receptor phenotypes.

Methods

We conducted a prospective cohort study and collected nasal and lingual tissue from healthy pediatric (n = 22) and adult (n = 25) patients undergoing general anesthesia for elective procedures. RNA isolation and qPCR were performed with primers targeting ACE2 and TAS2R38.

Results

A total of 25 adult (52% male; 44% obese) and 22 pediatric (50% male; 36% obese) patients were enrolled, pediatric tissue had 43% more nasal ACE2 RNA expression than adults with a median fold change of 0.69 (IQR 0.37, 0.98) in adults and 0.99 (IQR 0.74, 1.43) in children (p < .05). There were no differences between the age groups in ACE2 expression of lingual tissue (p = .14) or TAS2R38 expression collected from either nasal (p = 049) or lingual tissue (p = .49). Stratifying for obesity yielded similar differences between nasal ACE2 expression between adults and children with median fold change of 0.56 (IQR 0.32, 0.87) in adults and 1.0 (IQR 0.82, 1.52) in children (p < .05).

Conclusions

ACE2 receptor expression is higher in nasal tissue collected from children compared to adults, suggesting COVID-19 infectivity is more complicated than ACE2 and TAS2R38 mRNA expression.

Level of Evidence

NA.

Generalised Periodontitis: Examining TAS2R16 Serum Levels and Common Gene Polymorphisms (rs860170, rs978739, rs1357949)

The objective of this study was to evaluate and compare the associations between TAS2R16 serum levels and common gene rs860170, rs978739, and rs1357949 polymorphisms in patients affected by generalized periodontitis. The study enrolled 590 patients: 280 patients with periodontitis and 310 healthy controls as a reference group. Patients underwent periodontal examination and radiographic analysis to confirm the periodontitis diagnosis. Blood samples were collected, and the DNA salting-out method was used for DNA extraction from peripheral venous blood. Genotyping of TAS2R16 (rs860170, rs978739, and rs1357949) was performed using real-time polymerase chain reaction (RT-PCR), and serum level analysis was performed for both periodontitis-affected patients and reference group subjects. The analysis of TAS2R16 rs860170 (TT, CT, and CC) showed a statistically significant difference between generalized periodontitis and the reference group (41.8%, 58.2%, and 0% vs. 38.7%, 56.1%, and 5.2%, p < 0.001). TAS2R16 rs860170 (TT, CT, and CC) showed a statistically significant difference between males in generalized periodontitis and reference groups (38.4%, 61.6%, and 0% vs. 32.9%, 56.6%, and 10.5%, p = 0.002). Female-specific analysis showed that the TAS2R16 rs978739 C allele was more frequent in generalized periodontitis compared to the reference group (37.5% vs. 28.7%, p = 0.016). Subjects aged 70 years and older demonstrated a statistically significant difference in TAS2R16 rs860170 (TT, CT, and CC) between generalized periodontitis and the reference group (42.8%, 57.2%, and 0% vs. 38.6%, 53.8%, and 7.6%, p = 0.003). TAS2R16 serum levels were elevated in generalized periodontitis compared to the reference group (0.112 (0.06) ng/mL vs. 0.075 (0.03) ng/mL, p = 0.002). Females carrying the TAS2R16 rs978739 C allele were more prone to generalized periodontitis development. Associations were found between TAS2R16 rs860170 polymorphisms, elevated TAS2R16 serum levels, and generalized periodontitis development.

Tuft cells are required for a rhinovirus-induced asthma phenotype in immature mice

Infection of immature mice with rhinovirus (RV) induces an asthma-like phenotype consisting of type 2 inflammation, mucous metaplasia, eosinophilic inflammation, and airway hyperresponsiveness that is dependent on IL-25 and type 2 innate lymphoid cells (ILC2s). Doublecortin-like kinase 1-positive (DCLK1+) tuft cells are a major source of IL-25. We sought to determine the requirement of tuft cells for the RV-induced asthma phenotype in wild-type mice and mice deficient in Pou2f3, a transcription factor required for tuft cell development. C57BL/6J mice infected with RV-A1B on day 6 of life and RV-A2 on day 13 of life showed increased DCLK1+ tuft cells in the large airways. Compared with wild-type mice, RV-infected Pou2f3-/- mice showed reductions in IL-25 mRNA and protein expression, ILC2 expansion, type 2 cytokine expression, mucous metaplasia, lung eosinophils, and airway methacholine responsiveness. We conclude that airway tuft cells are required for the asthma phenotype observed in immature mice undergoing repeated RV infections. Furthermore, RV-induced tuft cell development provides a mechanism by which early-life viral infections could potentiate type 2 inflammatory responses to future infections.

Comparison of SARS-CoV-2 variants of concern in primary human nasal cultures demonstrates Delta as most cytopathic and Omicron as fastest replicating

The SARS-CoV-2 pandemic was marked with emerging viral variants, some of which were designated as variants of concern (VOCs) due to selection and rapid circulation in the human population. Here we elucidate functional features of each VOC linked to variations in replication rate. Patient-derived primary nasal cultures grown at air-liquid-interface (ALI) were used to model upper-respiratory infection and human lung epithelial cell lines used to model lower-respiratory infection. All VOCs replicated to higher titers than the ancestral virus, suggesting a selection for replication efficiency. In primary nasal cultures, Omicron replicated to the highest titers at early time points, followed by Delta, paralleling comparative studies of population sampling. All SARS-CoV-2 viruses entered the cell primarily via a transmembrane serine protease 2 (TMPRSS2)-dependent pathway, and Omicron was more likely to use an endosomal route of entry. All VOCs activated and overcame dsRNA-induced cellular responses including interferon (IFN) signaling, oligoadenylate ribonuclease L degradation and protein kinase R activation. Among the VOCs, Omicron infection induced expression of the most IFN and IFN stimulated genes. Infections in nasal cultures resulted in cellular damage, including a compromise of cell-barrier integrity and loss of nasal cilia and ciliary beating function, especially during Delta infection. Overall, Omicron was optimized for replication in the upper-respiratory system and least-favorable in the lower-respiratory cell line; and Delta was the most cytopathic for both upper and lower respiratory cells. Our findings highlight the functional differences among VOCs at the cellular level and imply distinct mechanisms of pathogenesis in infected individuals.

The Effects of Artificial Sweeteners on Intestinal Nutrient-Sensing Receptors: Dr. Jekyll or Mr. Hyde?

The consumption of artificial and low-calorie sweeteners (ASs, LCSs) is an important component of the Western diet. ASs play a role in the pathogenesis of metabolic syndrome, dysbiosis, inflammatory bowel diseases (IBDs), and various inflammatory conditions. Intestinal nutrient-sensing receptors act as a crosstalk between dietary components, the gut microbiota, and the regulation of immune, endocrinological, and neurological responses. This narrative review aimed to summarize the possible effects of ASs and LCSs on intestinal nutrient-sensing receptors and their related functions. Based on the findings of various studies, long-term AS consumption has effects on the gut microbiota and intestinal nutrient-sensing receptors in modulating incretin hormones, antimicrobial peptides, and cytokine secretion. These effects contribute to the regulation of glucose metabolism, ion transport, gut permeability, and inflammation and modulate the gut-brain, and gut-kidney axes. Based on the conflicting findings of several in vitro, in vivo, and randomized and controlled studies, artificial sweeteners may have a role in the pathogenesis of IBDs, functional bowel diseases, metabolic syndrome, and cancers via the modulation of nutrient-sensing receptors. Further studies are needed to explore the exact mechanisms underlying their effects to decide the risk/benefit ratio of sugar intake reduction via AS and LCS consumption.

Relevance of Phytochemical Taste for Anti-Cancer Activity: A Statistical Inquiry

Targeting inflammation and the pathways linking inflammation with cancer is an innovative therapeutic strategy. Tastants are potential candidates for this approach, since taste receptors display various biological functions, including anti-inflammatory activity (AIA). The present study aims to explore the power different tastes have to predict a phytochemical's anti-cancer properties. It also investigates whether anti-inflammatory phytocompounds also have anti-cancer effects, and whether there are tastes that can better predict a phytochemical's bivalent biological activity. Data from the PlantMolecularTasteDB, containing a total of 1527 phytochemicals, were used. Out of these, only 624 phytocompounds met the inclusion criterion of having 40 hits in a PubMed search, using the name of the phytochemical as the keyword. Among them, 461 phytochemicals were found to possess anti-cancer activity (ACA). The AIA and ACA of phytochemicals were strongly correlated, irrespective of taste/orosensation or chemical class. Bitter taste was positively correlated with ACA, while sweet taste was negatively correlated. Among chemical classes, only flavonoids (which are most frequently bitter) had a positive association with both AIA and ACA, a finding confirming that taste has predictive primacy over chemical class. Therefore, bitter taste receptor agonists and sweet taste receptor antagonists may have a beneficial effect in slowing down the progression of inflammation to cancer.

Human airway tuft cells influence the mucociliary clearance through cholinergic signalling

BACKGROUND

Airway tuft cells, formerly called brush cells have long been described only morphologically in human airways. More recent RNAseq studies described a chemosensory cell population, which includes tuft cells, by a distinct gene transcription signature. Yet, until which level in the tracheobronchial tree in native human airway epithelium tuft cells occur and if they function as regulators of innate immunity, e.g., by regulating mucociliary clearance, remained largely elusive.

METHODS

We performed immunohistochemistry, RT-PCR and immunoblotting analyses for various tuft cell markers to confirm the presence of this cell type in human tracheal samples. Immunohistochemistry was conducted to study the distribution of tuft cells along the intrapulmonary airways in humans. We assessed the influence of bitter substances and the taste transduction pathway on mucociliary clearance in mouse and human tracheal samples by measuring particle transport speed.

RESULTS

Tuft cells identified by the expression of their well-established marker POU class 2 homeobox 3 (POU2F3) were present from the trachea to the bronchioles. We identified choline acetyltransferase in POU2F3 expressing cells as well as the transient receptor potential melastatin 5 (TRPM5) channel in a small population of tracheal epithelial cells with morphological appearance of tuft cells. Application of bitter substances, such as denatonium, led to an increase in mucociliary clearance in human tracheal preparations. This was dependent on activation of the TRPM5 channel and involved cholinergic and nitric oxide signalling, indicating a functional role for human tuft cells in the regulation of mucociliary clearance.

CONCLUSIONS

We were able to detect tuft cells in the tracheobronchial tree down to the level of the bronchioles. Moreover, taste transduction and cholinergic signalling occur in the same cells and regulate mucociliary clearance. Thus, tuft cells are potentially involved in the regulation of innate immunity in human airways.

A novel sophorolipids extraction method by yeast fermentation process for enhanced skin efficacy

AIMS

Oriental herbs have been used as medicines in the folk remedy for their numerous phytochemicals and bioactivities. In this study, we have selected five Korean traditional medical herbs and applied bio conversion extraction technology, named it as Bioconversion Oji complex, to identify phytochemicals and evaluate skin related efficacies.

MATERIAL AND METHODS

The process of two-step bio conversion was sequentially conducted. The first step of fermentation was to produce biosurfactants using macadamia seed oil with Candida bombicola, and then five natural plants were added to carry out the main fermentation. To evaluate skin improvement efficacy of Bioconversion Oji complex, in vitro and in vivo studies were conducted. We studied HaCaT cells cultured to assess viability, skin anti-inflammatory, moisturizing and barrier improvement-related mRNA expression. For efficacy study, 21 participants were tested evaluating anti-inflammatory, skin moisturizing and skin barrier improving effects of Bioconversion Oji complex compared to Water extraction of Oji (placebo) for the 4 weeks test period.

RESULTS

The application of bioconversion technology highly increased the content of amino acids and lipids within Bioconversion Oji complex, and 23 flavonoids were also identified. Bioconversion Oji complex was found to be non-toxic and showed significant effects in all parameters tested, including anti-inflammation, skin moisture, and skin barrier in both in vitro and in clinical studies.

CONCLUSIONS

Bioconversion Oji complex has demonstrated skin-friendly properties with significant beneficial effects on anti-inflammatory, skin hydration and barrier function properties. This study provides evidence for the use of Bioconversion Oji complex as an active ingredient in cosmetics and skincare products.

The Dual Role of the Airway Epithelium in Asthma: Active Barrier and Regulator of Inflammation

Chronic airway inflammation is the cornerstone on which bronchial asthma arises, and in turn, chronic inflammation arises from a complex interplay between environmental factors such as allergens and pathogens and immune cells as well as structural cells constituting the airway mucosa. Airway epithelial cells (AECs) are at the center of these processes. On the one hand, they represent the borderline separating the body from its environment in order to keep inner homeostasis. The airway epithelium forms a multi-tiered, self-cleaning barrier that involves an unstirred, discontinuous mucous layer, the dense and rigid mesh of the glycocalyx, and the cellular layer itself, consisting of multiple, densely interconnected cell types. On the other hand, the airway epithelium represents an immunologically highly active tissue once its barrier has been penetrated: AECs play a pivotal role in releasing protective immunoglobulin A. They express a broad spectrum of pattern recognition receptors, enabling them to react to environmental stressors that overcome the mucosal barrier. By releasing alarmins-proinflammatory and regulatory cytokines-AECs play an active role in the formation, strategic orientation, and control of the subsequent defense reaction. Consequently, the airway epithelium is of vital importance to chronic inflammatory diseases, such as asthma.

Heterodimerization of Chemoreceptors TAS1R3 and mGlu2 in Human Blood Leukocytes

The expression of canonical chemosensory receptors of the tongue, such as the heteromeric sweet taste (TAS1R2/TAS1R3) and umami taste (TAS1R1/TAS1R3) receptors, has been demonstrated in many extra-oral cells and tissues. Gene expression studies have revealed transcripts for all TAS1 and metabotropic glutamate (mGlu) receptors in different types of immune cells, where they are involved, for example, in the chemotaxis of human neutrophils and the protection of T cells from activation-induced cell death. Like other class-C G protein-coupling receptors (GPCRs), TAS1Rs and mGlu receptors form heteromers within their families. Since mGlu receptors and TAS1R1/TAS1R3 share the same ligand, monosodium glutamate (MSG), we hypothesized their hitherto unknown heteromerization across receptor families in leukocytes. Here we show, by means of immunocytochemistry and co-IP/Western analysis, that across class-C GPCR families, mGlu2 and TAS1R3 co-localize and heterodimerize in blood leukocytes. Expressing the recombinant receptors in HEK-293 cells, we validated their heterodimerization by bioluminescence resonance energy transfer. We demonstrate MSG-induced, mGlu2/TAS1R3 heteromer-dependent gain-of-function and pertussis toxin-sensitive signaling in luminescence assays. Notably, we show that mGlu2/TAS1R3 is necessary and sufficient for MSG-induced facilitation of N-formyl-methionyl-leucyl-phenylalanine-stimulated IL-8 secretion in neutrophils, using receptor-specific antagonists. In summary, our results demonstrate mGlu2/TAS1R3 heterodimerization in leukocytes, suggesting cellular function-tailored chemoreceptor combinations to modulate cellular immune responses.

A succinate/SUCNR1-brush cell defense program in the tracheal epithelium

Host-derived succinate accumulates in the airways during bacterial infection. Here, we show that luminal succinate activates murine tracheal brush (tuft) cells through a signaling cascade involving the succinate receptor 1 (SUCNR1), phospholipase Cβ2, and the cation channel transient receptor potential channel subfamily M member 5 (TRPM5). Stimulated brush cells then trigger a long-range Ca2+ wave spreading radially over the tracheal epithelium through a sequential signaling process. First, brush cells release acetylcholine, which excites nearby cells via muscarinic acetylcholine receptors. From there, the Ca2+ wave propagates through gap junction signaling, reaching also distant ciliated and secretory cells. These effector cells translate activation into enhanced ciliary activity and Cl- secretion, which are synergistic in boosting mucociliary clearance, the major innate defense mechanism of the airways. Our data establish tracheal brush cells as a central hub in triggering a global epithelial defense program in response to a danger-associated metabolite.

Effect of Functional Endoscopic Sinus Surgery on Gustatory Function in Patients With Chronic Rhinosinusitis

OBJECTIVES

In this study, we investigated the effect of functional endoscopic sinus surgery (FESS) on gustatory function in patients with chronic rhinosinusitis (CRS).

METHODS

Forty-three patients with CRS who underwent FESS were included in this study. Prior to FESS and 3 months after surgery, the severity of rhinosinusitis was assessed using the Taiwanese version of the 22-item SNOT (SNOT-22), endoscopic examination, and acoustic rhinometry. The olfactory function was evaluated using the phenylethyl alcohol odor detection threshold test and the traditional Chinese version of the University of Pennsylvania Smell Identification Test, and the gustatory function was evaluated using the whole mouth suprathreshold taste test (WMTT) and the taste quad test (TQT). Subgroup analyses were performed based on CRS phenotypes and endotypes.

RESULTS

The SNOT-22 significantly improved 3 months after FESS for all patients with CRS. The endoscopic score and olfactory function significantly improved in patients with eosinophilic CRS and in patients with nasal polyps (CRSwNP). The WMTT sweet and bitter scores were significantly lower after FESS in CRSwNP, but the TQT sweet score was significantly higher in patients without nasal polyps. In addition, patients with noneosinophilic CRS had significantly decreased WMTT and salty scores 3 months after FESS.

CONCLUSION

Our results showed that the effect of FESS on gustatory function of patients with CRS was different with the different testing procedures, the association with nasal polyps, and the underlying inflammatory patterns.

Microbial metabolite succinate activates solitary chemosensory cells in the human sinonasal epithelium

BACKGROUND

Succinate, although most famous for its role in the Krebs cycle, can be released extracellularly as a signal of cellular distress, particularly in situations of metabolic stress and inflammation. Solitary chemosensory cells (SCCs) express SUCNR1, the succinate receptor, and modulate type 2 inflammatory responses in helminth and protozoal infections in the small intestine. SCCs are the dominant epithelial source of interleukin-25, as well as an important source of cysteinyl leukotrienes in the airway, and have been implicated as upstream agents in type 2 inflammation in chronic rhinosinusitis (CRS) and asthma.

METHODS

In this study, we used scRNAseq analysis, live cell imaging of intracellular calcium from primary sinonasal air-liquid interface (ALI) cultures from 1 donor, and measure antimicrobial peptide release from 5 donors to demonstrate preliminary evidence suggesting that succinate can act as a stimulant of SCCs in the human sinonasal epithelium.

RESULTS

Results from scRNAseq analysis show that approximately 10% of the SCC/ionocyte cluster of cells expressed SUCNR1 as well as a small population of immune cells. Using live cell imaging of intracellular calcium, we also demonstrate that clusters of cells on primary sinonasal ALI cultures initiated calcium-mediated signaling in response to succinate stimulation. Furthermore, we present evidence that primary sinonasal ALI cultures treated with succinate had increased levels of apical beta-defensin 2, an antimicrobial peptide, compared to treatment with a control solution.

CONCLUSION

Overall, these findings demonstrate the need for further investigation into the activation of the sinonasal epithelium by succinate in the pathogenesis of CRS.

Stem/Progenitor Cells and Related Therapy in Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease commonly seen in preterm infants, and is triggered by infection, mechanical ventilation, and oxygen toxicity. Among other problems, lifelong limitations in lung function and impaired psychomotor development may result. Despite major advances in understanding the disease pathologies, successful interventions are still limited to only a few drug therapies with a restricted therapeutic benefit, and which sometimes have significant side effects. As a more promising therapeutic option, mesenchymal stem cells (MSCs) have been in focus for several years due to their anti-inflammatory effects and their secretion of growth and development promoting factors. Preclinical studies provide evidence in that MSCs have the potential to contribute to the repair of lung injuries. This review provides an overview of MSCs, and other stem/progenitor cells present in the lung, their identifying characteristics, and their differentiation potential, including cytokine/growth factor involvement. Furthermore, animal studies and clinical trials using stem cells or their secretome are reviewed. To bring MSC-based therapeutic options further to clinical use, standardized protocols are needed, and upcoming side effects must be critically evaluated. To fill these gaps of knowledge, the MSCs' behavior and the effects of their secretome have to be examined in more (pre-) clinical studies, from which only few have been designed to date.

Sensory systems in the peripheral and central nervous systems shape host response during infections

The function of sensory cells has been largely investigated in the field of neuroscience for how they report the physical and chemical changes of the environment ("exteroception") and of internal physiology ("interoception"). Investigations over the last century have largely focused on the morphological, electrical and receptor properties of sensory cells in the nervous system focusing on conscious perception of external cues or homeostatic regulation upon detection of internal cues. Research in the last decade has uncovered that sensory cells can often sense polymodal cues, such as mechanical, chemical, and/ or thermal. Furthermore, sensory cells in the peripheral as well as in the central nervous system can detect evidence associated with the invasion of pathogenic bacteria or viruses. The corresponding neuronal activation associated with the presence of pathogens can impact their classical functions within the nervous system and trigger the release of compounds modulating the response to intruders, either triggering pain to raise awareness, enhancing host defense or sometimes, aggravating the infection. This perspective brings to light the need for interdisciplinary training in immunology, microbiology and neuroscience for the next generation of investigators in this field.

Lipopolysaccharide increases bitter taste sensitivity via epigenetic changes in Tas2r gene clusters

T2R bitter receptors, encoded by Tas2r genes, are not only critical for bitter taste signal transduction but also important for defense against bacteria and parasites. However, little is known about whether and how Tas2r gene expression are regulated. Here, we show that in an inflammation model mimicking bacterial infection using lipopolysaccharide, the expression of many Tas2rs was significantly upregulated and mice displayed markedly increased neural and behavioral responses to bitter compounds. Using single-cell assays for transposase-accessible chromatin with sequencing (scATAC-seq), we found that the chromatin accessibility of Tas2rs was highly celltype specific and lipopolysaccharide increased the accessibility of many Tas2rs. scATAC-seq also revealed substantial chromatin remodeling in immune response genes in taste tissue stem cells, suggesting potential long-lasting effects. Together, our results suggest an epigenetic mechanism connecting inflammation, Tas2r gene regulation, and altered bitter taste, which may explain heightened bitter taste that can occur with infections and cancer treatments.

Interkingdom Detection of Bacterial Quorum-Sensing Molecules by Mammalian Taste Receptors

Bitter and sweet taste G protein-coupled receptors (known as T2Rs and T1Rs, respectively) were originally identified in type II taste cells on the tongue, where they signal perception of bitter and sweet tastes, respectively. Over the past ~15 years, taste receptors have been identified in cells all over the body, demonstrating a more general chemosensory role beyond taste. Bitter and sweet taste receptors regulate gut epithelial function, pancreatic β cell secretion, thyroid hormone secretion, adipocyte function, and many other processes. Emerging data from a variety of tissues suggest that taste receptors are also used by mammalian cells to "eavesdrop" on bacterial communications. These receptors are activated by several quorum-sensing molecules, including acyl-homoserine lactones and quinolones from Gram-negative bacteria such as Pseudomonas aeruginosa, competence stimulating peptides from Streptococcus mutans, and D-amino acids from Staphylococcus aureus. Taste receptors are an arm of immune surveillance similar to Toll-like receptors and other pattern recognition receptors. Because they are activated by quorum-sensing molecules, taste receptors report information about microbial population density based on the chemical composition of the extracellular environment. This review summarizes current knowledge of bacterial activation of taste receptors and identifies important questions remaining in this field.

RSV-induced expanded ciliated cells contribute to bronchial wall thickening

Viral infection, particularly respiratory syncytial virus (RSV), causes inflammation in the bronchiolar airways (bronchial wall thickening, also known as bronchiolitis). This bronchial wall thickening is a common pathophysiological feature in RSV infection, but it causes more fatalities in infants than in children and adults. However, the molecular mechanism of RSV-induced bronchial wall thickening remains unknown, particularly in healthy adults. Using highly differentiated pseudostratified airway epithelium generated from primary human bronchial epithelial cells, we revealed RSV-infects primarily ciliated cells. The infected ciliated cells expanded substantially without compromising epithelial membrane integrity and ciliary functions and contributed to the increased height of the airway epithelium. Furthermore, we identified multiple factors, e.g., cytoskeletal (ARP2/3-complex-driven actin polymerization), immunological (IP10/CXCL10), and viral (NS2), contributing to RSV-induced uneven epithelium height increase in vitro. Thus, RSV-infected expanded cells contribute to a noncanonical inflammatory phenotype, which contributes to bronchial wall thickening in the airway, and is termed cytoskeletal inflammation.

Pathogenesis of Nasal Polyposis: Current Trends

Chronic Rhinosinusitis (CRS) is characterized by edema of the sub-epithelial layers, but, only specific types of CRS are developing polyps. Nasal polyposis may develop under different pathogenetic mechanisms rendering the typical macroscopic classification of CRS, with or without nasal polyps, rather deficient. Currently, we approach nasal polyposis, in terms of diagnosis and treatment, according to its endotype, which means that we focus on the specific cells and cytokines that are participating in its pathogenesis. It appears that the molecular procedures that contribute to polyp formation, initiating with a Th-2 response of the adaptive immune system, are local phenomena occurring in the sub-epithelial layers of the mucosa. Several hypotheses are trying to approach the etiology that drives the immune response towards Th-2 type. Extrinsic factors, like fungi, Staphylococcus superantigens, biofilms, and altered microbiome can contribute to a modified and intense local reaction of the immune system. Some hypotheses based on intrinsic factors like the elimination of Treg lymphocytes, low local vitamin-D levels, high levels of leukotrienes, epithelial to mesenchymal transition (EMT) induced by hypoxia, and altered levels of NO, add pieces to the puzzle of the pathogenesis of nasal polyposis. Currently, the most complete theory is that of epithelial immune barrier dysfunction. Intrinsic and extrinsic conditions can damage the epithelial barrier rendering sub-epithelial layers more vulnerable to invasion by pathogens that trigger a Th-2 response of the adaptive immune system. Th2 cytokines, subsequently, induce the accumulation of eosinophils and IgE together with the remodeling of the stroma in the sub-epithelial layers leading, eventually, to the formation of nasal polyps.

A Review on the Nasal Microbiome and Various Disease Conditions for Newer Approaches to Treatments

Introduction: Commensal bacteria have always played a significant role in the maintenance of health and disease but are being unravelled only recently. Studies suggest that the nasal microbiome has a significant role in the development of various disease conditions. Search engines were used for searching articles having a nasal microbiome and disease correlation. In olfactory dysfunction, dysbiosis of the microbiome may have a significant role to play in the pathogenesis. The nasal microbiome influences the phenotype of CRS and is also capable of modulating the immune response and plays a role in polyp formation. Microbiome dysbiosis has a pivotal role in the development of Allergic Rhinitis; but, yet known how is this role played. The nasal microbiome has a close association with the severity and phenotype of asthma. They contribute significantly to the onset, severity, and development of asthma. The nasal microbiome has a significant impact on the immunity and protection of its host. The nasal microbiome has been a stimulus in the development of Otitis Media and its manifestations. Studies suggest that the resident nasal microbiome is responsible for the initiation of neurodegenerative diseases like Parkinson's Disease.Materials and Methods: Literature search from PubMed, Medline, and Google with the Mesh terms: nasal microbiome AND diseases. Conclusion: With increasing evidence on the role of the nasal microbiome on various diseases, it would be interesting to see how this microbiome can be modulated by pro/pre/post biotics to prevent a disease or the severity of illness.

Human T2R38 Bitter Taste Receptor Expression and COVID-19: From Immunity to Prognosis

Background

Bitter taste-sensing type 2 receptor (T2Rs or TAS2Rs) found on ciliated epithelial cells and solitary chemosensory cells have a role in respiratory tract immunity. T2Rs have shown protection against SARS-CoV-2 by enhancing the innate immune response. The purpose of this review is to outline the current sphere of knowledge regarding this association.

Methods

A narrative review of the literature was done by searching (T2R38 OR bitter taste receptor) AND (COVID-19 OR SARS-CoV-2) keywords in PubMed and google scholar.

Results

T2R38, an isoform of T2Rs encoded by the TAS2R38 gene, may have a potential association between phenotypic expression of T2R38 and prognosis of COVID-19. Current studies suggest that due to different genotypes and widespread distributions of T2Rs within the respiratory tract and their role in innate immunity, treatment protocols for COVID-19 and other respiratory diseases may change accordingly. Based on the phenotypic expression of T2R38, it varies in innate immunity and host response to respiratory infection, systemic symptoms and hospitalization.

Conclusion

This review reveals that patients' innate immune response to SARS-COV-2 could be influenced by T2R38 receptor allelic variations.

Tuft cell-derived acetylcholine regulates epithelial fluid secretion

Tuft cells are solitary chemosensory epithelial cells that can sense lumenal stimuli at mucosal barriers and secrete effector molecules to regulate the physiology and immune state of their surrounding tissue. In the small intestine, tuft cells detect parasitic worms (helminths) and microbe-derived succinate, and signal to immune cells to trigger a Type 2 immune response that leads to extensive epithelial remodeling spanning several days. Acetylcholine (ACh) from airway tuft cells has been shown to stimulate acute changes in breathing and mucocilliary clearance, but its function in the intestine is unknown. Here we show that tuft cell chemosensing in the intestine leads to release of ACh, but that this does not contribute to immune cell activation or associated tissue remodeling. Instead, tuft cell-derived ACh triggers immediate fluid secretion from neighboring epithelial cells into the intestinal lumen. This tuft cell-regulated fluid secretion is amplified during Type 2 inflammation, and helminth clearance is delayed in mice lacking tuft cell ACh. The coupling of the chemosensory function of tuft cells with fluid secretion creates an epithelium-intrinsic response unit that effects a physiological change within seconds of activation. This response mechanism is shared by tuft cells across tissues, and serves to regulate the epithelial secretion that is both a hallmark of Type 2 immunity and an essential component of homeostatic maintenance at mucosal barriers.

CSF-contacting neurons respond to Streptococcus pneumoniae and promote host survival during central nervous system infection

The pathogenic bacterium Streptococcus pneumoniae (S. pneumoniae) can invade the cerebrospinal fluid (CSF) and cause meningitis with devastating consequences. Whether and how sensory cells in the central nervous system (CNS) become activated during bacterial infection, as recently reported for the peripheral nervous system, is not known. We find that CSF infection by S. pneumoniae in larval zebrafish leads to changes in posture and behavior that are reminiscent of pneumococcal meningitis, including dorsal arching and epileptic-like seizures. We show that during infection, invasion of the CSF by S. pneumoniae massively activates in vivo sensory neurons contacting the CSF, referred to as "CSF-cNs" and previously shown to detect spinal curvature and to control posture, locomotion, and spine morphogenesis. We find that CSF-cNs express orphan bitter taste receptors and respond in vitro to bacterial supernatant and metabolites via massive calcium transients, similar to the ones observed in vivo during infection. Upon infection, CSF-cNs also upregulate the expression of numerous cytokines and complement components involved in innate immunity. Accordingly, we demonstrate, using cell-specific ablation and blockade of neurotransmission, that CSF-cN neurosecretion enhances survival of the host during S. pneumoniae infection. Finally, we show that CSF-cNs respond to various pathogenic bacteria causing meningitis in humans, as well as to the supernatant of cells infected by a neurotropic virus. Altogether, our work uncovers that central sensory neurons in the spinal cord, previously involved in postural control and morphogenesis, contribute as well to host survival by responding to the invasion of the CSF by pathogenic bacteria during meningitis.

Promising applications of D-amino acids in periprosthetic joint infection

Due to the rise in our aging population, a disproportionate demand for total joint arthroplasty (TJA) in the elderly is forecast. Periprosthetic joint infection (PJI) represents one of the most challenging complications that can occur following TJA, and as the number of primary and revision TJAs continues to rise, an increasing PJI burden is projected. Despite advances in operating room sterility, antiseptic protocols, and surgical techniques, approaches to prevent and treat PJI remain difficult, primarily due to the formation of microbial biofilms. This difficulty motivates researchers to continue searching for an effective antimicrobial strategy. The dextrorotatory-isoforms of amino acids (D-AAs) are essential components of peptidoglycan within the bacterial cell wall, providing strength and structural integrity in a diverse range of species. Among many tasks, D-AAs regulate cell morphology, spore germination, and bacterial survival, evasion, subversion, and adhesion in the host immune system. When administered exogenously, accumulating data have demonstrated that D-AAs play a pivotal role against bacterial adhesion to abiotic surfaces and subsequent biofilm formation; furthermore, D-AAs have substantial efficacy in promoting biofilm disassembly. This presents D-AAs as promising and novel targets for future therapeutic approaches. Despite their emerging antibacterial efficacy, their role in disrupting PJI biofilm formation, the disassembly of established TJA biofilm, and the host bone tissue response remains largely unexplored. This review aims to examine the role of D-AAs in the context of TJAs. Data to date suggest that D-AA bioengineering may serve as a promising future strategy in the prevention and treatment of PJI.

Sweetener System Intervention Shifted Neutrophils from Homeostasis to Priming

BACKGROUND

Non-nutritive sweeteners (NNS) are part of personalized nutrition strategies supporting healthy glycemic control. In contrast, the consumption of non-nutritive sweeteners has been related to person-specific and microbiome-dependent glycemic impairments. Reports on the effects of NNS on our highly individual cellular immune system are sparse. The recent identification of taste receptor expression in a variety of immune cells, however, suggested their immune-modulatory relevance.

METHODS

We studied the influence of a beverage-typical NNS system on the transcriptional profiling of sweetener-cognate taste receptors, selected cytokines and their receptors, and on Ca²⁺ signaling in isolated blood neutrophils. We determined plasma concentrations of saccharin, acesulfame-K, and cyclamate by HPLC-MS/MS, upon ingestion of a soft drink-typical sweetener surrogate. In an open-labeled, randomized intervention study, we determined pre- versus post-intervention transcript levels by RT-qPCR of sweetener-cognate taste receptors and immune factors.

RESULTS

Here we show that the consumption of a food-typical sweetener system modulated the gene expression of cognate taste receptors and induced the transcriptional regulation signatures of early homeostasis- and late receptor/signaling- and inflammation-related genes in blood neutrophils, shifting their transcriptional profile from homeostasis to priming. Notably, sweeteners at postprandial plasma concentrations facilitated fMLF (N-formyl-Met-Leu-Phe)-induced Ca²⁺ signaling.

CONCLUSIONS

Our results support the notion of sweeteners priming neutrophils to higher alertness towards their adequate stimuli.