Increased expression of bitter taste receptors in human allergic nasal mucosa and their contribution to the shrinkage of human nasal mucosa

Deciphering the Systemic Impact of Herbal Medicines on Allergic Rhinitis: A Network Pharmacological Approach

Allergic rhinitis (AR) is a systemic allergic disease that has a considerable impact on patients' quality of life. Current treatments include antihistamines and nasal steroids; however, their long-term use often causes undesirable side effects. In this context, traditional Asian medicine (TAM), with its multi-compound, multi-target herbal medicines (medicinal plants), offers a promising alternative. However, the complexity of these multi-compound traits poses challenges in understanding the overall mechanisms and efficacy of herbal medicines. Here, we demonstrate the efficacy and underlying mechanisms of these multi-compound herbal medicines specifically used for AR at a systemic level. We utilized a modified term frequency-inverse document frequency method to select AR-specific herbs and constructed an herb-compound-target network using reliable databases and computational methods, such as the Quantitative Estimate of Drug-likeness for compound filtering, STITCH database for compound-target interaction prediction (with a high confidence score threshold of 0.7), and DisGeNET and CTD databases for disease-gene association analysis. Through this network, we conducted AR-related targets and pathway analyses, as well as clustering analysis based on target-level information of the herbs. Gene ontology enrichment analysis was conducted using a protein-protein interaction network. Our research identified 14 AR-specific herbs and analyzed whether AR-specific herbs are highly related to previously known AR-related genes and pathways. AR-specific herbs were found to target several genes related to inflammation and AR pathogenesis, such as PTGS2, HRH1, and TBXA2R. Pathway analysis revealed that AR-specific herbs were associated with multiple AR-related pathways, including cytokine signaling, immune response, and allergic inflammation. Additionally, clustering analysis based on target similarity identified three distinct subgroups of AR-specific herbs, corroborated by a protein-protein interaction network. Group 1 herbs were associated with the regulation of inflammatory responses to antigenic stimuli, while Group 2 herbs were related to the detection of chemical stimuli involved in the sensory perception of bitter taste. Group 3 herbs were distinctly associated with antigen processing and presentation and NIK/NF-kappa B signaling. This study decodes the principles of TAM herbal configurations for AR using a network pharmacological approach, providing a holistic understanding of drug effects beyond specific pathways.

The Hidden One: What We Know About Bitter Taste Receptor 39

Over thousands of years of evolution, animals have developed many ways to protect themselves. One of the most protective ways to avoid disease is to prevent the absorption of harmful components. This protective function is a basic role of bitter taste receptors (TAS2Rs), a G protein-coupled receptor family, whose presence in extraoral tissues has intrigued many researchers. In humans, there are 25 TAS2Rs, and although we know a great deal about some of them, others are still shrouded in mystery. One in this latter category is bitter taste receptor 39 (TAS2R39). Besides the oral cavity, it has also been found in the gastrointestinal tract and the respiratory, nervous and reproductive systems. TAS2R39 is a relatively non-selective receptor, which means that it can be activated by a range of mostly plant-derived compounds such as theaflavins, catechins and isoflavones. On the other hand, few antagonists for this receptor are available, since only some flavones have antagonistic properties (all of them detailed in the document). The primary role of TAS2R39 is to sense the bitter components of food and protect the organism from harmful compounds. There is also some indication that this bitter taste receptor regulates enterohormones and in turn, regulates food intake. In the respiratory system, it may be involved in the congestion process of allergic rhinitis and may stimulate inflammatory cytokines. However, more thorough research is needed to determine the precise role of TAS2R39 in these and other tissues.

Notch2 suppresses the development of allergic rhinitis by promoting FOXP3 expression and Treg cell differentiation

AIMS

Notch signaling is closely related to a variety of diseases, but the role of Notch2 in allergic rhinitis (AR) remain unclear. This study was performed to investigate the effects of Notch2 on the differentiation of Treg cells and on the inflammatory response of AR.

MATERIALS AND METHODS

Peripheral blood (including 101 AR patients and 66 Controls) and nasal mucosa (including 19 AR patients and 17 Controls) were collected to detect the expression levels of Notch2, NICD2 and FOXP3. CD4+ T cells of human origin were selected to detect the effects of Notch2 on the differentiation of Treg cells and FOXP3. An AR mouse model was established, and lentiviruses overexpressing Notch2 were administered. Then, allergic symptoms, OVA-sIgE titers, nasal mucosal inflammation, Th1/Th2/Th17 cytokines and splenic Treg cells were assessed.

KEY FINDINGS

Compared with that in the Control group, the expression of Notch2 in the AR group was decreased, and Notch2 expression was negatively correlated with the degree of allergy (P < 0.01). The expression levels of Notch2, NICD2 and FOXP3 were decreased in the nasal mucosa of AR patients. Notch2 can promote the differentiation of human Treg cells in vitro (P < 0.05), and Notch2 can directly promote FOXP3 transcription. Animal experiments showed after the upregulation of Notch2 expression, the allergic inflammatory of mice with AR was reduced, the differentiation of Treg cells was increased, and the imbalance of T cells was reversed (P < 0.05).

SIGNIFICANCE

Notch2 promotes the differentiation of Treg cells by upregulating FOXP3 expression, thus significantly inhibiting the inflammatory response of AR.

Taste Receptors: The Gatekeepers of the Airway Epithelium

Taste receptors are well known for their role in the sensation of taste. Surprisingly, the expression and involvement of taste receptors in chemosensory processes outside the tongue have been recently identified in many organs including the airways. Currently, a clear understanding of the airway-specific function of these receptors and the endogenous activating/inhibitory ligands is lagging. The focus of this review is on recent physiological and clinical data describing the taste receptors in the airways and their activation by secreted bacterial compounds. Taste receptors in the airways are potentially involved in three different immune pathways (i.e., the production of nitric oxide and antimicrobial peptides secretion, modulation of ciliary beat frequency, and bronchial smooth muscle cell relaxation). Moreover, genetic polymorphisms in these receptors may alter the patients’ susceptibility to certain types of respiratory infections as well as to differential outcomes in patients with chronic inflammatory airway diseases such as chronic rhinosinusitis and asthma. A better understanding of the function of taste receptors in the airways may lead to the development of a novel class of therapeutic molecules that can stimulate airway mucosal immune responses and could treat patients with chronic airway diseases.

Systematic prediction of the biological functions of TAS2R10 using positive co-expression analysis

Type 2 taste receptor 10 (TAS2R10), belonging to the TAS2R family of bitter receptors, is widely expressed in extra-oral tissues. However, its biological roles beyond bitterness sensing in the tongue have remained largely elusive. The present study aimed to perform a positive co-expression analysis using 60,000 Affymetrix expression arrays and 5,000 The Cancer Genome Atlas datasets to uncover such roles. Based on the functional enrichment analysis, it was indicated that in the Gene Ontology (GO) category biological process, TAS2R10 was mostly involved in 'cellular protein metabolic process', 'protein modification process', 'cellular protein modification process' and 'cellular component assembly'. In the GO category cellular component, the co-expressed genes were accumulated in 'Spt-Ada-Gcn5 acetyltransferase (SAGA)-type complex' and 'SAGA complex', and in the category molecular function, they were concentrated in 'hexosaminidase activity', 'cytoskeletal adaptor activity', 'cyclin binding' and 'β-N-acetylhexosaminidase activity'. Of note, it was indicated that TAS2R10 may be involved in 'ubiquitin-mediated proteolysis', which may provide a starting point to fully investigate the detailed functions of TAS2R10 in the future. TAS2R10 was also indicated to be associated with human diseases, i.e. 'Salmonella infection'. Overall, the present study was the first to perform a comprehensive bioinformatics analysis of the functions of TAS2R10 and provide insight regarding the notion that this gene may have crucial roles beyond bitterness sensing.

Epithelial Cell Regulation of Allergic Diseases

Allergic diseases, which have escalated in prevalence in recent years, arise as a result of maladaptive immune responses to ubiquitous environmental stimuli. Why only certain individuals mount inappropriate type 2 immune responses to these otherwise harmless allergens has remained an unanswered question. Mounting evidence suggests that the epithelium, by sensing its environment, is the central regulator of allergic diseases. Once considered to be a passive barrier to allergens, epithelial cells at mucosal surfaces are now considered to be the cornerstone of the allergic diathesis. Beyond their function as maintaining barrier at mucosal surfaces, mucosal epithelial cells through the secretion of mediators like IL-25, IL-33, and TSLP control the fate of downstream allergic immune responses. In this review, we will discuss the advances in recent years regarding the process of allergen recognition and secretion of soluble mediators by epithelial cells that shape the development of the allergic response.