Olfactory receptors in non-chemosensory tissues

Efficacy of Deferoxamine Mesylate in Serum and Serum-Free Media: Adult Ventral Root Schwann Cell Survival Following Hydrogen Peroxide-Induced Cell Death

Schwann cell (SC) transplantation shows promise in treating spinal cord injury as a pro-regenerative agent to allow host endogenous neurons to bridge over the lesion. However, SC transplants face significant oxidative stress facilitated by ROS in the lesion, leading to poor survival. deferoxamine mesylate (DFO) is a neuroprotective agent shown to reduce H2O2-induced cell death in serum-containing conditions. Here we show that DFO is not necessary to induce neuroprotection under serum-free conditions by cell survival quantification and phenotypic analysis via immunohistochemistry, Hif1α and collagen IV quantification via whole cell corrected total cell fluorescence, and cell death transcript changes via RT-qPCR. Our results indicate survival of SC regardless of DFO pretreatment in serum-free conditions and an increased survival facilitated by DFO in serum-containing conditions. Furthermore, our results showed strong nuclear expression of Hif1α in serum-free conditions regardless of DFO pre-treatment and a nuclear expression of Hif1α in DFO-treated SCs in serum conditions. Transcriptomic analysis reveals upregulation of autophagy transcripts in SCs grown in serum-free media relative to SCs in serum conditions, with and without DFO and H2O2. Thus, indicating a pro-repair and regenerative state of the SCs in serum-free conditions. Overall, results indicate the protectiveness of CDM in enhancing SC survival against ROS-induced cell death in vitro.

Microbiome-emitted scents activate olfactory neuron-independent airway-gut-brain axis to promote host growth in Drosophila

While it is now accepted that the microbiome has strong impacts on animal growth promotion, the exact mechanism has remained elusive. Here we show that microbiome-emitted scents contain volatile somatotrophic factors (VSFs), which promote host growth in an olfaction-independent manner in Drosophila. We found that inhaled VSFs are readily sensed by olfactory receptor 42b non-neuronally expressed in subsets of tracheal airway cells, enteroendocrine cells, and enterocytes. Olfaction-independent sensing of VSFs activates the airway-gut-brain axis by regulating Hippo, FGF and insulin-like growth factor signaling pathways, which are required for airway branching, organ oxygenation and body growth. We found that a mutant microbiome that did not produce (2R,3R)-2,3-butanediol failed to activate the airway-gut-brain axis for host growth. Importantly, forced inhalation of (2R,3R)-2,3-butanediol completely reversed these defects. Our discovery of contact-independent and olfaction-independent airborne interactions between host and microbiome provides a novel perspective on the role of the airway-gut-brain axis in microbiome-controlled host development.

Influence of MHC on genetic diversity and testicular expression of linked olfactory receptor genes

BACKGROUND

Olfactory receptor (OR) genes are highly polymorphic and form extensive families that recognize a wide range of vertebrate odorants. To explore the genetic diversity of MHC-linked OR genes and their connection to MHC genes, we conducted a combined haplotype analysis of MHC-linked OR and MHC class I genes to determine the influence of MHC on OR diversity, which could be associated with MHC-based mate selection.

RESULTS

We selected nine MHC-linked OR genes based on their expression levels in pig testes and developed a sequence-based typing method for these genes. We then performed high-resolution typing of these OR genes, along with three major classical MHC class I genes (SLA-1, -2, and - 3), in 48 pigs across six breeds. We observed significantly higher allelic diversity (P < 0.01) in ORs with strong linkage disequilibrium (LD) to SLA compared to those with weak or no LD, and we identified 48 SLA class I-OR haplotypes using the expectation-maximization algorithm. The genetic diversity of SLA-linked ORs was positively correlated with their expression levels in the testis. Specifically, SLA-linked ORs with higher testicular expression (FPKM ≥ 0.1) exhibited an increase in the number of codons under mutually diversifying selection with SLA compared to those with lower expression (FPKM < 0.1).

CONCLUSIONS

The presence of evolutionary interactions between MHC and linked OR genes supports the potential involvement of MHC-linked ORs in MHC-based mate selection. The use of combined haplotype information for MHC and linked ORs could provide new insights into the reproductive biology of animals.

Disruption of the odorant receptor co-receptor (Orco) reveals its critical role in multiple olfactory behaviors of a cosmopolitan pest

The olfactory system of insects plays a pivotal role in multiple, essential activities including feeding, mating, egg laying, and host localization. The capacity of odorant receptors to recognize odor molecules relies on odorant receptor co-receptors forming heterodimers. Here we report the successful engineering a homozygous mutant strain of diamondback moth (Plutella xylostella) in which the odorant receptor co-receptor PxOrco was silenced using CRISPR/Cas9. This insect is a globally important crop pest for which novel control methods are urgently required. Behavioral assays demonstrated that PxOrco knockout males exhibited abolished courtship behaviors, inability to mate, and loss of selective preference for P. xylostella's key sex pheromone components. Whilst female mating behavior and fecundity remained unaffected by PxOrco knockout, oviposition response to leaf alcohol, a key cue for normal oviposition behavior, was lost. Electroantennography revealed drastically reduced responses to sex pheromones and plant volatiles in PxOrco-deficient adults but food location by larvae was unaffected. Moreover, expression analysis of PxOrco-deficient pheromone receptors (PRs) indicated varied regulation patterns, with down-regulation observed in several PRs in both sexes. These findings underscore the critical role of PxOrco in regulating multiple olfactory aspects in P. xylostella, including feeding, mating, and host location. Our study identifies the potential of disrupting the Orco gene in this and other pest species to provide novel avenues for future pest control.

Protein-Protein Interactions of Odorant and G Protein-Coupled Receptors: A BRET Analysis Approach

Odorant receptors (ORs), the largest subfamily of G protein-coupled receptors, are pivotal not only for olfactory detection in the nose but also for various biological functions in extra-nasal tissues. The functional characterization of ORs presents significant challenges, especially due to the difficulty of achieving their surface expression in in vitro systems. Research indicates that interactions between ORs and other receptors, as well as OR multimerization, are crucial for their membrane localization and the modulation of signaling pathways. Utilizing the bioluminescence resonance energy transfer (BRET) assay, a technique for investigating protein-protein interactions, our study quantifies the interactions between ORs and various receptors. This approach provides novel insights into OR molecular dynamics, emphasizing the role of OR multimerization. By exploring into these complexities, our work aims to enhance the understanding of cellular signaling mechanisms and promote the development of innovative therapeutic strategies.

Yellow Fluorescent Protein Quenching Assay for Analyzing Odorant Receptor Activity

Odorant receptors (ORs), recognized as the largest subfamily of G protein-coupled receptors (GPCR), are increasingly identified as membrane proteins crucial not only in nasal but also in various extra-nasal biological processes. However, researching the functions of these extra-nasal ORs is challenging due to the limited availability of ligands, posing a significant barrier to comprehensive studies. Large-scale screening with in vitro assays, such as the halide-sensitive yellow fluorescent protein (YFP) quenching assay, is crucial for deorphanizing ORs. This protocol employs the YFP quenching assay to identify OR-ligand interactions, thereby advancing OR deorphanization research.

Image-Based cAMP Sensor Assay for Analyzing Odorant Receptor Activity

Odorant receptors (ORs), the largest subfamily of G-protein-coupled receptors (GPCRs), are transmembrane proteins essential for olfactory perception. Recent research has revealed their expression in nonolfactory tissues, highlighting their potential as novel drug targets. However, the functional analysis of ORs beyond nasal tissues is constrained by limited availability of suitable ligands. Conventional in vitro methods for studying OR-ligand interactions via cAMP often face challenges in large-scale applications. This protocol introduces an advanced cAMP assay employing the Pink Flamindo sensor, a cAMP fluorescence sensor that normally does not exhibit fluorescence but shows fluorescence when combined with cAMP. This enables the real-time visualization of OR-ligand interactions through an imaging-based method. This technique significantly aids in the deorphanization of ORs.

Comprehensive Transcriptomic Analysis Reveals Cell-Type-Specific Roles of Human Odorant Receptors in Glioblastoma and the Tumor Microenvironment

Odorant receptors (ORs), which constitute approximately 50% of all human G protein-coupled receptors, are increasingly recognized for their diverse roles beyond odor perception, including functions in various pathological conditions like brain diseases and cancers. However, the roles of ORs in glioblastoma (GBM), the most aggressive primary brain tumor with a median survival of only 15 months, remain largely unexplored. Here, we performed an integrated transcriptomic analysis combining The Cancer Genome Atlas RNA-seq and single-cell RNA sequencing data from GBM patients to uncover cell-type-specific roles of ORs within the tumor and its microenvironment. Our findings reveal that ORs display distinct expression patterns, with OR51E1 enriched in pericytes linked to vascular remodeling and angiogenesis, OR2B11 associated with tumor-associated macrophages supporting immunosuppressive phenotypes, and OR2L13 correlated with synaptic activity in recurrent tumors, potentially mediating treatment-induced neuronal adaptations. These results highlight ORs as potential therapeutic targets, offering new insights into their regulatory roles in GBM progression, immune modulation, and treatment resistance.

Study of the genomics and transcriptomics profiles of male-infertility genes in human prostate cancer: an in silico analysis

The World Health Organization has considered the infertility as an international public health problem. Infertility affect nearly 1 in 7 couples and male component contributes to 50% of infertility cases. There is a clear link between male infertility and some cancers such as testicular germ cell, prostate and colon cancers. Two possibilities support this finding: 1) Cancer treatments can affect the fertility factors 2) Genetic profile of infertility genes have been altered in cancer patients. Although the previously published researches have mostly focused on the first factor, no article has yet confirmed the role of genetic factors. In this in silico study, we collected the large number of genes (n = 17703) involved in infertility. These genes were collected from NGS panel tests of male infertility and comprehensive literature review or online data base. The Prostate Adenocarcinoma genomic and transcriptomics raw data were downloaded from the cBioPortal Cancer dataset. This included with 494 patients of Prostate Cancer with 494 mutation data, 489 with CNA and 493 with RNA seqV2 data. TCGA RNA-Seq raw data was extracted in R using the cgdsr extension package with a threshold of ±2 relative to normal samples. The observed data showed that male infertility genes have been distributed through the human genome. Among the 17703 analyzed genes of this study, the genomic profile of three genes including OR9Q1, H4C6 and PSG7 were changed approximately in 100% of (n = 493) patients. In most of patients (>98%), genetic alteration was related to change in gene expression. In conclusion, this study showed that the genomic and transcriptomics patterns of some male-infertility genes are notably altered in patients of prostate cancer and suggested a possible role of genetic factors in occurrence of infertility in cancer patients. Our information can be used as a source for the design of genetic database of male-infertility.

Human-specific epigenomic states in spermatogenesis

Infertility is becoming increasingly common, affecting one in six people globally. Half of these cases can be attributed to male factors, many driven by abnormalities in the process of sperm development. Emerging evidence from genome-wide association studies, genetic screening of patient cohorts, and animal models highlights an important genetic contribution to spermatogenic defects, but comprehensive identification and characterization of the genes critical for male fertility remain lacking. High divergence of gene regulation in spermatogenic cells across species poses challenges for delineating the genetic pathways required for human spermatogenesis using common model organisms. In this study, we leveraged post-translational histone modification and gene transcription data for 15,491 genes in four mammalian species (human, rhesus macaque, mouse, and opossum), to identify human-specific patterns of gene regulation during spermatogenesis. We combined H3K27me3 ChIP-seq, H3K4me3 ChIP-seq, and RNA-seq data to define epigenetic states for each gene at two stages of spermatogenesis, pachytene spermatocytes and round spermatids, in each species. We identified 239 genes that are uniquely active, poised, or dynamically regulated in human spermatogenic cells distinct from the other three species. While some of these genes have been implicated in reproductive functions, many more have not yet been associated with human infertility and may be candidates for further molecular and epidemiologic studies. Our analysis offers an example of the opportunities provided by evolutionary and epigenomic data for broadly screening candidate genes implicated in reproduction, which might lead to discoveries of novel genetic targets for diagnosis and management of male infertility and male contraception.

Recent Advances in Artificial Sensory Neurons: Biological Fundamentals, Devices, Applications, and Challenges

Spike-based neural networks, which use spikes or action potentials to represent information, have gained a lot of attention because of their high energy efficiency and low power consumption. To fully leverage its advantages, converting the external analog signals to spikes is an essential prerequisite. Conventional approaches including analog-to-digital converters or ring oscillators, and sensors suffer from high power and area costs. Recent efforts are devoted to constructing artificial sensory neurons based on emerging devices inspired by the biological sensory system. They can simultaneously perform sensing and spike conversion, overcoming the deficiencies of traditional sensory systems. This review summarizes and benchmarks the recent progress of artificial sensory neurons. It starts with the presentation of various mechanisms of biological signal transduction, followed by the systematic introduction of the emerging devices employed for artificial sensory neurons. Furthermore, the implementations with different perceptual capabilities are briefly outlined and the key metrics and potential applications are also provided. Finally, we highlight the challenges and perspectives for the future development of artificial sensory neurons.

Receptors Involved in COVID-19-Related Anosmia: An Update on the Pathophysiology and the Mechanistic Aspects

Olfactory perception is an important physiological function for human well-being and health. Loss of olfaction, or anosmia, caused by viral infections such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has received considerable attention, especially in persistent cases that take a long time to recover. This review discusses the integration of different components of the olfactory epithelium to serve as a structural and functional unit and explores how they are affected during viral infections, leading to the development of olfactory dysfunction. The review mainly focused on the role of receptors mediating the disruption of olfactory signal transduction pathways such as angiotensin converting enzyme 2 (ACE2), transmembrane protease serine type 2 (TMPRSS2), neuropilin 1 (NRP1), basigin (CD147), olfactory, transient receptor potential vanilloid 1 (TRPV1), purinergic, and interferon gamma receptors. Furthermore, the compromised function of the epithelial sodium channel (ENaC) induced by SARS-CoV-2 infection and its contribution to olfactory dysfunction are also discussed. Collectively, this review provides fundamental information about the many types of receptors that may modulate olfaction and participate in olfactory dysfunction. It will help to understand the underlying pathophysiology of virus-induced anosmia, which may help in finding and designing effective therapies targeting molecules involved in viral invasion and olfaction. To the best of our knowledge, this is the only review that covered all the receptors potentially involved in, or mediating, the disruption of olfactory signal transduction pathways during COVID-19 infection. This wide and complex spectrum of receptors that mediates the pathophysiology of olfactory dysfunction reflects the many ways in which anosmia can be therapeutically managed.

The Olfactory Receptor Olfr25 Mediates Sperm Dysfunction Induced by Low-Dose Bisphenol A through the CatSper-Ca2+ Signaling Pathway

Bisphenol A (BPA), a typical endocrine disruptor, is known to have various adverse effects on the male reproductive system. However, the toxic effects and mechanisms of low-dose BPA have not yet been fully explored. In this study, male Kunming mice were orally administered low-dose BPA (0.03, 0.3 and 3 mg/kg/d) for ten consecutive weeks. Pathological sections of testicular tissue showed no significant morphological differences after BPA exposure. An analysis of the functional parameters of sperm revealed that exposure to low-dose BPA significantly decreased sperm motility, chemotaxis, and the acrosome reaction. An in vitro BPA exposure model combined with an omics data analysis showed that the olfactory receptor-related pathway was significantly enriched after BPA treatment. Subsequent experiments verified the reduced mRNA level of a novel olfactory receptor gene, Olfr25, in vivo and in vitro exposure models. Meanwhile, exposure to low-dose BPA reduced the intracellular calcium ion concentration and the mRNA levels of pore-forming subunits of the CatSper channel in sperm. Importantly, the knockdown of Olfr25 inhibited calcium ion levels and CatSper subunit expression in GC-2 cells. Olfr25 overexpression attenuated the BPA-induced downregulation of CatSper subunit expression in GC-2 cells. These findings indicate that Olfr25 might participate in low-dose BPA-induced sperm dysfunction by affecting the CatSper-Ca2+ signaling pathway. This study reveals a new mechanism underlying the effects of low-dose BPA on sperm function and provides a reference for assessing the safety of low-dose BPA exposure.

Orco-dependent survival of odorant receptor neurons in ants

Olfaction is essential for complex social behavior in insects. To discriminate complex social cues, ants evolved an expanded number of odorant receptor (Or) genes. Mutations in the obligate odorant co-receptor gene orco lead to the loss of ~80% of the antennal lobe glomeruli in the jumping ant Harpegnathos saltator. However, the cellular mechanism remains unclear. Here, we demonstrate massive apoptosis of odorant receptor neurons (ORNs) in the mid to late stages of pupal development, possibly due to ER stress in the absence of Orco. Further bulk and single-nucleus transcriptome analysis shows that, although most orco-expressing ORNs die in orco mutants, a small proportion of them survive: They express ionotropic receptor (Ir) genes that form IR complexes. In addition, we found that some Or genes are expressed in mechanosensory neurons and nonneuronal cells, possibly due to leaky regulation from nearby non-Or genes. Our findings provide a comprehensive overview of ORN development and Or expression in H. saltator.

A family of olfactory receptors uniquely expanded in marsupial and monotreme genomes are expressed by a T cell subset also unique to marsupials and monotremes

Olfactory receptors (OR), expressed on olfactory neurons, mediate the sense of smell. Recently, OR have also been shown to be expressed in non-olfactory tissues, including cells of the immune system. An analysis of single-cell transcriptomes of splenocytes of the grey short-tailed opossum (Monodelphis domestica) found OR are expressed on a subset of T cells, the γμ T cells, that are unique to marsupials and monotremes. A majority of opossum γμ T cells transcriptomes contain OR family 14 transcripts, specifically, from the OR14C subfamily. Amongst the mammals, the OR14 gene family is expanded in the genomes of marsupials and monotremes, and rarer or absent in placental mammals. In summary, here we demonstrate the intriguing correlation that a family of OR genes, abundant in the genomes of marsupials and monotremes, are ectopically expressed in a particular subset of T cells unique to the marsupials and monotremes.

The Olfactory Trail of Neurodegenerative Diseases

Alterations in olfactory functions are proposed as possible early biomarkers of neurodegenerative diseases. Parkinson's and Alzheimer's diseases manifest olfactory dysfunction as a symptom, which is worth mentioning. The alterations do not occur in all patients, but they can serve to rule out neurodegenerative pathologies that are not associated with small deficits. Several prevalent neurodegenerative conditions, including impaired smell, arise in the early stages of Parkinson's and Alzheimer's diseases, presenting an attractive prospect as a snitch for early diagnosis. This review covers the current knowledge on the link between olfactory deficits and Parkinson's and Alzheimer's diseases. The review also covers the emergence of olfactory receptors as actors in the pathophysiology of these diseases. Olfactory receptors are not exclusively expressed in olfactory sensory neurons. Olfactory receptors are widespread in the human body; they are expressed, among others, in the testicles, lungs, intestines, kidneys, skin, heart, and blood cells. Although information on these ectopically expressed olfactory receptors is limited, they appear to be involved in cell recognition, migration, proliferation, wound healing, apoptosis, and exocytosis. Regarding expression in non-chemosensory regions of the central nervous system (CNS), future research should address the role, in both the glia and neurons, of olfactory receptors. Here, we review the limited but relevant information on the altered expression of olfactory receptor genes in Parkinson's and Alzheimer's diseases. By unraveling how olfactory receptor activation is involved in neurodegeneration and identifying links between olfactory structures and neuronal death, valuable information could be gained for early diagnosis and intervention strategies in neurodegenerative diseases.

Comparative genomic analysis of chemosensory-related gene families in gastropods

Chemoreception is critical for the survival and reproduction of animals. Except for a reduced group of insects and chelicerates, the molecular identity of chemosensory proteins is poorly understood in invertebrates. Gastropoda is the extant mollusk class with the greatest species richness, including marine, freshwater, and terrestrial lineages, and likely, highly diverse chemoreception systems. Here, we performed a comprehensive comparative genome analysis taking advantage of the chromosome-level information of two Gastropoda species, one of which belongs to a lineage that underwent a whole genome duplication event. We identified thousands of previously uncharacterized chemosensory-related genes, the majority of them encoding G protein-coupled receptors (GPCR), mostly organized into clusters distributed across all chromosomes. We also detected gene families encoding degenerin epithelial sodium channels (DEG-ENaC), ionotropic receptors (IR), sensory neuron membrane proteins (SNMP), Niemann-Pick type C2 (NPC2) proteins, and lipocalins, although with a lower number of members. Our phylogenetic analysis of the GPCR gene family across protostomes revealed: (i) remarkable gene family expansions in Gastropoda; (ii) clades including members from all protostomes; and (iii) species-specific clades with a substantial number of receptors. For the first time, we provide new and valuable knowledge into the evolution of the chemosensory gene families in invertebrates other than arthropods.

Global research Activity on olfactory marker protein (OMP): A bibliometric and visualized analysis

Olfactory marker protein (OMP) is extensively studied in mature olfactory receptor neurons (ORNs) for understanding olfaction physiology. However, no bibliometric analysis on this topic exists. We conducted a bibliometric analysis of OMP research articles, wherein the publication count was assessed by year, country, journal, and author, collaboration by country, and productivity of the authors. Additionally, key terms and research themes were identified. Using the search phrase "olfactory marker protein" in Scopus, we retrieved 691 original research articles by 2487 authors since 1974. Publications showed an increasing trend, with the United States leading in quantity and collaboration. Our thematic map highlights "Olfactory bulb, regeneration, olfactory" as the primary research domain, while "olfaction, olfactory sensory neuron, glomerulus" and "olfactory receptor neurons, apoptosis, olfactory dysfunction" emerge as essential future research topics. These bibliometric findings offer insights into the global OMP research landscape, guiding researchers in potential collaborations and intriguing future research fields.

Taste shaped the use of botanical drugs

The perception of taste and flavour (a combination of taste, smell, and chemesthesis), here also referred to as chemosensation, enables animals to find high-value foods and avoid toxins. Humans have learned to use unpalatable and toxic substances as medicines, yet the importance of chemosensation in this process is poorly understood. Here, we generate tasting-panel data for botanical drugs and apply phylogenetic generalised linear mixed models to test whether intensity and complexity of chemosensory qualities as well as particular tastes and flavours can predict ancient Graeco-Roman drug use. We found chemosensation to be strongly predictive of therapeutic use: botanical drugs with high therapeutic versatility have simple yet intense tastes and flavours, and 21 of 22 chemosensory qualities predicted at least one therapeutic use. In addition to the common notion of bitter tasting medicines, we also found starchy, musky, sweet, and soapy drugs associated with versatility. In ancient Greece and Rome, illness was thought to arise from imbalance in bodily fluids or humours, yet our study suggests that uses of drugs were based on observed physiological effects that are often consistent with modern understanding of chemesthesis and taste receptor pharmacology.

The Role of the Olfactory System in Obesity and Metabolism in Humans: A Systematic Review and Meta-Analysis

Obesity, linked to chronic diseases, poses a global health challenge. While the role of the olfactory system in energy homeostasis is well-documented in rodents, its role in metabolism regulation and obesity in humans remains understudied. This review examines the interplay between olfactory function and metabolic alterations in human obesity and the effects of bariatric surgery on olfactory capabilities in humans. Adhering to PRISMA guidelines, a systematic review and meta-analysis was conducted, focusing exclusively on original human studies. From 51 articles, 14 were selected for the meta-analysis. It was found that variations in olfactory receptor genes influence the susceptibility to odors and predisposition to weight gain and poor eating habits. Bariatric surgery, particularly sleeve gastrectomy, shows significant improvements in olfactory function (SMD 2.37, 95% CI [0.96, 3.77], I = 92%, p = 0.001), especially regarding the olfactory threshold (SMD -1.65, 95% CI [-3.03, -0.27], I = 81%, p = 0.02). There is a bidirectional relationship between olfactory function and metabolism in humans. Bariatric surgery improves olfactory perception in obese patients, but it is still unclear if impacting the olfactory system directly affects eating behavior and the energy balance. However, these findings open novel avenues for future studies addressing the olfactory system as a novel target to alter systemic metabolism in humans.

Exploring the Potential of Olfactory Receptor Circulating RNA Measurement for Preeclampsia Prediction and Its Linkage to Mild Gestational Hypothyroidism

Gestational hypothyroidism may lead to preeclampsia development. However, this pathophysiological is unknown. We expect to find a shared mechanism by comparing hypothyroidism and preeclampsia. From our transcriptome data, we recognized olfactory receptors as that fingerprint. The reduction of taste and smell in hypothyroid patients has been known for a long time. Therefore, we decided to look to the olfactory receptors and aimed to identify genes capable of predicting preeclampsia (PEC). Methods: An Ion Proton Sequencer (Thermo Fisher Scientific, Waltham, MA, USA) was used to construct the transcriptome databases. RStudio with packages Limma v.3.50.0, GEOquery v.2.62.2, and umap v.0.2.8.8 were used to analyze the differentially expressed genes in GSE149440 from the Gene Expression Omnibus (GEO). The 7500 Real-Time PCR System (Applied Biosystems, Foster City, CA, USA) was used for RT-qPCR amplification of OR6X1 and OR4E2. Results: Our transcriptomic datasets analysis revealed 25.08% and 26.75% downregulated olfactory receptor (ORs) in mild nontreated gestational hypothyroidism (GHT) and PEC, respectively. In the GSE149440 GEO dataset, we found OR5H1, OR5T3, OR51A7, OR51B6, OR10J5, OR6C6, and OR2AG2 as predictors of early-onset PEC. We also evaluate two chosen biomarkers' responses to levothyroxine. The RT-qPCR demonstrated a difference in OR6X1 and OR4E2 expression between GHT and healthy pregnancy (p < 0.05). Those genes presented a negative correlation with TSH (r: -0.51, p < 0.05; and r: -0.44, p < 0.05), a strong positive correlation with each other (r: 0.89; p < 0.01) and the levothyroxine-treated group had no difference from the healthy one. We conclude that ORs could be used as biomarkers at the beginning of gestation, and the downregulated ORs found in GHT may be improved with levothyroxine treatment.

Developing human olfactory network and exploring olfactory receptor-odorant interaction

The Olfactory receptor (OR)-odorant interactions are perplexed. ORs can bind to structurally diverse odorants associated with one or more odor percepts. Various attempts have been made to understand the intricacies of OR-odorant interaction. In this study, experimentally documented OR-odorant interactions are investigated comprehensively to; (a) suggest potential odor percepts for ORs based on the OR-OR network; (b) determine how odorants interacting with specific ORs differ in terms of inherent pharmacophoric features and molecular properties, (c) identify molecular interactions that explained OR-odorant interactions of selective ORs; and (d) predict the probable role of ORs other than olfaction. Human olfactory receptor network (hORnet) is developed to study possible odor percepts for ORs. We identified six molecular properties which showed variation and significant patterns to differentiate odorants binding with five ORs. The pharmacophore analysis revealed that odorants subset of five ORs follow similar pharmacophore hypothesis, (one hydrogen acceptor and two hydrophobic regions) but differ in terms of distance and orientation of pharmacophoric features. To ascertain the binding site residues and key interactions between the selected ORs and their interacting odorants, 3D-structure modelling, docking and molecular dynamics studies were carried out. Lastly, the potential role of ORs beyond olfaction is explored. A human OR-OR network was developed to suggest possible odor percepts for ORs using empirically proven OR-odorant interactions. We sought to find out significant characteristics, molecular properties, and molecular interactions that could explain OR-odorant interactions and add to the understanding of the complex issue of odor perception.Communicated by Ramaswamy H. Sarma.

Olfactory marker protein regulates adipogenesis via the cAMP-IκBα pathway

Olfactory marker protein (OMP) regulates olfactory transduction and is also expressed in adipose tissue. Since it serves as a regulatory buffer for cyclic AMP (cAMP) levels, we hypothesized that it plays a role in modulating adipocyte differentiation. To determine the role of OMP in adipogenesis, we examined the differences in body weight, adipose tissue mass, and adipogenic or thermogenic gene expression between high-fat diet-fed control and Omp-knockout (KO) mice. cAMP production, adipogenic gene expression, and cAMP response element binding protein (CREB) phosphorylation were measured during the differentiation of 3T3-L1 preadipocytes and mouse embryonic fibroblasts (MEFs). RNA sequencing was performed to determine the gene expression patterns responsible for the reduction in adipogenesis when Omp was deleted. Body weight, adipose tissue mass, and adipocyte size decreased in Omp-KO mice. Furthermore, cAMP production and CREB phosphorylation reduced during adipogenesis induced in Omp-/- MEFs, and the Nuclear factor kappa B was activated due to significantly reduced expression of its inhibitor. Collectively, our results suggest that loss of OMP function inhibits adipogenesis by affecting adipocyte differentiation.

Exploring olfactory receptor family 7 subfamily C member 1 as a novel oral cancer stem cell target for immunotherapy

The mortality rate of oral cancer has not improved over the past three decades despite remarkable advances in cancer therapies. Oral cancers contain a subpopulation of cancer stem cells (CSCs) that share characteristics associated with normal stem cells, including self-renewal and multi-differentiation potential. CSCs are tumorigenic, play a critical role in cancer infiltration, recurrence, and distant metastasis, and significantly contribute to drug resistance to current therapeutic strategies, including immunotherapy. Cytotoxic CD8+ T lymphocytes (CTLs) are key immune cells that effectively recognize peptide antigens presented by the major histocompatibility complex class I molecules. Increasing evidence suggests that cancer antigen-specific targeting by CTLs effectively regulates CSCs that drive cancer progression. In this study, we utilized data from public domains and performed various bioassays on human oral squamous cell carcinoma clinical samples and cell lines, including HSC-2 and HSC-3, to investigate the potential role of olfactory receptor family 7 subfamily C member 1 (OR7C1), a seven transmembrane G-protein-coupled olfactory receptor that is also expressed in nonolfactory tissues and was previously reported as a novel marker and target of colon cancer initiating cell-targeted immunotherapy, in CSC-targeted treatment against oral cancer. We found that the OR7C1 gene was expressed only in oral CSCs, and that CTLs reacted with human leukocyte antigen-A24-restricted OR7C1 oral CSC-specific peptides. Taken together, our findings suggest that OR7C1 represents a novel target for potent CSC-targeted immunotherapy in oral cancer.

Anaplastic Kaposi Sarcoma: A Clinicopathologic and Molecular Genetic Analysis

Kaposi sarcoma (KS) is a human herpesvirus 8 (HHV8)-associated vascular proliferation that most often involves the skin. Rarely, KS shows marked nuclear atypia or pleomorphism; such examples are known as "anaplastic" KS. This poorly characterized variant often pursues an aggressive course; little is known of its genetic landscape. This study evaluated the clinicopathologic and genomic features of anaplastic KS. We identified 9 anaplastic KS cases from 7 patients and 8 conventional KS cases, including a matched conventional KS and primary metastasis anaplastic KS pair from a single patient (anaplastic KS diagnosed 9 years after conventional KS). All patients with anaplastic KS were men, aged 51 to 82 years, who had locally aggressive tumors predominantly affecting the soft tissue and bone of the lower extremities (5/7 patients). Four patients were known to be HIV positive (all on antiretrovirals), 2 were HIV negative, and 1 was of unknown HIV status. The tumors showed angiosarcoma-like or pleomorphic spindle cell sarcoma morphology. Plasma cell-rich chronic inflammation and hemosiderin deposition were commonly present. Single-nucleotide polymorphism-based chromosomal microarray analysis showed the anaplastic KS cohort to demonstrate highly recurrent whole chromosome (chr) gains of chr 7, 11, 19, and 21, which primarily affected olfactory and G protein-coupled receptor signaling and losses of chr6_q and chrY. Compared with conventional KS, anaplastic KS cases showed significantly more total copy number alterations and more frequent gains of chr7 and chr11_q13.1 (MARK2, RELA, and ESRRA, including high copy number gain in 1 case). Pathway analysis demonstrated that these gains preferentially affected genes that facilitate cyclin-dependent cell signaling. Furthermore, anaplastic KS cases were phylogenetically distinct from conventional KS cases, including the patient-matched primary metastasis anaplastic KS pair and conventional KS. Our study is the first to demonstrate that a more complex genome and distinct copy number alterations distinguish anaplastic KS from conventional KS. Gains of chr7 and chr11_q13.1 appear central to biological transformation.

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

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

Distinct sets of olfactory receptors highly expressed in different human tissues evaluated by meta-transcriptome analysis: Association of OR10A6 in skin with keratinization

Olfactory receptors (ORs) are expressed in many tissues and have multiple functions. However, most studies have focused on individual ORs. Here, we aimed to conduct a comprehensive meta-transcriptome analysis of OR gene expression in human tissues by using open-source tools to search a large, publicly available genotype-tissue expression (GTEx) data set. Analysis of RNA-seq data from GTEx revealed that OR expression patterns were tissue-dependent, and we identified distinct sets of ORs that were highly expressed in 12 tissues, involving 97 ORs in total. Among them, OR5P2, OR5P3 and OR10A6 were associated with skin. We further examined the roles of these ORs in skin by performing weighted gene correlation network analysis (WGCNA) and c3net analysis. WGCNA suggested that the three ORs are involved in epidermal differentiation and water-impermeable barrier homeostasis, and OR10A6 showed the largest gene sub-network in the c3net network. Immunocytochemical examination of human skin keratinocytes revealed a sparse expression pattern of OR10A6, suggesting that it is not uniformly distributed among all keratinocytes. An OR10A6 agonist, 3-phenylpropyl propionate (3PPP), transiently increased intracellular Ca²⁺ concentration and increased cornified envelope (CE) production in cultured keratinocytes. Knock-down of OR10A6 diminished the effect of 3PPP. Overall, integration of meta-transcriptome analysis and functional analysis uncovered distinct expression patterns of ORs in various human tissues, providing basic data for future studies of the biological functions of highly expressed ORs in individual tissues. Our results further suggest that expression of OR10A6 in skin is related to epidermal differentiation, and OR10A6 may be a potential target for modulation of keratinization.

Modeling of Olfactory Receptors

Olfactory receptors (ORs) form the largest subfamily within class A G protein-coupled receptors (GPCRs). No experimental structural data of any OR is available to date. Homology modeling has become a popular strategy to propose plausible OR models, in order to study the structure-function relationships of the receptors and to aid the discovery and development of ligands capable of modulating receptor activity. In this chapter, we provide a general guideline for OR structure construction, including the collection of candidate templates, structure-based sequence alignment, 3D structure construction, ligand docking, and molecular dynamic simulation.

Short-Chain Fatty Acids Modulate Sperm Migration through Olfactory Receptor 51E2 Activity

The non-orthotopic expression of olfactory receptors (ORs) includes the male reproductive system, and in particular spermatozoa; their active ligands could be essential to sperm chemotaxis and chemical sperm-oocyte communication. OR51E2 expression has been previously reported on sperm cells' surface. It has been demonstrated in different cellular models that olfactory receptor 51E2 (OR51E2) binds volatile short-chain fatty acids (SCFAs) as specific ligands. In the present research, we make use of Western blot, confocal microscopy colocalization analysis, and the calcium-release assay to demonstrate the activation of sperm cells through OR51E2 upon SCFAs stimulus. Moreover, we perform a novel modified swim-up assay to study the involvement of OR51E2/SCFAs in sperm migration. Taking advantage of computer-assisted sperm analysis (CASA system), we determine the kinematics parameters of sperm cells migrating towards SCFAs-enriched medium, revealing that these ligands are able to promote a more linear sperm-cell orientation. Finally, we obtain SCFAs by mass spectrometry in cervico-vaginal mucus and show for the first time that a direct incubation between cervical mucus and sperm cells could promote their activation. This study can shed light on the possible function of chemosensory receptors in successful reproduction activity, laying the foundation for the development of new strategies for the treatment of infertile individuals.

Mutagenesis of the odorant receptor co-receptor (Orco) reveals severe olfactory defects in the crop pest moth Helicoverpa armigera

BACKGROUND

Odorant receptors (ORs) as odorant-gated ion channels play a crucial role in insect olfaction. They are formed by a heteromultimeric complex of the odorant receptor co-receptor (Orco) and a ligand-selective Or. Other types of olfactory receptor proteins, such as ionotropic receptors (IRs) and some gustatory receptors (GRs), are also involved in the olfactory system of insects. Orco as an obligatory subunit of ORs is highly conserved, providing an opportunity to systematically evaluate OR-dependent olfactory responses.

RESULTS

Herein, we successfully established a homozygous mutant (Orco^-/-) of Helicoverpa armigera, a notorious crop pest, using the CRISPR/Cas9 gene editing technique. We then compared the olfactory response characteristics of wild type (WT) and Orco^-/- adults and larvae. Orco^-/- males were infertile, while Orco^-/- females were fertile. The lifespan of Orco^-/- females was longer than that of WT females. The expressions of most Ors, Irs, and other olfaction-related genes in adult antennae of Orco^-/- moths were not obviously affected, but some of them were up- or down-regulated. In addition, there was no change in the neuroanatomical phenotype of Orco^-/- moths at the level of the antennal lobe (including the macroglomerular complex region of the male). Using EAG and SSR techniques, we discovered that electrophysiological responses of Orco^-/- moths to sex pheromone components and many host plant odorants were absent. The upwind flight behaviors toward sex pheromones of Orco^-/- males were severely reduced in a wind tunnel experiment. The oviposition selectivity of Orco^-/- females to the host plant (green pepper) has completely disappeared, and the chemotaxis toward green pepper was also lost in Orco^-/- larvae.

CONCLUSIONS

Our study indicates that OR-mediated olfaction is essential for pheromone communication, oviposition selection, and larval chemotaxis of H. armigera, suggesting a strategy in which mate searching and host-seeking behaviors of moth pests could be disrupted by inhibiting or silencing Orco expression.

Olfactory marker protein regulation of glucagon secretion in hyperglycemia

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

Extracellular loop 2 of G protein-coupled olfactory receptors is critical for odorant recognition

G protein–coupled olfactory receptors (ORs) enable us to detect innumerous odorants. They are also ectopically expressed in nonolfactory tissues and emerging as attractive drug targets. ORs can be promiscuous or highly specific, which is part of a larger mechanism for odor discrimination. Here, we demonstrate that the OR extracellular loop 2 (ECL2) plays critical roles in OR promiscuity and specificity. Using site-directed mutagenesis and molecular modeling, we constructed 3D OR models in which ECL2 forms a lid over the orthosteric pocket. We demonstrate using molecular dynamics simulations that ECL2 controls the shape and volume of the odorant-binding pocket, maintains the pocket hydrophobicity, and acts as a gatekeeper of odorant binding. Therefore, we propose the interplay between the specific orthosteric pocket and the variable, less specific ECL2 controls OR specificity and promiscuity. Furthermore, the 3D models created here enabled virtual screening of new OR agonists and antagonists, which exhibited a 70% hit rate in cell assays. Our approach can potentially be generalized to structure-based ligand screening for other G protein–coupled receptors that lack high-resolution 3D structures.

Impact of in Utero Rat Exposure to 17Alpha-Ethinylestradiol or Genistein on Testicular Development and Germ Cell Gene Expression

Although the decline in male fertility is believed to partially result from environmental exposures to xenoestrogens during critical developmental windows, the underlying mechanisms are still poorly understood. Experimental in utero exposures in rodents have demonstrated the negative impact of xenoestrogens on reproductive development, long-term adult reproductive function and offspring health. In addition, transcriptomic studies have demonstrated immediate effects on gene expression in fetal reproductive tissues, However, the immediate molecular effects on the developing germ cells have been poorly investigated. Here, we took advantage of a transgenic rat expressing the green fluorescent protein specifically in germ cells allowing purification of perinatal GFP-positive germ cells. Timed-pregnant rats were exposed to ethinylestradiol (EE2, 2 μg/kg/d), genistein (GE, 10 mg/kg/d) or vehicle by gavage, from gestational days (GD) 13–19; testes were sampled at GD20 or post-natal (PND) 5 for histological analysis and sorting of GFP-positive cells. While EE2-exposed females gained less weight during treatment compared to controls, neither treatment affected the number of pups per litter, sex ratio, anogenital distance, or body and gonadal weights of the offspring. Although GE significantly decreased circulating testosterone at GD20, no change was observed in either testicular histology or germ cell and sertoli cell densities. Gene expression was assessed in GFP-positive cells using Affymetrix Rat Gene 2.0 ST microarrays. Analysis of differentially expressed genes (DEGs) (p < 0.05; fold change 1.5) identified expression changes of 149 and 128 transcripts by EE2 and GE respectively at GD20, and 287 and 207 transcripts at PND5, revealing an increased effect after the end of treatment. Only about 1% of DEGs were common to both stages for each treatment. Functional analysis of coding DEG revealed an overrepresentation of olfactory transduction in all groups. In parallel, many non-coding RNAs were affected by both treatments, the most represented being small nucleolar and small nuclear RNAs. Our data suggest that despite no immediate toxic effects, fetal exposure to xenoestrogens can induce subtle immediate changes in germ cell gene expression. Moreover, the increased number of DEGs between GD20 and PND5 suggests an effect of early exposures with latent impact on later germ cell differentiation.

In Vivo Bioelectronic Nose Based on a Bioengineered Rat Realizes the Detection and Classification of Multiodorants

Inspired by the powerful capability of the biological olfactory system, we developed an in vivo bioelectronic nose based on a bioengineered rat by recording electrophysiological-responsive signals from the olfactory bulb with implanted multichannel microelectrodes. The bioengineered rat was prepared by overexpressing a selected olfactory receptor (OR3) on the rat olfactory epithelium, and multichannel electrophysiological signals were obtained from the mitral/tufted (M/T) cell population of the olfactory bulb. The classification of target multiodorants was realized by analyzing the redundant stimuli-responsive firing information. Ligand odorants induced significant firing changes with specific response patterns compared with nonligand odorants. The responsive curves were dependent on the concentration of target ligand odorants ranging from 10^-6 to 10^-3 M, and the detection limit was as low as 10^-5 M. In addition, different ligand odorants were successfully discriminated via principal component analysis. This in vivo bioelectronic nose provides a novel approach for the detection of specific target odorants and has promising application potential in the field of rapid on-site odor discrimination.

Association between olfactory pathway gene variants and obesity in Chinese Han population: A case-control study based on genetic score

BACKGROUND

Our previous bivariate genome-wide association study in dizygotic twins suggested that the olfactory transduction pathway genes were associated with obesity in Northern Han Chinese adults. In this study, we attempted to verify the associations of the olfactory transduction pathway genes score with obesity in population with the same genetic background, and to estimate the interaction between gene variants and potential environment factors.

METHODS

A case-control study was conducted in Qingdao, China in 2019-2021, which enrolled 301 obesity cases and 307 controls. Based on the candidate gene selection method, 29 single nucleotide polymorphisms (SNPs) in 7 olfactory pathway genes were selected. Genomic deoxyribonucleic acid (DNA) was isolated and purified from the peripheral blood leukocytes by using DNA extraction kits and was genotyped by the MassArray system. The weighted genetic score of each gene was calculated to analyze the effect of whole gene. The effect of gene scores on obesity and the gene-environment interaction were estimated by logistic regression.

RESULTS

After adjusting for age, sex, smoking, alcohol drinking, physical activity, we observed positive associations of OR4D1 (OR = 1.531, 95% CI = 1.083-2.164, P = 0.016) and OR52K1 (OR = 1.437, 95% CI = 1.055-1.957, P = 0.022) gene scores with obesity, as well as negative associations of OR2L8 (OR = 0.708, 95% CI = 0.504-0.995, P = 0.046) and CALML3 (OR = 0.601, 95% CI = 0.410-0.881, P = 0.009) gene scores with obesity. Significant multiplicative model interaction between OR4D1 and smoking (P_interaction = 0.041) as well as CALML3 and smoking (P_interaction = 0.026) on obesity were identified. Stratified analysis showed that in smokers, OR4D1 gene score was positively associated with obesity (OR = 2.673, 95% CI = 1.348-5.299, P = 0.005) and CALML3 gene score was negatively correlated with obesity (OR = 0.252, 95% CI = 0.103-0.618, P = 0.003). The relationships were not statistically significant in non-smokers (OR4D1: OR = 1.216, 95% CI = 0.806-1.836, P = 0.351; CALML3: OR = 0.764, 95% CI = 0.492-1.188, P = 0.232).

CONCLUSIONS

Genetic variations in the olfactory pathway were associated with obesity in Northern Han Chinese adults. Smoking modified the effect of OR4D1 and CALML3 gene variants on obesity.

Large-Scale G Protein-Coupled Olfactory Receptor-Ligand Pairing

G protein-coupled receptors (GPCRs) conserve common structural folds and activation mechanisms, yet their ligand spectra and functions are highly diverse. This work investigated how the amino-acid sequences of olfactory receptors (ORs)-the largest GPCR family-encode diversified responses to various ligands. We established a proteochemometric (PCM) model based on OR sequence similarities and ligand physicochemical features to predict OR responses to odorants using supervised machine learning. The PCM model was constructed with the aid of site-directed mutagenesis, in vitro functional assays, and molecular simulations. We found that the ligand selectivity of the ORs is mostly encoded in the residues up to 8 Å around the orthosteric pocket. Subsequent predictions using Random Forest (RF) showed a hit rate of up to 58%, as assessed by in vitro functional assays of 111 ORs and 7 odorants of distinct scaffolds. Sixty-four new OR-odorant pairs were discovered, and 25 ORs were deorphanized here. The best model demonstrated a 56% deorphanization rate. The PCM-RF approach will accelerate OR-odorant mapping and OR deorphanization.

Odorant receptors in cancer

Odorant receptors (ORs), the largest subfamily of G protein-coupled receptors, detect odorants in the nose. In addition, ORs were recently shown to be expressed in many nonolfactory tissues and cells, indicating that these receptors have physiological and pathophysiological roles beyond olfaction. Many ORs are expressed by tumor cells and tissues, suggesting that they may be associated with cancer progression or may be cancer biomarkers. This review describes OR expression in various types of cancer and the association of these receptors with various types of signaling mechanisms. In addition, the clinical relevance and significance of the levels of OR expression were evaluated. Namely, levels of OR expression in cancer were analyzed based on RNA-sequencing data reported in the Cancer Genome Atlas; OR expression patterns were visualized using t-distributed stochastic neighbor embedding (t-SNE); and the associations between patient survival and levels of OR expression were analyzed. These analyses of the relationships between patient survival and expression patterns obtained from an open mRNA database in cancer patients indicate that ORs may be cancer biomarkers and therapeutic targets.

Odorant receptors in cancer

Odorant receptors (ORs), the largest subfamily of G protein-coupled receptors, detect odorants in the nose. In addition, ORs were recently shown to be expressed in many nonolfactory tissues and cells, indicating that these receptors have physiological and pathophysiological roles beyond olfaction. Many ORs are expressed by tumor cells and tissues, suggesting that they may be associated with cancer progression or may be cancer biomarkers. This review describes OR expression in various types of cancer and the association of these receptors with various types of signaling mechanisms. In addition, the clinical relevance and significance of the levels of OR expression were evaluated. Namely, levels of OR expression in cancer were analyzed based on RNA-sequencing data reported in the Cancer Genome Atlas; OR expression patterns were visualized using t-distributed stochastic neighbor embedding (t-SNE); and the associations between patient survival and levels of OR expression were analyzed. These analyses of the relationships between patient survival and expression patterns obtained from an open mRNA database in cancer patients indicate that ORs may be cancer biomarkers and therapeutic targets. [BMB Reports 2022;55(2): 72-80].

Association between Olfactory Receptors and Skin Physiology

Olfactory receptors are chemosensory receptors that detect odorants and function in the initial perception of a smell. Intriguingly, olfactory receptors are also expressed in cells other than olfaction sensory cells, an expression pattern termed ectopic expression. Ectopically expressed olfactory receptors have a distinct role depending on the type of tissues or cells in which they are expressed. This review introduces current research on the ectopic expression and function of olfactory receptors in skin and provides insight into directions for future research.

Odorant G protein-coupled receptors as potential therapeutic targets for adult diffuse gliomas: a systematic analysis and review

Odorant receptors (ORs) account for about 60% of all human G protein-coupled receptors (GPCRs). OR expression outside of the nose has functions distinct from odor perception, and may contribute to the pathogenesis of disorders including brain diseases and cancers. Glioma is the most common adult malignant brain tumor and requires novel therapeutic strategies to improve clinical outcomes. Here, we outlined the expression of brain ORs and investigated OR expression levels in glioma. Although most ORs were not ubiquitously expressed in gliomas, a subset of ORs displayed glioma subtype-specific expression. Moreover, through systematic survival analysis on OR genes, OR51E1 (mouse Olfr558) was identified as a potential biomarker of unfavorable overall survival, and OR2C1 (mouse Olfr15) was identified as a potential biomarker of favorable overall survival in isocitrate dehydrogenase (IDH) wild-type glioma. In addition to transcriptomic analysis, mutational profiles revealed that somatic mutations in OR genes were detected in > 60% of glioma samples. OR5D18 (mouse Olfr1155) was the most frequently mutated OR gene, and OR5AR1 (mouse Olfr1019) showed IDH wild-type-specific mutation. Based on this systematic analysis and review of the genomic and transcriptomic profiles of ORs in glioma, we suggest that ORs are potential biomarkers and therapeutic targets for glioma.

A comprehensive genome-wide scan detects genomic regions related to local adaptation and climate resilience in Mediterranean domestic sheep

Background

The management of farm animal genetic resources and the adaptation of animals to climate change will probably have major effects on the long-term sustainability of the livestock sector. Genomic data harbour useful relevant information that needs to be harnessed for effectively managing genetic resources. In this paper, we report the genome characterization of the highly productive Mediterranean Chios dairy sheep and focus on genetic diversity measures related with local adaptation and selection and the genetic architecture of animal resilience to weather fluctuations as a novel adaptative trait linked to climate change.

Results

We detected runs of homozygosity (ROH) and heterozygosity (ROHet) that revealed multiple highly homozygous and heterozygous hotspots across the Chios sheep genome. A particularly highly homozygous region was identified on chromosome 13 as a candidate of directional genetic selection associated with milk traits, which includes annotated genes that were previously shown to be linked to local adaptation to harsh environmental conditions. Favourable heterozygosity related with a potentially protective role against livestock diseases and enhanced overall fitness was revealed in heterozygous-rich regions on sheep chromosomes 3, 10, 13 and 19. Furthermore, genomic analyses were conducted on sheep resilience phenotypes that display changes in milk production in response to weather variation. Sheep resilience to heat stress was a significantly heritable trait (h² = 0.26) and genetically antagonistic to milk production. Genome-wide association and regional heritability mapping analyses revealed novel genomic markers and regions on chromosome 5 that were significantly associated with sheep resilience to climate change. Subsequently, an annotation analysis detected a set of genes on chromosome 5 that were associated with olfactory receptor complexes that could participate in heat stress mitigation through changes in respiration rate and respiratory evaporation. Other genes were grouped in previously reported biological processes relevant to livestock heat dissipation, including stress and immune response.

Conclusions

Our results may contribute to the optimal management of sheep genetic resources and inform modern selective breeding programmes that aim at mitigating future environmental challenges towards sustainable farming, while better balancing animal adaptation and productivity. Our results are directly relevant to the studied breed and the respective environmental conditions; however, the methodology may be extended to other livestock species of interest.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12711-021-00682-7.

A Genome-Wide Association Study Identifies Novel Risk Loci for Sarcopenia in a Taiwanese Population

Purpose

A genome-wide association study (GWAS) of sarcopenia unraveled the importance of genetic contribution to decline in muscle. The current study investigated sarcopenia-related single nucleotide polymorphisms (SNPs) in Asian older adults, and further constructed a genotype score that tests the combined effect of these SNPs on risk of sarcopenia.

Patients and Methods

Ninety-six subjects aged 60 or above were recruited from the database of annual geriatric health examination at Tri-Service General Hospital during 2020. Eligible criteria included: 1) not having severe comorbidities; 2) agreed to join the Taiwan Precision Medicine Initiative project; and 3) having sufficient information of required sarcopenic measurements. Genotype–phenotype association analysis was performed to find SNPs that were significantly associated with each of three sarcopenic indices (low muscle mass, muscle strength, and physical performance). Subsequently, these SNPs comprised a sarcopenia-related genotype score that summed up the number of SNPs carrying unfavorable allele(s).

Results

Twelve SNPs revealed suggestive genome-wide significance with the three sarcopenic indices, and eight of them revealed a relationship with more than one index. Low muscle strength was the item that had the most (eight) related SNPs. Among them, rs10282247 affects cholesterol binding and rs7022373 participates in cellular apoptosis. In addition, higher genotype score demonstrated higher risk of sarcopenia (≥4 points: OR=630.6; 2–3 points: OR=408, p-value<0.001).

Conclusion

Several newly discovered SNPs suggest that genetic contribution plays a part in the pathogenesis of sarcopenia. Further studies are warranted to verify the underlying mechanisms. Moreover, a genotype score provides an estimate of the combined effect of genetic association with sarcopenia, which may modestly improve clinical risk classification.

The role of sensory and olfactory pathways in multiple chemical sensitivity

Multiple chemical sensitivity (MCS) is characterised by non-specific and recurring symptoms affecting multiple organs and associated with exposure to chemicals, even at low concentrations, which are, under normal circumstances, harmless to the general population. Symptoms include general discomfort, cardiovascular instability, irritation of the sensory organs, breath disorders, hypersensitivity affecting the skin and epithelial lining of the gut, throat and lungs, anxiety, and learning and memory loss. Chemical intolerance is a key distinguishing feature of MCS, limiting considerably patients' lifestyle with serious social, occupational and economic implications. Since no specific diagnostic markers are currently available for chemical intolerance, the diagnosis relies on clinical symptoms. Despite the formulation of several hypotheses regarding the pathophysiology of MCS, its mechanisms remain undefined. A person-centred care approach, based on multidisciplinary and individualised medical plans, has shown promising results. However, more definite treatment strategies are required. We have reviewed the main experimental studies on MCS pathophysiology, focusing on the brain networks involved, the impact of environmental pollution on the olfactory system and the correlation with other pathologies such as neurodegenerative diseases. Finally, we discuss treatment strategies targeting the olfactory system.

The macrophage odorant receptor Olfr78 mediates the lactate-induced M2 phenotype of tumor-associated macrophages

Expression and function of odorant receptors (ORs), which account for more than 50% of G protein-coupled receptors, are being increasingly reported in nonolfactory sites. However, ORs that can be targeted by drugs to treat diseases remain poorly identified. Tumor-derived lactate plays a crucial role in multiple signaling pathways leading to generation of tumor-associated macrophages (TAMs). In this study, we hypothesized that the macrophage OR Olfr78 functions as a lactate sensor and shapes the macrophage-tumor axis. Using Olfr78 ^+/+ and Olfr78 ^-/- bone marrow-derived macrophages with or without exogenous Olfr78 expression, we demonstrated that Olfr78 sensed tumor-derived lactate, which was the main factor in tumor-conditioned media responsible for generation of protumoral M2-TAMs. Olfr78 functioned together with Gpr132 to mediate lactate-induced generation of protumoral M2-TAMs. In addition, syngeneic Olfr78-deficient mice exhibited reduced tumor progression and metastasis together with an increased anti- versus protumoral immune cell population. We propose that the Olfr78-lactate interaction is a therapeutic target to reduce and prevent tumor progression and metastasis.

Ectopic Odorant Receptor Responding to Flavor Compounds: Versatile Roles in Health and Disease

Prompted by the ground-breaking discovery of the rodent odorant receptor (OR) gene family within the olfactory epithelium nearly 30 years ago, followed by that of OR genes in cells of the mammalian germ line, and potentiated by the identification of ORs throughout the body, our appreciation for ORs as general chemoreceptors responding to odorant compounds in the regulation of physiological or pathophysiological processes continues to expand. Ectopic ORs are now activated by a diversity of flavor compounds and are involved in diverse physiological phenomena varying from adipogenesis to myogenesis to hepatic lipid accumulation to serotonin secretion. In this review, we outline the key biological functions of the ectopic ORs responding to flavor compounds and the underlying molecular mechanisms. We also discuss research opportunities for utilizing ectopic ORs as therapeutic strategies in the treatment of human disease as well as challenges to be overcome in the future. The recognition of the potent function, signaling pathway, and pharmacology of ectopic ORs in diverse tissues and cell types, coupled with the fact that they belong to G protein-coupled receptors, a highly druggable protein family, unequivocally highlight the potential of ectopic ORs responding to flavor compounds, especially food-derived odorant compounds, as a promising therapeutic strategy for various diseases.

PathExt: a general framework for path-based mining of omics-integrated biological networks

MOTIVATION

Transcriptomes are routinely used to prioritize genes underlying specific phenotypes. Current approaches largely focus on differentially expressed genes (DEGs), despite the recognition that phenotypes emerge via a network of interactions between genes and proteins, many of which may not be differentially expressed. Furthermore, many practical applications lack sufficient samples or an appropriate control to robustly identify statistically significant DEGs.

RESULTS

We provide a computational tool-PathExt, which, in contrast to differential genes, identifies differentially active paths when a control is available, and most active paths otherwise, in an omics-integrated biological network. The sub-network comprising such paths, referred to as the TopNet, captures the most relevant genes and processes underlying the specific biological context. The TopNet forms a well-connected graph, reflecting the tight orchestration in biological systems. Two key advantages of PathExt are (i) it can extract characteristic genes and pathways even when only a single sample is available, and (ii) it can be used to study a system even in the absence of an appropriate control. We demonstrate the utility of PathExt via two diverse sets of case studies, to characterize (i) Mycobacterium tuberculosis response upon exposure to 18 antibacterial drugs where only one transcriptomic sample is available for each exposure; and (ii) tissue-relevant genes and processes using transcriptomic data for 39 human tissues. Overall, PathExt is a general tool for prioritizing context-relevant genes in any omics-integrated biological network for any condition(s) of interest, even with a single sample or in the absence of appropriate controls.

AVAILABILITYAND IMPLEMENTATION

The source code for PathExt is available at https://github.com/NarmadaSambaturu/PathExt.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Ectopically expressed olfactory receptors OR51E1 and OR51E2 suppress proliferation and promote cell death in a prostate cancer cell line

Olfactory receptors (ORs), the largest family of G protein–coupled receptors, are expressed in the nasal epithelium where they mediate the sense of smell. However, ORs are also found in other non-nasal tissues, but the role of these ectopic ORs in cell signaling, proliferation, and survival is not well understood. Here, using an inducible expression system in the lymph node carcinoma of the prostate (LNCaP) cell line, we investigated two ectopic ORs, OR51E1 and OR51E2, which have been shown to be upregulated in prostate cancer. We found that, consistent with previous studies, OR51E1 stimulated adenylyl cyclase in response to treatment by short-chain to medium-chain organic acids (C3–C9) but not by acetate. OR51E2 responded to acetate and propionate but not to the longer chain organic acids. Stimulation of LNCaP cells with butyrate inhibited their growth, and the knockdown of the endogenous OR51E1 negated this cytostatic effect. Most significantly, overexpression of OR51E1 or OR51E2 suppressed LNCaP cell proliferation. Overexpression of another ectopic OR OR2AT4, β2-adrenergic receptor, or treatment of cells with forskolin did not suppress cell proliferation, indicating that a rise in cAMP is not sufficient to induce cytostasis. Overexpression of OR51E1 caused an upregulation of cytostatic and cell death markers including p27, p21, and p53, strongly increased annexin V staining, and stimulated extracellular signal–regulated protein kinases 1 and 2. Overexpression and/or activation of OR51E1 did not affect human embryonic kidney 293 cell proliferation, indicating that cytotoxicity of OR51E1/OR51E2 is specific for LNCaP cells. Together, our results further our understanding of prostate cancer etiology and suggest that ectopic ORs may be useful therapeutic targets.

Expression pattern of olfactory receptor genes in human cumulus cells as an indicator for competent oocyte selection

Odorant or olfactory receptors are mainly localized in the olfactory epithelium for the perception of different odors. Interestingly, many ectopic olfactory receptors with low expression levels have recently been found in nonolfactory tissues to involve in local functions. Therefore, we investigated the probable role of the olfactory signaling pathway in the surrounding microenvironment of oocyte. This study included 22 women in intracytoplasmic sperm injection cycle. The expression of olfactory target molecules in cumulus cells surrounding the growing and mature oocytes was evaluated by Western blotting and real-time polymerase chain reaction. Additionally, integrated bioinformatics analyses were carried out and 6 ectopic olfactory receptors were selected for further evaluation. The initiation of olfactory transduction cascade in cumulus cells of competent oocytes was confirmed by analyzing the expression of adenylyl cyclase type 3 and olfactory market protein. Moreover, the expression pattern of the selected olfactory receptors was evaluated and OR10H2 was selected due to a high level of expression in mature fertile oocytes. We suggested that OR10H2 could be considered as a reliable biomarker for oocyte selection in assisted reproduction technique programs. However, further studies are required to elucidate the role of olfactory transduction cascade in embryo quality and implantation.

The leukocyte non-coding RNA landscape in critically ill patients with sepsis

The extent of non-coding RNA alterations in patients with sepsis and their relationship to clinical characteristics, soluble mediators of the host response to infection, as well as an advocated in vivo model of acute systemic inflammation is unknown. Here we obtained whole blood from 156 patients with sepsis and 82 healthy subjects among whom eight were challenged with lipopolysaccharide in a clinically controlled setting (human endotoxemia). Via next-generation microarray analysis of leukocyte RNA we found that long non-coding RNA and, to a lesser extent, small non-coding RNA were significantly altered in sepsis relative to health. Long non-coding RNA expression, but not small non-coding RNA, was largely recapitulated in human endotoxemia. Integrating RNA profiles and plasma protein levels revealed known as well as previously unobserved pathways, including non-sensory olfactory receptor activity. We provide a benchmark dissection of the blood leukocyte ‘regulome’ that can facilitate prioritization of future functional studies.