Small-chain fatty acid activates astrocytic odorant receptor Olfr920

Interplay of human gastrointestinal microbiota metabolites: Short-chain fatty acids and their correlation with Parkinson's disease

Short-chain fatty acids (SCFAs) are, the metabolic byproducts of intestinal microbiota that, are generated through anaerobic fermentation of undigested dietary fibers. SCFAs play a pivotal role in numerous physiological functions within the human body, including maintaining intestinal mucosal health, modulating immune functions, and regulating energy metabolism. In recent years, extensive research evidence has indicated that SCFAs are significantly involved in the onset and progression of Parkinson disease (PD). However, the precise mechanisms remain elusive. This review comprehensively summarizes the progress in understanding how SCFAs impact PD pathogenesis and the underlying mechanisms. Primarily, we delve into the synthesis, metabolism, and signal transduction of SCFAs within the human body. Subsequently, an analysis of SCFA levels in patients with PD is presented. Furthermore, we expound upon the mechanisms through which SCFAs induce inflammatory responses, oxidative stress, abnormal aggregation of alpha-synuclein, and the intricacies of the gut-brain axis. Finally, we provide a critical analysis and explore the potential therapeutic role of SCFAs as promising targets for treating PD.

VPrimer: A Method of Designing and Updating Primer and Probe With High Variant Coverage for RNA Virus Detection

Fatal infectious diseases caused by RNA viruses, such as COVID-19, have emerged around the world. RT-PCR is widely employed for virus detection, and its accuracy depends on the primers and probes since RT-PCR can detect a virus only when the primers and probes bind to the target gene of the virus. Most of primer design methods are for a single host and so require a great deal of effort to design for RNA virus detection, including homology tests among the host and all the viruses for the host using BLAST-like tools. Furthermore, they do not consider variant sequences, which are very common in viruses. In this study, we describe VPrimer, a method of designing high-quality primer-probe sets for RNA viruses. VPrimer can find primer-probe sets that cover more than 95% of the variants of a target virus but do not cover any sequences of other viruses or the host. With VPrimer, we found 381,698,582 primer-probe sets for 3,104 RNA viruses. Multiplex PCR assays using the top 2 primer-probe sets suggested by VPrimer usually cover 100% of variants. To address the rapid changes in viral genomes, VPrimer finds the best and up-to-date primer-probe sets incrementally against the most recently reported variants.

Short-chain fatty acid: An updated review on signaling, metabolism, and therapeutic effects

Fatty acids are good energy sources (9 kcal per gram) that aerobic tissues can use except for the brain (glucose is an alternative source). Apart from the energy source, fatty acids are necessary for cell signaling, learning-related memory, modulating gene expression, and functioning as cytokine precursors. Short-chain fatty acids (SCFAs) are saturated fatty acids arranged as a straight chain consisting minimum of 6 carbon atoms. SCFAs possess various beneficial effects like improving metabolic function, inhibiting insulin resistance, and ameliorating immune dysfunction. In this review, we discussed the biogenesis, absorption, and transport of SCFA. SCFAs can act as signaling molecules by stimulating G protein-coupled receptors (GPCRs) and suppressing histone deacetylases (HDACs). The role of SCFA on glucose metabolism, fatty acid metabolism, and its effect on the immune system is also reviewed with updated details. SCFA possess anticancer, anti-diabetic, and hepatoprotective effects. Additionally, the association of protective effects of SCFA against brain-related diseases, kidney diseases, cardiovascular damage, and inflammatory bowel diseases were also reviewed. Nanotherapy is a branch of nanotechnology that employs nanoparticles at the nanoscale level to treat various ailments with enhanced drug stability, solubility, and minimal side effects. The SCFA functions as drug carriers, and nanoparticles were also discussed. Still, much research was not focused on this area. SCFA functions in host gene expression through inhibition of HDAC inhibition. However, the study has to be focused on the molecular mechanism of SCFA against various diseases that still need to be investigated.

Mechanisms of Short-Chain Fatty Acids Derived from Gut Microbiota in Alzheimer's Disease

Short-chain fatty acids (SCFAs) are important metabolites derived from the gut microbiota through fermentation of dietary fiber. SCFAs participate a number of physiological and pathological processes in the human body, such as host metabolism, immune regulation, appetite regulation. Recent studies on gut-brain interaction have shown that SCFAs are important mediators of gut-brain interactions and are involved in the occurrence and development of many neurodegenerative diseases, including Alzheimer's disease. This review summarizes the current research on the potential roles and mechanisms of SCFAs in AD. First, we introduce the metabolic distribution, specific receptors and signaling pathways of SCFAs in human body. The concentration levels of SCFAs in AD patient/animal models are then summarized. In addition, we illustrate the effects and mechanisms of SCFAs on the cognitive level, pathological features (Aβ and tau) and neuroinflammation in AD. Finally, we analyze the translational value of SCFAs as potential therapeutic targets for the treatment of AD.

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 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.

Oral-Gut-Brain Axis in Experimental Models of Periodontitis: Associating Gut Dysbiosis With Neurodegenerative Diseases

Periodontitis is considered a non-communicable chronic disease caused by a dysbiotic microbiota, which generates a low-grade systemic inflammation that chronically damages the organism. Several studies have associated periodontitis with other chronic non-communicable diseases, such as cardiovascular or neurodegenerative diseases. Besides, the oral bacteria considered a keystone pathogen, Porphyromonas gingivalis, has been detected in the hippocampus and brain cortex. Likewise, gut microbiota dysbiosis triggers a low-grade systemic inflammation, which also favors the risk for both cardiovascular and neurodegenerative diseases. Recently, the existence of an axis of Oral-Gut communication has been proposed, whose possible involvement in the development of neurodegenerative diseases has not been uncovered yet. The present review aims to compile evidence that the dysbiosis of the oral microbiota triggers changes in the gut microbiota, which creates a higher predisposition for the development of neuroinflammatory or neurodegenerative diseases.The Oral-Gut-Brain axis could be defined based on anatomical communications, where the mouth and the intestine are in constant communication. The oral-brain axis is mainly established from the trigeminal nerve and the gut-brain axis from the vagus nerve. The oral-gut communication is defined from an anatomical relation and the constant swallowing of oral bacteria. The gut-brain communication is more complex and due to bacteria-cells, immune and nervous system interactions. Thus, the gut-brain and oral-brain axis are in a bi-directional relationship. Through the qualitative analysis of the selected papers, we conclude that experimental periodontitis could produce both neurodegenerative pathologies and intestinal dysbiosis, and that periodontitis is likely to induce both conditions simultaneously. The severity of the neurodegenerative disease could depend, at least in part, on the effects of periodontitis in the gut microbiota, which could strengthen the immune response and create an injurious inflammatory and dysbiotic cycle. Thus, dementias would have their onset in dysbiotic phenomena that affect the oral cavity or the intestine. The selected studies allow us to speculate that oral-gut-brain communication exists, and bacteria probably get to the brain via trigeminal and vagus nerves.

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.

The Intestinal Fatty Acid-Enteroendocrine Interplay, Emerging Roles for Olfactory Signaling and Serotonin Conjugates

Intestinal enteroendocrine cells (EECs) respond to fatty acids from dietary and microbial origin by releasing neurotransmitters and hormones with various paracrine and endocrine functions. Much has become known about the underlying signaling mechanisms, including the involvement of G-protein coupled receptors (GPCRs), like free fatty acids receptors (FFARs). This review focusses on two more recently emerging research lines: the roles of odorant receptors (ORs), and those of fatty acid conjugates in gut. Odorant receptors belong to a large family of GPCRs with functional roles that only lately have shown to reach beyond the nasal-oral cavity. In the intestinal tract, ORs are expressed on serotonin (5-HT) and glucagon-like-peptide-1 (GLP-1) producing enterochromaffin and enteroendocrine L cells, respectively. There, they appear to function as chemosensors of microbiologically produced short-, and branched-chain fatty acids. Another mechanism of fatty acid signaling in the intestine occurs via their conjugates. Among them, conjugates of unsaturated long chain fatty acids and acetate with 5-HT, N-acyl serotonins have recently emerged as mediators with immune-modulatory effects. In this review, novel findings in mechanisms and molecular players involved in intestinal fatty acid biology are highlighted and their potential relevance for EEC-mediated signaling to the pancreas, immune system, and brain is discussed.

A pathogen-derived metabolite induces microglial activation via odorant receptors

Microglia (MG), the principal neuroimmune sentinels in the brain, continuously sense changes in their environment and respond to invading pathogens, toxins, and cellular debris, thereby affecting neuroinflammation. Microbial pathogens produce small metabolites that influence neuroinflammation, but the molecular mechanisms that determine whether pathogen-derived small metabolites affect microglial activation of neuroinflammation remain to be elucidated. We hypothesized that odorant receptors (ORs), the largest subfamily of G protein-coupled receptors, are involved in microglial activation by pathogen-derived small metabolites. We found that MG express high levels of two mouse ORs, Olfr110 and Olfr111, which recognize a pathogenic metabolite, 2-pentylfuran, secreted by Streptococcus pneumoniae. These interactions activate MG to engage in chemotaxis, cytokine production, phagocytosis, and reactive oxygen species generation. These effects were mediated through the G_αs -cyclic adenosine monophosphate-protein kinase A-extracellular signal-regulated kinase and G_βγ -phospholipase C-Ca²⁺ pathways. Taken together, our results reveal a novel interplay between the pathogen-derived metabolite and ORs, which has major implications for our understanding of microglial activation by pathogen recognition. DATABASE: Model data are available in the PMDB database under the accession number PM0082389.