Toward manipulating serotonin signaling via the microbiota-gut-brain axis

A 5-HT-mediated urethral defense against urinary tract infections

The urethra is considered a passive conduit for urine. Here, we reveal a surprising multicellular signaling pathway guiding the urethra's dynamic response to an invading pathogen. Using a genetic approach in female mice, we deposited uropathogenic Escherichia coli into the distal urethra to establish a model of ascending urinary tract infection that progresses to the bladder within 4 h. We show that urethral neuroendocrine cells (UNECs), and the serotonin they synthesize, protect the bladder from bacterial colonization. We tested the hypothesis that serotonin initiates urethral contraction to expel ascending bacteria. We identified transient receptor potential cation channel subfamily A member 1, a noncanonical lipopolysaccharide receptor, in human and mouse UNECs and localized the serotonin receptors (HTR) 2B and 3, as well as the calcium-activated chloride channel anoctamin 1 (ANO1) to the pacemaker cells of the human and mouse urethra, the interstitial cells of Cajal (ICCs). HTR2B or ANO1 activation is sufficient for urethral contraction and is required for serotonin-induced mouse urethral contraction. Our results support the hypothesis that the urethra actively surveils its environment and responds to an ascending pathogen by evoking UNECs and ICC to induce urethral contraction and pathogen expulsion.

Toxic effects of deltamethrin on oxidative stress, behavioural, organosomatic indices and histopathological changes in Digitonthophagus gazella (Coleoptera: Scarabaeinae)

Pyrethroids pose a great concern to the declining population of dung beetles and the sustainability of ecosystem services. This study aimed to investigate the toxic effects of deltamethrin on Digitonthophagus gazella. First, the LC50 value (0.275 ppm) was determined, and sub-lethal concentrations (LD; low dose-0.014ppm, MD; medium dose-0.028ppm, and HD; high dose-0.055ppm) were assessed for physiological effects. The findings showed a significant dose and time dependent increase in fluorescence intensity (DCF-DA staining) and a decrease in antioxidant activity, including superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH). Furthermore, significant down regulation of cyp4g7, cyp6bq9, and cyp4q4 expression indicates enhanced oxidative stress. Additionally, a reduction in the organosomatic index, accompanied by histological changes in the brain, gut, and gonads, suggests potential functional disturbances. Overall, deltamethrin exposure had profound and irreversible pathological consequences on various vital organs and systems in D. gazella, affecting reproduction and nesting.

Interaction of the Vagus Nerve and Serotonin in the Gut-Brain Axis

The gut-brain axis represents an important bidirectional communication network, with the vagus nerve acting as a central conduit for peripheral signals from the various gut organs to the central nervous system. Among the molecular mediators involved, serotonin (5-HT), synthesized predominantly by enterochromaffin cells in the gut, plays a pivotal role. Gut-derived serotonin activates vagal afferent fibers, transmitting signals to the nucleus tractus solitarius (NTS) and modulating serotonergic neurons in the dorsal raphe nucleus (DRN) as well as the norepinephrinergic neurons in the locus coeruleus (LC). This interaction influences emotional regulation, stress responses, and immune modulation. Emerging evidence also highlights the role of microbial metabolites, particularly short-chain fatty acids (SCFAs), in enhancing serotonin synthesis and vagal activity, thereby shaping gut-brain communication. This review synthesizes the current knowledge on serotonin signaling, vagal nerve pathways, and central autonomic regulation, with an emphasis on their implications for neuropsychiatric and gastrointestinal disorders. By elucidating these pathways, novel therapeutic strategies targeting the gut-brain axis may be developed to improve mental and physical health outcomes.

Beyond digestion: Exploring how the gut microbiota modulates human social behaviors

For a long time, traditional medicine has acknowledged the gut's impact on general health. Contemporary science substantiates this association through investigations of the gut microbiota, the extensive community of microorganisms inhabiting our gastrointestinal system. These microscopic residents considerably improve digestive processes, nutritional absorption, immunological function, and pathogen defense. Nevertheless, a variety of gastrointestinal and extra-intestinal disorders can result from dysbiosis, an imbalance of the microbial composition of the gut microbiota. A groundbreaking discovery is the gut-brain axis, a complex communication network that links the enteric and central nervous system (CNS). This bidirectional communication allows the brain to influence gut activities and vice versa, impacting mental health and mood disorders like anxiety and depression. The gut microbiota can influence this communication by creating neurotransmitters and short-chain fatty acids, among other biochemical processes. These factors may affect our mental state, our ability to regulate our emotions, and the hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to explore the complex interrelationships between the brain and the gut microbiota. We also conducted a thorough examination of the existing understanding in the area of how microbiota affects social behaviors, including emotions, stress responses, and cognitive functions. We also explored the potential of interventions that focus on the connection between the gut and the brain, such as using probiotics to treat diseases of the CNS. This research opens up new possibilities for addressing mental health and neurological conditions in an innovative manner.

Harnessing Gut Microbiota for Biomimetic Innovations in Health and Biotechnology

The gut microbiota is a complex and dynamic ecosystem that plays a fundamental role in human health by regulating immunity, metabolism, and the gut-brain axis. Beyond its critical physiological functions, it has emerged as a rich source of inspiration for biomimetic innovations in healthcare and biotechnology. This review explores the transformative potential of microbiota-based biomimetics, focusing on key biological mechanisms such as resilience, self-regulation, and quorum sensing. These mechanisms have inspired the development of innovative applications, including personalized probiotics, synbiotics, artificial microbiomes, bioinspired biosensors, and bioremediation systems. Such technologies aim to emulate and optimize the intricate functions of microbial ecosystems, addressing challenges in healthcare and environmental sustainability. The integration of advanced technologies, such as artificial intelligence, bioengineering, and multi-omics approaches, has further accelerated the potential of microbiota biomimetics. These tools enable the development of precision therapies tailored to individual microbiota profiles, enhance the efficacy of diagnostic systems, and facilitate the design of environmentally sustainable solutions, such as waste-to-energy systems and bioremediation platforms. Emerging areas of innovation, including gut-on-chip models and synthetic biology, offer unprecedented opportunities for studying and applying microbiota principles in controlled environments. Despite these advancements, challenges remain. The replication of microbial complexity in artificial environments, ethical concerns regarding genetically engineered microorganisms, and equitable access to advanced therapies are critical hurdles that must be addressed. This review underscores the importance of interdisciplinary collaboration and public awareness in overcoming these barriers and ensuring the responsible development of microbiota-based solutions. By leveraging the principles of microbial ecosystems, microbiota biomimetics represents a promising frontier in healthcare and sustainability. This approach has the potential to revolutionize therapeutic strategies, redefine diagnostic tools, and address global challenges, paving the way for a more personalized, efficient, and sustainable future in medicine and biotechnology.

Multi-omics integration and immune profiling identify possible causal networks leading to uterine microbiome dysbiosis in dairy cows that develop metritis

BACKGROUND

Cows that develop metritis experience dysbiosis of their uterine microbiome, where opportunistic pathogens overtake uterine commensals. An effective immune response is critical for maintaining uterine health. Nonetheless, periparturient cows experience immune dysregulation, which seems to be intensified by prepartum over-condition. Herein, Bayesian networks were applied to investigate the directional correlations between prepartum body weight (BW), BW loss, pre- and postpartum systemic immune profiling and plasma metabolome, and postpartum uterine metabolome and microbiome.

RESULTS

The Bayesian network analysis showed a positive directional correlation between prepartum BW, prepartum BW loss, and plasma fatty acids at parturition, suggesting that heavier cows were in lower energy balance than lighter cows. There was a positive directional correlation between prepartum BW, prepartum systemic leukocyte death, immune activation, systemic inflammation, and metabolomic changes associated with oxidative stress prepartum and at parturition. Immune activation and systemic inflammation were characterized by increased proportion of circulating polymorphonuclear cells (PMN) prepartum, B-cell activation at parturition, interleukin-8 prepartum and at parturition, and interleukin-1β at parturition. These immune changes together with plasma fatty acids at parturition had a positive directional correlation with PMN extravasation postpartum, which had a positive directional correlation with uterine metabolites associated with tissue damage. These results suggest that excessive PMN migration to the uterus leads to excessive endometrial damage. The aforementioned changes had a positive directional correlation with Fusobacterium, Porphyromonas, and Bacteroides in cows that developed metritis, suggesting that excessive tissue damage may disrupt physical barriers or increase substrate availability for bacterial growth.

CONCLUSIONS

This work provides robust mechanistic hypotheses for how prepartum BW may impact peripartum immune and metabolic profiles, which may lead to uterine opportunistic pathogens overgrowth and metritis development.

The Intricate Interplay: Microbial Metabolites and the Gut-Liver-Brain Axis in Parkinson's Disease

Parkinson's Disease (PD) is a neurodegenerative disorder marked by the depletion of dopaminergic neurons. Recent studies highlight the gut-liver-brain (GLB) axis and its role in PD pathogenesis. The GLB axis forms a dynamic network facilitating bidirectional communication between the gastrointestinal tract, liver, and central nervous system. Dysregulation within this axis, encompassing gut dysbiosis and microbial metabolites, is emerging as a critical factor influencing PD progression. Our understanding of PD was traditionally centered on neurodegenerative processes within the brain. However, examining PD through the lens of the GLB axis provides new insights. This review provides a comprehensive analysis of microbial metabolites, such as short-chain fatty acids (SCFAs), trimethylamine-N-oxide (TMAO), kynurenine, serotonin, bile acids, indoles, and dopamine, which are integral to PD pathogenesis by modulation of the GLB axis. Our extensive research included a comprehensive literature review and database searches utilizing resources such as gutMGene and gutMDisorder. These databases have been instrumental in identifying specific microbes and their metabolites, shedding light on the intricate relationship between the GLB axis and PD. This review consolidates existing knowledge and underscores the potential for targeted therapeutic interventions based on the GLB axis and its components, which offer new avenues for future PD research and treatment strategies. While the GLB axis is not a novel concept, this review is the first to focus specifically on its role in PD, highlighting the importance of integrating the liver and microbial metabolites as central players in the PD puzzle.

Host-microbe serotonin metabolism

As a result of a long evolutionary history, serotonin plays a variety of physiological roles, including neurological, cardiovascular, gastrointestinal, and endocrine functions. While many of these activities can be accommodated within the serotoninergic activity, recent findings have revealed an unsuspected role of serotonin in orchestrating host and microbial dialogue at the tryptophan dining table, to the benefit of local and systemic homeostasis. Herein we review the dual role of serotonin at the host-microbe interface and discuss how unraveling the interconnections among the host and microbial pathways of tryptophan degradation may help to accommodate the versatility of serotonin in physiology and pathology.

The 5-HT-related gut-brain axis in obesity

AIMS

The incidence of obesity increases annually. It is closely related to the occurrence of cardiovascular diseases, malignant tumors, etc., and has become a major global health problem. 5-hydroxytryptamine (5-HT), a multifunctional monoamine neurotransmitter, is dispersed throughout the central nervous system and digestive tract. It is intimately related to the mechanism of obesity.

MATERIALS AND METHODS

PubMed, Web of Science and Embase were carefully searched. We collected articles that are closely related to 5-HT, the gut-brain axis, and obesity.

KEY FINGDINGS

The gut microbiota not only influences nutrient metabolism but also centrally meditates appetite and mood regulation. The gut-brain axis, a system connecting the gut and the brain, is known to participate in two-way communication between the gut flora and the central nervous system.

SIGNIFICANCE

There have been few reports on whether peripheral and central 5-HT interact bidirectionally via the gut-brain axis and jointly play a role in the pathogenesis of obesity. In this review, we summarize the rationale for the contribution of the 5-HT-related gut-brain axis to the development of obesity and explore feasible signaling pathways, which elucidates new targets for preventing and treating obesity.

An Investigation into the Relationship of Circulating Gut Microbiome Molecules and Inflammatory Markers with the Risk of Incident Dementia in Later Life

The gut microbiome may be involved in the occurrence of dementia primarily through the molecular mechanisms of producing bioactive molecules and promoting inflammation. Epidemiological evidence linking gut microbiome molecules and inflammatory markers to dementia risk has been mixed, and the intricate interplay between these groups of biomarkers suggests that their joint investigation in the context of dementia is warranted. We aimed to simultaneously investigate the association of circulating levels of selected gut microbiome molecules and inflammatory markers with dementia risk. This case-cohort epidemiological study included 805 individuals (83 years, 66% women) free of dementia at baseline. Plasma levels of 19 selected gut microbiome molecules comprising lipopolysaccharide, short-chain fatty acids, and indole-containing tryptophan metabolites as well as four inflammatory markers measured at baseline were linked to incident all-cause (ACD) and Alzheimer's disease dementia (AD) in binary outcomes and time-to-dementia analyses. Independent of several covariates, seven gut microbiome molecules, 5-hydroxyindole-3-acetic acid, indole-3-butyric acid, indole-3-acryloylglycine, indole-3-lactic acid, indole-3-acetic acid methyl ester, isobutyric acid, and 2-methylbutyric acid, but no inflammatory markers discriminated incident dementia cases from non-cases. Furthermore, 5-hydroxyindole-3-acetic acid (hazard ratio: 0.58; 0.36-0.94, P = 0.025) was associated with time-to-ACD. These molecules underpin gut microbiome-host interactions in the development of dementia and they may be crucial in its prevention and intervention strategies. Future larger epidemiological studies are needed to confirm our findings, specifically in exploring the repeatedly measured circulating levels of these molecules and investigating their causal relationship with dementia risk.

The aryl hydrocarbon receptor pathway: a linking bridge between the gut microbiome and neurodegenerative diseases

The Aryl hydrocarbon receptor (AHR) is a cytosolic receptor and ligand-activated transcription factor widely expressed across various cell types in the body. Its signaling is vital for host responses at barrier sites, regulating epithelial renewal, barrier integrity, and the activities of several types of immune cells. This makes AHR essential for various cellular responses during aging, especially those governing inflammation and immunity. In this review, we provided an overview of the mechanisms by which the AHR mediates inflammatory response at gut and brain level through signals from intestinal microbes. The age-related reduction of gut microbiota functions is perceived as a trigger of aberrant immune responses linking gut and brain inflammation to neurodegeneration. Thus, we explored gut microbiome impact on the nature and availability of AHR ligands and outcomes for several signaling pathways involved in neurodegenerative diseases and age-associated decline of brain functions, with an insight on Parkinson's and Alzheimer's diseases, the most common neurodegenerative diseases in the elderly. Specifically, we focused on microbial tryptophan catabolism responsible for the production of several AHR ligands. Perspectives for the development of microbiota-based interventions targeting AHR activity are presented for a healthy aging.

The gut microbiota-brain axis in neurological disorders

Previous studies have shown a bidirectional communication between human gut microbiota and the brain, known as the microbiota-gut-brain axis (MGBA). The MGBA influences the host's nervous system development, emotional regulation, and cognitive function through neurotransmitters, immune modulation, and metabolic pathways. Factors like diet, lifestyle, genetics, and environment shape the gut microbiota composition together. Most research have explored how gut microbiota regulates host physiology and its potential in preventing and treating neurological disorders. However, the individual heterogeneity of gut microbiota, strains playing a dominant role in neurological diseases, and the interactions of these microbial metabolites with the central/peripheral nervous systems still need exploration. This review summarizes the potential role of gut microbiota in driving neurodevelopmental disorders (autism spectrum disorder and attention deficit/hyperactivity disorder), neurodegenerative diseases (Alzheimer's and Parkinson's disease), and mood disorders (anxiety and depression) in recent years and discusses the current clinical and preclinical gut microbe-based interventions, including dietary intervention, probiotics, prebiotics, and fecal microbiota transplantation. It also puts forward the current insufficient research on gut microbiota in neurological disorders and provides a framework for further research on neurological disorders.

New insights into the effects of serotonin on Parkinson's disease and depression through its role in the gastrointestinal tract

Neuropsychiatric and neurodegenerative disorders are frequently associated with gastrointestinal (GI) co-pathologies. Although the central and enteric nervous systems (CNS and ENS, respectively) have been studied separately, there is increasing interest in factors that may contribute to conditions affecting both systems. There is compelling evidence that serotonin (5-HT) may play an important role in several gut-brain disorders. It is well known that 5-HT is essential for the development and functioning of the CNS. However, most of the body's 5-HT is produced in the GI tract. A deeper understanding of the specific effects of enteric 5-HT on gut-brain disorders may provide the basis for the development of new therapeutic targets. This review summarizes current data focusing on the important role of 5-HT in ENS development and motility, with particular emphasis on novel aspects of 5-HT signaling in conditions where CNS and ENS comorbidities are common, such as Parkinson's disease and depressive disorders.

Gut microbiota and intestinal immunity-A crosstalk in irritable bowel syndrome

Irritable bowel syndrome (IBS), one of the most prevalent functional gastrointestinal disorders, is characterized by recurrent abdominal pain and abnormal defecation habits, resulting in a severe healthcare burden worldwide. The pathophysiological mechanisms of IBS are multi-factorially involved, including food antigens, visceral hypersensitivity reactions, and the brain-gut axis. Numerous studies have found that gut microbiota and intestinal mucosal immunity play an important role in the development of IBS in crosstalk with multiple mechanisms. Therefore, based on existing evidence, this paper elaborates that the damage and activation of intestinal mucosal immunity and the disturbance of gut microbiota are closely related to the progression of IBS. Combined with the application prospect, it also provides references for further in-depth exploration and clinical practice.

Exploring the serotonin-probiotics-gut health axis: A review of current evidence and potential mechanisms

Modulatory effects of serotonin (5-Hydroxytryptamine [5-HT]) have been seen in hepatic, neurological/psychiatric, and gastrointestinal (GI) disorders. Probiotics are live microorganisms that confer health benefits to their host. Recent research has suggested that probiotics can promote serotonin signaling, a crucial pathway in the regulation of mood, cognition, and other physiological processes. Reviewing the literature, we find that peripheral serotonin increases nutrient uptake and storage, regulates the composition of the gut microbiota, and is involved in mediating neuronal disorders. This review explores the mechanisms underlying the probiotic-mediated increase in serotonin signaling, highlighting the role of gut microbiota in the regulation of serotonin production and the modulation of neurotransmitter receptors. Additionally, this review discusses the potential clinical implications of probiotics as a therapeutic strategy for disorders associated with altered serotonin signaling, such as GI and neurological disorders. Overall, this review demonstrates the potential of probiotics as a promising avenue for the treatment of serotonin-related disorders and signaling of serotonin.

EPA and DHA Alleviated Chronic Dextran Sulfate Sodium Exposure-Induced Depressive-like Behaviors in Mice and Potential Mechanisms Involved

Patients with ulcerative colitis (UC) have higher rates of depression. However, the mechanism of depression development remains unclear. The improvements of EPA and DHA on dextran sulfate sodium (DSS)-induced UC have been verified. Therefore, the present study mainly focused on the effects of EPA and DHA on UC-induced depression in C57BL/6 mice and the possible mechanisms involved. A forced swimming test and tail suspension experiment showed that EPA and DHA significantly improved DSS-induced depressive-like behavior. Further analysis demonstrated that EPA and DHA could significantly suppress the inflammation response of the gut and brain by regulating the NLRP3/ASC signal pathway. Moreover, intestine and brain barriers were maintained by enhancing ZO-1 and occludin expression. In addition, EPA and DHA also increased the serotonin (5-HT) concentration and synaptic proteins. Interestingly, EPA and DHA treatments increased the proportion of dominant bacteria, alpha diversity, and beta diversity. In conclusion, oral administration of EPA and DHA alleviated UC-induced depressive-like behavior in mice by modulating the inflammation, maintaining the mucosal and brain barriers, suppressing neuronal damage and reverting microbiota changes.

Traditional Chinese Medicine in Osteoporosis Intervention and the Related Regulatory Mechanism of Gut Microbiome

The gut microbiome (GM) has become a crucial factor that can affect the progression of osteoporosis. A number of studies have demonstrated the impact of Traditional Chinese Medicine (TCM) on GM and bone metabolism. In this review, we summarize the potential mechanisms of the relationship between osteoporosis and GM disorder and introduce several natural Chinese medicines that exert anti-osteoporosis effects by modulating the GM. It is underlined that, through the provision of the microbial associated molecular pattern (MAMP), the GM causes inflammatory reactions and alterations in the Treg-Th17 balance and ultimately leads to changes in bone mass. Serotonin and many hormones, especially estrogen, may play a crucial role in the interaction of the GM with bone metabolism. Additionally, the GM may affect the absorption of specific nutrients in the intestine, particularly minerals like calcium, magnesium, and phosphorus. Several natural Chinese herbs, such as Sambucus Williamsii, Achyranthes bidentata Blume, Pleurotus ostreatus and Ganoderma lucidum mushrooms, Pueraria Lobata, and Agaricus blazei Murill have exhibited anti-osteoporosis effects through regulating the distribution and metabolism of the GM. These herbs may increase the abundance of Firmicutes, decrease the abundance of Bacteroides, promote the GM to produce more SCFAs, modulate the immune response caused by harmful bacteria, and increase the proportion of Treg-Th17 to indirectly affect bone metabolism. Moreover, gut-derived 5-HT is an important target for TCM to prevent osteoporosis via the gut-bone axis. Puerarin could prevent osteoporosis by improving intestinal mucosal integrity and decrease systemic inflammation caused by estrogen deficiency.

Therapeutic potential of dietary phytochemicals from Drynaria quercifolia to modulate gut microbiome: an in silico approach

Drynaria quercifolia is one of the pioneer medicinal plants which exert many beneficial effects on humans. Fatty acids are hydrophobic ligands that act as membrane substrates, metabolic signalling molecules, and metabolic energy sources. It could enhance the mucus production in the intestine which maintain mucosal homeostasis. The inflammatory responses were also regulated by 5-HT receptors. Serotonin 2 A receptors are G-protein coupled receptors targeted by various types of ligands viz. antidepressants, antipsychotics and anti-migraine drugs. The interaction of mucin protein and fatty acid could increase the antimicrobial activity and anti-inflammatory activity of gut microbiome. In this study, dietary phytochemicals were extracted from D. quercifolia and characterized using GC-MS analysis. The result shows presence of 38 various compounds viz. decanoic acid, indole, and dodecanoic acid and etc., Among the all, dodecanoic acid showed good drug likeness and pharmaceutical properties. Target proteins viz. 3IFB (Intestinal fatty acid binding protein) and 7WC4 (5-hydroxytryptamine receptor 2 A) were docked with dodecanoic acid using Auto dock software. The fatty acids produced in the gut could interact with 3IFB and 7WC4 proteins to maintain intestinal integrity and improved gut-brain function respectively. Dodecanoic acid exhibits the highest binding energy with mutated 3IFB (-6.01) than native whereas 7WC4 native protein showed (-7.3 kal/mol) the highest affinity than mutated protein. Structural changes were predicted by using SOPMA and ProSA. Evaluation results indicate that 3IFB was having more stability, good quality, and enhanced affinity than 7WC4. Further, MD simulations were done for 3IFB to check the stability of protein-ligand complex using WebGro platform. The model was investigated by root mean square deviation and fluctuations. Therefore, dodecanoic acids have been considered as a potential agonists and offer opportunities for developing innovative medications for gastrointestinal diseases.Communicated by Ramaswamy H. Sarma.

Dietary Polyphenols as Prospective Natural-Compound Depression Treatment from the Perspective of Intestinal Microbiota Regulation

The broad beneficial effects of dietary polyphenols on human health have been confirmed. Current studies have shown that dietary polyphenols are important for maintaining the homeostasis of the intestinal microenvironment. Moreover, the corresponding metabolites of dietary polyphenols can effectively regulate intestinal micro-ecology and promote human health. Although the pathogenesis of depression has not been fully studied, it has been demonstrated that dysfunction of the microbiota-gut-brain axis may be its main pathological basis. This review discusses the interaction between dietary polyphenols and intestinal microbiota to allow us to better assess the potential preventive effects of dietary polyphenols on depression by modulating the host gut microbiota.