An intestinal commensal symbiosis factor controls neuroinflammation via TLR2-mediated CD39 signalling

Gut microbes-spinal connection is required for itch sensation

The gut microbiota has been linked to a number of neurological disorders. However, it is unclear whether the gut microbiota is involved in the genesis of chronic itch, a refractory condition that afflicts patients both physically and mentally. Here, we report that depletion of gut microbiota enhances tolerance to itch in mice orally administered with antibiotics (ABX) and mice free of germ. Of note, oral gavage with Bacteroides fragilis (B. fragilis), a prominent species of the genus Bacteroides with most differential change, corrected the ABX-induced itch dysfunction through its driven metabolite acetyl-l-carnitine (ALC). Mechanistically, gut microbiota or B. fragilis depletion caused a decrease in RNA N6-methyladenosine (m6A) demethylase FTO expression in the dorsal horn and a consequent increase in RNA m6A sites in Mas-related G protein-coupled receptor F (MrgprF) mRNA, leading to decreased MRGPRF protein. The downregulation of FTO was triggered by inactivation of ETS proto-oncogene 1 (ETS1), a transcription factor that binds to the Fto promoter. These findings support a gut microbe - spinal connection in modulation of itch sensation in RNA m6A epigenetic-dependent manner and highlight a critical role of ALC in linking the altered B. fragilis and itch dysfunction.

Microbiome Gut-Brain-Axis: Impact on Brain Development and Mental Health

The current discovery that the gut microbiome, which contains roughly 100 trillion microbes, affects health and disease has catalyzed a boom in multidisciplinary research efforts focused on understanding this relationship. Also, it is commonly demonstrated that the gut and the CNS are closely related in a bidirectional pathway. A balanced gut microbiome is essential for regular brain activities and emotional responses. On the other hand, the CNS regulates the majority of GI physiology. Any disruption in this bidirectional pathway led to a progression of health problems in both directions, neurological and gastrointestinal diseases. In this review, we hope to shed light on the complicated connections of the microbiome-gut-brain axis and the critical roles of gut microbiome in the early development of the brain in order to get a deeper knowledge of microbiome-mediated pathological conditions and management options through rebalancing of gut microbiome.

Gut microbiota in multiple sclerosis and animal models

Multiple sclerosis (MS) is a chronic central nervous system (CNS) neurodegenerative and neuroinflammatory disease marked by a host immune reaction that targets and destroys the neuronal myelin sheath. MS and correlating animal disease models show comorbidities, including intestinal barrier disruption and alterations of the commensal microbiome. It is accepted that diet plays a crucial role in shaping the microbiota composition and overall gastrointestinal (GI) tract health, suggesting an interplay between nutrition and neuroinflammation via the gut-brain axis. Unfortunately, poor host health and diet lead to microbiota modifications that could lead to significant responses in the host, including inflammation and neurobehavioral changes. Beneficial microbial metabolites are essential for host homeostasis and inflammation control. This review will highlight the importance of the gut microbiota in the context of host inflammatory responses in MS and MS animal models. Additionally, microbial community restoration and how it affects MS and GI barrier integrity will be discussed.

The impact of perinatal maternal stress on the maternal and infant gut and human milk microbiomes: A scoping review

BACKGROUND

Perinatal maternal stress, which includes both psychological and physiological stress experienced by healthy women during pregnancy and the postpartum period, is becoming increasingly prevalent. Infant early exposure to adverse environments such as perinatal stress has been shown to increase the long-term risk to metabolic, immunologic and neurobehavioral disorders. Evidence suggests that the human microbiome facilitates the transmission of maternal factors to infants via the vaginal, gut, and human milk microbiomes. The colonization of aberrant microorganisms in the mother's microbiome, influenced by the microbiome-brain-gut axis, may be transferred to infants during a critical early developmental period. This transfer may predispose infants to a more inflammatory-prone microbiome which is associated with dysregulated metabolic process leading to adverse health outcomes. Given the prevalence and potential impact of perinatal stress on maternal and infant health, with no systematic mapping or review of the data to date, the aim of this scoping review is to gather evidence on the relationship between perinatal maternal stress, and the human milk, maternal, and infant gut microbiomes.

METHODS

This is an exploratory mapping scoping review, guided by the Joanna Briggs Institute's methodology along with use of the Prisma Scr reporting guideline. A comprehensive search was conducted using the following databases, CINAHL Complete; MEDLINE; PsycINFO, Web of Science and Scopus with a protocol registered with Open Science Framework DOI 10.17605/OSF.IO/5SRMV.

RESULTS

After screening 1145 papers there were 7 paper that met the inclusion criteria. Statistically significant associations were found in five of the studies which identify higher abundance of potentially pathogenic bacteria such as Erwinia, Serratia, T mayombie, Bacteroides with higher maternal stress, and lower levels of stress linked to potentially beneficial bacteria such Lactococcus, Lactobacillus, Akkermansia. However, one study presents conflicting results where it was reported that higher maternal stress was linked to the prevalence of more beneficial bacteria.

CONCLUSION

This review suggests that maternal stress does have an impact on the alteration of abundance and diversity of influential bacteria in the gut microbiome, however, it can affect colonisation in different ways. These bacterial changes have the capacity to influence long term health and disease. The review analyses data collection tools and methods, offers potential reasons for these findings as well as suggestions for future research.

Unravelling the neuroimmune nexus: insights into epilepsy pathology and the role of S100b protein in brain-gut axis modulation: a literature review

Epilepsy, a chronic neurological condition marked by recurrent, unprovoked seizures, involves complex pathophysiological mechanisms. Recent advancements have expanded our understanding from traditional neuronal dysfunction to include neuroimmune interactions and the influence of the brain-gut-bio-axis. This review explores the role of the S100b protein within these contexts, noted for its involvement in neuroinflammatory processes and as a potential biomarker. Furthermore, it discusses the emerging significance of the gut microbiome in modulating neuroimmune responses and seizure activity. The review integrates findings from recent studies, emphasizing the critical role of the S100b signalling pathway and the gut-brain axis in epilepsy pathology. The interplay between neuroimmune mechanisms and gut microbiota offers novel insights and potential therapeutic targets, underlining the need for further research to exploit these connections for clinical benefit.

Multiple Sclerosis: A Story of the Interaction Between Gut Microbiome and Components of the Immune System

Multiple sclerosis (MS) is defined as an inflammatory disorder that chronically affects the central nervous system of young people mostly and is distributed globally. It is associated with degeneration and demyelination of the myelin sheath around the nerves, resulting in multiple neurological disability symptoms ranging from mild to severe cases that end with paralysis sometimes. MS is one of the rising diseases globally that is unfortunately associated with reduced quality of life and adding national economic burdens. The definite MS mechanism is not clearly defined; however, all the previous researches confirm the role of the immune system as the master contributor in the pathogenesis. Innate and adaptive immune cells are activated peripherally then attracted toward the central nervous system (CNS) due to the breakdown of the blood-brain barrier. Recently, the gut-brain axis was shown to depend on gut metabolites that are produced by different microorganisms in the colon. The difference in microbiota composition between individuals is responsible for diversity in secreted metabolites that affect immune responses locally in the gut or systemically when reach blood circulation to the brain. It may enhance or suppress immune responses in the central nervous system (CNS) (repeated short forms); consequently, it may exacerbate or ameliorate MS symptoms. Recent data showed that some metabolites can be used as adjuvant therapy in MS and other inflammatory diseases. This review sheds light on the nature of MS and the possible interaction between gut microbiota and immune system regulation through the gut-brain axis, hence contributing to MS pathogenesis.

Nurturing development: how a mother's nutrition shapes offspring's brain through the gut

Pregnancy is a transformative period marked by profound physical and emotional changes, with far-reaching consequences for both mother and child. Emerging research has illustrated the pivotal role of a mother's diet during pregnancy in influencing the prenatal gut microbiome and subsequently shaping the neurodevelopment of her offspring. The intricate interplay between maternal gut health, nutrition, and neurodevelopmental outcomes has emerged as a captivating field of investigation within developmental science. Acting as a dynamic bridge between mother and fetus, the maternal gut microbiome, directly and indirectly, impacts the offspring's neurodevelopment through diverse pathways. This comprehensive review delves into a spectrum of studies, clarifying putative mechanisms through which maternal nutrition, by modulating the gut microbiota, orchestrates the early stages of brain development. Drawing insights from animal models and human cohorts, this work underscores the profound implications of maternal gut health for neurodevelopmental trajectories and offers a glimpse into the formulation of targeted interventions able to optimize the health of both mother and offspring. The prospect of tailored dietary recommendations for expectant mothers emerges as a promising and accessible intervention to foster the growth of beneficial gut bacteria, potentially leading to enhanced cognitive outcomes and reduced risks of neurodevelopmental disorders.

Gut Microbiota and Gut-Brain Axis in Hypertension: Implications for Kidney and Cardiovascular Health-A Narrative Review

INTRODUCTION

Arterial hypertension is a major contributor to a wide range of health complications, with cardiac hypertrophy and chronic kidney disease being among the most prevalent. Consequently, novel strategies for the treatment and prevention of hypertension are actively being explored. Recent research has highlighted a potential link between hypertension and the gut-brain axis. A bidirectional communication between the microbiota and the brain via the vagus nerve, enteric nervous system, hypothalamus-pituitary-adrenal axis, secreted short-chain fatty acids, and neurotransmitter metabolism.

MATERIALS AND METHODS

A comprehensive literature search was conducted using databases such as PubMed to identify studies exploring the relationship between gut microbiota and hypertension, along with the effects of dietary interventions and probiotics on blood pressure regulation.

DISCUSSION

Studies in both animal models and human subjects have demonstrated a strong correlation between alterations in gut microbiota composition and the development of hypertension. By influencing blood pressure, the gut microbiota can potentially affect the progression of cardiovascular and kidney disorders. Modulating gut microbiota through dietary interventions and probiotics has shown promise in regulating blood pressure and reducing systemic inflammation, offering a novel approach to managing hypertension. Diets such as the Mediterranean diet, which is rich in polyphenols and omega-3 fatty acids and low in sodium, promote the growth of beneficial gut bacteria that support cardiovascular health. Additionally, probiotics have been found to enhance gut barrier function, reduce inflammation, and modulate the Renin-Angiotensin System, all of which contribute to lowering blood pressure.

CONCLUSIONS

Further research is needed to determine the mechanisms of action of the microbiota in hypertension. The aim of this study was to evaluate the influence of gut microbiota on blood pressure regulation and the progression of hypertension-related complications, such as cardiovascular and kidney disorders.

Relationship between gut microbiota and multiple sclerosis: a scientometric visual analysis from 2010 to 2023

Background

Numerous studies have investigated the relationship between gut microbiota (GM) and multiple sclerosis(MS), highlighting the significant role of GM in MS. However, there is a lack of systematic Scientometric analyses published in this specific research area to provide an overall understanding of the current research status.

Methods

Perform a scientometric analysis on research conducted between 2010 and 2023 concerning the link between GM and MS using quantitative and visual analysis software (CiteSpace and VOSviewer.).

Results

From January 1, 2010, and December 31, 2023, a total of 1019 records about GM and MS were retrieved. The number of publications exhibited a consistent upward trend annually. The United States led in publications, showed the strongest level of collaboration among countries. The University of California, San Francisco stands as the top institution in terms of output, and the most prolific and cited authors were Lloyd H. Kasper and Javier Ochoa-Reparaz from the USA. The research in this field primarily centers on investigating the alterations and associations of GM in MS or EAE, the molecular immunological mechanisms, and the potential of GM-based interventions to provide beneficial effects in MS or EAE. The Keywords co-occurrence network reveals five primary research directions in this field. The most frequently occurring keywords are inflammation, probiotics, diet, dysbiosis, and tryptophan. In recent years, neurodegeneration and neuropsychiatric disorders have been prominent, indicating that the investigation of the mechanisms and practical applications of GM in MS has emerged as a current research focus. Moreover, GM research is progressively extending into the realm of neurodegenerative and psychiatric diseases, potentially becoming future research hotspots.

Conclusions

This study revealed a data-driven systematic comprehension of research in the field of GM in MS over the past 13 years, highlighted noteworthy research within the field, provided us with a clear understanding of the current research status and future trends, providing a valuable reference for researchers venturing into this domain.

The interplay between microbiota and brain-gut axis in epilepsy treatment

The brain-gut axis plays a vital role in connecting the cognitive and emotional centers of the brain with the intricate workings of the intestines. An imbalance in the microbiota-mediated brain-gut axis extends far beyond conditions like Irritable Bowel Syndrome (IBS) and obesity, playing a critical role in the development and progression of various neurological disorders, including epilepsy, depression, Alzheimer's disease (AD), and Parkinson's disease (PD). Epilepsy, a brain disorder characterized by unprovoked seizures, affects approximately 50 million people worldwide. Accumulating evidence suggests that rebuilding the gut microbiota through interventions such as fecal microbiota transplantation, probiotics, and ketogenic diets (KD) can benefit drug-resistant epilepsy. The disturbances in the gut microbiota could contribute to the toxic side effects of antiepileptic drugs and the development of drug resistance in epilepsy patients. These findings imply the potential impact of the gut microbiota on epilepsy and suggest that interventions targeting the microbiota, such as the KD, hold promise for managing and treating epilepsy. However, the full extent of the importance of microbiota in epilepsy treatment is not yet fully understood, and many aspects of this field remain unclear. Therefore, this article aims to provide an overview of the clinical and animal evidence supporting the regulatory role of gut microbiota in epilepsy, and of potential pathways within the brain-gut axis that may be influenced by the gut microbiota in epilepsy. Furthermore, we will discuss the recent advancements in epilepsy treatment, including the KD, fecal microbiota transplantation, and antiseizure drugs, all from the perspective of the gut microbiota.

Gut microbiota dysbiosis-related susceptibility to nontuberculous mycobacterial lung disease

The role of gut microbiota in host defense against nontuberculous mycobacterial lung disease (NTM-LD) was poorly understood. Here, we showed significant gut microbiota dysbiosis in patients with NTM-LD. Reduced abundance of Prevotella copri was significantly associated with NTM-LD and its disease severity. Compromised TLR2 activation activity in feces and plasma in the NTM-LD patients was highlighted. In the antibiotics-treated mice as a study model, gut microbiota dysbiosis with reduction of TLR2 activation activity in feces, sera, and lung tissue occurred. Transcriptomic analysis demonstrated immunocompromised in lung which were closely associated with increased NTM-LD susceptibility. Oral administration of P. copri or its capsular polysaccharides enhanced TLR2 signaling, restored immune response, and ameliorated NTM-LD susceptibility. Our data highlighted the association of gut microbiota dysbiosis, systematically compromised immunity and NTM-LD development. TLR2 activation by P. copri or its capsular polysaccharides might help prevent NTM-LD.

The Gut-Brain Axis in Autoimmune Diseases: Emerging Insights and Therapeutic Implications

The gut-brain axis (GBA) is a two-way communication system that is influenced by signals from the nervous system, hormones, metabolism, the immune system, and microbes. The GBA may play a key role in gastrointestinal and neurological illnesses. Signaling events from the gut can regulate brain function. As a result, mounting data point to a connection between autoimmune disorders (AIDs), both neuroinflammatory and neurodegenerative diseases, and the GBA. Clinical, epidemiological, and experimental studies have shown that a variety of neurological illnesses are linked to alterations in the intestinal environment, which are suggestive of disease-mediated inter-organ communication between the gut and the brain. This review's objective is to draw attention to the clinical and biological relationship between the gut and the brain, as well as the clinical importance of this relationship for AIDs, neurodegeneration, and neuroinflammation. We also discuss the dysbiosis in the gut microbiota that has been linked to various AIDs, and we make some assumptions about how dietary changes such as prebiotics and probiotics may be able to prevent or treat AIDs by restoring the composition of the gut microbiota and regulating metabolites.

Farnesol brain transcriptomics in CNS inflammatory demyelination

BACKGROUND

Farnesol (FOL) prevents the onset of experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis (MS).

OBJECTIVE

We examined the transcriptomic profile of the brains of EAE mice treated with daily oral FOL using next-generation sequencing (RNA-seq).

METHODS

Transcriptomics from whole brains of treated and untreated EAE mice at the peak of EAE was performed.

RESULTS

EAE-induced mice, compared to naïve, healthy mice, overall showed increased expression in pathways for immune response, as well as an increased cytokine signaling pathway, with downregulation of cellular stress proteins. FOL downregulates pro-inflammatory pathways and attenuates the immune response in EAE. FOL downregulated the expression of genes involved in misfolded protein response, MAPK activation/signaling, and pro-inflammatory response.

CONCLUSION

This study provides insight into the molecular impact of FOL in the brain and identifies potential therapeutic targets of the isoprenoid pathway in MS patients.

Under the influence: environmental factors as modulators of neuroinflammation through the IL-10/IL-10R axis

The IL-10/IL-10 receptor (IL-10R) axis plays an important role in attenuating neuroinflammation in animal models of Multiple Sclerosis (MS) and increased IL-10 has been associated with a positive response to MS disease modifying therapy. Because environmental factors play an important role in MS susceptibility and disease course, identification of environmental factors that impact the IL-10/IL-10R axis has therapeutic potential. In this review, we provide historical and updated perspectives of how IL-10R signaling impacts neuroinflammation, discuss environmental factors and intestinal microbes with known impacts on the IL-10/IL-10R axis, and provide a hypothetical model for how B cells, via their production of IL-10, may be important in conveying environmental "information" to the inflamed central nervous system.

Gut microbiota in brain tumors: An emerging crucial player

In recent decades, various roles of the gut microbiota in physiological and pathological conditions have been uncovered. Among the many interacting pathways between the host and gut flora, the gut-brain axis has drawn increasing attention and is generally considered a promising way to understand and treat brain tumors, one of the most lethal neoplasms. In this narrative review, we aimed to unveil and dissect the sophisticated mechanisms by which the gut-brain axis exerts its influence on brain tumors. Furthermore, we summarized the latest research regarding the gastrointestinal microbial landscape and the effect of gut-brain axis malfunction on different brain tumors. Finally, we outlined the ongoing developing approaches of microbial manipulation and their corresponding research related to neuro-malignancies. Collectively, we recapitulated the advances in gut microbial alterations along with their potential interactive mechanisms in brain tumors and encouraged increased efforts in this area.

Feeding the gut microbiome: impact on multiple sclerosis

Multiple sclerosis (MS) is a multifactorial neurological disease characterized by chronic inflammation and immune-driven demyelination of the central nervous system (CNS). The rising number of MS cases in the last decade could be partially attributed to environmental changes, among which the alteration of the gut microbiome driven by novel dietary habits is now of particular interest. The intent of this review is to describe how diet can impact the development and course of MS by feeding the gut microbiome. We discuss the role of nutrition and the gut microbiota in MS disease, describing preclinical studies on experimental autoimmune encephalomyelitis (EAE) and clinical studies on dietary interventions in MS, with particular attention to gut metabolites-immune system interactions. Possible tools that target the gut microbiome in MS, such as the use of probiotics, prebiotics and postbiotics, are analyzed as well. Finally, we discuss the open questions and the prospects of these microbiome-targeted therapies for people with MS and for future research.

The immunomodulatory roles of the gut microbiome in autoimmune diseases of the central nervous system: Multiple sclerosis as a model

The gut-associated lymphoid tissue is a primary activation site for immune responses to infection and immunomodulation. Experimental evidence using animal disease models suggests that specific gut microbes significantly regulate inflammation and immunoregulatory pathways. Furthermore, recent clinical findings indicate that gut microbes' composition, collectively named gut microbiota, is altered under disease state. This review focuses on the functional mechanisms by which gut microbes promote immunomodulatory responses that could be relevant in balancing inflammation associated with autoimmunity in the central nervous system. We also propose therapeutic interventions that target the composition of the gut microbiota as immunomodulatory mechanisms to control neuroinflammation.

Dietary Polyphenols, Microbiome, and Multiple Sclerosis: From Molecular Anti-Inflammatory and Neuroprotective Mechanisms to Clinical Evidence

Multiple sclerosis (MS) is a multifactorial, immune-mediated disease caused by complex gene-environment interactions. Dietary factors modulating the inflammatory status through the control of the metabolic and inflammatory pathways and the composition of commensal gut microbiota, are among the main environmental factors involved in the pathogenesis of MS. There is no etiological therapy for MS and the drugs currently used, often accompanied by major side effects, are represented by immunomodulatory substances capable of modifying the course of the disease. For this reason, nowadays, more attention is paid to alternative therapies with natural substances with anti-inflammatory and antioxidant effects, as adjuvants of classical therapies. Among natural substances with beneficial effects on human health, polyphenols are assuming an increasing interest due to their powerful antioxidant, anti-inflammatory, and neuroprotective effects. Beneficial properties of polyphenols on the CNS are achieved through direct effects depending on their ability to cross the blood-brain barrier and indirect effects exerted in part via interaction with the microbiota. The aim of this review is to examine the literature about the molecular mechanism underlying the protective effects of polyphenols in MS achieved by experiments conducted in vitro and in animal models of the disease. Significant data have been accumulated for resveratrol, curcumin, luteolin, quercetin, and hydroxytyrosol, and therefore we will focus on the results obtained with these polyphenols. Clinical evidence for the use of polyphenols as adjuvant therapy in MS is restricted to a smaller number of substances, mainly curcumin and epigallocatechin gallate. In the last part of the review, a clinical trial studying the effects of these polyphenols in MS patients will also be revised.

Gut immune cell trafficking: inter-organ communication and immune-mediated inflammation

Immune cell trafficking is a complex and tightly regulated process that is indispensable for the body's fight against pathogens. However, it is also increasingly acknowledged that dysregulation of cell trafficking contributes to the pathogenesis of immune-mediated inflammatory diseases (IMIDs) in gastroenterology and hepatology, such as inflammatory bowel disease and primary sclerosing cholangitis. Moreover, altered cell trafficking has also been implicated as a crucial step in the immunopathogenesis of other IMIDs, such as rheumatoid arthritis and multiple sclerosis. Over the past few years, a central role of the gut in mediating these disorders has progressively emerged, and the partly microbiota-driven imprinting of particular cell trafficking phenotypes in the intestine seems to be crucially involved. Therefore, this Review highlights achievements in understanding immune cell trafficking to, within and from the intestine and delineates its consequences for immune-mediated pathology along the gut-liver, gut-joint and gut-brain axes. We also discuss implications for current and future therapeutic approaches that specifically interfere with homing, retention, egress and recirculation of immune cells.

Gut microbiome in type 1 diabetes: the immunological perspective

INTRODUCTION

Type 1 diabetes (T1D) is a prevalent, and yet uncurable, autoimmune disease targeting insulin-producing pancreatic β-cells. Despite a known genetic component in T1D onset, genetics alone cannot explain the alarming worldwide rise in T1D incidence, which is attributed to a growing impact of environmental factors, including perturbations of the gut microbiome.

AREAS COVERED

Intestinal commensal bacteria plays a crucial role in host physiology in health and disease by regulating endocrine and immune functions. An aberrant gut microbiome structure and metabolic function have been documented prior and during T1D onset. In this review, we summarize and discuss the current studies depicting the taxonomic profile and role of the gut microbial communities in murine models of T1D, diabetic patients and human interventional trials.

EXPERT OPINION

Compelling evidence have shown that the intestinal microbiota is instrumental in driving differentiation and functions of immune cells. Therefore, any alterations in the intestinal microbiome composition or microbial metabolite production, particularly early in life, may impact disease susceptibility and amplify inflammatory responses and hence accelerate the course of T1D pathogenesis.

Gut microbiota plays a role in irritable bowel syndrome by regulating 5-HT metabolism

Irritable bowel syndrome (IBS) is a common chronic functional gastrointestinal disorder. Brain-gut-microbiota axis dysfunction is an important pathogenic factor for IBS, in which neurotransmitters and gut microbes play key roles. The gastrointestinal tract contains large amounts of serotonin (5-hydroxytryptamine, 5-HT), a neurotransmitter that has been strongly linked to IBS-related symptoms. More than 90% of serotonin is synthesized in the gut by enterochromaffin cells (ECs), and certain intestinal flora can affect the occurrence and development of IBS by regulating 5-HT and its metabolism. In this review, we will discuss the role of gut microbiota in IBS by regulating 5-HT.

The adenosinergic signaling in the pathogenesis and treatment of multiple sclerosis

Multiple sclerosis (MS) is a highly disabling, progressive neurodegenerative disease with no curative treatment available. Although significant progress has been made in understanding how MS develops, there remain aspects of disease pathogenesis that are yet to be fully elucidated. In this regard, studies have shown that dysfunctional adenosinergic signaling plays a pivotal role, as patients with MS have altered levels adenosine (ADO), adenosine receptors and proteins involved in the generation and termination of ADO signaling, such as CD39 and adenosine deaminase (ADA). We have therefore performed a literature review regarding the involvement of the adenosinergic system in the development of MS and propose mechanisms by which the modulation of this system can support drug development and repurposing.

The Gut Microbiome-Brain Crosstalk in Neurodegenerative Diseases

The gut–brain axis (GBA) is a complex interactive network linking the gut to the brain. It involves the bidirectional communication between the gastrointestinal and the central nervous system, mediated by endocrinological, immunological, and neural signals. Perturbations of the GBA have been reported in many neurodegenerative diseases, suggesting a possible role in disease pathogenesis, making it a potential therapeutic target. The gut microbiome is a pivotal component of the GBA, and alterations in its composition have been linked to GBA dysfunction and CNS inflammation and degeneration. The gut microbiome might influence the homeostasis of the central nervous system homeostasis through the modulation of the immune system and, more directly, the production of molecules and metabolites. Small clinical and preclinical trials, in which microbial composition was manipulated using dietary changes, fecal microbiome transplantation, and probiotic supplements, have provided promising outcomes. However, results are not always consistent, and large-scale randomized control trials are lacking. Here, we give an overview of how the gut microbiome influences the GBA and could contribute to disease pathogenesis in neurodegenerative diseases.

The function of gut microbiota in immune-related neurological disorders: a review

This review provides an overview of the importance of microbiota in the regulation of gut–brain communication in immune-related neurological disorders. The gastrointestinal (GI) tract hosts a diverse abundance of microbiota, referred to as gut microbiota. The gut microbiota plays a role in the maintenance of GI tract homeostasis and is likely to have multiple effects on brain development and function. The bidirectional communication between the gut microbiota and the brain is termed the microbiota–gut–brain axis. This communication between the intestine and the brain appears to affect human health and behavior, as certain animal studies have demonstrated the association between alterations in the gut microbiota and neurological disorders. Most insights about the microbiota–gut–brain axis come from germ-free animal models, which reveal the importance of gut microbiota in neural function. To date, many studies have observed the impact of the gut microbiota in patients with neurological disorders. Although many studies have investigated the microbiota–gut–brain axis, there are still limitations in translating this research to humans given the complexities of the relationship between the gut microbiota and the brain. In this review, we discuss emerging evidence of how the microbiota–gut–brain axis regulates brain development and function through biological networks, as well as the possible contribution of the microbiota–gut–brain axis in immune-related neurological disorders.

Gut Microbial Antigenic Mimicry in Autoimmunity

The gut microbiota plays a major role in the developmental biology and homeostasis of cells belonging to the adaptive and innate arms of the immune system. Alterations in its composition, which are known to be regulated by both genetic and environmental factors, can either promote or suppress the pathogenic processes underlying the development of various autoimmune diseases, including inflammatory bowel disease, multiple sclerosis, systemic lupus erythematosus, type 1 diabetes and rheumatoid arthritis, to just name a few. Cross-recognition of gut microbial antigens by autoreactive T cells as well as gut microbe-driven alterations in the activation and homeostasis of effector and regulatory T cells have been implicated in this process. Here, we summarize our current understanding of the positive and negative associations between alterations in the composition of the gut microbiota and the development of various autoimmune disorders, with a special emphasis on antigenic mimicry.

Antigen presenting cell response to polysaccharide A is characterized by the generation of anti-inflammatory macrophages

Polysaccharide A (PSA) is the immunodominant capsular carbohydrate from the gram negative commensal microbe Bacteroides fragilis that has shown remarkable potency in ameliorating many rodent models of inflammatory disease by eliciting downstream suppressive CD4+ T cells. PSA is composed of a zwitterionic repeating unit that allows it to be processed by antigen presenting cells (APCs) and presented by MHCII in a glycosylation-dependent manner. While previous work has uncovered much about the interactions between MHCII and PSA, as well as the downstream T cell response, little is known about how PSA affects the phenotype of MHCII+ APCs, including macrophages. Here, we utilized an unbiased systems approach consisting of RNAseq transcriptomics, high-throughput flow cytometry, Luminex analysis and targeted validation experiments to characterize the impact of PSA-mediated stimulation of splenic MHCII+ cells. The data revealed that PSA potently elicited the upregulation of an alternatively activated M2 macrophage transcriptomic and cell surface signature. Cell-type-specific validation experiments further demonstrated that PSA-exposed bone marrow-derived macrophages (BMDMs) induced cell surface and intracellular markers associated with M2 macrophages compared with conventional peptide ovalbumin (ova)-exposed BMDMs. In contrast to macrophages, we also found that CD11c+ dendritic cells (DCs) upregulated the pro-T cell activation costimulatory molecule CD86 following PSA stimulation. Consistent with the divergent BMDM and DC changes, PSA-exposed DCs elicited an antigen-experienced T cell phenotype in co-cultures, whereas macrophages did not. These findings collectively demonstrate that the PSA-induced immune response is characterized by both T cell stimulation via presentation by DCs, and a previously unrecognized anti-inflammatory polarization of macrophages.

Microbiota and the gut-brain-axis: Implications for new therapeutic design in the CNS

The recent revelation that the gut microbiome, home to approximately 100 trillion microorganisms, is implicated in the development of both health and disease has spurred an exponential increase in interdisciplinary research involving gut microbiology. In all this hype, there is a need to better understand and contextualize the emerging evidence for the role of the gut microbiota in neurodegenerative and neurodevelopmental diseases, including central nervous system (CNS) malignancies. In this review, we aim to unravel the complex interactions of the microbiota-gut-brain-axis to pave a better understanding of microbiota-mediated pathogenesis, avenues for noninvasive prognosis, and therapeutic possibilities leveraging microbiota-gut-brain-axis modulations. We further provide insights of the ongoing transition from bench to bedside and discuss limitations of current approaches. Ultimately, we urge the continued development of synergistic therapeutic models with considerable consideration of the many gut-resident bacteria that will enable significant progress for the treatment of many neurological diseases.

The lung microbiome regulates brain autoimmunity

Lung infections and smoking are risk factors for multiple sclerosis, a T-cell-mediated autoimmune disease of the central nervous system¹. In addition, the lung serves as a niche for the disease-inducing T cells for long-term survival and for maturation into migration-competent effector T cells². Why the lung tissue in particular has such an important role in an autoimmune disease of the brain is not yet known. Here we detected a tight interconnection between the lung microbiota and the immune reactivity of the brain. A dysregulation in the lung microbiome significantly influenced the susceptibility of rats to developing autoimmune disease of the central nervous system. Shifting the microbiota towards lipopolysaccharide-enriched phyla by local treatment with neomycin induced a type-I-interferon-primed state in brain-resident microglial cells. Their responsiveness towards autoimmune-dominated stimulation by type II interferons was impaired, which led to decreased proinflammatory response, immune cell recruitment and clinical signs. Suppressing lipopolysaccharide-producing lung phyla with polymyxin B led to disease aggravation, whereas addition of lipopolysaccharide-enriched phyla or lipopolysaccharide recapitulated the neomycin effect. Our data demonstrate the existence of a lung-brain axis in which the pulmonary microbiome regulates the immune reactivity of the central nervous tissue and thereby influences its susceptibility to autoimmune disease development.

Reduced Gut Microbiome Diversity in People With HIV Who Have Distal Neuropathic Pain

Gut dysbiosis, defined as pathogenic alterations in the distribution and abundance of different microbial species, is associated with neuropathic pain in a variety of clinical conditions, but this has not been explored in the context of neuropathy in people with HIV (PWH). We assessed gut microbial diversity and dysbiosis in PWH and people without HIV (PWoH), some of whom reported distal neuropathic pain (DNP). DNP was graded on a standardized, validated severity scale. The gut microbiome was characterized using 16S rRNA sequencing and diversity was assessed using phylogenetic tree construction. Songbird analysis (https://github.com/mortonjt/songbird) was used to produce a multinomial regression model predicting counts of specific microbial taxa through metadata covariate columns. Participants were 226 PWH and 101 PWoH, mean (SD) age 52.0 (13.5), 21.1% female, 54.7% men who have sex with men, 44.7% non-white. Among PWH, median (interquartile range, IQR) nadir and current CD4 were 174 (21, 302) and 618 (448, 822), respectively; 90% were virally suppressed on antiretroviral therapy. PWH and PWoH did not differ with respect to microbiome diversity as indexed by Faith's phylogenetic diversity (PD). More severe DNP was associated with lower alpha diversity as indexed by Faith's phylogenetic diversity in PWH (Spearman's ρ = .224, P = 0.0007), but not in PWoH (Spearman's ρ = .032, P = .748). These relationships were not confounded by demographics or disease factors. In addition, the log-ratio of features identified at the genus level as Blautia to Lachnospira was statistically significantly higher in PWH with DNP than in PWH without DNP (t-test, P = 1.01e-3). Furthermore, the log-ratio of Clostridium features to Lachnospira features also was higher in PWH with DNP than in those without (t-test, P = 6.24e-5). Our results, in combination with previous findings in other neuropathic pain conditions, suggest that gut dysbiosis, particularly reductions in diversity and relative increases in the ratios of Blautia and Clostridium to Lachnospira, may contribute to prevalent DNP in PWH. Two candidate pathways for these associations, involving microbial pro-inflammatory components and microbially-produced anti-inflammatory short chain fatty acids, are discussed. Future studies might test interventions to re-establish a healthy gut microbiota and determine if this prevents or improves DNP. PERSPECTIVE: The association of neuropathic pain in people with HIV with reduced gut microbial diversity and dysbiosis raises the possibility that re-establishing a healthy gut microbiota might ameliorate neuropathic pain in HIV by reducing proinflammatory and increasing anti-inflammatory microbial products.

Alterations of host-gut microbiome interactions in multiple sclerosis

Background

Multiple sclerosis (MS) has a complex genetic, immune and metabolic pathophysiology. Recent studies implicated the gut microbiome in MS pathogenesis. However, interactions between the microbiome and host immune system, metabolism and diet have not been studied over time in this disorder.

Methods

We performed a six-month longitudinal multi-omics study of 49 participants (24 untreated relapse remitting MS patients and 25 age, sex, race matched healthy control individuals. Gut microbiome composition and function were characterized using 16S and metagenomic shotgun sequencing. Flow cytometry was used to characterize blood immune cell populations and cytokine profiles. Circulating metabolites were profiled by untargeted UPLC-MS. A four-day food diary was recorded to capture the habitual dietary pattern of study participants.

Findings

Together with changes in blood immune cells, metagenomic analysis identified a number of gut microbiota decreased in MS patients compared to healthy controls, and microbiota positively or negatively correlated with degree of disability in MS patients. MS patients demonstrated perturbations of their blood metabolome, such as linoleate metabolic pathway, fatty acid biosynthesis, chalcone, dihydrochalcone, 4-nitrocatechol and methionine. Global correlations between multi-omics demonstrated a disrupted immune-microbiome relationship and a positive blood metabolome-microbiome correlation in MS. Specific feature association analysis identified a potential correlation network linking meat servings with decreased gut microbe B. thetaiotaomicron, increased Th17 cell and greater abundance of meat-associated blood metabolites. The microbiome and metabolome profiles remained stable over six months in MS and control individuals.

Interpretation

Our study identified multi-system alterations in gut microbiota, immune and blood metabolome of MS patients at global and individual feature level. Multi-OMICS data integration deciphered a potential important biological network that links meat intakes with increased meat-associated blood metabolite, decreased polysaccharides digesting bacteria, and increased circulating proinflammatory marker.

Funding

This work was supported by the Washington University in St. Louis Institute of Clinical and Translational Sciences, funded, in part, by Grant Number # UL1 TR000448 from the National Institutes of Health, National Center for Advancing Translational Sciences, Clinical and Translational Sciences Award (Zhou Y, Piccio, L, Lovett-Racke A and Tarr PI); R01 NS10263304 (Zhou Y, Piccio L); the Leon and Harriet Felman Fund for Human MS Research (Piccio L and Cross AH). Cantoni C. was supported by the National MS Society Career Transition Fellowship (TA-180531003) and by donations from Whitelaw Terry, Jr. / Valerie Terry Fund. Ghezzi L. was supported by the Italian Multiple Sclerosis Society research fellowship (FISM 2018/B/1) and the National Multiple Sclerosis Society Post-Doctoral Fellowship (FG-190734474). Anne Cross was supported by The Manny & Rosalyn Rosenthal-Dr. John L. Trotter MS Center Chair in Neuroimmunology of the Barnes-Jewish Hospital Foundation. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Farnesol induces protection against murine CNS inflammatory demyelination and modifies gut microbiome

Farnesol is a 15‑carbon organic isoprenol synthesized by plants and mammals with anti-oxidant, anti-inflammatory, and neuroprotective activities. We sought to determine whether farnesol treatment would result in protection against murine experimental autoimmune encephalomyelitis (EAE), a well-established model of multiple sclerosis (MS). We compared disease progression and severity in C57BL/6 mice treated orally with 100 mg/kg/day farnesol solubilized in corn oil to corn-oil treated and untreated EAE mice. Farnesol significantly delayed the onset of EAE (by ~2 days) and dramatically decreased disease severity (~80%) compared to controls. Disease protection by farnesol was associated with a significant reduction in spinal cord infiltration by monocytes-macrophages, dendritic cells, CD4⁺ T cells, and a significant change in gut microbiota composition, including a decrease in the Firmicutes:Bacteroidetes ratio. The study suggests FOL could protect MS patients against CNS inflammatory demyelination by partially modulating the gut microbiome composition.

The Gut Microbiome as a Regulator of the Neuroimmune Landscape

The gut microbiome influences many host physiologies, spanning gastrointestinal function, metabolism, immune homeostasis, neuroactivity, and behavior. Many microbial effects on the host are orchestrated by bidirectional interactions between the microbiome and immune system. Imbalances in this dialogue can lead to immune dysfunction and immune-mediated conditions in distal organs including the brain. Dysbiosis of the gut microbiome and dysregulated neuroimmune responses are common comorbidities of neurodevelopmental, neuropsychiatric, and neurological disorders, highlighting the importance of the gut microbiome–neuroimmune axis as a regulator of central nervous system homeostasis. In this review, we discuss recent evidence supporting a role for the gut microbiome in regulating the neuroimmune landscape in health and disease.

Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Microbiome Methods in Experimental Autoimmune Encephalomyelitis

Microbiome composition studies are increasingly shedding light on animal models of disease. This paper describes a protocol for analyzing the gut microbiome composition prior to and after the induction of mice to experimental autoimmune encephalomyelitis (EAE), the principal animal model of the human neuroinflammatory demyelinating disease multiple sclerosis (MS). We also address and provide data assessing the impact of mice reared in different animal facilities on EAE induction. Furthermore, we discuss potential regulators of the gut-microbiome-brain axis (GMBA) in relation to neuroinflammation and implications on demyelinating disease states. Our results suggest that mice reared in different animal facilities produce different levels of EAE induction. These results highlight the importance of accounting for consistent environmental conditions when inducing EAE and other animal models of disease. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Study of the composition of the gut microbiome in the neuroinflammatory model of experimental autoimmune encephalomyelitis Basic Protocol 2: Experimental procedures for DNA extraction and microbiome analysis.

The Gut-Brain Axis

Preclinical evidence has firmly established bidirectional interactions among the brain, the gut, and the gut microbiome. Candidate signaling molecules and at least three communication channels have been identified. Communication within this system is nonlinear, is bidirectional with multiple feedback loops, and likely involves interactions between different channels. Alterations in gut-brain-microbiome interactions have been identified in rodent models of several digestive, psychiatric, and neurological disorders. While alterations in gut-brain interactions have clearly been established in irritable bowel syndrome, a causative role of the microbiome in irritable bowel syndrome remains to be determined. In the absence of specific microbial targets for more effective therapies, current approaches are limited to dietary interventions and centrally targeted pharmacological and behavioral approaches. A more comprehensive understanding of causative influences within the gut-brain-microbiome system and well-designed randomized controlled trials are needed to translate these exciting preclinical findings into effective therapies. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The Gut-Brain Axis in Multiple Sclerosis. Is Its Dysfunction a Pathological Trigger or a Consequence of the Disease?

A large and expending body of evidence indicates that the gut-brain axis likely plays a crucial role in neurological diseases, including multiple sclerosis (MS). As a whole, the gut-brain axis can be considered as a bi-directional multi-crosstalk pathway that governs the interaction between the gut microbiota and the organism. Perturbation in the commensal microbial population, referred to as dysbiosis, is frequently associated with an increased intestinal permeability, or "leaky gut", which allows the entrance of exogeneous molecules, in particular bacterial products and metabolites, that can disrupt tissue homeostasis and induce inflammation, promoting both local and systemic immune responses. An altered gut microbiota could therefore have significant repercussions not only on immune responses in the gut but also in distal effector immune sites such as the CNS. Indeed, the dysregulation of this bi-directional communication as a consequence of dysbiosis has been implicated as playing a possible role in the pathogenesis of neurological diseases. In multiple sclerosis (MS), the gut-brain axis is increasingly being considered as playing a crucial role in its pathogenesis, with a major focus on specific gut microbiota alterations associated with the disease. In both MS and its purported murine model, experimental autoimmune encephalomyelitis (EAE), gastrointestinal symptoms and/or an altered gut microbiota have been reported together with increased intestinal permeability. In both EAE and MS, specific components of the microbiota have been shown to modulate both effector and regulatory T-cell responses and therefore disease progression, and EAE experiments with germ-free and specific pathogen-free mice transferred with microbiota associated or not with disease have clearly demonstrated the possible role of the microbiota in disease pathogenesis and/or progression. Here, we review the evidence that can point to two possible consequences of the gut-brain axis dysfunction in MS and EAE: 1. A pro-inflammatory intestinal environment and "leaky" gut induced by dysbiosis could lead to an altered communication with the CNS through the cholinergic afferent fibers, thereby contributing to CNS inflammation and disease pathogenesis; and 2. Neuroinflammation affecting efferent cholinergic transmission could result in intestinal inflammation as disease progresses.

Mutual interaction of microbiota and host immunity during health and diseases

Microbiota-host interaction has attracted more and more attentions in recent years. The association between microbiota and host health is largely attributed to its influence on host immune system. Microbial-derived antigens and metabolites play a critical role in shaping the host immune system, including regulating its development, activation, and function. However, during various diseases the microbiota-host communication is frequently found to be disordered. In particular, gut microbiota dysbiosis associated with or led to the occurrence and progression of infectious diseases, autoimmune diseases, metabolic diseases, and neurological diseases. Pathogenic microbes and their metabolites disturb the protective function of immune system, and lead to disordered immune responses that usually correlate with disease exacerbation. In the other hand, the immune system also regulates microbiota composition to keep host homeostasis. Here, we will discuss the current advances of our knowledge about the interactions between microbiota and host immune system during health and diseases.

Contribution of Gut Microbiota to Immunological Changes in Alzheimer's Disease

Emerging evidence suggests that both central and peripheral immunological processes play an important role in the pathogenesis of Alzheimer's disease (AD), but regulatory mechanisms remain unknown. The gut microbiota and its key metabolites are known to affect neuroinflammation by modulating the activity of peripheral and brain-resident immune cells, yet an overview on how the gut microbiota contribute to immunological alterations in AD is lacking. In this review, we discuss current literature on microbiota composition in AD patients and relevant animal models. Next, we highlight how microbiota and their metabolites may contribute to peripheral and central immunological changes in AD. Finally, we offer a future perspective on the translation of these findings into clinical practice by targeting gut microbiota to modulate inflammation in AD. Since we find that gut microbiota alterations in AD can induce peripheral and central immunological changes via the release of microbial metabolites, we propose that modulating their composition may alter ongoing inflammation and could therefore be a promising future strategy to fight progression of AD.

A Janus-Faced Bacterium: Host-Beneficial and -Detrimental Roles of Cutibacterium acnes

The bacterial species Cutibacterium acnes (formerly known as Propionibacterium acnes) is tightly associated with humans. It is the dominant bacterium in sebaceous regions of the human skin, where it preferentially colonizes the pilosebaceous unit. Multiple strains of C. acnes that belong to phylogenetically distinct types can co-exist. In this review we summarize and discuss the current knowledge of C. acnes regarding bacterial properties and traits that allow host colonization and play major roles in host-bacterium interactions and also regarding the host responses that C. acnes can trigger. These responses can have beneficial or detrimental consequences for the host. In the first part of the review, we highlight and critically review disease associations of C. acnes, in particular acne vulgaris, implant-associated infections and native infections. Here, we also analyse the current evidence for a direct or indirect role of a C. acnes-related dysbiosis in disease development or progression, i.e., reduced C. acnes strain diversity and/or the predominance of a certain phylotype. In the second part of the review, we highlight historical and recent findings demonstrating beneficial aspects of colonization by C. acnes such as colonization resistance, immune system interactions, and oxidant protection, and discuss the molecular mechanisms behind these effects. This new insight led to efforts in skin microbiota manipulation, such as the use of C. acnes strains as probiotic options to treat skin disorders.

Exploring the Gut-Brain Axis for the Control of CNS Inflammatory Demyelination: Immunomodulation by Bacteroides fragilis' Polysaccharide A

The symbiotic relationship between animals and their resident microorganisms has profound effects on host immunity. The human microbiota comprises bacteria that reside in the gastrointestinal tract and are involved in a range of inflammatory and autoimmune diseases. The gut microbiota's immunomodulatory effects extend to extraintestinal tissues, including the central nervous system (CNS). Specific symbiotic antigens responsible for inducing immunoregulation have been isolated from different bacterial species. Polysaccharide A (PSA) of Bacteroides fragilis is an archetypical molecule for host-microbiota interactions. Studies have shown that PSA has beneficial effects in experimental disease models, including experimental autoimmune encephalomyelitis (EAE), the most widely used animal model for multiple sclerosis (MS). Furthermore, in vitro stimulation with PSA promotes an immunomodulatory phenotype in human T cells isolated from healthy and MS donors. In this review, we discuss the current understanding of the interactions between gut microbiota and the host in the context of CNS inflammatory demyelination, the immunomodulatory roles of gut symbionts. More specifically, we also discuss the immunomodulatory effects of B. fragilis PSA in the gut-brain axis and its therapeutic potential in MS. Elucidation of the molecular mechanisms responsible for the microbiota's impact on host physiology offers tremendous promise for discovering new therapies.

ILC3, a Central Innate Immune Component of the Gut-Brain Axis in Multiple Sclerosis

Gut immune cells have been increasingly appreciated as important players in the central nervous system (CNS) autoimmunity in animal models of multiple sclerosis (MS). Among the gut immune cells, innate lymphoid cell type 3 (ILC3) is of special interest in MS research, as they represent the innate cell counterpart of the major pathogenic cell population in MS, i.e. T helper (Th)17 cells. Importantly, these cells have been shown to stimulate regulatory T cells (Treg) and to counteract pathogenic Th17 cells in animal models of autoimmune diseases. Besides, they are also well known for their ability to stabilize the intestinal barrier and to shape the immune response to the gut microbiota. Thus, proper maintenance of the intestinal barrier and the establishment of the regulatory milieu in the gut performed by ILC3 may prevent activation of CNS antigen-specific Th17 cells by the molecular mimicry. Recent findings on the role of ILC3 in the gut-CNS axis and their relevance for MS pathogenesis will be discussed in this paper. Possibilities of ILC3 functional modulation for the benefit of MS patients will be addressed, as well.

Common Peripheral Immunity Mechanisms in Multiple Sclerosis and Alzheimer's Disease

Neurodegenerative diseases are closely related to inflammatory and autoimmune events, suggesting that the dysregulation of the immune system is a key pathological factor. Both multiple sclerosis (MS) and Alzheimer's disease (AD) are characterized by infiltrating immune cells, activated microglia, astrocyte proliferation, and neuronal damage. Moreover, MS and AD share a common pro-inflammatory signature, characterized by peripheral leukocyte activation and transmigration to the central nervous system (CNS). MS and AD are both characterized by the accumulation of activated neutrophils in the blood, leading to progressive impairment of the blood–brain barrier. Having migrated to the CNS during the early phases of MS and AD, neutrophils promote local inflammation that contributes to pathogenesis and clinical progression. The role of circulating T cells in MS is well-established, whereas the contribution of adaptive immunity to AD pathogenesis and progression is a more recent discovery. Even so, blocking the transmigration of T cells to the CNS can benefit both MS and AD patients, suggesting that common adaptive immunity mechanisms play a detrimental role in each disease. There is also growing evidence that regulatory T cells are beneficial during the initial stages of MS and AD, supporting the link between the modulatory immune compartments and these neurodegenerative disorders. The number of resting regulatory T cells declines in both diseases, indicating a common pathogenic mechanism involving the dysregulation of these cells, although their precise role in the control of neuroinflammation remains unclear. The modulation of leukocyte functions can benefit MS patients, so more insight into the role of peripheral immune cells may reveal new targets for pharmacological intervention in other neuroinflammatory and neurodegenerative diseases, including AD.

Host surface ectonucleotidase-CD73 and the opportunistic pathogen, Porphyromonas gingivalis, cross-modulation underlies a new homeostatic mechanism for chronic bacterial survival in human epithelial cells

Cell surface nucleotide-metabolizing enzyme, ectonucleotidase-CD73, has emerged as a central component of the cellular homeostatic-machinery that counterbalances the danger-molecule (extracellular-ATP)-driven proinflammatory response in immune cells. While the importance of CD73 in microbial host fitness and symbiosis is gradually being unraveled, there remains a significant gap in knowledge of CD73 and its putative role in epithelial cells. Here, we depict a novel host-pathogen adaptation mechanism where CD73 takes a center role in the intracellular persistence of Porphyromonas gingivalis, a major colonizer of oral mucosa, using human primary gingival epithelial cell (GEC) system. Temporal analyses revealed, upon invasion into the GECs, P. gingivalis can significantly elevate the host-surface CD73 activity and expression. The enhanced and active CD73 significantly increases P. gingivalis intracellular growth in the presence of substrate-AMP and simultaneously acts as a negative regulator of reactive oxygen species (ROS) generation upon eATP treatment. The inhibition of CD73 by siRNA or by a specific inhibitor markedly increases ROS production. Moreover, CD73 and P. gingivalis cross-signaling significantly modulates pro-inflammatory interleukin-6 (IL-6) in the GECs. Conversely, exogenous treatment of the infected GECs with IL-6 suppresses the intracellular bacteria via amplified ROS generation. However, the decreased bacterial levels can be restored by overexpressing functionally active CD73. Together, these findings illuminate how the local extracellular-purine-metabolism, in which CD73 serves as a core molecular switch, can alter intracellular microbial colonization resistance. Further, host-adaptive pathogens such as P. gingivalis can target host ectonucleotidases to disarm specific innate defenses for successful intracellular persistence in mucosal epithelia.

Gut hormones in microbiota-gut-brain cross-talk

The homeostasis of the gut-brain axis has been shown to exert several effects on physiological and psychological health. The gut hormones released by enteroendocrine cells scattered throughout the gastrointestinal tract are important signaling molecules within the gut-brain axis. The interaction between gut microbiota and gut hormones has been greatly appreciated in gut-brain cross-talk. The microbiota plays an essential role in modulating many gut-brain axis-related diseases, ranging from gastrointestinal disorders to psychiatric diseases. Similarly, gut hormones also play pleiotropic and important roles in maintaining health, and are key signals involved in gut-brain axis. More importantly, gut microbiota can affect the release and functions of gut hormones. This review highlights the role of gut microbiota in the gut-brain axis and focuses on how microbiota-related gut hormones modulate various physiological functions. Future studies could target the microbiota-hormones-gut brain axis to develop novel therapeutics for different psychiatric and gastrointestinal disorders, such as obesity, anxiety, and depression.

Modulating Gut Microbiota: An Emerging Approach in the Prevention and Treatment of Multiple Sclerosis

Multiple sclerosis (MS) is a progressive neuromuscular disorder characterized by demyelination of neurons of the central nervous system (CNS). The pathogenesis of the disorder is described as an autoimmune attack targeting the myelin sheath of nerve cell axons in the CNS. Available treatments only reduce the risk of relapse, prolonging the remissions of neurological symptoms and halt the progression of the disorder. Among the new ways of targeting neurological disorders, including MS, there is modulation of gut microbiota since the link between gut microbiota has been rethought within the term gut-brain axis. Gut microbiota is known to help the body with essential functions such as vitamin production and positive regulation of immune, inflammatory, and metabolic pathways. High consumption of saturated fatty acids, gluten, salt, alcohol, artificial sweeteners, or antibiotics is the responsible factor for causing gut dysbiosis. The latter can lead to dysregulation of immune and inflammatory pathways, which eventually results in leaky gut syndrome, systemic inflammation, autoimmune reactions, and increased susceptibility to infections. In modern medicine, scientists have mostly focused on the modulation of gut microbiota in the development of novel and effective therapeutic strategies for numerous disorders, with probiotics and prebiotics being the most widely studied in this regard. Several pieces of evidence from preclinical and clinical studies have supported the positive impact of probiotic and/or prebiotic intake on gut microbiota and MS. This review aims to link gut dysbiosis with the development/progression of MS, and the potential of modulation of gut microbiota in the therapeutics of the disease.

Probiotic and commensal gut microbial therapies in multiple sclerosis and its animal models: a comprehensive review

The need for alternative treatments for multiple sclerosis (MS) has triggered copious amounts of research into microbial therapies focused on manipulating the microbiota-gut-brain axis. This comprehensive review was intended to present and systematically evaluate the current clinical and preclinical evidence for various probiotic and commensal gut microbial therapies as treatments for MS, using the Bradford Hill criteria (BHC) as a multi-parameter assessment rubric. Literature searches were performed to identify a total of 37 relevant studies (6 human, 31 animal), including 28 probiotic therapy and 9 commensal therapy studies. In addition to presenting qualitative summaries of these findings, therapeutic evidence for each bacterial formulation was assessed using the BHC to generate summative scores. These scores, which encompassed study quality, replication, and other considerations, were used to rank the most promising therapies and highlight deficiencies. Several therapeutic formulations, including VSL#3, Lactobacillus paracasei, Bifidobacterium animalis, E. coli Nissle 1917, and Prevotella histicola, emerged as the most promising. In contrast, a number of other therapies were hindered by limited evidence of replicable findings and other criteria, which need to be addressed by future studies in order to harness gut microbial therapies to ultimately provide cheaper, safer, and more durable treatments for MS.

Probióticos na redução de sintomas de ansiedade e depressão: uma revisão integrativa

Objetivos: sumarizar estudos que avaliaram a suplementação de probióticos como estratégia terapêutica nos sintomas da ansiedade e depressão. Métodos: revisão integrativa de artigos indexados na base de dados PubMed, SciELO e Biblioteca Virtual em Saúde publicados de janeiro de 2010 a setembro de 2019. Para isso, utilizou-se a conjugação dos descritores: “intestino”, “cérebro”, “microbiota intestinal”, “ansiedade”, “depressão”, “probióticos”, nos idiomas português e inglês. Resultados: Após a aplicação dos critérios de inclusão e exclusão, 13 ensaios clínicos randomizados foram selecionados. O tempo de duração dos estudos, em sua maioria, foi de 8 ou 12 semanas (61,5%; n = 8), e a forma mais ofertada do suplemento foi o probiótico em pó (46,2%; n = 6) e em cápsula (30,8%; n = 4). Sobre a utilização de escalas como parâmetro de avaliação dos sintomas de ansiedade e depressão, 38,5% (n = 5) utilizaram apenas uma escala e 69,2% (n = 8) utilizaram a combinação de duas ou três escalas. Em relação ao gênero das bactérias, a maior parte dos estudos utilizou Lactobacillus e Bifidobacterium em conjunto (53,8%; n = 7). Apesar das limitações metodológicas e dos resultados inconsistentes, a maioria dos ensaios clínicos (76,9%; n = 10) evidenciaram uma redução significativa dos sintomas relacionados à ansiedade e depressão através da suplementação de probióticos. Conclusão: As evidências indicam que a suplementação com probióticos apresenta potencial promissor na redução dos sintomas de ansiedade e depressão, no entanto são necessárias pesquisas adicionais sobre essa estratégia como terapia adjuvante no tratamento efetivo para a saúde mental.

Mechanisms of microbial-neuronal interactions in pain and nociception

•

Molecular mechanisms of how microorganisms communicate with sensory afferent neurons.

•

How pathogenic microorganisms directly communicate with nociceptor neurons to inflict pain on the host.

•

Symbiotic bacterial communication with gut-extrinsic sensory afferent neurons.

•

Plausible roles on how gut symbionts directly mediate pain and nociception.

Nociceptor sensory neurons innervate barrier tissues that are constantly exposed to microbial stimuli. During infection, pathogenic microorganisms can breach barrier surfaces and produce pain by directly activating nociceptors. Microorganisms that live in symbiotic relationships with their hosts, commensals and mutualists, have also been associated with pain, but the molecular mechanisms of how symbionts act on nociceptor neurons to modulate pain remain largely unknown. In this review, we will discuss the known molecular mechanisms of how microbes directly interact with sensory afferent neurons affecting nociception in the gut, skin and lungs. We will touch on how bacterial, viral and fungal pathogens signal to the host to inflict or suppress pain. We will also discuss recent studies examining how gut symbionts affect pain. Specifically, we will discuss how gut symbionts may interact with sensory afferent neurons either directly, through secretion of metabolites or neurotransmitters, or indirectly,through first signaling to epithelial cells or immune cells, to regulate visceral, neuropathic and inflammatory pain. While this area of research is still in its infancy, more mechanistic studies to examine microbial-sensory neuron crosstalk in nociception may allow us to develop new therapies for the treatment of acute and chronic pain.

Gut-Brain-Skin Axis in Psoriasis: A Review

Introduction

Psoriasis is a common skin disease, with chronic inflammation and a complex etiology. It has long been recognized that chronic skin conditions and mental health disorders are often co-morbid. Thus, the concept of the gut–brain–skin axis emphasized in mental health disorders may also regulate the health of skin.

Results

The gut microbiota has been found to be the bridge between the immune system and nervous system. By leveraging clinical cases and animal models of psoriasis, an important communication pathway has been identified along the gut–brain–skin axis that is associated with the modulation of neurotransmitters from the microbiota. Furthermore, mammalian neurotransmitters, including dopamine, serotonin, or γ-aminobutyric acid (GABA), can be produced and/or consumed by several types of bacteria. Other studies suggest that manipulating these neurotransmitters by bacteria may have an effect on host physiology, and the levels of neurotransmitter can be altered by microbiota-based interventions.

Conclusions

Nonetheless, it is unknown whether or not the manipulation of neurotransmitter levels by bacteria can affect the occurrence and development of psoriasis. Notably, preliminary experiments found that oral consumption of probiotics improves the clinical symptoms in patients with psoriasis, perhaps correlated with the gut microbiome-mediated crosstalk between the immune system and the nervous system by secreting neurotransmitters in psoriasis. In this review, the communication along the gut–brain–skin axis is discussed.

Gut Microbiota-Bile Acid Crosstalk in Diarrhea-Irritable Bowel Syndrome

The occurrence of diarrhea-predominant irritable bowel syndrome (IBS-D) is the result of multiple factors, and its pathogenesis has not yet been clarified. Emerging evidence indicates abnormal changes in gut microbiota and bile acid (BA) metabolism have a close relationship with IBS-D. Gut microbiota is involved in the secondary BA production via deconjugation, 7α-dehydroxylation, oxidation, epimerization, desulfation, and esterification reactions respectively. Changes in the composition and quantity of gut microbiota have an important impact on the metabolism of BAs, which can lead to the occurrence of gastrointestinal diseases. BAs, synthesized in the hepatocytes, play an important role in maintaining the homeostasis of gut microbiota and the balance of glucose and lipid metabolism. In consideration of the complex biological functional connections among gut microbiota, BAs, and IBS-D, it is urgent to review the latest research progress in this field. In this review, we summarized the alterations of gut microbiota in IBS-D and discussed the mechanistic connections between gut microbiota and BA metabolism in IBS-D, which may be involved in activating two important bile acid receptors, G-protein coupled bile acid receptor 1 (TGR5) and farnesoid X receptor (FXR). We also highlight the strategies of prevention and treatment of IBS-D via regulating gut microbiota-bile acid axis, including probiotics, fecal microbiota transplantation (FMT), cholestyramine, and the cutting-edge technology about bacteria genetic engineering.