A bidirectional association between the gut microbiota and CNS disease in a biphasic murine model of multiple sclerosis

Gut flora in multiple sclerosis: implications for pathogenesis and treatment

ABSTRACT

Multiple sclerosis is an inflammatory disorder characterized by inflammation, demyelination, and neurodegeneration in the central nervous system. Although current first-line therapies can help manage symptoms and slow down disease progression, there is no cure for multiple sclerosis. The gut-brain axis refers to complex communications between the gut flora and the immune, nervous, and endocrine systems, which bridges the functions of the gut and the brain. Disruptions in the gut flora, termed dysbiosis, can lead to systemic inflammation, leaky gut syndrome, and increased susceptibility to infections. The pathogenesis of multiple sclerosis involves a combination of genetic and environmental factors, and gut flora may play a pivotal role in regulating immune responses related to multiple sclerosis. To develop more effective therapies for multiple sclerosis, we should further uncover the disease processes involved in multiple sclerosis and gain a better understanding of the gut-brain axis. This review provides an overview of the role of the gut flora in multiple sclerosis.

Targeting gut microbiota: new therapeutic opportunities in multiple sclerosis

Multiple sclerosis (MS) causes long-lasting, multifocal damage to the central nervous system. The complex background of MS is associated with autoimmune inflammation and neurodegeneration processes, and is potentially affected by many contributing factors, including altered composition and function of the gut microbiota. In this review, current experimental and clinical evidence is presented for the characteristics of gut dysbiosis found in MS, as well as for its relevant links with the course of the disease and the dysregulated immune response and metabolic pathways involved in MS pathology. Furthermore, therapeutic implications of these investigations are discussed, with a range of pharmacological, dietary and other interventions targeted at the gut microbiome and thus intended to have beneficial effects on the course of MS.

Endurance Exercise Attenuates Established Progressive Experimental Autoimmune Encephalomyelitis and Is Associated with an Amelioration of Innate Immune Responses in NOD Mice

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease causing axonal degeneration and demyelination. Exercise in mice with active monophasic experimental autoimmune encephalomyelitis (EAE) attenuates disease severity associated with diverse impacts on T cell-mediated immunity. However, studies have so far focused on preventive approaches. In this study, we investigated the impact of endurance exercise on established EAE disease in a model of secondary progressive MS. When the exercise program on motorized running wheels was started at disease manifestation, the disease course was significantly ameliorated. This was associated with a significant decrease in B cell, dendritic cell, and neutrophil cell counts in the central nervous system (CNS). Furthermore, we observed an increased expression of major histocompatibility complex class II (MHC-II) as well as alterations in costimulatory molecule expression in CNS B cells and dendritic cells. In contrast, T cell responses were not altered in the CNS or periphery. Thus, exercise training is capable of attenuating the disease course even in established secondary progressive EAE, potentially via modulation of the innate immune compartment. Further studies are warranted to corroborate our findings and assess the potential of this lifestyle intervention as a complementary therapeutic strategy in secondary progressive MS patients.

The gut microbiome: an important role in neurodegenerative diseases and their therapeutic advances

There are complex interactions between the gut and the brain. With increasing research on the relationship between gut microbiota and brain function, accumulated clinical and preclinical evidence suggests that gut microbiota is intimately involved in the pathogenesis of neurodegenerative diseases (NDs). Increasingly studies are beginning to focus on the association between gut microbiota and central nervous system (CNS) degenerative pathologies to find potential therapies for these refractory diseases. In this review, we summarize the changes in the gut microbiota in Alzheimer's disease, Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis and contribute to our understanding of the function of the gut microbiota in NDs and its possible involvement in the pathogenesis. We subsequently discuss therapeutic approaches targeting gut microbial abnormalities in these diseases, including antibiotics, diet, probiotics, and fecal microbiota transplantation (FMT). Furthermore, we summarize some completed and ongoing clinical trials of interventions with gut microbes for NDs, which may provide new ideas for studying NDs.

Unraveling the Gut-Brain Axis in Multiple Sclerosis: Exploring Dysbiosis, Oxidative Stress, and Therapeutic Insights

This comprehensive review delves into the intricate relationship between the gut microbiota and multiple sclerosis (MS), shedding light on the potential therapeutic avenues for this complex autoimmune disease. It emphasizes the multifactorial nature of MS, including genetic, environmental, and gender-related factors. Furthermore, the article highlights the emerging role of gut microbiota in MS pathophysiology, particularly in terms of gut dysbiosis, oxidative stress, and inflammasome activation within the gut-brain axis. This interplay raises intriguing questions about how the gut microbiota influences the onset and progression of MS. Environmental factors, such as diet and pollutants, add further layers of complexity to the connection between gut health and MS risk. This review also discusses promising therapeutic interventions, such as fecal microbiota transplantation, probiotics, dietary adjustments, and gut-derived metabolites that offer potential avenues for managing MS. It underscores the need for ongoing research to fully unravel the complexities of the role of the gut-brain axis in MS. Ultimately, this article provides a comprehensive exploration of the topic, offering hope for novel preventive and therapeutic strategies that could significantly improve the lives of individuals affected by this challenging autoimmune condition.

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.

Akkermansia muciniphila in neuropsychiatric disorders: friend or foe?

An accumulating body of evidence suggests that the bacterium Akkermansia muciniphila exhibits positive systemic effects on host health, mainly by improving immunological and metabolic functions, and it is therefore regarded as a promising potential probiotic. Recent clinical and preclinical studies have shown that A. muciniphila plays a vital role in a variety of neuropsychiatric disorders by influencing the host brain through the microbiota-gut-brain axis (MGBA). Numerous studies observed that A. muciniphila and its metabolic substances can effectively improve the symptoms of neuropsychiatric disorders by restoring the gut microbiota, reestablishing the integrity of the gut mucosal barrier, regulating host immunity, and modulating gut and neuroinflammation. However, A. muciniphila was also reported to participate in the development of neuropsychiatric disorders by aggravating inflammation and influencing mucus production. Therefore, the exact mechanism of action of A. muciniphila remains much controversial. This review summarizes the proposed roles and mechanisms of A. muciniphila in various neurological and psychiatric disorders such as depression, anxiety, Parkinson's disease, Alzheimer's disease, multiple sclerosis, strokes, and autism spectrum disorders, and provides insights into the potential therapeutic application of A. muciniphila for the treatment of these conditions.

The Role of Gut Microbiome in the Pathogenesis of Multiple Sclerosis and Related Disorders

Multiple sclerosis (MS) is a chronic, progressive neuroinflammatory disease with a complex pathophysiological background. A variety of diverse factors have been attributed to the propagation of inflammation and neurodegeneration in MS, mainly genetic, immunological, and environmental factors such as vitamin D deficiency, infections, or hormonal disbalance. Recently, the importance of the gut-brain axis for the development of many neurological conditions, including stroke, movement disorders, and neuroinflammatory disorders, has been postulated. The purpose of our paper was to summarize current evidence confirming the role of the gut microbiome in the pathophysiology of MS and related disorders, such as neuromyelitis optica spectrum disorder (NMO-SD). For this aim, we conducted a systematic review of the literature listed in the following databases: Medline, Pubmed, and Scopus, and were able to identify several studies demonstrating the involvement of the gut microbiome in the pathophysiology of MS and NMO-SD. It seems that the most relevant bacteria for the pathophysiology of MS are those belonging to Pseudomonas, Mycoplasma, Haemophilus, Blautia, Dorea, Faecalibacterium, Methanobrevibacter, Akkermansia, and Desulfovibrionaceae genera, while Clostridium perfringens and Streptoccocus have been demonstrated to play a role in the pathophysiology of NMO-SD. Following this line of evidence, there is also some preliminary data supporting the use of probiotics or other agents affecting the microbiome that could potentially have a beneficial effect on MS/NMO-SD symptoms and prognosis. The topic of the gut microbiome in the pathophysiology of MS is therefore relevant since it could be used as a biomarker of disease development and progression as well as a potential disease-modifying therapy.

Obesity, gut microbiota, and multiple sclerosis: Unraveling the connection

Obesity is associated with chronic mild-grade systemic inflammation and neuroinflammation. Obesity in early childhood and adolescence is also a significant risk factor for multiple sclerosis (MS) development. However, the underlying mechanisms that explain the link between obesity and MS development are not fully explored. An increasing number of studies call attention to the importance of gut microbiota as a leading environmental risk factor mediating inflammatory central nervous system demyelination, particularly in MS. Obesity and high-calorie diet are also associated with disturbances in gut microbiota. Therefore, gut microbiota alteration is a plausible connection between obesity and the increased risk of MS development. A greater understanding of this connection could provide additional therapeutic opportunities, like dietary interventions, microbiota-derived products, and exogenous antibiotics and probiotics. This review summarizes the current evidence regarding the relationships between MS, obesity, and gut microbiota. We discuss gut microbiota as a potential link between obesity and increased risk for MS. Additional experimental studies and controlled clinical trials targeting gut microbiota are warranted to unravel the possible causal relationship between obesity and increased risk of MS.

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.

Gut microbiome-modulated dietary strategies in EAE and multiple sclerosis

Over the last few decades, the incidence of multiple sclerosis has increased as society's dietary habits have switched from a whole foods approach to a high fat, high salt, low dietary fiber, and processed food diet, termed the "Western diet." Environmental factors, such as diet, could play a role in the pathogenesis of multiple sclerosis due to gut microbiota alterations, gut barrier leakage, and subsequent intestinal inflammation that could lead to exacerbated neuroinflammation. This mini-review explores the gut microbiome alterations of various dietary strategies that improve upon the "Western diet" as promising alternatives and targets to current multiple sclerosis treatments. We also provide evidence that gut microbiome modulation through diet can improve or exacerbate clinical symptoms of multiple sclerosis, highlighting the importance of including gut microbiome analyses in future studies of diet and disease.

Potential biological contributers to the sex difference in multiple sclerosis progression

Multiple sclerosis (MS) is an immune-mediated disease that targets the myelin sheath of central nervous system (CNS) neurons leading to axon injury, neuronal death, and neurological progression. Though women are more highly susceptible to developing MS, men that develop this disease exhibit greater cognitive impairment and accumulate disability more rapidly than women. Magnetic resonance imaging and pathology studies have revealed that the greater neurological progression seen in males correlates with chronic immune activation and increased iron accumulation at the rims of chronic white matter lesions as well as more intensive whole brain and grey matter atrophy and axon loss. Studies in humans and in animal models of MS suggest that male aged microglia do not have a higher propensity for inflammation, but may become more re-active at the rim of white matter lesions as a result of the presence of pro-inflammatory T cells, greater astrocyte activation or iron release from oligodendrocytes in the males. There is also evidence that remyelination is more efficient in aged female than aged male rodents and that male neurons are more susceptible to oxidative and nitrosative stress. Both sex chromosome complement and sex hormones contribute to these sex differences in biology.

The immunology of multiple sclerosis

Our incomplete understanding of the causes and pathways involved in the onset and progression of multiple sclerosis (MS) limits our ability to effectively treat this complex neurological disease. Recent studies explore the role of immune cells at different stages of MS and how they interact with cells of the central nervous system (CNS). The findings presented here begin to question the exclusivity of an antigen-specific cause and highlight how seemingly distinct immune cell types can share common functions that drive disease. Innovative techniques further expose new disease-associated immune cell populations and reinforce how environmental context is critical to their phenotype and subsequent role in disease. Importantly, the differentiation of immune cells into a pathogenic state is potentially reversible through therapeutic manipulation. As such, understanding the mechanisms that provide plasticity to causal cell types is likely key to uncoupling these disease processes and may identify novel therapeutic targets that replace the need for cell ablation.

Mining the microbiota to identify gut commensals modulating neuroinflammation in a mouse model of multiple sclerosis

BACKGROUND

The gut microbiome plays an important role in autoimmunity including multiple sclerosis and its mouse model called experimental autoimmune encephalomyelitis (EAE). Prior studies have demonstrated that the multiple sclerosis gut microbiota can contribute to disease, hence making it a potential therapeutic target. In addition, antibiotic treatment has been shown to ameliorate disease in the EAE mouse model of multiple sclerosis. Yet, to this date, the mechanisms mediating these antibiotic effects are not understood. Furthermore, there is no consensus on the gut-derived bacterial strains that drive neuroinflammation in multiple sclerosis.

RESULTS

Here, we characterized the gut microbiome of untreated and vancomycin-treated EAE mice over time to identify bacteria with neuroimmunomodulatory potential. We observed alterations in the gut microbiota composition following EAE induction. We found that vancomycin treatment ameliorates EAE, and that this protective effect is mediated via the microbiota. Notably, we observed increased abundance of bacteria known to be strong inducers of regulatory T cells, including members of Clostridium clusters XIVa and XVIII in vancomycin-treated mice during the presymptomatic phase of EAE, as well as at disease peak. We identified 50 bacterial taxa that correlate with EAE severity. Interestingly, several of these taxa exist in the human gut, and some of them have been implicated in multiple sclerosis including Anaerotruncus colihominis, a butyrate producer, which had a positive correlation with disease severity. We found that Anaerotruncus colihominis ameliorates EAE, and this is associated with induction of RORγt⁺ regulatory T cells in the mesenteric lymph nodes.

CONCLUSIONS

We identified vancomycin as a potent modulator of the gut-brain axis by promoting the proliferation of bacterial species that induce regulatory T cells. In addition, our findings reveal 50 gut commensals as regulator of the gut-brain axis that can be used to further characterize pathogenic and beneficial host-microbiota interactions in multiple sclerosis patients. Our findings suggest that elevated Anaerotruncus colihominis in multiple sclerosis patients may represent a protective mechanism associated with recovery from the disease. Video Abstract.

Fucoxanthin: A Promising Phytochemical on Diverse Pharmacological Targets

Fucoxanthin (FX) is a special carotenoid having an allenic bond in its structure. FX is extracted from a variety of algae and edible seaweeds. It has been proved to contain numerous health benefits and preventive effects against diseases like diabetes, obesity, liver cirrhosis, malignant cancer, etc. Thus, FX can be used as a potent source of both pharmacological and nutritional ingredient to prevent infectious diseases. In this review, we gathered the information regarding the current findings on antimicrobial, antioxidant, anti-inflammatory, skin protective, anti-obesity, antidiabetic, hepatoprotective, and other properties of FX including its bioavailability and stability characteristics. This review aims to assist further biochemical studies in order to develop further pharmaceutical assets and nutritional products in combination with FX and its various metabolites.

Probiotics: Protecting Our Health from the Gut

The gut microbiota (GM) comprises billions of microorganisms in the human gastrointestinal tract. This microbial community exerts numerous physiological functions. Prominent among these functions is the effect on host immunity through the uptake of nutrients that strengthen intestinal cells and cells involved in the immune response. The physiological functions of the GM are not limited to the gut, but bidirectional interactions between the gut microbiota and various extraintestinal organs have been identified. These interactions have been termed interorganic axes by several authors, among which the gut–brain, gut–skin, gut–lung, gut–heart, and gut–metabolism axes stand out. It has been shown that an organism is healthy or in homeostasis when the GM is in balance. However, altered GM or dysbiosis represents a critical factor in the pathogenesis of many local and systemic diseases. Therefore, probiotics intervene in this context, which, according to various published studies, allows balance to be maintained in the GM, leading to an individual’s good health.

The Role of Microbiome in Brain Development and Neurodegenerative Diseases

Hundreds of billions of commensal microorganisms live in and on our bodies, most of which colonize the gut shortly after birth and stay there for the rest of our lives. In animal models, bidirectional communications between the central nervous system and gut microbiota (Gut-Brain Axis) have been extensively studied, and it is clear that changes in microbiota composition play a vital role in the pathogenesis of various neurodevelopmental and neurodegenerative disorders, such as Autism Spectrum Disorder, Alzheimer's disease, Parkinson's disease, Multiple Sclerosis, Amyotrophic Lateral Sclerosis, anxiety, stress, and so on. The makeup of the microbiome is impacted by a variety of factors, such as genetics, health status, method of delivery, environment, nutrition, and exercise, and the present understanding of the role of gut microbiota and its metabolites in the preservation of brain functioning and the development of the aforementioned neurological illnesses is summarized in this review article. Furthermore, we discuss current breakthroughs in the use of probiotics, prebiotics, and synbiotics to address neurological illnesses. Moreover, we also discussed the role of boron-based diet in memory, boron and microbiome relation, boron as anti-inflammatory agents, and boron in neurodegenerative diseases. In addition, in the coming years, boron reagents will play a significant role to improve dysbiosis and will open new areas for researchers.

Focus on the Role of the NLRP3 Inflammasome in Multiple Sclerosis: Pathogenesis, Diagnosis, and Therapeutics

Neuroinflammation is initiated with an aberrant innate immune response in the central nervous system (CNS) and is involved in many neurological diseases. Inflammasomes are intracellular multiprotein complexes that can be used as platforms to induce the maturation and secretion of proinflammatory cytokines and pyroptosis, thus playing a pivotal role in neuroinflammation. Among the inflammasomes, the nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3) inflammasome is well-characterized and contributes to many neurological diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), and ischemic stroke. MS is a chronic autoimmune disease of the CNS, and its hallmarks include chronic inflammation, demyelination, and neurodegeneration. Studies have demonstrated a relationship between MS and the NLRP3 inflammasome. To date, the pathogenesis of MS is not fully understood, and clinical studies on novel therapies are still underway. Here, we review the activation mechanism of the NLRP3 inflammasome, its role in MS, and therapies targeting related molecules, which may be beneficial in MS.

Microbiota, IgA and Multiple Sclerosis

Multiple sclerosis (MS) is a neuroinflammatory disease characterized by immune cell infiltration in the central nervous system and destruction of myelin sheaths. Alterations of gut bacteria abundances are present in MS patients. In mouse models of neuroinflammation, depletion of microbiota results in amelioration of symptoms, and gavage with MS patient microbiota exacerbates the disease and inflammation via Th17 cells. On the other hand, depletion of B cells using anti-CD20 is an efficient therapy in MS, and growing evidence shows an important deleterious role of B cells in MS pathology. However, the failure of TACI-Ig treatment in MS highlighted the potential regulatory role of plasma cells. The mechanism was recently demonstrated involving IgA+ plasma cells, specific for gut microbiota and producing IL-10. IgA-coated bacteria in MS patient gut exhibit also modifications. We will focus our review on IgA interactions with gut microbiota and IgA+ B cells in MS. These recent data emphasize new pathways of neuroinflammation regulation in MS.

Multiple Sclerosis and Microbiome

The composition of microbiota and the gut-brain axis is increasingly considered a factor in the development of various pathological conditions. The etiology of multiple sclerosis (MS), a chronic autoimmune disease affecting the CNS, is complex and interactions within the gut-brain axis may be relevant in the development and the course of MS. In this article, we focus on the relationship between gut microbiota and the pathophysiology of MS. We review the contribution of germ-free mouse studies to our understanding of MS pathology and its implications for treatment strategies to modulate the microbiome in MS. This summary highlights the need for a better understanding of the role of the microbiota in patients’ responses to disease-modifying drugs in MS and disease activity overall.

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.

Dietary Isoflavones Alter Gut Microbiota and Lipopolysaccharide Biosynthesis to Reduce Inflammation

The etiopathogenesis of multiple sclerosis (MS) is strongly affected by environmental factors such as diet and the gut microbiota. An isoflavone-rich (ISO) diet was previously shown to reduce the severity of MS in the animal model experimental autoimmune encephalomyelitis (EAE). Translation of this concept to clinical trial where dietary isoflavones may be recommended for MS patients will require preliminary evidence that providing the isoflavone-rich diet to people with MS (PwMS) who lack phytoestrogen-metabolizing bacteria has beneficial effects. We have previously shown that the gut microbiota of PwMS resembles the gut microbiota of mice raised under a phytoestrogen-free (phyto-free) diet in that it lacks phytoestrogen-metabolizing bacteria. To investigate the effects of phytoestrogens on the microbiota inflammatory response and EAE disease severity we switched the diet of mice raised under a phyto-free (PF) diet to an isoflavone-rich diet. Microbiota analysis showed that the change in diet from one that is ISO to one that is PF reduces beneficial bacteria such as Bifidobacterium species. In addition we observed functional differences in lipopolysaccharide (LPS) biosynthesis pathways. Moreover LPS extracted from feces of mice fed an ISO diet induced increased production of anti-inflammatory cytokines from bone marrow-derived macrophages relative to fecal-LPS isolated from mice fed a PF diet. Eventually mice whose diet was switched from a PF diet to an ISO diet trended toward reduced EAE severity and mortality. Overall we show that an isoflavone-rich diet specifically modulates LPS biosynthesis of the gut microbiota imparts an anti-inflammatory response and decreases disease severity.

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 second brain: The connection between gut microbiota composition and multiple sclerosis

Gut microbiota composition may affect the central nervous system (CNS) and immune function. Several studies have recently examined the possible link between gut microbiota composition and multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Most of these studies agree that patients with MS suffer from dysbiosis. Moreover, an altered proportion of certain phyla of bacteria was detected in the digestive tracts of these patients compared to healthy individuals. This review article gathers information from research papers that have examined the relationship between gut microbiota composition and MS and its possible mechanisms.

The Impact of IgA and the Microbiota on CNS Disease

Although anatomically distant from the central nervous system (CNS), gut-derived signals can dynamically regulate both peripheral immune cells and CNS-resident glial cells to modulate disease. Recent discoveries of specific microbial taxa and microbial derived metabolites that modulate neuroinflammation and neurodegeneration have provided mechanistic insight into how the gut may modulate the CNS. Furthermore, the participation of the gut in regulation of peripheral and CNS immune activity introduces a potential therapeutic target. This review addresses emerging literature on how the microbiome can affect glia and circulating lymphocytes in preclinical models of human CNS disease. Critically, this review also discusses how the host may in turn influence the microbiome, and how this may impact CNS homeostasis and disease, potentially through the production of IgA.

HLA Class II Polymorphisms Modulate Gut Microbiota and Experimental Autoimmune Encephalomyelitis Phenotype

Multiple sclerosis (MS) is an autoimmune disease of the CNS in which the interaction between genetic and environmental factors plays an important role in disease pathogenesis. Although environmental factors account for 70% of disease risk, the exact environmental factors associated with MS are unknown. Recently, gut microbiota has emerged as a potential missing environmental factor linked with the pathobiology of MS. Yet, how genetic factors, such as HLA class II gene(s), interact with gut microbiota and influence MS is unclear. In the current study, we investigated whether HLA class II genes that regulate experimental autoimmune encephalomyelitis (EAE) and MS susceptibility also influence gut microbiota. Previously, we have shown that HLA-DR3 transgenic mice lacking endogenous mouse class II genes (AE-KO) were susceptible to myelin proteolipid protein (91-110)-induced EAE, an animal model of MS, whereas AE-KO.HLA-DQ8 transgenic mice were resistant. Surprisingly, HLA-DR3.DQ8 double transgenic mice showed higher disease prevalence and severity compared with HLA-DR3 mice. Gut microbiota analysis showed that HLA-DR3, HLA-DQ8, and HLA-DR3.DQ8 double transgenic mice microbiota are compositionally different from AE-KO mice. Within HLA class II transgenic mice, the microbiota of HLA-DQ8 mice were more similar to HLA-DR3.DQ8 than HLA-DR3. As the presence of DQ8 on an HLA-DR3 background increases disease severity, our data suggests that HLA-DQ8-specific microbiota may contribute to disease severity in HLA-DR3.DQ8 mice. Altogether, our study provides evidence that the HLA-DR and -DQ genes linked to specific gut microbiota contribute to EAE susceptibility or resistance in a transgenic animal model of MS.

Sepsis and multiple sclerosis: Causative links and outcomes

Sepsis is a life-threatening condition characterized by an acute cytokine storm followed by prolonged dysfunction of the immune system in the survivors. Post-septic lymphopenia and functional deficits of the remaining immune cells lead to increased susceptibility to secondary infections and other morbid conditions causing late death in the patients. This state of post-septic immunoparalysis may also influence disorders stemming from inappropriate or overactive immune responses, such as autoimmune and immunoinflammatory diseases, including multiple sclerosis. In addition, ongoing autoimmunity likely influences the susceptibility to and outcome of sepsis. This review article addresses the bidirectional relationship between sepsis and multiple sclerosis, with a focus on the immunologic mechanisms of the interaction and potential directions for future studies.

Targeting the gut to treat multiple sclerosis

The gut-brain axis (GBA) refers to the complex interactions between the gut microbiota and the nervous, immune, and endocrine systems, together linking brain and gut functions. Perturbations of the GBA have been reported in people with multiple sclerosis (pwMS), suggesting a possible role in disease pathogenesis and making it a potential therapeutic target. While research in the area is still in its infancy, a number of studies revealed that pwMS are more likely to exhibit altered microbiota, altered levels of short chain fatty acids and secondary bile products, and increased intestinal permeability. However, specific microbes and metabolites identified across studies and cohorts vary greatly. Small clinical and preclinical trials in pwMS and mouse models, in which microbial composition was manipulated through the use of antibiotics, fecal microbiota transplantation, and probiotic supplements, have provided promising outcomes in preventing CNS inflammation. However, results are not always consistent, and large-scale randomized controlled trials are lacking. Herein, we give an overview of how the GBA could contribute to MS pathogenesis, examine the different approaches tested to modulate the GBA, and discuss how they may impact neuroinflammation and demyelination in the CNS.

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.

Gut Microbiome in Progressive Multiple Sclerosis

OBJECTIVE

This study was undertaken to investigate the gut microbiome in progressive multiple sclerosis (MS) and how it relates to clinical disease.

METHODS

We sequenced the microbiota from healthy controls and relapsing-remitting MS (RRMS) and progressive MS patients and correlated the levels of bacteria with clinical features of disease, including Expanded Disability Status Scale (EDSS), quality of life, and brain magnetic resonance imaging lesions/atrophy. We colonized mice with MS-derived Akkermansia and induced experimental autoimmune encephalomyelitis (EAE).

RESULTS

Microbiota β-diversity differed between MS patients and controls but did not differ between RRMS and progressive MS or differ based on disease-modifying therapies. Disease status had the greatest effect on the microbiome β-diversity, followed by body mass index, race, and sex. In both progressive MS and RRMS, we found increased Clostridium bolteae, Ruthenibacterium lactatiformans, and Akkermansia and decreased Blautia wexlerae, Dorea formicigenerans, and Erysipelotrichaceae CCMM. Unique to progressive MS, we found elevated Enterobacteriaceae and Clostridium g24 FCEY and decreased Blautia and Agathobaculum. Several Clostridium species were associated with higher EDSS and fatigue scores. Contrary to the view that elevated Akkermansia in MS has a detrimental role, we found that Akkermansia was linked to lower disability, suggesting a beneficial role. Consistent with this, we found that Akkermansia isolated from MS patients ameliorated EAE, which was linked to a reduction in RORγt+ and IL-17-producing γδ T cells.

INTERPRETATION

Whereas some microbiota alterations are shared in relapsing and progressive MS, we identified unique bacteria associated with progressive MS and clinical measures of disease. Furthermore, elevated Akkermansia in MS may be a compensatory beneficial response in the MS microbiome. ANN NEUROL 2021;89:1195-1211.

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.

Bifidobacterium Lactis Probio-M8 regulates gut microbiota to alleviate Alzheimer's disease in the APP/PS1 mouse model

PURPOSE

Studies have shown that Alzheimer's disease is associated with significant alterations in the gut microbiota. But the effect of probiotics and/or prebiotics on Alzheimer's disease still remains to be explored. The aim of this study was to determine whether Bifidobacterium Lactis Probio-M8 could alleviate Alzheimer's disease pathophysiologies in the APP/PS1 transgenic mouse model.

METHODS

4-month old APP/PS1 mice were randomly put into two groups and fed with either Probio-M8 or saline water for 45 days. Fecal samples of mice were collected at the beginning and the end of the treatment period to determine the composition of the gut microbiota via 16S ribosomal RNA sequencing technology. The number and size of Aβ plaques in the brain were quantified. In addition, Y maze, novel object recognition and nest building were employed to access cognitive function in the 8-months old APP/PS1 mice at the end of the treatment period.

CONCLUSION

Our results demonstrated that Probio-M8 reduced Aβ plaque burden in the whole brain and protected against gut microbiota dysbiosis. Furthermore, Probio-M8 could alleviate cognitive impairment in the APP/PS1 mouse.

Sleep and Circadian Disruption and the Gut Microbiome-Possible Links to Dysregulated Metabolism

Insufficient sleep and circadian misalignment are associated with adverse metabolic health outcomes. Alterations in gut microbial diversity occur with insufficient sleep and circadian misalignment, which can lead to modifications in microbial structure and function. Changes in microbially produced and modified metabolites such as short chain fatty acids and secondary bile acids may contribute to chronic inflammation, positive energy balance and endocrine changes, and represent potential mechanisms linking insufficient sleep and circadian misalignment with metabolic dysregulation. Literature primarily from the last two years is reviewed here, examining the impact of sleep and circadian rhythms and their disruption on the gut microbiome in human and non-human models, with an emphasis on the hypothesis that the altered gut microbiome may be one pathway by which insufficient sleep and circadian misalignment dysregulate metabolism.

Gut Microbiota Changes in Experimental Autoimmune Encephalomyelitis and Cuprizone Mice Models

Multiple sclerosis (MS) is a chronic and neurodegenerative disease of the central nervous system (CNS) characterized by the immune mediated attack on axons and the subsequent demyelination. There is growing evidence that the gut microbiota of MS patients is altered; however, the connection between demyelination events and changes in the gut microbiota has not been determined. The objective of the current work was to characterize the microbial dysbiosis in two murine demyelinating models and to study the correlation between them. Concurrently, their suitability as predictors of microbial changes in MS patients was assessed. To this purpose, experimental autoimmune encephalomyelitis (EAE) and cuprizone (CPZ) models were induced in C57BL/6 mice that were monitored for 4 and 9 weeks, respectively. Fecal samples were collected during disease progression. Motor skill performance was evaluated by EAE scale measurement in EAE mice and demyelination by magnetic resonance imaging (MRI) in CPZ ones. EAE and CPZ mice revealed drastic microbial changes according to disease progression, adding a new layer of complexity to the understanding of demyelination and remyelination processes. Besides, the reported microbial changes replicate most of the characteristics that define the potential dysbiosis in MS patients. The controlled environment and stable diet that animals have in research centers offer an exceptional scenario to modify animal's microbiota and provide opportunities to study host microbiota interplay with restrained conditions not achievable in human studies. Nevertheless the slight differences from murine model's and patient's microbiota should be considered in the design of studies aiming to modulate the microbiota.

Dysbiosis of the intestinal microbiome as a component of pathophysiology in the inborn errors of metabolism

Inborn errors of metabolism (IEMs) represent monogenic disorders in which specific enzyme deficiencies, or a group of enzyme deficiencies (e.g., peroxisomal biogenesis disorders) result in either toxic accumulation of metabolic intermediates or deficiency in the production of key end-products (e.g., low cholesterol in Smith-Lemli-Opitz syndrome (Gedam et al., 2012 [1]); low creatine in guanidinoacetic acid methyltransferase deficiency (Stromberger, 2003 [2])). Some IEMs can be effectively treated by dietary restrictions (e.g., phenylketonuria (PKU), maple syrup urine disease (MSUD)), and/or dietary intervention to remove offending compounds (e.g., acylcarnitine excretion with the oral intake of l-carnitine in the disorders of fatty acid oxidation). While the IEMs are predominantly monogenic disorders, their phenotypic presentation is complex and pleiotropic, impacting multiple physiological systems (hepatic and neurological function, renal and musculoskeletal impairment, cardiovascular and pulmonary activity, etc.). The metabolic dysfunction induced by the IEMs, as well as the dietary interventions used to treat them, are predicted to impact the gut microbiome in patients, and it is highly likely that microbiome dysbiosis leads to further exacerbation of the clinical phenotype. That said, only recently has the gut microbiome been considered as a potential pathomechanistic consideration in the IEMs. In this review, we overview the function of the gut-brain axis, the crosstalk between these compartments, and the expanding reports of dysbiosis in the IEMs recently reported. The potential use of pre- and probiotics to improve clinical outcomes in IEMs is also highlighted.

The Microbiota-Gut-Brain Axis and Alzheimer's Disease: Neuroinflammation Is to Blame?

For years, it has been reported that Alzheimer’s disease (AD) is the most common cause of dementia. Various external and internal factors may contribute to the early onset of AD. This review highlights a contribution of the disturbances in the microbiota–gut–brain (MGB) axis to the development of AD. Alteration in the gut microbiota composition is determined by increase in the permeability of the gut barrier and immune cell activation, leading to impairment in the blood–brain barrier function that promotes neuroinflammation, neuronal loss, neural injury, and ultimately AD. Numerous studies have shown that the gut microbiota plays a crucial role in brain function and changes in the behavior of individuals and the formation of bacterial amyloids. Lipopolysaccharides and bacterial amyloids synthesized by the gut microbiota can trigger the immune cells residing in the brain and can activate the immune response leading to neuroinflammation. Growing experimental and clinical data indicate the prominent role of gut dysbiosis and microbiota–host interactions in AD. Modulation of the gut microbiota with antibiotics or probiotic supplementation may create new preventive and therapeutic options in AD. Accumulating evidences affirm that research on MGB involvement in AD is necessary for new treatment targets and therapies for AD.

Human Commensal Prevotella histicola Ameliorates Disease as Effectively as Interferon-Beta in the Experimental Autoimmune Encephalomyelitis

Gut microbiota has emerged as an important environmental factor in the pathobiology of multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system (CNS). Both genetic and environmental factors have been shown to play an important role in MS. Among genetic factors, the human leukocyte antigen (HLA) class II allele such as HLA-DR2, DR3, DR4, DQ6, and DQ8 show the association with the MS. We have previously used transgenic mice expressing MS susceptible HLA class II allele such as HLA-DR2, DR3, DQ6, and DQ8 to validate significance of HLA alleles in MS. Although environmental factors contribute to 2/3 of MS risk, less is known about them. Gut microbiota is emerging as an imporatnt environmental factor in MS pathogenesis. We and others have shown that MS patients have distinct gut microbiota compared to healthy control (HC) with a lower abundance of Prevotella. Additionally, the abundance of Prevotella increased in patients receiving disease-modifying therapies (DMTs) such as Copaxone and/or Interferon-beta (IFNβ). We have previously identified a specific strain of Prevotella (Prevotella histicola), which can suppress experimental autoimmune encephalomyelitis (EAE) disease in HLA-DR3.DQ8 transgenic mice. Since Interferon-β-1b [IFNβ (Betaseron)] is a major DMTs used in MS patients, we hypothesized that treatment with the combination of P. histicola and IFNβ would have an additive effect on the disease suppression. We observed that treatment with P. histicola suppressed disease as effectively as IFNβ. Surprisingly, the combination of P. histicola and IFNβ was not more effective than either treatment alone. P. histicola alone or in combination with IFNβ increased the frequency and number of CD4+FoxP3+ regulatory T cells in the gut-associated lymphoid tissue (GALT). Treatment with P. histicola alone, IFNβ alone, and in the combination decreased frequency of pro-inflammatory IFN-γ and IL17-producing CD4+ T cells in the CNS. Additionally, P. histicola alone or IFNβ alone or the combination treatments decreased CNS pathology, characterized by reduced microglia and astrocytic activation. In conclusion, our study indicates that the human gut commensal P. histicola can suppress disease as effectively as commonly used MS drug IFNβ and may provide an alternative treatment option for MS patients.

Potential role of the gut microbiota in neuromyelitis optica spectrum disorder: Implication for intervention

The gut microbiota plays an important role in the occurrence and development of neuroimmunological diseases. Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune disease of the central nervous system that is characterized by the peripheral production of the disease-specific serum autoantibody aquaporin-4 (AQP4)-IgG. Recently, accumulating evidence has provided insights into the associations of gut microbiota dysbiosis and intestinal mucosal barrier destruction with NMOSD, but the underlying pathogenesis remains unclear. Thus, a microbiota intervention might be a potential therapeutic strategy for NMOSD by regulating the gut microbiota, repairing the intestinal mucosal barrier, and modulating intestinal immunity and peripheral immunity.

A Gut Feeling: The Importance of the Intestinal Microbiota in Psychiatric Disorders

The intestinal microbiota constitutes a complex ecosystem in constant reciprocal interactions with the immune, neuroendocrine, and neural systems of the host. Recent molecular technological advances allow for the exploration of this living organ and better facilitates our understanding of the biological importance of intestinal microbes in health and disease. Clinical and experimental studies demonstrate that intestinal microbes may be intimately involved in the progression of diseases of the central nervous system (CNS), including those of affective and psychiatric nature. Gut microbes regulate neuroinflammatory processes, play a role in balancing the concentrations of neurotransmitters and could provide beneficial effects against neurodegeneration. In this review, we explore some of these reciprocal interactions between gut microbes and the CNS during experimental disease and suggest that therapeutic approaches impacting the gut-brain axis may represent the next avenue for the treatment of psychiatric disorders.

Gut microbiome and multiple sclerosis: New insights and perspective

The human gastrointestinal microbiota, also known as the gut microbiota living in the human gastrointestinal tract, has been shown to have a significant impact on several human disorders including rheumatoid arthritis, diabetes, obesity, and multiple sclerosis (MS). MS is an inflammatory disease characterized by the destruction of the spinal cord and nerve cells in the brain due to an attack of immune cells, causing a wide range of harmful symptoms related to inflammation in the central nervous system (CNS). Despite extensive studies on MS that have shown that many external and genetic factors are involved in its pathogenesis, the exact role of external factors in the pathophysiology of MS is still unclear. Recent studies on MS and experimental autoimmune encephalomyelitis (EAE), an animal model of encephalitis, have shown that intestinal microbiota may play a key role in the pathogenesis of MS. Therefore, modification of the intestinal microbiome could be a promising strategy for the future treatment of MS. In this study, the characteristics of intestinal microbiota, the relationship between intestine and brain despite the blood-brain barrier, various factors involved in intestinal microbiota modification, changes in intestinal microbial composition in MS, intestinal microbiome modification strategies, and possible use of intestinal microbiome and factors affecting it have been discussed.

The Microbiome as a Therapeutic Target for Multiple Sclerosis: Can Genetically Engineered Probiotics Treat the Disease?

There is an increasing interest in the intestinal microbiota as a critical regulator of the development and function of the immune, nervous, and endocrine systems. Experimental work in animal models has provided the foundation for clinical studies to investigate associations between microbiota composition and function and human disease, including multiple sclerosis (MS). Initial work done using an animal model of brain inflammation, experimental autoimmune encephalomyelitis (EAE), suggests the existence of a microbiota-gut-brain axis connection in the context of MS, and microbiome sequence analyses reveal increases and decreases of microbial taxa in MS intestines. In this review, we discuss the impact of the intestinal microbiota on the immune system and the role of the microbiome-gut-brain axis in the neuroinflammatory disease MS. We also discuss experimental evidence supporting the hypothesis that modulating the intestinal microbiota through genetically modified probiotics may provide immunomodulatory and protective effects as a novel therapeutic approach to treat this devastating disease.

Gut commensals, dysbiosis, and immune response imbalance in the pathogenesis of multiple sclerosis

Intestinal microbiota alterations have been found to be directly related to a wide range of disease states in humans, including multiple sclerosis (MS). The etiology of MS is highly debated and subsequently, there is no cure. Research dedicated to MS and its murine model, experimental autoimmune encephalomyelitis (EAE), have found that dysbiosis of the gut microbiota may play a role in the disease state and severity. In this review, we discuss the characteristic dysbiosis in MS, the role commensal-derived ligands may have in the pathogenesis of the disease, and the possibility of targeting the microbiota as a future therapy.

Gut-Brain Axis and Neurodegeneration: State-of-the-Art of Meta-Omics Sciences for Microbiota Characterization

Recent advances in the field of meta-omics sciences and related bioinformatics tools have allowed a comprehensive investigation of human-associated microbiota and its contribution to achieving and maintaining the homeostatic balance. Bioactive compounds from the microbial community harboring the human gut are involved in a finely tuned network of interconnections with the host, orchestrating a wide variety of physiological processes. These includes the bi-directional crosstalk between the central nervous system, the enteric nervous system, and the gastrointestinal tract (i.e., gut-brain axis). The increasing accumulation of evidence suggest a pivotal role of the composition and activity of the gut microbiota in neurodegeneration. In the present review we aim to provide an overview of the state-of-the-art of meta-omics sciences including metagenomics for the study of microbial genomes and taxa strains, metatranscriptomics for gene expression, metaproteomics and metabolomics to identify and/or quantify microbial proteins and metabolites, respectively. The potential and limitations of each discipline were highlighted, as well as the advantages of an integrated approach (multi-omics) to predict microbial functions and molecular mechanisms related to human diseases. Particular emphasis is given to the latest results obtained with these approaches in an attempt to elucidate the link between the gut microbiota and the most common neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS).

The proportion of myeloid-derived suppressor cells in the spleen is related to the severity of the clinical course and tissue damage extent in a murine model of multiple sclerosis

Multiple Sclerosis (MS) is the second cause of paraplegia among young adults, after all types of CNS traumatic lesions. In its most frequent relapsing-remitting form, the severity of the disease course is very heterogeneous, and its reliable evaluation remains a key issue for clinicians. Myeloid-Derived sSuppressor Cells (MDSCs) are immature myeloid cells that suppress the inflammatory response, a phenomenon related to the resolution or recovery of the clinical symptoms associated with experimental autoimmune encephalomyelitis (EAE), the most common model for MS. Here, we establish the severity index as a new parameter for the clinical assessment in EAE. It is derived from the relationship between the maximal clinical score and the time elapsed since disease onset. Moreover, we relate this new index with several histopathological hallmarks in EAE and with the peripheral content of MDSCs. Based on this new parameter, we show that the splenic MDSC content is related to the evolution of the clinical course of EAE, ranging from mild to severe. Indeed, when the severity index indicates a severe disease course, EAE mice display more intense lymphocyte infiltration, demyelination and axonal damage. A direct correlation was drawn between the MDSC population in the peripheral immune system, and the preservation of myelin and axons, which was also correlated with T cell apoptosis within the CNS (being these cells the main target for MDSC suppression). The data presented clearly indicated that the severity index is a suitable tool to analyze disease severity in EAE. Moreover, our data suggest a clear relationship between circulating MDSC enrichment and disease outcome, opening new perspectives for the future targeting of this population as an indicator of MS severity.

Repeated sleep disruption in mice leads to persistent shifts in the fecal microbiome and metabolome

It has been established in recent years that the gut microbiome plays a role in health and disease, potentially via alterations in metabolites that influence host physiology. Although sleep disruption and gut dysbiosis have been associated with many of the same diseases, studies investigating the gut microbiome in the context of sleep disruption have yielded inconsistent results, and have not assessed the fecal metabolome. We exposed mice to five days of sleep disruption followed by four days of ad libitum recovery sleep, and assessed the fecal microbiome and fecal metabolome at multiple timepoints using 16S rRNA gene amplicons and untargeted LC-MS/MS mass spectrometry. We found global shifts in both the microbiome and metabolome in the sleep-disrupted group on the second day of recovery sleep, when most sleep parameters had recovered to baseline levels. We observed an increase in the Firmicutes:Bacteroidetes ratio, along with decreases in the genus Lactobacillus, phylum Actinobacteria, and genus Bifidobacterium in sleep-disrupted mice compared to control mice. The latter two taxa remained low at the fourth day post-sleep disruption. We also identified multiple classes of fecal metabolites that were differentially abundant in sleep-disrupted mice, some of which are physiologically relevant and commonly influenced by the microbiome. This included bile acids, and inference of microbial functional gene content suggested reduced levels of the microbial bile salt hydrolase gene in sleep-disrupted mice. Overall, this study adds to the evidence base linking disrupted sleep to the gut microbiome and expands it to the fecal metabolome, identifying sleep disruption-sensitive bacterial taxa and classes of metabolites that may serve as therapeutic targets to improve health after poor sleep.

Alcohol shifts gut microbial networks and ameliorates a murine model of neuroinflammation in a sex-specific pattern

Alcohol is a widely consumed dietary component by patients with autoimmune neuroinflammatory diseases, but current evidence on the effects of alcohol in these conditions is confounding. Epidemiological studies suggest moderate consumption of alcohol may be protective in some autoimmune diseases; however, this correlation has not been directly investigated. Here, we characterize the effects of moderate-dose alcohol in a model system of autoimmune neuroinflammation, experimental autoimmune encephalomyelitis (EAE). Male and female C57BL/6J mice were fed a 2.6% alcohol or isocaloric diet for 3 wk prior to MOG_35-55 EAE induction. Surprisingly, alcohol-fed males experienced significantly greater disease remission compared to alcohol-fed females and control-fed counterparts. We observed a male-specific decrease in microglial density in alcohol-consuming animals in cervical and thoracic spinal cord in late-stage disease. In the gut, alcohol diet resulted in several sex-specific alterations in key microbiota known for their regulatory immune roles, including Turicibacter, Akkermansia, Prevotella, and Clostridium Using a correlation network modeling approach, we identified unique bacterial modules that are significantly enriched in response to treatment and sex, composed of Clostridial taxa and several Firmicutes known to be protective in EAE. Together, these data demonstrate the potential of alcohol to significantly alter the course of autoimmunity differentially in males and females via effects on gut bacterial networks and support further need to evaluate dose and sex-specific alcohol effects in multiple sclerosis (MS) and other autoimmune neuroinflammatory conditions.

TREM Receptors Connecting Bowel Inflammation to Neurodegenerative Disorders

Alterations in Triggering Receptors Expressed on Myeloid cells (TREM-1/2) are bound to a variety of infectious, sterile inflammatory, and degenerative conditions, ranging from inflammatory bowel disease (IBD) to neurodegenerative disorders. TREMs are emerging as key players in pivotal mechanisms often concurring in IBD and neurodegeneration, namely microbiota dysbiosis, leaky gut, and inflammation. In conditions of dysbiosis, compounds released by intestinal bacteria activate TREMs on macrophages, leading to an exuberant pro-inflammatory reaction up to damage in the gut barrier. In turn, TREM-positive activated macrophages along with inflammatory mediators may reach the brain through the blood, glymphatic system, circumventricular organs, or the vagus nerve via the microbiota-gut-brain axis. This leads to a systemic inflammatory response which, in turn, impairs the blood-brain barrier, while promoting further TREM-dependent neuroinflammation and, ultimately, neural injury. Nonetheless, controversial results still exist on the role of TREM-2 compared with TREM-1, depending on disease specificity, stage, and degree of inflammation. Therefore, the present review aimed to provide an update on the role of TREMs in the pathophysiology of IBD and neurodegeneration. The evidence here discussed the highlights of the potential role of TREMs, especially TREM-1, in bridging inflammatory processes in intestinal and neurodegenerative disorders.

Bidirectional regulatory potentials of short-chain fatty acids and their G-protein-coupled receptors in autoimmune neuroinflammation

Microbial metabolites, produced in the intestine, have significant effects on inflammatory diseases throughout the body. Short-chain fatty acids (SCFAs) have protective effects on experimental autoimmune encephalitis (EAE) responses but the detailed roles of SCFAs and their receptors in regulating autoimmune CNS inflammation have been unclear. SCFAs metabolically regulate T cells and change the phenotype of antigen presenting cells to efficiently induce IL-10⁺ regulatory T cells. In line with the overall protective effect, blood levels of major SCFAs, such as acetate, propionate and butyrate, are significantly decreased in long-term active progressive multiple sclerosis (MS) patients. Importantly, SCFAs can induce CD4⁺ effector T cells, which are highly inflammatory when transferred into mice, suggesting that the direct effect of SCFAs on T cells can even be pro-inflammatory in the CNS. In contrast to the moderate protective effect of SCFAs, mice deficient in GPR41 or GPR43 are more resistant to EAE pathogenesis. Thus, despite the overall protective function of SCFAs, SCFAs and their receptors have the potential to regulate autoimmune CNS inflammation both positively and negatively.