Role of gut microbiota in regulating gastrointestinal dysfunction and motor symptoms in a mouse model of Parkinson's disease

Gut microbiota promote the propagation of pathologic α-syn from gut to brain in a gut-originated mouse model of Parkinson's disease

The pathology of Parkinson's disease (PD) can originate in gut and gut microbiota is considered as important pathway in gut-brain axis of PD. However, no studies have delineated the interaction of gut microbiota with gut-originated PD. We established a gut-originated PD murine model and subsequently characterized changes in gut microbiota over an eight-month period. Progressive motor dysfunction, decreased dopaminergic neurons and spreading of α-syn pathology was observed at several time points during the 8-month disease progression, along with changes in the composition of the gut microbiota. Increases in Dubosiella at genus level occurred from 4 months, and was highly consistent with the time point of disease progression. Metabolic function prediction of gut microbiota suggested metabolic disorders of branched-chain-amino acids (BCAA), which resulted in accumulation of BCAA in peripheral blood. Removal of gut microbiota by antibiotic treatment reversed the progression of PD, as well as decreased the levels of Dubosiella and BCAA. Remarkably, Dubosiella newyorkensis disrupted the BCAA metabolism and mediated the accumulation of BCAA in mouse colon organoids. Consistent with the results observed in the animal model, abnormally elevated serum BCAA were also detected in the PD patients enrolled in this study. Furthermore, excessive BCAA caused lysosome dysfunction in microglia, suggesting that accumulated BCAA mediated by the gut microbiota may be an important mechanism in preventing the degradation of α-syn. These results show that microbiota-dependent BCAA function to inhibit α-syn degradation, thus enhancing PD progression, and provides compelling evidence for microbiota intervention therapy for PD. Our dynamic tracking of gut microbiota pioneers a new field of study in understanding the role of the gut-brain axis in development of PD, and provides compelling evidence for microbiota intervention therapy for PD.

Gut microbiota therapy in gastrointestinal diseases

The human gut microbiota, consisting of trillions of microorganisms, plays a crucial role in gastrointestinal (GI) health and disease. Dysbiosis, an imbalance in microbial composition, has been linked to a range of GI disorders, including inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), celiac disease, and colorectal cancer. These conditions are influenced by the interactions between the gut microbiota, the host immune system, and the gut-brain axis. Recent research has highlighted the potential for microbiome-based therapeutic strategies, such as probiotics, prebiotics, fecal microbiota transplantation (FMT), and dietary modifications, to restore microbial balance and alleviate disease symptoms. This review examines the role of gut microbiota in the pathogenesis of common gastrointestinal diseases and explores emerging therapeutic approaches aimed at modulating the microbiome. We discuss the scientific foundations of these interventions, their clinical effectiveness, and the challenges in their implementation. The review underscores the therapeutic potential of microbiome-targeted treatments as a novel approach to managing GI disorders, offering personalized and alternative options to conventional therapies. As research in this field continues to evolve, microbiome-based interventions hold promise for improving the treatment and prevention of gastrointestinal diseases.

Neurodegenerative diseases and neuroinflammation-induced apoptosis

Neuroinflammation represents a critical pathway in the brain for the clearance of foreign bodies and the maintenance of homeostasis. When the neuroinflammatory process is dysregulate, such as the over-activation of microglia, which results in the excessive accumulation of free oxygen and inflammatory factors in the brain, among other factors, it can lead to an imbalance in homeostasis and the development of various diseases. Recent research has indicated that the development of numerous neurodegenerative diseases is closely associated with neuroinflammation. The pathogenesis of neuroinflammation in the brain is intricate, involving alterations in numerous genes and proteins, as well as the activation and inhibition of signaling pathways. Furthermore, excessive inflammation can result in neuronal cell apoptosis, which can further exacerbate the extent of the disease. This article presents a summary of recent studies on the relationship between neuronal apoptosis caused by excessive neuroinflammation and neurodegenerative diseases. The aim is to identify the link between the two and to provide new ideas and targets for exploring the pathogenesis, as well as the prevention and treatment of neurodegenerative diseases.

Enterococcus faecalis Exerts Neuroprotective Effects via the Vagus Nerve in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease worldwide. Current treatment methods for PD are unable to halt disease progression. The gut microbiota contributes to the neurodevelopment of PD; however, the gut-brain connections and underlying neural bases that regulate this complex behavior are not yet clear. Enterococcus faecalis (EF) is a common commensal bacterium of the gut and a common pathogen associated with hospital-acquired infections. Here, we demonstrated the significant therapeutic effects of a non-pathogenic strain of EF (EF ATCC19433) on PD. In this study, we established a mouse model of PD by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We found that EF treatment alleviated behavioral impairment, dopaminergic neuronal loss, blood-brain barrier damage, and neuroinflammation induced by MPTP in the mice. Additionally, 16S rRNA sequencing revealed that dysbiosis of PD-related microbial communities induced by MPTP was reversed by EF treatment. Moreover, EF treatment relieved gastrointestinal dysfunction in the mice. The therapeutic efficacy of EF in MPTP-induced PD mice is markedly diminished when the activity of EF is lost. Further mechanistic studies indicated that the neuroprotective effects of EF in PD were associated with the vagus nerve pathway. Following the surgical severance of the vagus nerve through subdiaphragmatic vagotomy, the protective effects of EF on PD were markedly diminished. Our study suggests that EF can alleviate neurofunctional impairments and gastrointestinal disorders associated with PD, indicating that gut-derived microbes influence brain function through the vagus nerve pathway.

Alpha synuclein overexpression can drive microbiome dysbiosis in mice

Growing evidence indicates that persons with Parkinson disease (PD), have a unique composition of indigenous gut microbes. Given the long prodromal or pre-diagnosed period, longitudinal studies of the human and rodent gut microbiome before symptomatic onset and for the duration of the disease are currently lacking. PD is partially characterized by the accumulation of the protein α-synuclein (α-syn) into insoluble aggregates, in both the central and enteric nervous systems. As such, several experimental rodent and non-human primate models of α-syn overexpression recapitulate some of the hallmark pathophysiologies of PD. These animal models provide an opportunity to assess how the gut microbiome changes with age under disease-relevant conditions. Here, we used a transgenic mouse strain, which overexpress wild-type human α-syn to test how the gut microbiome composition responds in this model of PD pathology during aging. Using shotgun metagenomics, we find significant, age and genotype-dependent bacterial taxa whose abundance becomes altered with age. We reveal that α-syn overexpression can drive alterations to the gut microbiome composition and suggest that it limits diversity through age. Taxa that were most affected by genotype-age interaction were Lactobacillus and Bifidobacteria. In a mouse model, we showed direct link between alpha synuclein geneotype (hallmark of PD), a dysbiotic and low-diversity gut microbiome, and dysbiotic levels of Bifidobacteria and Lactobacillus (most robust features of PD microbiome). Given emerging data on the potential contributions of the gut microbiome to PD pathologies, our data provide an experimental foundation to understand how the PD-associated microbiome may arise as a trigger or co-pathology to disease.

Lewy body diseases and the gut

Gastrointestinal (GI) involvement in Lewy body diseases (LBDs) has been observed since the initial descriptions of patients by James Parkinson. Recent experimental and human observational studies raise the possibility that pathogenic alpha-synuclein (⍺-syn) might develop in the GI tract and subsequently spread to susceptible brain regions. The cellular and mechanistic origins of ⍺-syn propagation in disease are under intense investigation. Experimental LBD models have implicated important contributions from the intrinsic gut microbiome, the intestinal immune system, and environmental toxicants, acting as triggers and modifiers to GI pathologies. Here, we review the primary clinical observations that link GI dysfunctions to LBDs. We first provide an overview of GI anatomy and the cellular repertoire relevant for disease, with a focus on luminal-sensing cells of the intestinal epithelium including enteroendocrine cells that express ⍺-syn and make direct contact with nerves. We describe interactions within the GI tract with resident microbes and exogenous toxicants, and how these may directly contribute to ⍺-syn pathology along with related metabolic and immunological responses. Finally, critical knowledge gaps in the field are highlighted, focusing on pivotal questions that remain some 200 years after the first descriptions of GI tract dysfunction in LBDs. We predict that a better understanding of how pathophysiologies in the gut influence disease risk and progression will accelerate discoveries that will lead to a deeper overall mechanistic understanding of disease and potential therapeutic strategies targeting the gut-brain axis to delay, arrest, or prevent disease progression.

Regulatory effects of Lactobacillus zhachilii HBUAS52074T on depression-like behavior induced by chronic social defeat stress in mice: modulation of the gut microbiota

The gut microbiome has emerged as a growing focus of research and public health interest, leading to the frequent exploration of probiotic dietary supplements as potential treatments for various disorders, such as anxiety and depression. In the present report, changes in inflammation and microbiome composition were assessed in model mice exhibiting depressive-like behaviors that were exposed to the probiotic Lactobacillus zhachilii HBUAS52074T. It was found that L. zhachilii HBUAS52074T alleviated the severity of depressive-like behaviors while increasing serum 5-HT concentrations. Moreover, L. zhachilii HBUAS52074T modulated the composition of the gut microbiota, resulting in a decrease in the abundance of Prevotella and an increase in the abundance of Lactobacillus. Additionally, supplementation with L. zhachilii HBUAS52074T enhanced intestinal barrier function and reduced inflammation in peripheral blood, as well as in the hippocampal and prefrontal cortical tissues. Correlational analyses indicated that the abundance of Lactobacillus was positively correlated with the social interaction ratio, time spent in the center, entries into the center, as well as serum 5-HT and serum IL-10 levels but negatively correlated with immobility time. Overall, chronic social defeat stress was found to be associated with inflammation and the exacerbation of depressive-like behaviors. The above findings suggested that L. zhachilii HBUAS52074T supplementation was sufficient to alter the parameters. Collectively, these data suggest that L. zhachilii HBUAS52074T, derived from naturally fermented foods, may possess therapeutic potential for the treatment of depression.

Brazilin-Rich Extract from Caesalpinia sappan L. Attenuated the Motor Deficits and Neurodegeneration in MPTP/p-Induced Parkinson's Disease Mice by Regulating Gut Microbiota and Inhibiting Inflammatory Responses

Parkinson's disease (PD) is a complicated neurological disease with an unclear pathogenesis. However, dysregulation of gut microbiota and inflammation response play crucial roles in the progression of PD. Caesalpinia sappan L., a traditional medicinal plant containing brazilin as its primary active compound, is known for its anti-inflammatory and neuroprotective properties. However, the impact of C. sappan L. extract (SE) on PD through the regulation of the microbiota-gut-brain axis remains unclear. This study investigated the effects and mechanisms of a 91.23% brazilin-enriched SE on MPTP/p-induced PD mice. Results showed that SE significantly ameliorated motor deficits and protected dopaminergic neurons in PD mice. Additionally, SE reduced oxidative stress and inflammation in the brain. SE also restored gut microbiota by increasing Firmicutes and decreasing Bacteroidetes, alongside enhancing the production of short-chain fatty acids (SCFAs) like butyric acid. Furthermore, SE mitigated intestinal barrier damage by enhancing the expression of ZO-1 and occludin, thereby decreasing lipopolysaccharide leakage and inflammatory factor release. Molecular simulations suggested that butyric acid may maintain intestinal integrity by stabilizing ZO-I and occludin conformations. In conclusion, SE exhibited a protective effect on motor deficits and neurodegeneration in PD by regulating gut microbiota and SCFAs, repairing the intestinal barrier, and mitigating inflammatory responses.

Lycium ruthenicum Murray anthocyanin-driven neuroprotection modulates the gut microbiome and metabolome of MPTP-treated mice

Emerging evidence suggests that Parkinson's disease (PD) is strongly associated with altered gut microbiota. The present study investigated the prophylactic effects of anthocyanins (ACNs) from Lycium ruthenicum Murray on Parkinson's disease based on microbiomics and metabolomics. In this study, sixty-six adult male C57BL/6J mice were randomized into the control group, model group, positive drug (Madopar) group, and low-, medium- and high-dose ACN groups. Behavioral experiments were conducted and pathological indicators were determined. Fresh feces were collected for microbiomic analysis using 16S rRNA sequencing. Urine and serum were analyzed by the UPLC-MS method for untargeted metabolomics. The results demonstrated that ACNs ameliorated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced motor deficits, dopamine neuron death, and glial cell activation, while 100 mg kg-1 and 200 mg kg-1 ACNs were more neuroprotective than 50 mg kg-1. Mice with PD-like phenotypes have an altered gut microbiota composition, and ACNs may regulate this disorder by causing an increase in Firmicutes/Bacteroidota ratio and abundance of norank_f__Eubacterium_coprostanoligenes_group and a decrease in the abundance of norank_f__Muribaculaceae, Coriobacteriaceae_UCG-002 and Parvibacter. Furthermore, ACNs increased 14 urinary key metabolites such as DIMBOA-Glc and tauroursodeoxycholic acid, decreased N,N-dimethyllysine, and increased 12 serum key metabolites such as 1-methylguanine and 1-nitro-5-glutathionyl-6-hydroxy-5,6-dihydronaphthalene, and decreased lamivudine-monophosphate and 5-butyl-2- methylpyridine. The present study reveals that ACNs are protective against MPTP-induced PD in mice by modulating anti-inflammatory flora in the gut and endogenous metabolites in serum/urine, and the key mechanisms may be related to Coriobacteriaceae_UCG-002 and glycerophospholipid metabolic pathways. Our findings provide new insights into the pathogenesis and potential treatment of Parkinson's disease.

Cross-talk between adipose tissue and microbiota-gut-brain-axis in brain development and neurological disorder

The gut microbiota is an important factor responsible for the physiological processes as well as pathogenesis of host. The communication between central nervous system (CNS) and microbiota occurs by different pathways i.e., chemical, neural, immune, and endocrine. Alteration in gut microbiota i.e., gut dysbiosis causes alteration in the bidirectional communication between CNS and gut microbiota and linked to the pathogenesis of neurological and neurodevelopmental disorder. Therefore, now-a-days microbiota-gut-brain-axis (MGBA) has emerged as therapeutic target for the treatment of metabolic disorder. But, experimental data available on MGBA from basic research has limited application in clinical study. In present study we first summarized molecular mechanism of microbiota interaction with brain physiology and pathogenesis via collecting data from different sources i.e., PubMed, Scopus, Web of Science. Furthermore, evidence shows that adipose tissue (AT) is active during metabolic activities and may also interact with MGBA. Hence, in present study we have focused on the relationship among MGBA, brown adipose tissue, and white adipose tissue. Along with this, we have also studied functional specificity of AT, and understanding heterogeneity among MGBA and different types of AT. Therefore, molecular interaction among them may provide therapeutic target for the treatment of neurological disorder.

Retrospective analysis of diet and gut microbiota diversity and clinical pharmacology outcomes in patients with Parkinsonism syndrome

Background

Parkinson's disease (PD) is a global neurodegenerative ailment impacting millions, causes significant degeneration of dopaminergic neurons in the substantia nigra. Emerging research underscores the gut microbiota's role in PD onset. Yet, investigations in Chinese demographics are lacking. This study thus targets a retrospective examination of gut microbiota variety and clinical aspects in Chinese PD patients.

Methods

We retrospectively analyzed 50 PD patients' clinical data (admitted May 2021-April 2022) and compared their gut microbiota composition and abundance via 16S rDNA V3-V4 region sequencing against 50 healthy controls. The study also explored links between disease severity and PD patients' gut microbiota.

Results

We found that the gut microbiota diversity was increased in PD patients. Specifically, phyla Firmicutes, Actinobacteria, and Proteobacteria were more abundant, whereas Bacteroidetes was less abundant compared to controls. Gut microbiota diversity did not vary between early-vs. late-onset PD, tremor-dominant vs. non-tremor-dominant, or constipation-associated vs. non-constipation-associated subtypes. The abundance of Firmicutes was positively correlated with UPDRS (Unified Parkinson's Disease Rating Scale) III score, NMSS (Non-Motor Symptoms Scale) score, Wexner score, and PDQ-39 (Parkinson's Disease Questionnaire-39) score; the abundance of Actinobacteria was positively correlated with UPDRS III, NMSS, Wexner, and PDQ-39 scores; and the abundance of Bacteroidetes was negatively correlated with UPDRS III, NMSS, Wexner, and PDQ-39 scores. At the family level, the abundance of Bifidobacteriaceae, Enterobacteriaceae, and Porphyromonadaceae was positively correlated with UPDRS III, NMSS, and PDQ-39 scores.

Conclusion

Compared with healthy individuals, PD patients have increased gut microbiota diversity, and the abundance of Bifidobacteriaceae, Enterobacteriaceae, and Porphyromonadaceae is associated with the severity of both motor and non-motor symptoms in PD patients.

Dissecting Causal Links Between Gut Microbiota, Inflammatory Cytokines, and Parkinson's Disease: A Mendelian Randomization Study

BACKGROUND

The association between gut microbiota (GM) and Parkinson's disease (PD) has been well established, but whether there is a causal relationship between the two and whether inflammatory cytokines (ICs) act as mediators remain unclear.

METHODS

We utilized the summary databases of large-scale genome-wide association studies (GWAS) conducting Mendelian randomization (MR) analyses to investigate the causal relationships between GM, ICs, and PD. The inverse-variance weighted (IVW) method was primarily used to identify GM and ICs associated with PD and to examine the mediating role of ICs, supplemented by MR Egger and weighted median.

RESULTS

Through MR analysis, we identified three positive causal relationships and six negative causal relationships between GM and PD. Additionally, there were three positive associations and five negative associations between ICs and PD. However, after adjusting for FDR, none of these associations were significant. In reverse MR analysis, we also found causal relationships between PD and various GM and ICs. Further, two-step MR analysis indicated that the negative impact of phylum Actinobacteria on PD may be mediated through Fms-related tyrosine kinase 3 ligand levels.

CONCLUSION

This study strengthens the link between GM and the risk of PD, while also revealing the potential mediating role of ICs in the causal relationships between these factors.

Microbiome-based therapeutics for Parkinson's disease

Recent experimental and clinical data demonstrate a significant dysregulation of the gut microbiome in individuals with Parkinson's disease (PD). With an immense influence on all aspects of physiology, this dysregulation has potential to directly or indirectly contribute to disease pathology. Experimental models have bridged these associations toward defined contributions, identifying various microbiome-dependent impacts to PD pathology. These studies have laid the foundation for human translation, examining whether certain members of the microbiome and/or whole restoration of the gut microbiome community can provide therapeutic benefit for people living with PD. Here, we review recent and ongoing clinically-focused studies that use microbiome-targeted therapies to limit the severity and progression of PD. Fecal microbiome transplants, prebiotic interventions, and probiotic supplementation are each emerging as viable methodologies to augment the gut microbiome and potentially limit PD symptoms. While still early, the data in the field to date support continued cross-talk between experimental systems and human studies to identify key microbial factors that contribute to PD pathologies.

Gut microbiota modulates neurotransmitter and gut-brain signaling

Neurotransmitters, including 5-hydroxytryptamine (5-HT), dopamine (DA), gamma-aminobutyric acid (GABA), and glutamate, are essential transductors in the Gut-Brain Axis (GBA), playing critical roles both peripherally and centrally. Accumulating evidence suggests that the gut microbiota modulates intestinal neurotransmitter metabolism and gut-to-brain signaling, shedding light on the crucial role of the gut microbiota in brain function and the pathogenesis of various neuropsychiatric diseases, such as major depression disorder (MDD), anxiety, addiction and Parkinson's disease (PD). Despite the exciting findings, the mechanisms underlying the modulation of neurotransmitter metabolism and function by the gut microbiota are still being elucidated. In this review, we aim to provide a comprehensive overview of the existing knowledge about the role of the gut microbiota in neurotransmitter metabolism and function in animal and clinical experiments. Moreover, we will discuss the potential mechanisms through which gut microbiota-derived neurotransmitters contribute to the pathogenesis of neuropsychiatric diseases, thus highlighting a novel therapeutic target for these conditions.

Mind over matter: the microbial mindscapes of psychedelics and the gut-brain axis

Psychedelics have emerged as promising therapeutics for several psychiatric disorders. Hypotheses around their mechanisms have revolved around their partial agonism at the serotonin 2 A receptor, leading to enhanced neuroplasticity and brain connectivity changes that underlie positive mindset shifts. However, these accounts fail to recognise that the gut microbiota, acting via the gut-brain axis, may also have a role in mediating the positive effects of psychedelics on behaviour. In this review, we present existing evidence that the composition of the gut microbiota may be responsive to psychedelic drugs, and in turn, that the effect of psychedelics could be modulated by microbial metabolism. We discuss various alternative mechanistic models and emphasize the importance of incorporating hypotheses that address the contributions of the microbiome in future research. Awareness of the microbial contribution to psychedelic action has the potential to significantly shape clinical practice, for example, by allowing personalised psychedelic therapies based on the heterogeneity of the gut microbiota.

Gut microbiota: the indispensable player in neurodegenerative diseases

As one of the most urgent social and health problems in the world, neurodegenerative diseases have always been of interest to researchers. However, the pathological mechanisms and therapeutic approaches are not achieved. In addition to the established roles of oxidative stress, inflammation and immune response, changes of gut microbiota are also closely related to the pathogenesis of neurodegenerative diseases. Gut microbiota is the central player of the gut-brain axis, the dynamic bidirectional communication pathway between gut microbiota and central nervous system, and emerging insights have confirmed its indispensability in the development of neurodegenerative diseases. In this review, we discuss the complex relationship between gut microbiota and the central nervous system from the perspective of the gut-brain axis; review the mechanism of microbiota for the modulation different neurodegenerative diseases and discuss how different dietary patterns affect neurodegenerative diseases via gut microbiota; and prospect the employment of gut microbiota in the therapeutic approach to those diseases. © 2024 Society of Chemical Industry.

Deciphering the microbial map and its implications in the therapeutics of neurodegenerative disorder

Every facet of biological anthropology, including development, ageing, diseases, and even health maintenance, is influenced by gut microbiota's significant genetic and metabolic capabilities. With current advancements in sequencing technology and with new culture-independent approaches, researchers can surpass older correlative studies and develop mechanism-based studies on microbiome-host interactions. The microbiota-gut-brain axis (MGBA) regulates glial functioning, making it a possible target for the improvement of development and advancement of treatments for neurodegenerative diseases (NDDs). The gut-brain axis (GBA) is accountable for the reciprocal communication between the gastrointestinal and central nervous system, which plays an essential role in the regulation of physiological processes like controlling hunger, metabolism, and various gastrointestinal functions. Lately, studies have discovered the function of the gut microbiome for brain health-different microbiota through different pathways such as immunological, neurological and metabolic pathways. Additionally, we review the involvement of the neurotransmitters and the gut hormones related to gut microbiota. We also explore the MGBA in neurodegenerative disorders by focusing on metabolites. Further, targeting the blood-brain barrier (BBB), intestinal barrier, meninges, and peripheral immune system is investigated. Lastly, we discuss the therapeutics approach and evaluate the pre-clinical and clinical trial data regarding using prebiotics, probiotics, paraprobiotics, fecal microbiota transplantation, personalised medicine, and natural food bioactive in NDDs. A comprehensive study of the GBA will felicitate the creation of efficient therapeutic approaches for treating different NDDs.

Gut microbiota dysbiosis contributes to α-synuclein-related pathology associated with C/EBPβ/AEP signaling activation in a mouse model of Parkinson's disease

JOURNAL/nrgr/04.03/01300535-202409000-00042/figure1/v/2024-01-16T170235Z/r/image-tiff Parkinson's disease is a neurodegenerative disease characterized by motor and gastrointestinal dysfunction. Gastrointestinal dysfunction can precede the onset of motor symptoms by several years. Gut microbiota dysbiosis is involved in the pathogenesis of Parkinson's disease, whether it plays a causal role in motor dysfunction, and the mechanism underlying this potential effect, remain unknown. CCAAT/enhancer binding protein β/asparagine endopeptidase (C/EBPβ/AEP) signaling, activated by bacterial endotoxin, can promote α-synuclein transcription, thereby contributing to Parkinson's disease pathology. In this study, we aimed to investigate the role of the gut microbiota in C/EBPβ/AEP signaling, α-synuclein-related pathology, and motor symptoms using a rotenone-induced mouse model of Parkinson's disease combined with antibiotic-induced microbiome depletion and fecal microbiota transplantation. We found that rotenone administration resulted in gut microbiota dysbiosis and perturbation of the intestinal barrier, as well as activation of the C/EBP/AEP pathway, α-synuclein aggregation, and tyrosine hydroxylase-positive neuron loss in the substantia nigra in mice with motor deficits. However, treatment with rotenone did not have any of these adverse effects in mice whose gut microbiota was depleted by pretreatment with antibiotics. Importantly, we found that transplanting gut microbiota derived from mice treated with rotenone induced motor deficits, intestinal inflammation, and endotoxemia. Transplantation of fecal microbiota from healthy control mice alleviated rotenone-induced motor deficits, intestinal inflammation, endotoxemia, and intestinal barrier impairment. These results highlight the vital role that gut microbiota dysbiosis plays in inducing motor deficits, C/EBPβ/AEP signaling activation, and α-synuclein-related pathology in a rotenone-induced mouse model of Parkinson's disease. Additionally, our findings suggest that supplementing with healthy microbiota may be a safe and effective treatment that could help ameliorate the progression of motor deficits in patients with Parkinson's disease.

The role of gut microbiota in chronic restraint stress-induced cognitive deficits in mice

BACKGROUND

Chronic stress induces cognitive deficits. There is a well-established connection between the enteric and central nervous systems through the microbiota-gut-brain (MGB) axis. However, the effects of the gut microbiota on cognitive deficits remain unclear. The present study aimed to elucidate the microbiota composition in cognitive deficits and explore its potential in predicting chronic stress-induced cognitive deficits.

METHODS

Mice were randomly divided into control and chronic restraint stress (CRS) groups. The mice subjected to CRS were further divided into cognitive deficit (CRS-CD) and non-cognitive deficit (CRS-NCD) groups using hierarchical cluster analysis of novel object recognition test results. The composition and diversity of the gut microbiota were analyzed.

RESULTS

After being subjected to chronic restraint distress, the CRS-CD mice travelled shorter movement distances (p = 0.034 vs. CRS-NCD; p < 0.001 vs. control) and had a lower recognition index than the CRS-NCD (p < 0.0001 vs. CRS-NCD; p < 0.0001 vs. control) and control mice. The results revealed that 5 gut bacteria at genus levels were significantly different in the fecal samples of mice in the three groups. Further analyses demonstrated that Muricomes were not only significantly enriched in the CRS-CD group but also correlated with a decreased cognitive index. The area under the receiver operating curve of Muricomes for CRS-induced cognitive deficits was 0.96.

CONCLUSIONS

Our study indicates that the composition of the gut microbiota is involved in the development of cognitive deficits induced by chronic restraint stress. Further analysis revealed that Muricomes have the potential to predict the development of chronic stress-induced cognitive deficits in mice.

The interplay between gut microbiota and the brain-gut axis in Parkinson's disease treatment

This study delves into the pivotal role of the gut microbiota and the brain-gut axis in Parkinson's Disease (PD), a neurodegenerative disorder with significant motor and non-motor implications. It posits that disruptions in gut microbiota-dysbiosis-and alterations in the brain-gut axis contribute to PD's pathogenesis. Our findings highlight the potential of the gastrointestinal system's early involvement in PD, suggested by the precedence of gastrointestinal symptoms before motor symptoms emerge. This observation implies a possible gut-originated disease pathway. The analysis demonstrates that dysbiosis in PD patients leads to increased intestinal permeability and systemic inflammation, which in turn exacerbates neuroinflammation and neurodegeneration. Such insights into the interaction between gut microbiota and the brain-gut axis not only elucidate PD's underlying mechanisms but also pave the way for novel therapeutic interventions. We propose targeted treatment strategies, including dietary modifications and fecal microbiota transplantation, aimed at modulating the gut microbiota. These approaches hold promise for augmenting current PD treatment modalities by alleviating both motor and non-motor symptoms, thereby potentially improving patient quality of life. This research underscores the significance of the gut microbiota in the progression and treatment of PD, advocating for an integrated, multidisciplinary approach to develop personalized, efficacious management strategies for PD patients, combining insights from neurology, microbiology, and nutritional science.

Relationship of mTORC1 and ferroptosis in tumors

Ferroptosis is a novel form of programmed death, dependent on iron ions and oxidative stress, with a predominant intracellular form of lipid peroxidation. In recent years, ferroptosis has gained more and more interest of people in the treatment mechanism of targeted tumors. mTOR, always overexpressed in the tumor, and controlling cell growth and metabolic activities, has an important role in both autophagy and ferroptosis. Interestingly, the selective types of autophay plays an important role in promoting ferroptosis, which is related to mTOR and some metabolic pathways (especially in iron and amino acids). In this paper, we list the main mechanisms linking ferroptosis with mTOR signaling pathway and further summarize the current compounds targeting ferroptosis in these ways. There are growing experimental evidences that targeting mTOR and ferroptosis may have effective impact in many tumors, and understanding the mechanisms linking mTOR to ferroptosis could provide a potential therapeutic approach for tumor treatment.

Correlation between the gut microbiome and neurodegenerative diseases: a review of metagenomics evidence

A growing body of evidence suggests that the gut microbiota contributes to the development of neurodegenerative diseases via the microbiota-gut-brain axis. As a contributing factor, microbiota dysbiosis always occurs in pathological changes of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. High-throughput sequencing technology has helped to reveal that the bidirectional communication between the central nervous system and the enteric nervous system is facilitated by the microbiota's diverse microorganisms, and for both neuroimmune and neuroendocrine systems. Here, we summarize the bioinformatics analysis and wet-biology validation for the gut metagenomics in neurodegenerative diseases, with an emphasis on multi-omics studies and the gut virome. The pathogen-associated signaling biomarkers for identifying brain disorders and potential therapeutic targets are also elucidated. Finally, we discuss the role of diet, prebiotics, probiotics, postbiotics and exercise interventions in remodeling the microbiome and reducing the symptoms of neurodegenerative diseases.

Microbiota, Tryptophan and Aryl Hydrocarbon Receptors as the Target Triad in Parkinson's Disease-A Narrative Review

In the era of a steadily increasing lifespan, neurodegenerative diseases among the elderly present a significant therapeutic and socio-economic challenge. A properly balanced diet and microbiome diversity have been receiving increasing attention as targets for therapeutic interventions in neurodegeneration. Microbiota may affect cognitive function, neuronal survival and death, and gut dysbiosis was identified in Parkinson's disease (PD). Tryptophan (Trp), an essential amino acid, is degraded by microbiota and hosts numerous compounds with immune- and neuromodulating properties. This broad narrative review presents data supporting the concept that microbiota, the Trp-kynurenine (KYN) pathway and aryl hydrocarbon receptors (AhRs) form a triad involved in PD. A disturbed gut-brain axis allows the bidirectional spread of pro-inflammatory molecules and α-synuclein, which may contribute to the development/progression of the disease. We suggest that the peripheral levels of kynurenines and AhR ligands are strongly linked to the Trp metabolism in the gut and should be studied together with the composition of the microbiota. Such an approach can clearly delineate the sub-populations of PD patients manifesting with a disturbed microbiota-Trp-KYN-brain triad, who would benefit from modifications in the Trp metabolism. Analyses of the microbiome, Trp-KYN pathway metabolites and AhR signaling may shed light on the mechanisms of intestinal distress and identify new targets for the diagnosis and treatment in early-stage PD. Therapeutic interventions based on the combination of a well-defined food regimen, Trp and probiotics seem of potential benefit and require further experimental and clinical research.

Microbiota-microglia crosstalk between Blautia producta and neuroinflammation of Parkinson's disease: A bench-to-bedside translational approach

Parkinson's disease (PD) is intricately linked to abnormal gut microbiota, yet the specific microbiota influencing clinical outcomes remain poorly understood. Our study identified a deficiency in the microbiota genus Blautia and a reduction in fecal short-chain fatty acid (SCFA) butyrate level in PD patients compared to healthy controls. The abundance of Blautia correlated with the clinical severity of PD. Supplementation with butyrate-producing bacterium B. producta demonstrated neuroprotective effects, attenuating neuroinflammation and dopaminergic neuronal death in mice, consequently ameliorating motor dysfunction. A pivotal inflammatory signaling pathway, the RAS-related pathway, modulated by butyrate, emerged as a key mechanism inhibiting microglial activation in PD. The change of RAS-NF-κB pathway in PD patients was observed. Furthermore, B. producta-derived butyrate demonstrated the inhibition of microglial activation in PD through regulation of the RAS-NF-κB pathway. These findings elucidate the causal relationship between specific gut microbiota and PD, presenting a novel microbiota-based treatment perspective for PD.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

Relationship among Parkinson's disease, constipation, microbes, and microbiological therapy

This comprehensive review elucidates the complex interplay between gut microbiota and constipation in Parkinson's disease (PD), a prevalent non-motor symptom contributing significantly to patients' morbidity. A marked alteration in the gut microbiota, predominantly an increase in the abundance of Proteobacteria and Bacteroidetes, is observed in PD-related constipation. Conventional treatments, although safe, have failed to effectively alleviate symptoms, thereby necessitating the development of novel therapeutic strategies. Microbiological interventions such as prebiotics, probiotics, and fecal microbiota transplantation (FMT) hold therapeutic potential. While prebiotics improve bowel movements, probiotics are effective in enhancing stool consistency and alleviating abdominal discomfort. FMT shows potential for significantly alleviating constipation symptoms by restoring gut microbiota balance in patients with PD. Despite promising developments, the causal relationship between changes in gut microbiota and PD-related constipation remains elusive, highlighting the need for further research in this expanding field.

Gut microbiota-induced CXCL1 elevation triggers early neuroinflammation in the substantia nigra of Parkinsonian mice

Gut microbiota disturbance and systemic inflammation have been implicated in the degeneration of dopaminergic neurons in Parkinson's disease (PD). How the alteration of gut microbiota results in neuropathological events in PD remains elusive. In this study, we explored whether and how environmental insults caused early neuropathological events in the substantia nigra (SN) of a PD mouse model. Aged (12-month-old) mice were orally administered rotenone (6.25 mg·kg-1·d-1) 5 days per week for 2 months. We demonstrated that oral administration of rotenone to ageing mice was sufficient to establish a PD mouse model and that microglial activation and iron deposition selectively appeared in the SN of the mice prior to loss of motor coordination and dopaminergic neurons, and these events could be fully blocked by microglial elimination with a PLX5622-formulated diet. 16 S rDNA sequencing analysis showed that the gut microbiota in rotenone-treated mice was altered, and mice receiving faecal microbial transplantation (FMT) from ageing mice treated with rotenone for 2 months exhibited the same pathology in the SN. We demonstrated that C-X-C motif chemokine ligand-1 (CXCL1) was an essential molecule, as intravenous injection of CXCL1 mimicked almost all the pathology in serum and SN induced by oral rotenone and FMT. Using metabolomics and transcriptomics analyses, we identified the PPAR pathway as a key pathway involved in rotenone-induced neuronal damage. Inhibition of the PPARγ pathway was consistent in the above models, whereas its activation by linoleic acid (60 mg·kg-1·d-1, i.g. for 1 week) could block these pathological events in mice intravenously injected with CXCL1. Altogether, these results reveal that the altered gut microbiota resulted in neuroinflammation and iron deposition occurring early in the SN of ageing mice with oral administration of rotenone, much earlier than motor symptoms and dopaminergic neuron loss. We found that CXCL1 plays a crucial role in this process, possibly via PPARγ signalling inhibition. This study may pave the way for understanding the "brain-gut-microbiota" molecular regulatory networks in PD pathogenesis. The aged C57BL/6 male mice with rotenone intragastric administration showed altered gut microbiota, which caused systemic inflammation, PPARγ signalling inhibition and neuroinflammation, brain iron deposition and ferroptosis, and eventually dopaminergic neurodegeneration in PD.

Parkinson's disease and gut microbiota: from clinical to mechanistic and therapeutic studies

Parkinson's disease (PD) is one of the most prevalent neurodegenerative diseases. The typical symptomatology of PD includes motor symptoms; however, a range of nonmotor symptoms, such as intestinal issues, usually occur before the motor symptoms. Various microorganisms inhabiting the gastrointestinal tract can profoundly influence the physiopathology of the central nervous system through neurological, endocrine, and immune system pathways involved in the microbiota-gut-brain axis. In addition, extensive evidence suggests that the gut microbiota is strongly associated with PD. This review summarizes the latest findings on microbial changes in PD and their clinical relevance, describes the underlying mechanisms through which intestinal bacteria may mediate PD, and discusses the correlations between gut microbes and anti-PD drugs. In addition, this review outlines the status of research on microbial therapies for PD and the future directions of PD-gut microbiota research.

Gut-microbiome-brain axis: the crosstalk between the vagus nerve, alpha-synuclein and the brain in Parkinson's disease

This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease. The vagus nerve, the main component of the parasympathetic nervous system, is involved in the regulation of immune response, digestion, heart rate, and control of mood. It can detect microbiota metabolites through its afferents, transferring this gut information to the central nervous system. Preclinical and clinical studies have shown the important role played by the gut microbiome and gut-related factors in disease development and progression, as well as treatment responses. These findings suggest that the gut microbiome may be a valuable target for new therapeutic strategies for Parkinson's disease. More studies are needed to better understand the underlying biology and how this axis can be modulated for the patient's benefit.

The epithelial barrier: The gateway to allergic, autoimmune, and metabolic diseases and chronic neuropsychiatric conditions

Since the 1960 s, our health has been compromised by exposure to over 350,000 newly introduced toxic substances, contributing to the current pandemic in allergic, autoimmune and metabolic diseases. The "Epithelial Barrier Theory" postulates that these diseases are exacerbated by persistent periepithelial inflammation (epithelitis) triggered by exposure to a wide range of epithelial barrier-damaging substances as well as genetic susceptibility. The epithelial barrier serves as the body's primary physical, chemical, and immunological barrier against external stimuli. A leaky epithelial barrier facilitates the translocation of the microbiome from the surface of the afflicted tissues to interepithelial and even deeper subepithelial locations. In turn, opportunistic bacterial colonization, microbiota dysbiosis, local inflammation and impaired tissue regeneration and remodelling follow. Migration of inflammatory cells to susceptible tissues contributes to damage and inflammation, initiating and aggravating many chronic inflammatory diseases. The objective of this review is to highlight and evaluate recent studies on epithelial physiology and its role in the pathogenesis of chronic diseases in light of the epithelial barrier theory.

The impact of Parkinson's disease-associated gut microbiota on the transcriptome in Drosophila

Parkinson's disease (PD) is a common neurodegenerative disease in middle-aged and elderly people, and many studies have confirmed that the disorder of gut microbiota is involved in the pathophysiological process of PD. However, the molecular mechanism of gut microbiota in regulating the pathogenesis of PD is still lacking. In this study, to investigate the impact of PD-associated gut microbiota on host transcriptome, we established various PD models with fecal microbiota transplantation (FMT) in the model organism Drosophila followed by integrative data analysis of microbiome and transcriptome. We first constructed rotenone-induced PD models in Drosophila followed by FMT in different groups. Microbial analysis by 16S rDNA sequencing showed that gut microbiota from PD Drosophila could affect bacterial structure of normal Drosophila, and gut microbiota from normal Drosophila could affect bacterial structure of PD Drosophila. Transcriptome analysis revealed that PD-associated gut microbiota influenced expression patterns of genes enriched in neuroactive ligand-receptor interaction, lysosome, and diverse metabolic pathways. Importantly, to verify our findings, we transplanted Drosophila with fecal samples from clinical PD patients. Compared to the control, Drosophila transplanted with fecal samples from PD patients had reduced microbiota Acetobacter and Lactobacillus, and differentially expressed genes enriched in diverse metabolic pathways. In summary, our results reveal the influence of PD-associated gut microbiota on host gene expression, and this study can help better understand the link between gut microbiota and PD pathogenesis through gut-brain axis. IMPORTANCE Gut microbiota plays important roles in regulating host gene expression and physiology through complex mechanisms. Recently, it has been suggested that disorder of gut microbiota is involved in the pathophysiological process of Parkinson's disease (PD). However, the molecular mechanism of gut microbiota in regulating the pathogenesis of PD is still lacking. In this study, to investigate the impact of PD-associated gut microbiota on host transcriptome, we established various PD models with fecal microbiota transplantation in the model organism Drosophila followed by integrative data analysis of microbiome and transcriptome. We also verified our findings by transplanting Drosophila with fecal samples from clinical PD patients. Our results demonstrated that PD-associated gut microbiota can induce differentially expressed genes enriched in diverse metabolic pathways. This study can help better understand the link between gut microbiota and PD pathogenesis through gut-brain axis.

The intestinal immune system and gut barrier function in obesity and ageing

Obesity and ageing predispose to numerous, yet overlapping chronic diseases. For example, metabolic abnormalities, including insulin resistance (IR) and type 2 diabetes (T2D) are important causes of morbidity and mortality. Low-grade chronic inflammation of tissues, such as the liver, visceral adipose tissue and neurological tissues, is considered a significant contributor to these chronic diseases. Thus, it is becoming increasingly important to understand what drives this inflammation in affected tissues. Recent evidence, especially in the context of obesity, suggests that the intestine plays an important role as the gatekeeper of inflammatory stimuli that ultimately fuels low-grade chronic tissue inflammation. In addition to metabolic diseases, abnormalities in the intestinal mucosal barrier have been linked to a range of other chronic inflammatory conditions, such as neurodegeneration and ageing. The flow of inflammatory stimuli from the gut is in part controlled by local immunological inputs impacting the intestinal barrier. Here, we will review the impact of obesity and ageing on the intestinal immune system and its downstream consequences on gut barrier function, which is strongly implicated in the pathogenesis of obesity and age-related diseases. In particular, we will discuss the effects of age-related intestinal dysfunction on neurodegenerative diseases.

Fecal Microbiota Transplantation from Aged Mice Render Recipient Mice Resistant to MPTP-Induced Nigrostriatal Degeneration Via a Neurogenesis-Dependent but Inflammation-Independent Manner

Accumulating data support a crucial role of gut microbiota in Parkinson's disease (PD). However, gut microbiota vary with age and, thus, will affect PD in an age-dependent, but unknown manner. We examined the effects of fecal microbiota transplantation (FMT) pretreatment, using fecal microbiota from young (7 weeks) or aged mice (23 months), on MPTP-induced PD model. Motor function, pathological changes, striatal neurotransmitters, neuroinflammation, gut inflammation and gut permeability were examined. Gut microbiota composition and metabolites, namely short-chain fatty acids (SCFAs), were analyzed. Neurogenesis was also evaluated by measuring the number of doublecortin-positive (DCX+) neurons and Ki67-positive (Ki67+) cells in the hippocampus. Expression of Cd133 mRNA, a cellular stemness marker, in the hippocampus was also examined. Mice who received FMT from young mice showed MPTP-induced motor dysfunction, and reduction of striatal dopamine (DA), dopaminergic neurons and striatal tyrosine hydroxylase (TH) levels. Interestingly and unexpectedly, mice that received FMT from aged mice showed recovery of motor function and rescue of dopaminergic neurons and striatal 5-hydroxytryptamine (5-HT), as well as decreased DA metabolism after MPTP challenge. Further, they showed improved metabolic profiling and a decreased amount of fecal SCFAs. High-throughput sequencing revealed that FMT remarkably reshaped the gut microbiota of recipient mice. For instance, levels of genus Akkermansia and Candidatus Saccharimonas were elevated in fecal samples of recipient mice receiving aged microbiota (AM + MPTP mice) than YM + MPTP mice. Intriguingly, both young microbiota and aged microbiota had no effect on neuroinflammation, gut inflammation or gut permeability. Notably, AM + MPTP mice showed a marked increase in DCX+ neurons, as well as Ki67+ cells and Cd133 expression in the hippocampal dentate gyrus (DG) compared to YM + MPTP mice. These results suggest that FMT from aged mice augments neurogenesis, improves motor function and restores dopaminergic neurons and neurotransmitters in PD model mice, possibly through increasing neurogenesis.

Gut-to-brain spreading of pathology in synucleinopathies: A focus on molecular signalling mediators

Synucleinopathies are a group of neurodegenerative disorders, classically characterized by the accumulation of aggregated alpha synuclein (aSyn) in the central nervous system. Parkinson's disease (PD) and multiple system atrophy (MSA) are the two prominent members of this family. Current treatment options mainly focus on the motor symptoms of these diseases. However, non-motor symptoms, including gastrointestinal (GI) symptoms, have recently gained particular attention, as they are frequently associated with synucleinopathies and often arise before motor symptoms. The gut-origin hypothesis has been proposed based on evidence of an ascending spreading pattern of aggregated aSyn from the gut to the brain, as well as the comorbidity of inflammatory bowel disease and synucleinopathies. Recent advances have shed light on the mechanisms underlying the progression of synucleinopathies along the gut-brain axis. Given the rapidly expanding pace of research in the field, this review presents a summary of the latest findings on the gut-to-brain spreading of pathology and potential pathology-reinforcing mediators in synucleinopathies. Here, we focus on 1) gut-to-brain communication pathways, including neuronal pathways and blood circulation, and 2) potential molecular signalling mediators, including bacterial amyloid proteins, microbiota dysbiosis-induced alterations in gut metabolites, as well as host-derived effectors, including gut-derived peptides and hormones. We highlight the clinical relevance and implications of these molecular mediators and their possible mechanisms in synucleinopathies. Moreover, we discuss their potential as diagnostic markers in distinguishing the subtypes of synucleinopathies and other neurodegenerative diseases, as well as for developing novel individualized therapeutic options for synucleinopathies.

The gut microbiota-brain axis in neurological disorder

The gut microbiota (GM) plays an important role in the physiology and pathology of the host. Microbiota communicate with different organs of the organism by synthesizing hormones and regulating body activity. The interaction of the central nervous system (CNS) and gut signaling pathways includes chemical, neural immune and endocrine routes. Alteration or dysbiosis in the gut microbiota leads to different gastrointestinal tract disorders that ultimately impact host physiology because of the abnormal microbial metabolites that stimulate and trigger different physiologic reactions in the host body. Intestinal dysbiosis leads to a change in the bidirectional relationship between the CNS and GM, which is linked to the pathogenesis of neurodevelopmental and neurological disorders. Increasing preclinical and clinical studies/evidence indicate that gut microbes are a possible susceptibility factor for the progression of neurological disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and autism spectrum disorder (ASD). In this review, we discuss the crucial connection between the gut microbiota and the central nervous system, the signaling pathways of multiple biological systems and the contribution of gut microbiota-related neurological disorders.

Parkinson's disease: Are gut microbes involved?

INTRODUCTION

Parkinson's disease (PD) is a neurodegenerative disorder that affects more than 10 million individuals worldwide. It is characterized by motor and sensory deficits. Research studies have increasingly demonstrated a correlation between Parkinson's disease and alternations in the composition of the gut microbiota in affected patients. Also, the significant role of prebiotics and probiotics in gastrointestinal and neurological conditions is imperative to understand their relation to Parkinson's disease.

METHOD

To explore the scientific interaction of the gut-microbiota-brain axis and its association with Parkinson's disease, a comprehensive narrative review of the relevant literature was conducted. Articles were retrieved systematically from reputable sources, including PubMed, Science Direct, World Health Organization (WHO), and Advanced Google Scholar. Key search terms included are "Parkinson's Disease", "Gut Microbiome", "Braak's Theory", "Neurological Disorders", and "Gut-brain axis". Articles included in our review are published in English and they provide detailed information on the relationship between Parkinson's disease and gut microbiota RESULTS: This review highlights the impact of gut microbiota composition and associated factors on the progression of Parkinson's disease. Evidence-based studies highlighting the existing evidence of the relationship between Parkinson's disease and alteration in gut microbiota are discussed. Consequently, the potential mechanisms by which the gut microbiota may affect the composition of the gut microbiota were revealed, with a particular emphasis on the role of the gut-brain axis in this interplay.

CONCLUSION

Understanding the complex interplay between gut microbiota and Parkinson's disease is a potential implication for the development of novel therapeutics against Parkinson's disease. Following the existing relationship demonstrated by different evidence-based studies on Parkinson's disease and gut microbiota, our review concludes by providing recommendations and suggestions for future research studies with a particular emphasis on the impact of the microbiota-brain axis on Parkinson's disease.

The role of the microbiota-gut-brain axis and intestinal microbiome dysregulation in Parkinson's disease

Parkinson's disease (PD) is a complex progressive neurodegenerative disease associated with aging. Its main pathological feature is the degeneration and loss of dopaminergic neurons related to the misfolding and aggregation of α-synuclein. The pathogenesis of PD has not yet been fully elucidated, and its occurrence and development process are closely related to the microbiota-gut-brain axis. Dysregulation of intestinal microbiota may promote the damage of the intestinal epithelial barrier, intestinal inflammation, and the upward diffusion of phosphorylated α-synuclein from the enteric nervous system (ENS) to the brain in susceptible individuals and further lead to gastrointestinal dysfunction, neuroinflammation, and neurodegeneration of the central nervous system (CNS) through the disordered microbiota-gut-brain axis. The present review aimed to summarize recent advancements in studies focusing on the role of the microbiota-gut-brain axis in the pathogenesis of PD, especially the mechanism of intestinal microbiome dysregulation, intestinal inflammation, and gastrointestinal dysfunction in PD. Maintaining or restoring homeostasis in the gut microenvironment by targeting the gut microbiome may provide future direction for the development of new biomarkers for early diagnosis of PD and therapeutic strategies to slow disease progression.

Gut Microbiota in Autophagy Regulation: New Therapeutic Perspective in Neurodegeneration

Gut microbiota and the brain are related via a complex bidirectional interconnective network. Thus, intestinal homeostasis is a crucial factor for the brain, as it can control the environment of the central nervous system and play a significant role in disease progression. The link between neuropsychological behavior or neurodegeneration and gut dysbiosis is well established, but many involved pathways remain unknown. Accumulating studies showed that metabolites derived from gut microbiota are involved in the autophagy activation of various organs, including the brain, one of the major pathways of the protein clearance system that is essential for protein aggregate clearance. On the other hand, some metabolites are evidenced to disrupt the autophagy process, which can be a modulator of neurodegeneration. However, the detailed mechanism of autophagy regulation by gut microbiota remains elusive, and little research only focused on that. Here we tried to evaluate the crosstalk between gut microbiota metabolites and impaired autophagy of the central nervous system in neurodegeneration and the key to future research regarding gut dysbiosis and compromised autophagy in neurodegenerative diseases.

Neuroprotective Effects of Lactobacillus plantarum PS128 in a Mouse Model of Parkinson’s Disease: The Role of Gut Microbiota and MicroRNAs

Parkinson’s disease (PD) is a neurodegenerative disease characterized by motor deficits and marked neuroinflammation in various brain regions. The pathophysiology of PD is complex and mounting evidence has suggested an association with the dysregulation of microRNAs (miRNAs) and gut dysbiosis. Using a rotenone-induced PD mouse model, we observed that administration of Lactobacillus plantarum PS128 (PS128) significantly improved motor deficits in PD-like mice, accompanied by an increased level of dopamine, reduced dopaminergic neuron loss, reduced microglial activation, reduced levels of inflammatory factors, and enhanced expression of neurotrophic factor in the brain. Notably, the inflammation-related expression of miR-155-5p was significantly upregulated in the proximal colon, midbrain, and striatum of PD-like mice. PS128 reduced the level of miR-155-5p, whereas it increased the expression of suppressor of cytokine signaling 1 (SOCS1), a direct target of miR-155-5p and a critical inhibitor of the inflammatory response in the brain. Alteration of the fecal microbiota in PD-like mice was partially restored by PS128 administration. Among them, Bifidobacterium, Ruminiclostridium_6, Bacteroides, and Alistipes were statistically correlated with the improvement of rotenone-induced motor deficits and the expression of miR-155-5p and SOCS1. Our findings suggested that PS128 ameliorates motor deficits and exerts neuroprotective effects by regulating the gut microbiota and miR-155-5p/SOCS1 pathway in rotenone-induced PD-like mice.

Gut Dysbiosis: A Target for Protective Interventions against Parkinson’s Disease

Sub-chronic inflammation, caused by age-related dysbiosis, primes the brain to neuroinflammation and neurodegenerative diseases. Evidence revealed that Parkinson’s disease (PD) might originate in the gut, demonstrating gastro-intestinal disturbances, as reported by PD patients long before developing motor symptoms. In this study, we conducted comparative analyses in relatively young and old mice maintained in conventional or gnotobiotic conditions. We aimed to confirm that the effects induced by age-related dysbiosis, rather than aging itself, sensitize to PD onset. This hypothesis was confirmed in germ-free (GF) mice, which proved resistant to the pharmacological induction of PD, regardless of their age. Contrary to conventional animals, old GF mice did not develop an inflammatory phenotype or an accumulation of iron in the brain, two catalysts sensitizing to disease onset. The resistance of GF mice to PD is reverted when colonized with stool collected from conventional old animals, but not if receiving bacterial content from young mice. Hence, changes in gut microbiota composition are a risk factor for PD development and can be targeted preventively by iron chelators, shown to protect the brain from pro-inflammatory intestinal priming that sensitizes to neuroinflammation and the development of severe PD.

Quinpirole ameliorates nigral dopaminergic neuron damage in Parkinson's disease mouse model through activating GHS-R1a/D2R heterodimers

Growth hormone secretagogue receptor 1a (GHS-R1a) is an important G protein-coupled receptor (GPCR) that regulates a variety of functions by binding to ghrelin. It has been shown that the dimerization of GHS-R1a with other receptors also affects ingestion, energy metabolism, learning and memory. Dopamine type 2 receptor (D₂R) is a GPCR mainly distributed in the ventral tegmental area (VTA), substantia nigra (SN), striatum and other brain regions. In this study we investigated the existence and function of GHS-R1a/D₂R heterodimers in nigral dopaminergic neurons in Parkinson's disease (PD) models in vitro and in vivo. By conducting immunofluorescence staining, FRET and BRET analyses, we confirmed that GHS-R1a and D₂R could form heterodimers in PC-12 cells and in the nigral dopaminergic neurons of wild-type mice. This process was inhibited by MPP⁺ or MPTP treatment. Application of QNP (10 μM) alone significantly increased the viability of MPP⁺-treated PC-12 cells, and administration of quinpirole (QNP, 1 mg/kg, i.p. once before and twice after MPTP injection) significantly alleviated motor deficits in MPTP-induced PD mice model; the beneficial effects of QNP were abolished by GHS-R1a knockdown. We revealed that the GHS-R1a/D₂R heterodimers could increase the protein levels of tyrosine hydroxylase in the SN of MPTP-induced PD mice model through the cAMP response element binding protein (CREB) signaling pathway, ultimately promoting dopamine synthesis and release. These results demonstrate a protective role for GHS-R1a/D₂R heterodimers in dopaminergic neurons, providing evidence for the involvement of GHS-R1a in PD pathogenesis independent of ghrelin.

Dysfunction of the noradrenergic system drives inflammation, α-synucleinopathy, and neuronal loss in mouse colon

Clinical and pathological evidence revealed that α-synuclein (α-syn) pathology seen in PD patients starts in the gut and spreads via anatomically connected structures from the gut to the brain. Our previous study demonstrated that depletion of central norepinephrine (NE) disrupted brain immune homeostasis, producing a spatiotemporal order of neurodegeneration in the mouse brain. The purpose of this study was 1) to determine the role of peripheral noradrenergic system in the maintenance of gut immune homeostasis and in the pathogenesis of PD and 2) to investigate whether NE-depletion induced PD-like α-syn pathological changes starts from the gut. For these purposes, we investigated time-dependent changes of α-synucleinopathy and neuronal loss in the gut following a single injection of DSP-4 (a selective noradrenergic neurotoxin) to A53T-SNCA (human mutant α-syn) over-expression mice. We found DPS-4 significantly reduced the tissue level of NE and increased immune activities in gut, characterized by increased number of phagocytes and proinflammatory gene expression. Furthermore, a rapid-onset of α-syn pathology was observed in enteric neurons after 2 weeks and delayed dopaminergic neurodegeneration in the substantia nigra was detected after 3-5 months, associated with the appearance of constipation and impaired motor function, respectively. The increased α-syn pathology was only observed in large, but not in the small, intestine, which is similar to what was observed in PD patients. Mechanistic studies reveal that DSP-4-elicited upregulation of NADPH oxidase (NOX2) initially occurred only in immune cells during the acute intestinal inflammation stage, and then spread to enteric neurons and mucosal epithelial cells during the chronic inflammation stage. The upregulation of neuronal NOX2 correlated well with the extent of α-syn aggregation and subsequent enteric neuronal loss, suggesting that NOX2-generated reactive oxygen species play a key role in α-synucleinopathy. Moreover, inhibiting NOX2 by diphenyleneiodonium or restoring NE function by salmeterol (a β2-receptor agonist) significantly attenuated colon inflammation, α-syn aggregation/propagation, and enteric neurodegeneration in the colon and ameliorated subsequent behavioral deficits. Taken together, our model of PD shows a progressive pattern of pathological changes from the gut to the brain and suggests a potential role of the noradrenergic dysfunction in the pathogenesis of PD.

The intestinal barrier in disorders of the central nervous system

The intestinal barrier, which primarily consists of a mucus layer, an epithelial barrier, and a gut vascular barrier, has a crucial role in health and disease by facilitating nutrient absorption and preventing the entry of pathogens. The intestinal barrier is in close contact with gut microbiota on its luminal side and with enteric neurons and glial cells on its tissue side. Mounting evidence now suggests that the intestinal barrier is compromised not only in digestive disorders, but also in disorders of the central nervous system (CNS), such as Parkinson's disease, autism spectrum disorder, depression, multiple sclerosis, and Alzheimer's disease. After providing an overview of the structure and functions of the intestinal barrier, we review existing preclinical and clinical studies supporting the notion that intestinal barrier dysfunction is present in neurological, neurodevelopmental, and psychiatric disorders. On the basis of this evidence, we discuss the mechanisms that possibly link gut barrier dysfunction and CNS disorders and the potential impact that evaluating enteric barriers in brain disorders could have on clinical practice, in terms of novel diagnostic and therapeutic strategies, in the near future.

Pesticides and the Microbiome-Gut-Brain Axis: Convergent Pathways in the Pathogenesis of Parkinson's Disease

The increasing global burden of Parkinson's disease (PD), termed the PD pandemic, is exceeding expectations related purely to population aging and is likely driven in part by lifestyle changes and environmental factors. Pesticides are well recognized risk factors for PD, supported by both epidemiological and experimental evidence, with multiple detrimental effects beyond dopaminergic neuron damage alone. The microbiome-gut-brain axis has gained much attention in recent years and is considered to be a significant contributor and driver of PD pathogenesis. In this narrative review, we first focus on how both pesticides and the microbiome may influence PD initiation and progression independently, describing pesticide-related central and peripheral neurotoxicity and microbiome-related local and systemic effects due to dysbiosis and microbial metabolites. We then depict the bidirectional interplay between pesticides and the microbiome in the context of PD, synthesizing current knowledge about pesticide-induced dysbiosis, microbiome-mediated alterations in pesticide availability, metabolism and toxicity, and complex systemic pesticide-microbiome-host interactions related to inflammatory and metabolic pathways, insulin resistance and other mechanisms. An overview of the unknowns follows, and the role of pesticide-microbiome interactions in the proposed body-/brain-first phenotypes of PD, the complexity of environmental exposures and gene-environment interactions is discussed. The final part deals with possible further steps for translation, consisting of recommendations on future pesticide use and research as well as an outline of promising preventive/therapeutic approaches targeted on strengthening or restoring a healthy gut microbiome, closing with a summary of current gaps and future perspectives in the field.

Immunology and microbiome: Implications for motor systems

Immune-inflammatory mechanisms seem to play a relevant role in neurodegenerative disorders affecting motor systems, particularly Parkinson's disease, where activity changes in inflammatory cells and evidence of neuroinflammation in experimental models and patients is available. Amyotrophic lateral sclerosis is also characterized by neuroinflammatory changes that involve primarily glial cells, both microglia and astrocytes, as well as systemic immune dysregulation associated with more rapid progression. Similarly, the exploration of gut dysbiosis in these two prototypical neurodegenerative motor disorders is advancing rapidly. Altered composition of gut microbial constituents and related metabolic and putative functional pathways is supporting a pathophysiological link that is currently explored in preclinical, germ-free animal models. Less compelling, but still intriguing, evidence suggests that motor neurodevelopmental disorders, e.g., Tourette syndrome, are associated with abnormal trajectories of maturation that include also immune system development. Microglia has a key role also in these disorders, and new therapeutic avenues aiming at its modulation are exciting prospects. Preclinical and clinical research on the role of gut dysbiosis in Tourette syndrome and related behavioral disorders is still in its infancy, but early findings support the rationale to delve deeper into its contribution to neural and immune maturation abnormalities in its spectrum.

Role of gut microbiota-derived branched-chain amino acids in the pathogenesis of Parkinson's disease: An animal study

Neuroinflammation caused by the disorder of gut microbiota and its metabolites is associated with the pathogenesis of Parkinson's disease (PD). Thus, it is necessary to identify certain molecules derived from gut microbiota to verify whether they could become intervention targets for the treatment of PD. The branched-chain amino acids (BCAAs), as a common dietary supplement, could modulate brain function. Herein, we investigated the longitudinal shifts of microbial community in mice treated with rotenone for 0, 3 and 4 weeks by 16S rRNA gene sequencing to identify the microbial markers at different PD stages. Serum BCAAs were determined by gas chromatography-mass spectrometry. Then, rotenone-induced mice were given a high BCAA diet to evaluate the motor and non-motor functions, dopaminergic neuron loss, and inflammation levels. Using a PD mouse model, we discovered that during PD progression, the alterations of gut microbiota compositions led to the peripheral decrease of BCAAs. Based on the serum lipopolysaccharide binding protein concentrations and the levels of pro-inflammatory factors (including tumor necrosis factor-α, interleukin [IL]-1β, and IL-6) in the colon and substantia nigra, we found that the high BCAA diet could attenuate the inflammatory levels in PD mice, and reverse motor and non-motor dysfunctions and dopaminergic neuron impairment. Together, our results emphasize the dynamic changes of gut microbiota and BCAA metabolism and propose a novel strategy for PD therapy: a high BCAA diet intervention could improve PD progression by regulating the levels of inflammation.

Linking Puberty and the Gut Microbiome to the Pathogenesis of Neurodegenerative Disorders

Puberty is a critical period of development marked by the maturation of the central nervous system, immune system, and hypothalamic-pituitary-adrenal axis. Due to the maturation of these fundamental systems, this is a period of development that is particularly sensitive to stressors, increasing susceptibility to neurodevelopmental and neurodegenerative disorders later in life. The gut microbiome plays a critical role in the regulation of stress and immune responses, and gut dysbiosis has been implicated in the development of neurodevelopmental and neurodegenerative disorders. The purpose of this review is to summarize the current knowledge about puberty, neurodegeneration, and the gut microbiome. We also examine the consequences of pubertal exposure to stress and gut dysbiosis on the development of neurodevelopmental and neurodegenerative disorders. Understanding how alterations to the gut microbiome, particularly during critical periods of development (i.e., puberty), influence the pathogenesis of these disorders may allow for the development of therapeutic strategies to prevent them.

Non-Reproducibility of Oral Rotenone as a Model for Parkinson's Disease in Mice

Oral rotenone has been proposed as a model for Parkinson’s disease (PD) in mice. To establish the model in our lab and study complex behavior we followed a published treatment regimen. C57BL/6 mice received 30 mg/kg body weight of rotenone once daily via oral administration for 4 and 8 weeks. Motor functions were assessed by RotaRod running. Immunofluorescence studies were used to analyze the morphology of dopaminergic neurons, the expression of alpha-Synuclein (α-Syn), and inflammatory gliosis or infiltration in the substantia nigra. Rotenone-treated mice did not gain body weight during treatment compared with about 4 g in vehicle-treated mice, which was however the only robust manifestation of drug treatment and suggested local gut damage. Rotenone-treated mice had no deficits in motor behavior, no loss or sign of degeneration of dopaminergic neurons, no α-Syn accumulation, and only mild microgliosis, the latter likely an indirect remote effect of rotenone-evoked gut dysbiosis. Searching for explanations for the model failure, we analyzed rotenone plasma concentrations via LC-MS/MS 2 h after administration of the last dose to assess bioavailability. Rotenone was not detectable in plasma at a lower limit of quantification of 2 ng/mL (5 nM), showing that oral rotenone had insufficient bioavailability to achieve sustained systemic drug levels in mice. Hence, oral rotenone caused local gastrointestinal toxicity evident as lack of weight gain but failed to evoke behavioral or biological correlates of PD within 8 weeks.

Differential Response of Ileal and Colonic Microbiota in Rats with High-Fat Diet-Induced Atherosclerosis

Growing evidence suggests that gut microbiota are associated with atherosclerosis (AS). However, the functional heterogeneity of each gut segment gives rise to regional differences in gut microbiota. We established a rat model of AS by feeding the rats a high-fat diet for a long period. The pathological and microbiota changes in the ileum and colon of the rats were examined, and correlations between AS and microbiota were analyzed. The aortic mesothelium of the experimental rats was damaged. The intima showed evident calcium salt deposition, indicating that the AS rat model was successfully developed. We noted varying degrees of pathological damage in the ileum and colon of the experimental rats. The 16S rDNA high-throughput sequencing showed significant differences in α-diversity, β-diversity, and microbiota comparisons in the ileum and colon. Furthermore, the ileum and colon of AS rats showed varying degrees of intestinal microbiota disturbance. This article contributes to the study of the relationship between the microbiota in different regions of the gut and AS, and provides new approaches in gut microbiota intervention for the treatment of AS.