Absence of gut microbiota affects lipid metabolism in the prefrontal cortex of mice

Gut microbiota and microbial metabolites for osteoporosis

Osteoporosis is an age-related bone metabolic disease. As an essential endocrine organ, the skeletal system is intricately connected with extraosseous organs. The crosstalk between bones and other organs supports this view. In recent years, the link between the gut microecology and bone metabolism has become an important research topic, both in preclinical studies and in clinical trials. Many studies have shown that skeletal changes are accompanied by changes in the composition and structure of the gut microbiota (GM). At the same time, natural or artificial interventions targeting the GM can subsequently affect bone metabolism. Moreover, microbiome-related metabolites may have important effects on bone metabolism. We aim to review the relationships among the GM, microbial metabolites, and bone metabolism and to summarize the potential mechanisms involved and the theory of the gut‒bone axis. We also describe existing bottlenecks in laboratory studies, as well as existing challenges in clinical settings, and propose possible future research directions.

Gut microbiota regulates stress responsivity via the circadian system

Stress and circadian systems are interconnected through the hypothalamic-pituitary-adrenal (HPA) axis to maintain responses to external stimuli. Yet, the mechanisms of how such signals are orchestrated remain unknown. Here, we uncover the gut microbiota as a regulator of HPA-axis rhythmicity. Microbial depletion disturbs the brain transcriptome and metabolome in stress-responding pathways in the hippocampus and amygdala across the day. This is coupled with a dysregulation of the circadian pacemaker in the brain that results in perturbed glucocorticoid rhythmicity. The resulting hyper-activation of the HPA axis at the sleep/wake transition drives time-of-day-specific impairments of the stress response and stress-sensitive behaviors. Finally, microbiota transplantation confirmed that diurnal oscillations of gut microbes underlie altered glucocorticoid secretion and that L. reuteri is a candidate strain for such effects. Our data offer compelling evidence that the microbiota regulates stress responsiveness in a circadian manner and is necessary to respond adaptively to stressors throughout the day.

A study on the association between gut microbiota, inflammation, and type 2 diabetes

Type 2 diabetes mellitus (T2DM) was reported to be associated with impaired immune response and alterations in microbial composition and function. However, the underlying mechanism remains elusive. To investigate the association among retinoic acid-inducible gene-I-like receptors (RLRs) signaling pathway, intestinal bacterial microbiome, microbial tryptophan metabolites, inflammation, and a longer course of T2DM, 14 patients with T2DM and 7 healthy controls were enrolled. 16S rRNA amplicon sequencing and untargeted metabolomics were utilized to analyze the stool samples. RNA sequencing (RNA-seq) was carried out on the peripheral blood samples. Additionally, C57BL/6J specific pathogen-free (SPF) mice were used. It was found that the longer course of T2DM could lead to a decrease in the abundance of probiotics in the intestinal microbiome. In addition, the production of microbial tryptophan derivative skatole declined as a consequence of the reduced abundance of related intestinal microbes. Furthermore, low abundances of probiotics, such as Bacteroides and Faecalibacterium, could trigger the inflammatory response by activating the RLRs signaling pathway. The increased level of the member of TNF receptor-associated factors (TRAF) family, nuclear factor kappa-B (NF-κB) activator (TANK), in the animal colon activated nuclear factor kappa B subunit 2 (NFκB2), resulting in inflammatory damage. In summary, it was revealed that the low abundances of probiotics could activate the RLR signaling pathway, which could in turn activate its downstream signaling pathway, NF-κB, highlighting a relationship among gut microbes, inflammation, and a longer course of T2DM. KEY POINTS: Hyperglycemia may suppress tryptophanase activity. The low abundance of Bacteroides combined with the decrease of Dopa decarboxylase (DDC) activity may lead to the decrease of the production of tryptophan microbial derivative skatole, and the low abundance of Bacteroides or reduced skatole may further lead to the increase of blood glucose by downregulating the expression of glucagon-like peptide-1 (GLP1). A low abundance of anti-inflammatory bacteria may induce an inflammatory response by triggering the RLR signaling pathway and then activating its downstream NF-κB signaling pathway in prolonged T2DM.

Oral D-ribose causes depressive-like behavior by altering glycerophospholipid metabolism via the gut-brain axis

Our previous work has shown that D-ribose (RIB)-induced depressive-like behaviors in mice. However, the relationship between variations in RIB levels and depression as well as potential RIB participation in depressive disorder is yet unknown. Here, a reanalysis of metabonomics data from depressed patients and depression model rats is performed to clarify whether the increased RIB level is positively correlated with the severity of depression. Moreover, we characterize intestinal epithelial barrier damage, gut microbial composition and function, and microbiota-gut-brain metabolic signatures in RIB-fed mice using colonic histomorphology, 16 S rRNA gene sequencing, and untargeted metabolomics analysis. The results show that RIB caused intestinal epithelial barrier impairment and microbiota-gut-brain axis dysbiosis. These microbial and metabolic modules are consistently enriched in peripheral (fecal, colon wall, and serum) and central (hippocampus) glycerophospholipid metabolism. In addition, three differential genera (Lachnospiraceae_UCG-006, Turicibacter, and Akkermansia) and two types of glycerophospholipids (phosphatidylcholine and phosphatidylethanolamine) have greater contributions to the overall correlations between differential genera and glycerophospholipids. These findings suggest that the disturbances of gut microbiota by RIB may contribute to the onset of depressive-like behaviors via regulating glycerophospholipid metabolism, and providing new insight for understanding the function of microbiota-gut-brain axis in depression.

Intergenerational association of gut microbiota and metabolism with perinatal folate metabolism and neural tube defects

Disorders of folic acid metabolism during pregnancy lead to fetal neural tube defects (NTDs). However, the mechanisms still require further investigation. Here, we aim to analyze the brain metabolic profiles of 30 NTDs and 30 healthy fetuses. Our results indicated that low-folate diet during early life played a causal role in cerebral metabolism, especially in lipometabolic disturbance, highlighting the importance of folate in modulating brain development and metabolism. Next, we established a mouse model of NTDs. Interestingly, the differential metabolites are mainly involved in glycerophospholipid metabolism and biosynthesis of unsaturated fatty acids both in human and mice fetal brain. Since intestinal microbes could critically regulate neurofunction via the intestinal-brain axis, we further found the abundances of Firmicutes and Bacteroidetes in the gut of pregnant mice were correlated with the abundances of lipid metabolism related metabolites in the fetal brain. This finding probably reflects the intergenerational microbial-metabolism biomarkers of NTDs.

Short chain fatty acids: the messengers from down below

Short-chain fatty acids (SCFAs), produced by the metabolism of dietary fibers in the gut, have wide-ranging effects locally and throughout the body. They modulate the enteric and central nervous systems, benefit anti-inflammatory pathways, and serve as energy sources. Recent research reveals SCFAs as crucial communicators between the gut and brain, forming the gut-brain axis. This perspective highlights key findings and discusses signaling mechanisms connecting SCFAs to the brain. By shedding light on this link, the perspective aims to inspire innovative research in this rapidly developing field.

Microbiota-derived short-chain fatty acids may participate in post-stroke depression by regulating host's lipid metabolism

BACKGROUND

Post-stroke depression (PSD) is a common mental disorder of stroke survivors, its pathogenesis remains elusive. Previous studies suggested a role of the microbiota-gut-brain (MGB) axis in stroke and depression. In this study, we characterized microbial composition and function, and gut-brain metabolic signatures, in PSD rats. We aim to explore how disordered gut microbes participate in the pathogenesis of PSD through the MGB axis.

MATERIALS AND METHODS

16S rRNA gene sequence and fecal metabolome analysis were performed to identify the gut microbiome and their functional metabolites in PSD rats. Then, the lipid metabolic signatures in the prefrontal cortex (PFC) of PSD were conducted by liquid chromatography mass spectrometry. Finally, the potential pathway between gut and brain in the onset of PSD were explored.

RESULTS

Compared to control and stroke rats, there were 10 genera (most of them belonged to phylum Firmicutes) significantly changed and 3 short chain fatty acids (SCFAs: butyric acid, acetic acid and pentanoic acid) significantly decreased in PSD rats. Meanwhile, altered gut microbial in PSD rats was significantly associated with these SCFAs. Compared with control and stroke rats, 57 lipid metabolites in the PFC of PSD rats were significantly changed. In addition, the altered SCFAs in PSD rats were also significantly correlated with most of disordered lipid metabolites in PFC.

CONCLUSIONS

Our findings suggest that the SCFAs may be a bridge of gut-brain communication. The Firmicutes-SCFAs-lipid metabolism might be a potential pathway to further investigate the MGB axis and pathogenesis of PSD.

Decoding the neurocircuitry of gut feelings: Region-specific microbiome-mediated brain alterations

Research in the last decade has unveiled a crucial role for the trillions of microorganisms that reside in the gut in influencing host neurodevelopment across the lifespan via the microbiota-gut-brain axis. Studies have linked alterations in the composition, complexity, and diversity of the gut microbiota to changes in behaviour including abnormal social interactions, cognitive deficits, and anxiety- and depressive-like phenotypes. Moreover, the microbiota has been linked with neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. Interestingly, there appears to be specific brain regions governing the neurocircuitry driving higher cognitive function that are susceptible to influence from manipulations to the host microbiome. This review will aim to elucidate the region-specific effects mediated by the gut microbiota, with a focus on translational animal models and some existing human neuroimaging data. Compelling preclinical evidence suggests disruption to normal microbiota-gut-brain signalling can have detrimental effects on the prefrontal cortex, amygdala, hippocampus, hypothalamus, and striatum. Furthermore, human neuroimaging studies have unveiled a role for the microbiota in mediating functional connectivity and structure of specific brain regions that can be traced back to neurocognition and behavioural output. Understanding these microbiota-mediated changes will aid in identifying unique therapeutic targets for treating neurological disorders associated with these regions.

ROLE OF GUT MICROBIOTA IN DEPRESSION: UNDERSTANDING MOLECULAR PATHWAYS, RECENT RESEARCH, AND FUTURE DIRECTION

Gut microbiota, also known as the "second brain" in humans because of the regulatory role it has on the central nervous system via neuronal, chemical and immune pathways. It has been proven that there exists a bidirectional communication between the gut and the brain. Increasing evidence supports that this crosstalk is linked to the etiology and treatment of depression. Reports suggest that the gut microbiota control the host epigenetic machinery in depression and gut dysbiosis causes negative epigenetic modifications via mechanisms like histone acetylation, DNA methylation and non-coding RNA mediated gene inhibition. The gut microbiome can be a promising approach for the management of depression. The diet and dietary metabolites like kynurenine, tryptophan, and propionic acid also greatly influence the microbiome composition and thereby, the physiological activities. This review gives a bird-eye view on the pathological updates and currently used treatment approaches targeting the gut microbiota in depression.

Gut dysbiosis impairs hippocampal plasticity and behaviors by remodeling serum metabolome

Accumulating evidence suggests that gut microbiota as a critical mediator of gut-brain axis plays an important role in human health. Altered gut microbial profiles have been implicated in increasing the vulnerability of psychiatric disorders, such as autism, depression, and schizophrenia. However, the cellular and molecular mechanisms underlying the association remain unknown. Here, we modified the gut microbiome with antibiotics in newborn mice, and found that gut microbial alteration induced behavioral impairment by decreasing adult neurogenesis and long-term potentiation of synaptic transmission, and altering the gene expression profile in hippocampus. Reconstitution with normal gut flora produced therapeutic effects against both adult neurogenesis and behavioral deficits in the dysbiosis mice. Furthermore, our results show that circulating metabolites changes mediate the effect of gut dysbiosis on hippocampal plasticity and behavior outcomes. Elevating the serum 4-methylphenol, a small aromatic metabolite produced by gut bacteria, was found to induce autism spectrum disorder (ASD)-like behavior impairment and hippocampal dysfunction. Together our finding demonstrates that early-life gut dysbiosis and its correlated metabolites change contribute to hippocampal dysfunction and behavior impairment, hence highlight the potential microbiome-mediated therapies for treating psychiatric disorders.

Alteration of Glycerophospholipid Metabolism in Hippocampus of Post-stroke Depression Rats

Post-stroke depression (PSD) is the most common mental disorder in stroke survivors. However, its specific pathophysiology remains largely unknown. Previous studies suggested a role of hippocampus in PSD. Therefore, we conducted this study to investigate the lipid metabolic signatures in hippocampus of PSD rats. Here, the liquid chromatography mass spectrometry was used to identify the lipid metabolic signatures in the hippocampus of PSD, control and stroke rats. Then, correlations between behavior indices and differential lipid metabolites in PSD rats were explored. Pathway and enrichment analysis were further conducted to uncover the crucial metabolic pathways related to PSD. Finally, we found that the lipid metabolic phenotype in hippocampus of PSD rats was substantially different from that in control and stroke rats, and identified 50 key lipid metabolites that were significantly decreased in PSD rats. These differential metabolites were mainly involved in glycerophospholipid metabolism. Meanwhile, the sucrose preference and immobility time were found to be significantly positively and negatively, respectively, correlated with glycerophospholipid metabolites. The pathway and enrichment analysis showed that the glycerophospholipid metabolism, especially cardiolipin metabolism, was significantly disturbed in PSD rats. These results suggested that the down-regulated glycerophospholipids in hippocampus, especially cardiolipin, might participate in the pathophysiology of PSD. Our findings would be helpful for future exploring the pathophysiology of PSD.

Curcumin Alleviates DSS-Induced Anxiety-Like Behaviors via the Microbial-Brain-Gut Axis

The anxiety and depression caused by inflammatory bowel diseases (IBD) are known to greatly affect the mental health of patients. The mechanism of psychiatric disorders caused by IBD is not fully understood. Previous research has suggested that the gut microbiome plays a key role in IBD. Curcumin is a yellow polyphenol extracted from the rhizome of the ginger plant, which has been shown to have effects against both depression and anxiety. Research has indicated that curcumin affects the gut microbiome and exerts antianxiety and neuroprotective effects through the microbiota-gut-brain axis (MGB). However, whether curcumin can alleviate the psychiatric disorders caused by IBD and how curcumin affects the MGB axis through the gut microbiota have not been fully understood. Therefore, this study was aimed at determining the metabolic parameters and microbiological environment in the peripheral and central nervous system to determine the effects of curcumin against anxiety induced by dextran sulfate sodium salt (DSS) in mice. To elaborate on the link between the gut microbiota and how curcumin alleviates anxiety-like behaviors, we performed a fecal microbiota transplantation (FMT) experiment. The results suggested that curcumin can effectively relieve anxiety-like behaviors caused by DSS in mice. Further, curcumin treatment can alleviate disturbances in the gut microbiota and systemic disorders of lipid metabolism caused by DSS. Finally, through FMT, we verified that curcumin increased phosphatidylcholine in the prefrontal cortex of the mice and alleviated DSS-induced anxiety-like behaviors by modulating specific gut microbiota. We also revealed that Muribaculaceae may be a key part of the gut microbiota for curcumin to alleviate DSS-induced anxiety-like behaviors through the MGB axis.

Changes in gut viral and bacterial species correlate with altered 1,2-diacylglyceride levels and structure in the prefrontal cortex in a depression-like non-human primate model

Major depressive disorder (MDD) is a debilitating mental disease, but its underlying molecular mechanisms remain obscure. Our previously established model of naturally occurring depression-like (DL) behaviors in Macaca fascicularis, which is characterized by microbiota-gut-brain (MGB) axis disturbances, can be used to interrogate how a disturbed gut ecosystem may impact the molecular pathology of MDD. Here, gut metagenomics were used to characterize how gut virus and bacterial species, and associated metabolites, change in depression-like monkey model. We identified a panel of 33 gut virus and 14 bacterial species that could discriminate the depression-like from control macaques. In addition, using lipidomic analyses of central and peripheral samples obtained from these animals, we found that the DL macaque were characterized by alterations in the relative abundance, carbon-chain length, and unsaturation degree of 1,2-diacylglyceride (DG) in the prefrontal cortex (PFC), in a brain region-specific manner. In addition, lipid-reaction analysis identified more active and inactive lipid pathways in PFC than in amygdala or hippocampus, with DG being a key nodal player in these lipid pathways. Significantly, co-occurrence network analysis showed that the DG levels may be relevant to the onset of negative emotions behaviors in PFC. Together our findings suggest that altered DG levels and structure in the PFC are hallmarks of the DL macaque, thus providing a new framework for understanding the gut microbiome's role in depression.

Electroacupuncture at Lower He-Sea and Front-Mu Acupoints Ameliorates Insulin Resistance in Type 2 Diabetes Mellitus by Regulating the Intestinal Flora and Gut Barrier

INTRODUCTION

The study objective was to investigate the effects of electroacupuncture performed at the he-sea and front-mu acupoints on the intestinal microflora and intestinal barrier in db/db mice and to explore the related mechanism in type 2 diabetes mellitus.

METHODS

Db/m mice in the normal control group (NOC), electroacupuncture group (EA), metformin group (MET) and T2DM group (T2DM) were used as model controls, and db/db mice were used in all three groups, with 8 mice in each group. The treatment period was 2 weeks. Fasting blood glucose (FBG) and triglyceride (TG) levels were measured. Lipopolysaccharide (LPS) and tumor necrosis factor-α (TNF-α) levels were detected by enzyme-linked immune sorbent assay (ELISA). The ileal tissue was stained with hematoxylin-eosin staining (H&E), and histopathological changes were observed under a light microscope. Illumina sequencing was used to analyze the V4 region of the 16S rRNA gene to evaluate the effect of EA on the intestinal flora.

RESULTS

Our results suggest that EA treatment can reduce the expression of diabetes-related markers, with an effect similar to that of metformin. After EA intervention, the abundance of Firmicutes and the ratio of Firmicutes to Bacteroidetes increased, while the abundances of Bacteroidetes and Eubacterium decreased. In addition, the serum levels of LPS and TNF-α in the electroacupuncture group were downregulated, and ileal tissue damage was alleviated under an electron microscope.

CONCLUSION

EA combined with acupoints can restore the intestinal flora structure, decrease the blood LPS level, reduce levels of inflammation, maintain the integrity of the intestinal barrier, and play a therapeutic role in the treatment of T2DM, mainly by increasing the abundance of Firmicutes and the ratio of Firmicutes to Bacteroidetes and decreasing the abundances of Bacteroidetes and Eubacterium.

Jasmine Tea Attenuates Chronic Unpredictable Mild Stress-Induced Depressive-like Behavior in Rats via the Gut-Brain Axis

The number of depressed people has increased worldwide. Dysfunction of the gut microbiota has been closely related to depression. The mechanism by which jasmine tea ameliorates depression via the brain-gut-microbiome (BGM) axis remains unclear. Here, the effects of jasmine tea on rats with depressive-like symptoms via the gut microbiome were investigated. We first established a chronic unpredictable mild stress (CUMS) rat model to induce depressive symptoms and measured the changes in depression-related indicators. Simultaneously, the changes in gut microbiota were investigated by 16S rRNA sequencing. Jasmine tea treatment improved depressive-like behaviors and neurotransmitters in CUMS rats. Jasmine tea increased the gut microbiota diversity and richness of depressed rats induced by CUMS. Spearman’s analysis showed correlations between the differential microbiota (Patescibacteria, Firmicutes, Bacteroidetes, Spirochaetes, Elusimicrobia, and Proteobacteria) and depressive-related indicators (BDNF, GLP-1, and 5-HT in the hippocampus and cerebral cortex). Combined with the correlation analysis of gut microbiota, the result indicated that jasmine tea could attenuate depression in rats via the brain- gut-microbiome axis.

Multi-omics data reveals the disturbance of glycerophospholipid metabolism caused by disordered gut microbiota in depressed mice

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Three important ”metabolite type-bacterial genus” correlated pairs were identified.

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Peripheral and central GP metabolism was disordered in depressed mice.

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Four differential NEs from tryptophan pathway in hippocampus were found.

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“Firmicutes-SCFAs-GP metabolism-Tryptophan pathway” was possible way in gut-brain.

Introduction

Although researchers have done intensive research on depression, its pathogenesis is still not fully explained. More and more evidence suggests that gut microbiota is closely related to the onset of depression; but its specific functional ways are not clearly identified.

Objectives

The purpose of our work was to find out how the gut microbiota was involved in the onset of depression, and to identify the potential ways to link the gut and brain in mice with depressive-like behaviors (DLB).

Methods

We used the chronic restraint stress (CRS)-induced depression model here. Gut microbiota compositions in fecal samples, lipid metabolism (in fecal, serum and hippocampus samples) and neurotransmitters in hippocampus samples were detected.

Results

We found that the 7 of 13 differential genera that significantly correlated with DLB belonged to phylum Firmicutes. The differential lipid metabolites in fecal samples mainly belonged to glycerophospholipids (GP) and fatty acids (FA) metabolism, and three important “metabolite type-bacterial taxa” correlated pairs were identified: “FA/GP-Firmicutes”, “FA/GP-Akkermansia”, and “FA/GP-Bifidobacterium”. The key differential lipid metabolites significantly correlated with DLB mainly belonged to FA and GP, and the DLB-related metagenomic genes were consistently enriched in GP metabolism and FA metabolism. Three significantly changed short-chain fatty acids (SCFAs) were significantly correlated with the majority of differential genera. Meanwhile, we found that the differential lipid metabolites in serum and hippocampus samples were mainly mapped into the GP metabolism, and there were four differential neurotransmitters from the tryptophan pathway in hippocampus samples.

Conclusion

Together, our findings could provide novel insights into the role of “microbiota-gut-brain” (MGB) axis in depression, and indicate that the gut microbiota might have a vital role in the onset of DLB by affecting the peripheral/central GP metabolism and tryptophan pathway. The “Firmicutes-SCFAs-GP metabolism-Tryptophan pathway” might be a possible way to link the gut and brain in depressed mice.

Stress and the Role of the Gut-Brain Axis in the Pathogenesis of Schizophrenia: A Literature Review

Schizophrenia is a severe neuropsychiatric disorder, and its etiology remains largely unknown. Environmental factors have been reported to play roles in the pathogenesis of schizophrenia, and one of the major environmental factors identified for this disorder is psychosocial stress. Several studies have suggested that stressful life events, as well as the chronic social stress associated with city life, may lead to the development of schizophrenia. The other factor is the gut–brain axis. The composition of the gut microbiome and alterations thereof may affect the brain and may lead to schizophrenia. The main interest of this review article is in overviewing the major recent findings on the effects of stress and the gut–brain axis, as well as their possible bidirectional effects, in the pathogenesis of schizophrenia.

Impact of Gut Microbiota and Microbiota-Related Metabolites on Hyperlipidemia

Hyperlipidemia, defined as the presence of excess fat or lipids in the blood, has been considered as a high-risk factor and key indicator of many metabolic diseases. The gut microbiota has been reported playing a vital role in regulating host lipid metabolism. The pathogenic role of gut microbiota in the development of hyperlipidemia has been revealed through fecal microbiota transplantation experiment to germ-free mice. The effector mechanism of microbiota-related metabolites such as bile acids, lipopolysaccharide, and short-chain fatty acids in the regulation of hyperlipidemia has been partially unveiled. Moreover, studies on gut-microbiota-targeted hyperlipidemia interventions, including the use of prebiotics, probiotics, fecal microbiota transplantation, and natural herbal medicines, also have shown their efficacy in the treatment of hyperlipidemia. In this review, we summarize the relationship between gut microbiota and hyperlipidemia, the impact of gut microbiota and microbiota-related metabolites on the development and progression of hyperlipidemia, and the potential therapeutic management of hyperlipidemia targeted at gut microbiota.

Altered Fecal Metabolites and Colonic Glycerophospholipids Were Associated With Abnormal Composition of Gut Microbiota in a Depression Model of Mice

The microbiota–gut–brain axis has been considered to play an important role in the development of depression, but the underlying mechanism remains unclear. The gastrointestinal tract is home to trillions of microbiota and the colon is considered an important site for the interaction between microbiota and host, but few studies have been conducted to evaluate the alterations in the colon. Accordingly, in this study, we established a chronic social defeated stress (CSDS) mice model of depression. We applied 16S rRNA gene sequencing to assess the gut microbial composition and gas and liquid chromatography–mass spectroscopy to identify fecal metabolites and colonic lipids, respectively. Meanwhile, we used Spearman’s correlation analysis method to evaluate the associations between the gut microbiota, fecal metabolites, colonic lipids, and behavioral index. In total, there were 20 bacterial taxa and 18 bacterial taxa significantly increased and decreased, respectively, in the CSDS mice. Further, microbial functional prediction demonstrated a disturbance of lipid, carbohydrate, and amino acid metabolism in the CSDS mice. We also found 20 differential fecal metabolites and 36 differential colonic lipids (in the category of glycerolipids, glycerophospholipids, and sphingolipids) in the CSDS mice. Moreover, correlation analysis showed that fecal metabolomic signature was associated with the alterations in the gut microbiota composition and colonic lipidomic profile. Of note, three lipids [PC(16:0/20:4), PG(22:6/22:6), and PI(18:0/20:3), all in the category of glycerophospholipids] were significantly associated with anxiety- and depression-like phenotypes in mice. Taken together, our results indicated that the gut microbiota might be involved in the pathogenesis of depression via influencing fecal metabolites and colonic glycerophospholipid metabolism.

Regulation of Gut Microbiota Disrupts the Glucocorticoid Receptor Pathway and Inflammation-related Pathways in the Mouse Hippocampus

An increasing number of studies have recently indicated the important effects of gut microbes on various functions of the central nervous system. However, the underlying mechanisms by which gut microbiota regulate brain functions and behavioral phenotypes remain largely unknown. We therefore used isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis to obtain proteomic profiles of the hippocampus in germ-free (GF), colonized GF, and specific pathogen-free (SPF) mice. We then integrated the resulting proteomic data with previously reported mRNA microarray data, to further explore the effects of gut microbes on host brain functions. We identified that 61 proteins were upregulated and 242 proteins were downregulated in GF mice compared with SPF mice. Of these, 124 proteins were significantly restored following gut microbiota colonization. Bioinformatic analysis of these significant proteins indicated that the glucocorticoid receptor signaling pathway and inflammation-related pathways were the most enriched disrupted pathways. This study provides new insights into the pathological mechanisms of gut microbiota-regulated diseases.

Circulating microRNA 134 sheds light on the diagnosis of major depressive disorder

Major depressive disorder (MDD) is a prevalent and debilitating psychiatric mood disorder that lacks objective laboratory-based tests to support its diagnosis. A class of microRNAs (miRNAs) has been found to be centrally involved in regulating many molecular processes fundamental to central nervous system function. Among these miRNAs, miRNA-134 (miR-134) has been reported to be related to neurogenesis and synaptic plasticity. In this study, the hypothesis that plasma miR-134 can be used to diagnose MDD was tested. Perturbation of peripheral and central miR-134 in a depressive-like rat model was also examined. By reverse-transcription quantitative PCR, miR-134 was comparatively measured in a small set of plasma samples from MDD and healthy control (HC) subjects. To determine its diagnostic efficacy, plasma miR-134 levels were assessed in 100 MDD, 50 bipolar disorder (BD), 50 schizophrenic (SCZ), and 100 HC subjects. A chronic unpredictable mild stress (CUMS) rat model was also developed to evaluate miR-134 expression in plasma, hippocampus (HIP), prefrontal cortex (PFC), and olfactory bulb. We found that plasma miR-134 was significantly downregulated in MDD subjects. Diagnostically, plasma miR-134 levels could effectively distinguish MDD from HC with 79% sensitivity and 84% specificity, while distinguishing MDD from HC, BD, and SCZ subjects with 79% sensitivity and 76.5% specificity. Congruent with these clinical findings, CUMS significantly reduced miR-134 levels in the rat plasma, HIP, and PFC. Although limited by the relatively small sample size, these results demonstrated that plasma miR-134 displays potential ability as a biomarker for MDD.

Age-specific differential changes on gut microbiota composition in patients with major depressive disorder

Emerging evidence has shown the age-related changes in gut microbiota, but few studies were conducted to explore the effects of age on the gut microbiota in patients with major depressive disorder (MDD). This study was performed to identify the age-specific differential gut microbiota in MDD patients. In total, 70 MDD patients and 71 healthy controls (HCs) were recruited and divided into two groups: young group (age 18-29 years) and middle-aged group (age 30-59 years). The 16S rRNA gene sequences were extracted from the collected fecal samples. Finally, we found that the relative abundances of Firmicutes and Bacteroidetes were significantly decreased and increased, respectively, in young MDD patients as compared with young HCs, and the relative abundances of Bacteroidetes and Actinobacteria were significantly decreased and increased, respectively, in middle-aged MDD patients as compared with middle-aged HCs. Meanwhile, six and 25 differentially abundant bacterial taxa responsible for the differences between MDD patients (young and middle-aged, respectively) and their respective HCs were identified. Our results demonstrated that there were age-specific differential changes on gut microbiota composition in patients with MDD. Our findings would provide a novel perspective to uncover the pathogenesis underlying MDD.

Identification of Potential Metabolite Markers for Middle-Aged Patients with Post-Stroke Depression Using Urine Metabolomics

BACKGROUND

Post-stroke depression (PSD) is one of the most common complications in stroke survivors. But, there are still no objective methods to diagnose PSD. This study aims to identify potential biomarkers for diagnosing PSD in middle-aged stroke survivors.

METHODS

Middle-aged subjects aged 30 to 59 years (92 PSD patients and 89 stroke survivors without depression) were included in this study. Urinary metabolites were detected by gas chromatography-mass spectrometry (GC-MS). Differential urinary metabolites and potential biomarkers were screened by applying statistical analysis.

RESULTS

The different urinary metabolic phenotypes between PSD patients and stroke survivors without depression were identified. A total of 12 differential urinary metabolites were accurately identified by using orthogonal partial least-squares-discriminant analysis. After analyzing those 12 differential urinary metabolites by step-wise logistic regression analysis, only seven metabolites (palmitic acid, hydroxylamine, myristic acid, glyceric acid, lactic acid, tyrosine and azelaic acid) were finally selected as potential biomarkers for diagnosing PSD in middle-aged stroke survivors. A panel consisting of these potential biomarkers could effectively diagnose middle-aged PSD patients.

CONCLUSION

Urinary metabolic profiles were different between middle-aged PSD patients and stroke survivors without depression. Our results would be helpful in future for developing an objective method to diagnose PSD in middle-aged stroke survivors.

Dual Metabolomic Platforms Identified a Novel Urinary Metabolite Signature for Hepatitis B Virus-Infected Patients with Depression

OBJECTIVE

Depression could make the treatment outcome worse. However, up to now, no objective methods were developed to diagnose depression in hepatitis B virus (HBV)-infected patients. Therefore, the dual metabolomic platforms were used here to identify potential biomarkers for diagnosing HBV-infected patients with depression (dHB).

METHODS

Both gas chromatography-mass spectrometry-based and nuclear magnetic resonance-based metabolomic platforms were used to conduct urine metabolic profiling of dHB subjects and HBV-infected patients without depression (HB). Orthogonal partial least-squares discriminant analysis was used to identify the differential metabolites between dHB subjects and HB subjects, and the step-wise logistic regression analysis was used to identify potential biomarkers.

RESULTS

In total, 21 important metabolites responsible for distinguishing dHB subjects from HB subjects were identified. Meanwhile, seven potential biomarkers (α-ydroxyisobutyric acid, hippuric acid, azelaic acid, isobutyric acid, malonic acid, levulinic acid, and phenylacetylglycine) were viewed as potential biomarkers. The simplified biomarker panel consisting of these seven metabolites had an excellent diagnostic performance in discriminating dHB subjects from HB subjects. Moreover, this panel could yield a higher accuracy in separating dHB subjects from HB subjects than our previous panels (identified by single metabolomic platform) did.

CONCLUSION

These results suggested that the dual metabolomic platforms could yield a better urinary biomarker panel for dHB subjects than any single metabolomic platform did, and our results could be helpful for developing an objective method in future to diagnose depression in HBV-infected patients.