Fishing for obesity-related gut microbiome enterotype.

Despite debate, the concept of enterotype-like clusters remains valuable for exploring the human gut microbiome and associated environmental factors. In this issue of Cell Host & Microbe, Wu et al. robustly identified an obesity-related enterotype-like cluster, Megamonas, and demonstrated its clinical relevance through cohort studies, mice, and cell experiments.

MicroRNA-Messenger RNA Regulatory Network Mediates Disrupted TH17 Cell Differentiation in Depression.

Accumulating evidence indicates an important role for microRNA (miRNA)-messenger RNA (mRNA) regulatory networks in human depression. However, the mechanisms by which these networks act are complex and remain poorly understood. We used data mining to identify differentially expressed miRNAs from GSE81152 and GSE152267 datasets, and differentially expressed mRNAs were identified from the Netherlands Study of Depression and Anxiety, the GlaxoSmithKline-High-Throughput Disease-specific target Identification Program, and the Janssen-Brain Resource Company study. We constructed a miRNA-mRNA regulatory network based on differentially expressed mRNAs that intersected with target genes of differentially expressed miRNAs, and then performed bioinformatics analysis of the network. The key candidate genes were assessed in the prefrontal cortex of chronic social defeat stress (CSDS) depression mice by quantitative real-time polymerase chain reaction (qRT-PCR). Three differentially expressed miRNAs were commonly identified across the two datasets, and 119 intersecting differentially expressed mRNAs were identified. A miRNA-mRNA regulatory network including these three key differentially expressed miRNAs and 119 intersecting differentially expressed mRNAs was constructed. Functional analysis of the intersecting differentially expressed mRNAs revealed that an abnormal inflammatory response characterized by disturbed T-helper cell 17 (Th17) differentiation was the primary altered biological function. qRT-PCR validated the decreased expression of Th17 cell differentiation-related genes, including interleukin (IL)17A, IL21, IL22, and IL1ß, and the increased expression of retinoic acid receptor-related orphan receptor gamma-t (RORγt) in CSDS mice, which showed significant depressive- and anxiety-like behaviors. This study indicates that an abnormal inflammatory response characterized by disturbed Th17 cell differentiation is the primary altered biological process in major depressive disorder. Our findings indicate possible biomarkers and treatment targets and provide novel clues to understand the pathogenesis of major depressive disorder.

Comprehensive analysis of the lysine acetylome and succinylome in the hippocampus of gut microbiota-dysbiosis mice.

Introduction: Major depressive disorder is caused by gene-environment interactions, and the host microbiome has been recognized as an important environmental factor. However, the underlying mechanisms of the host-microbiota interactions that lead to depression are complex and remain poorly understood. Objectives: The present study aimed to explore the possible mechanisms underlying gut microbiota dysbiosis-induced depressive-like behaviors. Methods: We used high-performance liquid chromatography-tandem mass spectrometry to analyze alterations in the hippocampal lysine acetylome and succinylome in male mice that had received gut microbiota from fecal samples of either patients with major depressive disorder or healthy controls. This was followed by bioinformatic analyses. Results: A total of 315 acetylation sites on 223 proteins and 624 succinylation sites on 494 proteins were differentially expressed in the gut microbiota-dysbiosis mice. The significantly acetylated proteins were primarily associated with carbon metabolism disruption and gene transcription suppression, while the synaptic vesicle cycle and protein translation were the most significantly altered functions for succinylated proteins. Additionally, our findings suggest that gut microbiota dysbiosis disturbs mitochondria-mediated biological processes and the MAPK signaling pathway through crosstalk between acetylation and succinylation on relevant proteins. Conclusions: This is the first study to demonstrate modifications in acetylation and succinylation in gut microbiota-dysbiosis mice. Our findings provide new avenues for exploring the pathogenesis of gut microbiota dysbiosis-related depression, and highlight potential targets for depression treatment.

Proteomic Profiling of Lysine Acetylation Indicates Mitochondrial Dysfunction in the Hippocampus of Gut Microbiota-Absent Mice.

Major depressive disorder (MDD) is a leading cause of disability around the world and contributes greatly to the global burden of disease. Mounting evidence suggests that gut microbiota dysbiosis may be involved in the pathophysiology of MDD through the microbiota-gut-brain axis. Recent research suggests that epigenetic modifications might relate to depression. However, our knowledge of the role of epigenetics in host-microbe interactions remains limited. In the present study, we used a combination of affinity enrichment and high-resolution liquid chromatography tandem mass spectrometry analysis to identify hippocampal acetylated proteins in germ-free and specific pathogen-free mice. In total, 986 lysine acetylation sites in 543 proteins were identified, of which 747 sites in 427 proteins were quantified. Motif analysis identified several conserved sequences surrounding the acetylation sites, including D∗Kac, DKac, KacY, KacD, and D∗∗Kac. Gene ontology annotations revealed that these differentially expressed acetylated proteins were involved in multiple biological functions and were mainly located in mitochondria. In addition, pathway enrichment analysis demonstrated that oxidative phosphorylation and the tricarboxylic acid cycle II (eukaryotic), both of which are exclusively localized to the mitochondria, were the primarily disturbed functions. Taken together, this study indicates that lysine acetylation alterations may play a pivotal role in mitochondrial dysfunction and may be a mechanism by which gut microbiota regulate brain function and behavioral phenotypes.

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.

Integrative Analysis of Long Non-coding RNAs, Messenger RNAs, and MicroRNAs Indicates the Neurodevelopmental Dysfunction in the Hippocampus of Gut Microbiota-Dysbiosis Mice.

Major depressive disorder is caused by gene-environment interactions and the gut microbiota plays a pivotal role in the development of depression. However, the underlying mechanisms remain elusive. Herein, the differentially expressed hippocampal long non-coding RNAs (lncRNAs), messenger RNAs (mRNAs), and microRNAs (miRNAs) between mice inoculated with gut microbiota from major depressive disorder patients or healthy controls were detected, to identify the effects of gut microbiota-dysbiosis on gene regulation patterns at the transcriptome level, and in further to explore the microbial-regulated pathological mechanisms of depression. As a result, 200 mRNAs, 358 lncRNAs, and 4 miRNAs were differentially expressed between the two groups. Functional analysis of these differential mRNAs indicated dysregulated inflammatory response to be the primary pathological change. Intersecting these differential mRNAs with targets of differentially expressed miRNAs identified 47 intersected mRNAs, which were mainly related to neurodevelopment. Additionally, a microbial-regulated lncRNA-miRNA-mRNA network based on RNA-RNA interactions was constructed. Subsequently, according to the competitive endogenous RNAs (ceRNA) hypothesis and the biological functions of these intersected genes, two neurodevelopmental ceRNA sub-networks implicating in depression were identified, one including two lncRNAs (4930417H01Rik and AI480526), one miRNA (mmu-miR-883b-3p) and two mRNAs (Adcy1 and Nr4a2), and the other including six lncRNAs (5930412G12Rik, 6430628N08Rik, A530013C23Rik, A930007I19Rik, Gm15489, and Gm16251), one miRNA (mmu-miR-377-3p) and three mRNAs (Six4, Stx16, and Ube3a), and these molecules could be recognized as potential genetic and epigenetic biomarkers in microbial-associated depression. This study provides new understanding of the pathogenesis of depression induced by gut microbiota-dysbiosis and may act as a theoretical basis for the development of gut microbiota-based antidepressants.

Integrated phosphoproteomic and metabolomic profiling reveals perturbed pathways in the hippocampus of gut microbiota dysbiosis mice.

The dysbiosis of gut microbiota is an important environmental factor that can induce mental disorders, such as depression, through the microbiota-gut-brain axis. However, the underlying pathogenic mechanisms are complex and not completely understood. Here we utilized mass spectrometry to identify the global phosphorylation dynamics in hippocampus tissue in germ-free mice and specific pathogen-free mice (GF vs SPF), fecal microbiota transplantation (FMT) model ("depression microbiota" and the "healthy microbiota" recipient mice). As a result, 327 phosphosites of 237 proteins in GF vs SPF, and 478 phosphosites of 334 proteins in "depression microbiota" vs "healthy microbiota" recipient mice were identified as significant. These phosphorylation dysregulations were consistently associated with glutamatergic neurotransmitter system disturbances. The FMT mice exhibited disturbances in lipid metabolism and amino acid metabolism in both the periphery and brain through integrating phosphoproteomic and metabolomic analysis. Moreover, CAMKII-CREB signaling pathway, in response to these disturbances, was the primary common perturbed cellular process. In addition, we demonstrated that the spliceosome, never directly implicated in mental disorders previously, was a substantially neuronal function disrupted by gut microbiota dysbiosis, and the NCBP1 phosphorylation was identified as a novel pathogenic target. These results present a new perspective to study the pathologic mechanisms of gut microbiota dysbiosis related depression and highlight potential gut-mediated therapies for depression.

Microbial regulation of a lincRNA-miRNA-mRNA network in the mouse hippocampus.

Aim: To comprehensively understand microbiota-regulated lincRNA-miRNA-mRNA networks in psychiatric disorders. Materials & methods: Integrated analyses of lincRNAs, mRNAs and miRNAs, obtained by microarray analysis of hippocampus from specific pathogen-free, germ-free and colonized germ-free mice, were performed. Results: Expression of 139 mRNAs, seven miRNAs and one lincRNA was restored following colonization. The restored transcripts were mainly involved in CREB and Ras/MAPK signaling pathways. RNA transcription and post-transcriptional regulation were the primary perturbed functions. Finally, 12 lincRNAs, six miRNAs and 47 mRNAs were included in a lincRNA-miRNA-mRNA network, and lincRNA0926-miR-190a-5p-Celf4 interactions may play a pivotal role in this regulatory network. Conclusion: This study provides clues for understanding the molecular basis of gut microbiota-brain interactions in depressive- and anxiety-like behaviors.

Commensal Microbiota Regulation of Metabolic Networks During Olfactory Dysfunction in Mice.

INTRODUCTION: Recently, an increasing number of studies have focused on commensal microbiota. These microorganisms have been suggested to impact human health and disease. However, only a small amount of data exists to support the assessment of the influences that commensal microbiota exert on olfactory function. METHODS: We used a buried food pellet test (BFPT) to investigate and compare olfactory functions in adult, male, germ-free (GF) and specific-pathogen-free (SPF) mice, then examined and compared the metabolomic profiles for olfactory bulbs (OBs) isolated from GF and SPF mice to uncover the mechanisms associated with olfactory dysfunction. RESULTS: We found that the absence of commensal microbiota was able to influence olfactory function and the metabolic signatures of OBs, with 38 metabolites presenting significant differences between the two groups. These metabolites were primarily associated with disturbances in glycolysis, the tricarboxylic acid (TCA) cycle, amino acid metabolism, and purine catabolism. Finally, the commensal microbiota regulation of metabolic networks during olfactory dysfunction was identified, based on an integrated analysis of metabolite, protein, and mRNA levels. CONCLUSION: This study demonstrated that the absence of commensal microbiota may impair olfactory function and disrupt metabolic networks. These findings provide a new entry-point for understanding olfactory-associated disorders and their potential underlying mechanisms.

Hippocampus-specific regulation of long non-coding RNA and mRNA expression in germ-free mice.

Gut microbiota can affect multiple brain functions and cause behavioral alterations through the microbiota-gut-brain axis. In our previous study, we found that the absence of gut microbiota can influence the expression of microRNAs and mRNAs in the hippocampal region of the germ-free (GF) mice. Long non-coding RNAs (lncRNAs) are increasingly being recognized as an important functional transcriptional regulator in the brain. In the present study, we aim to identify possible biological pathways and functional networks for lncRNA-associated transcript of the gut microbiota in relation to the brain function. The profiles of lncRNA and mRNA from specific pathogen-free (SPF), colonized GF (CGF), and GF mice were generated using the Agilent Mouse LncRNA Array v2.0. Differentially expressed (DE) lncRNAs and mRNAs were identified, and lncRNA target genes were also predicted. Ingenuity pathway analysis (IPA) was performed to analyze related signaling pathways and biological functions associated with these dysregulated mRNAs and target genes. Validation with quantitative real-time PCR was performed on several key genes. Compared with SPF mice a total of 2230 DE lncRNAs were found in GF mice. Among these, 1355 were upregulated and 875 were downregulated. After comparing the target genes of DE lncRNAs with mRNA datasets, 669 overlapping genes were identified. IPA core analyses revealed that most of these genes were highly associated with cardiac hypertrophy, nuclear factors of activated T cells (NFAT) gonadotropin-releasing hormone (GnRH), calcium, and cAMP-response element-binding protein (CREB) signaling pathways. Additionally, mRNA expression levels of APP, CASP9, IGFBP2, PTGDS, and TGFBR2 genes that are involved in central nervous system functions were significantly changed in the GF mouse hippocampus. Through this study, for the first time, we describe the effect of gut microbiota on the hippocampal lncRNA regulation. This will help in enhancing the overall knowledge about microbiota-gut-brain axis.