Mouse Gut Research Articles

Inactivation of the riboswitch-controlled GMP synthase GuaA in Clostridioides difficile is associated with severe growth defects and poor infectivity in a mouse model of infection

ABSTRACT Clostridioides difficile is the main cause of nosocomial antibiotic-associated diarrhoea. There is a need for new antimicrobials to tackle this pathogen. Guanine riboswitches have been proposed as promising new antimicrobial targets, but experimental evidence of their importance in C. difficile is missing. The genome of C. difficile encodes four distinct guanine riboswitches, each controlling a single gene involved in purine metabolism and transport. One of them controls the expression of guaA, encoding a guanosine monophosphate (GMP) synthase. Here, using in-line probing and GusA reporter assays, we show that these riboswitches are functional in C. difficile and cause premature transcription termination upon binding of guanine. All riboswitches exhibit a high affinity for guanine characterized by Kd values in the low nanomolar range. Xanthine and guanosine also bind the guanine riboswitches, although with less affinity. Inactivating the GMP synthase (guaA) in C. difficile strain 630 led to cell death in minimal growth conditions, but not in rich medium. Importantly, the capacity of a guaA mutant to colonize the mouse gut was significantly reduced. Together, these results demonstrate the importance of de novo GMP biosynthesis in C. difficile during infection, suggesting that targeting guanine riboswitches with analogues could be a viable therapeutic strategy.

Impact of Bead-Beating Intensity on the Genus- and Species-Level Characterization of the Gut Microbiome Using Amplicon and Complete 16S rRNA Gene Sequencing.

Bead-beating within a DNA extraction protocol is critical for complete microbial cell lysis and accurate assessment of the abundance and composition of the microbiome. While the impact of bead-beating on the recovery of OTUs at the phylum and class level have been studied, its influence on species-level microbiome recovery is not clear. Recent advances in sequencing technology has allowed species-level resolution of the microbiome using full length 16S rRNA gene sequencing instead of smaller amplicons that only capture a few hypervariable regions of the gene. We sequenced the v3-v4 hypervariable region as well as the full length 16S rRNA gene in mouse and human stool samples and discovered major clusters of gut bacteria that exhibit different levels of sensitivity to bead-beating treatment. Full length 16S rRNA gene sequencing unraveled vast species diversity in the mouse and human gut microbiome and enabled characterization of several unclassified OTUs in amplicon data. Many species of major gut commensals such as Bacteroides, Lactobacillus, Blautia, Clostridium, Escherichia, Roseburia, Helicobacter, and Ruminococcus were identified. Interestingly, v3-v4 amplicon data classified about 50% of Ruminococcus reads as Ruminococcus gnavus species which showed maximum abundance in a 9 min beaten sample. However, the remaining 50% of reads could not be assigned to any species. Full length 16S rRNA gene sequencing data showed that the majority of the unclassified reads were Ruminococcus albus species which unlike R. gnavus showed maximum recovery in the unbeaten sample instead. Furthermore, we found that the Blautia hominis and Streptococcus parasanguinis species were differently sensitive to bead-beating treatment than the rest of the species in these genera. Thus, the present study demonstrates species level variations in sensitivity to bead-beating treatment that could only be resolved with full length 16S rRNA sequencing. This study identifies species of common gut commensals and potential pathogens that require minimum (0-1 min) or extensive (4-9 min) bead-beating for their maximal recovery.

High‐efficiency delivery of CRISPR‐Cas9 by engineered probiotics enables precise microbiome editing

Antibiotic resistance threatens our ability to treat infectious diseases, spurring interest in alternative antimicrobial technologies. The use of bacterial conjugation to deliver CRISPR‐cas systems programmed to precisely eliminate antibiotic‐resistant bacteria represents a promising approach but requires high in situ DNA transfer rates. We have optimized the transfer efficiency of conjugative plasmid TP114 using accelerated laboratory evolution. We hence generated a potent conjugative delivery vehicle for CRISPR‐cas9 that can eliminate > 99.9% of targeted antibiotic‐resistant Escherichia coli in the mouse gut microbiota using a single dose. We then applied this system to a Citrobacter rodentium infection model, achieving full clearance within four consecutive days of treatment.

Malvidin Protects against and Repairs Peptic Ulcers in Mice by Alleviating Oxidative Stress and Inflammation.

Peptic ulcer episodes cause damage to the stomach and intestine, with inflammatory cell infiltration and oxidative stress as the main players. In this study, we investigated the potential of anthocyanidin malvidin for preventive and curative peptic ulcer treatment. The anthocyanidin effects were examined in gastric ulcer mouse models induced by ethanol, non-steroidal anti-inflammatory drugs (NSAIDs), ischemia-reperfusion (IR), acetic acid and duodenal ulcer induced by polypharmacy. Expression levels of oxidative and inflammatory genes were measured to investigate the mechanism of anthocyanin activity. At a dose of 5 mg·kg−1, Malvidin prevented gastric ulcer induction by ethanol, NSAID and repaired the tissue after 6 days of IR. Moreover, the anthocyanidin accelerated the healing of acetic acid-induced ulcer, increased the gene expression of EGF and COX-1, and downregulated MMP-9. Anthocyanin treatment mitigated the effect of polypharmacy on inflammation and oxidative stress observed in the intestine. Additionally, the compound downregulated cytokine expression and TLR4 and upregulated HMOX-1 and IL-10, exhibiting protective activity in the mouse gut. Malvidin thus prevented gastric and duodenal ulcers due to prominent anti-inflammatory and antioxidative effects on the gastrointestinal tract that were related to gene expression modulation and an increase in endogenous defense mechanisms.

Exopolysaccharides from a Scandinavian fermented milk viili increase butyric acid and Muribaculum members in the mouse gut

Starter culture of viili contains lactic acid bacteria belonging to Lactococcus lactis. These bacteria secrete large polysaccharides (EPSs) into milk, resulting in a ropy texture of viili. In mouse experiments, a large dose of EPS (5–140 mg/day) has been shown to alleviate severity of artificially induced illness through modulation of the gut microbiota. The present study investigated whether supplementary amounts of EPS affects the gut microbiota of normal mouse. EPS with high glucosamine content (VEPS) was isolated from home-made viili. C57BL/6J male mice fed ordinary diet took 49 ± 1 μg VEPS/day for 28 days by drinking ad libitum tap water containing 8 μg/mL VEPS. The relative abundance of Muribaculum increased significantly by VEPS supplementation. The relative abundance of fecal butyric acid decreased in control mice, and VEPS prevented this decrease. These findings indicated that the gut microbiota can be modulated by a small dose of VEPS.

Gut Microbiota Predicts Healthy Late-Life Aging in Male Mice.

Calorie restriction (CR) extends lifespan and retards age-related chronic diseases in most species. There is growing evidence that the gut microbiota has a pivotal role in host health and age-related pathological conditions. Yet, it is still unclear how CR and the gut microbiota are related to healthy aging. Here, we report findings from a small longitudinal study of male C57BL/6 mice maintained on either ad libitum or mild (15%) CR diets from 21 months of age and tracked until natural death. We demonstrate that CR results in a significantly reduced rate of increase in the frailty index (FI), a well-established indicator of aging. We observed significant alterations in diversity, as well as compositional patterns of the mouse gut microbiota during the aging process. Interrogating the FI-related microbial features using machine learning techniques, we show that gut microbial signatures from 21-month-old mice can predict the healthy aging of 30-month-old mice with reasonable accuracy. This study deepens our understanding of the links between CR, gut microbiota, and frailty in the aging process of mice.

The Gut Microbiota Protects Bees from Invasion by a Bacterial Pathogen.

ABSTRACTCommensal microbes in animal guts often help to exclude bacterial pathogens. In honey bees, perturbing or depleting the gut microbiota increases host mortality rates upon challenge with the opportunistic pathogen Serratia marcescens, suggesting antagonism between S. marcescens and one or more members of the bee gut microbiota. In laboratory culture, S. marcescens uses a type VI secretion system (T6SS) to kill bacterial competitors, but the role of this T6SS within hosts is unknown. Using infection assays, we determined how the microbiota impacts the abundance and persistence of S. marcescens in the gut and visualized colocalization of S. marcescens with specific community members in situ. Using T6SS-deficient S. marcescens strains, we measured T6SS-dependent killing of gut isolates in vitro and compared the persistence of mutant and wild-type strains in the gut. We found that S. marcescens is rapidly eliminated in the presence of the microbiota but persists in microbiota-free guts. Protection is reduced in monocolonized and antibiotic-treated bees, possibly because different symbionts occupy distinct niches. Serratia marcescens uses a T6SS to antagonize Escherichia coli and other S. marcescens strains but shows limited ability to kill bee symbionts. Furthermore, wild-type and T6SS-deficient S. marcescens strains achieved similar abundance and persistence in bee guts. Thus, an intact gut microbiota offers robust protection against this common pathogen, whose T6SSs do not confer the ability to compete with commensal species.IMPORTANCE Bacteria living within guts of animals can provide protection against infection by pathogens. Some pathogens have been shown to use a molecular weapon known as a T6SS to kill beneficial bacteria during invasion of the mouse gut. In this study, we examined how bacteria native to the honey bee gut work together to exclude the opportunistic pathogen Serratia marcescens. Although S. marcescens has a T6SS that can kill bacteria, bee gut bacteria seem resistant to its effects. This limitation may partially explain why ingestion of S. marcescens is rarely lethal to insects with healthy gut communities.

The enriched gut commensal Faeciroseburia intestinalis contributes to the anti-metabolic disorders effects of the Ganoderma meroterpene derivative

Previous study demonstrated that Ganoderma meroterpene derivative (GMD) increased the abundance of butyrate-producing bacteria in gut and subsequently delivered anti-metabolic disorder effect of host. To specify the key commensal bacteria associating with the beneficial effects, we tried to isolate and compare the microbiota from the cecal samples of GMD- and vehicle-treated ob/ob mice, and further identified butyrate-producing bacterial strains. It was found that Faeciroseburia intestinalis was enriched and 11 strains affiliated to F. intestinalis were cultivated from the gut of GMD-treated mice. In vitro assay attested butyrate production by representative strain of F. intestinalis. Oral administration with F. intestinalis further demonstrated its benefits on regulating hyperglycemia and hyperlipidemia, on decreasing plasma lipopolysaccharide (LPS) and inflammation, and on improving hepatic injuries. Treatment with F. intestinalis effectively enhanced the level of gut butyrate, which subsequently ameliorated the intestinal barrier function and activated epithelial PPAR-γ signaling pathway to regulate microbiome homeostasis in gut. Our study demonstrated that the causal relationship between the butyrate-producing bacteria and the GMD's therapeutic effects and confirmed the important function of the butyrate-producing F. intestinalis in maintaining host metabolism homeostasis.

Construction of a sustainable 3-hydroxybutyrate-producing probiotic Escherichia coli for treatment of colitis.

Colitis is a common disease of the colon that is very difficult to treat. Probiotic bacteria could be an effective treatment. The probiotic Escherichia coli Nissle 1917 (EcN) was engineered to synthesize the ketone body (R)-3-hydroxybutyrate (3HB) for sustainable production in the gut lumen of mice suffering from colitis. Components of heterologous 3HB synthesis routes were constructed, expressed, optimized, and inserted into the EcN genome, combined with deletions in competitive branch pathways. The genome-engineered EcN produced the highest 3HB level of 0.6 g/L under microaerobic conditions. The live therapeutic was found to colonize the mouse gastrointestinal tract over 14 days, elevating gut 3HB and short-chain-length fatty acid (SCFA) levels 8.7- and 3.1-fold compared to those of wild-type EcN, respectively. The sustainable presence of 3HB in mouse guts promoted the growth of probiotic bacteria, especially Akkermansia spp., to over 31% from the initial 2% of all the microbiome. As a result, the engineered EcN termed EcNL4 ameliorated colitis induced via dextran sulfate sodium (DSS) in mice. Compared to wild-type EcN or oral administration of 3HB, oral EcNL4 uptake demonstrated better effects on mouse weights, colon lengths, occult blood levels, gut tissue myeloperoxidase activity and proinflammatory cytokine concentrations. Thus, a promising live bacterium was developed to improve colonic microenvironments and further treat colitis. This proof-of-concept design can be employed to treat other diseases of the colon.

Natural Nano-Drug Delivery System in Coptidis Rhizoma Extract with Modified Berberine Hydrochloride Pharmacokinetics.

PurposeThis study aimed to evaluate the pharmaceutical and pharmacokinetic effects of the natural nanoparticles (Nnps) isolated from Coptidis Rhizoma extract on berberine hydrochloride (BBR) and systematically explore the related mechanisms.MethodsFirstly, Nnps were isolated from Coptidis Rhizoma extract and then an Nnps-BBR complex was prepared. After qualitative and quantitative analysis in terms of size, Zeta potential, morphology, and composition of the Nnps and the Nnps-BBR complex, the effects of the Nnps on the crystallization of BBR were characterized. The effects of the Nnps on the solubility and dissolution of BBR were then evaluated. In addition, the effects of the Nnps on BBR in terms of cellular uptake, transmembrane transport, metabolic stability, and pharmacokinetics in mice were studied.ResultsThe Nnps had an average size of 166.6 ± 1.3 nm and Zeta potential of −12.5 ± 0.2 mV. The Nnps were formed by denaturation of co-existing plant proteins with molecular weight < 30 kDa. The Nnps adsorbed or dispersed BBR, thereby promoting BBR transformation from crystal to amorphous form and improving its solubility and dissolution. The Nnps carried and promoted BBR uptake by human colonic adenocarcinoma (Caco-2) cells via caveolae-mediated endocytosis, reducing P-gp-mediated efflux of BBR in mice gut sacs and Madin-Darby canine kidney cells stably expressing the transporter P-gp (MDCK-MDR1) cells. Moreover, the Nnps improved BBR metabolic stability in mouse intestinal S9, promoting BBR intestinal absorption in mice, as shown by increased peak BBR concentration (Cmax, 1182.3 vs 310.2 ng/mL) and exposure level (AUC0–12 h, 2842.8 vs 1447.0 ng·h/mL) in mouse portal vein. In addition, the Nnps increased BBR exposure level in mouse livers (95,443.2 vs 43,586.2 ng·h/g liver).ConclusionThe proteinaceous nanoparticles isolated from Coptidis Rhizoma extract can form a natural nano-drug delivery system with BBR, thereby significantly improving the pharmacokinetics of oral BBR.

Anti-inflammatory Effect of Probiotic Limosilactobacillus reuteri KUB-AC5 Against Salmonella Infection in a Mouse Colitis Model.

Acute non-typhoidal salmonellosis (NTS) caused by Salmonella enterica Typhimurium (STM) is among the most prevalent of foodborne diseases. A global rising of antibiotic resistance strains of STM raises an urgent need for alternative methods to control this important pathogen. Major human food animals which harbor STM in their gut are cattle, swine, and poultry. Previous studies showed that the probiotic Limosilactobacillus (Lactobacillus) reuteri KUB-AC5 (AC5) exhibited anti-Salmonella activities in chicken by modulating gut microbiota and the immune response. However, the immunobiotic effect of AC5 in a mammalian host is still not known. Here, we investigated the anti-Salmonella and anti-inflammatory effects of AC5 on STM infection using a mouse colitis model. Three groups of C57BL/6 mice (prophylactic, therapeutic, and combined) were fed with 109 colony-forming units (cfu) AC5 daily for 7, 4, and 11 days, respectively. Then, the mice were challenged with STM compared to the untreated group. By using a specific primer pair, we found that AC5 can transiently colonize mouse gut (colon, cecum, and ileum). Interestingly, AC5 reduced STM gut proliferation and invasion together with attenuated gut inflammation and systemic dissemination in mice. The decreased STM numbers in mouse gut lumen, gut tissues, and spleen possibly came from longer AC5 feeding duration and/or the combinatorial (direct and indirect inhibitory) effect of AC5 on STM. However, AC5 attenuated inflammation (both in the gut and in the spleen) with no difference between these three approaches. This study demonstrated that AC5 confers both direct and indirect inhibitory effects on STM in the inflamed gut.

Low-dose oral pyrethroid exposure induces gastrointestinal dysfunction and alters nigrostriatal dopamine signaling pathways in mice

BACKGROUND AND AIM: Insecticide exposure is associated with greater risk for developing Parkinson’s disease (PD). PD is characterized by motor impairments due to loss of nigrostriatal dopamine (DA) neurons in the midbrain, and patients commonly experience gastrointestinal (GI) dysfunction long before the onset of motor symptoms. Pyrethroids, synthetic insecticides commonly used around the world, disrupt DA signaling pathways. One of the most common routes of pyrethroid exposure is ingestion, so it is plausible that oral exposure acts locally within the GI tract and facilitates PD pathogenesis via the gut-brain axis. Here, we sought to determine the functional and molecular consequences of oral pyrethroid exposure in the adult mouse gut and brain in the context of idiopathic PD. METHODS: Adult mice were orally gavaged with 3 mg/kg deltamethrin weekly for 3 weeks. Intestinal behaviors were assessed to determine constipation phenotypes. Gut microbiome composition was determined by 16S rRNA sequencing. Intestinal and brain tissues were collected following the final dose to assess changes in gene expression and protein production pathways related to DA and other monoamine signaling, as determined by qPCR and western blot. RESULTS:Oral deltamethrin exposure significantly impaired GI function compared to vehicle controls. We observed reduced fecal output, changed gene and protein levels important for normal gut function, and altered gut microbial composition in deltamethrin-exposed mice, all of which are reflective of changes observed in PD patients. In the brain, oral deltamethrin exposure significantly altered production of proteins important for DA synthesis and reuptake compared to controls. CONCLUSIONS:Low-dose oral pyrethroid exposure induces GI dysfunction and alters DA pathways in the brain. These findings support the idea that pyrethroids induce functional and molecular changes relevant to PD pathology from within the gut, and further investigation is warranted to fully understand this phenomenon as a potential trigger in the etiology of PD. KEYWORDS: Pesticides, Chemical exposures, Neurodegenerative outcomes, Microbes/Microbiome

Effects of Andrographolide on Mouse Intestinal Microflora Based on High-Throughput Sequence Analysis.

The intestinal flora is a micro-ecosystem that is closely linked to the overall health of the host. We examined the diversity and abundance of intestinal microorganisms in mice following the administration of andrographolide, a component of the Chinese medical herb Andrographis paniculata. Administration of andrographolide produces multiple beneficial effects including anti-inflammatory, antiviral and antibacterial effects but whether it directly influences the gut microbiota is not known. This study investigated whether the oral administration of andrographolide influences the intestinal microbiota and was compared with amoxicillin treatment as a positive control and water only as a negative control. We examined 21 cecal samples and conducted a high-throughput sequencing analysis based on V3-V4 variable region of the 16S rDNA genes. We found that the diversity and abundance of mouse gut microbiota decreased in direct proportion with the amoxicillin dose whereas andrographolide administration did not affect intestinal microbial community structure. The composition of intestinal microbes following andrographolide treatment was dominated by the Firmicutes while Bacteroidetes dominated the amoxicillin treatment group compared with the negative controls. Specifically, the f__Lachnospiraceae_ Unclassified, Lachnospiraceae_ NK4A136_group and Ruminococcaceae_ UCG-014 were enriched with andrographolide administration while Bacteroides, Klebsiella and Escherichia-Shigella significantly increased in the amoxicillin test groups. Amoxicillin administration altered the microbial community composition and structure by increasing the proportion of pathogenic to beneficial bacteria whereas andrographolide administration led to increases in the proportions and abundance of beneficial bacteria. This study provides a theoretical basis for finding alternatives to antibiotics to decrease bacterial resistance and restore intestinal floral imbalances.

Characterization of an in vitro 3D intestinal organoid model\xa0by using massive RNAseq-based transcriptome profiling

Organoids culture provides unique opportunities to study human diseases and to complement animal models. Several organs and tissues can be in vitro cultured in 3D structures resembling in vivo tissue organization. Organoids culture contains most of the cell types of the original tissue and are maintained by growth factors mimicking the in vivo state. However, the system is yet not fully understood, and specific in vivo features especially those driven by cell-extrinsic factors may be lost in culture. Here we show a comprehensive transcriptome-wide characterization of mouse gut organoids derived from different intestinal compartments and from mice of different gender and age. RNA-seq analysis showed that the in vitro culture strongly influences the global transcriptome of the intestinal epithelial cells (~ 60% of the total variance). Several compartment-, age- and gender-related transcriptome features are lost after culturing indicating that they are driven by niche or systemic factors. However, certain intrinsic transcriptional programs, for example, some compartment-related features and a minority of gender- and aging- related features are maintained in vitro which suggested possibilities for these features to be studied in this system. Moreover, our study provides knowledge about the cell-extrinsic or cell-intrinsic origin of intestinal epithelial transcriptional programs. We anticipated that our characterization of this in vitro system is an important reference for scientists and clinicians using intestinal organoids as a research model.

Polysaccharides Obtained from Cordyceps militaris Alleviate Hyperglycemia by Regulating Gut Microbiota in Mice Fed a High-Fat/Sucrose Diet

Polysaccharides isolated from fungus Cordyceps militaris display multi-biofunctions, such as immunostimulation, down-regulation of hyperlipidemia, and anti-cancer function. The occurrence of obesity and metabolic syndrome is related to the imbalance of gut microbiota. In this study, the effects of C. militaris and its fractions on modifying metabolic syndrome in mice were evaluated. Mice were fed a high-fat/high-sucrose diet (HFSD) for 14 weeks to induce body weight increase and hyperlipidemia symptoms in mice, and then the mice were simultaneously given a HFSD and C. militaris samples for a further 8 weeks. The results indicated that the fruit body, polysaccharides, and cordycepin obtained from C. militaris had different efficacies on regulating metabolic syndrome and gut microbiota in HFSD-treated mice. Polysaccharides derived from C. militaris decreased the levels of blood sugar and serum lipids in mice fed HFSD. In addition, C. militaris-polysaccharide treatment obviously improved intestinal dysbiosis through promoting the population of next generation probiotic Akkermansia muciniphila in the gut of mice fed HFSD. In conclusion, polysaccharides derived from C. militaris have the potential to act as dietary supplements and health food products for modifying the gut microbiota to improve the metabolic syndrome.

A comprehensive approach for microbiota and health monitoring in mouse colonies using metagenomic shotgun sequencing

BackgroundHealth surveillance of murine colonies employed for scientific purposes aim at detecting unwanted infection that can affect the well-being of animals and personnel, and potentially undermine scientific results. In this study, we investigated the use of a next-generation sequencing (NGS) metagenomic approach for monitoring the microbiota composition and uncovering the possible presence of pathogens in mice housed in specific pathogen-free (SPF) or conventional (non-SPF) facilities.ResultsAnalysis of metagenomic NGS assay through public and free algorithms and databases allowed to precisely assess the composition of mouse gut microbiome and quantify the contribution of the different microorganisms at the species level. Sequence analysis allowed the uncovering of pathogens or the presence of imbalances in the microbiota composition. In several cases, fecal pellets taken from conventional facilities were found to carry gene sequences from bacterial pathogens (Helicobacter hepaticus, Helicobacter typhlonius, Chlamydia muridarum, Streptococcus pyogenes, Rodentibacter pneumotropicus, Citrobacter rodentium, Staphylococcus aureus), intestinal protozoa (Entamoeba muris, Tritrichomonas muris, Spironucleus muris) nematoda (Aspiculuris tetraptera, Syphacia obvelata), eukaryotic parasites (Myocoptes musculinus) and RNA virus (Norwalk virus). Thus, the use of NGS metagenomics can reduce the number of tests required for the detection of pathogens and avoid the use of sentinel mice.ConclusionsIn summary, in comparison with standard approaches, which require multiple types of test, NGS assay can detect bacteria, fungi, DNA and RNA viruses, and eukaryotic parasites from fecal pellets in a single test. Considering the need to protect animal well-being and to improve the success and reproducibility of preclinical studies, this work provides the proof-of-concept that the use of NGS metagenomics for health monitoring of laboratory mice is a feasible and dependable approach, that is able to broaden the current concept of health monitoring of laboratory mice from “pathogen surveillance” to a more inclusive “microbiota surveillance”.

GW9508 ameliorates cognitive dysfunction via the external treatment of encephalopathy in Aβ1-42 induced mouse model of Alzheimer's disease

The functions and mechanisms of GPR40 receptor to ameliorating the Alzheimer's disease (AD) by external treatment of encephalopathy remain unknown. In present study, the typical Aβ1-42 induced mice model was applied to explore the functions and mechanisms of GPR40 receptor by external treatment of encephalopathy in AD. GPR40 agonist GW9508 and antagonist GW1100 were given by i.g injection to activate/inhibit the GPR40 receptor respectively in the gut of AD mouse which illustrated the function and mechanism of GPR40 receptor in ameliorating AD symptoms by external treatment of encephalopathy. A series of behavioral experiments were used to investigate the cognitive function and memory ability of mice, while molecular biology experiments such as Western blot, ELISA, flow cytometry were used to detect the corresponding changes of signaling pathways. The results revealed that intragastric administrated GW9508 could significantly ameliorate cognitive deficits of AD mouse, up-regulate the expression levels of gut-brain peptides both in blood circulation and hypothalamus thus up-regulate the expression levels of α-MSH in hypothalamus, while the negative autophagy-related proteins and inflammation-related proteins were down-regulated correspondingly. Meanwhile, GW9508 could also inhibit the pathological process of neuroinflammation in microglia. GW1100 reversed the effects of GW9508 significantly. These results suggested that GPR40 was an underlying therapeutic target for the external treatment of encephalopathy related to AD and GPR40 agonist could be explored as the emerging AD therapeutic drug.

The Selective Advantage of the lac Operon for Escherichia coli Is Conditional on Diet and Microbiota Composition.

The lac operon is one of the best known gene regulatory circuits and constitutes a landmark example of how bacteria tune their metabolism to nutritional conditions. It is nearly ubiquitous in Escherichia coli strains justifying the use of its phenotype, the ability to consume lactose, for species identification. Lactose is the primary sugar found in milk, which is abundant in mammals during the first weeks of life. However, lactose is virtually non-existent after the weaning period, with humans being an exception as many consume dairy products throughout their lives. The absence of lactose during adulthood in most mammals and the rarity of lactose in the environment, means that the selective pressure for maintaining the lac operon could be weak for long periods of time. Despite the ability to metabolize lactose being a hallmark of E. coli’s success when colonizing its primary habitat, the mammalian intestine, the selective value of this trait remains unknown in this ecosystem during adulthood. Here we determine the competitive advantage conferred by the lac operon to a commensal strain of E. coli when colonizing the mouse gut. We find that its benefit, which can be as high as 11%, is contingent on the presence of lactose in the diet and on the presence of other microbiota members in the gut, but the operon is never deleterious. These results help explaining the pervasiveness of the lac operon in E. coli, but also its polymorphism, as lac-negative E. coli strains albeit rare can naturally occur in the gut.

Vibrio vulnificus induces the death of a major bacterial species in the mouse gut via cyclo-Phe-Pro

BackgroundA foodborne pathogen, Vibrio vulnificus, encounters normal microflora inhabiting the gut environments prior to causing fatal septicemia or gastroenteritis and should overcome the barriers derived from the gut commensals for successful infection. Its interactions with gut commensals during the infection process, however, have not yet been understood. In the present study, the effect of V. vulnificus on the community structures of gut microbiota in mice was examined.ResultsAnalyses of microbiota in the fecal samples of mice that died due to V. vulnificus infection revealed the decreased abundance of bacteria belonged to Bacteroidetes, notably, the species Bacteroides vulgatus. In vitro coculturing of the two bacterial species resulted in the decreased survival of B. vulgatus. The antagonistic effect of V. vulnificus against B. vulgatus was found to be mediated by cyclo-Phe-Pro (cFP), one of the major compounds secreted by V. vulnificus. cFP-treated B. vulgatus showed collapsed cellular morphology with an undulated cell surface, enlarged periplasmic space, and lysed membranes, suggesting the occurrence of membrane disruption. The degree of membrane disruption caused by cFP was dependent upon the cellular levels of ObgE in B. vulgatus. Recombinant ObgE exhibited a high affinity to cFP at a 1:1 ratio. When mice were orally injected with cFP, their feces contained significantly reduced B. vulgatus levels, and their susceptibility to V. vulnificus infection was considerably increased.ConclusionsThis study demonstrates that V. vulnificus-derived cFP modulates the abundance of the predominant species among gut commensals, which made V. vulnificus increase its pathogenicity in the hosts.2SB4iqYCk6h9vi_xizs4mWVideo abstract

Gut inflammation triggers C/EBPβ/δ-secretase-dependent gut-to-brain propagation of Aβ and Tau fibrils in Alzheimer's disease.

Inflammation plays an important role in the pathogenesis of Alzheimer's disease (AD). Some evidence suggests that misfolded protein aggregates found in AD brains may have originated from the gut, but the mechanism underlying this phenomenon is not fully understood. C/EBPβ/δ-secretase signaling in the colon was investigated in a 3xTg AD mouse model in an age-dependent manner. We applied chronic administration of 1% dextran sodium sulfate (DSS) to trigger gut leakage or colonic injection of Aβ or Tau fibrils or AD patient brain lysates in 3xTg mice and combined it with excision/cutting of the gut-brain connecting vagus nerve (vagotomy), in order to explore the role of the gut-brain axis in the development of AD-like pathologies and to monitor C/EBPβ/δ-secretase signaling under those conditions. We found that C/EBPβ/δ-secretase signaling is temporally activated in the gut of AD patients and 3xTg mice, initiating formation of Aβ and Tau fibrils that spread to the brain. DSS treatment promotes gut leakage and facilitates AD-like pathologies in both the gut and the brain of 3xTg mice in a C/EBPβ/δ-secretase-dependent manner. Vagotomy selectively blunts this signaling, attenuates Aβ and Tau pathologies, and restores learning and memory. Aβ or Tau fibrils or AD patient brain lysates injected into the colon propagate from the gut into the brain via the vagus nerve, triggering AD pathology and cognitive dysfunction. The results indicate that inflammation activates C/EBPβ/δ-secretase and initiates AD-associated pathologies in the gut, which are subsequently transmitted to the brain via the vagus nerve.