Gut Epithelial Cells Research Articles

Influence of bisphenol A and its analogues on human gut microbiota composition and metabolic activity: Insights from an in vitro model

Food contamination is a primary route of human exposure to bisphenols (BPs), which are known to affect gut microbiota (GM) and intestinal health. This study comprehensively assessed the impact of bisphenol A (BPA) and three of its substitutes—bisphenol S (BPS), bisphenol F (BPF), and tetramethyl bisphenol F (TMBPF, the monomer of valPure V70) — on the taxonomic and functional profile of human GM using an in vitro model. Human GM was acutely exposed to 1 mM concentrations of these BPs during a 48 h anaerobic cultivation. We first examined the effects of BPA, BPS, BPF, and TMBPF on GM taxonomic and metabolic profiles, mainly focusing on short-chain fatty acids (SCFAs) production. We then evaluated the degradation potential of these BPs by GM and its influence on their estrogenic activity. Finally, we assessed the impact of GM metabolites from BPs-exposed cultures on the viability of intestinal epithelial cells (Caco-2). BPA, BPS, and BPF severely disrupted GM taxonomic composition and metabolite profiles, significantly reducing SCFAs production. In contrast, TMBPF exhibited the least disruptive effects, suggesting it may be a safer alternative. Although the GM did not biotransform the BPs, bioadsorption occurred, with affinity correlating to hydrophobicity in the order of TMBPF > BPA > BPF > BPS. GM reduced the estrogenic activity of BPs primarily through bioadsorption. However, exposure of gut epithelial cells to Post-Culture Supernatants of BPA, BPF, and TMBPF significantly reduced Caco-2 cell viability, indicating the potential formation of harmful GM-derived metabolites and/or a depletion of beneficial GM metabolites.

Type III interferons induce pyroptosis in gut epithelial cells and impair mucosal repair.

Tissue damage and repair are hallmarks of inflammation. Despite a wealth of information on the mechanisms that govern tissue damage, mechanistic insight into how inflammation affects repair is lacking. Here, we investigated how interferons influence tissue repair after damage to the intestinal mucosa. We found that type III, not type I or type II, interferons delay epithelial cell regeneration by inducing the upregulation of Z-DNA-binding protein 1 (ZBP1). Z-nucleic acids formed following intestinal damage are sensed by ZBP1, leading to caspase-8 activation and the cleavage of gasdermin C (GSDMC). Cleaved GSDMC drives epithelial cell death by pyroptosis and delays repair of the large or small intestine after colitis or irradiation, respectively. The type III interferon/ZBP1/caspase-8/GSDMC axis is also active in patients with inflammatory bowel disease (IBD). Our findings highlight the capacity of type III interferons to delay gut repair, which has implications for IBD patients or individuals exposed to radiation therapies.

Description and functional validation of human enteroendocrine cell sensors.

Enteroendocrine cells (EECs) are gut epithelial cells that respond to intestinal contents by secreting hormones, including the incretins glucagon-like peptide 1 (GLP-1) and gastric inhibitory protein (GIP), which regulate multiple physiological processes. Hormone release is controlled through metabolite-sensing proteins. Low expression, interspecies differences, and the existence of multiple EEC subtypes have posed challenges to the study of these sensors. We describe differentiation of stomach EECs to complement existing intestinal organoid protocols. CD200 emerged as a pan-EEC surface marker, allowing deep transcriptomic profiling from primary human tissue along the stomach-intestinal tract. We generated loss-of-function mutations in 22 receptors and subjected organoids to ligand-induced secretion experiments. We delineate the role of individual human EEC sensors in the secretion of hormones, including GLP-1. These represent potential pharmacological targets to influence appetite, bowel movement, insulin sensitivity, and mucosal immunity.

Genomic and phenotypic characterization of a Clostridioides difficile strain of the epidemic ST37 type from China.

Clostridioides difficile strains of sequence type (ST) 37, primarily including PCR ribotype (RT) 017, are prevalent in mainland China. Our study aimed to compare the major virulence factors of an epidemic C. difficile isolate of ST37 type (Xy06) from China with the well-characterized C. difficile reference strains R20291 (RT027) and CD630E (ST54), as well as a Chinese ST54 strain (Xy07) isolated from the same hospital. The Xy06 genome was predicted to harbor two complete prophages and several transposon-like elements. Comparative analysis of PaLoc revealed a truncated tcdA gene, a functional tcdB gene, a functional tcdC gene, and well-conserved tcdR and tcdE genes. Phenotypic comparisons showed that Xy06 was a robust producer of TcdB, readily sporulated and germinated, and strongly bound to human gut epithelial cells. In a mouse model of C. difficile infection, Xy06 was more virulent than strains CD630E and Xy07 and was comparable to strain R20291 in virulence. Our data suggest the potential threat of the epidemic ST37 strains in China.

Pathogenic diversification of the gut commensal Providencia alcalifaciens via acquisition of a second type III secretion system.

Providencia alcalifaciens is a Gram-negative bacterium found in various water and land environments and organisms, including insects and mammals. Some P. alcalifaciens strains encode gene homologs of virulence factors found in pathogenic Enterobacterales members, such as Salmonella enterica serovar Typhimurium and Shigella flexneri. Whether these genes are pathogenic determinants in P. alcalifaciens is not known. In this study, we investigated P. alcalifaciens-host interactions at the cellular level, focusing on the role of two type III secretion systems (T3SS) belonging to the Inv-Mxi/Spa family. T3SS1b is widespread in Providencia spp. and encoded on the chromosome. A large plasmid that is present in a subset of P. alcalifaciens strains, primarily isolated from diarrheal patients, encodes for T3SS1a. We show that P. alcalifaciens 205/92 is internalized into eukaryotic cells, lyses its internalization vacuole, and proliferates in the cytosol. This triggers caspase-4-dependent inflammasome responses in gut epithelial cells. The requirement for the T3SS1a in entry, vacuole lysis, and cytosolic proliferation is host cell type-specific, playing a more prominent role in intestinal epithelial cells than in macrophages or insect cells. In a bovine ligated intestinal loop model, P. alcalifaciens colonizes the intestinal mucosa and induces mild epithelial damage with negligible fluid accumulation in a T3SS1a- and T3SS1b-independent manner. However, T3SS1b was required for the rapid killing of Drosophila melanogaster. We propose that the acquisition of two T3SS has allowed P. alcalifaciens to diversify its host range, from a highly virulent pathogen of insects to an opportunistic gastrointestinal pathogen of animals.

Effects of Prebiotic Dietary Fibers on the Stimulation of the Mucin Secretion in Host Cells by In Vitro Gut Microbiome Consortia.

The gastrointestinal microbiota are important for human health. Dietary intake may modulate the composition and metabolic function of the gut microbiome. We examined how the breakdown of prebiotic dietary fibers by the gut microbiome affects mucin secretion by intestinal epithelial cells. Metagenomic analyses of in vitro gut microbiome consortia revealed taxonomic profiles and genetic diversity of carbohydrate-active enzymes that digest polysaccharides. Two independent consortia exhibited different abilities to produce acetic acid, propionic acid, and butyric acid via the fermentation of polysaccharides derived from dietary fibers of grains and mushrooms. Although acetic acid generally had the highest concentration, the ratios of butyric acid and propionic acid to acetic acid varied depending on the polysaccharide source. These short-chain fatty acids affected morphological differentiation and mucin secretion in HT-29 human intestinal epithelial cells. These results suggest that prebiotic dietary fibers can be digested and metabolized by the gut microbiome to short-chain fatty acids, which can affect gut epithelial cells both directly and indirectly via the modulation of the gut microbiota and their enzymes.

Semaglutide treatment for PRevention Of Toxicity in high-dosE Chemotherapy with autologous haematopoietic stem-cell Transplantation (PROTECT): study protocol for a randomised, double-blind, placebo-controlled, investigator-initiated study

IntroductionCancer treatment with high-dose chemotherapy damages the mucosal barrier of the gastrointestinal (GI) tract and is associated with severe toxicity involving mucositis, severe inflammation and organ dysfunction. Currently, there is...

Development of in vitro model of exosome transport in microfluidic gut-brain axis-on-a-chip.

The gut communicates with the brain in a variety of ways known as the gut-brain axis (GBA), which is known to affect neurophysiological functions as well as neuronal disorders. Exosomes capable of passing through the blood-brain-barrier (BBB) have received attention as a mediator of gut-brain signaling and drug delivery vehicles. In conventional well plate-based experiments, it is difficult to observe the exosome movement in real time. Here, we developed a microfluidic-based GBA chip for co-culturing gut epithelial cells and neuronal cells and simultaneously observing exosome transport. The GBA-chip is aimed to mimic the in vivo situation of convective flow in blood vessels and convective and diffusive transport in the tissue interstitium. Here, fluorescence-labeled exosome was produced by transfection of HEK-293T cells with CD63-GFP plasmid. We observed in real time the secretion of CD63-GFP-exosomes by the transfected HEK-293T cells in the chip, and transport of the exosomes to neuronal cells and analyzed the dynamics of GFP-exosome movement. Our model is expected to enhance understanding of the roles of exosome in GBA.

Bacterial lipopolysaccharide inhibits free thiamin uptake along the intestinal tract via interference with membrane expression of thiamin transporters 1 and 2.

This study examined the effect of exposure of small and large intestinal epithelial cells to the bacterial lipopolysaccharide (LPS) on uptake of free form of vitamin B1, i.e., thiamin. The intestinal tract encounters two sources of thiamin: diet and the gut microbiota. Absorption of thiamin in both the small and large intestine occurs via a carrier-mediated process that involves thiamin transporters 1 and 2 (THTR-1 and -2). Complementary in vitro (human duodenal epithelial HuTu-80 cells and human colonic epithelial NCM460 cells), in vivo (mice), and ex vivo (human primary differentiated enteroid and colonoid monolayers) models were used. The results showed that exposure to LPS causes a significant inhibition in carrier-mediated [3H]-thiamin uptake by small and large intestinal epithelia, with no change in the levels of expression of THTR-1 and -2 mRNAs and their total cellular proteins. However, a significant decrease in the fractions of the THTR-1 and -2 proteins that are expressed at the cell membranes of these epithelial cells was observed. These effects of LPS appeared to involve a protein kinase A (PKA) signaling pathway as activating this pathway caused a reversal in the inhibition of thiamin uptake and level of expression of its transporters at the cell membrane. These findings demonstrate that exposure of gut epithelia to LPS (a situation that occurs under different pathological conditions) leads to inhibition in thiamin uptake due to a decrease in level of expression of its transporters at the cell membrane that is likely mediated via a PKA signaling pathway. NEW & NOTEWORTHY This study shows that the exposure of gut epithelial cells to bacterial LPS negatively impact the uptake process of the free form of vitamin B1 (i.e., thiamin). This appears to be mediated via suppression in the level of thiamin transporters 1 and 2 (THTR-1 and -2) expression at the cell membrane and involves a protein kinase A (PKA) signaling pathway.

Assessment of microbial safety of fresh vegetables through Caenorhabditis elegans model

Caenorhabditis elegans is widely used as a model to predict the virulence of animal-origin human pathogens, as C. elegans and humans share similar intestinal epithelial cells. A study was undertaken to assess the feasibility of C. elegans for surveillance of foodborne pathogens in fresh vegetables. First, the virulent strains of four foodborne pathogens viz., Pseudomonas aeruginosa (PAO1), Escherichia coli (O157), Salmonella enterica (CI1), and Staphylococcus aureus (ATCC25923) were fed to the worm as sole diet and compared the survival, phenome traits, and gut integrity with standard E. coli OP50. Secondly, the vegetable surface microbiota (tomato) was enriched with gradient concentrations of PAO1, and the worm's survival and gut distension and leakage were assessed. Thirdly, the total microbiota of fresh vegetables (tomato, brinjal, and lablab) were evaluated for the worm's survival. The gut epithelial cell damage and leakage were monitored by blue dye-based smurf assay. Foodborne pathogens reduced the median lifespan (LT50) of the worm drastically, with PAO1 had 2.5 days, O157 (6 days), CI1 (8 days), ATCC25923 (6 days), while the standard diet OP50 had 16 days. The phenome traits of worms, viz., pharyngeal pumping, defecation cycle, body bends, head thrashes, touch stimulus, paralysis, gut leakage, and reproduction, were significantly negatively affected due to pathogen feeding. The gut epithelial integrity was severely affected, and blue dye leakage was the highest in O157 (73 %), followed by PAO1 (55 %), CI1 (40 %) and ATCC25923 (38 %), while the gut epithelial cells were intact in OP50 fed worms. The pathogen enrichment in tomato surface microbiota diet showed that LT50 of the worms was reduced from 8 days to 2.5 days and 10 to 8 days with increasing gradient of PAO1 in fresh tomato microbiota and 24-hours pre-enriched tomato microbiota, respectively. Smurf test also confirmed that an increase in PAO1 proportion in total microbiota distended the gut with high dye leakage. The total microbiota extracted from tomato, brinjal, and lablab did not affect the worm's health and had an extended median life span (11 – 13 days) when they were devoid of any foodborne pathogens. These findings provide a novel and straightforward approach for assessing foodborne pathogens using animal models.

A newborn's perspective on immune responses to food.

In this review, we will highlight infants' immune responses to food, emphasizing the unique aspects of early-life immunity and the critical role of breast milk as a food dedicated to infants. Infants are susceptible to inflammatory responses rather than immune tolerance at the mucosal and skin barriers, necessitating strategies to promote oral tolerance that consider this susceptibility. Breast milk provides nutrients for growth and cell metabolism, including immune cells. The content of breast milk, influenced by maternal genetics and environmental exposures, prepares the infant's immune system for the outside world, including solid foods. To do this, breast milk promotes immune system development through antigen-specific and non-antigen-specific immune education by exposing the newborn to food and respiratory allergens and acting on three key targets for food allergy prevention: the gut microbiota, epithelial cells, and immune cells. Building knowledge of how the maternal exposome and human milk composition influence offspring's healthy immune development will lead to recommendations that meet the specific needs of the developing immune system and increase the chances of promoting an appropriate immune response to food in the long term.

Bacillus subtilis-derived peptides disrupt quorum sensing and biofilm assembly in multidrug-resistant Staphylococcus aureus.

The formation of biofilms by multidrug-resistant bacterial pathogens, such as Staphylococcus aureus, increases these microorganisms' virulence and decreases the efficacy of common antibiotic regimens. Probiotics possess a variety of strain-specific strategies to reduce biofilm formation in competing organisms; however, the mechanisms and compounds responsible for these phenomena often go uncharacterized. In this study, we identified a mixture of small probiotic-derived peptides capable of Agr quorum sensing interference as one of the mechanisms driving antibiofilm activity against S. aureus. This collection of peptides also improved antibiotic killing and protected human gut epithelial cells from S. aureus-induced toxicity by stimulating an adaptive cytokine response. We conclude that purposeful strain screening and selection efforts can be used to identify unique probiotic strains that possess specially desired mechanisms of action. This information can be used to further improve our understanding of the ways in which probiotic and probiotic-derived compounds can be applied to prevent bacterial infections or improve bacterial sensitivity to antibiotics in clinical and agricultural settings.

Desulfovibrio vulgaris caused gut inflammation and aggravated DSS-induced colitis in C57BL/6 mice model

BackgroundSulfate-reducing bacteria (SRB) is a potential pathogen usually detected in patients with gastrointestinal diseases. Hydrogen sulfide (H2S), a metabolic byproduct of SRB, was considered the main causative agent that disrupted the morphology and function of gut epithelial cells. Associated study also showed that flagellin from Desulfovibrio vulgaris (DVF), the representative bacterium of the Desulfovibrio genus, could exacerbate colitis due to the interaction of DVF and LRRC19, leading to the secretion of pro-inflammatory cytokines. However, we still have limited understanding about the change of gut microbiota (GM) composition caused by overgrowth of SRB and its exacerbating effects on colitis.ResultsIn this study, we transplanted D. vulgaris into the mice treated with or without DSS, and set a one-week recovery period to investigate the impact of D. vulgaris on the mice model. The outcomes showed that transplanted D. vulgaris into the normal mice could cause the gut inflammation, disrupt gut barrier and reduce the level of short-chain fatty acids (SCFAs). Moreover, D. vulgaris also significantly augmented DSS-induced colitis by exacerbating the damage of gut barrier and the secretion of inflammatory cytokines, for instance, IL-1β, iNOS, and TNF-α. Furthermore, results also showed that D. vulgaris could markedly change GM composition, especially decrease the relative abundance of SCFAs-producing bacteria. Additionally, D. vulgaris significantly stimulated the growth of Akkermansia muciniphila probably via its metabolic byproduct, H2S, in vivo.ConclusionsCollectively, this study indicated that transplantation of D. vulgaris could cause gut inflammation and aggravate the colitis induced by DSS.

Mechanistic Insight into Intestinal α-Synuclein Aggregation in Parkinson's Disease Using a Laser-Printed Electrochemical Sensor.

Aggregated deposits of the protein α-synuclein and depleting levels of dopamine in the brain correlate with Parkinson's disease development. Treatments often focus on replenishing dopamine in the brain; however, the brain might not be the only site requiring attention. Aggregates of α-synuclein appear to accumulate in the gut years prior to the onset of any motor symptoms. Enteroendocrine cells (specialized gut epithelial cells) may be the source of intestinal α-synuclein, as they natively express this protein. Enteroendocrine cells are constantly exposed to gut bacteria and their metabolites because they border the gut lumen. These cells also express the dopamine metabolic pathway and form synapses with vagal neurons, which innervate the gut and brain. Through this connection, Parkinson's disease pathology may originate in the gut and spread to the brain over time. Effective therapeutics to prevent this disease progression are lacking due to a limited understanding of the mechanisms by which α-synuclein aggregation occurs in the gut. We previously proposed a gut bacterial metabolic pathway responsible for the initiation of α-synuclein aggregation that is dependent on the oxidation of dopamine. Here, we develop a new tool, a laser-induced graphene-based electrochemical sensor chip, to track α-synuclein aggregation and dopamine level over time. Using these sensor chips, we evaluated diet-derived catechols dihydrocaffeic acid and caffeic acid as potential inhibitors of α-synuclein aggregation. Our results suggest that these molecules inhibit dopamine oxidation. We also found that these dietary catechols inhibit α-synuclein aggregation in STC-1 enteroendocrine cells. These findings are critical next steps to reveal new avenues for targeted therapeutics to treat Parkinson's disease, specifically in the context of functional foods that may be used to reshape the gut environment.

AMPK Deficiency Increases DNA Methylation and Aggravates Colorectal Tumorigenesis in AOM/DSS Mice.

The incidence of colorectal cancer (CRC) is closely linked to metabolic diseases. Accumulating evidence suggests the regulatory role of AMP-activated protein kinase (AMPK) in cancer metabolic reprogramming. In this study, wild-type and AMPK knockout mice were subjected to azoxymethane-induced and dextran sulfate sodium (AOM/DSS)-promoted colitis-associated CRC induction. A stable AMPK-deficient Caco-2 cell line was also established for the mechanistic studies. The data showed that AMPK deficiency accelerated CRC development, characterized by increased tumor number, tumor size, and hyperplasia in AOM/DSS-treated mice. The aggravated colorectal tumorigenesis resulting from AMPK ablation was associated with reduced α-ketoglutarate production and ten-eleven translocation hydroxylase 2 (TET2) transcription, correlated with the reduced mismatch repair protein mutL homolog 1 (MLH1) protein. Furthermore, in AMPK-deficient Caco-2 cells, the mRNA expression of mismatch repair and tumor suppressor genes, intracellular α-ketoglutarate, and the protein level of TET2 were also downregulated. AMPK deficiency also increased hypermethylation in the CpG islands of Mlh1 in both colonic tissues and Caco-2 cells. In conclusion, AMPK deficiency leads to reduced α-ketoglutarate concentration and elevates the suppressive epigenetic modifications of tumor suppressor genes in gut epithelial cells, thereby increasing the risk of colorectal tumorigenesis. Given the modifiable nature of AMPK activity, it holds promise as a prospective molecular target for the prevention and treatment of CRC.

Pathogenic diversification of the gut commensal Providencia alcalifaciens via acquisition of a second type III secretion system.

Providencia alcalifaciens is a Gram-negative bacterium found in a wide variety of water and land environments and organisms. It has been isolated as part of the gut microbiome of animals and insects, as well as from stool samples of patients with diarrhea. Specific P. alcalifaciens strains encode gene homologs of virulence factors found in other pathogenic members of the same Enterobacterales order, such as Salmonella enterica serovar Typhimurium and Shigella flexneri. Whether these genes are also pathogenic determinants in P. alcalifaciens is not known. Here we have used P. alcalifaciens 205/92, a clinical isolate, with in vitro and in vivo infection models to investigate P. alcalifaciens -host interactions at the cellular level. Our particular focus was the role of two type III secretion systems (T3SS) belonging to the Inv-Mxi/Spa family. T3SS 1b is widespread in Providencia spp. and encoded on the chromosome. T3SS 1a is encoded on a large plasmid that is present in a subset of P. alcalifaciens strains, which are primarily isolates from diarrheal patients. Using a combination of electron and fluorescence microscopy and gentamicin protection assays we show that P. alcalifaciens 205/92 is internalized into eukaryotic cells, rapidly lyses its internalization vacuole and proliferates in the cytosol. This triggers caspase-4 dependent inflammasome responses in gut epithelial cells. The requirement for the T3SS 1a in entry, vacuole lysis and cytosolic proliferation is host-cell type specific, playing a more prominent role in human intestinal epithelial cells as compared to macrophages. In a bovine ligated intestinal loop model, P. alcalifaciens colonizes the intestinal mucosa, inducing mild epithelial damage with negligible fluid accumulation. No overt role for T3SS 1a or T3SS 1b was seen in the calf infection model. However, T3SS 1b was required for the rapid killing of Drosophila melanogaster . We propose that the acquisition of two T3SS by horizontal gene transfer has allowed P. alcalifaciens to diversify its host range, from a highly virulent pathogen of insects to an opportunistic gastrointestinal pathogen of animals.

Impact of secreted glucanases upon the cell surface and fitness of Candida albicans during colonisation and infection

Host recognition of the pathogen-associated molecular pattern (PAMP), β-1,3-glucan, plays a major role in antifungal immunity. β-1,3-glucan is an essential component of the inner cell wall of the opportunistic pathogen Candida albicans. Most β-1,3-glucan is shielded by the outer cell wall layer of mannan fibrils, but some can become exposed at the cell surface. In response to host signals such as lactate, C. albicans shaves the exposed β-1,3-glucan from its cell surface, thereby reducing the ability of innate immune cells to recognise and kill the fungus. We have used sets of barcoded xog1 and eng1 mutants to compare the impacts of the secreted β-glucanases Xog1 and Eng1 upon C. albicans in vitro and in vivo. Flow cytometry of Fc-dectin-1-stained strains revealed that Eng1 plays the greater role in lactate-induced β-1,3-glucan masking. Transmission electron microscopy and stress assays showed that neither Eng1 nor Xog1 are essential for cell wall maintenance, but the inactivation of either enzyme compromised fungal adhesion to gut and vaginal epithelial cells. Competitive barcode sequencing suggested that neither Eng1 nor Xog1 strongly influence C. albicans fitness during systemic infection or vaginal colonisation in mice. However, the deletion of XOG1 enhanced C. albicans fitness during gut colonisation. We conclude that both Eng1 and Xog1 exert subtle effects on the C. albicans cell surface that influence fungal adhesion to host cells and that affect fungal colonisation in certain host niches.

Gut Epithelial Barrier Function is Impacted by Hyperglycemia and Secondary Bile Acids in Vitro: Possible Rescuing Effects of Specific Pectins.

Gut epithelial barrier disruption is commonly observed in Western diseases like diabetes and inflammatory bowel disease (IBD). Enhanced epithelial permeability triggers inflammatory responses and gut microbiota dysbiosis. Reduced bacterial diversity in IBD affects gut microbiota metabolism, altering microbial products such as secondary bile acids (BAs), which potentially play a role in gut barrier regulation and immunity. Dietary fibers such as pectin may substitute effects of these BAs. The study examines transepithelial electrical resistance of gut epithelial T84 cells and the gene expression of tight junctions after exposure to (un)sulfated secondary BAs. This is compared to the impact of the dietary fiber pectin with different degrees of methylation (DM) and blockiness (DB), with disruption induced by calcium ionophore A23187 under both normal and hyperglycemic conditions. Unsulfated lithocholic acid (LCA) and deoxycholic acid (DCA) show a stronger rescuing effect, particularly evident under 20mM glucose levels. DM19 with high DB (HB) and DM43HB pectin exhibit rescuing effects under both glucose conditions. Notably, DM19HB and DM43HB display higher rescue effects under 20mM glucose compared to 5mM glucose. The study demonstrates that specific pectins such as DM19HB and DM43HB may serve as alternatives for preventing barrier disruption in the case of disturbed DCA metabolism.

Two-component system RstAB promotes the pathogenicity of adherent-invasive Escherichia coli in response to acidic conditions within macrophages

ABSTRACT Adherent-invasive Escherichia coli (AIEC) strain LF82, isolated from patients with Crohn’s disease, invades gut epithelial cells, and replicates in macrophages contributing to chronic inflammation. In this study, we found that RstAB contributing to the colonization of LF82 in a mouse model of chronic colitis by promoting bacterial replication in macrophages. By comparing the transcriptomes of rstAB mutant- and wild-type when infected macrophages, 83 significant differentially expressed genes in LF82 were identified. And we identified two possible RstA target genes (csgD and asr) among the differentially expressed genes. The electrophoretic mobility shift assay and quantitative real-time PCR confirmed that RstA binds to the promoters of csgD and asr and activates their expression. csgD deletion attenuated LF82 intracellular biofilm formation, and asr deletion reduced acid tolerance compared with the wild-type. Acidic pH was shown by quantitative real-time PCR to be the signal sensed by RstAB to activate the expression of csgD and asr. We uncovered a signal transduction pathway whereby LF82, in response to the acidic environment within macrophages, activates transcription of the csgD to promote biofilm formation, and activates transcription of the asr to promote acid tolerance, promoting its replication within macrophages and colonization of the intestine. This finding deepens our understanding of the LF82 replication regulation mechanism in macrophages and offers new perspectives for further studies on AIEC virulence mechanisms.

Roles of airway and intestinal epithelia in responding to pathogens and maintaining tissue homeostasis.

Epithelial cells form a resilient barrier and orchestrate defensive and reparative mechanisms to maintain tissue stability. This review focuses on gut and airway epithelia, which are positioned where the body interfaces with the outside world. We review the many signaling pathways and mechanisms by which epithelial cells at the interface respond to invading pathogens to mount an innate immune response and initiate adaptive immunity and communicate with other cells, including resident microbiota, to heal damaged tissue and maintain homeostasis. We compare and contrast how airway and gut epithelial cells detect pathogens, release antimicrobial effectors, collaborate with macrophages, Tregs and epithelial stem cells to mount an immune response and orchestrate tissue repair. We also describe advanced research models for studying epithelial communication and behaviors during inflammation, tissue injury and disease.