Altered expression and localization of ion transporters contribute to diarrhea in mice with Salmonella-induced enteritis

Temporal transcriptome profiling in the response to Salmonella enterica serovar enteritidis infection in chicken cecum

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a common zoonotic pathogen that not only causes gastroenteritis or death of livestock and poultry but also poses a serious threat to human health, causing severe economic losses to the poultry industry and society. Herein, RNA-sequencing (RNA-seq) was used to analyze the transcriptome variation of chicken cecum at four different time points (1, 3, 7, and 14 days) following S. Enteritidis infection. There were 529, 1477, 476, and 432 differentially expressed genes (DEGs) in the cecum at four different days post-infection (dpi), respectively. The DEGs were significantly enriched in various immune-related pathways on 3 dpi and 7 dpi, such as cytokine-cytokine-receptor interaction and Toll-like receptor signaling pathway. DEGs were significantly enriched in several metabolic pathways on 14 dpi. Gene ontology (GO) enrichment of DEGs showed that up-regulated genes were significantly enriched in immune-related terms on 3 and 7 dpi. On 14 dpi, up-regulated genes were mainly enriched in the signaling-related terms, while the down-regulated genes were primarily enriched in the metabolic-related terms. Based on weighted gene co-expression network analysis (WGCNA), the key modules related to energy, non-coding processes, immunity, and development-related functions were identified at 1, 3, 7, and 14 dpi, respectively, and 5, 8, 6, and 5 hub genes were screened out, respectively. This study demonstrated that the chicken cecal transcriptome regulation responding to S. Enteritidis infection is time-dependent. The regulation of S. Enteritidis infection in chickens is coordinated by multiple systems, mainly involving immunity, metabolism, and signal transduction. Both 3 and 7 dpi are key time points for immune response. As the infection progresses, metabolism-related pathways were increasingly identified. This change reflects the dynamic adjustment between immune response and metabolism in Jining Bairi chickens following S. Enteritidis infection. These results suggested that starting from 3 dpi, the chickens gradually transition from an immune response triggered by S. Enteritidis infection to a state where they adapt to the infection by modulating their metabolism.

Decreased expression of DRA (SLC26A3) by a p38-driven IL-1α response contributes to diarrheal disease following in vivo challenge with Brachyspira spp

In this study, we uncovered the novel mechanism of IL-1α-mediated downregulated in adenoma (DRA) (SLC26A3) downregulation in the context of Brachyspira spp.-induced malabsorptive diarrhea. Experimentally infected pigs with Brachyspira spp. had significantly reduced DRA expression in the colon accompanied by IL-1α upregulation. This response was recapitulated in vitro by exposing Caco-2 cells to either Brachyspira lysate or IL-1α. Both p38 and MAPK-activated protein kinase 2 (MAPKAPK-2 also referred as MK-2) showed an increased phosphorylation after exposure to either. SB203580 application, a p38 inhibitor blocked the MK-2 phosphorylation and attenuated the DRA and IL-1α response to both lysate and IL-1α. Exposure to IL-1 receptor antagonist (IL-1RA) produced a similar response. In addition, exposure of cells to either of these blockers without IL-1α or lysate results in increased DRA and decreased IL-1α expression, revealing that DRA needs IL-1α signaling for basal physiological expression. Dual inhibition with both blockers completely inhibited the effect from IL-1α while significantly attenuating the response from Brachyspira lysate, suggesting a minor contribution from another pathway. Together this demonstrates that Brachyspira activates p38 MAPK signaling driving IL-1α expression, which activates IL-1R1 causing DRA downregulation while also driving upregulation of IL-1α through p38 in a positive feedback mechanism. In conclusion, we elucidated a major pathway involved in DRA downregulation and its role in Brachyspira-induced diarrhea. In addition, these observations will aid in our understanding of other inflammatory and infectious diarrhea conditions.NEW & NOTEWORTHY The diarrheal disease caused by the two infectious spirochete spp. B. hyodysenteriae and B. hampsonii reduced the expression of DRA (SLC26A3), a major Cl-/HCO-3 exchanger involved in Cl- absorption. This is attributed to the upregulation of IL-1α driven by p38 MAPK. This work also describes a potential new mechanism in inflammatory diseases while showing the importance of IL-1α in maintaining DRA levels.

A Review of Epithelial Ion Transporters and Their Roles in Equine Infectious Colitis

Equine colitis is a devastating disease with a high mortality rate. Infectious pathogens associated with colitis in the adult horse include Clostridioides difficile, Clostridium perfringens, Salmonella spp., Neorickettsia risticii/findlaynesis, and equine coronavirus. Antimicrobial-associated colitis can be associated with the presence of infectious pathogens. Colitis can also be due to non-infectious causes, including non-steroidal anti-inflammatory drug administration, sand ingestion, and infiltrative bowel disease. Current treatments focus on symptomatic treatment (restoring fluid and electrolyte balance, preventing laminitis and sepsis). Intestinal epithelial ion channels are key regulators of electrolyte (especially sodium and chloride) and water movement into the lumen. Dysfunctional ion channels play a key role in the development of diarrhea. Infectious pathogens, including Salmonella spp. and C. difficile, have been shown to regulate ion channels in a variety of ways. In other species, there has been an increased interest in ion channel manipulation as an anti-diarrheal treatment. While targeting ion channels also represents a promising way to manage diarrhea associated with equine colitis, ion channels have not been well studied in the equine colon. This review provides an overview of what is known about colonic ion channels and their known or putative role in specific types of equine colitis due to various pathogens.

Milk and Lacticaseibacillus paracasei BL23 effects on intestinal responses in a murine model of colitis

Probiotic-containing fermented dairy foods have the potential to benefit human health, but the importance of the dairy matrix for efficacy remains unclear. We investigated the capacity of Lacticaseibacillus paracasei BL23 in phosphate-buffered saline (BL23-PBS), BL23-fermented milk (BL23-milk), and milk to modify intestinal and behavioral responses in a dextran sodium sulfate (DSS, 3% wt/vol) mouse model of colitis. Significant sex-dependent differences were found such that female mice exhibited more severe colitis, greater weight loss, and higher mortality rates. Sex differences were also found for ion transport ex vivo, colonic cytokine and tight junction gene expression, and fecal microbiota composition. Measurements of milk and BL23 effects showed BL23-PBS consumption improved weight recovery in females, whereas milk resulted in better body weight recovery in males. Occludin and Claudin-2 gene transcript levels indicated barrier function was impaired in males, but BL23-milk was still found to improve colonic ion transport in those mice. Proinflammatory and anti-inflammatory gene expression levels were increased in both male and female mice fed BL23, and to a more variable extent, milk, compared with controls. The female mouse fecal microbiota contained high proportions of Akkermansia (average of 18.1%) at baseline, and females exhibited more changes in gut microbiota composition following BL23 and milk intake. Male fecal microbiota harbored significantly more Parasutterella and less Blautia and Roseburia after DSS treatment, independent of BL23 or milk consumption. These findings show the complex interplay between dietary components and sex-dependent responses in mitigating inflammation in the digestive tract.NEW & NOTEWORTHY Sex-dependent responses to probiotic Lacticaseibacillus paracasei and milk and the potential of the dairy matrix to enhance probiotic protection against colitis in this context have not been previously explored. Female mice were more sensitive than males to colonic injury, and neither treatment effectively alleviated inflammation in both sexes. These sex-dependent responses may result from differences in the higher baseline proportions of Akkermansia in the gut microbiome of female mice.

SLC26A3 (DRA) is stimulated in a synergistic, intracellular Ca2+-dependent manner by cAMP and ATP in intestinal epithelial cells

In polarized intestinal epithelial cells, downregulated in adenoma (DRA) is an apical Cl-/[Formula: see text] exchanger that is part of neutral NaCl absorption under baseline conditions, but in cyclic adenosine monophosphate (cAMP)-driven diarrheas, it is stimulated and contributes to increased anion secretion. To further understand the regulation of DRA in conditions mimicking some diarrheal diseases, Caco-2/BBE cells were exposed to forskolin (FSK) and adenosine 5'-triphosphate (ATP). FSK and ATP stimulated DRA in a concentration-dependent manner, with ATP acting via P2Y1 receptors. FSK at 1 µM and ATP at 0.25 µM had minimal to no effect on DRA given individually; however, together, they stimulated DRA to levels seen with maximum concentrations of FSK and ATP alone. In Caco-2/BBE cells expressing the Ca2+ indicator GCaMP6s, ATP increased intracellular Ca2+ (Ca2+i) in a concentration-dependent manner, whereas FSK (1 µM), which by itself did not significantly alter Ca2+i, followed by 0.25 µM ATP produced a large increase in Ca2+ that was approximately equal to the elevation caused by 1 µM ATP. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA-AM) pretreatment prevented the ATP and FSK/ATP synergistically increased the DRA activity and the increase in Ca2+i caused by FSK/ATP. FSK/ATP synergistic stimulation of DRA was similarly observed in human colonoids. In Caco-2/BBE cells, subthreshold concentrations of FSK (cAMP) and ATP (Ca2+) synergistically increased Ca2+i and stimulated DRA activity with both being blocked by BAPTA-AM pretreatment. Diarrheal diseases, such as bile acid diarrhea, in which both cAMP and Ca2+ are elevated, are likely to be associated with stimulated DRA activity contributing to increased anion secretion, whereas separation of DRA from Na+/H+ exchanger isoform-3 (NHE3) contributes to reduced NaCl absorption.NEW & NOTEWORTHY The BB Cl-/[Formula: see text] exchanger DRA takes part in both neutral NaCl absorption and stimulated anion secretion. Using intestinal cell line, Caco-2/BBE high concentrations of cAMP and Ca2+ individually stimulated DRA activity, whereas low concentrations, which had no/minimal effect, synergistically stimulated DRA activity that required a synergistic increase in intracellular Ca2+. This study increases understanding of diarrheal diseases, such as bile salt diarrhea, in which both cAMP and elevated Ca2+ are involved.

The hypoxic tissue microenvironment as a driver of mucosal inflammatory resolution

On the backdrop of all acute inflammatory processes lies the activation of the resolution response. Recent years have witnessed an emerging interest in defining molecular factors that influence the resolution of inflammation. A keystone feature of the mucosal inflammatory microenvironment is hypoxia. The gastrointestinal tract, particularly the colon, exists in a state of physiological hypoxia and during active inflammation, this hypoxic state is enhanced as a result of infiltrating leukocyte oxygen consumption and the activation of oxygen consuming enzymes. Most evidence suggests that mucosal hypoxia promotes the active resolution of inflammation through a variety of mechanisms, including extracellular acidification, purine biosynthesis/salvage, the generation of specialized pro-resolving lipid mediators (ie. resolvins) and altered chemokine/cytokine expression. It is now appreciated that infiltrating innate immune cells (neutrophils, eosinophils, macrophages) have an important role in molding the tissue microenvironment to program an active resolution response. Structural or functional dysregulation of this inflammatory microenvironment can result in the loss of tissue homeostasis and ultimately progression toward chronicity. In this review, we will discuss how inflammatory hypoxia drives mucosal inflammatory resolution and its impact on other microenvironmental factors that influence resolution.

Increased intestinal permeability and downregulation of absorptive ion transporters Nhe3, Dra, and Sglt1 contribute to diarrhea during Clostridioides difficile infection

BACKGROUND & AIM

Clostridioides difficile infection (CDI) is the leading cause of hospital-acquired diarrhea and pseudomembranous colitis. Two protein toxins, TcdA and TcdB, produced by C. difficile are the major determinants of disease. However, the pathophysiological causes of diarrhea during CDI are not well understood. Here, we investigated the effects of C. difficile toxins on paracellular permeability and apical ion transporters in the context of an acute physiological infection.

METHODS

We studied intestinal permeability and apical membrane transporters in female C57BL/6J mice. Üssing chambers were used to measure paracellular permeability and ion transporter function across the intestinal tract. Infected intestinal tissues were analyzed by immunofluorescence microscopy and RNA-sequencing to uncover mechanisms of transporter dysregulation.

RESULTS

Intestinal permeability was increased through the size-selective leak pathway in vivo during acute CDI in a 2-day-post infection model. Chloride secretory activity was reduced in the cecum and distal colon during infection by decreased CaCC and CFTR function, respectively. SGLT1 activity was significantly reduced in the cecum and colon, accompanied by ablated SGLT1 expression in colonocytes and increased luminal glucose concentrations. SGLT1 and DRA expression was ablated by either TcdA or TcdB during acute infection, but NHE3 was decreased in a TcdB-dependent manner. The localization of key proteins that link filamentous actin to the ion transporters in the apical plasma membrane was unchanged. However, Sglt1, Nhe3, and Dra were drastically reduced at the transcript level, implicating downregulation of ion transporters in the mechanism of diarrhea during CDI.

CONCLUSIONS

CDI increases intestinal permeability and decreases apical abundance of NHE3, SGLT1, and DRA. This combination likely leads to dysfunctional water and solute absorption in the large bowel, causing osmotic diarrhea. These findings provide insights into the pathophysiological mechanisms underlying diarrhea and may open novel avenues for attenuating CDI-associated diarrhea.

The effect of a fennel seed extract on the STAT signaling and intestinal barrier function

BACKGROUND

Foeniculum vulgare, F. vulgare, commonly known as fennel, is believed to be one of the world's oldest medicinal herbs and has been exploited by people for centuries as a nutritional aid for digestive disorders. In many southeast Asian countries, it is ingested as an after-meal snack, mukhvas, due to its breath-freshening and digestive aid properties. F. vulgare is used in some countries, such as Iran, as a complementary and alternative treatment for inflammatory bowel disease (IBD).

METHODS

This study investigated the effects of fennel seed extract on intestinal epithelium barrier function and the Signal Transducer and Activator of Transcription (STAT) pathway. This pathway is active in inflammatory bowel disease. To study the protective effects of fennel seed extract in vitro, monolayers derived from the T84 colonic cell line were challenged with interferon-gamma (IFN-γ) and monitored with and without fennel seed extract. To complement our in vitro studies, the dextran sodium sulfate induced murine colitis model was employed to ascertain whether the protective effect of fennel seed extract can be recapitulated in vivo.

RESULTS

Fennel seed extract was shown to exert a protective effect on transepithelial electrical resistance (TEER) in both T84 and murine models and showed increases in tight junction-associated mRNA in T84 cell monolayers. Both models demonstrated significant decreases in phosphorylated STAT1 (pSTAT1), indicating reduced activation of the STAT pathway. Additionally, mice treated with fennel seed showed significantly lower ulcer indices than control mice.

CONCLUSIONS

We conclude barrier function of the gastrointestinal tract is improved by fennel seed extract, suggesting the potential utility of this agent as an alternative or adjunctive therapy in IBD.

Cross-Talk Between the Intestinal Epithelium and Salmonella Typhimurium

Salmonella enterica serovars are invasive gram-negative bacteria, causing a wide range of diseases from gastroenteritis to typhoid fever, representing a public health threat around the world. Salmonella gains access to the intestinal lumen after oral ingestion of contaminated food or water. The crucial initial step to establish infection is the interaction with the intestinal epithelium. Human-adapted serovars such as S. Typhi or S. Paratyphi disseminate to systemic organs and induce life-threatening disease known as typhoid fever, whereas broad-host serovars such as S. Typhimurium usually are limited to the intestine and responsible for gastroenteritis in humans. To overcome intestinal epithelial barrier, Salmonella developed mechanisms to induce cellular invasion, intracellular replication and to face host defence mechanisms. Depending on the serovar and the respective host organism, disease symptoms differ and are linked to the ability of the bacteria to manipulate the epithelial barrier for its own profit and cross the intestinal epithelium.

This review will focus on S. Typhimurium (STm). To better understand STm pathogenesis, it is crucial to characterize the crosstalk between STm and the intestinal epithelium and decipher the mechanisms and epithelial cell types involved. Thus, the purpose of this review is to summarize our current knowledge on the molecular dialogue between STm and the various cell types constituting the intestinal epithelium with a focus on the mechanisms developed by STm to cross the intestinal epithelium and access to subepithelial or systemic sites and survive host defense mechanisms.

Diarrheal pathogenesis in Salmonella infection may result from an imbalance in intestinal epithelial differentiation through reduced Notch signaling

KEY POINTS

Salmonella is a leading foodborne pathogen known to cause high chloride content diarrhea. Salmonella infection of murine enteroid-derived monolayers decreased DRA expression. Salmonella infection resulted in upregulation of the secretory epithelial marker ATOH1, the goblet cell marker Muc2, and the enteroendocrine cell marker ChgA. Downregulation of DRA may result from infection-induced Notch inhibition, as reflected by decreased expression of Notch intracellular domain and Hes1, as well as from decreased HNF1α signaling. The imbalance in intestinal epithelial differentiation favoring secretory over absorptive cell types is a possible mechanism by which Salmonella elicits diarrhea and may be relevant therapeutically.

ABSTRACT

Infections with non-typhoidal Salmonella spp. represent the most burdensome foodborne illnesses worldwide, yet despite their prevalence, the mechanism through which Salmonella elicits diarrhea is not entirely known. Intestinal ion transporters play important roles in fluid and electrolyte homeostasis in the intestine. We have previously shown that infection with Salmonella caused decreased colonic expression of the chloride/bicarbonate exchanger SLC26A3 (Down-Regulated in Adenoma; DRA) in a mouse model. In this study, we focused on the mechanism of DRA downregulation during Salmonella infection, by using murine epithelial enteroid-derived monolayers (EDM). The decrease in DRA expression caused by infection was recapitulated in EDM and accompanied by increased expression of ATOH1, the goblet cell marker Muc2, and the enteroendocrine cell marker ChgA. This suggested biased epithelial differentiation towards the secretory, rather than absorptive phenotype. In addition, the downstream Notch effector, Notch Intracellular Domain (NICD) and Hes1 were decreased following Salmonella infection. The relevance of Notch signaling was further investigated using a γ-secretase inhibitor, which recapitulated the downregulation in Hes1 and DRA as well as upregulation in ATOH1 and Muc2 seen following infection. Our findings suggest that Salmonella infection may result in a shift from absorptive to secretory cell types through Notch inhibition, which explains why there is a decreased capacity for absorption and ultimately the accumulation of diarrheal fluid. Our work also shows the value of EDM as a model to investigate mechanisms that might be targeted for therapy of diarrhea caused by Salmonella infection. Abstract figure legend Upon infection of the intestinal epithelium with Salmonella, diarrhea may be explained by an imbalance of intestinal epithelial differentiation. Downregulation of cell-fate commitment to the absorptive lineage, as reflected by decreased Hes1 and DRA, was observed. Conversely, upregulation of epithelial differentiation into secretory cell types was observed, as reflected by increased ATOH1, Muc2, and ChgA. This article is protected by copyright. All rights reserved.

Slc26a3 (DRA) in the Gut: Expression, Function, Regulation, Role in Infectious Diarrhea and Inflammatory Bowel Disease

BACKGROUND

The transport of transepithelial Cl- and HCO3- is crucial for the function of the intestinal epithelium and maintains the acid-based homeostasis. Slc26a3 (DRA), as a key chloride-bicarbonate exchanger protein in the intestinal epithelial luminal membrane, participates in the electroneutral NaCl absorption of intestine, together with Na+/H+ exchangers. Increasing recent evidence supports the essential role of decreased DRA function or expression in infectious diarrhea and inflammatory bowel disease (IBD).

METHOD

In this review, we give an overview of the current knowledge of Slc26a3, including its cloning and expression, function, roles in infectious diarrhea and IBD, and mechanisms of actions. A better understanding of the physiological and pathophysiological relevance of Slc26a3 in infectious diarrhea and IBD may reveal novel targets for future therapy.

CONCLUSION

Understanding the physiological function, regulatory interactions, and the potential mechanisms of Slc26a3 in the pathophysiology of infectious diarrhea and IBD will define novel therapeutic approaches in future.

Fluid shear stress enhances differentiation of jejunal human enteroids in Intestine-Chip

There is increasing evidence that the study of normal human enteroids duplicates many known aspects of human intestinal physiology. However, this epithelial cell-only model lacks the many nonepithelial intestinal cells present in the gastrointestinal tract and exposure to the mechanical forces to which the intestine is exposed. We tested the hypothesis that physical shear forces produced by luminal and blood flow would provide an intestinal model more closely resembling normal human jejunum. Jejunal enteroid monolayers were studied in the Emulate, Inc. Intestine-Chip under conditions of constant luminal and basolateral flow that was designed to mimic normal intestinal fluid flow, with human umbilical vein endothelial cells (HUVECs) on the basolateral surface and with Wnt3A, R-spondin, and Noggin only on the luminal surface. The jejunal enteroids formed monolayers that remained confluent for 6-8 days, began differentiating at least as early as day 2 post plating, and demonstrated continuing differentiation over the entire time of the study, as shown by quantitative real-time polymerase chain reaction and Western blot analysis. Differentiation impacted villus genes and proteins differently with early expression of regenerating family member 1α (REG1A), early reduction to a low but constant level of expression of Na⁺-K⁺-2Cl^- cotransporter 1 (NKCC1), and increasing expression of sucrase-isomaltase (SI) and downregulated in adenoma (DRA). These results were consistent with continual differentiation, as was shown to occur in mouse villus enterocytes. Compared with differentiated enteroid monolayers grown on Transwell inserts, enteroids exposed to flow were more differentiated but exhibited increased apoptosis and reduced carbohydrate metabolism, as shown by proteomic analysis. This study of human jejunal enteroids-on-chip suggests that luminal and basolateral flow produce a model of continual differentiation over time and NaCl absorption that mimics normal intestine and should provide new insights in intestinal physiology.NEW & NOTEWORTHY This study showed that polarized enteroid models in which there is no basolateral Wnt3a, are differentiated, regardless of the Wnt3a status of the apical media. The study supports the concept that in the human intestine villus differentiation is not an all or none phenomenon, demonstrating that at different days after lack of basolateral Wnt exposure, clusters of genes and proteins exist geographically along the villus with different domains having different functions.

Interleukin-8 Receptor 2 (IL-8R2)-Deficient Mice Are More Resistant to Pulmonary Coccidioidomycosis than Control Mice

The pathology of human coccidioidomycosis is granulomatous inflammation with many neutrophils surrounding ruptured spherules, but the chemotactic pathways that draw neutrophils into the infected tissues are not known. We previously showed that formalin-killed spherules (FKS) stimulate mouse macrophages to secret macrophage inflammatory protein 2 (MIP-2), which suggested that CXC ELR+ chemokines might be involved in neutrophil recruitment in vivo To test that hypothesis, we intranasally infected interleukin-8R2 (IL-8R2) (Cxcr2)-deficient mice on a BALB/c background with Coccidioides immitis RS. IL-8R2-deficient mice had fewer neutrophils in infected lungs than controls, but unexpectedly the IL-8R2-deficient mice had fewer organisms in their lungs than the control mice. Infected IL-8R2-deficient mouse lungs had higher expression of genes associated with lymphocyte activation, including the Th1 and Th17-related cytokines Ifnγ and Il17a and the transcription factors Stat1 and Rorc Additionally, bronchial alveolar lavage fluid from infected IL-8R2-deficient mice contained more IL-17A and interferon-γ (IFN-γ). We postulate that neutrophils in the lung directly or indirectly interfere with the development of a protective Th1/Th17 immune response to C. immitis at the site of infection.

Epithelial transport in digestive diseases: mice, monolayers, and mechanisms

The transport of electrolytes and fluid by the intestinal epithelium is critical in health to maintain appropriate levels of fluidity of the intestinal contents. The transport mechanisms that underlie this physiological process are also subject to derangement in various digestive disease states, such as diarrheal illnesses. This article summarizes the 2019 Hans Ussing Lecture of the Epithelial Transport Group of the American Physiological Society and discusses some pathways by which intestinal transport is dysregulated, particularly in the setting of infection with the diarrheal pathogen, Salmonella, and in patients treated with small-molecule inhibitors of the tyrosine kinase activity of the epidermal growth factor receptor (EGFr-TKI). The burdensome diarrhea in patients infected with Salmonella may be attributable to decreased expression of the chloride-bicarbonate exchanger downregulated in adenoma (DRA) that participates in electroneutral NaCl absorption. This outcome is possibly secondary to increased epithelial proliferation and/or decreased epithelial differentiation that occurs following infection. Conversely, the diarrheal side effects of cancer treatment with EGFr-TKI may be related to the known ability of EGFr-associated signaling to reduce calcium-dependent chloride secretion. Overall, the findings described may suggest targets for therapeutic intervention in a variety of diarrheal disease states.

Genistein antagonizes gliadin-induced CFTR malfunction in models of celiac disease

In celiac disease (CD), an intolerance to dietary gluten/gliadin, antigenic gliadin peptides trigger an HLA-DQ2/DQ8-restricted adaptive Th1 immune response. Epithelial stress, induced by other non-antigenic gliadin peptides, is required for gliadin to become fully immunogenic. We found that cystic-fibrosis-transmembrane-conductance-regulator (CFTR) acts as membrane receptor for gliadin-derived peptide P31-43, as it binds to CFTR and impairs its channel function. P31-43-induced CFTR malfunction generates epithelial stress and intestinal inflammation. Maintaining CFTR in an active open conformation by the CFTR potentiators VX-770 (Ivacaftor) or Vrx-532, prevents P31-43 binding to CFTR and controls gliadin-induced manifestations. Here, we evaluated the possibility that the over-the-counter nutraceutical genistein, known to potentiate CFTR function, would allow to control gliadin-induced alterations. We demonstrated that pre-treatment with genistein prevented P31-43-induced CFTR malfunction and an epithelial stress response in Caco-2 cells. These effects were abrogated when the CFTR gene was knocked out by CRISP/Cas9 technology, indicating that genistein protects intestinal epithelial cells by potentiating CFTR function. Notably, genistein protected gliadin-sensitive mice from intestinal CFTR malfunction and gliadin-induced inflammation as it prevented gliadin-induced IFN-γ production by celiac peripheral-blood-mononuclear-cells (PBMC) cultured ex-vivo in the presence of P31-43-challenged Caco-2 cells. Our results indicate that natural compounds capable to increase CFTR channel gating might be used for the treatment of CD.

NHERF3 is necessary for Escherichia coli heat-stable enterotoxin-induced inhibition of NHE3: differences in signaling in mouse small intestine and Caco-2 cells

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of childhood death from diarrhea and the leading cause of Traveler's diarrhea. E. coli heat-stable enterotoxin (ST) is a major virulence factor of ETEC and inhibits the brush border Na/H exchanger NHE3 in producing diarrhea. NHE3 regulation involves multiprotein signaling complexes that form on its COOH terminus. In this study, the hypothesis was tested that ST signals via members of the Na/H exchanger regulatory factor (NHERF) family of scaffolding proteins, NHERF2, which had been previously shown to have a role, and now with concentration on a role for NHERF3. Two models were used: mouse small intestine and Caco-2/BBe cells. In both models, ST rapidly increased intracellular cGMP, inhibited NHE3 activity, and caused a quantitatively similar decrease in apical expression of NHE3. The transport effects were NHERF3 and NHERF2 dependent. Also, mutation of the COOH-terminal amino acids of NHERF3 supported that NHERF3-NHERF2 heterodimerization was likely to account for this dual dependence. The ST increase in cGMP in both models was partially dependent on NHERF3. The intracellular signaling pathways by which ST-cGMP inhibits NHE3 were different in mouse jejunum (activation of cGMP kinase II, cGKII) and Caco-2 cells, which do not express cGKII (elevation of intracellular Ca²⁺ concentration [Ca²⁺]_i). The ST elevation of [Ca²⁺]_i was from intracellular stores and was dependent on NHERF3-NHERF2. This study shows that intracellular signaling in the same diarrheal model in multiple cell types may be different; this has implications for therapeutic strategies, which often assume that models have similar signaling mechanisms.

cAMP Stimulates SLC26A3 Activity in Human Colon by a CFTR-Dependent Mechanism That Does Not Require CFTR Activity

BACKGROUND & AIMS

SLC26A3 (DRA) is an electroneutral Cl^-/HCO₃^- exchanger that is present in the apical domain of multiple intestinal segments. An area that has continued to be poorly understood is related to DRA regulation in acute adenosine 3',5'-cyclic monophosphate (cAMP)-related diarrheas, in which DRA appears to be both inhibited as part of NaCl absorption and stimulated to contribute to increased HCO₃^- secretion. Different cell models expressing DRA have shown that cAMP inhibits, stimulates, or does not affect its activity.

METHODS

This study re-evaluated cAMP regulation of DRA using new tools, including a successful knockout cell model, a specific DRA inhibitor (DRA_inh-A250), specific antibodies, and a transport assay that did not rely on nonspecific inhibitors. The studies compared DRA regulation in colonoids made from normal human colon with regulation in the colon cancer cell line, Caco-2.

RESULTS

DRA is an apical protein in human proximal colon, differentiated colonoid monolayers, and Caco-2 cells. It is glycosylated and appears as 2 bands. cAMP (forskolin) acutely stimulated DRA activity in human colonoids and Caco-2 cells. In these cells, DRA is the predominant apical Cl^-/HCO₃^- exchanger and is inhibited by DRA_inh-A250 with a median inhibitory concentration of 0.5 and 0.2 μmol/L, respectively. However, there was no effect of cAMP in HEK293/DRA cells that lacked a cystic fibrosis transmembrane conductance regulator (CFTR). When CFTR was expressed in HEK293/DRA cells, cAMP also stimulated DRA activity. In all cases, cAMP stimulation of DRA was not inhibited by CFTR_inh-172.

CONCLUSIONS

DRA is acutely stimulated by cAMP by a process that is CFTR-dependent, but appears to be one of multiple regulatory effects of CFTR that does not require CFTR activity.

A pathogenic role for cystic fibrosis transmembrane conductance regulator in celiac disease

Intestinal handling of dietary proteins usually prevents local inflammatory and immune responses and promotes oral tolerance. However, in ~ 1% of the world population, gluten proteins from wheat and related cereals trigger an HLA DQ2/8‐restricted T_H1 immune and antibody response leading to celiac disease. Prior epithelial stress and innate immune activation are essential for breaking oral tolerance to the gluten component gliadin. How gliadin subverts host intestinal mucosal defenses remains elusive. Here, we show that the α‐gliadin‐derived LGQQQPFPPQQPY peptide (P31–43) inhibits the function of cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel pivotal for epithelial adaptation to cell‐autonomous or environmental stress. P31–43 binds to, and reduces ATPase activity of, the nucleotide‐binding domain‐1 (NBD1) of CFTR, thus impairing CFTR function. This generates epithelial stress, tissue transglutaminase and inflammasome activation, NF‐κB nuclear translocation and IL‐15 production, that all can be prevented by potentiators of CFTR channel gating. The CFTR potentiator VX‐770 attenuates gliadin‐induced inflammation and promotes a tolerogenic response in gluten‐sensitive mice and cells from celiac patients. Our results unveil a primordial role for CFTR as a central hub orchestrating gliadin activities and identify a novel therapeutic option for celiac disease.

Lactobacillus acidophilus Alleviated Salmonella-Induced Goblet Cells Loss and Colitis by Notch Pathway

SCOPE

The intestinal mucosal barrier, including the mucus layer, protects against invasion of enteropathogens, thereby inhibiting infection. In this study, the protective effect of Lactobacillus on the intestinal barrier against Salmonella infection is investigated. The underlying mechanism of its effect, specifically on the regulation of goblet cells through the Notch pathway, is also elucidated.

METHODS AND RESULTS

Here, the protective effect of Lactobacillus on alleviating changes in the intestinal barrier caused by Salmonella infection is explored. It has been found that Salmonella typhimurium colonizes the colon and damages colonic mucosa. However, Lactobacillus acidophilus ATCC 4356 alleviates the colitis caused by Salmonella infection. Moreover, S. typhimurium infection causes colonic crypt hyperplasia with increased PCNA⁺ cells, while L. acidophilus administration resolves these pathological changes. In addition, it has been further demonstrated that Salmonella results in severe colitis associated with goblet cells, and Lactobacillus improves colitis similarly associated with goblet cells. Salmonella infection induces goblet cell loss and reduces MUC2 expression by increasing Dll1, Dll4, and HES1 expression, while L. acidophilus reverses epithelial damage by balancing the Notch pathway.

CONCLUSION

The study demonstrates that colitis improvement is controlled by Lactobacillus ATCC 4356 by regulation of the Notch pathway; this finding will be useful for prevention against animal S. typhimurium infection.

Human evolutionary loss of epithelial Neu5Gc expression and species-specific susceptibility to cholera

While infectious agents have typical host preferences, the noninvasive enteric bacterium Vibrio cholerae is remarkable for its ability to survive in many environments, yet cause diarrheal disease (cholera) only in humans. One key V. cholerae virulence factor is its neuraminidase (VcN), which releases host intestinal epithelial sialic acids as a nutrition source and simultaneously remodels intestinal polysialylated gangliosides into monosialoganglioside GM1. GM1 is the optimal binding target for the B subunit of a second virulence factor, the AB5 cholera toxin (Ctx). This coordinated process delivers the CtxA subunit into host epithelia, triggering fluid loss via cAMP-mediated activation of anion secretion and inhibition of electroneutral NaCl absorption. We hypothesized that human-specific and human-universal evolutionary loss of the sialic acid N-glycolylneuraminic acid (Neu5Gc) and the consequent excess of N-acetylneuraminic acid (Neu5Ac) contributes to specificity at one or more steps in pathogenesis. Indeed, VcN was less efficient in releasing Neu5Gc than Neu5Ac. We show enhanced binding of Ctx to sections of small intestine and isolated polysialogangliosides from human-like Neu5Gc-deficient Cmah-/- mice compared to wild-type, suggesting that Neu5Gc impeded generation of the GM1 target. Human epithelial cells artificially expressing Neu5Gc were also less susceptible to Ctx binding and CtxA intoxication following VcN treatment. Finally, we found increased fluid secretion into loops of Cmah-/- mouse small intestine injected with Ctx, indicating an additional direct effect on ion transport. Thus, V. cholerae evolved into a human-specific pathogen partly by adapting to the human evolutionary loss of Neu5Gc, optimizing multiple steps in cholera pathogenesis.

Differential expression of intestinal ion transporters and water channel aquaporins in young piglets challenged with enterotoxigenic Escherichia coli K88

The study was to determine whether the expression of genes involved in intestinal water and ion transport would be affected by enterotoxigenic (ETEC) K88 both in vitro and in vivo. First, 36 male piglets (4 d old) were randomly allotted to either the control or the ETEC K88 group. Each group had 6 replicates with 3 piglets per replicate. All piglets were fed with the same diets for 17 d. On d 15, piglets in the ETEC K88 group were challenged with ETEC K88 (serotype O149:K91:K88ac) at 1 × 10 cfu per pig, whereas those in the control group received the same volume of sterile PBS. After being challenged with ETEC K88 for 72 h (d 18), 1 piglet from each replicate was selected for slaughter to collect samples from the jejunum, ileum, and colon. The mRNA expression and protein abundance of cystic fibrosis transmembrane conductance regulator (CFTR) in the ileum and colon were increased compared with that in the control group ( < 0.05). Furthermore, the mRNA expression of () in the ileum and colon was increased by ETEC K88 challenge ( < 0.05), whereas in the jejunum, both its mRNA and protein expression were increased by ETEC K88 treatment ( < 0.05). Additionally, an established porcine intestinal epithelial cell line (IPEC-J2) was used to investigate the effect and possible mechanism of ETEC K88 on expression of water channel aquaporins (AQP) and ion transporters. Cells (1.17 × 10 per well) were grown in 6-well plates and treated with ETEC K88 at a multiplicity of infection of 50:1 for 3 h. The mRNA expression of , , and () in IPEC-J2 cells was reduced after ETEC K88 treatment ( < 0.05). Further analyses using western blotting also demonstrated that ETEC K88 decreased the protein expression of AQP3, AQP9, and AQP11 in IPEC-J2 cells ( < 0.05). Moreover, the phosphorylation levels of protein kinase A (PKA) and cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB) were decreased by ETEC K88 challenge ( < 0.05). The results indicate that ETEC K88 challenge induced differential expression of intestinal ion transporters and AQP in young piglets, probably by regulation of the cAMP-PKA signaling pathway. This study might provide new insights about the importance of fluid homeostasis in control of ETEC-induced diarrhea in young piglets.

Infection with enteric pathogens Salmonella typhimurium and Citrobacter rodentium modulate TGF-beta/Smad signaling pathways in the intestine

Salmonella and Citrobacter are gram negative, members of Enterobacteriaceae family that are important causative agents of diarrhea and intestinal inflammation. TGF-β1 is a pleiotropic multifunctional cytokine that has been implicated in modulating the severity of microbial infections. How these pathogens alter the TGF-β1 signaling pathways in the intestine is largely unknown. Streptomycin-pretreated C57BL/6J mouse model colonized with S. typhimurium for 8 hours (acute) and 4 days (chronic) infection and FVB/N mice infected with C. rodentium for 6 days were utilized. Results demonstrated an increase in TGF-β1 receptor I expression (p<0.05) in S. typhimurium infected mouse ileum at both acute and chronic post-infection vs control. This was associated with activation of Smad pathways as evidenced by increased phosphorylated (p)-Smad2 and p-Smad3 levels in the nucleus. The inhibitory Smad7 mRNA levels showed a significant up regulation during acute phase of Salmonella infection but no change at 4d post-infection. In contrast to Salmonella, infection with Citrobacter caused drastic downregulation of TGF receptor I and II concomitant with a decrease in levels of Smad 2, 3, 4 and 7 expression in the mouse colon. We speculate that increased TGF-β1 signaling in response to Salmonella may be a host compensatory response to promote mucosal healing; while C. rodentium decreases TGF-β1 signaling pathways to promote inflammation and contribute to disease pathogenesis. These findings increase our understanding of how enteric pathogens subvert specific aspects of the host-cellular pathways to cause disease.

The Role of Ion Transporters in the Pathophysiology of Infectious Diarrhea

Every year, enteric infections and associated diarrhea kill millions of people. The situation is compounded by increases in the number of enteric pathogens that are acquiring resistance to antibiotics, as well as (hitherto) a relative paucity of information on host molecular targets that may contribute to diarrhea. Many forms of diarrheal disease depend on the dysregulation of intestinal ion transporters, and an associated imbalance between secretory and absorptive functions of the intestinal epithelium. A number of major transporters have been implicated in the pathogenesis of diarrheal diseases and thus an understanding of their expression, localization, and regulation after infection with various bacteria, viruses, and protozoa likely will prove critical in designing new therapies. This article surveys our understanding of transporters that are modulated by specific pathogens and the mechanism(s) involved, thereby illuminating targets that might be exploited for new therapeutic approaches.

Campylobacter jejuni impairs sodium transport and epithelial barrier function via cytokine release in human colon

This corrects the article DOI: 10.1038/mi.2017.66.

Campylobacter jejuni impairs sodium transport and epithelial barrier function via cytokine release in human colon

Campylobacter jejuni is the most prevalent cause of foodborne bacterial enteritis worldwide. Patients present with diarrhea and immune responses lead to complications like arthritis and irritable bowel syndrome. Although studies exist in animal and cell models, we aimed at a functional and structural characterization of intestinal dysfunction and the involved regulatory mechanisms in human colon. First, in patients' colonic biopsies, sodium malabsorption was identified as an important diarrheal mechanism resulting from hampered epithelial ion transport via impaired epithelial sodium channel (ENaC) β- and γ-subunit. In addition, barrier dysfunction from disrupted epithelial tight junction proteins (claudin-1, -3, -4, -5, and -8), epithelial apoptosis, and appearance of lesions was detected, which cause leak-flux diarrhea and can perpetuate immune responses. Importantly, these effects in human biopsies either represent direct action of Campylobacter jejuni (ENaC impairment) or are caused by proinflammatory signaling (barrier dysfunction). This was revealed by regulator analysis from RNA-sequencing (cytometric bead array-checked) and confirmed in cell models, which identified interferon-γ, TNFα, IL-13, and IL-1β. Finally, bioinformatics' predictions yielded additional information on protective influences like vitamin D, which was confirmed in cell models. Thus, these are candidates for intervention strategies against C. jejuni infection and post-infectious sequelae, which result from the permissive barrier defect along the leaky gut.

Restoration of CFTR Activity in Ducts Rescues Acinar Cell Function and Reduces Inflammation in Pancreatic and Salivary Glands of Mice

BACKGROUND & AIMS

Sjögren's syndrome and autoimmune pancreatitis are disorders with decreased function of salivary, lacrimal glands, and the exocrine pancreas. Nonobese diabetic/ShiLTJ mice and mice transduced with the cytokine BMP6 develop Sjögren's syndrome and chronic pancreatitis and MRL/Mp mice are models of autoimmune pancreatitis. Cystic fibrosis transmembrane conductance regulator (CFTR) is a ductal Cl^- channel essential for ductal fluid and HCO₃^- secretion. We used these models to ask the following questions: is CFTR expression altered in these diseases, does correction of CFTR correct gland function, and most notably, does correcting ductal function correct acinar function?

METHODS

We treated the mice models with the CFTR corrector C18 and the potentiator VX770. Glandular, ductal, and acinar cells damage, infiltration, immune cells and function were measured in vivo and in isolated duct/acini.

RESULTS

In the disease models, CFTR expression is markedly reduced. The salivary glands and pancreas are inflamed with increased fibrosis and tissue damage. Treatment with VX770 and, in particular, C18 restored salivation, rescued CFTR expression and localization, and nearly eliminated the inflammation and tissue damage. Transgenic overexpression of CFTR exclusively in the duct had similar effects. Most notably, the markedly reduced acinar cell Ca²⁺ signaling, Orai1, inositol triphosphate receptors, Aquaporin 5 expression, and fluid secretion were restored by rescuing ductal CFTR.

CONCLUSIONS

Our findings reveal that correcting ductal function is sufficient to rescue acinar cell function and suggests that CFTR correctors are strong candidates for the treatment of Sjögren's syndrome and pancreatitis.

Hydrogen peroxide scavenger, catalase, alleviates ion transport dysfunction in murine colitis

Reactive oxygen species (ROS) such as hydrogen peroxide (H₂ O₂ ) contribute to epithelial damage and ion transport dysfunction (key events in inflammatory diarrhoea) in inflammatory bowel disease (IBD). The aim of this study was to identify if H₂ O₂ mediates suppression of colonic ion transport function in the murine dextran sulfate sodium (DSS) colitis model by using the H₂ O₂ degrading enzyme, catalase. Colitis was induced by administering DSS (4%) in drinking water for 5 days followed by 3 days on normal H₂ O. Mice were administered either pegylated catalase or saline at day -1, 0 and +1 of DSS treatment. Ion transport responses to the Ca²⁺ -dependent agonist, carbachol (CCh), or the cAMP-dependent agonist, forskolin, were measured across distal colonic mucosa mounted in Ussing chambers. Parameters of DSS-induced inflammation (loss in body weight, decreased colon length, altered stool consistency), were only partially alleviated by catalase while histology was only minimally improved. However, catalase significantly reversed the DSS-induced reduction in baseline ion transport as well as colonic I_sc responses to CCh. However, ion transport responses to forskolin were not significantly restored. Catalase also reduced activation of ERK MAP kinase in the setting of colitis, and increased expression of the Na⁺ -K⁺ -2Cl^- cotransporter, NKCC1, consistent with restoration of ion transport function. Ex vivo treatment of inflamed colonic mucosae with catalase also partially restored ion transport function. Therefore, catalase partially prevents, and rescues, the loss of ion transport properties in DSS colitis even in the setting of unresolved tissue inflammation. These findings indicate a prominent role for ROS in ion transport dysfunction in colitis and may suggest novel strategies for the treatment of inflammatory diarrhoea.

Anti-inflammatory capacity of Lactobacillus rhamnosus GG in monophasic variant Salmonella infected piglets is correlated with impeding NLRP6-mediated host inflammatory responses

In this study, we investigated the effect of Lactobacillus rhamnosus GG strain (LGG) in ameliorating enteritis in newly weaned pigs following challenge with a monophasic variant of Salmonella enterica serovar Typhimurium (serotyped as 4,[5],12:i:-), which has been linked to disease in humans and livestocks over the past 10 years. In weaned pigs, S. enterica serovar 4,[5],12:i:- induced the mRNA expression of toll like receptor (TLR) 5 and TLR4, while increasing interleukin (IL)-8 and IL-6 mRNA expression in the jejunum. The monophasic variant Salmonella stimulated the expression of nucleotide-binding oligomerization domain-containing protein 1/2 (NOD1/2) mRNA in the ileum, which was accompanied by phosphorylation of IκB-α, an inhibitor of NF-κB, activating the NF-κB pathway and promoting the release of inflammatory cytokines. Oral administration of LGG attenuated the Salmonella-induced increases in the expression of NOD1 mRNA of jejunal and ileal tissues. LGG promoted the secretion of immunoglobulin A in different intestinal segments but did not induce expression of polymeric immunoglobulin receptor. LGG also impeded the activation of the Nod-like receptor protein (NLRP) 6/apoptosis-associated speck-like protein/caspase-1 inflammasome and decreased the production of IL-18 in the ileum during Salmonella infection. In contrast, activation of the NLRP3 inflammasome was not altered. Our data indicate that LGG accelerated the clearance of Salmonella in the early phase of infection and prevented the excessive inflammatory responses in S. enterica serovar 4,[5],12:i:- model. LGG ameliorates inflammation induced by infection with the monophasic variant Salmonella via inhibition of the canonical NF-κB pathway and attenuation of the NLRP6-mediated inflammasome in the intestine.

Cystic Fibrosis Transmembrane Conductance Regulator Reduces Microtubule-Dependent Campylobacter jejuni Invasion

Campylobacterjejuni is a foodborne pathogen that induces gastroenteritis. Invasion and adhesion are essential in the process of C. jejuni infection leading to gastroenteritis. The mucosal layer plays a key role in the system of defense against efficient invasion and adhesion by bacteria, which is modulated by several ion channels and transporters mediated by water flux in the intestine. The cystic fibrosis transmembrane conductance regulator (CFTR) plays the main role in water flux in the intestine, and it is closely associated with bacterial clearance. We previously reported that C. jejuni infection suppresses CFTR channel activity in intestinal epithelial cells; however, the mechanism and importance of this suppression are unclear. This study sought to elucidate the role of CFTR in C. jejuni infection. Using HEK293 cells that stably express wild-type and mutated CFTR, we found that CFTR attenuated C. jejuni invasion and that it was not involved in bacterial adhesion or intracellular survival but was associated with microtubule-dependent intracellular transport. Moreover, we revealed that CFTR attenuated the function of the microtubule motor protein, which caused inhibition of C. jejuni invasion, but did not affect microtubule stability. Meanwhile, the CFTR mutant G551D-CFTR, which had defects in channel activity, suppressed C. jejuni invasion, whereas the ΔF508-CFTR mutant, which had defects in maturation, did not suppress C. jejuni invasion, suggesting that CFTR suppression of C. jejuni invasion is related to CFTR maturation but not channel activity. When these findings are taken together, it may be seen that mature CFTR inhibits C. jejuni invasion by regulating microtubule-mediated pathways. We suggest that CFTR plays a critical role in cellular defenses against C. jejuni invasion and that suppression of CFTR may be an initial step in promoting cell invasion during C. jejuni infection.

AMPK/α-Ketoglutarate Axis Regulates Intestinal Water and Ion Homeostasis in Young Pigs

Water and ion absorption via sensitive aquaporins (AQPs) and ion channels is of critical importance in intestinal health. However, whether α-ketoglutarate (AKG) could improve intestinal water and ion homeostasis in lipopolysaccharide (LPS)-challenged piglets and whether the AMP-activated protein kinase (AMPK) pathway is involved remains largely unknown. This study was conducted to investigate the effect of dietary AKG supplementation on the small intestinal water and ion homeostasis through modulating the AMPK pathway in a piglet diarrhea model. A total of 32 weaned piglets were used in a 2 × 2 factorial design; the major factors were diet (basal diet or 1% AKG diet) and challenge (Escherichia coli LPS or saline). The results showed that LPS challenge increased the diarrhea index and affected the concentrations of serum Na⁺, K⁺, Cl^-, glucose, and AKG and its metabolites in piglets fed the basal or AKG diet. However, the addition of AKG attenuated diarrhea incidence and reversed these serum parameter concentrations. Most AQPs (e.g., AQP1, AQP3, AQP4, AQP5, AQP8, AQP10, and AQP11) and ion transporters (NHE3, ENaC, and DRA/PAT1) were widely distributed in the duodenum and jejunum of piglets. We also found that AKG up-regulated the expression of intestinal epithelial AQPs while inhibiting the expression of ion transporters. LPS challenge decreased (P < 0.05) the gene and protein expression of the AMPK pathway (AMPKα1, AMPKα2, SIRT1, PGC-1α, ACC, and TORC2) in the jejunum and ileum. Notably, AKG supplementation enhanced the abundance of these proteins in the LPS-challenged piglets. Collectively, AKG plays an important role in increasing water and ion homeostasis through modulating the AMPK pathway. Our novel finding has important implications for the prevention and treatment of gut dysfunction in neonates.

Lawsonia intracellularis exploits β-catenin/Wnt and Notch signalling pathways during infection of intestinal crypt to alter cell homeostasis and promote cell proliferation

Lawsonia intracellularis is an obligate intracellular bacterial pathogen that causes proliferative enteropathy (PE) in pigs. L. intracellularis infection causes extensive intestinal crypt cell proliferation and inhibits secretory and absorptive cell differentiation. However, the affected host upstream cellular pathways leading to PE are still unknown. β-catenin/Wnt signalling is essential in maintaining intestinal stem cell (ISC) proliferation and self-renewal capacity, while Notch signalling governs differentiation of secretory and absorptive lineage specification. Therefore, in this report we used immunofluorescence (IF) and quantitative reverse transcriptase PCR (RTqPCR) to examine β-catenin/Wnt and Notch-1 signalling levels in uninfected and L. intracellularis infected pig ileums at 3, 7, 14, 21 and 28 days post challenge (dpc). We found that while the significant increase in Ki67+ nuclei in crypts at the peak of L. intracellularis infection suggested enhanced cell proliferation, the expression of c-MYC and ASCL2, promoters of cell growth and ISC proliferation respectively, was down-regulated. Peak infection also coincided with enhanced cytosolic and membrane-associated β-catenin staining and induction of AXIN2 and SOX9 transcripts, both encoding negative regulators of β-catenin/Wnt signalling and suggesting a potential alteration to β-catenin/Wnt signalling levels, with differential regulation of the expression of its target genes. We found that induction of HES1 and OLFM4 and the down-regulation of ATOH1 transcript levels was consistent with the increased Notch-1 signalling in crypts at the peak of infection. Interestingly, the significant down-regulation of ATOH1 transcript levels coincided with the depletion of MUC2 expression at 14 dpc, consistent with the role of ATOH1 in promoting goblet cell maturation. The lack of significant change to LGR5 transcript levels at the peak of infection suggested that the crypt hyperplasia was not due to the expansion of ISC population. Overall, simultaneous induction of Notch-1 signalling and the attenuation of β-catenin/Wnt pathway appear to be associated with the inhibition of goblet cell maturation and enhanced crypt cell proliferation at the peak of L. intracellularis infection. Moreover, the apparent differential regulation of apoptosis between crypt and lumen cells together with the strong induction of Notch-1 signalling and the enhanced SOX9 expression along crypts 14 dpc suggest an expansion of actively dividing transit amplifying and/or absorptive progenitor cells and provide a potential basis for understanding the development and maintenance of PE.

Three-dimensional organotypic co-culture model of intestinal epithelial cells and macrophages to study Salmonella enterica colonization patterns

Three-dimensional models of human intestinal epithelium mimic the differentiated form and function of parental tissues often not exhibited by two-dimensional monolayers and respond to Salmonella in key ways that reflect in vivo infections. To further enhance the physiological relevance of three-dimensional models to more closely approximate in vivo intestinal microenvironments encountered by Salmonella, we developed and validated a novel three-dimensional co-culture infection model of colonic epithelial cells and macrophages using the NASA Rotating Wall Vessel bioreactor. First, U937 cells were activated upon collagen-coated scaffolds. HT-29 epithelial cells were then added and the three-dimensional model was cultured in the bioreactor until optimal differentiation was reached, as assessed by immunohistochemical profiling and bead uptake assays. The new co-culture model exhibited in vivo-like structural and phenotypic characteristics, including three-dimensional architecture, apical-basolateral polarity, well-formed tight/adherens junctions, mucin, multiple epithelial cell types, and functional macrophages. Phagocytic activity of macrophages was confirmed by uptake of inert, bacteria-sized beads. Contribution of macrophages to infection was assessed by colonization studies of Salmonella pathovars with different host adaptations and disease phenotypes (Typhimurium ST19 strain SL1344 and ST313 strain D23580; Typhi Ty2). In addition, Salmonella were cultured aerobically or microaerobically, recapitulating environments encountered prior to and during intestinal infection, respectively. All Salmonella strains exhibited decreased colonization in co-culture (HT-29-U937) relative to epithelial (HT-29) models, indicating antimicrobial function of macrophages. Interestingly, D23580 exhibited enhanced replication/survival in both models following invasion. Pathovar-specific differences in colonization and intracellular co-localization patterns were observed. These findings emphasize the power of incorporating a series of related three-dimensional models within a study to identify microenvironmental factors important for regulating infection.

The effect of porcine reproductive and respiratory syndrome virus and porcine epidemic diarrhea virus challenge on growing pigs I: Growth performance and digestibility

Porcine reproductive and respiratory syndrome (PRRS) and porcine epidemic diarrhea (PED) are two diseases costly to the U.S. swine industry. The objective of this study was to determine the impact of PRRS virus and PED virus, alone or in combination, on growth performance, feed efficiency, and digestibility in grower pigs. Forty-two gilts (16 ± 0.98 kg BW) naïve for PRRS and PED were selected and allocated to 1 of 4 treatments. Treatments included 1) a control, 2) PRRS virus infected, 3) PED virus infected, and 4) PRRS+PED coinfection (PRP). Pigs in treatments 2 and 4 were inoculated with a live field strain of PRRS virus via intramuscular and intranasal routes at 0 d after inoculation (dpi). Treatments 3 and 4 were orally inoculated with a cloned PED virus at 15 dpi. Infection with PRRS virus was confirmed by quantitative PCR and seroconversion. Infection with PED virus was confirmed with PCR. Control pigs remained PRRS and PED virus negative throughout the study. All pigs were offered, ad libitum, a standard diet with free access to water. During the test period, PRRS reduced ADG and ADFI by 30 and 26%, respectively (P < 0.05), compared with control pigs, whereas PRP decreased ADG, ADFI, and G:F by 45, 30, and 23%, respectively (P < 0.05). Additional reductions in ADG and G:F were detected in PRP pigs compared with singular PED or PRRS treatments (33 and 16%, respectively). The impact of PED, alone or in combination, on performance (15–21 dpi) reduced ADG (0.66 vs. 0.35 vs. 0.20 kg/d; P < 0.01), ADFI (1.22 vs. 0.88 vs. 0.67 kg/d; P = 0.003), and G:F (0.54 vs. 0.39 vs. 0.31; P = 0.001) compared with control pigs. Compared with control pigs, PRRS infection did not reduce apparent total tract digestibility (ATTD) of nutrients and energy. However, PED infection, alone or in combination, decreased ATTD of DM and energy by 8 and 12%, respectively (P < 0.05). Compared with control pigs, PRP reduced N and OM ATTD by 13 and 3%, respectively (P < 0.05). No significant differences in apparent ileal digestibility (AID) were detected between virus challenges. However, Lys AID tended to be reduced in both PED treatments compared with the control (10 and 12%; P = 0.095). Altogether, PRRS reduced growth but did not alter digestibility. Pigs challenged with PED and, to a greater extent, the coinfection of PED and PRRS viruses had reduced ADG, ADFI, G:F, and ATTD of nutrients and energy.

Effects of Salmonella infection on hepatic damage following acute liver injury in rats

BACKGROUND

Acute liver injury is a common clinical disorder associated with intestinal barrier injury and disturbance of intestinal microbiota. Probiotic supplementation has been reported to reduce liver injury; however, it is unclear whether enteropathogen infection exacerbates liver injury. The purpose of this study was to address this unanswered question using a rat model.

METHODS

Oral supplementation with Salmonella enterica serovar enteritidis (S. enteritidis) was given to rats for 7 days. Different degrees of acute liver injury were then induced by intraperitoneal injection of D-galactosamine. The presence and extent of liver injury was assayed by measuring the concentrations of serum alanine aminotransferase, aspartate aminotransferase, and total bilirubin. Histology was used to observe liver tissue damage. Additionally, we measured the changes in plasma endotoxin, serum cytokines and bacterial translocation to clarify the mechanisms underlying intestinal microbiota associated liver injury.

RESULTS

The levels of liver damage and endotoxin were significantly increased in the Salmonella infected rats with severe liver injury compared with the no infection rats with severe liver injury (P<0.01); The peyer's patch CD3+ T cell counts were increased significantly when the Salmonella infection with severe injury group was compared with the normal group (P<0.05). S. enteritidis pretreatment enhanced intestinal barrier impairment and bacterial translocation.

CONCLUSIONS

Oral S. enteritidis administration exacerbates acute liver injury, especially when injury was severe. Major factors of the exacerbation include inflammatory and oxidative stress injuries induced by the translocated bacteria and associated endotoxins, as well as over-activation of the immune system in the intestine and liver.

Endogenous and exogenous control of gastrointestinal epithelial function: building on the legacy of Bayliss and Starling

Transport of fluid and electrolytes in the intestine allows for appropriate adjustments in luminal fluidity while reclaiming water used in digesting and absorbing a meal, and is closely regulated. This article discusses various endogenous and exogenous mechanisms whereby transport is controlled in the gut, placing these in the context of the ideas about the neurohumoral control of alimentary physiology that were promulgated by William Bayliss and Ernest Starling. The article considers three themes. First, mechanisms that intrinsically regulate chloride secretion, centred on the epidermal growth factor receptor (EGFr), are discussed. These may be important in ensuring that excessive chloride secretion, with the accompanying loss of fluid, is not normally stimulated by intestinal distension as the meal passes through the gastrointestinal tract. Second, mechanisms whereby probiotic microorganisms can impart beneficial effects on the gut are described, with a focus on targets at the level of the epithelium. These findings imply that the commensal microbiota exert important influences on the epithelium in health and disease. Finally, mechanisms that lead to diarrhoea in patients infected with an invasive pathogen, Salmonella, are considered, based on recent studies in a novel mouse model. Diarrhoea is most likely attributable to reduced expression of absorptive transporters and may not require the influx of neutrophils that accompanies infection. Overall, the goal of the article is to highlight the many ways in which critical functions of the intestinal epithelium are regulated under physiological and pathophysiological conditions, and to suggest possible targets for new therapies for digestive disease states.

A novel treatment of cystic fibrosis acting on-target: cysteamine plus epigallocatechin gallate for the autophagy-dependent rescue of class II-mutated CFTR

We previously reported that the combination of two safe proteostasis regulators, cysteamine and epigallocatechin gallate (EGCG), can be used to improve deficient expression of the cystic fibrosis transmembrane conductance regulator (CFTR) in patients homozygous for the CFTR Phe508del mutation. Here we provide the proof-of-concept that this combination treatment restored CFTR function and reduced lung inflammation (P<0.001) in Phe508del/Phe508del or Phe508del/null-Cftr (but not in Cftr-null mice), provided that such mice were autophagy-competent. Primary nasal cells from patients bearing different class II CFTR mutations, either in homozygous or compound heterozygous form, responded to the treatment in vitro. We assessed individual responses to cysteamine plus EGCG in a single-centre, open-label phase-2 trial. The combination treatment decreased sweat chloride from baseline, increased both CFTR protein and function in nasal cells, restored autophagy in such cells, decreased CXCL8 and TNF-α in the sputum, and tended to improve respiratory function. These positive effects were particularly strong in patients carrying Phe508del CFTR mutations in homozygosity or heterozygosity. However, a fraction of patients bearing other CFTR mutations failed to respond to therapy. Importantly, the same patients whose primary nasal brushed cells did not respond to cysteamine plus EGCG in vitro also exhibited deficient therapeutic responses in vivo. Altogether, these results suggest that the combination treatment of cysteamine plus EGCG acts 'on-target' because it can only rescue CFTR function when autophagy is functional (in mice) and improves CFTR function when a rescuable protein is expressed (in mice and men). These results should spur the further clinical development of the combination treatment.

Sulfonamide inhibition studies of the β-carbonic anhydrase from the pathogenic bacterium Vibrio cholerae

The genome of the pathogenic bacterium Vibrio cholerae encodes for three carbonic anhydrases (CAs, EC 4.2.1.1) belonging to the α-, β- and γ-classes. VchCA, the α-CA from this species was investigated earlier, whereas the β-class enzyme, VchCAβ was recently cloned, characterized kinetically and its X-ray crystal structure reported by this group. Here we report an inhibition study with sulfonamides and one sulfamate of this enzyme. The best VchCAβ inhibitors were deacetylated acetazolamide and methazolamide and hydrochlorothiazide, which showed inhibition constants of 68.2-87.0nM. Other compounds, with medium potency against VchCAβ, (KIs in the range of 275-463nM), were sulfanilamide, metanilamide, sulthiame and saccharin whereas the clinically used agents such as acetazolamide, methazolamide, ethoxzolamide, dorzolamide, zonisamide and celecoxib were micromolar inhibitors (KIs in the range of 4.51-8.57μM). Identification of potent and possibly selective inhibitors of VchCA and VchCAβ over the human CA isoforms, may lead to pharmacological tools useful for understanding the physiological role(s) of this under-investigated enzymes.

Secretory diarrhoea: mechanisms and emerging therapies

Diarrhoeal disease remains a major health burden worldwide. Secretory diarrhoeas are caused by certain bacterial and viral infections, inflammatory processes, drugs and genetic disorders. Fluid secretion across the intestinal epithelium in secretory diarrhoeas involves multiple ion and solute transporters, as well as activation of cyclic nucleotide and Ca(2+) signalling pathways. In many secretory diarrhoeas, activation of Cl(-) channels in the apical membrane of enterocytes, including the cystic fibrosis transmembrane conductance regulator and Ca(2+)-activated Cl(-) channels, increases fluid secretion, while inhibition of Na(+) transport reduces fluid absorption. Current treatment of diarrhoea includes replacement of fluid and electrolyte losses using oral rehydration solutions, and drugs targeting intestinal motility or fluid secretion. Therapeutics in the development pipeline target intestinal ion channels and transporters, regulatory proteins and cell surface receptors. This Review describes pathogenic mechanisms of secretory diarrhoea, current and emerging therapeutics, and the challenges in developing antidiarrhoeal therapeutics.

TRPM8 on mucosal sensory nerves regulates colitogenic responses by innate immune cells via CGRP

TRPM8 is the molecular sensor for cold; however, the physiological role of TRPM8+ neurons at mucosal surfaces is unclear. Here we evaluated the distribution and peptidergic properties of TRPM8+ fibers in naive and inflamed colons, as well as their role in mucosal inflammation. We found that Trpm8(-/-) mice were hypersusceptible to dextran sodium sulfate (DSS)-induced colitis, and that Trpm8(-/-) CD11c+ DCs (dendritic cells) showed hyperinflammatory responses to toll-like receptor (TLR) stimulation. This was phenocopied in calcitonin gene-related peptide (CGRP) receptor-deficient mice, but not in substance P receptor-deficient mice, suggesting a functional link between TRPM8 and CGRP. The DSS phenotype of CGRP receptor-deficient mice could be adoptively transferred to wild-type (WT) mice, suggesting that CGRP suppresses the colitogenic activity of bone marrow-derived cells. TRPM8+ mucosal fibers expressed CGRP in human and mouse colon. Furthermore, neuronal CGRP contents were increased in colons from naive and DSS-treated Trpm8(-/-) mice, suggesting deficient CGRP release in the absence of TRPM8 triggering. Finally, treatment of Trpm8(-/-) mice with CGRP reversed their hyperinflammatory phenotype. These results suggest that TRPM8 signaling in mucosal sensory neurons is indispensable for the regulation of innate inflammatory responses via the neuropeptide CGRP.

Early-life dietary spray-dried plasma influences immunological and intestinal injury responses to later-life Salmonella typhimurium challenge

Increasing evidence supports the concept that early-life environmental influences, including nutrition and stress, have an impact on long-term health outcomes and disease susceptibility. The objective of the present study was to determine whether dietary spray-dried plasma (SDP), fed during the first 2 weeks post-weaning (PW), influences subsequent immunological and intestinal injury responses to Salmonella typhimurium challenge. A total of thirty-two piglets (age 16-17 d) were weaned onto nursery diets containing 0, 2·5 % SDP (fed for 7 d PW) or 5 % SDP (fed for 14 d PW), and were then fed control diets (without SDP), for the remainder of the experiment. At 34 d PW (age 50 d), pigs were challenged with 3 × 10⁹ colony-forming units of S. typhimurium. A control group (non-challenged) that was fed 0 % SDP in the nursery was included. At 2 d post-challenge, the distal ileum was harvested for the measurement of inflammatory, histological and intestinal physiological parameters. S. typhimurium challenge induced elevated ileal histological scores, myeloperoxidase (MPO), IL-8 and TNF, and increased intestinal permeability (indicated by reduced transepithelial voltage (potential difference) and elevated 4 kDa fluorescein isothiocyanate dextran (FD4) flux rates). Compared with S. typhimurium-challenged controls (0 % SDP), pigs fed the 5 % SDP-14 d diet exhibited reduced ileal histological scores, MPO levels, IL-8 levels and FD4 flux rates. Pigs fed the 5 % SDP-14 d nursery diet exhibited increased levels of plasma and ileal TNF-α in response to the challenge, compared with the other treatments. These results indicate that inclusion of SDP in PW diets can have an influence on subsequent immunological and intestinal injury responses induced by later-life S. typhimurium challenge.

Salmonella-induced Diarrhea Occurs in the Absence of IL-8 Receptor (CXCR2)-Dependent Neutrophilic Inflammation

BACKGROUND

Gastroenteritis is the most common manifestation of nontyphoidal Salmonella enterica infections, but little is known about the pathogenesis of diarrhea in this infection

METHODS

To determine whether polymorphonuclear neutrophils (PMNs) are required for diarrhea for Salmonella colitis, we infected kanamycin-pretreated interleukin 8R (IL-8R) mutant mice and controls, both with nonmutant Slc11a1 (Nramp1, ItyR). We compared the 2 mouse strains for increases in fecal water content (diarrhea) 3 days after infection, changes in expression of ion transporters in colonic epithelial cells, proliferation of epithelial cells, and severity of infection as measured by colony-forming units (CFUs).

RESULTS

The IL-8R knockout mice had fewer PMNs in the colon but the other variables we measured were unaffected except for an increase in CFUs in the colon. The pathologic changes in the cecum were similar in both groups except for the lack of PMNs in the IL-8R knockout mice. There was minimal damage to the colon more distally.

CONCLUSIONS

In the early stage of Salmonella colitis, PMNs are not required for diarrhea or for the decrease in expression of colonic epithelial cell apical ion transporters. They contribute to defense against infection in the cecum but not extracolonically at this stage of Salmonella colitis.

Mutation of EpCAM leads to intestinal barrier and ion transport dysfunction

Congenital tufting enteropathy (CTE) is a devastating diarrheal disease seen in infancy that is typically associated with villous changes and the appearance of epithelial tufts. We previously found mutations in epithelial cell adhesion molecule (EpCAM) to be causative in CTE. We developed a knock-down cell model of CTE through transfection of an EpCAM shRNA construct into T84 colonic epithelial cells to elucidate the in vitro role of EpCAM in barrier function and ion transport. Cells with EpCAM deficiency exhibited decreased electrical resistance, increased permeability, and decreased ion transport. Based on mutations in CTE patients, an in vivo mouse model was developed, with tamoxifen-inducible deletion of exon 4 in Epcam resulting in mutant protein with decreased expression. Tamoxifen treatment of Epcam (Δ4/Δ4) mice resulted in pathological features of villous atrophy and epithelial tufts, similar to those in human CTE patients, within 4 days post induction. Epcam (Δ4/Δ4) mice also showed decreased expression of tight junctional proteins, increased permeability, and decreased ion transport in the intestines. Taken together, these findings reveal mechanisms that may underlie disease in CTE.

KEY MESSAGES

Knock-down EpCAM cell model of congenital tufting enteropathy was developed. In vivo inducible mouse model was developed resulting in mutant EpCAM protein. Cells with EpCAM deficiency demonstrated barrier and ion transport dysfunction. Tamoxifen-treated Epcam (Δ4/Δ4) mice demonstrated pathological features. Epcam (Δ4/Δ4) mice showed improper barrier function and ion transport.

Campylobacter jejuni infection suppressed Cl⁻ secretion induced by CFTR activation in T-84 cells

Campylobacter jejuni causes foodborne disease associated with abdominal pain, gastroenteritis, and diarrhea. These symptoms are induced by bacterial adherence and invasion of host epithelial cells. C. jejuni infection can occur with a low infective dose, suggesting that C. jejuni may have evolved strategies to cope with the bacterial clearance system in the gastrointestinal tract. The mucosa layer is the first line of defense against bacteria. Mucus conditions are maintained by water and anion (especially Cl(-)) movement. Cystic fibrosis transmembrane conductance regulator (CFTR) is the main Cl(-) channel transporting Cl(-) to the lumen. Mutations in CFTR result in dehydrated secreted mucus and bacterial accumulation in the lungs, and recent studies suggest that closely related pathogenic bacteria also may survive in the intestine. However, the relationship between C. jejuni infection and CFTR has been little studied. Here, we used an (125)I(-) efflux assay and measurement of short-circuit current to measure Cl(-) secretion in C. jejuni-infected T-84 human intestinal epithelial cells. The basic state of Cl(-) secretion was unchanged by C. jejuni infection, but CFTR activator was observed to induce Cl(-) secretion suppressed in C. jejuni-infected T-84 cells. The suppression of activated Cl(-) secretion was bacterial dose-dependent and duration-dependent. A similar result was observed during infection with other C. jejuni strains. The mechanism of suppression may occur by affecting water movement or mucus condition in the intestinal tract. A failure of mucus barrier function may promote bacterial adhesion or invasion of host intestinal epithelial cells, thereby causing bacterial preservation in the host intestinal tract.

Fluid and electrolyte secretion in the inflamed gut: novel targets for treatment of inflammation-induced diarrhea

Diarrheal disease can occur in the context of both inflammatory and infectious challenges. Inflammation can result in changes in ion transporter expression or simply mislocalization of the protein. In addition to development of diarrhea, an altered secretory state can lead to changes in mucus secretion and luminal pH. Bacterial infection can lead to subversion of host cell signaling, leading to transporter mislocalization and hyposecretion, promoting bacterial colonization. Novel therapeutic strategies are currently being developed to ameliorate transporter defects in the setting of inflammation or bacterial infection including, for example, administration of probiotics and fecal microbiota transplantation. This review will highlight recent findings in the literature detailing these aspects of ion transport in the inflamed gut.