Xylobiose treatment strengthens intestinal barrier function by regulating claudin 2 and heat shock protein 27 expression in human Caco-2 cells

BACKGROUND

Xylobiose, a non-digestible disaccharide, largely contributes to the beneficial physiological effects of xylooligosaccharides. However, there is insufficient evidence to assess the direct effect of xylobiose on intestinal barrier function. Here, we investigated the intestinal barrier function in human intestinal Caco-2 cells treated with xylobiose.

RESULTS

In total, 283 genes were upregulated and 256 genes were downregulated in xylobiose-treated Caco-2 cells relative to the controls. We focused on genes related to intestinal barrier function, such as tight junction (TJ) and heat shock protein (HSP). Xylobiose decreased the expression of the TJ gene Claudin 2 (CLDN2) and increased the expression of the cytoprotective HSP genes HSPB1 and HSPA1A, which encode HSP27 and HSP70, respectively. Immunoblot analysis confirmed that xylobiose suppressed CLDN2 expression and enhanced HSP27 and HSP70 expression. A quantitative reverse transcription-PCR and promoter assays indicated that xylobiose post-transcriptionally regulated CLDN2 and HSPB1 levels. Additionally, selective inhibition of phosphatidyl-3-inositol kinase (PI3K) inhibited xylobiose-mediated CLDN2 expression, whereas HSP27 expression induced by xylobiose was sensitive to the inhibition of PI3K, mitogen-activated protein kinase kinase and Src.

CONCLUSION

The results of the present study reveal that xylobiose suppresses CLDN2 and increases HSP27 expression in intestinal Caco-2 cells via post-transcriptional regulation, potentially strengthening intestinal barrier integrity; however, these effects seem to occur via different signaling pathways. Our findings may help to assess the physiological role of xylobiose. © 2023 Society of Chemical Industry.

SLC16a6, mTORC1, and Autophagy Regulate Ketone Body Excretion in the Intestinal Cells

Ketone bodies serve several functions in the intestinal epithelium, such as stem cell maintenance, cell proliferation and differentiation, and cancer growth. Nevertheless, there is limited understanding of the mechanisms governing the regulation of intestinal ketone body concentration. In this study, we elucidated the factors responsible for ketone body production and excretion using shRNA-mediated or pharmacological inhibition of specific genes or functions in the intestinal cells. We revealed that a fasting-mimicked culture medium, which excluded glucose, pyruvate, and glutamine, augmented ketone body production and excretion in the Caco2 and HT29 colorectal cells. This effect was attenuated by glucose or glutamine supplementation. On the other hand, the inhibition of the mammalian target of rapamycin complex1 (mTORC1) recovered a fraction of the excreted ketone bodies. In addition, the pharmacological or shbeclin1-mediated inhibition of autophagy suppressed ketone body excretion. The knockdown of basigin, a transmembrane protein responsible for targeting monocarboxylate transporters (MCTs), such as MCT1 and MCT4, suppressed lactic acid and pyruvic acid excretion but increased ketone body excretion. Finally, we found that MCT7 (SLC16a6) knockdown suppressed ketone body excretion. Our findings indicate that the mTORC1-autophagy axis and MCT7 are potential targets to regulate ketone body excretion from the intestinal epithelium.

Partially hydrolyzed guar gum upregulates heat shock protein 27 in intestinal Caco-2 cells and mouse intestine via mTOR and ERK signaling

BACKGROUND

The intestinal epithelium acts as a barrier against harmful luminal materials, thus preventing intestinal diseases and maintaining intestinal health. Heat shock protein 27 (HSP27) promotes intestinal epithelial integrity under both physiological and stressed conditions. The effects of partially hydrolyzed guar gum (PHGG) on HSP27 expression in intestinal Caco-2 cells and mouse intestines were investigated.

RESULTS

The present study showed that PHGG upregulated HSP27 expression in Caco-2 cells without upregulating Hspb1, the gene encoding HSP27. Feeding PHGG increased HSP25 expression in epithelial cells of the small intestine of mice. Inhibition of protein translation using cycloheximide suppressed PHGG-mediated HSP27 expression, indicating that PHGG upregulated HSP27 via translational modulation. Signaling inhibition of the mechanistic target of rapamycin (mTOR) and phosphatidyl 3-inositol kinase reduced PHGG-mediated HSP27 expression, whereas mitogen-activated protein kinase kinase inhibition by U0126 increased HSP27 expression, irrespective of PHGG administration. PHGG increases mTOR phosphorylation and reduces extracellular signal-regulated protein kinase (ERK) phosphorylation.

CONCLUSION

PHGG-mediated translation of HSP27 in intestinal Caco-2 cells and mouse intestine via the mTOR and ERK signaling pathways may promote intestinal epithelial integrity. These findings help us better understand how dietary fibers regulate the physiological function of the intestines. © 2023 Society of Chemical Industry.

Propofol Affects EGF's Activity in Intestinal Cell by Down-Regulating EGFR-Mediated Intracellular Signaling

Propofol is a commonly used anesthetic drug in clinic. In recent years, a series of non-anesthetic effects of propofol have been discovered. Studies have shown that propofol has many effects on the intestine. Epidermal growth factor (EGF) is one of the most important growth factors that could regulate intestinal growth and development. In the current study, we studied the effect of protocol on the biological activity of EGF on intestinal tissue and cell models. Through flow cytometry, indirect immunofluorescence and Western-blot and other technologies, it was found that propofol reduced the activity of EGF on intestinal cells, which inhibited EGF-induced intestinal cell proliferation and changed the cell behavior of EGF. To further explore the potential mechanism by which propofol down-regulated epidermal growth factor receptor (EGFR)-induced signaling, we carried out a series of related experiments, and found that propofol may inhibit the proliferation of intestinal cells by inhibiting the EGFR-mediated intracellular signaling pathway. The current research will lay the theoretical and experimental basis for further study of the effect of propofol on the intestine.

The Hippo Pathway Effector YAP1 Regulates Intestinal Epithelial Cell Differentiation

The human intestine is covered by epithelium, which is continuously replaced by new cells provided by stem cells located at the bottom of the glands. The maintenance of intestinal stem cells is supported by a niche which is composed of several signaling proteins including the Hippo pathway effectors YAP1/TAZ. The role of YAP1/TAZ in cell proliferation and regeneration is well documented but their involvement on the differentiation of intestinal epithelial cells is unclear. In the present study, the role of YAP1/TAZ on the differentiation of intestinal epithelial cells was investigated using the HT29 cell line, the only multipotent intestinal cell line available, with a combination of knockdown approaches. The expression of intestinal differentiation cell markers was tested by qPCR, Western blot, indirect immunofluorescence and electron microscopy analyses. The results show that TAZ is not expressed while the abolition of YAP1 expression led to a sharp increase in goblet and absorptive cell differentiation and reduction of some stem cell markers. Further studies using double knockdown experiments revealed that most of these effects resulting from YAP1 abolition are mediated by CDX2, a key intestinal cell transcription factor. In conclusion, our results indicate that YAP1/TAZ negatively regulate the differentiation of intestinal epithelial cells through the inhibition of CDX2 expression.

A Novel Role for the Klebsiella pneumoniae Sap (Sensitivity to Antimicrobial Peptides) Transporter in Intestinal Cell Interactions, Innate Immune Responses, Liver Abscess, and Virulence

Klebsiella pneumoniae is an important human pathogen causing hospital-acquired and community-acquired infections. Systemic K. pneumoniae infections may be preceded by gastrointestinal colonization, but the basis of this bacterium’s interaction with the intestinal epithelium remains unclear. Here, we report that the K. pneumoniae Sap (sensitivity to antimicrobial peptides) transporter contributes to bacterial–host cell interactions and in vivo virulence. Gene deletion showed that sapA is required for the adherence of a K. pneumoniae blood isolate to intestinal epithelial, lung epithelial, urinary bladder epithelial, and liver cells. The ΔsapA mutant was deficient for translocation across intestinal epithelial monolayers, macrophage interactions, and induction of proinflammatory cytokines. In a mouse gastrointestinal infection model, ΔsapA yielded significantly decreased bacterial loads in liver, spleen and intestine, reduced liver abscess generation, and decreased mortality. These findings offer new insights into the pathogenic interaction of K. pneumoniae with the host gastrointestinal tract to cause systemic infection.

Enterococcus faecalis Isolated From Infant Feces Inhibits Toxigenic Clostridioides (Clostridium) difficile

Clostridioides (Clostridium) difficile infection is implicated as a major cause of antibiotic-associated diarrhea in hospitals worldwide. Probiotics, especially lactic acid bacteria, are the most frequently used alternative treatment. This study aims to identify potential probiotic enterococci strains that act against C. difficile strains and exert a protective effect on colon adenocarcinoma cells (HT-29 cells). To this end, nine Enterococcus strains isolated from the feces of breast-fed infants were investigated. They were identified as E. faecalis by 16s rRNA sequencing and MALDI-TOF. The probiotic properties including their viabilities in simulated gastrointestinal condition, cell adhesion ability, and their safety were evaluated. All strains exhibited more tolerance toward both pepsin and bile salts and adhered more tightly to HT-29 cells compared with the reference probiotic strain Lactobacillus plantarum ATCC 14917. Polymerase chain reaction (PCR) results exhibited that six of nine strains carried at least one virulence determinant gene; however, none exhibited virulence phenotypes or carried transferable antibiotic resistance genes. These strains did not infect Galleria mellonella when compared to pathogenic E. faecalis strain (p < 0.05). Moreover, their antibacterial activities against C. difficile were examined using agar well-diffusion, spore production, and germination tests. The six safe strains inhibited spore germination (100 - 98.20% ± 2.17%) and sporulation, particularly in C. difficile ATCC 630 treated with E. faecalis PK 1302. Furthermore, immunofluorescence assay showed that the cytopathic effects of C. difficile of HT-29 cells were reduced by the treatment with the cell-free supernatant of E. faecalis strains. These strains prevented rounding of HT-29 cells and preserved the F-actin microstructure and tight junctions between adjacent cells, which indicated their ability to reduce the clostridial cytopathic effects. Thus, the study identified six E. faecalis isolates that have anti-C. difficile activity. These could be promising probiotics with potential applications in the prevention of C. difficile colonization and treatment of C. difficile infection.

Invited review: Dairy proteins and bioactive peptides: Modeling digestion and the intestinal barrier

Dairy products are one of the most important sources of biologically active proteins and peptides. The health-promoting functions of these peptides are related to their primary structure, which depends on the parent protein composition. A crucial issue in this field is the demonstration of a cause-effect relationship from the ingested protein form to the bioactive form in vivo. Intervention studies represent the gold standard in nutritional research; however, attention has increasingly been focused on the development of sophisticated in vitro models of digestion to elucidate the mechanism of action of dairy nutrients in a mechanistic way and significantly reduce the number of in vivo trials. On the other hand, the epithelial intestinal barrier is the first gate that actively interacts with digestion metabolites, making the intestinal cells the first target tissue of dairy nutrients and respective metabolites. An evolution of the in vitro digestion approach in the study of dairy proteins and derived bioactive compounds is the setup of combined in vitro digestion and cell culture models taking into consideration the endpoint to measure the target organism (e.g., animal, human) and the key concepts of bioaccessibility, bioavailability, and bioactivity. This review discusses the relevance and challenges of modeling digestion and the intestinal barrier, focusing on the implications for the modeling of dairy protein digestion for bioactivity evaluation.

High Iron-Sequestrating Bifidobacteria Inhibit Enteropathogen Growth and Adhesion to Intestinal Epithelial Cells In vitro

The gut microbiota plays an important role in host health, in particular by its barrier effect and competition with exogenous pathogenic bacteria. In the present study, the competition of Bifidobacterium pseudolongum PV8-2 (Bp PV8-2) and Bifidobacterium kashiwanohense PV20-2 (Bk PV20-2), isolated from anemic infant gut microbiota and selected for their high iron sequestration properties, was investigated against Salmonella Typhimurium (S. Typhi) and Escherichia coli O157:H45 (EHEC) by using co-culture tests and assays with intestinal cell lines. Single and co-cultures were carried out anaerobically in chemically semi-defined low iron (1.5 μM Fe) medium (CSDLIM) without and with added ferrous iron (30 μM Fe). Surface properties of the tested strains were measured by bacterial adhesion to solvent xylene, chloroform, ethyl acetate, and to extracellular matrix molecules, mucus II, collagen I, fibrinogen, fibronectin. HT29-MTX mucus-secreting intestinal cell cultures were used to study bifidobacteria competition, inhibition and displacement of the enteropathogens. During co-cultures in CSDLIM we observed strain-dependent inhibition of bifidobacterial strains on enteropathogens, independent of pH, organic acid production and supplemented iron. Bp PV8-2 significantly (P < 0.05) inhibited S. Typhi N15 and EHEC after 24 h compared to single culture growth. In contrast Bk PV20-2 showed less inhibition on S. Typhi N15 than Bp PV8-2, and no inhibition on EHEC. Affinity for intestinal cell surface glycoproteins was strain-specific, with high affinity of Bp PV8-2 for mucin and Bk PV20-2 for fibronectin. Bk PV20-2 showed high adhesion potential (15.6 ± 6.0%) to HT29-MTX cell layer compared to Bp PV8-2 (1.4 ± 0.4%). In competition, inhibition and displacement tests, Bp PV8-2 significantly (P < 0.05) reduced S. Typhi N15 and EHEC adhesion, while Bk PV20-2 was only active on S. Typhi N15 adhesion. To conclude, bifidobacterial strains selected for their high iron binding properties inhibited S. Typhi N15 and EHEC in co-culture experiments and efficiently competed with the enteropathogens on mucus-producing HT29-MTX cell lines. Further studies in complex gut ecosystems should explore host protection effects of Bp PV8-2 and Bk PV20-2 mediated by nutritional immunity mechanism associated with iron-binding.

Endotoxin and Kupffer cell activation in alcoholic liver disease

One central component in the complex network of processes leading to the development of alcoholic liver disease is the activation of immune cells residing in the liver (i.e., Kupffer cells) by a substance called endotoxin, which is released by bacteria living in the intestine. Alcohol consumption can lead to increased endotoxin levels in the blood and liver. When activated, Kupffer cells produce signaling molecules (i.e., cytokines) that promote inflammatory reactions as well as molecules called reactive oxygen species (ROS), which can damage liver cells. Endotoxin activates Kupffer cells by interacting with a complex of protein molecules that are located on the outside of the Kupffer cell or which extend into the cell. Binding of endotoxin alters the activities of the proteins in this complex so that they trigger a cascade of biochemical signals in the Kupffer cell, resulting in cytokine and ROS production and, ultimately, liver damage. Because alcohol can enhance endotoxin release and, therefore, Kupffer cell activation, novel approaches to inhibit these processes might help prevent or ameliorate alcoholic liver disease.

Growth of fastidious adenovirus serotype 40 in HRT 18 cells: interactions with E1A and E1B deletion mutants of subgenus C adenoviruses

Growth of fastidious adenovirus serotype 40 (Ad40) in several cell lines was investigated. Ad40 was able to readily propagate in human intestinal cell line, HRT 18. Coinfection assays were made in non-permissive and permissive cells between Ad40 and Ad5dl312 or dl1520, mutants deleted in E1A and E1B regions, respectively, to test the ability of Ad40 to complement these mutants and vice versa. Ad40 could enhance Ad5dl312 DNA synthesis in HRT18 and HeLa cells, although its own DNA disappeared in the presence of this mutant in HRT18 cells. In coinfection with dl1520, Ad40 DNA synthesis was inhibited by dl1520 in HRT18 cells and dl1520 DNA synthesis was inhibited by Ad40 in 293 cells. This might reflect the presence of unusual products encoded by Ad40 E1B region.