Transcriptome Analysis Identifies Strategies Targeting Immune Response-Related Pathways to Control Enterotoxigenic Escherichia coli Infection in Porcine Intestinal Epithelial Cells

Uncovering the mechanism of Clostridium butyricum CBX 2021 to improve pig health based on in vivo and in vitro studies

Introduction

As a symbiotic probiotic for the host, Clostridium butyricum (CB) has the potential to strengthen the body's immune system and improve intestinal health. However, the probiotic mechanism of CB is not completely understood. The Clostridium butyricum CBX 2021 strain isolated by our team from a health pig independently exhibits strong butyric acid production ability and stress resistance. Therefore, this study comprehensively investigated the efficacy of CBX 2021 in pigs and its mechanism of improving pig health.

Methods

In this study, we systematically revealed the probiotic effect and potential mechanism of the strain by using various methods such as microbiome, metabolites and transcriptome through animal experiments in vivo and cell experiments in vitro.

Results

Our in vivo study showed that CBX 2021 improved growth indicators such as daily weight gain in weaned piglets and also reduced diarrhea rates. Meanwhile, CBX 2021 significantly increased immunoglobulin levels in piglets, reduced contents of inflammatory factors and improved the intestinal barrier. Subsequently, 16S rRNA sequencing showed that CBX 2021 treatment implanted more butyric acid-producing bacteria (such as Faecalibacterium) in piglets and reduced the number of potentially pathogenic bacteria (like Rikenellaceae RC9_gut_group). With significant changes in the microbial community, CBX 2021 improved tryptophan metabolism and several alkaloids synthesis in piglets. Further in vitro experiments showed that CBX 2021 adhesion directly promoted the proliferation of a porcine intestinal epithelial cell line (IPEC-J2). Moreover, transcriptome analysis revealed that bacterial adhesion increased the expression of intracellular G protein-coupled receptors, inhibited the Notch signaling pathway, and led to a decrease in intracellular pro-inflammatory molecules.

Discussion

These results suggest that CBX 2021 may accelerate piglet growth by optimizing the intestinal microbiota, improving metabolic function and enhancing intestinal health.

Antimicrobial Activity and Mechanisms of Walnut Green Husk Extract

Walnut green husks (WGHs), by-products of walnut production, are believed to possess antimicrobial properties, making them a potential alternative to antibiotics. In this study, the antibacterial activities of three extracts, derived from WGH, against Staphylococcus aureus, Bacillus subtilis, and Escherichia coli were investigated, and the antibacterial mechanisms of an anhydrous ethanol extract of WGH (WGHa) were examined. The results showed that WGHa exhibited inhibitory effects on all tested bacteria. The ultrahigh-performance liquid chromatography-tandem mass spectrometry analysis revealed that the major active compounds present in WGHa were terpenoids, phenols, and flavonoids. Treatment with WGHa resulted in the leakage of intracellular ions and alkaline phosphatase; a reduction in intracellular ATP content, ATPase activity, and nucleic acid content; as well as cellular metabolic viability. The transmission electron microscopy images showed varying degrees of cell deformation and membrane damage following WGHa treatment. The transcriptome sequencing and differentially expressed gene enrichment analyses revealed an up-regulation in pathways associated with RNA degradation, translation, protein export, and oxidative phosphorylation. Conversely, pathways involved in cell movement and localization, as well as cell wall organization and carbohydrate transport, were found to be down-regulated. These findings suggest that WGHa alters cell membrane permeability and causes damage to the cell wall. Additionally, WGHa interferes with cellular energy metabolism, compromises RNA integrity, and induces DNA replication stress, consequently inhibiting the normal growth and proliferation of bacteria. These findings unveiled the antimicrobial mechanisms of WGHa, highlighting its potential application as an antibiotic alternative.

Effects on the intestinal morphology, inflammatory response and microflora in piglets challenged with enterotoxigenic Escherichia coli K88

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea in piglets, which leads to great economic losses. In this study, the ternary crossbred weaned piglets were orally administered with 1.5 × 10¹¹ CFU ETEC K88 for three days. The results showed the ratio of villus length to crypt depth decreased in the duodenum and ileum after ETEC K88 infection. The expression of tight junction proteins ZO-1 in the jejunum and ileum, occludin in the jejunum and colon, and claudin-1 in the colon were down-regulated. The expression of IL-8 in the duodenum and jejunum, IL-13 in the colon, and TNF-α in the jejunum and colon were up-regulated. The expression of pBD1 in the colon, pBD2 in the jejunum, and pBD3 in the duodenum increased after infection. Meanwhile, the expression of TLR4, p38 MAPK and NF-κB p65 increased in all intestinal segments. Moreover, the expression of IL-8 in superficial cervical lymph nodes (SCLN), TNF-α in mesenteric lymph nodes (MLN), and IL-13 in inguinal lymph nodes (ILN) and MLN were up-regulated. The expression of pBD1 and pBD2 in SCLN and MLN, and pBD3 in SCLN were up-regulated. Acidobacteria and Proteobacteria were the most abundant phyla in both groups by analysis of intestinal microflora using 16 s rRNA sequencing, and the relative abundances of bacteria were found to be changed by Metastats software and LEfSe analysis. Our results indicated that cytokines and pBDs had different roles in different intestinal segments or different lymph nodes against ETEC K88, and gut microbiota was influenced after infection.

Integration of the Microbiome, Metabolome and Transcriptome Reveals Escherichia coli F17 Susceptibility of Sheep

Escherichia coli (E. coli) F17 is one of the most common pathogens causing diarrhea in farm livestock. In the previous study, we accessed the transcriptomic and microbiomic profile of E. coli F17-antagonism (AN) and -sensitive (SE) lambs; however, the biological mechanism underlying E. coli F17 infection has not been fully elucidated. Therefore, the present study first analyzed the metabolite data obtained with UHPLC-MS/MS. A total of 1957 metabolites were profiled in the present study, and 11 differential metabolites were identified between E. coli F17 AN and SE lambs (i.e., FAHFAs and propionylcarnitine). Functional enrichment analyses showed that most of the identified metabolites were related to the lipid metabolism. Then, we presented a machine-learning approach (Random Forest) to integrate the microbiome, metabolome and transcriptome data, which identified subsets of potential biomarkers for E. coli F17 infection (i.e., GlcADG 18:0-18:2, ethylmalonic acid and FBLIM1); furthermore, the PCCs were calculated and the interaction network was constructed to gain insight into the crosstalk between the genes, metabolites and bacteria in E. coli F17 AN/SE lambs. By combing classic statistical approaches and a machine-learning approach, our results revealed subsets of metabolites, genes and bacteria that could be potentially developed as candidate biomarkers for E. coli F17 infection in lambs.

Lactiplantibacillus plantarum Strains Modulate Intestinal Innate Immune Response and Increase Resistance to Enterotoxigenic Escherichia coli Infection

Currently, probiotic bacteria with not transferable antibiotic resistance represent a sustainable strategy for the treatment and prevention of enterotoxigenic Escherichia coli (ETEC) in farm animals. Lactiplantibacillus plantarum is among the most versatile species used in the food industry, either as starter cultures or probiotics. In the present work, the immunobiotic potential of L. plantarum CRL681 and CRL1506 was studied to evaluate their capability to improve the resistance to ETEC infection. In vitro studies using porcine intestinal epithelial (PIE) cells and in vivo experiments in mice were undertaken. Expression analysis indicated that both strains were able to trigger IL-6 and IL-8 expression in PIE cells in steady-state conditions. Furthermore, mice orally treated with these strains had significantly improved levels of IFN-γ and TNF-α in the intestine as well as enhanced activity of peritoneal macrophages. The ability of CRL681 and CRL1506 to beneficially modulate intestinal immunity was further evidenced in ETEC-challenge experiments. In vitro, the CRL1506 and CRL681 strains modulated the expression of inflammatory cytokines (IL-6) and chemokines (IL-8, CCL2, CXCL5 and CXCL9) in ETEC-stimulated PIE cells. In vivo experiments demonstrated the ability of both strains to beneficially regulate the immune response against this pathogen. Moreover, the oral treatment of mice with lactic acid bacteria (LAB) strains significantly reduced ETEC counts in jejunum and ileum and prevented the spread of the pathogen to the spleen and liver. Additionally, LAB treated-mice had improved levels of intestinal IL-10 both at steady state and after the challenge with ETEC. The protective effect against ETEC infection was not observed for the non-immunomodulatory TL2677 strain. Furthermore, the study showed that L. plantarum CRL1506 was more efficient than the CRL681 strain to modulate mucosal immunity highlighting the strain specific character of this probiotic activity. Our results suggest that the improved intestinal epithelial defenses and innate immunity induced by L. plantarum CRL1506 and CRL681 would increase the clearance of ETEC and at the same time, protect the host against detrimental inflammation. These constitute valuable features for future probiotic products able to improve the resistance to ETEC infection.

Recombinant porcine beta defensin 2 alleviates inflammatory responses induced by Escherichia coli in IPEC-J2 cells

pBD2 is one of the porcine beta defensins with broad antimicrobial activity, and plays an important role in immune regulation. However, the activities and mechanisms of pBD2 regulating host resistance to Escherichia coli infection are unclear. In this study, the immunomodulatory activity and mechanisms of recombinant pBD2 against Escherichia coli infection were explored in IPEC-J2 cells. Recombinant pBD2 had no obvious effect on the growth of cells below 80 μg/mL, however, it reduced the number of E. coli adhering to cells. Furthermore, pBD2 restored the abnormal expression of ZO-1 and occludin in cells challenged with E. coli. pBD2 treatment also reduced cell apoptosis and decreased the expression of the apoptosis-related genes Cox-2 and Caspase-3, and decreased the expression of the pro-inflammatory IL-6, IL-8, IL-1α and TNF-α, and Cxcl2 and Ccl20. pBD2 also reduced the expression of TAK1, and inhibited the phosphorylation of NF-κB p65 following E. coli infection. In addition, pBD2 was localized in the cytoplasm. Collectively, pBD2 appeared to penetrate cells and alleviate inflammatory responses via the TAK1-NF-κB signaling pathway. Our results revealed the immunomodulatory activity of recombinant pBD2 against E. coli and provided insights into the molecular mechanisms that protected cells from E. coli infection.

Barrier Perturbation in Porcine Peyer’s Patches by Tumor Necrosis Factor is Associated With a Dysregulation of Claudins

The proinflammatory cytokine tumor necrosis factor (TNF) has been described as one of the main mediators of intestinal inflammatory diseases, affecting the composition of tight junction (TJ) proteins and leading to a disruption of the epithelial barrier. An intact intestinal barrier is mandatory, because the follicle-associated epithelium of Peyer’s patches represents the first defense line of the intestinal immune system and ensures a controlled uptake of antigens from the gut lumen. In the current study, we have analyzed the detailed effects of TNF on the follicle-associated epithelium of porcine Peyer’s patches by applying the Ussing chamber technique. Epithelial tissue specimens of Peyer’s patches and the surrounding villus epithelium were mounted into conventional Ussing chambers and incubated with TNF for 10 h. The transepithelial resistance, representing epithelial barrier function of the tissue, was recorded. A reduction of transepithelial resistance was detected after 8 h in Peyer’s patch tissue specimens, whereas the villus epithelium was not significantly affected by TNF. Subsequent molecular analysis of TJ protein expression revealed a marked decrease of claudin-1 and -4, and an increase of claudin-2. In neighboring villus epithelium, no significant changes in the expression of TJ proteins could be shown. A strong increase of TNF receptor-2 (TNFR-2) could also be detected in Peyer’s patches, in agreement with the major role of this receptor in Peyer’s patches. Our findings were in accordance with changes detected by confocal laser scanning immunofluorescence microscopy. The regulation of TNF effects via myosin light chain kinase (MLCK) was analyzed in blocking experiments. Our detailed analysis is the first to show that TNF affects the barrier function of the follicle-associated epithelium of porcine Peyer’s patches but has no effects on the villus epithelium. These findings reveal not only the basic differences of epithelial barrier function between the two structures, but also the significance of Peyer’s patches as a primary mucosal immune defense.