Effects of Clostridium perfringens beta2 toxin on apoptosis, inflammation, and barrier function of intestinal porcine epithelial cells

Injury of Macrophages Induced by Clostridium perfringens Type C Exotoxins

Clostridium perfringens is a kind of anaerobic Gram-positive bacterium that widely exists in the intestinal tissue of humans and animals. And the main virulence factor in Clostridium perfringens is its exotoxins. Clostridium perfringens type C is the main strain of livestock disease, its exotoxins can induce necrotizing enteritis and enterotoxemia, which lead to the reduction in feed conversion, and a serious impact on breeding production performance. Our study found that treatment with exotoxins reduced cell viability and triggered intracellular reactive oxygen species (ROS) in human mononuclear leukemia cells (THP-1) cells. Through transcriptome sequencing analysis, we found that the levels of related proteins such as heme oxygenase 1 (HO-1) and ferroptosis signaling pathway increased significantly after treatment with exotoxins. To investigate whether ferroptosis occurred after exotoxin treatment in macrophages, we confirmed that the protein expression levels of antioxidant factors glutathione peroxidase 4/ferroptosis-suppressor-protein 1/the cystine/glutamate antiporter solute carrier family 7 member 11 (GPX4/FSP1/xCT), ferroptosis-related protein nuclear receptor coactivator 4/transferrin/transferrin receptor (NCOA4/TF/TFR)/ferritin and the level of lipid peroxidation were significantly changed. Based on the above results, our study suggested that Clostridium perfringens type C exotoxins can induce macrophage injury through oxidative stress and ferroptosis.

Lipopolysaccharides from a Shiraia fruiting body-associated bacterium elicit host fungal hypocrellin A biosynthesis through nitric oxide generation

Hypocrellin A (HA) is an excellent perylenequinone photosensitizer from Shiraia fruiting bodies. A dominant bacterium Pseudomonas fulva SB1 in the fruiting body was found to promote HA biosynthesis. The bacterial LPS were purified and the O-specific polysaccharide (OPS) consisted of rhamnose (Rha), galactose (Gal) and N-acetyl-galactosamine (GalNAc) with an average molecular weight of 282.8 kDa. Although the OPS composing of Rhap and Galp backbone showed elicitation capability on fungal HA accumulation, the highest HA production (303.76 mg/L) was achieved by LPS treatment at 20 μg/mL on day 3 of the mycelium culture. The generation of nitric oxide (NO) in Shiraia mycelia was triggered by LPS, which was partially blocked by inhibitors of nitric oxide synthase (NOS) and nitrate reductase (NR), leading to the depressed HA production. Transcriptome analysis revealed that NO mediated LPS-induced HA production via upregulating the expressions of critical genes associated with central carbon metabolism and downstream HA biosynthesis genes. This is the first report of LPS-induced NO to regulate fungal secondary metabolite production, which provides new insights on the role of bacterial LPS in bacterium-fungus interactions and an effective strategy to enhance hypocrellin production.

High Prevalence of Multidrug-Resistant, Biofilm-Forming Virulent Clostridium perfringens in Broiler Chicken Retail Points in Northeast India

In light of the significant public health and food safety implications associated with Clostridium perfringens, this study aimed to isolate and characterize C. perfringens in samples obtained from broiler chicken retail points in Meghalaya, northeastern India. A total of 280 samples comprising meat, intestinal contents, water, and hand swabs were processed to detect contamination by C. perfringens. The isolates were subjected to toxinotyping, antimicrobial susceptibility testing, and biofilm-forming ability test. The overall occurrence of C. perfringens was 22.5% (17.74-27.85, 95% CI) with the highest recovery from intestine samples (31%; 22.13-41.03, 95% CI), followed by meat (23%, 15.17-32.49, 95% CI) and water samples (18%, 8.58-31.44, 95% CI). Type A was the predominant toxinotype (71.43%, 58.65-82.11, 95% CI), followed by Type A with beta2 toxin (17.46%, 9.05-29.10, 95% CI), Type C (7.94%, 2.63-17.56, 95% CI), and Type C with beta2 toxin (3.17%, 0.39-11.0, 95% CI). Nearly all (95.24%) isolates were multidrug resistant and 68.25% were biofilm formers. The predominance of multidrug-resistant and virulent Type A and Type C C. perfringens in retail broiler meat and intestines in the tribal-dominated northeastern region of India is of great concern from food safety and public health perspectives.

Longan Polysaccharides with Covalent Selenylation Combat the Fumonisin B1-Induced Cell Toxicity and Barrier Disruption in Intestinal Epithelial (IEC-6) Cells

In this study, the soluble, but non-digestible, longan (Dimocarpus longan Lour.) polysaccharides (LP) were extracted from dried longan fruits and then chemically selenylated to produce two selenylated products, namely SeLP1 and SeLP2, with different selenylation extents. The aim was to investigate their protective effects on rat intestinal epithelial (IEC-6) cells exposed to the food toxin fumonisin B1 (FB1). LP only contained total Se content of less than 0.01 g/kg, while SeLP1 and SeLP2 were measured with respective total Se content of up to 1.46 and 4.79 g/kg. The cell viability results showed that these two selenylated products were more efficient than LP in the IEC-6 cells in alleviating FB1-induced cell toxicity, suppressing lactate dehydrogenase (LDH) release, and decreasing the generation of intracellular reactive oxygen species (ROS). These two selenylated products were also more effective than LP in combating FB1-induced barrier disruption via increasing the transepithelial electric resistance (TEER), reducing the paracellular permeability, decreasing the mitochondrial membrane potential (MMP) loss, and maintaining cell barrier integrity by upregulating the tight-junction-related genes and proteins. FB1 caused cell oxidative stress and barrier dysfunction by activating the MAPK and mitochondrial apoptosis signaling pathways, while SeLP1 and SeLP2 could regulate the tMAPK- and apoptosis-related proteins to suppress the FB1-mediated activation of the two pathways. Overall, SeLP2 was observed to be more active than SeLP1 in the IEC-6 cells. In conclusion, the chemical selenylation of LP caused an activity enhancement to ameliorate the FB1-induced cell cytotoxicity and intestinal barrier disruption. Meanwhile, the increased selenylation of LP would endow the selenylated product SeLP2 with more activity.

Molecular mechanism of Enteroaggregative Escherichia coli induced apoptosis in cultured human intestinal epithelial cells

Background. Enteroaggregative Escherichia coli (EAEC) is an evolving etiological agent of acute and persistent diarrhoea worldwide. The previous study from our laboratory has reported the apoptosis-inducing activity of EAEC in human small intestinal and colonic epithelial cell lines. In the present investigation, we have explored the underlying mechanism of EAEC-induced apoptosis in human intestinal epithelial cell lines.Methods. INT-407 and HCT-15 cells were infected with EAEC-T8 and EAEC-pT8 (plasmid cured strain of EAEC-T8) separately. Cells cultured in the absence of bacteria served as a negative control in all the experiments. For the subsequent experiments, the molecular mechanism(s) of epithelial cell aposptosis was measured in EAEC infecting both the cell lines by flow cytometry, real-time PCR and Western blotting.Results and conclusions. EAEC was found to activate the intrinsic/mitochondrial apoptotic pathway in both the cell lines through upregulation of pro-apoptotic Bax and Bak, un-alteration/reduction in the level of anti-apoptotic Bcl-2 and Bcl-XL, decrease in mitochondrial transmembrane potential, accumulation of cytosolic cytochrome c leading to activation of procaspase-9 and procaspase-3, which ultimately resulted in DNA fragmentation and apoptosis. Further, an increased expression of Fas, activation of procaspase-8 and upregulation of pro-apoptotic Bid in the EAEC-infected cells indicated the involvement of extrinsic apoptotic pathway too in this process. Our finding has undoubtedly led to an increased understanding of EAEC pathogenesis, which may be helpful to develop an improved strategy to combat the infection.

Gut Microbiota Taxon-Dependent Transformation of Microglial M1/M2 Phenotypes Underlying Mechanisms of Spatial Learning and Memory Impairment after Chronic Methamphetamine Exposure

Methamphetamine (METH) exposure may lead to cognitive impairment. Currently, evidence suggests that METH exposure alters the configuration of the gut microbiota. However, the role and mechanism of the gut microbiota in cognitive impairment after METH exposure are still largely unknown. Here, we investigated the impact of the gut microbiota on the phenotype status of microglia (microglial phenotypes M1 and microglial M2) and their secreting factors, the subsequent hippocampal neural processes, and the resulting influence on spatial learning and memory of chronically METH-exposed mice. We determined that gut microbiota perturbation triggered the transformation of microglial M2 to M1 and a subsequent change of pro-brain-derived neurotrophic factor (proBDNF)-p75NTR-mature BDNF (mBDNF)-TrkB signaling, which caused reduction of hippocampal neurogenesis and synaptic plasticity-related proteins (SYN, PSD95, and MAP2) and, consequently, deteriorated spatial learning and memory. More specifically, we found that Clostridia, Bacteroides, Lactobacillus, and Muribaculaceae might dramatically affect the homeostasis of microglial M1/M2 phenotypes and eventually contribute to spatial learning and memory decline after chronic METH exposure. Finally, we found that fecal microbial transplantation could protect against spatial learning and memory decline by restoring the microglial M1/M2 phenotype status and the subsequent proBDNF-p75NTR/mBDNF-TrkB signaling in the hippocampi of chronically METH-exposed mice. IMPORTANCE Our study indicated that the gut microbiota contributes to spatial learning and memory dysfunction after chronic METH exposure, in which microglial phenotype status plays an intermediary role. The elucidated "specific microbiota taxa-microglial M1/M2 phenotypes-spatial learning and memory impairment" pathway would provide a novel mechanism and elucidate potential gut microbiota taxon targets for the no-drug treatment of cognitive deterioration after chronic METH exposure.

Overexpression of SIRT1 alleviates oxidative damage and barrier dysfunction in CPB2 toxin-infected IPEC-J2 cells

Clostridium perfringens (C. perfringens) beta2 (CPB2) toxin may induce necrotizing enteritis (NE) in pigs. Sirtuin1 (SIRT1) is involved in inflammatory intestinal diseases and affects intestinal barrier function. However, the effects of SIRT1 on piglet intestinal disease caused by CPB2 toxin are unclear. This study revealed the role of pig SIRT1 in CPB2 toxin-exposed intestinal porcine epithelial cells (IPEC-J2). Herein, we manifested that SIRT1 was dramatically decreased in IPEC-J2 cells infected with CPB2 toxin. Subsequently, we silenced and overexpressed SIRT1 using siRNA and a overexpression vector in CPB2 toxin-treated IPEC-J2 cells. The results indicated that overexpression of SIRT1 suppressed reactive oxygen species (ROS) generates, the expression tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and Bax, nuclear factor-kappa B (NF-κB p65), phospho (p)-NF-kB p65 and lactate dehydrogenase (LDH) activity and apoptosis in CPB2 toxin-treated IPEC-J2 cells, and increased IL-10, mitochondrial membrane potential (ΔΨm), Bcl-2, Claudin1 and Occludin levels and cell viability. These results indicated that SIRT1 protects IPEC-J2 cells against CPB2 toxin-induced oxidative damage and tight junction (TJ) disruption, which provides a theoretical basis for further study of the molecular regulatory mechanism of SIRT1 in C. perfringens-infected NE in piglets.

Identification of a Novel lncRNA LNC_001186 and Its Effects on CPB2 Toxin-Induced Apoptosis of IPEC-J2 Cells

The Clostridium perfringens (C. perfringen) beta2 (CPB2) toxin produced by C. perfringens type C (CpC) can cause necrotizing enteritis in piglets. Immune system activation in response to inflammation and pathogen infection is aided by long non-coding RNAs (lncRNAs). In our previous work, we revealed the differential expression of the novel lncRNA LNC_001186 in CpC-infected ileum versus healthy piglets. This implied that LNC_001186 may be a regulatory factor essential for CpC infection in piglets. Herein, we analyzed the coding ability, chromosomal location and subcellular localization of LNC_001186 and explored its regulatory role in CPB2 toxin-induced apoptosis of porcine small intestinal epithelial (IPEC-J2) cells. RT-qPCR results indicated that LNC_001186 expression was highly enriched in the intestines of healthy piglets and significantly increased in CpC-infected piglets' ileum tissue and CPB2 toxin-treated IPEC-J2 cells. The total sequence length of LNC_001186 was 1323 bp through RACE assay. CPC and CPAT, two online databases, both confirmed that LNC_001186 had a low coding ability. It was present on pig chromosome 3. Cytoplasmic and nuclear RNA isolation and RNA-FISH assays showed that LNC_001186 was present in the nucleus and cytoplasm of IPEC-J2 cells. Furthermore, six target genes of LNC_001186 were predicted using cis and trans approaches. Meanwhile, we constructed ceRNA regulatory networks with LNC_001186 as the center. Finally, LNC_001186 overexpression inhibited IPEC-J2 cells' apoptosis caused by CPB2 toxin and promoted cell viability. In summary, we determined the role of LNC_001186 in IPEC-J2 cells' apoptosis caused by CPB2 toxin, which assisted us in exploring the molecular mechanism of LNC_001186 in CpC-induced diarrhea in piglets.

TLR/MyD88-Mediated Inflammation Induced in Porcine Intestinal Epithelial Cells by Ochratoxin A Affects Intestinal Barrier Function

The intestinal epithelium performs vital functions such as nutrient absorption and acting as an intestinal barrier to maintain the host's homeostasis. Mycotoxin, which affects the processing and storage of animal feedstuff, is a problematic pollutant in farming products. Ochratoxin A generated by Aspergillus and Penicillium fungi causes inflammation, intestinal dysfunction, decline in growth, and reduced intake in porcine and other livestock. Despite these ongoing problems, OTA-related studies in intestinal epithelium are lacking. This study aimed to demonstrate that OTA regulates TLR/MyD88 signaling in IPEC-J2 cells and induces barrier function impairment through tight junction reduction. We measured expression of TLR/MyD88 signaling-related mRNAs and proteins. The indicator of intestinal barrier integrity was confirmed through immunofluorescence and transepithelial electrical resistance. Additionally, we confirmed whether inflammatory cytokines and barrier function were affected by MyD88 inhibition. MyD88 inhibition alleviated inflammatory cytokine levels, tight junction reduction, and damage to barrier function due to OTA. These results indicate that OTA induces TLR/MyD88 signaling-related genes and impairs tight junctions and intestinal barrier function in IPEC-J2 cells. MyD88 regulation in OTA-treated IPEC-J2 cells mitigates the tight junction and intestinal barrier function impairments. Our findings provide a molecular understanding of OTA toxicity in porcine intestinal epithelial cells.

lnc001776 Affects CPB2 Toxin-Induced Excessive Injury of Porcine Intestinal Epithelial Cells via Activating JNK/NF-kB Pathway through ssc-let-7i-5p/IL-6 Axis

Piglet diarrhea caused by Clostridium perfringens (C. perfringens) type C (CpC) seriously endangers the development of the pig production industry. C. perfringens beta2 (CPB2) toxin is a virulent toxin produced by CpC. Long non-coding RNAs (lncRNAs) are key regulators in the immune inflammatory response to bacterial infection. Nevertheless, the functional mechanism of lncRNAs in bacterial piglet diarrhea is unclear. Herein, a novel lncRNA lnc001776 expression was confirmed to be substantially elevated in the ileum tissue of CpC-infected diarrhea piglets and in CPB2 toxin-treated porcine small intestinal epithelial cells (IPEC-J2). lnc001776 knockdown restrained CPB2 toxin-induced apoptosis, inflammatory injury, barrier dysfunction and activation of JNK/NF-kB pathway in IPEC-J2 cells. Additionally, ssc-let-7i-5p was identified as sponge for lnc001776. Overexpression of ssc-let-7i-5p repressed CPB2-induced injury in IPEC-J2 cells. Interleukin 6 (IL-6), a target gene of ssc-let-7i-5p, was enhanced in CPB2 toxin-treated IPEC-J2 cells. Rescue experiments demonstrated that a ssc-let-7i-5p mimic reversed the effect of lnc001776 overexpression on CPB2 toxin-induced IPEC-J2 cell injury and JNK/NF-kB pathway, whereas IL-6 overexpression partially restored the impact of lnc001776. Overall, lnc001776 overexpression exacerbated CPB2 toxin-induced IPEC-J2 cell damage by sponging ssc-let-7i-5p to regulate IL-6 to activate JNK/NF-kB pathway, indicating that lnc001776 could be a key target for piglet resistance to CpC-induced diarrhea.

METTL3-Mediated LncRNA EN_42575 m6A Modification Alleviates CPB2 Toxin-Induced Damage in IPEC-J2 Cells

Long non-coding RNAs (lncRNAs) modified by n6-methyladenosine (m6A) have been implicated in the development and progression of several diseases. However, the mechanism responsible for the role of m6A-modified lncRNAs in Clostridium perfringens type C piglet diarrhea has remained largely unknown. We previously developed an in vitro model of CPB2 toxin-induced piglet diarrhea in IPEC-J2 cells. In addition, we previously performed RNA immunoprecipitation sequencing (MeRIP-seq), which demonstrated lncRNA EN_42575 as one of the most regulated m6A-modified lncRNAs in CPB2 toxin-exposed IPEC-J2 cells. In this study, we used MeRIP-qPCR, FISH, EdU, and RNA pull-down assays to determine the function of lncRNA EN_42575 in CPB2 toxin-exposed IPEC-J2 cells. LncRNA EN_42575 was significantly downregulated at different time points in CPB2 toxin-treated cells. Functionally, lncRNA EN_42575 overexpression reduced cytotoxicity, promoted cell proliferation, and inhibited apoptosis and oxidative damage, whereas the knockdown of lncRNA EN_42575 reversed these results. Furthermore, the dual-luciferase analysis revealed that METTL3 regulated lncRNA EN_42575 expression in an m6A-dependent manner. In conclusion, METTL3-mediated lncRNA EN_42575 exerted a regulatory effect on IPEC-J2 cells exposed to CPB2 toxins. These findings offer novel perspectives to further investigate the function of m6A-modified lncRNAs in piglet diarrhea.

Decreased S100A9 expression alleviates Clostridium perfringens beta2 toxin-induced inflammatory injury in IPEC-J2 cells

Background

S100 calcium-binding protein A9 (S100A9) is a commonly known pro-inflammatory factor involved in various inflammatory responses. Clostridium perfringens (C. perfringens ) type C is known to cause diarrhea in piglets. However, the role of S100A9 in C. perfringens type C-induced infectious diarrhea is unclear.

Methods

Here, the S100A9 gene was overexpressed and knocked down in the IPEC-J2 cells, which were treated with C. perfringens beta2 (CPB2) toxin. The role of S100A9 in CPB2 toxin-induced injury in IPEC-J2 cells was assessed by measuring the levels of inflammatory cytokines, reactive oxygen species (ROS), lactate dehydrogenase (LDH), cell proliferation, and tight junction-related proteins.

Results

The results showed elevated expression of S100A9 in diarrhea-affected piglet tissues, and the elevation of S100A9 expression after CPB2 toxin treatment of IPEC-J2 was time-dependent. In CPB2 toxin-induced IPEC-J2 cells, overexpression of S100A9 had the following effects: the relative expression of inflammatory factors IL-6, IL8, TNF-α, and IL-1β was increased; the ROS levels and LDH viability were significantly increased; cell viability and proliferation were inhibited; the G0/G1 phase cell ratio was significantly increased. Furthermore, overexpression of S100A9 reduced the expression of tight junction proteins in CPB2-induced IPEC-J2 cells. The knockdown of S100A9 had an inverse effect. In conclusion, our results confirmed that S100A9 exacerbated inflammatory injury in CPB2 toxin-induced IPEC-J2 cells, inhibited cell viability and cell proliferation, and disrupted the tight junctions between cells. Thus, decreased S100A9 expression alleviates CPB2 toxin-induced inflammatory injury in IPEC-J2 cells.

S100A9 plays a key role in Clostridium perfringens beta2 toxin-induced inflammatory damage in porcine IPEC-J2 intestinal epithelial cells

BACKGROUND

As an important regulator of autoimmune responses and inflammation, S100A9 may serve as a therapeutic target in inflammatory diseases. However, the role of S100A9 in Clostridium perfringens type C infectious diarrhea is poorly studied. The aim of our study was to screen downstream target genes regulated by S100A9 in Clostridium perfringens beta2 (CPB2) toxin-induced IPEC-J2 cell injury. We constructed IPEC-J2 cells with S100A9 knockdown and a CPB2-induced cell injury model, screened downstream genes regulated by S100A9 using RNA-Seq technique, and performed functional enrichment analysis. The function of S100A9 was verified using molecular biology techniques.

RESULTS

We identified 316 differentially expressed genes (DEGs), of which 221 were upregulated and 95 were downregulated. Functional enrichment analysis revealed that the DEGs were significantly enriched in cilium movement, negative regulation of cell differentiation, immune response, protein digestion and absorption, and complement and coagulation cascades. The key genes of immune response were TNF, CCL1, CCR7, CSF2, and CXCL9. When CPB2 toxin-induced IPEC-J2 cells overexpressed S100A9, Bax expression increased, Bcl-2 expression and mitochondrial membrane potential decreased, and SOD activity was inhibited.

CONCLUSION

In conclusion, S100A9 was involved in CPB2-induced inflammatory response in IPEC-J2 cells by regulating the expression of downstream target genes, namely, TNF, CCL1, CCR7, CSF2, and CXCL9; promoting apoptosis; and aggravating oxidative cell damage. This study laid the foundation for further study on the regulatory mechanism underlying piglet diarrhea.

LncRNA EN-90756 promotes CPB2-induced proliferation and inhibits apoptosis in IPEC-J2 cells by affecting the JAK-STAT signaling pathway activation

Background

Long non-coding RNAs (lncRNAs), as key regulators, are closely associated with the development of a variety of disease. However, the mechanisms by which lncRNAs regulate Clostridium perfringens type C induced piglet diarrhea are unclear.

Methods

In the present study, we explored the expression and characterization of lncRNAs in a C. perfringens beta2 (CPB2) toxin-treated intestinal porcine epithelial cell line-J2 (IPEC-J2) using RNA-sequencing (RNA-seq).

Results

A total of 6,558 lncRNAs were identified, of which 49 lncRNAs were significantly differentially expressed between the control and CPB2 groups. Functional enrichment analysis showed that the target genes of differentially expressed lncRNA EN-90756 were mainly associated with defense response to virus, and negative regulation of apoptotic process. LncRNA EN-90756 was significantly up-regulated in IPEC-J2 cells at different time points after CPB2 treatment. Functionally, knockdown of lncRNA EN-90756 might regulate the proliferation and apoptosis of IPEC-J2 cells by affecting the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway. LncRNA EN-90756 may be involved in CPB2 toxin-induced piglet diarrhea by regulating the expression of its target gene MX1 (encoding MX dynamin like GTPase 1).

Conclusion

Long non-coding RNA EN-90756 affected the antiviral ability of IPEC-J2 cells by regulating the expression of MX1. Meanwhile, lncRNA EN-90756 might regulate cell proliferation and apoptosis by affecting JAK-STAT signaling pathway activation. These findings provide novel perspectives and directions for further exploration of the regulatory mechanisms of lncRNAs on CPB2 toxin-induced diarrhea in piglets.

METTL3 Regulates the Inflammatory Response in CPB2 Toxin-Exposed IPEC-J2 Cells through the TLR2/NF-κB Signaling Pathway

Clostridium perfringens beta2 (CPB2) toxin is one of the main pathogenic toxins produced by Clostridium perfringens, which causes intestinal diseases in animals and humans. The N6-methyladenosine (m6A) modification is the most common reversible modification in eukaryotic disease processes. Methyltransferase-like 3 (METTL3) regulates immunity and inflammatory responses induced by the bacterial infections in animals. However, METTL3's involvement in CPB2-treated intestinal porcine epithelial cell line-J2 (IPEC-J2) remains unclear. In the current study, we used methylated RNA immunoprecipitation-quantitative polymerase chain reaction, Western blotting and immunofluorescence assay to determine the role of METTL3 in CPB2-exposed IPEC-J2 cells. The findings revealed that m6A and METTL3 levels were increased in CPB2 treated IPEC-J2 cells. Functionally, METTL3 overexpression promoted the release of inflammatory factors, increased cytotoxicity, decreased cell viability and disrupted tight junctions between cells, while the knockdown of METTL3 reversed these results. Furthermore, METTL3 was involved in the inflammatory response of IPEC-J2 cells by activating the TLR2/NF-κB signaling pathway through regulating TLR2 m6A levels. In conclusion, METTL3 overexpression triggered the TLR2/NF-κB signaling pathway and promoted CPB2-induced inflammatory responses in IPEC-J2 cells. These findings may provide a new strategy for the prevention and treatment of diarrhea caused by Clostridium perfringens.

Identification and Characterization of Clostridium perfringens Atypical CPB2 Toxin in Cell Cultures and Field Samples Using Monoclonal Antibodies

A direct sandwich enzyme-linked immunosorbent assay (sELISA) was developed for the detection of the atypical β2-toxin (CPB2) of Clostridium perfringens. Polyclonal (PAbs) and monoclonal (MAbs) antibodies were previously obtained employing recombinant CPB2 produced in the baculovirus system as antigen. In the current study, PAbs were used as capture molecules, while purified MAbs conjugated to horseradish peroxidase (MAbs-HRP) were used for the detection of atypical CPB2 toxin. MAbs 5C11E6 and 2G3G6 showed high reactivity, sensitivity and specificity when tested on 232 C. perfringens cell culture isolates. In addition, a reactivity variation among different strains producing atypical CPB2 toxin was observed using the conformation-dependent MAb 23E6E6, suggesting the hypothesis of high instability and/or the existence of different three-dimensional structures of this toxin. Results obtained by sELISA and Western blotting performed on experimentally CPB2-contaminated feces revealed a time-dependent proteolytic degradation as previously observed with the consensus allelic form of CPB2. Finally, the sELISA and an end-point PCR, specific for the atypical cpb2 gene, were used to test field samples (feces, rectal swabs and intestinal contents) from different dead animal species with suspected or confirmed clostridiosis. The comparison of sELISA data with those obtained with end-point PCR suggests this method as a promising tool for the detection of atypical CPB2 toxin.

FTO Regulates Apoptosis in CPB2-Treated IPEC-J2 Cells by Targeting Caspase 3 Apoptotic Protein

N6-methyladenosine (m6A) modification can accommodate mRNA processing, stability, and translation in mammals, and fat mass and obesity associated protein (FTO) is a vital demethylase in the m6A modification pathway. Clostridium perfringens type C (C. perfringens type C) causes diarrhea in piglets and has a serious impact on the pig industry. However, our understanding of the effect of m6A in the process of C. perfringens type C infectious piglet diarrhea (CPTCIPD) is limited. Here, an in vitro model of CPTCIPD was constructed by treating the intestinal porcine epithelial cell line-J2 (IPEC-J2) with Clostridium perfringens beta2 (CPB2) toxin, and the role of FTO was analyzed using quantitative real-time polymerase chain reaction, Western blotting, and flow cytometry. The results revealed that the overall RNA m6A contents at the tissue and cell levels were significantly up-regulated after C. perfringens infection (p < 0.05). FTO expression was significantly reduced in CPB2-treated IPEC-J2 cells. Functionally, FTO knockdown in the treated cells inhibited their proliferation and promoted apoptosis and the inflammation phenotype, whereas FTO overexpression had the opposite effects. Inhibiting FTO prolonged the half-life and up-regulated the expression of Caspase 3, leading to apoptosis. Therefore, this work explored the regulation of FTO in IPEC-J2 cells after CPB2 treatment and enhanced our understanding of the effect of the m6A modification in CPTCIPD.

miR-30d Inhibition Protects IPEC-J2 Cells Against Clostridium perfringens Beta2 Toxin-Induced Inflammatory Injury

Clostridium perfringens beta2 (CPB2) toxin, one of the virulence factors of Clostridium perfringens (C. perfringens), can cause necrotizing enterocolitis in piglets. Accumulating pieces of evidence indicate that microRNAs (miRNAs) refer to the regulation of inflammatory processes. Previously, we have discovered that miR-30d was differentially expressed between the ileum of normal piglets and C. perfringens type C-infected diarrheal piglets. Here, we found that miR-30d expression was lowered in CPB2 toxin-treated intestinal porcine epithelial cells (IPEC-J2) at different time points. Subsequently, we determined that miR-30d inhibitor attenuated CPB2 toxin revulsive inflammatory damage in IPEC-J2 cells and promoted cell proliferation and cell cycle progression, whereas miR-30d mimic had opposite results. In addition, we confirmed that Proteasome activator subunit 3 (PSME3) was a downstream target gene of miR-30d via a dual luciferase reporter assay, qPCR, and western blot. We also found that overexpression of PSME3 suppressed CPB2 toxin-induced inflammatory damage and promoted cell proliferation and cycle progression. Our results demonstrate that miR-30d aggravates CPB2 toxin revulsive IPEC-J2 cells inflammatory injury via targeting PSME3, thereby providing a novel perspective for the prevention and treatment of piglet diarrhea at the molecular level.

ssc-microRNA-132 targets DACH1 to exert anti-inflammatory and anti-apoptotic effects in Clostridium perfringens beta2 toxin-treated porcine intestinal epithelial cells

Clostridium perfringens (C. perfringens) type C (CPC) is one of the chief pathogens that causes diarrhea in piglets, and C. perfringens beta2 (CPB2) toxin is the main virulence factor of CPC. Our previous research demonstrated that ssc-microR-132 was differentially expressed in ileal tissues of CPC-mediated diarrheic piglets and healthy piglets, which implied a potential role of ssc-microR-132 in this process. Here, we found that ssc-microR-132 was notably down-regulated in CPB2-exposed intestinal porcine epithelial cells (IPEC-J2), which was consistent with the ileal tissue expression. Moreover, ssc-microR-132 upregulation alleviated CPB2-induced inflammatory damage and apoptosis in IPEC-J2, whereas ssc-microR-132 knockdown presented the opposite effects. Furthermore, the dual-luciferase reporter assay indicated that ssc-microR-132 directly targeted Dachshund homolog 1 (DACH1). Moreover, DACH1 overexpression intensified CPB2-induced inflammatory injury and apoptosis in IPEC-J2. Remarkably, the introduction of DACH1 weakened the anti-inflammatory and anti-apoptotic effects of ssc-microR-132 in CPB2-exposed IPEC-J2. Overall, the results reveal that ssc-microR-132 targeted DACH1 to alleviate CPB2-mediated inflammation and apoptosis in IPEC-J2.

Clostridium perfringens Beta2 toxin forms highly cation-selective channels in lipid bilayers

Clostridium perfringens is a potent producer of a variety of toxins. Well studied from these are five toxins (alpha, Beta (CPB), epsilon, iota and CPE) that are produced by seven toxinotype strains (A–G) of C. perfringens. Besides these toxins, C. perfringens produces also another toxin that causes necrotizing enterocolitis in piglets. This toxin termed consensus Beta2 toxin (cCPB2) has a molecular mass of 27,620 Da and shows only little homology to CPB and no one to the other toxins of C. perfringens. Its primary action on cells remained unknown to date. cCPB2 was heterogeneously expressed as fusion protein with GST in Escherichia coli and purified to homogeneity. Although cCPB2 does not exhibit the typical structure of beta-stranded pore-forming proteins and contains no indication for the presence of amphipathic alpha-helices we could demonstrate that cCPB2 is a pore-forming component with an extremely high activity in lipid bilayers. The channels have a single-channel conductance of about 700 pS in 1 M KCl and are highly cation-selective as judged from selectivity measurements in the presence of salt gradients. The high cation selectivity is caused by the presence of net negative charges in or near the channel that allowed an estimate of the channel size being about 1.4 nm wide. Our measurements suggest that the primary effect of cCPB2 is the formation of cation-selective channels followed by necrotic enteritis in humans and animals. We searched in databases for homologs of cCPB2 and constructed a cladogram representing the phylogenetic relationship to the next relatives of cCPB2.

Prevalence and Genetic Diversity of Clostridium perfringens Isolates in Hospitalized Diarrheal Patients from Central China

Objective

This study aimed to investigate the prevalence, genetic diversity and clinical characteristics of Clostridium perfringens isolates from hospitalized clinical diarrheal patients.

Methods

A prospective study was conducted on 1108 patients with diarrhea during hospitalization. Stool samples were cultured for C. perfringens, and the toxin genes were detected by PCR. The available clinical data of 112 patients were analyzed to study the clinical features of various isolates. Multi-locus sequence typing (MLST) was performed to assess phylogenetic relationship between different isolates.

Results

A total of 153 (13.8%) isolates were obtained from patients’ stools. C. perfringens type F (49.0%) was the major toxin type in the isolates, followed by type A (n = 59, 38.6%) and type C (n = 14, 9.2%). Patients older than 50 years and those with underlying diseases of cancer, hepatobiliary system, and ulcerative colitis (UC) were more predisposed to C. perfringens type F and type A infection than to type C. The patients infected with type C experienced more severe clinical symptoms compared to those with type A infection. There was a significant association between type F^C and foodborne gastrointestinal (GI) diseases (p = 0.018), between type F^P and antibiotic-associated diarrhea (AAD) (p < 0.001), and between type A and sporadic diarrhea (SD) (p < 0.001). Phylogenetic analysis indicated that type F isolates carrying a chromosomal cpe gene mainly belonged to ST77 (6/15 isolates). Type F isolates with cpe gene on a plasmid exhibited high genetic diversity.

Conclusion

High prevalence and considerable genetic diversity of C. perfringens type F were found in clinical diarrheal patients. Elderly people and patients with cancer, hepatobiliary diseases or UC, or suspected of having food poisoning (FP) may be targeted for routine testing of C. perfringens toxin genes and may benefit from early detection of C. perfringens type C isolates that cause more severe clinical symptoms.

N6-Methyladenosine Methylation Analysis of Long Noncoding RNAs and mRNAs in IPEC-J2 Cells Treated With Clostridium perfringens beta2 Toxin

Background

The n6-methyladenosine (m6A) modification is present widely in mRNAs and long non-coding RNAs (lncRNAs), and is related to the occurrence and development of certain diseases. However, the role of m6A methylation in Clostridium perfringens type C infectious diarrhea remains unclear.

Methods

Here, we treated intestinal porcine jejunum epithelial cells (IPEC-J2 cells) with Clostridium perfringens beta2 (CPB2) toxin to construct an in vitro model of Clostridium perfringens type C (C. perfringens type C) infectious diarrhea, and then used methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-seq) to identify the methylation profiles of mRNAs and lncRNAs in IPEC-J2 cells.

Results

We identified 6,413 peaks, representing 5,825 m6A-modified mRNAs and 433 modified lncRNAs, of which 4,356 m6A modified mRNAs and 221 m6A modified lncRNAs were significantly differential expressed between the control group and CPB2 group. The motif GGACU was enriched significantly in both the control group and the CPB2 group. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation analysis showed that the differentially methylated modified mRNAs were mainly enriched in Hippo signaling pathway and Wnt signaling pathway. In addition, the target genes of the differentially m6A modified lncRNAs were related to defense response to virus and immune response. For example, ENSSSCG00000042575, ENSSSCG00000048701 and ENSSSCG00000048785 might regulate the defense response to virus, immune and inflammatory response to resist the harmful effects of viruses on cells.

Conclusion

In summary, this study established the m6A transcription profile of mRNAs and lncRNAs in IPEC-J2 cells treated by CPB2 toxin. Further analysis showed that m6A-modified RNAs were related to defense against viruses and immune response after CPB2 toxin treatment of the cells. Threem6A-modified lncRNAs, ENSSSCG00000042575, ENSSSCG00000048785 and ENSSSCG00000048701, were most likely to play a key role in CPB2 toxin-treated IPEC-J2 cells. The results provide a theoretical basis for further research on the role of m6A modification in piglet diarrhea.

Comprehensive Analysis of Transcriptome-wide m6A Methylome Upon Clostridium perfringens Beta2 Toxin Exposure in Porcine Intestinal Epithelial Cells by m6A Sequencing

Piglet diarrhea is a swine disease responsible for serious economic impacts in the pig industry. Clostridium perfringens beta2 toxin (CPB2), which is a major toxin of C. perfringens type C, may cause intestinal diseases in many domestic animals. N6-methyladenosine (m6A) RNA methylation plays critical roles in many immune and inflammatory diseases in livestock and other animals. However, the role of m6A methylation in porcine intestinal epithelial (IPEC-J2) cells exposed to CPB2 has not been studied. To address this issue, we treated IPEC-J2 cells with CPB2 toxin and then quantified methylation-related enzyme expression by RT-qPCR and assessed the m6A methylation status of the samples by colorimetric N6-methyladenosine quantification. The results showed that the methylation enzymes changed to varying degrees while the m6A methylation level increased (p < 0.01). On this basis, we performed N6-methyladenosine sequencing (m6A-seq) and RNA sequencing (RNA-seq) to examine the detailed m6A modifications and gene expression of the IPEC-J2 cells following CPB2 toxin exposure. Our results indicated that 1,448 m6A modification sites, including 437 up-regulated and 1,011 down-regulated, differed significantly between CPB2 toxin exposed cells and non-exposed cells (p < 0.05). KEGG pathway analysis results showed that m6A peaks up-regulated genes (n = 394) were mainly enriched in cancer, Cushing syndrome and Wnt signaling pathways, while m6A peaks down-regulated genes (n = 920) were mainly associated with apoptosis, small cell lung cancer, and the herpes simplex virus 1 infection signaling pathway. Furthermore, gene expression (RNA-seq data) analysis identified 1,636 differentially expressed genes (DEGs), of which 1,094 were up-regulated and 542 were down-regulated in the toxin exposed group compared with the control group. In addition, the down-regulated genes were involved in the Hippo and Wnt signaling pathways. Interestingly, the combined results of m6A-seq and RNA-seq identified genes with up-regulated m6A peaks but with down-regulated expression, here referred to as "hyper-down" genes (n = 18), which were mainly enriched in the Wnt signaling pathway. Therefore, we speculate that the genes in the Wnt signaling pathway may be modified by m6A methylation in CPB2-induced IPEC-J2 cells. These findings provide new insights enabling further exploration of the mechanisms underlying piglet diarrhea caused by CPB2 toxin.

Effects of miR-204 on apoptosis and inflammatory response of Clostridium perfringens beta2 toxin induced IPEC-J2 cells via targeting BCL2L2

Clostridium perfringens beta2 (CPB2) toxin can cause intestinal damage and inflammatory responses in a variety of animals, which seriously endanger the healthy development of animal husbandry. Increasing evidence has demonstrated that microRNAs (miRNAs) can play an important regulatory role in the process of pathogenic infection. In our previous study, we found that miR-204 was highly expressed in the ileum tissues of the susceptible group diarrhea piglets after infection with Clostridium perfringens (C. perfringens) type C. In this study, we found that miR-204 was also up-regulated in different time points after CPB2 toxin treatment. Overexpression of miR-204 promoted apoptosis and inflammatory response of intestinal porcine epithelial cells (IPEC-J2), whereas the opposite results were displayed after transfected with miR-204 inhibitor. Furthermore, the luciferase reporter assays confirmed that BCL2L2 was a direct target gene of miR-204. Interestingly, we found that overexpression BCL2L2 attenuated the apoptosis and inflammatory response of CPB2 toxin induced IPEC-J2 cells. In conclusion, these results find that miR-204 promotes the apoptosis and intensify inflammatory response of CPB2 toxin induced IPEC-J2 cells via targeting BCL2L2. These data provide a valuable reference for the piglets resistance diarrhea at the molecular level.

MicroRNA-21-5p targets PDCD4 to modulate apoptosis and inflammatory response to Clostridium perfringens beta2 toxin infection in IPEC-J2 cells

Clostridium perfringens (C. perfringens), a toxin-producing enteric pathogen, causes a variety of intestinal infections in humans and animals. C. perfringens beta2 (CPB2) toxin has been considered to be a strong virulence factor for C. perfringens infectious enteric diseases (CPED). Altered levels and functions of microRNA-21-5p (miR-21-5p) have been associated with apoptosis and inflammation response in pathological processes. However, little is known about its functional mechanism in CPED. Here, we found that miR-21-5p expressed in multiple tissues of pig, had a highest level in jejunum, and significantly upregulated in intestinal porcine epithelial cells (IPEC-J2) exposed to CPB2 toxin. Noteworthily, transfection of CPB2-treated IPEC-J2 cells with miR-21-5p mimic increased cell viability and Bcl2 expression, as well as reduced cytotoxicity, apoptosis rates and Bax level. Moreover, overexpression of miR-21-5p significantly suppressed the levels of interleukin (IL)-6, IL-8, TNF-α, IL-1β and nuclear factor-kappa B (NF-κB p65) activity induced by CPB2 toxin, whereas that of the IL-10 was increased in IPEC-J2 cells. On the contrary, transfection of miR-21-5p inhibitor promoted CPB2-induced cell apoptosis and inflammation. Furthermore, we validated that programmed cell death 4 (PDCD4) was strikingly downregulated in CPB2-treated IPEC-J2 cells. PDCD4 exhibited opposing effects to those of miR-21-5p mimic on IPEC-J2 cells, and restoration of PDCD4 expression counteracted the suppressive effect of miR-21-5p on CPB2-induced apoptosis and inflammatory response. Collectively, our findings demonstrated that miR-21-5p was involved in regulating the immune response triggered by CPB2 toxin and contributed to protective effects in CPB2-induced CPED cell model by targeting PDCD4.