Cytolethal distending toxin: from genotoxin to a potential biomarker and anti-tumor target

Helicobacter mastomyrinus infection induces autoimmune hepatitis in mice

Background

Autoimmune hepatitis (AIH) is a chronic progressive liver disease caused by the immune system mistakenly attacking its own hepatocytes. The role of the gut microbiome in the pathogenesis and progression of AIH is of considerable significance. However, the dearth of suitable animal models has significantly constrained advancements in the pathogenesis and the development of therapeutic strategies for AIH. Helicobacter mastomyrinus (H. mastomyrinus, Hm) is a potentially zoonotic pathogenic microorganism capable of causing diseases of the enterohepatic system in rodent laboratory animals. Nevertheless, research on its role and mechanisms in causing liver disease is severely limited.

Methods

In this study, male BALB/c mice were infected with Hm isolate Hm-17, and were sacrificed at 4 w, 8 w, 14 w and 22 w after infection, respectively. The serum was collected for detecting a number of AIH indicators, including the aminotransferases level, IgG content and autoantibody level. Additionally, the liver tissue was examined for pathological analysis, fibrosis, bacterial content, and the distribution of immune cells.

Results

It was observed that the infection initially caused focal necrotizing hepatitis and subsequently progressed to interface hepatitis with lymphocyte/plasma cell infiltration, as well as hypergammaglobulinemia and autoantibody reactions, predominantly to Anti-nuclear and anti-smooth muscle antibodies. Furthermore, as the infection persisted, the mice exhibited a progressive increase in liver fibrosis and mild steatosis. Despite the maintenance of a low level of Hm colonization in the liver, there was a notable infiltrate of macrophages, T and B lymphocytes. In particular, the inflammatory foci in the Hm-infected liver were highly enriched for IL17+ cells.

Conclusion

The present study provides an animal model of immunological liver injury induced by Hm infection that exhibits main characteristics similar to those observed in AIH-1 patients. This model may serve as a novel animal model for the study of the pathogenesis and potential therapeutic strategies for human AIH.

The role of cytolethal distending toxin in Glaesserella parasuis JS0135 strain infection: Cytotoxicity, phagocytic resistance and pathogenicity

Glaesserella parasuis is an important porcine pathogen that commonly colonizes the upper respiratory tract of pigs and is prone to causing Glässer's disease under complex conditions. As yet, the disease has led to serious economic losses to the swine industry worldwide. Studies so far have found that several virulence factors are associated with the pathogenicity of G. parasuis, but the pathogenic mechanism is still not fully understood. Cytolethal distending toxin (CDT), a potential virulence factor in G. parasuis, is involved in cytotoxicity, serum resistance, adherence to and invasion of host cells in vitro. Here, to further investigate the pathogenic role of CDT during G. parasuis infection in vitro and in vivo, a double cdt1 and cdt2 deletion mutant (Δcdt1Δcdt2) without selectable marker was first generated in G. parasuis JS0135 strain by continuous natural transformations and replica plating. Morphological observation and lactate dehydrogenase assay showed that the Δcdt1Δcdt2 mutant was defective in cytotoxicity. Additionally, the Δcdt1Δcdt2 mutant was more susceptible to phagocytosis caused by 3D4/2 macrophages compared to the wild-type JS0135 strain. Moreover, by focusing on clinical signs, necropsy, bacterial recovery and pathological observation, we found that the deletion of cdt1 and cdt2 genes led to a significant attenuation of virulence in G. parasuis. Taken together, these findings suggest that as an important virulence factor, CDT can significantly affect the pathogenicity of G. parasuis.

Unravelling bacterial virulence factors in yeast: From identification to the elucidation of their mechanisms of action

Pathogenic bacteria employ virulence factors (VF) to establish infection and cause disease in their host. Yeasts, Saccharomyces cerevisiae and Saccharomyces pombe, are useful model organisms to study the functions of bacterial VFs and their interaction with targeted cellular processes because yeast processes and organelle structures are highly conserved and similar to higher eukaryotes. In this review, we describe the principles and applications of the yeast model for the identification and functional characterisation of bacterial VFs to investigate bacterial pathogenesis. The growth inhibition phenotype caused by the heterologous expression of bacterial VFs in yeast is commonly used to identify candidate VFs. Then, subcellular localisation patterns of bacterial VFs can provide further clues about their target molecules and functions during infection. Yeast knockout and overexpression libraries are also used to investigate VF interactions with conserved eukaryotic cell structures (e.g., cytoskeleton and plasma membrane), and cellular processes (e.g., vesicle trafficking, signalling pathways, and programmed cell death). In addition, the yeast growth inhibition phenotype is also useful for screening new drug leads that target and inhibit bacterial VFs. This review provides an updated overview of new tools, principles and applications to study bacterial VFs in yeast.

Increased IgA-mediated responses to the gut paracellular pathway and blood-brain barrier proteins predict delirium due to hip fracture in older adults

Introduction

Delirium is accompanied by immune response system activation, which may, in theory, cause a breakdown of the gut barrier and blood-brain barrier (BBB). Some results suggest that the BBB is compromised in delirium, but there is no data regarding the gut barrier. This study investigates whether delirium is associated with impaired BBB and gut barriers in elderly adults undergoing hip fracture surgery.

Methods

We recruited 59 older adults and measured peak Delirium Rating Scale (DRS) scores 2-3 days after surgery, and assessed plasma IgG/IgA levels (using ELISA techniques) for zonulin, occludin, claudin-6, β-catenin, actin (indicating damage to the gut paracellular pathway), claudin-5 and S100B (reflecting BBB damage), bacterial cytolethal distending toxin (CDT), LPS-binding protein (LBP), lipopolysaccharides (LPS), Porphyromonas gingivalis, and Helicobacter pylori.

Results

Results from univariate analyses showed that delirium is linked to increased IgA responses to all the self-epitopes and antigens listed above, except for LPS. Part of the variance (between 45-48.3%) in the peak DRS score measured 2-3 days post-surgery was explained by independent effects of IgA directed to LPS and LBP (or bacterial CDT), baseline DRS scores, and previous mild stroke. Increased IgA reactivity to the paracellular pathway and BBB proteins and bacterial antigens is significantly associated with the activation of M1 macrophage, T helper-1, and 17 cytokine profiles.

Conclusion

Heightened bacterial translocation, disruption of the tight and adherens junctions of the gut and BBB barriers, elevated CDT and LPS load in the bloodstream, and aberrations in cell-cell interactions may be risk factors for delirium.