Rat hepatocyte invasion by Listeria monocytogenes and analysis of TNF-alpha role in apoptosis

New insights into iNKT cells and their roles in liver diseases

Natural killer T cells (NKTs) are an important part of the immune system. Since their discovery in the 1990s, researchers have gained deeper insights into the physiology and functions of these cells in many liver diseases. NKT cells are divided into two subsets, type I and type II. Type I NKT cells are also named iNKT cells as they express a semi-invariant T cell-receptor (TCR) α chain. As part of the innate immune system, hepatic iNKT cells interact with hepatocytes, macrophages (Kupffer cells), T cells, and dendritic cells through direct cell-to-cell contact and cytokine secretion, bridging the innate and adaptive immune systems. A better understanding of hepatic iNKT cells is necessary for finding new methods of treating liver disease including autoimmune liver diseases, alcoholic liver diseases (ALDs), non-alcoholic fatty liver diseases (NAFLDs), and liver tumors. Here we summarize how iNKT cells are activated, how they interact with other cells, and how they function in the presence of liver disease.

Escherichia coli Affects Expression of Circadian Clock Genes in Human Hepatoma Cells

Recent research has indicated that dysbiosis of the gut microbiota can lead to an altered circadian clock of the mammalian host. Herein we developed an original system that allows real-time circadian studies of human HepG2 hepatoma cells co-cultured with bacteria. The HepG2 cells with stably integrated firefly luciferase reporter under the control of PERIOD2 promoter were co-cultured with E. coli strains isolated from human fecal samples from healthy individuals. The two E. coli strains differ in the phylogenetic group and the number of ExPEC virulence-associated genes: BJ17 has only two, and BJ23 has 15 of 23 tested. In the first 24 h, the E. coli BJ17 affected the HepG2 circadian clock more than BJ23. Cosinor analysis shows a statistically significant change in the amplitude of PER1 and 2 and the phase advance of PER3. A high percentage of necrotic and apoptotic cells occurred at 72 h, while a correlation between the number of ExPEC genes and the influence on the HepG2 core clock gene expression was observed. Our study reveals that the E. coli genetic background is important for the effect on the mammalian circadian clock genes, indicating possible future use of probiotic E. coli strains to influence the host circadian clock.

Role of ADAMTS-13 and nNOS expression in neuropathogenesis of listeric encephalitis of small ruminants

We investigated the expression of A disintegrin and metalloprotease with thrombospondin type I repeats-13 (ADAMTS-13) in the central nervous system (CNS), because it is related to blood-brain barrier (BBB) permeability. We also investigated 8-OHdG, caspase-3 and neuronal nitric oxide synthase (nNOS) expression for the cytotoxic effects of oxidative stress (OS) and nNOS, and their relation to apoptosis. We also investigated the neuroimmunopathology caused by L. monocytogenes. Brain tissues were obtained from 10 lambs and 10 kids with listeric meningoencephalitis, and healthy brain tissue from six lambs and six kids. Serial sections of brain were stained by hematoxylin and eosin (H & E), and using immunohistochemistry (IHC) for L. monocytogenes antigen, ADAMTS-13, 8-hydroxy-2'-deoxyguanosine (8-OHdG), nNOS and caspase-3. We found that ADAMTS-13, 8-OHdG, nNOS and caspase-3 expression in the brain was increased in L. Monocytogenes infected animals compared to uninfected controls. Intense staining for 8-OHdG was observed only in neurons and glia that were exposed to OS. ADAMTS-13 was increased significantly, which may play a role in regulating and protecting BBB integrity and cells of the CNS in cases of listeric encephalitis. Increased expression of ADAMTS-13 may be critical for supporting the survival of neurons and glia. We found that L. monocytogenes-related increases in OS and nNOS, and that the associated apoptosis, may participate in neurodegeneration and neuropathology in listeric encephalitis.

Immunopathogenesis of Hepatic Brucellosis

The hepatic immune system can induce rapid and controlled responses to pathogenic microorganisms and tumor cells. Accordingly, most of the microorganisms that reach the liver through the blood are eliminated. However, some of them, including Brucella spp., take advantage of the immunotolerant capacity of the liver to persist in the host. Brucella has a predilection for surviving in the reticuloendothelial system, with the liver being the largest organ of this system in the human body. Therefore, its involvement in brucellosis is practically invariable. In patients with active brucellosis, the liver is commonly affected, and the most frequent clinical manifestation is hepatosplenomegaly. The molecular mechanisms implicated in liver damage have been recently elucidated. It has been demonstrated how Brucella interacts with hepatocytes inducing its death by apoptosis. The inflammatory microenvironment and the direct effect of Brucella on hepatic stellate cells (HSC) induce their activation and turn these cells from its quiescent form to their fibrogenic phenotype. This HSC activation induced by Brucella infection relies on the presence of a functional type IV secretion system and the effector protein BPE005 through a mechanism involved in the activation of the autophagic pathway. Finally, the molecular mechanisms of liver brucellosis observed so far are shedding light on how the interaction of Brucella with liver cells may play an important role in the discovery of new targets to control the infection. In this review, we report the current understanding of the interaction between liver structural cells and immune system cells during Brucella infection.

Listeria monocytogenes: The Impact of Cell Death on Infection and Immunity

Listeria monocytogenes has evolved exquisite mechanisms for invading host cells and spreading from cell-to-cell to ensure maintenance of its intracellular lifecycle. As such, it is not surprising that loss of the intracellular replication niche through induction of host cell death has significant implications on the development of disease and the subsequent immune response. Although L. monocytogenes can activate multiple pathways of host cell death, including necrosis, apoptosis, and pyroptosis, like most intracellular pathogens L. monocytogenes has evolved a series of adaptations that minimize host cell death to promote its virulence. Understanding how L. monocytogenes modulates cell death during infection could lead to novel therapeutic approaches. In addition, as L. monocytogenes is currently being developed as a tumor immunotherapy platform, understanding how cell death pathways influence the priming and quality of cell-mediated immunity is critical. This review will focus on the mechanisms by which L. monocytogenes modulates cell death, as well as the implications of cell death on acute infection and the generation of adaptive immunity.

Restraining reactive oxygen species in Listeria monocytogenes promotes the apoptosis of glial cells

OBJECTIVES

Listeria monocytogenes is a facultative anaerobic foodborne pathogen that can traverse the blood-brain barrier and cause brain infection. L. monocytogenes infection induces host cell apoptosis in several cell types. In this study, we investigated the apoptosis of human glioma cell line U251 invaded by L. monocytogenes and evaluated the function of bacterial reactive oxygen species (ROS) during infection.

METHODS

Bacterial ROS level was reduced by carrying out treatment with N-acetyl cysteine (NAC) and diphenyleneiodonium chloride (DPI). After infection, the apoptosis of U251 cells was examined by flow cytometry assay and propidium iodide staining.

RESULTS

DPI and NAC efficiently decreased ROS level in L. monocytogenes without affecting bacterial growth. Moreover, the apoptosis of glial cells was enhanced upon invasion of DPI- and NAC-pretreated L. monocytogenes.

DISCUSSION

Results indicate that the apoptosis of glial cells can be induced by L. monocytogenes, and that the inhibition of bacterial ROS increases the apoptosis of host cells.

Crucial roles of TNFAIP8 protein in regulating apoptosis and Listeria infection

TNF-α-induced protein 8 (TNFAIP8 or TIPE) is a newly described regulator of cancer and infection. However, its precise roles and mechanisms of actions are not well understood. We report in this article that TNFAIP8 regulates Listeria monocytogenes infection by controlling pathogen invasion and host cell apoptosis in a RAC1 GTPase-dependent manner. TNFAIP8-knockout mice were resistant to lethal L. monocytogenes infection and had reduced bacterial load in the liver and spleen. TNFAIP8 knockdown in murine liver HEPA1-6 cells increased apoptosis, reduced bacterial invasion into cells, and resulted in dysregulated RAC1 activation. TNFAIP8 could translocate to plasma membrane and preferentially associate with activated RAC1-GTP. The combined effect of reduced bacterial invasion and increased sensitivity to TNF-α-induced clearance likely protected the TNFAIP8-knockout mice from lethal listeriosis. Thus, by controlling bacterial invasion and the death of infected cells through RAC1, TNFAIP8 regulates the pathogenesis of L. monocytogenes infection.

Defense Mechanisms of Hepatocytes Against Burkholderia pseudomallei

The Gram-negative facultative intracellular rod Burkholderia pseudomallei causes melioidosis, an infectious disease with a wide range of clinical presentations. Among the observed visceral abscesses, the liver is commonly affected. However, neither this organotropism of B. pseudomallei nor local hepatic defense mechanisms have been thoroughly investigated so far. Own previous studies using electron microscopy of the murine liver after systemic infection of mice indicated that hepatocytes might be capable of killing B. pseudomallei. Therefore, the aim of this study was to further elucidate the interaction of B. pseudomallei with these cells and to analyze the role of hepatocytes in anti-B. pseudomallei host defense. In vitro studies using the human hepatocyte cell line HepG2 revealed that B. pseudomallei can invade these cells. Subsequently, B. pseudomallei is able to escape from the vacuole, to replicate within the cytosol of HepG2 cells involving its type 3 and type 6 secretion systems, and to induce actin tail formation. Furthermore, stimulation of HepG2 cells showed that IFNγ can restrict growth of B. pseudomallei in the early and late phase of infection whereas the combination of IFNγ, IL-1β, and TNFα is required for the maximal antibacterial activity. This anti-B. pseudomallei defense of HepG2 cells did not seem to be mediated by inducible nitric oxide synthase-derived nitric oxide or NADPH oxidase-derived superoxide. In summary, this is the first study describing B. pseudomallei intracellular life cycle characteristics in hepatocytes and showing that IFNγ-mediated, but nitric oxide- and reactive oxygen species-independent, effector mechanisms are important in anti-B. pseudomallei host defense of hepatocytes.

TNF-α production and apoptosis in hepatocytes after Listeria monocytogenes and Salmonella Typhimurium invasion

Invasion of hepatocytes by Listeria monocytogenes (LM) and Salmonella Typhimurium (ST) can stimulate tumor necrosis factor alpha (TNF-α) release and induce apoptosis. In this study, we compared the behavior of hepatocytes invaded by three L. monocytogenes serotypes (LM-4a, LM-4b and LM-1/2a) and by ST to understand which bacterium is more effective in the infectious process. We quantified TNF-α release by ELISA, apoptosis rates by annexin V (early apoptosis) and TUNEL (late apoptosis) techniques. The cell morphology was studied too. TNF-α release rate was highest in ST-invaded hepatocytes. ST and LM-1/2a induced the highest apoptosis production rates evaluated by TUNEL. LM-4b produced the highest apoptosis rate measured by annexin. Invaded hepatocytes presented various morphological alterations. Overall, LM-4b and LM-1/2a proved to be the most efficient at cell invasion, although ST adapted faster to the environment and induced earlier hepatocyte TNF-α release.

Expression of cytokines and their regulation during amoebic liver abscess development

Amoebic liver abscess (ALA) is the most important extraintestinal complication of Entamoeba histolytica infection. Amoebic liver abscess development causes severe destruction of the liver tissue concomitant with a strong inflammatory reaction. We analyse the in situ expression of TNF-α, IFN-γ, IL-1β, 1L-8 and IL-10 at different stages of ALA development in a susceptible animal model. Results showed that after inoculation, neutrophils (PMN) and some macrophages infiltrated the liver and were positive for TNF-α and IFN-γ at the acute phase of amoeba infection. The presence of these cytokines was transient and decreased as tissue damage progressed. In contrast, IL-1β and IL-8 were detected mainly in neutrophils and macrophages from the periods of acute infection to subacute and chronic infection and decreased when granulomas were formed. The IL-10 was expressed in PMN and mononuclear cells and only during a short period at the onset of acute infection. The qRT-PCR of mRNA revealed a relationship with the expression of the cytokines in cells found in the ALA. Furthermore, our data suggest that IL-10 does not regulate local production of these cytokines. Our results indicate that an exacerbated inflammatory milieu is established and contributes to liver tissue damage and probably supports the survival of the parasites.

Brucella-infected hepatocytes mediate potentially tissue-damaging immune responses

BACKGROUND & AIMS

Hepatic involvement is frequent in human brucellosis. While different histopathological lesions have been reported in these patients, the underlying cellular and molecular mechanisms have not been addressed.

METHODS

This study assessed whether Brucella abortus can infect a human hepatoma cell line and induce a proinflammatory response in these cells.

RESULTS

The bacterium not only infected the human hepatoma cell line HepG2 but also exhibited intracellular replication. The infection induced hepatoma cells to secrete IL-8, and supernatants from Brucella-infected hepatoma cells were shown to induce the migration of human neutrophils. The infection also induced the expression of the intercellular adhesion molecule ICAM-1 on hepatoma cells, and the adhesion of neutrophils to these cells was significantly higher than to uninfected hepatoma cells. ICAM-1 expression was also induced by stimulation of hepatoma cells with supernatants from Brucella-infected neutrophils. While Brucella infection did not induce the expression of matrix metalloproteinases (MMPs) in hepatoma cells, it significantly induced MMP-9 in neutrophils. Hepatoma cell apoptosis was significantly induced by B. abortus infection and also by stimulation with supernatants from Brucella-infected neutrophils.

CONCLUSIONS

The present study provides clues regarding potential mechanisms of tissue damage during liver brucellosis.