Endogenous glucocorticoids attenuate Shiga toxin-2-induced toxicity in a mouse model of haemolytic uraemic syndrome

Glucocorticoid receptor-targeting antagomirs alleviates AFB1-induced hepatotoxicity in mice

Aflatoxin B1 (AFB1) exhibits hepatotoxic properties in both humans and animals. Contradictory findings regarding corticosterone suggest that it may either aggravate AFB1 toxicity or reduce its Lethal Dose 50 % (LD50), potentially through the role of the glucocorticoid receptor (GR). Additionally, microRNAs (miRNAs) are known to modulate the toxic effects of AFB1. Nevertheless, whether the modulation of GR-targeting miRNAs can alleviate AFB1-induced hepatotoxicity has not been thoroughly investigated. This study examined the expression of GR and its associated microRNAs in AFB1-induced hepatotoxicity in mice, using GR-targeting antagomirs to mitigate AFB1 toxicity. AFB1 exposure elicited liver inflammation and oxidative stress in mice, while also reducing detoxification capacity. Notably, a decrease in GR protein expression was observed in liver tissue and hepatocytes. Additionally, miR141-3p, miR200a-3p, miR384-5p, miR183-5p, miR181a-5p, and miR181b-5p were upregulated and identified as regulators of GR expression. AFB1 induced cytotoxicity in AML12 cells, as evidenced by decreased GR protein levels and increased expression of miR141-3p, miR200a-3p, and miR495-3p. Inhibition of miR141/200a/495-3p reduced AFB1-induced cytotoxicity in AML12 cells. Furthermore, GR-targeting antagomirs (antagomir141/200a/495-3p) alleviated AFB1-induced hepatotoxicity in mice. This study highlights potential therapeutic targets for AFB1-induced liver diseases and offers new insights into strategies to mitigate the harmful effects of aflatoxin exposure.

Evolutionary Significance of the Neuroendocrine Stress Axis on Vertebrate Immunity and the Influence of the Microbiome on Early-Life Stress Regulation and Health Outcomes

Stress is broadly defined as the non-specific biological response to changes in homeostatic demands and is mediated by the evolutionarily conserved neuroendocrine networks of the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system. Activation of these networks results in transient release of glucocorticoids (cortisol) and catecholamines (epinephrine) into circulation, as well as activation of sympathetic fibers innervating end organs. These interventions thus regulate numerous physiological processes, including energy metabolism, cardiovascular physiology, and immunity, thereby adapting to cope with the perceived stressors. The developmental trajectory of the stress-axis is influenced by a number of factors, including the gut microbiome, which is the community of microbes that colonizes the gastrointestinal tract immediately following birth. The gut microbiome communicates with the brain through the production of metabolites and microbially derived signals, which are essential to human stress response network development. Ecological perturbations to the gut microbiome during early life may result in the alteration of signals implicated in developmental programming during this critical window, predisposing individuals to numerous diseases later in life. The vulnerability of stress response networks to maladaptive development has been exemplified through animal models determining a causal role for gut microbial ecosystems in HPA axis activity, stress reactivity, and brain development. In this review, we explore the evolutionary significance of the stress-axis system for health maintenance and review recent findings that connect early-life microbiome disturbances to alterations in the development of stress response networks.

Therapeutic Strategies to Protect the Central Nervous System against Shiga Toxin from Enterohemorrhagic Escherichia coli

Infection with Shiga toxin-producing Escherichia coli (STEC) may cause hemorrhagic colitis, hemolytic uremic syndrome (HUS) and encephalopathy. The mortality rate derived from HUS adds up to 5% of the cases, and up to 40% when the central nervous system (CNS) is involved. In addition to the well-known deleterious effect of Stx, the gram-negative STEC releases lipopolysaccharides (LPS) and may induce a variety of inflammatory responses when released in the gut. Common clinical signs of severe CNS injury include sensorimotor, cognitive, emotional and/or autonomic alterations. In the last few years, a number of drugs have been experimentally employed to establish the pathogenesis of, prevent or treat CNS injury by STEC. The strategies in these approaches focus on: 1) inhibition of Stx production and release by STEC, 2) inhibition of Stx bloodstream transport, 3) inhibition of Stx entry into the CNS parenchyma, 4) blockade of deleterious Stx action in neural cells, and 5) inhibition of immune system activation and CNS inflammation. Fast diagnosis of STEC infection, as well as the establishment of early CNS biomarkers of damage, may be determinants of adequate neuropharmacological treatment in time.

Pathogenic role of inflammatory response during Shiga toxin-associated hemolytic uremic syndrome (HUS)

Hemolytic uremic syndrome (HUS) is defined as a triad of noninmune microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. The most frequent presentation is secondary to Shiga toxin (Stx)-producing Escherichia coli (STEC) infections, which is termed postdiarrheal, epidemiologic or Stx-HUS, considering that Stx is the necessary etiological factor. After ingestion, STEC colonize the intestine and produce Stx, which translocates across the intestinal epithelium. Once Stx enters the bloodstream, it interacts with renal endothelial and epithelial cells, and leukocytes. This review summarizes the current evidence about the involvement of inflammatory components as central pathogenic factors that could determine outcome of STEC infections. Intestinal inflammation may favor epithelial leakage and subsequent passage of Stx to the systemic circulation. Vascular damage triggered by Stx promotes not only release of thrombin and increased fibrin concentration but also production of cytokines and chemokines by endothelial cells. Recent evidence from animal models and patients strongly indicate that several immune cells types may participate in HUS physiopathology: neutrophils, through release of proteases and reactive oxygen species (ROS); monocytes/macrophages through secretion of cytokines and chemokines. In addition, high levels of Bb factor and soluble C5b-9 (sC5b-9) in plasma as well as complement factors adhered to platelet-leukocyte complexes, microparticles and microvesicles, suggest activation of the alternative pathway of complement. Thus, acute immune response secondary to STEC infection, the Stx stimulatory effect on different immune cells, and inflammatory stimulus secondary to endothelial damage all together converge to define a strong inflammatory status that worsens Stx toxicity and disease.

Role of transcriptional coregulator GRIP1 in the anti-inflammatory actions of glucocorticoids

Inhibition of cytokine gene expression by the hormone-activated glucocorticoid receptor (GR) is the key component of the anti-inflammatory actions of glucocorticoids, yet the underlying molecular mechanisms remain obscure. Here we report that glucocorticoid repression of cytokine genes in primary macrophages is mediated by GR-interacting protein (GRIP)1, a transcriptional coregulator of the p160 family, which is recruited to the p65-occupied genomic NFκB-binding sites in conjunction with liganded GR. We created a mouse strain enabling a conditional hematopoietic cell-restricted deletion of GRIP1 in adult animals. In this model, GRIP1 depletion in macrophages attenuated in a dose-dependent manner repression of NFκB target genes by GR irrespective of the upstream Toll-like receptor pathway responsible for their activation. Furthermore, genome-wide transcriptome analysis revealed a broad derepression of lipopolysaccharide (LPS)-induced glucocorticoid-sensitive targets in GRIP1-depleted macrophages without affecting their activation by LPS. Consistently, conditional GRIP1-deficient mice were sensitized, relative to the wild type, to a systemic inflammatory challenge developing characteristic signs of LPS-induced shock. Thus, by serving as a GR corepressor, GRIP1 facilitates the anti-inflammatory effects of glucocorticoids in vivo.

Lipopolysaccharide renders transgenic mice expressing human serum amyloid P component sensitive to Shiga toxin 2

Transgenic C57BL/6 mice expressing human serum amyloid P component (HuSAP) are resistant to Shiga toxin 2 (Stx2) at dosages that are lethal in HuSAP-negative wild-type mice. However, it is well established that Stx2 initiates extra-intestinal complications such as the haemolytic-uremic syndrome despite the presence of HuSAP in human sera. We now demonstrate that co-administering purified Escherichia coli O55 lipopolysaccharide (LPS), at a dosage of 300 ng/g body weight, to HuSAP-transgenic mice increases their susceptibility to the lethal effects of Stx2. The enhanced susceptibility to Stx2 correlated with an increased expression of genes encoding the pro-inflammatory cytokine TNFα and chemokines of the CXC and CC families in the kidneys of LPS-treated mice, 48 hours after the Stx2/LPS challenge. Co-administering the glucocorticoid dexamethasone, but not the LPS neutralizing cationic peptide LL-37, protected LPS-sensitized HuSAP-transgenic mice from lethal doses of Stx2. Dexamethasone protection was specifically associated with decreased expression of the same inflammatory mediators (CXC and CC-type chemokines and TNFα) linked to enhanced susceptibility caused by LPS. The studies reveal further details about the complex cascade of host-related events that are initiated by Stx2 as well as establish a new animal model system in which to investigate strategies for diminishing serious Stx2-mediated complications in humans infected with enterohemorrhagic E. coli strains.

The glucocorticoid receptor: a revisited target for toxins

The hypothalamic-pituitary-adrenal (HPA) axis activation and glucocorticoid responses are critical for survival from a number of bacterial, viral and toxic insults, demonstrated by the fact that removal of the HPA axis or GR blockade enhances mortality rates. Replacement with synthetic glucocorticoids reverses these effects by providing protection against lethal effects. Glucocorticoid resistance/insensitivity is a common problem in the treatment of many diseases. Much research has focused on the molecular mechanism behind this resistance, but an area that has been neglected is the role of infectious agents and toxins. We have recently shown that the anthrax lethal toxin is able to repress glucocorticoid receptor function. Data suggesting that the glucocorticoid receptor may be a target for a variety of toxins is reviewed here. These studies have important implications for glucocorticoid therapy.

Bacillus anthracis lethal toxin represses MMTV promoter activity through transcription factors

We have recently shown that the anthrax lethal toxin (LeTx) selectively represses nuclear hormone receptors. In this study, we found that LeTx repressed the activation of the mouse mammary tumor virus promoter related to overexpression of the transcription factors hepatocyte nuclear factor 3, octamer-binding protein 1, and c-Jun. LeTx transcriptional repression was associated with a decrease in the protein levels of these transcription factors in a lethal factor protease activity-dependent manner. Early administration of LeTx antagonists partially or completely abolished the repressive effects of LeTx. In contrast to the rapid cleavage of mitogen-activated protein kinase kinases by LeTx, the degradation of these transcription factors occurred at a relatively late stage after LeTx treatment. In addition, LeTx repressed phorbol-12-myristate-13-acetate-induced mouse mammary tumor virus promoter activity and phorbol 12-myristate 13-acetate induction of endogenous c-Jun protein. Collectively, these findings suggest that transcription factors are intracellular targets of LeTx and expand our understanding of the molecular action of LeTx at a later stage of low-dose exposure.

Posttraumatic stress and immune dissonance

Stress or neuroendocrine response usually occurs soon after trauma, which is central to the maintenance of post-traumatic homeostasis. Immune inflammatory response has been recognized to be a key element both in the pathogenesis of post-traumatic complications and in tissue repair. Despite the existence of multiple and intricate interconnected neuroendocrine pathways, the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system have been considered to be the most important in trauma. Although the short-term and appropriate activation of these stress responses is vital to the host's adaptation, prolonged duration and exaggerative magnitude of their activity leads to deleterious effects on immune function in trauma, causing immune dissonance. The overall appropriate and controlled activation and termination of the neuroendocrine responses that mediate the necessary physiological functions involved in maintaining and restoring homeostasis in the event of trauma are of critical importance. This review will describe the effects of some important neuroendocrine responses on immune system. Present evidences indicate that the neuroendocrine and immune systems form a cohesive and integrated early host response to trauma, and identify areas for further research to fully elucidate the regulatory role of neuroendocrine system in trauma.

Pathogenesis of renal disease due to enterohemorrhagic Escherichia coli in germ-free mice

Enterohemorrhagic Escherichia coli (EHEC) is a food-borne pathogen that causes hemorrhagic colitis and acute renal failure. We used a germ-free mouse model to investigate the role of host factors, Shiga toxin 2 (Stx2), and bacterial strain in disease due to EHEC. Germ-free male and female Swiss-Webster mice that were 3 days to 12 weeks old were orally inoculated with 1 of 10 EHEC strains or derivatives of two of these strains with Stx2 deleted. All inoculated mice became infected regardless of the inoculum dose. All bacterial strains colonized the intestines, reaching levels of 10(9) to 10(12) CFU/g of feces by 4 days after inoculation. Seven of the 10 wild-type strains caused disease. However, the two Stx2 deletion mutants, unlike the Stx2(+) parental strains, did not cause disease. The clinical signs of disease in mice included lethargy, dehydration, polyuria, polydypsia, and death. Postmortem examination of affected mice revealed dehydration and luminal cecal fluid accumulation. Histologic examination revealed close adherence of bacteria to the intestinal epithelium in the ileum and cecum but not in the colon. Other lesions included progressive renal tubular necrosis, glomerular fibrin thrombosis, and red blood cell sludging. The severity of disease varied according to the bacterial strain and age, but not sex, of the host. This study demonstrated that EHEC colonizes germ-free mice in large numbers, adheres to the intestinal epithelium, and causes luminal cecal fluid accumulation and progressive renal failure. The disease in mice was Stx2 and bacterial strain dependent. This animal model should be a useful tool for studying the pathogenesis of renal disease secondary to EHEC infection.

Neural regulation of innate immunity: a coordinated nonspecific host response to pathogens

The central nervous system (CNS) regulates innate immune responses through hormonal and neuronal routes. The neuroendocrine stress response and the sympathetic and parasympathetic nervous systems generally inhibit innate immune responses at systemic and regional levels, whereas the peripheral nervous system tends to amplify local innate immune responses. These systems work together to first activate and amplify local inflammatory responses that contain or eliminate invading pathogens, and subsequently to terminate inflammation and restore host homeostasis. Here, I review these regulatory mechanisms and discuss the evidence indicating that the CNS can be considered as integral to acute-phase inflammatory responses to pathogens as the innate immune system.

Anthrax lethal toxin represses glucocorticoid receptor (GR) transactivation by inhibiting GR-DNA binding in vivo

Anthrax lethal factor (LF) is a non-competitive repressor of glucocorticoid (GR) and progesterone receptor (PR) transactivation. This repression was shown to be specific and selective and was dependent on promoter context and receptor subtype. Anthrax lethal toxin (LeTx) selectively repressed GR-mediated transactivation but not transrepression. The DNA binding region of GR was required for repression by LeTx and LeTx prevented GR-DNA binding in vivo, which had downstream consequences on polymerase II binding and histone acetylation. In addition, LeTx also prevented the accessory protein C/EBP from binding to a GR-responsive promoter. We hypothesize that LeTx may remove/inactivate one of the many co-factors or accessory proteins that are required to stabilize the GR-DNA complex. These findings enhance the current knowledge of the molecular mechanism by which the anthrax lethal factor represses nuclear hormone receptors and could provide an approach to overcome some of LeTx's effects.

Endogenous glucocorticoids modulate neutrophil function in a murine model of haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS) is caused by Shiga-toxin-producing Escherichia coli (STEC). Although, Shiga toxin type 2 (Stx2) is responsible for the renal pathogenesis observed in patients, the inflammatory response, including cytokines and polymorphonuclear neutrophils (PMN), plays a key role in the development of HUS. Previously, we demonstrated that Stx2 injection generates an anti-inflammatory reaction characterized by endogenous glucocorticoid (GC) secretion, which attenuates HUS severity in mice. Here, we analysed the effects of Stx2 on the pathogenic function of PMN and the potential role of endogenous GC to limit PMN activation during HUS development in a murine model. For this purpose we assessed the functional activity of isolated PMN after in vivo treatment with Stx2 alone or in simultaneous treatment with Ru486 (GC receptor antagonist). We found that Stx2 increased the generation of reactive oxygen intermediates (ROI) under phobol-myristate-acetate (PMA) stimulation and that the simultaneous treatment with Ru486 strengthened this effect. Conversely, both treatments significantly inhibited in vitro phagocytosis. Furthermore, Stx2 augmented in vitro PMN adhesion to fibrinogen (FGN) and bovine serum albumin (BSA) but not to collagen type I (CTI). Stx2 + Ru486 caused enhanced adhesion to BSA and CTI compared to Stx2. Whereas Stx2 significantly increased migration towards N-formyl-methionyl-leucyl-phenylalanine (fMLP), Stx2 + Ru486 treatment enhanced and accelerated this process. The percentage of apoptotic PMN from Stx2-treated mice was higher compared with controls, but equal to Stx2 + Ru486 treated mice. We conclude that Stx2 activates PMN and that the absence of endogenous GC enhances this activation suggesting that endogenous GC can, at least partially, counteract PMN inflammatory functions.

Antibody therapy in the management of shiga toxin-induced hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is a disease that can lead to acute renal failure and often to other serious sequelae, including death. The majority of cases are attributed to infections with Escherichia coli, serotype O157:H7 strains in particular, which cause bloody diarrhea and liberate one or two toxins known as Shiga toxins 1 and 2. These toxins are thought to directly be responsible for the manifestations of HUS. Currently, supportive nonspecific treatment is the only available option for the management of individuals presenting with HUS. The benefit of antimicrobial therapy remains uncertain because of several reports which claim that such intervention can in fact exacerbate the syndrome. There have been only a few specific therapies directed against neutralizing the activities of these toxins, but none so far has been shown to be effective. This article reviews the literature on the mechanism of action of these toxins and the clinical manifestations and current management and treatment of HUS. The major focus of the article, however, is the development and rationale for using neutralizing human antibodies to combat this toxin-induced disease. Several groups are currently pursuing this approach with either humanized, chimeric, or human antitoxin antibodies produced in transgenic mice. They are at different phases of development, ranging from preclinical evaluation to human clinical trials. The information available from preclinical studies indicates that neutralizing specific antibodies directed against the A subunit of the toxin can be highly protective. Such antibodies, even when administered well after exposure to bacterial infection and onset of diarrhea, can prevent the occurrence of systemic complications.

Neural immune pathways and their connection to inflammatory diseases

Inflammation and inflammatory responses are modulated by a bidirectional communication between the neuroendocrine and immune system. Many lines of research have established the numerous routes by which the immune system and the central nervous system (CNS) communicate. The CNS signals the immune system through hormonal pathways, including the hypothalamic-pituitary-adrenal axis and the hormones of the neuroendocrine stress response, and through neuronal pathways, including the autonomic nervous system. The hypothalamic-pituitary-gonadal axis and sex hormones also have an important immunoregulatory role. The immune system signals the CNS through immune mediators and cytokines that can cross the blood-brain barrier, or signal indirectly through the vagus nerve or second messengers. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. This review discusses neuroimmune interactions and evidence for the role of such neural immune regulation of inflammation, rather than a discussion of the individual inflammatory mediators, in rheumatoid arthritis.

Anthrax lethal factor represses glucocorticoid and progesterone receptor activity

We report here that a bacterial toxin, anthrax lethal toxin (LeTx), at very low concentrations represses glucocorticoid receptor (GR) transactivation in a transient transfection system and the activity of an endogenous GR-regulated gene in both a cellular system and an animal model. This repression is noncompetitive and does not affect ligand binding or DNA binding, suggesting that anthrax lethal toxin (LeTx) probably exerts its effects through a cofactor(s) involved in the interaction between GR and the basal transcription machinery. LeTx-nuclear receptor repression is selective, repressing GR, progesterone receptor B (PR-B), and estrogen receptor alpha (ERalpha), but not the mineralocorticoid receptor (MR) or ERbeta. GR repression was also caused by selected p38 mitogen-activated protein (MAP) kinase inhibitors, suggesting that the LeTx action may result in part from its known inactivation of MAP kinases. Simultaneous loss of GR and other nuclear receptor activities could render an animal more susceptible to lethal or toxic effects of anthrax infection by removing the normally protective antiinflammatory effects of these hormones, similar to the increased mortality seen in animals exposed to both GR antagonists and infectious agents or bacterial products. These finding have implications for development of new treatments and prevention of the toxic effects of anthrax.