Characterization of the baboon responses to Shiga-like toxin: descriptive study of a new primate model of toxic responses to Stx-1

Shiga Toxin 2 Triggers C3a-Dependent Glomerular and Tubular Injury through Mitochondrial Dysfunction in Hemolytic Uremic Syndrome

Shiga toxin (Stx)-producing Escherichia coli is the predominant offending agent of post-diarrheal hemolytic uremic syndrome (HUS), a rare disorder of microvascular thrombosis and acute kidney injury possibly leading to long-term renal sequelae. We previously showed that C3a has a critical role in the development of glomerular damage in experimental HUS. Based on the evidence that activation of C3a/C3a receptor (C3aR) signaling induces mitochondrial dysregulation and cell injury, here we investigated whether C3a caused podocyte and tubular injury through induction of mitochondrial dysfunction in a mouse model of HUS. Mice coinjected with Stx2/LPS exhibited glomerular podocyte and tubular C3 deposits and C3aR overexpression associated with cell damage, which were limited by C3aR antagonist treatment. C3a promoted renal injury by affecting mitochondrial wellness as demonstrated by data showing that C3aR blockade reduced mitochondrial ultrastructural abnormalities and preserved mitochondrial mass and energy production. In cultured podocytes and tubular cells, C3a caused altered mitochondrial fragmentation and distribution, and reduced anti-oxidant SOD2 activity. Stx2 potentiated the responsiveness of renal cells to the detrimental effects of C3a through increased C3aR protein expression. These results indicate that C3aR may represent a novel target in Stx-associated HUS for the preservation of renal cell integrity through the maintenance of mitochondrial function.

Therapeutic Uses of Bacterial Subunit Toxins

The B subunit pentamer verotoxin (VT aka Shiga toxin-Stx) binding to its cellular glycosphingolipid (GSL) receptor, globotriaosyl ceramide (Gb₃) mediates internalization and the subsequent receptor mediated retrograde intracellular traffic of the AB5 subunit holotoxin to the endoplasmic reticulum. Subunit separation and cytosolic A subunit transit via the ER retrotranslocon as a misfolded protein mimic, then inhibits protein synthesis to kill cells, which can cause hemolytic uremic syndrome clinically. This represents one of the most studied systems of prokaryotic hijacking of eukaryotic biology. Similarly, the interaction of cholera AB5 toxin with its GSL receptor, GM1 ganglioside, is the key component of the gastrointestinal pathogenesis of cholera and follows the same retrograde transport pathway for A subunit cytosol access. Although both VT and CT are the cause of major pathology worldwide, the toxin–receptor interaction is itself being manipulated to generate new approaches to control, rather than cause, disease. This arena comprises two areas: anti neoplasia, and protein misfolding diseases. CT/CTB subunit immunomodulatory function and anti-cancer toxin immunoconjugates will not be considered here. In the verotoxin case, it is clear that Gb₃ (and VT targeting) is upregulated in many human cancers and that there is a relationship between GSL expression and cancer drug resistance. While both verotoxin and cholera toxin similarly hijack the intracellular ERAD quality control system of nascent protein folding, the more widespread cell expression of GM1 makes cholera the toxin of choice as the means to more widely utilise ERAD targeting to ameliorate genetic diseases of protein misfolding. Gb₃ is primarily expressed in human renal tissue. Glomerular endothelial cells are the primary VT target but Gb₃ is expressed in other endothelial beds, notably brain endothelial cells which can mediate the encephalopathy primarily associated with VT2-producing E. coli infection. The Gb₃ levels can be regulated by cytokines released during EHEC infection, which complicate pathogenesis. Significantly Gb₃ is upregulated in the neovasculature of many tumours, irrespective of tumour Gb₃ status. Gb₃ is markedly increased in pancreatic, ovarian, breast, testicular, renal, astrocytic, gastric, colorectal, cervical, sarcoma and meningeal cancer relative to the normal tissue. VT has been shown to be effective in mouse xenograft models of renal, astrocytoma, ovarian, colorectal, meningioma, and breast cancer. These studies are herein reviewed. Both CT and VT (and several other bacterial toxins) access the cell cytosol via cell surface ->ER transport. Once in the ER they interface with the protein folding homeostatic quality control pathway of the cell -ERAD, (ER associated degradation), which ensures that only correctly folded nascent proteins are allowed to progress to their cellular destinations. Misfolded proteins are translocated through the ER membrane and degraded by cytosolic proteosome. VT and CT A subunits have a C terminal misfolded protein mimic sequence to hijack this transporter to enter the cytosol. This interface between exogenous toxin and genetically encoded endogenous mutant misfolded proteins, provides a new therapeutic basis for the treatment of such genetic diseases, e.g., Cystic fibrosis, Gaucher disease, Krabbe disease, Fabry disease, Tay-Sachs disease and many more. Studies showing the efficacy of this approach in animal models of such diseases are presented.

Shiga Toxins: An Update on Host Factors and Biomedical Applications

Shiga toxins (Stxs) are classic bacterial toxins and major virulence factors of toxigenic Shigella dysenteriae and enterohemorrhagic Escherichia coli (EHEC). These toxins recognize a glycosphingolipid globotriaosylceramide (Gb3/CD77) as their receptor and inhibit protein synthesis in cells by cleaving 28S ribosomal RNA. They are the major cause of life-threatening complications such as hemolytic uremic syndrome (HUS), associated with severe cases of EHEC infection, which is the leading cause of acute kidney injury in children. The threat of Stxs is exacerbated by the lack of toxin inhibitors and effective treatment for HUS. Here, we briefly summarize the Stx structure, subtypes, in vitro and in vivo models, Gb3 expression and HUS, and then introduce recent studies using CRISPR-Cas9-mediated genome-wide screens to identify the host cell factors required for Stx action. We also summarize the latest progress in utilizing and engineering Stx components for biomedical applications.

A One Health Perspective for Defining and Deciphering Escherichia coli Pathogenic Potential in Multiple Hosts

E. coli is one of the most common species of bacteria colonizing humans and animals. The singularity of E. coli 's genus and species underestimates its multifaceted nature, which is represented by different strains, each with different combinations of distinct virulence factors. In fact, several E. coli pathotypes, or hybrid strains, may be associated with both subclinical infection and a range of clinical conditions, including enteric, urinary, and systemic infections. E. coli may also express DNA-damaging toxins that could impact cancer development. This review summarizes the different E. coli pathotypes in the context of their history, hosts, clinical signs, epidemiology, and control. The pathotypic characterization of E. coli in the context of disease in different animals, including humans, provides comparative and One Health perspectives that will guide future clinical and research investigations of E. coli infections.

Involvement of high mobility group box 1 in the pathogenesis of severe hemolytic uremic syndrome in a murine model

Typical hemolytic uremic syndrome is caused by Shiga toxin (Stx2) and lipopolysaccharide (LPS) of Escherichia coli and leads to acute kidney injury. The role of innate immunity in this pathogenesis is unclear. We analyzed the role of high mobility group box 1 (HMGB1) at the onset of disease in a murine model. C57BL/6 mice were intraperitoneally administered saline ( group A), anti-HMGB1 monoclonal antibody ( group B), Stx2 and LPS to elicit severe disease ( group C), or Stx2, LPS, and anti-HMGB1 antibody ( group D). While all mice in group C died by day 5 of the experiment, all mice in group D survived. Anemia and thrombocytopenia were pronounced and plasma creatinine levels were significantly elevated in group C only at 72 h. While at 72 h after toxin administration the glomerulus tissue in group C showed pathology similar to that of humans, mesangial cell proliferation was seen in group D. Plasma HMGB1 levels in group C peaked 3 h after administration and were higher than those in other groups. Expression of the receptor of advanced glycation end products and NF-κB, involved in HMGB1 signaling, was significantly elevated in group C but not in group D. Administration of anti-HMGB1 antibody in a murine model of severe disease inhibited plasma HMGB1 and promoted amelioration of tissue damage. HMGB1 was found to be involved in the disease pathology; therefore, controlling HMGB1 activity might inhibit disease progression.

Roles of Shiga Toxins in Immunopathology

Shigella species and Shiga toxin-producing Escherichia coli (STEC) are agents of bloody diarrhea that may progress to potentially lethal complications such as diarrhea-associated hemolytic uremic syndrome (D+HUS) and neurological disorders. The bacteria share the ability to produce virulence factors called Shiga toxins (Stxs). Research over the past two decades has identified Stxs as multifunctional toxins capable of inducing cell stress responses in addition to their canonical ribotoxic function inhibiting protein synthesis. Notably, Stxs are not only potent inducers of cell death, but also activate innate immune responses that may lead to inflammation, and these effects may increase the severity of organ injury in patients infected with Stx-producing bacteria. In the intestines, kidneys, and central nervous system, excessive or uncontrolled host innate and cellular immune responses triggered by Stxs may result in sensitization of cells to toxin mediated damage, leading to immunopathology and increased morbidity and mortality in animal models (including primates) and human patients. Here, we review studies describing Stx-induced innate immune responses that may be associated with tissue damage, inflammation, and complement activation. We speculate on how these processes may contribute to immunopathological responses to the toxins.

Shiga toxin triggers endothelial and podocyte injury: the role of complement activation

Shiga toxin (Stx)-producing Escherichia coli (STEC) is the offending agent in post-diarrhea-associated hemolytic uremic syndrome (HUS), a disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute kidney failure, with thrombi occluding the renal microvasculature. Endothelial dysfunction has been recognized as the trigger event in the development of microangiopathic processes. Glomerular endothelial cells are susceptible to the toxic effects of Stxs that, via nuclear factor kappa B (NF-κB) activation, induce the expression of genes encoding for adhesion molecules and chemokines, culminating in leukocyte adhesion and platelet thrombus formation on the activated endothelium. Complement activation via the alternative pathway has been seen in patients during the acute phase of STEC-associated HUS. Experimental evidence has highlighted the role of complement proteins in driving glomerular endothelium toward a thrombogenic phenotype. At the glomerular level, podocytes are also an important target of Stx-induced complement activation. Glomerular injury as a consequence of podocyte dysfunction and loss is thus a mechanism that might affect long-term renal outcomes in the disease. New approaches to targeting the complement system may be useful therapeutic options for patients with STEC-HUS.

Complement Activation Contributes to the Pathophysiology of Shiga Toxin-Associated Hemolytic Uremic Syndrome

Shiga toxin (Stx)-producing Escherichia coli (STEC) infections have become a threat to public health globally because of the severe illnesses that they can trigger, such as hemorrhagic colitis and the post-diarrheal hemolytic uremic syndrome (HUS), characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney failure. Glomerular endothelial cells are primary targets of Stx which, after binding to its specific receptor globotriaosylceramide, upregulates proinflammatory proteins involved both in the recruitment and adhesion of leukocytes and thrombus formation at the site of endothelial injury. In this review, we discuss the role of complement activation in promoting glomerular microvascular dysfunction, providing evidence from experimental models and patients with STEC-HUS. Within the glomerulus, an important target for Stx-induced complement activation is the podocyte, a cell type that is in close contact with endothelial cells and participates in maintaining the filtration barrier. Recently, podocyte injury and loss have been indicated as potential risk factors for long-term renal sequelae in patients with STEC-HUS. Therapeutic approaches targeting the complement system, that may be useful options for patients with STEC-HUS, will also be discussed.

Pathogenic and non-pathogenic Escherichia coli colonization and host inflammatory response in a defined microbiota mouse model

Most Escherichia coli strains in the human intestine are harmless. However, enterohemorrhagic Ecoli (EHEC) is a foodborne pathogen that causes intestinal disease in humans. Conventionally reared (CONV) mice are inconsistent models for human infections with EHEC because they are often resistant to Ecoli colonization, in part due to their gastrointestinal (GI) microbiota. Although antibiotic manipulation of the mouse microbiota has been a common means to overcome colonization resistance, these models have limitations. Currently, there are no licensed treatments for clinical EHEC infections and, thus, new tools to study EHEC colonization need to be developed. Here, we used a defined microbiota mouse model, consisting of the altered Schaedler flora (ASF), to characterize intestinal colonization and compare host responses following colonization with EHEC strain 278F2 or non-pathogenic Ecoli strain MG1655. Significantly higher (P<0.05) levels of both strains were found in feces and cecal and colonic contents of C3H/HeN ASF compared to C3H/HeN CONV mice. GI inflammation was significantly elevated (P<0.05) in the cecum of EHEC 278F2-colonized compared to E. coli MG1655-colonized C3H/HeN ASF mice. In addition, EHEC 278F2 differentially modulated inflammatory-associated genes in colonic tissue of C3H/HeN ASF mice compared to E. coli MG1655-colonized mice. This approach allowed for prolonged colonization of the murine GI tract by pathogenic and non-pathogenic Ecoli strains, and for evaluation of host inflammatory processes. Overall, this system can be used as a powerful tool for future studies to assess therapeutics, microbe-microbe interactions, and strategies for preventing EHEC infections.

Modeling Hemolytic-Uremic Syndrome: In-Depth Characterization of Distinct Murine Models Reflecting Different Features of Human Disease

Diarrhea-positive hemolytic-uremic syndrome (HUS) is a renal disorder that results from infections with Shiga-toxin (Stx)-producing Escherichia coli. The aim of this study was to establish well-defined refined murine models of HUS that can serve as preclinical tools to elucidate molecular mechanisms of disease development. C57BL/6J mice were subjected to different doses of Stx2 purified from an E. coli O157:H7 patient isolate. Animals received 300 ng/kg Stx2 and were sacrificed on day 3 to establish an acute model with fast disease progression. Alternatively, mice received 25 ng/kg Stx2 on days 0, 3, and 6, and were sacrificed on day 7 to establish a subacute model with moderate disease progression. Indicated by a rise in hematocrit, we observed dehydration despite volume substitution in both models, which was less pronounced in mice that underwent the 7-day regime. Compared with sham-treated animals, mice subjected to Stx2 developed profound weight loss, kidney dysfunction (elevation of plasma urea, creatinine, and neutrophil gelatinase-associated lipocalin), kidney injury (tubular injury and loss of endothelial cells), thrombotic microangiopathy (arteriolar microthrombi), and hemolysis (elevation of plasma bilirubin, lactate dehydrogenase, and free hemoglobin). The degree of complement activation (C3c deposition), immune cell invasion (macrophages and T lymphocytes), apoptosis, and proliferation were significantly increased in kidneys of mice subjected to the 7-day but not in kidneys of mice subjected to the 3-day regime. However, glomerular and kidney volume remained mainly unchanged, as assessed by 3D analysis of whole mount kidneys using CD31 staining with light sheet fluorescence microscopy. Gene expression analysis of kidneys revealed a total of only 91 overlapping genes altered in both Stx2 models. In conclusion, we have developed two refined mouse models with different disease progression, both leading to hemolysis, thrombotic microangiopathy, and acute kidney dysfunction and damage as key clinical features of human HUS. While intrarenal changes (apoptosis, proliferation, complement deposition, and immune cell invasion) mainly contribute to the pathophysiology of the subacute model, prerenal pathomechanisms (hypovolemia) play a predominant role in the acute model. Both models allow the further study of the pathomechanisms of most aspects of human HUS and the testing of distinct novel treatment strategies.

Shiga Toxins Induce Apoptosis and ER Stress in Human Retinal Pigment Epithelial Cells

Shiga toxins (Stxs) produced by Shiga toxin-producing bacteria Shigella dysenteriae serotype 1 and select serotypes of Escherichia coli are the most potent known virulence factors in the pathogenesis of hemorrhagic colitis progressing to potentially fatal systemic complications such as acute renal failure, blindness and neurological abnormalities. Although numerous studies have defined apoptotic responses to Shiga toxin type 1 (Stx1) or Shiga toxin type 2 (Stx2) in a variety of cell types, the potential significance of Stx-induced apoptosis of photoreceptor and pigmented cells of the eye following intoxication is unknown. We explored the use of immortalized human retinal pigment epithelial (RPE) cells as an in vitro model of Stx-induced retinal damage. To the best of our knowledge, this study is the first report that intoxication of RPE cells with Stxs activates both apoptotic cell death signaling and the endoplasmic reticulum (ER) stress response. Using live-cell imaging analysis, fluorescently labeled Stx1 or Stx2 were internalized and routed to the RPE cell endoplasmic reticulum. RPE cells were significantly sensitive to wild type Stxs by 72 h, while the cells survived challenge with enzymatically deficient mutant toxins (Stx1A⁻ or Stx2A⁻). Upon exposure to purified Stxs, RPE cells showed activation of a caspase-dependent apoptotic program involving a reduction of mitochondrial transmembrane potential (Δψ_m), increased activation of ER stress sensors IRE1, PERK and ATF6, and overexpression CHOP and DR5. Finally, we demonstrated that treatment of RPE cells with Stxs resulted in the activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38MAPK), suggesting that the ribotoxic stress response may be triggered. Collectively, these data support the involvement of Stx-induced apoptosis in ocular complications of intoxication. The evaluation of apoptotic responses to Stxs by cells isolated from multiple organs may reveal unique functional patterns of the cytotoxic actions of these toxins in the systemic complications that follow ingestion of toxin-producing bacteria.

Comparison of clinical and immunological findings in gnotobiotic piglets infected with Escherichia coli O104:H4 outbreak strain and EHEC O157:H7

Background

Shiga toxin (Stx) producing Escherichia coli (E. coli) (STEC) is the most frequent cause of diarrhoea-positive haemolytic uraemic syndrome (D + HUS) in humans. In 2011, a huge outbreak with an STEC O104:H4 strain in Germany highlighted the limited possibilities for causative treatment of this syndrome. The responsible STEC strain was found to combine Stx production with adherence mechanisms normally found in enteroaggregative E. coli (EAEC). Pathotypes of E. coli evolve and can exhibit different adhesion mechanisms. It has been shown previously that neonatal gnotobiotic piglets are susceptible for infection with STEC, such as STEC O157:H7 as well as for EAEC, which are considered to be the phylogenetic origin of E. coli O104:H4. This study was designed to characterise the host response to infection with the STEC O104:H4 outbreak strain in comparison to an STEC O157:H7 isolate by evaluating clinical parameters (scoring) and markers of organ dysfunction (biochemistry), as well as immunological (flow cytometry, assessment of cytokines/chemokines and acute phase proteins) and histological alterations (light- and electron microscopy) in a gnotobiotic piglet model of haemolytic uraemic syndrome.

Results

We observed severe clinical symptoms, such as diarrhoea, dehydration and neurological disorders as well as attaching-and-effacing lesions (A/E) in the colon in STEC O157:H7 infected piglets. In contrast, STEC O104:H4 challenged animals exhibited only mild clinical symptoms including diarrhoea and dehydration and HUS-specific/severe histopathological, haematological and biochemical alterations were only inconsistently presented by individual piglets. A specific adherence phenotype of STEC O104:H4 could not be observed. Flow cytometric analyses of lymphocytes derived from infected animals revealed an increase of natural killer cells (NK cells) during the course of infection revealing a potential role of this subset in the anti-bacterial activity in STEC disease.

Conclusions

Unexpectedly, E. coli O104:H4 infection caused only mild symptoms and minor changes in histology and blood parameters in piglets. Outcome of the infection trial does not reflect E. coli O104:H4 associated human disease as observed during the outbreak in 2011. The potential role of cells of the innate immune system for STEC related disease pathogenesis should be further elucidated.

Animal Models of Enterohemorrhagic Escherichia coli Infection

The first major outbreaks caused by enterohemorrhagic Escherichia coli (EHEC) raised public and medical awareness of the risks associated with acquiring this potentially deadly infection. The widespread presence of these organisms in the environment, the severity of the clinical sequelae, and the lack of treatment options and effective preventive measures demand that we obtain a better understanding of how this group of organisms cause disease. Animal models allow study of the processes and factors that contribute to disease and, as such, form a valuable tool in the repertoire of infectious disease researchers. Yet despite more than 30 years of research, it seems that no single model host reproduces the full spectrum of clinical disease induced by EHEC in humans. In the first part of this review, a synopsis of what is known about EHEC infections is garnered from human outbreaks and biopsy specimens. The main features and limitations of EHEC infection models that are based on the three most commonly used species (pigs, rabbits, and mice) are described within a historical context. Recent advances are highlighted, and a brief overview of models based on other species is given. Finally, the impact of the host on moderating EHEC infection is considered in light of growing evidence for the need to consider the biology and virulence strategies of EHEC in the context of its niche within the intestine.

Sub-Lethal Dose of Shiga Toxin 2 from Enterohemorrhagic Escherichia coli Affects Balance and Cerebellar Cytoarchitecture

Shiga toxin producing Escherichia coli may damage the central nervous system before or concomitantly to manifested hemolytic–uremic syndrome symptoms. The cerebellum is frequently damaged during this syndrome, however, the deleterious effects of Shiga toxin 2 has never been integrally reported by ultrastructural, physiological and behavioral means. The aim of this study was to determine the cerebellar compromise after intravenous administration of a sub-lethal dose of Shiga toxin 2 by measuring the cerebellar blood–brain barrier permeability, behavioral task of cerebellar functionality (inclined plane test), and ultrastructural analysis (transmission electron microscope). Intravenous administration of vehicle (control group), sub-lethal dose of 0.5 and 1 ηg of Stx2 per mouse were tested for behavioral and ultrastructural studies. A set of three independent experiments were performed for each study (n = 6). Blood–brain barrier resulted damaged and consequently its permeability was significantly increased. Lower scores obtained in the inclined plane task denoted poor cerebellar functionality in comparison to their controls. The most significant lower score was obtained after 5 days of 1 ηg of toxin administration. Transmission electron microscope micrographs from the Stx2-treated groups showed neurons with a progressive neurodegenerative condition in a dose dependent manner. As sub-lethal intravenous Shiga toxin 2 altered the blood brain barrier permeability in the cerebellum the toxin penetrated the cerebellar parenchyma and produced cell damaged with significant functional implications in the test balance.

Enterohemorrhagic Escherichia coli Pathogenesis and the Host Response

Enterohemorrhagic Escherichia coli (EHEC) is a highly pathogenic bacterial strain capable of causing watery or bloody diarrhea, the latter termed hemorrhagic colitis, and hemolytic-uremic syndrome (HUS). HUS is defined as the simultaneous development of non-immune hemolytic anemia, thrombocytopenia, and acute renal failure. The mechanism by which EHEC bacteria colonize and cause severe colitis, followed by renal failure with activated blood cells, as well as neurological symptoms, involves the interaction of bacterial virulence factors and specific pathogen-associated molecular patterns with host cells as well as the host response. The innate immune host response comprises the release of antimicrobial peptides as well as cytokines and chemokines in addition to activation and/or injury to leukocytes, platelets, and erythrocytes and activation of the complement system. Some of the bacterial interactions with the host may be protective in nature, but, when excessive, contribute to extensive tissue injury, inflammation, and thrombosis, effects that may worsen the clinical outcome of EHEC infection. This article describes aspects of the host response occurring during EHEC infection and their effects on specific organs.

Shiga Toxins: Potent Poisons, Pathogenicity Determinants, and Pharmacological Agents

The Shiga toxins (Stxs), also known as Vero toxins and previously called Shiga-like toxins, are a family of potent protein synthesis inhibitors made by Shigella dysenteriae type 1 and some serogroups of Escherichia coli that cause bloody diarrhea in humans. Stxs act as virulence factors for both S. dysenteriae and E. coli and contribute to the disease process initiated by those organisms both directly and indirectly. A handful of methods exist for toxin purification, and the toxins can now even be purchased commercially. However, the Stxs are now classified as select agents, and specific rules govern the distribution of both the toxin and clones of the toxin. Toxin delivery into the host in S. dysenteriae type 1 is most likely aided by the invasiveness of that organism. Although the Stxs are made and produced by bacteria, they do not appear to act against either their host organism or other bacteria under normal circumstances, most likely because the A subunit is secreted from the cytoplasm as soon as it is synthesized and because the holotoxin cannot enter intact bacterial cells. The effectiveness of antibiotic therapy in patients infected with Stx-producing E. coli (STEC) such as O157:H7 as well as the potential risks of such treatment are areas of controversy. Several studies indicate that the course of the diarrhea stage of the disease is unaltered by antibiotic treatment. Several groups anticipate that a therapy that targets the Stxs is an important component of trying to alleviate disease caused by Stx-producing bacteria.

Pro-Coagulant Endothelial Dysfunction Results from EHEC Shiga Toxins and Host Damage-Associated Molecular Patterns

Hemolytic uremic syndrome (HUS) from enterohemorrhagic Escherichia coli infection is a leading cause of kidney failure in otherwise healthy U.S. children. The bacterial Shiga toxins (Stx) induce the characteristic coagulopathy of HUS, but the damage to toxin-receptor expressing cells and organ injury due to ischemia likely also releases inflammatory damage-associated molecular patterns (DAMPs), which may exacerbate injury along with the toxins. To examine this, human aortic and renal glomerular cell anti-coagulant and barrier functions were studied after in vitro challenge with Stx1, Stx2, and DAMPs. There was significant loss of surface anti-coagulant protein C pathway molecules, increased expression of pro-thrombotic PAR1 and reduced protein C activation capability by 15-27%. Histones nearly completely prevented the activated protein C protection of endothelial cells from thrombin-induced permeability. In mice, lethal Stx2 challenge elevated plasma HMGB1 (day 2, 321 ± 118%; p < 0.01) and extracellular histones (day 3, 158 ± 62%; p < 0.01). Mice colonized with Stx2-expressing Citrobacter rodentium developed increased HMGB1 (day 5, 155 ± 55%; p < 0.01) and histones (day 3, 378 ± 188%; p < 0.01). Anti-histone antibody reduced both DAMPs to baseline, but was not sufficient to improve survival outcome or kidney function. Together, these data suggest a potential role Stx to produce DAMPs, and DAMPs to produce endothelial injury and a pro-thrombotic environment.

Translational value of animal models of kidney failure

Acute kidney injury (AKI) and chronic kidney disease (CKD) are associated with decreased renal function and increased mortality risk, while the therapeutic armamentarium is unsatisfactory. The availability of adequate animal models may speed up the discovery of biomarkers for disease staging and therapy individualization as well as design and testing of novel therapeutic strategies. Some longstanding animal models have failed to result in therapeutic advances in the clinical setting, such as kidney ischemia-reperfusion injury and diabetic nephropathy models. In this regard, most models for diabetic nephropathy are unsatisfactory in that they do not evolve to renal failure. Satisfactory models for additional nephropathies are needed. These include anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis, IgA nephropathy, anti-phospholipase-A2-receptor (PLA2R) membranous nephropathy and Fabry nephropathy. However, recent novel models hold promise for clinical translation. Thus, the AKI to CKD translation has been modeled, in some cases with toxins of interest for human CKD such as aristolochic acid. Genetically modified mice provide models for Alport syndrome evolving to renal failure that have resulted in clinical recommendations, polycystic kidney disease models that have provided clues for the development of tolvaptan, that was recently approved for the human disease in Japan; and animal models also contributed to target C5 with eculizumab in hemolytic uremic syndrome. Some ongoing trials explore novel concepts derived from models, such TWEAK targeting as tissue protection for lupus nephritis. We now review animal models reproducing diverse, genetic and acquired, causes of AKI and CKD evolving to kidney failure and discuss the contribution to clinical translation and prospects for the future.

The efficacy of recombinant human soluble thrombomodulin for the treatment of shiga toxin-associated hemolytic uremic syndrome model mice

BACKGROUND

Recombinant human soluble thrombomodulin (rhTM) is a promising therapeutic natural anticoagulant that is comparable to antithrombin, tissue factor pathway inhibitor and activated protein C. In order to clarify the efficacy of rhTM for the treatment of typical hemolytic uremic syndrome (t-HUS), we examined changes in renal damage in t-HUS mice treated with rhTM or vehicle alone.

METHODS

We used severe and moderate t-HUS mice injected with shiga toxin (Stx) and lipopolysaccharide (LPS). The severe t-HUS mice were divided into two subgroups [an rhTM subgroup (Group A) and a saline subgroup (Group B)] along with the moderate t-HUS mice [an rhTM subgroup (Group C) and a saline subgroup (Group D)]. Groups E and F were healthy mice treated with rhTM or saline, respectively.

RESULTS

All mice in Group B died at 80-90 h post-administration of Stx2 and LPS whereas all mice in Group A remained alive. Loss of body weight, serum creatinine level, endothelial injury and mesangiolysis scores at 24 h after administration in the t-HUS mice treated with rhTM were lower than those in t-HUS mice treated with saline. The levels of hemoglobin at 6 h and platelet counts at 24 h after administration in Group A were higher than those in Group B. Serum interleukin (IL)-6, IL-1β and tumor necrotic factor (TNF)-α levels at 24 h after administration in Group A were lower than those in Group B. Serum C5b-9 levels at 24 h after the administration and serum fibrinogen degradation product (FDP) at 72 h after the administration of Stx2 and LPS were lower in Group A than in Group B.

CONCLUSIONS

These results indicate that rhTM might afford an efficacious treatment for t-HUS model mice via the inhibition of further thrombin formation and amelioration of hypercoagulant status.

Animal Reservoirs of Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) strains have been detected in a wide diversity of mammals, birds, fish, and several insects. Carriage by most animals is asymptomatic, thus allowing for dissemination of the bacterium in the environment without detection. Replication of the organism may occur in the gastrointestinal tract of some animals, notably ruminants. Carriage may also be passive or transient, without significant amplification of bacterial numbers while in the animal host. Animals may be classified as reservoir species, spillover hosts, or dead-end hosts. This classification is based on the animal's ability to (i) transmit STEC to other animal species and (ii) maintain STEC infection in the absence of continuous exposure. Animal reservoirs are able to maintain STEC infections in the absence of continuous STEC exposure and transmit infection to other species. Spillover hosts, although capable of transmitting STEC to other animals, are unable to maintain infection in the absence of repeated exposure. The large diversity of reservoir and spillover host species and the survival of the organism in environmental niches result in complex pathways of transmission that are difficult to interrupt.

Shiga toxin promotes podocyte injury in experimental hemolytic uremic syndrome via activation of the alternative pathway of complement

Shiga toxin (Stx)-producing Escherichia coli is the offending agent of postdiarrhea-associated hemolytic uremic syndrome (HUS), a disorder of glomerular ischemic damage and widespread microvascular thrombosis. We previously documented that Stx induces glomerular complement activation, generating C3a responsible for microvascular thrombosis in experimental HUS. Here, we show that the presence of C3 deposits on podocytes is associated with podocyte damage and loss in HUS mice generated by the coinjection of Stx2 and LPS. Because podocyte adhesion to the glomerular basement membrane is mediated by integrins, the relevance of integrin-linked kinase (ILK) signals in podocyte dysfunction was evaluated. Podocyte expression of ILK increased after the injection of Stx2/LPS and preceded the upregulation of Snail and downregulation of nephrin and α-actinin-4. Factor B deficiency or pretreatment with an inhibitory antibody to factor B protected mice against Stx2/LPS-induced podocyte dysregulation. Similarly, pretreatment with a C3a receptor antagonist limited podocyte loss and changes in ILK, Snail, and α-actinin-4 expression. In cultured podocytes, treatment with C3a reduced α-actinin-4 expression and promoted ILK-dependent nuclear expression of Snail and cell motility. These results suggest that Stx-induced activation of the alternative pathway of complement and generation of C3a promotes ILK signaling, leading to podocyte dysfunction and loss in Stx-HUS.

Protection of human podocytes from shiga toxin 2-induced phosphorylation of mitogen-activated protein kinases and apoptosis by human serum amyloid P component

Hemolytic uremic syndrome (HUS) is mainly induced by Shiga toxin 2 (Stx2)-producing Escherichia coli. Proteinuria can occur in the early phase of the disease, and its persistence determines the renal prognosis. Stx2 may injure podocytes and induce proteinuria. Human serum amyloid P component (SAP), a member of the pentraxin family, has been shown to protect against Stx2-induced lethality in mice in vivo, presumably by specific binding to the toxin. We therefore tested the hypothesis that SAP can protect against Stx2-induced injury of human podocytes. To elucidate the mechanisms underlying podocyte injury in HUS-associated proteinuria, we assessed Stx2-induced activation of mitogen-activated protein kinases (MAPKs) and apoptosis in immortalized human podocytes and evaluated the impact of SAP on Stx2-induced damage. Human podocytes express Stx2-binding globotriaosylceramide 3. Stx2 applied to cultured podocytes was internalized and then activated p38α MAPK and c-Jun N-terminal kinase (JNK), important signaling steps in cell differentiation and apoptosis. Stx2 also activated caspase 3, resulting in an increased level of apoptosis. Coincubation of podocytes with SAP and Stx2 mitigated the effects of Stx2 and induced upregulation of antiapoptotic Bcl2. These data suggest that podocytes are a target of Stx2 and that SAP protects podocytes against Stx2-induced injury. SAP may therefore be a useful therapeutic option.

Treatment and prevention of enterohemorrhagicEscherichia coliinfection and hemolytic uremic syndrome

Over a quarter century after the discovery of verocytotoxin and the first report by Karmali and colleagues of cases of postdiarrheal hemolytic uremic syndrome (HUS) caused by verotoxigenic Escherichia coli (VTEC), otherwise known as Shiga-toxigenic E. coli (STEC), successful treatment of these infections has remained elusive. This is because the pathological insult producing the clinical picture of HUS occurs early in the disease process and curtails quickly, making treatment intervention a largely vain hope. Nevertheless, understanding of the pathogenesis of HUS has expanded and, as a result, we can expect a future breakthrough in the treatment of this life-threatening condition. This review examines the pathogenesis of HUS and explores targets for treatment, including the reasons why certain therapies have failed and why future therapies could be successful. This review also examines the status of vaccine development in prevention of VTEC/STEC disease.

Plasma bacterial and mitochondrial DNA distinguish bacterial sepsis from sterile systemic inflammatory response syndrome and quantify inflammatory tissue injury in nonhuman primates

Systemic inflammatory response syndrome (SIRS) is a fundamental host response common to bacterial infection and sterile tissue injury. Systemic inflammatory response syndrome can cause organ dysfunction and death, but its mechanisms are incompletely understood. Moreover, SIRS can progress to organ failure or death despite being sterile or after control of the inciting infection. Biomarkers discriminating between sepsis, sterile SIRS, and postinfective SIRS would therefore help direct care. Circulating mitochondrial DNA (mtDNA) is a damage-associated molecular pattern reflecting cellular injury. Circulating bacterial 16S DNA (bDNA) is a pathogen-associated pattern (PAMP) reflecting ongoing infection. We developed quantitative polymerase chain reaction assays to quantify these markers, and predicting their plasma levels might help distinguish sterile injury from infection. To study these events in primates, we assayed banked serum from Papio baboons that had undergone a brief challenge of intravenous Bacillus anthracis delta Sterne (modified to remove toxins) followed by antibiotics (anthrax) that causes organ failure and death. To investigate the progression of sepsis to "severe" sepsis and death, we studied animals where anthrax was pretreated with drotrecogin alfa (activated protein C), which attenuates sepsis in baboons. We also contrasted lethal anthrax bacteremia against nonlethal E. coli bacteremia and against sterile tissue injury from Shiga-like toxin 1. Bacterial DNA and mtDNA levels in timed samples were correlated with blood culture results and assays of organ function. Sterile injury by Shiga-like toxin 1 increased mtDNA, but bDNA was undetectable: consistent with the absence of infection. The bacterial challenges caused parallel early bDNA and mtDNA increases, but bDNA detected pathogens even after bacteria were undetectable by culture. Sublethal E. coli challenge only caused transient rises in mtDNA consistent with a self-limited injury. In lethal anthrax challenge (n = 4), bDNA increased transiently, but mtDNA levels remained elevated until death, consistent with persistent septic tissue damage after bacterial clearance. Critically, activated protein C pretreatment (n = 4) allowed mtDNA levels to decay after bacterial clearance with sparing of organ function and survival. In summary, host tissue injury correlates with mtDNA whether infective or sterile. Mitochondrial DNA and bDNA polymerase chain reactions can quantify tissue injury incurred by septic or sterile mechanisms and suggest the source of SIRS of unknown origin.

Distinct renal pathology and a chemotactic phenotype after enterohemorrhagic Escherichia coli shiga toxins in non-human primate models of hemolytic uremic syndrome

Enterohemorrhagic Escherichia coli cause approximately 1.5 million infections globally with 176,000 cases occurring in the United States annually from ingesting contaminated food, most frequently E. coli O157:H7 in ground beef or fresh produce. In severe cases, the painful prodromal hemorrhagic colitis is complicated by potentially lethal hemolytic uremic syndrome (HUS), particularly in children. Bacterial Shiga-like toxins (Stx1, Stx2) are primarily responsible for HUS and the kidney and neurologic damage that ensue. Small animal models are hampered by the inability to reproduce HUS with thrombotic microangiopathy, hemolytic anemia, and acute kidney injury. Earlier, we showed that nonhuman primates (Papio) recapitulated clinical HUS after Stx challenge and that novel therapeutic intervention rescued the animals. Here, we present detailed light and electron microscopic pathology examination of the kidneys from these Stx studies. Stx1 challenge resulted in more severe glomerular endothelial injury, whereas the glomerular injury after Stx2 also included prominent mesangiolysis and an eosinophilic inflammatory infiltration. Both toxins induced glomerular platelet-rich thrombi, interstitial hemorrhage, and tubular injury. Analysis of kidney and other organs for inflammation biomarkers showed a striking chemotactic profile, with extremely high mRNA levels for IL-8, monocyte chemoattractant protein 1, and macrophage inflammatory protein 1α and elevated urine chemokines at 48 hours after challenge. These observations give unique insight into the pathologic consequences of each toxin in a near human setting and present potential pathways for therapeutic intervention.

A translational murine model of sub-lethal intoxication with Shiga toxin 2 reveals novel ultrastructural findings in the brain striatum

Infection by Shiga toxin-producing Escherichia coli causes hemorrhagic colitis, hemolytic uremic syndrome (HUS), acute renal failure, and also central nervous system complications in around 30% of the children affected. Besides, neurological deficits are one of the most unrepairable and untreatable outcomes of HUS. Study of the striatum is relevant because basal ganglia are one of the brain areas most commonly affected in patients that have suffered from HUS and since the deleterious effects of a sub-lethal dose of Shiga toxin have never been studied in the striatum, the purpose of this study was to attempt to simulate an infection by Shiga toxin-producing E. coli in a murine model. To this end, intravenous administration of a sub-lethal dose of Shiga toxin 2 (0.5 ηg per mouse) was used and the correlation between neurological manifestations and ultrastructural changes in striatal brain cells was studied in detail. Neurological manifestations included significant motor behavior abnormalities in spontaneous motor activity, gait, pelvic elevation and hind limb activity eight days after administration of the toxin. Transmission electron microscopy revealed that the toxin caused early perivascular edema two days after administration, as well as significant damage in astrocytes four days after administration and significant damage in neurons and oligodendrocytes eight days after administration. Interrupted synapses and mast cell extravasation were also found eight days after administration of the toxin. We thus conclude that the chronological order of events observed in the striatum could explain the neurological disorders found eight days after administration of the toxin.

Shiga toxins and the pathophysiology of hemolytic uremic syndrome in humans and animals

Food-borne diseases are estimated at 76 million illnesses and 5000 deaths every year in the United States with the greatest burden on young children, the elderly and immunocompromised populations. The impact of efficient food distribution systems and a truly global food supply ensures that outbreaks, previously sporadic and contained locally, are far more widespread and emerging pathogens have far more frequent infection opportunities. Enterohemorrhagic E. coli is an emerging food- and water-borne pathogen family whose Shiga-like toxins induce painful hemorrhagic colitis with potentially lethal complications of hemolytic uremic syndrome (HUS). The clinical manifestations of Shiga toxin-induced HUS overlap with other related syndromes yet molecular mechanisms differ considerably. As discussed herein, understanding these differences and the novel properties of the toxins is imperative for clinical management decisions, design of appropriate animal models, and choices of adjunctive therapeutics. The emergence of new strains with rapidly aggressive virulence makes clinical and research initiatives in this field a high public health priority.

The interactions of human neutrophils with shiga toxins and related plant toxins: danger or safety?

Shiga toxins and ricin are well characterized similar toxins belonging to quite different biological kingdoms. Plant and bacteria have evolved the ability to produce these powerful toxins in parallel, while humans have evolved a defense system that recognizes molecular patterns common to foreign molecules through specific receptors expressed on the surface of the main actors of innate immunity, namely monocytes and neutrophils. The interactions between these toxins and neutrophils have been widely described and have stimulated intense debate. This paper is aimed at reviewing the topic, focusing particularly on implications for the pathogenesis and diagnosis of hemolytic uremic syndrome.

Shiga toxin pathogenesis: kidney complications and renal failure

The kidneys are the major organs affected in diarrhea-associated hemolytic uremic syndrome (D(+)HUS). The pathophysiology of renal disease in D(+)HUS is largely the result of the interaction between bacterial virulence factors such as Shiga toxin and lipopolysaccharide and host cells in the kidney and in the blood circulation. This chapter describes in detail the current knowledge of how these bacterial toxins may lead to kidney disease and renal failure. The toxin receptors expressed by specific blood and resident renal cell types are also discussed as are the actions of the toxins on these cells.

Rescue from lethal Shiga toxin 2-induced renal failure with a cell-permeable peptide

Intestinal infection with Shiga toxin (Stx)-producing E.coli is a leading cause of hemolytic uremic syndrome and acute renal injury in otherwise healthy children in the US. Antibiotics are contraindicated and a therapeutic priority is agents that act intracellularly against the bacterial toxins that drive kidney injury. Our aim was to evaluate whether intravenous administration of a cell-permeable peptide (TVP) that binds to Stx2 will reduce disease severity and rescue juvenile baboons from a lethal Stx2 dose (50 ng/kg). TVP (5 mg/kg) was delivered i.v. simultaneously with toxin (prevention protocol) or at 6 or 24 h after toxin with daily 1 mg/kg supplements up to day 4 (rescue protocols). Biomarkers were monitored in blood and urine up to 28 days. TVP therapy resulted in either absence of clinical signs of acute kidney injury and normal urine output (prevention), or delayed and reduced BUN and creatinine levels (rescue) with concomitant survival. Delayed peptide administration significantly reduced thrombocytopenia, but surprisingly did not alter anemia even when monitored for 28 days in rescued survivors. This is the first successful cell-permeable therapeutic that counteracts Stx2 lethality in an animal model, which recapitulates many of the human responses to enteric infection.

Patterns in early diffusion-weighted MRI in children with haemolytic uraemic syndrome and CNS involvement

OBJECTIVES

Diffusion-weighted imaging (DWI) in children with diarrhoea associated haemolytic uraemic syndrome (D+HUS) and cerebral involvement was evaluated retrospectively.

METHODS

DWI within 24 h of onset of neurological symptoms. The apparent diffusion coefficient (ADC) was measured in grey/white matter and correlated with clinical and laboratory findings.

RESULTS

DWI was abnormal in all. Abnormal ADC was detected in the supratentorial white matter (6/12) and cortex (1/12), the basal ganglia (5/12), the thalami (4/12), and the cerebellum (1/12). ADC was reduced in 5/12, increased in 4/12, and both in 3/12. Mean serum sodium was lower in patients with DWI abnormalities affecting the white matter (6/12), than in those with basal ganglia/thalamic involvement (6/12). Neurological outcome was normal in 4/11 and abnormal in 7/11, and 1 patient died, outcome did not correlate to either localisation or type of DWI abnormality.

CONCLUSIONS

In D+HUS with neurological symptoms, early DWI may reveal abnormal ADC not only in the basal ganglia/thalami, but also in the white matter/cortex. Besides thrombotic microangiopathy, toxic effects of shiga toxin, azotaemia and hyponatraemia / hypoosmolality may be involved in cerebral involvement in children with D+HUS. Findings on early MRI seem not to predict clinical course or outcome.

KEY POINTS

• DWI MR imaging may detect early CNS involvement in haemolytic uraemic syndrome • Different pathogenetical mechanisms may contribute to the CNS disease in HUS • Early MRI findings do not seem to allow prediction of clinical outcome.

Clinical relevance of shiga toxin concentrations in the blood of patients with hemolytic uremic syndrome

BACKGROUND

Intestinal infections with Shiga toxin-producing Escherichia coli (STEC) in children can lead to the hemolytic uremic syndrome (HUS). Shiga toxins (Stx) released in the gut by bacteria enter the blood stream and target the kidney causing endothelial injury. Free toxins have never been detected in the blood of HUS patients, but they have been found on the surface of polymorphonuclear leukocytes (PMN).

METHODS

With respect to their clinical features, the clinical relevance of the amounts of serum Stx (cytotoxicity assay with human endothelial cells) and PMN-bound Stx (cytofluorimetric assay) in 46 patients with STEC-associated HUS was evaluated.

RESULTS

Stx-positive PMN were found in 60% of patients, whereas negligible amounts of free Stx were detected in the sera. Patients with high amounts of Stx on PMN showed preserved or slightly impaired renal function (incomplete form of HUS), whereas cases with low amounts of Stx usually presented evidence of acute renal failure.

CONCLUSIONS

These observations suggest that the extent of renal damage in children with STEC-associated HUS could depend on the concentration of Stx present on their PMN and presumably delivered by them to the kidney. As previously shown by experimental models from our laboratory, high amounts of Stx could induce a reduced release of cytokines by the renal endothelium, with a consequent lower degree of inflammation. Conversely, low toxin amounts can trigger the cytokine cascade, provoking inflammation, thereby leading to tissue damage.

Mouse models of Escherichia coli O157:H7 infection and shiga toxin injection

Escherichia coli O157:H7 has been responsible for multiple food- and waterborne outbreaks of diarrhea and/or hemorrhagic colitis (HC) worldwide. More importantly, a portion of E. coli O157:H7-infected individuals, particularly young children, develop a life-threatening sequela of infection called hemolytic uremic syndrome (HUS). Shiga toxin (Stx), a potent cytotoxin, is the major virulence factor linked to the presentation of both HC and HUS. Currently, treatment of E. coli O157:H7 and other Stx-producing E. coli (STEC) infections is limited to supportive care. To facilitate development of therapeutic strategies and vaccines for humans against these agents, animal models that mimic one or more aspect of STEC infection and disease are needed. In this paper, we focus on the characteristics of various mouse models that have been developed and that can be used to monitor STEC colonization, disease, pathology, or combinations of these features as well as the impact of Stx alone.

Escherichia coli Shiga Toxin Mechanisms of Action in Renal Disease

Shiga toxin-producing Escherichia coli is a contaminant of food and water that in humans causes a diarrheal prodrome followed by more severe disease of the kidneys and an array of symptoms of the central nervous system. The systemic disease is a complex referred to as diarrhea-associated hemolytic uremic syndrome (D⁺HUS). D⁺HUS is characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure. This review focuses on the renal aspects of D⁺HUS. Current knowledge of this renal disease is derived from a combination of human samples, animal models of D⁺HUS, and interaction of Shiga toxin with isolated renal cell types. Shiga toxin is a multi-subunit protein complex that binds to a glycosphingolipid receptor, Gb3, on select eukaryotic cell types. Location of Gb3 in the kidney is predictive of the sites of action of Shiga toxin. However, the toxin is cytotoxic to some, but not all cell types that express Gb3. It also can cause apoptosis or generate an inflammatory response in some cells. Together, this myriad of results is responsible for D⁺HUS disease.

Role of tumor necrosis factor alpha in disease using a mouse model of Shiga toxin-mediated renal damage

Mice have been extensively employed as an animal model of renal damage caused by Shiga toxins. In this study, we examined the role of the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) in the development of toxin-mediated renal disease in mice. Mice pretreated with TNF-alpha and challenged with Shiga toxin type 1 (Stx1) showed increased survival compared to that of mice treated with Stx1 alone. Conversely, mice treated with Stx1 before TNF-alpha administration succumbed more quickly than mice given Stx1 alone. Increased lethality in mice treated with Stx1 followed by TNF-alpha was associated with evidence of glomerular damage and the loss of renal function. No differences in renal histopathology were noted between animals treated with Stx1 alone and the TNF-alpha pretreatment group, although we noted a sparing of renal function when TNF-alpha was administered before toxin. Compared to that of treatment with Stx1 alone, treatment with TNF-alpha after toxin altered the renal cytokine profile so that the expression of proinflammatory cytokines TNF-alpha and interleukin-1beta (IL-1beta) increased, and the expression of the anti-inflammatory cytokine IL-10 decreased. Increased lethality in mice treated with Stx1 followed by TNF-alpha was associated with higher numbers of dUTP-biotin nick end labeling-positive renal tubule cells, suggesting that increased lethality involved enhanced apoptosis. These data suggest that the early administration of TNF-alpha is a candidate interventional strategy blocking disease progression, while TNF-alpha production after intoxication exacerbates disease.

Shiga toxins: intracellular trafficking to the ER leading to activation of host cell stress responses

Despite efforts to improve hygenic conditions and regulate food and drinking water safety, the enteric pathogens, Shiga toxin-producing Escherichia coli (STEC) and Shigella dysenteriae serotype 1 remain major public health concerns due to widespread outbreaks and the severity of extra-intestinal diseases they cause, including acute renal failure and central nervous system complications. Shiga toxins are the key virulence factors expressed by these pathogens mediating extra-intestinal disease. Delivery of the toxins to the endoplasmic reticulum (ER) results in host cell protein synthesis inhibition, activation of the ribotoxic stress response, the ER stress response, and in some cases, the induction of apoptosis. Intrinsic and/or extrinsic apoptosis inducing pathways are involved in executing cell death following intoxication. In this review we provide an overview of the current understanding Shiga toxin intracellular trafficking, host cellular responses to the toxin and ER stress-induced apoptosis with an emphasis on recent findings.

Signaling through C/EBP homologous protein and death receptor 5 and calpain activation differentially regulate THP-1 cell maturation-dependent apoptosis induced by Shiga toxin type 1

Shiga toxins (Stxs) induce apoptosis via activation of the intrinsic and extrinsic pathways in many cell types. Toxin-mediated activation of the endoplasmic reticulum (ER) stress response was shown to be instrumental in initiating apoptosis in THP-1 myeloid leukemia cells. THP-1 cells responded to Shiga toxin type 1 (Stx1) in a cell maturation-dependent manner, undergoing rapid apoptosis in the undifferentiated state but reduced and delayed apoptosis in differentiated cells. The onset of apoptosis was associated with calpain activation and changes in expression of C/EBP homologous protein (CHOP), Bcl-2 family members, and death receptor 5 (DR5). Ligation of DR5 by tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) activates the extrinsic pathway of apoptosis. We show here that expression of TRAIL and DR5 is increased by Stx1 treatment. Addition of exogenous TRAIL enhances, and anti-TRAIL antibodies inhibit, Stx1-induced apoptosis of THP-1 cells. Silencing of CHOP or DR5 expression selectively prevented caspase activation, loss of mitochondrial membrane potential, and Stx1-induced apoptosis of macrophage-like THP-1 cells. In contrast, the rapid kinetics of apoptosis induction in monocytic THP-1 cells correlated with rates of calpain cleavage. The results suggest that CHOP-DR5 signaling and calpain activation differentially contribute to cell maturation-dependent Stx1-induced apoptosis. Inhibition of these signaling pathways may protect cells from Stx cytotoxicity.

Distinct physiologic and inflammatory responses elicited in baboons after challenge with Shiga toxin type 1 or 2 from enterohemorrhagic Escherichia coli

Shiga toxin-producing Escherichia coli is a principal source of regional outbreaks of bloody diarrhea and hemolytic-uremic syndrome in the United States and worldwide. Primary bacterial virulence factors are Shiga toxin types 1 and 2 (Stx1 and Stx2), and we performed parallel analyses of the pathophysiologies elicited by the toxins in nonhuman primate models to identify shared and unique consequences of the toxemias. After a single intravenous challenge with purified Stx1 or Stx2, baboons (Papio) developed thrombocytopenia, anemia, and acute renal failure with loss of glomerular function, in a dose-dependent manner. Differences in the timing and magnitude of physiologic responses were observed between the toxins. The animals were more sensitive to Stx2, with mortality at lower doses, but Stx2-induced renal injury and mortality were delayed 2 to 3 days compared to those after Stx1 challenge. Multiplex analyses of plasma inflammatory cytokines revealed similarities (macrophage chemoattractant protein 1 [MCP-1] and tumor necrosis factor alpha [TNF-alpha]) and differences (interleukin-6 [IL-6] and granulocyte colony-stimulating factor [G-CSF]) elicited by the toxins with respect to the mediator induced and timing of the responses. Neither toxin induced detectable levels of plasma TNF-alpha. To our knowledge, this is the first time that the in vivo consequences of the toxins have been compared in a parallel and reproducible manner in nonhuman primates, and the data show similarities to patient observations. The availability of experimental nonhuman primate models for Stx toxemias provides a reproducible platform for testing antitoxin compounds and immunotherapeutics with outcome criteria that have clinical meaning.

Down-regulation of platelet surface CD47 expression in Escherichia coli O157:H7 infection-induced thrombocytopenia

Background

Platelet depletion is a key feature of hemolytic uremic syndrome (HUS) caused by Shiga toxin-producing Escherichia coli (STEC) infection. The mechanism underlying STEC-induced platelet depletion, however, is not completely understood.

Methodology/Principal Findings

Here we demonstrated for the first time that platelet surface expression of CD47 was significantly decreased in C57BL6 mice treated with concentrated culture filtrates (CCF) from STEC O157:H7. STEC O157:H7 CCF treatment also led to a sharp drop of platelet counts. The reduction of cell surface CD47 was specific for platelets but not for neutrophil, monocytes and red blood cells. Down-regulation of platelet surface CD47 was also observed in isolated human platelets treated with O157:H7 CCF. Platelet surface CD47 reduction by O157:H7 CCF could be blocked by anti-TLR4 antibody but not anti-CD62 antibody. Down-regulation of platelet surface CD47 was positively correlated with platelet activation and phagocytosis by human monocyte-derived macrophages. Furthermore, the enhanced phagocytosis process of O157:H7 CCF-treated platelets was abolished by addition of soluble CD47 recombinants.

Conclusions/Significance

Our results suggest that platelet CD47 down-regulation may be a novel mechanism underneath STEC-induced platelet depletion, and that the interactions between CD47 and its receptor, signal regulatory protein α (SIRPα), play an essential role in modulating platelet homeostasis.

Shiga-like toxins and HIV-1 'go through' glycosphingolipids and lipid rafts in renal cells

The binding of Shiga-like toxins (Stx) to globotriaosyl ceramide (Gb(3)) in renal cells plays a central role in Stx-induced hemolytic uremic syndrome (Stx-HUS). Khan et al. show that the presence of Gb(3) within lipid raft microdomains in glomerular but not tubular cells may be the basis for the glomerular- and age-restricted pathology of Stx-HUS. They also propose that the binding of the HIV-1 glycoprotein gp120 to Gb(3) in renal tubules may play a role in HIV nephropathy.

Shiga toxin 1-induced proinflammatory cytokine production is regulated by the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling pathway

Shiga toxin 1 (Stx1) transiently increases the expression of proinflammatory cytokines by macrophage-like THP-1 cells in vitro. Increased cytokine production is partly due to activation of the translation initiation factor eIF4E through a mitogen-activated protein kinase (MAPK)- and Mnk1-dependent pathway. eIF4E availability for translation initiation is regulated by association with eIF4E binding proteins (4E-BP). In this study, we showed that Stx1 transiently induced 4E-BP hyperphosphorylation, which may release eIF4E for translation initiation. Phosphorylation of 4E-BP at priming sites T37 and T46 was not altered by Stx1 but was transiently increased at S65, concomitant with increased cytokine expression. Using kinase inhibitors, we showed that 4E-BP phosphorylation was dependent on phosphatidylinositol 3-kinase (PI3K), Akt, and mammalian target of rapamycin (mTOR) activation but did not require MAPKs. Stx1 treatment resulted in increased levels of cytosolic Ca(2+). PI3K and Akt activation led to the phosphorylation and inactivation of the positive cytokine regulator glycogen synthase kinase 3alpha/beta (GSK-3alpha/beta). PI3K, Akt, and mTOR inhibitors and small interfering RNA knockdown of Akt expression all increased, whereas a GSK-3alpha/beta inhibitor decreased, Stx1-induced soluble tumor necrosis factor alpha and interleukin-1beta production. Overall, these findings suggest that despite transient activation of 4E-BP, the PI3K/Akt/mTOR pathway negatively influences cytokine induction by inactivating the positive regulator GSK-3alpha/beta.

Reduced Nitric Oxide Bioavailability In a Baboon Model of Shiga Toxin Mediated Hemolytic Uremic Syndrome (HUS)

BACKGROUND

Although there is agreement that post-diarrheal hemolytic uremic syndrome (D+ HUS) is caused by Shiga toxin (Stx)-producing E. coli, little is known about factors that mediate the host response to these toxins and potentially contribute to pathogenesis. Nitric oxide (NO) is a candidate mediator by virtue of its antiplatelet and renal vasodilatory properties.

METHODS

We used a baboon model of HUS to measure plasma and urinary NO metabolites and expression of NO synthase (eNOS and iNOS) in renal tissue following the intravenous administration of Stx-1.

RESULTS

Plasma concentrations through 60 hours of observation did not differ significantly from controls. Urinary values (indexed against urinary creatinine) tended, however, to rise during the initial 12 hours following administration of Stx-1. This was followed by a sustained reduction that coincided with the development of hemolytic anemia (schistocytosis) and other features of HUS. However, immunohistochemical staining for eNOS and iNOS in tissue obtained immediately after death at a median of 59 hours showed similar levels in control and Stx-treated animals, despite the presence of a florid thrombotic microangiopathy and tubular injury in the Stx-treated group.

CONCLUSION

We propose that urinary NO metabolite reduction was due to NO inactivation subsequent to its avid binding to free hemoglobin released from lysed red blood cells, and that this contributed to the acute renal failure by facilitating vasoconstriction and platelet aggregation and adhesion within the renal microvasculature.

Inhibition of water absorption in human proximal tubular epithelial cells in response to Shiga toxin-2

Postdiarrhea hemolytic uremic syndrome (HUS) is the most common cause of acute renal failure in children in Argentina. It is well established that Shiga toxin type 2 (Stx2) causes direct damage to glomerular endothelial cells and tubular epithelial cells, leading to a reduction in the water handling capacity of the kidney. In this study, we demonstrate that Stx2 and its B subunit (Stx2B) were able to inhibit water absorption across human renal tubular epithelial cell (HRTEC) monolayers without altering the short circuit current and the (3)H-mannitol permeability. Quantitative evaluation of (14)C-inulin transport across HRTEC monolayers showed a similar transport rate both before and after HRTEC treatment with Stx2 that confirmed the integrity of the paracellular pathway. Furthermore, Stx2 produced significant protein synthesis inhibition of HRTEC at concentrations as low as 0.001 ng/ml and 1 h of incubation, whereas Stx2B did not modify it at concentrations as high as 10,000 ng/ml and 6 h of incubation. Our findings suggest that whereas the action of Stx2 appears to be caused mainly by the inhibition of protein synthesis mediated by the A subunit, the binding of Stx2B subunit to the Gb3 receptor may affect the membrane mechanisms related to water absorption. We speculate that inhibition of water absorption may occur in proximal tubular cells in vivo in response to Stx2 and may contribute to the early event of HUS pathogenesis.

Shiga toxin-mediated disease in MyD88-deficient mice infected with Escherichia coli O157:H7

Toll-like receptors (TLRs) are key factors of innate immunity that detect pathogen invasion and trigger a host response. TLR4 can mediate a response through adaptor molecules, MyD88 or TRIF. In the present study, streptomycin-treated MyD88(-/-), Tlr4(-/-), Trif (Lps2/Lps2), and C57BL/6 wild-type (WT) mice were infected with either Shiga toxin (Stx)-producing or non-producing Escherichia coli O157:H7. Moderate to severe clinical signs of disease developed in MyD88(-/-) (n = 21/21), Tlr4(-/-) (n = 12/16), Trif (Lps2/Lps2) (n = 7/15) and WT mice (n = 6/20) infected with Stx-producing E. coli O157:H7 but not in mice inoculated with the Stx non-producing strain (n = 0/54, P < 0.001). MyD88(-/-) mice infected with Stx-producing E. coli O157:H7 developed the most severe disease and had the highest bacterial burden. Hematological analysis of sick MyD88(-/-) mice showed reduced red blood cell counts and reticulocytosis, suggesting hemolysis. Thrombocytopenia developed in MyD88(-/-), Trif (Lps2/Lps2), and WT mice, and creatinine levels were elevated in both MyD88(-/-) and WT mice infected with the Stx-producing strain. Renal histopathology showed evidence of glomerular capillary congestion, tubular desquamation, and fibrinogen deposition, and intestinal histopathology showed mucosal injury, edema, and inflammation in sick mice. Administration of purified Stx2 to MyD88(-/-) and WT mice led to severe disease in both groups, suggesting that MyD88(-/-) mice are not more sensitive to Stx than WT mice. As MyD88(-/-) mice developed the most severe disease hematological and pathological changes, the results suggest that dysfunctional innate immune responses via MyD88 enhanced Stx-induced disease.

Development of an experimental hemolytic uremic syndrome in rats

Escherichia coli strains producing Shiga toxins (Stxs) colonize the lower gastrointestinal tract and cause watery diarrhea, hemorrhagic colitis, and hemolytic-uremic syndrome (HUS). HUS is characterized by hemolytic anemia, thrombocytopenia, and acute renal failure. Oliguria associated with acute tubular necrosis and microangiopathic thrombosis has been reported as the most common cause of renal failure in Argentinean children. Our study was undertaken to obtain a model of HUS in rats that was similar to the clinical and renal histopathology findings described in humans. Rats were intraperitoneally inoculated with culture supernatant from recombinant E. coli expressing Stx2. Glomerular filtrate volume evaluated from clearance of creatinine resulted in a progressive reduction (from 53% at 24 h to 90% at 48 h). Urine volume increased significantly at 24 h but returned to normal levels at 48 h. Evidence of thrombocytopenia, anemia and leukocytosis was documented. Macroscopic analysis revealed a hyperemic peritoneal face with intestinal water accumulation. The kidneys were friable and congestive. Histopathological analysis showed glomerular and tubular necrosis as well as microangiopathic thrombosis. Our findings indicated vascular damage and kidney lesions similar to those described in humans with HUS.