Fabry Disease in Mice Protects against Lethal Disease Caused by Shiga Toxin–Expressing EnterohemorrhagicEscherichia coli

Shiga toxin targets the podocyte causing hemolytic uremic syndrome through endothelial complement activation

BACKGROUND

Shiga toxin (Stx)-producing Escherichia coli hemolytic uremic syndrome (STEC-HUS) is the leading cause of acute kidney injury in children, with an associated mortality of up to 5%. The mechanisms underlying STEC-HUS and why the glomerular microvasculature is so susceptible to injury following systemic Stx infection are unclear.

METHODS

Transgenic mice were engineered to express the Stx receptor (Gb3) exclusively in their kidney podocytes (Pod-Gb3) and challenged with systemic Stx. Human glomerular cell models and kidney biopsies from patients with STEC-HUS were also studied.

FINDINGS

Stx-challenged Pod-Gb3 mice developed STEC-HUS. This was mediated by a reduction in podocyte vascular endothelial growth factor A (VEGF-A), which led to loss of glomerular endothelial cell (GEnC) glycocalyx, a reduction in GEnC inhibitory complement factor H binding, and local activation of the complement pathway. Early therapeutic inhibition of the terminal complement pathway with a C5 inhibitor rescued this podocyte-driven, Stx-induced HUS phenotype.

CONCLUSIONS

This study potentially explains why systemic Stx exposure targets the glomerulus and supports the early use of terminal complement pathway inhibition in this devastating disease.

FUNDING

This work was supported by the UK Medical Research Council (MRC) (grant nos. G0901987 and MR/K010492/1) and Kidney Research UK (grant nos. TF_007_20151127, RP42/2012, and SP/FSGS1/2013). The Mary Lyon Center is part of the MRC Harwell Institute and is funded by the MRC (A410).

Molecular mechanisms of Shigella effector proteins: a common pathogen among diarrheic pediatric population

Different gastrointestinal pathogens cause diarrhea which is a very common problem in children aged under 5 years. Among bacterial pathogens, Shigella is one of the main causes of diarrhea among children, and it accounts for approximately 11% of all deaths among children aged under 5 years. The case-fatality rates for Shigella among the infants and children aged 1 to 4 years are 13.9% and 9.4%, respectively. Shigella uses unique effector proteins to modulate intracellular pathways. Shigella cannot invade epithelial cells on the apical site; therefore, it needs to pass epithelium through other cells rather than the epithelial cell. After passing epithelium, macrophage swallows Shigella, and the latter should prepare itself to exhibit at least two types of responses: (I) escaping phagocyte and (II) mediating invasion of and injury to the recurrent PMN. The presence of PMN and invitation to a greater degree resulted in gut membrane injuries and greater bacterial penetration. Infiltration of Shigella to the basolateral space mediates (A) cell attachment, (B) cell entry, (C) evasion of autophagy recognition, (D) vacuole formation and and vacuole rapture, (E) intracellular life, (F) Shiga toxin, and (G) immune response. In this review, an attempt is made to explain the role of each factor in Shigella infection.

Fabry Disease: Molecular Basis, Pathophysiology, Diagnostics and Potential Therapeutic Directions

Fabry disease (FD) is a lysosomal storage disorder (LSD) characterized by the deficiency of α-galactosidase A (α-GalA) and the consequent accumulation of toxic metabolites such as globotriaosylceramide (Gb3) and globotriaosylsphingosine (lysoGb3). Early diagnosis and appropriate timely treatment of FD patients are crucial to prevent tissue damage and organ failure which no treatment can reverse. LSDs might profit from four main therapeutic strategies, but hitherto there is no cure. Among the therapeutic possibilities are intravenous administered enzyme replacement therapy (ERT), oral pharmacological chaperone therapy (PCT) or enzyme stabilizers, substrate reduction therapy (SRT) and the more recent gene/RNA therapy. Unfortunately, FD patients can only benefit from ERT and, since 2016, PCT, both always combined with supportive adjunctive and preventive therapies to clinically manage FD-related chronic renal, cardiac and neurological complications. Gene therapy for FD is currently studied and further strategies such as substrate reduction therapy (SRT) and novel PCTs are under investigation. In this review, we discuss the molecular basis of FD, the pathophysiology and diagnostic procedures, together with the current treatments and potential therapeutic avenues that FD patients could benefit from in the future.

Assessing the role of glycosphingolipids in the phenotype severity of Fabry disease mouse model

Fabry disease is caused by deficient activity of α-galactosidase A, an enzyme that hydrolyzes the terminal α-galactosyl moieties from glycolipids and glycoproteins, and subsequent accumulation of glycosphingolipids, mainly globotriaosylceramide (Gb₃), globotriaosylsphingosine (lyso-Gb₃), and galabiosylceramide. However, there is no known link between these compounds and disease severity. In this study, we compared Gb₃ isoforms (various fatty acids) and lyso-Gb₃ analogs (various sphingosine modifications) in two strains of Fabry disease mouse models: a pure C57BL/6 (B6) background or a B6/129 mixed background, with the latter exhibiting more prominent cardiac and renal hypertrophy and thermosensation deficits. Total Gb₃ and lyso-Gb₃ levels in the heart, kidney, and dorsal root ganglion (DRG) were similar in the two strains. However, levels of the C20-fatty acid isoform of Gb₃ and particular lyso-Gb₃ analogs (+18, +34) were significantly higher in Fabry-B6/129 heart tissue when compared with Fabry-B6. By contrast, there was no difference in Gb₃ and lyso-Gb₃ isoforms/analogs in the kidneys and DRG between the two strains. Furthermore, using immunohistochemistry, we found that Gb₃ massively accumulated in DRG mechanoreceptors, a sensory neuron subpopulation with preserved function in Fabry disease. However, Gb₃ accumulation was not observed in nonpeptidergic nociceptors, the disease-relevant subpopulation that has remarkably increased isolectin-B4 (the marker of nonpeptidergic nociceptors) binding and enlarged cell size. These findings suggest that specific species of Gb₃ or lyso-Gb₃ may play major roles in the pathogenesis of Fabry disease, and that Gb₃ and lyso-Gb₃ are not responsible for the pathology in all tissues or cell types.

Progress in the understanding and treatment of Fabry disease

BACKGROUND

Fabry disease is caused by α-galactosidase A deficiency. Substrates of this lysosomal enzyme accumulate, resulting in cellular dysfunction. Patients experience neuropathic pain, kidney failure, heart disease, and strokes.

SCOPE OF REVIEW

The clinical picture and molecular features of Fabry disease are described, along with updates on disease mechanisms, animal models, and therapies.

MAJOR CONCLUSIONS

How the accumulation of α-galactosidase A substrates, mainly glycosphingolipids, leads to organ damage is incompletely understood. Enzyme replacement and chaperone therapies are clinically available to patients, while substrate reduction, mRNA-based, and gene therapies are on the horizon. Animal models exist to optimize these therapies and elucidate disease mechanisms for novel treatments.

GENERAL SIGNIFICANCE

Recent newborn screening studies demonstrate that Fabry disease is the most common lysosomal storage disease. As many countries now include Fabry disease in their screening panels, the number of identified patients is expected to increase significantly. Better knowledge of disease pathogenesis is needed to improve treatment options.

Protein Toxins That Utilize Gangliosides as Host Receptors

Subsets of protein toxins utilize gangliosides as host receptors. Gangliosides are preferred receptors due to their extracellular localization on the eukaryotic cell and due to their essential nature in host physiology. Glycosphingolipids, including gangliosides, are mediators of signal transduction within and between eukaryotic cells. Protein toxins possess AB structure-function organization, where the A domain encodes a catalytic function for the posttranslational modification of a host macromolecule, including proteins and nucleic acids, and a B domain, which encodes host receptor recognition, including proteins and glycosphingolipids, alone or in combination. Protein toxins use similar strategies to bind glycans by pockets and loops, generally employing hydrogen bonding and aromatic stacking to stabilize interactions with sugars. In some cases, glycan binding facilitates uptake, while in other cases, cross-linking or a second receptor is necessary to stimulate entry. The affinity that protein toxins have for host glycans is necessary for tissue targeting, but not always sufficient to cause disease. In addition to affinity for binding the glycan, the lipid moiety also plays an important role in productive uptake and tissue tropism. Upon endocytosis, the protein toxin must escape to another intracellular compartment or into cytosol to modify a host substrate, modulating host signaling, often resulting in cytotoxic or apoptotic events in the cell, and a unique morbidity for the organism. The study of protein toxins that utilize gangliosides as host receptors has illuminated numerous eukaryotic cellular processes, identified the basis for developing interventions to prevent disease through vaccines and control bacterial diseases through therapies. In addition, subsets of these protein toxins have been utilized as therapeutic agents to treat numerous human inflictions.

Fabry Disease: A Disorder of Childhood Onset

BACKGROUND

Fabry disease, an X-linked disorder of glycosphingolipids, markedly increases the risk of systemic vasculopathy, ischemic stroke, small-fiber peripheral neuropathy, cardiac dysfunction, and chronic kidney disease.

METHODS

We performed an extensive PubMed search on the topic of Fabry disease and drew from our cumulative 43 years of experience.

RESULTS

Most of these complications are nonspecific in nature and clinically indistinguishable from similar abnormalities that occur in the context of more common disorders in the general population. This disease is caused by variants of the GLA gene, and its incidence may have been underestimated. However, one must also guard against overdiagnosis of Fabry disease and unjustified enzyme replacement therapy, because some of the gene variants are benign. Specific therapy for Fabry disease has been developed in the last few years, but its clinical effect has been modest. Novel therapeutic agents are being developed. Standard "nonspecific" medical and surgical therapy is necessary and effective in slowing deterioration or compensating for organ failure in patients with Fabry disease.

CONCLUSIONS

Fabry disease is a treatable and modifiable genetic risk factor for a myriad of clinical organ complications. Fabry disease may be frequently overlooked but on occasion overdiagnosed.

Efficacy of Plant-Derived Antimicrobials in Controlling Enterohemorrhagic Escherichia coli Virulence In Vitro

Escherichia coli O157:H7 is a major foodborne pathogen that can cause serious human illness characterized by hemorrhagic diarrhea and kidney failure. The pathology of enterohemorrhagic E. coli O157:H7 (EHEC) infection is primarily mediated by verotoxins, which bind to the globotriaosylceramide receptor on host cells. Antibiotics are contraindicated for treating EHEC infection because they lead to increased verotoxin release, thereby increasing the risk of renal failure and death in patients. Thus, alternative strategies are needed for controlling EHEC infections in humans. This study investigated the effect of subinhibitory concentrations of five plant-derived antimicrobial agents (PDAs) that are generally considered as safe, i.e., trans-cinnamaldehyde, eugenol, carvacrol, thymol, and β-resorcylic acid, on EHEC motility, adhesion to human intestinal epithelial cells, verotoxin production, and virulence gene expression. All tested PDAs reduced EHEC motility and attachment to human intestinal epithelial cells (P < 0.05) and decreased verotoxin synthesis by EHEC. The reverse transcription real-time PCR data revealed that PDAs decreased the expression of critical virulence genes in EHEC (P < 0.05). The results collectively suggest that these PDAs could be used to reduce EHEC virulence, but follow-up studies in animal models are necessary to validate these findings.

Selenium reduces enterohemorrhagic Escherichia coli O157:H7 verotoxin production and globotriaosylceramide receptor expression on host cells

Aim: This study investigated the efficacy of selenium (Se) in reducing Escherichia coli O157:H7 verotoxin production and toxin gene expression. Additionally, the effect of Se on globotriaosylceramide (Gb3) receptor in human lymphoma cells was determined. Materials & methods: The effect of Se on verotoxin synthesis was determined by standard ELISA, whereas its effect on Gb3 receptor was determined by flow cytometry and real-time quantitative PCR. Results & conclusions: Se reduced extracellular and intracellular verotoxin concentration by 40–60% and 80–90%, respectively (p < 0.05), and downregulated verotoxin genes (p < 0.05). Se reduced Gb3 receptor synthesis in lymphoma cells, and real-time quantitative PCR data revealed a significant downregulation of LacCer synthase gene (GalT2) involved in Gb3 synthesis. Further studies are warranted to validate these results in an appropriate animal model.

Shiga toxin induces membrane reorganization and formation of long range lipid order

Lateral variation of the in-plane orientation of lipids in a bilayer is referred to as texture. The influence of the protein Shiga toxin on orientational membrane texture was studied in phosphatidylcholine lipid bilayers using polarization two-photon fluorescence microscopy and atomic force microscopy. A content of 1% of glycosphingolipid globotriaosylceramide (Gb3) receptor lipids in a bilayer was used to bind the Shiga toxin B-subunit to the surface of gel domains. Binding of the Shiga toxin B-subunit to lipids led to the modulation of orientational membrane texture in gel domains and induced membrane reordering. When Shiga toxin was added above the lipid chain melting temperature, the toxin interaction with the membrane induced rearrangement and clustering of Gb3 lipids that resulted in the long range order and alignment of lipids in gel domains. The toxin induced redistribution of Gb3 lipids inside gel domains is governed by the temperature at which Shiga toxin was added to the membrane: above or below the phase transition. The temperature is thus one of the critical factors controlling lipid organization and texture in the presence of Shiga toxin. Lipid chain ordering imposed by Shiga toxin binding can be another factor driving the reconstruction of lipid organization and crystallization of lipids inside gel domains.

Upregulation of Shiga toxin receptor CD77/Gb3 and interleukin-1β expression in the brain of EHEC patients with hemolytic uremic syndrome and neurologic symptoms

In 2011, a large outbreak of Shiga toxin-producing enterohemorrhagic Escherichia coli (EHEC) infections occurred in northern Germany, which mainly affected adults. Out of 3842 patients, 104 experienced a complicated course comprising hemolytic uremic syndrome and neurological complications, including cognitive impairment, aphasia, seizures and coma. T2 hyperintensities on magnet resonance imaging (MRI) bilateral in the thalami and in the dorsal pons were found suggestive of a metabolic toxic effect. Five of the 104 patients died because of toxic heart failure. In the present study, the post-mortem neuropathological findings of the five EHEC patients are described. Histological investigation of 13 brain regions (frontal, temporal, occipital cortex, corpora mammillaria, thalamus, frontal operculum, corona radiata, gyrus angularis, pons, medulla oblongata, cerebellar vermis and cerebellar hemisphere) showed no thrombosis, ischemic changes or fresh infarctions. Further, no changes were found in electron microscopy. In comparison with five age-matched controls, slightly increased activation of microglia and a higher neuronal expression of interleukin-1β and of Shiga toxin receptor CD77/globotriaosylceramide 3 was observed. The findings were confirmed by Western blot analyses. It is suggested that CD77/globotriaosylceramide upregulation may be a consequence to Shiga toxin exposure, whereas increased interleukin-1β expression may point to activation of inflammatory cascades.

Shiga Toxin (Stx) Classification, Structure, and Function

Shiga toxin (Stx) is one of the most potent bacterial toxins known. Stx is found in Shigella dysenteriae 1 and in some serogroups of Escherichia coli (called Stx1 in E. coli). In addition to or instead of Stx1, some E. coli strains produce a second type of Stx, Stx2, that has the same mode of action as Stx/Stx1 but is antigenically distinct. Because subtypes of each toxin have been identified, the prototype toxin for each group is now designated Stx1a or Stx2a. The Stxs consist of two major subunits, an A subunit that joins noncovalently to a pentamer of five identical B subunits. The A subunit of the toxin injures the eukaryotic ribosome and halts protein synthesis in target cells. The function of the B pentamer is to bind to the cellular receptor, globotriaosylceramide, Gb3, found primarily on endothelial cells. The Stxs traffic in a retrograde manner within the cell, such that the A subunit of the toxin reaches the cytosol only after the toxin moves from the endosome to the Golgi and then to the endoplasmic reticulum. In humans infected with Stx-producing E. coli, the most serious manifestation of the disease, hemolytic-uremic syndrome, is more often associated with strains that produce Stx2a rather than Stx1a, and that relative toxicity is replicated in mice and baboons. Stx1a and Stx2a also exhibit differences in cytotoxicity to various cell types, bind dissimilarly to receptor analogs or mimics, induce differential chemokine responses, and have several distinctive structural characteristics.

A view on sphingolipids and disease

Sphingolipid and glycosphingolipid levels and expression of sphingolipid metabolizing enzymes are altered in a variety of diseases or in response to drug treatment. Inherited defects of enzymes and other proteins required for the lysosomal degradation of these lipids lead to human sphingolipidoses. Also genetic defects that affect sphingolipid biosynthesis are known. Although the molecular details are often far from clear, (glyco)sphingolipids have been implicated to play a role in atherosclerosis, insulin resistance, cancer, and infections by pathogens. More general aspects of selected diseases are discussed.

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.

Shiga toxin as a bacterial defense against a eukaryotic predator, Tetrahymena thermophila

Bacterially derived exotoxins kill eukaryotic cells by inactivating factors and/or pathways that are universally conserved among eukaryotic organisms. The genes that encode these exotoxins are commonly found in bacterial viruses (bacteriophages). In the context of mammals, these toxins cause diseases ranging from cholera to diphtheria to enterohemorrhagic diarrhea. Phage-carried exotoxin genes are widespread in the environment and are found with unexpectedly high frequency in regions lacking the presumed mammalian "targets," suggesting that mammals are not the primary targets of these exotoxins. We suggest that such exotoxins may have evolved for the purpose of bacterial antipredator defense. We show here that Tetrahymena thermophila, a bacterivorous predator, is killed when cocultured with bacteria bearing a Shiga toxin (Stx)-encoding temperate bacteriophage. In cocultures with Tetrahymena, the Stx-encoding bacteria display a growth advantage over those that do not produce Stx. Tetrahymena is also killed by purified Stx. Disruption of the gene encoding the StxB subunit or addition of an excess of the nontoxic StxB subunit substantially reduced Stx holotoxin toxicity, suggesting that this subunit mediates intake and/or trafficking of Stx by Tetrahymena. Bacterially mediated Tetrahymena killing was blocked by mutations that prevented the bacterial SOS response (recA mutations) or by enzymes that breakdown H(2)O(2) (catalase), suggesting that the production of H(2)O(2) by Tetrahymena signals its presence to the bacteria, leading to bacteriophage induction and production of Stx.

Fabry disease

Fabry disease, an X-linked disorder of glycosphingolipids that is caused by the deficiency of alpha-galactosidase A, is associated with dysfunction of many cell types and includes a systemic vasculopathy. As a result, patients have a markedly increased risk of developing small-fiber peripheral neuropathy, stroke, myriad cardiac manifestations and chronic renal disease. Virtually all complications of Fabry disease are non-specific in nature and clinically indistinguishable from similar abnormalities that occur in the context of more common disorders in the general population. Although Fabry disease was originally thought to be very rare, recent studies have found a much higher incidence of mutations of the GLA gene, suggesting that this disorder is under-diagnosed. Although the etiology of Fabry disease has been known for many years, the mechanism by which the accumulating alpha-D-galactosyl moieties cause this multi-organ disorder has only recently been studied and is yet to be completely elucidated. Specific therapy for Fabry disease has been developed in the last few years but its role in the management of the disorder is still being investigated. Fortunately, standard 'non-specific' medical and surgical therapy is effective in slowing deterioration or compensating for organ failure in patients with Fabry disease. All these aspects are discussed in detail in the present review.