Pathogenic mechanisms in VTEC-associated HUS Maurizio Brigotti Department of Experimental Pathology University of Bologna, Italy
The main cause of acute renal failure in children under 2-3 years is the hemolytic uremic syndrome (HUS), a consequence of intestinal infection by Escherichia coli strains (VTEC) producing Vero toxins (also called Shiga toxins, Stx).
Hemolytic Uremic Syndrome (HUS) acute renal failure (dialysis) thrombocytopenia microangiopathic hemolytic anemia 70% of HUS cases are associated with VTEC infections Occurrence of HUS: 5-10% VTEC infection cases
HUS is characterized by widespread thrombotic microvascular lesions in the renal glomeruli, the gastrointestinal tract and other organs, such as the brain.
Pathogen virulence factors Shiga toxins (Stx1, Stx2) Type III secretion system encoded on LEE (locus for enterocyte effacement)
Components of type III secretion system Alves de Brito et al., Genet, Mol Research (2004)
Molecular syringe Troisfontaines and Cornelis, 2005
Pathogen virulence factors Shiga toxins (Stx1, Stx2) Type III secretion system encoded on LEE (locus for enterocyte effacement) Several secreted effector proteins (LEE or non-lee encoded)
Systemic Stx toxemia is considered to be central to the genesis of HUS Stx-induced endothelial injury is the primary pathogenic event in HUS even though Stx also damage mesangial cells and tubular epithelial cells in the kidney
Cells targeted by Stx through Gb3 receptor Microvascular endothelial cells in the kidney, the intestine and the brain express Gb3 receptor for Stx
Structure of Shiga toxins A 1 peptide: contains the activity Two units A A 2 peptide: binds the A 1 to B B (pentamer( pentamer) binds the toxin to the specific receptor Gb 3
Stx are enzymes which cleave the bond connecting adenine to sugar in ribosomal RNA (Endo et al., 1988 Eur J. Biochem 171, 45) and DNA (Brigotti et al., 1998 Nucleic Acids Res. 26, 4306) (Brigotti et al., 2002 FASEB J. 16, 365) Adenine X Stx Adenine Adenine X Adenine X X X Adenine Stx 28S rrna DNA Inhibition of translation Formation of AP sites APOPTOSIS
Stx also induce cellular response not related to apoptosis such as the expression of pro-inflammatory cytokines involved in HUS pathogenesis Endothelial cells increased mrna levels and protein expression of about 25 genes: chemokines (such as IL-8 and MCP-1) adhesion molecules other cytokines involved in HUS pathogenesis Transcription factors (Matussek et al., 2003 Blood, 102, 1323)
Ribosomal damage is the molecular link between the enzymatic activity of Stx and the up-regulation of pro-inflammatory cytokines
Relationship between inhibition of translation and expression of pro-inflammatory cytokines Maximal expression Brigotti et al., Infection and Immunity (2007)
Naylor et al., 2005 VTEC 3-4 days Abdominal cramps, non-bloody diarrhoea 1-2 days Stx Bloody diarrhoea 5-7 days 90-95% Resolution HUS 5-10%
Non-endothelial cells targeted by Stx through Gb3 receptor Circulating monocytes Platelets TNF-α and IL-1 Up-regulation of Gb3 in renal endothelial cells
Histopathology Thrombotic microvascular lesions in renal glomeruli Dickinson et al., 2008
The triad of HUS acute renal failure (dialysis) thrombocytopenia microangiopathic hemolytic anemia
Peripheral blood smear from a patient with HUS Kumar: Robbins and Cotran pathological bases of diseases
STEC 3-4 days Abdominal cramps, non-bloody diarrhoea 1-2 days Stx 90-95% Resolution Bloody diarrhoea 5-7 days 5-10% HUS The route of transport of Stx from the intestine to the kidney has been greatly debated. plasma neutrophils
During their journey to the kidney, are Stx free in the plasma? Renal endothelium
The presence of Stx has never been reported in the soluble blood fraction of HUS patients with concomitant detectable fecal Stx
Stx bind to neutrophils from healthy donors Brigotti et al., Journal of Leukocyte Biology (2008)
The interaction Stx/neutrophils is specific Stx bind to the surface of human mature neutrophils, but not to immature cells Brigotti et al., Journal of Leukocyte Biology (2008) The plant toxin ricin, which has the same mechanism of action and structural homology with Stx, interacts with neutrophils competing for the same receptor Arfilli et al., Biochem J. (2010)
Stx bound to neutrophils has been detected in patients with HUS Brigotti et al., Journal of Clinical Microbiology (2006) 5 FEBRUARY 2003 7 FEBRUARY 2003 11 FEBRUARY 2003 13 FEBRUARY 2003 15 FEBRUARY 2003 CONTROL
PMN Stx receptor
Experimental model of neutrophil transmigration through an endothelial cell monolayer Neutrophils Endothelial cells IL-8
Neutrophils might transfer Stx to renal endothelium during transmigration Renal endothelium Brigotti et al., Journal of Leukocyte Biology (2010)
Understanding the mechanism of Stx delivery from the gut to the kidney could have an important impact on the therapeutic strategies for preventing the onset of HUS plasmaexchange prevention of neutrophil/endothelium interactions
HUS connected people: Alfredo Caprioli, Gaia Scavia Fabio Minelli Alfonso V. Ferretti Carmine Pecoraro A. E. Tozzi, M. A. Procaccino Maurizio Brigotti, Domenica Carnicelli Valentina Arfilli Laura Rocchi Pier Luigi Tazzari, Francesca Ricci, P. Pagliaro Fabio Paglialonga Alberto Edefonti Pier Giorgio Petronini Roberta Alfieri
Inhibition of protein synthesis in endothelial cells after transmigration of neutrophils loaded with Stx as found in patients Up-regulation of cytokines APOPTOSIS Brigotti et al., Journal of Leukocyte Biology (2010)
The quantitative detection of blood Stx in the early phases of HUS could represent a predictor of renal outcome and a useful tool in the management of HUS patients