| Summary: | Enterohemorrhagic E. coli (EHEC) infection is a leading cause of acute kidney
failure in otherwise healthy children, and a leading cause of foodborne illness with an
outsized economic impact from outbreaks. EHEC secrete two Shiga-like toxins (Stx1
and Stx2) which are AB5 holotoxins that inhibit protein synthesis in cells expressing the
toxin receptor Gb3. Infection with EHEC typically begins with a diarrheal prodrome that
can progress in 5-15% of cases to hemolytic uremic syndrome (HUS), a clinical diagnosis
characterized by thrombocytopenia, hemolytic anemia, and thrombotic microangiopathy.
Historically, strains of EHEC expressing Stx2 have been associated with more severe
disease. We hypothesized that tissue injury due to the toxins leads to the release of
damage-associated molecular patterns (DAMPs), which act through inflammatory
receptors to promote the endothelial dysfunction that drives this disease alongside the
inciting Shiga toxins. Here we demonstrate that two well-characterized DAMPs,
extracellular histones and HMGB1, are produced in two different mouse models when
Stx2 is present; one model represents challenge with the toxin alone, and the second
model introduces toxin through secretion with a lysogenized bacterium, C. rodentium,
mimicking EHEC colonization. We investigate whether Stx1, Stx2, or histones affect the
endothelial expression of well-characterized members of the protein C pathway, namely
the endothelial protein C receptor (ECPR), protease-activated receptor 1 (PAR1), and
thrombomodulin (TM), on human aortic (HAEC) and human renal glomerular
endothelial cells (HRGEC). We show that Stx and/or histones reduce endothelial
expression of these anti-coagulant molecules and histones dramatically increase
expression of pro-thrombotic PAR-1. These changes lead to physiologically important
decreases in activated protein C (APC), a critical anti-coagulant and cytoprotective
molecule. Finally, we demonstrate that histones exacerbate thrombin's barrier-disruptive
effects on the endothelium, and prevent APC's protective effects. These data provide
novel mechanistic insight into the endothelial dysfunction that characterizes HUS and
also provide a new perspective on systemic consequences of the bacterial Shiga toxins
that might drive organ injury in susceptible patients.
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