Von Willebrand Factor and Von Willebrand Factor-Cleaving Metalloprotease Activity in Escherichia coli O157:H7-Associated Hemolytic Uremic Syndrome

Abstract

Hemolytic uremic syndrome (HUS) usually occurs after infection with Shiga toxin-producing bacteria. Thrombotic thrombocytopenic purpura, a disorder with similar clinical manifestations, is associated with deficient activity of a circulating metalloprotease that cleaves von Willebrand factor at the Tyr842-Met843 peptide bond in a shear stress-dependent manner. We analyzed von Willebrand factor-cleaving metalloprotease activity and the status of von Willebrand factor in 16 children who developed HUS after Escherichia coli O157:H7 infection and in 29 infected children who did not develop this complication. Von Willebrand factor-cleaving metalloprotease activity was normal in all subjects, but von Willebrand factor size was decreased in the plasma of each of 16 patients with HUS. The decrease in circulating von Willebrand factor size correlated with the severity of thrombocytopenia and was proportional to an increase in von Willebrand factor proteolytic fragments in plasma. Immunohistochemical studies of the kidneys in four additional patients who died of HUS demonstrated glomerular thrombi in three patients, and arterial and arteriolar thrombi in one patient. The glomerular thrombi contained fibrin but little or no von Willebrand factor. A decrease in large von Willebrand factor multimers, presumably caused by enhanced proteolysis from abnormal shear stress in the microcirculation, is common in HUS. HUS, characterized by acute renal failure, hemolysis with schistocytes on blood smears, and thrombocytopenia, is accompanied by thrombotic microangiopathy of the kidneys and of other organs (1). The syndrome covers a diverse spectrum of microangiopathic disorders (2-4), but most cases occur after infection with Shiga toxin-producing bacteria, such as Escherichia coli O157:H7 (5) or Shigella dysenteriae serotype 1 (6).TTP, a disorder with some clinical, laboratory, and histopathologic similarities to HUS, has been associated with abnormal homeostasis of von Willebrand factor, a protein that is secreted from endothelial cells as a disulfide-linked polymer of a polypeptide with 2050 amino acid residues. Circulating von Willebrand factor is normally cleaved between Tyr842 and Met843 (7) in a shear stress-dependent manner (8) by a plasma metalloprotease (9, 10), generating a series of multimers. Without this metalloprotease activity, von Willebrand factor, when unfolded by shear stress (11), has increased platelet-aggregating activity (12). It is postulated that this increased activity facilitates the formation of arteriolar and capillary platelet thrombi in TTP. Indeed, acquired TTP has been associated with deficient von Willebrand factor-cleaving metalloprotease activity caused by inhibitory antibodies (12, 13).

Renal Thrombotic Microangiopathies Induced by Severe Hypertension

“…In most patients with familial or acquired types of thrombotic thrombocytopenic purpura, plasma ADAMTS13 activity is less than 5% of normal. On the other hand, ADAMTS13 plays little or no role in the pathogenesis of TMA, and there is no deficiency of ADAMTS13 in typical diarrhea-associated HUS (18). In most patients with a diagnosis of TTP, ADAMTS13 activity, measured on a pretreatment citrated plasma sample, is 0-5% of normal (1).…”

Thrombotic Thrombocytopenic Purpura: A Thrombotic Disorder Caused by ADAMTS13 Deficiency

“…VWF multimer is normal during the stage of colitis but shows a gradient of decreased large multimers at the onset of HUS. The VWF fragments are markedly increased, which are attributable to both increased VWF antigen level and increased proteolysis by ADAMTS13 [74]. VWF multimers are separated by SDS agarose gel electrophoresis and visualized.…”

“…Large VWF multimers are also decreased in patients with HUS, aortic stenosis or pulmonary arterial hypertension (Figure 3, panel C) [74][75][76]. In these conditions, ADAMTS13 levels are normal or mildly decreased.…”

von Willebrand factor cleaving protease (ADAMTS13) is deficient in recurrent and familial thrombotic thrombocytopenic purpura and hemolytic uremic syndrome

“…24,25 That patients with HUS have normal ADAMTS13 activity was taken to indicate that the presence or absence of this activity could be used to classify patients as having HUS or TTP. 26 However, a few recent studies [27][28][29][30][31] have challenged this paradigm, showing that patients with a diagnosis of HUS may have complete ADAMTS13 deficiency.…”