ABSTRACT
Essentials von Willebrands factor (VWF) glycosylation plays a key role in modulating in vivo clearance. VWF glycoforms were used to examine the role of specific glycan moieties in regulating clearance. Reduction in sialylation resulted in enhanced VWF clearance through asialoglycoprotein receptor. Progressive VWF N-linked glycan trimming resulted in increased macrophage-mediated clearance. Click to hear Dr Denis discuss clearance of von Willebrand factor in a free presentation from the ISTH Academy SUMMARY: Background Enhanced von Willebrand factor (VWF) clearance is important in the etiology of both type 1 and type 2 von Willebrand disease (VWD). In addition, previous studies have demonstrated that VWF glycans play a key role in regulating in vivo clearance. However, the molecular mechanisms underlying VWF clearance remain poorly understood. Objective To define the molecular mechanisms through which VWF N-linked glycan structures influence in vivo clearance. Methods By use of a series of exoglycosidases, different plasma-derived VWF (pd-VWF) glycoforms were generated. In vivo clearance of these glycoforms was then assessed in VWF-/- mice in the presence or absence of inhibitors of asialoglycoprotein receptor (ASGPR), or following clodronate-induced macrophage depletion. Results Reduced amounts of N-linked and O-linked sialylation resulted in enhanced pd-VWF clearance modulated via ASGPR. In addition to this role of terminal sialylation, we further observed that progressive N-linked glycan trimming also resulted in markedly enhanced VWF clearance. Furthermore, these additional N-linked glycan effects on clearance were ASGPR-independent, and instead involved enhanced macrophage clearance that was mediated, at least in part, through LDL receptor-related protein 1. Conclusion The carbohydrate determinants expressed on VWF regulate susceptibility to proteolysis by ADAMTS-13. In addition, our findings now further demonstrate that non-sialic acid carbohydrate determinants expressed on VWF also play an unexpectedly important role in modulating in vivo clearance through both hepatic ASGPR-dependent and macrophage-dependent pathways. In addition, these data further support the hypothesis that variation in VWF glycosylation may be important in the pathophysiology underlying type 1C VWD.
Subject(s)
Polysaccharides/chemistry , von Willebrand Factor/chemistry , ADAMTS13 Protein/metabolism , Animals , Asialoglycoproteins/chemistry , Blood Platelets/metabolism , Glycosylation , Humans , LDL-Receptor Related Protein-Associated Protein/chemistry , Low Density Lipoprotein Receptor-Related Protein-1/metabolism , Macrophages/metabolism , Mice , Mice, Inbred C57BL , Mice, Transgenic , Plasma/metabolism , Protein Binding , Protein Domains , Protein Processing, Post-TranslationalABSTRACT
Based on the formalisms of Langmuir and Fowler, theoretical adsorption isotherms are calculated for different bundle geometries of single wall carbon nanotubes in a triangular lattice. The authors show the dependence of the adsorption properties on the nanotube diameter and on the specific morphology of the bundles they constitute. The authors demonstrate how isotherm curve analysis can help to experimentally determine what kinds of tubes form a given bundle and the ratio of open to closed tubes in a sample having undergone a complete or incomplete opening protocol. In spite of the model's simplicity, quite satisfactory agreement is observed between experiments and the authors' calculations.
ABSTRACT
To better define the bovine reservoir of Escherichia coli O157:H7, cattle were tested monthly by bacteriologic culture for fecal excretion of E. coli. E. coli O157:H7 was isolated from feces of 56 cattle sampled an average of 6.98 times (2-12 samples). By broth enrichment culture, immunomagnetic separation, or both, 35 cattle had 1 positive sample, 12 had 2, 7 had 3, and 1 each had 4 and 5. Five cattle with > or = 2 positive samples were in a herd in which 5 pulsed-field gel electrophoretic (PFGE) types were simultaneously present; in 3 of these cattle, different PFGE types were detected in different samples. The duration of detected excretion E. coli O157:H7 by individual cattle in this study was <1 month in 35 (63%) of 56 cattle. Both serial and concurrent excretion of different E. coli O157:H7 strains by individual cattle was observed.
