To cite this article: Leytin V, Allen DJ, Mykhaylov S, Lyubimov E, Freedman J. Thrombin-triggered platelet apoptosis. J Thromb Haemost 2006; 4: 2656-63.Summary. Background: Thrombin is primarily known as a coagulation factor and as an inducer of platelet activation and aggregation. It has been reported that thrombin modulates apoptosis of nucleated cells. Objectives: The current study investigated whether thrombin can affect apoptosis in anucleated human platelets. Methods: Using flow cytometry, we studied platelet apoptosis at the single-cell level, analyzing markers of mitochondrial and cytoplasmic apoptosis. Western blotting was also employed, in addition to flow cytometry, for determining the expression of Bcl-2 family proteins. Results: We found that human a-thrombin induced four key manifestations of apoptosis in human platelets: (i) mitochondrial inner transmembrane potential (DWm) depolarization; (ii) strong expression of pro-apoptotic Bax and Bak proteins but only weak expression of anti-apoptotic Bcl-2 protein; (iii) caspase-3 activation; and (iv) phosphatidylserine (PS) exposure. Conclusions: This study demonstrates that, aside from its ÔclassicalÕ function as an inducer of platelet activation, thrombin can trigger platelet apoptosis, where it acts as a death ligand. These data indicate that thrombin triggers platelet apoptosis by impacting on several intracellular apoptotic targets, including shifting the balance between Bcl-2 regulatory proteins in a proapoptotic direction, depolarizing the inner mitochondrial membrane, activating the executioner caspase-3, and stimulating aberrant exposure of PS on the platelet surface.

European Union's Horizon 2020 grant COMPARE, ZonMw TOP grant, the Virgo Consortium funded by the Dutch Government, and the Hungarian Scientific Research Fund.

BackgroundHuman noroviruses are a highly diverse group of viruses classified into three of the five currently recognised Norovirus genogroups, and contain numerous genotypes or genetic clusters. Noroviruses are the major aetiological agent of endemic gastroenteritis in all age groups, as well as the cause of periodic epidemic gastroenteritis. The noroviruses most commonly associated with outbreaks of gastroenteritis are genogroup II genotype 4 (GII-4) strains. The relationship between genotypes of noroviruses with their phenotypes and antigenic profile remains poorly understood through an inability to culture these viruses and the lack of a suitable animal model.Methodology/Principal FindingsHere we describe a study of the diversity of amino acid sequences of the highly variable P2 region in the major capsid protein, VP1, of the GII-4 human noroviruses strains using sequence analysis and homology modelling techniques.Conclusions/SignificanceOur data identifies two sites in this region, which show significant amino acid substitutions associated with the appearance of variant strains responsible for epidemics with major public health impact. Homology modelling studies revealed the exposed nature of these sites on the capsid surface, providing supportive structural data that these two sites are likely to be associated with putative variant-specific epitopes. Furthermore, the patterns in the evolution of these viruses at these sites suggests that noroviruses follow a neutral network pattern of evolution.