Human platelet activation by Escherichia coli: roles for FcγRIIA and integrin αIIbβ3

Gram-negative Escherichia coli cause diseases such as sepsis and hemolytic uremic syndrome in which thrombotic disorders can be found. Direct platelet–bacterium interactions might contribute to some of these conditions; however, mechanisms of human platelet activation by E. coli leading to thrombus formation are poorly understood. While the IgG receptor FcγRIIA has a key role in platelet response to various Gram-positive species, its role in activation to Gram-negative bacteria is poorly defined. This study aimed to investigate the molecular mechanisms of human platelet activation by E. coli, including the potential role of FcγRIIA. Using light-transmission aggregometry, measurements of ATP release and tyrosine-phosphorylation, we investigated the ability of two E. coli clinical isolates to activate platelets in plasma, in the presence or absence of specific receptors and signaling inhibitors. Aggregation assays with washed platelets supplemented with IgGs were performed to evaluate the requirement of this plasma component in activation. We found a critical role for the immune receptor FcγRIIA, αIIbβ3, and Src and Syk tyrosine kinases in platelet activation in response to E. coli. IgG and αIIbβ3 engagement was required for FcγRIIA activation. Moreover, feedback mediators adenosine 5’-diphosphate (ADP) and thromboxane A₂ (TxA₂) were essential for platelet aggregation. These findings suggest that human platelet responses to E. coli isolates are similar to those induced by Gram-positive organisms. Our observations support the existence of a central FcγRIIA-mediated pathway by which human platelets respond to both Gram-negative and Gram-positive bacteria

Neutrophil extracellular traps (NETS): role in disease

Neutrophil extracellular traps (NETs) are web-like structures composed by a chromatin backbone, histones and antimicrobial proteins. NETs constitute yet another mechanism deployed by neutrophils to immobilise and kill microorganisms, thus contributing to the host innate immunity. Neutrophils cast NETs upon stimulation by a variety of stimuli, including bacteria, protozoa, fungi, viruses, their products and also host factors like chemokines, complement and activated platelets. NETs production or NETosis occurs as a result of activation of neutrophil PKC, Raf-MEK-ERK and NADPH oxydase signalling pathways. Driven mostly by peptidylarginine deiminase 4 (PAD4) citrullination of histones, the hallmark of NETosis is chromatin decondensation, rupture of nuclear membrane and release of nuclear and granular contents into the cytoplasm, prior their release into the extracellular space. NETs control propagation of pathogens by entrapping them within the lose chromatin web and kills them with the antimicrobial molecules –granule proteins and histones- present in high concentrations within the chromatin network. Despite contributing to host defence, aberrant NET formation may damage tissues and activate inflammatory cells, contributing to several pathologies, including sepsis, systemic inflammatory response syndrome, autoimmune diseases and thrombosis. This review presents an overview of our current knowledge of NETs physiology and their role in fighting and propagating disease.Sociedad Argentina de FisiologíaFacultad de Ciencias Médica

Concerted functions of<i> Streptococcus gordonii</i> surface proteins PadA and Hsa mediate activation of human platelets and interactions with extracellular matrix

A range of Streptococcus bacteria are able to interact with blood platelets to form a thrombus (clot). Streptococcus gordonii is ubiquitous within the human oral cavity and amongst the common pathogens isolated from subjects with infective endocarditis. Two cell surface proteins, Hsa and Platelet adherence protein A (PadA), in S. gordonii mediate adherence and activation of platelets. In this study, we demonstrate that PadA binds activated platelets and that an NGR (Asparagine-Glycine-Arginine) motif within a 657 amino acid residue N-terminal fragment of PadA is responsible for this, together with two other integrin-like recognition motifs RGT and AGD. PadA also acts in concert with Hsa to mediate binding of S. gordonii to cellular fibronectin and vitronectin, and to promote formation of biofilms. Evidence is presented that PadA and Hsa are each reliant on the other\u27s active presentation on the bacterial cell surface, suggesting cooperativity in functions impacting both colonization and pathogenesis

Towards 3D in vitro models for the study of cardiovascular tissues and disease

The field of tissue engineering is developing biomimetic biomaterial scaffolds which are showing increasing therapeutic potential for the repair of cardiovascular tissues. However, a major opportunity exists to use them as 3D in vitro models for the study of cardiovascular tissues and disease in addition to drug development and testing. These in vitro models can span the gap between 2D culture and in vivo testing thus reducing cost, time and the ethical burden of current approaches. This review outlines the progress to date and requirements for the development of ideal in vitro 3D models for blood vessels, heart valves and myocardial tissue

Amplification of bacteria-induced platelet activation is triggered by FcγRIIA, integrin αiIbβ3, and platelet factor 4

Bacterial adhesion to platelets is mediated via a range of strain-specific bacterial surface proteins that bind to a variety of platelet receptors. It is unclear how these interactions lead to platelet activation. We demonstrate a critical role for the immune receptor FcγRIIA, αIIbβ3, and Src and Syk tyrosine kinases in platelet activation by Staphylococcus aureus, Streptococcus sanguinis, Streptococcus gordonii, Streptococcus oralis, and Streptococcus pneumoniae. FcγRIIA activation is dependent on immunoglobulin G (IgG) and αIIbβ3 engagement. Moreover, feedback agonists adenosine 59-diphosphate and thromboxane A2 aremandatory for platelet aggregation. Additionally, platelet factor 4 (PF4) binds to bacteria and reduces the lag time for aggregation, and gray platelet syndromea-granule-deficient platelets do not aggregate to 4 of 5 bacterial strains. We propose that FcγRIIA-mediated activation is a common response mechanism used against a wide range of bacteria, and that release of secondary mediators and PF4 serve as a positive feedback mechanism for activation through an IgG-dependent pathway. © 2014 by The American Society of Hematology

The female condom: Dynamics of use in urban Zimbabwe

In July 1997, Population Services International (PSI), at the request of the Zimbabwe National AIDS Coordination Programme, launched a social marketing program for the female condom in Zimbabwe. To avoid stigma associated with condoms and STI prevention, the female condom was marketed as a family planning product or “contraceptive sheath” under the brand name “Care.” It was initially sold through pharmacies and clinics at a heavily subsidized retail price of US $0.24 for two; distribution has since expanded to other urban outlets, including supermarkets and convenience stores. Approximately one year after the start of the social marketing program, the Horizons Project and PSI conducted a descriptive, cross-sectional study of female condom users, male condom users, and nonusers of either barrier method. The goal is to increase understanding of the patterns and dynamics of female condom use to inform policymakers and program planners involved in decisions about promotion and distribution in Zimbabwe. In total, 493 female condom users, 633 male condom users, and 624 nonusers are included in the analyses upon which this report is based

Clinical controversies in abdominal sepsis : insights for critical care settings

International audienc

Phosphorylation of CLEC-2 is dependent on lipid rafts, actin polymerization,secondary mediators, and Rac

The C-type lectin-like receptor 2 (CLEC-2)activates platelets through Src and Syk tyrosine kinases via a single cytoplasmic YxxL motif known as a hem immunoreceptor tyrosine-based activation motif (hemITAM).Here, we demonstrate using sucrose gradient ultracentrifugation and methyl--cyclodextrin treatment that CLEC-2 translocates to lipid rafts upon ligand engagement and that translocation is essential for hemITAM phosphorylation and signal initiation. HemITAM phosphorylation, but not translocation, is also critically dependent on actin polymerization,Rac1 activation, and release of ADP and thromboxane A2 (TxA2). The role of ADP and TxA2 in mediating hosphorylation is dependent on ligand engagement and rac activation but is independent of platelet aggregation. In contrast,tyrosine phosphorylation of the GPVIFcR -chain ITAM, which has 2 YxxL motifs,is independent of actin polymerization and secondary mediators. These results reveal a unique series of proximal events in CLEC-2 phosphorylation involving actin polymerization, secondary mediators,and Rac activation