Platelet mitochondrial transfer via extracellular vesicles modulates neutrophil phenotype and function.

Background: Platelet activation causes the release of extracellular vesicles, of which a small proportion contain respiratory competent mitochondria. Mitochondria are integral for energy production and in the regulation of apoptotic pathways, however the existence of extracellular mitochondria highlights a potential new role in intercellular communication. Indeed, mitochondrial transfer has gained significant research interest in recent years, highlighting mechanisms through which cellular function and metabolism may be augmented.

Involvement of peptidylarginine deiminase 4 in eosinophil extracellular trap formation and contribution to citrullinated histone signal in thrombi.

Background: Extracellular traps formed by neutrophils (NETs) and eosinophils (EETs) have been described in coronary thrombi, contributing to thrombus stability. A key mechanism during NET formation is histone modification by the enzyme PAD4. Citrullinated histones, the product of PAD4 activity, are often attributed to neutrophils.

Transcriptional response of the heart to vagus nerve stimulation.

Heart failure is a major clinical problem, with treatments involving medication, devices, and emerging neuromodulation therapies such as vagus nerve stimulation (VNS). Considering the ongoing interest in using VNS to treat cardiovascular disease, it is important to understand the genetic and molecular changes developing in the heart in response to this form of autonomic neuromodulation. This experimental animal (rat) study investigated the immediate transcriptional response of the ventricular myocardium to selective stimulation of vagal efferent activity using an optogenetic approach.

Renal Function Underpins the Cyclooxygenase-2: Asymmetric Dimethylarginine Axis in Mouse and Man.

Introduction: Through the production of prostacyclin, cyclooxygenase (COX)-2 protects the cardiorenal system. Asymmetric dimethylarginine (ADMA), is a biomarker of cardiovascular and renal disease. Here we determined the relationship between COX-2/prostacyclin, ADMA, and renal function in mouse and human models.

Neutrophils Protect Against Endocarditis Progression Independent of Extracellular Trap Release.

Background: Infective endocarditis (IE) is characterized by an infected thrombus at the heart valves. How bacteria bypass the immune system and cause these thrombi remains unclear. Neutrophils releasing NETs (neutrophil extracellular traps) lie at this interface between host defense and coagulation.

Temporal in vivo platelet labeling in mice reveals age-dependent receptor expression and conservation of specific mRNAs.

The proportion of young platelets, also known as newly formed or reticulated, within the overall platelet population has been clinically correlated with adverse cardiovascular outcomes. However, our understanding of this is incomplete because of limitations in the technical approaches available to study platelets of different ages. In this study, we have developed and validated an in vivo temporal labeling approach using injectable fluorescent antiplatelet antibodies to subdivide platelets by age and assess differences in functional and molecular characteristics.

A pilot study assessing the implementation of 96-well plate-based aggregometry (Optimul) in Australia.

Identification of disordered platelet function is important to guide peri-operative bleeding management as well as long term treatment and prognostic strategies in individuals with platelet bleeding disorders. Light transmission aggregometry (LTA), the current gold standard diagnostic test of platelet function is a time consuming technique almost exclusively performed in specialised laboratories and almost universally unavailable in regional centres in Australia, where there is an unmet need for access to specialised platelet function diagnostic services. 96-well plate-based aggregometry (Optimul, UK), has been utilised in research laboratories as a novel platform to investigate platelet function.

and Neutrophil Extracellular Traps: The Master Manipulator Meets Its Match in Immunothrombosis.

Over the past 10 years, neutrophil extracellular traps (NETs) have become widely accepted as an integral player in immunothrombosis, due to their complex interplay with both pathogens and components of the coagulation system. While the release of NETs is an attempt by neutrophils to trap pathogens and constrain infections, NETs can have bystander effects on the host by inducing uncontrolled thrombosis, inflammation, and tissue damage. From an evolutionary perspective, pathogens have adapted to bypass the host innate immune response.

Proteome and functional decline as platelets age in the circulation.

Background: Platelets circulate in the blood of healthy individuals for approximately 7-10 days regulated by finely balanced processes of production and destruction. As platelets are anucleate we reasoned that their protein composition would change as they age and that this change would be linked to alterations in structure and function.

Objective: To isolate platelets of different ages from healthy individuals to test the hypothesis that changes in protein content cause alterations in platelet structure and function.

Proteomic signatures for perioperative oxygen delivery in skin after major elective surgery: mechanistic sub-study of a randomised controlled trial.

Background: Maintaining adequate oxygen delivery (DO) after major surgery is associated with minimising organ dysfunction. Skin is particularly vulnerable to reduced DO. We tested the hypothesis that reduced perioperative DO fuels inflammation in metabolically compromised skin after major surgery.

Cyclooxygenases and the cardiovascular system.

Cyclooxygenase (COX)-1 and COX-2 are centrally important enzymes within the cardiovascular system with a range of diverse, sometimes opposing, functions. Through the production of thromboxane, COX in platelets is a pro-thrombotic enzyme. By contrast, through the production of prostacyclin, COX in endothelial cells is antithrombotic and in the kidney regulates renal function and blood pressure.

Identification of a homozygous recessive variant in resulting in a congenital aspirin-like defect in platelet function.

We have identified a rare missense variant on chromosome 9, position 125145990 (GRCh37), in exon 8 in PTGS1 (the gene encoding cyclo-oxygenase 1, COX-1, the target of anti-thrombotic aspirin therapy). We report that in the homozygous state within a large consanguineous family this variant is associated with a bleeding phenotype and alterations in platelet reactivity and eicosanoid production. Western blotting and confocal imaging demonstrated that COX-1 was absent in the platelets of three family members homozygous for the PTGS1 variant but present in their leukocytes.

Combination of cyclic nucleotide modulators with P2Y receptor antagonists as anti-platelet therapy.

Background: Endothelium-derived prostacyclin and nitric oxide elevate platelet cyclic nucleotide levels and maintain quiescence. We previously demonstrated that a synergistic relationship exists between cyclic nucleotides and P2Y receptor inhibition. A number of clinically approved drug classes can modulate cyclic nucleotide tone in platelets including activators of NO-sensitive guanylyl cyclase (GC) and phosphodiesterase (PDE) inhibitors.

Cell-Specific Gene Deletion Reveals the Antithrombotic Function of COX1 and Explains the Vascular COX1/Prostacyclin Paradox.

Rationale: Endothelial cells (ECs) and platelets, which respectively produce antithrombotic prostacyclin and prothrombotic thromboxane A, both express COX1 (cyclooxygenase1). Consequently, there has been no way to delineate any antithrombotic role for COX1-derived prostacyclin from the prothrombotic effects of platelet COX1. By contrast, an antithrombotic role for COX2, which is absent in platelets, is straightforward to demonstrate.

Eicosanoids in platelets and the effect of their modulation by aspirin in the cardiovascular system (and beyond).

Platelets are important players in thrombosis and haemostasis with their function being modulated by mediators in the blood and the vascular wall. Among these, eicosanoids can both stimulate and inhibit platelet reactivity. Platelet Cyclooxygenase (COX)-1-generated Thromboxane (TX)A is the primary prostanoid that stimulates platelet aggregation; its action is counter-balanced by prostacyclin, a product of vascular COX.

Farnesoid X Receptor and Liver X Receptor Ligands Initiate Formation of Coated Platelets.

Objectives: The liver X receptors (LXRs) and farnesoid X receptor (FXR) have been identified in human platelets. Ligands of these receptors have been shown to have nongenomic inhibitory effects on platelet activation by platelet agonists. This, however, seems contradictory with the platelet hyper-reactivity that is associated with several pathological conditions that are associated with increased circulating levels of molecules that are LXR and FXR ligands, such as hyperlipidemia, type 2 diabetes mellitus, and obesity.

RXR Ligands Negatively Regulate Thrombosis and Hemostasis.

Objective: Platelets have been found to express intracellular nuclear receptors including the retinoid X receptors (RXRα and RXRβ). Treatment of platelets with ligands of RXR has been shown to inhibit platelet responses to ADP and thromboxane A2; however, the effects on responses to other platelet agonists and the underlying mechanism have not been fully characterized.

Approach And Results: The effect of 9--retinoic acid, docosahexaenoic acid and methoprene acid on collagen receptor (glycoprotein VI [GPVI]) agonists and thrombin-stimulated platelet function; including aggregation, granule secretion, integrin activation, calcium mobilization, integrin αIIbβ3 outside-in signaling and thrombus formation in vitro and in vivo were determined.

Intracellular Trafficking, Localization, and Mobilization of Platelet-Borne Thiol Isomerases.

Objective: Thiol isomerases facilitate protein folding in the endoplasmic reticulum, and several of these enzymes, including protein disulfide isomerase and ERp57, are mobilized to the surface of activated platelets, where they influence platelet aggregation, blood coagulation, and thrombus formation. In this study, we examined the synthesis and trafficking of thiol isomerases in megakaryocytes, determined their subcellular localization in platelets, and identified the cellular events responsible for their movement to the platelet surface on activation.

Approach And Results: Immunofluorescence microscopy imaging was used to localize protein disulfide isomerase and ERp57 in murine and human megakaryocytes at various developmental stages.

Pharmacological actions of nobiletin in the modulation of platelet function.

Background And Purpose: The discovery that flavonoids are capable of inhibiting platelet function has led to their investigation as potential antithrombotic agents. However, despite the range of studies on the antiplatelet properties of flavonoids, little is known about the mechanisms by which flavonoids inhibit platelet function. In this study, we aimed to explore the pharmacological effects of a polymethoxy flavonoid, nobiletin, in the modulation of platelet function.