Exploring the Role of PI3P in Platelets: Insights from a Novel External PI3P Pool.

Phosphoinositides (PIs) play a crucial role in regulating intracellular signaling, actin cytoskeleton rearrangements, and membrane trafficking by binding to specific domains of effector proteins. They are primarily found in the membrane leaflets facing the cytosol. Our study demonstrates the presence of a pool of phosphatidylinositol 3-monophosphate (PI3P) in the outer leaflet of the plasma membrane of resting human and mouse platelets.

Phosphatidylinositol 3 monophosphate metabolizing enzymes in blood platelet production and in thrombosis.

Blood platelets, produced by the fragmentation of megakaryocytes, play a key role in hemostasis and thrombosis. Being implicated in atherothrombosis and other thromboembolic disorders, they represent a major therapeutic target for antithrombotic drug development. Several recent studies have highlighted an important role for the lipid phosphatidylinositol 3 monophosphate (PtdIns3P) in megakaryocytes and platelets.

Profiling of phosphoinositide molecular species in human and mouse platelets identifies new species increasing following stimulation.

Phosphoinositides are bioactive lipids essential in the regulation of cell signaling as well as cytoskeleton and membrane dynamics. Their metabolism is highly active in blood platelets where they play a critical role during activation, at least through two well identified pathways involving phospholipase C and phosphoinositide 3-kinases (PI3K). Here, using a sensitive high-performance liquid chromatography-mass spectrometry method recently developed, we monitored for the first time the profiling of phosphatidylinositol (PI), PIP, PIP and PIP molecular species (fatty-acyl profiles) in human and mouse platelets during the course of stimulation by thrombin and collagen-related peptide.

The class I phosphoinositide 3-kinases α and β control antiphospholipid antibodies-induced platelet activation.

Antiphospholipid syndrome (APS) is an autoimmune disease characterised by the presence of antiphospholipid antibodies (aPL) associated with increased thrombotic risk and pregnancy morbidity. Although aPL are heterogeneous auto-antibodies, the major pathogenic target is the plasma protein β2-glycoprotein 1. The molecular mechanisms of platelet activation by aPL remain poorly understood.

Phosphoinositides: Important lipids in the coordination of cell dynamics.

By interacting specifically with proteins, phosphoinositides organize the spatiotemporal formation of protein complexes involved in the control of intracellular signaling, vesicular trafficking and cytoskeleton dynamics. A set of specific kinases and phosphatases ensures the production, degradation and inter-conversion of phosphoinositides to achieve a high level of precision in the regulation of cellular dynamics coordinated by these lipids. The direct involvement of these enzymes in cancer, genetic or infectious diseases, and the recent arrival of inhibitors targeting specific phosphoinositide kinases in clinic, emphasize the importance of these lipids and their metabolism in the biomedical field.

A novel mass assay to quantify the bioactive lipid PtdIns3P in various biological samples.

PtdIns3P is recognized as an important player in the control of the endocytotic pathway and in autophagy. Recent data also suggest that PtdIns3P contributes to molecular mechanisms taking place at the plasma membrane and at the midbody during cytokinesis. This lipid is present in low amounts in mammalian cells and remains difficult to quantify either by traditional techniques based on radiolabelling followed by HPLC to separate the different phosphatidylinositol monophosphates, or by high-sensitive liquid chromatography coupled to MS, which is still under development.

Microparticles from apoptotic monocytes induce transient platelet recruitment and tissue factor expression by cultured human vascular endothelial cells via a redox-sensitive mechanism.

Circulating microparticles derived from different types of blood cells have been reported to impair endothelial function and to induce pro-inflammatory and prothrombotic endothelial phenotypes. Although the number of monocyte-derived microparticles (M-MPs) is elevated in the blood of patients with various inflammatory conditions, their interaction with endothelial cells has been poorly investigated so far. In this study, we produced microparticles in vitro from apoptotic human monocytes and examined the effects of their interaction with cultured human umbilical vascular endothelial cells (HUVECs).

Microparticles from apoptotic vascular smooth muscle cells induce endothelial dysfunction, a phenomenon prevented by beta3-integrin antagonists.

Fragile atherosclerotic plaques are rich in apoptotic smooth muscle cells (SMCs) and macrophages, generating microparticules (MPs) which accumulate locally and may be released in blood in case of mechanical or spontaneous plaque disruption. Besides being highly procoagulant, this material may interact with downstream endothelium. Using a model of mouse aorta vaso-reactivity, we have investigated the effects of apoptotic MPs prepared in vitro from Fas-ligand sensitive SMCs.

Cytoprotective effect of glucosylceramide synthase inhibition against daunorubicin-induced apoptosis in human leukemic cell lines.

Several studies have shown that ceramide (CER) glucosylation contributes to drug resistance in multidrug-resistant cells and that inhibition of glucosylceramide synthase sensitizes cells to various drug treatments. However, the role of glucosylceramide synthase has not been studied in drug-sensitive cancer cells. We have demonstrated previously that the anthracycline daunorubicin (DNR) rapidly induces interphasic apoptosis through neutral sphingomyelinase-mediated CER generation in human leukemic cell lines.

Shedding of active tissue factor by aortic smooth muscle cells (SMCs) undergoing apoptosis.

As apoptosis of neo-intimal SMCs is a feature of advanced atherosclerotic plaques, the procoagulant properties of SMCs of synthetic phenotype undergoing apoptosis were investigated. SMCs isolated from rat aorta obtained 10 days after balloon injury, previously found to up-regulate Tissue Factor (TF) and Tissue Factor Inhibitor (TFPI) and to release large amounts of TFPI (Ghrib et al. Thromb Haemost 2002;87:1043-50), were sensitive to the apoptosis induced by Fas-ligand.

Daunorubicin- and Ara-C-induced interphasic apoptosis of human type II leukemia cells is caspase-8-independent.

Drug-induced interphasic apoptosis in human leukemia cells is mediated through intracellular signaling pathways, of which the most proximal (initiating) event remains unclear. Indeed, both early ceramide generation and procaspase-8 cleavage have been individually identified as the initial apoptotic signaling events which precede the mitochondrial control of the apoptotic execution phase in Type II cells. In order to evaluate whether or not procaspase-8 cleavage is requisite for initial ceramide generation and rapid interphasic apoptosis, we investigated the chronological ordering of early ceramide generation and caspase-8 cleavage induced by daunorubicin (DNR) and 1-beta-D-arabinofuranosylcytosine (Ara-C) in U937 cells.

The expression of tissue factor and tissue factor pathway inhibitor in aortic smooth muscle cells is up-regulated in synthetic compared to contractile phenotype.

Tissue factor (TF) and its specific inhibitor TF pathway inhibitor (TFPI) are produced by vascular smooth muscle cells (SMCs) in vitro and are increased in vivo in atherosclerotic compared to normal vessels. Besides local regulation of the hemostatic balance, this may be related to non-hemostatic TF/protease dependent functions such as SMC proliferation, adhesion and migration. The aim of the study was to compare the expression of both proteins between the contractile (normal adult) and synthetic (neo-intimal) SMC phenotypes.