Giuseppe Montrucchio

Resistance to thromboembolism in PI3Kγ-deficient mice

Platelet aggregation and subsequent thrombosis are the major cause of ischemic diseases such as heart attack and stroke. ADP, acting via G protein‐coupled receptors (GPCRs), is an important signal in thrombus formation and involves activation of phosphoinositide 3‐kinases (PI3K). When platelets from mice lacking the G protein‐activated PI3Kγ isoform were stimulated with ADP, aggregation was impaired. Collagen or thrombin, however, evoked a normal response. ADP stimulation of PI3Kγ‐deficient platelets resulted in decreased PKB/Akt phosphorylation and αIIbβ3 fibrinogen receptor activation. These effects did not influence bleeding time but protected PI3Kγ‐null mice from death caused by ADP‐induced platelet‐dependent thromboembolic vascular occlusion. This result demonstrates an unsuspected, well‐defined role for PI3Kγ downstream of ADP and suggests that pharmacological targeting of PI3Kγ has a potential use as antithrombotic therapy.

PAF Produced by Human Breast Cancer Cells Promotes Migration and Proliferation of Tumor Cells and Neo-Angiogenesis

Platelet-activating factor (PAF), a phospholipid mediator of inflammation, is present in breast cancer tissue and correlates with microvessel density. In the present study, we investigated the biological significance of PAF synthesized within breast cancer. In vitro, we observed the production of PAF by two estrogen-dependent (MCF7 and T-47D) and an estrogen-independent (MDA-MB231) breast cancer cell lines after stimulation with vascular endothelial growth factor, basic fibroblast growth factor, hepatocyte growth factor, tumor necrosis factor, thrombin but not with estrogen, progesterone, and oxytocin. The sensitivity to agonist stimulation and the amount of PAF synthesized as cell-associated or released varied in different cell lines, being higher in MDA-MB231 cells, which are known to be highly invasive. We further demonstrate, by reverse transcriptase-polymerase chain reaction and cytofluorimetry, that all of the breast cancer cells express the PAF receptor and respond to PAF stimulation in terms of proliferation. Moreover, in MDA-MB231 cells PAF elicited cell motility. In vivo, two structurally different PAF receptor antagonists WEB 2170 and CV 3988 significantly reduced the formation of new vessels in a tumor induced by subcutaneous implantation of MDA-MB231 cells into SCID mice. In conclusion, these results suggest that PAF, produced and released by breast cancer cells, can contribute to tumor development by enhancing cell motility and proliferation and by stimulating the angiogenic response.

Platelet activating factor produced in vitro by Kaposi's sarcoma cells induces and sustains in vivo angiogenesis.

Imbalance in the network of soluble mediators may play a pivotal role in the pathogenesis of Kaposis sarcoma (KS). In this study, we demonstrated that KS cells grown in vitro produced and in part released platelet activating factor (PAF), a powerful lipid mediator of inflammation and cell-to-cell communication. IL-1, TNF, and thrombin enhanced the synthesis of PAF. PAF receptor mRNA and specific, high affinity binding site for PAF were present in KS cells. Nanomolar concentration of PAF stimulated the chemotaxis and chemokinesis of KS cells, endothelial cells, and vascular smooth muscle cells. The migration response to PAF was inhibited by WEB 2170, a hetrazepinoic PAF receptor antagonist. Because neoangiogenesis is essential for the growth and progression of KS and since PAF can activate vascular endothelial cells, we examined the potential role of PAF as an instrumental mediator of angiogenesis associated with KS. Conditioned medium (CM) from KS cells (KS-CM) or KS cells themselves induced angiogenesis and macrophage recruitment in a murine model in which Matrigel was injected subcutaneously. These effects were inhibited by treating mice with WEB 2170. Synthetic PAF or natural PAF extracted from plasma of patients with classical KS also induced angiogenesis, which in turn was inhibited by WEB 2170. The action of PAF was amplified by expression of other angiogenic factors and chemokines: these included basic and acidic fibroblast growth factor, placental growth factor, vascular endothelial growth factor and its specific receptor flk-1, hepatocyte growth factor, KC, and macrophage inflammatory protein-2. Treatment with WEB 2170 abolished the expression of the transcripts of these molecules within Matrigel containing KS-CM. These results indicate that PAF may cooperate with other angiogenic molecules and chemokines in inducing vascular development in KS.

Thrombopoietin Stimulates Endothelial Cell Motility and Neoangiogenesis by a Platelet-Activating Factor–Dependent Mechanism

In this study, we demonstrate that human umbilical cord vein-derived endothelial cells (HUVECs) expressed c-Mpl, the thrombopoietin (TPO) receptor, and that TPO activates HUVECs in vitro, as indicated by directional migration, synthesis of 1-alkyl-/1-acyl-platelet-activating factor (PAF) and interleukin-8 (IL-8), and phosphorylation of the signal transducers and activators of transcription (STAT) STAT1 and STAT5B. The observation that WEB 2170 and CV3988, 2 structurally unrelated PAF receptor antagonists, prevented the motility of HUVECs induced by TPO suggests a role of PAF as secondary mediator. Moreover, kinetic analysis of TPO-induced tyrosine phosphorylation of STAT demonstrated that STAT5B activation temporally correlated with the synthesis of PAF. PAF, in turn, induced a rapid tyrosine phosphorylation of STAT5B and PAF receptor blockade, by WEB 2170, preventing both TPO- and PAF-mediated STAT5B activation. The in vivo angiogenic effect of TPO, studied in a mouse model of Matrigel implantation, demonstrated that TPO induced a dose-dependent angiogenic response that required the presence of heparin. Moreover, the in vivo angiogenic effect of TPO was inhibited by the PAF receptor antagonist WEB 2170 but not by the anti-basic fibroblast growth factor neutralizing antibody. These results indicate that the effects of TPO are not restricted to cells of hematopoietic lineages, because TPO is able to activate endothelial cells and to induce an angiogenic response in which the recruitment of endothelial cells is mediated by the synthesis of PAF. Moreover, biochemical analysis supports the hypothesis that STAT5B may be involved in the signaling pathway leading to PAF-dependent angiogenesis.

Release of Platelet-Activating Factor in Systemic Lupus erythematosus

The biologically active 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (platelet-activating factor; PAF) is inactivated in plasma mainly by a specific PAF acetylhydrolase (1-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine acetylhydrolase; EC 3.1.1.48). In the present study, PAF was released in detectable amounts (5.4 +/- 2.9 ng/ml; mean +/- 1 SD) in the plasma of 8 out of 10 patients with systemic lupus erythematosus (SLE) during the most active phases of the disease. PAF was never detectable in the plasma of patients with inactive SLE or of healthy subjects. PAF acetylhydrolase activity was markedly reduced in sera of 10 patients with active SLE as compared to 7 patients with inactive SLE, 16 patients with rheumatoid arthritis (RA), 5 patients with nephrotic syndrome (NS) and 15 healthy subjects. A kinetic study of the enzyme in patients with active SLE suggested an overall reduced activity rather than an intrinsic defect of the enzyme. PAF acetylhydrolase in sera of patients with active SLE shared with that of healthy subjects the same substrate specificity, sensitivity to enzymatic and chemicophysical treatments and association to low-density lipoprotein (LDL), acting as carrier of PAF acetylhydrolase in plasma. However, the protein concentration of LDL was significantly reduced in patients with active SLE as compared to patients with inactive SLE, RA and NS and to healthy subjects, thereby suggesting that the reduction of PAF acetylhydrolase activity in active SLE might be due at least in part to a carrier defect related to the activity of the disease. In addition, experiments in which serum of patients with active SLE and serum of healthy subjects were mixed in different combinations indicated the absence of factors inhibiting PAF acetylhydrolase activity in SLE patients.

Platelet-Activating Factor Enhances Vascular Endothelial Growth Factor–Induced Endothelial Cell Motility and Neoangiogenesis in a Murine Matrigel Model

We previously reported that platelet-activating factor (PAF) enhances the angiogenic activity of certain polypeptide mediators such as tumor necrosis factor and hepatocyte growth factor by promoting endothelial cell motility. The purpose of the present study was to evaluate whether the synthesis of PAF induced by vascular endothelial growth factor (VEGF) might affect endothelial cell motility, microvascular permeability, and angiogenesis. The neoangiogenesis and synthesis of PAF induced by VEGF were studied in vivo in a murine Matrigel model. Dermal permeability was studied in mice by injection of (125)I-albumin. The synthesis of PAF, cell motility, and the increased (125)I-albumin transfer across endothelial monolayers were studied in vitro by using cultures of human umbilical cord vein-derived endothelial cells (HUVECs). The results obtained demonstrate that the neoangiogenesis induced by VEGF in vivo was associated with a local synthesis of PAF and was inhibited by WEB2170 and CV3988, 2 chemically unrelated, specific PAF-receptor antagonists. In contrast, WEB2170 did not inhibit VEGF-enhanced dermal permeability, suggesting that the latter was independent of the synthesis of PAF. In vitro, it was found that VEGF induced the synthesis of PAF by HUVECs in a dose- and time-dependent manner. The cell motility induced by VEGF was inhibited by PAF-receptor antagonists. In contrast, VEGF-induced proliferation of HUVECs and albumin transfer through HUVEC monolayer were unaffected by PAF-receptor antagonists. These results suggest that the synthesis of PAF induced by VEGF enhances endothelial cell migration and contributes to the angiogenic effect of VEGF in the in vivo Matrigel model.

Potential angiogenic role of platelet-activating factor in human breast cancer.

This study investigated the presence of platelet-activating factor (PAF) in the lipid extracts of 18 primary breast carcinomas and 20 control breast tissues. The amount of PAF detected in breast carcinomas was significantly higher than in controls. The mass spectrometric analysis of PAF-bioactive lipid extract from breast carcinomas showed the presence of several molecular species of PAF, including C16-alkylPAF, C18-lysophosphatidylcholine (LPC), C16-LPC, lyso-PAF, and C16-acylPAF. The amount of bioactive PAF extracted from breast specimens significantly correlated with tumor vascularization revealed by the number of CD34-and CD31-positive cells. As C16-alkylPAF was previously shown to induce angiogenesis in vivo, we evaluated whether the thin layer chromatography-purified lipid extracts of breast specimens elicited neoangiogenesis in a murine model of subcutaneous Matrigel injection. The lipid extracts from specimens of breast carcinoma containing high levels of PAF bioactivity, but not from breast carcinomas containing low levels of PAF bioactivity or from normal breast tissue, induced a significant angiogenic response. This angiogenic response was significantly inhibited by the PAF receptor antagonist WEB 2170. T47D and MCF7 breast cancer cell lines, but not an immortalized nontumor breast cell line (MCF10), released PAF in the culture medium. A significant in vivo neoangiogenic response, inhibited by WEB 2170, was elicited by T47D and MCF7 but not by MCF10 culture medium. These results indicate that an increased concentration of PAF is present in tumors with high microvessel density and that PAF may account for the neoangiogenic activity induced in mice by the lipid extracts obtained from breast cancer. A contribution of PAF in the neovascularization of human breast cancer is suggested.

Plasmin Promotes an Endothelium-Dependent Adhesion of Neutrophils Involvement of Platelet Activating Factor and P-Selectin

BACKGROUND The adhesion of leukocytes to the endothelium and the edema of vessel wall may cause vascular reocclusion after thrombolytic therapy. The aim of this study was to evaluate the role of platelet activating factor (PAF) and P-selectin on the adherence of polymorphonuclear neutrophils (PMN) to the endothelium and of PAF on the increased vascular permeability induced by tissue-type plasminogen activator, streptokinase, and plasmin. METHODS AND RESULTS We studied (1) the adhesion of 111Inlabeled PMN to human umbilical cord vein-derived cultured endothelial cells (HUVEC), (2) the transfer of 125I-labeled albumin across HUVEC monolayers, and (3) the adhesion of PMN to isolated bovine coronary arteries under flow conditions. It was found that the adhesion of PMN, induced by tissue-type plasminogen activator, streptokinase, and plasmin, correlated with the synthesis of PAF by HUVEC and was inhibited by WEB 2170, a PAF receptor antagonist. The adhesion of PMN was also inhibited by the treatment of HUVEC with anti-P-selectin antibodies or of PMN with soluble P-selectin or with anti-CD18 monoclonal antibodies. Plasmin also increased the permeability of HUVEC monolayers, an effect that was partially prevented by WEB 2170. Moreover, plasmin promoted the synthesis of PAF from isolated bovine coronary arteries and the adherence of PMN to the endothelium under flow conditions. The pretreatment of PMN with WEB 2170 or with soluble P-selectin prevented adhesion. CONCLUSIONS The synthesis of PAF by endothelial cells at the site of plasmin generation and the endothelial expression of P-selectin may render the endothelial cell surface proadhesive for neutrophils and may favor a local increase in vascular permeability.

Signaling through PI3Kγ: a common platform for leukocyte, platelet and cardiovascular stress sensing

The concerted activation of leukocytes and vessels shapes multiple physiological and pathological responses. A large number of these processes shares a common signal transduction platform involving the activation of plasma membrane bound G protein-coupled receptors (GPCRs). This event is usually amplified by the production of different intra-cellular second messenger molecules. Among these mediators, the phosphorylated lipid phosphatidylinositol (3,4,5)-trisphosphate (PIP3) produced by phosphoinositide 3-kinase gamma (PI3Kgamma) has recently emerged as a crucial signal in both vascular and white blood cells. The generation of mice lacking PI3Kgamma showed that the GPCR/PI3Kgamma/PIP3 signaling pathway controls diverse immune modulatory and vascular functions like respiratory burst, cell recruitment, mast cell reactivity, platelet aggregation, endothelial activation as well as smooth muscle contractility. The relative specificity of these events suggests that blocking PI3Kgamma function might turn out beneficial for diseases like inflammation, allergy, thrombosis, and major cardiovascular disorders like hypertension, thus offering a wide range of therapeutic opportunities.

Mechanisms of the priming effect of low doses of lipopoly-saccharides on leukocyte-dependent platelet aggregation in whole blood

Several studies focused on the ability of bacterial lipopolysac-charides (LPS) in triggering platelet and/or leukocyte activation. The aim of this study was to investigate the molecular mechanisms involved in the aggregation of platelets and in their interaction with leukocytes in whole blood after stimulation with low doses of LPS. LPS did not directly induce platelet aggregation in whole blood, but they primed the aggregation of platelets induced by epinephrine, adenosine diphosphate and arachidonic acid. As shown by cytofluorimetry, platelets neither bind FITC-LPS, nor express the LPS-receptors CD14 and toll-like receptor 4 (TLR4). On the contrary, LPS primed monocytes and to a lesser extent polymorphonuclear neutrophils to adhere to platelets. Both platelet-leukocyte interaction and platelet aggregation in whole blood were inhibited by blockade of CD14 and TLR4. Moreover, the interaction between platelets and leukocytes was inhibited by P-selectin, and by blockade of PAF and reactive oxygen species, suggesting a role of P-selectin and of leukocyte-derived mediators. In conclusion, these results elucidate the mechanisms leading to platelet activation and interaction with leukocytes triggered by LPS. They suggest that the activation of platelets by LPS is mainly dependent on leukocytes and especially monocytes as a result of CD14 and TLR4 engagement. Moreover, we found that leukocyte-platelet interaction was triggered by the synthesis of PAF and the generation of oxygen radicals that induced upregulation of surface expression of P-selectin.