Microparticles: targets and tools in cardiovascular disease

Cells communicate with other cells not only via direct cell–cell contact and the production of signaling molecules but also through release of microparticles (MPs). MPs are small vesicles released from stimulated and/or apoptotic cells. They harbor membrane proteins that are characteristic of the original parent cell and intracellular components involved in cell signaling. MPs are considered to be both biomarkers and effectors of cell signaling that maintain and/or initiate cell dysfunction. Thus, MPs can evoke endothelial dysfunction by decreasing nitric oxide (NO) production and promoting vascular inflammation which favor the prothrombotic state in atherosclerosis. Novel pharmacological approaches targeting MP production or properties could be used to treat cardiovascular pathologies. Paradoxically, another useful approach might be to employ engineered MPs with modified compositions as therapeutic agents to correct cardiovascular pathologies. This review is focused on the mechanisms of MP formation and their effects on target cells under physiological or pathophysiological conditions

Circulating microparticles from pulmonary hypertensive rats are vectors of oxidative stress

Date du colloque : 04/2010National audienc

Increased Oxidative Stress Induces Apoptosis in Human Cystic Fibrosis Cells

Oxidative stress results in deleterious cell function in pathologies associated with inflammation. Here, we investigated the generation of superoxide anion as well as the anti-oxidant defense systems related to the isoforms of superoxide dismutases (SOD) in cystic fibrosis (CF) cells. Pro-apoptotic agents induced apoptosis in CF but not in control cells that was reduced by treatment with SOD mimetic. These effects were associated with increased superoxide anion production, sensitive to the inhibition of IκB-α phosphorylation, in pancreatic but not tracheal CF cells, and reduced upon inhibition of either mitochondrial complex I or NADPH oxidase. CF cells exhibited reduced expression, but not activity, of both Mn-SOD and Cu/Zn-SOD when compared to control cells. Although, expression of EC-SOD was similar in normal and CF cells, its activity was reduced in CF cells. We provide evidence that high levels of oxidative stress are associated with increased apoptosis in CFTR-mutated cells, the sources being different depending on the cell type. These observations underscore a reduced anti-oxidant defense mechanism, at least in part, via diminished EC-SOD activity and regulation of Cu/Zn-SOD and Mn-SOD expressions. These data point to new therapeutic possibilities in targeting anti-oxidant pathways to reduce oxidative stress and apoptosis in CF cells

Microvesicles: Intercellular Vectors of Biological Messages

Cells communicate directly by cell-cell contact and indirectly via the release of mediators. But gaining a greater appreciation recently is the identification and characterization of intercellular communication through the secretion of microvesicles (MVs). MVs—small vesicles that comprise microparticles (MPs) and exosomes (1) —released from a wide variety of cells, can be considered micro-messengers. Whereas exosomes are released into the extracellular compartment by exocytosis, MPs are shed from the blebbing plasma membrane, and the composition and effects of both on target cells differ depending on the cell from which originate and the type of stimulus involved in their formation. MVs are obtained after several steps of centrifugation, whereby MPs are defined as the MVs obtained by centrifugation at < 100,000 × g, whereas exosomes are isolated by centrifugation at > 100,000 × g. Because the processes by which exosomes and MPs work are different, some researchers have claimed that such broad observations impede the defining and understanding of MV actions (2)

Microparticle release in remote ischemic conditioning mechanism

Remote ischemic conditioning (RCond) induced by short periods of ischemia and reperfusion of an organ or tissue before myocardial reperfusion is an attractive strategy of cardioprotection in the context of acute myocardial infarction. Nonetheless, its mechanism remains unknown. A humoral factor appears to be involved, although its identity is currently unknown. We hypothesized that the circulating microparticles (MPs) are the link between the remote tissue and the heart. MPs from rats and healthy humans undergoing RCond were characterized. In rats, RCond was induced by 10 min of limb ischemia. In humans, RCond was induced by three cycles of 5-min inflation and 5-min deflation of a blood-pressure cuff. In the second part of the study, rats underwent 40 min myocardial ischemia followed by 2 h reperfusion. Infarct size was measured and compared among three groups of rats: 1) myocardial infarction alone (MI) (n = 6); 2) MI + RCond started 20 min after coronary ligation (n = 6); and 3) MI + injection of RCond-derived rat MPs (MI + MPs) (n = 5). MPs from endothelial cells (CD54(+) and CD146(+) for rats and humans, respectively) and procoagulant MPs (Annexin V(+)) markedly increased after RCond, both in rats and humans. RCond reduced infarct size (24.4 ± 5.9% in MI + RCond vs. 54.6 ± 4.7% in MI alone; P < 0.01). Infarct size did not decrease in MI + MPs compared with MI alone (50.2 ± 6.4% vs. 54.6 ± 4.7%, not significantly different). RCond increased endothelium-derived and procoagulant MPs in both rats and humans. However, MP release did not appear to be a biological vector of RCond in our model

Circulating microparticles from a rat model of pulmonary arterial hypertension induce endothelial dysfunction

Pulmonary arterial hypertension (PAH) is a rare and severe disease characterized by an increase of pulmonary vascular resistance and right heart failure. Chronic hypoxia induces PAH, which is accompanied by functional (endothelial dysfunction, increased vasoconstriction) and structural (thickening of media) changes in pulmonary arteries. However, the mechanisms of these alterations remain unsolved. Among biological hallmark of this disease, level of circulating microparticles (MPs), small vesicles of plasma membrane released during cell activation and apoptosis, is increased in PAH patients. Although MPs can act as biological vectors of endothelial dysfunction, their role in PAH are not elucidated yet. We studied circulating MP effects on endothelial function during hypoxic PAH. Male Wistar rats were exposed or not to chronic hypoxia (3 weeks, 0.5 atmosphere) and normoxic or hypoxic MPs were isolated from peripheral blood and characterized by flow cytometry. Endothelial cells from rat normoxic aorta or pulmonary arteries were incubated for 24 h with MPs. We studied also effects of in vivo treatment of MPs on vasomotricity, for this, normoxic or hypoxic MPs or vehicle were i.v. injected into rats, and 24 h after, endothelial function were studied. Levels of circulating MPs from hypoxic rats was twice than MPs from normoxic rats (1568 ± 174 vs 852 ± 80 MPs/Âμl of plasma). In vitro treatment of endothelial cells with hypoxic MPs reduced NO production both in aortas and pulmonary arteries ; these effects were associated with enhanced phosphorylation of endothelial NO-synthase at their inhibitory site. By contrast, O2- production was increased only in endothelial cells from pulmonary arteries. In vivo injection of normoxic or hypoxic MPs into rats impaired to the same extent the endotheliumdependent relaxation induced by acetylcholine in aorta. Although pulmonary arteries from rat treated either with normoxic or hypoxic MPs displayed reduction of endothelium-dependent relaxation to carbachol compared to control, the deleterious effect of hypoxic MPs was greater than normoxic MPs. These data provide evidence that hypoxic circulating MPs induce in vitro and in vivo endothelial dysfunction by increasing oxydative stress and by decreasing NO production

Circulating microparticles from pulmonary hypertensive rats induce endothelial dysfunction

RATIONALE: Pulmonary arterial hypertension (PAH) is a severe disease characterized by an increase of pulmonary vascular resistance, which is accompanied by functional and structural changes in pulmonary arteries. Microparticles (MPs) have been described as biological vector of endothelial dysfunction in other pathologies.OBJECTIVES: The purpose of this work was to characterize circulating MPs during hypoxic PAH and to study their effects on endothelial function. METHODS: Male Wistar rats were exposed or not to chronic hypoxia, and normoxic or hypoxic MPs from blood were characterized by flow cytometry. Endothelial cells (ECs) from rat aorta or pulmonary arteries were incubated with MPs, and then expression and phosphorylation of enzymes involved in nitric oxide (NO) and reactive oxygen species productions were analyzed. Hypoxic MPs were injected into rats, and endothelium-dependent relaxation was assessed. MEASUREMENTS AND MAIN RESULTS: Circulating levels of MPs from hypoxic rats were twofold higher than those present in normoxic rats. In vitro treatment of ECs with hypoxic MPs reduced NO production in aortas and pulmonary arteries by enhancing phosphorylation of endothelial NO synthase at the inhibitory site. Hypoxic MPs increased oxidative stress only in pulmonary ECs via xanthine oxidase and mitochondrial implication. In vivo injection of hypoxic MPs into rat impaired endothelium-dependent relaxation both in aorta and pulmonary arteries. CONCLUSIONS: These data provide evidence that hypoxic circulating MPs induce endothelial dysfunction in rat aorta and pulmonary arteries by decreasing NO production. Moreover, MPs display tissue specificity with respect to increased oxidative stress, which occurs only in pulmonary ECs