Platelet Microvesicles

描述（由申请人提供）： 微囊泡是亚微米大小的、膜封闭的片段，在细胞激活或凋亡过程中从细胞中释放出来。血小板活化后释放的血小板衍生微泡构成循环血液中微泡的主要部分。在 血小板微泡除了在止血中的公知作用外，还显示出刺激造血细胞、将血小板特异性受体转移到其它细胞的表面并引发滑膜成纤维细胞的细胞因子应答。在流动的血液中，微泡由于其大小而被推向血浆-内皮界面，并且它们准备与内皮相互作用。血小板和内皮细胞之间的相互作用已经知道很久了。严重血小板减少症改变内皮细胞的通透性和完整性。严重血小板减少症患者的紫癜性血管破裂是由于内皮细胞破裂而不是通过内皮连接处外渗所致。血小板衍生的生长因子调节血管生成。血小板微泡可能介导一些归因于血小板的作用。最近的研究结果还表明，血小板微泡诱导血管生成和内皮细胞迁移。我们最近表明，发育内皮基因座-1（Del-1）是一种52 kDa的糖蛋白，在体外和体内介导内皮对血小板微泡的吸收。我们建议，内皮细胞是微泡清除的生理介质。内皮细胞对微泡的摄取诱导内皮细胞的几种功能和形态学变化。最近，我们已经表明，血小板微泡可以提供微RNA内皮细胞提高微泡可以通过修改基因表达调节内皮细胞功能的可能性。我们建议描述这一新发现的意义。本提案的具体目的是（1）进一步表征内皮细胞对血小板微泡的磷脂酰丝氨酸依赖性摄取和清除中涉及的分子（2）确定微泡相关microRNA对内皮功能的影响和（3）确定血浆Del-1和乳凝集素水平是否是微泡清除的生物标志物。

DESCRIPTION (provided by applicant): Project Summary Microvesicles are submicron size, membrane enclosed fragments, released from cells in response to activation or during apoptosis. Platelet-derived microvesicles, released upon platelet activation, constitute a major fraction of microvesicles in the circulating blood. In addition to their well-known role in hemostasis, platelet microvesicles have been shown to stimulate hematopoietic cells, transfer platelet-specific receptors to the surface of other cells and elicit cytokine responses from synovial fibroblasts. In flowing blood, microvesicles are pushed towards the plasma-endothelial interface because of their size and they are poised to interact with endothelium. Interactions between platelets and endothelium have been known for a long time. Severe thrombocytopenia alters endothelial cell permeability and integrity. Purpuric hemorrhages in severe thrombocytopenia occur by rupture of endothelial cells rather than by extravasation through endothelial junction. Platelets derived growth factors regulate angiogenesis. Platelet microvesicles may mediate some of the effects attributed to platelets. The recent findings also suggest that platelet microvesicles induce angiogenesis and endothelial cell migration. We have recently shown that (developmental endothelial locus-1 (Del-1), a 52 kDa glycoprotein mediates the uptake of platelet microvesicles by endothelium both in vitro and in vivo. We propose that endothelium is the physiological mediator of microvesicles clearance. Uptake of microvesicles by the endothelial cells induces several functional and morphological changes in endothelium. More recently, we have shown that platelet microvesicles can deliver microRNAs endothelium raising the possibility that microvesicles can modulate endothelial cells function by modifying gene expression. We propose to characterize the significance of this novel finding. The specific aims of this proposal are (1) To further characterize the molecules involved in phosphatidylserine-dependent uptake and clearance of platelet microvesicles by endothelium (2) To determine the effect of microvesicles associated microRNAs on endothelial function and (3) to determine whether plasma levels of Del-1 and lactadherin are biomarkers of microvesicles clearance.