Biology of Platelet Factor 4

血小板含有一种独特的趋化因子血小板因子4（PF 4），它在血小板活化部位大量释放。 虽然基于体外数据已经提出了PF 4在心血管系统中的许多潜在作用，但其体内生物学作用尚不清楚。 在本申请中，我们将定义PF 4在血小板生物学中的作用，扩展我们初步的体外数据PF 4与低密度脂蛋白（LDL），其受体LDL-R和相关受体LRP的相互作用。 我们还将在体内扩展这些观察结果。具体目标包括：第1：表征PF 4与LDL-R和LRP的体外相互作用。 这些研究将表征PF 4与LDL结合LDL-受体（R）的相互作用，使用定义的嵌合体和突变体鉴定PF 4和LDL-R内的负责结构域，并探索细胞蛋白聚糖引起的PF 4寡聚化阻碍LDL/LDL-R复合物内吞作用的假设。我们还将研究PF 4与LRP相互作用的特异性，并进一步表征其影响尿激酶进入细胞的能力。 第2号：PF 4对动脉粥样硬化发展的影响，重点是转基因小鼠方法。 我们已经创建了PF 4敲除小鼠（mPF 4）和过表达人PF 4的小鼠（hPF 4+）。 将对这些动物进行研究，以观察PF 4水平对LDL代谢的影响。 这些动物也将被交叉到几个定义明确的致动脉粥样硬化模型中，这些模型将测试与PF 4对LDL代谢和动脉粥样硬化发展的影响相关的特定问题。 第3号：PF 4对心血管生物学的影响，重点是转基因小鼠方法。 由我们小组和其他人开发的强有力的体外数据表明PF 4在血栓形成、血管生成和巨核细胞生成的发展中的作用。 然而，PF 4在这些过程中的生理作用尚未得到证实。 在这一特定目标中，我们计划使用mPF 4-/-和hPF 4+小鼠开始定义文献中和第1个特定目标中所述体外研究的生物学相关性。 交叉到其他转基因动物模型，这将提高我们的理解的分子机制（S），PF 4有助于这些生物过程也提出了。 我们认为，该应用程序获得的新信息将具有临床意义。 PF 4的生物学研究将为心血管相关过程的调控提供新的见解，并可能为心血管疾病的治疗提供新的方法。

Platelets contain a unique chemokine Platelet Factor 4 (PF4), which is released in large amounts at sites of platelet activation. While a number of potential roles of PF4 in the cardiovascular system have been suggested based on in vitro data, its in vivo biological role(s) is unclear. In this application we will define the role of PF4 in platelet biology, extending our preliminary in vitro data of PF4's interaction with low-density lipoprotein (LDL), with its receptor LDL-R and with the related receptor LRP. We will also extend these observations in vivo. Specific aims include: Number 1: Characterize PF4's interactions with LDL-R and LRP in vitro. These studies will characterize the interactions of PF4 with LDL binding to the LDL-receptor (R), identifying the responsible domains within PF4 and LDL-R using defined chimeras and mutants, and exploring the hypothesis that oligomerization of PF4 by cellular proteoglycans frustrates the endocytosis of LDL/LDL-R complexes. We will also examine the specificity of PF4's interactions with LRP and further characterize its ability to influence the uptake of urokinase into cells. Number 2: Effect of PF4 on the development of atherosclerosis focusing on a transgenic mice approach. We have created PF4 null mice (mPF4) and mice overexpressing human PF4 (hPF4+). These animals will be studied to see the effect of PF4 level on LDL metabolism. The animals will also be crossed onto several well-defined atherogenic models that will test specific issues related to PF4's affect on LDL metabolism and the development of atherosclerosis. Number 3: Effect of PF4 on the cardiovascular biology focusing on a transgenic mice approach. Strong in vitro data developed by our group and others have suggested a role of PF4 in the development of thrombosis, angiogenesis and megakaryopoiesis. However, a physiologic role of PF4 in these processes has yet to be demonstrated. In this specific aim, we plan to use the mPF4-/- and hPF4+ mice to begin to define the biological relevance of the in vitro studies in the literature and presented in the 1st specific aim. Crosses onto other transgenic animal models that will enhance our understanding of the molecular mechanism(s) by which PF4 contributes to these biological processes are also proposed. We believe that new information derived by this application will have clinical relevance. The biological studies of PF4 should provide new insights into the regulation of several cardiovascular-related processes, and may offer novel approaches for the treatment of cardiovascular diseases.