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(PF4)，它在血小板激活的部位大量释放。虽然基于体外数据已经提出了PF4在心血管系统中的一些潜在作用，但它在体内的生物学作用尚不清楚(S)。在这一应用中，我们将确定Pf4在血小板生物学中的作用，扩展我们的初步体外数据，即Pf4‘S与低密度脂蛋白及其受体低密度脂蛋白-R和相关受体Lrp的相互作用。我们还将在活体内扩展这些观察。具体目标包括：1：体外研究PF4‘S与低密度脂蛋白受体和LRP的相互作用。这些研究将描述PF4与与低密度脂蛋白受体(R)结合的低密度脂蛋白的相互作用，使用已定义的嵌合体和突变体确定PF4和低密度脂蛋白受体中的负责区域，并探索细胞蛋白多糖对PF4的寡聚抑制低密度脂蛋白/低密度脂蛋白-R复合体的内吞作用的假设。我们还将研究Pf4‘S与Lrp相互作用的特异性，并进一步表征其影响细胞对尿激酶摄取的能力。数字2：转基因小鼠研究PF4在动脉粥样硬化发展中的作用。我们创造了pf4缺失小鼠(Mpf4)和高表达人pf4的小鼠(hpf4+)。将对这些动物进行研究，以了解PF4水平对低密度脂蛋白代谢的影响。这些动物还将被交叉到几个定义明确的致动脉粥样硬化模型上，以测试与PF4‘S对低密度脂蛋白代谢和动脉粥样硬化发展的影响相关的具体问题。第三：PF4对心血管生物学的影响，重点放在转基因小鼠方法上。我们团队和其他人开发的强大的体外数据表明，PF4在血栓形成、血管生成和巨核细胞生成中发挥作用。然而，PF4在这些过程中的生理作用尚未得到证实。在这个特定的目标中，我们计划使用mPF4-/-和HPF4+小鼠来开始定义文献中和第一个特定目标中提出的体外研究的生物学相关性。与其他转基因动物模型的交叉也将加强我们对PF4参与这些生物学过程的分子机制的理解(S)。我们相信，通过这一应用获得的新信息将具有临床意义。PF4的生物学研究将为几个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.