Cellular Lipids and Leukocyte Function

 描述(申请人提供)：败血症的特征是细菌结构成分和毒素的释放，这些毒素激活了靶细胞中的炎症级联反应。中性粒细胞的募集及其与血管内皮细胞的结合是败血症早期的重要反应。中性粒细胞和驻留巨噬细胞通过分泌细胞因子、趋化因子和消化酶启动修复过程。然而，免疫反应的失调可导致以白细胞增多(中性粒细胞增多/单核细胞增多)为特征的广泛和失控的炎症损伤。这种失调导致多器官功能障碍综合征(MODS)，并过渡到明显的感染性休克。呼吸衰竭进展迅速，与大约40%-50%的死亡率有关。高密度脂蛋白是多种蛋白质的载体，包括载脂蛋白(Apo)A-I和apoE，它们在介导胆固醇反向运输中发挥作用。几项研究表明，载脂蛋白E具有抗炎作用，包括调节免疫细胞功能，这与其降低血浆胆固醇水平的能力无关。在这方面，apoE最近被证明可以限制造血干细胞和多潜能祖细胞(HSPC)的扩张，导致中性粒细胞和单核细胞增殖减少。载脂蛋白E对白细胞激活的抑制作用与细胞胆固醇含量本身的降低有关。高密度脂蛋白相关的载脂蛋白E在减少脓毒症时炎性细胞损伤方面起着关键作用。然而，载脂蛋白E的这种保护作用可能受到脓毒症特征的高密度脂蛋白水平降低的限制。申请中提出的初步数据显示，一种模拟天然载脂蛋白E效应的合成肽(Ac-hE18A-NH2)可以防止白细胞的激活，并提高脓毒症啮齿动物模型的存活率。AC-hE18A-NH2还能诱导含有抗氧化剂对氧磷酶和载脂蛋白E本身的前高密度脂蛋白颗粒的释放。我们的数据还表明，apoE模拟物与细胞表面的蛋白多糖结合，并介导白细胞的胆固醇外流，这一反应与内毒素诱导的细胞因子/趋化因子释放减少有关。在这一应用中，我们将检验这一新的假设，即Ac-hE18A-NH2和相关的apoE模拟肽通过降低细胞胆固醇含量的机制抑制HSPC的扩张和白细胞的增殖/激活，从而减轻脓毒症引起的炎性损伤。其他研究将测试体外用apoE模拟多肽治疗是否改变败血症患者分离的白细胞的表型/功能。

 DESCRIPTION (provided by applicant): Sepsis is characterized by the release of bacterial structural components and toxins that activate inflammatory cascades in target cells. The recruitment of neutrophils and their binding to the vascular endothelium is an important, early response to sepsis. Neutrophils and resident macrophages initiate repair processes via the secretion of cytokines, chemokines and digestive enzymes. Dysregulation of the immune response, however, can lead to widespread and uncontrolled inflammatory injury characterized by leukocytosis (neutrophilia/monocytosis). This dysregulation results in multiple organ dysfunction syndrome (MODS) with the transition to overt septic shock. Respiratory failure progresses rapidly and is associated with approximately 40- 50% mortality. HDL serves as a carrier for diverse proteins, including apolipoprotein (apo) A-I and apoE, that play a role in mediating reverse cholesterol transport. Several studies suggest that apoE exerts anti-inflammatory effects, including the modulation of immune cell function, that are independent of its ability to lower plasma cholesterol levels. In this regard, apoE was recently shown to limit th expansion of hematopoietic stem and multipotential progenitor cells (HSPCs), resulting in a decrease in neutrophil and monocyte proliferation. The inhibitory effect of apoE on leukocyte activation was linked to a reduction in cellular cholesterol content per se. It is proposed that HDL-associated apoE plays a critical role in reducing inflammatory cell injury in the context of sepsis. This protective effect of apoE, however, may be limited by reduced levels of HDL that characterize sepsis. Preliminary data presented in the application show that a synthetic peptide (Ac-hE18A-NH2) that mimics effects of native apoE prevents the activation of leukocytes and improves survival in a rodent model of sepsis. Ac-hE18A-NH2 also induces the release of preß-HDL particles containing the antioxidant paraoxonase and apoE itself. Our data also show that apoE mimetics bind to cell surface proteoglycans and mediate cholesterol efflux from leukocytes, a response that is associated with a reduction in lipopolysaccharide-induced cytokine/chemokine release. In this application, we will test the novel hypothesis that Ac-hE18A-NH2 and related apoE mimetic peptides attenuate sepsis-induced inflammatory injury by inhibiting HSPC expansion and leukocyte proliferation/activation by a mechanism involving a reduction in cellular cholesterol content. Additional studies will test whether in vitro treatment with apoE mimetic peptides alters the phenotype/function of leukocytes isolated from septic patients.