Angiotensin II, oxidative stress and aneurysm formation

描述(申请人提供)：腹主动脉瘤(AAA)常见于老年人群，是发病率和死亡率的主要原因。对动脉瘤形成的机制了解甚少，这阻碍了对这种疾病的有效药物治疗的确定。在人类AAA和实验动物模型的研究中，越来越多的证据表明，氧化应激在AAA的发病机制中发挥着关键作用。虽然许多酶途径能够诱导血管氧化应激，并可能导致AAA，但我们假设髓过氧化物酶(MPO)在这一过程中起着重要作用。MPO是一种主要在中性粒细胞(PMN)中表达的酶，在单核/巨噬细胞中表达较少，它催化强氧化性物种HOCl2的形成，并诱导蛋白质硝化。此外，MPO可以被带入血管壁，从而放大炎症、氧化应激和蛋白酶降解。使用两种不同的小鼠模型(弹性酶诱导和血管紧张素II注射在高脂血症小鼠中)，我们的数据表明，在实验性AAA形成过程中，主动脉MPO活性和氯酪氨酸(HOCl介导的氧化应激的标志)的表达增加。我们的数据还表明，血管紧张素II有一个潜在的新作用，可以加剧HOCl2介导的血管壁氧化应激。此外，补充牛磺酸，一种与HOCl反应并解毒的β氨基酸，可以防止这些实验模型中AAA的形成。为了检验我们的假设，我们提出了三个具体目标。在目标1中，我们将对对照或MPO缺陷小鼠的PMN进行选择性免疫耗竭和过继转移，以验证在弹性酶模型中PMN中MPO表达有助于实验性AAA形成的假设。此外，我们将免疫耗竭中性粒细胞，以确定它们在血管紧张素II输注模型中AAA形成中的作用。在目标2中，我们将在弹性蛋白酶诱导和血管紧张素II输注模型中检验MPO基因缺陷改善AAA形成的假设。在目标3中，我们将检验人类MPO转基因表达增加实验性AAA形成的假设。在目标2和目标3中，我们还将确定血管紧张素II是否上调白细胞中MPO的表达和活性，以及MPO是否调节血管紧张素II诱导的高血压和动脉粥样硬化。我们的研究将为AAA的形成机制以及心血管疾病发病机制中关键的氧化应激生成途径之间的联系提供新的见解。 与公共卫生相关：腹主动脉瘤在美国老年人中很常见，可导致体内最大的血管--主动脉--进行性增大甚至破裂。我们的研究表明，存在于白细胞中的一种名为髓过氧化物酶的酶有助于炎症和主动脉内的组织损伤，从而导致动脉瘤的形成。本研究的目的是探讨髓过氧化物酶在实验性动物模型动脉瘤形成中的作用，进而确定髓过氧化物酶的对策在治疗人类动脉瘤中是否有效。

DESCRIPTION (provided by applicant): Abdominal aortic aneurysms (AAA) occur commonly in the elderly population and are a major cause of morbidity and mortality. The mechanisms responsible for aneurysm formation are poorly understood, which has impeded identification of effective medical therapies for this disease. Mounting evidence from studies in human AAA, and in experimental animal models, suggests that oxidative stress plays a key role in the pathogenesis of AAA. While a number of enzymatic pathways are capable of inducing vascular oxidant stress and potentially contributing to AAA, we hypothesis that myeloperoxidase (MPO) is instrumental in this process. MPO is an enzyme expressed primarily in neutrophils (PMNs) and to a lesser extent in monocytes/macrophages, that catalyzes the formation of HOCl, a powerful oxidizing specie, and induces protein nitration. In addition, MPO can be taken up into the blood vessel wall, thus amplifying inflammation, oxidative stress and protease degradation. Using two distinct murine models (elastase-induced and angiotensin II infusion in hyperlipidemic mice), we present data showing that aortic MPO activity and chlorotyrosine expression (a marker of HOCl-mediated oxidative stress) are increased during experimental AAA formation. Our data also suggest a potentially novel role for angiotensin II to exacerbate HOCl-mediated oxidative stress in the blood vessel wall. Moreover, supplementation with taurine, a beta amino acid that reacts with and detoxifies HOCl, prevents AAA formation in these experimental models. To test our hypothesis, we propose three specific aims. In aim 1, we will perform selective immunodepletion and adoptive transfer of PMNs from control or MPO- deficient mice.to test the hypothesis that MPO expression in PMNs contributes to experimental AAA formation in the elastase model. Also, we will immnuodeplete PMNs to determine their role in AAA formation in the angiotensin II infusion model. In aim 2, we will test the hypothesis that genetic deficiency of MPO ameliorates AAA formation in the elastase-induced and angiotensin II infusion models. In aim 3, we will test the hypothesis that transgenic expression of human MPO augments experimental AAA formation. In aims 2 and 3, we will also determine whether angiotensin II upregulates expression and activity of MPO in leukocytes, and whether MPO modulates hypertension and atherosclerosis induced by angiotensin II infusion. Our studies will provide novel insight into mechanisms of AAA formation and linkages between key oxidant stress generating pathways in the pathogenesis of cardiovascular disease. PUBLIC HEALTH RELEVANCE: Abdominal aortic aneurysms are common in elderly Americans and can lead to progressive enlargement and even rupture of the aorta, the largest blood vessel in the body. Our research suggests that an enzyme known as myeloperoxidase, which is present in white blood cells, contributes to inflammation and tissue damage within the aorta, leading to aneurysm formation. The purpose of our research is to investigate the role of myeloperoxidase in aneurysm formation in experimental animal models, and then to determine whether countermeasures against myeloperoxidase may be effective in treating aneurysms in humans.