Platelet ERK5 regulates myocardial infarct expansion

 描述(申请人提供)：背景血小板的激活和募集是血管系统血栓形成和血管闭塞的关键，发生在血栓形成的紧急情况下，包括急性冠脉综合征(ACS)、中风、深静脉血栓形成(DVT)和肺血栓(PE)。在美国，血栓突发事件极大地增加了发病率和死亡率。有许多典型的血小板表面受体可启动细胞内信号转导事件，从而触发血小板活化和血栓形成。其中一些受体被用于临床使用抗血小板药物，用于经历心肌梗死(MI)的患者。阿司匹林和氯吡格雷是两种用于治疗心肌梗死的抗血小板药物，然而一项前瞻性研究显示，在阿司匹林的基础上加入氯吡格雷，不良血管事件仅减少20%。在急性心肌梗塞期间，可以使用支架打开冠状动脉。最近的数据表明，冠状动脉支架植入--即使使用氯吡格雷和阿司匹林治疗--在大约50%的患者中会导致“无复流”现象。没有复流，即使在移除管腔阻塞后，也被认为涉及下游微血管阻塞--这是一个血小板最活跃的区域。抗血小板药物的失败和观察到没有复流有时会导致临床医生条件反射地增加现有的药物剂量，联合使用抗血小板药物，或者寻找针对相同的血小板受体的新药，以期看到更好的疗效。创新观察另一种策略可能是考虑到，在无复流和糖尿病等疾病条件下，血小板活性在某种程度上是不同的(失调)，在这些疾病条件下，传统的抗血小板药物可能会产生不可预测的效果。在缺血的微血管系统中，血小板暴露于浓度丰富的活性氧物种(ROS)中，ROS可以激活不依赖于表面受体的血小板。我们首次在血小板中发现了一种名为ERK5的蛋白质。ERK5对ROS非常敏感，似乎是一种血小板缺血感受器，可以触发不适应的血小板行为。ERK5是一种丝裂原活化蛋白激酶(MAPK)家族成员，通常存在于增殖细胞中，因为它推动细胞周期的进展。在无核血小板中，我们发现ERK5对正常的血小板激活以及ROS反应中的血小板激活都是重要的。使用ROS和血小板激活剂显著升高的小鼠MI模型，血小板特异性ERK5-/-小鼠缩小了梗塞面积并改善了心功能。此外，对血小板活化至关重要的蛋白质的表达和泛素化也发生了显著的变化，这表明在炎症和脑梗塞后的环境中，可能存在着将血小板转变为失调状态的开关。导师研究奖的重要性我治疗心血管疾病患者，因此我敏锐地意识到目前可用的治疗方法的局限性和需求。传统上，血液学家为血小板研究做出了贡献，而心脏病学家通常会开出抗血小板药物。我的目标是在基础血栓研究和临床心血管护理之间进行操作。在开发用于心脏病发作患者的血小板抑制药物方面进展甚微，我认为这是因为人们对调节失调的血小板功能还不了解。我建议从机制上证明血小板ERK5作为“缺血感受器”的关键作用，是心肌梗塞后血小板活性失调的媒介，也是治疗血栓急症的潜在新药靶点。这项研究的初步数据表明，在确定心肌梗塞后的血小板功能以及为药物治疗建议新的相关血小板靶点方面，这是一项重大的技术进步。目的是利用导师职业科学家奖专注于并发展独立的研究路线，以启动作为内科科学家的职业生涯。为了实现这一目标，我将致力于描述ERK5在缺血性损伤后调节体内血小板激活的机制。这将使我能够学习以前我无法接触到的疾病的动物模型，并以一种有凝聚力和有组织的方式补充我之前在生物化学和细胞信号方面的培训。

 DESCRIPTION (provided by applicant): Background Platelet activation and recruitment are critical for thrombus formation and blood vessel occlusion in the vasculature, occurring in thrombotic emergencies including acute coronary syndromes (ACS), stroke, Deep Vein Thrombosis (DVT), and Pulmonary Embolus (PE). Thrombotic emergencies contribute greatly to morbidity and mortality in the U.S. There are well-characterized platelet surface receptors initiating intracellular signal transduction events which trigger platelet activation and thrombus formation. Some of these receptors are exploited clinically using anti-platelet medications for patients who experience a myocardial infarction (MI). Aspirin and clopidogrel are two anti-platelet agents used to treat MI yet one prospective study showed only a 20% reduction in adverse vascular events with the addition of clopidogrel to aspirin. During an acute MI, coronary arteries can be opened using stents. Recent data indicates that stenting a coronary artery-even with clopidogrel and aspirin therapy-leads to a `no reflow' phenomenon in around 50% of patients. No reflow, even after removing luminal obstruction, is thought to involve downstream microvascular obstruction-a region where platelets are most active. Failure of anti-platelet medications and observing no reflow sometimes leads clinicians to reflexively increase the existing drug dose, to combine anti-platelet medications, or to search for new medications against the same platelet receptors in the hope of seeing enhanced efficacy. Innovative Observation Another strategy may be to consider that platelet activity is somehow different (dysregulated) in disease conditions such as no reflow and diabetes where traditional anti-platelet medications can have unpredictable effects. In the ischemic microvasculature, platelets are exposed to enriched concentrations of reactive oxygen species (ROS) which can activate platelets independent of surface receptors. We have, for the first time, identified a protein in platelets called ERK5. ERK5 is exquisitely sensitive to ROS, and appears to act as a platelet ischemic sensor, which triggers maladaptive platelet behavior. ERK5 is a Mitogen-Activated Protein Kinase (MAPK) family member usually found in proliferating cells because it drives cell cycle progression. In the anucleate platelet, we found that ERK5 is important for normal platelet activation as well as platelet activation in response to ROS. Using a mouse MI model in which ROS and platelet activators are greatly elevated, platelet specific ERK5-/- mice have reduced infarct size and improved heart function. In addition, the expression and ubiquitination of proteins important for platelet activation are dramatically altered, suggesting there may be a switch which transforms platelets into a dysregulated state in inflammatory, post-infarct environment. Importance of the Mentored Research Award I treat patients with cardiovascular disorders and so I am acutely aware of the limitations and needs of currently available therapeutics. Traditionally, hematologists have contributed to platelet research while cardiologists typically prescribe anti-platelet medications. I aim operate at the interface of basi thrombosis research and clinical cardiovascular care. There has been little advance in the development of platelet inhibiting drugs to use in patients with heart attack and I feel this is because dysregulated platelet function is not understood. I propose to mechanistically demonstrate a key role for platelet ERK5 as an `ischemia sensor', a mediator of dysregulated platelet activity following MI, and a potentially new drug target for thrombotic emergencies. The preliminary data for this study represents a significant technological advancement in terms of defining platelet function following MI as well as suggesting new relevant platelet targets for drug therapy. The aim to use the mentored career scientist award to focus and to develop independent lines of investigation needed to launch a career as a physician scientist. To achieve this goal I will aim to characterize the mechanism by which ERK5 regulates platelet activation in the body following an ischemic insult. This will allow me to learn animal models of disease previously inaccessible to me and to complement my previous training in biochemistry and cellular signaling in a cohesive and organized manner.