Aging, Adenosine and Platelet-Mediated Thrombosis

描述(由申请人提供)：缺血预适应(PC)是一种广为人知的现象，在这种现象中，短暂的心肌缺血发作使心肌细胞对后来持续的缺血损伤具有抵抗力。来自我们团队的证据表明，PC的益处超出了心肌细胞本身：即，先前的PC缺血减弱了血小板的激活-聚集，并改善了受损和狭窄动脉的血管通畅性--这一有利效果至少部分是由刺激血小板表面的腺苷A2受体触发的。这些数据表明，腺苷A2介导的对血小板活化-聚集的抑制可能在未来用于设计新的临床疗法，以减轻急性缺血综合征患者的血栓形成事件。然而：(1)到目前为止的所有研究都是在成人队列中进行的；(2)最近的体外初步结果表明，A2受体刺激的有益抗血栓作用可能在老年人群的血液样本中消失。因此，我们目前的目标是：(1)确定我们的初步发现与体内复发血栓形成的生理学相关性；以及(2)初步了解老年人群中血小板腺苷A2受体反应性明显降低的机制。为了解决目标1(并测试我们的主要假设，即PC/A2刺激的抗血栓作用随着年龄的增长而减弱)，我们将利用新的大鼠和小鼠自发的、复发性动脉(股和冠状动脉)血栓形成模型-模拟不稳定心绞痛中复发性缺血的关键病理生理特征。我们将通过测量血流和组织灌注量，比较PC缺血和CGS 21680(一种有效的A2受体激动剂)预防治疗对2岁衰老动物和成年动物动脉通畅的影响。为了探索目标2，我们将采集2岁大鼠和成年大鼠的血小板来测试我们的第二个辅助假设：PC/A2刺激的抗血栓作用的年龄相关丧失是以下结果：(1)A2受体蛋白减少；(2)A2受体反应性减弱，和/或(3)远端信号传导缺陷。这些问题的解决对于A2受体刺激未来的临床应用至关重要，因为中老年人正是急性冠状动脉综合征最常见的人群，因此抗血栓治疗策略是最相关的。

DESCRIPTION (provided by applicant): Ischemic preconditioning (PC) is the well-described phenomenon whereby brief episodes of myocardial ischemia render cardiomyocytes resistant to a later, sustained ischemic insult. Evidence from our group has shown that the benefits of PC extend beyond the myocyte per se: i.e., antecedent PC ischemia attenuates platelet activation-aggregation and improves vessel patency in damaged and stenotic arteries - a favorable effect that is triggered, at least in part, by stimulation of adenosine A2 receptors on the platelets' surface. These data suggest that adenosine A2-mediated inhibition of platelet activation-aggregation may, in future, be used in the design of new clinical therapies to attenuate thrombotic events in patients with acute ischemic syndromes. However: (1) all studies to date have been conducted in adult cohorts; and (2) recent preliminary in vitro results suggest that the beneficial anti-thrombotic effect of A2 receptor stimulation may be lost in blood samples obtained from aging populations. Accordingly, our current aims are to: (1) establish the physiologic relevance of our preliminary findings to the in vivo setting of recurrent thrombosis; and (2) obtain initial insight into the mechanisms that underlie the apparently diminished responsiveness of platelet adenosine A2 receptors in old cohorts. To address Aim 1 (and test our primary hypothesis that the anti- thrombotic effects of PC/A2 stimulation wane with age), we will utilize novel rat and mouse models of spontaneous, recurrent arterial (femoral and coronary) thrombosis - models that mimic the key pathophysiologic features of recurrent ischemia seen in unstable angina. We will, via measurement of blood flow and tissue perfusion, compare the effects of prophylactic treatment with PC ischemia and CGS 21680 (a potent A2 receptor agonist) on arterial patency in senescent 2-year old animals versus adults. To explore Aim 2, we will harvest platelets from 2-year old versus adult rats to test our second ancillary hypothesis: that the age-associated loss of the anti-thrombotic effects of PC/A2 stimulation is a consequence of: (1) a reduction in A2 receptor protein; (2) diminished A2 receptor responsiveness, and/or (3) defects in distal signaling. Resolution of these issues is crucial for any future clinical application of A2 receptor stimulation, as the middle-aged and elderly are precisely the population in whom acute coronary syndromes are most common and thus anti-thrombotic treatment strategies are most relevant.