Aging, Adenosine and Platelet-Mediated Thrombosis

描述（由申请人提供）：缺血预处理（PC）是一种描述良好的现象，即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。我们小组的证据表明，PC的益处超出了心肌细胞本身：即，先前的PC缺血会减弱血小板激活聚集并改善受损和狭窄动脉的血管扩张——至少部分是通过刺激血小板表面的腺苷A2受体触发的有利效果。这些数据表明，在未来，腺苷a2介导的血小板活化聚集抑制可能被用于设计新的临床疗法，以减轻急性缺血性综合征患者的血栓事件。然而：(1)迄今为止所有的研究都是在成人队列中进行的；(2)最近的初步体外实验结果表明，在老年人群的血液样本中，A2受体刺激的有益抗血栓作用可能会消失。因此，我们目前的目标是：(1)建立我们的初步发现与复发性血栓形成的体内环境的生理学相关性；(2)初步了解老年人群血小板腺苷A2受体反应性明显降低的机制。为了解决第一个目标（并验证我们的主要假设，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性、复发性动脉（股动脉和冠状动脉）血栓形成模型，这些模型模拟了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，比较预防性治疗PC缺血和CGS 21680（一种强效A2受体激动剂）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，我们将收集2岁大鼠和成年大鼠的血小板，以验证我们的第二个辅助假设：与年龄相关的PC/A2刺激抗血栓作用的丧失是：(1)A2受体蛋白减少的结果；(2) A2受体反应性降低，和/或(3)远端信号缺陷。这些问题的解决对于A2受体刺激的任何未来临床应用至关重要，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最相关。

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.