Aging, Adenosine and Platelet-Mediated Thrombosis

描述（由申请人提供）：缺血预处理（PC）是一种描述充分的现象，即短暂的心肌缺血事件使心肌细胞对随后的持续缺血损伤具有抵抗力。我们小组的证据表明，PC的益处超出了肌细胞本身：即，在受损和狭窄的动脉中，先前的PC缺血减弱血小板活化-聚集并改善血管开放性-这是一种有利的作用，至少部分地由血小板表面上的腺苷A2受体的刺激触发。这些数据表明，腺苷A2介导的抑制血小板活化-聚集，在未来，可能会被用于设计新的临床治疗，以减轻急性缺血综合征患者的血栓事件。然而：（1）迄今为止的所有研究都是在成人队列中进行的;（2）最近的初步体外结果表明，A2受体刺激的有益抗血栓形成作用可能在从老年人群中获得的血液样品中丧失。因此，我们目前的目标是：（1）建立我们的初步研究结果的生理相关性，在体内设置的复发性血栓形成;（2）获得初步了解的机制，血小板腺苷A2受体的反应性明显降低，在老年队列。为了解决目标1（并测试我们的主要假设，即PC/A2刺激的抗血栓形成作用随年龄而减弱），我们将利用自发性复发性动脉（股动脉和冠状动脉）血栓形成的新型大鼠和小鼠模型-模拟不稳定型心绞痛中观察到的复发性缺血的关键病理生理学特征的模型。我们将通过测量血流量和组织灌注，比较PC缺血和CGS 21680（一种有效的A2受体激动剂）预防性治疗对衰老2岁动物与成年动物动脉通畅性的影响。为了探索目标2，我们将从2岁大鼠与成年大鼠中收获血小板，以检验我们的第二个辅助假设：PC/A2刺激的抗血栓形成作用的年龄相关性丧失是以下因素的结果：（1）A2受体蛋白减少;（2）A2受体反应性降低，和/或（3）远端信号传导缺陷。这些问题的解决对于A2受体刺激的任何未来临床应用至关重要，因为中年和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.