CHRONIC HYPOXIA AND RESISTANCE TO MYOCARDIAL ISCHEMIA

描述（由申请人提供）：血小板生成素（Tpo）是通过Tpo受体mpl调节巨核细胞和血小板发育的主要生理调节剂。最近，我们有了一个新奇而偶然的发现，即Tpo是一种非常有效的心脏保护剂。这些原始的观察结果可能会导致我们如何看待Tpo的机制和生物学效应的范式转变。因此，本提案的总体目标是确定Tpo提供早期和延迟心脏保护的细胞内信号通路。虽然关于血小板功能中mpl受体的组成、分布和信号传导的文献大量，但关于Tpo与mpl结合的途径赋予心脏保护作用以及该途径如何在心脏缺氧时被招募的信息却没有。我们假设Tpo受体的激活触发促生存途径并抑制细胞凋亡，从而通过打开线粒体KATp通道和/或线粒体赋予早期和延迟的心脏保护！王者文化频道。具体来说，我们将：1)确定Tpo赋予早期心脏保护的途径。我们将确定Tpo是否通过其受体（mpl）信号激活促生存激酶信号级联：JAK/STAT、Ras、Raf、磷脂酰肌醇-3- oh激酶(PI3K)/Akt、PKC、JNK、p38 MARK和p42/44 MARK。我们将确定在再灌注后立即给予Tpo是否通过激活促生存风险通路起保护作用，以及Tpo是否保护慢性缺氧心脏。2)确定线粒体KATP通道、KCa通道和肌层KATP通道在Tpo产生的早期心脏保护中的相对重要性。我们将确定早期心脏保护中的Tpo信号是否通过线粒体KATP和KCa通道的打开介导。我们将测量从tpo处理过的心脏中分离的线粒体的线粒体膜电位、呼吸和ATP合成，以确定KATP通道与线粒体功能之间的关系。3)测定慢性缺氧对兔和人心脏Tpo及Tpo受体（mpl）表达的影响。我们将利用我们的慢性缺氧模型来确定婴儿和兔心脏对慢性缺氧的适应是否会增加mpl的信息和蛋白质表达以及血小板循环水平。4)确定Tpo产生的延迟心脏保护的介质。我们将确定NO是否作为Tpo延迟心脏保护的中介。然后，我们将确定Tpo是否通过打开肌层和/或线粒体KATP通道介导延迟的心脏保护。这些研究的结果有望对我们对心脏中Tpo生物学的理解产生影响，并可能导致心肌梗死治疗新疗法的发展。

DESCRIPTION (provided by applicant): Thrombopoietin (Tpo) is the primary physiologic regulator of megakaryocyte and platelet development through the Tpo receptor mpl. Recently we have made the novel and serendipitous observation that Tpo is an extraordinarily potent cardioprotective agent. These original observations may cause a paradigm shift in how we view the mechanisms and biological effects of Tpo. Thus the overall objective of this proposal is to define the intracellular signaling pathways by which Tpo confers early and delayed cardioprotection. Whereas there is a substantial body of literature regarding the mpl receptor composition, distribution and signaling in platelet function, there is no information about the pathway by which binding of Tpo to mpl confers cardioprotection and how this pathway is recruited by hypoxia in the heart. We hypothesize that activation of the Tpo receptor triggers pro-survival pathways and suppresses apoptosis to confer early and delayed cardioprotection by opening of mitochondrial KATp channels and/or mitochondria! KCa channels. Specifically we shall: 1) Determine the pathways that confer early cardioprotection by Tpo. We shall determine whether Tpo signals through its receptor (mpl) to activate the pro-survival kinase signaling cascade: JAK/STAT, Ras, Raf, phosphatidylinositol-3-OH kinase (PI3K)/Akt, PKC, JNK, p38 MARK and p42/44 MARK. We shall determine whether protection by Tpo given immediately following reperfusion acts by activating the pro-survival RISK pathway and whether Tpo protects the chronically hypoxic heart. 2) Determine the relative importance of the mitochondrial KATP channel, KCa channel and the sarcolemmal KATP channel in early cardioprotection produced by Tpo. We shall determine if Tpo signaling in early cardioprotection is mediated by opening of mitochondrial KATP and KCa channels. We shall measure mitochondrial membrane potential, respiration and ATP synthesis in mitochondria isolated from Tpo-treated hearts to determine the relationship between KATP channels to mitochondrial function. 3) Determine the effect of chronic hypoxia on the expression of Tpo and the Tpo receptor (mpl) in rabbit and human heart. We shall utilize our model of chronic hypoxia to determine in both infant human and rabbit hearts whether adaptation to chronic hypoxia increases expression of message and protein for mpl and circulating levels of platelets. 4) Determine the mediators of delayed cardioprotection produced by Tpo. We shall determine if "NO acts as a mediator of delayed cardioprotection by Tpo. We shall then determine if mediation of delayed cardioprotection by Tpo occurs by opening sarcolemmal and/or mitochondrial KATP channels. The results of these studies are expected to have an impact on our understanding of the biology of Tpo in heart and may lead to the development of new therapeutics for the treatment of myocardial infarction.