The Role of Adenosine in Retinal Ischemia

描述(申请人提供)：视网膜动脉或静脉阻塞的视网膜缺血，青光眼，动脉粥样硬化，或糖尿病等全身性疾病可能导致严重的视力丧失。发病机制涉及细胞生化和能量水平、血流和基因表达的变化。 在这个项目的过去11年中，我们记录了该复合体的广泛的生化、功能、结构和血流动力学证据，但主要涉及嘌呤核苷腺苷在视网膜缺血再灌注损伤中的作用。最近，我们还发现，在活体视网膜中，由于短暂的非损伤性缺血，即缺血预适应(IPC)，对缺血损伤具有完整的功能和组织学保护。IPC的其他重要伴随保护机制包括减弱低灌注率、蛋白磷酸化和细胞凋亡。我们证明了腺苷是IPC的触发因素，我们开始发现下游信号转导因子，包括线粒体KATP通道、PKC、丝裂原活化蛋白激酶p38、一氧化氮和活性氧在这种神经保护中的作用。这些令人兴奋的结果扩展了我们早期的发现，即IPC对缺血损伤具有显著的功能和组织保护作用，表明IPC对细胞信号转导和生存具有深远的影响。在我们已建立的视网膜缺血模型中，对IPC机制的研究为了解视网膜内源性抗缺血损伤的能力提供了一个独特的、创新的窗口。 第一个目标将描述IPC涉及线粒体KATP通道的信号通路和相关的信号转导因子。第二个目标将描述一氧化氮合酶和蛋白激酶C亚型在IPC中作为重要的信号中介的参与。第三个目标将研究这一矛盾效应的机制，即瞬时MAPK p38的表达保护视网膜，而在缺血之前阻断它则保护缺血损伤。我们的实验将明确地检验IPC的主要机制，并应使我们更接近于了解这种强大、耐人寻味和临床相关的神经保护背后的分子事件。

DESCRIPTION (provided by applicant): Significant visual loss may result from retinal ischemia in retinal arterial or venous occlusion, glaucoma, atherosclerosis, or in systemic disorders such as diabetes mellitus. The pathogenesis involves changes in cellular biochemistry and energy level, blood flow, and gene expression. During the past 11 years of this project, we documented extensive biochemical, functional, structural, and hemodynamic evidence for the complex, but major involvement of the purine nucleoside adenosine in retinal ischemia-reperfusion injury. More recently, we also discovered the closely related and dramatic finding of complete functional and histological protection from ischemic damage in the in vivo retina conferred by a brief period of non damaging ischemia, i.e., ischemic preconditioning (IPC). Other significant accompanying protective mechanisms of IPC include the attenuation of hypoperfusion, protein phosphorylation, and apoptosis. We demonstrated that adenosine is a trigger for IPC, and we began to uncover the roles of downstream signal transduction factors, including mitochondrial KATP channels, PKC, mitogen-activated protein kinase p38, nitric oxide, and reactive oxygen species, in this neuroprotection. These exciting results extend our earlier findings of the remarkable functional and histological protection from ischemic damage afforded by IPC, indicating that IPC has a profound influence upon cell signaling and survival. Examination of the mechanisms responsible for IPC in our established retinal ischemia model provides a unique and innovative window into the retina's endogenous ability to counter ischemic injury. The first aim will characterize the signaling pathways for IPC involving mitochondrial KATP channels and the associated signal transduction factors. The second aim will characterize the involvement of NOS and PKC subtypes as essential signaling intermediaries in IPC. The third aim will examine the mechanisms of the paradoxical effect whereby transient MAPK p38 expression protects the retina, while its blockade prior to ischemia protects against ischemic damage. Our experiments will definitively examine major mechanisms of IPC and should bring us closer to understanding molecular events underlying this robust, intriguing, and clinically relevant neuroprotection.