ISCHEMIC PROTECTION OF RETINA BY HYPOXIC PRECONDITIONING

描述(由申请人提供)：适应压力的能力是一个基本的生理学原理。通过故意对动物、组织或细胞施加特定的压力，并研究由此诱导的内源性保护反应，研究人员可以发现治疗干预的新策略。最近，这种方法被应用于缺血再灌注领域，通过预先暴露于短暂的、非损伤性的缺血或缺氧，可以触发对缺血损伤的强大的“耐受性”，这种耐受性依赖于基因表达的变化。 到目前为止，这种“预适应”治疗本质上是单一的，由此产生的耐受持续时间很短。我们假设，重复的预适应治疗将使组织中的缺血耐受期延长得多。事实上，我们最近在小鼠身上进行的研究结果支持这一假设，这些研究使用重复呈现轻度全身低氧或多次注射模拟低氧的去铁胺来预调节视网膜。根据形态和功能标准，我们可以证明神经保护表型持续数月而不是数天。如此漫长的适应变化期，以及从药理上触发这种反应的能力，都是前所未有的发现。 本申请中提出的研究旨在开始系统地阐明诱导这一长期表型适应的诱导机制；我们将重点关注转录因子‘低氧诱导因子-1α’(HIF-1a)的参与。第一个目标的研究将检验HIF-1a蛋白表达如何受到我们单一和重复的基于低氧和去铁胺的预适应方案的影响。HIF-1a参与预适应反应的因果证据将在利用HIF-1a基因敲除小鼠和该转录因子的寡核苷酸阻断的AIM 2研究中出现。HIF-1a信号与预适应诱导的一氧化氮产生变化的关系将在AIM 3研究中阐明，这是基于我们观察到一氧化氮合酶缺失小鼠无法实现视网膜缺血耐受。了解这些内源性适应性反应的分子基础具有巨大的临床前景，因为这些机制可以作为缺血性视网膜病变和青光眼风险患者的新治疗靶点。

DESCRIPTION (provided by applicant): The ability to adapt to a stress is a fundamental physiologic principle. By intentionally imposing a particular stress on animals, tissues, or cells, and studying the endogenous protective responses so induced, investigators can uncover new strategies for therapeutic intervention. Recently, this approach has been leveraged in the field of ischemia-reperfusion, where a robust "tolerance" to ischemic injury that is dependent on changes in gene expression can be triggered by pre-exposure to brief, noninjurious ischemia or hypoxia. To date, such "preconditioning" treatments are singular in nature, and the resulting duration of tolerance is short lasting. We hypothesized that repetitive preconditioning treatments would confer a much longer lasting period of ischemic tolerance in the tissue. Indeed, results of our recent studies in mice using repetitive presentations of mild systemic hypoxia or multiple injections of the hypoxia-mimetic deferroxamine to precondition the retina support this hypothesis. By both morphologic and functional criteria, we can document a neuroprotective phenotype that lasts for months instead of days. Such protracted periods of adaptive change, and the ability to trigger this response pharmacologically, are unprecedented findings. Studies proposed in this application are designed to begin to systematically elucidate the induction mechanisms whereby this long-lasting period of phenotypic adaptation is induced; we will focus on the involvement of the transcription factor 'hypoxia-inducible factor-1 alpha' (HIF-1a). Studies in the first aim will examine how HIF-1a protein expression is affected by our single and repetitive hypoxic and deferroxamine-based preconditioning regimens. Causal evidence for HIF-1a involvement in the preconditioning response will be forthcoming in Aim 2 studies utilizing HIF-1a knockout mice and oligonucleotide blockade of this transcription factor. The relationship of HIF-1a signaling to preconditioning-induced changes in nitric oxide production will be elucidated in Aim 3 studies, based on our observation that retinal ischemic tolerance cannot be achieved in nitric oxide synthase null mice. Understanding the molecular basis of these endogenous adaptive responses holds tremendous clinical promise, as these mechanisms can serve as new therapeutic targets for patients at risk for ischemic retinopathies and glaucoma.