Vascular Mechanisms of Cerebral Ischemic Tolerance

描述（由申请方提供）：血管功能障碍和血管损伤，表现为微血管灌注、自动调节和血管反应性受损，以及血管源性水肿、出血、炎症和凝血，对局灶性卒中后的结局有重要影响。治疗策略可以源自“缺血耐受性”的研究，其中内源性保护机制被不同的“预处理”刺激激活。本提案中概述的研究将侧重于阐明缺氧预处理后脑血管内皮保护的先天机制，利用我们实验室开发和表征的小鼠局灶性卒中诱导耐受模型和人脑血管内皮细胞缺血耐受培养模型。低氧预处理减弱缺血诱导的血管/内皮功能障碍和损伤的不同终点的关键诱导和表达机制将在每个模型中阐明。 具体目标1：阐明内皮型一氧化氮合酶（eNOS）在缺氧预处理诱导脑血管缺血耐受的诱导和表达途径中的作用。我们假设eNOS衍生的NO是负责诱导血管保护基因转录/翻译的信号通路的组成部分。我们还假设eNOS是一种效应蛋白，有助于预处理脑微循环的缺血耐受表型。 具体目标二：描述转录因子HIF-2 α在体内和体外对低氧和化学预处理的内皮细胞中介导细胞保护基因表达的参与。我们将检验这样的假设：在内皮细胞中高度表达的HIF-2 α的活性被这些预处理刺激上调，受到eNOS衍生的NO和磷酸化Akt的调节，并且对于介导细胞保护基因的表达至关重要。内皮细胞导致缺血耐受。 具体目标3：阐明存活素，一个特定的细胞凋亡家族成员，在体内和体外预处理的内皮细胞缺血性损伤的阻力的参与，以及这种蛋白质提供保护的机制。我们推测低氧预处理上调生存素的表达，从而阻断半胱天冬酶介导的内皮损伤，从而保持缺血后微循环的稳态。 内皮细胞抵抗缺血性损伤的内源性机制的鉴定可能为治疗局灶性卒中后血管功能障碍和血管损伤提供新的分子靶点。

DESCRIPTION (provided by applicant): Vascular dysfunction and vascular injury, as manifested by impairments in microvascular perfusion, autoregulation, and vascular reactivity, as well as by vasogenic edema, hemorrhage, inflammation, and coagulation, contribute importantly to outcome following focal stroke. Treatment strategies may derive from studies of "ischemic tolerance", wherein endogenous mechanisms of protection are activated by different "preconditioning" stimuli. Studies outlined in this proposal will focus on elucidating the innate mechanisms responsible for protection of cerebrovascular endothelium following hypoxic preconditioning, utilizing a mouse model of induced tolerance to focal stroke and a human cerebrovascular endothelial cell culture model of ischemic tolerance, both developed and characterized in our laboratory. Key induction and expression mechanisms whereby hypoxic preconditioning attenuates diverse endpoints of ischemia-induced vascular/endothelial dysfunction and injury will be elucidated in each model. Specific Aim 1: Elucidate the role of endothelial nitric oxide synthase (eNOS) in the induction and expression pathways responsible for hypoxic preconditioning-induced cerebrovascular ischemic tolerance in vivo and in vitro. We hypothesize that eNOS-derived NO is integral to the signaling pathways responsible for inducing the transcription/translation of vasculoprotective genes. We also hypothesize that eNOS is an effector protein contributing to the ischemia-tolerant phenotype of the preconditioned cerebral microcirculation. Specific Aim 2: Delineate the involvement of the transcription factor HIF-2alpha in mediating cytoprotective gene expression in endothelial cells in vivo and in vitro in response to hypoxic and chemical preconditioning. We will test the hypothesis that the activity of HIF-2alpha, highly expressed in endothelial cells, is upregulated by these preconditioning stimuli, is modulated by eNOS-derived NO and phosphorylated Akt, and is critical to mediating the expression of cytoprotective genes in endothelium that lead to ischemic tolerance. Specific Aim 3: Elucidate the participation of survivin, a specific inhibitor-of-apoptosis family member, in the resistance of in vivo- and in vitro-preconditioned endothelium to ischemic injury, and the mechanisms by which this protein affords protection. We hypothesize that hypoxic preconditioning upregulates survivin expression, which blocks caspase-mediated endothelial injury, thereby preserving post-ischemic microcirculatory homeostasis. Identification of endogenous mechanisms of endothelial cell resistance to ischemic injury may provide novel molecular targets for the therapeutic treatment of vascular dysfunction and vascular injury following focal stroke.