STRUCTURE AND FUNCTION OF CEREBRAL BLOOD VESSELS IN HYPERHOMOCYSTEINEMIA

高同型半胱氨酸血症现在被认为是脑血管疾病的流行危险因素。尽管高同型半胱氨酸血症与颈动脉内膜增厚和卒中有很强的临床相关性，但高同型半胱氨酸血症对脑血管结构或功能的影响却知之甚少。新的证据表明，高同型半胱氨酸血症增加了氧化应激，同型半胱氨酸诱导的超氧化物的产生可能是内皮来源的一氧化氮介导的血管扩张功能受损的主要机制。然而，支持这一假说的大部分证据都来自于体外研究，还没有进行过在体内明确检验这一假说的研究。我们已经开发了新的遗传和饮食方法来产生高同型半胱氨酸血症，我们已经证明，中度高同型半胱氨酸血症会导致脑小动脉内皮功能障碍和肥大。我们现在建议使用这些小鼠模型来研究脑循环中损伤的机制以及血管结构和功能。该项目的总体目标是检验这一假说，即高同型半胱氨酸血症通过一种涉及超氧化物的机制导致血管功能障碍和脑循环结构变化。我们实验设计的一个关键方面是，将在高同型结晶小鼠中检测超氧化物歧化酶(SOD)表达变化对血管的影响。在目标1中，我们将验证高同型半胱氨酸血症时颈动脉和脑小动脉内皮细胞功能受损，超氧化物水平增加的假设，并探讨叶酸在这种损害中的作用。在目标2中，我们将检验这一假说，即超氧化物是高同型半胱氨酸血症小鼠脑循环内皮细胞功能障碍的关键介质，以及超氧化物歧化酶的过度表达是否能保护功能障碍。在目标3中，我们将检验超氧化物在高同型半胱氨酸血症时导致脑血管肥大的假说。

Hyperhomocysteinemia is now recognized as a prevalent risk factor for cerebrovascular disease. Despite strong clinical correlations between hyperhomocysteinemia and carotid intimal thickening and stroke, little is known about effects of hyperhomocysteinemia on vascular structure or function in cerebral blood vessels. Emerging evidence suggests that hyperhomocysteinemia increases oxidative stress, and that homocysteine- induced production of superoxide may be a major mechanism for impairment of vasodilation mediated by endothelium-derived nitric oxide. Most of the evidence to support5 this hypothesis has been derived from studies performed in vitro, however, and no studies have been performed to definitively test this hypothesis in vivo. We have developed novel genetic and dietary approaches to produce hyperhomocysteinemia in mice, and we have demonstrated that moderate hyperhomocysteinemia produces endothelial dysfunction and hypertrophy in cerebral arterioles. We now propose to use these murine models to examine mechanisms of impairment and vascular structure and function in the cerebral circulation. The overall goal of this project is to test the hypothesis that hyperhomocysteinemia produces vascular dysfunction and changes in structure in the cerebral circulation through a mechanism that involves superoxide. A key aspect of our experimental design is that vascular effects of altered expression of superoxide dismutase (SOD) will be examined in hyperhomocystemic mice. In Aim 1, we will test the hypothesis that endothelial function in the carotid artery and cerebral arterioles is impaired, and levels of superoxide are increased, during hyperhomocysteinemia, and examine the role of folate in this impairment. In Aim 2, we will test the hypothesis that superoxide is a key mediator of endothelial dysfunction in the cerebral circulation during hyperhomocysteinemia in mice, and whether over- expression of SOD protects from dysfunction. In Aim 3, we will test the hypothesis that superoxide contributes to cerebral vascular hypertrophy during hyperhomocysteinemia.