5Lipoxygenase-mediated vasculopathy in HHcy

描述(由申请人提供)：血浆总同型半胱氨酸(Hcy)水平升高，称为高同型半胱氨酸血症(HHcy)，与包括冠心病和中风在内的慢性血管疾病的发病率和死亡率增加有关。然而，潜在的生化机制仍不清楚。同型半胱氨酸导致细胞内S-腺苷同型半胱氨酸水平显著升高，这是一种有效的内源性甲基转移反应抑制物。最近，我们发现HHcy上调了5-脂氧合酶(5-LO)，这是一种丰富存在于血管系统中的酶，它诱导内皮细胞(EC)内淀粉样β蛋白(Abeta)的形成增加。一旦形成，Abeta就会沿着血管周围淋巴引流途径迅速消除。然而，如果产生的Abeta总量超过了这种能力，多肽将在动脉壁中积聚，导致血管炎症和功能障碍。随着时间的推移，这种情况将发展为淀粉样血管病，其特征是Abeta过度沉积在动脉壁细胞外间隙，平滑肌细胞丢失和循环炎症细胞募集。综上所述，这些数据提示5-LO可能参与了HHcy依赖的血管功能障碍和淀粉样血管病的发展，并支持我们的中心假设：HHcy导致细胞内SAH升高，而细胞内SAH通过激活5-LO诱导Abeta的过度产生和在血管中的积聚，从而导致随后的血管炎症、内皮功能障碍(ED)和最终的淀粉样血管病变。为了检验我们的假设，我们提出了三个相互关联的具体目标。在第一个实验中，我们将评估5-LO的激活及其在血管炎症、ED和淀粉样血管病变中的作用。在第二个实验中，我们将确定HHcy诱导5-LO上调的机制，并研究激活的5-LO调节EC中Abeta形成的作用和机制。在第三个实验中，我们将确定HHcy和5-LO上调在TG-HCBS CBS-/-小鼠病理血管表型形成中的作用。

DESCRIPTION (provided by applicant): Elevated levels of total plasma homocysteine (Hcy), termed hyperhomocysteinemia (HHcy), are associated with increased incidence and mortality of chronic vascular diseases including coronary heart disease and stroke. However, the underlying biochemical mechanisms remain unknown. HHcy results in a significant elevation of intracellular levels of S- adenosylhomocysteine (SAH), a potent endogenous inhibitor of methyl-transfer reactions. Recently, we found that HHcy up-regulates the 5-Lipoxygenase (5- LO), an enzyme abundantly present in the vasculature, where it induces an increased formation of the amyloid beta peptide (Abeta) within the endothelial cells (EC). Once formed Abeta is rapidly eliminated along perivascular lymphatic drainage pathways. However, if the total amount of Abeta produced overcomes this ability, the peptide will accumulate in the arterial walls resulting in vascular inflammation and dysfunction. With time this condition will develop in amyloid angiopathy, which is characterized by excessive Abeta deposited also in the extracellular space of the artery wall, loss of smooth muscle cells and recruitment of circulating inflammatory cells. Taken together these data suggest a possible involvement of 5-LO in the HHcy-dependent vascular dysfunction and development of amyloid angiopathy, and support our central hypothesis: HHcy results in elevated intracellular SAH which by activating 5-LO induces an over- production of Abeta and its accumulation in the vasculature with subsequent vascular inflammation, endothelial dysfunction (ED) and ultimately amyloid angiopathy. To test our hypothesis we propose 3 linked specific Aims. In the first one, we will assess 5-LO activation and its contribution to vascular inflammation, ED and amyloid angiopathy in a mouse model of HHcy, the Tg-hCBS Cbs-/- mice. In the second one, we will determine the mechanisms by which HHcy induces 5-LO upregulation, and examine the role and mechanisms by which activated 5-LO regulates Abeta formation in EC. In the third one, we will establish the role of HHcy, and 5-LO upregulation in the development of the pathological vascular phenotype of the Tg-hCBS Cbs-/- mice.