Hypertension and Glomerular Injury in Hyperhomocysteinemia

描述（由申请人提供）：在目前的资助期内，我们已经证明高同型半胱氨酸血症（hHcys）是一个独立于动脉压升高的致病因素，可以启动或促进与高血压相关的肾小球硬化的发展。研究发现，hHcys的这种致病作用归因于hHcys早期与Rac-NAD(P)H氧化酶（Rac-NOX）激活相关的局部氧化应激。本研究试图进一步探索Hcys依次激活Rac-GTPase和NOX从而导致肾小球损伤的细胞和分子机制。在初步研究中，我们发现Vav2和Vav3，两种鸟嘌呤核苷酸交换因子（GEF）在大鼠肾小球中选择性表达，负责hcys诱导的Rac-GTPase和NOX的激活。阻断Vav2表达或活性可显著降低肾小球氧化应激和硬化。因此，我们假设GEF Vav作为Hcys的靶信号分子激活Rac- NOX，从而触发肾小球损伤和硬化的级联反应，包括局部氧化应激、足细胞功能障碍、ECM沉积和纤维化。在Dahl S （DS）高血压大鼠中，这种vav触发的信号有助于hhcys诱导的肾小球损伤，而不依赖于动脉压升高。为了验证这一假设，提出了三个具体目标。Specific Aim 1将探讨Hcys通过vav介导的信号通路诱导Rac-GTPase和NOX顺序激活的机制。不同的肾小球细胞包括内皮细胞、系膜细胞和足细胞将被用来解剖Hcys的作用部位。特异性目的2将在无叶酸饮食诱导的实验性hHcys大鼠模型中确定Vav介导的Rac-NOX激活是否有助于肾小球损伤或硬化，并探索该动物模型中Vav活性增加的相关机制。特异性目的3将探讨vav激活的Rac-NOX信号通路通过伺服控制肾灌注压对DS大鼠肾小球损伤的贡献，而不依赖于动脉压升高。这些拟议的研究一旦完成，将首次将hhcys诱导的肾小球损伤与vav介导的氧化还原信号机制联系起来。对DS特征的机制的理解可以揭示人类的状况，特别是非洲裔美国人对终末期肾脏疾病的高易感性。

DESCRIPTION (provided by applicant): Over the current funding period, we have demonstrated that hyperhomocysteinemia (hHcys) is a pathogenic factor independent of elevated arterial pressure to initiate or promote the development of glomerular sclerosis associated with hypertension. This pathogenic action of hHcys was found to be attributed to a local oxidative stress associated with Rac-NAD(P)H oxidase (Rac-NOX) activation at the early stage of hHcys. This proposal attempts to further explore the cell and molecular mechanisms by which Hcys sequentially activates Rac-GTPase and NOX and thereby produce glomerular injury. In preliminary studies, we found that Vav2 and Vav3, two guanine nucleotide exchange factors (GEF) that are selectively expressed in rat glomeruli, are responsible for Hcys-induced activation of Rac-GTPase and NOX. Blockade of Vav2 expression or activity significantly reduced glomerular oxidative stress and sclerosis. Therefore, we hypothesized that the GEF Vav as a target signaling molecule of Hcys activates Rac- NOX and thereby triggers the cascade of glomerular injury and sclerosis including local oxidative stress, podocytes dysfunction, ECM deposition and fibrosis. This Vav-triggered signaling contributes to hHcys-induced glomerular injury independent of elevation of arterial pressure in Dahl S (DS) hypertensive rats. To test this hypothesis, three specific Aims are proposed. Specific Aim 1 will explore the mechanism by which Hcys induces a sequential activation of Rac-GTPase and NOX via Vav-mediated signaling pathway. Different glomerular cells including endothelial cells, mesangial cells and podocytes will be used to dissect the action site of Hcys. Specific Aim 2 will determine whether Vav- mediated activation of Rac-NOX contributes to glomerular injury or sclerosis in a rat model with experimental hHcys induced by folate-free diet and to explore related mechanisms responsible for increases in Vav activity in this animal model. Specific Aim 3 will address the contribution of Vav-activated Rac-NOX signaling pathway to glomerular injury independent of elevated arterial pressure in DS rats by servo-control of renal perfusion pressure. These proposed studies, when completed, will for the first time link hHcys-induced glomerular injury with Vav-mediated redox signaling mechanism. An understanding of the mechanism responsible for the DS trait could shed light on the human condition, in particular, on the high susceptibility to end-stage renal disease in African American populations. PUBLIC HEALTH RELEVANCE Elevations of plasma homocysteine (Hcys), a toxic amino acid, are demonstrated to cause renal dysfunction and chronic renal failure. This project attempts to determine how Hcys produces injury to the kidney, focusing on a novel targeting molecule, Vav protein. Clarification of the action of this protein will help develop new therapeutic strategy for prevention and treatment of Hcys-induced chronic renal failure.