Genetics of Angiotensinogen-Mediated Hypertension: Stage, Background & Gender

描述（申请人提供）：血管紧张素原（AGT）基因的常见遗传变异易导致人类原发性高血压（EH）和血浆AGT升高。Smithies及其同事的基因滴定实验证实了小鼠中的这一推断，进一步表征有限。各种啮齿动物实验模型表明，显着激活的肾素-血管紧张素系统（RAS）和高血压之间的关系，通过全身或肾脏机制。是否以及如何在AGT表达的主要增加，在正常的稳态发挥作用，介导高血压提出了几个问题。这些包括全身或肾脏AGT表达增加对EH不同阶段表型表现的相对贡献。 我们的中心假设是，AGT过表达可以在没有人为伴随的肾素表达增加的情况下促进疾病的发生和进展（a）通过全身和肾小管机制中的一种或两种，以及（B）疾病的持续时间、遗传背景、性别和暴露（如饮食和生活方式）调节临床表现和进展。 本申请旨在填补II.13中阐述的关于AGT基因表达的原发性、同种特异性改变与AGT介导的高血压表型表现之间关系的知识空白，特别关注EH发展早期和晚期全身和肾小管AGT变化对基因表达的相对贡献。在此处拟定的研究中，分析将仅限于钠敏感遗传背景的雄性动物（C57 BL/6 J品系）。 我们已经产生了在肝脏（L）或近端小管（PT）中过表达小鼠（m）AGT的动物。我们已经验证了我们的L-mAGT模型，并发现表型表达随遗传背景而变化。我们还开发并验证了一种新的PT-mAGT模型，在该模型中，我们通过同源重组（基因靶向）改变了KAP基因，以在其天然基因组环境中的KAP启动子下游插入mAGT。该模型依赖于内源性小鼠肾素的生理、自然调节。我们的新的初步数据记录了PT中靶向过表达对幼龄动物2周钠负荷的显著影响（III.1）。 这一最终的1年重新提交的目的是实现长期的最低目标，NIH和犹他州大学的有限桥梁资金多年来进行了非常有价值的投资，以测试（1）在血压调节和AGT介导的高血压的发病机制中，肝脏、肾脏或两个部位的同种特异性AGT过表达的相对贡献，（2）慢性饮食摄入和/或疾病或衰老的持续时间在这些模型中对EH及其进展的解释程度。拟议的实验将阐明AGT的主要，持续表达易患高血压的方式在人类，伴随着临床和治疗管理的影响。 公共卫生相关性：超过50%的美国人口在达到65岁时患有原发性高血压或不明原因的高血压，并且这些患者中只有一小部分的血压得到控制。肾素-血管紧张素系统（RAS）是血压及其与膳食盐的关系的主要控制器，但其功能是复杂的，因为它涉及重叠的循环和组织系统。我们已经表明，血管紧张素原基因（AGT）的常见遗传变异，RAS的一个组成部分，导致血浆中蛋白水平的增加，易患EH。由于AGT在多个位点表达，其参与全身和肾功能。我们将使用转基因小鼠来操纵基因在两个主要位点的表达，即肝脏和肾脏，并测试这两个来源作为遗传背景，性别，饮食盐，衰老和肾素调节的功能的相对意义。我们的目标是提高高血压临床管理和治疗的特异性。

DESCRIPTION (provided by applicant): Common genetic variation in the angiotensinogen (AGT) gene predisposes to essential hypertension (EH) and increased plasma AGT in humans. Gene titration experiments by Smithies and colleagues have confirmed this inference in mouse, with limited further characterization. Various rodent experimental models demonstrate a relation between marked activation of the renin-angiotensin system (RAS) and hypertension through either systemic or renal mechanisms. Whether and how a primary increase in AGT expression alone, with normal homeostasis at play, mediates EH raises several questions. These include the relative contributions of systemic or renal increases in AGT expression to phenotypic manifestation at various stages of EH. Our central hypothesis is that AGT overexpression can, without artificial concomitant increase in renin expression, contributes to disease initiation and progression (a) through either or both systemic and tubular mechanisms and (b) that duration of disease, genetic background, gender, and exposures such as diet and lifestyle modulate clinical manifestation and progression. This application is intended to fill specific gaps in knowledge, spelled out in II.13, about the relationship between primary, homospecific alterations in AGT gene expression and phenotypic manifestation in AGT- mediated hypertension, with a particular focus on the relative contributions of systemic and tubular AGT changes in gene expression in early and late stages of EH development. In the studies proposed here, analysis will be restricted to male animals of the sodium-sensitive genetic background, the C57BL/6J strain. We have generated animals that overexpress mouse (m) AGT either in liver (L) or in proximal tubule (PT). We have validated our L-mAGT model and found that phenotypic expression varies with genetic background. We have also developed and validated a new PT-mAGT model where we have altered the KAP gene by homologous recombination (gene targeting) to insert mAGT downstream from the KAP promoter in its natural genomic environment. This model relies on physiologic, natural regulation of endogenous mouse renin. Our new preliminary data document a significant effect of targeted overexpression in PT in response to 2- week sodium loading in young animals (III.1). The purpose of this final, 1-year resubmission is to achieve minimal objectives on long-term, very valuable investment made over years of both NIH and limited bridge funding from the University of Utah to test (1) the relative contributions of homospecific AGT overexpression in either liver, kidney or at both sites in blood pressure regulation and the pathogenesis of AGT-mediated hypertension, (2) the extent to which chronic dietary intake and/or duration of disease or aging account for EH and its progression in these models . The proposed experiments will clarify the manner in which primary, sustained expression of AGT predisposes to EH in humans, with attendant implications for clinical and therapeutic management. PUBLIC HEALTH RELEVANCE: Over 50% of the population of the United States have essential hypertension, or high blood pressure of unknown cause, by the time they reach 65 years of age, and only a fraction of these patients have their blood pressure under control. The renin-angiotensin system (RAS) is a major controller of blood pressure and of its relationship to dietary salt, but its function is complex because it involves overlapping circulating and tissue systems. We have shown that common genetic variants in the angiotensinogen gene (AGT), a component of the RAS, lead to increased plasma levels of the protein and predisposes to EH. As a result of its expression at multiple sites, AGT is involved in both systemic and renal function. We will use transgenic mice to manipulate expression of the gene at two major sites, namely the liver and the kidney, and test the relative significance of these two sources as a function of genetic background, gender, dietary salt, aging and renin regulation. Our goal is to advance the specificity of clinical management and treatment of EH.