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

描述（由申请人提供）：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在小鼠中证实了这一推断，但进一步的表征有限。各种啮齿类动物实验模型表明肾素-血管紧张素系统（RAS）的显著激活与高血压之间的关系通过全身或肾脏机制。在正常体内平衡的作用下，单纯AGT表达的原发性增加是否以及如何介导EH引发了几个问题。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的肾素表达增加的情况下促进疾病的发生和进展(a)通过系统和管状机制或两者；(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。本应用程序旨在填补在II.13中阐明的关于AGT介导的高血压中AGT基因表达的原发性、同源性改变与表型表现之间关系的知识空白，特别关注在EH发展的早期和晚期，全体性和管状AGT基因表达变化的相对贡献。在这里提出的研究中，分析将仅限于具有钠敏感遗传背景的雄性动物，C57BL/6J菌株。我们已经产生了在肝脏(L)或近端小管（PT）中过表达小鼠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，我们通过同源重组（基因靶向）改变KAP基因，将KAP启动子下游的mAGT插入其自然基因组环境中。该模型依赖于内源性小鼠肾素的生理、自然调节。我们新的初步数据表明，在幼龄动物中，PT靶向过表达对2周钠负荷的反应有显著影响（III.1）。这项为期1年的最终重新提交的目的是通过NIH和犹他大学有限的过桥基金多年来的长期非常有价值的投资来实现最小的目标，以测试(1)肝脏、肾脏或两个部位的同源AGT过表达在血压调节和AGT介导的高血压发病机制中的相对贡献；(2)在这些模型中，慢性饮食摄入和/或疾病持续时间或衰老对EH及其进展的影响程度。拟议的实验将阐明人类中AGT的原发、持续表达易导致EH的方式，并对临床和治疗管理产生影响。

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.