Beta2-Adrenergic Receptor Gene Variation and Cardiovascular Control in Humans

描述（由申请人提供）：本次A1再提交的总体目标是促进对人类¿2-肾上腺素能受体（¿2-AR）基因单倍型变异和心血管表型的理解。在人类中，¿2-AR单倍型、对交感神经兴奋运动（如精神压力和握力）的加压反应、¿2介导的心脏和血管功能以及饮食钠控制之间存在着一种新兴但尚未确定的关系。编码¿2- AR基因第16和第27个氨基酸的单核苷酸多态性（SNP）已经被组合表征，然而，需要在种族同质队列中检查三种最常见的单倍型的功能相关性，从而控制SNP和种族/民族的变化。我们的策略是对高加索人高血压和心血管疾病发病机制相关的¿2-AR单倍型的生理和药理反应进行假设驱动的方案。在AIM 1中，我们测试了个体在¿2-AR中常见单倍型的纯合是否影响正常钠饮食后对交感神经兴奋运动的心血管和区域血管舒张剂反应。我们假设，与精氨酸(Arg16) +谷氨酰胺（Gln27）（单倍型2）和Gly16 + Gln27（单倍型3）单倍型纯合的个体相比，携带16号位置甘氨酸（Gly16）和27号位置谷氨酸（Glu27）（单倍型1）单倍型纯合的健康个体在精神应激和等距握力运动中表现出更大的心输出量和更低的全身血管阻力。在AIM 2中，我们测试了在5天的饮食钠限制和5天的饮食钠负荷后，¿2- ar中的常见单倍型是否影响心血管和区域血管舒张剂对交感神经兴奋运动的反应。我们假设，在正常饮食钠摄入后，单倍型1中更大的心输出量和系统性¿2-AR介导的血管舒张在饮食钠限制后将不再出现，这些反应将在钠负荷后增强。在AIM 3中，我们测试了在暂时药物消融循环的压力反射控制后，在全身输注¿2-AR激动剂时，¿2-AR的常见单倍型是否影响心血管和局部血管扩张剂的反应。我们假设a)在压力反射消融后，单倍型1比单倍型2和3在全身2- ar激动剂输注期间与更大的心输出量和更大的全身2- ar介导的血管舒张相关；b)¿2-AR单倍型变异对全身血管阻力的影响将取决于¿2-AR介导的一氧化氮的产生。最后，我们假设在体外测定高亲和结合构象中的淋巴细胞¿2-AR将从机制上解释饮食钠操纵对单倍型依赖性心血管功能差异的影响。本研究提出的机制高分辨率表型将为心血管疾病的发病机制提供重要的遗传学新见解。

DESCRIPTION (provided by applicant): The overall goal of this A1 resubmission is to advance the understanding of human ¿2-adrenergic receptor (¿2-AR) gene haplotype variation and cardiovascular phenotype. An emerging but yet to be defined relationship exists in humans between ¿2-AR haplotype, the pressor response to sympathoexcitatory maneuvers like mental stress and handgrip, ¿2-mediated cardiac and vascular function, and dietary sodium manipulation. Single nucleotide polymorphisms (SNP's) encoding the 16th and 27th amino acid in the ¿2- AR gene have been characterized in combination, whereas the need exists to examine the functional relevance of the three, most common haplotypes in an ethnically homogenous cohort, thus controlling for variation in SNP's and race/ethnicity. Our strategy is to perform hypothesis-driven protocols with respect to ¿2-AR haplotype on physiological and pharmacological responses pertinent to the pathogenesis of hypertension and cardiovascular disease in Caucasians. In AIM 1 we test whether individuals homozygous for common haplotypes in the ¿2-AR influence the cardiovascular and regional vasodilator responses to sympathoexcitatory maneuvers following a normal sodium diet. We hypothesize that healthy individuals carrying the haplotype homozygous for glycine at position 16 (Gly16) and glutamate at position 27 (Glu27) (haplotype 1) will demonstrate greater cardiac output and lower systemic vascular resistance during mental stress and isometric handgrip exercise than individuals with haplotypes homozygous for arginine (Arg16) + glutamine (Gln27) (haplotype 2) and Gly16 + Gln27 (haplotype 3). In AIM 2 we test whether common haplotypes in ¿2-AR influence the cardiovascular and regional vasodilator responses to sympathoexcitatory maneuvers after 5 days of dietary sodium restriction, followed by 5 days of dietary sodium loading. We hypothesize the greater cardiac output and systemic ¿2-AR mediated vasodilation in haplotype 1 following normal dietary sodium intake will no longer be seen following dietary sodium restriction, and these responses will be augmented following sodium loading. In AIM 3 we test whether common haplotypes in ¿2- AR influence the cardiovascular and regional vasodilator responses to systemic infusions of ¿2-AR agonist, after temporary pharmacological ablation of baroreflex control of the circulation. We hypothesize a) that after baroreflex ablation, the haplotype 1 will be associated with greater cardiac output and greater systemic ¿2-AR mediated vasodilation than haplotypes 2 and 3 during systemic ¿2-AR agonist infusion; b) that effects of ¿2- AR haplotype variation on systemic vascular resistance will be dependent on ¿2-AR mediated production of nitric oxide. Finally, we hypothesize that ex vivo determination of lymphocyte ¿2-AR's present in the high affinity binding conformation will mechanistically explain the influence of dietary sodium manipulation on haplotype-dependent differences in cardiovascular function. The mechanistic high-resolution phenotyping in this proposal will provide important new genetic insight about the pathogenesis of cardiovascular disorders. PUBLIC HEALTH RELEVANCE The overall goal of this project is to advance the understanding of how genetic variation in a major heart and blood vessel receptor (the beta-2 adrenergic receptor) influences cardiovascular regulation. Healthy young adult volunteers will be grouped according to diverse yet commonly inherited forms of the beta-2 receptor. By determining the genetic influence of blood pressure regulation in response to stressful maneuvers, medication infusions, and dietary sodium intake, this strategy will provide mechanistic detail of how genes interact with intermediate physiological traits pertinent to the development of hypertension and cardiovascular disease.