Smooth Muscle Mineralocorticoid Receptors in Vascular Aging and Hypertension

描述(申请人提供)：高血压(HTN)的发病率随着年龄的增长而急剧增加，在老年人中得不到很好的治疗，并且对发病率有显著的影响。 以及我们老龄化社会中的死亡率。血管老化的特征是血管紧张素II(AngII)信号增强，血管氧化应激增加，血管张力和收缩增加。驱动这种老化的血管表型的刺激因素还不是很清楚，也没有已知的策略来延缓人类的动脉衰老。盐皮质激素受体(MR)通过结合肾脏中的激素醛固酮(ALDO)来调节血压(BP)，从而促进钠滞留。我们以前在人血管平滑肌细胞(SMC)中发现了功能性MR，发现SMC-MR可以被血管紧张素转换酶II直接激活，并发展了一种新的小鼠模型，该模型具有可诱导的SMC特异性MR缺失(SMC-MR-KO)。SMC-MR缺失可阻止血管紧张素转换酶抑制剂诱导的HTN、血管氧化应激和肠系膜血管收缩以及衰老引起的血压升高。初步数据显示，AngII以PKC依赖的方式激活人SMC的MR，提示SMC-MR的激活是一种新的配体非依赖的机制。新的数据显示，老年SMC-MR-KO小鼠肠系膜细胞和血管中L型钙通道(LTCC)的表达和电流密度降低，钙激活的氯通道TMEM16A的表达随增龄而减少，并且对LTCC激活的钙和收缩反应降低。此外，老年SMC-MR-KO小鼠的血管减少了NADPH-氧化酶亚基NOX2的表达，降低了基础和血管紧张素Ⅱ诱导的氧化应激。基于这些数据，我们提出了一种新的假设，即在衰老的血管系统中，SMC-MR通过PKC介导的磷酸化直接被Angii激活，并调节LTCC、TMEM16A和NOX2的表达和活性，促进与年龄相关的血管氧化应激和收缩增加，从而导致高血压。我们建议用三个具体的研究目的来检验这一假设：SA1)。SMC-MR激活血管紧张素Ⅱ的机制；SA2)SMC-MR对血管离子通道的调节以及随年龄增长对血管张力和收缩的影响；以及SA3)SMC-MR对随年龄增长的血管氧化应激的贡献以及在调节血管张力和血压中的作用。我们建议在每个目标中使用新分离的细胞和整个血管的分子方法，并在SA3中进行体内遥测研究，以探索对血压的影响。由于SMC-MR缺失在阻断Angii诱导的HTN方面比药物上的MR拮抗剂更有效，而MR拮抗剂的广泛使用受到肾MR阻断引起的高钾血症的限制，了解SMC-MR被激活并直接参与全身血压的机制可以找到比现有药物更有效、更安全的HTN新疗法，尤其是在老年人中。

DESCRIPTION (provided by applicant): The incidence of hypertension (HTN) increases dramatically with age, is poorly treated in the elderly, and contributes significantly to morbidity and mortality in our aging society. Vascular aging is characterized by enhanced angiotensin II (AngII) signaling, increased vascular oxidative stress, and increased vascular tone and contraction. The stimuli driving this aging vascular phenotype are not well understood and no strategy is known to retard arterial aging in humans. Mineralocorticoid receptors (MR) regulate blood pressure (BP) by binding the hormone aldosterone (Aldo) in the kidney to promote sodium retention. We previously identified functional MR in human vascular smooth muscle cells (SMC), discovered that SMC-MR can be directly activated by AngII, and developed a novel mouse model with inducible, SMC-specific deletion of MR (SMC- MR-KO). SMC-MR deletion prevented AngII-induced HTN, vascular oxidative stress and mesenteric vessel contraction and the aging-induced rise in BP. Preliminary data show that AngII activates MR in human SMC in a PKC -dependent manner suggesting a novel ligand-independent mechanism of SMC-MR activation. New data reveals decreased L-type calcium channel (LTCC) expression and current density, a loss of the rise in expression of the Ca-activated Cl channel TMEM16A with aging, and decreased calcium and contractile responses to LTCC activation in mesenteric cells and vessels from aged SMC-MR-KO mice. Furthermore vessels from aged SMC-MR-KO mice have decreased expression of the NADPH-oxidase subunit Nox2 and lower basal and AngII-induced oxidative stress. Based on these data, we propose to test the novel hypothesis that in the aging vasculature, SMC-MR is directly activated by AngII via PKC -mediated phosphorylation and regulates LTCC, TMEM16A and Nox2 expression and activity, promoting the age-associated increase in vascular oxidative stress and contraction, thereby contributing to hypertension. We propose to test this hypothesis with three specific aims investigating: SA1). The mechanism of AngII activation of SMC-MR; SA2) SMC-MR regulation of vascular ion channels and the impact on vascular tone and contraction with aging; and SA3) SMC-MR contribution to vascular oxidative stress with aging and the role in modulating vascular tone and BP. We propose to use molecular approaches in freshly isolated cells and whole vessels in each aim and in vivo telemetry studies in SA3 to explore the impact on blood pressure. Since SMC-MR deletion was more effective in blocking AngII-induced HTN than pharmacologic MR antagonist and widespread use of MR antagonists is limited by hyperkalemia from renal MR blockade, understanding the mechanisms by which SMC-MR is activated and directly contributes to systemic BP could identify novel HTN therapies that are more effective and safer than current drugs, particularly in the elderly.