Smooth Muscle Mineralocorticoid Receptors in Vascular Aging and Hypertension

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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.