Mineralocorticoid receptor-dependent coronary vascular dysfunction in obesity

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Impaired coronary flow control is an independent predictor of cardiac mortality in obesity/MetS. Recent studies from our laboratory and others demonstrate a deleterious role for mineralocorticoid receptor (MR) signaling in coronary vascular dysfunction in obesity and the metabolic syndrome (MetS). Specifically, MR antagonism improves coronary vasodilator responsiveness by unclear mechanisms. Recent evidence suggests that vascular cell, specifically smooth muscle cell (SMC), MR signaling plays a role in vascular ion channel expression and function. Overall coronary flow control is dependent on the functional expression of microvascular K+ channels, in particular voltage-gated K+ (Kv) channels, which are critical mediators of SMC electromechanical coupling and microvascular tone. Our preliminary data provide the first evidence of MR-dependent impairment of coronary Kv channels, specifically Kv1, consistent with MetS-associated impaired functional expression of these channels. Based on these preliminary findings we propose to examine the central hypothesis that SMC MR-dependent signaling significantly contributes to coronary microvascular dysfunction in MetS. To accomplish our goal, we will examine the following set of Specific Aims: Aim 1 will determine SMC MR-dependent cellular and molecular mechanisms responsible for coronary dysfunction in MetS utilizing tissues from male and female mice treated with the MR agonist aldosterone or after western diet (WD) feeding to induce MetS. Involvement of SMC MR signaling will be evaluated in mice with SMC-specific MR deletion. Specifically, these studies will evaluate SMC MR-dependent modulation of Kv/Kv1 channel functional expression in cultured SMC, freshly isolated microvessel studies, patch clamp electrophysiology, and molecular/cellular/genomic techniques as well as coronary flow imaging/echocardiography in vivo. Studies in Aim 2 will utilize lean and MetS Ossabaw swine with and without MR antagonism to elucidate the contribution of MR-dependent signaling to augmented coronary vascular resistance and impaired control of myocardial blood flow and oxygen balance in vivo in MetS. These studies will involve in vivo studies in conscious, chronically instrumented and open-chest swine to evaluate coronary vasomotor responses to (patho)physiologic stimuli including increased cardiac metabolism (i.e., exercise), increased coronary perfusion pressure (i.e., autoregulation), and myocardial ischemia. Additional studies will evaluate if changes in flow control correspond to changes in cardiac function. These conceptually innovative studies will combine mechanistic cell-type specific knockout mouse studies with clinically relevant in vivo studies of myocardial oxygen balance thereby providing integrative and complementary measures to address the central hypothesis and Aims. Together, the proposed Aims will provide novel insight into mechanisms of (patho)physiologic electromechanical coupling and coronary flow regulation in MetS. Further, results stand to provide direct rationale for innovative therapeutic interventions to reduce the incidence and impact of coronary and cardiac complications in the ever increasing population of obese/MetS patients.