e108T he endothelium plays important roles in modulating vascular tone by synthesizing and releasing an array of endothelium-derived relaxing factors, including vasodilator prostaglandins, NO, and endothelium-dependent hyperpolarization (EDH) factors, as well as endothelium-derived contracting factors.1,2 Such redundant mechanisms, like endogenous hyperglycemic hormones, are advantageous for ensuring proper maintenance of vascular tone under pathological conditions, where one of the vasoactive factor-mediated responses is compromised favoring a vasoconstrictor, prothrombotic, and proinflammatory state. Endothelial dysfunction is mainly caused by reduced production or action of endothelium-derived relaxing factors and could be an initial step toward cardiovascular disease.1 Indeed, evaluation of endothelial functions in humans has attracted much attention in the clinical settings because it serves as an excellent surrogate marker of cardiovascular events. For instance, endothelial dysfunction, as evaluated by impaired flow-mediated dilation of the brachial artery or digital reactive hyperemia index in peripheral arterial tonometry, is associated with future cardiovascular events in patients with coronary artery disease, 3-5 and 1-SD decrease in flow-mediated dilation or reactive hyperemia index is associated with doubling of cardiovascular event risk. 6 These observations suggest that endothelial function in peripheral vascular beds could predict future cardiovascular events.In this review, we will sum up the current advances and trends in the research on endothelial functions from bench to bedside with particular focus on recent publications in Arteriosclerosis, Thrombosis, and Vascular Biology. Earlier highlights of the journal on endothelial biology are extensively summarized in some review articles. 7-9 Emerging Modulators of Endothelial Functions Shear StressAs Lüscher and Corti 10 described in an editorial, flow is the signal of life. This physical force is sensed by the endothelium lining internal surface of the whole cardiovascular system to be translated into numerous downstream signaling pathways in a moment to moment manner in response to diverse physiological demands in the body. Indeed, shear stress is one of the important physiological cues that make endothelial cells synthesize and release endothelium-derived relaxing factors to cause relaxation of underlying vascular smooth muscle and vasodilatation. In this context, novel mechanisms of endothelial mechanotransduction in health and disease have been unveiled and summarized in a review series published recently in Arteriosclerosis, Thrombosis, and Vascular Biology. 11,12 Briefly, Zhou et al 12 emphasized the distinct roles of atheroprotective laminar or pulsatile shear stress versus atheroprone oscillatory shear stress or disturbed flow and discussed in detail the underlying molecular mechanisms that are dependent on these patterns of flow. Abe and Berk 11 further reviewed the current knowledge on the dual roles of shear stress with emphasis plac...

BackgroundMetabolic disorders, caused by excessive calorie intake and low physical activity, are important cardiovascular risk factors. Rho-kinase, an effector protein of the small GTP-binding protein RhoA, is an important cardiovascular therapeutic target and its activity is increased in patients with metabolic syndrome. We aimed to examine whether Rho-kinase inhibition improves high-fat diet (HFD)-induced metabolic disorders, and if so, to elucidate the involvement of AMP-activated kinase (AMPK), a key molecule of metabolic conditions.Methods and ResultsMice were fed a high-fat diet, which induced metabolic phenotypes, such as obesity, hypercholesterolemia and glucose intolerance. These phenotypes are suppressed by treatment with selective Rho-kinase inhibitor, associated with increased whole body O2 consumption and AMPK activation in the skeletal muscle and liver. Moreover, Rho-kinase inhibition increased mRNA expression of the molecules linked to fatty acid oxidation, mitochondrial energy production and glucose metabolism, all of which are known as targets of AMPK in those tissues. In systemic overexpression of dominant-negative Rho-kinase mice, body weight, serum lipid levels and glucose metabolism were improved compared with littermate control mice. Furthermore, in AMPKα2-deficient mice, the beneficial effects of fasudil, a Rho-kinase inhibitor, on body weight, hypercholesterolemia, mRNA expression of the AMPK targets and increase of whole body O2 consumption were absent, whereas glucose metabolism was restored by fasudil to the level in wild-type mice. In cultured mouse myocytes, pharmacological and genetic inhibition of Rho-kinase increased AMPK activity through liver kinase b1 (LKB1), with up-regulation of its targets, which effects were abolished by an AMPK inhibitor, compound C.ConclusionsThese results indicate that Rho-kinase inhibition ameliorates metabolic disorders through activation of the LKB1/AMPK pathway, suggesting that Rho-kinase is also a novel therapeutic target of metabolic disorders.

T he endothelium plays an important role in modulating vascular tone by synthesizing and releasing endotheliumderived relaxing factors, including vasodilator prostaglandins, nitric oxide (NO), and endothelium-dependent hyperpolarization (EDH) factors. [1][2][3][4][5] In 1988, Feletou and Vanhoutte 6 and Chen et al 7 independently demonstrated that a diffusible substance released by the endothelium causes relaxation and hyperpolarization of underlying vascular smooth muscle cells (VSMCs), attributing to the existence of putative EDH factors. A quarter century has passed since then and now several candidates have been proposed for the nature of EDH factors. It is widely accepted that the nature of EDH factors varies depending on species and vascular beds examined, including epoxyeicosatrienoic acids, metabolites of arachidonic P450 epoxygenase pathway, 8,9 electric communication through gap junctions, 10 K + ions, 11 hydrogen sulfide, 12 and as we have originally identified 13 and other researchers have subsequently confirmed, 14 endotheliumderived hydrogen peroxide (H 2 O 2 ). Intriguingly, the contribution of endothelium-derived relaxing factors to endothelium-dependent vasodilatation markedly varies depending on vessel size with the physiological balance between NO and EDH; NO predominantly regulates the tone of large conduit vessels and the contribution of NO decreases as vessel size decreases, whereas that of EDH increases as vessel size decreases. 15,16 Thus, EDH rather than NO plays a dominant role in small resistance vessels where blood pressure and organ perfusion are finely regulated. Indeed, accumulating evidence has demonstrated the critical roles of EDH in modulating blood pressure 17 and vascular metabolic functions 18 in general and coronary autoregulation 19 and metabolic dilatation 20 in particular. We have previously demonstrated the diverse roles of the NO synthases (NOSs) system in the endothelium depending © 2015 American Heart Association, Inc. Objective-Endothelium-derived nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) play important roles in modulating vascular tone in a distinct vessel size-dependent manner; NO plays a dominant role in conduit arteries and EDH in resistance vessels. We have recently demonstrated that endothelial NO synthase (eNOS) is functionally suppressed in resistance vessels through caveolin-1 (Cav-1)-dependent mechanism, switching its function from NO to EDH/hydrogen peroxide generation in mice. Here, we examined the possible importance of the physiological balance between NO and EDH in cardiovascular homeostasis. Approach and Results-We used 2 genotypes of mice in which eNOS activity is genetically upregulated; Cav-1-knockout (Cav-1-KO) and endothelium-specific eNOS transgenic (eNOS-Tg) mice. Isometric tension recordings and Langendorff experiments with isolated perfused hearts showed that NO-mediated relaxations were significantly enhanced, whereas EDH-mediated relaxations were markedly reduced in microcirculations. Importantly, impaired EDH-...

Objective— Vascular endothelium plays an important role to maintain cardiovascular homeostasis through several mechanisms, including endothelium-dependent hyperpolarization (EDH). We have recently demonstrated that EDH is involved in endothelial metabolic regulation in mice. However, it remains to be examined whether AMP-activated protein kinase (AMPK), an important metabolic regulator, is involved in EDH and if so, whether endothelial AMPK (eAMPK) plays a role for circulatory regulation. Approach and Results— We examined the role of eAMPK in EDH, using mice with endothelium-specific deficiency of α-catalytic subunit of AMPK, either α 1 (eAMPKα 1 −/− α 2 +/+ ) or α 2 (eAMPKα 1 +/+ α 2 −/− ) alone or both of them (eAMPKα 1 −/− α 2 −/− ). We performed telemetry, organ chamber, electrophysiological, and Langendorff experiments to examine blood pressure, vascular responses, hyperpolarization of membrane potential, and coronary flow responses, respectively. Hypertension was noted throughout the day in eAMPKα 1 −/− α 2 −/− and eAMPKα 1 −/− α 2 +/+ but not in eAMPKα 1 +/+ α 2 −/− mice when compared with respective control. Importantly, endothelium-dependent relaxations, EDH, and coronary flow increase were all significantly reduced in eAMPKα 1 −/− α 2 −/− and eAMPKα 1 −/− α 2 +/+ but not in eAMPKα 1 +/+ α 2 −/− mice. In contrast, endothelium-independent relaxations to sodium nitroprusside (a NO donor), NS-1619 (a Ca 2+ -activated K + channel opener), and exogenous H 2 O 2 were almost comparable among the groups. In eAMPKα 1 −/− α 2 −/− mice, antihypertensive treatment with hydralazine or long-term treatment with metformin (a stimulator of AMPK) failed to restore EDH-mediated responses. Conclusions— These results provide the first direct evidence that α 1 subunit of eAMPK substantially mediates EDH responses of microvessels and regulates blood pressure and coronary flow responses in mice in vivo, demonstrating the novel role of eAMPK in cardiovascular homeostasis.

Over the past couple of decades, accumulating evidence has shown that structural and functional abnormalities of coronary microvasculature are highly prevalent, associated with adverse clinical outcomes in patients with various cardiovascular diseases. The term coronary microvascular dysfunction (CMD) has been coined to refer to this clinical condition and is increasingly recognized as an important clinical entity in many clinical settings. The potential mechanisms of CMD appear to be heterogenous, including enhanced coronary vasoconstrictive reactivity at microvascular level, impaired endothelium-dependent and independent coronary vasodilator capacities, and increased coronary microvascular resistance secondary to structural factors. Recent experimental and clinical studies have highlighted emerging modulators of vascular functions, vital insight into the pathogenesis of cardiovascular diseases associated with CMD, and potential therapeutic interventions to CMD with major clinical implications. In this article, we will briefly review the current progress on pathophysiology, molecular mechanisms, and clinical management of CMD from bench to bedside.