Flow-induced dilation is mediated by Akt-dependent activation of endothelial nitric oxide synthase-derived hydrogen peroxide in mouse cerebral arteries

Sex, Endothelial Cell Functions, and Peripheral Artery Disease

Peripheral artery disease (PAD) is caused by blocked arteries due to atherosclerosis and/or thrombosis which reduce blood flow to the lower limbs. It results in major morbidity, including ischemic limb, claudication, and amputation, with patients also suffering a heightened risk of heart attack, stroke, and death. Recent studies suggest women have a higher prevalence of PAD than men, and with worse outcomes after intervention. In addition to a potential unconscious bias faced by women with PAD in the health system, with underdiagnosis, and lower rates of guideline-based therapy, fundamental biological differences between men and women may be important. In this review, we highlight sexual dimorphisms in endothelial cell functions and how they may impact PAD pathophysiology in women. Understanding sex-specific mechanisms in PAD is essential for the development of new therapies and personalized care for patients with PAD.

Hesperetin-7-O-glucoside/β-cyclodextrin Inclusion Complex Induces Acute Vasodilator Effect to Inhibit the Cold Sensation Response during Localized Cold-Stimulate Stress in Healthy Human Subjects: A Randomized, Double-Blind, Crossover, and Placebo-Controlled Study

Hesperetin, a citrus flavonoid, exerts vasodilation and is expected to improve endothelial function and alleviate cold sensation by activating nervous system thermal transduction pathways. In this randomized, double-blind, crossover, and placebo-controlled study, the purpose was to assess the effect of an orally administered highly bioavailable soluble inclusion complex of hesperetine-7-O-glucoside with β-cyclodextrin (HEPT7G/βCD; SunActive® HES/HCD) on cold sensation response during localized cold-stimulated stress in healthy humans. A significant (p ≤ 0.05) dose-dependent increase in skin cutaneous blood flow following relatively small doses of HEPT7G/βCD inclusion complex ingestion was confirmed, which led to a relatively effective recovery of peripheral skin temperature. The time delay of an increase in blood flow during rewarming varied significantly between low- and high-dose HEPT7G/βCD inclusion complex consumption (e.g., 150 mg and 300 mg contain 19.5 mg and 39 mg of HEPT7G, respectively). In conclusion, the substantial alteration in peripheral skin blood flow observed during local cooling stress compared to placebo suggested that deconjugated hesperetin metabolites may have a distinct capacity for thermoregulatory control of human skin blood flow to maintain a constant body temperature during cold stress exposure via cutaneous vasodilation and vasoconstriction systems.

The role of nitric oxide in flow-induced and myogenic responses in 1A, 2A, and 3A branches of the porcine middle cerebral artery

Myogenic and flow-induced reactivity contribute to cerebral autoregulation, with potentially divergent roles for smaller versus larger arteries. The present study tested the hypotheses that compared with first-order (1A) branches of the middle cerebral artery, second- and third-order branches (2A and 3A, respectively) exhibit greater myogenic reactivity but reduced flow-induced constriction. Furthermore, nitric oxide synthase (NOS) inhibition may amplify myogenic reactivity and abolish instances of flow-induced dilation. Isolated porcine cerebral arteries mounted in a pressure myograph were exposed to incremental increases in intraluminal pressure (40-120 mmHg; n = 41) or flow (1-1,170 µL/min; n = 31). Intraluminal flows were adjusted to achieve 5, 10, 20, and 40 dyn/cm2 of wall shear stress at 60 mmHg. Myogenic tone was greater in 3A versus 1A arteries (P < 0.05). There was an inverse relationship between myogenic reactivity and passive arterial diameter (P < 0.01). NOS inhibition increased basal tone to a lesser extent in 3A versus 1A arteries (P < 0.01) but did not influence myogenic reactivity (P = 0.49). Increasing flow decreased luminal diameter (P ≤ 0.01), with increased vasoconstriction at 10-40 dyn/cm2 of shear stress (P < 0.01). However, relative responses were similar between 1A, 2A, and 3A arteries (P = 0.40) with and without NOS inhibition conditions (P ≥ 0.29). Whereas NOS inhibition increases basal myogenic tone, and myogenic reactivity was less in smaller versus larger arteries (range = ∼100-550 µM), neither NOS inhibition nor luminal diameter influences flow-induced constriction in porcine cerebral arteries.NEW & NOTEWORTHY This study demonstrated size-dependent heterogeneity in myogenic reactivity in porcine cerebral arteries. Smaller branches of the middle cerebral artery exhibited increased myogenic reactivity, but attenuated NOS-dependent increases in myogenic tone compared with larger branches. Flow-dependent regulation does not exhibit the same variation; diameter-independent flow-induced vasoconstrictions occur across all branch orders and are not affected by NOS inhibition. Conceptually, flow-induced vasoconstriction contributes to cerebral autoregulation, particularly in larger arteries with low myogenic tone.

Reactive Oxygen Species Are Essential for Vasoconstriction upon Cold Exposure

Purpose

We explored the role of ROS in cold-induced vasoconstriction and corresponding mechanism.

Methods

Three experiments were performed. First, we measured blood flow in human hands before and after cold exposure. Second, 24 mice were randomly divided into 3 groups: 8 mice received saline injection, 8 received subcutaneous Tempol injection, and 8 received intrathecal Tempol injection. After 30 min, we determined blood flow in the skin before and after cold exposure. Finally, we used Tempol, CCG-1423, and Go 6983 to pretreat HAVSMCs and HUVECs for 24 h. Then, cells in the corresponding groups were exposed to cold (6 h, 4°C). After cold exposure, the cytoskeleton was stained. Intracellular Ca²⁺ and ROS levels were measured by flow cytometry and fluorescence microscopy. We measured protein expression via Western blotting.

Results

In the first experiment, after cold exposure, maximum skin blood flow decreased to 118.4 ± 50.97 flux units. Then, Tempol or normal saline pretreatment did not change skin blood flow. Unlike intrathecal Tempol injection, subcutaneous Tempol injection increased skin blood flow after cold exposure. Finally, cold exposure for 6 h shrank the cells, making them narrower, and increased intracellular Ca²⁺ and ROS levels in HUVECs and HAVSMCs. Tempol reduced cell shrinkage and decreased intracellular Ca²⁺ levels. In addition, Tempol decreased intracellular ROS levels. Cold exposure increased RhoA, Rock1, p-MLC-2, ET-1, iNOS, and p-PKC expression and decreased eNOS expression. Tempol or CCG-1423 pretreatment decreased RhoA, Rock1, and p-MLC-2 levels in HAVSMCs. Furthermore, Tempol or Go 6983 pretreatment decreased ET-1, iNOS, and p-PKC expression and increased eNOS expression in HUVECs.

Conclusion

ROS mediate the vasoconstrictor response within the cold-induced vascular response, and ROS in blood vessel tissues rather than nerve fibers are involved in vasoconstriction via the ROS/RhoA/ROCK1 and ROS/PKC/ET-1 pathways in VSMCs and endothelial cells.

Endothelial TrkB receptor activation controls vascular tone of rat middle cerebral artery

Little is known on the cerebrovascular BDNF (brain-derived neurotrophic factor)/TrkB (tropomyosin related kinase B) pathway. This study investigated the contribution of endogenous endothelial BDNF to the control of vascular tone of rat middle cerebral artery (MCA) and the capacity of exogenous agonist of TrkB receptors to induce their relaxation. Endothelial cells constitutively expressed both BDNF and activated TrkB receptors. Supporting endothelial BDNF as an autocrine regulator of basal myogenic tone, incubation of MCA with the TrkB antagonist cyclotraxin B induced contraction as observed with incubation in the presence of inhibitors of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) production. Exposure of MCA with the TrkB agonist LM22A-4 that increased expression of TrkB receptors phosphorylated at tyrosine 816 induced relaxation of preconstricted MCA (EC₅₀ 6.7 × 10^-8 mol/L) as efficiently than acetylcholine (EC₅₀ 5.3 × 10^-8 mol/L). Finally, endothelium removal, exposure to a TrkB antagonist or to inhibitors of NO and EDHF production prevented the relaxant effect of LM22A-4. In conclusion, our study identified endothelial BDNF as a new autocrine regulator of vascular tone of MCA, thus making the endothelial BDNF/TrkB pathway an attractive target for strategies aiming to improve blood supply to the brain.

Therapeutic Potential of Quercetin to Alleviate Endothelial Dysfunction in Age-Related Cardiovascular Diseases

The vascular endothelium occupies a catalog of functions that contribute to the homeostasis of the cardiovascular system. It is a physically active barrier between circulating blood and tissue, a regulator of the vascular tone, a biochemical processor and a modulator of coagulation, inflammation, and immunity. Given these essential roles, it comes to no surprise that endothelial dysfunction is prodromal to chronic age-related diseases of the heart and arteries, globally termed cardiovascular diseases (CVD). An example would be ischemic heart disease (IHD), which is the main cause of death from CVD. We have made phenomenal advances in treating CVD, but the aging endothelium, as it senesces, always seems to out-run the benefits of medical and surgical therapies. Remarkably, many epidemiological studies have detected a correlation between a flavonoid-rich diet and a lower incidence of mortality from CVD. Quercetin, a member of the flavonoid class, is a natural compound ubiquitously found in various food sources such as fruits, vegetables, seeds, nuts, and wine. It has been reported to have a wide range of health promoting effects and has gained significant attention over the years. A growing body of evidence suggests quercetin could lower the risk of IHD by mitigating endothelial dysfunction and its risk factors, such as hypertension, atherosclerosis, accumulation of senescent endothelial cells, and endothelial-mesenchymal transition (EndoMT). In this review, we will explore these pathophysiological cascades and their interrelation with endothelial dysfunction. We will then present the scientific evidence to quercetin's anti-atherosclerotic, anti-hypertensive, senolytic, and anti-EndoMT effects. Finally, we will discuss the prospect for its clinical use in alleviating myocardial ischemic injuries in IHD.

Vasoconstrictor Mechanisms in Chronic Hypoxia-Induced Pulmonary Hypertension: Role of Oxidant Signaling

Elevated resistance of pulmonary circulation after chronic hypoxia exposure leads to pulmonary hypertension. Contributing to this pathological process is enhanced pulmonary vasoconstriction through both calcium-dependent and calcium sensitization mechanisms. Reactive oxygen species (ROS), as a result of increased enzymatic production and/or decreased scavenging, participate in augmentation of pulmonary arterial constriction by potentiating calcium influx as well as activation of myofilament sensitization, therefore mediating the development of pulmonary hypertension. Here, we review the effects of chronic hypoxia on sources of ROS within the pulmonary vasculature including NADPH oxidases, mitochondria, uncoupled endothelial nitric oxide synthase, xanthine oxidase, monoamine oxidases and dysfunctional superoxide dismutases. We also summarize the ROS-induced functional alterations of various Ca2+ and K+ channels involved in regulating Ca2+ influx, and of Rho kinase that is responsible for myofilament Ca2+ sensitivity. A variety of antioxidants have been shown to have beneficial therapeutic effects in animal models of pulmonary hypertension, supporting the role of ROS in the development of pulmonary hypertension. A better understanding of the mechanisms by which ROS enhance vasoconstriction will be useful in evaluating the efficacy of antioxidants for the treatment of pulmonary hypertension.

KIR channels in the microvasculature: Regulatory properties and the lipid-hemodynamic environment

Basal tone and perfusion control is set in cerebral arteries by the sensing of pressure and flow, key hemodynamic stimuli. These forces establish a contractile foundation within arterial networks upon which local neurovascular stimuli operate. This fundamental process is intimately tied to arterial V_M and the rise in cytosolic [Ca²⁺] by the graded opening of voltage-operated Ca²⁺ channels. Arterial V_M is in turn controlled by a dynamic interaction among several resident ion channels, K_IR being one of particular significance. As the name suggests, K_IR displays strong inward rectification, retains a small outward component, potentiated by extracellular K⁺ and blocked by micromolar Ba²⁺. Cerebrovascular K_IR is unique from other K⁺ currents as it is present in both smooth muscle and endothelium yet lacking in classical regulatory modulation. Such observations have fostered the view that K_IR is nothing more than a background conductance, activated by extracellular K⁺ and which passively facilitates dilation. Recent work in cell model systems has; however, identified two membrane lipids, phosphatidylinositol 4,5-bisphosphate (PIP₂) and cholesterol, that interact with K_IR2.x, to stabilize the channel in the preferred open or silent state, respectively. Translating this unique form of regulation, recent studies have demonstrated that specific lipid-protein interactions enable unique K_IR populations to sense distinct hemodynamic stimuli and set basal tone. This review summarizes the current knowledge of vascular K_IR channels and how the lipid and hemodynamic impact their activity.

Nitric oxide and endothelium-dependent hyperpolarization mediated by hydrogen peroxide in health and disease

The endothelium plays crucial roles in modulating vascular tone by synthesizing and releasing endothelium-derived relaxing factors (EDRFs), including vasodilator prostaglandins, nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) factors. Thus, endothelial dysfunction is the hallmark of atherosclerotic cardiovascular diseases. Importantly, the contribution of EDRFs to endothelium-dependent vasodilatation varies in a distinct vessel size-dependent manner; NO mainly mediates vasodilatation of relatively large, conduit vessels (eg epicardial coronary arteries), while EDH factors in small resistance vessels (eg coronary microvessels). Endothelium-derived hydrogen peroxide (H₂ O₂ ) is a physiological signalling molecule serving as one of the major EDH factors especially in microcirculations and has gained increasing attention in view of its emerging relevance for cardiovascular diseases. In the clinical settings, therapeutic approaches targeting NO (eg NO donors) or non-specific elimination of reactive oxygen species (eg antioxidant supplements) are disappointingly ineffective for the treatment of various cardiovascular diseases, in which endothelial dysfunction and coronary microvascular dysfunction are substantially involved. These lines of evidence indicate the potential importance of the physiological balance between NO and H₂ O₂ /EDH factor. Further characterization and better understanding of endothelium-dependent vasodilatations are important to develop novel therapeutic strategies in cardiovascular medicine. In this MiniReview, we will briefly summarize the current knowledge on the emerging regulatory roles of endothelium-dependent vasodilatations in the cardiovascular system, with a special reference to the two major EDRFs, NO and H₂ O₂ /EDH factor, in health and disease.

Membrane Lipid-K IR 2.x Channel Interactions Enable Hemodynamic Sensing in Cerebral Arteries

Objective—

Inward rectifying K + (K IR ) channels are present in cerebral arterial smooth muscle and endothelial cells, a tandem arrangement suggestive of a dynamic yet undiscovered role for this channel. This study defined whether distinct pools of cerebral arterial K IR channels were uniquely modulated by membrane lipids and hemodynamic stimuli.

Approach and Results—

A Ba 2+ -sensitive K IR current was isolated in smooth muscle and endothelial cells of rat cerebral arteries; molecular analyses subsequently confirmed K IR 2.1/K IR 2.2 mRNA and protein expression in both cells. Patch-clamp electrophysiology next demonstrated that each population of K IR channels was sensitive to key membrane lipids and hemodynamic stimuli. In this regard, endothelial K IR was sensitive to phosphatidylinositol 4,5-bisphosphate content, with depletion impairing the ability of laminar shear stress to activate this channel pool. In contrast, smooth muscle K IR was sensitive to membrane cholesterol content, with sequestration blocking the ability of pressure to inhibit channel activity. The idea that membrane lipids help confer shear stress and pressure sensitivity of K IR channels was confirmed in intact arteries using myography. Virtual models integrating structural/electrical observations reconceptualized K IR as a dynamic regulator of membrane potential working in concert with other currents to set basal tone across a range of shear stresses and intravascular pressures.

Conclusions—

The data show for the first time that specific membrane lipid-K IR interactions enable unique channel populations to sense hemodynamic stimuli and drive vasomotor responses to set basal perfusion in the cerebral circulation.

Systolic hypertension-induced neurovascular unit disruption magnifies vascular cognitive impairment in middle-age atherosclerotic LDLr-/-:hApoB+/+ mice

Cognitive functions are dependent upon intercommunications between the cellular components of the neurovascular unit (NVU). Vascular risk factors are associated with a more rapid rate of cognitive decline with aging and cerebrovascular diseases magnify both the incidence and the rate of cognitive decline. The causal relationship between vascular risk factors and injury to the NVU is, however, lacking. We hypothesized that vascular risk factors, such as hypertension and dyslipidemia, promote disruption of the NVU leading to early cognitive impairment. We compared brain structure and cerebrovascular functions of 1-year old (middle-aged) male wild-type (WT) and atherosclerotic hypertensive (LDLr^-/-:hApoB^+/+, ATX) mice. In addition, mice were subjected, or not, to a transverse aortic constriction (TAC) for 6 weeks to assess the acute impact of an increase in systolic blood pressure on the NVU and cognitive functions. Compared with WT mice, ATX mice prematurely developed cognitive decline associated with cerebral micro-hemorrhages, loss of microvessel density and brain atrophy, cerebral endothelial cell senescence and dysfunction, brain inflammation, and oxidative stress associated with blood-brain barrier leakage and brain hypoperfusion. These data suggest functional disturbances in both vascular and parenchymal components of the NVU. Exposure to TAC-induced systolic hypertension promoted cerebrovascular damage and cognitive decline in WT mice, similar to those observed in sham-operated ATX mice; TAC exacerbated the existing cerebrovascular dysfunctions and cognitive failure in ATX mice. Thus, a hemodynamic stress such as systolic hypertension could initiate the cascade involving cerebrovascular injury and NVU deregulation and lead to cognitive decline, a process accelerated in atherosclerotic mice.

The Effects of Flavonoids on Cardiovascular Health: A Review of Human Intervention Trials and Implications for Cerebrovascular Function

Research has suggested a number of beneficial effects arising from the consumption of dietary flavonoids, found in foods such as cocoa, apples, tea, citrus fruits and berries on cardiovascular risk factors such as high blood pressure and endothelial dysfunction. These effects are thought to have a significant impact upon both vascular and cerebrovascular health, ultimately with the potential to prevent cardiovascular and potentially neurodegenerative disease with a vascular component, for example vascular dementia. This review explores the current evidence for the effects of flavonoid supplementation on human endothelial function and both peripheral and cerebral blood flow (CBF). Evidence presented includes their potential to reduce blood pressure in hypertensive individuals, as well as increasing peripheral blood perfusion and promoting CBF in both healthy and at-risk populations. However, there is great variation in the literature due to the heterogeneous nature of the randomised controlled trials conducted. As such, there is a clear need for further research and understanding within this area in order to maximise potential health benefits.

Microvascular NADPH oxidase in health and disease

The systemic and cerebral microcirculation contribute critically to regulation of local and global blood flow and perfusion pressure. Microvascular dysfunction, commonly seen in numerous cardiovascular pathologies, is associated with alterations in the oxidative environment including potentiated production of reactive oxygen species (ROS) and subsequent activation of redox signaling pathways. NADPH oxidases (Noxs) are a primary source of ROS in the vascular system and play a central role in cardiovascular health and disease. In this review, we focus on the roles of Noxs in ROS generation in resistance arterioles and capillaries, and summarize their contributions to microvascular physiology and pathophysiology in both systemic and cerebral microcirculation. In light of the accumulating evidence that Noxs are pivotal players in vascular dysfunction of resistance arterioles, selectively targeting Nox isozymes could emerge as a novel and effective therapeutic strategy for preventing and treating microvascular diseases.

Context-dependent function of ROS in the vascular endothelium: The role of the Notch pathway and shear stress

Reactive oxygen species (ROS) act as signal molecules in several biological processes whereas excessive, unregulated, ROS production contributes to the development of pathological conditions including endothelial dysfunction and atherosclerosis. The maintenance of a healthy endothelium depends on many factors and on their reciprocal interactions; in this framework, the Notch pathway and shear stress (SS) play two lead roles. Recently, evidence of a crosstalk between ROS, Notch, and SS, is emerging. The aim of this review is to describe the way ROS interact with the Notch pathway and SS protecting from-or promoting-the development of endothelial dysfunction. © 2017 BioFactors, 43(4):475-485, 2017.

Pulse pressure-dependent cerebrovascular eNOS regulation in mice

Arterial blood pressure is oscillatory; whether pulse pressure (PP) regulates cerebral artery myogenic tone (MT) and endothelial function is currently unknown. To test the impact of PP on MT and dilation to flow (FMD) or to acetylcholine (Ach), isolated pressurized mouse posterior cerebral arteries were subjected to either static pressure (SP) or a physiological PP (amplitude: 30 mm Hg; frequency: 550 bpm). Under PP, MT was significantly higher than in SP conditions ( p < 0.05) and was not affected by eNOS inhibition. In contrast, under SP, eNOS inhibition increased ( p < 0.05) MT to levels observed under PP, suggesting that PP may inhibit eNOS. At a shear stress of 20 dyn/cm², FMD was lower ( p < 0.05) under SP than PP. Under SP, eNOS-dependent [Formula: see text] production contributed to FMD, while under PP, eNOS-dependent NO was responsible for FMD, indicating that PP favours eNOS coupling. Differences in FMD between pressure conditions were abolished after NOX2 inhibition. In contrast to FMD, Ach-induced dilations were higher ( p < 0.05) under SP than PP. Reactive oxygen species scavenging reduced ( p < 0.05) Ach-dependent dilations under SP, but increased ( p < 0.05) them under PP; hence, under PP, Ach promotes ROS production and limits eNOS-derived NO activity. In conclusion, PP finely regulates eNOS, controlling cerebral artery reactivity.

Attenuated flow-induced dilatation of middle cerebral arteries is related to increased vascular oxidative stress in rats on a short-term high salt diet

KEY POINTS

Recent studies have shown that high salt (HS) intake leads to endothelial dysfunction and impaired vascular reactivity in different vascular beds in both animal and human models, due to increased oxidative stress. The objective of this study was to assess vascular response to flow-induced dilatation (FID) and to elucidate the role of vascular oxidative stress/antioxidative capacity in middle cerebral arteries (MCAs) of HS-fed rats in vitro. The novelty of this study is in demonstrating impaired flow-induced dilatation of MCAs and down-regulation of vascular antioxidant genes with HS intake, leading to increased levels of oxidative stress in blood vessels and peripheral lymph organs, which together contribute to impaired FID. In addition, results show increased oxidative stress in leukocytes of peripheral lymph organs, suggesting the occurrence of inflammatory processes due to HS intake. Recirculation of leukocytes might additionally increase vascular oxidative stress in vivo.

ABSTRACT

The aim of this study was to determine flow-induced dilatation (FID) and the role of oxidative stress/antioxidative capacity in isolated, pressurized middle cerebral arteries (MCAs) of high salt (HS)-fed rats. Healthy male Sprague-Dawley rats (11 weeks old) were fed low salt (0.4% NaCl; LS group) or high salt (4% NaCl; HS group) diets for 1 week. Reactivity of MCAs in response to stepwise increases in pressure gradient (Δ10-Δ100 mmHg) was determined in the absence or presence of the superoxide dismutase (SOD) mimetic TEMPOL and/or the nitric oxide synthases (NOS) inhibitor N(ω) -nitro-l-arginine methyl ester (l-NAME). mRNA levels of antioxidative enzymes, NAPDH-oxidase components, inducible (iNOS) and endothelial nitric oxide synthases (eNOS) were determined by quantitative real-time PCR. Blood pressure (BP), antioxidant enzymes activity, oxidative stress in peripheral leukocytes, lipid peroxidation products and the antioxidant capacity of plasma were measured for both groups. FID was reduced in the HS group compared to the LS group. The presence of TEMPOL restored dilatation in the HS group, with no effect in the LS group. Expression of glutathione peroxidase 4 (GPx4) and iNOS in the HS group was significantly decreased; oxidative stress was significantly higher in the HS group compared to the LS group. HS intake significantly induced basal reactive oxygen species production in the leukocytes of mesenteric lymph nodes and splenocytes, and intracellular production after stimulation in peripheral lymph nodes. Antioxidant enzyme activity and BP were not affected by HS diet. Low GPx4 expression, increased superoxide production in leukocytes, and decreased iNOS expression are likely to underlie increased oxidative stress and reduced nitric oxide bioavailability, leading to impairment of FID in the HS group without changes in BP values.

Exercise and NO production: relevance and implications in the cardiopulmonary system

This article reviews the existing knowledge about the effects of physical exercise on nitric oxide (NO) production in the cardiopulmonary system. The authors review the sources of NO in the cardiopulmonary system; involvement of three forms of NO synthases (eNOS, nNOS, and iNOS) in exercise physiology; exercise-induced modulation of NO and/or NOS in physiological and pathophysiological conditions in human subjects and animal models in the absence and presence of pharmacological modulators; and significance of exercise-induced NO production in health and disease. The authors suggest that physical activity significantly improves functioning of the cardiovascular system through an increase in NO bioavailability, potentiation of antioxidant defense, and decrease in the expression of reactive oxygen species-forming enzymes. Regular physical exercises are considered a useful approach to treat cardiovascular diseases. Future studies should focus on detailed identification of (i) the exercise-mediated mechanisms of NO exchange; (ii) optimal exercise approaches to improve cardiovascular function in health and disease; and (iii) physical effort thresholds.

Vascular oxidative stress, nitric oxide and atherosclerosis

In the vascular wall, reactive oxygen species (ROS) are produced by several enzyme systems including NADPH oxidase, xanthine oxidase, uncoupled endothelial nitric oxide synthase (eNOS) and the mitochondrial electron transport chain. On the other hand, the vasculature is protected by antioxidant enzyme systems, including superoxide dismutases, catalase, glutathione peroxidases and paraoxonases, which detoxify ROS. Cardiovascular risk factors such as hypercholesterolemia, hypertension, and diabetes mellitus enhance ROS generation, resulting in oxidative stress. This leads to oxidative modification of lipoproteins and phospholipids, mechanisms that contribute to atherogenesis. In addition, oxidation of tetrahydrobiopterin may cause eNOS uncoupling and thus potentiation of oxidative stress and reduction of eNOS-derived NO, which is a protective principle in the vasculature. This review summarizes the latest advances in the role of ROS-producing enzymes, antioxidative enzymes as well as NO synthases in the initiation and development of atherosclerosis.

Nitric oxide and cerebrovascular regulation

The cerebrovascular regulation involves highly complex mechanisms to assure that the brain is perfused at all times. These mechanisms depend on all components of the neurovascular units: neurons, glia, and vascular cells. All these cell types can produce nitric oxide (NO), a powerful vasodilator through different NO synthases. Many studies underlined the key role of NO in the maintenance of resting cerebral blood flow (CBF) as well as in the mechanisms that control cerebrovascular tone: autoregulation and neurovascular coupling. However, although the role of NO in the control of CBF has been largely investigated, the complexity of the NO system and the lack of specific NO synthase inhibitors led to still unresolved questions such as the origin of NO and the pathways by which it controls the vascular tone. In this chapter, the role of NO in the regulation of CBF is critically reviewed and discussed in the context of the neurovascular unit and the general principles of cerebrovascular regulation.

Endothelium-dependent control of cerebrovascular functions through age: exercise for healthy cerebrovascular aging

Cognitive performances are tightly associated with the maximal aerobic exercise capacity, both of which decline with age. The benefits on mental health of regular exercise, which slows the age-dependent decline in maximal aerobic exercise capacity, have been established for centuries. In addition, the maintenance of an optimal cerebrovascular endothelial function through regular exercise, part of a healthy lifestyle, emerges as one of the key and primary elements of successful brain aging. Physical exercise requires the activation of specific brain areas that trigger a local increase in cerebral blood flow to match neuronal metabolic needs. In this review, we propose three ways by which exercise could maintain the cerebrovascular endothelial function, a premise to a healthy cerebrovascular function and an optimal regulation of cerebral blood flow. First, exercise increases blood flow locally and increases shear stress temporarily, a known stimulus for endothelial cell maintenance of Akt-dependent expression of endothelial nitric oxide synthase, nitric oxide generation, and the expression of antioxidant defenses. Second, the rise in circulating catecholamines during exercise not only facilitates adequate blood and nutrient delivery by stimulating heart function and mobilizing energy supplies but also enhances endothelial repair mechanisms and angiogenesis. Third, in the long term, regular exercise sustains a low resting heart rate that reduces the mechanical stress imposed to the endothelium of cerebral arteries by the cardiac cycle. Any chronic variation from a healthy environment will perturb metabolism and thus hasten endothelial damage, favoring hypoperfusion and neuronal stress.

Postnatal exposure to voluntary exercise but not the antioxidant catechin protects the vasculature after a switch to an atherogenic environment in middle-age mice

We aimed to evaluate the lasting functional imprinting of exercise (EX) and catechin (CAT) on the vascular function of middle-age mice switched to a proatherogenic environment. C57BL/6J mice (n = 10-15 in each group) fed a regular diet (RD) were exposed from the age of 1 to 9 months either to EX (voluntary running; 2.7 ± 0.2 km/day), to the polyphenol CAT (30 mg/kg/day in drinking water), or to physical inactivity (PI). At 9 months of age, EX and CAT were stopped and mice either remained on the RD or were fed a Western diet (WD) for an additional 3 months. At 12 months of age, mice from all groups fed a WD had similar body mass, systolic blood pressure, and plasma total cholesterol, glucose, insulin, and isoprostane. Compared to the RD, the WD induced an indomethacin-sensitive aortic endothelium-dependent and independent dysfunction in PI mice (p < 0.05) that was prevented by both EX and CAT; this benefit was associated with a higher (p < 0.05) non-nitric oxide/non-prostacyclin endothelium-dependent relaxation. While EX, but not PI or CAT, prevented vascular dysfunction induced by the WD in cerebral arteries, it had no effect in femoral arteries. The profiles of activity of antioxidant enzymes and of proinflammatory gene expression in the aorta suggest a better adaptation of EX > CAT > PI mice to stress. In conclusion, our data suggest that a postnatal exposure to EX, but not to CAT, imprints an adaptive defense capacity in the vasculature against a deleterious change in lifestyle.

Genetically engineered pig models for human diseases

Although pigs are used widely as models of human disease, their utility as models has been enhanced by genetic engineering. Initially, transgenes were added randomly to the genome, but with the application of homologous recombination, zinc finger nucleases, and transcription activator-like effector nuclease (TALEN) technologies, now most any genetic change that can be envisioned can be completed. To date these genetic modifications have resulted in animals that have the potential to provide new insights into human diseases for which a good animal model did not exist previously. These new animal models should provide the preclinical data for treatments that are developed for diseases such as Alzheimer's disease, cystic fibrosis, retinitis pigmentosa, spinal muscular atrophy, diabetes, and organ failure. These new models will help to uncover aspects and treatments of these diseases that were otherwise unattainable. The focus of this review is to describe genetically engineered pigs that have resulted in models of human diseases.

Contribution of flow-dependent vasomotor mechanisms to the autoregulation of cerebral blood flow

Regulation of cerebral blood flow (CBF) is the result of multilevel mechanisms to maintain the appropriate blood supply to the brain while having to comply with the limited space available in the cranium. The latter requirement is ensured by the autoregulation of CBF, in which the pressure-sensitive myogenic response is known to play a pivotal role. However, in vivo increases in pressure are accompanied by increases in flow; yet the effects of flow on the vasomotor tone of cerebral vessels are less known. Earlier studies showed flow-sensitive dilation and/or constriction or both, but no clear picture emerged. Recently, the important role of flow-sensitive mechanism(s) eliciting the constriction of cerebral vessels has been demonstrated. This review focuses on the effect of hemodynamic forces (especially intraluminal flow) on the vasomotor tone of cerebral vessels and the underlying cellular and molecular mechanisms. A novel concept of autoregulation of CBF is proposed, suggesting that (in certain areas of the cerebrovascular tree) pressure- and flow-induced constrictions together maintain an effective autoregulation, and that alterations in these mechanisms may contribute to the development of cerebrovascular disorders. Future studies are warranted to explore the signals, the details of signaling processes and the in vivo importance of these mechanisms.

Role of endothelial nitric oxide in cerebrovascular regulation

Endothelial nitric oxide (NO) plays important roles in the vascular system. Animal models that show vascular dysfunction demonstrate the protective role of endothelial NO dependent pathways. This review focuses on the role of endothelial NO in the regulation of cerebral blood flow and vascular tone. We will discuss the importance of NO in cerebrovascular function using animal models with altered endothelial NO production under normal, ischemic and reperfusion conditions, as well as in hyperoxia. Pharmacological and genetic manipulations of the endothelial NO system demonstrate the essential roles of endothelial NO synthase in maintenance of vascular tone and cerebral perfusion under normal and pathological conditions.

Effect of exercise training on nitric oxide and superoxide/H₂O₂ signaling pathways in collateral-dependent porcine coronary arterioles

Endothelial nitric oxide (NO) synthase (NOS) has been shown to contribute to enhanced vascular function after exercise training. Recent studies have revealed that relatively low concentrations of reactive oxygen species can contribute to endothelium-dependent vasodilation under physiological conditions. We tested the hypothesis that exercise training enhances endothelial function via endothelium-derived vasodilators, NO and superoxide/H(2)O(2), in the underlying setting of chronic coronary artery occlusion. An ameroid constrictor was placed around the proximal left circumflex coronary artery to induce gradual occlusion in Yucatan miniature swine. At 8 wk postoperatively, pigs were randomly assigned to sedentary (pen-confined) or exercise-training (treadmill-run: 5 days/wk for 14 wk) regimens. Exercise training significantly enhanced concentration-dependent, bradykinin-mediated dilation in cannulated collateral-dependent arterioles (∼130 μm diameter) compared with sedentary pigs. NOS inhibition reversed training-enhanced dilation at low bradykinin concentrations in collateral-dependent arterioles, although increased dilation persisted at higher bradykinin concentrations. Total and phosphorylated (Ser(1179)) endothelial NOS protein levels were significantly increased in arterioles from collateral-dependent compared with the nonoccluded region, independent of exercise. The H(2)O(2) scavenger polyethylene glycol-catalase abolished the training-enhanced bradykinin-mediated dilation in collateral-dependent arterioles; similar results were observed with the SOD inhibitor diethyldithiocarbamate. Fluorescence measures of bradykinin-stimulated H(2)O(2) levels were significantly increased by exercise training, independent of occlusion. The NADPH inhibitor apocynin significantly attenuated bradykinin-mediated dilation in arterioles of exercise-trained, but not sedentary, pigs and was associated with significantly increased protein levels of the NADPH subunit p67phox. These data provide evidence that, in addition to NO, the superoxide/H(2)O(2) signaling pathway significantly contributes to exercise training-enhanced endothelium-mediated dilation in collateral-dependent coronary arterioles.

Catechin prevents severe dyslipidemia-associated changes in wall biomechanics of cerebral arteries in LDLr-/-:hApoB+/+ mice and improves cerebral blood flow

Endothelial dysfunction and oxidative stress contribute to the atherosclerotic process that includes stiffening of large peripheral arteries. In contrast, our laboratory previously reported a paradoxical increase in cerebrovascular compliance in LDLr(-/-):hApoB(+/+) atherosclerotic (ATX) mice (7). We hypothesized that prevention of cerebral artery endothelial dysfunction with a chronic dietary antioxidant intake would normalize the changes in cerebral artery wall structure and biomechanics and prevent the decline in basal cerebral blood flow associated with atherosclerosis. Three-month-old ATX mice were treated, or not, for 3 mo with the polyphenol (+)-catechin (CAT; 30 mg·kg(-1)·day(-1)) and compared with wild-type controls. In isolated, pressurized cerebral arteries from ATX mice, CAT prevented endothelial dysfunction (deterioration of endothelium-dependent, flow-mediated dilations; P < 0.05), the inward hypertrophic structural remodeling (increase in the wall-to-lumen ratio; P < 0.05), and the rise in cerebrovascular compliance (rightward shift of the stress-strain curve measured in passive conditions, reflecting mechanical properties of the arterial wall; P < 0.05). Doppler optical coherence tomography imaging in vivo confirmed these findings, showing that cerebral compliance was higher in ATX mice and normalized by CAT (P < 0.05). CAT also prevented basal cerebral hypoperfusion in ATX mice (P < 0.05). Active remodeling of the cerebrovascular wall in ATX mice was further suggested by the increase (P < 0.05) in pro-metalloproteinase-9 activity, which was normalized by CAT. We conclude that, by preserving the endothelial function, a chronic treatment with CAT prevents the deleterious effect of severe dyslipidemia on cerebral artery wall structure and biomechanical properties, contributing to preserving resting cerebral blood flow.

Lithium attenuates bupivacaine-induced neurotoxicity in vitro through phosphatidylinositol-3-kinase/threonine-serine protein kinase B- and extracellular signal-regulated kinase-dependent mechanisms

Local anesthetics (LAs) are necessary for the regional anesthesia, spinal anesthesia, and pain management. However, the application of LAs may cause neurotoxicity and result in postoperative neurological complications. Lithium is a mood stabilizer for the treatment of bipolar disorder and may exert neuroprotective effects. In this study, we evaluated the effects of lithium on bupivacaine (a frequently used LAs)-induced injury in mouse neuroblastoma neuro 2a (N2a) cells. N2a cells were treated with bupivacaine in the presence or absence of lithium. After treatment, the cell injury was evaluated by examination of viability, morphology changes, and nuclear condensation. The levels of mitochondrial transmembrane potential (ΔΨm) and activation of phosphatidylinositol-3-kinase (PI3K)/ threonine-serine protein kinase B (Akt) and extracellular signal-regulated kinase (ERK) were also examined. In a separate experiment, we investigated the effect of Akt and ERK inhibition on cell injury after bupivacaine and lithium treatment. Pretreatment of N2a cells with lithium significantly attenuated bupivacaine-induced cell injury. Lithium pretreatment completely reversed the suppression of PI3K/Akt and ERK signalings and significantly prevented the decline of ΔΨm in N2a cells after bupivacaine treatment. More importantly, pharmacological inhibition of Akt and ERK diminished the protective effect of lithium against bupivacaine-induced neuronal death. Our data suggest that lithium pretreatment provides a protective effect on bupivacaine-induced neuronal cell injury. This action of lithium is mediated through, at least in part, the activating of PI3K/Akt- and ERK-dependent mechanisms. Because lithium is a clinically proved safety drug for neurons, it is worthwhile to identify whether coadministration of LAs with lithium will decrease the risks of LAs-induced postoperative neurological complications in clinic practice.

Isolated human and rat cerebral arteries constrict to increases in flow: role of 20-HETE and TP receptors

Elevation of intraluminal pressure increases vasomotor tone, which thought to have a substantial role in regulation of cerebral blood flow (CBF). Interestingly, responses of cerebral vessels to increases in flow varied and have not been studied in human cerebral arteries. We hypothesized that increases in flow elicit constrictions of isolated human and rat cerebral arteries and aimed to elucidate the underlying mechanisms. Human cerebral arteries and rat middle cerebral arteries constricted to increases in flow (P<0.05). Simultaneous increase in intraluminal flow+pressure further reduced the diameter compared with pressure-induced changes (P<0.05), leading to constant estimated CBF. Flow-induced constrictions were abolished by HET0016 (inhibitor of synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) or inhibition of COXs or blocking TP (thromboxane A(2)/prostaglandin H(2), receptors and attenuated by scavenging reactive oxygen species (ROS). Flow-enhanced ROS formation was significantly reduced by HET0016. In conclusion, in human and rat cerebral arteries (1) increases in flow elicit constrictions, (2) signaling mechanism of flow-induced constriction of cerebral arteries involves enhanced production of ROS, COX activity, and mediated by 20-HETE via TP receptors, and (3) we propose that simultaneous operation of pressure- and flow-induced constrictions is necessary to provide an effective autoregulation of CBF.

Genetic modifications of pigs for medicine and agriculture

Genetically modified swine hold great promise in the fields of agriculture and medicine. Currently, these swine are being used to optimize production of quality meat, to improve our understanding of the biology of disease resistance, and to reduced waste. In the field of biomedicine, swine are anatomically and physiologically analogous to humans. Alterations of key swine genes in disease pathways provide model animals to improve our understanding of the causes and potential treatments of many human genetic disorders. The completed sequencing of the swine genome will significantly enhance the specificity of genetic modifications, and allow for more accurate representations of human disease based on syntenic genes between the two species. Improvements in both methods of gene alteration and efficiency of model animal production are key to enabling routine use of these swine models in medicine and agriculture.

Heart rate-associated mechanical stress impairs carotid but not cerebral artery compliance in dyslipidemic atherosclerotic mice

The cardiac cycle imposes a mechanical stress that dilates elastic carotid arteries, while shear stress largely contributes to the endothelium-dependent dilation of downstream cerebral arteries. In the presence of dyslipidemia, carotid arteries stiffen while the endothelial function declines. We reasoned that stiffening of carotid arteries would be prevented by reducing resting heart rate (HR), while improving the endothelial function would regulate cerebral artery compliance and function. Thus we treated or not 3-mo-old male atherosclerotic mice (ATX; LDLr(-/-):hApoB(+/+)) for 3 mo with the sinoatrial pacemaker current inhibitor ivabradine (IVA), the β-blocker metoprolol (METO), or subjected mice to voluntary physical training (PT). Arterial (carotid and cerebral artery) compliance and endothelium-dependent flow-mediated cerebral dilation were measured in isolated pressurized arteries. IVA and METO similarly reduced (P < 0.05) 24-h HR by ≈15%, while PT had no impact. As expected, carotid artery stiffness increased (P < 0.05) in ATX mice compared with wild-type mice, while cerebral artery stiffness decreased (P < 0.05); this paradoxical increase in cerebrovascular compliance was associated with endothelial dysfunction and an augmented metalloproteinase-9 (MMP-9) activity (P < 0.05), without changing the lipid composition of the wall. Reducing HR (IVA and METO) limited carotid artery stiffening, but plaque progression was prevented by IVA only. In contrast, IVA maintained and PT improved cerebral endothelial nitric oxide synthase-dependent flow-mediated dilation and wall compliance, and both interventions reduced MMP-9 activity (P < 0.05); METO worsened endothelial dysfunction and compliance and did not reduce MMP-9 activity. In conclusion, HR-dependent mechanical stress contributes to carotid artery wall stiffening in severely dyslipidemic mice while cerebrovascular compliance is mostly regulated by the endothelium.

Cigarette smoke-induced kinin B1 receptor promotes NADPH oxidase activity in cultured human alveolar epithelial cells

Pulmonary inflammation is an important pathological feature of tobacco smoke-related lung diseases. Kinin B1 receptor (B1R) is up-regulated in the rat trachea chronically exposed to cigarette-smoke. This study aimed at determining (1) whether exposure to total particulate matter of the cigarette smoke (TPM) can induce B1R in human alveolar epithelial A549 cells, (2) the mechanism of B1R induction, (3) the functionality of de novo synthesized B1R, and (4) the role of B1R in TPM-induced increase of superoxide anion (O₂(●⁻)) level. Results show that A549 cells exposed to 10 μg/ml TPM increased O₂(●⁻) level along with B1R (protein and mRNA) and IL-1β mRNA. In contrast, B2R and TNF-α mRNA were not affected by TPM. The increasing effect of TPM on O₂(●⁻) level was not significantly affected by the B1R antagonist SSR240612. TPM-increased B1R mRNA was prevented by co-treatments with N-acetyl-l-cysteine (potent antioxidant), diphenyleneiodonium (NADPH oxidase inhibitor), IL-1Ra (interleukin-1R antagonist) and SN-50 (specific inhibitor of NF-kB activation) but not by pentoxifylline (TNF-α release inhibitor), indomethacin and niflumic acid (COX-1 and -2 inhibitors). Stimulation of B1R with a selective agonist (des-Arg⁹-BK, 10 μM; 30 min) increased O₂(●⁻)production which was prevented by apocynin and diphenyleneiodonium (NADPH oxidase inhibitors). Data suggest that the increased expression of B1R by TPM in A549 cells is mediated by oxidative stress, IL-1β and NF-kB but not by cyclooxygenases or TNF-α. The amplification of O₂(●⁻) levels via the activation of B1R-NADPH oxidase may exacerbate pulmonary inflammation and contribute to the chronicity of tobacco smoke-related lung diseases.

Up-regulation of thromboxane A₂ impairs cerebrovascular eNOS function in aging atherosclerotic mice

We previously reported that in healthy mouse cerebral arteries, endothelial nitric oxide synthase (eNOS) produces H₂O₂, leading to endothelium-dependent dilation. In contrast, thromboxane A₂ (TXA₂), a potent pro-oxidant and pro-inflammatory endogenous vasoconstrictor, is associated with eNOS dysfunction. Our objectives were to elucidate whether (1) the cerebrovascular eNOS-H₂O₂ pathway was sensitive to oxidative stress associated with aging and dyslipidemia and (2) TXA₂ contributed to cerebral eNOS dysfunction. Atherosclerotic (ATX = LDLR(-/-); hApoB(+/+)) and wild-type (WT) control mice were used at 3 and 12 months old (m/o). Three-m/o ATX mice were treated with the cardio-protective polyphenol catechin for 9 months. Dilations to ACh and the simultaneous eNOS-derived H₂O₂ production were recorded in isolated pressurized cerebral arteries. The age-associated decrease in cerebral eNOS-H₂O₂ pathway observed in WT was premature in ATX mice, decreasing at 3 m/o and abolished at 12 m/o. Thromboxane synthase inhibition by furegrelate increased dilations at 12 months in WT and at 3 and 12 months in ATX mice, suggesting an anti-dilatory role of TXA₂ with age hastened by dyslipidemia. In addition, the non-selective NADP(H) oxidase inhibitor apocynin improved the eNOS-H₂O₂ pathway only in 12-m/o ATX mice. Catechin normalized the function of this pathway, which became sensitive to L-NNA and insensitive to furegrelate or apocynin; catechin also prevented the rise in TXA₂ synthase expression. In conclusion, the age-dependent cerebral endothelial dysfunction is precocious in dyslipidemia and involves TXA₂ production that limits eNOS activity. Preventive catechin treatment reduced the impact of endogenous TXA₂ on the control of cerebral tone and maintained eNOS function.

Catechin treatment improves cerebrovascular flow-mediated dilation and learning abilities in atherosclerotic mice

Severe dyslipidemia and the associated oxidative stress could accelerate the age-related decline in cerebrovascular endothelial function and cerebral blood flow (CBF), leading to neuronal loss and impaired learning abilities. We hypothesized that a chronic treatment with the polyphenol catechin would prevent endothelial dysfunction, maintain CBF responses, and protect learning abilities in atherosclerotic (ATX) mice. We treated ATX (C57Bl/6-LDLR(-/-)hApoB(+/+); 3 mo old) mice with catechin (30 mg · kg(-1) · day(-1)) for 3 mo, and C57Bl/6 [wild type (WT), 3 and 6 mo old] mice were used as controls. ACh- and flow-mediated dilations (FMD) were recorded in pressurized cerebral arteries. Basal CBF and increases in CBF induced by whisker stimulation were measured by optical coherence tomography and Doppler, respectively. Learning capacities were evaluated with the Morris water maze test. Compared with 6-mo-old WT mice, cerebral arteries from 6-mo-old ATX mice displayed a higher myogenic tone, lower responses to ACh and FMD, and were insensitive to NOS inhibition (P < 0.05), suggesting endothelial dysfunction. Basal and increases in CBF were lower in 6-mo-old ATX than WT mice (P < 0.05). A decline in the learning capabilities was also observed in ATX mice (P < 0.05). Catechin 1) reduced cerebral superoxide staining (P < 0.05) in ATX mice, 2) restored endothelial function by reducing myogenic tone, improving ACh- and FMD and restoring the sensitivity to nitric oxide synthase inhibition (P < 0.05), 3) increased the changes in CBF during stimulation but not basal CBF, and 4) prevented the decline in learning abilities (P < 0.05). In conclusion, catechin treatment of ATX mice prevents cerebrovascular dysfunctions and the associated decline in learning capacities.

Vascular endothelium-specific overexpression of human catalase in cloned pigs

The objective of this study was to develop transgenic Yucatan minipigs that overexpress human catalase (hCat) in an endothelial-specific manner. Catalase metabolizes hydrogen peroxide (H(2)O(2)), an important regulator of vascular tone that contributes to diseases such as atherosclerosis and preeclampsia. A large animal model to study reduced endothelium-derived H(2)O(2) would therefore generate valuable translational data on vascular regulation in health and disease. Yucatan minipig fetal fibroblasts stably co-transfected with human catalase (Tie2-hCat) and eGFP expression constructs were isolated into single-cell populations. The presence of the Tie2-hCat transgene in individual colonies of fibroblasts was determined by PCR. Transgenic fibroblasts were used for nuclear transfer into enucleated oocytes by electrofusion. A minimum of 140 cloned embryos were transferred per surrogate sow (n = 4). All four surrogates maintained pregnancies and piglets were delivered by cesarean section. Nine male piglets from three of the four litters carried the Tie2-hCat transgene. Expression of human catalase mRNA and overall elevated catalase protein in isolated umbilical endothelial cells from transgenic piglets were verified by RT-PCR and western blot, respectively, and endothelial localization was confirmed by immunohistochemistry. Increased enzymatic activity of catalase in transgenic versus wild-type endothelial cells was inferred based on significantly reduced levels of H(2)O(2) in culture. The similarities in swine and human cardiovascular anatomy and physiology will make this pig model a valuable source of information on the putative role of endothelium-derived H(2)O(2) in vasodilation and in the mechanisms underlying vascular health and disease.

PKG and PKC Are Down-Regulated during Cardiomyocyte Differentiation from Embryonic Stem Cells: Manipulation of These Pathways Enhances Cardiomyocyte Production

Understanding signal transduction mechanisms that drive differentiation of adult or embryonic stem cells (ESCs) is imperative if they are to be used to cure disease. While the list of signaling pathways regulating stem cell differentiation is growing, it is far from complete. Indentifying regulatory mechanisms and timecourse commitment to cell lineages is needed for generating pure populations terminally differentiated cell types, and in ESCs, suppression of teratoma formation. To this end, we investigated specific signaling mechanisms involved in cardiomyogenesis, followed by manipulation of these pathways to enhance differentiation of ESCs into cardiomyocytes. Subjecting nascent ESC-derived cardiomyocytes to a proteomics assay, we found that cardiomyogenesis is influenced by up- and down-regulation of a number of kinases, one of which, cGMP-dependent protein kinase (PKG), is markedly down-regulated during differentiation. Delving further, we found that manipulating the PKG pathway using PKG-specific inhibitors produced significantly more cardiomyocytes from ESCs when compared to ESCs left to differentiate without inhibitors. In addition, we found combinatorial effects when culturing ESCs in inhibitors to PKG and PKC isotypes. Consequently, we have generated a novel hypothesis: Down-regulation of PKG and specific PKC pathways are necessary for cardiomyogenesis, and when manipulated, these pathways produce significantly more cardiomyocytes than untreated ESCs.

Age-dependent endothelial nitric oxide synthase uncoupling in pulmonary arteries of endoglin heterozygous mice

Endoglin is a TGF-β superfamily receptor critical for endothelial cell function. Mutations in this gene are associated with hereditary hemorrhagic telangiectasia type I (HHT1), and clinical signs of disease are generally more evident later in life. We previously showed that systemic vessels of adult Eng heterozygous ( Eng+/−) mice exhibit increased vasorelaxation due to uncoupling of endothelial nitric oxide synthase (eNOS). We postulated that these changes may develop with age and evaluated pulmonary arteries from newborn and adult Eng+/− mice for eNOS-dependent, acetylcholine (ACh-induced) vasorelaxation, compared with that of age-matched littermate controls. While ACh-induced vasorelaxation was similar in all newborn mice, it was significantly increased in the adult Eng+/− vs. control vessels. The vasodilatory responses were inhibited by l-NAME suggesting eNOS dependence. eNOS uncoupling was observed in lung tissues of adult, but not newborn, heterozygous mice and was associated with increased production of reactive O2 species (ROS) in adult Eng +/− vs. control lungs. Interestingly, ROS generation was higher in adult than newborn mice and so were the levels of NADPH oxidase 4 and SOD 1, 2, 3 isoforms. However, enzyme protein levels and NADPH activity were normal in adult Eng+/− lungs indicating that the developmental maturation of ROS generation and scavenging cannot account for the increased vasodilatation observed in adult Eng+/− mice. Our data suggest that eNOS-dependent H2O2 generation in Eng+/− lungs accounts for the heightened pulmonary vasorelaxation. To the extent that these mice mimic human HHT1, age-associated pulmonary vascular eNOS uncoupling may explain the late childhood and adult onset of clinical lung manifestations.

Vascular endothelial ageing, heartbeat after heartbeat

The vascular endothelium starts to age at the first heartbeat. There is no longer a need to demonstrate that an increased resting heart rate--above 70 b.p.m.--is associated with the onset of cardiovascular events and reduces lifespan in humans. Each cardiac cycle imposes a mechanical constraint on the arteries, and we would like to propose that this mechanical stress damages the vascular endothelium, its dysfunction being the prerequisite for atherogenesis. Consequently, reducing heart rate could protect the endothelium and slow the onset of atherosclerosis. The potential mechanisms by which reducing heart rate could be beneficial to the endothelium are likely a combination of a reduction in mechanical stress and tissue fatigue and a prolongation of the period of steady laminar flow, and thus sustained shear stress, between each systole. With age, irreparable damage accumulates in endothelial cells and leads to senescence, which is characterized by a pro-atherogenic phenotype. In the body, the highest mechanical stress occurs in the coronary vessels, where blood only flows during diastole and even reverses during systole; thus, coronary arteries are the prime site of atherosclerosis. All classical risk factors for cardiovascular diseases add up, to accelerate atherogenesis, but hypertension, which further raises mechanical stress, is likely the most damaging. By inducing flow through the arteries, the heart rate determines shear stress and its stability: mechanical stress and the associated damage induced by each systole are efficiently counteracted by the repair capacities of a healthy endothelium. The maintenance of a physiological, low heart rate may be key to prolonging the endothelial healthy lifespan and thus, vascular health.