Interference with PPARγ in endothelium accelerates angiotensin II-induced endothelial dysfunction

The 2023 Walter B. Cannon Award Lecture: Mechanisms Regulating Vascular Function and Blood Pressure by the PPARγ-RhoBTB1-CUL3 Pathway

Human genetic and clinical trial data suggest that peroxisome proliferator activated receptor γ (PPARγ), a nuclear receptor transcription factor plays an important role in the regulation of arterial blood pressure. The examination of a series of novel animal models, coupled with transcriptomic and proteomic analysis, has revealed that PPARγ and its target genes employ diverse pathways to regulate vascular function and blood pressure. In endothelium, PPARγ target genes promote an antioxidant state, stimulating both nitric oxide (NO) synthesis and bioavailability, essential components of endothelial-smooth muscle communication. In vascular smooth muscle, PPARγ induces the expression of a number of genes that promote an antiinflammatory state and tightly control the level of cGMP, thus promoting responsiveness to endothelial-derived NO. One of the PPARγ targets in smooth muscle, Rho related BTB domain containing 1 (RhoBTB1) acts as a substrate adaptor for proteins to be ubiquitinated by the E3 ubiquitin ligase Cullin-3 and targeted for proteasomal degradation. One of these proteins, phosphodiesterase 5 (PDE5) is a target of the Cullin-3/RhoBTB1 pathway. Phosphodiesterase 5 degrades cGMP to GMP and thus regulates the smooth muscle response to NO. Moreover, expression of RhoBTB1 under condition of RhoBTB1 deficiency reverses established arterial stiffness. In conclusion, the coordinated action of PPARγ in endothelium and smooth muscle is needed to maintain NO bioavailability and activity, is an essential regulator of vasodilator/vasoconstrictor balance, and regulates blood vessel structure and stiffness.

Oxidative Stress, Reductive Stress and Antioxidants in Vascular Pathogenesis and Aging

This review is focused on the mechanisms that regulate health, disease and aging redox status, the signal pathways that counteract oxidative and reductive stress, the role of food components and additives with antioxidant properties (curcumin, polyphenols, vitamins, carotenoids, flavonoids, etc.), and the role of the hormones irisin and melatonin in the redox homeostasis of animal and human cells. The correlations between the deviation from optimal redox conditions and inflammation, allergic, aging and autoimmune responses are discussed. Special attention is given to the vascular system, kidney, liver and brain oxidative stress processes. The role of hydrogen peroxide as an intracellular and paracrine signal molecule is also reviewed. The cyanotoxins β-N-methylamino-l-alanine (BMAA), cylindrospermopsin, microcystins and nodularins are introduced as potentially dangerous food and environment pro-oxidants.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Rosiglitazone restores nitric oxide synthase-dependent reactivity of cerebral arterioles in rats exposed to prenatal alcohol

BACKGROUND

Prenatal exposure to alcohol leads to a greater incidence of many cardiovascular-related diseases, presumably via a mechanism that may involve increased oxidative stress. An agonist of peroxisome proliferator-activated receptor gamma (PPARγ; rosiglitazone) has been shown to suppress alcohol-induced neuroinflammation and oxidative stress. The goal of this study was to determine whether acute and chronic treatment with rosiglitazone could restore or prevent impaired nitric oxide synthase (NOS)-dependent responses of cerebral arterioles in male and female adult (14-16 weeks old) rats exposed to alcohol in utero.

METHODS

We fed Sprague-Dawley dams a liquid diet with or without 3% ethanol for the duration of their pregnancy (21-23 days). In the first series of studies, we examined the reactivity of cerebral arterioles to eNOS- (ADP), nNOS-dependent (NMDA), and NOS-independent agonists in male and female adult rats before and during acute (1 hour) topical application of rosiglitazone (1 µM). In a second series of studies, we examined the influence of chronic treatment with rosiglitazone (3 mg/kg/day in drinking water for 2-3 weeks) on the responses of cerebral arterioles in male and female adult rats exposed to alcohol in utero.

RESULTS

We found that in utero exposure to alcohol similarly reduced responses of cerebral arterioles to ADP and NMDA, but not to nitroglycerin in male and female adult rats. In addition, acute treatment of the male and female adult rats with rosiglitazone similarly restored this impairment in cerebral vascular function to that observed in controls. We also found that chronic treatment with rosiglitazone prevented impaired vascular function in male and female adult rats that were exposed to alcohol in utero.

CONCLUSIONS

PPARγ activation may be an effective and relevant treatment to reverse or prevent cerebral vascular abnormalities associated with prenatal exposure to alcohol.

Role of the Peroxisome Proliferator Activated Receptors in Hypertension

Nuclear receptors represent a large family of ligand-activated transcription factors which sense the physiological environment and make long-term adaptations by mediating changes in gene expression. In this review, we will first discuss the fundamental mechanisms by which nuclear receptors mediate their transcriptional responses. We will focus on the PPAR (peroxisome proliferator-activated receptor) family of adopted orphan receptors paying special attention to PPARγ, the isoform with the most compelling evidence as an important regulator of arterial blood pressure. We will review genetic data showing that rare mutations in PPARγ cause severe hypertension and clinical trial data which show that PPARγ activators have beneficial effects on blood pressure. We will detail the tissue- and cell-specific molecular mechanisms by which PPARs in the brain, kidney, vasculature, and immune system modulate blood pressure and related phenotypes, such as endothelial function. Finally, we will discuss the role of placental PPARs in preeclampsia, a life threatening form of hypertension during pregnancy. We will close with a viewpoint on future research directions and implications for developing novel therapies.

Impact of the Renin-Angiotensin System on the Endothelium in Vascular Dementia: Unresolved Issues and Future Perspectives

The effects of the renin-angiotensin system (RAS) surpass the renal and cardiovascular systems to encompass other body tissues and organs, including the brain. Angiotensin II (Ang II), the most potent mediator of RAS in the brain, contributes to vascular dementia via different mechanisms, including neuronal homeostasis disruption, vascular remodeling, and endothelial dysfunction caused by increased inflammation and oxidative stress. Other RAS components of emerging significance at the level of the blood-brain barrier include angiotensin-converting enzyme 2 (ACE2), Ang(1-7), and the AT2, Mas, and AT4 receptors. The various angiotensin hormones perform complex actions on brain endothelial cells and pericytes through specific receptors that have either detrimental or beneficial actions. Increasing evidence indicates that the ACE2/Ang(1-7)/Mas axis constitutes a protective arm of RAS on the blood-brain barrier. This review provides an update of studies assessing the different effects of angiotensins on cerebral endothelial cells. The involved signaling pathways are presented and help highlight the potential pharmacological targets for the management of cognitive and behavioral dysfunctions associated with vascular dementia.

Increased Susceptibility of Mice Lacking Renin-b to Angiotensin II-Induced Organ Damage

Several cardiac and renal diseases are attributed to a dysregulation of the renin-angiotensin system. Renin, the rate-limiting enzyme of the renin-angiotensin system, has 2 isoforms. The classical renin isoform (renin-a) encoding preprorenin is mainly confined to the juxtaglomerular cells and released into the circulation upon stimulation. Alternatively, renin-b is predicted to remain intracellular and is expressed in the brain, heart, and adrenal gland. In the brain, ablation of renin-b (Ren-b^Null mice) results in increased brain renin-angiotensin system activity. However, the consequences of renin-b ablation in tissues outside the brain remain unknown. Therefore, we hypothesized that renin-b protects from hypertensive cardiac and renal end-organ damage in mice. Ren-b^Null mice exhibited normal blood pressure at baseline. Thus, we induced hypertension by using a slow pressor dose of Ang II (angiotensin II). Ang II increased blood pressure in both wild type and Ren-b^Null to the same degree. Although the blood pressure between Ren-b^Null and wild-type mice was elevated equally, 4-week infusion of Ang II resulted in exacerbated cardiac remodeling in Ren-b^Null mice compared with wild type. Ren-b^Null mice also exhibited a modest increase in renal glomerular matrix deposition, elevated plasma aldosterone, and a modestly enhanced dipsogenic response to Ang II. Interestingly, ablation of renin-b strongly suppressed plasma renin, but renal cortical renin mRNA was preserved. Altogether, these data indicate that renin-b might play a protective role in the heart, and thus renin-b could be a potential target to treat hypertensive heart disease.

Biomechanical Forces and Oxidative Stress: Implications for Pulmonary Vascular Disease

Significance: Oxidative stress in the cell is characterized by excessive generation of reactive oxygen species (ROS). Superoxide (O₂^-) and hydrogen peroxide (H₂O₂) are the main ROS involved in the regulation of cellular metabolism. As our fundamental understanding of the underlying causes of lung disease has increased it has become evident that oxidative stress plays a critical role. Recent Advances: A number of cells in the lung both produce, and respond to, ROS. These include vascular endothelial and smooth muscle cells, fibroblasts, and epithelial cells as well as the cells involved in the inflammatory response, including macrophages, neutrophils, eosinophils. The redox system is involved in multiple aspects of cell metabolism and cell homeostasis. Critical Issues: Dysregulation of the cellular redox system has consequential effects on cell signaling pathways that are intimately involved in disease progression. The lung is exposed to biomechanical forces (fluid shear stress, cyclic stretch, and pressure) due to the passage of blood through the pulmonary vessels and the distension of the lungs during the breathing cycle. Cells within the lung respond to these forces by activating signal transduction pathways that alter their redox state with both physiologic and pathologic consequences. Future Directions: Here, we will discuss the intimate relationship between biomechanical forces and redox signaling and its role in the development of pulmonary disease. An understanding of the molecular mechanisms induced by biomechanical forces in the pulmonary vasculature is necessary for the development of new therapeutic strategies.

[Role of PPARγ, a transcription factor in cardiovascular disease]

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand activated transcription factor known to regulate fatty acid metabolism. Thiazolidinediones (TZDs), PPARγ synthetic agonists, currently used to treat patients with type 2 diabetes, have been shown to lower the blood pressure and protect against vascular diseases such as atherosclerosis. In line with these findings, it has been reported that individuals with loss-of-function mutations of PPARγ developed sever early-onset hypertension in addition to metabolic abnormalities. Accumulating evidences suggest PPARγ in the vasculature has protective effects on cardiovascular disease despite unclear mechanism. Because of ubiquitous expression of PPARγ, TZDs are well-known to be associated with serious side effects such as weight gain, fluid retention, and bone fractures. Thus identification of mechanisms on tissue-specific PPARγ activity may lead to the development of targeted treatment which is characterized by no deleterious effects. This review discusses role of PPARγ in cardiovascular disease.

Conditional deletion of smooth muscle Cullin-3 causes severe progressive hypertension

Patients with mutations in Cullin-3 (CUL3) exhibit severe early onset hypertension but the contribution of the smooth muscle remains unclear. Conditional genetic ablation of CUL3 in vascular smooth muscle (S-CUL3KO) causes progressive impairment in responsiveness to nitric oxide (NO), rapid development of severe hypertension, and increased arterial stiffness. Loss of CUL3 in primary aortic smooth muscle cells or aorta resulted in decreased expression of the NO receptor, soluble guanylate cyclase (sGC), causing a marked reduction in cGMP production and impaired vasodilation to cGMP analogues. Vasodilation responses to a selective large conductance Ca2+-activated K+-channel activator were normal suggesting that downstream signals which promote smooth muscle-dependent relaxation remained intact. We conclude that smooth muscle specific CUL3 ablation impairs both cGMP production and cGMP responses and that loss of CUL3 function selectively in smooth muscle is sufficient to cause severe hypertension by interfering with the NO-sGC-cGMP pathway. Our study provides compelling evidence for the sufficiency of vascular smooth muscle CUL3 as a major regulator of BP. CUL3 mutations cause severe vascular dysfunction, arterial stiffness and hypertension due to defects in vascular smooth muscle.

Endothelial PPARγ (Peroxisome Proliferator-Activated Receptor-γ) Protects From Angiotensin II-Induced Endothelial Dysfunction in Adult Offspring Born From Pregnancies Complicated by Hypertension

Preeclampsia is a hypertensive disorder of pregnancy associated with vascular dysfunction and cardiovascular risk to offspring. We hypothesize that endothelial PPARγ (peroxisome proliferator-activated receptor-γ) provides cardiovascular protection in offspring from pregnancies complicated by hypertension. C57BL/6J dams were bred with E-V290M sires, which express a dominant-negative allele of PPARγ selectively in the endothelium. Arginine vasopressin was infused throughout gestation. Vasopressin elevated maternal blood pressure at gestational day 14 to 15 and urinary protein at day 17 consistent. Systolic blood pressure and vasodilation responses to acetylcholine were similar in vasopressin-exposed offspring compared to offspring from control pregnancies. We treated offspring with a subpressor dose of angiotensin II to test if hypertension during pregnancy predisposes offspring to hypertension. Male and female angiotensin II-treated E-V290M offspring from vasopressin-exposed but not control pregnancy exhibited significant impairment in acetylcholine-induced relaxation in carotid artery. Endothelial dysfunction in angiotensin II-treated E-V290M vasopressin-exposed offspring was attenuated by tempol, an effect which was more prominent in male offspring. Nrf2 (nuclear factor-E2-related factor) protein levels were significantly elevated in aorta from male E-V290M offspring, but not female offspring compared to controls. Blockade of ROCK (Rho-kinase) signaling and incubation with a ROCK2-specific inhibitor improved endothelial function in both male and female E-V290M offspring from vasopressin-exposed pregnancy. Our data suggest that interference with endothelial PPARγ in offspring from vasopressin-exposed pregnancies increases the risk for endothelial dysfunction on exposure to a cardiovascular stressor in adulthood. This implies that endothelial PPARγ provides protection to cardiovascular stressors in offspring of a pregnancy complicated by hypertension and perhaps in preeclampsia.

Interference With Endothelial PPAR (Peroxisome Proliferator-Activated Receptor)-γ Causes Accelerated Cerebral Vascular Dysfunction in Response to Endogenous Renin-Angiotensin System Activation

Low-salt diet is beneficial in salt-sensitive hypertension but may provoke cardiovascular risk in patients with heart failure, diabetes mellitus, or other cardiovascular abnormalities because of endogenous renin-angiotensin system activation. PPAR (peroxisome proliferator-activated receptor)-γ is a transcription factor which promotes an antioxidant pathway in the endothelium. We studied transgenic mice expressing a dominant-negative mutation in PPAR-γ selectively in the endothelium (E-V290M) to test the hypothesis that endothelial PPAR-γ plays a protective role in response to low salt-mediated renin-angiotensin system activation. Plasma renin and Ang II (angiotensin II) were significantly and equally increased in all mice fed low salt for 6 weeks. Vasorelaxation to acetylcholine was not affected in basilar artery from E-V290M at baseline but was significantly and selectively impaired in E-V290M after low salt. Unlike basilar artery, low salt was not sufficient to induce vascular dysfunction in carotid artery or aorta. Endothelial dysfunction in the basilar artery from E-V290M mice fed low salt was attenuated by scavengers of superoxide, inhibitors of NADPH oxidase, or blockade of the Ang II AT1 (angiotensin type-1) receptor. Simultaneous AT1 and AT2 receptor blockade revealed that the restoration of endothelial function after AT1 receptor blockade was not a consequence of AT2 receptor activation. We conclude that interference with PPAR-γ in the endothelium produces endothelial dysfunction in the cerebral circulation in response to low salt-mediated activation of the endogenous renin-angiotensin system, mediated at least in part, through AT1 receptor activation and perturbed redox homeostasis. Moreover, our data suggest that the cerebral circulation may be particularly sensitive to inhibition of PPAR-γ activity and renin-angiotensin system activation.

The Nuclear Export and Ubiquitin-Proteasome-Dependent Degradation of PPARγ Induced By Angiotensin II

Evidence has documented local angiotensin II (Ang II) as a pro-oxidant and pro-inflammatory molecule contributes to progressive deterioration of organ function in diseases. Peroxisome proliferator-activated receptor γ (PPARγ), a ligand-activated transcription factor, plays crucial roles in protection against oxidative stress and inflammation. Ang II stimulation decreases PPARγ protein in multiple types of cells, while the regulatory role of Ang II on PPARγ is not clear. Here we show that Ang II down-regulated PPARγ in ECV304 cells through 2 actions, inducing nuclear export and loss of protein. The nuclear export of PPARγ occurred transiently in the early phase, while the reduction in PPARγ protein happened in the later phase and was more persistent. Both alterations in PPARγ were accompanied by the decrease in PPARγ-DNA binding activity. Reduction of PPARγ protein levels was also coupled with the inhibition of PPARγ target genes. In addition, activation of PPARγ by its ligand troglitazone could completely counteract both 2 actions of Ang II on PPARγ. Further studies demonstrated that the decline of PPARγ protein was in association with ubiquitin-proteasome-dependent degradation, which was supported by the increase in polyubiquitin-PPARγ conjugates and the inhibitory effect of lactacystin, a specific proteasome inhibitor, on the loss of PPARγ. Taken together, this study uncovers a novel means by which Ang II down-regulates PPARγ. This down-regulation disrupts nuclear PPARγ function, which may lead to the loss of beneficial effects of PPARγ in response to Ang II stress.

Endothelial PPARγ Is Crucial for Averting Age-Related Vascular Dysfunction by Stalling Oxidative Stress and ROCK

Aging plays a significant role in the progression of vascular diseases and vascular dysfunction. Activation of the ADP-ribosylation factor 6 and small GTPases by inflammatory signals may cause vascular permeability and endothelial leakage. Pro-inflammatory molecules have a significant effect on smooth muscle cells (SMC). The migration and proliferation of SMC can be promoted by tumor necrosis factor alpha (TNF-α). TNF-α can also increase oxidative stress in SMCs, which has been identified to persuade DNA damage resulting in apoptosis and cellular senescence. Peroxisome proliferator-activated receptor (PPAR) acts as a ligand-dependent transcription factor and a member of the nuclear receptor superfamily. They play key roles in a wide range of biological processes, including cell differentiation and proliferation, bone formation, cell metabolism, tissue remodeling, insulin sensitivity, and eicosanoid signaling. The PPARγ activation regulates inflammatory responses, which can exert protective effects in the vasculature. In addition, loss of function of PPARγ enhances cardiovascular events and atherosclerosis in the vascular endothelium. This appraisal, therefore, discusses the critical linkage of PPARγ in the inflammatory process and highlights a crucial defensive role for endothelial PPARγ in vascular dysfunction and disease, as well as therapy for vascular aging.

RhoBTB1 protects against hypertension and arterial stiffness by restraining phosphodiesterase 5 activity

Mice selectively expressing PPARγ dominant negative mutation in vascular smooth muscle exhibit RhoBTB1-deficiency and hypertension. Our rationale was to employ genetic complementation to uncover the mechanism of action of RhoBTB1 in vascular smooth muscle. Inducible smooth muscle-specific restoration of RhoBTB1 fully corrected the hypertension and arterial stiffness by improving vasodilator function. Notably, the cardiovascular protection occurred despite preservation of increased agonist-mediated contraction and RhoA/Rho kinase activity, suggesting RhoBTB1 selectively controls vasodilation. RhoBTB1 augmented the cGMP response to nitric oxide by restraining the activity of phosphodiesterase 5 (PDE5) by acting as a substrate adaptor delivering PDE5 to the Cullin-3 E3 Ring ubiquitin ligase complex for ubiquitination inhibiting PDE5. Angiotensin-II infusion also caused RhoBTB1-deficiency and hypertension which was prevented by smooth muscle specific RhoBTB1 restoration. We conclude that RhoBTB1 protected from hypertension, vascular smooth muscle dysfunction, and arterial stiffness in at least two models of hypertension.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Endothelial PPARγ (Peroxisome Proliferator-Activated Receptor-γ) Is Essential for Preventing Endothelial Dysfunction With Aging

Little is known about mechanisms that control vascular aging, particularly at the cell-specific level. PPARγ (peroxisome proliferator-activated receptor-γ) exerts protective effects in the vasculature when activated pharmacologically. To gain insight into the cell-specific impact of PPARγ, we examined the hypothesis that genetic interference with endothelial PPARγ would augment age-induced vascular dysfunction. We studied carotid arteries from adult (11.6±0.3 months) and old (24.7±0.6 months) mice with endothelial-specific expression of a human dominant negative mutation in PPARγ driven by the vascular cadherin promoter (E-V290M), along with age-matched, nontransgenic littermates. Acetylcholine (an endothelium-dependent agonist) produced similar relaxation in arteries from adult nontransgenic and E-V290M mice and old nontransgenic mice. In contrast, responses to acetylcholine were reduced by >50% in old male and female E-V290M mice (P<0.01). Endothelial function in old E-V290M mice was not altered by an inhibitor of COX (cyclooxygenase) but was restored to normal by a superoxide scavenger, an inhibitor of NADPH oxidase, or inhibition of ROCK (Rho kinase). Relaxation of arteries to nitroprusside, which acts directly on vascular muscle, was similar in all groups. Vascular expression of IL (interleukin)-6, Nox-2, and CDKN2A (a marker of senescence) was significantly increased in old E-V290M mice compared with controls (P<0.05). These findings provide the first evidence that age-related vascular dysfunction, inflammation, and senescence is accelerated after interference with endothelial PPARγ via mechanisms involving oxidative stress and ROCK. The finding of an essential protective role for endothelial PPARγ has implications for vascular disease and therapy for vascular aging.

Effect of captopril on radiation-induced TGF-β1 secretion in EA.Hy926 human umbilical vein endothelial cells

The pathophysiological mechanism involved in the sustained endothelial secretion of cytokines that leads to fibrosis 6–16 months after radiotherapy remains unclear. Angiotensin II (Ang II) is produced by the endothelium in response to stressing stimuli, like radiation, and may induce the synthesis of TGF-β, a profibrotic cytokine. In this study we tested the hypothesis that captopril, an angiotensin-converting enzyme (ACE) inhibitor, inhibits or attenuates radiation-induced endothelial TGF-β1 secretion. The human endothelial hybrid cell line EA.HY926 was irradiated with split doses of x-rays (28 Gy delivered in 14 fractions of 2 Gy). TGF-β1 mRNA, TNF-α mRNA and TGF-β1 protein levels were evaluated by RT-PCR and western blotting each month until the fifth month post radiation. Ang II was detected using radioimmunoassays, NF-κB activity was examined using EMSA, and western blotting was used to detect the expression of Iκ-Bα. To explore the role of Ang II on radiation-induced TGF-β1 release and Iκ-Bα expression, captopril was added to cultured cells before, during, or after irradiation. Sustained strong expression of TGF-β1 was observed after conventional fractionated irradiation. TNF-α, Ang II, and NF-κB activity were also increased in EA.Hy926 cells after radiation. Captopril decreased Ang II expression, inhibited the NF-κB pathway and reduced TGF-β1 expression. These data suggest that captopril might protect the endothelium from radiation-induced injury.

PPARγ and retinol binding protein 7 form a regulatory hub promoting antioxidant properties of the endothelium

Peroxisome proliferator-activated receptors (PPARs) are a family of conserved ligand-activated nuclear receptor transcription factors heterogeneously expressed in mammalian tissues. PPARγ is recognized as a master regulator of adipogenesis, fatty acid metabolism, and glucose homeostasis, but genetic evidence also supports the concept that PPARγ regulates the cardiovascular system, particularly vascular function and blood pressure. There is now compelling evidence that the beneficial blood pressure-lowering effects of PPARγ activation are due to its activity in vascular smooth muscle and endothelium, through its modulation of nitric oxide-dependent vasomotor function. Endothelial PPARγ regulates the production and bioavailability of nitric oxide, while PPARγ in the smooth muscle regulates the vasomotor response to nitric oxide. We recently identified retinol binding protein 7 (RBP7) as a PPARγ target gene that is specifically and selectively expressed in the endothelium. In this review, we will discuss the evidence that RBP7 is required to mediate the antioxidant effects of PPARγ and mediate PPARγ target gene selectivity in the endothelium.

Genetic Interference With Endothelial PPAR-γ (Peroxisome Proliferator-Activated Receptor-γ) Augments Effects of Angiotensin II While Impairing Responses to Angiotensin 1-7

Pharmacological activation of PPAR-γ (peroxisome proliferator-activated receptor-γ) protects the vasculature. Much less is known on the cell-specific impact of PPAR-γ when driven by endogenous ligands. Recently, we found that endothelial PPAR-γ protects against angiotensin II-induced endothelial dysfunction. Here, we explored that concept further examining whether effects were sex dependent along with underlying mechanisms. We studied mice expressing a human dominant-negative mutation in PPAR-γ driven by the endothelial-specific vascular cadherin promoter (E-V290M), using nontransgenic littermates as controls. Acetylcholine (an endothelium-dependent agonist) produced similar relaxation of carotid arteries from nontransgenic and E-V290M mice. Incubation of isolated arteries with angiotensin II (1 nmol/L) overnight had no effect in nontransgenic, but reduced responses to acetylcholine by about 50% in male and female E-V290M mice (P<0.05). Endothelial function in E-V290M mice was restored to normal by inhibitors of superoxide (tempol), NADPH oxidase (VAS-2870), Rho kinase (Y-27632), ROCK2 (SLX-2119), NF-κB (nuclear factor-kappa B essential modulator-binding domain peptide), or interleukin-6 (neutralizing antibody). In addition, we hypothesized that PPAR-γ may influence the angiotensin 1-7 arm of the renin-angiotensin system. In the basilar artery, dilation to angiotensin 1-7 was selectively reduced in E-V290M mice by >50% (P<0.05), an effect reversed by Y-27632. Thus, effects of angiotensin II are augmented by interference with endothelial PPAR-γ through sex-independent mechanisms, involving oxidant-inflammatory signaling and ROCK2 (Rho kinase). The study also provides the first evidence that endothelial PPAR-γ interacts with angiotensin 1-7 responses. These critical roles for endothelial PPAR-γ have implications for pathophysiology and therapeutic approaches for vascular disease.

AT1 receptor signaling pathways in the cardiovascular system

The importance of the renin angiotensin aldosterone system in cardiovascular physiology and pathophysiology has been well described whereas the detailed molecular mechanisms remain elusive. The angiotensin II type 1 receptor (AT1 receptor) is one of the key players in the renin angiotensin aldosterone system. The AT1 receptor promotes various intracellular signaling pathways resulting in hypertension, endothelial dysfunction, vascular remodeling and end organ damage. Accumulating evidence shows the complex picture of AT1 receptor-mediated signaling; AT1 receptor-mediated heterotrimeric G protein-dependent signaling, transactivation of growth factor receptors, NADPH oxidase and ROS signaling, G protein-independent signaling, including the β-arrestin signals and interaction with several AT1 receptor interacting proteins. In addition, there is functional cross-talk between the AT1 receptor signaling pathway and other signaling pathways. In this review, we will summarize an up to date overview of essential AT1 receptor signaling events and their functional significances in the cardiovascular system.

Hypertension-Causing Mutation in Peroxisome Proliferator-Activated Receptor γ Impairs Nuclear Export of Nuclear Factor-κB p65 in Vascular Smooth Muscle

Selective expression of dominant negative (DN) peroxisome proliferator-activated receptor γ (PPARγ) in vascular smooth muscle cells (SMC) results in hypertension, atherosclerosis, and increased nuclear factor-κB (NF-κB) target gene expression. Mesenteric SMC were cultured from mice designed to conditionally express wild-type (WT) or DN-PPARγ in response to Cre recombinase to determine how SMC PPARγ regulates expression of NF-κB target inflammatory genes. SMC-specific overexpression of WT-PPARγ or agonist-induced activation of endogenous PPARγ blunted tumor necrosis factor α (TNF-α)-induced NF-κB target gene expression and activity of an NF-κB-responsive promoter. TNF-α-induced gene expression responses were enhanced by DN-PPARγ in SMC. Although expression of NF-κB p65 was unchanged, nuclear export of p65 was accelerated by WT-PPARγ and prevented by DN-PPARγ in SMC. Leptomycin B, a nuclear export inhibitor, blocked p65 nuclear export and inhibited the anti-inflammatory action of PPARγ. Consistent with a role in facilitating p65 nuclear export, WT-PPARγ coimmunoprecipitated with p65, and WT-PPARγ was also exported from the nucleus after TNF-α treatment. Conversely, DN-PPARγ does not bind to p65 and was retained in the nucleus after TNF-α treatment. Transgenic mice expressing WT-PPARγ or DN-PPARγ specifically in SMC (S-WT or S-DN) were bred with mice expressing luciferase controlled by an NF-κB-responsive promoter to assess effects on NF-κB activity in whole tissue. TNF-α-induced NF-κB activity was decreased in aorta and carotid artery from S-WT but was increased in vessels from S-DN mice. We conclude that SMC PPARγ blunts expression of proinflammatory genes by inhibition of NF-κB activity through a mechanism promoting nuclear export of p65, which is abolished by DN mutation in PPARγ.

Retinol-binding protein 7 is an endothelium-specific PPAR cofactor mediating an antioxidant response through adiponectin

Impaired PPARγ activity in endothelial cells causes oxidative stress and endothelial dysfunction which causes a predisposition to hypertension, but the identity of key PPARγ target genes that protect the endothelium remain unclear. Retinol-binding protein 7 (RBP7) is a PPARγ target gene that is essentially endothelium specific. Whereas RBP7-deficient mice exhibit normal endothelial function at baseline, they exhibit severe endothelial dysfunction in response to cardiovascular stressors, including high-fat diet and subpressor angiotensin II. Endothelial dysfunction was not due to differences in weight gain, impaired glucose homeostasis, or hepatosteatosis, but occurred through an oxidative stress-dependent mechanism which can be rescued by scavengers of superoxide. RNA sequencing revealed that RBP7 was required to mediate induction of a subset of PPARγ target genes by rosiglitazone in the endothelium including adiponectin. Adiponectin was selectively induced in the endothelium of control mice by high-fat diet and rosiglitazone, whereas RBP7 deficiency abolished this induction. Adiponectin inhibition caused endothelial dysfunction in control vessels, whereas adiponectin treatment of RBP7-deficient vessels improved endothelium-dependent relaxation and reduced oxidative stress. We conclude that RBP7 is required to mediate the protective effects of PPARγ in the endothelium through adiponectin, and RBP7 is an endothelium-specific PPARγ target and regulator of PPARγ activity.

Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke

The consequences of cerebrovascular disease are among the leading health issues worldwide. Large and small cerebral vessel disease can trigger stroke and contribute to the vascular component of other forms of neurological dysfunction and degeneration. Both forms of vascular disease are driven by diverse risk factors, with hypertension as the leading contributor. Despite the importance of neurovascular disease and subsequent injury after ischemic events, fundamental knowledge in these areas lag behind our current understanding of neuroprotection and vascular biology in general. The goal of this review is to address select key structural and functional changes in the vasculature that promote hypoperfusion and ischemia, while also affecting the extent of injury and effectiveness of therapy. In addition, as damage to the blood-brain barrier is one of the major consequences of ischemia, we discuss cellular and molecular mechanisms underlying ischemia-induced changes in blood-brain barrier integrity and function, including alterations in endothelial cells and the contribution of pericytes, immune cells, and matrix metalloproteinases. Identification of cell types, pathways, and molecules that control vascular changes before and after ischemia may result in novel approaches to slow the progression of cerebrovascular disease and lessen both the frequency and impact of ischemic events.

Genetic Regulation of Endothelial Vasomotor Function

The endothelium plays an important role in the regulation of vasomotor tone and the maintenance of vascular integrity. Endothelial dysfunction, i.e., impaired endothelial dependent dilation, is a fundamental component of the pathogenesis of cardiovascular disease. Although endothelial dysfunction is associated with a number of cardiovascular disease risk factors, those risk factors are not the only determinants of endothelial dysfunction. Despite knowing many molecules involved in endothelial signaling pathways, the genetic contribution to endothelial function has yet to be fully elucidated. This mini-review summarizes current evidence supporting the genetic contribution to endothelial vasomotor function. Findings from population-based studies, association studies for candidate genes, and unbiased large genomic scale studies in humans and rodent models are discussed. A brief synopsis of the current studies addressing the genetic regulation of endothelial responses to exercise training is also included.

Adipokine CTRP6 improves PPARγ activation to alleviate angiotensin II-induced hypertension and vascular endothelial dysfunction in spontaneously hypertensive rats

Angiotensin II (AngII) is the most important component of angiotensin, which has been regarded as a major contributor to the incidence of hypertension and vascular endothelial dysfunction. The adipocytokine C1q/TNF-related protein 6 (CTRP6) was recently reported to have multiple protective effects on cardiac and cardiovascular function. However, the exact role of CTRP6 in the progression of AngII induced hypertension and vascular endothelial function remains unclear. Here, we showed that serum CTRP6 content was significantly downregulated in SHRs, accompanied by a marked increase in arterial systolic pressure and serum AngII, CRP and ET-1 content. Then, pcDNA3.1-mediated CTRP6 delivery or CTRP6 siRNA was injected into SHRs. CTRP6 overexpression caused a significant decrease in AngII expression and AngII-mediated hypertension and vascular endothelial inflammation. In contrast, CTRP6 knockdown had the opposite effect to CTRP6 overexpression. Moreover, we found that CTRP6 positively regulated the activation of the ERK1/2 signaling pathway and the expression of peroxisome proliferator-activated receptor γ (PPARγ), a recently proven negative regulator of AngII, in the brain and vascular endothelium of SHRs. Finally, CTRP6 was overexpressed in endothelial cells, and caused a significant increase in PPARγ activation and suppression in AngII-mediated vascular endothelial dysfunction and apoptosis. The effect of that could be rescued by the ERK inhibitor PD98059. In contrast, silencing CTRP6 suppressed PPARγ activation and exacerbated AngII-mediated vascular endothelial dysfunction and apoptosis. In conclusion, CTRP6 improves PPARγ activation and alleviates AngII-induced hypertension and vascular endothelial dysfunction.

Cullin-3 mutation causes arterial stiffness and hypertension through a vascular smooth muscle mechanism

Cullin-3 (CUL3) mutations (CUL3Δ9) were previously identified in hypertensive patients with pseudohypoaldosteronism type-II (PHAII), but the mechanism causing hypertension and whether this is driven by renal tubular or extratubular mechanisms remains unknown. We report that selective expression of CUL3Δ9 in smooth muscle acts by interfering with expression and function of endogenous CUL3, resulting in impaired turnover of the CUL3 substrate RhoA, increased RhoA activity, and augmented RhoA/Rho kinase signaling. This caused vascular dysfunction and increased arterial pressure under baseline conditions and a marked increase in arterial pressure, collagen deposition, and vascular stiffness in response to a subpressor dose of angiotensin II, which did not cause hypertension in control mice. Inhibition of total cullin activity increased the level of CUL3 substrates cyclin E and RhoA, and expression of CUL3Δ9 decreased the level of the active form of endogenous CUL3 in human aortic smooth muscle cells. These data indicate that selective expression of the Cul3Δ9 mutation in vascular smooth muscle phenocopies the hypertension observed in Cul3Δ9 human subjects and suggest that mutations in CUL3 cause human hypertension in part through a mechanism involving smooth muscle dysfunction initiated by a loss of CUL3-mediated degradation of RhoA.