Key role of the NO-pathway and matrix metalloprotease-9 in high blood flow-induced remodeling of rat resistance arteries

Autophagy protein 5 controls flow-dependent endothelial functions

Dysregulated autophagy is associated with cardiovascular and metabolic diseases, where impaired flow-mediated endothelial cell responses promote cardiovascular risk. The mechanism by which the autophagy machinery regulates endothelial functions is complex. We applied multi-omics approaches and in vitro and in vivo functional assays to decipher the diverse roles of autophagy in endothelial cells. We demonstrate that autophagy regulates VEGF-dependent VEGFR signaling and VEGFR-mediated and flow-mediated eNOS activation. Endothelial ATG5 deficiency in vivo results in selective loss of flow-induced vasodilation in mesenteric arteries and kidneys and increased cerebral and renal vascular resistance in vivo. We found a crucial pathophysiological role for autophagy in endothelial cells in flow-mediated outward arterial remodeling, prevention of neointima formation following wire injury, and recovery after myocardial infarction. Together, these findings unravel a fundamental role of autophagy in endothelial function, linking cell proteostasis to mechanosensing.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Sildenafil-Induced Revascularization of Rat Hindlimb Involves Arteriogenesis through PI3K/AKT and eNOS Activation

Hypoxia and inflammation play a major role in revascularization following ischemia. Sildenafil inhibits phosphodiesterase-5, increases intracellular cGMP and induces revascularization through a pathway which remains incompletely understood. Thus, we investigated the effect of sildenafil on post-ischemic revascularization. The left femoral artery was ligated in control and sildenafil-treated (25 mg/kg per day) rats. Vascular density was evaluated and expressed as the left/right leg (L/R) ratio. In control rats, L/R ratio was 33 ± 2% and 54 ± 9%, at 7- and 21-days post-ligation, respectively, and was significantly increased in sildenafil-treated rats to 47 ± 4% and 128 ± 11%, respectively. A neutralizing anti-VEGF antibody significantly decreased vascular density (by 0.48-fold) in control without effect in sildenafil-treated animals. Blood flow and arteriolar density followed the same pattern. In the ischemic leg, HIF-1α and VEGF expression levels increased in control, but not in sildenafil–treated rats, suggesting that sildenafil did not induce angiogenesis. PI3-kinase, Akt and eNOS increased after 7 days, with down-regulation after 21 days. Sildenafil induced outward remodeling or arteriogenesis in mesenteric resistance arteries in association with eNOS protein activation. We conclude that sildenafil treatment increased tissue blood flow and arteriogenesis independently of VEGF, but in association with PI3-kinase, Akt and eNOS activation.

Membrane estrogen receptor alpha (ERα) participates in flow-mediated dilation in a ligand-independent manner

Estrogen receptor alpha (ERα) activation by estrogens prevents atheroma through its nuclear action, whereas plasma membrane-located ERα accelerates endothelial healing. The genetic deficiency of ERα was associated with a reduction in flow-mediated dilation (FMD) in one man. Here, we evaluated ex vivo the role of ERα on FMD of resistance arteries. FMD, but not agonist (acetylcholine, insulin)-mediated dilation, was reduced in male and female mice lacking ERα (Esr1-/- mice) compared to wild-type mice and was not dependent on the presence of estrogens. In C451A-ERα mice lacking membrane ERα, not in mice lacking AF2-dependent nuclear ERα actions, FMD was reduced, and restored by antioxidant treatments. Compared to wild-type mice, isolated perfused kidneys of C451A-ERα mice revealed a decreased flow-mediated nitrate production and an increased H₂O₂ production. Thus, endothelial membrane ERα promotes NO bioavailability through inhibition of oxidative stress and thereby participates in FMD in a ligand-independent manner.

Dual Role of Thrombospondin-1 in Flow-Induced Remodeling

(1) Background: Chronic increases in blood flow, as in cardiovascular diseases, induce outward arterial remodeling. Thrombospondin-1 (TSP-1) is known to interact with matrix proteins and immune cell-surface receptors, but its contribution to flow-mediated remodeling in the microcirculation remains unknown. (2) Methods: Mesenteric arteries were ligated in vivo to generate high- (HF) and normal-flow (NF) arteries in wild-type (WT) and TSP-1-deleted mice (TSP-1-/-). After 7 days, arteries were isolated and studied ex vivo. (3) Results: Chronic increases in blood flow induced outward remodeling in WT mice (increasing diameter from 221 ± 10 to 280 ± 10 µm with 75 mmHg intraluminal pressure) without significant effect in TSP-1-/- (296 ± 18 to 303 ± 14 µm), neutropenic or adoptive bone marrow transfer mice. Four days after ligature, pro inflammatory gene expression levels (CD68, Cox2, Gp91phox, p47phox and p22phox) increased in WT HF arteries but not in TSP-1-/- mice. Perivascular neutrophil accumulation at day 4 was significantly lower in TSP-1-/- than in WT mice. (4) Conclusions: TSP-1 origin is important; indeed, circulating TSP-1 participates in vasodilation, whereas both circulating and tissue TSP-1 are involved in arterial wall thickness and diameter expansion.

Identification of intima-to-media signals for flow-induced vascular remodeling using correlative gene expression analysis

Changes in blood flow can induce arterial remodeling. Intimal cells sense flow and send signals to the media to initiate remodeling. However, the nature of such intima-media signaling is not fully understood. To identify potential signals, New Zealand white rabbits underwent bilateral carotid ligation to increase flow in the basilar artery or sham surgery (n = 2 ligated, n = 2 sham). Flow was measured by transcranial Doppler ultrasonography, vessel geometry was determined by 3D angiography, and hemodynamics were quantified by computational fluid dynamics. 24 h post-surgery, the basilar artery and terminus were embedded for sectioning. Intima and media were separately microdissected from the sections, and whole transcriptomes were obtained by RNA-seq. Correlation analysis of expression across all possible intima-media gene pairs revealed potential remodeling signals. Carotid ligation increased flow in the basilar artery and terminus and caused differential expression of 194 intimal genes and 529 medial genes. 29,777 intima-media gene pairs exhibited correlated expression. 18 intimal genes had > 200 medial correlates and coded for extracellular products. Gene ontology of the medial correlates showed enrichment of organonitrogen metabolism, leukocyte activation/immune response, and secretion/exocytosis processes. This demonstrates correlative expression analysis of intimal and medial genes can reveal novel signals that may regulate flow-induced arterial remodeling.

Organ-on-a-chip systems for vascular biology

Organ-on-a-chip (OOC) platforms involve the miniaturization of cell culture systems and enable a variety of novel experimental approaches. These range from modeling the independent effects of biophysical forces on cells to screening novel drugs in multi-organ microphysiological systems, all within microscale devices. As in living systems, the incorporation of vascular structure is a key feature common to almost all organ-on-a-chip systems. In this review we highlight recent advances in organ-on-a-chip technologies with a focus on the vasculature. We first present the developmental process of the blood vessels through which vascular cells assemble into networks and remodel to form complex vascular beds under flow. We then review self-assembled vascular models and flow systems for the study of vascular development and biology as well as pre-patterned vascular models for the generation of perfusable microvessels for modeling vascular and tissue function. We finally conclude with a perspective on developing future OOC approaches for studying different aspects of vascular biology. We highlight the fit for purpose selection of OOC models towards either simple but powerful testbeds for therapeutic development, or complex vasculature to accurately replicate human physiology for specific disease modeling and tissue regeneration.

Pathophysiological adaptations of resistance arteries in rat offspring exposed in utero to maternal obesity is associated with sex-specific epigenetic alterations

BACKGROUND/OBJECTIVES

Maternal obesity impacts vascular functions linked to metabolic disorders in offspring, leading to cardiovascular diseases during adulthood. Even if the relation between prenatal conditioning of cardiovascular diseases by maternal obesity and vascular function begins to be documented, little is known about resistance arteries. They are of particular interest because of their specific role in the regulation of local blood flow. Then our study aims to determine if maternal obesity can directly program fetal vascular dysfunction of resistance arteries, independently of metabolic disorders.

METHODS

With a model of rats exposed in utero to mild maternal diet-induced obesity (OMO), we investigated third-order mesenteric arteries of 4-month old rats in absence of metabolic disorders. The methylation profile of these vessels was determined by reduced representation bisulfite sequencing (RRBS). Vascular structure and reactivity were investigated using histomorphometry analysis and wire-myography. The metabolic function was evaluated by insulin and glucose tolerance tests, plasma lipid profile, and adipose tissue analysis.

RESULTS

At 4 months of age, small mesenteric arteries of OMO presented specific epigenetic modulations of matrix metalloproteinases (MMPs), collagens, and potassium channels genes in association with an outward remodeling and perturbations in the endothelium-dependent vasodilation pathways (greater contribution of EDHFs pathway in OMO males compared to control rats, and greater implication of PGI₂ in OMO females compared to control rats). These vascular modifications were detected in absence of metabolic disorders.

CONCLUSIONS

Our study reports a specific methylation profile of resistance arteries associated with vascular remodeling and vasodilation balance perturbations in offspring exposed in utero to maternal obesity, in absence of metabolic dysfunctions.

Kinetics of Postpartum Mesenteric Artery Structure and Function Relative to Pregnancy and Lactation in Mice

Epidemiological evidence suggests that normal pregnancy in women is associated with decreased cardiovascular risk in later life. Clinical studies have provided evidence that alterations in vascular function and structure are detectable long after delivery. To understand these findings, we examined mesenteric artery reactivity at both early (3 days and 2–4 weeks) and late (12 weeks) postpartum (PP) time points in relation to late pregnancy (LP) and lactation. Vessels from virgin controls, LP, PP, and nursing and non-nursing mothers were tested for responses to phenylephrine (PE), high potassium solutions (high K⁺), and acetylcholine (ACh). Passive arterial distensibility, vessel dimensions, and collagen and elastin content were evaluated for the studied groups. We observed that (1) there was a significant inhibition of vascular reactivity to PE in LP, 3 days and 2 weeks PP vessels that returned to pre-pregnancy levels at 4 and 12 weeks PP; (2) inhibition of NO production in PP vessels restored PE-induced constriction to pre-pregnancy levels; (3) vasodilator responses to ACh were similar at all PP periods; (4) LP and early PP was associated with a persistent increase in arterial distensibility that correlates with a PP-induced reduction in wall collagen, and regressed to pre-conception levels at 12 weeks PP; (5) vessels from non-nursing PP mice demonstrated an increased PE reactivity, diminished responses to ACh, and reduced distensibility compared to breastfeeding mice. These studies provide a timeframe for mesenteric artery adaptations that occur during pregnancy and extend to the PP period, but which may be modified by PP events.

Flow-mediated outward arterial remodeling in aging

The present review focuses on the effect of aging on flow-mediated outward remodeling (FMR) via alterations in estrogen metabolism, oxidative stress and inflammation. In ischemic disorders, the ability of the vasculature to adapt or remodel determines the quality of the recovery. FMR, which has a key role in revascularization, is a complex phenomenon that recruits endothelial and smooth muscle cells as well as the immune system. FMR becomes progressively less with age as a result of an increase in inflammation and oxidative stress, in part of mitochondrial origin. The alteration in FMR is greater in older individuals with risk factors and thus the therapy cannot merely amount to exercise with or without a mild vasodilating drug. Interestingly, the reduction in FMR occurs later in females. Estrogen and its alpha receptor (ERα) play a key role in FMR through the control of dilatory pathways including the angiotensin II type 2 receptor, thus providing possible tools to activate FMR in older subjects although only experimental data is available. Indeed, the main issue is the reversibility of the vascular damage induced over time, and to date promoting prevention and limiting exposure to the risk factors remain the best options in this regard.

Estrogens and the Angiotensin II Type 2 Receptor Control Flow-Mediated Outward Remodeling in the Female Mouse Mesenteric Artery

Flow-mediated outward remodeling (FMR) is involved in postischemic revascularization. Angiotensin II type 2 receptor (AT2R), through activation of T-cell-mediated IL-17 production, and estrogens are involved in FMR. Thus, we investigated the interplay between estrogens and AT2R in FMR using a model of ligation of feed arteries supplying collateral pathways in mouse mesenteric arteries in vivo. Arteries were collected after 2 (inflammatory phase), 4 (diameter expansion phase), and 7 days (remodeling completed). We used AT2R+/+ and AT2R-/- ovariectomized (OVX) female mice treated or not with 17-beta-estradiol (E2). Seven days after ligation, arterial diameter was larger in high flow (HF) compared to normal flow (NF) arteries. FMR was absent in OVX mice and restored by E2. AT2R gene expression was higher in HF than in NF arteries only in E2-treated OVX AT2R+/+ mice. CD11b and TNF alpha levels (inflammatory phase), MMP2 and TIMP1 (extracellular matrix digestion), and NOS3 (diameter expansion phase) expression levels were higher in HF than in NF arteries only in E2-treated AT2R+/+ mice, not in the other groups. Thus, E2 is necessary for AT2R-dependent diameter expansion, possibly through activation of T-cell AT2R, in arteries submitted chronically to high blood flow.

Carotid artery plaque composition and distribution: near-infrared spectroscopy and intravascular ultrasound analysis

Most atherosclerotic plaques (APs) form in typical predilection areas of low endothelial shear stress (ESS). On the contrary, previous data hinted that plaques rupture in their proximal parts where accelerated blood flow causes high ESS. It was postulated that high ESS plays an important role in the latter stages of AP formation and in its destabilization. Here, we used near-infrared spectroscopy (NIRS) to analyse the distribution of lipid core based on the presumed exposure to ESS. A total of 117 carotid arteries were evaluated using NIRS and intravascular ultrasound (IVUS) prior to carotid artery stenting. The point of minimal luminal area (MLA) was determined using IVUS. A stepwise analysis of the presence of lipid core was then performed using NIRS. The lipid core presence was quantified as the lipid core burden index (LCBI) within 2 mm wide segments both proximally and distally to the MLA. The analysed vessel was then divided into three 20 mm long thirds (proximal, middle, and distal) for further analysis. The maximal value of LCBI (231.9 ± 245.7) was noted in the segment localized just 2 mm proximally to MLA. The mean LCBI in the middle third was significantly higher than both the proximal (121.4 ± 185.6 vs. 47.0 ± 96.5, P < 0.01) and distal regions (121.4 ± 185.6 vs. 32.4 ± 89.6, P < 0.01). Lipid core was more common in the proximal region when compared with the distal region (mean LCBI 47.0 ± 96.5 vs. 32.4 ± 89.6, P < 0.01).

Hyperglycemia-induced transcriptional regulation of ROCK1 and TGM2 expression is involved in small artery remodeling in obese diabetic Göttingen Minipigs

Obesity and diabetes in humans are associated with hypertrophic remodeling and increased media:lumen ratio of small resistance arteries, which is an independent predictor of cardiovascular events. In order to minimize increases in media:lumen ratio, hypertrophic remodeling should be accompanied by outward remodeling. We aimed to investigate the mechanisms of structural remodeling in small pial arteries (PAs) and terminal mesenteric arteries (TMAs) from obese Göttingen Minipigs with or without diabetes. Göttingen Minipigs received either control diet (lean control (LC)), high fat/high fructose/high cholesterol diet (FFC), or FFC diet with streptozotocin (STZ)-induced diabetes (FFC/STZ) for 13 months. At the end of the study (20 months), we assessed body weight, fasting plasma biochemistry, passive vessel dimensions, mRNA expression (matrix metallopeptidases 2/9 (MMP2, MMP9), tissue inhibitor of metallopeptidase 1 (TIMP1), transglutaminase 2 (TGM2), Rho-kinase 1 (ROCK1), TGFβ-receptor 2 (TGFBR2), and IGF1-receptor (IGFR1) genes), and immunofluorescence in PAs and TMAs. We performed multiple linear correlation analyses using plasma values, structural data, and gene expression data. We detected outward hypertrophic remodeling in TMAs and hypertrophic remodeling in PAs from FFC/STZ animals. ROCK1 and TGM2 genes were up-regulated in PAs and TMAs from the FFC/STZ group. Passive lumen diameter (PLD) of TMAs was correlated with plasma values of glucose (GLU), fructosamine (FRA), total cholesterol (TC), and triglycerides (TGs). ROCK1 and TGM2 expressions in TMAs were correlated with PLD, plasma GLU, fructosamine, and TC. ROCK1 and TGM2 proteins were immunolocalized in the media of PAs and TMAs, and their fluorescence levels were increased in the FFC/STZ group. Hyperglycemia/hyperlipidemia is involved in regulation of ROCK1 and TGM2 expression leading to outward remodeling of small resistance arteries in obese diabetic Göttingen Minipigs.

The Impact of Estrogen Receptor in Arterial and Lymphatic Vascular Diseases

The lower incidence of cardiovascular diseases in pre-menopausal women compared to men is well-known documented. This protection has been largely attributed to the protective effect of estrogens, which exert many beneficial effects against arterial diseases, including vasodilatation, acceleration of healing in response to arterial injury, arterial collateral growth and atheroprotection. More recently, with the visualization of the lymphatic vessels, the impact of estrogens on lymphedema and lymphatic diseases started to be elucidated. These estrogenic effects are mediated not only by the classic nuclear/genomic actions via the specific estrogen receptor (ER) α and β, but also by rapid extra-nuclear membrane-initiated steroid signaling (MISS). The ERs are expressed by endothelial, lymphatic and smooth muscle cells in the different vessels. In this review, we will summarize the complex vascular effects of estrogens and selective estrogen receptor modulators (SERMs) that have been described using different transgenic mouse models with selective loss of ERα function and numerous animal models of vascular and lymphatic diseases.

Influence of Estrogens on Uterine Vascular Adaptation in Normal and Preeclamptic Pregnancies

During pregnancy, the maternal cardiovascular system undergoes significant changes, including increased heart rate, cardiac output, plasma volume, and uteroplacental blood flow (UPBF) that are required for a successful pregnancy outcome. The increased UPBF is secondary to profound circumferential growth that extends from the downstream small spiral arteries to the upstream conduit main uterine artery. Although some of the mechanisms underlying uterine vascular remodeling are, in part, known, the factors that drive the remodeling are less clear. That higher circulating levels of estrogens are positively correlated with gestational uterine vascular remodeling suggests their involvement in this process. Estrogens binding to the estrogen receptors expressed in cytotrophoblast cells and in the uterine artery wall stimulate an outward hypertrophic remodeling of uterine vasculature. In preeclampsia, generally lower concentrations of estrogens limit the proper uterine remodeling, thereby reducing UPBF increases and restricting the growth of the fetus. This review aims to report estrogenic regulation of the maternal uterine circulatory adaptation in physiological and pathological pregnancy that favors vasodilation, and to consider the underlying molecular mechanisms by which estrogens regulate uteroplacental hemodynamics.

Nuclear Activation Function 2 Estrogen Receptor α Attenuates Arterial and Renal Alterations Due to Aging and Hypertension in Female Mice

Background

The cardiovascular protective effects of estrogens in premenopausal women depend mainly on estrogen receptor α (ERα). ERα activates nuclear gene transcription regulation and membrane‐initiated signaling. The latter plays a key role in estrogen‐dependent activation of endothelial NO synthase. The goal of the present work was to determine the respective roles of the 2 ERα activities in endothelial function and cardiac and kidney damage in young and old female mice with hypertension, which is a major risk factor in postmenopausal women.

Methods and Results

Five‐ and 18‐month‐old female mice lacking either ERα (ERα^−/−), the nuclear activating function AF2 of ERα (AF2°), or membrane‐located ERα (C451A) were treated with angiotensin II (0.5 mg/kg per day) for 1 month. Systolic blood pressure, left ventricle weight, vascular reactivity, and kidney function were then assessed. Angiotensin II increased systolic blood pressure, ventricle weight, and vascular contractility in ERα^−/− and AF2° mice more than in wild‐type and C451A mice, independent of age. In both the aorta and mesenteric resistance arteries, angiotensin II and aging reduced endothelium‐dependent relaxation in all groups, but this effect was more pronounced in ERα^−/− and AF2° than in the wild‐type and C451A mice. Kidney inflammation and oxidative stress, as well as blood urea and creatinine levels, were also more pronounced in old hypertensive ERα^−/− and AF2° than in old hypertensive wild‐type and C451A mice.

Conclusions

The nuclear ERα‐AF2 dependent function attenuates angiotensin II–dependent hypertension and protects target organs in aging mice, whereas membrane ERα signaling does not seem to play a role.

Shear Stress Attenuates Inward Remodeling in Cultured Mouse Thoracodorsal Arteries in an eNOS-Dependent, but Not Hemodynamic Manner, and Increases Cx37 Expression

BACKGROUND

Arteries chronically constricted in culture remodel to smaller diameters. Conversely, elevated luminal shear stress (SS) promotes outward remodeling of arteries in vivo and prevents inward remodeling in culture in a nitric oxide synthase (NOS)-dependent manner.

OBJECTIVES

To determine whether SS-induced prevention of inward remodeling in cultured arteries is specifically eNOS-dependent and requires dilation, and whether SS alters the expression of eNOS and other genes potentially involved in remodeling.

METHODS

Female mouse thoracodorsal arteries were cannulated, pressurized to 80 mm Hg, and cultured for 2 days with low SS (<7 dyn/cm2), high SS (≥15 dyn/cm2), high SS + L-NAME (NOS inhibitor, 10-4 M), or high SS in arteries from eNOS-/- mice. In separate arteries cultured 1 day with low or high SS, eNOS and connexin (Cx) 37, Cx40, and Cx43 mRNA were assessed with real-time PCR.

RESULTS

High SS caused little change in passive diameters after culture (-4.7 ± 2.0%), which was less than low SS (-18.9 ± 1.4%; p < 0.0001), high SS eNOS-/- (-18.0 ± 1.5; p < 0.001), or high SS + L-NAME (-12.0 ± 0.6%; nonsignificant) despite similar constriction during culture. Cx37 mRNA expression was increased (p < 0.05) with high SS, but other gene levels were not different.

CONCLUSIONS

eNOS is involved in SS-induced prevention of inward remodeling in cultured small arteries. This effect does not require NO-mediated dilation. SS increased Cx37.

High shear stress on the coronary arterial wall is related to computed tomography-derived high-risk plaque: a three-dimensional computed tomography and color-coded tissue-characterizing intravascular ultrasonography study

Low wall shear stress (WSS) is associated with plaque formation. However, the relationship between WSS and coronary plaque vulnerability remains unclear. Therefore, this study aimed to clarify the in vivo relationship between luminal WSS derived from three-dimensional (3D) computed tomography (CT) and plaque vulnerability within the coronary artery. Forty-three consecutive patients with ischemic heart disease and coronary stenotic lesions were enrolled and underwent coronary angiography and color-coded intravascular ultrasonography (iMap™) followed by multi-slice coronary CT angiography. CT-derived high-risk plaque was defined by specific CT characteristics, including low CT intensity (< 30 HU) and positive remodeling. The Student's t test, Mann-Whitney U test, χ² test, repeated measures analysis of variance, and logistic and multiple regression were used for statistical analyses. CT-derived high-risk plaque (n = 15) had higher values of maximum and average shear stress than CT-derived stable plaque (474 ± 453 vs. 158 ± 138 Pa, p = 0.018; 4.2 ± 3.1 vs. 1.6 ± 1.2 Pa, p = 0.007, respectively). Compared with patients with CT-derived stable plaque, those with CT-derived high-risk plaque had a higher prevalence of necrotic and lipidic characteristics (44 ± 13 vs. 31 ± 11%, p = 0.001) based on iMap™. Multivariate logistic regression analysis showed that the average WSS and necrotic plus lipidic content were independent determinants of CT-derived high-risk plaque (average WSS: odds ratio 2.996, p = 0.014; necrotic plus lipidic content: odds ratio 1.306, p = 0.036). Our findings suggested that CT-derived high-risk plaque may coexist with high shear stress on the plaque surface.

Netrin-1 plays a role in the effect of moderate exercise on myocardial fibrosis in rats

INTRODUCTION

This study aimed to investigate the effect of aerobic exercise on the expression of neitrin-1,DCC receptor and myocardial fibrosis in rats with acute myocardial infarction.

METHODS

Twenty-four rats were randomly divided into three groups: the sham group (n = 8), the acute myocardial infarction (AMI) model group (n = 8), and the aerobic exercise treatment after acute myocardial infarction group (ET) (n = 8). After 10 weeks, the serum levels of netrin-1, tumor necrosis factor alpha α (TNF-α), and interleukin 6 (IL-6) were measured. The expression of matrix metalloproteinase 2 and 9 (MMP2, 9), and their inhibitor, tissue inhibitor of metalloproteinase 2 (TIMP2), myocardial netrin-1, and the deleted in colorectal cancer (DCC) receptor were evaluated. Histopathological results were also evaluated. The collagen volume fraction of the myocardial tissues was also calculated.

RESULTS

Compared with the sham group, in the AMI and ET groups, left ventricular end diastolic pressure (LVEDP) were increased, while left ventricular systolic pressure (LVSP), and left ventricular pressure maximal rate of rise and fall (± dp/dtmax) were significantly decreased (P<0.05,). Compared with the AMI group, in the ET group, LVSP, and ±dp/dtmax were significantly increased while LVEDP was decreased (P<0.05). Compared with the sham group, the AMI group and ET groups showed increased levels of serum TNF-α, IL-6 and significantly reduced levels of netrin-1. Levels of TNF-α and IL-6 were significantly reduced in the ET group compared with the AMI group, whereas the level of netrin-1 was increased. The expression of myocardial MMP2 and MMP9 was significantly increased in the AMI group compared with the sham group, whereas that of myocardial netrin-1, TIMP2 and the DCC receptor, was significantly reduced. Compared with the AMI group, the ET group showed reduced expression of myocardial MMP2 and MMP9 proteins, whereas expression of myocardial netrin-1, TIMP2 and the DCC receptor, was significantly increased. The collagen volume fraction of the myocardial tissues was significantly increased in the AMI group and the ET group compared with the sham group, with a greater increase in the AMI group.

CONCLUSIONS

Aerobic exercise increased levels of serum netrin-1, myocardial netrin-1, and the DCC receptor and reduced the expression of myocardial MMP2 and MMP9 proteins, to improve the degree of fibrosis following myocardial infarction in rats.

Lack of tone in mouse small mesenteric arteries leads to outward remodeling, which can be prevented by prolonged agonist-induced vasoconstriction

Inward remodeling of resistance vessels is an independent risk factor for cardiovascular events. Thus far, the remodeling process remains incompletely elucidated, but the activation level of the vascular smooth muscle cell appears to play a central role. Accordingly, previous data have suggested that an antagonistic and supposedly beneficial response, outward remodeling, may follow prolonged vasodilatation. The present study aimed to determine whether 1) outward remodeling follows 3 days of vessel culture without tone, 2) a similar response can be elicited in a much shorter 4-h timeframe, and, finally, 3) whether a 4-h response can be prevented or reversed by the presence of vasoconstrictors in the medium. Cannulated mouse small mesenteric arteries were organocultured for 3 days in the absence of tone, leading to outward remodeling that continued throughout the culture period. In more acute experiments in which cannulated small mesenteric arteries were maintained in physiological saline without tone for 4 h, we detected a similar outward remodeling that proceeded at a rate several times faster. In the 4-h experimental setting, continuous vasoconstriction to ~50% tone by abluminal application of UTP or norepinephrine + neuropeptide Y prevented outward remodeling but did not cause inward remodeling. Computational modeling was used to simulate and interpret these findings and to derive time constants of the remodeling processes. It is suggested that depriving resistance arteries of activation will lead to eutrophic outward remodeling, which can be prevented by vascular smooth muscle cell activation induced by prolonged vasoconstrictor exposure. NEW & NOTEWORTHY We have established an effective 4-h method for studying outward remodeling in pressurized mouse resistance vessels ex vivo and have determined conditions that block the remodeling response. This allows for investigating the subtle but clinically highly relevant phenomenon of outward remodeling while avoiding both laborious 3-day organoid culture of cannulated vessels and in vivo experiments lasting several weeks.

Endothelial glycocalyx as a critical signalling platform integrating the extracellular haemodynamic forces and chemical signalling

The glycocalyx covers the human mammalian cells and plays important roles in stroke, inflammation and atherosclerosis. It has also been shown to be involved in endothelial mechanotransduction of shear stress. Shear stress induces the remodelling of the major component of the glycocalyx including glypican‐1, a cell membrane heparan sulphate proteoglycan. Other factors, such as sphingosine‐1‐phosphate (S1P), protect the glycocalyx against syndecan‐1 ectodomain shedding and induce the synthesis of heparan sulphate. In this study, we reviewed the role of shear stress and S1P in glycocalyx remodelling and revealed that the glycocalyx is a critical signalling platform, integrating the extracellular haemodynamic forces and chemical signalling, such as S1P, for determining the fate of endothelial cells and vascular diseases. This review integrated our current understanding of the structure and function of the glycocalyx and provided new insight into the role of the glycocalyx that might be helpful for investigating the underlying biological mechanisms in certain human diseases, such as atherosclerosis.

High pressure–low flow remodeling of the rat saphenous vein wall

Objective

To better understand factors that may play a role in the development of varicosities.

Methods

We induced combined flow-pressure disturbance in the saphenous system of the rat by performing chronic partial clipping of the main branch. Biomechanical and quantitative histological testing was undertaken.

Results

A rich microvenous network developed. Bloodflow decreased to 0.65 ± 0.18 µl/s (control side, 3.5 ± 1.4 µl/s) and pressure elevated to 6.8 ± 0.7 mmHg (control side, 2.3 ± 0.2 mmHg, p < 0.05). Involution of the wall and lumen was observed (16.5%, 28.7% and 35.5% reduction in outer diameter, wall thickness and wall mass respectively, p < 0.05). Elevated macrophage (CD68) and cell division (Ki67) activity was observed. Elastic tissue and smooth muscle actin became less concentrated in the inner medial layers.

Conclusions

Low-flow induced morphological shrinking of the lumen in veins may override pressure-induced morphological distension. Loosening of the force-bearing elements during flow-induced wall remodeling may be an important pathological component in varicosity.

PI16 is a shear stress and inflammation-regulated inhibitor of MMP2

Raised endothelial shear stress is protective against atherosclerosis but such protection may be lost at sites of inflammation. We found that four splice variants of the peptidase inhibitor 16 (PI16) mRNA are among the most highly shear stress regulated transcripts in human coronary artery endothelial cells (HCAECs), in vitro but that expression is reduced by inflammatory mediators TNFα and IL-1β. Immunohistochemistry demonstrated that PI16 is expressed in human coronary endothelium and in a subset of neointimal cells and medial smooth muscle cells. Adenovirus-mediated PI16 overexpression inhibits HCAEC migration and secreted matrix metalloproteinase (MMP) activity. Moreover, PI16 inhibits MMP2 in part by binding an exposed peptide loop above the active site. Our results imply that, at high endothelial shear stress, PI16 contributes to inhibition of protease activity; protection that can be reversed during inflammation.

High shear stress induces atherosclerotic vulnerable plaque formation through angiogenesis

Rupture of atherosclerotic plaques causing thrombosis is the main cause of acute coronary syndrome and ischemic strokes. Inhibition of thrombosis is one of the important tasks developing biomedical materials such as intravascular stents and vascular grafts. Shear stress (SS) influences the formation and development of atherosclerosis. The current review focuses on the vulnerable plaques observed in the high shear stress (HSS) regions, which localizes at the proximal region of the plaque intruding into the lumen. The vascular outward remodelling occurs in the HSS region for vascular compensation and that angiogenesis is a critical factor for HSS which induces atherosclerotic vulnerable plaque formation. These results greatly challenge the established belief that low shear stress is important for expansive remodelling, which provides a new perspective for preventing the transition of stable plaques to high-risk atherosclerotic lesions.

Biomechanics of vascular mechanosensation and remodeling

Flowing blood exerts a frictional force, fluid shear stress (FSS), on the endothelial cells that line the blood and lymphatic vessels. The magnitude, pulsatility, and directional characteristics of FSS are constantly sensed by the endothelium. Sustained increases or decreases in FSS induce vessel remodeling to maintain proper perfusion of tissue. In this review, we discuss these mechanisms and their relevance to physiology and disease, and propose a model for how information from different mechanosensors might be integrated to govern remodeling.

The angiotensin II type 2 receptor activates flow-mediated outward remodelling through T cells-dependent interleukin-17 production

AIMS

The angiotensin II type 1 receptor (AT1R) through the activation of immune cells plays a key role in arterial inward remodelling and reduced blood flow in cardiovascular disorders. On the other side, flow (shear stress)-mediated outward remodelling (FMR), involved in collateral arteries growth in ischaemic diseases, allows revascularization. We hypothesized that the type 2 receptor (AT2R), described as opposing the effects of AT1R, could be involved in FMR.

METHODS AND RESULTS

We studied FMR using a model of ligation of feed arteries supplying collateral pathways in the mouse mesenteric arterial bed in vivo. Seven days after ligation, diameter increased by 30% in high flow (HF) arteries compared with normal flow vessels. FMR was absent in mice lacking AT2R. At Day 2, T lymphocytes expressing AT2R were present preferentially around HF arteries. FMR did not occur in athymic (nude) mice lacking T cells and in mice treated with anti-CD3ε antibodies. AT2R activation induced interleukin-17 production by memory T cells. Treatment of nude mice or AT2R-deficient mice with interleukin-17 restored diameter enlargement in HF arteries. Interleukin-17 increased NO-dependent relaxation and matrix metalloproteinases activity, both important in FMR. Remodelling of feeding arteries in the skin flap model of ischaemia was also absent in AT2R-deficient mice and in anti-interleukin-17-treated mice. Finally, remodelling, absent in 12-month-old mice, was restored by a treatment with the AT2R non-peptidic agonist C21.

CONCLUSION

AT2R-dependent interleukin-17 production by T lymphocyte is necessary for collateral artery growth and could represent a new therapeutic target in ischaemic disorders.

Genetic Associations of Primary Angle-Closure Disease: A Systematic Review and Meta-analysis

TOPIC

Systematic review and meta-analysis of the genetic associations of primary angle-closure disease (PACD).

CLINICAL RELEVANCE

To confirm the genetic biomarkers for PACD, including primary angle-closure glaucoma (PACG) and related phenotypes.

METHODS

We searched in the MEDLINE and EMBASE databases for genetic studies of PACG or other PACD published from the start dates of the databases to May 11, 2015. We estimated the summary odds ratios (ORs) and 95% confidence intervals (CIs) for each polymorphism in PACG, primary angle-closure suspect (PACS), and primary angle-closure (PAC) using fixed- or random-effect models. We also performed sensitivity analysis to test the robustness of the results.

RESULTS

Our literature search yielded 6463 reports. Among them, we identified 24 studies that fulfilled the eligibility criteria for meta-analysis, involving 28 polymorphisms in 11 genes/loci. We affirmed the association of PACG and combined PACS/PAC/PACG with 10 polymorphisms in 8 genes/loci, including COL11A1 (rs3753841-G, OR, 1.22; P = 0.00046), HGF (rs17427817-C, OR, 2.02; P = 6.9E-07; rs5745718-A, OR, 2.11; P = 9.9E-07), HSP70 (rs1043618, GG+GC, OR, 0.52; P = 0.0010), MFRP (rs2510143-C, OR, 0.66; P = 0.012; rs3814762-G, OR, 1.40; P = 0.0090), MMP9 (rs3918249-C, OR, 1.35; P = 0.034), NOS3 (rs7830-A, OR, 0.80; P = 0.036), PLEKHA7 (rs11024102-G, OR, 1.24; P = 8.3E-05), and PCMTD1-ST18 (rs1015213-A, OR, 1.59; P = 0.00013). Sensitivity analysis indicated that the results were robust.

CONCLUSIONS

In this study, we confirmed multiple polymorphisms in 8 genes/loci as genetic biomarkers for PACD, among which 3 were identified in a genome-wide association study (COL11A1, PLEKHA7, and PCMTD1-ST18), and 5 were identified in candidate gene studies (HGF, HSP70, MFRP, MMP9, and NOS3).

Resveratrol Improved Flow-Mediated Outward Arterial Remodeling in Ovariectomized Rats with Hypertrophic Effect at High Dose

Objectives

Chronic increases in blood flow in resistance arteries induce outward remodeling associated with increased wall thickness and endothelium-mediated dilatation. This remodeling is essential for collateral arteries growth following occlusion of a large artery. As estrogens have a major role in this remodeling, we hypothesized that resveratrol, described as possessing phytoestrogen properties, could improve remodeling in ovariectomized rats.

Methods

Blood flow was increased in vivo in mesenteric arteries after ligation of adjacent arteries in 3-month old ovariectomized rats treated with resveratrol (5 or 37.5 mg/kg per day: RESV5 or RESV37.5) or vehicle. After 2 weeks arterial structure and function were measured in vitro in high flow (HF) and normal flow (NF) arteries isolated from each rat.

Results

Arterial diameter was greater in HF than in NF arteries in ovariectomized rats treated with RESV5 or RESV37.5, not in vehicle-treated rats. In mice lacking estrogen receptor alpha diameter was equivalent in HF and NF arteries whereas in mice treated with RESV5 diameter was greater in HF than in NF vessels. A compensatory increase in wall thickness and a greater phenylephrine-mediated contraction were observed in HF arteries. This was more pronounced in HF arteries from RESV37.5-treated rats. ERK1/2 phosphorylation, involved in hypertrophy and contraction, were higher in RESV37.5-treated rats than in RESV5- and vehicle-treated rats. Endothelium-dependent relaxation was greater in HF than in NF arteries in RESV5-treated rats only. In HF arteries from RESV37.5-treated rats relaxation was increased by superoxide reduction and markers of oxidative stress (p67phox, GP91phox) were higher than in the 2 other groups.

Conclusion

Resveratrol improved flow-mediated outward remodeling in ovariectomized rats thus providing a potential therapeutic tool in menopause-associated ischemic disorders. This effect seems independent of the estrogen receptor alpha. Nevertheless, caution should be taken with high doses inducing excessive contractility and hypertrophy in association with oxidative stress in HF arteries.

Arterial stiffness is associated with adipokine dysregulation in non-hypertensive obese mice

The aim of this study was to characterize alterations in vascular structure and mechanics in murine mesenteric arteries from obese non-hypertensive mice, as well as their relationship with adipokines. Four-week old C57BL/6J male mice were assigned either to a control (C, 10% kcal from fat) or a high-fat diet (HFD, 45% kcal from fat) for 32weeks. HFD animals weighed 30% more than controls (p<0.001), exhibited similar blood pressure, increased leptin, insulin and superoxide anion (O2(-)) levels, and reduced adiponectin levels and nitric oxide (NO) bioavailability. Arterial structure showed an outward remodeling with an increase in total number of both adventitial and smooth muscle cells in HFD. Moreover, HFD mice exhibited an increased arterial stiffness assessed by β-values (C=2.4±0.5 vs HFD=5.3±0.8; p<0.05) and aortic pulse wave velocity (PWV, C=3.4±0.1 vs HFD=3.9±0.1; p<0.05). β-Values and PWV positively correlated with leptin, insulin or O2(-) levels, whereas they negatively correlated with adiponectin levels and NO bioavailability (p<0.01). A reduction in fenestrae number together with an increase in type-I collagen amount (p<0.05) were observed in HFD. These data demonstrate that HFD accounts for the development of vascular remodeling and arterial stiffness associated with adipokine dysregulation and oxidative stress, independently of hypertension development.

Mechanisms of the inward remodeling process in resistance vessels: is the actin cytoskeleton involved?

The resistance arteries and arterioles are the vascular components of the circulatory system where the greatest drop in blood pressure takes place. Consequently, these vessels play a preponderant role in the regulation of blood flow and the modulation of blood pressure. For this reason, the inward remodeling process of the resistance vasculature, as it occurs in hypertension, has profound consequences on the incidence of life-threatening cardiovascular events. In this manuscript, we review some of the most prominent characteristics of inwardly remodeled resistance arteries including their changes in vascular passive diameter, wall thickness, and elastic properties. Then, we explore the known contribution of the different components of the vascular wall to the characteristics of inwardly remodeled vessels, and pay particular attention to the role the vascular smooth muscle actin cytoskeleton may play on the initial stages of the remodeling process. We end by proposing potential ways by which many of the factors and mechanisms known to participate in the inward remodeling process may be associated with cytoskeletal modifications and participate in reducing the passive diameter of resistance vessels.

Central Pulse Pressure and Variability in Matrix Metalloproteinases Genes and Their Inhibitors in Patients With Ischemic Heart Disease

Matrix metalloproteinases (MMPs) as well as their inhibitors (TIMPs) play a crucial role in controlling extracellular matrix turnover and have recently been associated with atherosclerosis, myocardial and vascular injury. Moreover, the genetic variability of MMP genes has been suggested to play an important role in vascular remodeling and age-related arterial stiffening. This study aims to describe associations of 14 selected polymorphisms in genes for MMPs and TIMPs with selected cardiovascular parameters (including central pulse pressure), clinical conditions and drug treatment profiles in 411 stable ischemic patients with preserved systolic function of the left ventricle. The genotyping of 14 single-nucleotide polymorphisms in 8 genes was carried out either using 5′ exonuclease (TaqMan®) reagents or by restriction analysis. Numerous associations of the investigated polymorphisms with systolic and diastolic blood pressure, maximum left ventricular end diastolic pressure and ejection fraction were observed. While some of the observed effects were found to be age-dependent, associations with clinical conditions (hypertension, diabetes mellitus, angina pectoris) were only observed in women and associations with four groups of drugs (statins, nitrates, calcium channel blockers, anti-aggregation drugs) were only observed in men. The results of this study indicate that the genetic variability of MMPs and TIMPs is an important factor which influences cardiovascular functions and may have important consequences for individual therapy customization in the future.

How do we prevent the vulnerable atherosclerotic plaque from rupturing? Insights from in vivo assessments of plaque, vascular remodeling, and local endothelial shear stress

Coronary atherosclerosis progresses both as slow, gradual enlargement of focal plaque and also as a more dynamic process with periodic abrupt changes in plaque geometry, size, and morphology. Systemic vasculoprotective therapies such as statins, angiotensin-converting enzyme inhibitors, and antiplatelet agents are the cornerstone of prevention of plaque rupture and new adverse clinical outcomes, but such systemic therapies are insufficient to prevent the majority of new cardiac events. Invasive imaging methods have been able to identify both the anatomic features of high-risk plaque and the ongoing pathobiological stimuli responsible for progressive plaque inflammation and instability and may provide sufficient information to formulate preventive local mechanical strategies (eg, preemptive percutaneous coronary interventions) to avert cardiac events. Local endothelial shear stress (ESS) triggers vascular phenomena that synergistically exacerbate atherosclerosis toward an unstable phenotype. Specifically, low ESS augments lipid uptake and catabolism, induces plaque inflammation and oxidation, downregulates the production, upregulates the degradation of extracellular matrix, and increases cellular apoptosis ultimately leading to thin-cap fibroatheromas and/or endothelial erosions. Increases in blood thrombogenicity that result from either high or low ESS also contribute to plaque destabilization. An understanding of the actively evolving vascular phenomena, as well as the development of in vivo imaging methodologies to identify the presence and severity of the different processes, may enable early identification of a coronary plaque destined to acquire a high-risk state and allow for highly selective, focal preventive interventions to avert the adverse natural history of that particular plaque. In this review, we focus on the role of ESS in the pathobiologic processes responsible for plaque destabilization, leading either to accelerated plaque growth or to acute coronary events, and emphasize the potential to utilize in vivo risk stratification of individual coronary plaques to optimize prevention strategies to preclude new cardiac events.

Maternal uterine vascular remodeling during pregnancy

Remodeling of the maternal uterine vasculature during pregnancy is a unique cardiovascular process that occurs in the adult and results in significant structural and functional changes in large and small arteries and veins, and in the creation of the placenta--a new fetomaternal vascular organ. This expansive, hypertrophic process results in increases in both lumen circumference and length, and is effected through a combination of tissue and cellular hypertrophy, endothelial and vascular smooth muscle hyperplasia, and matrix remodeling. This review summarizes what is currently known about the time course and extent of the remodeling process, and how local vs. systemic factors influence its genesis. The main focus is on upstream maternal vessels rather than spiral artery changes, although the latter are considered from the overall hemodynamic perspective. We also consider some of the underlying mechanisms and provide a hypothetical scenario that integrates our current knowledge. Abrogation of this adaptive vascular process is associated with several human gestational pathologies such as preeclampsia and intrauterine growth restriction (IUGR), which not only raise the risk of infant mortality and morbidity but are also a significant source of maternal mortality and susceptibility to cardiovascular and other diseases for both mother and neonate later in life.

Role of estrogens and age in flow-mediated outward remodeling of rat mesenteric resistance arteries

In resistance arteries, a chronic increase in blood flow induces hypertrophic outward remodeling. This flow-mediated remodeling (FMR) is absent in male rats aged 10 mo and more. As FMR depends on estrogens in 3-mo-old female rats, we hypothesized that it might be preserved in 12-mo-old female rats. Blood flow was increased in vivo in mesenteric resistance arteries after ligation of the side arteries in 3- and 12-mo-old male and female rats. After 2 wk, high-flow (HF) and normal-flow (NF) arteries were isolated for in vitro analysis. Arterial diameter and cross-sectional area increased in HF arteries compared with NF arteries in 3-mo-old male and female rats. In 12-mo-old rats, diameter increased only in female rats. Endothelial nitric oxide synthase expression and endothelium-mediated relaxation were higher in HF arteries than in NF arteries in all groups. ERK1/2 phosphorylation, NADPH oxidase subunit expression levels, and arterial contractility to KCl and to phenylephrine were greater in HF vessels than in NF vessels in 12-mo-old male rats only. Ovariectomy in 12-mo-old female rats induced a similar pattern with an increased contractility without diameter increase in HF arteries. Treatment of 12-mo-old male rats and ovariectomized female rats with hydralazine, the antioxidant tempol, or the angiotensin II type 1 receptor blocker candesartan restored HF remodeling and normalized arterial contractility in HF vessels. Thus, we found that FMR of resistance arteries remains efficient in 12-mo-old female rats compared with age-matched male rats. A balance between estrogens and vascular contractility might preserve FMR in mature female rats.

Endothelial nitric oxide synthase and superoxide mediate hemodynamic initiation of intracranial aneurysms

Background

Hemodynamic insults at arterial bifurcations are believed to play a critical role in initiating intracranial aneurysms. Recent studies in a rabbit model indicate that aneurysmal damage initiates under specific wall shear stress conditions when smooth muscle cells (SMCs) become pro-inflammatory and produce matrix metalloproteinases (MMPs). The mechanisms leading to SMC activation and MMP production during hemodynamic aneurysm initiation are unknown. The goal is to determine if nitric oxide and/or superoxide induce SMC changes, MMP production and aneurysmal remodeling following hemodynamic insult.

Methods

Bilateral common carotid artery ligation was performed on rabbits (n = 19, plus 5 sham operations) to induce aneurysmal damage at the basilar terminus. Ligated animals were treated with the nitric oxide synthase (NOS) inhibitor LNAME (n = 7) or the superoxide scavenger TEMPOL (n = 5) and compared to untreated animals (n = 7). Aneurysm development was assessed histologically 5 days after ligation. Changes in NOS isoforms, peroxynitrite, reactive oxygen species (ROS), MMP-2, MMP-9, and smooth muscle α-actin were analyzed by immunohistochemistry.

Results

LNAME attenuated ligation-induced IEL loss, media thinning and bulge formation. In untreated animals, immunofluorescence showed increased endothelial NOS (eNOS) after ligation, but no change in inducible or neuronal NOS. Furthermore, during aneurysm initiation ROS increased in the media, but not the intima, and there was no change in peroxynitrite. In LNAME-treated animals, ROS production did not change. Together, this suggests that eNOS is important for aneurysm initiation but not by producing superoxide. TEMPOL treatment reduced aneurysm development, indicating that the increased medial superoxide is also necessary for aneurysm initiation. LNAME and TEMPOL treatment in ligated animals restored α-actin and decreased MMPs, suggesting that eNOS and superoxide both lead to SMC de-differentiation and MMP production.

Conclusion

Aneurysm-inducing hemodynamics lead to increased eNOS and superoxide, which both affect SMC phenotype, increasing MMP production and aneurysmal damage.

Time-related alteration in flow- (shear stress-) mediated remodeling in resistance arteries from spontaneously hypertensive rats

Hypertension is a major risk factor for cardiovascular disorders. As flow-mediated outward remodeling has a key role in postischemic revascularization, we investigated this remodeling in mesenteric resistance arteries of normotensive (WKY) and spontaneously hypertensive rats (SHRs) aged 3 to 9 months. Sequential ligation of mesenteric resistance arteries allowed modifying blood flow in vivo, thus exposing arteries to low, normal, or high flow. After 1, 3, 8, or 24 weeks, arteries were isolated for in vitro study. High flow (HF) induced outward hypertrophic remodeling in WKY rats after 1 week and persisted until 24 weeks without change in wall to lumen ratio. In SHRs, diameter increase was delayed, occurring only after 3 weeks. Nevertheless, it was reduced at 8 weeks and no longer significant after 24 weeks. In parallel, media cross-section area increased more with time in SHRs than in WKY rats and this was associated with increased contractility and oxidative stress with decreased NO-dependent relaxation. Low flow induced progressive inward remodeling until 24 weeks in both strains with excessive hypertrophy in SHRs. Thus, a chronic increase in flow induced transitory diameter expansion and long-lasting hypertrophy in SHRs. This could contribute to the higher susceptibility of hypertensive subjects to ischemic diseases.

Determinants of flow-mediated outward remodeling in female rodents: respective roles of age, estrogens, and timing

OBJECTIVE

Flow (shear stress)-mediated outward remodeling (FMR) of resistance arteries is a key adaptive process allowing collateral growth after arterial occlusion but declining with age. 17-β-estradiol (E2) has a key role in this process through activation of estrogen receptor α (ERα). Thus, we investigated the impact of age and timing for estrogen efficacy on FMR.

APPROACH AND RESULTS

Female rats, 3 to 18 months old, were submitted to surgery to increase blood flow locally in 1 mesenteric artery in vivo. High-flow and normal-flow arteries were collected 2 weeks later for in vitro analysis. Diameter increased by 27% in high-flow arteries compared with normal-flow arteries in 3-month-old rats. The amplitude of remodeling declined with age (12% in 18-month-old rats) in parallel with E2 blood level and E2 substitution failed restoring remodeling in 18-month-old rats. Ovariectomy of 3-, 9-, and 12-month-old rats abolished FMR, which was restored by immediate E2 replacement. Nevertheless, this effect of E2 was absent 9 months after ovariectomy. In this latter group, ERα and endothelial nitric oxide synthase expression were reduced by half compared with age-matched rats recently ovariectomized. FMR did not occur in ERα(-/-) mice, whereas it was decreased by 50% in ERα(+/-) mice, emphasizing the importance of gene dosage in high-flow remodeling.

CONCLUSIONS

E2 deprivation, rather than age, leads to decline in FMR, which can be prevented by early exogenous E2. However, delayed E2 replacement was ineffective on FMR, underlining the importance of timing of this estrogen action.

Association of eNOS polymorphisms with anterior chamber depth in han chinese: jiangsu eye study

Recently, a study reported that single nucleotide polymorphisms (SNP) in endothelial nitric oxide synthase (eNOS) were associated with primary angle closure glaucoma (PACG) in Australian cohort. In this study, we aimed to investigate whether those eNOS SNPs are associated with primary angle closure (PAC) or ocular biometric characteristics such as axial length (AL), anterior chamber depth (ACD), and diopter of spherical power (DS) in Han Chinese. The samples consisted of 232 PAC subjects and 306 controls collected from a population-based prevalence survey conducted in Funing County of Jiangsu, China. The rs3793342 and rs11771443 in eNOS were genotyped by TaqMan-MGB probe using the RT-PCR system. Our data did not identify any association of the eNOS SNPs with PAC. However, the analysis on the quantitative traits of ocular biometrics showed that the ACD of rs11771443 AA and GA carriers is significantly deeper than that of rs11771443 GG carriers (P = 0.0025), even though the AL and DS are not associated with rs11771443 genotypes. Rs3793342 was not associated with any biometric parameters including ACD, AL and DS. In summary, our data indicates that eNOS rs11771443 is associated with ACD and its role in the pathogenesis of PACG warranted further study.

AGEs breaking and antioxidant treatment improves endothelium-dependent dilation without effect on flow-mediated remodeling of resistance arteries in old Zucker diabetic rats

BACKGROUND

A chronic increase in blood flow in resistance arteries is associated with increased lumen diameter (outward remodeling) and improved endothelium (NO)-mediated relaxation. Flow-mediated remodeling of resistance arteries is essential for revascularization in ischemic diseases. Nevertheless, it is impaired in 12 to 24-month old rats and in young Zucker Diabetic Fatty (ZDF) rats due to advanced glycation end products (AGEs) and oxidative stress. As type 2 diabetes occurs preferentially in older subjects we investigated flow-mediated remodeling and the effect of the AGEs breaker ALT-711 associated or not to the antioxidant TEMPOL in one-year old lean (LZ) and ZDF rats.

METHODS

Mesenteric resistance arteries were exposed to high (HF) or normal blood flow (NF) in vivo. They were collected after 2 weeks for in vitro analysis.

RESULTS

In LZ rats, diameter expansion did not occur despite a significant increase in blood flow in HF arteries. Nevertheless, endothelium-mediated relaxation was higher in HF than in NF arteries. ALT-711, alone or in combination with TEMPOL, restored outward remodeling in HF arteries in association with AGEs reduction. TEMPOL alone had no effect. ALT-711, TEMPOL or the combination of the 2 drugs did not significantly affect endothelium-mediated relaxation in HF and NF arteries.In ZDF rats, diameter did not increase despite the increase in blood flow and endothelium-mediated relaxation was further decreased in HF arteries in association with AGEs accumulation and excessive oxidative stress. In both NF and HF arteries, endothelium-mediated relaxation was lower in ZDF than in LZ rats. ALT-711, TEMPOL or their combination did not improve remodeling (diameter equivalent in HF and NF arteries). In parallel, they did not reduce AGEs level and did not improve MMPs activity. Nevertheless, ALT-711 and TEMPOL partly improved endothelium-mediated relaxation through a reduction of oxidative stress and the association of ALT-711 and TEMPOL fully restored relaxation to the level found in LZ rats.

CONCLUSIONS

ALT-711 did not improve outward remodeling in mature ZDF rats but it reduced oxidative stress and consequently improved endothelium-dependent relaxation. In mature LZ rats, ALT-711 improved outward remodeling and reduced AGEs level. Consequently, AGEs breaking is differently useful in ageing whether it is associated with diabetes or not.

COX-2-derived prostanoids and oxidative stress additionally reduce endothelium-mediated relaxation in old type 2 diabetic rats

Endothelial dysfunction in resistance arteries alters end organ perfusion in type 2 diabetes. Superoxides and cyclooxygenase-2 (COX-2) derivatives have been shown separately to alter endothelium-mediated relaxation in aging and diabetes but their role in the alteration of vascular tone in old diabetic subjects is not clear, especially in resistance arteries. Consequently, we investigated the role of superoxide and COX-2-derivatives on endothelium-dependent relaxation in 3 and 12 month-old Zucker diabetic fatty (ZDF) and lean (LZ) rats. Mesenteric resistance arteries were isolated and vascular tone was investigated using wire-myography. Endothelium (acetylcholine)-dependent relaxation was lower in ZDF than in LZ rats (60 versus 84% maximal relaxation in young rats and 41 versus 69% in old rats). Blocking NO production with L-NAME was less efficient in old than in young rats. L-NAME had no effect in old ZDF rats although eNOS expression level in old ZDF rats was similar to that in old LZ rats. Superoxide level and NADPH-oxidase subunits (p67phox and gp91phox) expression level were greater in ZDF than in LZ rats and were further increased by aging in ZDF rats. In young ZDF rats reducing superoxide level with tempol restored acetylcholine-dependent relaxation to the level of LZ rats. In old ZDF rats tempol improved acetylcholine-dependent relaxation without increasing it to the level of LZ rats. COX-2 (immunolabelling and Western-blot) was present in arteries of ZDF rats and absent in LZ rats. In old ZDF rats arterial COX-2 level was higher than in young ZDF rats. COX-2 blockade with NS398 restored in part acetylcholine-dependent relaxation in arteries of old ZDF rats and the combination of tempol and NS398 fully restored relaxation in control (LZ rats) level. Accordingly, superoxide production and COX-2 derivatives together reduced endothelium-dependent relaxation in old ZDF rats whereas superoxides alone attenuated relaxation in young ZDF or old LZ rats.

Key role of estrogens and endothelial estrogen receptor α in blood flow-mediated remodeling of resistance arteries

OBJECTIVE

Flow- (shear stress-)mediated outward remodeling of resistance arteries is involved in collateral growth during postischemic revascularization. As this remodeling is especially important during pregnancy, we hypothesized that estrogens may be involved. A surgical model eliciting a local increase in blood flow in 1 mesenteric resistance artery was used in 3-month-old ovariectomized female rats either treated with 17-β-estradiol (E2) or left untreated.

METHODS AND RESULTS

After 14 days, arterial diameter was greater in high-flow arteries than in normal-flow vessels. An ovariectomy suppressed high-flow remodeling, while E2 restored it. High-flow remodeling was absent in mice lacking the estrogen receptor α but not estrogen receptor β. The kinetics of inflammatory marker expression, macrophage infiltration, oxidative stress, and metaloproteinases expression were not altered by the absence of E2 after 2 and 4 days, that is, during remodeling. Nevertheless, E2 was required for the increase in endothelial nitric oxide synthase expression and activation at day 4 when diameter expansion occurs. Finally, the impact of E2 on the endothelium appeared crucial for high-flow remodeling, as this E2 action was abrogated in mice lacking endothelial NOS, as well as in Tie2-Cre(+) ERα(f/f) mice.

CONCLUSIONS

We demonstrate the essential role of E2 and endothelial estrogen receptor α in flow-mediated remodeling of resistance arteries in vivo.

High wall shear stress and spatial gradients in vascular pathology: a review

Cardiovascular pathologies such as intracranial aneurysms (IAs) and atherosclerosis preferentially localize to bifurcations and curvatures where hemodynamics are complex. While extensive knowledge about low wall shear stress (WSS) has been generated in the past, due to its strong relevance to atherogenesis, high WSS (typically >3 Pa) has emerged as a key regulator of vascular biology and pathology as well, receiving renewed interests. As reviewed here, chronic high WSS not only stimulates adaptive outward remodeling, but also contributes to saccular IA formation (at bifurcation apices or outer curves) and atherosclerotic plaque destabilization (in stenosed vessels). Recent advances in understanding IA pathogenesis have shed new light on the role of high WSS in pathological vascular remodeling. In complex geometries, high WSS can couple with significant spatial WSS gradient (WSSG). A combination of high WSS and positive WSSG has been shown to trigger aneurysm initiation. Since endothelial cells (ECs) are sensors of WSS, we have begun to elucidate EC responses to high WSS alone and in combination with WSSG. Understanding such responses will provide insight into not only aneurysm formation, but also plaque destabilization and other vascular pathologies and potentially lead to improved strategies for disease management and novel targets for pharmacological intervention.

17ß-estradiol antagonizes the down-regulation of ERα/NOS-3 signaling in vascular endothelial dysfunction of female diabetic rats

Previous studies indicated that estrogen could improve endothelial function. However, whether estrogen protects vascular complications of diabetes has yet to be clarified. The study was designed to investigate the action of 17ß-estradiol on vascular endothelium in streptozotocin (STZ)-induced diabetic rats. Ovariectomized female Sprague-Dawley rats were administered with streptozotocin to produce an ovariectomized-diabetic (OVS) model which manifested as dysfunction of aortic dilation and contraction ability. Meanwhile, OVS animals with 17ß-estradiol supplementation significantly improved aortic function. Accordingly, nitric oxide synthase-3 (NOS-3), Akt, PI3K and estrogen receptor α (ERα) protein expression in aorta declined in the OVS group. Such effects were partially restored by estrogen replacement. The presence of 17ß-estradiol similarly counteracted the reduction of cyclic guanosine monophosphate (cGMP), the enhanced expression of inducible NOS (NOS-2) and NO metabolites (nitrite and nitrate), as well as the increase of matrix metalloproteinase-9/tissue inhibitor of metalloproteinase-1 (MMP-9/TIMP-1), which is an index of arterial compliance. 17ß-estradiol could also decrease ROS production in vascular endothelium. In EA hy 926 cells we found that ER antagonist, wortmannin and Akt inhibitor could block improvement effects of 17ß-estradiol. These results strongly suggest that functional impairment of the ERα/NOS-3 signaling network in OVS animals was partially restored by 17ß-estradiol administration, which provides experimental support for estrogen recruitment to improve vascular outcomes in female diabetes after endogenous hormone depletion.