Oscillatory shear stress stimulates adhesion molecule expression in cultured human endothelium

Brachial artery flow-mediated dilation following exercise with augmented oscillatory and retrograde shear rate

Background

Acute doses of elevated retrograde shear rate (SR) appear to be detrimental to endothelial function in resting humans. However, retrograde shear increases during moderate intensity exercise which also enhances post-exercise endothelial function. Since SR patterns differ with the modality of exercise, it is important to determine if augmented retrograde SR during exercise influences post-exercise endothelial function. This study tested the hypothesis that (1) increased doses of retrograde SR in the brachial artery during lower body supine cycle ergometer exercise would attenuate post-exercise flow-mediated dilation (FMD) in a dose-dependent manner, and (2) antioxidant vitamin C supplementation would prevent the attenuated post-exercise FMD response.

Methods

Twelve men participated in four randomized exercise sessions (90 W for 20 minutes) on separate days. During three of the sessions, one arm was subjected to increased oscillatory and retrograde SR using three different forearm cuff pressures (20, 40, 60 mmHg) (contralateral arm served as the control) and subjects ingested placebo capsules prior to exercise. A fourth session with 60 mmHg cuff pressure was performed with 1 g of vitamin C ingested prior to the session.

Results

Post-exercise FMD following the placebo conditions were lower in the cuffed arm versus the control arm (arm main effect: P < 0.05) and without differences between cuff pressures (20 mmHg: 5.7 ± 2.2%; 40 mmHg: 4.7 ± 1.3%; 60 mmHg: 5.4 ± 2.4%) (P > 0.05). Following vitamin C treatment, post-exercise FMD in the cuffed and control arm increased from baseline (P < 0.05) but were not different (control: 7.1 ± 3.5% vs. cuffed: 6.6 ± 3.3%) (P > 0.05).

Conclusions

These results indicate that augmented oscillatory and retrograde SR in non-working limbs during lower body exercise attenuates post-exercise FMD without an evident dose–response in the range of cuff pressures evaluated. Vitamin C supplementation prevented the attenuation of FMD following exercise with augmented oscillatory and retrograde SR suggesting that oxidative stress contributes to the adverse effects of oscillatory and retrograde shear during exercise on FMD.

The induction of autophagy by mechanical stress

The ability to respond and adapt to changes in the physical environment is a universal and essential cellular property. Here we demonstrated that cells respond to mechanical compressive stress by rapidly inducing autophagosome formation. We measured this response in both Dictyostelium and mammalian cells, indicating that this is an evolutionarily conserved, general response to mechanical stress. In Dictyostelium, the number of autophagosomes increased 20-fold within 10 min of 1 kPa pressure being applied and a similar response was seen in mammalian cells after 30 min. We showed in both cell types that autophagy is highly sensitive to changes in mechanical pressure and the response is graduated, with half-maximal responses at ~0.2 kPa, similar to other mechano-sensitive responses. We further showed that the mechanical induction of autophagy is TOR-independent and transient, lasting until the cells adapt to their new environment and recover their shape. The autophagic response is therefore part of an integrated response to mechanical challenge, allowing cells to cope with a continuously changing physical environment.

Force-specific activation of Smad1/5 regulates vascular endothelial cell cycle progression in response to disturbed flow

Vascular endothelial cells (ECs) are constantly exposed to blood flow-induced shear stress, but the mechanism of force-specific activation of their signaling to modulate cellular function remains unclear. We have demonstrated that bone morphogenetic protein receptor (BMPR)-specific Smad1/5 can be force-specifically activated by oscillatory shear stress (OSS) in ECs to cause cell cycle progression. Smad1/5 is highly activated in ECs of atherosclerotic lesions in diseased human coronary arteries from patients with end-stage heart failure undergoing heart transplantation and from apolipoprotein E-deficient mice. Application of OSS (0.5 ± 4 dyn/cm(2)) causes the sustained activation of Smad1/5 in ECs through activations of mammalian target of rapamycin and p70S6 kinase, leading to up-regulation of cyclin A and down-regulations of p21(CIP1) and p27(KIP1) and, hence, EC cycle progression. En face examination of rat aortas reveals high levels of phospho-Smad1/5 in ECs of the inner, but not the outer, curvature of aortic arch, nor the straight segment of thoracic aorta [corrected]. Immunohistochemical and en face examinations of the experimentally stenosed abdominal aorta in rats show high levels of phospho-Smad1/5 in ECs at poststenotic sites, where OSS occurs. These OSS activations of EC Smad1/5 in vitro and in vivo are not inhibited by the BMP-specific antagonist Noggin and, hence, are independent of BMP ligand. Transfecting ECs with Smad1/5-specific small interfering RNAs inhibits the OSS-induced EC cycle progression. Our findings demonstrate the force-specificity of the activation of Smad1/5 and its contribution to cell cycle progression in ECs induced by disturbed flow.

Dynamics of mechanical signal transmission through prestressed stress fibers

Transmission of mechanical stimuli through the actin cytoskeleton has been proposed as a mechanism for rapid long-distance mechanotransduction in cells; however, a quantitative understanding of the dynamics of this transmission and the physical factors governing it remains lacking. Two key features of the actin cytoskeleton are its viscoelastic nature and the presence of prestress due to actomyosin motor activity. We develop a model of mechanical signal transmission through prestressed viscoelastic actin stress fibers that directly connect the cell surface to the nucleus. The analysis considers both temporally stationary and oscillatory mechanical signals and accounts for cytosolic drag on the stress fibers. To elucidate the physical parameters that govern mechanical signal transmission, we initially focus on the highly simplified case of a single stress fiber. The results demonstrate that the dynamics of mechanical signal transmission depend on whether the applied force leads to transverse or axial motion of the stress fiber. For transverse motion, mechanical signal transmission is dominated by prestress while fiber elasticity has a negligible effect. Conversely, signal transmission for axial motion is mediated uniquely by elasticity due to the absence of a prestress restoring force. Mechanical signal transmission is significantly delayed by stress fiber material viscosity, while cytosolic damping becomes important only for longer stress fibers. Only transverse motion yields the rapid and long-distance mechanical signal transmission dynamics observed experimentally. For simple networks of stress fibers, mechanical signals are transmitted rapidly to the nucleus when the fibers are oriented largely orthogonal to the applied force, whereas the presence of fibers parallel to the applied force slows down mechanical signal transmission significantly. The present results suggest that cytoskeletal prestress mediates rapid mechanical signal transmission and allows temporally oscillatory signals in the physiological frequency range to travel a long distance without significant decay due to material viscosity and/or cytosolic drag.

Anterograde and retrograde blood velocity profiles in the intact human cardiovascular system

Current assessments of the effects of shear patterns on vascular function assume that a parabolic velocity profile is always present. Any substantial deviation in the profile away from this may result in misinterpretation of the importance that shear patterns have on vascular function. The present investigation tested the hypothesis that anterograde and retrograde blood flow would have a parabolic velocity profile at rest, during cold pressor test and exercise. Eight healthy subjects completed a cold pressor test and a graded knee-extension exercise test. Doppler ultrasound was used to determine time-averaged mean velocity (V(mean)) and time-averaged peak velocity (V(peak)) for both anterograde and retrograde flow in the femoral artery (FA) and brachial artery (BA). The V(mean)/V(peak) ratio was used to interpret the shape of the blood velocity profile (parabolic, V(mean)/V(peak) = 0.5; plug-like, V(mean)/V(peak) = 1.0). At rest, BA and FA V(mean)/V(peak) ratios of anterograde and retrograde flow were not significantly different from 0.5. During cold pressor test, anterograde V(mean)/V(peak) in the BA (0.56 ± 0.02) and FA (0.58 ± 0.03) were significantly greater than 0.5. During peak exercise, the V(mean)/V(peak) ratio of anterograde flow in the FA (0.53 ± 0.04) was not significantly different from 0.5. In all conditions, the retrograde V(mean)/V(peak) ratio was lower than anterograde. These data demonstrate that blood flow through two different conduit arteries during two different physiological stressors maintains a velocity profile that resembles a slightly blunted parabolic velocity profile.

Shear stress modulates RAGE-mediated inflammation in a model of diabetes-induced metabolic stress

Atherosclerosis occurs preferentially at sites of disturbed blood flow despite the influence of risk factors contributing to systemic inflammation. The receptor for advanced glycation endproducts (RAGE) is a prominent mediator of inflammation in diabetes that is upregulated in atherosclerotic plaques. Our goal was to elucidate a role for arterial hemodynamics in the regulation of RAGE expression and activity. Endothelial RAGE expression was elevated at sites of flow disturbance in the aortas of healthy swine. To demonstrate a direct role for physiological shear stress (SS) in modulating RAGE expression, human aortic endothelial cells (HAEC) were exposed to high SS (HSS; 15 dyn/cm(2)), which downregulated RAGE by fourfold, or oscillatory SS (OSS; 0 ± 5 dyn/cm(2)), which upregulated RAGE by threefold, compared with static culture at 4 h. In a model of diabetes-induced metabolic stress, HAEC were chronically conditioned under high glucose (25 mM) and then simultaneously stimulated with TNF-α (0.5 ng/ml) and the RAGE ligand high mobility group box 1 (HMGB1). A 50% increase in VCAM-1 expression over TNF-α was associated with increased cytoplasmic and mitochondrial reactive oxygen species and NF-κB activity. This increase was RAGE-specific and NADPH oxidase dependent. In activated HAEC, OSS amplified HMGB1-induced VCAM-1 (3-fold) and RAGE (1.6-fold) expression and proportionally enhanced monocyte adhesion to HAEC in a RAGE-dependent manner, while HSS mitigated these increases to the level of TNF-α alone. We demonstrate that SS plays a fundamental role in regulating RAGE expression and inflammatory responses in the endothelium. These findings may provide mechanistic insight into how diabetes accelerates the nonrandom distribution of atherosclerosis in arteries.

Mechanotransduction of shear in the endothelium: basic studies and clinical implications

The endothelium plays an integral role in the development and progression of atherosclerosis. Hemodynamic forces, particularly shear stress, have a powerful influence on endothelial phenotype and function; however, there is no clear consensus on how endothelial cells sense shear. Nevertheless, multiple endothelial cell signal transduction pathways are activated when exposed to shear stress in vitro. The type of shear, laminar or oscillatory, impacts which signal transduction pathways are initiated as well as which subsequent genes are up- or down-regulated, thereby influencing endothelial phenotype and function. Recently, human studies have examined the impact of shear stress and different shear patterns at rest and during exercise on endothelial function. Current evidence supports the theory that augmented exercise-induced shear stress contributes to improved endothelial function following acute exercise and exercise training, whereas retrograde shear initiates vascular dysfunction. The purpose of this review is to examine the current theories on how endothelial cells sense shear stress, to provide an overview on shear stress-induced signal transduction pathways and subsequent gene expression, and to review the current literature pertaining to shear stress and shear patterns at rest as well as during exercise in humans and the related effects on endothelial function.

Thioredoxin interacting protein promotes endothelial cell inflammation in response to disturbed flow by increasing leukocyte adhesion and repressing Kruppel-like factor 2

RATIONALE

Endothelial cells (EC) at regions exposed to disturbed flow (d-flow) are predisposed to inflammation and the subsequent development of atherosclerosis. We previously showed that thioredoxin interacting protein (TXNIP) was required for tumor necrosis factor-mediated expression of vascular cell adhesion molecule-1.

OBJECTIVE

We sought to investigate the role of TXNIP in d-flow-induced cell adhesion molecule expression and leukocyte interaction with vessels, and the mechanisms by which TXNIP suppresses athero-protective gene expression.

METHODS AND RESULTS

Using en face staining of mouse aorta, we found a dramatic increase of TXNIP in EC at sites exposed to d-flow as compared to steady flow. EC-specific TXNIP (EC-TXNIP) knockout mice showed significant decreases in vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 mRNA expression in the d-flow regions of mouse aorta. Intravital microscopy of mesenteric venules showed that leukocyte rolling time was decreased, whereas rolling velocity was increased significantly in EC-TXNIP knockout mice. In vitro experiments using a cutout flow chamber to generate varying flow patterns showed that increased TXNIP was required for d-flow-induced EC-monocyte adhesion. Furthermore, we found that the expression of Kruppel-like factor 2, a key anti-inflammatory transcription factor in EC, was inhibited by TXNIP. Luciferase and chromatin immunoprecipitation assays showed that TXNIP was present within a repressing complex on the Kruppel-like factor 2 promoter.

CONCLUSIONS

These data demonstrate the essential role for TXNIP in mediating EC-leukocyte adhesion under d-flow, as well as define a novel mechanism by which TXNIP acts as a transcriptional corepressor to regulate Kruppel-like factor 2-dependent gene expression.

Elevated resting heart rate is associated with white blood cell count in middle-aged and elderly individuals without apparent cardiovascular disease

We investigated the association between resting heart rate (HR) and inflammation markers in a healthy population. White blood cell (WBC) count was used as a surrogate marker of subclinical inflammation. Smoking status, body mass index, resting HR, high-density lipoprotein cholesterol, triglycerides, uric acid, and glycated hemoglobin were significantly associated with WBC in both men and women. Blood pressure and fasting plasma glucose levels, however, were associated with WBC only in women. Logistic regression analysis indicated that for every 10 beats per minute increase in HR, the odds ratio of an increase in the WBC was approximately 1.3 in both men and women. These findings indicate the clinical significance of resting HR for identifying individuals at risk of subclinical inflammation and a future cardiovascular event.

Effects of biaxial oscillatory shear stress on endothelial cell proliferation and morphology

Wall shear stress (WSS) on anchored cells affects their responses, including cell proliferation and morphology. In this study, the effects of the directionality of pulsatile WSS on endothelial cell proliferation and morphology were investigated for cells grown in a Petri dish orbiting on a shaker platform. Time and location dependent WSS was determined by computational fluid dynamics (CFD). At low orbital speed (50 rpm), WSS was shown to be uniform (0-1 dyne/cm(2)) across the bottom of the dish, while at higher orbital speed (100 and 150 rpm), WSS remained fairly uniform near the center and fluctuated significantly (0-9 dyne/cm(2)) near the side walls of the dish. Since WSS on the bottom of the dish is two-dimensional, a new directional oscillatory shear index (DOSI) was developed to quantify the directionality of oscillating shear. DOSI approached zero for biaxial oscillatory shear of equal magnitudes near the center and approached one for uniaxial pulsatile shear near the wall, where large tangential WSS dominated a much smaller radial component. Near the center (low DOSI), more, smaller and less elongated cells grew, whereas larger cells with greater elongation were observed in the more uniaxial oscillatory shear (high DOSI) near the periphery of the dish. Further, cells aligned with the direction of the largest component of shear but were randomly oriented in low magnitude biaxial shear. Statistical analyses of the individual and interacting effects of multiple factors (DOSI, shear magnitudes and orbital speeds) showed that DOSI significantly affected all the responses, indicating that directionality is an important determinant of cellular responses.

Evaluation of aortic geometries created by magnetic resonance imaging data in healthy volunteers

INTRODUCTION

The development of atherosclerotic plaques has been associated with the patterns of wall shear stress (WSS). However, much is still uncertain with the methods used to calculate WSS. Correct vessel geometries are mandatory to get reliable estimations, and the purpose of this study was to evaluate an in vivo method for creating aortic 3D geometry in human based on data from magnetic resonance imaging (MRI) with ultrasound as reference.

METHODS

The aortas of ten healthy men, 23·4 ± 1·6 years of age, were examined with a 1·5 T MRI system using a 3D gadolinium-enhanced gradient-echo sequence. Three-dimensional geometries were created using manual segmentation of images. Lumen diameters (LD) were measured in the abdominal aorta (AA) and the thoracic aorta (TA) with non-invasive B-mode ultrasound as a reference.

RESULTS

The anteroposterior diameter of the AA was 13·6 ± 1·1 mm for the MRI and 13·8 ± 1·3 mm for the ultrasound (NS). Intraobserver variability (CV) for MRI and ultrasound was <0·92% and <0·40%, respectively. Interobserver variability for MRI and ultrasound was 0·96% and 0·56%, respectively. The diameter of the TA was 19·2 ± 1·4 mm for the MRI, and the intraobserver variability (CV) was <0·78% and interobserver variability (CV) was 0·92%.

CONCLUSION

  Specific arterial geometries can be constructed with a high degree of accuracy using MRI. This indicates that the MRI geometries may be used to create realistic and correct geometries in the calculation of WSS in the aorta of human.

Ambulatory blood pressure variability is associated with restenosis after percutaneous coronary intervention in normotensive patients

BACKGROUND

Previous studies have showed that BP variability is associated with cardiovascular events. However, no data were available regarding binary restenosis as an end-point after percutenous coronary intervention (PCI).

METHODS AND RESULTS

This multicenter study included 100 consecutive normotensive patients with stable coronary artery disease who were planned for PCI. Before the index procedure, office BP and 24-h ambulatory BP measurements were performed. BP variability indices including systolic and diastolic 24-h average, the day and the night values of standard deviation (SD) and variation coefficient (VC) were measured and calculated. All patients underwent repeat coronary angiography at 6-month. According to angiographic results, 2 groups were formed; a restenosis group (n=30) with binary restenosis of the stented segment and a control group (n=70) with a stenosis diameter of <50% in stented segment. Systolic SD and VC values for 24-h average (14.0±2.8mmHg vs. 9.5±1.6mmHg, p<0.001 and 16%±3 vs. 11%±2, p<0.001, respectively), the day (15.2±3.9mmHg vs. 10.6±1.7mmHg, p<0.001 and 17%±4 vs. 12%±2, p<0.001, respectively), and the night (12.8±4.1mmHg vs. 8.4±2.4mmHg, p<0.001 and 14%±5 vs. 11%±3, p=0.004, respectively) values were significantly higher in restenosis group compared to control group. Similarly, diastolic SD and VC values for 24-h average (10.6±2.5mmHg vs. 8.1±1.5mmHg, p<0.001 and 12%±3 vs. 9%±2, p=0.001, respectively), the day (11.1±2.9mmHg vs. 9.0±1.8mmHg, p=0.003 and 12%±3 vs. 10%±2, p=0.006, respectively), and the night (10.0±3.6mmHg vs. 7.2±2.0mmHg, p=0.001 and 11%±5 vs. 9%±3, p=0.059, respectively) values were significantly higher in restenosis group compared to no restenosis group except for diastolic VC night. All systolic and diastolic BP variability indices except diastolic VC night were found to be independent predictors of risk of restenosis in multivariate analysis. In addition, the cut-off values of 11.4mmHg and 13% for 24-h systolic SD and VC, respectively, were found to be highly sensitive (93% for both) and specific (94% and 91%, respectively) for predicting binary restenosis at 6-month after PCI.

CONCLUSIONS

BP variability indices are significantly and independently associated with binary restenosis and higher values can predict restenosis after PCI sensitively and specifically.

Blood pressure in relation to neurogenic, inflammatory and endothelial dysfunction biomarkers in patients with treated essential arterial hypertension

PURPOSE

Clinical relevance of relations among blood pressure (BP), inflammation, endothelial dysfunction and sympathetic activation is unknown. Study aimed, whether in patients with diagnosed and treated essential arterial hypertension (HTN) biomarkers of inflammation (hs-C-reactive protein, hs-CRP), endothelial dysfunction (endothelin-1, ET-1), and sympathetic nervous system modulation (epinephrine, E and norepinephrine, NE) could be related to BP values.

MATERIAL AND METHODS

In 62 patients with diagnosed and treated HTN (mean time of disease 5±3.2 years), serum hs-CRP and ET-1 as well as plasma E and NE concentrations were measured. 24-hour ambulatory blood pressure measurement device (ABPM) was used to estimate efficacy of treatment.

RESULTS

A positive correlation between epinephrine and norepinephrine concentrations was found (r=0.246, p=0.05), however such a statistically significant correlation neither to hs-CRP, nor ET-1 were found. Patients with the highest hs-CRP and NE concentrations had the highest systolic (SBP) and diastolic (DBP) blood pressure values. Similar relation was found in subgroup of patients with suboptimal blood pressure values (SPB ł 130mmHg, DBP ł 80mmHg). In a group of optimal treated patients, elevated levels of ET-1 and NE related to increased blood pressure values. ROC analysis identified ET-1 as statistically significant to diagnose elevated blood pressure: 0.665 (95% Confidence interval 0.512 to 0.796).

CONCLUSIONS

In patients with diagnosed and treated arterial hypertension, there are relations among measurements of hs-CRP, ET-1, NE and blood pressure values in spite of treatment, which may improve understanding of mechanisms involving inflammation, endothelial dysfunction and sympathetic nerve activation and may identify patients with refractory hypertension.

Time rate of blood pressure variation: a new factor associated with coronary atherosclerosis

OBJECTIVES

Previous studies have demonstrated that the time rate of blood pressure (BP) variation was associated with early carotid atherosclerosis, independent of peripheral and central BP levels. We evaluated the association between the rate of BP variation, derived from ambulatory BP monitoring (ABPM) data analysis, and the severity and topography of coronary artery lesion in a cohort of normotensive patients with suspected coronary artery disease.

METHODS

ABPM and coronary angiography were performed in 162 normotensive patients with suspected coronary artery disease. The topography and severity of coronary artery lesions were assessed by Gensini score. The time rate of BP variation was defined as the first derivative of the BP values against time.

RESULTS

Patients with coronary artery disease (n = 123) presented significantly (P = 0.005) higher daytime rate of systolic BP variation than control patients (n = 39). Multiple linear regression models revealed independent determinants of Gensini score in the following rank order: diabetes mellitus (β: +0.286, P < 0.001), daytime rate of systolic BP variation (β: +0.277, P < 0.001), daytime systolic BP (β: +0.216, P = 0.002), smoking (β: +0.178, P = 0.008) and hypercholesterolemia (β: +0.158, P = 0.020). A 0.1 mmHg/min increase in the daytime rate of systolic BP variation correlated with an increment of 4.935 in the Gensini score (95% CI 2.432-7.438).

CONCLUSION

Steeper BP variations may produce a greater stress on the arterial wall and may have an additive role to vascular risk factors and BP parameters in the detection of the severity of coronary artery lesions in normotensive individuals with suspected coronary artery disease.

Microfluidic endothelial cell culture model to replicate disturbed flow conditions seen in atherosclerosis susceptible regions

Atherosclerotic lesions occur non-randomly at vascular niches in bends and bifurcations where fluid flow can be characterized as "disturbed" (low shear stress with both forward and retrograde flow). Endothelial cells (ECs) at these locations experience significantly lower average shear stress without change in the levels of pressure or strain, which affects the local balance in mechanical stresses. Common in vitro models of atherosclerosis focus primarily on shear stress without accounting for pressure and strain loading. To overcome this limitation, we used our microfluidic endothelial cell culture model (ECCM) to achieve accurate replication of pressure, strain, and shear stress waveforms associated with both normal flow seen in straight sections of arteries and disturbed flow seen in the abdominal aorta in the infrarenal segment at the wall distal to the inferior mesenteric artery (IMA), which is associated with high incidence of atherosclerotic lesion formation. Human aortic endothelial cells (HAECs) were cultured within the ECCM under both normal and disturbed flow and evaluated for cell shape, cytoskeletal alignment, endothelial barrier function, and inflammation using immunofluorescence microscopy and flow cytometry. Results clearly demonstrate quantifiable differences between cells cultured under disturbed flow conditions, which are cuboidal with short and randomly oriented actin microfilaments and show intermittent expression of β-Catenin and cells cultured under normal flow. However, in the absence of pro-inflammatory stimulation, the levels of expression of activation markers: intra cellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), platelet endothelial cell adhesion molecule-1 (PECAM-1), and vascular endothelial cell growth factor - receptor 2 (VEGF-R2) known to be involved in the initiation of plaque formation were only slightly higher in HAECs cultured under disturbed flow in comparison to cells cultured under normal flow.

Anti-atherogenic effect of laminar shear stress via Nrf2 activation

Fluid shear stress plays a critical role in the regulation of vascular biology and its pathology, such as atherosclerosis, via modulation of redox balance. Both pro-atherogenic (either oscillatory or turbulent, nonunidirectional) shear stress and anti-atherogenic (either steady or pulsatile, unidirectional laminar) shear stress stimulate production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that are involved in signal transduction of gene expression. Nonunidirectional shear stress induces pro-atherogenic genes encoding adhesion molecules and chemokines in a manner dependent on production of both superoxide and nitric oxide. Steady or pulsatile laminar shear stress induces expression of genes encoding cytoprotective enzymes for glutathione biosynthesis and detoxification, which are regulated by the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2). We show that pulsatile laminar shear stress (PLSS)-induced expression of adhesion molecules and chemokines was enhanced in human umbilical vein endothelial cells (HUVEC) treated with Nrf2 siRNA and arterial endothelial cells isolated from Nrf2 knockout mice. Hence, we propose the hypothesis that PLSS maintains the endothelium in an anti-atherogenic state via intracellular antioxidant levels increased as a result of Nrf2 activation, thereby preventing excess ROS/RNS production required for pro-atherogenic gene expression.

Redox signaling in an in vivo murine model of low magnitude oscillatory wall shear stress

Wall Shear Stress (WSS) has been identified as an important factor in the pathogenesis of atherosclerosis. We utilized a novel murine aortic coarctation model to acutely create a region of low magnitude oscillatory WSS in vivo. We employed this model to test the hypothesis that acute changes in WSS in vivo induce upregulation of inflammatory proteins, mediated by reactive oxygen species (ROS). Superoxide generation and VCAM-1 expression both increased in regions of low magnitude oscillatory WSS. WSS-dependent superoxide formation was attenuated by tempol treatment, but was unchanged in p47 phox knockout (ko) mice. However, in both the p47 phox ko mice and the tempol-treated mice, low magnitude oscillatory WSS produced an increase in VCAM-1 expression comparable to control mice. Additionally, this same VCAM-1 expression was observed in ebselen-treated mice and catalase overexpressing mice. These results suggest that although the redox state is important to the overall pathogenesis of atherosclerosis, the initial WSS-dependent inflammatory response leading to lesion localization is not dependent on ROS.

Visit-to-visit blood pressure variations: new independent determinants for carotid artery measures in the elderly at high risk of cardiovascular disease

Recently, visit-to-visit variability in systolic blood pressure (SBP) has been shown to be a predictor of stroke. In this study, we investigated the relationship of visit-to-visit blood pressure (BP) variations (based on 12 visits once a month) with intima-media thickness (IMT) and stiffness in common carotid artery among the 201 high-risk elderly (female 75%) at cardiovascular disease. Max-IMT was significantly positively correlated with age, smoking, renin-angiotensin system inhibitor use, coefficient of variation (CV), and delta (maximum-minimum) in SBP, and CV in diastolic BP (DBP) but was significantly negatively correlated with female, high-density lipoprotein (HDL), and minimum in SBP. Stiffness parameter β was significantly positively correlated with age, standard deviation (SD), CV, maximum, and delta in SBP, and SD, CV, and delta in DBP but was significantly negatively correlated with smoking, HDL, average, and minimum in DBP. In a multiple regression analysis, delta SBP (P < .001) was associated with max-IMT independently of average SBP. CV (P < .05) and delta (P < .05) in SBP, and CV (P < .001) and delta (P < .01) in DBP were associated with stiffness parameter β independently of average BP. In the high-risk elderly, exaggerated visit-to-visit BP fluctuations were significant indicators for carotid artery atherosclerosis and stiffness independently of average BP.

Application of autologous bone marrow mononuclear cells in six patients with advanced chronic critical limb ischemia as a result of diabetes: our experience

BACKGROUND AIMS

Previous clinical studies have reported that the injection of bone marrow (BM)-derived mononuclear cells (MNC) results in improvement in symptoms and healing of ulcers in patients with critical limb ischemia (CLI) up to stage IV of Fontaine's classification. However, most patients with Fontaine stage IV CLI limbs had to undergo amputation even after stem cell therapy. We report on six patients, who had poorly controlled diabetes with extensive ulceration and gangrene of limbs because of Fontaine stage IV CLI and had been advised amputation elsewhere, who underwent injection of autologous BM MNC.

METHODS

In all six patients, BM was aspirated and the isolated MNC from the BM were injected intralesionally at various sites of the ulcer and its surroundings after necessary debridement. The patients were followed up at regular intervals for at least 6 months.

RESULTS

At the end of the 6-month follow-up, the lower limb pain and ulcers had improved significantly in all patients. The mean toe-brachial index had increased from 0.26 to 0.36. One patient died a month after therapy because of causes unrelated to the procedure. Limb salvage was possible in the remaining five patients and they had a pain-free walking distance of 100 m within 6 months.

CONCLUSIONS

Limb salvage was possible in all six diabetic patients with Fontaine stage IV CLI following autologous BM MNC injection. The procedure was safe without any adverse outcomes.

Malignancies confined to disused arteriovenous fistulae in renal transplant patients: an important differential diagnosis

BACKGROUND

Swelling in an arteriovenous fistula (AVF) is commonly caused by thrombosis, aneurysm and infection. However, due to the increased risk of malignancy after transplantation, this should also be considered.

PATIENTS

We discuss 4 patients with malignancy confined to an AVF after renal transplantation presenting in a 2-year period. Angiosarcoma was diagnosed in 3 patients and the other had post-transplant lymphoproliferative disorder (PTLD). Angiosarcoma behaves aggressively and 2 of our patients died within 6 months of diagnosis. There are 6 previous cases and 5 died within 16 months of diagnosis. PTLD at AVFs has not been documented previously.

CONCLUSION

Malignancy at an AVF is a rare but important differential that can impact significantly on patient morbidity and mortality. Predilection for malignancy at an AVF is not understood. We review the literature and discuss possible aetiologies.

MicroRNA-21 targets peroxisome proliferators-activated receptor-alpha in an autoregulatory loop to modulate flow-induced endothelial inflammation

Adhesion of circulating monocytes to vascular endothelial cells (ECs) is a critical event leading to vascular inflammation and, hence, development of atherosclerosis. MicroRNAs (miRs) are a class of endogenous, highly conserved, noncoding small RNAs that play important roles in regulating gene expression and cellular function, as well as pathogenesis of atherosclerosis. Here, we showed that oscillatory shear stress (OSS) induces the expression of miR-21 at the transcriptional level in cultured human umbilical vein ECs via an increased binding of c-Jun, which is a component of transcription factor activator protein-1 (AP-1), to the promoter region of miR-21. OSS induction of miR-21 inhibited the translation, but not transcription, of peroxisome proliferators-activated receptor-α (PPARα) by 3'-UTR targeting. Overexpression of miR-21 up-regulated AP-1 activation, which was attenuated by exogenous expression of PPARα. OSS and overexpression of miR-21 enhanced the expression of adhesion molecules vascular cell adhesion molecule-1 and monocyte chemotactic protein-1 and the consequential adhesion of monocytes to ECs. Overexpression of PPARα significantly attenuated the AP-1-mediated miR-21 expression. These results demonstrate a unique mechanism by which OSS induces AP-1-dependent miR-21 expression, which directly targets PPARα to inhibit its expression, thereby allowing activation of AP-1 and the promotion of monocyte adhesion. Our findings suggest the presence of a positive feedback loop that enables the sustained induction of miR-21, thus contributing to the proinflammatory responses of vascular endothelium under OSS.

Computational analysis of nanoparticle adhesion to endothelium: effects of kinetic rate constants and wall shear rates

Various nanoparticles have been developed as imaging probes and drug carriers, and their selectivity in binding to target cells determines the efficacy of these functionalized nanoparticles. Since target cells in different arterial segments experience different hemodynamic environments, we study the effects of wall shear rate waveforms on particle binding. We also explore the effects of the kinetic rate constant, which is determined by particle design parameters, on particle binding. A transport and reaction model is used to evaluate nanoparticle binding to the substrate in a laminar flow chamber. Flow and particle concentration fields are solved by using a computational fluid dynamics. The particle binding rate increases as the mean value of wall shear increases, and the amplitudes of sinusoidal shear waveform do not affect the bound particle density profiles significantly. Particle binding rates increase with the rate constant of attachment (k(A)), and are more sensitively affected by low k(A) values and less by k(A) values higher than 1 × 10⁻⁶ m s⁻¹. Since binding selectivity is affected by k(A) and the wall shear rate, the results of this study can be used for designing functionalized nanoparticles targeting for the specific cells that experience a specific shear rate.

Effects of exercise on endothelium and endothelium/smooth muscle cross talk: role of exercise-induced hemodynamics

Physical activity, exercise training, and fitness are associated with decreased cardiovascular risk. In the context that a risk factor "gap" exists in the explanation for the beneficial effects of exercise on cardiovascular disease, it has recently been proposed that exercise generates hemodynamic stimuli which exert direct effects on the vasculature that are antiatherogenic. In this review we briefly introduce some of the in vitro and in vivo evidence relating exercise hemodynamic modulation and vascular adaptation. In vitro data clearly demonstrate the importance of shear stress as a potential mechanism underlying vascular adaptations associated with exercise. Supporting this is in vivo human data demonstrating that exercise-mediated shear stress induces localized impacts on arterial function and diameter. Emerging evidence suggests that exercise-related changes in hemodynamic stimuli other than shear stress may also be associated with arterial remodeling. Taken together, in vitro and in vivo data strongly imply that hemodynamic influences combine to orchestrate a response to exercise and training that regulates wall stress and peripheral vascular resistance and contributes to the antiatherogenic impacts of physical activity, fitness, and training.

Effects of disturbed flow on vascular endothelium: pathophysiological basis and clinical perspectives

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

Time rate of blood pressure variation is associated with impaired renal function in hypertensive patients

OBJECTIVES

The rate of blood pressure (BP) variation has been positively associated with intima-media thickness of common carotid arteries and left ventricular mass. We evaluated the association between the rate of BP variation derived from ambulatory blood pressure monitoring (ABPM) data analysis and impaired renal function.

METHODS

Twenty-four-hour ABPM was performed in 803 untreated hypertensive patients. The estimated glomerular filtration rate (eGFR) was assessed using the abbreviated equation of the Modification Diet for Renal Disease study. Patients were divided into two groups: those with an eGFR less than 60 ml/min per 1.73 m(2) (group A) and those with an eGFR 60 ml/min per 1.73 m(2) or more (group B).

RESULTS

The 24-h rate of systolic BP variation was significantly (P = 0.004) higher in group A [0.616 mmHg/min; 95% confidence interval (CI) 0.596-0.636] than in group B patients (0.585 mmHg/min; 95% CI 0.578-0.591), even after adjusting for baseline characteristics and ABPM parameters. In the entire study population, the multiple logistic regression models revealed the following variables as independent determinants of impaired renal function: age, male sex, office systolic BP and 24-h rate of systolic BP variation. In this model, the odds ratio for impaired renal function associated with each 0.1 mmHg/min increase in 24-h rate of systolic BP variation was 1.49 (95% CI 1.18-1.88, P = 0.001).

CONCLUSION

The 24-h rate of SBP variation is independently associated with impaired renal function. Target-organ damage in hypertensive patients, in addition to BP levels, dipping status and BP variability, may also be related to a steeper rate of BP fluctuations.

Endothelial differentiation of adipose-derived stem cells from elderly patients with cardiovascular disease

Adipose-derived stem cells (ASCs) possess significant therapeutic potential for tissue engineering and regeneration. This study investigates the endothelial differentiation and functional capacity of ASCs isolated from elderly patients. Isolation of ASCs from 53 patients (50-89 years) revealed that advanced age or comorbidity did not negatively impact stem cell harvest; rather, higher numbers were observed in older donors (>70 years) than in younger. ASCs cultured in endothelial growth medium-2 for up to 3 weeks formed cords upon Matrigel and demonstrated acetylated-low-density lipoprotein and lectin uptake. Further stimulation with vascular endothelial growth factor and shear stress upregulated endothelial cell-specific markers (CD31, von Willebrand factor, endothelial nitric oxide synthase, and VE-cadherin). Inhibition of the PI(3)K but not mitogen-activated protein kinase pathway blocked the observed endothelial differentiation. Shear stress promoted an anti-thrombogenic phenotype as demonstrated by production of tissue-plasminogen activator and nitric oxide, and inhibition of plasminogen activator inhibitor-1. Shear stress augmented integrin α(5)β(1) expression and subsequently increased attachment of differentiated ASCs to basement membrane components. Finally, ASCs seeded onto a decellularized vein graft resisted detachment despite application of shear force up to 9 dynes. These results suggest that (1) advanced age and comorbidity do not negatively impact isolation of ASCs, and (2) these stem cells retain significant capacity to acquire key endothelial cell traits throughout life. As such, adipose tissue is a practical source of autologous stem cells for vascular tissue engineering.

Expression of Endothelial Adhesion Molecules After Radiosurgery in an Animal Model of Arteriovenous Malformation

BACKGROUND:

Endothelial adhesion molecules may be important in the response of brain arteriovenous malformations (AVMs) to radiosurgery. In addition to a putative role in the occlusive process after radiosurgery, they may serve as potential targets for biological strategies to accelerate intravascular thrombosis.

OBJECTIVE:

To determine the temporal expression of E-selectin and vascular cell adhesion molecule-1 in an animal model of AVMs.

METHODS:

Forty-one Sprague-Dawley rats underwent surgical creation of a carotid-to-jugular anastomosis. Radiosurgery (25 Gy) was delivered to the model “nidus” after 6 weeks, and the tissue was harvested 1 to 84 days after radiosurgery. Control groups received sham irradiation. Immunofluorescence was used to study the expression of E-selectin and vascular cell adhesion molecule-1.

RESULTS:

Endothelial E-selectin expression was limited to regions receiving radiosurgery. E-selectin expression reached maximal expression at 24 hours after radiosurgery and was sustained for another 24 hours before gradually reducing to baseline at 84 days post-radiosurgery (P &lt; .01). Vascular cell adhesion molecule-1 expression remained at the baseline level for the first week; a 50% increase was observed at 21 days after radiosurgery, which was sustained for another 3 weeks before returning to the baseline at 84 days after radiosurgery (P &lt; .05).

CONCLUSION:

Radiosurgery stimulates early expression of E-selectin and delayed up-regulation of vascular cell adhesion molecule-1 on the endothelial surface of the AVM model nidus. Cell adhesion molecule expression may play an important role in the process leading to vascular obliteration after irradiation. These molecular alterations may be harnessed to promote thrombosis in the irradiated vasculature using a vascular targeting agent.

Role of hemodynamic shear stress in cardiovascular disease

Atherosclerosis is the main cause of morbidity and mortality in the Western world. Inflammation and blood flow alterations are new markers emerging as possible determinants for the development of atherosclerotic lesions. In particular, blood flow exerts a shear stress on vessel walls that alters cell physiology. Shear stress arises from the friction between two virtual layers of a fluid and is induced by the difference in motion and viscosity between these layers. Regions of the arterial tree with uniform geometry are exposed to a unidirectional and constant flow, which determines a physiologic shear stress, while arches and bifurcations are exposed to an oscillatory and disturbed flow, which determines a low shear stress. Atherosclerotic lesions develop mainly in areas of low shear stress, while those exposed to a physiologic shear stress are protected. The presence of areas of the arterial tree with different wall shear stress may explain, in part, the different localization of atherosclerotic lesions in both coronary and extracoronary arteries. The measurement of this parameter may help in identifying atherosclerotic plaques at higher risk as well as in evaluating the efficacy of different pharmacological interventions. Moreover, an altered shear stress is associated with the occurrence of both aortic and intracranial aneurysms, possibly leading to their growth and rupture. Finally, the evaluation of shear stress may be useful for predicting the risk of developing restenosis after coronary and peripheral angioplasty and for devising a coronary stent with a strut design less thrombogenic and more conducive to endothelization.

Perfusion and characterization of an endothelial cell-seeded modular tissue engineered construct formed in a microfluidic remodeling chamber

Tissue engineered constructs containing tortuous endothelial cell-lined perfusion channels were formed by randomly assembling endothelial cell-seeded submillimeter-sized collagen cylinders (modules) into a microfluidic perfusion chamber. The interconnected void space produced by random module packing created flow channels that were lined with endothelial cells. The effect of perfusion (0.5 mL min(-1), Re( *) = 27.78 and shear stress = 0.16 dyn cm(-2)) through the tortuous channels on construct remodeling and endothelium quiescence was studied. Over time, modules fused at their points of contact and as they contracted, decreased the internal void space, which reduced the overall perfusion through the construct. As compared to static controls, perfusion caused a transient increase in activation (ICAM-1 and VCAM-1 expression) after 1 h followed by a decrease after 24 h. Proliferation (by BrdU) was reduced significantly, while KLF2, which is upregulated with atheroprotective laminar shear stress, was upregulated significantly after 24 h. VE-cadherin became discontinuous and was significantly downregulated after 24 h, which was likely caused by the dismantling of the endothelial cell adherens junctions during remodeling. Collectively, these outcomes suggest that flow through the construct did not drive the endothelial cells towards an inflamed, "atherosclerotic like" disturbed flow pathology.

Shear-induced endothelial cell-cell junction inclination

Atheroprone regions of the arterial circulation are characterized by time-varying, reversing, and oscillatory wall shear stress. Several in vivo and in vitro studies have demonstrated that flow reversal (retrograde flow) is atherogenic and proinflammatory. The molecular and structural basis for the sensitivity of the endothelium to flow direction, however, has yet to be determined. It has been hypothesized that the ability to sense flow direction is dependent on the direction of inclination of the interendothelial junction. Immunostaining of the mouse aorta revealed an inclination of the cell-cell junction by 13 degrees in direction of flow in the descending aorta where flow is unidirectional. In contrast, polygonal cells of the inner curvature where flow is disturbed did not have any preferential inclination. Using a membrane specific dye, the angle of inclination of the junction was dynamically monitored using live cell confocal microscopy in confluent human endothelial cell monolayers. Upon application of shear the junctions began inclining within minutes to a final angle of 10 degrees in direction of flow. Retrograde flow led to a reversal of junctional inclination. Flow-induced junctional inclination was shown to be independent of the cytoskeleton or glycocalyx. Additionally, within seconds, retrograde flow led to significantly higher intracellular calcium responses than orthograde flow. Together, these results show for the first time that the endothelial intercellular junction inclination is dynamically responsive to flow direction and confers the ability to endothelial cells to rapidly sense and adapt to flow direction.

Effect of endothelial cell proliferation on atherogenesis: a role of p21(Sdi/Cip/Waf1) in monocyte adhesion to endothelial cells

OBJECTIVE

Uniform laminar shear stress (LS) and disturbed turbulent shear stress (DS) are thought to play opposite roles in preventing or inducing atherosclerosis. Endothelial cell (EC) growth and monocyte adhesion to ECs, an early event in atherosclerosis, are also oppositely regulated by LS and DS. However, how atherogenesis is affected by the regulation of growth by blood flow is unknown. Here we examined the role of p21(Sdi/Cip/Waf1) (p21), a growth inhibitor induced by LS, in monocyte adhesion to ECs.

METHODS

p21 was overexpressed by transfecting a p21-expressing adenoviral vector into ECs. Factors linking EC growth, monocyte adhesion, and p21 were examined by microarray analysis, PCR and Western blotting.

RESULTS

Compared with DS, in the presence or absence of TNFalpha, LS significantly inhibited EC growth and monocyte adhesion to ECs. Both EC proliferation and monocyte adhesion induced by DS were inhibited by p21-overexpression. LS suppressed the expression of thioredoxin-interacting protein (TXNIP). Thioredoxin (TRX) activity, which is suppressed by TXNIP, was therefore higher under LS than DS, as reported previously. p21-overexpression significantly suppressed the DS-induced TXNIP expression, and inhibited the expression of vascular cell adhesion molecule 1 and chemokine (C-C motif) ligand 5 (CCL5/RANTES), which stimulates leukocyte recruitment and is downregulated by ROS scavenging.

CONCLUSION

p21 may function to prevent atherogenesis by regulating the redox balance, which leads to the inhibition of adhesion molecule and chemokine expression in ECs under LS.

Angiosarcoma developing in a non-functioning arteriovenous fistula post-renal transplant

BACKGROUND

Angiosarcomas comprise less than 1% of all sarcomas, arising from endothelial cells of blood or lymph vessels. Chronic immunosuppression increases the risk of many malignancies and an association between the development of angiosarcoma with an immunosuppressed state is established. A few cases have been reported of angiosarcomas arising in the post-renal transplant patient. Specifically, there have been six cases of an angiosarcoma arising in arteriovenous (AV) fistulae in this patient population. We describe a further case and review the relevant literature with specific emphasis on a possible mechanism for the development of angiosarcoma in the post-transplant patient.

CASE PRESENTATION

We report the case of a 48-year-old male who developed an angiosarcoma in a ligated native AV fistula. The lesion arose on the background of immunosuppression following a successful ABO-incompatible renal transplant for chronic renal failure.

CONCLUSION

Angiosarcomas are extremely rare tumours but should be considered as a differential diagnosis for an evolving mass near the site of an AV fistula. Diagnosis relies on an index of suspicion and obtaining a definitive histological diagnosis. Both clinicians and patients should be aware that an evolving mass within or around an AV fistula should prompt urgent biopsy.

An in vitro perfusion system to examine the responses of endothelial cells to simulated flow and inflammatory stimulation

Atherosclerosis is a disease process which develops at the arterial branches and curvatures of medium to large arteries. Local haemodynamic flow patterns in these vessels play an essential role in the formation of atherosclerotic lesions. To simulate pro-atherogenic blood flow patterns, we have developed a perfusion system with the ability to simulate in vivo patterns of blood flow in vitro. In this system, human umbilical vein endothelial cells were seeded in y-shaped microslides, in which they were exposed to a variety of flow patterns. Besides being able to reproduce the disturbed flow involved in the development of pro-atherogenic events within the arterial wall, the system also permitted the assessment of the pre-conditioning/priming effect of oscillatory flow on endothelial cells. The system was further capable of integrating multi-endpoint assays relevant to cardiovascular disease. We show that oscillatory flow primed endothelial cells, making them more sensitive to subsequent treatments. The treatment of oscillatory flow primed cells with TNFalpha resulted in the detection of enhanced levels of pro-inflammatory and chemoattractant factors such as IL-8 and MCP-1. These measurements were facilitated by the small volumes of medium circulating within the perfusion system. Oscillatory flow also altered the characteristics of monocyte adhesion to the endothelial layer. In summary, this system allows the monitoring of multiple endpoints and biomarkers, and provides an alternative to the use of in vivo and ex vivo models of cardiovascular disease.

Identification of CD44 as a senescence-induced cell adhesion gene responsible for the enhanced monocyte recruitment to senescent endothelial cells

The mechanism that is responsible for progression of atherosclerosis seen with increasing age remains controversial. This issue was addressed in the present study, by searching for genes that are uniquely expressed in senescent endothelial cells and functionally involved in inflammatory leukocyte adhesion recognized as a critical step in the initiation of atherogenesis. Senescent human umbilical vein endothelial cells (HUVECs) prepared by continuous subculturing in vitro showed higher binding affinity for monocytes (THP-1 cells, human acute monocytic leukemia cell line) compared with young cells. Gene expression profiles between young and senescent endothelial cells were compared by the cDNA microarray method, and CD44 was identified as one of the "senescence-induced cell adhesion genes" whose expression was upregulated in senescent cells and whose gene ontology annotation indicated their role in cell adhesion. The enhanced gene expression of CD44 in senescent endothelial cells was verified both at the mRNA and protein levels. Adhesion of monocytes to senescent endothelial cells was significantly reduced following pretreatment of endothelial cells with the CD44 antibody or small-interfering RNA, thus reinforcing the critical role of CD44 in the inflammatory event. Exogenous expression of CD44 in young HUVECs and in human aortic endothelial cells led to an increase in monocyte adhesion. CD44 expression levels in the rat aorta endothelium were found to increase in an age-dependent manner, as determined by immunohistochemistry and Western blotting. CD44 and other senescence-induced cell adhesion genes identified in this study may provide the novel targets for the prevention of inflammatory leukocyte adhesion leading to the development atherosclerosis.

HUVEC ICAM-1 and VCAM-1 synthesis in response to potentially athero-prone and athero-protective mechanical and nicotine chemical stimuli

Previous mechano-transduction studies have investigated the endothelial cell (EC) morphological response to mechanical stimuli; generally consisting of a wall shear stress (WSS) and a cyclic tensile hoop strain (THS). More recent studies have investigated the EC biochemical response (intercellular adhesion molecule, ICAM-1, and vascular cellular adhesion molecule, VCAM-1, expression) to idealized mechanical stimuli. However, current literature is lacking in the area of EC biochemical response to combinations of physiological WSS and THS mechanical stimuli. The objective of this study is to investigate the EC response to physiological WSS and THS stimuli and to compare this response to that of ECs exposed to idealized steady WSS and cyclic THS of the same magnitudes. This study also investigated the EC response to a nicotine chemical stimulus combined with a suspected athero-prone physiological mechanical stimulus. A bioreactor was designed to apply a range of combinations of physiological WSS and THS waveforms. The bioreactor was calibrated and validated using computational fluid dynamics and video extensometry techniques. The bioreactor was used to investigated the biochemical response exhibited by human umbilical vein endothelial cells (HUVECs) exposed to physiological athero-protective (first bioreactor test case, pulsatile WSS combined with pulsatile THS) and athero-prone (second bioreactor test case, oscillating WSS combined with pulsatile THS) mechanical environments. The final testing environment (third bioreactor test case) combined a nicotine chemical stimulus with the mechanical stimuli of the second bioreactor test case. In first and second bioreactor test cases, the addition of a pulsatile THS to the WSS resulted in opposite trends of ICAM-1 down-regulation and up-regulation, respectively. This outcome suggests that the effect of the additional pulsatile THS depends on the state of the applied WSS waveform. Similarly, in first and second bioreactor test cases, the addition of a pulsatile THS to the WSS resulted in a VCAM-1 up-regulation. However, it has been previously shown that the addition of a cyclic THS to a high- or low-steady WSS resulted in a VCAM-1 down-regulation, indicating that the EC response to idealized mechanical stimuli (steady WSS and cyclic THS) is not comparable to physiological mechanical stimuli (unsteady WSS and pulsatile THS), even though in both situations the average magnitude of WSS and THS applied were similar. In third bioreactor test case, a nicotine chemical stimulus induced a substantial VCAM-1 up-regulation and a moderate ICAM-1 up-regulation. The addition of the mechanical stimuli of the second bioreactors test case resulted in a greater VCAM-1 up-regulation than what was expected, considering the observations of the previous second bioreactor test case alone. This study found that the EC biochemical response to physiological mechanical stimuli is not comparable to the previously observed EC response to idealized mechanical stimuli, even though in both environments the mechanical stimuli were of a similar magnitude. Also, the level of VCAM-1 expressed by the nicotine stimulated ECs showed an elevated level of sensitivity to the athero-prone mechanical stimuli.

Genetic and cellular evidence of vascular inflammation in neurofibromin-deficient mice and humans

Neurofibromatosis type 1 (NF1) results from mutations in the NF1 tumor suppressor gene, which encodes the protein neurofibromin. NF1 patients display diverse clinical manifestations, including vascular disease, which results from neointima formation and vessel occlusion. However, the pathogenesis of NF1 vascular disease remains unclear. Vessel wall homeostasis is maintained by complex interactions between vascular and bone marrow-derived cells (BMDCs), and neurofibromin regulates the function of each cell type. Therefore, utilizing cre/lox techniques and hematopoietic stem cell transplantation to delete 1 allele of Nf1 in endothelial cells, vascular smooth muscle cells, and BMDCs alone, we determined which cell lineage is critical for neointima formation in vivo in mice. Here we demonstrate that heterozygous inactivation of Nf1 in BMDCs alone was necessary and sufficient for neointima formation after vascular injury and provide evidence of vascular inflammation in Nf1+/- mice. Further, analysis of peripheral blood from NF1 patients without overt vascular disease revealed increased concentrations of inflammatory cells and cytokines previously linked to vascular inflammation and vasoocclusive disease. These data provide genetic and cellular evidence of vascular inflammation in NF1 patients and Nf1+/- mice and provide a framework for understanding the pathogenesis of NF1 vasculopathy and potential therapeutic and diagnostic interventions.

Endothelial cell responses to atheroprone flow are driven by two separate flow components: low time-average shear stress and fluid flow reversal

To simulate the effects of shear stress in regions of the vasculature prone to developing atherosclerosis, we subjected human umbilical vein endothelial cells to reversing shear stress to mimic the hemodynamic conditions at the wall of the carotid sinus, a site of complex, reversing blood flow and commonly observed atherosclerosis. We compared the effects of reversing shear stress (time-average: 1 dyn/cm(2), maximum: +11 dyn/cm(2), minimum: -11 dyn/cm(2), 1 Hz), arterial steady shear stress (15 dyn/cm(2)), and low steady shear stress (1 dyn/cm(2)) on gene expression, cell proliferation, and monocyte adhesiveness. Microarray analysis revealed that most differentially expressed genes were similarly regulated by all three shear stress regimens compared with static culture. Comparisons of the three shear stress regimens to each other identified 138 genes regulated by low average shear stress and 22 genes regulated by fluid reversal. Low average shear stress induced increased cell proliferation compared with high shear stress. Only reversing shear stress exposure induced monocyte adhesion. The adhesion of monocytes was partially inhibited by the incubation of endothelial cells with ICAM-1 blocking antibody. Increased heparan sulfate proteoglycan expression was observed on the surface of cells exposed to reversing shear stress. Heparinase III treatment significantly reduced monocyte adhesion. Our results suggest that low steady shear stress is the major impetus for differential gene expression and cell proliferation, whereas reversing flow regulates monocyte adhesion.

Integrated microfluidic chip for endothelial cells culture and analysis exposed to a pulsatile and oscillatory shear stress

For a comprehensive understanding of cells or tissues, it is important to enable multiple studies under the controllable microenvironment of a chip. In this report, we present an integrated microfluidic cell culture platform in which endothelial cells (ECs) are under static conditions or exposed to a pulsatile and oscillatory shear stress. Through the integration of a microgap, self-contained flow loop, pneumatic pumps, and valves, the novel microfluidic chip achieved multiple functions: pulsatile and oscillatory fluid circulation, cell trapping, cell culture, the formation of ECs barrier, and adding shear stress on cells. After being introduced into the chip by gravity, the ECs arranged along the microgap with the help of hydrodynamic forces and grew in the microchannel for more than 7 days. The cells proliferated and migrated to form a barrier at the microgap to mimic the vessel wall, which separated the microenvironment into two compartments, microchannel and microchamber. An optimized pneumatic micropump was embedded to actuate flow circulation in a self-contained loop that induced a pulsatile and oscillatory shear stress at physiological levels on the ECs in the microchannel. All the analyses were performed under either static or dynamic conditions. The performance of the barrier was evaluated by the diffusion and distribution behaviors of fluorescently labeled albumin. The permeability of the barrier was comparable to that in traditional in vitro assays. The concentration gradients of the tracer formed in the microchamber can potentially be used to study cell polarization, migration and communications in the future. Additionally, the morphology and cytoskeleton of the ECs response to the pulsatile and oscillatory shear stress were analyzed. The microfluidic chip provided a multifunctional platform to enable comprehensive studies of blood vessels at the cell or tissue level.

Vascular cell adhesion molecule-1 expression in endothelial cells exposed to physiological coronary wall shear stresses

Atherosclerosis is consistently found in bifurcations and curved segments of the circulatory system, indicating disturbed hemodynamics may participate in disease development. In vivo and in vitro studies have shown that endothelial cells (ECs) alter their gene expression in response to their hemodynamic environment, in a manner that is highly dependent on the exact nature of the applied forces. This research exposes cultured ECs to flow patterns present in the coronary arterial network, in order to determine the role of hemodynamic forces in plaque initiation. Vascular cell adhesion molecule-1 (VCAM-1) was examined as an indicator of plaque growth, as it participates in monocyte adhesion, which is one of the initial steps in the formation of fatty lesions. The hemodynamics of a healthy right and left coronary artery were determined by reconstructing 3D models from cineangiograms and employing computational fluid dynamic models to establish physiological coronary flow patterns. Wall shear stress (WSS) profiles selected from these studies were applied to ECs in a cone and plate bioreactor. The cone and plate system was specifically designed to be capable of reproducing the high frequency harmonics present in physiological waveforms. The shear stresses chosen represent those from regions prone to disease development and healthier arterial segments. The levels of the transcriptional and cell surface anchored VCAM-1 were quantified by flow cytometry and real time RT-PCR over a number of timepoints to obtain a complete picture of the relationship between this adhesion molecule and the applied shear stress. The WSS profiles from regions consistently displaying a higher incidence of plaques in vivo, induced greater levels of VCAM-1, particularly at the earlier timepoints. Conversely, the WSS profile from a straight section of vessel with undisturbed flow indicated no upregulation in VCAM-1 and a significant downregulation after 24 h, when compared with static controls. Low shear stress from the outer wall of a bifurcation induced four times the levels of VCAM-1 messenger ribonucleic acid (mRNA) after four hours when compared with levels of mRNA induced by WSS from a straight arterial section. This shear profile also induced prolonged expression of the surface protein of this molecule. The current study has provided insight into the possible influences of coronary hemodynamics on plaque localization, with VCAM-1 only significantly induced by the WSS from disease prone regions.

Partial carotid ligation is a model of acutely induced disturbed flow, leading to rapid endothelial dysfunction and atherosclerosis

Atherosclerosis is closely associated with disturbed flow characterized by low and oscillatory shear stress, but studies directly linking disturbed flow to atherogenesis is lacking. The major reason for this has been a lack of an animal model in which disturbed flow can be acutely induced and cause atherosclerosis. Here, we characterize partial carotid ligation as a model of disturbed flow with characteristics of low and oscillatory wall shear stress. We also describe a method of isolating intimal RNA in sufficient quantity from mouse carotid arteries. Using this model and method, we found that partial ligation causes upregulation of proatherogenic genes, downregulation of antiatherogenic genes, endothelial dysfunction, and rapid atherosclerosis in 2 wk in a p47(phox)-dependent manner and advanced lesions by 4 wk. We found that partial ligation results in endothelial dysfunction, rapid atherosclerosis, and advanced lesion development in a physiologically relevant model of disturbed flow. It also allows for easy and rapid intimal RNA isolation. This novel model and method could be used for genome-wide studies to determine molecular mechanisms underlying flow-dependent regulation of vascular biology and diseases.

Laminar shear stress regulates endothelial kinin B1 receptor expression and function: potential implication in atherogenesis

OBJECTIVE

The proinflammatory phenotype induced by low laminar shear stress (LSS) is implicated in atherogenesis. The kinin B1 receptor (B1R), known to be induced by inflammatory stimuli, exerts many proinflammatory effects including vasodilatation and leukocyte recruitment. We investigated whether low LSS is a stimulus for endothelial B1R expression and function.

METHODS AND RESULTS

Human and mouse atherosclerotic plaques expressed high level of B1R mRNA and protein. In addition, B1R expression was upregulated in the aortic arch (low LSS region) of ApoE(-/-) mice fed a high-fat diet compared to vascular regions of high LSS and animals fed normal chow. Of interest, a greater expression of B1R was noticed in endothelial cells from regions of low LSS in aortic arch of ApoE(-/-) mice. B1R was also upregulated in human umbilical vein endothelial cells (HUVECs) exposed to low LSS (0 to 2 dyn/cm(2)) compared to physiological LSS (6 to 10 dyn/cm(2)): an effect similarly evident in murine vascular tissue perfused ex vivo. Functionally, B1R activation increased prostaglandin and CXCL5 expression in cells exposed to low, but not physiological, LSS. IL-1beta and ox-LDL induced B1R expression and function in HUVECs, a response substantially enhanced under low LSS conditions and inhibited by blockade of NFkappaB activation.

CONCLUSIONS

Herein, we show that LSS is a major determinant of functional B1R expression in endothelium. Furthermore, whereas physiological high LSS is a powerful repressor of this inflammatory receptor, low LSS occurring [corrected] at sites of atheroma is associated with substantial upregulation, identifying this receptor as a potential therapeutic target.

Recent advances in the application of computational mechanics to the diagnosis and treatment of cardiovascular disease

During the last 30 years, research into the pathogenesis and progression of cardiovascular disease has had to employ a multidisciplinary approach involving a wide range of subject areas, from molecular and cell biology to computational mechanics and experimental solid and fluid mechanics. In general, research was driven by the need to provide answers to questions of critical importance for disease management. Ongoing improvements in the spatial resolution of medical imaging equipment coupled to an exponential growth in the capacity, flexibility and speed of computational techniques have provided a valuable opportunity for numerical simulations and complex experimental techniques to make a contribution to improving the diagnosis and clinical management of many forms of cardiovascular disease. This paper contains a review of recent progress in the numerical simulation of cardiovascular mechanics, focusing on three particular areas: patient-specific modeling and the optimization of surgery in pediatric cardiology, evaluating the risk of rupture in aortic aneurysms, and noninvasive characterization of intraventricular flow in the management of heart failure.

Impact of shear rate modulation on vascular function in humans

Shear stress is an important stimulus to arterial adaptation in response to exercise and training in humans. We recently observed significant reverse arterial flow and shear during exercise and different antegrade/retrograde patterns of shear and flow in response to different types of exercise. The purpose of this study was to simultaneously examine flow-mediated dilation, a largely NO-mediated vasodilator response, in both brachial arteries of healthy young men before and after 30-minute interventions consisting of bilateral forearm heating, recumbent leg cycling, and bilateral handgrip exercise. During each intervention, a cuff inflated to 60 mm Hg was placed on 1 arm to unilaterally manipulate the shear rate stimulus. In the noncuffed arm, antegrade flow and shear increased similarly in response to each intervention (ANOVA; P<0.001, no interaction between interventions; P=0.71). Baseline flow-mediated dilation (4.6%, 6.9%, and 6.7%) increased similarly in response to heating, handgrip, and cycling (8.1%, 10.4%, and 8.9%, ANOVA; P<0.001, no interaction; P=0.89). In contrast, cuffed arm antegrade shear rate was lower than in the noncuffed arm for all of the conditions (P<0.05), and the increase in flow-mediated dilation was abolished in this arm (4.7%, 6.7%, and 6.1%; 2-way ANOVA: all conditions interacted P<0.05). These results suggest that differences in the magnitude of antegrade shear rate transduce differences in endothelial vasodilator function in humans, a finding that may have relevance for the impact of different exercise interventions on vascular adaptation in humans.