Strain-Dependent Vascular Remodeling

Genetic background influences arterial vasomotor function in male and female mice

The purpose of this study was to assess the influence of genetic background and sex on nitric oxide (NO)-mediated vasomotor function in arteries from different vascular territories. Vasomotor function was assessed in thoracic aorta, abdominal aorta, carotid arteries, and femoral arteries from the following mouse strains: SJL/J, DBA/2J, NZW/LacJ, and C57BL/6J. Contractile responses were assessed using the α1-adrenergic receptor agonist phenylephrine (PE, 10-9 -10-5  M). Vasorelaxation responses were assessed by examining relaxation to an endothelium-dependent vasodilator acetylcholine (ACh, 10-9 -10-5  M) and an endothelium-independent vasodilator sodium nitroprusside (SNP, 10-9 -10-5  M). To evaluate the role of NO, relaxation responses to ACh and SNP were assessed in the absence or presence of a nitric oxide synthase inhibitor (N omega-nitro-l-arginine methyl ester hydrochloride: 10-4  M). Vasomotor responses to ACh and PE varied across strains and among the arteries tested with some strains exhibiting artery-specific impairment. Results indicated some concentration-response heterogeneity in response to ACh and SNP between vessels from females and males, but no significant differences in responses to PE. Collectively, these findings indicate that vasomotor responses vary by genetic background, sex, and artery type.

Beiging of perivascular adipose tissue regulates its inflammation and vascular remodeling

Although inflammation plays critical roles in the development of atherosclerosis, its regulatory mechanisms remain incompletely understood. Perivascular adipose tissue (PVAT) has been reported to undergo inflammatory changes in response to vascular injury. Here, we show that vascular injury induces the beiging (brown adipose tissue-like phenotype change) of PVAT, which fine-tunes inflammatory response and thus vascular remodeling as a protective mechanism. In a mouse model of endovascular injury, macrophages accumulate in PVAT, causing beiging phenotype change. Inhibition of PVAT beiging by genetically silencing PRDM16, a key regulator to beiging, exacerbates inflammation and vascular remodeling following injury. Conversely, activation of PVAT beiging attenuates inflammation and pathological vascular remodeling. Single-cell RNA sequencing reveals that beige adipocytes abundantly express neuregulin 4 (Nrg4) which critically regulate alternative macrophage activation. Importantly, significant beiging is observed in the diseased aortic PVAT in patients with acute aortic dissection. Taken together, vascular injury induces the beiging of adjacent PVAT with macrophage accumulation, where NRG4 secreted from the beige PVAT facilitates alternative activation of macrophages, leading to the resolution of vascular inflammation. Our study demonstrates the pivotal roles of PVAT in vascular inflammation and remodeling and will open a new avenue for treating atherosclerosis.

Perivascular adipose tissue (PVAT) has been reported to undergo inflammatory changes in response to vascular injury. Here, the authors show that vascular injury induces the beiging (brown adipose tissue-like phenotype change) of PVAT, which fine-tunes inflammatory response as a protective mechanism.

Physalin B inhibits PDGF-BB-induced VSMC proliferation, migration and phenotypic transformation by activating the Nrf2 pathway

Vascular intimal hyperplasia is a hallmark event in vascular restenosis. The excessive proliferation, migration and phenotypic transformation of vascular smooth muscle cells (VSMCs) play important roles in the pathological mechanism of vascular intimal hyperplasia. Physalin B is an alcoholate isolated from Physalis (Solanaceae) that has a wide range of biological activities. However, the effect of physalin B on VSMCs is currently unclear. In this study, we demonstrated that physalin B significantly inhibited the proliferation, migration and phenotypic transformation of VSMCs induced by PDGF-BB. Physalin B also reduced inflammation and oxidative stress in VSMCs induced by PDGF-BB. Mechanistic studies showed that physalin B plays a role mainly by activating Nrf2. After Nrf2 activation, physalin B mitigates oxidative stress by enhancing the expression of the antioxidant gene HO-1; on the other hand, physalin B inhibits the NF-κB pathway to alleviate the inflammatory response. These two effects ultimately reduce the proliferation, migration and phenotypic transformation of VSMCs induced by PDGF-BB. In addition, in the mouse carotid artery ligation model, physalin B prevented intimal hyperplasia and inhibited the proliferation, migration and phenotypic transformation of cells in the hyperplastic intima. In conclusion, we provided significant evidence that physalin B abrogates PDGF-BB-induced VSMC proliferation, migration, phenotypic transformation and intimal hyperplasia by activating Nrf2-mediated signal transduction. Therefore, physalin B may be a potential therapeutic agent for preventing or treating restenosis.

KCa3.1 Inhibition Decreases Size and Alters Composition of Atherosclerotic Lesions Induced by Low, Oscillatory Flow

Low, oscillatory flow/shear patterns are associated with atherosclerotic lesion development. Increased expression of K_Ca3.1 has been found in Vascular Smooth Muscle (VSM), macrophages and T-cells in lesions from humans and mice. Increased expression of K_Ca3.1, is also required for VSM cell proliferation and migration. Previously, we showed that the specific K_Ca3.1 inhibitor, TRAM-34, could inhibit coronary neointimal development following balloon injury in swine. Atherosclerosis develops in regions with a low, oscillatory (i.e. atheroprone) flow pattern. Therefore, we used the Partial Carotid Ligation (PCL) model in high-fat fed, Apoe^−/− mice to determine the role of K_Ca3.1 in atherosclerotic lesion composition and development. PCL was performed on 8–10 week old male Apoe^−/− mice and subsequently placed on a Western diet (TD.88137, Teklad) for 4 weeks. Mice received daily s.c. injections of TRAM-34 (120 mg/kg) or equal volumes of vehicle (peanut oil, PO). 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) treatment reduced lesion size ~50% (p < 0.05). In addition, lesions from TRAM-34 treated mice contained less collagen (6% ± 1% vs. 15% ± 2%; p < 0.05), fibronectin (14% ± 3% vs. 32% ± 3%; p < 0.05) and smooth muscle content (19% ± 2% vs. 29% ± 3%; p < 0.05). Conversely, TRAM-34 had no effect on total cholesterol (1455 vs. 1334 mg/dl, PO and TRAM, resp.) or body weight (29.1 vs. 28.8 g, PO and TRAM, resp.). Medial smooth muscle of atherosclerotic carotids showed diminished RE1-Silencing Transcription Factor (REST)/Neural Restrictive Silencing Factor (NRSF) expression, while REST overexpression in vitro inhibited smooth muscle migration. Together, these data support a downregulation of REST/NRSF and upregulation of K_Ca3.1 in determining smooth muscle and matrix content of atherosclerotic lesions.

Simple model of atherosclerosis in cylindrical arteries: impact of anisotropic growth on Glagov remodeling

In 1987, Seymour Glagov observed that arteries went through a two-stage remodeling process as a result of plaque growth: first, a compensatory phase where the lumen area remains approximately constant and second, an encroachment phase where the lumen area decreases over time. In this paper, we investigate the effect of growth anisotropy on Glagov remodeling in five different cases: pure radial, pure circumferential, pure axial, isotropic and general anisotropic growth where the elements of the growth tensor are chosen to minimize the total energy. We suggest that the nature of anisotropy is inclined towards the growth direction that requires the least amount of energy. Our framework is the theory of morphoelasticity on an axisymmetric arterial domain. For each case, we explore their specific effect on the Glagov curves. For the latter two cases, we also provide the changes in collagen fiber orientation and length in the intima, media and adventitia. In addition, we compare the total energy produced by growth in radial, circumferential and axial direction and deduce that using a radially dominant anisotropic growth leads to lower strain energy than isotropic growth.

Natriuretic Peptide Receptor 2 Locus Contributes to Carotid Remodeling

Background Carotid artery intima/media thickness (IMT) is a hallmark trait associated with future cardiovascular events. The goal of this study was to map new genes that regulate carotid IMT by genome-wide association. Methods and Results We induced IMT by ligation procedure of the left carotid artery in 30 inbred mouse strains. Histologic reconstruction revealed significant variation in left carotid artery intima, media, adventitia, external elastic lamina volumes, intima-to-media ratio, and (intima+media)/external elastic lamina percent ratio in inbred mice. The carotid remodeling trait was regulated by distinct genomic signatures with a dozen common single-nucleotide polymorphisms associated with left carotid artery intima volume, intima-to-media ratio, and (intima+media)/external elastic lamina percent ratio. Among genetic loci on mouse chromosomes 1, 4, and 12, there was natriuretic peptide receptor 2 (Npr2), a strong candidate gene. We observed that only male, not female, mice heterozygous for a targeted Npr2 deletion (Npr2^+/-) exhibited defective carotid artery remodeling compared with Npr2 wild-type (Npr2^+/+) littermates. Fibrosis in carotid IMT was significantly increased in Npr2^+/- males compared with Npr2^+/- females or Npr2^+/+ mice. We also detected decreased Npr2 expression in human atherosclerotic plaques, similar to that seen in studies in Npr2^+/- mice. Conclusions We found that components of carotid IMT were regulated by distinct genetic factors. We also showed a critical role for Npr2 in genetic regulation of vascular fibrosis associated with defective carotid remodeling.

Label-free photoacoustic and ultrasound imaging for murine atherosclerosis characterization

Dual-modality photoacoustic tomography (PAT) and 4D ultrasound (4DUS) imaging have shown promise for cardiovascular applications, but their use in murine atherosclerosis imaging is limited. This study used PAT and 4DUS to correlate altered arterial strain and hemodynamics to morphological changes and lipid localization in a murine partial carotid ligation (PCL) model of atherosclerosis. Validation experiments showed a positive correlation between the PAT signal-to-noise ratio and plaque lipid composition obtained from oil-red O histology. Cross-sectional in situ PAT and longitudinal in vivo ultrasound imaging was performed using a 40 MHz transducer. Ultrasound timepoints included days 0, 1, 4, 7, 10, and 14 for hemodynamic and strain assessment, and 1100 nm and 1210 nm PAT was implemented at the study end point for hemoglobin and lipid characterization. These study groups were then separated into day 4 post-PCL with (n = 5) and without (n = 6) Western diet feeding, as well as days 7 (n = 8), 10 (n = 8), and 14 (n = 8) post-PCL, in addition to a sham control group on a Western diet (n = 5). Overall, our data revealed a substantial decrease in left carotid artery pulsatility by day 7. The hemodynamic results suggested greater disturbed flow in the caudal regions resulting in earlier vessel stenosis and greater lipid deposition than cranial regions. Morphological and compositional data revealed heterogeneous vascular remodeling between days 0 and 7, with a rapid decrease in the vessel volume/length and the presence of both intraplaque hematoma and lipid deposition at day 10 post-PCL. These results highlight the utility of utilizing dual-modality PAT and 4DUS to study atherosclerosis progression.

Differential Consequences of Bmp9 Deletion on Sinusoidal Endothelial Cell Differentiation and Liver Fibrosis in 129/Ola and C57BL/6 Mice

The aim of the present work was to address the role of BMP9 in different genetic backgrounds (C57BL/6, BALB/c, and 129/Ola) of mice deleted for Bmp9. We found that Bmp9 deletion led to premature mortality only in the 129/Ola strain. We have previously shown that Bmp9 deletion led to liver sinusoidal endothelial cells (LSEC) capillarization and liver fibrosis in the 129/Ola background. Here, we showed that this is not the case in the C57BL/6 background. Analysis of LSEC from Wild-type (WT) versus Bmp9-KO mice in the C57BL/6 background showed no difference in LSEC fenestration and in the expression of differentiation markers. Comparison of the mRNA expression of LSEC differentiation markers between WT C57BL/6 and 129/Ola mice showed a significant decrease in Stabilin2, Plvap, and CD209b, suggesting a more capillary-like phenotype in WT C57BL/6 LSECs. C57BL/6 mice also had lower BMP9 circulating concentrations and hepatic Vegfr2 mRNA levels, compared to the 129/Ola mice. Taken together, our observations support a role for BMP9 in liver endothelial cell fenestration and prevention of fibrosis that is dependent on genetic background. It also suggests that 129/Ola mice are a more suitable model than C57BL/6 for the study of liver fibrosis subsequent to LSEC capillarization.

Cystathionine γ-Lyase Modulates Flow-Dependent Vascular Remodeling

Objective- Flow patterns differentially regulate endothelial cell phenotype, with laminar flow promoting vasodilation and disturbed flow promoting endothelial proinflammatory activation. CSE (cystathionine γ-lyase), a major source of hydrogen sulfide (H₂S) in endothelial cells, critically regulates cardiovascular function, by both promoting vasodilation and reducing endothelial activation. Therefore, we sought to investigate the role of CSE in the endothelial response to flow. Approach and Results- Wild-type C57Bl/6J and CSE knockout ( CSE^-/-) mice underwent partial carotid ligation to induce disturbed flow in the left carotid. In addition, endothelial cells isolated from wild-type and CSE ^-/- mice were exposed to either laminar or oscillatory flow, an in vitro model of disturbed flow. Interestingly, laminar flow significantly reduced CSE expression in vitro, and only disturbed flow regions show discernable CSE protein expression in vivo, correlating with enhanced H₂S production in wild-type C57BL/6J but not CSE^-/- mice. Lack of CSE limited disturbed flow-induced proinflammatory gene expression (ICAM-1[intercellular adhesion molecule 1], VCAM-1 [vascular cell adhesion molecular 1]) and monocyte infiltration and CSE^-/- endothelial cells showed reduced NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activation and proinflammatory gene expression in response to oscillatory flow in vitro. In addition, CSE^-/- mice showed reduced inward remodeling after partial carotid ligation. CSE^-/- mice showed elevated vascular nitrite levels (measure of nitric oxide [NO]) in the unligated carotids, suggesting an elevation in baseline NO production, and the NO scavenger 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxy-3-oxide normalized the reduced inward remodeling, but not inflammation, of ligated carotids in CSE^-/- mice. Conclusions- CSE expression in disturbed flow regions critically regulates both endothelial activation and flow-dependent vascular remodeling, in part through altered NO availability.

Strain-selective efficacy of sacubitril/valsartan on carotid fibrosis in response to injury in two inbred mouse strains

BACKGROUND AND PURPOSE

Sacubitril/valsartan (Sac/val) is more effective than valsartan in lowering BP and mortality in patients with heart failure. Here, we proposed that Sac/val treatment would be more effective in preventing pathological vascular remodelling in 129X1/SvJ (129X1), than in C57BL/6J (B6) inbred mice.

EXPERIMENTAL APPROACH

Sac/val (60 mg·kg^-1 ·day^-1 ) and valsartan (27 mg·kg^-1 ·day^-1 ) were given as prophylactic or therapeutic treatments, to 129X1 or B6 mice with carotid artery ligation for 14 days. Blood flow was measured by ultrasound. Ex vivo, carotid tissue was analysed with histological and morphometric techniques, together with RNA sequencing and gene ontology.

KEY RESULTS

Sac/val was more effective than valsartan in lowering BP in 129X1 compared with B6 mice. Liver expression of CYP2C9 and plasma cGMP levels were similar across treatments. A reduction in carotid thickening after prophylactic treatment with valsartan or Sac/val also resulted in significant arterial shrinkage in B6 mice. In 129X1 mice, Sac/val and prophylactic treatment with valsartan had no effect on carotid thickening but preserved carotid size. BP lowering significantly correlated with a decline in carotid stiffness (R²  = .37, P = .0096) in 129X1 but not in B6 mice. The gene expression signature associated with hyalurononglucosaminidase activity was down-regulated in injured arteries after both regimens of Sac/val only in 129X1 mice. Administration of Sac/val but not valsartan significantly reduced deposition of hyaluronic acid and carotid fibrosis in 129X1 mice.

CONCLUSION AND IMPLICATIONS

These results underscore the importance of the genetic background in the efficacy of the Sac/val on vascular fibrosis.

Genetic and Environmental Contributions to Variation in the Posterior Communicating Collaterals of the Circle of Willis

Variation in blood flow mediated by the posterior communicating collateral arteries (PComs) contributes to variation in the severity of tissue injury in obstructive disease. Evidence in animals and humans indicates that differences in the extent of PComs, i.e., their anatomic lumen diameter and whether they are present bilaterally, unilaterally, or absent, are a major factor. These differences arise during development since they are present at birth. However, the causal mechanisms are unknown. We used angiography after maximal dilation to examine involvement of genetic, environmental, and stochastic factors. The extent of PComs varied widely among seven genetically diverse strains of mice. Like pial collaterals in the microcirculation, aging and hypertension reduced PCom diameter, while in contrast, obesity, hyperlipidemia, metabolic syndrome, and diabetes mellitus had no effect. Naturally occurring intrauterine growth restriction had no effect on extent of PCom or pial collaterals in the adult. The number and diameter of PComs evidenced much larger apparent stochastic-dependent variation than pial collaterals. In addition, both PComs underwent flow-mediated outward remodeling after unilateral permanent MCA occlusion that varied with genetic background and was greater on the ipsilesional side. These findings indicate that variation in the number and diameter of PCom collateral arteries arises from stochastic factors and naturally occurring genetic variants that differ from those that cause variation in pial collateral arterioles. Environmental factors also contribute: aging and hypertension reduce PCom diameter. Our results suggest possible sources of variation of PComs in humans and provide information relevant when studying mouse models of occlusive cerebrovascular disease.

Biomechanical Phenotyping of the Murine Aorta: What Is the Best Control?

The availability of diverse mouse models is revealing increasingly greater information on arterial mechanics, including homeostatic adaptations and pathologic maladaptations to genetic, pharmacological, and surgical manipulations. Fundamental to understanding such biomechanical changes, however, is reliable information on appropriate control vessels. In this paper, we contrast 15 different geometrical and mechanical metrics of biaxial wall mechanics for the ascending aorta across seven different types of possible control mice. We show that there is a comforting similarity across these multiple controls for most, though not all, metrics. In particular, three potential controls, namely, noninduced conditional mice, exhibit higher values of distensibility, an important clinical metric of structural stiffness, and two of these potential controls also have higher values of intrinsic circumferential material stiffness. There is motivation, therefore, to understand better the biomechanical changes that can arise with noninduced Cre-lox or similar approaches for generating mutations conditionally. In cases of germline mutations generated by breeding heterozygous +/- mice, however, the resulting homozygous +/+ mice tend to exhibit properties similar to traditional (C57BL/6) controls.

Model-based vascular elastography improves the detection of flow-induced carotid artery remodeling in mice

Increased arterial thickness measured with ultrasound correlates with future cardiovascular events, but conventional ultrasound imaging techniques cannot distinguish between intima, media, or atherosclerotic plaque in the carotid artery. In this work, we evaluated how well vascular elastography can detect intimal changes in a mouse model of carotid remodeling. We ligated the left external and internal branches of the carotid artery of male FVB mice and performed sham operations for 2 weeks. High-resolution ultrasound imaging accurately detected lower blood velocities and low blood volume flow in the carotid arteries after ligation in FVB mice. However, ultrasound could not detect differences in the carotid wall even at 2 weeks post-surgery. The Young’s modulus was measured based on displacements of the carotid artery wall, and Young’s modulus was 2-fold greater in shams at 1 week post ligation, and 3-fold greater 2 weeks after ligation. Finally, the higher Young’s modulus was most associated with higher intimal thickness but not medial or adventitial thickness as measured by histology. In conclusion, we developed a robust ultrasound-based elastography method for early detection of intimal changes in small animals.

Vascular remodeling: A redox-modulated mechanism of vessel caliber regulation

Vascular remodeling, i.e. whole-vessel structural reshaping, determines lumen caliber in (patho)physiology. Here we review mechanisms underlying vessel remodeling, with emphasis in redox regulation. First, we discuss confusing terminology and focus on strictu sensu remodeling. Second, we propose a mechanobiological remodeling paradigm based on the concept of tensional homeostasis as a setpoint regulator. We first focus on shear-mediated models as prototypes of remodeling closely dominated by highly redox-sensitive endothelial function. More detailed discussions focus on mechanosensors, integrins, extracellular matrix, cytoskeleton and inflammatory pathways as potential of mechanisms potentially coupling tensional homeostasis to redox regulation. Further discussion of remodeling associated with atherosclerosis and injury repair highlights important aspects of redox vascular responses. While neointima formation has not shown consistent responsiveness to antioxidants, vessel remodeling has been more clearly responsive, indicating that despite the multilevel redox signaling pathways, there is a coordinated response of the whole vessel. Among mechanisms that may orchestrate redox pathways, we discuss roles of superoxide dismutase activity and extracellular protein disulfide isomerase. We then discuss redox modulation of aneurysms, a special case of expansive remodeling. We propose that the redox modulation of vascular remodeling may reflect (1) remodeling pathophysiology is dominated by a particularly redox-sensitive cell type, e.g., endothelial cells (2) redox pathways are temporospatially coordinated at an organ level across distinct cellular and acellular structures or (3) the tensional homeostasis setpoint is closely connected to redox signaling. The mechanobiological/redox model discussed here can be a basis for improved understanding of remodeling and helps clarifying mechanisms underlying prevalent hard-to-treat diseases.

Low Endothelial Shear Stress Predicts Evolution to High-Risk Coronary Plaque Phenotype in the Future

Background—

Low endothelial shear stress (ESS) is associated with plaque progression and vulnerability. To date, changes in plaque phenotype over time in relation to ESS have not been studied in humans. The aim of this study was to investigate whether local ESS can predict subsequent changes to plaque phenotype using optical coherence tomography.

Methods and Results—

A total of 25 coronary arteries from 20 patients who underwent baseline and 6-month follow-up optical coherence tomography were included. Arteries were divided into serial 3-mm segments, and plaque characteristics were evaluated in each segment. A total of 145 segments were divided into low-ESS group (ESS <1 Pa) and higher-ESS group (ESS ≥1 Pa) based on baseline computational flow dynamics analyses. At baseline, low-ESS segments had significantly thinner fibrous cap thickness compared with higher-ESS segments (128.2±12.3 versus 165.0±12.0 μm; P =0.03), although lipid arc was similar. At follow-up, fibrous cap thickness remained thin in low-ESS segments, whereas it significantly increased in higher-ESS segments (165.0±12.0 to 182.2±14.1 μm; P =0.04). Lipid arc widened only in plaques with low ESS (126.4±15.2° to 141.1±14.0°; P =0.01). After adjustment, baseline ESS was associated with fibrous cap thickness (β, 9.089; 95% confidence interval, 2.539–15.640; P =0.007) and lipid arc (β, −4.381; 95% confidence interval, −6.946 to −1.815; P =0.001) at follow-up.

Conclusions—

Low ESS is significantly associated with baseline high-risk plaque phenotype and progression to higher-risk phenotype at 6 months.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01110538.

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.

Vascular Imaging Outcomes of Childhood Primary Angiitis of the Central Nervous System

BACKGROUND

Inflammation affecting cerebral blood vessels is a common cause of stroke in children. Arterial abnormalities on vascular imaging are an important risk factor for stroke recurrence. We aimed to describe the vascular imaging outcomes in children with primary angiitis of the central nervous system after 12 months and identify factors associated with vascular progression and stroke recurrence.

METHODS

We retrospectively analyzed clinical and neuroimaging data from the BrainWorks Registry of children with large-vessel primary angiitis of the central nervous system. Neuroimaging was collected at baseline and at least 12-month follow-up, and vascular outcome was categorized as improved, stable, or progressed based on comparison of magnetic resonance angiography. Univariate clinical and neuroimaging predictors were associated with outcome by Fisher exact test.

RESULTS

Our study consisted of 27 children; 20 male; median age was 7.92 years (range, two to 15 years). Twelve patients received steroids (44%). Median follow-up time was 16 months (range, 12 to 56 months). Vascular imaging outcome was categorized as improved in 37%, stable in 22%, and progressed in 41% of patients. Discordant progression, defined as progression and improvement occurring simultaneously across multiple vessels, was observed in 26%. Stroke recurred in 15%, occurring exclusively in the group with progression on follow-up imaging (P = 0.02).

CONCLUSIONS

After 12 months, 40% of children with primary angiitis of the central nervous system demonstrated progression on vascular imaging, without apparent clinical or angiographic predictors. Stroke recurrence was associated with vascular progression. Discordant progression is a newly described angiographic finding. Further studies are necessary to determine if this represents a unique characteristic of inflammatory arteriopathies.

Multi-Layer Mechanical Model of Glagov Remodeling in Coronary Arteries: Differences between In-Vivo and Ex-Vivo Measurements

When blood vessels undergo remodeling because of the buildup of atherosclerotic plaque, it is thought that they first undergo compensatory or outward remodeling, followed by inward remodeling: the lumen area stays roughly constant or increases slightly and then decreases rapidly. The second phase of remodeling is supposed to start after the plaque burden exceeds about 40%. These changes in the vessel were first observed by S. Glagov who examined cross-sections of coronary arteries at different stages of the disease. In this paper, we use a mathematical model based on growth and elasticity theory to verify the main aspects of Glagov’s result. However, both our model and curve-fitting to the data suggest that the critical stenosis is around 20% rather than 40%. Our model and data from the PROSPECT trial also show that Glagov remodeling is qualitatively different depending on whether measurements are taken ex-vivo or in-vivo. Our results suggest that the first outward phase of “Glagov remodeling” is largely absent for in-vivo measurements: that is, the lumen area always decreases as plaque builds up. We advocate that care must be taken when infering how in-vivo vessels remodel from ex-vivo data.

Morphometric analysis of calcification and fibrous layer thickness in carotid endarterectomy tissues

BACKGROUND

Advanced atherosclerotic lesions are commonly characterized by the presence of calcification. Several studies indicate that extensive calcification is associated with plaque stability, yet recent studies suggest that calcification morphology and location may adversely affect the mechanical stability of atherosclerotic plaques. The underlying cause of atherosclerotic calcification and the importance of intra-plaque calcium distribution remains poorly understood.

METHOD

The goal of this study was the characterization of calcification morphology based on histological features in 20 human carotid endarterectomy (CEA) specimens. Representative frozen sections (10μm thick) were cut from the common, bulb, internal and external segments of CEA tissues and stained with von Kossa׳s reagent for calcium phosphate. The morphology of calcification (calcified patches) and fibrous layer thickness were quantified in 135 histological sections.

RESULTS

Intra-plaque calcification was distributed heterogeneously (calcification %-area: bulb segment: 14.2±2.1%; internal segment: 12.9±2.8%; common segment: 4.6±1.1%; p=0.001). Calcified patches were found in 20 CEAs (patch size: <0.1mm(2) to >1.0mm(2)). Calcified patches were most abundant in the bulb and least in the common segment (bulb n=7.30±1.08; internal n=4.81±1.17; common n=2.56±0.56; p=0.0007). Calcified patch circularity decreased with increasing size (<0.1mm(2): 0.77±0.01, 0.1-1mm(2): 0.62±0.01, >1.0mm(2): 0.51±0.02; p=0.0001). A reduced fibrous layer thickness was associated with increased calcium patch size (p<0.0001).

CONCLUSIONS

In advanced carotid atherosclerosis, calcification appears to be a heterogeneous and dynamic atherosclerotic plaque component, as indicated by the simultaneous presence of few large stabilizing calcified patches and numerous small calcific patches. Future studies are needed to elucidate the associations of intra-plaque calcification size and distribution with atherothrombotic events.

Fasudil, a Rho‑kinase inhibitor, prevents intima‑media thickening in a partially ligated carotid artery mouse model: Effects of fasudil in flow‑induced vascular remodeling

Vascular remodeling in response to hemodynamic alterations is a physiological process that requires coordinated signaling between endothelial, inflammatory and vascular smooth muscle cells (VSMCs). Extensive experimental and clinical studies have indicated the critical role of the Ras homolog gene family, member A/Rho‑associated kinase (ROCK) signaling pathway in the pathogenesis of cardiovascular disease, where ROCK activation has been demonstrated to promote inflammation and remodeling through inducing the expression of proinflammatory cytokines and adhesion molecules in endothelial cells and VSMCs. However, the role of ROCK in flow‑induced vascular remodeling has not been fully defined. The current study aimed to investigate the effect of the ROCK signaling pathway in flow‑induced vascular remodeling by comparing the responses to partial carotid artery ligation in mice treated with fasudil (a ROCK inhibitor) and untreated mice. Intima‑media thickness and neointima formation were evaluated by morphology. VSMC proliferation and inflammation of the vessel wall were assessed by immunohistochemistry. In addition, the expression levels of ROCK and the downstream effectors of ROCK, myosin light chain (MLC) and phosphorylated‑MLC (p‑MLC), were quantified by western blot analysis. Following a reduction in blood flow, ROCK1 and p‑MLC expression increased in the untreated left common carotid arteries (LCA). Fasudil‑treated mice developed a significantly smaller intima‑media thickness compared with the untreated mice. Quantitative immunohistochemistry of the fasudil‑treated LCA indicated that there was a reduction in proliferation when compared with untreated vessels. There were fewer CD45+ cells observed in the fasudil‑treated LCA compared with the untreated LCA. In conclusion, the expression of ROCK was enhanced in flow‑induced carotid artery remodeling and ROCK inhibition as a result of fasudil treatment may attenuate flow‑induced carotid artery remodeling.

Autonomic dysfunction determines stress-induced cardiovascular and immune complications in mice

BACKGROUND

Clinical studies suggest that acute inflammation in patients with elevated heart rate (HR) increases morbidity and mortality. The SJL/J (SJL) inbred mouse strain is a unique genetic model that has higher HR and systemic and vascular inflammation compared with C3HeB/FeJ (C3HeB) mice. The goal of this study was to investigate the role of stress on cardiac and vascular complications between 2 strains.

METHODS AND RESULTS

Radiotelemetry was used for continuous recordings of HR and blood pressure in mice. Hemodynamic differences between mouse strains were very small without stress; however, tail-cuff training generated mild stress and significantly increased HR (≈2-fold) in SJL compared with C3HeB mice. Circulating proinflammatory monocytes (CD11b(+)Ly6C(H) (i)) significantly increased in SJL mice but not in C3HeB mice after stress. Presence of Ly6C(+) cells in injured carotids was elevated only in SJL mice after stress; however, a transfer of bone marrow cells from SJL/C3HeB to C3HeB/SJL chimeras had no effect on HR or vascular inflammation following stress. Arterial inflammation (VCAM-1(+)) was greater in SJL inbred mice or SJL recipient chimeras, even without stress or injury. HR variability was reduced in SJL mice compared with C3HeB mice.

CONCLUSIONS

We found that impaired parasympathetic activity is central for stress-induced elevation of HR and systemic and vascular inflammation; however, immune cells from stress-susceptible mice had no effect on HR or vascular inflammation in stress-protected mice.

Animal models of surgically manipulated flow velocities to study shear stress-induced atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial tree that develops at predisposed sites, coinciding with locations that are exposed to low or oscillating shear stress. Manipulating flow velocity, and concomitantly shear stress, has proven adequate to promote endothelial activation and subsequent plaque formation in animals. In this article, we will give an overview of the animal models that have been designed to study the causal relationship between shear stress and atherosclerosis by surgically manipulating blood flow velocity profiles. These surgically manipulated models include arteriovenous fistulas, vascular grafts, arterial ligation, and perivascular devices. We review these models of manipulated blood flow velocity from an engineering and biological perspective, focusing on the shear stress profiles they induce and the vascular pathology that is observed.

Markers of inflammation associated with plaque progression and instability in patients with carotid atherosclerosis

Atherosclerosis is the focal expression of a systemic disease affecting medium- and large-sized arteries, in which traditional cardiovascular risk factor and immune factors play a key role. It is well accepted that circulating biomarkers, including C-reactive protein and interleukin-6, reliably predict major cardiovascular events, including myocardial infarction or death. However, the relevance of biomarkers of systemic inflammation to atherosclerosis progression in the carotid artery is less established. The large majority of clinical studies focused on the association between biomarkers and subclinical atherosclerosis, that is, carotid intima-media thickening (cIMT), which represents an earlier stage of the disease. The aim of this work is to review inflammatory biomarkers that were associated with a higher atherosclerotic burden, a faster disease progression, and features of plaque instability, such as inflammation or neovascularization, in patients with carotid atherosclerotic plaque, which represents an advanced stage of disease compared with cIMT. The association of biomarkers with the occurrence of cerebrovascular events, secondary to carotid plaque rupture, will also be presented. Currently, the degree of carotid artery stenosis is used to predict the risk of future cerebrovascular events in patients affected by carotid atherosclerosis. However, this strategy appears suboptimal. The identification of suitable biomarkers could provide a useful adjunctive criterion to ensure better risk stratification and optimize management.

Collagen inhibitory peptide R1R2 mediates vascular remodeling by decreasing inflammation and smooth muscle cell activation

The extracellular matrix (ECM) is a major constituent of the vessel wall. In addition to providing a structural scaffold, the ECM controls numerous cellular functions in both physiologic and pathologic settings. Vascular remodeling occurs after injury and is characterized by endothelial cell activation, inflammatory cell infiltration, phenotypic modulation of smooth muscle cells (SMCs), and augmented deposition of collagen-rich ECM. R1R2, a peptide derived from the bacterial adhesin SFS, with sequence homology to collagen, is known to inhibit collagen type I deposition in vitro by inhibiting the binding of fibronectin to collagen. However, the inhibitory effects of R1R2 during vascular remodeling have not been explored. We periadventitially delivered R1R2 to carotid arteries using pluronic gel in a vascular remodeling mouse model induced by blood flow cessation, and evaluated its effects on intima-media thickening, ECM deposition, SMC activation, and inflammatory cell infiltration. Morphometric analysis demonstrated that R1R2 reduced intima-media thickening compared to the control groups. R1R2 treatment also decreased collagen type I deposition in the vessel wall, and maintained SMC in the contractile phenotype. Interestingly, R1R2 dramatically reduced inflammatory cell infiltration into the vessel by ∼78%. This decrease was accompanied by decreased VCAM-1 and ICAM-1 expression. Our in vitro studies revealed that R1R2 attenuated SMC proliferation and migration, and also decreased monocyte adhesion and transendothelial migration through endothelial cells. Together, these data suggest that R1R2 attenuates vascular remodeling responses by decreasing inflammation and by modulating SMC proliferation and migration, and suggest that the R1R2 peptide may have therapeutic potential in treating occlusive vascular diseases.

Alternative splicing of endothelial fibronectin is induced by disturbed hemodynamics and protects against hemorrhage of the vessel wall

OBJECTIVE

Abnormally low-flow conditions, sensed by the arterial endothelium, promote aneurysm rupture. Fibronectin (FN) is among the most abundant extracellular matrix proteins and is strongly upregulated in human aneurysms, suggesting a possible role in disease progression. Altered FN splicing can result in the inclusion of EIIIA and EIIIB exons, generally not expressed in adult tissues. We sought to explore the regulation of FN and its splicing and their possible roles in the vascular response to disturbed flow.

APPROACH AND RESULTS

We induced low and reversing flow in mice by partial carotid ligation and assayed FN splicing in an endothelium-enriched intimal preparation. Inclusion of EIIIA and EIIIB was increased as early as 48 hours, with negligible increases in total FN expression. To test the function of EIIIA and EIIIB inclusion, we induced disturbed flow in EIIIAB(-/-) mice unable to include these exons and found that they developed focal lesions with hemorrhage and hypertrophy of the vessel wall. Acute deletion of floxed FN caused similar defects in response to disturbed flow, consistent with a requirement for the upregulation of the spliced isoforms, rather than a developmental defect. Recruited macrophages promote FN splicing because their depletion by clodronate liposomes blocked the increase in endothelial EIIIA and EIIIB inclusion in the carotid model.

CONCLUSIONS

These results uncover a protective mechanism in the inflamed intima that develops under disturbed flow, by showing that splicing of FN mRNA in the endothelium, induced by macrophages, inhibits hemorrhage of the vessel wall.

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

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

Inhibition of patched-1 prevents injury-induced neointimal hyperplasia

OBJECTIVE

To determine the role of patched receptor (Ptc)-1 in mediating pulsatile flow-induced changes in vascular smooth muscle cell growth and vascular remodeling.

APPROACH AND RESULTS

In vitro, human coronary arterial smooth muscle cells were exposed to normal or pathological low pulsatile flow conditions for 24 hours using a perfused transcapillary flow system. Low pulsatile flow increased vascular smooth muscle cell proliferation when compared with normal flow conditions. Inhibition of Ptc-1 by cyclopamine attenuated low flow-induced increases in Notch expression while concomitantly decreasing human coronary arterial smooth muscle cell growth to that similar under normal flow conditions. In vivo, ligation injury-induced low flow increased vascular smooth muscle cell growth and vascular remodeling, while increasing Ptc-1/Notch expression. Perivascular delivery of Ptc-1 small interfering RNA by pluronic gel inhibited the pathological low flow-induced increases in Ptc-1/Notch expression and markedly reduced the subsequent vascular remodeling.

CONCLUSIONS

These results suggest that pathological low flow stimulates smooth muscle cell growth in vitro and vascular remodeling in vivo via Ptc-1 regulation of Notch signaling.

Blood pressure, artery size, and artery compliance parallel bone size and strength in mice with differing ece1 expression

The recombinant congenic mouse strains HcB-8 and HcB-23 differ in femoral shape, size, and strength, with HcB-8 femora being more gracile, more cylindrical, weaker, and having higher Young's modulus. In previous work, we mapped a robust, pleiotropic quantitative trait locus for these bone traits. Ece1, encoding endothelin converting enzyme 1, is a positional candidate gene for this locus, and was less expressed in HcB-8 bone. We hypothesized that the same genetic factors would impose analogous developmental trajectories on arteries to those in bones. Cardiovascular hemodynamics and biomechanics of carotids were measured in adult HcB-8 and HcB-23 mice. Biological differences in heart and arteries were examined at mRNA and protein levels. As in bone, Ece1 expression was higher in HcB-23 heart and arteries (p &lt; 0.05), and its expression was correlated with that of the endothelin B type receptor target Nos3, encoding endothelial nitric oxide synthase. HcB-8 mice had higher ambulatory blood pressure (p &lt; 0.005) than HcB-23 mice. Ex vivo, at identical pressures, HcB-8 carotid arteries had smaller diameters and lower compliance (p &lt; 0.05), but the same elastic modulus compared to HcB-23 carotid arteries. HcB-8 hearts were heavier than HcB-23 hearts (p &lt; 0.01). HcB-8 has both small, stiff bones and small, stiff arteries, lower expression of Ece1 and Nos3, associated in each case with less favorable function. These findings suggest that endothelin signaling could serve as a nexus for the convergence of skeletal and vascular modeling, providing a potential mechanism for the epidemiologic association between skeletal fragility and atherosclerosis.

Identification of a genetic locus on chromosome 11 that regulates leukocyte infiltration in mouse carotid artery

OBJECTIVE

We demonstrated that inflammatory cells and intima-media thickening are increased in carotids exposed to low-blood flow in the SJL/J (SJL) strain compared with other mouse strains. We hypothesized that the extent of inflammation associated with intima-media thickening is a genetically regulated trait.

APPROACH AND RESULTS

We performed a whole genome approach to measure leukocyte infiltration in the carotid intima as a quantitative trait in a genetic cross between C3HeB/FeJ (C3H/F) and SJL mice. Immunostaining for CD45(+) (a pan-specific leukocyte marker) was performed on carotids from C3H/F, SJL, F1, and N2 progeny to measure leukocyte infiltration. We identified a nearly significant quantitative trait locus for CD45(+) on chromosome (chr) 11 (17 cM, LOD=2.3; significance was considered at threshold P=0.05). Interval mapping showed that the CD45(+) locus on chr 11 accounted for 8% of the variation in the logarithm of odds backcross. Importantly, the CD45(+) locus colocalized with the intima-modifier 2 (Im2) locus, which controls 17% of intima variation. We created 2 Im2 congenic lines of mice (C3H/F.SJL.11.1 and C3H/F.SJL.11.2) to better understand the regulation of intima-media thickening by the chr 11 locus. The C3H/F.SJL.11.1 congenic mouse showed ≈30% of the SJL trait, confirming that CD45(+) cell infiltration contributed to the intima trait.

CONCLUSIONS

We discovered a novel locus on chr 11 that controls leukocyte infiltration in the carotid. Importantly, this locus overlaps with our previously published Im2 locus on chr 11. Our study reveals a potential mechanistic relationship between leukocyte infiltration and intima-media thickening in response to decreased blood flow.

Ribosomal protein L17, RpL17, is an inhibitor of vascular smooth muscle growth and carotid intima formation

BACKGROUND

Carotid intima-media thickening is associated with increased cardiovascular risk in humans. We discovered that intima formation and cell proliferation in response to carotid injury is greater in SJL/J (SJL) in comparison with C3HeB/FeJ (C3H/F) mice. The purpose of this study was to identify candidate genes contributing to intima formation.

METHODS AND RESULTS

We performed microarray and bioinformatic analyses of carotid arteries from C3H/F and SJL mice. Kyoto Encyclopedia of Genes and Genomes analysis showed that the ribosome pathway was significantly up-regulated in C3H/F in comparison with SJL mice. Expression of a ribosomal protein, RpL17, was >40-fold higher in C3H/F carotids in comparison with SJL. Aortic vascular smooth muscle cells from C3H/F grew slower in comparison to SJL. To determine the role of RpL17 in vascular smooth muscle cell growth regulation, we analyzed the relationship between RpL17 expression and cell cycle progression. Cultured vascular smooth muscle cells from mice, rats, and humans showed that RpL17 expression inversely correlated with growth as shown by decreased cells in S phase and increased cells in G(0)/G(1). To prove that RpL17 acted as a growth inhibitor in vivo, we used pluronic gel delivery of RpL17 small interfering RNA to C3H/F carotid arteries. This resulted in an 8-fold increase in the number of proliferating cells. Furthermore, following partial carotid ligation in SJL mice, RpL17 expression in the intima and media decreased, but the number of proliferating cells increased.

CONCLUSIONS

RpL17 acts as a vascular smooth muscle cell growth inhibitor (akin to a tumor suppressor) and represents a potential therapeutic target to limit carotid intima-media thickening.

Immune modulation of vascular resident cells by Axl orchestrates carotid intima-media thickening

Cellular mechanisms of carotid intima-media thickening (IMT) are largely unknown. The receptor tyrosine kinase Axl is essential for function of both bone marrow (BM) and non-BM cells. We studied the mechanisms by which Axl expression in BM-derived cells (compared with non-BM-derived cells) mediates carotid IMT. Partial ligation of the left carotid artery resulted in a similar carotid blood flow reduction in Axl chimeras. Neither irradiation nor bone marrow transplantation had any effect on the 40% difference in carotid IMT between Axl genotypes. Axl-dependent survival is very important for intimal leukocytes; however, Axl expression in BM cells contributes to <30% of carotid IMT. Axl in non-BM cells has a greater effect on carotid remodeling. Expression of Axl in non-BM cells is crucial for the up-regulation of several key proinflammatory signals (eg, IL-1) in the carotid. We found that Axl is involved in immune activation of cultured smooth muscle cells and in immune heterogeneity of medial cells (measured by major histocompatibility complex class II) after carotid injury. Finally, a lack of Axl in non-BM cells increased collagen Iα expression, which may play a critical role in carotid remodeling. Our data suggest that Axl contributes to carotid remodeling not only by inhibition of apoptosis but also via regulation of immune heterogeneity of vascular cells, cytokine/chemokine expression, and extracellular matrix remodeling.

Lack of interleukin-1 signaling results in perturbed early vein graft wall adaptations

BACKGROUND

Vein grafts fail as the result of wall maladaptations to surgical injury and hemodynamic perturbations. Interleukin-1 signaling has emerged as an important mediator of the vascular response to trauma and hemodynamically induced vascular lesions. We therefore hypothesized that interleukin-1 signaling drives early vein graft wall adaptations.

METHODS

Using interleukin-1 type I receptor knockout (IL-1RI(-/-)) and wild-type (B6129SF2/J) mice, we investigated morphologic changes 28 days after interposition isograft from donor inferior vena cava to recipient carotid artery, without (n = 19) or with (n = 13) outflow restriction. The impact of mouse strain on the response to vein arterialization also was evaluated between B6129SF2/J (n = 18) and C57BL/6J (n = 19) mice.

RESULTS

No differences were observed in the traditional end points of intimal thickness and calculated luminal area, yet media+adventitia thickness of the vein graft wall of IL-1RI(-/-) mice was 44% to 52% less than wild-type mice, at the both proximal (P < .01, P < .01) and distal (P = .054, P < .01) portions of vein grafts, for both normal flow and low flow, respectively. Compared with the C57BL/6J strain, B6129SF2/J mice exhibited no difference in vein graft intimal thickness but 2-fold greater media+adventitia thickness (P < .01).

CONCLUSION

When lacking IL-1 signaling, the vein graft wall adapts differently compared with the injured artery, showing typical intima hyperplasia although attenuated media+adventitia thickening. B6129SF2/J mice exhibit more media+adventitia response than C57BL/6J mice. The inflammatory networks that underlie the vein response to arterialization hold many roles in the adaptation of the total wall; thus, the utility of anti-inflammatory approaches to extend the durability of vein grafts comes into question.

Genetic locus on mouse chromosome 7 controls elevated heart rate

Elevated heart rate (HR) is a risk factor for cardiovascular diseases. The goal of the study was to map HR trait in mice using quantitative trait locus (QTL) analysis followed by genome-wide association (GWA) analysis. The first approach provides mapping power and the second increases genome resolution. QTL analyses were performed in a C3HeB×SJL backcross. HR and systolic blood pressure (SBP) were measured by the tail-cuff plethysmography. HR was ∼80 beats/min higher in SJL compared with C3HeB. There was a wide distribution of the HR (536-763 beats/min) in N2 mice. We discovered a highly significant QTL (logarithm of odds = 6.7, P < 0.001) on chromosome 7 (41 cM) for HR in the C3HeB×SJL backcross. In the Hybrid Mouse Diversity Panel (58 strains, n = 5-6/strain) we found that HR (beats/min) ranged from 546 ± 12 in C58/J to 717 ± 7 in MA/MyJ mice. SBP (mmHg) ranged from 99 ± 6 in strain I/LnJ to 151 ± 4 in strain BXA4/PgnJ. GWA analyses were done using the HMDP, which revealed a locus (64.2-65.1 Mb) on chromosome 7 that colocalized with the QTL for elevated HR found in the C3HeB×SJL backcross. The peak association was observed for 17 SNPs that are localized within three GABA(A) receptor genes. In summary, we used a combined genetic approach to fine map a novel elevated HR locus on mouse chromosome 7.

In vivo bioluminescence imaging of inducible nitric oxide synthase gene expression in vascular inflammation

PURPOSE

Inflammation plays a critical role in atherosclerosis and is associated with upregulation of inducible nitric oxide synthase (iNOS). We studied bioluminescence imaging (BLI) to track iNOS gene expression in a murine model of vascular inflammation.

PROCEDURES

Macrophage-rich vascular lesions were induced by carotid ligation plus high-fat diet and streptozotocin-induced diabetes in 18 iNOS-luc reporter mice. In vivo iNOS expression was imaged serially by BLI over 14 days, followed by in situ BLI and histology.

RESULTS

BLI signal from ligated carotids increased over 14 days (9.7 ± 4.4 × 10(3 ) vs. 4.4 ± 1.7 × 10(3) photons/s/cm(2)/sr at baseline, p < 0.001 vs. baseline, p < 0.05 vs. sham controls). Histology confirmed substantial macrophage infiltration, with iNOS and luciferase expression, only in ligated left carotid arteries and not controls.

CONCLUSIONS

BLI allows in vivo detection of iNOS expression in murine carotid lesions and may provide a valuable approach for monitoring vascular gene expression and inflammation in small animal models.

Relationship between hemodynamics and atherosclerosis in aortic arches of apolipoprotein E-null mice on 129S6/SvEvTac and C57BL/6J genetic backgrounds

OBJECTIVE

We investigated the relationships between hemodynamics and differential plaque development at the aortic arch of apolipoprotein E (apoE)-null mice on 129S6/SvEvTac (129) and C57BL/6J (B6) genetic backgrounds.

METHODS

Mean flow velocities at the ascending and descending aorta (mVAA and mVDA) were measured by Doppler ultrasound in wild type and apoE-null male mice at 3 and 9 months of age. Following dissection of the aortic arches, anatomical parameters and plaque areas were evaluated.

RESULTS

Arch plaques were five times bigger in 129-apoE than in B6-apoE mice at 3 months, and twice as large at 9 months. The geometric differences, namely larger vessel diameter in the B6 strain and broader inner curvature of the aortic arch in the 129 strain, were exaggerated in 9-month-old apoE-null mice. Cardiac output and heart rate under anesthesia were significantly higher in the B6 strain than in the 129 strain. The values of mVAA were similar in the two strains, while mVDA was lower in the 129 strain. However, there was a 129-apoE-specific reduction of flow velocities with age, and both mVAA and mVDA were significantly lower in 129-apoE than in B6-apoE mice at 9 months. The mean relative wall shear stress (rWSS) over the aortic arch in 129-apoE and B6-apoE mice were not different, but animals with lower mean rWSS had larger arch plaques within each strain.

CONCLUSIONS

The plaque formation in the arch of apoE-null mice is accompanied by strain-dependent changes in both arch geometry and hemodynamics. While arch plaque sizes negatively correlate with mean rWSS, additional factors are necessary to account for the strain differences in arch plaque development.

Mouse vein graft hemodynamic manipulations to enhance experimental utility

Mouse models serve as a tool to study vein graft failure. However, in wild-type mice, there is limited intimal hyperplasia, hampering efforts to identify anti-intimal hyperplasia therapies. Furthermore, vein graft wall remodeling has not been well quantified in mice. We hypothesized that simple hemodynamic manipulations can reproducibly augment intimal hyperplasia and remodeling end points in mouse vein grafts, thereby enhancing their experimental utility. Mouse inferior vena cava-to-carotid interposition isografts were completed using an anastomotic cuff technique. Three flow restriction manipulations were executed by ligating outflow carotid branches, creating an outflow common carotid stenosis, and constructing a midgraft stenosis. Flowmetry and ultrasonography were used perioperatively and at day 28. All ligation strategies decreased the graft flow rate and wall shear stress. Morphometry showed that intimal thickness increased by 26% via carotid branch ligation and by 80% via common carotid stenosis. Despite similar mean flow rates and shear stresses among the three manipulations, the flow waveform amplitudes were lowest with common carotid stenosis. The disordered flow of the midgraft stenosis yielded poststenotic dilatation. The creation of an outflow common carotid stenosis generates clinically relevant (poor runoff) vein graft low wall shear stress and offers a technically flexible method for enhancing the intimal hyperplasia response. Midgraft stenosis exhibits poststenotic positive wall remodeling. These reproducible approaches offer novel strategies for increasing the utility of mouse vein graft models.

Animal, in vitro, and ex vivo models of flow-dependent atherosclerosis: role of oxidative stress

Atherosclerosis is an inflammatory disease preferentially occurring in curved or branched arterial regions, whereas straight parts of the arteries are protected, suggesting a close relationship between flow and atherosclerosis. However, evidence directly linking disturbed flow to atherogenesis is just emerging, thanks to the recent development of suitable animal models. In this article, we review the status of various animal, in vitro, and ex vivo models that have been used to study flow-dependent vascular biology and atherosclerosis. For animal models, naturally flow-disturbed regions such as branched or curved arterial regions as well as surgically created models, including arterio-venous fistulas, vascular grafts, perivascular cuffs, and complete, incomplete, or partial ligation of arteries, are used. Although in vivo models provide the environment needed to mimic the complex pathophysiological processes, in vitro models provide simple conditions that allow the study of isolated factors. Typical in vitro models use cultured endothelial cells exposed to various flow conditions, using devices such as cone-and-plate and parallel-plate chambers. Ex vivo models using isolated vessels have been used to bridge the gap between complex in vivo models and simple in vitro systems. Here, we review these flow models in the context of the role of oxidative stress in flow-dependent inflammation, a critical proatherogenic step, and atherosclerosis.

Coronary artery wall shear stress is associated with progression and transformation of atherosclerotic plaque and arterial remodeling in patients with coronary artery disease

BACKGROUND

Experimental studies suggest that low wall shear stress (WSS) promotes plaque development and high WSS is associated with plaque destabilization. We hypothesized that low-WSS segments in patients with coronary artery disease develop plaque progression and high-WSS segments develop necrotic core progression with fibrous tissue regression.

METHODS AND RESULTS

Twenty patients with coronary artery disease underwent baseline and 6-month radiofrequency intravascular ultrasound (virtual histology intravascular ultrasound) and computational fluid dynamics modeling for WSS calculation. For each virtual histology intravascular ultrasound segment (n=2249), changes in plaque area, virtual histology intravascular ultrasound-derived plaque composition, and remodeling were compared in low-, intermediate-, and high-WSS categories. Compared with intermediate-WSS segments, low-WSS segments developed progression of plaque area (P=0.027) and necrotic core (P<0.001), whereas high-WSS segments had progression of necrotic core (P<0.001) and dense calcium (P<0.001) and regression of fibrous (P<0.001) and fibrofatty (P<0.001) tissue. Compared with intermediate-WSS segments, low-WSS segments demonstrated greater reduction in vessel (P<0.001) and lumen area (P<0.001), and high-WSS segments demonstrated an increase in vessel (P<0.001) and lumen (P<0.001) area. These changes resulted in a trend toward more constrictive remodeling in low- compared with high-WSS segments (73% versus 30%; P=0.06) and more excessive expansive remodeling in high- compared with low-WSS segments (42% versus 15%; P=0.16).

CONCLUSIONS

Compared with intermediate-WSS coronary segments, low-WSS segments develop greater plaque and necrotic core progression and constrictive remodeling, and high-WSS segments develop greater necrotic core and calcium progression, regression of fibrous and fibrofatty tissue, and excessive expansive remodeling, suggestive of transformation to a more vulnerable phenotype. Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT00576576.

In-vivo assessment of the natural history of coronary atherosclerosis: vascular remodeling and endothelial shear stress determine the complexity of atherosclerotic disease progression

PURPOSE OF REVIEW

Atherosclerotic disease progression is determined by localized plaque growth, which is induced by systemic and local hemodynamic factors, and the nature of the wall remodeling response. The purpose of this review is to summarize the processes underlying the heterogeneity of coronary atherosclerosis progression in relation to the local hemodynamic and arterial remodeling environment.

RECENT FINDINGS

Multiple competing biological processes in the extracellular matrix define the extent of vascular remodeling and disease progression. The remodeling phenomenon is not consistent but is characterized by great phenotypical heterogeneity which reflects the complex effect of systemic, genetic and hemodynamic factors on the arterial wall response to plaque formation and progression. The exaggeration of expansive remodeling (i.e., excessive expansive remodeling) likely contributes to the transformation of an initially favorable action into an excessive course of vessel expansion, continued disease progression and plaque instability. Extremely low endothelial shear stress and excessive expansive remodeling establish a vicious cycle which leads to the formation of severe plaques with high-risk characteristics.

SUMMARY

The dynamic interplay between the local hemodynamic environment and the wall remodeling behavior determines the complexity of the natural history of atherosclerosis and explains the development of localized plaque vulnerability.

A critical role for chloride channel-3 (CIC-3) in smooth muscle cell activation and neointima formation

OBJECTIVE

We have shown that the chloride-proton antiporter chloride channel-3 (ClC-3) is required for endosome-dependent signaling by the Nox1 NADPH oxidase in SMCs. In this study, we tested the hypothesis that ClC-3 is necessary for proliferation of smooth muscle cells (SMCs) and contributes to neointimal hyperplasia following vascular injury.

METHODS AND RESULTS

Studies were performed in SMCs isolated from the aorta of ClC-3-null and littermate control (wild-type [WT]) mice. Thrombin and tumor necrosis factor-α (TNF-α) each caused activation of both mitogen activated protein kinase extracellular signal-regulated kinases 1 and 2 and the matrix-degrading enzyme matrix metalloproteinase-9 and cell proliferation of WT SMCs. Whereas responses to thrombin were preserved in ClC-3-null SMCs, the responses to TNF-α were markedly impaired. These defects normalized following gene transfer of ClC-3. Carotid injury increased vascular ClC-3 expression, and compared with WT mice, ClC-3-null mice exhibited a reduction in neointimal area of the carotid artery 28 days after injury.

CONCLUSIONS

ClC-3 is necessary for the activation of SMCs by TNF-α but not thrombin. Deficiency of ClC-3 markedly reduces neointimal hyperplasia following vascular injury. In view of our previous findings, this observation is consistent with a role for ClC-3 in endosomal Nox1-dependent signaling. These findings identify ClC-3 as a novel target for the prevention of inflammatory and proliferative vascular diseases.

p190 RhoGTPase-activating protein links the β1 integrin/caveolin-1 mechanosignaling complex to RhoA and actin remodeling

OBJECTIVE

To determine whether the β1 integrin/caveolin-1 signaling complex plays a role in shear stress regulation of RhoA activity .

METHODS AND RESULTS

Hemodynamic shear stress influences the phenotype of the endothelium. Integrins and RhoA are essential components in the process that allows endothelial cells to adapt to flow. However, the signaling mechanisms that relay from integrins to RhoA are not well defined. Bovine aortic endothelial cells were subjected to laminar shear stress (10 dyne/cm(2)) for up to 6 hours. β1 integrin blockade inhibited Src family kinases and p190RhoGAP tyrosine phosphorylation observed after the immediate onset of shear stress. Depletion of caveolin-1 blocked the decline in p190RhoGAP tyrosine phosphorylation observed at later points by sustaining Src family kinase activity. The manipulation of β1 integrin and caveolin-1 also altered shear regulation of RhoA activity. More importantly, cells depleted of p190RhoGAP showed faulty temporal regulation of RhoA activity. Each of these treatments attenuated actin reorganization induced by flow. Similarly, stress fibers failed to form in endothelial cells exposed to enhanced blood flow in caveolin-1 knockout mice.

CONCLUSIONS

Our studies demonstrate that p190RhoGAP links integrins and caveolin-1/caveolae to RhoA in a mechanotransduction cascade that participates in endothelial adaptation to flow.

Rationale and practical techniques for mouse models of early vein graft adaptations

Mouse models serve as relatively new yet powerful research tools to study intimal hyperplasia and wall remodeling of vein bypass graft failure. Several model variations have been reported in the past decade. However, the approach demands thoughtful preparation, selected sophisticated equipment, microsurgical technical expertise, advanced tissue processing, and data acquisition. This review compares several described models and aims (building on our personal experiences) to practically aid the investigators who want to utilize mouse models of vein graft failure.

Natural history of experimental coronary atherosclerosis and vascular remodeling in relation to endothelial shear stress: a serial, in vivo intravascular ultrasound study

BACKGROUND

The natural history of heterogeneous atherosclerotic plaques and the role of local hemodynamic factors throughout their development are unknown. We performed a serial study to assess the role of endothelial shear stress (ESS) and vascular remodeling in the natural history of coronary atherosclerosis.

METHODS AND RESULTS

Intravascular ultrasound-based 3-dimensional reconstruction of all major coronary arteries (n=15) was performed serially in vivo in 5 swine 4, 11, 16, 23, and 36 weeks after induction of diabetes mellitus and hyperlipidemia. The reconstructed arteries were divided into 3-mm-long segments (n=304). ESS was calculated in all segments at all time points through the use of computational fluid dynamics. Vascular remodeling was assessed at each time point in all segments containing significant plaque, defined as maximal intima-media thickness >/=0.5 mm, at week 36 (n=220). Plaque started to develop at week 11 and progressively advanced toward heterogeneous, multifocal lesions at all subsequent time points. Low ESS promoted the initiation and subsequent progression of plaques. The local remodeling response changed substantially over time and determined future plaque evolution. Excessive expansive remodeling developed in regions of very low ESS, further exacerbated the low ESS, and was associated with the most marked plaque progression. The combined assessment of ESS, remodeling, and plaque severity enabled the early identification of plaques that evolved to high-risk lesions at week 36.

CONCLUSIONS

The synergistic effect of local ESS and the remodeling response to plaque formation determine the natural history of individual lesions. Combined in vivo assessment of ESS and remodeling may predict the focal formation of high-risk coronary plaque.

Soluble epoxide hydrolase inhibition modulates vascular remodeling

The soluble epoxide hydrolase enzyme (SEH) and vascular remodeling are associated with cardiovascular disease. Although inhibition of SEH prevents smooth muscle cell proliferation in vitro, the effects of SEH inhibition on vascular remodeling in vivo and mechanisms of these effects remain unclear. Herein we determined the effects of SEH antagonism in an endothelium intact model of vascular remodeling induced by flow reduction and an endothelium denuded model of vascular injury. We demonstrated that chronic treatment of spontaneously hypertensive stroke-prone rats with 12-(3-adamantan-1-yl-ureido) dodecanoic acid, an inhibitor of SEH, improved the increment of inward remodeling induced by common carotid ligation to a level that was comparable with normotensive Wistar Kyoto rats. Similarly, mice with deletion of the gene responsible for the production of the SEH enzyme (Ephx2(-/-)) demonstrated enhanced inward vascular remodeling induced by carotid ligation. However, the hyperplastic response induced by vascular injury that denudes the endothelium was unabated by SEH inhibition or Ephx2 gene deletion. These results suggest that SEH inhibition or Ephx2 gene deletion antagonizes neointimal formation in vivo by mechanisms that are endothelium dependent. Thus SEH inhibition may have therapeutic potential for flow-induced remodeling and neointimal formation.

Nuclear receptor Nur77 inhibits vascular outward remodelling and reduces macrophage accumulation and matrix metalloproteinase levels

AIMS

Structural adaptation of the vessel wall in response to sustained alterations in haemodynamic forces is known as vascular remodelling. Detailed knowledge on the mechanism underlying this vascular response is limited, and we aimed to study the function of Nur77 in smooth muscle cells (SMCs) in arterial remodelling.

METHODS AND RESULTS

Carotid artery ligation in mice results in flow-induced, outward remodelling of the contralateral carotid artery, and we observed enhanced Nur77 expression during this process. Transgenic mice that express Nur77 or its dominant-negative variant, denoted as 'DeltaTA' in arterial SMCs, were exposed to carotid artery ligation, and after 4 weeks pressure-diameter relationships were measured. Structural outward remodelling is inhibited in Nur77-transgenic mice when compared with wild-type and DeltaTA-transgenic mice. The key determinants of remodelling vascular tone and macrophage accumulation were studied. No difference in contractile and relaxant responses was detected in isolated aorta, carotid, and mesenteric artery segments between transgenic and wild-type mice. SMC-specific overexpression of Nur77 in transgenic mice reduced macrophage accumulation and repressed matrix metalloproteinase (MMP)1 and MMP9 expression at early time points. MMP2 protein expression was reduced in Nur77-transgenic mice, whereas in DeltaTA-transgenic mice MMP2 expression was increased.

CONCLUSION

Nur77 is induced during outward remodelling and inhibits this vascular adaptation in mice. Nur77-mediated inhibition of arterial remodelling involves a reduction in both macrophage accumulation and MMP expression levels.