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

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

Cerebral and peripheral vascular differences between pre- and postmenopausal women.

OBJECTIVE: Menopause is associated with lower peripheral vascular function; however, cerebrovascular responses to this time-period are unclear. We aimed to describe peripheral vascular and cerebrovascular differences between pre- and postmenopausal women. METHODS: Fifty pre- and postmenopausal women (N = 100) underwent assessments of cerebral blood flow; cerebrovascular reactivity and autoregulation; carotid artery reactivity; brachial and femoral artery flow-mediated dilation; and carotid, brachial, and femoral artery intima-media thickness. Comparisons were made between pre- and postmenopausal women followed by a secondary analysis (N = 20) between late premenopausal women and those within 5 years of menopause using a general linear model. RESULTS: Cerebral blood flow (-11 [-17, -4 cm/s]; P = 0.03) and carotid reactivity (-2.3 [-4.3, -0.3%] P = 0.03) were lower postmenopause compared to premenopause, whereas cerebrovascular reactivity and autoregulation did not differ (P > 0.05). Postmenopausal women had a larger carotid (0.16 [0.13, 0.20 mm] P < 0.001), brachial (0.07 [0.03, 0.11 mm] P = 0.004), and femoral artery intima-media thickness (0.09 [0.05, 0.14 mm] P = 0.04), alongside lower brachial (-2.3 [-3.9, -0.7%] P = 0.004) and femoral artery flow-mediated dilation (-3.0 [-4.3, -1.8%] P < 0.001). In the secondary-analysis, early postmenopausal women had a lower femoral artery flow-mediated dilation (-1.9 [-3.9, -0.0%] P = 0.05) and larger carotid intima-media thickness (0.07 [0.00, 0.14 mm] P = 0.03) compared to late premenopausal women. CONCLUSIONS: Cerebral blood flow, carotid artery reactivity, peripheral vascular function, and structure are negatively affected by age. Preliminary data indicate that femoral artery function and carotid artery structure may be potentially impaired in early postmenopause compared with late premenopause. These findings suggest that conduit arteries susceptible to atherosclerosis may be important targets for lifestyle intervention in early menopause.

S100B is required for maintaining an intermediate state with double-positive Sca-1+ progenitor and vascular smooth muscle cells during neointimal formation.

INTRODUCTION: Accumulation of vascular smooth muscle cells (VSMCs) within the neointimal region is a hallmark of atherosclerosis and vessel injury. Evidence has shown that Sca-1-positive (Sca-1+) progenitor cells residing in the vascular adventitia play a crucial role in VSMC assemblages and intimal lesions. However, the underlying mechanisms, especially in the circumstances of vascular injury, remain unknown. METHODS AND RESULTS: The neointimal formation model in rats was established by carotid artery balloon injury using a 2F-Forgaty catheter. Most Sca-1+ cells first appeared at the adventitia of the vascular wall. S100B expressions were highest within the adventitia on the first day after vessel injury. Along with the sequentially increasing trend of S100B expression in the intima, media, and adventitia, respectively, the numbers of Sca-1+ cells were prominently increased at the media or neointima during the time course of neointimal formation. Furthermore, the Sca-1+ cells were markedly increased in the tunica media on the third day of vessel injury, SDF-1α expressions were obviously increased, and SDF-1α levels and Sca-1+ cells were almost synchronously increased within the neointima on the seventh day of vessel injury. These effects could effectually be reversed by knockdown of S100B by shRNA, RAGE inhibitor (SPF-ZM1), or CXCR4 blocker (AMD3100), indicating that migration of Sca-1+ cells from the adventitia into the neointima was associated with S100B/RAGE and SDF-1α/CXCR4. More importantly, the intermediate state of double-positive Sca-1+ and α-SMA cells was first found in the neointima of injured arteries, which could be substantially abrogated by using shRNA for S100B or blockade of CXCR4. S100B dose-dependently regulated SDF-1α expressions in VSMCs by activating PI3K/AKT and NF-κB, which were markedly abolished by PI3K/AKT inhibitor wortmannin and enhanced by p65 blocker PDTC. Furthermore, S100B was involved in human umbilical cord-derived Sca-1+ progenitor cells' differentiation into VSMCs, especially in maintaining the intermediate state of double-positive Sca-1+ and α-SMA. CONCLUSIONS: S100B triggered neointimal formation in rat injured arteries by maintaining the intermediate state of double-positive Sca-1+ progenitor and VSMCs, which were associated with direct activation of RAGE by S100B and indirect induction of SDF-1α by activating PI3K/AKT and NF-κB.

Regional distribution of layer-specific circumferential residual deformations and opening angles in the porcine aorta.

Information on the layer-specific residual deformations of aortic tissue and how these vary throughout the vessel is important for understanding the regionally-varying aortic functions and pathophysiology, but not so much can be found in the literature. Toward this end, porcine aortas were sectioned into eighteen rings, with one ring from each anatomical position radially cut to obtain the zero-stress state for the intact wall and the other ring dissected into intimal-medial and adventitial layers; these rings were then radially cut to reach the zero-stress state for the intima-media and adventitia. Peripheral variations in internal/external circumferences, thickness, and opening angle of the intact wall and its layers were measured through image analysis at the no-load and zero-stress states. Intact wall and layer circumferences at both states significantly declined along the aorta, as did intact wall and intimal-medial but not adventitial thickness. Adventitia exhibited the greatest opening angles, approaching 180 deg all over the aorta. The opening angles of the intima-media and intact wall were quite similar, with the highest values in the ascending aorta, the lowest at the diaphragm, and increasing subsequently. Bending-related residual stretches were released by radial cutting that were compressive internally and tensile externally, displaying distinct axial variation for the intima-media and intact wall, and non-significant variation for the adventitia. Evidence is provided for the release upon layer separation of compressive stretches in the intima-media and of tensile stretches in the adventitia, whose values were smallest in the descending thoracic aorta and highest near the iliac artery bifurcation.

Modeling the effects of muscle contraction on the mechanical response and circumferential stability of coronary arteries.

Smooth muscle contraction regulates the size of the blood vessel lumen which directly affects the mechanical response of the vessel. Folding in arteries has been observed in arteries during excessive contraction, known as a coronary artery spasm. The interplay of muscle contraction, geometry, and material responses and their effects on stability can be understood through mathematical models. Here, we consider a three-layer cross-sectional model of a coronary artery with anisotropic properties and intimal thickening, and perform a linear stability analysis to investigate the circumferential folding patterns that emerge due to muscle contraction. Our model shows that a critical level of contractile activity yields a uniform strain distribution across the arterial wall. When the muscle is contracted above this critical level, the tissue behaves isotropically and it is more prone to circumferential instability. This theoretical framework could serve as a valuable tool to understand the relationship between arterial lumen morphology and wall contraction in health and disease.

Recipient c-Kit Lineage Cells Repopulate Smooth Muscle Cells of Transplant Arteriosclerosis in Mouse Models.

RATIONALE: Transplantation-accelerated arteriosclerosis is one of the major challenges for long-term survival of patients with solid organ transplantation. Although stem/progenitor cells have been implicated to participate in this process, the cells of origin and underlying mechanisms have not been fully defined. OBJECTIVE: The objective of our study was to investigate the role of c-Kit lineage cells in allograft-induced neointima formation and to explore the mechanisms underlying this process. METHODS AND RESULTS: Using an inducible lineage tracing Kit-CreER;Rosa26-tdTomato mouse model, we observed that c-Kit is expressed in multiple cell types in the blood vessels, rather than a specific stem/progenitor cell marker. We performed allograft transplantation between different donor and recipient mice, as well as bone marrow transplantation experiments, demonstrating that recipient c-Kit+ cells repopulate neointimal smooth muscle cells (SMCs) and leukocytes, and contribute to neointima formation in an allograft transplantation model. c-Kit-derived SMCs originate from nonbone marrow tissues, whereas bone marrow-derived c-Kit+ cells mainly generate CD45+ leukocytes. However, the exact identity of c-Kit lineage cells contributing to neointimal SMCs remains unclear. ACK2 (anti-c-Kit antibody), which specifically binds and blocks c-Kit function, ameliorates allograft-induced arteriosclerosis. Stem cell factor and TGF (transforming growth factor)-ß1 levels were significantly increased in blood and neointimal lesions after allograft transplantation, by which stem cell factor facilitated c-Kit+ cell migration through the stem cell factor/c-Kit axis and downstream activation of small GTPases, MEK (mitogen-activated protein kinase kinase)/ERK (extracellular signal-regulated kinase)/MLC (myosin light chain), and JNK (c-Jun N-terminal kinase)/c-Jun signaling pathways, whereas TGF-ß1 induces c-Kit+ cell differentiation into SMCs via HK (hexokinase)-1-dependent metabolic reprogramming and a possible downstream O-GlcNAcylation of myocardin and serum response factor. CONCLUSIONS: Our findings provide evidence that recipient c-Kit lineage cells contribute to vascular remodeling in an allograft transplantation model, in which the stem cell factor/c-Kit axis is responsible for cell migration and HK-1-dependent metabolic reprogramming for SMC differentiation.

Layer-specific arterial micromechanics and microstructure: Influences of age, anatomical location, and processing technique.

The importance of matrix micromechanics is increasingly recognized in cardiovascular research due to the intimate role they play in local vascular cell physiology. However, variations in micromechanics among arterial layers (i.e. intima, media, adventitia), as well as dependency on local matrix composition and/or structure, anatomical location or developmental stage remain largely unknown. This study determined layer-specific stiffness in elastic arteries, including the main pulmonary artery, ascending aorta, and carotid artery using atomic force indentation. To compare stiffness with age and frozen processing techniques, neonatal and adult pulmonary arteries were tested, while fresh (vibratomed) and frozen (cryotomed) tissues were tested from the adult aorta. Results revealed that the mean compressive modulus varied among the intima, sub-luminal media, inner-middle media, and adventitia layers in the range of 1-10 kPa for adult arteries. Adult samples, when compared to neonatal pulmonary arteries, exhibited increased stiffness in all layers except adventitia. Compared to freshly isolated samples, frozen preparation yielded small stiffness increases in each layer to varied degrees, thus inaccurately representing physiological stiffness. To interpret micromechanics measurements, composition and structure analyses of structural matrix proteins were conducted with histology and multiphoton imaging modalities including second harmonic generation and two-photon fluorescence. Composition analysis of matrix protein area density demonstrated that decrease in the elastin-to-collagen and/or glycosaminoglycan-to-collagen ratios corresponded to stiffness increases in identical layers among different types of arteries. However, composition analysis was insufficient to interpret stiffness variations between layers which had dissimilar microstructure. Detailed microstructure analyses may contribute to more complete understanding of arterial micromechanics.

Elucidating the role of graft compliance mismatch on intimal hyperplasia using an ex vivo organ culture model.

There is a growing clinical need to address high failure rates of small diameter (<6 mm) synthetic vascular grafts. Although there is a strong empirical correlation between low patency rates and low compliance of synthetic grafts, the mechanism by which compliance mismatch leads to intimal hyperplasia is poorly understood. To elucidate this relationship, synthetic vascular grafts were fabricated that varied compliance independent of other graft variables. A computational model was then used to estimate changes in fluid flow and wall shear stress as a function of graft compliance. The effect of compliance on arterial remodeling in an ex vivo organ culture model was then examined to identify early markers of intimal hyperplasia. The computational model prediction of low wall shear stress of low compliance grafts and clinical control correlated well with alterations in arterial smooth muscle cell marker, extracellular matrix, and inflammatory marker staining patterns at the distal anastomoses. Conversely, high compliance grafts displayed minimal changes in fluid flow and arterial remodeling, similar to the sham control. Overall, this work supports the intrinsic link between compliance mismatch and intimal hyperplasia and highlights the utility of this ex vivo organ culture model for rapid screening of small diameter vascular grafts. STATEMENT OF SIGNIFICANCE: We present an ex vivo organ culture model as a means to screen vascular grafts for early markers of intimal hyperplasia, a leading cause of small diameter vascular graft failure. Furthermore, a computational model was used to predict the effect of graft compliance on wall shear stress and then correlate these values to changes in arterial remodeling in the organ culture model. Combined, the ex vivo bioreactor system and computational model provide insight into the mechanistic relationship between graft-arterial compliance mismatch and the onset of intimal hyperplasia.

Intimal regeneration after coronary endarterectomy and onlay grafting in coronary artery bypass grafting.

OBJECTIVES: Coronary onlay grafting, with or without endarterectomy, has been widely used for the treatment of diffuse lesions. Recent studies have demonstrated excellent long-term patency and favorable remodeling of onlay anastomosis; however, the underlying mechanisms remain unknown. Here, we describe the mechanism of intimal regeneration based on postmortem pathological evaluation of a patient who had undergone onlay grafting with coronary endarterectomy. METHODS: The onlay anastomosis was analyzed using a combination of immunohistological stainings, namely, H&E, vimentin, α-SMA, factor VIII, and Ki-67, to identify the source and mechanism of intimal regeneration after onlay grafting with endarterectomy. RESULTS: Our results suggest that the regenerated endothelium derives from the smooth muscle cells of the endarterectomized media of the coronary artery and that it circumferentially covers the internal lumen of the arterial graft. CONCLUSIONS: Intimal regeneration, derived from the smooth muscle cells of the endarterectomized coronary artery that proliferate toward the graft lumen, may be a key mechanism that underlies the observed favorable remodeling after onlay grafting during coronary endarterectomy.

A hybrid small-diameter tube fabricated from decellularized aortic intima-media and electrospun fiber for artificial small-diameter blood vessel.

Hybrid small-diameter tubes were fabricated by wrapping decellularized aortic intima-media sheets around a tubular stainless steel mandrel with diameter 4 mm, and then by coating with electrospun segmented polyurethane. The synthetic coat was deposited uniformly to a thickness of about 0.5-3.5 µm depending on the duration of electrospinning. Resistance to luminal pressure, burst strength, and stiffness increased with the thickness of the electrospun coat, suggesting that the synthetic fabric reinforces the reconstructed acellular aortic intima-media. Human umbilical vein endothelial cells seeded on the inner surface acquired flagstone morphology, while normal human dermal fibroblasts seeded on the outer surface proliferated well and partly migrated into deeper layers. Collectively, the data suggest that reinforcing decellularized aortic intima-media with electrospun fibers generates a small-diameter hybrid blood vessel with good biocompatibility and suitable mechanical properties. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1064-1070, 2019.

Identification of regional/layer differences in failure properties and thickness as important biomechanical factors responsible for the initiation of aortic dissections.

Thoracic aortic dissections involving the ascending aorta represent one of the most dramatic and lethal emergencies in cardiovascular surgery. It is therefore critical to identify the mechanisms driving them and biomechanical analyses hold great clinical promise, since rupture/dissection occur when aortic wall strength is unable to withstand hemodynamic stresses. Although several studies have been done on the biomechanical properties of thoracic aortic aneurysms, few data are available about thoracic aortic dissections. Detailed mechanical tests with measurement of tissue thickness and failure properties were performed with a tensile-testing device on 445 standardized specimens, corresponding to 19 measurement sites per inner (intima with most of media)/outer layer (leftover media with adventitia); harvested from twelve patients undergoing emergent surgical repair for type A dissection. Our data suggested inherent differences in tissue properties between the origin of dissection and distal locations, i.e. thinner and stiffer inner layers that might render them more vulnerable to tearing despite their increased strength. The strength of tissue circumferentially was greater than that longitudinally, likely determining the direction of tear. The relative strengths of the inner: ∼{65,40}N/cm2 and outer layer: ∼{350,270}N/cm2 in the two principal directions of dissected tissue were differentiated from the intima: ∼{100,75}N/cm2, media: ∼{150,55}N/cm2, and adventitia: ∼{270,190}N/cm2 of non-dissected ascending aortic aneurysms (Sokolis et al., 2012), in favor of weaker inner and stronger outer layers, allowing an explanation as to why the presently-studied tissue suffered dissection, i.e. tear of the inner layers, and not rupture, i.e. full tearing across the entire wall thickness.

Biomechanical relevance of the microstructure in artery walls with a focus on passive and active components.

The microstructure of arteries, consisting, in particular, of collagen, elastin, and vascular smooth muscle cells, plays a very significant role in their biomechanical response during a cardiac cycle. In this article, we highlight the microstructure and the contributions of each of its components to the overall mechanical behavior. We also describe the changes of the microstructure that occur as a result of abdominal aortic aneurysms and disease, such as atherosclerosis. We also focus on how the passive and active constituents are incorporated into a mathematical model without going into detail of the mathematical formulation. We conclude by mentioning open problems toward a better characterization of the biomechanical aspects of arteries that will be beneficial for a better understanding of cardiovascular pathophysiology.

PET Assessment of Epicardial Intimal Disease and Microvascular Dysfunction in Cardiac Allograft Vasculopathy.

BACKGROUND: Cardiac allograft vasculopathy (CAV) is a leading cause of graft failure and death after heart transplantation. Absolute myocardial blood flow (MBF) quantification using rubidium 82 (Rb-82) positron emission tomography (PET) could enable evaluation of diagnostically challenging diffuse epicardial and microvascular disease in CAV. OBJECTIVES: The authors aimed to evaluate Rb-82 PET detection of CAV. METHODS: Consecutive transplant recipients undergoing coronary angiography were prospectively evaluated with PET, multivessel intravascular ultrasound (IVUS), and intracoronary hemodynamics. CAV was defined as International Society of Heart and Lung Transplantation CAV1-3 on angiography and maximal intimal thickness ≥0.5 mm on IVUS. RESULTS: Forty patients (mean age 56 years, 4.8 years post-transplant) completed evaluation. CAV was detected in 32 patients (80%) by IVUS and 14 (35%) by angiography. PET correlated significantly with invasive coronary flow indices: r = 0.29, rate-pressure product-adjusted myocardial flow reserve (cMFR) versus coronary flow reserve; r = 0.28, relative flow reserve versus fractional flow reserve; and r = 0.37, coronary vascular resistance (CVR) versus index of microcirculatory resistance. Patients with CAV or microvascular dysfunction had reduced cMFR and stress MBF and increased CVR. Receiver operator characteristic curves demonstrated good accuracy of PET for CAV on IVUS (area under the curve 0.77 to 0.81) and optimal diagnostic cutoffs of cMFR <2.9, stress MBF <2.3, and CVR >55. Combined PET assessment for CAV yielded excellent >93% sensitivity (>65% specificity) for 1 abnormal parameter and >96% specificity (>55% sensitivity) for 2 abnormal parameters. CONCLUSIONS: Rb-82 PET flow quantification has high diagnostic accuracy for CAV, with potential for noninvasive evaluation after heart transplantation.

A single nucleotide polymorphism of cyclin-dependent kinase inhibitor 1B (p27Kip1) associated with human vein graft failure affects growth of human venous adventitial cells but not smooth muscle cells.

BACKGROUND: Cyclin-dependent kinase inhibitor 1B (p27Kip1) is a cell-cycle inhibitor whose -838C>A single nucleotide polymorphism (rs36228499; hereafter called p27 SNP) has been associated with the clinical failure of peripheral vein grafts, but the functional effects of this SNP have not been demonstrated. METHODS: Human saphenous vein adventitial cells and intimal/medial smooth muscle cells (SMCs) were derived from explants obtained at the time of lower extremity bypass operations. We determined the following in adventitial cells and SMCs as a function of the p27 SNP genotype: (1) p27 promoter activity, (2) p27 messenger (m)RNA and protein levels, and (3) growth and collagen gel contraction. Deoxyribonuclease I footprinting was also performed in adventitial cells and SMCs. RESULTS: p27 promoter activity, deoxyribonuclease I footprinting, p27 mRNA levels, and p27 protein levels demonstrated that the p27 SNP is functional in adventitial cells and SMCs. Both cell types with the graft failure protective AA genotype had more p27 mRNA and protein. As predicted because of higher levels of p27 protein, adventitial cells with the AA genotype grew slower than those of the CC genotype. Unexpectedly, SMCs did not show this genotype-dependent growth response. CONCLUSIONS: These results support the functionality of the p27 SNP in venous SMCs and adventitial cells, but an effect of the SNP on cell proliferation is limited to only adventitial cells. These data point to a potential role for adventitial cells in human vein graft failure and also suggest that SMCs express factors that interfere with the activity of p27.

Impact of Age and Aerobic Exercise Training on Conduit Artery Wall Thickness: Role of the Shear Pattern.

Hemodynamic shear stress is the frictional force of blood on the arterial wall. The shear pattern in the conduit artery affects the endothelium and may participate in the development and progression of atherosclerosis. We investigated the role of the shear pattern in age- and aerobic exercise-induced changes in conduit artery wall thickness via cross-sectional and interventional studies. In a cross-sectional study, we found that brachial shear rate patterns and brachial artery intima-media thickness (IMT) correlated with age. Additionally, brachial artery shear rate patterns were associated with brachial artery IMT in 102 middle-aged and older individuals. In an interventional study, 39 middle-aged and older subjects were divided into 2 groups: control and exercise. The exercise group completed 12 weeks of aerobic exercise training. Aerobic exercise training significantly increased the antegrade shear rate and decreased the retrograde shear rate and brachial artery IMT. Moreover, changes in the brachial artery antegrade shear rate and the retrograde shear rate correlated with the change in brachial artery IMT. The results of the present study indicate that changes in brachial artery shear rate patterns may contribute to age- and aerobic exercise training-induced changes in brachial artery wall thickness.

Cytoglobin regulates blood pressure and vascular tone through nitric oxide metabolism in the vascular wall.

The identity of the specific nitric oxide dioxygenase (NOD) that serves as the main in vivo regulator of O2-dependent NO degradation in smooth muscle remains elusive. Cytoglobin (Cygb) is a recently discovered globin expressed in fibroblasts and smooth muscle cells with unknown function. Cygb, coupled with a cellular reducing system, efficiently regulates the rate of NO consumption by metabolizing NO in an O2-dependent manner with decreased NO consumption in physiological hypoxia. Here we show that Cygb is a major regulator of NO degradation and cardiovascular tone. Knockout of Cygb greatly prolongs NO decay, increases vascular relaxation, and lowers blood pressure and systemic vascular resistance. We further demonstrate that downregulation of Cygb prevents angiotensin-mediated hypertension. Thus, Cygb has a critical role in the regulation of vascular tone and disease. We suggest that modulation of the expression and NOD activity of Cygb represents a strategy for the treatment of cardiovascular disease.

Noradrenaline has opposing effects on the hydraulic conductance of arterial intima and media.

The uptake of circulating macromolecules by the arterial intima is thought to be a key step in atherogenesis. Such transport is dominantly advective, so elucidating the mechanisms of water transport is important. The relation between vasoactive agents and water transport in the arterial wall is incompletely understood. Here we applied our recently-developed combination of computational and experimental methods to investigate the effects of noradrenaline (NA) on hydraulic conductance of the wall (Lp), medial extracellular matrix volume fraction (ϕECM) and medial permeability (K11) in the rat abdominal aorta. Experimentally, we found that physiological NA concentrations were sufficient to induce SMC contraction and produced significant decreases in Lp and increases in ϕECM. Simulation results based on 3D confocal images of the extracellular volume showed a corresponding increase in K11, attributed to the opening of the ECM. Conversion of permeabilities to layer-specific resistances revealed that although the total wall resistance increased, medial resistance decreased, suggesting an increase in intimal resistance upon application of NA.

Hemodynamic Influence on Smooth Muscle Cell Kinetics and Phenotype During Early Vein Graft Adaptation.

Pathologic vascular adaptation following local injury is the primary driver for accelerated intimal hyperplasia and an occlusive phenotype. Smooth muscle cell (SMC) proliferation within the wall, and migration into the developing intima, is a major component of this remodeling response. The primary objective in the current study was to investigate the effect of the local biomechanical forces on early vein graft adaptation, specifically focusing on the spatial and temporal response of SMC proliferation and conversion from a contractile to synthetic architecture. Taking advantage of the differential adaptation that occurs during exposure to divergent flow environments, vein grafts were implanted in rabbits to create two distinct flow environments and harvested at times ranging from 2 h to 28 days. Using an algorithm for the virtual reconstruction of unfixed, histologic specimens, immunohistochemical tracking of DNA synthesis, and high-throughput transcriptional analysis, the spatial and temporal changes in graft morphology, cell proliferation, and SMC phenotype were catalogued. Notable findings include a burst of cell proliferation at 7 days post-implantation, which was significantly augmented by exposure to a reduced flow environment. Compared to the adjacent media, proliferation rates were 3-fold greater in the intima, and a specific spatial distribution of these proliferating cells was identified, with a major peak in the sub-endothelial region and a second peak centering on the internal elastic lamina. Genomic markers of a contractile SMC phenotype were reduced as early as 2 h post-implantation and reached a nadir at 7 days. Network analysis of upstream regulatory pathways identified GATA6 and KLF5 as important transcription factors that regulate this shift in SMC phenotype.

Circulating level of pigment epithelium-derived factor is associated with vascular function and structure: A cross-sectional study.

BACKGROUND: Pigment epithelium-derived factor (PEDF) is a glycoprotein that belongs to the superfamily of serine protease inhibitors. It is thought that PEDF plays a protective role against atherosclerosis. Clinical studies have shown that serum levels of PEDF are increased in subjects with cardiovascular risk factors. The role of PEDF in cardiovascular disease is still controversial. The purpose of this study was to evaluate the associations between serum levels of PEDF and vascular function and structure. METHODS: We measured serum levels of PEDF, assessed vascular function by measurements of flow-mediated vasodilation (FMD) and nitroglycerine-induced vasodilation in the brachial artery, and measured brachial artery intima-media thickness (IMT) in 150 subjects who underwent health examinations. RESULTS AND CONCLUSIONS: Univariate regression analysis revealed that serum level of PEDF was significantly correlated with body mass index, high-density lipoprotein cholesterol, glucose, FMD, nitroglycerine-induced vasodilation, and brachial artery IMT. Multivariate analysis revealed that serum levels of PEDF remained an independent predictor of nitroglycerine-induced vasodilation (ß=-0.20, P=0.02) and brachial artery IMT (ß=0.14, P=0.03) after adjustment of cardiovascular risk factors, while serum level of PEDF was not associated with FMD (ß=-0.02, P=0.79). These findings suggest that PEDF may be a factor directly associated with atherosclerosis. The serum level of PEDF may be a new biochemical marker of atherosclerosis.

Intimal and medial contributions to the hydraulic resistance of the arterial wall at different pressures: a combined computational and experimental study.

The hydraulic resistances of the intima and media determine water flux and the advection of macromolecules into and across the arterial wall. Despite several experimental and computational studies, these transport processes and their dependence on transmural pressure remain incompletely understood. Here, we use a combination of experimental and computational methods to ascertain how the hydraulic permeability of the rat abdominal aorta depends on these two layers and how it is affected by structural rearrangement of the media under pressure. Ex vivo experiments determined the conductance of the whole wall, the thickness of the media and the geometry of medial smooth muscle cells (SMCs) and extracellular matrix (ECM). Numerical methods were used to compute water flux through the media. Intimal values were obtained by subtraction. A mechanism was identified that modulates pressure-induced changes in medial transport properties: compaction of the ECM leading to spatial reorganization of SMCs. This is summarized in an empirical constitutive law for permeability and volumetric strain. It led to the physiologically interesting observation that, as a consequence of the changes in medial microstructure, the relative contributions of the intima and media to the hydraulic resistance of the wall depend on the applied pressure; medial resistance dominated at pressures above approximately 93 mmHg in this vessel.