Vascular Remodeling In Response Research Articles

Abstract 5682: Novel Role of Copper Transporters CTR1 and ATP7A in PDGF-induced Vascular Smooth Muscle Cell Migration and Vascular Remodeling

Platelet-derived growth factor (PDGF) stimulates vascular smooth muscle cell (VSMC) migration primary through the PDGF receptor-beta (PDGFR), which contributes to vascular remodeling in vivo. Previous study shows that copper chelation inhibits neointimal formation in response to injury. However, underlying mechanisms remain unknown. Intracellular copper levels are tightly regulated by the copper importer CTR1 which localizes at plasma membrane (PM) and the copper exporter ATP7A which traffics between trans-Golgi network (TGN) to PM. Here we show that both CTR1 and ATP7A are expressed in cultured VSMC. Co-immunoprecipitation assay shows that ATP7A binds to PDGFR basally and PDGF stimulation rapidly promotes their association within 5 min, which is prevented by knockdown of CTR1 with siRNA (85%). Proteomic analysis in caveolae/lipid raft (C/LR) fraction reveals that ATP7A is localized in C/LR where PDGFR is found. PDGF stimulation promotes recruitment of ATP7A to C/LR fraction, which is inhibited by CTR1 siRNA (95%). Furthermore, inductively coupled plasma mass spectrometry (ICP-MS) shows that C/LR contains high amount of copper (139.7 (C/LR) vs. 17.9 (non-C/LR) ppb/mg proteins). In response to wound injury or PDGF stimulation, ATP7A translocates from TGN to PM at the leading edge where it colocalizes with PDGFR and the LR marker cholera toxin subunit B in actively migrating VSMCs, which is prevented by CTR1 siRNA or C/LR disruptor methyl-beta cyclodextrin. Note that this ATP7A translocation is associated with decrease in copper levels in C/LR, suggesting increase in copper efflux in C/LR during active VSMC migration. Functionally, PDGF-induced VSMC migration is significantly inhibited by knockdown of CTR1 or ATP7A with siRNAs (84% and 68%, respectively) as well as treatment with cell permeable copper chelator TTM (50.2%) and cell impermeable copper chelator BCS (39.1%). Moreover, ATP7A expression is dramatically increased in the neointima in a mouse wire injury model. In summary, CTR1-dependent translocation of the copper exporter ATP7A to C/LR and its binding to PDGFR plays an important role in PDGF-induced VSMC migration, which may contributes to vascular remodeling in response to injury and development of atherosclerosis. This research has received full or partial funding support from the American Heart Association, Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota & Wisconsin).

Vascular Remodeling in Response to 12 wk of Upper Arm Unilateral Resistance Training

Participation in regular aerobic exercise has been shown to increase arterial size and that exercise-induced vascular remodeling may be regional rather than systemic. However, these issues have been minimally investigated concerning resistance training. To determine whether 1) resistance training of the nondominant arm elicits an increase in diameter of the brachial artery and 2) unilateral training induces arterial remodeling in the contralateral arm. Twenty-four previously untrained participants, consisting of 18 females (aged 22.3 +/- 5.1 yr) and 6 males (aged 21.7 +/- 1.8 yr), participated in unilateral strength training of the biceps and triceps for 12 wk using their nondominant arm. Isotonic (one-repetition maximum, 1RM) and isometric (ISO) strength of the biceps were assessed before and after training on both arms. Brachial artery diameter and biceps muscle cross-sectional area (CSA) of both arms were also measured before and after training using magnetic resonance imaging (MRI). Brachial artery diameter increased 5.47% (P < 0.05) in the nondominant trained arm with no change observed in the dominant untrained arm. Biceps CSA increased 18.3% (P < 0.05) in the trained arm with no change (P > 0.05) in the untrained limb. Nondominant 1RM and ISO strength increased by 35.1% and 16.8%, respectively (P < 0.05 for both), although there were no significant changes (P > 0.05) in the contralateral arm. A modest correlation was found between the increases in CSA and in brachial artery diameter (r2 = 0.19, P = 0.039). These results indicate that upper arm vascular remodeling, manifesting as increased brachial artery diameter, can result from resistance training and that these changes are localized to the trained limb and associated with increases in CSA.

Fibronectin Is an Important Regulator of Flow-Induced Vascular Remodeling

Fibronectin is an important regulator of cell migration, differentiation, growth, and survival. Our data show that fibronectin also plays an important role in regulating extracellular matrix (ECM) remodeling. Fibronectin circulates in the plasma and is also deposited into the ECM by a cell dependent process. To determine whether fibronectin affects vascular remodeling in vivo, we asked whether the fibronectin polymerization inhibitor, pUR4, inhibits intima-media thickening, and prevents excess ECM deposition in arteries using a mouse model of vascular remodeling. To induce vascular remodeling, partial ligation of the left external and internal carotid arteries was performed in mice. pUR4 and the control peptide were applied periadventitially in pluronic gel immediately after surgery. Animals were euthanized 7 or 14 days after surgery. Morphometric analysis demonstrated that the pUR4 fibronectin inhibitor reduced carotid intima (63%), media (27%), and adventitial thickening (40%) compared to the control peptide (III-11C). Treatment with pUR4 also resulted in a dramatic decrease in leukocyte infiltration into the vessel wall (80%), decreased ICAM-1 and VCAM-1 levels, inhibited cell proliferation (60% to 70%), and reduced fibronectin and collagen I accumulation in the vessel wall. In addition, the fibronectin inhibitor prevented SMC phenotypic modulation, as evidenced by the maintenance of smooth muscle (SM) alpha-actin and SM myosin heavy chain levels in medial cells. These data are the first to demonstrate that fibronectin plays an important role in regulating the vascular remodeling response. Collectively, these data suggest a therapeutic benefit of periadventitial pUR4 in reducing pathological vascular remodeling.

Krüppel-like Factor 5 Shows Proliferation-specific Roles in Vascular Remodeling, Direct Stimulation of Cell Growth, and Inhibition of Apoptosis

Krüppel-like factor 5 (KLF5), originally isolated as a regulator of phenotypic modulation of vascular smooth muscle cells, induces pathological cell growth and is expressed in the neointima. Although induction of KLF5 up-regulates growth factors like platelet-derived growth factor-A chain, how KLF5 actually contributes to vascular remodeling, notably its direct effects on cell proliferation, had been poorly clarified. To investigate the effects of KLF5 on neointimal formation, we at first performed adenoviral overexpression of KLF5 to rats subjected to carotid balloon injury. Neointimal formation and proliferating cell nuclear antigen-positive rate were significantly increased at 14 days after injury in the KLF5-treated animals. At the cellular level, overexpression of KLF5 also resulted in markedly increased cell proliferation and cell cycle progression. As a molecular mechanism, we showed that KLF5 directly bound to the promoter and up-regulated gene expression of cyclin D1, as well as showing specific transactivation of cyclins and cyclin-dependent kinase inhibitors in cardiovascular cells. Conversely, knockdown of KLF5 by RNA interference specifically down-regulated cyclin D1 and impaired vascular smooth muscle cell proliferation. Furthermore, KLF5 attenuated cleavage of caspase-3 under conditions of apoptotic stimulation. Moreover, KLF5-administered animals exhibited a significant decrease in terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling-positive cells in the medial layer, suggesting inhibition of apoptosis in the early phase after denudation. These findings collectively suggest that KLF5 plays a central role in cardiovascular pathologies through direct and specific stimulation of cell growth as well as inhibition of apoptosis.

Correlation of soluble gp130 serum concentrations with arterial blood pressure

An increased blood pressure can elicit remodeling of the cardiovascular system. Experimental data have implicated gp130, a subunit of the receptor for interleukin-6 (IL-6)-related cytokines, in the regulation of proliferation and apoptosis of cardiomyocytes and vascular smooth muscle cells (VSMC). Here, we investigate whether serum soluble gp130 concentrations correlate with blood pressure in humans, whether gp130 expression in the aorta differs between hypertensive and control rats, and whether angiotensin II or endothelin regulate gp130 expression in human VSMC. We measured serum concentrations of soluble gp130, IL-6, the soluble IL-6 receptor, and the intima-media thickness of the common carotid artery in stroke patients (n = 48) and in elderly controls (n = 48). Furthermore, soluble gp130 levels were measured in young controls (n = 200). Expression of gp130 in Wistar-Kyoto (n = 12), spontaneously hypertensive rats (n = 12), and human VSMC was detected by real-time reverse transcription-PCR and immunohistochemistry. Soluble gp130 serum concentrations correlated with blood pressure in stroke patients and in elderly and young controls and with the intima-media thickness of the common carotid artery in stroke patients. The hypothesis that elevated soluble gp130 derives from the vascular system was supported by the enhanced expression of gp130 in the aortic wall of spontaneously hypertensive rats. Furthermore, treatment of human VSMC with angiotensin II stimulated gp130 expression. Our data suggest that soluble gp130 serum concentrations are correlated with blood pressure and may reflect vascular remodeling in response to arterial hypertension.

Neprilysin Null Mice Develop Exaggerated Pulmonary Vascular Remodeling in Response to Chronic Hypoxia

Neprilysin is a transmembrane metalloendopeptidase that degrades neuropeptides that are important for both growth and contraction. In addition to promoting carcinogenesis, decreased levels of neprilysin increases inflammation and neuroendocrine cell hyperplasia, which may predispose to vascular remodeling. Early pharmacological studies showed a decrease in chronic hypoxic pulmonary hypertension with neprilysin inhibition. We used a genetic approach to test the alternate hypothesis that neprilysin depletion increases chronic hypoxic pulmonary hypertension. Loss of neprilysin had no effect on baseline airway or alveolar wall architecture, vessel density, cardiac function, hematocrit, or other relevant peptidases. Only lung neuroendocrine cell hyperplasia and a subtle neuropeptide imbalance were found. After chronic hypoxia, neprilysin-null mice exhibited exaggerated pulmonary hypertension and striking increases in muscularization of distal vessels. Subtle thickening of proximal media/adventitia not typically seen in mice was also detected. In contrast, adaptive right ventricular hypertrophy was less than anticipated. Hypoxic wild-type pulmonary vessels displayed close temporal and spatial relationships between decreased neprilysin and increased cell growth. Smooth muscle cells from neprilysin-null pulmonary arteries had increased proliferation compared with controls, which was decreased by neprilysin replacement. These data suggest that neprilysin may be protective against chronic hypoxic pulmonary hypertension in the lung, at least in part by attenuating the growth of smooth muscle cells. Lung-targeted strategies to increase neprilysin levels could have therapeutic benefits in the treatment of this disorder.

Roflumilast, a phosphodiesterase 4 inhibitor, alleviates bleomycin‐induced lung injury

The effects of a phosphodiesterase 4 (PDE4) inhibitor, roflumilast, on bleomycin-induced lung injury were explored in 'preventive' and 'therapeutic' protocols and compared with glucocorticoids. Roflumilast (1 and 5 mg.kg(-1).d(-1), p.o.) or dexamethasone (2.5 mg.kg(-1).d(-1), p.o.) was given to C57Bl/6J mice from day 1 to 14 (preventive) or day 7 to 21 (therapeutic) after intratracheal bleomycin (3.75 U.kg(-1)). In Wistar rats, roflumilast (1 mg.kg(-1).d(-1), p.o.) was compared with methylprednisolone (10 mg.kg(-1).d(-1), p.o.) from day 1 to 21 (preventive) or from day 10 to 21 (therapeutic), following intratracheal instillation of bleomycin (7.5 U.kg(-1)). Analyses were performed at the end of the treatment periods. Preventive. Roflumilast reduced bleomycin-induced lung hydroxyproline, lung fibrosis and right ventricular hypertrophy; muscularization of intraacinar pulmonary vessels was also attenuated. The PDE4 inhibitor diminished bleomycin-induced transcripts for tumour necrosis factor (TNFalpha), transforming growth factor (TGFbeta), connective tissue growth factor, alphaI(I)collagen, endothelin-1 and the mucin, Muc5ac, in lung, and reduced bronchoalveolar lavage fluid levels of TNFalpha, interleukin-13, TGFbeta, Muc5ac, lipid hydroperoxides and inflammatory cell counts. Therapeutic. In mice, roflumilast but not dexamethasone reduced bleomycin-induced lung alphaI(I)collagen transcripts, fibrosis and right ventricular hypertrophy. Similar results were found in the rat. Roflumilast prevented the development of bleomycin-induced lung injury, and alleviated the lung fibrotic and vascular remodeling response to bleomycin in a therapeutic protocol, the latter being resistant to glucocorticoids.

Flow-Mediated Vascular Remodeling in Hypertension

Changes in shear and medial wall stress induced by blood flow contribute to vascular remodeling, but details of these relations remain undefined. We hypothesized that remodeling has a strong genetic component and that phenotypic responses to hemodynamic stress will differ among rat strains. Here, we characterized phenotypic traits related to carotid remodeling in the 2 rat strains that we previously showed the greatest difference in shear stress regulation: Genetically Hypertensive (GH) and Brown Norway (BN) rat strains. Left internal and external carotid arteries were ligated and blood flow was reduced in the left common (LCA) by 90% and increased in the right common carotid artery (RCA) by 60%. Rats were studied for up to 28 days after flow modification and carotid outer diameters were measured in vivo, and wall and luminal components by histomorphometry, to obtain indices of remodeling. Blood flow and pressure measurements were made at corresponding time points. By day 28, remodeling in the GH was greater in response to high flow than in BN, and shear stress was normalized. In contrast, remodeling in the BN was greater in the low flow LCA than in GH. Media stress was greater in GH than BN for any value of carotid shear stress and remained relatively unchanged in low flow, but markedly increased in high flow remodeling. Importantly, pressure was not a major determinant of flow remodeling in these conditions. There are key differences in the ability of carotids in GH and BN rats to adhere to hemodynamic laws during vascular remodeling. GH rats exhibit intact regulatory mechanisms for increased, but not reduced, shear stress. Moreover, the ability to maintain physiological shear and media stresses during vascular remodeling in response to modified flow appears to be intrinsically "genetically" determined.

Roles of Macrophages in Flow-Induced Outward Vascular Remodeling

Sustained hemodynamic stresses, especially sustained high blood flow, result in flow-induced outward vascular remodeling. Mechanisms that link hemodynamic stresses to vascular remodeling are not well understood. Inflammatory cells, known for their release of proteinases, including matrix metalloproteinases (MMPs), are emerging as key mediators for various tissue remodeling. Using a flow-augmented common carotid artery model in rats, we tested whether macrophages play critical roles in adaptive outward vascular remodeling in response to an increase in blood flow. Left common carotid artery ligation caused a sustained increase in blood flow with a gradual increase in luminal diameter in the right common carotid artery. Macrophages infiltrated into the vascular wall that peaked 3 days after flow augmentation. The time course of MMP-9 expression coincided with infiltration of macrophages. Macrophage depletion by liposome-encapsulated dichloromethylene diphosphonate significantly reduced flow-induced outward vascular remodeling, as indicated by the smaller luminal diameter of flow-augmented right common carotid artery in the clodronate-treated group compared with the phosphate-buffered saline-treated group (P<0.05). These data show critical roles of macrophages in flow-induced outward vascular remodeling. Inflammatory cell infiltration and their subsequent release of cytokines may be key processes for flow-induced outward vascular remodeling.

Invited review: activity-induced angiogenesis

The dynamic biochemical and mechanical environment around blood vessels during muscle activity generates powerful stimuli for vascular remodelling. Ultimately, this must lead to a coordinated expansion of various elements of the cardiovascular system in order to support enhanced aerobic exercise. Vascular endothelial growth factor plays a central role, and understanding how this is regulated in vivo by changes in transcription and stability of mRNA, production of protein and interaction with other growth factors, is a continuing challenge. Exercise hyperaemia leads to an increase in microvascular shear stress, which stimulates endothelial release of nitric oxide, whilst proteolytic modification of the extracellular matrix is induced by mechanical deformation during cyclical contractions or muscle overload. These components of the exercise response lead to different forms of capillary growth, and subsequent expansion of the microcirculation may not have the same functional outcome. In vitro and in vivo studies have shown a complex interplay between different cytokines, receptors and mural cells in directing the necessary tissue re-organisation. The mechanisms involved in arteriogenesis are less well-understood than those of angiogenesis, but application of these data to understanding vascular remodelling in response to exercise may help resolve a range of cardiovascular dysfunction.

Proteomic Analysis Permits the Identification of New Biomarkers of Arterial Wall Remodeling in Hypertension

Hypertension represents one of the main risk factors for vascular diseases. Genetic susceptibility may influence the rate of its development and the associated vascular remodeling. To explore markers of hypertension-related morbidity, we have used surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometry to study changes in proteins released by the aorta of two rat strains with different susceptibilities to hypertension. Fischer and Brown Norway (BN) rats were divided into a control group and a group receiving low-dose N(Omega)-nitro-L-arginine methyl ester (L-NAME), a hypertensive drug, interfering with endothelial function. In spite of a significant elevation of blood pressure in both strains in response to L-NAME, BN rats exhibited a lower vascular remodeling in response to hypertension. Proteomic analysis of secreted aortic proteins by SELDI-TOF MS allowed detection of four mass-to-charge ratio (m/z) peaks whose corresponding proteins were identified as ubiquitin, smooth muscle (SM) 22alpha, thymosin beta4, and C-terminal fragment of filamin A, differentially secreted in Fischer rats in response to L-NAME. We have confirmed a strain-dependent difference in susceptibility to L-NAME-induced hypertension between BN and Fischer rats. The greater susceptibility of Fischer rats is associated with aortic wall hypertrophic remodeling, reflected by increased aortic secretion of four identified biomarkers. Similar variations in one of them, SM22alpha, also were observed in plasma, suggesting that this marker could be used to assess vascular damage induced by hypertension.

Alpha2-Antiplasmin Is a Critical Regulator of Angiotensin II–Mediated Vascular Remodeling

Alpha2-antiplasmin (alpha2-AP) is the major circulating inhibitor of plasmin, which plays a determining role in the regulation of intravascular fibrinolysis. We investigated the role of alpha(2)-AP on vascular remodeling in response to angiotensin II (Ang II). alpha2-AP-deficient mice were performed. Ang II and N(omega)-nitro- L-arginine methyl ester (L-NAME)-induced perivascular fibrosis was significantly decreased in alpha2-AP-/- mice compared with wild-type mice. In situ gelatinolytic activity analysis shows that perivascular gelatinolytic activity was increased in alpha2-AP-/- mice, which was responsible for decreased perivascular fibrosis in response to Ang II and L-NAME. Ang II-induced arterial wall thickening, vascular cell proliferation, apoptosis, c-Myc, and collagen I expression were significantly decreased in alpha2-AP-/- mice compared with wild-type mice. Further analysis shows that increased p53 and p21 expression were responsible for inhibition of Ang II-induced vascular remodeling in alpha2-AP-/- mice. The results show that alpha2-AP is a critical regulator for vascular remodeling by inhibiting p53/p21 pathway, suggesting that alpha2-AP is proposed to be a potential therapeutic target for vascular remodeling.

Endothelial Expression of Beta‐1 Integrin Is Required for Embryonic Vascular Patterning and Postnatal Vascular Remodeling

The largest subgroup of integrins is that containing the β1 subunit. Global deletion of β1 integrin expression results in embryonic lethality at ~E5, a developmental time point too early to determine the effects of this integrin on vascular development. To elucidate the specific role of β1 integrin in the vasculature, we conditionally deleted the β1 gene in the endothelium using Cre/LoxP techniques. Homozygous deletion of β1 integrins in the endothelium resulted in failure of normal vascular patterning, severe fetal growth retardation, and embryonic death at E9.5‐10, although there were no overt effects on vasculogenesis (Fig. 1). Heterozygous endothelial β1 gene deletion did not diminish fetal or postnatal survival, but reduced β1 subunit expression in endothelial cells from adult mice approximately 40%. These mice demonstrated abnormal vascular remodeling in response to experimentally altered in vivo blood flow, and diminished vascularization in healing wounds (Fig. 2). These data demonstrate that endothelial expression of β1 integrin is required for developmental vascular patterning, and that endothelial β1 gene dosing has significant functional effects on vascular remodeling in the adult. Understanding how β1 integrin expression is modulated may have significant clinical importance.

Connexin37 Regulation of Vascular Remodeling Following Ischemic Injury

Gap junction proteins Connexin37 (Cx37) and Connexin40 (Cx40) are strongly expressed in normal vascular endothelium, although their specific function(s) in this tissue are poorly understood. Previously, we have shown by dual‐dye injection of oppositely‐charged dyes that both Cx37 and Cx40 channels are similarly cation‐selective. Despite similarities in permselectivity, expression of Cx37 – but not Cx40 – suppresses proliferation of otherwise connexin‐deficient rat insulinoma cells, suggesting that Cx37 may be uniquely suited to regulating endothelial cell proliferation in vivo. Indeed, animals lacking both Cx37 and Cx40 experience profound vascular abnormalities resembling hemangiomas. Using the unilateral hindlimb ischemia model to induce a vascular remodeling response in wild‐type and Cx37‐deficient animals, we show that revascularization following induction of ischemia (as determined by comparison of vascular density in the ischemic versus non‐ischemic hindlimb) is enhanced (~50%) in Cx37‐deficient animals compared to wild‐type controls. These findings are consistent with the hypothesis that in mature endothelium, Cx37 suppresses cell proliferation and controls remodeling of the vasculature. Further, we hypothesize that the inhibitory effect of Cx37 is temporarily relieved by downregulation of its expression during the revascularization response induced by ischemia. Support: AHA 550158Z (JMB), HL064232 (AMS) and AHA 0715532Z (JSF).

Induction of Vascular Remodeling in the Lung by Chronic House Dust Mite Exposure

Structural changes to the lung are associated with chronic asthma. In addition to alterations to the airway wall, asthma is associated with vascular modifications, although this aspect of remodeling is poorly understood. We sought to evaluate the character and kinetics of vascular remodeling in response to chronic aeroallergen exposure. Because many ovalbumin-driven models used to investigate allergic airway disease do so in the absence of persistent airway inflammation, we used a protocol of chronic respiratory exposure to house dust mite extract (HDME), which has been shown to induce persistent airway inflammation consistent with that seen in humans with asthma. Mice were exposed to HDME intranasally for 7 or 20 consecutive weeks, and resolution of the inflammatory and remodeling response to allergen was investigated 4 weeks after the end of a 7-week exposure protocol. Measures of vascular remodeling, including total collagen deposition, procollagen I production, endothelial and smooth muscle cell proliferation, smooth muscle area, and presence of myofibroblasts, were investigated histologically in lung vessels of different sizes and locations. We observed an increase in total collagen content, which did not resolve upon cessation of allergen exposure. Other parameters were significantly increased after 7 and/or 20 weeks of allergen exposure but returned to baseline after allergen withdrawal. We conclude that respiratory HDME exposure induces airway remodeling and pulmonary vascular remodeling, and, in accordance with airway remodeling, some components of these structural changes may be irreversible.

Endothelial Expression of β1 Integrin Is Required for Embryonic Vascular Patterning and Postnatal Vascular Remodeling

The largest subgroup of integrins is that containing the beta1 subunit. beta1 integrins have been implicated in a wide array of biological processes ranging from adhesion to cell growth, organogenesis, and mechanotransduction. Global deletion of beta1 integrin expression results in embryonic death at ca. embryonic day 5 (E5), a developmental time point too early to determine the effects of this integrin on vascular development. To elucidate the specific role of beta1 integrin in the vasculature, we conditionally deleted the beta1 gene in the endothelium. Homozygous deletion of beta1 integrins in the endothelium resulted in failure of normal vascular patterning, severe fetal growth retardation, and embryonic death at E9.5 to 10, although there were no overt effects on vasculogenesis. Heterozygous endothelial beta1 gene deletion did not diminish fetal or postnatal survival, but it reduced beta1 subunit expression in endothelial cells from adult mice by approximately 40%. These mice demonstrated abnormal vascular remodeling in response to experimentally altered in vivo blood flow and diminished vascularization in healing wounds. These data demonstrate that endothelial expression of beta1 integrin is required for developmental vascular patterning and that endothelial beta1 gene dosing has significant functional effects on vascular remodeling in the adult. Understanding how beta1 integrin expression is modulated may have significant clinical importance.

Risk stratification of individual coronary lesions using local endothelial shear stress: a new paradigm for managing coronary artery disease

The purpose of this review is to summarize the role of endothelial shear stress in the natural history of coronary atherosclerosis, and to propose an individualized risk-stratification strategy of atherosclerotic lesions based on the in-vivo characterization of local endothelial shear stress and wall morphology. Low endothelial shear stress promotes the development of early fibroatheromas, which subsequently follow an individualized natural history of progression. This individual natural history is critically dependent on the magnitude of low endothelial shear stress, which subsequently regulates the severity of inflammation within the wall and ultimately the vascular remodeling response. Very low endothelial shear stress enhances plaque inflammation, leading to excessive expansive remodeling. Excessive expansive remodeling leads to perpetuation, or even exacerbation, of the local low endothelial shear stress environment, thereby setting up a self-perpetuating vicious cycle among low local endothelial shear stress, inflammation, and excessive expansive remodeling, which transforms an early fibroatheroma to a high-risk plaque. In-vivo assessment of the local endothelial shear stress environment, severity of inflammation and vascular remodeling response, all responsible for individual plaque behavior and natural history, in combination with systemic biomarkers of vulnerability, may allow for detailed risk stratification of individual early atherosclerotic plaques, thereby guiding both systemic and local, lesion-specific therapeutic strategies.

Axl Mediates Vascular Remodeling Induced by Deoxycorticosterone Acetate–Salt Hypertension

Axl, a receptor tyrosine kinase, was recently identified as a novel candidate gene in a genetic model of salt-sensitive hypertension (Sabra rat). Our group first reported that Axl plays a significant role in vascular remodeling in response to injury. Here we investigated the role of Axl in the pathogenesis of hypertension in a deoxycorticosterone acetate (DOCA)-salt model. Hypertension was induced in Axl wild-type (Axl(+/+)) mice and Axl-deficient (Axl(-/-)) mice by uninephrectomy and DOCA-salt for 6 weeks. Controls were uninephrectomized and received tap water and regular chow ad libitum. DOCA-salt treatment increased systolic blood pressure by 25 mm Hg in both genotypes after 1 week. Systolic blood pressure remained significantly elevated in Axl(+/+) DOCA, whereas systolic blood pressure levels in Axl(-/-) DOCA mice were the same as controls at 6 weeks. DOCA-salt increased relative kidney weight and glomerular hypertrophy by 40% compared with controls in both genotypes. Consistent with levels of systolic blood pressure, endothelium-dependent vasorelaxation was impaired in Axl(+/+) DOCA mice compared with Axl(+/+) controls, whereas in Axl(-/-) DOCA mice relaxation responses were similar to Axl(-/-) controls. In addition, endothelium-independent vasorelaxation was improved in Axl(-/-) DOCA mice compared with Axl(+/+) DOCA mice. Nitrotyrosine and phospho-Akt immunoreactivity was significantly reduced in arteries from Axl(-/-) DOCA mice compared with Axl(+/+) DOCA mice. The remodeling index of the mesenteric artery (media:lumen ratio) was significantly increased in Axl(+/+) DOCA mice compared with Axl(-/-) DOCA mice. Finally, increased vascular apoptosis in the Axl(-/-) DOCA mice suggests a likely mechanism for Axl-dependent effects on hypertension. These data strengthen the pathogenic role for Axl in salt-sensitive hypertension.

Counterpoint: Chronic Hypoxia-induced Pulmonary Hypertension does not Lead to Loss of Pulmonary Vasculature

Exposure of native sea level dwellers to chronic hypoxia due to migration to high altitude leads to the development of increased pulmonary vascular resistance causing pulmonary hypertension. In some susceptible individuals this progressively worsens causing right ventricular failure and ultimately

Soluble Guanylate Cyclase-α1 Deficiency Selectively Inhibits the Pulmonary Vasodilator Response to Nitric Oxide and Increases the Pulmonary Vascular Remodeling Response to Chronic Hypoxia

Nitric oxide (NO) activates soluble guanylate cyclase (sGC), a heterodimer composed of alpha- and beta-subunits, to produce cGMP. NO reduces pulmonary vascular remodeling, but the role of sGC in vascular responses to acute and chronic hypoxia remains incompletely elucidated. We therefore studied pulmonary vascular responses to acute and chronic hypoxia in wild-type (WT) mice and mice with a nonfunctional alpha1-subunit (sGCalpha1-/-). sGCalpha1-/- mice had significantly reduced lung sGC activity and vasodilator-stimulated phosphoprotein phosphorylation. Right ventricular systolic pressure did not differ between genotypes at baseline and increased similarly in WT (22+/-2 to 34+/-2 mm Hg) and sGCalpha1-/- (23+/-2 to 34+/-1 mm Hg) mice in response to acute hypoxia. Inhaled NO (40 ppm) blunted the increase in right ventricular systolic pressure in WT mice (22+/-2 to 24+/-2 mm Hg, P<0.01 versus hypoxia without NO) but not in sGCalpha1-/- mice (22+/-1 to 33+/-1 mm Hg) and was accompanied by a significant rise in lung cGMP content only in WT mice. In contrast, the NO-donor sodium nitroprusside (1.5 mg/kg) decreased systemic blood pressure similarly in awake WT and sGCalpha1-/- mice as measured by telemetry (-37+/-2 versus -42+/-4 mm Hg). After 3 weeks of hypoxia, the increases in right ventricular systolic pressure, right ventricular hypertrophy, and muscularization of intra-acinar pulmonary vessels were 43%, 135%, and 46% greater, respectively, in sGCalpha1-/- than in WT mice (P<0.01). Increased remodeling in sGCalpha1-/- mice was associated with an increased frequency of 5'-bromo-deoxyuridine-positive vessels after 1 and 3 weeks (P<0.01 versus WT). Deficiency of sGCalpha1 does not alter hypoxic pulmonary vasoconstriction. sGCalpha1 is essential for NO-mediated pulmonary vasodilation and limits chronic hypoxia-induced pulmonary vascular remodeling.