Pressure and angiotensin II synergistically induce aortic fibronectin expression in organ culture model of rabbit aorta. Evidence for a pressure-induced tissue renin-angiotensin system

Cyclic stretch enhances neutrophil extracellular trap formation

BACKGROUND

Neutrophils, the most abundant leukocytes circulating in blood, contribute to host defense and play a significant role in chronic inflammatory disorders. They can release their DNA in the form of extracellular traps (NETs), which serve as scaffolds for capturing bacteria and various blood cells. However, uncontrolled formation of NETs (NETosis) can lead to excessive activation of coagulation pathways and thrombosis. Once neutrophils are migrated to infected or injured tissues, they become exposed to mechanical forces from their surrounding environment. However, the impact of transient changes in tissue mechanics due to the natural process of aging, infection, tissue injury, and cancer on neutrophils remains unknown. To address this gap, we explored the interactive effects of changes in substrate stiffness and cyclic stretch on NETosis. Primary neutrophils were cultured on a silicon-based substrate with stiffness levels of 30 and 300 kPa for at least 3 h under static conditions or cyclic stretch levels of 5% and 10%, mirroring the biomechanics of aged and young arteries.

RESULTS

Using this approach, we found that neutrophils are sensitive to cyclic stretch and that increases in stretch intensity and substrate stiffness enhance nuclei decondensation and histone H3 citrullination (CitH3). In addition, stretch intensity and substrate stiffness promote the response of neutrophils to the NET-inducing agents phorbol 12-myristate 13-acetate (PMA), adenosine triphosphate (ATP), and lipopolysaccharides (LPS). Stretch-induced activation of neutrophils was dependent on calpain activity, the phosphatidylinositol 3-kinase (PI3K)/focal adhesion kinase (FAK) signalling and actin polymerization.

CONCLUSIONS

In summary, these results demonstrate that the mechanical forces originating from the surrounding tissue influence NETosis, an important neutrophil function, and thus identify a potential novel therapeutic target.

Excessive adventitial stress drives inflammation-mediated fibrosis in hypertensive aortic remodelling in mice

Hypertension induces significant aortic remodelling, often adaptive but sometimes not. To identify immuno-mechanical mechanisms responsible for differential remodelling, we studied thoracic aortas from 129S6/SvEvTac and C57BL/6 J mice before and after continuous 14-day angiotensin II infusion, which elevated blood pressure similarly in both strains. Histological and biomechanical assessments of excised vessels were similar at baseline, suggesting a common homeostatic set-point for mean wall stress. Histology further revealed near mechano-adaptive remodelling of the hypertensive 129S6/SvEvTac aortas, but a grossly maladaptive remodelling of C57BL/6 J aortas. Bulk RNA sequencing suggested that increased smooth muscle contractile processes promoted mechano-adaptation of 129S6/SvEvTac aortas while immune processes prevented adaptation of C57BL/6 J aortas. Functional studies confirmed an increased vasoconstrictive capacity of the former while immunohistochemistry demonstrated marked increases in inflammatory cells in the latter. We then used multiple computational biomechanical models to test the hypothesis that excessive adventitial wall stress correlates with inflammatory cell infiltration. These models consistently predicted that increased vasoconstriction against an increased pressure coupled with modest deposition of new matrix thickens the wall appropriately, restoring wall stress towards homeostatic consistent with adaptive remodelling. By contrast, insufficient vasoconstriction permits high wall stresses and exuberant inflammation-driven matrix deposition, especially in the adventitia, reflecting compromised homeostasis and gross maladaptation.

Complementary roles of mechanotransduction and inflammation in vascular homeostasis

Arteries are exposed to relentless pulsatile haemodynamic loads, but via mechanical homeostasis they tend to maintain near optimal structure, properties and function over long periods in maturity in health. Numerous insults can compromise such homeostatic tendencies, however, resulting in maladaptations or disease. Chronic inflammation can be counted among the detrimental insults experienced by arteries, yet inflammation can also play important homeostatic roles. In this paper, we present a new theoretical model of complementary mechanobiological and immunobiological control of vascular geometry and composition, and thus properties and function. We motivate and illustrate the model using data for aortic remodelling in a common mouse model of induced hypertension. Predictions match the available data well, noting a need for increased data for further parameter refinement. The overall approach and conclusions are general, however, and help to unify two previously disparate literatures, thus leading to deeper insight into the separate and overlapping roles of mechanobiology and immunobiology in vascular health and disease.

Computational Modeling Predicts Immuno-Mechanical Mechanisms of Maladaptive Aortic Remodeling in Hypertension

Uncontrolled hypertension is a major risk factor for myriad cardiovascular diseases. Among its many effects, hypertension increases central artery stiffness which in turn is both an initiator and indicator of disease. Despite extensive clinical, animal, and basic science studies, the biochemomechanical mechanisms by which hypertension drives aortic stiffening remain unclear. In this paper, we show that a new computational model of aortic growth and remodeling can capture differential effects of induced hypertension on the thoracic and abdominal aorta in a common mouse model of disease. Because the simulations treat the aortic wall as a constrained mixture of different constituents having different material properties and rates of turnover, one can gain increased insight into underlying constituent-level mechanisms of aortic remodeling. Model results suggest that the aorta can mechano-adapt locally to blood pressure elevation in the absence of marked inflammation, but large increases in inflammation drive a persistent maladaptive phenotype characterized primarily by adventitial fibrosis. Moreover, this fibrosis appears to occur via a marked increase in the rate of deposition of collagen having different material properties in the absence of a compensatory increase in the rate of matrix degradation. Controlling inflammation thus appears to be key to reducing fibrosis, but therapeutic strategies should not compromise the proteolytic activity of the wall that is essential to mechanical homeostasis.

The cofilin phosphatase slingshot homolog 1 restrains angiotensin II-induced vascular hypertrophy and fibrosis in vivo

The dual specificity phosphatase slingshot homolog 1 (SSH1) contributes to actin remodeling by dephosphorylating and activating the actin-severing protein cofilin. The reorganization of the actin cytoskeleton has been implicated in chronic hypertension and the subsequent mechano-adaptive rearrangement of vessel wall components. Therefore, using a novel Ssh1^-/- mouse model, we investigated the potential role of SSH1 in angiotensin II (Ang II)-induced hypertension, and vascular remodeling. We found that loss of SSH1 did not produce overt phenotypic changes and that baseline blood pressures as well as heart rates were comparable between Ssh1^+/+ and Ssh1^-/- mice. Although 14 days of Ang II treatment equally increased systolic blood pressure in both genotypes, histological assessment of aortic samples indicated that medial thickening was exacerbated by the loss of SSH1. Consequently, reverse-transcription quantitative PCR analysis of the transcripts from Ang II-infused animals confirmed increased aortic expression levels of fibronectin, and osteopontin in Ssh1^-/- when compared to wild-type mice. Mechanistically, our data suggest that fibrosis in SSH1-deficient mice occurs by a process that involves aberrant responses to Ang II-induced TGFβ1. Taken together, our work indicates that Ang II-dependent fibrotic gene expression and vascular remodeling, but not the Ang II-induced pressor response, are modulated by SSH1-mediated signaling pathways and SSH1 activity is protective against Ang II-induced remodeling in the vasculature.

Differential cell-matrix mechanoadaptations and inflammation drive regional propensities to aortic fibrosis, aneurysm or dissection in hypertension

The embryonic lineage of intramural cells, microstructural organization of the extracellular matrix, local luminal and wall geometry, and haemodynamic loads vary along the length of the aorta. Yet, it remains unclear why certain diseases manifest differentially along the aorta. Toward this end, myriad animal models provide insight into diverse disease conditions-including fibrosis, aneurysm and dissection-but inherent differences across models impede general interpretations. We examined region-specific cellular, matrix, and biomechanical changes in a single experimental model of hypertension and atherosclerosis, which commonly coexist. Our findings suggest that (i) intramural cells within the ascending aorta are unable to maintain the intrinsic material stiffness of the wall, which ultimately drives aneurysmal dilatation, (ii) a mechanical stress-initiated, inflammation-driven remodelling within the descending aorta results in excessive fibrosis, and (iii) a transient loss of adventitial collagen within the suprarenal aorta contributes to dissection propensity. Smooth muscle contractility helps to control wall stress in the infrarenal aorta, which maintains mechanical properties near homeostatic levels despite elevated blood pressure. This early mechanoadaptation of the infrarenal aorta does not preclude subsequent acceleration of neointimal formation, however. Because region-specific conditions may be interdependent, as, for example, diffuse central arterial stiffening can increase cyclic haemodynamic loads on an aneurysm that is developing proximally, there is a clear need for more systematic assessments of aortic disease progression, not simply a singular focus on a particular region or condition.

Excessive Adventitial Remodeling Leads to Early Aortic Maladaptation in Angiotensin-Induced Hypertension

The primary function of central arteries is to store elastic energy during systole and to use it to sustain blood flow during diastole. Arterial stiffening compromises this normal mechanical function and adversely affects end organs, such as the brain, heart, and kidneys. Using an angiotensin II infusion model of hypertension in wild-type mice, we show that the thoracic aorta exhibits a dramatic loss of energy storage within 2 weeks that persists for at least 4 weeks. This diminished mechanical functionality results from increased structural stiffening as a result of an excessive accumulation of adventitial collagen, not a change in the intrinsic stiffness of the wall. A detailed analysis of the transmural biaxial wall stress suggests that the exuberant production of collagen results more from an inflammatory response than from a mechano-adaptation, hence reinforcing the need to control inflammation, not just blood pressure. Although most clinical assessments of arterial stiffening focus on intimal-medial thickening, these results suggest a need to measure and control the highly active and important adventitia.

Elevated pressure causes endothelial dysfunction in mouse carotid arteries by increasing local angiotensin signaling

Experiments were performed to determine whether or not acute exposure to elevated pressure would disrupt endothelium-dependent dilatation by increasing local angiotensin II (ANG II) signaling. Vasomotor responses of mouse-isolated carotid arteries were analyzed in a pressure myograph at a control transmural pressure (PTM) of 80 mmHg. Acetylcholine-induced dilatation was reduced by endothelial denudation or by inhibition of nitric oxide synthase (NG-nitro-L-arginine methyl ester, 100 μM). Transient exposure to elevated PTM (150 mmHg, 180 min) inhibited dilatation to acetylcholine but did not affect responses to the nitric oxide donor diethylamine NONOate. Elevated PTM also increased endothelial reactive oxygen species, and the pressure-induced endothelial dysfunction was prevented by the direct antioxidant and NADPH oxidase inhibitor apocynin (100 μM). The increase in endothelial reactive oxygen species in response to elevated PTM was reduced by the ANG II type 1 receptor (AT1R) antagonists losartan (3 μM) or valsartan (1 μM). Indeed, elevated PTM caused marked expression of angiotensinogen, the precursor of ANG II. Inhibition of ANG II signaling, by blocking angiotensin-converting enzyme (1 μM perindoprilat or 10 μM captopril) or blocking AT1Rs prevented the impaired response to acetylcholine in arteries exposed to 150 mmHg but did not affect dilatation to the muscarinic agonist in arteries maintained at 80 mmHg. After the inhibition of ANG II, elevated pressure no longer impaired endothelial dilatation. In arteries treated with perindoprilat to inhibit endogenous formation of the peptide, exogenous ANG II (0.3 μM, 180 min) inhibited dilatation to acetylcholine. Therefore, elevated pressure rapidly impairs endothelium-dependent dilatation by causing ANG expression and enabling ANG II-dependent activation of AT1Rs. These processes may contribute to the pathogenesis of hypertension-induced vascular dysfunction and organ injury.

Modulation of haemodynamics, endogeneous antioxidant enzymes, and pathophysiological changes by selective inhibition of angiotensin II type 1 receptors in pressureoverload rats

Background

Constriction of the thoracic or abdominal aorta provides an experimental model of pressure-overload cardiac hypertrophy. Blockade of AT₁ receptors is beneficial in preventing target-organ damage in hypertension.

Objective

To examine the effect of angiotensin II receptor antagonists on blood pressure, endogenous antioxidant enzyme and histopathological changes in pressure-overload rats.

Methods

Pressure overload was produced by abdominal aortic banding (AAB) using a blunt 22-guage needle in male rats as a model of cardiac hypertrophy. After surgery, the AAB-induced hypertension (AABIH) rats were treated with losartan 40 mg/kg/day, candesartan 10 mg/kg/day, irbesartan 10 mg/kg/day per os for 16 weeks. At 16 weeks of surgery, the rats were observed for general characteristics and mortality, and we determined non-invasive blood pressure (NIBP), endogenous antioxidant enzyme catalase and superoxide dismutase (SOD) activities, and histology of the target organs.

Results

In the AABIH group, significant increase in systolic blood pressure was observed from weeks 3 to 16 compared with the control group, along with reduced serum catalase and SOD activities. The treated groups showed significant reduction in systolic BP and increase in serum SOD and catalase activities. The histological changes induced in the target organs, namely heart, liver, kidneys and thoracic aorta in the AABIH rats were attenuated in the treated rats.

Conclusion

Blockade of the AT₁ receptor caused an improvement in the myocardial antioxidant reserve and decreased oxidative stress in the hypertensive rats, which was evidenced by the protection observed in the treatment groups.

The roles of integrins in mediating the effects of mechanical force and growth factors on blood vessels in hypertension

Hypertension is characterized by a sustained increase in vasoconstriction and attenuated vasodilation in the face of elevated mechanical stress in the blood vessel wall. To adapt to the increased stress, the vascular smooth muscle cell and its surrounding environment undergo structural and functional changes known as vascular remodeling. Multiple mechanisms underlie the remodeling process, including increased expression of humoral factors and their receptors as well as adhesion molecules and their receptors, all of which appear to collaborate and interact in the response to pressure elevation. In this review, we focus on the interactions between integrin signaling pathways and the activation of growth factor receptors in the response to the increased mechanical stress experienced by blood vessels in hypertension.

Alterations of pulse pressure stimulate arterial wall matrix remodeling

The effect of pulse pressure on arterial wall remodeling has not been clearly defined. The objective of this study was to evaluate matrix remodeling in arteries under nonpulsatile and hyperpulsatile pressure as compared with arteries under normal pulsatile pressure. Porcine carotid arteries were cultured for 3 and 7 days under normal, nonpulsatile, and hyperpulsatile pressures with the same mean pressure and flow rate using an ex vivo organ culture model. Fenestrae in the internal elastic lamina, collagen, fibronectin, and gap junction protein connexin 43 were examined in these arteries using confocal microscopy, immunoblotting, and immunohistochemistry. Our results showed that after 7 days, the mean fenestrae size and the area fraction of fenestrae decreased significantly in nonpulsatile arteries (51% and 45%, respectively) and hyperpulsatile arteries (45% and 54%, respectively) when compared with normal pulsatile arteries. Fibronectin decreased (29.9%) in nonpulsatile arteries after 3 days but showed no change after 7 days, while collagen I levels increased significantly (106%) in hyperpulsatile arteries after 7 days. The expression of connexin 43 increased by 35.3% in hyperpulsatile arteries after 7 days but showed no difference in nonpulsatile arteries. In conclusion, our results demonstrated, for the first time, that an increase or a decrease in pulse pressure from its normal physiologic level stimulates structural changes in the arterial wall matrix. However, hyperpulsatile pressure has a more pronounced effect than the diminished pulse pressure. This effect helps to explain the correlation between increasing wall stiffness and increasing pulse pressure in vivo.

The effect of angiotensin II on the proliferation of human gingival fibroblasts

Angiotensin not only raises blood pressure and modifies body fluids and electrolytes but also induces differentiation and proliferation of fibroblasts in the circulatory system in order to repair damage. The purpose of the present study was to observe the influence of the addition of angiotensin II (AngII) or nifedipine (NIF) alone or both sequentially on proliferative activity, the intracellular Ca(2+) concentration ([Ca(2+)]i), and the inositol-1,4,5-triphosphate (IP3) level in cultivated human gingival fibroblasts. Addition of 10(-8)-10(-4) M NIF or 10(-5)-10(-4) M AngII alone increased the proliferation of cultivated gingival fibroblasts, and the interaction of NIF and AngII suppressed proliferation. Addition of AngII alone increased [Ca(2+)]i, with a peak 60 s afterward and a return to a level slightly higher than the pretreatment level at 120 s. Addition of both AngII and NIF did not increase [Ca(2+)]i as much as the addition of AngII alone. When Ca(2+) was absent from the extracellular environment, the AngII-induced increase in [Ca(2+)]i was suppressed. AngII increased the concentration of IP(3), with a peak at 120 s after its addition. From these results we concluded that AngII increased the proliferation of gingival fibroblasts by causing an influx of Ca(2+), which increased [Ca(2+)]i.

Cyclic stretch, reactive oxygen species, and vascular remodeling

Blood vessels respond to changes in mechanical load from circulating blood in the form of shear stress and mechanical strain as the result of heart propulsions by changes in intracellular signaling leading to changes in vascular tone, production of vasoactive molecules, and changes in vascular permeability, gene regulation, and vascular remodeling. In addition to hemodynamic forces, microvasculature in the lung is also exposed to stretch resulting from respiratory cycles during autonomous breathing or mechanical ventilation. Among various cell signaling pathways induced by mechanical forces and reported to date, a role of reactive oxygen species (ROS) produced by vascular cells receives increasing attention. ROS play an essential role in signal transduction and physiologic regulation of vascular function. However, in the settings of chronic hypertension, inflammation, or acute injury, ROS may trigger signaling events that further exacerbate smooth muscle hypercontractility and vascular remodeling associated with hypertension and endothelial barrier dysfunction associated with acute lung injury and pulmonary edema. These conditions are also characterized by altered patterns of mechanical stimulation experienced by vasculature. This review will discuss signaling pathways regulated by ROS and mechanical stretch in the pulmonary and systemic vasculature and will summarize functional interactions between cyclic stretch- and ROS-induced signaling in mechanochemical regulation of vascular structure and function.

Selective reduction of central pulse pressure under angiotensin blockage in SHR: role of the fibronectin-alpha5beta1 integrin complex

BACKGROUND

Meta-analyses of antihypertensive therapy suggest that, independently of blood pressure (BP) level, stroke prevention is influenced mainly by calcium-entry blockers (CEB) and cardiac risk prevention by angiotensin-converting enzyme inhibitors (ACEIs). The possibility that central systolic and pulse pressure (PP) reduction differs between the two drug classes for the same mean BP (MBP) has never been explored. Our aim was to compare carotid PP at the same MBP obtained with the CEB, amlodipine, and the ACEI, trandolapril, in spontaneously hypertensive rats (SHR), and to evaluate the resulting changes of fibronectin (Fn) and its integrin alpha5beta1 receptor on central PP and arterial stiffness.

METHODS

Amlodipine and trandolapril were administered chronically to achieve the same MBP. Carotid arterial systolic BP (SBP) and PP, diameter and incremental elastic modulus (E(inc)) were determined using echo Doppler techniques, and complemented with vascular histomorphometry, and Fn and alpha5beta1-integrin immunolabeling.

RESULTS

Both drugs produced the same MBP, carotid wall thickness, and stress. Trandolapril reduced PP and E(inc) significantly more than amlodipine, while both agents comparably lowered EIIIA-Fn. Total Fn and alpha-subunit were lowered significantly by trandolapril, but unaffected by amlodipine, indicating that ACEI alone contributed to both diminished carotid stiffness and decrease of the Fn-integrin complex.

CONCLUSIONS

Results showed that amlodipine and trandolapril have different effects on carotid mechanical properties for comparable MBP reduction. Changes in Fn-integrin complex not only modify consistently ACEI mechanotransduction but also are associated with selective central PP reduction. Whether this property has consequences on cardiovascular (CV) risk remains to be investigated.

Increased static pressure promotes migration of vascular smooth muscle cells: involvement of the Rho-kinase pathway

Vascular smooth muscle cell (VSMC) migration plays a pivotal role in the pathogenesis of arteriosclerosis, under influences of various mechanical factors. Thus, we examined whether static pressure promotes VSMC migration and if so, whether Rho-kinase is involved. Rat VSMCs were cultured on chambers coated on fibronectin, vitronectin, laminin, or type IV collagen, under pressure-free conditions and at 90 and 180 mm Hg. In monolayer-wounding assay, VSMC migration was significantly increased after 72 hours at 180 mm Hg on both fibronectin (11.3 +/- 3.4-fold vs. pressure-free conditions) and vitronectin (10.6 +/- 0.7-fold; both P < 0.05). In Boyden chamber assay, the VSMC migration was again significantly increased at 180 mm Hg on both fibronectin (4.0 +/- 0.5-fold) and vitronectin (5.0 +/- 0.8-fold; both P < 0.05). Neutralizing antibodies against beta1-, beta3- and beta5-integrins, all of which play an important role in cell migration, significantly inhibited the pressure-promoted VSMC migration. Static pressure also significantly increased Rho-kinase activity in VSMC, as evaluated by the extent of phosphorylation of its downstream substrate, ezrin-radixin-moesin. Fasudil, a selective Rho-kinase inhibitor, significantly suppressed the pressure-promoted VSMC migration with reduced Rho-kinase activity. These results indicate that increased static pressure promotes VSMC migration through the integrin/Rho-kinase signaling, suggesting the therapeutic importance of this mechanism for the treatment of hypertensive vascular diseases.

Role of the renin–angiotensin–aldosterone system in vascular remodeling and inflammation: a clinical review

The concept of hypertension as primarily a consequence of altered hemodynamics has changed. Many factors are now implicated in the development of hypertensive vascular disease, and the renin-angiotensin-aldosterone system (RAAS) appears to be one of the most significant. Angiotensin II, the principal effector peptide of the RAAS, has far-reaching effects on vascular structure, growth and fibrosis, and is a key regulator of vascular remodeling and inflammation. Reactive oxygen species and a network of signaling pathways mediate angiotensin II and cellular mechanisms that promote remodeling and inflammation. The involvement of aldosterone in vessel-wall and myocardial remodeling has also come under intensive research scrutiny. Treatments that block the pathologic effects of the RAAS at several points have been shown to limit target-organ damage in hypertension and to decrease cardiovascular morbidity and mortality. Understanding the molecular and cellular mechanisms that participate in the early development of hypertensive vascular disease may lead to more targeted treatment and improved outcomes.

Leptin induces vascular smooth muscle cell hypertrophy through angiotensin II- and endothelin-1-dependent mechanisms and mediates stretch-induced hypertrophy

Various cardiovascular pathologies are associated with vascular smooth muscle cell (VSMC) hypertrophy and elevated plasma leptin levels. We used the rat portal vein (RPV) cultured for three days to investigate the effect of mechanical stretch on autocrine secretion of leptin and the effect of exogenous leptin (3.1 nM) on VSMC. Stretching the RPV significantly up-regulated leptin production by greater than 100-fold and leptin receptor expression by up to 10-fold. In addition, stretch increased tissue weight by 23 +/- 1.3 and 30 +/- 1% (P < 0.05), respectively, in the absence or presence of leptin, although this was significantly attenuated by an antileptin antibody (166 ng/ml). Unstretched RPV weight decreased by 7.5 +/- 1.8% in the absence of leptin, whereas in the presence of leptin, weight increased by 6.5 +/- 1.8% (P < 0.05). VSMC size and [3H]leucine incorporation rates were significantly increased by leptin in stretched and unstretched tissues. Leptin-induced hypertrophy was associated with significant extracellular signal-regulated kinase (ERK1/2) activation as well as increased expression of angiotensinogen, the angiotensin type 1 receptor as well as preproendothelin-1, and the endothelin type A receptor, whereas ERK inhibition or inhibition of either the angiotensin II or endothelin-1 systems at both the synthesis and receptor levels blocked the hypertrophic response. The effects of leptin were also completely blocked by the cholesterol-chelating agent methyl-beta-cyclodextrin. Therefore, our study demonstrates stretch-dependent leptin release and a direct hypertrophic effect of leptin on RPV, the latter likely dependent on intact cholesterol-rich membrane microdomains and locally produced paracrine factors.

Extracellular matrix and growth factors during heart growth

The effects of growth factors on tissue remodeling and cell differentiation depend on the nature of the extracellular matrix, the type and organization of integrins, the activation of metalloproteinases and the presence of secreted proteins associated to the matrix. These interactions are actually poorly known in the cardiovascular system. We describe here: 1) the main components of extracellular matrix within the cardiovascular system; 2) the role of integrins in the transmission of growth signals; 3) the shift in the expression of the components of the extracellular matrix (fibronectin and collagens) and the stimulation of the synthesis of metalloproteinases during normal and hypertrophic growth of the myocardium; 4) the effects of growth factors, such as Angiotensin II, Fibroblast Growth Factors (FGF), Transforming Growth Factor-beta (TGF-beta), on the synthesis of proteins of the extracellular matrix in the heart.

Different patterns of extracellular matrix protein expression in the convexity and the concavity of the dilated aorta with bicuspid aortic valve: preliminary results

OBJECTIVE

This study aimed to assess extracellular matrix protein expression patterns at the convexity (right anterolateral wall) and the concavity of the dilated ascending aorta in patients with bicuspid aortic valve disease.

METHODS

Aortic wall specimens were retrieved from the convexity and the concavity in 27 bicuspid aortic valve patients (12 with stenosis and 15 with regurgitation) and 6 heart donors (controls). Morphometry, immunohistochemistry, Western blot, and polymerase chain reaction were performed, focusing on matrix proteins involved in vascular remodeling.

RESULTS

Type I and III collagens were significantly decreased in bicuspid-associated dilated aortas versus controls (P < .001), particularly at the convexity (P < .05 vs concavity). Expression of messenger RNA for collagens was lower than normal only in the regurgitant subgroup. At immunohistochemistry, proteins whose overproduction has been demonstrated in response to abnormal wall stress, such as tenascin and fibronectin, were more expressed in the convexity than in the concavity, especially in the stenosis subgroup. Tenascin, which is produced by smooth muscle cells in the synthetic phenotype, was nearly undetectable in controls. Fewer smooth muscle cells (stenosis, P = .017; regurgitation, P = .008) and more severe elastic fiber fragmentation (P = .029 and P < .001) were observed in the convexity versus the concavity.

CONCLUSIONS

In bicuspid-associated aortic dilations, an asymmetric pattern of matrix protein expression was found that was consistent with the asymmetry in wall-stress distribution reported previously. Differences exist between patients with stenosis and those with regurgitation in terms of protein expression and content in the aortic wall. Further studies could clarify the relations between these findings and the pathogenesis of aortic dilatation in bicuspid aortic valve patients.

Stretch-dependent growth and differentiation in vascular smooth muscle: role of the actin cytoskeleton

The smooth muscle cells in the vascular wall are constantly exposed to distending forces from the intraluminal pressure. A rise in blood pressure triggers growth of the vessel wall, which is characterized primarily by hypertrophy of smooth muscle cells with maintained differentiation in a contractile phenotype. Growth factor stimulation of dissociated smooth muscle cells, on the other hand, causes proliferative growth with loss of contractility. This type of response is also found in neointima development following angioplasty and in atherosclerotic lesions. An intact tissue environment is therefore critical for preserved differentiation. Recent advances point to a role of actin polymerization in the expression of smooth muscle differentiation marker genes, in concert with serum response factor (SRF) and cofactors, such as myocardin. Stretch of intact venous smooth muscle activates Rho and inhibits the actin filament severing factor cofilin, resulting in increased actin polymerization. Concomitantly, the rates of synthesis of SRF-regulated differentiation markers, such as SM22α, calponin, and α-actin, are increased. This increase in differentiation signals is parallel with activation of the mitogen-activated protein (MAP) kinase pathway. Thus stretch-induced growth in a maintained contractile phenotype occurs by dual activation of signal pathways regulating both growth and differentiation. A current challenge is to identify sites of crosstalk between these pathways in intact smooth muscle tissue.Key words: stretch, hypertension, ERK, Rho, caveolae.

Sustained axial loading lengthens arteries in organ culture

Although it has been recognized for many years that arteries in vivo exist under significant axial strain, studies of the adaptation of arteries to elevated axial strain have only recently been conducted. To determine the effects of sustained elevation of axial loading on arterial structure and function, axial stresses of 250 kPa or greater were applied to porcine common carotid arteries maintained in a perfusion organ culture system for 7 days at physiologic pressure and flow conditions. Our results demonstrated that axial stretch could lead to an increase in unloaded length that was proportional to the axial stretch ratio (stretched length divided by unloaded length) when the axial stretch ratio was above a threshold value of 2.14. Below this threshold, no significant length change occurred. Above this threshold, a significant increase in unloaded length (13 +/- 7%,) and the number of smooth muscle cell nuclei (20 +/- 7%) was observed. Permanent length change was associated with a significant decrease in axial stiffness, and the maximum elongation achieved was limited by rupture of the arterial wall. All tested arteries demonstrated good viability and strong vasomotor responses. These results show that arteries in organ culture can elongate under sustained axial loading.

Comparative assessment of intimal hyperplasia development after 14 days in two different experimental settings: tissue culture versus ex vivo continuous perfusion of human saphenous vein

BACKGROUND

Intimal hyperplasia (IH) is a vascular remodeling process which often leads to failure of arterial bypass or hemodialysis access. Experimental and clinical work have provided insight in IH development; however, further studies under precise controlled conditions are required to improve therapeutic strategies to inhibit IH development. Ex vivo perfusion of human vessel segments under standardized hemodynamic conditions may provide an adequate experimental approach for this purpose. Therefore, chronically perfused venous segments were studied and compared to traditional static culture procedures with regard to functional and histomorphologic characteristics as well as gene expression.

MATERIALS AND METHODS

Static vein culture allowing high tissue viability was performed as previously described. Ex vivo vein support system (EVVSS) was performed using a vein support system consisting of an incubator with a perfusion chamber and a pump. EVVSS allows vessel perfusion under continuous flow while maintaining controlled hemodynamic conditions. Each human saphenous vein was divided in two parts, one cultured in a Pyrex dish and the other part perfused in EVVSS for 14days. Testing of vasomotion, histomorphometry, expression of CD 31, Factor VIII, MIB 1, alpha-actin, and PAI-l were determined before and after 14days of either experimental conditions.

RESULTS

Human venous segments cultured under traditional or perfused conditions exhibited similar IH after 14 days as shown by histomorphometry. Smooth-muscle cell (SMC) was preserved after chronic perfusion. Although integrity of both endothelial and smooth-muscle cells appears to be maintained in both culture conditions as confirmed by CD31, factor VIII, and alpha-actin expression, a few smooth-muscle cells in the media stained positive for factor VIII. Cell-proliferation marker MIB-1 was also detected in the two settings and PAI-1 mRNA expression and activity increased significantly after 14 days of culture and perfusion.

CONCLUSION

This study demonstrates the feasibility to chronically perfuse human vessels under sterile conditions with preservation of cellular integrity and vascular contractility. To gain insights into the mechanisms leading to IH, it will now be possible to study vascular remodeling not only under static conditions but also in hemodynamic environment mimicking as closely as possible the flow conditions encountered in reconstructive vascular surgery.

Chronic high pressure-induced arterial oxidative stress: involvement of protein kinase C-dependent NAD(P)H oxidase and local renin-angiotensin system

Regardless of the underlying pathological mechanisms oxidative stress seems to be present in all forms of hypertension. Thus, we tested the hypothesis that chronic presence of high pressure itself elicits increased arterial O(2)(.-) production. Hypertension was induced in rats by abdominal aortic banding (Ab). Rats with Ab had elevated pressure in vessels proximal and normal pressure in vessels distal to the coarctation, yet both vascular beds were exposed to the same circulating factors. Compared to normotensive hind limb arteries (HLAs) hypertensive forelimb arteries (FLAs) exhibited 1) impaired dilations to acetylcholine and the nitric oxide donor S-nitroso-N-acetyl-D,L-penicillamine that were restored by administration of superoxide dismutase; 2) an increased production of O(2)(.-) (measured by lucigenin chemiluminescence and ethidium bromide fluorescence) that was inhibited or reduced by superoxide dismutase, the NAD(P)H oxidase inhibitors diphenyleneiodonium and apocynin, or the protein kinase C (PKC) inhibitors chelerythrine and staurosporine or by the angiotensin-converting enzyme (ACE) inhibitor captopril; and 3) increased ACE activity. In organ culture, exposure of isolated arteries of normotensive rats to high pressure (160 mmHg, for 24 hours) significantly increased O(2)(.-) production compared to that in arteries exposed to 80 mmHg. High pressure-induced O(2)(.-) generation was reduced by inhibitors of ACE and PKC. Incubation of cultured arteries with angiotensin II elicited significantly increased O(2)(.-) generation that was inhibited by chelerythrine. Thus, we propose that chronic presence of high pressure itself can elicit arterial oxidative stress, primarily by activating directly a PKC-dependent NAD(P)H oxidase pathway, but also, in part, via activation of the local renin-angiotensin system.

A potential role of smooth muscle tone in early hypertension: a theoretical study

A conspicuous long-term consequence of hypertension is a thickening of the arterial wall, which many suggest returns the circumferential wall stress toward its normal value. This thickening results from an increase in smooth muscle and extracellular matrix, with the associated growth and remodeling processes depending on a host of regulatory signals that likely include the altered mechanical environment. Although the precise mechanotransduction pathways remain unknown, we propose that vasoconstriction may be an early response of the arterial wall to a step-change in pressure. In particular, computations suggest that such a response can decrease the magnitude and transmural gradients of the pressure-induced wall stresses and return the mean wall shear stress toward its homeostatic value. Such an initial 'compensatory vasoconstriction' could also help set into motion subsequent growth and remodeling responses due to growth regulatory characteristics of the vasoactive molecules (e.g., nitric oxide, endothelin-1, angiotensin-II). Although the consequences of growth and remodeling have been the focus of prior biomechanical and histological studies, early responses dictate subsequent developments and therefore deserve increased attention in vascular biomechanics and mechanobiology.

Force-independent expression of c-fos mRNA by endothelin-1 in rat intact small mesenteric arteries

AIM

Wall stress-independent signalling pathways were studied for endothelin-1 (ET-1)-induced c-fos expression in rat intact mesenteric small arteries.

METHODS

Arteries were kept unmounted in Krebs buffer, equilibrated for 1 h and stimulated with vasoactive substances for 15-60 min. The c-fos mRNA expression was determined by real-time polymerase chain reaction.

RESULTS

Stimulation with fetal bovine serum (FBS), phorbol 12-myristate 13-acetate (PMA) and ET-1 caused about a doubling of c-fos mRNA. The ET-1-induced c-fos expression was steady (15-60 min) and was inhibited by the inhibitor of the ET(A) receptor, BQ-123. Platelet-derived growth factor-B, angiotensin II and U46619 did not cause increased c-fos mRNA levels. The broad specificity inhibitor staurosporine inhibited the response to ET-1, but inhibitors of Rho-A kinase and phosphatidylinositol 3-kinase had no effect. However, inhibitors to tyrosine kinases, the MAP kinases [extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun amino-terminal kinase, p38], and to conventional protein kinase C showed no inhibition. Consistent with these findings, ET-1 did not cause activation of ERK1/2, a finding also seen in vessels held under pressure. In contrast, ET-1-induced c-fos expression was inhibited by the calcium chelator BAPTA, suggesting a role for intracellular calcium. This possibility was supported by the finding that raising the extracellular K(+) concentration caused increased expression of c-fos in a concentration-dependent manner.

CONCLUSION

The results suggest that in the absence of wall stress, ET-1 is able to induce increased expression of c-fos independent of traditional growth pathways, such as MAP kinase. The mechanism appears to be calcium-dependent.

Up-regulation of angiotensin II type 2 receptor in rat thoracic aorta by pressure-overload

We have examined whether expression of angiotensin II (Ang II) type 1 (AT(1)) and/or type 2 (AT(2)) receptors are changed in thoracic aorta under pressure-overload by abdominal aortic banding in rats and determined whether their changes are accompanied by alteration in contractile response of thoracic aorta to Ang II. AT(2) receptor mRNA levels determined by reverse transcription-polymerase chain reaction or quantitative real-time polymerase chain reaction were increased by about 300% in aortas 4, 7, 14, and 28 days after banding without changes in AT(1) receptor mRNA levels. Contractile response of aortic rings to Ang II was decreased in thoracic aortas 7 days after banding, and AT(2) receptor antagonist PD123319 (1-[[4-(dimethulamino)-3-methylphenyl]methyl]-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid ditrifluoroacetate) (10(-6) M) increased the Ang II responsiveness in pressure-loaded but not in sham rings. After removal of the endothelium or treatment with N(G)-nitro-L-arginine methyl ester (L-NAME), no differences were observed in Ang II responsiveness between sham and pressure-loaded rings. Either losartan (1 mg/kg/day i.p.) or candesartan (2 mg/kg/day p.o.) for 7 days after banding not only abolished the up-regulation of AT(2) receptor mRNA in aortas but also recovered their Ang II responsiveness. Basal cGMP levels were 2 times higher in pressure-loaded than in sham rings; both levels were not affected by Ang II (10(-7) M; 5 min), but greatly decreased by L-NAME (10(-4) M, 30 min). These results suggest that pressure-overload induces the up-regulation of AT(2) receptor expression in aortas via AT(1) receptor and thereby negatively modulates the vasoconstrictor sensitivity to Ang II, probably mediated by the mechanisms independent of the nitric oxide-cGMP system.

Functional, mechanical and geometrical adaptation of the arterial wall of a non-axisymmetric artery in vitro

OBJECTIVE

Vascular remodeling is an adaptive response to variations in the hemodynamic environment acting on the arterial wall. Remodeling translates into changes of structure, geometry and mechanical properties of the artery. Our aim was to study the remodeling response of pig right common carotid arteries in vitro.

METHODS

In vivo right carotid arteries are exposed to a non-uniform hemodynamic environment and exhibit a strong wall asymmetry in the circumferential direction that allows the study of two regions separately, as the artery remodels under in vitro perfusion. Porcine right common carotid arteries were cultured during 1 day (n = 6), 3 days (n = 6) or 8 days (n = 6) in an in vitro organ culture system, at a constant perfusion pressure of 100 mmHg. Geometrical, histological, biomechanical and biological analysis of the perfused segments was performed at the end of each study.

RESULTS

Smooth muscle cell nuclei density and wall thickness remain constant along the culture periods. Elastin and collagen are significantly redistributed to equilibrate their relative content along the vessel circumference. The distensibility profile is significantly different at day 8. Matrix metalloproteinase-2 expression and activity increase significantly at days 3 and 8.

CONCLUSION

The non-axisymmetric arterial wall adapts to a uniform hemodynamic environment by redistributing the structural components of the extracellular matrix. The changes of collagen and elastin density may result from a vascular remodeling process involving matrix metalloproteinase-2 up-regulation and enzymatic activity. The remodeling response results in a new vascular wall configuration that is more distensible at physiological pressures (30-120 mmHg) and stiffer at higher pressures.

Stretch-induced contractile differentiation of vascular smooth muscle: sensitivity to actin polymerization inhibitors

Signaling mechanisms for stretch-dependent growth and differentiation of vascular smooth muscle were investigated in mechanically loaded rat portal veins in organ culture. Stretch-dependent protein synthesis was found to depend on endogenous release of angiotensin II. Autoradiography after [(35)S]methionine incorporation revealed stretch-dependent synthesis of several proteins, of which SM22 and actin were particularly prominent. Inhibition of RhoA activity by cell-permeant C3 toxin increased tissue mechanical compliance and reduced stretch-dependent extracellular signal-regulated kinase (ERK)1/2 activation, growth, and synthesis of actin and SM22, suggesting a role of the actin cytoskeleton. In contrast, inhibition of Rho-associated kinase by Y-27632 did not reduce ERK1/2 phosphorylation or actin and SM22 synthesis and did not affect tissue mechanical compliance but still inhibited overall growth. The actin polymerization inhibitors latrunculin B and cytochalasin D both inhibited growth and caused increased tissue compliance. Whereas latrunculin B concentration-dependently reduced actin and SM22 synthesis, cytochalasin D did so at low (10(-8) M) but not at high (10(-6) M) concentration. The results show that stretch stabilizes the contractile smooth muscle phenotype. Stretch-dependent differentiation marker expression requires an intact cytoskeleton for stretch sensing, control of protein expression via the level of unpolymerized G-actin, or both.

Oxidation of tetrahydrobiopterin leads to uncoupling of endothelial cell nitric oxide synthase in hypertension

Tetrahydrobiopterin is a critical cofactor for the NO synthases, and in its absence these enzymes become "uncoupled," producing reactive oxygen species (ROSs) rather than NO. In aortas of mice with deoxycorticosterone acetate-salt (DOCA-salt) hypertension, ROS production from NO synthase is markedly increased, and tetrahydrobiopterin oxidation is evident. Using mice deficient in the NADPH oxidase subunit p47(phox) and mice lacking either the endothelial or neuronal NO synthase, we obtained evidence that hypertension produces a cascade involving production of ROSs from the NADPH oxidase leading to oxidation of tetrahydrobiopterin and uncoupling of endothelial NO synthase (eNOS). This decreases NO production and increases ROS production from eNOS. Treatment of mice with oral tetrahydrobiopterin reduces vascular ROS production, increases NO production as determined by electron spin resonance measurements of nitrosyl hemoglobin, and blunts the increase in blood pressure due to DOCA-salt hypertension. Endothelium-dependent vasodilation is only minimally altered in vessels of mice with DOCA-salt hypertension but seems to be mediated by hydrogen peroxide released from uncoupled eNOS, since it is inhibited by catalase. Tetrahydrobiopterin oxidation may represent an important abnormality in hypertension. Treatment strategies that increase tetrahydrobiopterin or prevent its oxidation may prove useful in preventing vascular complications of this common disease.

Oxidation of tetrahydrobiopterin leads to uncoupling of endothelial cell nitric oxide synthase in hypertension

Tetrahydrobiopterin is a critical cofactor for the NO synthases, and in its absence these enzymes become "uncoupled," producing reactive oxygen species (ROSs) rather than NO. In aortas of mice with deoxycorticosterone acetate-salt (DOCA-salt) hypertension, ROS production from NO synthase is markedly increased, and tetrahydrobiopterin oxidation is evident. Using mice deficient in the NADPH oxidase subunit p47(phox) and mice lacking either the endothelial or neuronal NO synthase, we obtained evidence that hypertension produces a cascade involving production of ROSs from the NADPH oxidase leading to oxidation of tetrahydrobiopterin and uncoupling of endothelial NO synthase (eNOS). This decreases NO production and increases ROS production from eNOS. Treatment of mice with oral tetrahydrobiopterin reduces vascular ROS production, increases NO production as determined by electron spin resonance measurements of nitrosyl hemoglobin, and blunts the increase in blood pressure due to DOCA-salt hypertension. Endothelium-dependent vasodilation is only minimally altered in vessels of mice with DOCA-salt hypertension but seems to be mediated by hydrogen peroxide released from uncoupled eNOS, since it is inhibited by catalase. Tetrahydrobiopterin oxidation may represent an important abnormality in hypertension. Treatment strategies that increase tetrahydrobiopterin or prevent its oxidation may prove useful in preventing vascular complications of this common disease.

Intraluminal pressure increases vascular neuronal nitric oxide synthase expression

BACKGROUND

Development of high blood pressure (BP) is associated with an increased expression of neuronal nitric oxide synthase (nNOS) in vascular smooth muscle cells.

METHODS

We investigated whether or not changes in intraluminal pressure affect nNOS expression in carotid arteries of normotensive rats. Expression of nNOS and other NOS isoforms was determined by Western blot analysis in rat carotid arteries maintained up to 24 h at different levels of intraluminal pressure in an organ culture system.

RESULTS

Expression of nNOS in arteries exposed to 80 mmHg was stable for the duration of the experiment. Increasing intraluminal pressure to 200 mmHg transiently augmented nNOS expression at 9 h, both in intact arteries and in arteries where the endothelium and the adventitia were removed. The expression of endothelial NOS (eNOS) was also augmented under similar experimental conditions, but only after 24 h exposure. The ERK1/2 kinase cascade inhibitor PD 98059 significantly impaired the expression of nNOS in arteries exposed to 200 mmHg for 9 h. However, the angiotensin AT(1) antagonist candesartan and the angiotensin converting enzyme inhibitor perindoprilat did not have any effect under the same experimental conditions. Finally, the preferential nNOS inhibitor S-methyl-L-thiocitrulline significantly augmented the contraction evoked by angiotensin II in arteries exposed to 200 mmHg, but not in those maintained at 80 mmHg intraluminal pressure for 9 h.

CONCLUSION

These results show that transmural pressure increases nNOS expression and NO release in rat smooth muscle cells by a mechanism involving the mitogen-activated protein kinase pathway, but independent from the local formation of angiotensin II.

Oxidation of tetrahydrobiopterin leads to uncoupling of endothelial cell nitric oxide synthase in hypertension

Tetrahydrobiopterin is a critical cofactor for the NO synthases, and in its absence these enzymes become "uncoupled," producing reactive oxygen species (ROSs) rather than NO. In aortas of mice with deoxycorticosterone acetate-salt (DOCA-salt) hypertension, ROS production from NO synthase is markedly increased, and tetrahydrobiopterin oxidation is evident. Using mice deficient in the NADPH oxidase subunit p47(phox) and mice lacking either the endothelial or neuronal NO synthase, we obtained evidence that hypertension produces a cascade involving production of ROSs from the NADPH oxidase leading to oxidation of tetrahydrobiopterin and uncoupling of endothelial NO synthase (eNOS). This decreases NO production and increases ROS production from eNOS. Treatment of mice with oral tetrahydrobiopterin reduces vascular ROS production, increases NO production as determined by electron spin resonance measurements of nitrosyl hemoglobin, and blunts the increase in blood pressure due to DOCA-salt hypertension. Endothelium-dependent vasodilation is only minimally altered in vessels of mice with DOCA-salt hypertension but seems to be mediated by hydrogen peroxide released from uncoupled eNOS, since it is inhibited by catalase. Tetrahydrobiopterin oxidation may represent an important abnormality in hypertension. Treatment strategies that increase tetrahydrobiopterin or prevent its oxidation may prove useful in preventing vascular complications of this common disease.

NAD(P)H oxidase-derived reactive oxygen species as mediators of angiotensin II signaling

Angiotensin II has been shown to participate in both physiological processes, such as sodium and water homeostasis and vascular contraction, and pathophysiological processes, including atherosclerosis and hypertension. The effects of this molecule on vascular tissue are mediated at least in part by the modification of the redox milieu of its target cells. Angiotensin II has been shown to activate the vascular NAD(P)H oxidase(s) resulting in the production of reactive oxygen species, namely superoxide and hydrogen peroxide. In this article, we review what is known about the molecular steps that link angiotensin II and its receptor to production of reactive oxygen species and subsequent redox-mediated events, focusing on the structural and functional properties of the vascular NAD(P)H oxidases and their downstream mediators. As such, we provide a framework linking angiotensin II to crucial vascular pathologies, such as hypertension, atherosclerosis, and restenosis after angioplasty, by means of the NAD(P)H-dependent oxidases and their effector molecules.

Contrasting effects of angiotensin type 1 and 2 receptors on nitric oxide release under pressure

This study was designed to test the hypothesis that increased pressure itself could cause endothelial dysfunction and lead to decreased nitric oxide (NO) release, partly through effects on the tissue renin angiotensin system in hypertension. Cultured endothelial cells (ECs) isolated from the aortas of WKY rats were continuously exposed to a pressure of 150 mmHg in a CO2 incubator for 72 h using a pressure system, and the NOx (NO2 and NO3) and angiotensin II (Ang II) concentrations in the supernatant were measured. An Ang II type 1 receptor (AT1R) antagonist (losartan) and an Ang II type 2 receptor (AT2R) antagonist (PD123319) were added to the medium. The expression of AT1R and AT2R mRNAs was also examined. Pressure loading significantly decreased the NO release from ECs. Concomitant administration of losartan restored NO release to the level before the application of pressure (p<0.001). This effect of losartan was blocked by simultaneous administration of PD123319, bradykinin type 2 receptor antagonist, and NO synthase inhibitor (p<0.05). The Ang II concentration was increased by pressure and was further increased by losartan. The gene expression of AT1R was not changed by pressure, but AT2R mRNA was increased almost 2-fold. These results indicate that high pressure itself attenuates NO release from ECs, and that losartan improves NO release by activating the bradykinin system via AT2R stimulation. In addition, the increase of AT2R gene expression in ECs during exposure to pressure may compensate for the reduction of NO.

Biomechanical adaptation of porcine carotid vascular smooth muscle to hypo and hypertension in vitro

Previous research in arterial remodeling in response to changes in blood pressure seldom included both hyper- and hypotension. To compare the effects of low and high pressure on arterial remodeling and vascular smooth muscle tone and performance, we have utilized an in vitro model. Porcine carotid arteries were cultured for 3 days at 30 and 170mmHg and compared to controls cultured at 100mmHg for 1 and 3 days. On the first and last day of culture, pressure-diameter and pressure-wall thickness curves were measured under normal smooth muscle tone using a high-resolution ultrasonic device. Last-day experiments included measurements where vascular smooth muscle was contracted or totally relaxed. From the data wall cross-sectional area, Hudetz elastic modulus and a contraction index related to the diameter reduction under normal smooth muscle tone were calculated. We found that although wall cross-sectional area (indicating wall mass) did not change much, Hudetz elastic modulus was significantly reduced in the 3-day hypotension group. Inspection of the wall contraction index suggests that this is due to a reduction in the vascular smooth muscle tone. Further, the peak of contraction index was found to be shifted to higher pressures in the 3-day 170mmHg group. We conclude that vascular smooth muscle performance adapts to both hypo- and hypertension at short time scales and can alter the biomechanics of the vascular wall in vitro.

The regulation of human vascular smooth muscle extracellular matrix protein production by alpha- and beta-adrenoceptor stimulation

OBJECTIVE

The sympathetic nervous system (SNS) is commonly activated in hypertension; however, the role of SNS activation in the pathogenesis of cardiovascular structural changes remains poorly defined. In particular, the effect of adrenergic stimulation on extracellular matrix (ECM) protein production by human cardiovascular cells is unknown. The present study thus investigated the direct effect of adrenergic stimulation on ECM protein production by cultured human vascular smooth muscle (VSM) cells.

METHODS AND RESULTS

Exposing human VSM cells to norepinephrine increased collagen protein production by 42%, P < 0.01, when compared to control (unstimulated) cells. This effect was mediated by the alpha1-adrenoceptor, since it was inhibited by the selective alpha1-adrenoceptor antagonist; prazosin (2 micromol/l) and reproduced by the selective alpha1-adrenoceptor agonist; phenylephrine (10 micromol/l). In contrast, beta-adrenoceptor stimulation - isoprenaline (1 micromol/l) or norepinephrine (10 micromol/l) + prazosin (2 micromol/l) - inhibited collagen production by 12%, P < 0.01. This inhibitory effect was mediated via the beta1-adrenoceptor, since it was blocked by atenolol (beta1-adrenoceptor antagonist) but not butoxamine (beta2-adrenoceptor antagonist). Fibronectin, another ECM protein, was similarly regulated by alpha- and beta-adrenoceptor stimulation. Transforming growth factor beta1 (TGFbeta1) mRNA expression by human VSM cells was also significantly influenced by adrenergic stimulation, being increased by phenylephrine (alpha-agonist) and inhibited by isoprenaline (beta-agonist).

CONCLUSIONS

These results uniquely demonstrate the capacity for adrenergic stimulation to directly modulate TGFbeta1 expression and ECM protein synthesis by the human cardiovascular system.

Angiotensin and cytoskeletal proteins: role in vascular remodeling

Vascular remodeling occurs during normal development and is involved in various physiologic events. However, the adaptive structural changes of the vasculature can also be pathologic, leading to vascular disease such as hypertension, atherosclerosis, and vein graft disease. Pre-eclampsia may develop as a consequence of inappropriate vascular remodeling during pregnancy. Angiotensin II contributes to vascular remodeling by activating signal transduction cascades that promote vasoconstriction, growth, and inflammation. The cytoskeleton also participates in structural adaptation responses of the vasculature; cytoskeletal filaments may mediate vasoactive responses, transduce mechanical stimuli, and are involved in pharmacologic signal transduction. It has become clear that many of the cytoskeletal changes during vascular remodeling can be induced by angiotensin II. Recently, the small G-protein Rho has attracted much attention. The Rho/Rho-kinase system is activated by angiotensin II, is a prominent regulator of the cytoskeleton, and is involved in pathologic vascular remodeling.

Molecular mechanism of fibronectin gene activation by cyclic stretch in vascular smooth muscle cells

Fibronectin plays an important role in vascular remodeling. A functional interaction between mechanical stimuli and locally produced vasoactive agents is suggested to be crucial for vascular remodeling. We examined the effect of mechanical stretch on fibronectin gene expression in vascular smooth muscle cells and the role of vascular angiotensin II in the regulation of the fibronectin gene in response to stretch. Cyclic stretch induced an increase in vascular fibronectin mRNA levels that was inhibited by actinomycin D and CV11974, an angiotensin II type 1 receptor antagonist; cycloheximide and PD123319, an angiotensin II type 2 receptor antagonist, did not affect the induction. In transfection experiments, fibronectin promoter activity was stimulated by stretch and inhibited by CV11974 but not by PD123319. DNA-protein binding experiments revealed that cyclic stretch enhanced nuclear binding to the AP-1 site, which was partially supershifted by antibody to c-Jun. Site-directed mutation of the AP-1 site significantly decreased the cyclic stretch-mediated activation of fibronectin promoter. Furthermore, antisense c-jun oligonucleotides decreased the stretch-induced stimulation of the fibronectin promoter activity and the mRNA expression. These results suggest that cyclic stretch stimulates vascular fibronectin gene expression mainly via the activation of AP-1 through the angiotensin II type 1 receptor.

Effect of mitogens on growth and contractile responses of rat small arteries: In vitro studies

Rat mesenteric and epigastric small arteries were cultured to investigate influences of mitogens on contractility, proliferation and protein synthesis. Wistar rat arteries were cultured in serum-free Dulbecco's Modified Eagle Medium, first, for 24 h to equilibrate and then for a further 24-48 h either in the absence or presence of test substances: angiotensin II (AII), 1 microM; AII, 1 microM + platelet derived growth factor BB-chain (PDGF-BB), 1 ng mL-1; PDGF-BB, 1 ng mL-1; PDGF-BB, 30 ng mL-1. No mechanical stress was applied. Viability was assessed by myography, protein synthesis by 6-h incorporation of 35S-methionine and proliferation by both 48-h 3H-thymidine-incorporation and immunohistochemical analysis using the thymidine analogue 5-bromo-2'-deoxyuridine. After 3 days in culture, the contractile responses of arteries to phenylephrine, serotonin, AII and PDGF-BB were preserved. Stimulation with PDGF-BB (30 ng mL-1) increased protein synthesis 1.5- (mesenteric) and 1. 9-fold (epigastric). Similarly, stimulation with PDGF-BB (30 ng mL-1) increased 3H-thymidine incorporation of unstimulated arteries 3.4- (mesenteric) and 2.8-fold (epigastric). The other treatments affected neither protein synthesis nor proliferation. Immunohistochemical analysis showed that the proliferation was occurring primarily in the adventitia and that the levels of apoptosis were unaltered by culture. The effects of AII and PDGF-BB on remodelling did not correlate with their contractile effects: epigastric arteries responded strongly to AII and PDGF-BB, while mesenteric arteries responded weakly. The results suggest that organ culture conditions which preserve contractile function may not be sufficient to preserve trophic mechanisms.

Organoid culture of cannulated rat resistance arteries: effect of serum factors on vasoactivity and remodeling

We developed an organoid culture technique to study the mechanisms involved in arterial remodeling. Resistance arteries were isolated from rat cremaster muscle and mounted in a pressure myograph at 75 mmHg. Vessels were studied during a 4-day culture period in DMEM with either 2% albumin, 10% heat-inactivated FCS (HI-FCS) or 10% dialyzed HI-FCS (12 kDa cut off) added to the perfusate. The albumin group showed a gradual loss of endothelial function and integrity, whereas smooth muscle agonist and myogenic responses were retained. No remodeling was observed. Vessels cultured in the presence of serum showed a progressive constriction. Smooth muscle responses and substance P-induced endothelium-dependent dilation were maintained. An inward remodeling of 17 +/- 4% in the HI-FCS group and 26 +/- 3% in the dialyzed HI-FCS group was found, while media cross-sectional areas were unchanged. These data show that pressurized resistance arteries can be maintained in culture for several days and undergo eutrophic remodeling in vitro in the presence of high molecular weight serum factors.

Mechanical strain-induced human vascular matrix synthesis: the role of angiotensin II

INTRODUCTION

Reduced vascular compliance in patients with hypertension results from an increase in extra-cellular matrix (ECM) protein deposition in blood vessels. At least two key factors, namely mechanical strain and neurohumoral mediators, for example Angiotensin II (Ang II), promote fibrogenesis within vessel walls; however potential interactions between these have not been clearly defined. This work examined the direct effect of mechanical strain on matrix mRNA expression and protein synthesis by human vascular smooth muscle (VSM) cells and identified the importance of renin-angiotensin system (RAS) activation in stretch-induced matrix production.

METHODS

Human VSM cells were exposed either to a cyclical mechanical strain regimen or to Ang II in the presence or absence of the Ang II receptor (AT(1) R) antagonist losartan or its more potent metabolite EXP3174. Analysis of matrix mRNA expression (Northerns) and protein synthesis (ELISA) and cellular AT(1)-receptor protein expression (Westerns) were determined.

RESULTS

Ang II increased both collagen alpha1 (92%, SEM +/- 20%) mRNA expression and fibronectin (21% +/- 6%) protein synthesis in static VSM cells compared with unstimulated controls. The effect of Ang II was attenuated by antagonism of the AT(1)-receptor (AT(1) R). Similarly, mechanical strain induced an increase in both collagen alpha1 (102% +/- 30%) mRNA expression and fibronectin (50% +/-21%) protein synthesis. Surprisingly, in the absence of exogenous Ang II, AT(1)-receptor blockade attenuated this stretch-induced increase in matrix synthesis. Mechanical strain also induced an increase in total cellular AT(1)-receptor protein (30.7% +/- 3.5%) compared with static cells.

CONCLUSION

Both mechanical strain and Ang II increased matrix gene expression and protein synthesis by human VSM cells. The effect of strain was attenuated by AT(1)-receptor antagonism. Our results further suggest that mechanical strain may sensitise human VSM cells to the fibrogenic actions of Ang II, perhaps via upregulation of the AT(1)-receptor.

Atorvastatin reduces NF-kappaB activation and chemokine expression in vascular smooth muscle cells and mononuclear cells

Cardiovascular mortality, mainly due to the rupture of unstable atherosclerotic plaques, is reduced by 3-hydroxy-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors. Inflammatory cells, attracted to the vascular lesion by chemokines, have been implicated in the process of the plaque rupture. In cultured vascular smooth muscle cells (VSMC) and U937 mononuclear cells we have studied the effect of Atorvastatin (Atv) on nuclear factor kappaB (NF-kappaB) activity, an inducer of the mRNA expression of chemokines such as interferon-inducible protein 10 (IP-10) and monocyte chemoattractant protein 1 (MCP-1). Angiotensin II (Ang II) and tumor necrosis factor alpha (TNF-alpha) increased NF-kappaB activity in VSMC (2 and 5-fold, respectively). Preincubation of cells with 10(-7) mol/l Atv diminished this activation (44 and 53%). The inhibition was reversed by mevalonate, farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP), but not by other isoprenoids. Coinciding with the NF-kappaB activation in VSMC, there was a diminution of cytoplasmic IkappaB levels that was recovered by pretreatment with Atv. Ang II and TNF-alpha induced the expression of IP-10 (1.5 and 3.4-fold) and MCP-1 (2.4 and 4-fold) in VSMC. Atv reduced this overexpression around 38 and 35% (IP-10), and 54 and 39% (MCP-1), respectively. Our results strongly suggest that Atv, through the inhibition of NF-kappaB activity and chemokine gene expression, could reduce the inflammation within the atherosclerotic lesion and play a role in the stabilization of the lesion.

Differences in aortic response to vasoactive stimuli in Japanese and Lyon rats. The role of hypertension

OBJECTIVE

We have previously shown that conduit arteries of normotensive (WKY) and hypertensive (SHR) Japanese rats differ from normotensive (LN) and hypertensive (LH) Lyon rats in terms of lower aortic thickness and higher collagen III content, whereas differences in vasoactive properties are unknown.

METHODS

Aortic rings with (E+) and without (E-) endothelium were studied under resting and noradrenaline-stimulated conditions in the presence of N(omega)-nitro-L-arginine (L-NNA) alone or in association with indomethacin, bosentan and/or BQ123.

RESULTS

Under resting conditions, aortas of normotensive and hypertensive Japanese rats differed from Lyon rats by higher developed tension in the presence of L-NNA and endothelium. In the absence of endothelium, normotensives differed from hypertensives in terms of stronger developed tensions in the presence of L-NNA in the two strains. Addition of indomethacin to L-NNA induced relaxation in E+ SHR and E- WKY and contraction in E-LH. By contrast, tensions were unchanged after addition of bosentan and BQ123. Under stimulated conditions, tensions were equally increased by L-NNA in E+ and unchanged in E- both in Japanese and Lyon rats whether they were normotensive or hypertensive, and indomethacin (but not bosentan) elicited higher response in Lyon than in Japanese rats in E+ and E- aorta.

CONCLUSION

Under NO synthase inhibition, the vasoactive properties of Japanese and Lyon aorta differ in the presence of a cyclo-oxygenase blocker but not endothelin blockers. These results indicate that the aorta vasorelaxant tone is associated to prostanoid regulation in Lyon but not in Japanese rats. This observation appears dependent on the genetic and/or environmental background linked to the origin and not the presence of hypertension.

Mechanical and dimensional adaptation of rabbit carotid artery cultured in vitro

The effects of the mechanical environment on arterial walls were investigated in rabbit common carotid arteries, cultured for six days under three different intraluminal pressures (0, 80 and 160 mmHg) in a perfusion culture system. The mechanical responses following the culture were examined using a quasi-static pressure-diameter test. Specimen viability was determined by smooth muscle contraction induced with KCl. Eighteen out of 21 cultured segments showed a peak reduction in diameter of more than 10% and were used for the analysis. The arterial segments cultured at 0 mmHg had a significantly smaller diameter than those cultured at other pressures. The segments cultured at higher pressure had lower incremental elastic moduli at 20 and 80 mmHg and higher moduli at 160 mmHg. The walls of the cultured segments were thicker in groups with higher pressure. These results indicate that, even in culture, the mechanical environment is a major determinant for the mechanical property and dimensions of the arterial wall. Arterial walls may respond to their mechanical environment even if other factors, such as hormonal environment and nervous stimuli, are kept unchanged.