Time courses of growth and remodeling of porcine aortic media during hypertension: a quantitative immunohistochemical examination

Renal denervation restores biomechanics of carotid arteries in a rat model of hypertension

The prevalence of hypertension increases with aging and is associated with increased arterial stiffness. Resistant hypertension is presented when drug treatments fail to regulate a sustained increased blood pressure. Given that the mechanisms between the sympathetic nervous system and the kidney play an important role in blood regulation, renal denervation (RDN) has emerged as a therapeutic potential in resistant hypertension. In this study, we investigated the effects of RDN on the biomechanical response and microstructure of elastic arteries. Common carotid arteries (CCA) excised from 3-month, 8-month, and 8-month denervated rats were subjected to biaxial extension-inflation test. Our results showed that hypertension developed in the 8-month-old rats. The sustained elevated blood pressure resulted in arterial remodeling which was manifested as a significant stress increase in both axial and circumferential directions after 8 months. RDN had a favorable impact on CCAs with a restoration of stresses in values similar to control arteries at 3 months. After biomechanical testing, arteries were imaged under a multi-photon microscope to identify microstructural changes in extracellular matrix (ECM). Quantification of multi-photon images showed no significant alterations of the main ECM components, elastic and collagen fibers, indicating that arteries remained intact after RDN. Regardless of the experimental group, our microstructural analysis of the multi-photon images revealed that reorientation of the collagen fibers might be the main microstructural mechanism taking place during pressurization with their straightening happening during axial stretching.

The immune response to arterial damage in a mouse model of intermittent hypoxia: a transcriptomics analysis

PURPOSE

Mice can develop arterial damage and even atherosclerosis under intermittent hypoxia (IH); however, the specific mechanism of arterial damage induced by IH remains unclear. Hence, this research aimed to illustrate the underlying mechanism linking IH to arterial injury.

MATERIALS AND METHODS

The differential gene expression of the thoracic aorta under normoxia or IH mice was analyzed utilizing RNA sequencing. Furthermore, GO, KEGG pathway, and CIBERSORT analyses were carried out. For verification of the expression of candidate genes affected by IH, quantitative RT-qPCR (qRT-PCR) was conducted. Immunohistochemical (IHC) staining revealed immune cell infiltration in the thoracic aorta.

RESULTS

The thickness of the intima-media of the mouse aorta was increased, and the fiber structure was disordered under IH. Transcriptomics analysis showed that in the aorta, 1137 upregulated genes and 707 downregulated genes were affected by IH, significantly related to the activation of the immune system and cell adhesion. Furthermore, B cell infiltration around the aorta was observed under IH.

CONCLUSIONS

IH might lead to structural changes in the aorta by activating the immune response and enhancing cell adhesion.

Renal denervation restores biomechanics of carotid arteries in a rat model of hypertension

The prevalence of hypertension increases with aging and is associated with increased arterial stiffness. Resistant hypertension is presented when drug treatments fail to regulate a sustained increased blood pressure. Given that the mechanisms between the sympathetic nervous system and the kidney play an important role in blood regulation, renal denervation (RDN) has emerged as a therapeutic potential in resistant hypertension. In this study, we investigated the effects of RDN on the biomechanical response and microstructure of elastic arteries. Common carotid arteries (CCA) were excised from 3-, 8- and 8-month-old denervated rats, and subjected to biaxial extension-inflation test. Our results showed that hypertension developed in the 8-month-old rats. The sustained elevated blood pressure resulted in arterial remodeling which was manifested as a significant stress increase in both axial and circumferential directions after 8 months. RDN had a favorable impact on CCAs with a restoration of stresses in values similar to control arteries at 3 months. After biomechanical testing, arteries were imaged under a multi-photon microscope to identify microstructural changes in extracellular matrix (ECM). Quantification of multi-photon images showed no significant alterations of the main ECM components, elastic and collagen fibers, indicating that arteries remained intact after RDN. Regardless of the experimental group, our microstructural analysis of the multi-photon images revealed that reorientation of the collagen fibers might be the main microstructural mechanism taking place during pressurization with their straightening happening during axial stretching.

Removal of an abluminal lining improves decellularization of human umbilical arteries

The decellularization of long segments of tubular tissues such as blood vessels may be improved by perfusing decellularization solution into their lumen. Particularly, transmural flow that may be introduced by the perfusion, if any, is beneficial to removing immunogenic cellular components in the vessel wall. When human umbilical arteries (HUAs) were perfused at a transmural pressure, however, very little transmural flow was observed. We hypothesized that a watertight lining at the abluminal surface of HUAs hampered the transmural flow and tested the hypothesis by subjecting the abluminal surface to enzyme digestion. Specifically, a highly viscous collagenase solution was applied onto the surface, thereby restricting the digestion to the surface. The localized digestion resulted in a water-permeable vessel without damaging the vessel wall. The presence of the abluminal lining and its successful removal were also supported by evidence from SEM, TEM, and mechanical testing. The collagenase-treated HUAs were decellularized with 1% sodium dodecyl sulfate (SDS) solution under either rotary agitation, simple perfusion, or pressurized perfusion. Regardless of decellularization conditions, the decellularization of HUAs was significantly enhanced after the abluminal lining removal. Particularly, complete removal of DNA was accomplished in 24 h by pressurized perfusion of the SDS solution. We conclude that the removal of the abluminal lining can improve the perfusion-assisted decellularization.

Progression of vascular remodeling in pulmonary vein obstruction

OBJECTIVES

Pulmonary vein obstruction (PVO) frequently occurs after repair of total anomalous pulmonary vein connection with progression of intimal hyperplasia from the anastomotic site toward upstream pulmonary veins (PVs). However, the understanding of mechanism in PVO progression is constrained by lack of data derived from a physiological model of the disease, and no prophylaxis has been established. We developed a new PVO animal model, investigated the mechanisms of PVO progression, and examined a new prophylactic strategy.

METHODS

We developed a chronic PVO model using infant domestic pigs by cutting and resuturing the left lower PV followed by weekly hemodynamic parameter measurement and angiographic assessment of the anastomosed PV. Subsequently, we tested a novel therapeutic strategy with external application of rapamycin-eluting film to the anastomotic site.

RESULTS

We found the pig PVO model mimicked human PVO hemodynamically and histopathologically. This model exhibited increased expression levels of Ki-67 and phospho-mammalian target of rapamycin in smooth muscle-like cells at the anastomotic neointima. In addition, contractile to synthetic phenotypic transition; that is, dedifferentiation of smooth muscle cells and mammalian target of rapamycin pathway activation in the neointima of upstream PVs were observed. Rapamycin-eluting films externally applied around the anastomotic site inhibited the activation of mammalian target of rapamycin in the smooth muscle-like cells of neointima, and delayed PV anastomotic stenosis.

CONCLUSIONS

We demonstrate the evidence on dedifferentiation of smooth muscle-like cells and mammalian target of rapamycin pathway activation in the pathogenesis of PVO progression. Delivery of rapamycin to the anastomotic site from the external side delayed PV anastomotic stenosis, implicating a new therapeutic strategy to prevent PVO progression.

Oxidative stress and vascular stiffness in hypertension: A renewed interest for antioxidant therapies?

Since the first successful launch of the Veterans Administration(VA) cooperative studies in the late 1960s, the increasing access to blood pressure lowering medications has significantly contributed to improving longevity and quality of life in hypertensive patients. Since then, insights into the pathogenesis of hypertension have shown a mechanistic role for reactive oxygen species (ROS) in all phases of disease progression, suggesting the potential utility of antioxidant therapies to counteract symptoms and, at the same time, treat a fundamental mechanism of the disease. Despite these progresses, hypertension still remains the main contributor to the global incidence of cardiovascular disease and the leading cause of morbidity and mortality worldwide. We here briefly review and update the role of ROS and ROS-dependent metalloproteinase activation in the maladaptive remodeling of the vascular wall in hypertension. Such understanding should provide new Potential sites of action for antioxidant therapies as an integrated therapeutic approach to hypertension and its consequences.

Matrix Metalloproteinase-2 Activity is Associated with Divergent Regulation of Calponin-1 in Conductance and Resistance Arteries in Hypertension-induced Early Vascular Dysfunction and Remodelling

Matrix metalloproteinase (MMP)-2 participates in hypertension-induced maladaptive vascular remodelling by degrading extra- and intracellular proteins. The consequent extracellular matrix rearrangement and phenotype switch of vascular smooth muscle cells (VSMCs) lead to increased cellular migration and proliferation. As calponin-1 degradation by MMP-2 may lead to VSMC proliferation during hypertension, the hypothesis of this study is that increased MMP-2 activity contributes to early hypertension-induced maladaptive remodelling in conductance and resistance arteries via regulation of calponin-1. The main objective was to analyse whether MMP-2 exerts similar effects on the structure and function of the resistance and conductance arteries during early hypertension. Two-kidney, one-clip (2K-1C) hypertensive male rats and corresponding controls were treated with doxycycline (30 mg/kg/day) or water until reaching one week of hypertension. Systolic blood pressure was increased in 2K-1C rats, and doxycycline did not reduce it. Aortas and mesenteric arteries were analysed. MMP-2 activity and expression were increased in both arteries, and doxycycline reduced it. Significant hypertrophic remodelling and VSMC proliferation were observed in aortas but not in mesenteric arteries of 2K-1C rats. The contractility of mesenteric arteries to phenylephrine was increased in 2K-1C rats, and doxycycline prevented this alteration. The potency of phenylephrine to contract aortas of 2K-1C rats was increased, and doxycycline decreased it. Whereas calponin-1 expression was increased in 2K-1C mesenteric arteries, calponin-1 was reduced in aortas. Doxycycline treatment reverted changes in calponin-1 expression. MMP-2 contributes to hypertrophic remodelling in aortas by decreasing calponin-1 levels, which may result in VSMC proliferation. On the other hand, MMP-2-dependent increased calponin-1 in mesenteric arteries may contribute to vascular hypercontractility in 2K-1C rats. Divergent regulation of calponin-1 by MMP-2 may be an important mechanism that leads to maladaptive vascular effects in hypertension.

Mechanobiological model of arterial growth and remodeling

A coupled agent-based model (ABM) and finite element analysis (FEA) computational framework is developed to study the interplay of bio-chemo-mechanical factors in blood vessels and their role in maintaining homeostasis. The agent-based model implements the power of REPAST Simphony libraries and adapts its environment for biological simulations. Coupling a continuum-level model (FEA) to a cellular-level model (ABM) has enabled this computational framework to capture the response of blood vessels to increased or decreased levels of growth factors, proteases and other signaling molecules (on the micro scale) as well as altered blood pressure. Performance of the model is assessed by simulating porcine left anterior descending artery under normotensive conditions and transient increases in blood pressure and by analyzing sensitivity of the model to variations in the rule parameters of the ABM. These simulations proved that the model is stable under normotensive conditions and can recover from transient increases in blood pressure. Sensitivity studies revealed that the model is most sensitive to variations in the concentration of growth factors that affect cellular proliferation and regulate extracellular matrix composition (mainly collagen).

Matrix metalloproteinase (MMP)-2 decreases calponin-1 levels and contributes to arterial remodeling in early hypertension

Increased matrix metalloproteinase (MMP)-2 is implicated in the vascular remodeling of hypertension. Calponin-1 is a contractile protein, and its absence is associated with vascular smooth muscle cell (VSMC) phenotype switch, which leads to migration and remodeling. We evaluated whether increased MMP-2 activity precedes chronic vascular remodeling by decreasing calponin-1 and inducing VSMC proliferation. Sham or two kidney-one clip (2K1C) rats were treated with doxycycline at 30mg/kg/day. Systolic blood pressure was increased in the 2K1C rats after 1 and 2weeks post-surgery, and doxycycline was effective to reduce it only at 2weeks of hypertension (p<0.05). Increased activity of MMP-2 was observed in aortas from 2K1C at 1 and 2weeks of hypertension, followed by increased VSMC proliferation, and those effects were abolished by treating 2K1C rats with doxycycline (p<0.05). Increased aortic media to lumen ratio started to emerge in 2K1C rats at 1week of hypertension, and it was established by 2weeks. MMP-2 and calponin-1 co-localized in the cytosol of VSMC. Aortas from 2K1C rats showed a significant reduction in calponin-1 levels at 1week of hypertension, and doxycycline prevented its loss (p<0.05). However, at 2weeks of hypertension, calponin-1 was upregulated in 2K1C (p<0.05 vs. Sham groups). The mRNA levels of calponin-1 were not altered in the aortas of 2K1C at 1week of hypertension. MMP-2 may contribute to the post-translational decrease in calponin-1, thus culminating in hypertension-induced maladaptive arterial remodeling.

Matrix Metalloproteinase 2 as a Potential Mediator of Vascular Smooth Muscle Cell Migration and Chronic Vascular Remodeling in Hypertension

For vascular remodeling in hypertension, it is essential that vascular smooth muscle cells (VSMCs) reshape in order to proliferate and migrate. The extracellular matrix (ECM) needs to be degraded to favor VSMC migration. Many proteases, including matrix metalloproteinases (MMPs), contribute to ECM proteolysis and VSMC migration. Bioactive peptides, hemodynamic forces and reactive oxygen-nitrogen species regulate MMP-2 expression and activity. Increased MMP-2 activity contributes to hypertension-induced maladaptive arterial changes and sustained hypertension. New ECM is synthesized to supply VSMCs with bioactive mediators, which stimulate hypertrophy. MMP-2 stimulates the interaction of VSMCs with newly formed ECM, which triggers intracellular signaling via integrins to induce a phenotypic switch and persistent migration. VSMCs switch from a contractile to a synthetic phenotype in order to migrate and contribute to vascular remodeling in hypertension. MMPs also disrupt growth factors bound to ECM, thus contributing to their capacity to regulate VSMC migration. This review sheds light on the proteolytic effects of MMP-2 on ECM and non-ECM substrates in the vasculature and how these effects contribute to VSMC migration in hypertension. The inhibition of MMP activity as a therapeutic target may make it possible to reduce arterial maladaptation caused by hypertension and prevent the resulting fatal cardiovascular events.

"Smooth Muscle Cell Stiffness Syndrome"-Revisiting the Structural Basis of Arterial Stiffness

In recent decades, the pervasiveness of increased arterial stiffness in patients with cardiovascular disease has become increasingly apparent. Though, this phenomenon has been well documented in humans and animal models of disease for well over a century, there has been surprisingly limited development in a deeper mechanistic understanding of arterial stiffness. Much of the historical literature has focused on changes in extracellular matrix proteins—collagen and elastin. However, extracellular matrix changes alone appear insufficient to consistently account for observed changes in vascular stiffness, which we observed in our studies of aortic stiffness in aging monkeys. This led us to examine novel mechanisms operating at the level of the vascular smooth muscle cell (VSMC)—that include increased cell stiffness and adhesion to extracellular matrix—which that may be interrelated with other mechanisms contributing to arterial stiffness. We introduce these observations as a new concept—the Smooth Muscle Cell Stiffness Syndrome (SMCSS)—within the field of arterial stiffness and posit that stiffening of vascular cells impairs vascular function and may contribute stiffening to the vasculature with aging and cardiovascular disease. Importantly, this review article revisits the structural basis of arterial stiffness in light of these novel findings. Such classification of SMCSS and its contextualization into our current understanding of vascular mechanics may be useful in the development of strategic therapeutics to directly target arterial stiffness.

Computational model of collagen turnover in carotid arteries during hypertension

It is well known that biological tissues adapt their properties because of different mechanical and chemical stimuli. The goal of this work is to study the collagen turnover in the arterial tissue of hypertensive patients through a coupled computational mechano-chemical model. Although it has been widely studied experimentally, computational models dealing with the mechano-chemical approach are not. The present approach can be extended easily to study other aspects of bone remodeling or collagen degradation in heart diseases. The model can be divided into three different stages. First, we study the smooth muscle cell synthesis of different biological substances due to over-stretching during hypertension. Next, we study the mass-transport of these substances along the arterial wall. The last step is to compute the turnover of collagen based on the amount of these substances in the arterial wall which interact with each other to modify the turnover rate of collagen. We simulate this process in a finite element model of a real human carotid artery. The final results show the well-known stiffening of the arterial wall due to the increase in the collagen content.

Augmented vascular smooth muscle cell stiffness and adhesion when hypertension is superimposed on aging

Hypertension and aging are both recognized to increase aortic stiffness, but their interactions are not completely understood. Most previous studies have attributed increased aortic stiffness to changes in extracellular matrix proteins that alter the mechanical properties of the vascular wall. Alternatively, we hypothesized that a significant component of increased vascular stiffness in hypertension is due to changes in the mechanical and adhesive properties of vascular smooth muscle cells, and that aging would augment the contribution from vascular smooth muscle cells when compared with the extracellular matrix. Accordingly, we studied aortic stiffness in young (16-week-old) and old (64-week-old) spontaneously hypertensive rats and Wistar-Kyoto wild-type controls. Systolic and pulse pressures were significantly increased in young spontaneously hypertensive rats when compared with young Wistar-Kyoto rats, and these continued to rise in old spontaneously hypertensive rats when compared with age-matched controls. Excised aortic ring segments exhibited significantly greater elastic moduli in both young and old spontaneously hypertensive rats versus Wistar-Kyoto rats. were isolated from the thoracic aorta, and stiffness and adhesion to fibronectin were measured by atomic force microscopy. Hypertension increased both vascular smooth muscle cell stiffness and vascular smooth muscle cell adhesion, and these increases were both augmented with aging. By contrast, hypertension did not affect histological measures of aortic collagen and elastin, which were predominantly changed by aging. These findings support the concept that stiffness and adhesive properties of vascular smooth muscle cells are novel mechanisms contributing to the increased aortic stiffness occurring with hypertension superimposed on aging.

Nonclinical Safety Biomarkers of Drug-induced Vascular Injury

Better biomarkers are needed to identify, characterize, and/or monitor drug-induced vascular injury (DIVI) in nonclinical species and patients. The Predictive Safety Testing Consortium (PSTC), a precompetitive collaboration of pharmaceutical companies and the U.S. Food and Drug Administration (FDA), formed the Vascular Injury Working Group (VIWG) to develop and qualify translatable biomarkers of DIVI. The VIWG focused its research on acute DIVI because early detection for clinical and nonclinical safety monitoring is desirable. The VIWG developed a strategy based on the premise that biomarkers of DIVI in rat would be translatable to humans due to the morphologic similarity of vascular injury between species regardless of mechanism. The histomorphologic lexicon for DIVI in rat defines degenerative and adaptive findings of the vascular endothelium and smooth muscles, and characterizes inflammatory components. We describe the mechanisms of these changes and their associations with candidate biomarkers for which advanced analytical method validation was completed. Further development is recommended for circulating microRNAs, endothelial microparticles, and imaging techniques. Recommendations for sample collection and processing, analytical methods, and confirmation of target localization using immunohistochemistry and in situ hybridization are described. The methods described are anticipated to aid in the identification and qualification of translational biomarkers for DIVI.

On the decellularization of fresh or frozen human umbilical arteries: implications for small-diameter tissue engineered vascular grafts

Most tissues, including those to be decellularized for tissue engineering applications, are frozen for long term preservation. Such conventional cryopreservation has been shown to alter the structure and mechanical properties of tissues. Little is known, however, how freezing affects decellularization of tissues. The purpose of this study was two-fold: to examine the effects of freezing on decellularization of human umbilical arteries (HUAs), which represent a potential scaffolding material for small-diameter tissue-engineered vascular grafts, and to examine how decellularization affects the mechanical properties of frozen HUAs. Among many decellularization methods, hypotonic sodium dodecyl sulfate solution was selected as the decellularizing agent and tested on fresh HUAs to optimize decellularization conditions. The efficiency of decellularization was evaluated by DNA assay and histology every 12 up to 48 h. The optimized decellularization protocol was then performed on frozen HUAs. The stiffness, burst pressure, and suture retention strength of fresh HUAs and frozen HUAs before and after decellularization were also examined. It appeared that freezing decreased the efficiency of decellularization, which may be attributed to the condensed extracellular matrix caused by freezing. While the stiffness of fresh HUAs did not change significantly after decellularization, decellularization reduced the compliance of frozen HUAs. Interestingly, the stiffness of decellularized frozen HUAs was similar to that of decellularized fresh HUAs. Although little difference in stiffness was observed, we suggest avoiding freezing if more efficient and complete decellularization is desired.

Disparate Changes in the Mechanical Properties of Murine Carotid Arteries and Aorta in Response to Chronic Infusion of Angiotensin-II

Chronic infusion of angiotensin-II has proved useful for generating dissecting aortic aneurysms in atheroprone mice. These lesions preferentially form in the suprarenal abdominal aorta and sometimes in the ascending aorta, but reasons for such localization remain unknown. This study focused on why these lesions do not form in other large (central) arteries. Toward this end, we quantified and compared the geometry, composition, and biaxial material behavior (using a nonlinear constitutive relation) of common carotid arteries from three groups of mice: non-treated controls as well as mice receiving a subcutaneous infusion of angiotensin-II for 28 days that either did or did not lead to the development of a dissecting aortic aneurysm. Consistent with the mild hypertension induced by the angiotensin-II, the carotid wall thickened as expected and remodeled modestly. There was no evidence, however, of a marked loss of elastic fibers or smooth muscle cells, each of which appear to be initiating events for the development of aneurysms, and there was no evidence of intramural discontinuities that might give rise to dissections.

Hypertensive changes within the aortic arch of infants and children with isolated coarctation

BACKGROUND

Despite repair, a significant proportion of patients with coarctation of the aorta (CoA) present with late hypertension. Increased gene expression of aortic wall collagen and vascular smooth muscle cell markers occurs in the presence of hypertension. Before repair, a patent ductus arteriosus (PDA) limits hypertension proximal to the coarctation. We hypothesize that preoperative collagen and vascular smooth muscle expression from the aortic arch in children is variable, depending on the presence or absence of a PDA.

METHODS

We analyzed the expression patterns of collagen and vascular smooth muscle cell markers in 25 children with CoA using a quantitative polymerase chain reaction. Aortic arch tissue proximal to the CoA was normalized to descending aortic tissue distal to the coarctation. Collagen-I, transforming growth factor-β, elastin, and calponin were analyzed.

RESULTS

At repair, 19 patients were aged younger than 3 months (14 with a PDA, 5 with a ligamentum arteriosum), and the remaining 6 were older than 1 year. There was no difference in age or weight between infants with or without a PDA. Infants without a PDA had the greatest difference in collagen-I expression compared with infants with a PDA (7.0 ± 1.6-fold vs 0.8 ± 1.1-fold, p = 0.01). Expression of transforming growth factor-β (4.3 ± 1.4 vs 2.6 ± 2.3, p = 0.01) and calponin (3.7 ± 0.7 vs 0.6 ± 1.1, p = 0.05) was lower from infants with vs without a PDA.

CONCLUSIONS

Our findings provide evidence of preoperative changes in the aortic arch before repair, particularly in the absence of a PDA.

Elastin and collagen fibre microstructure of the human aorta in ageing and disease: a review

Aortic disease is a significant cause of death in developed countries. The most common forms of aortic disease are aneurysm, dissection, atherosclerotic occlusion and ageing-induced stiffening. The microstructure of the aortic tissue has been studied with great interest, because alteration of the quantity and/or architecture of the connective fibres (elastin and collagen) within the aortic wall, which directly imparts elasticity and strength, can lead to the mechanical and functional changes associated with these conditions. This review article summarizes the state of the art with respect to characterization of connective fibre microstructure in the wall of the human aorta in ageing and disease, with emphasis on the ascending thoracic aorta and abdominal aorta where the most common forms of aortic disease tend to occur.

Biomechanical phenotyping of central arteries in health and disease: advantages of and methods for murine models

The stiffness and structural integrity of the arterial wall depends primarily on the organization of the extracellular matrix and the cells that fashion and maintain this matrix. Fundamental to the latter is a delicate balance in the continuous production and removal of structural constituents and the mechanical state in which such turnover occurs. Perturbations in this balance due to genetic mutations, altered hemodynamics, or pathological processes result in diverse vascular phenotypes, many of which have yet to be well characterized biomechanically. In this paper, we emphasize the particular need to understand regional variations in the biaxial biomechanical properties of central arteries in health and disease and, in addition, the need for standardization in the associated biaxial testing and quantification. As an example of possible experimental methods, we summarize testing protocols that have evolved in our laboratory over the past 8 years. Moreover, we note advantages of a four fiber family stress-stretch relation for quantifying passive biaxial behaviors, the use of stored energy as a convenient scalar metric of the associated material stiffness, and the utility of appropriate linearizations of the nonlinear, anisotropic relations both for purposes of comparison across laboratories and to inform computational fluid-solid-interaction models. We conclude that, notwithstanding prior advances, there remain many opportunities to advance our understanding of arterial mechanics and mechanobiology, particularly via the diverse genetic, pharmacological, and surgical models that are, or soon will be, available in the mouse.

Hyperelastic remodeling in the intrauterine growth restricted (IUGR) carotid artery in the near-term fetus

A constitutive model for a fiber reinforced hyperelastic material was applied to understand arterial fiber remodeling in a sheep model of Intrauterine Growth Restriction (IUGR). IUGR is associated altered hemodynamics characterized by increased resistance to blood flow in the placenta and elevated fetal arterial pressure and pulsatility. The constitutive model describes the collagen contribution to the mechanics within the arterial wall in both control and IUGR carotid artery through defining the material modulus and the orientation of the microstructure. A sheep model of placental insufficiency induced IUGR (PI-IUGR) was created by exposure of the pregnant ewe to elevated ambient temperatures. Experimental data was collected using pressure-diameter measurements to measure passive compliance in control and PI-IUGR carotid arteries. The constitutive model was optimized to fit the experimental data predicting the material parameters. Specifically, the collagen fiber predicted angle (γ) in the control artery was 49.9° from the circumferential axis while the PI-IUGR was 16.6° with a 23.5% increase in fiber orientation (κ). Quantitative assessment of collagen fiber orientation in secondary harmonic generation images confirmed the shift in orientation between the two groups. Together these suggest vascular remodeling of the ECM fiber orientation plays a major role in arterial stiffening in the PI-IUGR near-term fetal sheep.

Altered hemodynamics, endothelial function, and protein expression occur with aortic coarctation and persist after repair

Coarctation of the aorta (CoA) is associated with substantial morbidity despite treatment. Mechanically induced structural and functional vascular changes are implicated; however, their relationship with smooth muscle (SM) phenotypic expression is not fully understood. Using a clinically representative rabbit model of CoA and correction, we quantified mechanical alterations from a 20-mmHg blood pressure (BP) gradient in the thoracic aorta and related the expression of key SM contractile and focal adhesion proteins with remodeling, relaxation, and stiffness. Systolic and mean BP were elevated for CoA rabbits compared with controls leading to remodeling, stiffening, an altered force response, and endothelial dysfunction both proximally and distally. The proximal changes persisted for corrected rabbits despite >12 wk of normal BP (~4 human years). Computational fluid dynamic simulations revealed reduced wall shear stress (WSS) proximally in CoA compared with control and corrected rabbits. Distally, WSS was markedly increased in CoA rabbits due to a stenotic velocity jet, which has persistent effects as WSS was significantly reduced in corrected rabbits. Immunohistochemistry revealed significantly increased nonmuscle myosin and reduced SM myosin heavy chain expression in the proximal arteries of CoA and corrected rabbits but no differences in SM α-actin, talin, or fibronectin. These findings indicate that CoA can cause alterations in the SM phenotype contributing to structural and functional changes in the proximal arteries that accompany the mechanical stimuli of elevated BP and altered WSS. Importantly, these changes are not reversed upon BP correction and may serve as markers of disease severity, which explains the persistent morbidity observed in CoA patients.

Alterations in Pulse Pressure Affect Artery Function

Pulse pressure changes in response to cardiovascular diseases and interventions, but its effect on vascular wall structure and function is poorly understood. We examined the effect of increased or decreased pulse pressure on artery function, cellular function, and extracellular matrix remodeling. Porcine carotid arteries were cultured under non-pulsatile (100 mmHg), pulsatile (70-130 mmHg), or hyper-pulsatile pressure (50-150 mmHg) for 1 to 3 days. Vasomotor response, wall permeability, cell proliferation, apoptosis, extracellular matrix remodeling, and proteins involved in atherogenesis were examined. Our results showed that hyper-pulsatile pressure decreased the artery response to sodium nitroprusside, basal tone, and wall permeability after three days. Non-pulsatile pressure increased cell proliferation. Neither hyper-pulsatile nor non-pulsatile pressure caused a change in the extracellular matrix or in the expression of matrix metalloproteinase-2 (MMP-2), MMP-9, caveolin-1, or α-actin. Hyper-pulsatile pressure increased monocyte chemotactic protein-1 gene expression. Taken together, these changes indicate that pulse pressure has a limited effect on the artery immediately after its application. Specifically an increase in pulse pressure alters the artery tone and wall permeability while a decrease in pulse pressure alters cell proliferation. Overall these results provide insight into how the artery initially responds to changes in pulse pressure.

Applications of 'TissueQuant'- a color intensity quantification tool for medical research

This paper demonstrates the use of TissueQuant - an image analysis tool for quantification of color intensities which was developed for use in medical research where the stained biological specimen such as tissue or antigen needs to be quantified. TissueQuant provides facilities for user interaction to choose and quantify the color of interest and its shades. Gaussian weighting functions are used to provide a color score which quantifies how close the shade is to the user specified reference color. We describe two studies in medical research which use TissueQuant for quantification. The first study evaluated the effect of petroleum-ether extract of Cissus quadrangularis (CQ) on osteoporotic rats. It was found that the analysis results correlated well with the manual evaluation, p < 0.001. The second study evaluated the nerve morphometry and it was found that the adipose and non adipose tissue content was maximum in radial nerve among the five nerves studied.

Computational simulations of hemodynamic changes within thoracic, coronary, and cerebral arteries following early wall remodeling in response to distal aortic coarctation

Mounting evidence suggests that the pulsatile character of blood pressure and flow within large arteries plays a particularly important role as a mechano-biological stimulus for wall growth and remodeling. Nevertheless, understanding better the highly coupled interactions between evolving wall geometry, structure, and properties and the hemodynamics will require significantly more experimental data. Computational fluid-solid-growth models promise to aid in the design and interpretation of such experiments and to identify candidate mechanobiological mechanisms for the observed arterial adaptations. Motivated by recent aortic coarctation models in animals, we used a computational fluid-solid interaction model to study possible local and systemic effects on the hemodynamics within the thoracic aorta and coronary, carotid, and cerebral arteries due to a distal aortic coarctation and subsequent spatial variations in wall adaptation. In particular, we studied an initial stage of acute cardiac compensation (i.e., maintenance of cardiac output) followed by early arterial wall remodeling (i.e., spatially varying wall thickening and stiffening). Results suggested, for example, that while coarctation increased both the mean and pulse pressure in the proximal vessels, the locations nearest to the coarctation experienced the greatest changes in pulse pressure. In addition, after introducing a spatially varying wall adaptation, pressure, left ventricular work, and wave speed all increased. Finally, vessel wall strain similarly experienced spatial variations consistent with the degree of vascular wall adaptation.

Tissue engineering and regenerative strategies to replicate biocomplexity of vascular elastic matrix assembly

Cardiovascular tissues exhibit architecturally complex extracellular matrices, of which the elastic matrix forms a major component. The elastic matrix critically maintains native structural configurations of vascular tissues, determines their ability to recoil after stretch, and regulates cell signaling pathways involved in morphogenesis, injury response, and inflammation via biomechanical transduction. The ability to tissue engineer vascular replacements that incorporate elastic matrix superstructures unique to cardiac and vascular tissues is thus important to maintaining vascular homeostasis. However, the vascular elastic matrix is particularly difficult to tissue engineer due to the inherently poor ability of adult vascular cells to synthesize elastin precursors and organize them into mature structures in a manner that replicates the biocomplexity of elastic matrix assembly during development. This review discusses current tissue engineering materials (e.g., growth factors and scaffolds) and methods (e.g., dynamic stretch and contact guidance) used to promote cellular synthesis and assembly of elastic matrix superstructures, and the limitations of these approaches when applied to smooth muscle cells, the primary elastin-generating cell type in vascular tissues. The potential application of these methods for in situ regeneration of disrupted elastic matrix at sites of proteolytic vascular disease (e.g., abdominal aortic aneurysms) is also discussed. Finally, the review describes the potential utility of alternative cell types to elastic tissue engineering and regenerative matrix repair. Future progress in the field is contingent on developing a thorough understanding of developmental elastogenesis and then mimicking the spatiotemporal changes in the cellular microenvironment that occur during that phase. This will enable us to tissue engineer clinically applicable elastic vascular tissue replacements and to develop elastogenic therapies to restore homeostasis in de-elasticized vessels.

Time course involvement of matrix metalloproteinases in the vascular alterations of renovascular hypertension

Increased vascular matrix metalloproteinases (MMPs) levels play a role in late phases of hypertensive vascular remodeling. However, no previous study has examined the time course of MMPs in the various phases of two-kidney, one-clip hypertension (2K1C). We examined structural vascular changes, collagen and elastin content, vascular oxidative stress, and MMPs levels/activities during the development of 2K1C hypertension. Plasma angiotensin converting enzyme (ACE) activity was measured to assess renin-angiotensin system activation. Sham or 2K1C hypertensive rats were studied after 2, 4, 6, and 10weeks of hypertension. Systolic blood pressure (SBP) was monitored weekly. Morphometry of structural changes in the aortic wall was studied in hematoxylin/eosin, orcein and picrosirius red sections. Aortic NADPH activity and superoxide production was evaluated. Aortic gelatinolytic activity was determined by in situ zymography, and MMP-2, MMP-14, and tissue inhibitor of MMPs (TIMP)-2 levels were determined by gelatin zymography, immunofluorescence and immunohistochemistry. 2K1C hypertension was associated with increased ACE activity, which decreased to normal after 10 weeks. We found increased aortic collagen and elastin content in the early phase of hypertension, which were associated with vascular hypertrophy, increased vascular MMP-2 and MMP-14 (but not TIMP-2) levels, and increased gelatinolytic activity, possibly as a result of increased vascular NADPH oxidase activity and oxidative stress. These results indicate that vascular remodeling of renovascular hypertension is an early process associated with early increases in MMPs activities, enhanced matrix deposition and oxidative stress. Using antioxidants or MMPs inhibitors in the early phase of hypertension may prevent the vascular alterations of hypertension.

Arteriolar vascular smooth muscle cell differentiation in benign nephrosclerosis

BACKGROUND

Benign nephrosclerosis (bN) is the most prevalent form of hypertensive damage in kidney biopsies. It is defined by early hyalinosis and later fibrosis of renal arterioles. Despite its high prevalence, very little is known about the contribution of arteriolar vascular smooth muscle cells (VSMCs) to bN. We examined classical and novel candidate markers of the normal contractile and the pro-fibrotic secretory phenotype of VSMCs in arterioles in bN.

METHODS

Sixty-three renal tissue specimens with bN and eight control specimens were examined by immunohistochemistry for the contractile markers caldesmon, alpha-smooth muscle actin (alpha-SMA), JunB, smoothelin and the secretory marker S100A4 and by double stains for caldesmon or smoothelin with S100A4.

RESULTS

Smoothelin immunostaining showed an inverse correlation with hyalinosis and fibrosis scores, while S100A4 correlated with fibrosis scores only. Neither caldesmon, alpha-SMA nor JunB correlated with hyalinosis or fibrosis scores. Cells in the arteriolar wall were exclusively positive either for caldesmon/smoothelin or S100A4.

CONCLUSIONS

This is the first systematic analysis of VSMC differentiation in bN. The results suggest that smoothelin is the most sensitive marker for the contractile phenotype and that S100A4 could be a novel marker for the secretory phenotype in vivo. The other markers did not seem to differentiate these phenotypes in bN. Thus, VSMC phenotype markers should be defined in the context of the vessel segment and disease under examination. S100A4 could not only be a marker of pro-fibrotic secretory VSMCs in bN but also an important mediator of arteriolar fibrosis.

Spice up the hypertension diet - curcumin and piperine prevent remodeling of aorta in experimental L-NAME induced hypertension

Background

Increase of blood pressure is accompanied by functional and morphological changes in the vascular wall. The presented study explored the effects of curcuma and black pepper compounds on increased blood pressure and remodeling of aorta in the rat model of experimental NO-deficient hypertension.

Methods

Wistar rats were administered for 6 weeks clear water or L-NAME (40 mg/kg/day) dissolved in water, piperine (20 mg/kg/day), curcumin (100 mg/kg/day) or their combination in corn oil by oral gavage. The systolic blood pressure was measured weekly. Histological slices of thoracic aorta were stained with hematoxylin and eosin, Mallory's phosphotungstic acid hematoxylin (PTAH), orcein, picrosirius red and van Gieson staining and with antibodies against smooth muscle cells actin. Microscopic pictures were digitally processed and morphometrically evaluated.

Results

The increase of blood pressure caused by L-NAME was partially prevented by piperine and curcumin, but the effect of their combination was less significant. Animals with hypertension had increased wall thickness and cross-sectional area of the aorta, accompanied by relative increase of PTAH positive myofibrils and decrease of elastin, collagen and actin content. Piperine was able to decrease the content of myofibrils and slightly increase actin, while curcumin also prevented elastin decrease. The combination of spices had similar effects on aortic morphology as curcumin itself.

Conclusions

Administration of piperine or curcumin, less their combination, is able to partially prevent the increase of blood pressure caused by chronic L-NAME administration. The spices modify the remodeling of the wall of the aorta induced by hypertension. Our results show that independent administration of curcumin is more effective in preventing negative changes in blood vessel morphology accompanying hypertensive disease.

Aligned electrospun scaffolds and elastogenic factors for vascular cell-mediated elastic matrix assembly

Strategies to enhance the production of organized elastic matrix by smooth muscle cells (SMCs) are critical in engineering functional vascular conduits. Therefore, the goal of this study was to determine the effect of different surfaces, i.e. random and aligned electrospun poly(ε-caprolactone) meshes and two-dimensional (2D) controls, and exogenous elastogenic factors on the cultured rat aortic SMC phenotype and production of extracellular matrix. This study demonstrated that aligned electrospun fibres guide cell alignment, induce a more elongated cell morphology and promote a more synthetic phenotype. Importantly, these cells produced greater amounts of elastin-rich matrix per cell on the electrospun scaffolds. In addition, exogenous elastogenic factors severely limited rat aortic smooth muscle cells (RASMCs) proliferation and promoted a more synthetic SMC phenotype on electrospun meshes, but they had less effect on 2D controls. Finally, the elastogenic factors induced the SMCs to generate more matrix collagen and elastin on a per cell basis. Together, these results demonstrate the elastogenic benefits of electrospun meshes.

The inflammatory preatherosclerotic remodeling induced by intermittent hypoxia is attenuated by RANTES/CCL5 inhibition

RATIONALE

The highly prevalent obstructive sleep apnea syndrome (OSA) with its main component intermittent hypoxia (IH) is a risk factor for cardiovascular mortality. The poor knowledge of its pathophysiology has limited the development of specific treatments, whereas the gold standard treatment, continuous positive airway pressure, may not fully reverse the chronic consequences of OSA and has limited acceptance in some patients.

OBJECTIVES

To examine the contribution of IH-induced inflammation to the cardiovascular complications of OSA.

METHODS

We investigated systemic and vascular inflammatory changes in C57BL6 mice exposed to IH (21-5% Fi(O(2)), 60-s cycle) or normoxia 8 hours per day up to 14 days. Vascular alterations were reassessed in mice treated with a blocking antibody of regulated upon activation, normal T-cell expressed and secreted (RANTES)/CC chemokine ligand 5 (CCL5) signaling pathway, or with the IgG isotype control throughout the IH exposure.

MEASUREMENTS AND MAIN RESULTS

IH induced systemic inflammation combining increased splenic lymphocyte proliferation and chemokine expression, with early and predominant RANTES/CCL5 alterations, and enhanced splenocyte migration toward RANTES/CCL5. IH also induced structural and inflammatory vascular alterations. Leukocyte-endothelium adhesive interactions were increased, attested by leukocyte rolling and intercellular adhesion molecule-1 expression in mesenteric vessels. Aortas had increased intima-media thickness with elastic fiber alterations, mucoid depositions, nuclear factor-κB-p50 and intercellular adhesion molecule-1 overexpression, hypertrophy of smooth-muscle cells overexpressing RANTES/CCL5, and adventitial-periadventitial T-lymphocyte infiltration. RANTES/CCL5 neutralization prevented both intima-media thickening and inflammatory alterations, independently of the IH-associated proatherogenic dyslipidemia.

CONCLUSIONS

Inflammation is a determinant mechanism for IH-induced preatherosclerotic remodeling involving RANTES/CCL5, a key chemokine in atherogenesis. Characterization of the inflammatory response could allow identifying at-risk patients for complications, and its pharmacologic manipulation may represent a potential complementary treatment of sleep apnea consequences.

Image analysis tools for evaluation of microscopic views of immunohistochemically stained specimen in medical research-a review

The aim of this study is to review the methods being used for image analysis of microscopic views of immunohistochemically stained specimen in medical research. The solutions available range from general purpose software to commercial packages. Many studies have developed their own custom written programs based on some general purpose software available. Many groups have reported development of computer aided image analysis programs aiming at obtaining faster, simpler and cheaper solutions. Image analysis tools namely Aperio, Lucia, Metaview, Metamorph, ImageJ, Scion, Adobe Photoshop, Image Pro Plus are also used for evaluation of expressions using immunohistochemical staining. An overview of such methods used for image analysis is provided in this paper. This study concludes that there is good scope for development of freely available software for staining intensity quantification, which a medical researcher could easily use without requiring high level computer skills.

Image analysis tools for evaluation of microscopic views of immunohistochemically stained specimen in medical research-a review

The aim of this study is to review the methods being used for image analysis of microscopic views of immunohistochemically stained specimen in medical research. The solutions available range from general purpose software to commercial packages. Many studies have developed their own custom written programs based on some general purpose software available. Many groups have reported development of computer aided image analysis programs aiming at obtaining faster, simpler and cheaper solutions. Image analysis tools namely Aperio, Lucia, Metaview, Metamorph, ImageJ, Scion, Adobe Photoshop, Image Pro Plus are also used for evaluation of expressions using immunohistochemical staining. An overview of such methods used for image analysis is provided in this paper. This study concludes that there is good scope for development of freely available software for staining intensity quantification, which a medical researcher could easily use without requiring high level computer skills.

Toward a multi-scale computational model of arterial adaptation in hypertension: verification of a multi-cell agent based model

Agent-based models (ABMs) represent a novel approach to study and simulate complex mechano chemo-biological responses at the cellular level. Such models have been used to simulate a variety of emergent responses in the vasculature, including angiogenesis and vasculogenesis. Although not used previously to study large vessel adaptations, we submit that ABMs will prove equally useful in such studies when combined with well-established continuum models to form multi-scale models of tissue-level phenomena. In order to couple agent-based and continuum models, however, there is a need to ensure that each model faithfully represents the best data available at the relevant scale and that there is consistency between models under baseline conditions. Toward this end, we describe the development and verification of an ABM of endothelial and smooth muscle cell responses to mechanical stimuli in a large artery. A refined rule-set is proposed based on a broad literature search, a new scoring system for assigning confidence in the rules, and a parameter sensitivity study. To illustrate the utility of these new methods for rule selection, as well as the consistency achieved with continuum-level models, we simulate the behavior of a mouse aorta during homeostasis and in response to both transient and sustained increases in pressure. The simulated responses depend on the altered cellular production of seven key mitogenic, synthetic, and proteolytic biomolecules, which in turn control the turnover of intramural cells and extracellular matrix. These events are responsible for gross changes in vessel wall morphology. This new ABM is shown to be appropriately stable under homeostatic conditions, insensitive to transient elevations in blood pressure, and responsive to increased intramural wall stress in hypertension.

A 3-D Framework for Arterial Growth and Remodeling in Response to Altered Hemodynamics

We present a three-dimensional mathematical framework for modeling the evolving geometry, structure, and mechanical properties of a representative straight cylindrical artery subjected to changes in mean blood pressure and flow. We show that numerical predictions recover prior findings from a validated two-dimensional framework, but extend those findings by allowing effects of transmural gradients in wall constituents and vasoactive molecules to be simulated directly. Of particular note, we show that the predicted evolution of the residual stress related opening angle in response to an abrupt, sustained increase in blood pressure is qualitatively similar to measured changes when one accounts for a nonlinear transmural distribution of pre-stretched elastin. We submit that continuum-based constrained mixture models of arterial adaptation hold significant promise for deepening our basic understanding of arterial mechanobiology and thus for designing improved clinical interventions to treat many different types of arterial disease and injury.

Time course of carotid artery growth and remodeling in response to altered pulsatility

Elucidating early time courses of biomechanical responses by arteries to altered mechanical stimuli is paramount to understanding and eventually predicting long-term adaptations. In a previous study, we reported marked long-term (at 35-56 days) consequences of increased pulsatile hemodynamics on arterial structure and mechanics. Motivated by those findings, we focus herein on arterial responses over shorter periods (at 7, 10, and 14 days) following placement of a constrictive band on the aortic arch between the innominate and left carotid arteries of wild-type mice, which significantly increases pulsatility in the right carotid artery. We quantified hemodynamics in vivo using noninvasive ultrasound and measured wall properties and composition in vitro using biaxial mechanical testing and standard (immuno)histology. Compared with both baseline carotid arteries and left carotids after banding, right carotids after banding experienced a significant increase in both pulse pressure, which peaked at day 7, and a pulsatility index for velocity, which continued to rise over the 42-day study despite a transient increase in mean flow that peaked at day 7. Wall thickness and inner diameter also increased significantly in the right carotids, both peaking at day 14, with an associated marked early reduction in the in vivo axial stretch and a persistent decrease in smooth muscle contractility. Glycosaminoglycan content also increased within the wall, peaking at day 14, whereas increases in monocyte chemoattractant protein-1 activity and the collagen-to-elastin ratio continued to rise. These findings confirm that pulsatility is an important modulator of wall geometry, structure, and properties but reveal different early time courses for different microscopic and macroscopic metrics, presumably due to the separate degrees of influence of pressure and flow.

Immunohistochemistry in diagnostic surgical pathology: contributions of protein life-cycle, use of evidence-based methods and data normalization on interpretation of immunohistochemical stains

Immunohistochemical (IHC) staining of formalin-fixed and paraffin-embedded tissues (FFPE) is widely used in diagnostic surgical pathology. All anatomical and surgical pathologists use IHC to confirm cancer cell type and possible origin of metastatic cancer of unknown primary site. What kinds of improvements in IHC are needed to boost and strengthen the use of IHC in future diagnostic pathology practice? The aim of this perspective is to suggest that continuing reliance on immunohistochemistry in cancer diagnosis, search and validation of biomarkers for predictive and prognostic studies and utility in cancer treatment selection means that minimum IHC data sets including "normalization methods" for IHC scoring, use of relative protein expression levels, use of protein functional pathways and modifications and protein cell type specificity may be needed when markers are proposed for use in diagnostic pathology. Furthermore evidence based methods (EBM), minimum criteria for diagnostic accuracy (STARD), will help in selecting antibodies for use in diagnostic pathology. In the near future, quantitative methods of proteomics, quantitative real-time polymerase chain reaction (qRT-PCR) and the use of high-throughput genomics for diagnosis and predictive decisions may become preferred tools in medicine.

Extracellular matrix alterations in hypertensive vascular remodeling

Vascular cells are very sensitive to their hemodynamic environment. Any change in blood pressure or blood flow can be sensed by endothelial and vascular smooth muscle cells and ultimately results in structural modifications within the vascular wall that accommodate the new conditions. In the case of hypertension, the increase in arterial stretch stimulates vessel thickening to normalize the tensile forces. This process requires modification of the extracellular matrix and of cell-matrix interactions, which mainly involves extracellular proteases. In hypertension, chronic exposure of the arterial wall to stretch leads to vascular remodeling, arterial stiffness and calcification, which finally affect target organ function. This review surveys how mechanical stretch regulates extracellular proteases, considering the signaling pathways involved and the consequences on the cardiovascular system.

On the Mechanical Role of De Novo Synthesized Elastin in the Urinary Bladder Wall

The urinary bladder wall (UBW), which is composed of smooth muscle, collagen, and elastin, undergoes profound remodeling in response to changes in mechanical loading resulting from various pathologies. In our laboratory, we have observed the production of fibrillar elastin in the extracellular matrix (ECM), which makes the UBW a particularly attractive tissue to investigate smooth muscle tissue remodeling. In the present study, we explored the mechanical role that de novo elastin fibers play in altering UBW ECM mechanical behavior using a structural constitutive modeling approach. The mechanical behavior of the collagen fiber component of the UBW ECM was determined from the biaxial stress-stretch response of normal UBW ECM, based on bimodal fiber recruitment that was motivated by the UBW’s unique collagen fiber structure. The resulting fiber ensemble model was then combined with an experimentally derived fiber angular distribution to predict the biaxial mechanical behavior of normal and the elastin-rich UBW ECM to elucidate the underlying mechanisms of elastin production. Results indicated that UBW ECM exhibited a distinct structure with highly coiled collagen fiber bundles and visible elastic fibers in the pathological situation. Elastin-rich UBW ECM had a distinct mechanical behavior with higher compliance, attributable to the indirect effect of elastin fibers contracting the collagen fiber network, resulting in a retracted unloaded reference state of the tissue. In conclusion, our results suggest that the urinary bladder responds to prolonged periods of high strain by increasing its effective compliance through the interaction between collagen and de novo synthesized elastic fibers.

Importance of pulsatility in hypertensive carotid artery growth and remodeling

Arteries experience marked variations in blood pressure and flow during the cardiac cycle that can intensify during exercise, in disease, or with aging. Diverse observations increasingly suggest the importance of such pulsatility in arterial homeostasis and adaptations. We used a transverse aortic arch banding model to quantify chronic effects of increased pulsatile pressure and flow on wall morphology, composition, and biaxial mechanical properties in paired mouse arteries: the highly pulsatile right common carotid artery proximal to the band (RCCA-B) and the nearly normal left common carotid artery distal to the band (LCCA-B). Increased pulsatile mechanical stimuli in RCCA-B increased wall thickness compared with LCCA-B, which correlated more strongly with pulse (r* = 0.632; P < 0.01) than mean (r* = 0.020; P = 0.47) or systolic (r* = 0.466; P < 0.05) pressure. Similarly, inner diameter at mean pressure increased in RCCA-B and correlated slightly more strongly with a normalized index of blood velocity pulsatility (r* = 0.915; P < <0.001) than mean flow (r* = 0.834; P < 0.001). Increased wall thickness and luminal diameter in RCCA-B resulted from significant increases in cell number per cross-sectional area (P < 0.001) and collagen-to-elastin ratio (P < 0.05) as well as a moderate (1.7-fold) increase in glycosaminoglycan content, which appears to have contributed to the significant decrease (P < 0.001) in the in-vivo axial stretch in RCCA-B compared with LCCA-B. Changes in RCCA-B also associated with a signficant increase in monocyte chemoattractant protein-1 (P < 0.05) whereas LCCA-B did not. Pulsatile pressure and flow are thus important stimuli in the observed three-dimensional arterial adaptations, and there is a need for increased attention to the roles of both axial wall stress and adventitial remodeling.

A Structure-Based Model of Arterial Remodeling in Response to Sustained Hypertension

A novel structure-based mathematical model of arterial remodeling in response to a sustained increase in pressure is proposed. The model includes two major aspects of remodeling in a healthy matured vessel. First, the deviation of the wall stress and flow-induced shear stress from their normal physiological values drives the changes in the arterial geometry. Second, the new mass that is produced during remodeling results from an increase in the mass of smooth muscle cells and collagen fibers. The model additionally accounts for the effect of the average pulsatile strain on the recruitment of collagen fibers in load bearing. The model was used to simulate remodeling of a human thoracic aorta, and the results are in good agreement with previously published model predictions and experimental data. The model predicts that the total arterial volume rapidly increases during the early stages of remodeling and remains virtually constant thereafter, despite the continuing stress-driven geometrical remodeling. Moreover, the effects of a perfect or incomplete restoration of the arterial compliance on the remodeling outputs were analyzed. For instance, the model predicts that the pattern of the time course of the opening angle depends on the extent to which the average pulsatile strain is restored at the end of the remodeling process. Future experimental studies on the time course of compliance, opening angle, and mass fractions of collagen, elastin, and smooth muscle cells can validate and improve the introduced hypotheses of the model.

Transforming growth factor-beta signaling in hypertensive remodeling of porcine aorta

A porcine aortic coarctation model was used to examine regulation of gene expression in early hypertensive vascular remodeling. Aortic segments were collected proximal (high pressure) and distal (low pressure) to the coarctation after 2 wk of sustained hypertension (mean arterial pressure>150 mmHg). Porcine 10K oligoarrays used for gene expression profiling of the two regions of aorta revealed downregulation of cytoskeletal and upregulation of extracellular region genes relative to the whole genome. A genomic database search for transforming growth factor-beta (TGF-beta) control elements showed that 19% of the genes that changed expression due to hypertension contained putative TGF-beta control elements. Real-time RT-PCR and microarray analysis showed no change in expression of TGF-beta1, TGF-beta2, TGF-beta3, or bone morphogenetic proteins-2 and -4, yet immunohistochemical staining for phosphorylated SMAD2, an indicator of TGF-beta signaling, and for phosphorylated SMAD1/5/8, an indicator of signaling through the bone morphogenetic proteins, showed the highest percentage of positively stained cells in the proximal aortic segments of occluded animals. For TGF-beta signaling, this increase was significantly different than for sham-operated controls. Western blot analysis showed no difference in total TGF-beta1 protein levels with respect to treatment or aortic segment. Immunohistochemistry showed that the protein levels of latency-associated peptide was decreased in proximal segments of occluded animals. Collectively, these results suggest that activation of TGF-beta, but not altered expression, may be a major mechanism regulating early hypertensive vascular remodeling.

Calponin control of cerebrovascular reactivity: therapeutic implications in brain trauma

Calponin (Cp) is an actin-binding protein first characterized in chicken gizzard smooth muscle (SM). This review discusses the role of Cp in mediating SM contraction, the biochemical process by which Cp facilitates SM contraction and the function of Cp in the brain. Recent work on the role of Cp in pathological states with emphasis on traumatic brain injury is also discussed. Based on past and present data, the case is presented for targeting Cp for novel genetic and pharmacological therapies aimed at improving outcome following traumatic brain injury (TBI).

Elevated epidermal growth factor receptor phosphorylation induces resistance artery dysfunction in diabetic db/db mice

OBJECTIVE

We previously showed epidermal growth factor receptor (EGFR) transactivation to be key mechanism in the regulation of resistance artery myogenic tone. Type 2 diabetes is associated with microvascular complications. We hypothesized that elevated EGFR phosphorylation contributes to resistance artery dysfunction in type 2 diabetes.

RESEARCH DESIGN AND METHODS AND RESULTS

Diabetic db/db and nondiabetic (control) mice were treated with EGFR inhibitor (AG1478; 10 mg x kg(-1) x day(-1)) for 2 weeks. Isolated coronary artery and mesenteric resistance artery (MRA) were mounted in an arteriograph. Pressure-induced myogenic tone was increased in MRA and coronary artery from diabetic mice and normalized by AG1478. Phenylephrine-induced contraction and nitric oxide donor-induced relaxation were similar in all groups. Endothelium-dependent relaxation in response to shear stress and acetylcholine of MRA and coronary artery from diabetic mice was altered and associated with reduced endothelial nitric oxide synthase (eNOS) expression and phosphorylation. Treated diabetic mice with AG1478 improved coronary artery and MRA endothelial function and restored eNOS expression. Immunostaining and Western blot analysis showed increased endothelial and smooth muscle cell EGFR phosphorylation of MRA and coronary artery from diabetic mouse, which was reduced by AG1478. Primary cultured endothelial cells from resistance arteries treated with high glucose for 48 h showed an increase of EGFR phosphorylation associated with eNOS expression and phosphorylation decrease in response to calcium ionophore. Pretreatment of endothelial cells with AG1478 prevented the effect of high glucose.

CONCLUSIONS

This study provides evidence of the role of elevated EGFR phosphorylation in coronary artery and MRA dysfunction in diabetic db/db mice. Therefore, EGFR should be a potential target for overcoming diabetic small artery complications.