Shear stress downregulation of platelet-derived growth factor receptor-beta and matrix metalloprotease-2 is associated with inhibition of smooth muscle cell invasion and migration

Mechanical and chemical cues synergistically promote human venous smooth muscle cell osteogenesis through integrin β1-ERK1/2 signaling: A cell model of hemodialysis fistula calcification

Arteriovenous fistula (AVF) is the vascular access of choice for renal replacement therapy. However, AVF is susceptible to calcification with a high prevalence of 40%-65% in chronic hemodialysis patients. Repeated needle puncture for hemodialysis cannulation results in intimal denudation of AVF. We hypothesized that exposure to blood shear stress in the medial layer promotes venous smooth muscle cell (SMC) osteogenesis. While previous studies of shear stress focused on arterial-type SMCs, SMCs isolated from the vein had not been investigated. This study established a venous cell model of AVF using the fluid shear device, combined with a high phosphate medium to mimic the uremic milieu. Osteogenic gene expression of venous SMCs upon mechanical and chemical cues was analyzed in addition to the activated cell signaling pathways. Our findings indicated that upon shear stress and high phosphate environment, mechanical stimulation (shear stress) had an additive effect in up-regulation of an early osteogenic marker, Runx2. We further identified that the integrin β1-ERK1/2 signaling pathway was responsible for the molecular basis of venous SMC osteogenesis upon shear stress exposure. Mitochondrial biogenesis also took part in the early stage of this venopathy pathogenesis, evident by the up-regulated mitochondrial transcription factor A and mitochondrial DNA polymerase γ in venous SMCs. In conclusion, synergistic effects of fluid shear stress and high phosphate induce venous SMC osteogenesis via the ERK1/2 pathway through activating the mechanosensing integrin β1 signaling. The present study identified a promising druggable target for reducing AVF calcification, which deserves further in vivo investigations.

Mechanisms of Action of MiRNAs and LncRNAs in Extracellular Vesicle in Atherosclerosis

Atherosclerosis, a complex chronic inflammatory disease, involves multiple alterations of diverse cells, including endothelial cells (ECs), vascular smooth muscle cells (VSMCs), monocytes, macrophages, dendritic cells (DCs), platelets, and even mesenchymal stem cells (MSCs). Globally, it is a common cause of morbidity as well as mortality. It leads to myocardial infarctions, stroke and disabling peripheral artery disease. Extracellular vesicles (EVs) are a heterogeneous group of cell-derived membranous structures that secreted by multiple cell types and play a central role in cell-to-cell communication by delivering various bioactive cargos, especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Emerging evidence demonstrated that miRNAs and lncRNAs in EVs are tightly associated with the initiation and development of atherosclerosis. In this review, we will outline and compile the cumulative roles of miRNAs and lncRNAs encapsulated in EVs derived from diverse cells in the progression of atherosclerosis. We also discuss intercellular communications via EVs. In addition, we focused on clinical applications and evaluation of miRNAs and lncRNAs in EVs as potential diagnostic biomarkers and therapeutic targets for atherosclerosis.

Fluid shear stress-mediated mechanotransduction in circulating leukocytes and its defect in microvascular dysfunction

Leukocytes (neutrophils, monocytes) in the active circulation exhibit multiple phenotypic indicators for a low level of cellular activity, like lack of pseudopods and minimal amounts of activated, cell-adhesive integrins on their surfaces. In contrast, before these cells enter the circulation in the bone marrow or when they recross the endothelium into extravascular tissues of peripheral organs they are fully activated. We review here a multifaceted mechanism mediated by fluid shear stress that can serve to deactivate leukocytes in the circulation. The fluid shear stress controls pseudopod formation via the FPR receptor, the same receptor responsible for pseudopod projection by localized actin polymerization. The bioactivity of macromolecular factors in the blood plasma that interfere with receptor stimulation by fluid flow, such as proteolytic cleavage in the extracellular domain of the receptor or the membrane actions of cholesterol, leads to a defective ability to respond to fluid shear stress by actin depolymerization. The cell reaction to fluid shear involves CD18 integrins, nitric oxide, cGMP and Rho GTPases, is attenuated in the presence of inflammatory mediators and modified by glucocorticoids. The mechanism is abolished in disease models (genetic hypertension and hypercholesterolemia) leading to an increased number of activated leukocytes in the circulation with enhanced microvascular resistance and cell entrapment. In addition to their role in binding to biochemical agonists/antagonists, membrane receptors appear to play a second role: to monitor local fluid shear stress levels. The fluid shear stress control of many circulating cell types such as lymphocytes, stem cells, tumor cells remains to be elucidated.

Cell signaling model for arterial mechanobiology

Arterial growth and remodeling at the tissue level is driven by mechanobiological processes at cellular and sub-cellular levels. Although it is widely accepted that cells seek to promote tissue homeostasis in response to biochemical and biomechanical cues—such as increased wall stress in hypertension—the ways by which these cues translate into tissue maintenance, adaptation, or maladaptation are far from understood. In this paper, we present a logic-based computational model for cell signaling within the arterial wall, aiming to predict changes in extracellular matrix turnover and cell phenotype in response to pressure-induced wall stress, flow-induced wall shear stress, and exogenous sources of angiotensin II, with particular interest in mouse models of hypertension. We simulate a number of experiments from the literature at both the cell and tissue level, involving single or combined inputs, and achieve high qualitative agreement in most cases. Additionally, we demonstrate the utility of this modeling approach for simulating alterations (in this case knockdowns) of individual nodes within the signaling network. Continued modeling of cellular signaling will enable improved mechanistic understanding of arterial growth and remodeling in health and disease, and will be crucial when considering potential pharmacological interventions.

Biological soft tissues are characterized by continuous production and removal of material, which endows them with a remarkable ability to adapt to changes in their biochemical and biomechanical environments. For arteries, mechanical stimuli result primarily from changes in blood pressure or flow, and biochemical changes are induced by multiple factors, including pharmacological intervention. In order to understand how arterial properties are maintained in health, or how they adapt or fail to adapt in disease, we must understand better how these diverse stimuli affect material turnover. Extracellular matrix is tightly regulated by mechano-sensing and mechano-regulation, and therefore cell signaling, thus we present a computational model of relevant signaling pathways within the vascular wall, with the aim of predicting changes in wall composition and function in response to three main inputs: pressure-induced wall stress, flow-induced wall shear stress, and exogenous angiotensin II. We obtain qualitative agreement with a range of experimental studies from the literature, and provide illustrative examples demonstrating how such models can be used to further our understanding of arterial remodeling.

Platelet-Derived Growth Factor Receptor-α and β are Involved in Fluid Shear Stress Regulated Cell Migration in Human Periodontal Ligament Cells

Introduction

Fluid shear stress (FSS) is the most common stress produced by mastication, speech, or tooth movement. However, how FSS regulates human periodontal ligament (PDL) cell proliferation and migration as well as the underlying mechanism remains unknown.

Methods

FSS (6 dyn/cm²) was produced in a flow chamber. Cell proliferation was tested by the 5-ethynyl-2'-deoxyuridine assay. Cell migration was tested by the wound healing assay. Gene and protein expression of platelet-derived growth factors (PDGFs) and matrix metalloproteinase (MMP)-2 were measured by reverse transcription-polymerase chain reaction and western blot analyses.

Results

We investigated the effect of 4 h of 6 dyn/cm² FSS on proliferation and migration of PDL cells. FSS promoted PDL cell proliferation but inhibited migration. The gene and protein expression of PDGF receptor (PDGFR)-α and β both decreased in response to FSS. Activating and inhibiting the PDGFRs did not affect the FSS-induced increase in cell proliferation. However, activating PDGFRs with PDGF-BB, which bound both PDGFR-α and β, and PDGF-CC and DD, which had high affinities for PDGFR-α and PDGFR-β, individually rescued FSS-inhibited migration. FSS also inhibited MMP-2 gene expression, which was the most important factor for matrix turnover and migration of PDLs. PDGF-BB, CC, and DD increased the FSS-induced decline in MMP-2 expression. These results indicate that MMP-2 is regulated by FSS and contributes to the FSS-induced decrease in cell migration.

Conclusions

Our study suggests a role for PDGFR-α and β in short-term FSS-regulated cell proliferation and migration. These results will help provide the scientific foundation for revealing the mechanisms clinical tooth movement and PDL regeneration.

Cardiovascular Risk Factors and Markers

Cardiovascular risk is assessed for the prediction and appropriate management of patients using collections of identified risk markers obtained from clinical questionnaire information, concentrations of certain blood molecules (e.g., N-terminal proB-type natriuretic peptide fragment and soluble receptors of tumor-necrosis factor-α and interleukin-2), imaging data using various modalities, and electrocardiographic variables, in addition to traditional risk factors.

Making the cut: Innovative methods for optimizing perfusion-based migration assays

Application of fluid shear stress to adherent cells dramatically influences their cytoskeletal makeup and differentially regulates their migratory phenotype. Because cytoskeletal rearrangements are necessary for cell motility and migration, preserving these adaptations under in vitro conditions and in the presence of fluid flow are physiologically essential. With this in mind, parallel plate flow chambers and microchannels are often used to conduct in vitro perfusion experiments. However, both of these systems currently lack capacity to accurately study cell migration in the same location where cells were perfused. The most common perfusion/migration assays involve cell perfusion followed by trypsinization which can compromise adaptive cytoskeletal geometry and lead to misleading phenotypic conclusions. The purpose of this study was to quantitatively highlight some limitations commonly found with currently used cell migration approaches and to introduce two new advances which use additive manufacturing (3D printing) or laser capture microdissection (LCM) technology. The residue-free 3D printed insert allows accurate cell seeding within defined areas, increases cell yield for downstream analyses, and more closely resembles the reported levels of fluid shear stress calculated with computational fluid dynamics as compared to other residue-free cell seeding techniques. The LCM approach uses an ultraviolet laser for "touchless technology" to rapidly and accurately introduce a custom-sized wound area in otherwise inaccessible perfusion microchannels. The wound area introduced by LCM elicits comparable migration characteristics compared to traditional pipette tip-induced injuries. When used in perfusion experiments, both of these newly characterized tools were effective in yielding similar results yet without the limitations of the traditional modalities. These innovative methods provide valuable tools for exploring mechanisms of clinically important aspects of cell migration fundamental to the pathogenesis of many flow-mediated disorders and are applicable to other perfusion-based models where migration is of central importance. © 2016 International Society for Advancement of Cytometry.

The effects of fluid shear stress on proliferation and osteogenesis of human periodontal ligament cells

Shear stress is one of the main stress type produced by speech, mastication or tooth movement. The mechano-response of human periodontal ligament (PDL) cells by shear stress and the mechanism are largely unknown. In our study, we investigated the effects of fluid shear stress on proliferation, migration and osteogenic potential of human PDL cells. 6dyn/cm(2) of fluid shear stress was produced in a parallel plate flow chamber. Our results demonstrated that fluid shear stress rearranged the orientation of human PDL cells. In addition, fluid shear stress inhibited human PDL cell proliferation and migration, but increased the osteogenic potential and expression of several growth factors and cytokines. Our study suggested that shear stress is involved in homeostasis regulation in human PDL cells. Inhibiting proliferation and migration potentially induce PDL cells to respond to mechanical stimuli in order to undergo osteogenic differentiation.

Sonographic findings associated with stenosis progression and vascular complications in moyamoya disease

OBJECT The progression of arterial stenosis in patients with moyamoya disease (MMD) has variable courses and an unclear mechanism. The authors hypothesized that elevated wall shear stress (WSS) at the terminal internal carotid artery (ICA) and proximal middle cerebral artery (MCA) may facilitate MMD progression. They indirectly evaluated the relative magnitude of WSS (WSS value [WSSV]) with MR angiography (MRA) and transcranial Doppler to determine its predictive value for stenosis progression (SP) and the development of vascular complications. METHODS Thirty-one medically treated patients (58 hemispheres and 95 nonoccluded vessels) were analyzed with serial MRA (median follow-up 23 months). The parameters studied were SP, SP rates (SPRs) for individual ICAs/MCAs, and their mean values from the ipsilateral hemispheres as mean SP (MSP) and MSP rates (MSPRs). Significant progression was defined as decrements of ≥ 20% for SP and MSP and ≥ 10%/year for SPR and MSPR. The development of vascular complications in relevant hemispheres was also recorded. The WSSV (dyne/cm(2)) was defined as the shear rate multiplied by blood viscosity. RESULTS After adjusting the initial stenosis degree and MRA stage of MMD, an SP of ≥ 20% and an SPR of ≥ 10%/year were associated with the highest-quartile WSSVs for all individual vessels and for MCAs and ICAs separately. For each hemisphere, an MSP of ≥ 20% and an MSPR of ≥ 10%/year were associated with the highest-quartile mean WSSVs. Furthermore, significant SP was highly correlated with vascular complications, and the highest-quartile mean WSSV was independently associated with vascular complications in relevant hemispheres. CONCLUSIONS An elevated WSSV is an independent predictor for SP and vascular complications in nonoccluded MMD.

Vascular smooth muscle cell in atherosclerosis

Vascular smooth muscle cells (VSMCs) exhibit phenotypic and functional plasticity in order to respond to vascular injury. In case of the vessel damage, VSMCs are able to switch from the quiescent 'contractile' phenotype to the 'proinflammatory' phenotype. This change is accompanied by decrease in expression of smooth muscle (SM)-specific markers responsible for SM contraction and production of proinflammatory mediators that modulate induction of proliferation and chemotaxis. Indeed, activated VSMCs could efficiently proliferate and migrate contributing to the vascular wall repair. However, in chronic inflammation that occurs in atherosclerosis, arterial VSMCs become aberrantly regulated and this leads to increased VSMC dedifferentiation and extracellular matrix formation in plaque areas. Proatherosclerotic switch in VSMC phenotype is a complex and multistep mechanism that may be induced by a variety of proinflammatory stimuli and hemodynamic alterations. Disturbances in hemodynamic forces could initiate the proinflammatory switch in VSMC phenotype even in pre-clinical stages of atherosclerosis. Proinflammatory signals play a crucial role in further dedifferentiation of VSMCs in affected vessels and propagation of pathological vascular remodelling.

Cyclic mechanical stretching promotes migration but inhibits invasion of rat bone marrow stromal cells

Bone marrow stromal cells (BMSCs, also broadly known as bone marrow-derived mesenchymal stem cells) are multipotent stem cells that have a self-renewal capacity and multilineage differentiation potential. Mechanical stretching plays a vital role in regulating the proliferation and differentiation of BMSCs. However, little is known about the effects of cyclic stretching on BMSC migration and invasion. In this study, using a custom-made cell-stretching device, we studied the effects of cyclic mechanical stretching on rat BMSC migration and invasion using a Transwell Boyden Chamber. The protein secretion of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) was detected by gelatin zymography, and the activation of focal adhesion kinase (FAK) and extracellular signal regulated kinase1/2 (ERK1/2) was measured by western blot. We found that cyclic mechanical stretching with 10% amplitude at 1Hz frequency for 8h promotes BMSC migration, but reduces BMSC invasion. FAK and ERK1/2 signals were activated in BMSCs after exposure to cyclic stretching. In the presence of the FAK phosphorylation blocker PF573228 or the ERK1/2 phosphorylation blocker PD98059, the cyclic-stretch-promoted migration of BMSCs was completely suppressed. On the other hand, cyclic mechanical stretching reduced the secretion of MMP-2 and MMP-9 in BMSCs, and PF573228 suppressed the cyclic-stretch-reduced secretion of MMP-2 and MMP-9. The decrease of BMSC invasion induced by mechanical stretching is partially restored by PF573228 but remained unaffected by PD98059. Taken together, these data show that cyclic mechanical stretching promotes BMSC migration via the FAK-ERK1/2 signalling pathway, but reduces BMSC invasion by decreasing secretion of MMP-2 and MMP-9 via FAK, independent of the ERK1/2 signal.

Proposed new lymphology combined with lymphatic physiology, innate immunology, and oncology

As one of the lymphatic functions, it is well known that the transport and drainage of hydrophilic substances including plasma protein through the lymphatic system play pivotal roles in maintaining the homeostasis of the internal environment between the cells in tissues in collaboration with the exchange of the substances through the blood capillaries and venules. The physiological functions of the lymphatic system have been studied by many investigations of microcirculation, i.e., Yoffey and Courtice, Ruszunyak et al., Földie and Casley-Smigh et al., Roddie, Schmid-Schönbein et al., and Ohhashi et al. On the other hand, it is also well known that the initial clinical signs of primary diseases such as inflammation, tumors, and circulatory disorders including infarction and thrombosis appear as functional abnormalities of the internal environment in tissues. These abnormalities of the functions are strongly related to immunological defense reactions around the internal environment and abnormal actions of the transport and drainage of the lymphatic system. Taking into consideration the current inspired findings in lymphatic physiology, innate immunology, and oncology, we have proposed a new lymphology combined with new knowledge of the three above-mentioned academic fields from a defense mechanism points of view. In this review, we would like to demonstrate comprehensively our latest studies related to the possibility of establishing a new lymphology, hoping the readers will evaluate this possibility.

Shear enhances thrombopoiesis and formation of microparticles that induce megakaryocytic differentiation of stem cells

In vivo visualization of thrombopoiesis suggests an important role for shear flow in platelet biogenesis. In vitro, shear stress was shown to accelerate proplatelet formation from mature megakaryocytes (Mks). Yet, the role of biomechanical forces on Mk biology and platelet biogenesis remains largely unexplored. In this study, we investigated the impact of shear stress on Mk maturation and formation of platelet-like particles (PLPs), pro/preplatelets (PPTs), and Mk microparticles (MkMPs), and furthermore, we explored a physiological role for MkMPs. We found that shear accelerated DNA synthesis of immature Mks in an exposure time- and shear stress level-dependent manner. Both phosphatidylserine exposure and caspase-3 activation were enhanced by shear stress. Exposure to physiological shear dramatically increased generation of PLPs/PPTs and MkMPs by up to 10.8 and 47-fold, respectively. Caspase-3 inhibition reduced shear-induced PLP/PPT and MkMP formation. PLPs generated under shear flow displayed improved functionality as assessed by CD62P exposure and fibrinogen binding. Significantly, coculture of MkMPs with hematopoietic stem and progenitor cells promoted hematopoietic stem and progenitor cell differentiation to mature Mks synthesizing α- and dense-granules, and forming PPTs without exogenous thrombopoietin, thus identifying a novel and unexplored potential physiological role for MkMPs.

A PARAMETRIC NUMERICAL INVESTIGATION OF LOCAL HAEMODYNAMICS IN THE END-TO-SIDE ANASTOMOSIS OF CERVICAL-TO-PETROUS BYPASS BASED ON REAL GEOMETRY OF INTERNAL CAROTID ARTERY

Bypass reconstructed from the cervical segment of internal carotid artery (ICA) to its petrous segment allows high-volume bypass flow without any risk of intracranial dissection. The purpose of this study was to investigate the geometric effect on the end-to-side anastomosis of cervical-to-petrous bypass, for its close relationship to local haemodynamic and the long-term performance of bypass. We focused on two controllable geometric parameters: diameter ratio (Φ) and angle (α) between the graft and host arteries. Different models covering a range of Φ (0.75, 1 and 1.25) and α (30°, 45°, 60° and 90°) were constructed based on real geometry of human ICA. Numerical simulations of blood flow were performed in physiological flow condition. The flow patterns, flow distributions, time-average wall shear stress (TAWSS) and oscillatory shear index (OSI) in different models were compared. Our results showed geometric factors have influence on both the local haemodynamic parameters and the flow velocity through downstream branches. Of models with different geometric parameters, the model with Φ ≥ 1 or α = 45° were the most optimized considering haemodynamic performance.

Interfacial biology of in-stent restenosis

Percutaneous angioplasty is a nonsurgical method able to restore patency in atherosclerotic blood vessels through the expansion of a balloon. The clinical outcome of this technique has been significantly enhanced by the combined deployment of a stent. Although stents are successful in the majority of cases, a large percentage of patients (20-30%) still suffer a second vessel lumen reduction known as in-stent restenosis. In-stent restenosis is recognized to be caused by the mechanical and foreign body challenges elicited by the device. Drug-eluting stents have been recently made available to tackle restenosis, but their short clinical history and high costs may limit their future use. The present review links the most recent biologic findings related to in-stent restenosis to the devices' phyisico-chemical features in an attempt to demonstrate that a new generation of stents may be developed without the need of drug elution.

Fluid Mechanics, Arterial Disease, and Gene Expression

This review places modern research developments in vascular mechanobiology in the context of hemodynamic phenomena in the cardiovascular system and the discrete localization of vascular disease. The modern origins of this field are traced, beginning in the 1960s when associations between flow characteristics, particularly blood flow-induced wall shear stress, and the localization of atherosclerotic plaques were uncovered, and continuing to fluid shear stress effects on the vascular lining endothelial) cells (ECs), including their effects on EC morphology, biochemical production, and gene expression. The earliest single-gene studies and genome-wide analyses are considered. The final section moves from the ECs lining the vessel wall to the smooth muscle cells and fibroblasts within the wall that are fluid me chanically activated by interstitial flow that imposes shear stresses on their surfaces comparable with those of flowing blood on EC surfaces. Interstitial flow stimulates biochemical production and gene expression, much like blood flow on ECs.

Biomechanical regulation of vascular smooth muscle cell functions: from in vitro to in vivo understanding

Vascular smooth muscle cells (VSMCs) have critical functions in vascular diseases. Haemodynamic factors are important regulators of VSMC functions in vascular pathophysiology. VSMCs are physiologically active in the three-dimensional matrix and interact with the shear stress sensor of endothelial cells (ECs). The purpose of this review is to illustrate how haemodynamic factors regulate VSMC functions under two-dimensional conditions in vitro or three-dimensional co-culture conditions in vivo. Recent advances show that high shear stress induces VSMC apoptosis through endothelial-released nitric oxide and low shear stress upregulates VSMC proliferation and migration through platelet-derived growth factor released by ECs. This differential regulation emphasizes the need to construct more actual environments for future research on vascular diseases (such as atherosclerosis and hypertension) and cardiovascular tissue engineering.

Cell surface F1/FO ATP synthase contributes to interstitial flow-mediated development of the acidic microenvironment in tumor tissues

To address pivotal roles of cell surface F1/FO ATP synthase in the development of acidic microenvironment in tumor tissues, we investigated effects of shear stress stimulation on the cultured human breast cancer cells, MDA-MB-231 and MDA-MB-157, or human melanoma cells, SK-Mel-1. Shear stress stimulation (0.5-5.0 dyn/cm(2)), the levels of which are similar to those produced by the interstitial flow, induced strength-dependent corelease of ATP and H(+) from the cells, which triggered CO2 gas excretion. In contrast, the same level of shear stress stimulation did not induce significant ATP release and CO2 gas excretion from the control human mammary epithelial cells (HMEC). Marked immunocytochemical and mRNA expression of cell surface F1/FO ATP synthase, vacuolar-ATPase (V-ATPase), carbonic anhydrase type IX, and ectonucleoside triphosphate diphosphohydrolase (ENTPDase) 3 were detected in MDA-MB-231 cells, but little or no expression on the HMEC. Pretreatment with cell surface F1/FO ATP synthase inhibitors, but not cell surface V-ATPase inhibitors, caused a significant reduction of the shear stress stimulation-mediated ATP release and CO2 gas excretion from MDA-MB-231 cells. The ENTPDase activity in the shear stress-loaded MDA-MB-231 cell culture medium supernatant increased significantly in a time-dependent manner. In addition, MDA-MB-231 cells displayed strong staining for purinergic 2Y1 (P2Y1) receptors on their surfaces, and the receptors partially colocalized with ENTPDase 3. These findings suggest that cell surface F1/FO ATP synthase, but not V-ATPase, may play key roles in the development of interstitial flow-mediated acidic microenvironment in tumor tissues through the shear stress stimulation-induced ATP and H(+) corelease and CO2 gas production.

The effects of stenting on shear stress: relevance to endothelial injury and repair

Stent deployment following balloon angioplasty is used routinely to treat coronary artery disease. These interventions cause damage and loss of endothelial cells (EC), and thus promote in-stent thrombosis and restenosis. Injured arteries are repaired (intrinsically) by locally derived EC and by circulating endothelial progenitor cells which migrate and proliferate to re-populate denuded regions. However, re-endothelialization is not always complete and often dysfunctional. Moreover, the molecular and biomechanical mechanisms that control EC repair and function in stented segments are poorly understood. Here, we propose that stents modify endothelial repair processes, in part, by altering fluid shear stress, a mechanical force that influences EC migration and proliferation. A more detailed understanding of the biomechanical processes that control endothelial healing would provide a platform for the development of novel therapeutic approaches to minimize damage and promote vascular repair in stented arteries.

Migration of human mesenchymal stem cells under low shear stress mediated by mitogen-activated protein kinase signaling

Human mesenchymal stem cells (hMSCs) are attractive candidates for cell-based tissue repair approaches and have been used as vectors for delivering therapeutic genes to sites of injury. It is believed that hMSCs are able to detect and respond to shear stress due to blood and interstitial fluid flow through mechanotransduction pathways after transplantation. However, information regarding hMSC migration under shear stress and its mechanism is still limited. In this study, we examined the effect of shear stress on hMSC migration and the role of mitogen-activated protein kinases (MAPKs) in their migration. Shear stress between 0.2 and 10 Pa, which was produced by the flow medium, was exerted on fluorescently labeled hMSCs. Cell migration was evaluated using the scratch wound assay, and images were captured using a microscope equipped with a digital 3CCD camera. The results showed that hMSCs subjected to a shear stress of 0.2 Pa caused notably faster wound closure than statically cultured hMSCs, while migration in the 0.5- and 1-Pa shear stress group did not differ significantly from that in the control group. Shear stress >2 Pa markedly inhibited hMSC migration. hMSCs subjected to a shear stress of 0.2 Pa displayed an increase in extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNK), and p38 MAPK activation for up to 60 min, while a shear stress of 2 Pa abrogated the activation. JNK and p38 MAPK inhibitors completely abolished the effect of shear stress on hMSC migration, while significant differences were observed between the ERK1/2 inhibitor-treated static control and shear stress groups. Taken together, these results demonstrate that low shear stress effectively induces hMSC migration and that JNK and p38 MAPK play more prominent roles in shear stress-induced migration than ERK1/2.

Cellular plasticity: the good, the bad, and the ugly? Microenvironmental influences on progenitor cell therapy

Progenitor cell based therapies have emerged for the treatment of ischemic cardiovascular diseases where there is insufficient endogenous repair. However, clinical success has been limited, which challenges the original premise that transplanted progenitor cells would orchestrate repair. In this review, we discuss the basics of endothelial progenitor cell therapy and describe how microenvironmental changes (i.e., trophic and mechano-structural factors) in the damaged myocardium influence progenitor cell plasticity and hamper beneficial therapeutic outcome. Further understanding of these microenvironmental clues will enable optimization of cell therapy at all levels. We discuss current concepts and provide future perspectives for the enhancement of progenitor cell therapy, and merge these advances into a combined approach for ischemic tissue repair.

Reduced NO signaling during pregnancy attenuates outward uterine artery remodeling by altering MMP expression and collagen and elastin deposition

Recent findings indicate that endothelial nitric oxide (NO) plays a key role in uterine artery outward circumferential remodeling during pregnancy. Although the underlying mechanisms are not known, they likely involve matrix metalloproteinases (MMPs). The goal of this study was to examine the linkage among NO inhibition, expansive remodeling, and MMP expression within the uterine vascular wall. Adult female rats were treated with N(G)-nitro-L-arginine methyl ester [L-NAME (LPLN)] beginning on day 10 of pregnancy and until death at day 20 and compared with age-matched controls [late pregnant (LP)]. Mean arterial pressure of LPLN rats was significantly higher than controls. LPLN fetal and placental weights were significantly reduced compared with controls. Main uterine arteries (mUA) were collected to determine dimensional properties (lumen area and wall thickness), collagen and elastin content, and levels of endothelial nitric oxide synthase (eNOS) and MMP expression. Circumferential remodeling was attenuated, as evidenced by significantly smaller lumen diameters. eNOS RNA and protein were significantly (>90%) decreased in the LPLN mUA compared with LP. Collagen and elastin contents were significantly increased in LPLN rats by ∼10 and 25%, respectively, compared with LP (P < 0.05). Both MMP-2 and tissue inhibitors of metalloproteinase-2 as assessed by immunofluorescence were lower in the endothelium (reduction of 60%) and adventitia (reduction of 50%) of LPLN compared with LP mUA. Membrane bound MMP-1 (MT1-MMP) as assessed by immunoblot was significantly decreased in LPLN. These data suggest a novel contribution of MMPs to gestational uterine vascular remodeling and substantiate the linkage between NO signaling and gestational remodeling of the uterine circulation via altered MMP, TIMP-2, and MT1-MMP expression and activity.

Fluid flow mechanotransduction in vascular smooth muscle cells and fibroblasts

Understanding how vascular wall endothelial cells (ECs), smooth muscle cells (SMCs), and fibroblasts (FBs) sense and transduce the stimuli of hemodynamic forces (shear stress, cyclic strain, and hydrostatic pressure) into intracellular biochemical signals is critical to prevent vascular disease development and progression. ECs lining the vessel lumen directly sense alterations in blood flow shear stress and then communicate with medial SMCs and adventitial FBs to regulate vessel function and disease. Shear stress mechanotransduction in ECs has been extensively studied and reviewed. In the case of endothelial damage, blood flow shear stress may directly act on the superficial layer of SMCs and transmural interstitial flow may be elevated on medial SMCs and adventitial FBs. Therefore, it is also important to investigate direct shear effects on vascular SMCs as well as FBs. The work published in the last two decades has shown that shear stress and interstitial flow have significant influences on vascular SMCs and FBs. This review summarizes work that considered direct shear effects on SMCs and FBs and provides the first comprehensive overview of the underlying mechanisms that modulate SMC secretion, alignment, contraction, proliferation, apoptosis, differentiation, and migration in response to 2-dimensional (2D) laminar, pulsatile, and oscillating flow shear stresses and 3D interstitial flow. A mechanistic model of flow sensing by SMCs is also provided to elucidate possible mechanotransduction pathways through surface glycocalyx, integrins, membrane receptors, ion channels, and primary cilia. Understanding flow-mediated mechanotransduction in SMCs and FBs and the interplay with ECs should be helpful in exploring strategies to prevent flow-initiated atherosclerosis and neointima formation and has implications in vascular tissue engineering.

A local proinflammatory signalling loop facilitates adverse age-associated arterial remodeling

Background

The coincidence of vascular smooth muscle cells (VSMC) infiltration and collagen deposition within a diffusely thickened intima is a salient feature of central arterial wall inflammation that accompanies advancing age. However, the molecular mechanisms involved remain undefined.

Methodology/Principal Findings

Immunostaining and immunoblotting of rat aortae demonstrate that a triad of proinflammatory molecules, MCP-1, TGF-β1, and MMP-2 increases within the aortic wall with aging. Exposure of VSMC isolated from 8-mo-old rats (young) to MCP-1 effects, via CCR-2 signaling, both an increase in TGF-β1 activity, up to levels of untreated VSMC from 30-mo-old (old) rats, and a concurrent increase in MMP-2 activation. Furthermore, exposure of young VSMC to TGF-β1 increases levels of MCP-1, and MMP-2 activation, to levels of untreated VSMC from old rats. This autocatalytic signaling loop that enhances collagen production and invasiveness of VSMC is effectively suppressed by si-MCP-1, a CCR2 antagonist, or MMP-2 inhibition.

Conclusions/Significance

Threshold levels of MCP-1, MMP-2, or TGF-β1 activity trigger a feed-forward signaling mechanism that is implicated in the initiation and progression of adverse age-associated arterial wall remodeling. Intervention that suppressed this signaling loop may potentially retard age-associated adverse arterial remodeling.

Vascular smooth muscle cell glycocalyx modulates shear-induced proliferation, migration, and NO production responses

The endothelial cell glycocalyx, a structure coating the luminal surface of the vascular endothelium, and its related mechanotransduction have been studied by many over the last decade. However, the role of vascular smooth muscle cells (SMCs) glycocalyx in cell mechanotransduction has triggered little attention. This study addressed the role of heparan sulfate proteoglycans (HSPGs), a major component of the glycocalyx, in the shear-induced proliferation, migration, and nitric oxide (NO) production of the rat aortic smooth muscle cells (RASMCs). A parallel plate flow chamber and a peristaltic pump were employed to expose RASMC monolayers to a physiological level of shear stress (12 dyn/cm(2)). Heparinase III (Hep.III) was applied to selectively degrade heparan sulfate on the SMC surface. Cell proliferation, migration, and NO production rates were determined and compared among the following four groups of cells: 1) untreated with no flow, 2) Hep.III treatment with no flow, 3) untreated with flow of 12 dyn/cm(2) exposure, and 4) Hep.III treatment with flow of 12 dyn/cm(2) exposure. It was observed that flow-induced shear stress significantly suppressed SMC proliferation and migration, whereas cells preferred to aligning along the direction of flow and NO production were enhanced substantially. However, those responses were not found in the cells with Hep.III treatment. Under flow condition, the heparinase III-treated cells remained randomly oriented and proliferated as if there were no flow presence. Disruption of HSPG also enhanced wound closure and inhibited shear-induced NO production significantly. This study suggests that HSPG may play a pivotal role in mechanotransduction of SMCs.

Alteration of vaginal elastin metabolism in women with pelvic organ prolapse

OBJECTIVE

To compare elastin metabolism in the vagina of women with and without pelvic organ prolapse and to define the regulation of this process by hormone therapy (HT).

METHODS

Eighty-seven histologically confirmed full-thickness vaginal biopsies were procured from study participants at time of surgery. Premenopausal women with no prolapse served as controls. Women with prolapse were divided into three groups: premenopausal, postmenopausal not on HT, and postmenopausal on HT. The epithelium was excised leaving the subepithelium, muscularis, and adventitia for analyses. The elastin precursor, tropoelastin, was measured by immunoblotting and mature elastin protein via a desmosine cross-link radioimmunoassay. Matrix metalloproteinases (MMPs)-2 and -9 were quantitated by gelatin zymography. Data were analyzed using Kruskal-Wallis test and post hoc analysis using the Mann-Whitney U test.

RESULTS

Tropoelastin (432%), mature elastin (55%), proMMP-9 (90%), and active MMP-9 (106%) were increased in women with prolapse relative to those in the control group while active MMP-2 (41%) was decreased. Comparison of tropoelastin and mature elastin values obtained from the same women showed them to be independently regulated (r=0.19). Interestingly, the highest amount of both proteins occurred in postmenopausal patients not on HT.

CONCLUSION

Elastin metabolism is altered in the vagina of women with prolapse relative to those in the control group, suggesting that vaginal tissue is rapidly remodeling in response to mechanical stretch. We found that elastin levels are highest in the absence of hormones.

Shear stress and plaque development

Although traditional cardiovascular risk factors 'prime the soil' for atherogenesis systemically, atherosclerosis primarily occurs in a site-specific manner with a predilection towards the inner wall of curvatures and outer wall of bifurcations with sparing of flow-dividers. Wall shear stress is a frictional force exerted parallel to the vessel wall that leads to alteration of the endothelial phenotype, endothelial cell signaling, gene and protein expression leading to a proinflammatory phenotype, reduced nitric oxide availability and disruption of the extracellular matrix, which in turn leads to plaque development. Clinical and experimental data are emerging that suggest the pathobiology associated with abnormal wall shear stress results in atherosclerotic plaque development and progression.

Adaptive changes in autogenous vein grafts for arterial reconstruction: clinical implications

For patients with the most severe manifestations of lower extremity arterial occlusive disease, bypass surgery using autogenous vein has been the most durable reconstruction. However, the incidence of bypass graft stenosis and graft failure remains substantial and wholesale improvements in patency are lacking. One potential explanation is that stenosis arises not only from over exuberant intimal hyperplasia, but also due to insufficient adaptation or remodeling of the vein to the arterial environment. Although in vivo human studies are difficult to conduct, recent advances in imaging technology have made possible a more comprehensive structural examination of vein bypass maturation. This review summarizes recent translational efforts to understand the structural and functional properties of human vein grafts and places it within the context of the rich existing literature of vein graft failure.

Impact of endothelial cells and mechanical conditioning on smooth muscle cell extracellular matrix production and differentiation

The aim of the current study was to explore the separate and coupled effects of endothelial cell (EC) presence and mechanical conditioning on smooth muscle cell (SMC) responses by combining bilayered poly(ethylene glycol) diacrylate (PEGDA) hydrogels with a pulsatile flow bioreactor. Each construct was composed of an outer PEGDA layer containing SMC and an inner PEGDA layer, either with or without EC. After an initial 3 days of static culture, EC(+) and EC(-) constructs were each further divided into two subgroups, half of which received mechanical conditioning mimetic of late gestation (mean pressures of approximately 50 mmHg and peak-to-trough pressure differentials of approximately 20 mmHg at approximately 140-180 beats/min) and half of which were cultured statically. After 18 additional days of culture, the SMC-containing layer of each construct was harvested, and western blots and quantitative histology were conducted to compare collagen type I, collagen type III, and elastin levels among treatment groups. SMC differentiation was evaluated by focusing on SMC marker calponin h1 and direct regulators of its gene expression-the transcription factor serum response factor (SRF) and two of its binding partners, myocardin and Elk-1. Combined EC and pulsatile flow conditioning increased elastin production, but decreased collagen type I deposition. Further, combined EC presence and mechanical stimulation increased SRF levels and the ratio of myocardin to active, phosphorylated Elk-1. This modulation of SRF and its binding partners appeared to result in a net increase in SMC differentiation, as evidenced by an associated increase in calponin h1 levels.

Interstitial flow promotes vascular fibroblast, myofibroblast, and smooth muscle cell motility in 3-D collagen I via upregulation of MMP-1

Neointima formation often occurs in regions where the endothelium has been damaged and the transmural interstitial flow is elevated. Vascular smooth muscle cells (SMCs) and fibroblasts/myofibroblasts (FBs/MFBs) contribute to intimal thickening by migrating from the media and adventitia into the site of injury. In this study, for the first time, the direct effects of interstitial flow on SMC and FB/MFB migration were investigated in an in vitro three-dimensional system. Collagen I gels were used to mimic three-dimensional extracellular matrix (ECM) for rat aortic SMCs and FBs/MFBs. Exposure to interstitial flow induced by 1 cmH(2)O pressure differential (shear stress, approximately 0.05 dyn/cm(2); flow velocity, approximately 0.5 microm/s; and Darcy permeability, approximately 10(-11) cm(2)) substantially enhanced cell motility. Matrix metalloproteinase (MMP) inhibitor (GM-6001) abolished flow-induced migration augmentation, which suggested that the enhanced motility was MMP dependent. The upregulation of MMP-1 played a critical role for the flow-enhanced motility, which was further confirmed by silencing MMP-1 gene expression. Longer exposures to higher flows suppressed the number of migrated cells, although MMP-1 gene expression remained high. This suppression was a result of both flow-induced tissue inhibitor of metalloproteinase-1 upregulation and increased apoptotic and necrotic cell death. Interstitial flow did not affect MMP-2 gene expression or activity in the collagen I gel for any cell type. Our findings shed light on the mechanism by which vascular SMCs and FBs/MFBs contribute to intimal thickening in regions of vascular injury where interstitial flow is elevated.

Membrane type-1 matrix metalloproteinase is induced following cyclic compression of in vitro grown bovine chondrocytes

OBJECTIVE

To determine if membrane type-1 matrix metalloproteinase (MT1-MMP) will respond to cyclic compression of chondrocytes grown in vitro and the regulatory mechanisms underlying this response.

METHODS

Cyclic compression (30min, 1kPa, 1Hz) was applied to bovine chondrocytes (6-9-month-old animals) grown on top of a biodegradable substrate within 3 days of initiating culture. Luciferase assays using bovine articular chondrocytes were undertaken to demonstrate the mechanosensitivity of MT1-MMP. Semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) and western blot analysis were used to establish the time course of gene and protein upregulation in response to cyclic compression. The regulation of MT1-MMP was assessed by electrophoretic mobility shift assays, RT-PCR and western blot analysis. As well, an MT1-MMP decoy oligonucleotide and an extracellular signal-regulated kinase 1/2 (ERK1/2) pharmacological inhibitor were utilized to further characterize MT1-MMP regulation.

RESULTS

After cyclic compression, MT1-MMP showed a rapid and transient increase in gene expression. Elevated protein levels were detected within 2h of stimulation which returned to baseline by 6h. During cyclic compression, phosphorylation of the mitogen activated protein kinase ERK1/2 increased significantly. This was followed by increased gene and protein expression of the transcription factor; early growth factor-1 (Egr-1) and Egr-1 binding to the MT1-MMP promoter. Blocking Egr-1 DNA binding with a decoy MT1-MMP oligonucleotide, downregulated MT1-MMP gene expression. The ERK1/2 inhibitor U0126 also reduced Egr-1 DNA binding activity to MT1-MMP promoter sequences and subsequent transcription of MT1-MMP.

CONCLUSIONS

These data suggest that cyclic compression of chondrocytes in vitro upregulates MT1-MMP via ERK1/2 dependent activation of Egr-1 binding. Delineation of the regulatory pathways activated by mechanical stimulation will further our understating of the mechanisms influencing tissue remodeling.

Atherogenic Endothelial Cell eNOS and ET-1 Responses to Asynchronous Hemodynamics are Mitigated by Conjugated Linoleic Acid

Although local wall shear stress (WSS) induced by blood flow has been implicated in atherogenesis, another prominent and often neglected hemodynamic feature, circumferential strain (CS) driven by pressure, is induced concurrently. To investigate endothelial cell (EC) responses to pathologic hemodynamics and their possible manipulation by pharmaceuticals, we simulated complete hemodynamic conditions comprised of simultaneous WSS and CS during treatment with conjugated linoleic acid (CLA), a known PPAR (-alpha and -gamma) activator and anti-atherogenic agent, on cultured EC and examined effects on gene and metabolite expression. Two hemodynamic conditions representative of distinct regions of the circulation, coronary arteries: pro-atherogenic (asynchronous WSS and CS) and straight descending aorta: non-atherogenic (synchronous WSS and CS), were applied to cultured EC during treatment with the nutraceutical CLA. Competitive-quantitative RT-PCR showed that asynchronous hemodynamics significantly reduced ( approximately 2-fold) eNOS and PPAR-gamma mRNA levels compared to synchronous hemodynamics at 5 and 12 h. ET-1 showed an opposite trend at 12 h. CLA treatment mitigated pro-atherogenic eNOS, ET-1, PPAR-alpha and -gamma mRNA expression profiles and NO and ET-1 secretion patterns during asynchronous hemodynamics. This study demonstrates the potential for a pharmacological treatment (CLA) to normalize pro-atherogenic gene expression profiles induced by hemodynamics inherent to the circulation.

Effects of fluid shear stress on adventitial fibroblast migration: implications for flow-mediated mechanisms of arterialization and intimal hyperplasia

The involvement of vascular fibroblasts (FBs) and smooth muscle (SM)-like cells in physiological and pathological processes in large vessels (intimal hyperplasia) and microvessels (capillary arterialization), and the realization that these cells are exposed to interstitial flow shear stress (SS), motivate this study of SS on FB migratory activity. Rat adventitial FBs were grown to either 30-50% confluence (subconfluent FBs; SFBs) or full confluence (confluent FBs; CFBs) in culture. Immunofluorescence and Western blotting assays were conducted to evaluate the expression of two phenotype markers: SM alpha-actin and SM myosin heavy chain (MHC). Both assays indicated a significant increase in SM alpha-actin expression in CFBs compared with SFBs, suggesting a phenotype difference between the two cell populations. SFBs and CFBs both expressed minimal SM MHC. Both cell populations were seeded on Matrigel-coated cell culture inserts and exposed to 4 h of either 1 or 20 dyn/cm(2) SS via a rotating disk apparatus in the presence of the chemoattractant platelet-derived growth factor-BB to quantify the effect of SS on SFB and CFB migration. Four hours of 20 dyn/cm(2) SS significantly enhanced SFB migration while it suppressed CFB migratory activity. Four hours of 1 dyn/cm(2) SS did not significantly alter either SFB or CFB migration levels. Because of the distinct migratory responses of SFBs and CFBs in response to SS, phenotype modulation appears to be one way to regulate their involvement in both physiological and pathological remodeling processes.

Negative regulation of vascular smooth muscle cell migration by blood shear stress

Vortex blood flow with reduced blood shear stress in a vein graft has been hypothesized to promote smooth muscle cell (SMC) migration and intimal hyperplasia, pathological events leading to vein graft restenosis. To demonstrate that blood shear stress regulates these processes, we developed a modified vein graft model where the SMC response to reduced vortex blood flow was compared with that of control vein grafts. Vortex blood flow induced SMC migration and neointimal hyperplasia in control vein grafts, whereas reduction of vortex blood flow in the modified vein graft strongly suppressed these effects. A venous polymer implant with known fluid shear stress was employed to clarify the molecular mechanism of shear-dependent SMC migration in vivo. In the polymer implant, the phosphorylation of extracellular signal-regulated kinase (ERK1/2) and myosin light chain kinase (MLCK), found primarily in SMCs, increased from day 3 to day 5 and returned toward the control level from day 5 to day 10, with the peak phosphorylation associated with the maximal speed of SMC migration. Treatment with PD-98059 (an inhibitor specific to the ERK1/2 activator MEK1/2) significantly suppressed the phosphorylation of MLCK, suggesting a role for ERK1/2 in regulating the activity of MLCK. Treatment with PD-98059 or ML-7 (an inhibitor specific to MLCK) reduced shear stress-dependent SMC migration, resulting in an SMC distribution independent of fluid shear stress. These results suggest that fluid shear stress regulates SMC migration via the mediation of ERK1/2 and MLCK.

Mechanical stress-initiated signal transduction in vascular smooth muscle cells in vitro and in vivo

Increasing evidence has been demonstrated that hypertension-initiated abnormal biomechanical stress is strongly associated with cardio-/cerebrovascular diseases e.g. atherosclerosis, stroke, and heart failure, which is main cause of morbidity and mortality. How the cells in the cardiovascular system sense and transduce the extracellular physical stimuli into intracellular biochemical signals is a crucial issue for understanding the mechanisms of the disease development. Recently, collecting data derived from our and other laboratories showed that many kinds of molecules in the cells such as receptors, ion channels, caveolin, G proteins, cell cytoskeleton, kinases and transcriptional factors could serve as mechanoceptors directly or indirectly in response to mechanical stimulation implying that the activation of mechanoceptors represents a non-specific manner. The sensed signals can be further sorted and/or modulated by processing of the molecules both on the cell surface and by the network of intracellular signaling pathways resulting in a sophisticated and dynamic set of cues that enable cardiovascular cell responses. The present review will summarise the data on mechanotransduction in vascular smooth muscle cells and formulate a new hypothesis, i.e. a non-specific activation of mechanoceptors followed by a variety of signal cascade activation. The hypothesis could provide us some clues for exploring new therapeutic targets for the disturbed mechanical stress-initiated diseases such as hypertension and atherosclerosis.

Smooth muscle cells in human atherosclerotic plaques secrete and proliferate in response to high mobility group box 1 protein

High mobility group box 1 protein (HMGB1) is a chromatin component leaked out by necrotic cells and actively secreted by activated myeloid cells. The extracellular protein is a potent mediator of tissue remodeling. We show here that human atherosclerotic plaques, but not normal arteries, produce extracellular HMGB1. Secreted HMGB1 originates from endothelial cells, by neointimal foam cells, and also smooth muscle cells (SMCs). SMCs are an unexpected source for secreted HMGB1, since they normally express much lower amounts of HMGB1 than other cells types, and they do not secrete it. However, cultured SMCs actively secrete HMGB1 after cholesterol loading. In turn, in response to HMGB1, SMCs proliferate, migrate, and secrete more HMGB1. Thus, SMCs are both a source and a target of HMGB1; blocking HMGB1 secretion by SMCs can be an important strategy for treatment of atherosclerotic disease and in particular restenosis.

Large Negative Stress Phase Angle (SPA) attenuates nitric oxide production in bovine aortic endothelial cells

Hemodynamics plays an important role in cardiovascular physiology and pathology. Pulsatile flow (Q), pressure (P), and diameter (D) waveforms exert wall shear stress (WSS), normal stress, and circumferential strain (CS) on blood vessels. Most in vitro studies to date have focused on either WSS or CS but not their interaction. Recently, we have shown that concomitant WSS and CS affect EC biochemical response modulated by the temporal phase angle between WSS and CS (stress phase angle, SPA). Large negative SPA has been shown to occur in regions of the circulation where atherosclerosis and intimal hyperplasia are prevalent. Here, we report that nitric oxide (NO) biochemical secretion was significantly decreased in response to a large negative SPA of -180 deg with respect to an SPA of 0 degrees in bovine aortic endothelial cells (BAEC) at 5 h. A new hemodynamic simulator for the study of the physiologic SPA was used to provide the hemodynamic conditions of pro-atherogenic (SPA = -180 deg) and normopathic (SPA = 0 deg) states. The role of complex hemodynamics in vascular remodeling, homeostasis, and pathogenesis can be advanced by further assessment of the hypothesis that a large negative SPA is pro-atherogenic.

High-Flow-Induced Arterial Remodeling in Rats with Different Susceptibilities to Cerebral Aneurysms

BACKGROUND

The higher incidence of cerebral aneurysms (CAs) induced by enhanced arterial blood flow in Long Evans (LE) compared to Brown Norway (BN) rats suggests that intrinsic differences in high-flow arterial remodeling may be involved in determining CA susceptibility. Some aspects of this remodeling were compared in LE and BN rats after creation of an abdominal aortocaval fistula (ACF).

METHODS AND RESULTS

At 4 days with ACF, aortic luminal cross-sectional area (LCSA) determined by morphometry was increased by 20% in LE but not in BN rats. mRNA levels, determined by RT-PCR, were higher in LE than in BN rats for collagen alpha1(I), collagen alpha1(III), MMP2 and its inhibitor TIMP1 at 19 days with ACF. Nitric oxide synthase (NOS) mRNA levels were higher in LE rats at 4 days for the inducible (NOS2) isoform and at 4 and 19 days for the neuronal (NOS1) isoform. Aortic LCSA and NOS1 mRNA levels were tightly correlated and NOS inhibition prevented ACF-induced aortic remodeling in the LE rat. MMP2 and MMP7 activity, evaluated by zymography at 4 days with ACF, did not greatly differ between BN and LE.

CONCLUSIONS

These data suggest that a higher intrinsic ability for high-flow-induced arterial enlargement associated with NOS gene overexpression may be a possible genetic determinant in CA susceptibility.