Pulsatile Shear Stress Research Articles

Exercise mitigates flow recirculation and activates metabolic transducer SCD1 to catalyze vascular protective metabolites.

Exercise promotes pulsatile shear stress in the arterial circulation and ameliorates cardiometabolic diseases. However, exercise-mediated metabolic transducers for vascular protection remain under-investigated. Untargeted metabolomic analysis demonstrated that wild-type mice undergoing voluntary wheel running exercise expressed increased endothelial stearoyl-CoA desaturase 1 (SCD1) that catalyzes anti-inflammatory lipid metabolites, namely, oleic (OA) and palmitoleic acids (PA), to mitigate NF-κB-mediated inflammatory responses. In silico analysis revealed that exercise augmented time-averaged wall shear stress but mitigated flow recirculation and oscillatory shear index in the lesser curvature of the mouse aortic arch. Following exercise, endothelial Scd1-deleted mice (Ldlr-/- Scd1EC-/-) on high-fat diet developed persistent VCAM1-positive endothelium in the lesser curvature and the descending aorta, whereas SCD1 overexpression via adenovirus transfection mitigated endoplasmic reticulum stress and inflammatory biomarkers. Single-cell transcriptomics of the aorta identified Scd1-positive and Vcam1-negative endothelial subclusters interacting with other candidate genes. Thus, exercise mitigates flow recirculation and activates endothelial SCD1 to catalyze OA and PA for vascular endothelial protection.

Enhanced External Counterpulsation for Management of Postacute Sequelae of SARS-CoV-2 Associated Microvascular Angina and Fatigue: An Interventional Pilot Study.

Postacute sequelae of SARS-CoV-2 infection (PASC) are a novel clinical syndrome characterized in part by endothelial dysfunction. Enhanced external counterpulsation (EECP) produces pulsatile shear stress, which has been associated with improvements in systemic endothelial function. To explore the effects of EECP on symptom burden, physical capacity, mental health, and health-related quality of life (HRQoL) in patients with PASC-associated angina and microvascular dysfunction (MVD). An interventional pilot study was performed, including 10 patients (male = 5, mean age 50.3 years) recruited from a tertiary specialized PASC clinic. Patients with angina and MVD, defined as index of microcirculatory resistance (IMR) ≥25 and/or diagnosed through stress perfusion cardiac magnetic resonance imaging, were included. Patients underwent one modified EECP course (15 one-hour sessions over five weeks). Symptom burden, six-minute walk test, and validated generic self-reported instruments for measuring psychological distress and HRQoL were assessed before and one month after treatment. At baseline, most commonly reported PASC symptoms were angina (100%), fatigue (80%), and dyspnea (80%). Other symptoms included palpitations (50%), concentration impairment (50%), muscle pain (30%), and brain fog (30%). Mean IMR was 63.6. After EECP, 6MWD increased (mean 29.5 m, median 21 m) and angina and fatigue improved. Mean depression scores showed reduced symptoms (-0.8). Mean HRQoL scores improved in seven out of eight subscales (+0.2 to 10.5). Patients with PASC-associated angina and evidence of MVD experienced subjective and objective benefits from EECP. The treatment was well-tolerated. These findings warrant controlled studies in a larger cohort.

Platelet and endothelial cell responses under concurrent shear stress and tensile strain

Thrombosis can lead to significant mortality and morbidity. Both platelets and vascular endothelial cells play significant roles in thrombosis. Platelets' response to blood flow-induced shear stress can vary greatly depending on shear stress magnitude, pattern and shear exposure time. Endothelial cells are also sensitive to the biomechanical environment. Endothelial cell activation and dysfunction can occur under low oscillatory shear stress and low tensile strain. Platelet and endothelial cell interaction can also be affected by mechanical conditions. The goal of this study was to investigate how blood flow-induced shear stress, vascular wall tensile strain, platelet-endothelial cell stress history, and platelet-endothelial cell interaction affect platelet thrombogenicity. Platelets and human coronary artery endothelial cells were pretreated with physiological and pathological shear stress and/or tensile strain separately. The pretreated cells were then put together and exposed to pulsatile shear stress and cyclic tensile strain simultaneously in a shearing-stretching device. Following treatment, platelet thrombin generation rate, platelet and endothelial cell activation, and platelet adhesion to endothelial cells was measured. The results demonstrated that shear stress pretreatment of endothelial cells and platelets caused a significant increase in platelet thrombin generation rate, cell surface phosphatidylserine expression, and adhesion to endothelial cells. Shear stress pretreatment of platelets and endothelial cells attenuated endothelial cell ICAM-1 expression under stenosis conditions, as well as vWF expression under recirculation conditions. These results indicate that platelets are sensitized by prior shearing, while in comparison, the interaction with shear stress-pretreated platelets may reduce endothelial cell sensitivity to pathological shear stress and tensile strain.

Enhancing Muscle Intracellular Ca2+ Homeostasis and Glucose Uptake: Passive Pulsatile Shear Stress Treatment in Type 2 Diabetes.

Type 2 diabetes mellitus (T2D) is a significant global public health problem that has seen a substantial increase in the number of affected individuals in recent decades. In a murine model of T2D (db/db), we found several abnormalities, including aberrant intracellular calcium concentration ([Ca2+]i), decreased glucose transport, increased production of reactive oxygen species (ROS), elevated levels of pro-inflammatory interleukins and creatine phosphokinase (CK), and muscle weakness. Previously, we demonstrated that passive pulsatile shear stress, generated by sinusoidal (headward-forward) motion, using a motion platform that provides periodic acceleration of the whole body in the Z plane (pGz), induces the synthesis of nitric oxide (NO) mediated by constitutive nitric oxide synthase (eNOS and nNOS). We investigated the effect of pGz on db/db a rodent model of T2D. The treatment of db/db mice with pGz resulted in several beneficial effects. It reduced [Ca2+]i overload; enhanced muscle glucose transport; and decreased ROS levels, interleukins, and CK. Furthermore, pGz treatment increased the expression of endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS), and neuronal nitric oxide synthase (nNOS); reduced inducible nitric oxide synthase (iNOS); and improved muscle strength. The cytoprotective effects of pGz appear to be mediated by NO, since pretreatment with L-NAME, a nonspecific NOS inhibitor, abolished the effects of pGz on [Ca2+]i and ROS production. Our findings suggest that a non-pharmacological strategy such as pGz has therapeutic potential as an adjunct treatment to T2D.

Non-Invasive Pulsatile Shear Stress Modifies Endothelial Activation; A Narrative Review.

The monolayer of cells that line both the heart and the entire vasculature is the endothelial cell (EC). These cells respond to external and internal signals, producing a wide array of primary or secondary messengers involved in coagulation, vascular tone, inflammation, and cell-to-cell signaling. Endothelial cell activation is the process by which EC changes from a quiescent cell phenotype, which maintains cellular integrity, antithrombotic, and anti-inflammatory properties, to a phenotype that is prothrombotic, pro-inflammatory, and permeable, in addition to repair and leukocyte trafficking at the site of injury or infection. Pathological activation of EC leads to increased vascular permeability, thrombosis, and an uncontrolled inflammatory response that leads to endothelial dysfunction. This pathological activation can be observed during ischemia reperfusion injury (IRI) and sepsis. Shear stress (SS) and pulsatile shear stress (PSS) are produced by mechanical frictional forces of blood flow and contraction of the heart, respectively, and are well-known mechanical signals that affect EC function, morphology, and gene expression. PSS promotes EC homeostasis and cardiovascular health. The archetype of inducing PSS is exercise (i.e., jogging, which introduces pulsations to the body as a function of the foot striking the pavement), or mechanical devices which induce external pulsations to the body (Enhanced External Pulsation (EECP), Whole-body vibration (WBV), and Whole-body periodic acceleration (WBPA aka pGz)). The purpose of this narrative review is to focus on the aforementioned noninvasive methods to increase PSS, review how each of these modify specific diseases that have been shown to induce endothelial activation and microcirculatory dysfunction (Ischemia reperfusion injury-myocardial infarction and cardiac arrest and resuscitation), sepsis, and lipopolysaccharide-induced sepsis syndrome (LPS)), and review current evidence and insight into how each may modify endothelial activation and how these may be beneficial in the acute and chronic setting of endothelial activation and microvascular dysfunction.

Abstract P3008: Endothelial Stearoyl-CoA Desaturase-1 Catalyzes Fatty Acid Metabolites To Mitigate Arterial Inflammation And Stiffness

Introduction: Vascular metabolic plasticity is intimately linked with endothelial homeostasis. Stearoyl-CoA desaturase-1 (SCD1), the enzyme that catalyzes the saturated long-chain fatty acids (FA) into monounsaturated FA (MUFA), is responsive to pulsatile shear stress (PSS), and is associated with cancer cell metabolism. We assessed whether exercise-mediated PSS activates PPARγ-SCD1 to mediate anti-inflammatory metabolites for vascular protection. Methods and Results: Human aortic endothelial cells (HAEC) were subjected to PSS (τ avg = 23±8 dyne/cm 2 at 1 Hz) for 4 hours, followed by metabolomic analysis. SCD1-mediated fatty acid metabolites, azelaic acid (AZA) and oleic acid (OA), were identified to mitigate NFκB luciferase activity and monocyte binding ( p < 0.05, n= 5, vs. static condition). PSS upregulated PPARγ and SCD1 mRNA expression, whereas knockdown of PPARγ using siRNA downregulated SCD1. Wild type mice (C57BL/6J) undergoing 2-wk voluntary exercise developed increased perinuclear SCD1 expression in the aortic endothelium ( p < 0.05, n=6, vs. sedentary controls), whereas SCD1 expression was reduced in PPARγ -dominant negative mice following exercise. LDLR -/- mice with endothelial-specific SCD1 deletion (SCD1 EC-KO : Cdh5 Cre , Scd1 f/f ) on 4-wk high-fat diet (HFD) developed significantly increased VCAM-1 and Oil Red O positive lesions in the aortic arch, whereas exercise or selective overexpression (OE) of SCD1 in endothelial cells by pAd5/F35/CD144 adenoviral vector mitigated the lesions ( p < 0.05, n=5, HFD + exercise or HFD+Ad-SCD1 vs. HFD). Arterial stiffness as measured by Pulse Wave Velocity of the left common carotid was elevated in LDLR -/- SCD1 EC-KO on HF diet, but was decreased with exercise or SCD1 OE. Conclusion: PPARγ-SCD1 signaling is flow-responsive to mitigate arterial inflammation and stiffness. Despite SCD1-associated cancer cell metabolism, endothelial-specific SCD1 confers vascular protection, consistent with the reported skeletal muscle-specific model. Thus, we demonstrate that exercise activates PPARγ-SCD1 and SCD1 catalyzes AZA and OA as biomarkers with therapeutic potential.

Peripheral blood derived endothelial colony forming cells as suitable cell source for pre-endothelialization of arterial vascular grafts under dynamic flow conditions

In regenerative medicine, autologous peripheral blood derived endothelial colony forming cells (PB-derived ECFC) represent a promising source of endothelial cells (EC) for pre-endothelialization of arterial tissue engineered vascular grafts (TEVG) since they are readily attainable, can easily be isolated and possess a high proliferation potential. The aim of this study was to compare the phenotype of PB-derived ECFC with arterial and venous model cells such as human aortic endothelial cells (HAEC) and human umbilical vein endothelial cells (HUVEC) under dynamic cell culture conditions to find a suitable cell source of EC for pre-endothelialization. In this study PB-derived ECFC were cultivated over 24 h under a high pulsatile shear stress (20 dyn/cm2, 1 Hz) and subsequently analyzed. ECFC oriented and elongated in the direction of flow and expressed similar anti-thrombotic and endothelial differentiation markers compared to HAEC. There were significant differences observable in gene expression levels of CD31, CD34 and NOTCH4 between ECFC and HUVEC. These results therefore suggest an arterial phenotype for PB-derived ECFC both under static and flow conditions, and this was supported by NOTCH4 protein expression profiles. ECFC also significantly up-regulated gene expression levels of anti-thrombotic genes such as krueppel-like factor 2, endothelial nitric oxide synthase 3 and thrombomodulin under shear stress cultivation as compared to static conditions. Dynamically cultured PB-derived ECFC therefore may be a promising cell source for pre-endothelialization of arterial TEVGs.

Shear stress regulates the SNAP23-mediated endothelial secretion of VWF through the GPR68/PKA/vimentin mechanotransduction pathway

Von Willebrand Factor (VWF) can promote platelet adhesion to the post-atherosclerotic regions to initiate thrombosis. The synthesis and secretion of VWF are important functions of endothelial cells (ECs). However, the mechanism through which blood flow regulates endothelial secretion of VWF remains unclear. We utilized a parallel-plate flow apparatus to apply fluid shear stress to human umbilical vein endothelial cells (HUVECs). Compared with pulsatile shear stress that mimics laminar flow in the straight parts of arteries or upstream of atherosclerotic stenosis sites, short-term exposure to oscillatory shear stress (OS) that mimics disturbed flow increased VWF secretion independent of affecting synaptosomal-associated protein 23 (SNAP23) expression and promoted the translocation of SNAP23 to the cell membrane. Vimentin associated with SNAP23, and this association was enhanced by OS or histamine. Acrylamide, a reagent that disrupts vimentin intermediate filaments, prevented histamine/OS-induced SNAP23 translocation, as well as VWF secretion. Immunofluorescence analysis revealed that the polarity of the vimentin intermediate filament network decreased after stimulation with histamine or OS. In addition, inhibition of protein kinase A (PKA) or G protein coupled receptor 68 (GPR68) eliminated the histamine/OS-induced phosphorylation of vimentin at Ser38 and secretion of VWF. Furthermore, syntaxin 7 might assist with the translocation of SNAP23 to the cell membrane, thus playing a role in promoting VWF secretion. The GPR68/PKA/vimentin signaling pathway may represent a novel mechanism for the regulation of SNAP23-mediated VWF secretion by ECs under OS and provide strategies for the prevention of atherosclerosis-related thrombosis.

Volumetric lattice Boltzmann method for wall stresses of image-based pulsatile flows

Image-based computational fluid dynamics (CFD) has become a new capability for determining wall stresses of pulsatile flows. However, a computational platform that directly connects image information to pulsatile wall stresses is lacking. Prevailing methods rely on manual crafting of a hodgepodge of multidisciplinary software packages, which is usually laborious and error-prone. We present a new computational platform, to compute wall stresses in image-based pulsatile flows using the volumetric lattice Boltzmann method (VLBM). The novelty includes: (1) a unique image processing to extract flow domain and local wall normality, (2) a seamless connection between image extraction and VLBM, (3) an en-route calculation of strain-rate tensor, and (4) GPU acceleration (not included here). We first generalize the streaming operation in the VLBM and then conduct application studies to demonstrate its reliability and applicability. A benchmark study is for laminar and turbulent pulsatile flows in an image-based pipe (Reynolds number: 10 to 5000). The computed pulsatile velocity and shear stress are in good agreements with Womersley's analytical solutions for laminar pulsatile flows and concurrent laboratory measurements for turbulent pulsatile flows. An application study is to quantify the pulsatile hemodynamics in image-based human vertebral and carotid arteries including velocity vector, pressure, and wall-shear stress. The computed velocity vector fields are in reasonably well agreement with MRA (magnetic resonance angiography) measured ones. This computational platform is good for image-based CFD with medical applications and pore-scale porous media flows in various natural and engineering systems.

Endothelial Cell Activation Mediates Platelet Response to Pulsatile Shear Stress

Thrombin plays critical roles in both hemostasis and thrombosis. Many studies were carried out to examine the effects of different thrombogenic surfaces on thrombin generation. In the present study, how activated endothelial cells affected platelet thrombin generation under dynamic shear stress was investigated. Human platelets were exposed to pulsatile shear stress (physiological, low or elevated) in a cone-and-plate shearing device for 30 minutes in the presence of quiescent or activated human coronary artery endothelial cells. Coagulation factors including Factor II, Factor Xa and calcium were immediately available.

Endothelial Yin Yang 1 Phosphorylation at S118 Induces Atherosclerosis Under Flow.

Disturbed flow occurring in arterial branches and curvatures induces vascular endothelial cell (EC) dysfunction and atherosclerosis. We postulated that disturbed flow plays important role in modulating phosphoprotein expression profiles to regulate endothelial functions and atherogenesis. The goal of this study is to discover novel site-specific phosphorylation alterations induced by disturbed flow in ECs to contribute to atherosclerosis. Quantitative phosphoproteomics analysis of ECs exposed to disturbed flow with low and oscillatory shear stress (0.5±4 dynes/cm2) versus pulsatile shear stress (12±4 dynes/cm2) revealed that oscillatory shear stress induces phospho-YY1S118 (serine [S]118 phosphorylation of Yin Yang 1) in ECs. Elevated phospho-YY1S118 level in ECs was further confirmed to be present in the disturbed flow regions in experimental animals and human atherosclerotic arteries. This disturbed flow-induced EC phospho-YY1S118 is mediated by CK2α (casein kinase 2α) through its direct interaction with YY1. Yeast 2-hybrid library screening and in situ proximity ligation assays demonstrate that phospho-YY1S118 directly binds ZKSCAN4 (zinc finger with KRAB [krüppel-associated box] and SCAN [SRE-ZBP, CTfin51, AW-1 and Number 18 cDNA] domains 4) to induce promoter activity and gene expression of HDM2 (human double minute 2), which consequently induces EC proliferation through downregulation of p53 and p21CIP1. Administration of apoE-deficient (ApoE-/-) mice with CK2-specific inhibitor tetrabromocinnamic acid or atorvastatin inhibits atherosclerosis formation through downregulations of EC phospho-YY1S118 and HDM2. Generation of novel transgenic mice bearing EC-specific overexpression of S118-nonphosphorylatable mutant of YY1 in ApoE-/- mice confirms the critical role of phospho-YY1S118 in promoting atherosclerosis through EC HDM2. Our findings provide new insights into the mechanisms by which disturbed flow induces endothelial phospho-YY1S118 to promote atherosclerosis, thus indicating phospho-YY1S118 as a potential molecular target for atherosclerosis treatment.

In Vitro Flow Chamber Design for the Study of Endothelial Cell (Patho)Physiology.

In the native vasculature, flowing blood produces a frictional force on vessel walls that affects endothelial cell function and phenotype. In the arterial system, the vasculature's local geometry directly influences variations in flow profiles and shear stress magnitudes. Straight arterial sections with pulsatile shear stress have been shown to promote an athero-protective endothelial phenotype. Conversely, areas with more complex geometry, such as arterial bifurcations and branch points with disturbed flow patterns and lower, oscillatory shear stress, typically lead to endothelial dysfunction and the pathogenesis of cardiovascular diseases. Many studies have investigated the regulation of endothelial responses to various shear stress environments. Importantly, the accurate in vitro simulation of in vivo hemodynamics is critical to the deeper understanding of mechanotransduction through the proper design and use of flow chamber devices. In this review, we describe several flow chamber apparatuses and their fluid mechanics design parameters, including parallel-plate flow chambers, cone-and-plate devices, and microfluidic devices. In addition, chamber-specific design criteria and relevant equations are defined in detail for the accurate simulation of shear stress environments to study endothelial cell responses.

Pulsatility protects the endothelial glycocalyx during extracorporeal membrane oxygenation.

Pulsatile flow protects vital organ function and improves microcirculatory perfusion during extracorporeal membrane oxygenation (ECMO). Studies revealed that pulsatile shear stress plays a vital role in microcirculatory function and integrity. The objective of this study was to investigate how pulsatility affects wall shear stress and endothelial glycocalyx components during ECMO. Using the i-Cor system, sixteen canine ECMO models were randomly allocated into the pulsatile or the non-pulsatile group (eight canines for each). Hemodynamic parameters, peak wall shear stress (PWSS), serum concentration of syndecan-1, and heparan sulfate were measured at different time points during ECMO. Pulsatile shear stress experiments were also performed in endothelial cells exposed to different magnitudes of pulsatility (five plates for each condition), with cell viability, the expressions of syndecan-1, and endothelial-to-mesenchymal transformation (EndMT) markers analyzed. The pulsatile flow generated more surplus hemodynamic energy and preserved higher PWSS during ECMO. Serum concentrations of both syndecan-1 and heparan sulfate were negatively correlated with PWSS, and significantly lower levels were observed in the pulsatile group. Besides, non-pulsatility triggered EndMT and endothelial cells exposed to low pulsatility had the lowest possibility of EndMT. The maintenance of the PWSS by pulsatility during ECMO possesses beneficial effects on glycocalyx integrity. Moreover, pulsatility prevents EndMT in endothelial cells, and low pulsatility exhibits the best protective effects. The augmentation of pulsatility may be a plausible future direction to improve the clinical outcome in ECMO.

Roles of KLF4 and AMPK in the inhibition of glycolysis by pulsatile shear stress in endothelial cells

Vascular endothelial cells (ECs) sense and respond to hemodynamic forces such as pulsatile shear stress (PS) and oscillatory shear stress (OS). Among the metabolic pathways, glycolysis is differentially regulated by atheroprone OS and atheroprotective PS. Studying the molecular mechanisms by which PS suppresses glycolytic flux at the epigenetic, transcriptomic, and kinomic levels, we have demonstrated that glucokinase regulatory protein (GCKR) was markedly induced by PS in vitro and in vivo, although PS down-regulates other glycolysis enzymes such as hexokinase (HK1). Using next-generation sequencing data, we identified the binding of PS-induced Krüppel-like factor 4 (KLF4), which functions as a pioneer transcription factor, binding to the GCKR promoter to change the chromatin structure for transactivation of GCKR. At the posttranslational level, PS-activated AMP-activated protein kinase (AMPK) phosphorylates GCKR at Ser-481, thereby enhancing the interaction between GCKR and HK1 in ECs. In vivo, the level of phosphorylated GCKR Ser-481 and the interaction between GCKR and HK1 were increased in the thoracic aorta of wild-type AMPKα2+/+ mice in comparison with littermates with EC ablation of AMPKα2 (AMPKα2-/-). In addition, the level of GCKR was elevated in the aortas of mice with a high level of voluntary wheel running. The underlying mechanisms for the PS induction of GCKR involve regulation at the epigenetic level by KLF4 and at the posttranslational level by AMPK.

Cardioprotective Effect of Whole Body Periodic Acceleration in Dystrophic Phenotype mdx Rodent.

Duchenne muscular dystrophy (DMD) is characterized by progressive muscle wasting and the development of a dilated cardiomyopathy (DCM), which is the leading cause of death in DMD patients. Despite knowing the cause of DMD, there are currently no therapies which can prevent or reverse its inevitable progression. We have used whole body periodic acceleration (WBPA) as a novel tool to enhance intracellular constitutive nitric oxide (NO) production. WBPA adds small pulses to the circulation to increase pulsatile shear stress, thereby upregulating endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) and subsequently elevating the production of NO. Myocardial cells from dystrophin-deficient 15-month old mdx mice have contractile deficiency, which is associated with elevated concentrations of diastolic Ca2+ ([Ca2+]d), Na+ ([Na+]d), and reactive oxygen species (ROS), increased cell injury, and decreased cell viability. Treating 12-month old mdx mice with WBPA for 3 months reduced cardiomyocyte [Ca2+]d and [Na+]d overload, decreased ROS production, and upregulated expression of the protein utrophin resulting in increased cell viability, reduced cardiomyocyte damage, and improved contractile function compared to untreated mdx mice.

MiR-137 regulates low-intensity shear stress-induced human aortic endothelial cell apoptosis via JNK/AP-1 signaling.

The objective of this study is to evaluate the role of miR-137 in low-intensity shear stress-induced endoplasmic reticulum (ER) stress and cell apoptosis in human aortic endothelial cells (HAECs). HAECs were transfected with miR-137 mimic, miR-137 inhibitor, or the corresponding negative control and then exposed to pulsatile shear stress in a parallel-plate flow chamber at 1, 2, 5, 10, and 15 dyn/cm2 for 3 h. Real-time polymerase chain reaction was used to detect mRNA expression of miR-137 and SDS22. A dual-luciferase reporter assay was employed to verify the direct interaction between miR-137 and SDS22. The internal morphology of cells and cell apoptosis was assessed by TUNEL staining observed under a transmission electron microscope. Meanwhile, the protein expression of oxidative stress-related, apoptosis-related, and activated c-Jun N-terminal kinase (JNK)/activator protein-1 (AP-1) signaling-related genes were analyzed by western blotting. Low strength shear stress (0-5 dyn/cm2) caused a negative change of HAEC surface and internal morphology in an intensity-dependent manner, and these changes were gradually weakened when shear stress was increased more than 5 dyn/cm2. Furthermore, low-intensity shear stress promoted oxidative stress response, accelerated cell apoptosis, and upregulated miR-137 expression and JNK/AP-1 signaling in HAECs. MiR-137 directly targets SDS22. Knockdown of miR-137 noticeably reduced activation of JNK/AP-1 signaling, oxidative stress response, and cell apoptosis induced by shear stress. MiR-137 regulated low-intensity shear stress-induced human aortic endothelial cell ER stress and cell apoptosis via JNK/AP-1 signaling.

Mechanoresponsive Smad5 Enhances MiR-487a Processing to Promote Vascular Endothelial Proliferation in Response to Disturbed Flow.

MicroRNAs (miRs) and bone morphogenetic protein receptor–specific Smads are mechano-responsive molecules that play vital roles in modulating endothelial cell (EC) functions in response to blood flow. However, the roles of interplay between these molecules in modulating EC functions under flows remain unclear. We elucidated the regulatory roles of the interplay between miR-487a and Smad5 in EC proliferation in response to different flow patterns. Microarray and quantitative RT-PCR showed that disturbed flow with low and oscillatory shear stress (OS, 0.5 ± 4 dynes/cm2) upregulates EC miR-487a in comparison to static controls and pulsatile shear stress (12 ± 4 dynes/cm2). MiR-487a expression was higher in ECs in the inner curvature (OS region) than the outer curvature of the rat aortic arch and thoracic aorta and also elevated in diseased human coronary arteries. MiR-487a expression was promoted by nuclear phospho-Smad5, which bound to primary-miR-487a to facilitate miR-487a processing. Algorithm prediction and luciferase reporter and argonaute 2-immunoprecipitation assays demonstrated that miR-487a binds to 3′UTR of CREB binding protein (CBP) and p53. Knockdown and overexpression of miR-487a decreased and increased, respectively, phospho-Rb and cyclin A expressions through CBP and p53. A BrdU incorporation assay showed that miR-487a enhanced EC proliferation under OS in vitro and in disturbed flow regions of experimentally stenosed rat abdominal aorta in vivo. These results demonstrate that disturbed flow with OS induces EC expression of miR-487a through its enhanced processing by activated-Smad5. MiR-487 inhibits its direct targets CBP and p53 to induce EC cycle progression and proliferation. Our findings suggest that EC miR-487 may serve as an important molecular target for intervention against disturbed flow–associated vascular disorders resulting from atherosclerosis.

The Endothelium as a Therapeutic Target in Diabetes: A Narrative Review and Perspective.

Diabetes has reached worldwide epidemic proportions, and threatens to be a significant economic burden to both patients and healthcare systems, and an important driver of cardiovascular mortality and morbidity. Improvement in lifestyle interventions (which includes increase in physical activity via exercise) can reduce diabetes and cardiovascular disease mortality and morbidity. Encouraging a population to increase physical activity and exercise is not a simple feat particularly in individuals with co-morbidities (obesity, heart disease, stroke, peripheral vascular disease, and those with cognitive and physical limitations). Translation of the physiological benefits of exercise within that vulnerable population would be an important step for improving physical activity goals and a stopgap measure to exercise. In large part many of the beneficial effects of exercise are due to the introduction of pulsatile shear stress (PSS) to the vascular endothelium. PSS is a well-known stimulus for endothelial homeostasis, and induction of a myriad of pathways which include vasoreactivity, paracrine/endocrine function, fibrinolysis, inflammation, barrier function, and vessel growth and formation. The endothelial cell mediates the balance between vasoconstriction and relaxation via the major vasodilator endothelial derived nitric oxide (eNO). eNO is critical for vasorelaxation, increasing blood flow, and an important signaling molecule that downregulates the inflammatory cascade. A salient feature of diabetes, is endothelial dysfunction which is characterized by a reduction of the bioavailability of vasodilators, particularly nitric oxide (NO). Cellular derangements in diabetes are also related to dysregulation in Ca2+ handling with increased intracellular Ca2+overload, and oxidative stress. PSS increases eNO bioavailability, reduces inflammatory phenotype, decreases intracellular Ca2+ overload, and increases antioxidant capacity. This narrative review and perspective will outline four methods to non-invasively increase PSS; Exercise (the prototype for increasing PSS), Enhanced External Counterpulsation (EECP), Whole Body Vibration (WBV), Passive Simulated Jogging and its predicate device Whole Body Periodic Acceleration, and will discuss current knowledge on their use in diabetes.

Platelet Dysfunction During Mechanical Circulatory Support: Elevated Shear Stress Promotes Downregulation of αIIbβ3 and GPIb via Microparticle Shedding Decreasing Platelet Aggregability.

[Figure: see text].

The ocular pulse decreases aqueous humor outflow resistance by stimulating nitric oxide production.

Intraocular pressure (IOP) is not static, but rather oscillates by 2-3 mmHg because of cardiac pulsations in ocular blood volume known as the ocular pulse. The ocular pulse induces pulsatile shear stress in Schlemm's canal (SC). We hypothesize that the ocular pulse modulates outflow facility by stimulating shear-induced nitric oxide (NO) production by SC cells. We confirmed that living mice exhibit an ocular pulse with a peak-to-peak (pk-pk) amplitude of 0.5 mmHg under anesthesia. Using iPerfusion, we measured outflow facility (flow/pressure) during alternating periods of steady or pulsatile IOP in both eyes of 16 cadaveric C57BL/6J mice (13-14 weeks). Eyes were retained in situ, with an applied mean pressure of 8 mmHg and 1.0 mmHg pk-pk pressure amplitude at 10 Hz to mimic the murine heart rate. One eye of each cadaver was perfused with 100 µM L-NAME to inhibit NO synthase, whereas the contralateral eye was perfused with vehicle. During the pulsatile period in the vehicle-treated eye, outflow facility increased by 16 [12, 20] % (P < 0.001) relative to the facility measured during the preceding and subsequent steady periods. This effect was partly inhibited by L-NAME, where pressure pulsations increased outflow facility by 8% [4, 12] (P < 0.001). Thus, the ocular pulse causes an immediate increase in outflow facility in mice, with roughly one-half of the facility increase attributable to NO production. These studies reveal a dynamic component to outflow function that responds instantly to the ocular pulse and may be important for outflow regulation and IOP homeostasis.