Molecular basis of the effects of mechanical stretch on vascular smooth muscle cells

Hemodynamics regulate spatiotemporal artery muscularization in the developing circle of Willis

Vascular smooth muscle cells (VSMCs) envelop vertebrate brain arteries and play a crucial role in regulating cerebral blood flow and neurovascular coupling. The dedifferentiation of VSMCs is implicated in cerebrovascular disease and neurodegeneration. Despite its importance, the process of VSMC differentiation on brain arteries during development remains inadequately characterized. Understanding this process could aid in reprogramming and regenerating dedifferentiated VSMCs in cerebrovascular diseases. In this study, we investigated VSMC differentiation on zebrafish circle of Willis (CoW), comprising major arteries that supply blood to the vertebrate brain. We observed that arterial specification of CoW endothelial cells (ECs) occurs after their migration from cranial venous plexus to form CoW arteries. Subsequently, acta2+ VSMCs differentiate from pdgfrb+ mural cell progenitors after they were recruited to CoW arteries. The progression of VSMC differentiation exhibits a spatiotemporal pattern, advancing from anterior to posterior CoW arteries. Analysis of blood flow suggests that earlier VSMC differentiation in anterior CoW arteries correlates with higher red blood cell velocity and wall shear stress. Furthermore, pulsatile flow induces differentiation of human brain PDGFRB+ mural cells into VSMCs, and blood flow is required for VSMC differentiation on zebrafish CoW arteries. Consistently, flow-responsive transcription factor klf2a is activated in ECs of CoW arteries prior to VSMC differentiation, and klf2a knockdown delays VSMC differentiation on anterior CoW arteries. In summary, our findings highlight blood flow activation of endothelial klf2a as a mechanism regulating initial VSMC differentiation on vertebrate brain arteries.

Impact of Cyclic Strain on Elastin Synthesis in a 3D Human Myometrial Culture Model

The synthesis and assembly of mature, organized elastic fibers remains a limitation to the clinical use of many engineered tissue replacements. There is a critical need for a more in-depth understanding of elastogenesis regulation for the advancement of methods to induce and guide production of elastic matrix structures in engineered tissues that meet the structural and functional requirements of native tissue. The dramatic increase in elastic fibers through normal pregnancy has led us to explore the potential role of mechanical stretch in combination with pregnancy levels of the steroid hormones 17β-estradiol and progesterone on elastic fiber production by human uterine myometrial smooth muscle cells in a three-dimensional (3D) culture model. Opposed to a single strain regimen, we sought to better understand how the amplitude and frequency parameters of cyclic strain influence elastic fiber production in these myometrial tissue constructs (MTC). Mechanical stretch was applied to MTC at a range of strain amplitudes (5%, 10%, and 15% at 0.5 Hz frequency) and frequencies (0.1 Hz, 0.5 Hz, 1 Hz, and constant 0 Hz at 10% amplitude), with and without pregnancy-level hormones, for 6 days. MTC were assessed for cell proliferation, matrix elastin protein content, and expression of the main elastic fiber genes, tropoelastin (ELN) and fibrillin-1 (FBN1). Significant increases in elastin protein and ELN and FBN1 mRNA were produced from samples subjected to a 0.5 Hz, 10% strain regimen, as well as samples stretched at higher amplitude (15%, 0.5 Hz) and higher frequency (1 Hz, 10%); however, no significant effects because of third-trimester mimetic hormone treatment were determined. These results establish that a minimum level of strain is required to stimulate the synthesis of elastic fiber components in our culture model and show this response can be similarly enhanced by increasing either the amplitude or frequency parameter of applied strain. Further, our results demonstrate strain alone is sufficient to stimulate elastic fiber production and suggest hormones may not be a significant factor in regulating elastin synthesis. This 3D culture model will provide a useful tool to further investigate mechanisms underlying pregnancy-induced de novo elastic fiber synthesis and assembly by uterine smooth muscle cells.

Mechanical stress induced mitochondrial dysfunction in cardiovascular diseases: Novel mechanisms and therapeutic targets

Cardiovascular diseases (CVDs) are the leading cause of mortality worldwide. Others and our studies have shown that mechanical stresses (forces) including shear stress and cyclic stretch, occur in various pathological conditions, play significant roles in the development and progression of CVDs. Mitochondria regulate the physiological processes of cardiac and vascular cells mainly through adenosine triphosphate (ATP) production, calcium flux and redox control while promote cell death through electron transport complex (ETC) related cellular stress response. Mounting evidence reveal that mechanical stress-induced mitochondrial dysfunction plays a vital role in the pathogenesis of many CVDs including heart failure and atherosclerosis. This review summarized mitochondrial functions in cardiovascular system under physiological mechanical stress and mitochondrial dysfunction under pathological mechanical stress in CVDs (graphical abstract). The study of mitochondrial dysfunction under mechanical stress can further our understanding of the underlying mechanisms, identify potential therapeutic targets, and aid the development of novel treatments of CVDs.

Transient low shear-stress preconditioning influences long-term endothelial traction and alignment under high shear flow

Endothelial cells (ECs) within the vascular system encounter fluid shear stress (FSS). High, laminar FSS promotes vasodilation and anti-inflammatory responses, whereas low or disturbed FSS induces dysfunction and inflammation. However, the adaptation of endothelial cells (ECs) to dynamically changing FSS patterns remains underexplored. Here, by combining traction force microscopy with a custom flow chamber, we examined human umbilical vein endothelial cells adapting their traction during transitions from short-term low shear to long-term high shear stress. We discovered that the initial low FSS elevates the traction by only half of the amount in response to direct high FSS even after flow changes to high FSS. However, in the long term under high FSS, the flow started with low FSS triggers a substantial second rise in traction for over 10 h. In contrast, the flow started directly with high FSS results in a quick traction surge followed by a huge reduction below the baseline traction in <30 min. Importantly, we find that the orientation of traction vectors is steered by initial shear exposure. Using Granger causality analysis, we show that the traction that aligns in the flow direction under direct high FSS functionally causes cell alignment toward the flow direction. However, EC traction that orients perpendicular to the flow that starts with temporary low FSS functionally causes cell orientation perpendicular to the flow. Taken together, our findings elucidate the significant influence of initial short-term low FSS on lasting changes in endothelial traction that induces EC alignment.NEW & NOTEWORTHY In our study, we uncover that preconditioning with low shear stress yields enduring impacts on endothelial cell traction and orientation, persisting even after transitioning to high-shear conditions. Using Granger causality analysis, we demonstrate a functional link between the direction of cell traction and subsequent cellular alignment across varying shear environments.

A novel view to varicose veins pathogenesis: Proteomic profiling suggests a pivotal role of extracellular matrix degradation

INTRODUCTION

Although morphological and anatomical studies indicate that venous wall weakening and subendothelial fibrosis characterize varicose veins (VV), the pathogenesis of VV remains poorly understood. The aim of this study is to obtain protein expression profiles in patients with VV and thereby get a step closer to understanding the pathogenesis of VV.

METHODS

Specimens were obtained from total of 10 patients, that is, from 5 patients undergoing VV surgical stripping and from 5 non-VV patients undergoing bypass surgery. Specimens were collected from the same layers of venous wall. Proteins were extracted from each specimen and analyzed by ion mobility spectrometry (IMS-MS). In total, 1387 were identified and 486 proteins were identified in all samples. From these, 15 proteins were differentially expressed between VV and non-VV samples (p < .05) and 12 of these showed a fold change >1.5.

RESULTS

Interestingly, among the differentially expressed proteins, only two proteins were significantly increased in the VV tissue, that is, GAPDH (p = .028, fold change 2.74), where several proteins involved in maintaining the homeostasis in the extracellular matrix, that is, the CXXC zinc finger protein 5 (CXXC5) and nucleoporin (SEH1) were prominently downregulated (p = .049, fold change 37.8, and p = .040, fold change 3.46). The downregulation in protein expression of CXXC5 and SEH1 as well as upregulation of GAPDH were validated by Western blotting.

CONCLUSION

The identified differentially expressed proteins suggest an altered profile of the connective tissue proteins as well as an increased proteolytic enzyme activity which both may be central in the pathophysiology of varicose veins.

The Effects of Simulated and Real Microgravity on Vascular Smooth Muscle Cells

As considerations are being made for the limitations and safety of long-term human spaceflight, the vasculature is important given its connection to and impact on numerous organ systems. As a major constituent of blood vessels, vascular smooth muscle cells are of interest due to their influence over vascular tone and function. Additionally, vascular smooth muscle cells are responsive to pressure and flow changes. Therefore, alterations in these parameters under conditions of microgravity can be functionally disruptive. As such, here we review and discuss the existing literature that assesses the effects of microgravity, both actual and simulated, on smooth muscle cells. This includes the various methods for achieving or simulating microgravity, the animal models or cells used, and the various durations of microgravity assessed. We also discuss the various reported findings in the field, which include changes to cell proliferation, gene expression and phenotypic shifts, and renin-angiotensin-aldosterone system (RAAS), nitric oxide synthase (NOS), and Ca2+ signaling. Additionally, we briefly summarize the literature on smooth muscle tissue engineering in microgravity as well as considerations of radiation as another key component of spaceflight to contextualize spaceflight experiments, which by their nature include radiation exposure. Finally, we provide general recommendations based on the existing literature's focus and limitations.

Effects of Mechanical Stress on Endothelial Cells In Situ and In Vitro

Endothelial cells lining blood vessels are essential for maintaining vascular homeostasis and mediate several pathological and physiological processes. Mechanical stresses generated by blood flow and other biomechanical factors significantly affect endothelial cell activity. Here, we review how mechanical stresses, both in situ and in vitro, affect endothelial cells. We review the basic principles underlying the cellular response to mechanical stresses. We also consider the implications of these findings for understanding the mechanisms of mechanotransducer and mechano-signal transduction systems by cytoskeletal components.

Vascular smooth muscle cell mechanotransduction through serum and glucocorticoid inducible kinase-1 promotes interleukin-6 production and macrophage accumulation in murine hypertension

Objective

The objective of this investigation was to demonstrate that in vivo induction of hypertension (HTN) and in vitro cyclic stretch of aortic vascular smooth muscle cells (VSMCs) can cause serum and glucocorticoid-inducible kinase (SGK-1)-dependent production of cytokines to promote macrophage accumulation that may promote vascular pathology.

Methods

HTN was induced in C57Bl/6 mice with angiotensin II infusion (1.46 mg/kg/day × 21 days) with or without systemic infusion of EMD638683 (2.5 mg/kg/day × 21 days), a selective SGK-1 inhibitor. Systolic blood pressure was recorded. Abdominal aortas were harvested to quantify SGK-1 activity (pSGK-1/SGK-1) by immunoblot. Flow cytometry quantified the abundance of CD11b+/F480+ cells (macrophages). Plasma interleukin (IL)-6 and monocyte chemoattractant protein-1 (MCP-1) was assessed by enzyme-linked immunosorbent assay. Aortic VSMCs from wild-type mice were subjected to 12% biaxial cyclic stretch (Stretch) for 3 or 12 hours with or without EMD638683 (10 μM) and with or without SGK-1 small interfering RNA with subsequent quantitative polymerase chain reaction for IL-6 and MCP-1 expression. IL-6 and MCP-1 in culture media were analyzed by enzyme-linked immunosorbent assay. Aortic VSMCs from SGK-1flox+/+ mice were transfected with Cre-Adenovirus to knockdown SGK-1 (SGK-1KD VSMCs) and underwent parallel tension experimentation. Computational modeling was used to simulate VSMC signaling. Statistical analysis included analysis of variance with significance at a P value of <.05.

Results

SGK-1 activity, abundance of CD11b+/F4-80+ cells, and plasma IL-6 were increased in the abdominal aorta of mice with HTN and significantly reduced by treatment with EMD638683. This outcome mirrored the increased abundance of IL-6 in media from Stretch C57Bl/6 VSMCs and attenuation of the effect with EMD638683 or SGK-1 small interfering RNA. C57Bl/6 VSMCs also responded to Stretch with increased MCP-1 expression and secretion into the culture media. Further supporting the integral role of mechanical signaling through SGK-1, target gene expression and cytokine secretion was unchanged in SGK-1KD VSMCs with Stretch, and computer modeling confirmed SGK-1 as an intersecting node of signaling owing to mechanical strain and angiotensin II.

Conclusions

Mechanical activation of SGK-1 in aortic VSMCs can promote inflammatory signaling and increased macrophage abundance, therefore this kinase warrants further exploration as a pharmacotherapeutic target to abrogate hypertensive vascular pathology.

A new approach of using organ-on-a-chip and fluid-structure interaction modeling to investigate biomechanical characteristics in tissue-engineered blood vessels

The tissue-engineered blood vessel (TEBV) has been developed and used in cardiovascular disease modeling, preclinical drug screening, and for replacement of native diseased arteries. Increasing attention has been paid to biomechanical cues in TEBV and other tissue-engineered organs to better recapitulate the functional properties of the native organs. Currently, computational fluid dynamics models were employed to reveal the hydrodynamics in TEBV-on-a-chip. However, the biomechanical wall stress/strain conditions in the TEBV wall have never been investigated. In this paper, a straight cylindrical TEBV was placed into a polydimethylsiloxane-made microfluidic device to construct the TEBV-on-a-chip. The chip was then perfused with cell culture media flow driven by a peristaltic pump. A three-dimensional fluid-structure interaction (FSI) model was generated to simulate the biomechanical conditions in TEBV and mimic both the dynamic TEBV movement and pulsatile fluid flow. The material stiffness of the TEBV wall was determined by uniaxial tensile testing, while the viscosity of cell culture media was measured using a rheometer. Comparison analysis between the perfusion experiment and FSI model results showed that the average relative error in diameter expansion of TEBV from both approaches was 10.0% in one period. For fluid flow, the average flow velocity over a period was 2.52 cm/s from the FSI model, 10.5% higher than the average velocity of the observed cell clusters (2.28 mm/s) in the experiment. These results demonstrated the facility to apply the FSI modeling approach in TEBV to obtain more comprehensive biomechanical results for investigating mechanical mechanisms of cardiovascular disease development.

Building Blood Vessel Chips with Enhanced Physiological Relevance

Blood vessel chips are bioengineered microdevices, consisting of biomaterials, human cells, and microstructures, which recapitulate essential vascular structure and physiology and allow a well-controlled microenvironment and spatial-temporal readouts. Blood vessel chips afford promising opportunities to understand molecular and cellular mechanisms underlying a range of vascular diseases. The physiological relevance is key to these blood vessel chips that rely on bioinspired strategies and bioengineering approaches to translate vascular physiology into artificial units. Here, we discuss several critical aspects of vascular physiology, including morphology, material composition, mechanical properties, flow dynamics, and mass transport, which provide essential guidelines and a valuable source of bioinspiration for the rational design of blood vessel chips. We also review state-of-art blood vessel chips that exhibit important physiological features of the vessel and reveal crucial insights into the biological processes and disease pathogenesis, including rare diseases, with notable implications for drug screening and clinical trials. We envision that the advances in biomaterials, biofabrication, and stem cells improve the physiological relevance of blood vessel chips, which, along with the close collaborations between clinicians and bioengineers, enable their widespread utility.

Biomechanical and Mechanobiological Drivers of the Transition From PostCapillary Pulmonary Hypertension to Combined Pre-/PostCapillary Pulmonary Hypertension

Combined pre-/postcapillary pulmonary hypertension (Cpc-PH), a complication of left heart failure, is associated with higher mortality rates than isolated postcapillary pulmonary hypertension alone. Currently, knowledge gaps persist on the mechanisms responsible for the progression of isolated postcapillary pulmonary hypertension (Ipc-PH) to Cpc-PH. Here, we review the biomechanical and mechanobiological impact of left heart failure on pulmonary circulation, including mechanotransduction of these pathological forces, which lead to altered biological signaling and detrimental remodeling, driving the progression to Cpc-PH. We focus on pathologically increased cyclic stretch and decreased wall shear stress; mechanotransduction by endothelial cells, smooth muscle cells, and pulmonary arterial fibroblasts; and signaling-stimulated remodeling of the pulmonary veins, capillaries, and arteries that propel the transition from Ipc-PH to Cpc-PH. Identifying biomechanical and mechanobiological mechanisms of Cpc-PH progression may highlight potential pharmacologic avenues to prevent right heart failure and subsequent mortality.

Esophageal wound healing by aligned smooth muscle cell-laden nanofibrous patch

The esophagus exhibits peristalsis via contraction of circularly and longitudinally aligned smooth muscles, and esophageal replacement is required if there is a critical-sized wound. In this study, we proposed to reconstruct esophageal tissues using cell electrospinning (CE), an advanced technique for encapsulating living cells into fibers that allows control of the direction of fiber deposition. After treatment with transforming growth factor-β, mesenchymal stem cell-derived smooth muscle cells (SMCs) were utilized for cell electrospinning or three-dimensional bioprinting to compare the effects of aligned micropatterns on cell morphology. CE resulted in SMCs with uniaxially arranged and elongated cell morphology with upregulated expression levels of SMC-specific markers, including connexin 43, smooth muscle protein 22 alpha (SM22α), desmin, and smoothelin. When SMC-laden nanofibrous patches were transplanted into a rat esophageal defect model, the SMC patch promoted regeneration of esophageal wounds with an increased number of newly formed blood vessels and enhanced the SMC-specific markers of SM22α and vimentin. Taken together, CE with its advantages, such as guidance of highly elongated, aligned cell morphology and accelerated SMC differentiation, can be an efficient strategy to reconstruct smooth muscle tissues and treat esophageal perforation.

Computer Model-Driven Design in Cardiovascular Regenerative Medicine

Continuing advances in genomics, molecular and cellular mechanobiology and immunobiology, including transcriptomics and proteomics, and biomechanics increasingly reveal the complexity underlying native tissue and organ structure and function. Identifying methods to repair, regenerate, or replace vital tissues and organs remains one of the greatest challenges of modern biomedical engineering, one that deserves our very best effort. Notwithstanding the continuing need for improving standard methods of investigation, including cell, organoid, and tissue culture, biomaterials development and fabrication, animal models, and clinical research, it is increasingly evident that modern computational methods should play increasingly greater roles in advancing the basic science, bioengineering, and clinical application of regenerative medicine. This brief review focuses on the development and application of computational models of tissue and organ mechanobiology and mechanics for purposes of designing tissue engineered constructs and understanding their development in vitro and in situ. Although the basic approaches are general, for illustrative purposes we describe two recent examples from cardiovascular medicine-tissue engineered heart valves (TEHVs) and tissue engineered vascular grafts (TEVGs)-to highlight current methods of approach as well as continuing needs.

Vascular smooth muscle cell dysfunction in neurodegeneration

Vascular smooth muscle cells (VSMCs) are the key moderators of cerebrovascular dynamics in response to the brain's oxygen and nutrient demands. Crucially, VSMCs may provide a sensitive biomarker for neurodegenerative pathologies where vasculature is compromised. An increasing body of research suggests that VSMCs have remarkable plasticity and their pathophysiology may play a key role in the complex process of neurodegeneration. Furthermore, extrinsic risk factors, including environmental conditions and traumatic events can impact vascular function through changes in VSMC morphology. VSMC dysfunction can be characterised at the molecular level both preclinically, and clinically ex vivo. However the identification of VSMC dysfunction in living individuals is important to understand changes in vascular function at the onset and progression of neurological disorders such as dementia, Alzheimer's disease, and Parkinson's disease. A promising technique to identify changes in the state of cerebral smooth muscle is cerebrovascular reactivity (CVR) which reflects the intrinsic dynamic response of blood vessels in the brain to vasoactive stimuli in order to modulate regional cerebral blood flow (CBF). In this work, we review the role of VSMCs in the most common neurodegenerative disorders and identify physiological systems that may contribute to VSMC dysfunction. The evidence collected here identifies VSMC dysfunction as a strong candidate for novel therapeutics to combat the development and progression of neurodegeneration, and highlights the need for more research on the role of VSMCs and cerebrovascular dynamics in healthy and diseased states.

Molecular and genetic mechanisms in brain arteriovenous malformations: new insights and future perspectives

Brain arteriovenous malformations (bAVMs) are rare vascular lesions made of shunts between cerebral arteries and veins without the interposition of a capillary bed. The majority of bAVMs are asymptomatic, but some may be revealed by seizures and potentially life-threatening brain hemorrhage. The management of unruptured bAVMs remains a matter of debate. Significant progress in the understanding of their pathogenesis has been made during the last decade, particularly using genome sequencing and biomolecular analysis. Herein, we comprehensively review the recent molecular and genetic advances in the study of bAVMs that not only allow a better understanding of the genesis and growth of bAVMs, but also open new insights in medical treatment perspectives.

Multiscale simulations suggest a protective role of neo-adventitia in abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are a dangerous cardiovascular disease, the pathogenesis of which is not yet fully understood. In the present work a recent mechanopathological theory, which correlates AAA progression with microstructural and mechanical alterations in the tissue, is investigated using multiscale models. The goal is to combine these changes, within the framework of mechanobiology, with possible mechanical cues that are sensed by vascular cells along the AAA pathogenesis. Particular attention is paid to the formation of a 'neo-adventitia' on the abluminal side of the aortic wall, which is characterized by a highly random (isotropic) distribution of collagen fibers. Macro- and micro-scale results suggest that the formation of an AAA, as expected, perturbs the micromechanical state of the aortic tissue and triggers a growth and remodeling (G&R) reaction by mechanosensing cells such as fibroblasts. This G&R then leads to the formation of a thick neo-adventitia that appears to bring the micromechanical state of the tissue closer to the original homeostatic level. In this context, this new layer could act like a protective sheath, similar to the tunica adventitia in healthy aortas. This potential 'attempt at healing' by vascular cells would have important implications on the stability of the AAA wall and thus on the risk of rupture. STATEMENT OF SIGNIFICANCE: Current clinical criteria for risk assessment in AAAs are still empirical, as the causes and mechanisms of the disease are not yet fully understood. The strength of the arterial tissue is closely related to its microstructure, which in turn is remodeled by mechanosensing cells in the course of the disease. In this study, multiscale simulations show a possible connection between mechanical cues at the microscopic level and collagen G&R in AAA tissue. It should be emphasized that these micromechanical cues cannot be visualized in vivo. Therefore, the results presented here will help to advance our current understanding of the disease and motivate future experimental studies, with important implications for AAA risk assessment.

Natural Flavonoids Derived From Fruits Are Potential Agents Against Atherosclerosis

Atherosclerosis, as a chronic inflammatory response, is one of the main causes of cardiovascular diseases. Atherosclerosis is induced by endothelial cell dysfunction, migration and proliferation of smooth muscle cells, accumulation of foam cells and inflammatory response, resulting in plaque accumulation, narrowing and hardening of the artery wall, and ultimately leading to myocardial infarction or sudden death and other serious consequences. Flavonoid is a kind of natural polyphenol compound widely existing in fruits with various structures, mainly including flavonols, flavones, flavanones, flavanols, anthocyanins, isoflavones, and chalcone, etc. Because of its potential health benefits, it is now used in supplements, cosmetics and medicines, and researchers are increasingly paying attention to its role in atherosclerosis. In this paper, we will focus on several important nodes in the development of atherosclerotic disease, including endothelial cell dysfunction, smooth muscle cell migration and proliferation, foam cell accumulation and inflammatory response. At the same time, through the classification of flavonoids from fruits, the role and potential mechanism of flavonoids in atherosclerosis were reviewed, providing a certain direction for the development of fruit flavonoids in the treatment of atherosclerosis drugs.

Adaptation of Arterial Wall Viscosity to the Short-Term Reduction of Heart Rate: Impact of Aging

Background Changes in arterial wall viscosity, which dissipates the energy stored within the arterial wall, may contribute to the beneficial effect of heart rate (HR) reduction on arterial stiffness and cardiovascular coupling. However, it has never been assessed in humans and could be altered by aging. We evaluated the effect of a selective HR-lowering agent on carotid arterial wall viscosity and the impact of aging on this effect. Methods and Results This randomized, placebo-controlled, double-blind, crossover study performed in 19 healthy volunteers evaluated the effects of ivabradine (5 mg BID, 1-week) on carotid arterial wall viscosity, mechanics, hemodynamics, and cardiovascular coupling. Arterial wall viscosity was evaluated by the area of the hysteresis loop of the pressure-lumen cross-sectional area relationship, representing the energy dissipated (W_V), and by the relative viscosity (W_V/W_E), with W_E representing the elastic energy stored. HR reduction by ivabradine increased W_V and W_E whereas W_V/W_E remained stable. In middle-aged subjects (n=11), baseline arterial stiffness and cardiovascular coupling were less favorable, and W_E was similar but W_V and therefore W_V/W_E were lower than in youth (n=8). HR reduction increased W_V/W_E in middle-aged but not in young subjects, owing to a larger increase in W_V than W_E. These results were supported by the age-related linear increase in W_V/W_E after HR reduction (P=0.009), explained by a linear increase in W_V. Conclusion HR reduction increases arterial wall energy dissipation proportionally to the increase in W_E, suggesting an adaptive process to bradycardia. This mechanism is altered during aging resulting in a larger than expected energy dissipation, the impact of which should be assessed. Registration URL: https://www.clinicaltrials.gov; Unique identifier: 2015/077/HP. URL: https://www. eudract.ema.europa.eu; Unique identifier: 2015-002060-17.

Vascular Smooth Muscle Cells Mechanosensitive Regulators and Vascular Remodeling

Blood vessels are subjected to mechanical loads of pressure and flow, inducing smooth muscle circumferential and endothelial shear stresses. The perception and response of vascular tissue and living cells to these stresses and the microenvironment they are exposed to are critical to their function and survival. These mechanical stimuli not only cause morphological changes in cells and vessel walls but also can interfere with biochemical homeostasis, leading to vascular remodeling and dysfunction. However, the mechanisms underlying how these stimuli affect tissue and cellular function, including mechanical stimulation-induced biochemical signaling and mechanical transduction that relies on cytoskeletal integrity, are unclear. This review focuses on signaling pathways that regulate multiple biochemical processes in vascular mesangial smooth muscle cells in response to circumferential stress and are involved in mechanosensitive regulatory molecules in response to mechanotransduction, including ion channels, membrane receptors, integrins, cytoskeletal proteins, nuclear structures, and cascades. Mechanoactivation of these signaling pathways is closely associated with vascular remodeling in physiological or pathophysiological states.

Cyclic tensile strain facilitates proliferation and migration of human aortic smooth muscle cells and reduces their apoptosis via miRNA-187-3p

The cardiovascular is a system that contains extremely complex mechanical factors, in which the circulatory flow of blood has rich mechanical laws. Many studies have revealed that mechanical factors play a very important role in the process of revascularization. Hence, it is essential to investigate the mechanical factors in the process of revascularization in depth. A cyclic tensile strain (CTS) was applied to human aortic smooth muscle cells (HASMCs) at a frequency of 1 Hz and amplitudes of 5%, 10% and 15%, respectively. SmallRNA-seq was used to identify differentially expressed miRNAs (DE-miRNAs) responding to CTS in HASMCs. Starbase database predicted the target genes of DE-miRNAs. Metascape was applied for GO and KEGG pathway enrichment analysis and protein–protein interaction network construction. The proliferation and migration of CTS-treated HASMCs were significantly enhanced, and apoptosis were significantly reduced compared to the control group. SmallRNA-seq results demonstrated that 55, 16 and 16 DE-miRNAs were present in 5%, 10% and 15% CTS-treated HASMCs, respectively. Compared to controls, with miR-26a-2-3p and miR-187-3p being the intersection of these DE-miRNAs. Starbase database identified 189 common target genes for miR-26a-2-3p and miR-187-3p. Common target genes are mainly enriched in the basolateral plasma membrane and endocytosis. Further, in vitro experiments exhibited that CTS upregulated miR-187-3p expression, and miR-187-3p enhanced the proliferation and migration of HASMCs and reduced their apoptosis. It is suggested that miR-187-3p may be an important target for CTS participate in the process of cardiovascular disease.

Establishment of a Modular Hemodynamic Simulator for Accurate In Vitro Simulation of Physiological and Pathological Pressure Waveforms in Native and Bioartificial Blood Vessels

Purpose

In vitro stimulation of native and bioartificial vessels in perfusable systems simulating natural mechanical environments of the human vasculature represents an emerging approach in cardiovascular research. Promising results have been achieved for applications in both regenerative medicine and etiopathogenetic investigations. However, accurate and reliable simulation of the wide variety of physiological and pathological pressure environments observed in different vessels still remains an unmet challenge.

Methods

We established a modular hemodynamic simulator (MHS) with interchangeable and modifiable components suitable for the perfusion of native porcine—(i.e. the aorta, brachial and radial arteries and the inferior vena cava) and bioartificial fibrin-based vessels with anatomical site specific pressure curves. Additionally, different pathological pressure waveforms associated with cardiovascular diseases including hyper- and hypotension, tachy- and bradycardia, aortic valve stenosis and insufficiency, heart failure, obstructive cardiomyopathy and arterial stiffening were simulated. Pressure curves, cyclic distension and shear stress were measured for each vessel and compared to ideal clinical pressure waveforms.

Results

The pressure waveforms obtained in the MHS showed high similarity to the ideal anatomical site specific pressure curves of different vessel types. Moreover, the system facilitated accurate emulation of physiological and different pathological pressure conditions in small diameter fibrin-based vessels.

Conclusion

The MHS serves as a variable in vitro platform for accurate emulation of physiological and pathological pressure environments in biological probes. Potential applications of the system include bioartificial vessel maturation in cardiovascular tissue engineering approaches as well as etiopathogenetic investigations of various cardiovascular pathologies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13239-021-00577-0.

Crosstalk Between CD11b and Piezo1 Mediates Macrophage Responses to Mechanical Cues

Macrophages are versatile cells of the innate immune system that perform diverse functions by responding to dynamic changes in their microenvironment. While the effects of soluble cues, including cytokines and chemokines, have been widely studied, the effects of physical cues, including mechanical stimuli, in regulating macrophage form and function are less well understood. In this study, we examined the effects of static and cyclic uniaxial stretch on macrophage inflammatory and healing activation. We found that cyclic stretch altered macrophage morphology and responses to IFNγ/LPS and IL4/IL13. Interestingly, we found that both static and cyclic stretch suppressed IFNγ/LPS induced inflammation. In contrast, IL4/IL13 mediated healing responses were suppressed with cyclic but enhanced with static stretch conditions. Mechanistically, both static and cyclic stretch increased expression of the integrin CD11b (αM integrin), decreased expression of the mechanosensitive ion channel Piezo1, and knock down of either CD11b or Piezo1 through siRNA abrogated stretch-mediated changes in inflammatory responses. Moreover, we found that knock down of CD11b enhanced the expression of Piezo1, and conversely knock down of Piezo1 enhanced CD11b expression, suggesting the potential for crosstalk between integrins and ion channels. Finally, stretch-mediated differences in macrophage activation were also dependent on actin, since pharmacological inhibition of actin polymerization abrogated the changes in activation with stretch. Together, this study demonstrates that the physical environment synergizes with biochemical cues to regulate macrophage morphology and function, and suggests a role for CD11b and Piezo1 crosstalk in mechanotransduction in macrophages.

Vascular Mechanobiology: Homeostasis, Adaptation, and Disease

Cells of the vascular wall are exquisitely sensitive to changes in their mechanical environment. In healthy vessels, mechanical forces regulate signaling and gene expression to direct the remodeling needed for the vessel wall to maintain optimal function. Major diseases of arteries involve maladaptive remodeling with compromised or lost homeostatic mechanisms. Whereas homeostasis invokes negative feedback loops at multiple scales to mediate mechanobiological stability, disease progression often occurs via positive feedback that generates mechanobiological instabilities. In this review, we focus on the cell biology, wall mechanics, and regulatory pathways associated with arterial health and how changes in these processes lead to disease. We discuss how positive feedback loops arise via biomechanical and biochemical means. We conclude that inflammation plays a central role in overriding homeostatic pathways and suggest future directions for addressing therapeutic needs.

Anti-Atherosclerotic Effect of Afrocyclamin A against Vascular Smooth Muscle Cells Is Mediated via p38 MAPK Signaling Pathway

OBJECTIVE

Research suggests that fine particulate matter (PM2.5) contributes to the expansion and development of atherosclerosis. Infiltration and proliferation of vascular smooth muscle cells (VSMCs) from the blood vessel media into the intima, is an important step in the atherosclerosis pathophysiology. Afrocyclamin A, is an oleanane-type triterpene saponin, isolated from Androsace umbellate, which is commonly used in Chinese herbal medicine. In the study, we examined the effect of Afrocyclamin A on PM2.5-induced VSMCs proliferation and scrutinized possible mechanisms of action.

MATERIALS AND METHODS

In the experimental study, counting Kit-8 (CCK-8) assay was used for estimation of VSMCs viability. BrdU immunofluorescence was used for estimation of VSMCs proliferation. The levels of antioxidant parameters such as malonaldehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH); proinflammatory cytokines such as interleukin-1β (IL-1β), IL-6, tumor necrosis factor-α (TNF-α), nitric oxide (NO), endothelin-1 (ET-1), and vascular cell adhesion molecule-1 (VCAM-1), were estimated. The expression of proliferating cell nuclear antigen (PCNA) and phospho-p38 MAPK (p-p38 MAPK) was assessed.

RESULTS

Compared to PM2.5-treated cells, in addition to reducing PM2.5-induced VSMCs proliferation, Afrocyclamin A reduced the expression of PCNA and p-p38 MAPK, down-regulated the level of TNF-α, IL-1β, IL-6, VCAM-1, MDA and ET-1, and up-regulated SOD, GSH and NO level. Furthermore, the anti-proliferative effect of Afrocyclamin A was considerably increased following co-incubation of Afrocyclamin A with SB203580 (p38 MAPK inhibitor) in comparison with Afrocyclamin A-treated cells.

CONCLUSION

Based on the results, we can conclude that Afrocyclamin A might reduce PM2.5-induced VSMCs proliferation via reduction of p38 MAPK signaling pathway.

Functional assistance for stress distribution in cell culture membrane under periodically stretching

Dynamic cell cultures simulate the in vivo cell environment for a regular loading system with curtain strains. However, it is difficult to obtain strains that are suitable for cells without conducting multiple trials. This study develops a device that increases the strain gradient by changing the tensile section, in order to determine the effect of various cyclic strains on cultured human keratinocytes (HK) cells. This device is used to determine the effect of 3% and 5% cyclic strain and shear strain on cell proliferation and arrangement at 1 Hz. The results show that compared with static and 3% strain, a 5% cyclic strain better inhibits the proliferation of HK cells. Compared to the initial cell attachment when there is no specific directionality, the cells are aligned in the vertical stretching direction after cyclic stretching. This equipment increases the efficiency of the experiment and more intuitively maps the cell behavior and shape to the strain field and the response to the shear strain.

Recent advancements in the bioprinting of vascular grafts

Recent advancements in the bioinks and three-dimensional (3D) bioprinting methods used to fabricate vascular constructs are summarized herein. Critical biomechanical properties required to fabricate an ideal vascular graft are highlighted, as well as various testing methods have been outlined to evaluate the bio-fabricated grafts as per the Food and Drug Administration (FDA) and International Organization for Standardization (ISO) guidelines. Occlusive artery disease and cardiovascular disease are the major causes of death globally. These diseases are caused by the blockage in the arteries, which results in a decreased blood flow to the tissues of major organs in the body, such as the heart. Bypass surgery is often performed using a vascular graft to re-route the blood flow. Autologous grafts represent a gold standard for such bypass surgeries; however, these grafts may be unavailable due to the previous harvesting or possess a poor quality. Synthetic grafts serve well for medium to large-sized vessels, but they fail when used to replace small-diameter vessels, generally smaller than 6 mm. Various tissue engineering approaches have been used to address the urgent need for vascular graft that can withstand hemodynamic blood pressure and has the ability to grow and remodel. Among these approaches, 3D bioprinting offers an attractive solution to construct patient-specific vessel grafts with layered biomimetic structures.

Calcium signaling mediates a biphasic mechanoadaptive response of endothelial cells to cyclic mechanical stretch

The vascular system is precisely regulated to adjust blood flow to organismal demand, thereby guaranteeing adequate perfusion under varying physiological conditions. Mechanical forces, such as cyclic circumferential stretch, are among the critical stimuli that dynamically adjust vessel distribution and diameter, but the precise mechanisms of adaptation to changing forces are unclear. We find that endothelial monolayers respond to cyclic stretch by transient remodeling of the vascular endothelial cadherin–based adherens junctions and the associated actomyosin cytoskeleton. Time-resolved proteomic profiling reveals that this remodeling is driven by calcium influx through the mechanosensitive Piezo1 channel, triggering Rho activation to increase actomyosin contraction. As the mechanical stimulus persists, calcium signaling is attenuated through transient down-regulation of Piezo1 protein. At the same time, filamins are phosphorylated to increase monolayer stiffness, allowing mechanoadaptation to restore junctional integrity despite continuing exposure to stretch. Collectively, this study identifies a biphasic response to cyclic stretch, consisting of an initial calcium-driven junctional mechanoresponse, followed by mechanoadaptation facilitated by monolayer stiffening.

A computational bio-chemo-mechanical model of in vivo tissue-engineered vascular graft development

Stenosis is the primary complication of current tissue-engineered vascular grafts used in pediatric congenital cardiac surgery. Murine models provide considerable insight into the possible mechanisms underlying this situation, but they are not efficient for identifying optimal changes in scaffold design or therapeutic strategies to prevent narrowing. In contrast, computational modeling promises to enable time- and cost-efficient examinations of factors leading to narrowing. Whereas past models have been limited by their phenomenological basis, we present a new mechanistic model that integrates molecular- and cellular-driven immuno- and mechano-mediated contributions to in vivo neotissue development within implanted polymeric scaffolds. Model parameters are inferred directly from in vivo measurements for an inferior vena cava interposition graft model in the mouse that are augmented by data from the literature. By complementing Bayesian estimation with identifiability analysis and simplex optimization, we found optimal parameter values that match model outputs with experimental targets and quantify variability due to measurement uncertainty. Utility is illustrated by parametrically exploring possible graft narrowing as a function of scaffold pore size, macrophage activity, and the immunomodulatory cytokine transforming growth factor beta 1 (TGF-β1). The model captures salient temporal profiles of infiltrating immune and synthetic cells and associated secretion of cytokines, proteases, and matrix constituents throughout neovessel evolution, and parametric studies suggest that modulating scaffold immunogenicity with early immunomodulatory therapies may reduce graft narrowing without compromising compliance.

Physiological cyclic stretch up-regulates angiotensin-converting enzyme 2 expression to reduce proliferation and migration of vascular smooth muscle cells

Angiotensin-converting enzyme 2 (ACE2) is considered as an endogenous negative regulator of renin–angiotensin system (RAS), exerting multiple cardiovascular protective roles. Whether mechanical stretch modulates ACE2 expression remains unknown. The present study aimed at investigating whether ACE2 is involved in physiological stretch (10% elongation, 1 Hz) mediated cellular functions and the underlying mechanism. Cultured human aortic smooth muscle cells (HASMCs) were exposed to 10% stretch for indicated time, and real-time PCR and Western blot analysis showed 10% stretch increased ACE2 expression and activity significantly compared with static conditions and increased Ang-(1-7) level, but decreased Ang II level; Brdu incorporation assay and Scratch test showed that ACE2 was involved in the inhibition of HASMCs proliferation and migration by 10% stretch; the Dual-Luciferase Reporter Assay demonstrated that 10% increased ACE2 promoter activity, but had no effect on ACE2 mRNA stability; kinase inhibition study and Electrophoretic mobility shift assay (EMSA) showed that JNK1/2 and PKCβII pathway, as well as their downstream transcription factors, AP-1 and NF-κB, were involved in 10% stretch induced ACE2 expression. In conclusion, our study indicates ACE2 is a mechanosensitive gene, and may represent a potential therapeutic target for mechanical forces related vascular diseases.

Dickkopf-1 promotes Vascular Smooth Muscle Cell proliferation and migration through upregulating UHRF1 during Cyclic Stretch application

Dickkopf-1 (DKK1) was recently shown to play an important role in cardiovascular disease. The aim of this work was to assess the role of DKK1 in the regulation of smooth muscle cell function by mechanical stretch and the mechanisms underlying this process.

Methods: Wild-type C57BL/6J mice were subjected to sham or abdominal aortic constriction (AAC) surgery. The expression level of DKK1 was examined by immunohistochemical staining and Western blotting. Analyses of DKK1 function in vascular smooth muscle cell (VSMC) proliferation and migration were performed. Transcriptome sequencing analysis was performed to identify the differentially expressed genes and pathways regulated by DKK1. Smooth muscle-specific Dkk1 knockout mice were used to confirm the function of DKK1 in vivo. Chromatin immunoprecipitation (ChIP) was used to confirm DNA-protein interactions. Promoter luciferase analysis was used to detect transcription factor activity.

Results: We found that AAC significantly increased DKK1 protein levels in the thoracic aorta and coronary artery in vivo. In vitro, high-level stretch (18%) induced the expression of DKK1 in VSMCs. Knocking down DKK1 inhibited VSMC proliferation and migration under high-level stretch (18%). We identified ubiquitin-like containing PHD and RING finger domains 1 (UHRF1) as a target gene of DKK1. Knockdown of UHRF1 with small interfering RNAs partially reversed the regulatory effect of recombinant DKK1 on VSMCs. Specific deletion of DKK1 in VSMCs was sufficient to attenuate the AAC-induced upregulation of UHRF1, thickening of arterial media and increase in VSMC proliferation. Furthermore, we found that DKK1 regulated UHRF1 expression through the YAP-TEAD pathway. TEAD1 and TEAD4 bound directly to the promoter of UHRF1, and blocking the YAP-TEAD interaction inhibited UHRF1 upregulation due to DKK1.

Conclusions: This study reveals that DKK1 mediates the mechanical stretch regulation of smooth muscle cell function by modulating UHRF1 expression through the YAP-TEAD pathway.

Platelet-Derived Extracellular Vesicles Increase Col8a1 Secretion and Vascular Stiffness in Intimal Injury

The arterial mechanical microenvironment, including stiffness, is a crucial pathophysiological feature of vascular remodeling, such as neointimal hyperplasia after carotid endarterectomy and balloon dilatation surgeries. In this study, we examined changes in neointimal stiffness in a Sprague-Dawley rat carotid artery intimal injury model and revealed that extracellular matrix (ECM) secretion and vascular stiffness were increased. Once the endothelial layer is damaged in vivo, activated platelets adhere to the intima and may secrete platelet-derived extracellular vesicles (pEVs) and communicate with vascular smooth muscle cells (VSMCs). In vitro, pEVs stimulated VSMCs to promote collagen secretion and cell adhesion. MRNA sequencing analysis of a carotid artery intimal injury model showed that ECM factors, including col8a1, col8a2, col12a1, and elastin, were upregulated. Subsequently, ingenuity pathway analysis (IPA) was used to examine the possible signaling pathways involved in the formation of ECM, of which the Akt pathway played a central role. In vitro, pEVs activated Akt signaling through the PIP₃ pathway and induced the production of Col8a1. MicroRNA (miR) sequencing of pEVs released from activated platelets revealed that 14 of the top 30 miRs in pEVs targeted PTEN, which could promote the activation of the Akt pathway. Further research showed that the most abundant miR targeting PTEN was miR-92a-3p, which promoted Col8a1 expression. Interestingly, knockdown of Col8a1 expression in vivo abrogated the increase in carotid artery stiffness and simultaneously increased the degree of neointimal hyperplasia. Our results revealed that pEVs may deliver miR-92a-3p to VSMCs to induce the production and secretion of Col8a1 via the PTEN/PIP3/Akt pathway, subsequently increasing vascular stiffness. Therefore, pEVs and key molecules may be potential therapeutic targets for treating neointimal hyperplasia.

Stimulation of vascular smooth muscle cell proliferation by stiff matrix via the IKCa channel-dependent Ca2+ signaling

Vascular stiffening, an early and common characteristic of cardiovascular diseases (CVDs), stimulates vascular smooth muscle cell (VSMC) proliferation which reciprocally accelerates the progression of CVDs. However, the mechanisms by which extracellular matrix stiffness accompanying vascular stiffening regulates VSMC proliferation remain largely unknown. In the present study, we examined the role of the intermediate-conductance Ca²⁺ -activated K⁺  (IK_Ca ) channel in the matrix stiffness regulation of VSMC proliferation by growing A7r5 cells on soft and stiff polydimethylsiloxane substrates with stiffness close to these of arteries under physiological and pathological conditions, respectively. Stiff substrates stimulated cell proliferation and upregulated the expression of the IK_Ca channel. Stiff substrate-induced cell proliferation was suppressed by pharmacological inhibition using TRAM34, an IK_Ca channel blocker, or genetic depletion of the IK_Ca channel. In addition, stiff substrate-induced cell proliferation was also suppressed by reducing extracellular Ca²⁺ concentration using EGTA or intracellular Ca²⁺ concentration using BAPTA-AM. Moreover, stiff substrate induced activation of extracellular signal-regulated kinases (ERKs), which was inhibited by treatment with TRAM34 or BAPTA-AM. Stiff substrate-induced cell proliferation was suppressed by treatment with PD98059, an ERK inhibitor. Taken together, these results show that substrates with pathologically relevant stiffness upregulate the IK_Ca channel expression to enhance intracellular Ca²⁺ signaling and subsequent activation of the ERK signal pathway to drive cell proliferation. These findings provide a novel mechanism by which vascular stiffening regulates VSMC function.

Challenges and Possibilities of Cell-Based Tissue-Engineered Vascular Grafts

There is urgent demand for biologically compatible vascular grafts for both adult and pediatric patients. The utility of conventional nonbiodegradable materials is limited because of their thrombogenicity and inability to grow, while autologous vascular grafts involve considerable disadvantages, including the invasive procedures required to obtain these healthy vessels from patients and insufficient availability in patients with systemic atherosclerosis. All of these issues could be overcome by tissue-engineered vascular grafts (TEVGs). A large body of evidence has recently emerged in support of TEVG technologies, introducing diverse cell sources (e.g., somatic cells and stem cells) and novel fabrication methods (e.g., scaffold-guided and self-assembled approaches). Before TEVG can be applied in a clinical setting, however, several aspects of the technology must be improved, such as the feasibility of obtaining cells, their biocompatibility and mechanical properties, and the time needed for fabrication, while the safety of supplemented materials, the patency and nonthrombogenicity of TEVGs, their growth potential, and the long-term influence of implanted TEVGs in the body must be assessed. Although recent advances in TEVG fabrication have yielded promising results, more research is needed to achieve the most feasible methods for generating optimal TEVGs. This article reviews multiple aspects of TEVG fabrication, including mechanical requirements, extracellular matrix components, cell sources, and tissue engineering approaches. The potential of periodic hydrostatic pressurization in the production of scaffold-free TEVGs with optimal elasticity and stiffness is also discussed. In the future, the integration of multiple technologies is expected to enable improved TEVG performance.

Transient Receptor Potential Melastatin 7 Promotes Vascular Adventitial Fibroblasts Phenotypic Transformation and Inflammatory Reaction Induced by Mechanical Stretching Stress via p38 MAPK/JNK Pathway

Remodeling of the arteries is one of the pathological bases of hypertension. We have previously shown that transient receptor potential melastatin 7 (TRPM7) aggravates the vascular adventitial remodeling caused by pressure overload in the transverse aortic constriction (TAC) model. In this study, we sought to explore the functional expression and downstream signaling of TRPM7 in vascular adventitial fibroblasts (AFs) stimulated by mechanical stretching stress (MSS). The expression of TRPM7 was upregulated with a concomitant translocation to the cytoplasm in the AFs stimulated with 20% MSS. Meanwhile, the expression of α-smooth muscle actin (α-SMA), a marker of transformation from AFs to myofibroblasts (MFs) was also increased. Moreover, AF-conditioned medium caused a significant migration of macrophages after treatment with MSS and contained high levels of monocyte chemotactic protein-1 (MCP-1), interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α). Pharmacological and RNA interference approaches using the TRPM7 inhibitor 2-aminoethoxydiphenyl borate (2-APB) and specific anti-TRPM7 small interfering RNA (si-RNA-TRPM7) abrogated these changes significantly. Further exploration uncloaked that inhibition of TRPM7 reduced the phosphorylation of p38 MAP kinase (p38MAPK) and c-Jun N-terminal kinase (JNK) in the AFs stimulated with MSS. Furthermore, inhibition of the phosphorylation of p38MAPK or JNK could also alleviate the MSS-induced expression of α-SMA and secretion of inflammatory factors. These observations indicate that activated TRPM7 participates in the phenotypic transformation and inflammatory action of AFs in response to MSS through the p38MAPK/JNK pathway and suggest that TRPM7 may be a potential therapeutic target for vascular remodeling caused by hemodynamic changes in hypertension.

Study on the association of wall shear stress and vessel structural stress with atherosclerosis: An experimental animal study

BACKGROUND AND AIMS

Artery is subject to wall shear stress (WSS) and vessel structural stress (VSS) simultaneously. This study is designed to explore the role of VSS in development of atherosclerosis.

METHODS

Silastic collars were deployed on the carotid to create two constrictions on 13 rabbits for a distinct mechanical environment at the constriction. MRI was performed to visualize arteries' configuration. Animals with high fat (n = 9; Model-group) and normal diet (n = 4; Control-group) were sacrificed after 16 weeks. 3D fluid-structure interaction analysis was performed to quantify WSS and VSS simultaneously.

RESULTS

Twenty plaques were found in Model-group and 3 in Control-group. In Model-group, 8 plaques located proximally to the first constriction (Region-1, close to the heart) and 7 distally to the second (Region-2, close to the head) and 5 plaques were found on the contralateral side of 3 rabbits. Plaques at Region-1 tended to be bigger than those at Region-2 and the macrophage density at these locations was comparable. Minimum time-averaged WSS (TAWSS) in Region-1 was significantly higher than that in Region-2, and both maximum oscillatory shear index (OSI) and particle relative residence time (RRT) were significantly lower. Peak and mean VSS in Region-1 were significantly higher than those in Region-2. Correlation analyses indicated that low TAWSS, high OSI and RRT were only associated with plaque in Region-2, while lesions in Region-1 were only associated with high VSS. Moreover, only VSS was associated with wall thickness of plaque-free regions in both regions.

CONCLUSIONS

VSS might contribute to the initialization and development of atherosclerosis solely or in combination with WSS.

Mechanical Stretch Induces Smooth Muscle Cell Dysfunction by Regulating ACE2 via P38/ATF3 and Post-transcriptional Regulation by miR-421

Mechanical stretch promotes deregulation of vascular smooth muscle cell (VSMC) functions during hypertension-induced vascular remodeling. ACE2 has a wide range of cardiovascular and renal protective effects. Loss of ACE2 is associated with cardiovascular disease, but little is known about the regulation of its expression, especially by abnormal mechanical stretch during hypertension. The present study was designed to investigate the contribution of ACE2 to vascular remodeling under mechanical stretch and to assess the possible underlying mechanisms. The abdominal aortic constriction model was established to mimic the environment in vivo. FX-5000T Strain Unit provided mechanical stretch in vitro. Overexpression was used to analyze the role of ACE2 played in the proliferation, migration, apoptosis, and collagen metabolism of the VSMCs. RT-qPCR, Western blot, luciferase assay, and ChIP assay were used to elucidate the molecular mechanism of ACE2 expression regulated by stretch. We found that mechanical stretch modulated the expression of the ACE2/Ang-(1–7) and ACE/AngII axis. ACE2 was mechanically sensitive and was involved in the stretch-induced dysfunction of VSMCs. The p38 MAPK/ATF3 pathway and miR-421 participated in the regulation of ACE2. Thus, ACE2 may contribute to the development of vascular remodeling under conditions of mechanical stretch.

Upregulation of iNOS Protects Cyclic Mechanical Stretch-Induced Cell Death in Rat Aorta Smooth Muscle Cells

Aortic dissection and aneurysm are associated with abnormal hemodynamic loads originating from hypertension. Our previous study demonstrated that cyclic mechanical stretch (CMS, mimicked hypertension) caused the death of rat aortic smooth muscle cells (RASMCs) in a mitogen activated-protein kinases (MAPKs)-dependent manner. The current study investigated the effects of inducible nitric oxide synthase (iNOS) on CMS-induced RASMC death. cDNA microarrays for CMS-treated RASMCs showed that iNOS expression levels were increased in response to CMS. Real-time polymerase chain reaction (PCR) analysis demonstrated that this increase was p38 MAPK (p38)-dependent. NO production was also increased. This increase could be inhibited by p38 and iNOS inhibitors. Thus, CMS-induced iNOS synthesized NO. CMS-induced cell death in RASMCs was increased by the iNOS inhibitor but abrogated by the long-acting NO donor DETA-NONOate. Increased iNOS expression was confirmed in the abdominal aortic constriction mouse model. Signal transducers and activators of transcription 1 (STAT1) was activated in stretched RASMCs, and iNOS expression and NO production were inhibited by the STAT1 inhibitor nifuroxazide. Our findings suggest that RASMCs were protected by iNOS from CMS-stimulated cell death through the STAT1 and p38 signal pathways independently.

Histone Deacetylases (HDACs) and Atherosclerosis: A Mechanistic and Pharmacological Review

Atherosclerosis (AS), the most common underlying pathology for coronary artery disease, is a chronic inflammatory, proliferative disease in large- and medium-sized arteries. The vascular endothelium is important for maintaining vascular health. Endothelial dysfunction is a critical early event leading to AS, which is a major risk factor for stroke and myocardial infarction. Accumulating evidence has suggested the critical roles of histone deacetylases (HDACs) in regulating vascular cell homeostasis and AS. The purpose of this review is to present an updated view on the roles of HDACs (Class I, Class II, Class IV) and HDAC inhibitors in vascular dysfunction and AS. We also elaborate on the novel therapeutic targets and agents in atherosclerotic cardiovascular diseases.

Aortic "Disease-in-a-Dish": Mechanistic Insights and Drug Development Using iPSC-Based Disease Modeling

Thoracic aortic diseases, whether sporadic or due to a genetic disorder such as Marfan syndrome, lack effective medical therapies, with limited translation of treatments that are highly successful in mouse models into the clinic. Patient-derived induced pluripotent stem cells (iPSCs) offer the opportunity to establish new human models of aortic diseases. Here we review the power and potential of these systems to identify cellular and molecular mechanisms underlying disease and discuss recent advances, such as gene editing, and smooth muscle cell embryonic lineage. In particular, we discuss the practical aspects of vascular smooth muscle cell derivation and characterization, and provide our personal insights into the challenges and limitations of this approach. Future applications, such as genotype-phenotype association, drug screening, and precision medicine are discussed. We propose that iPSC-derived aortic disease models could guide future clinical trials via “clinical-trials-in-a-dish”, thus paving the way for new and improved therapies for patients.

Current understanding of intimal hyperplasia and effect of compliance in synthetic small diameter vascular grafts

Despite much effort, synthetic small diameter vascular grafts still face limited success due to vascular wall thickening known as intimal hyperplasia (IH). Compliance mismatch between graft and native vessels has been proposed to be one of a key mechanical factors of synthetic vascular grafts that could contribute to the formation of IH. While many methods have been developed to determine compliance both in vivo and in vitro, the effects of compliance mismatch still remain uncertain. This review aims to explain the biomechanical factors that are responsible for the formation and development of IH and their relationship with compliance mismatch. Furthermore, this review will address the current methods used to measure compliance both in vitro and in vivo. Lastly, current limitations in understanding the connection between the compliance of vascular grafts and the role it plays in the development and progression of IH will be discussed.

Phosphorylated GSK‑3β protects stress‑induced apoptosis of myoblasts via the PI3K/Akt signaling pathway

Facial jaw muscle is involved in the occurrence, development, treatment and maintenance of maxillofacial deformities. The structure and function of this tissue can be altered by changes in external stimuli, and orthodontists can regulate its reconstruction using orthopedic forces. The PI3K/Akt signaling pathway is most well‑known for its biological functions in cell proliferation, survival and apoptosis. In the present study, the effects of the PI3K/Akt signaling pathway in cyclic stretch‑induced myoblast apoptosis were investigated. For this purpose, L6 rat myoblasts were cultured under mechanical stimulation and treated with the PI3K kinase inhibitor, LY294002, to elucidate the role of the PI3K/Akt signaling pathway. Cells were stained with Hoechst 33258 to visualize morphological changes and apoptosis of myoblasts, and western blotting was performed to detect expression of Akt, phosphorylated (p)‑Akt (Ser473), glycogen synthase kinase 3β (GSK‑3β) and p‑GSK‑3β (Ser9). After addition of PI3K inhibitor, the expression of total Akt and GSK‑3β did not significantly differ among groups; however, the levels of p‑Akt and p‑GSK‑3β were lower in inhibitor‑treated groups than in those treated with loading stress alone. In addition, the rate of apoptosis in myoblasts subjected to cyclic stretch increased in a time‑dependent manner, peaking at 24 h. Collectively, it was also demonstrated that the PI3K/Akt/GSK‑3β pathway plays an important role in stretch‑induced myoblast apoptosis.

Intermedin promotes vessel fusion by inducing VE-cadherin accumulation at potential fusion sites and to achieve a dynamic balance between VE-cadherin-complex dissociation/reconstitution

To create a closed vascular system, angiogenic sprouts must meet and connect in a process called vessel fusion, which is a prerequisite for establishment of proper blood flow in nascent vessels. However, the molecular machinery underlying this process remains largely unknown. Herein, we report that intermedin (IMD), a calcitonin family member, promotes vessel fusion by inducing endothelial cells (ECs) to enter a "ready-to-anchor" state. IMD promotes vascular endothelial cadherin (VEC) accumulation at the potential fusion site to facilitate anchoring of approaching vessels to each other. Simultaneously, IMD fine-tunes VEC activity to achieve a dynamic balance between VEC complex dissociation and reconstitution in order to widen the anastomotic point. IMD induces persistent VEC phosphorylation. Internalized phospho-VEC preferentially binds to Rab4 and Rab11, which facilitate VEC vesicle recycling back to the cell-cell contact for reconstruction of the VEC complex. This novel mechanism may explain how neovessels contact and fuse to adjacent vessels to create a closed vascular system.

MicroRNA-29a Involvement in Phenotypic Transformation of Venous Smooth Muscle Cells Via Ten-Eleven Translocation Methylcytosinedioxygenase 1 in Response to Mechanical Cyclic Stretch

Mechanical stimuli play an important role in vein graft restenosis and the abnormal migration and proliferation of vascular smooth muscle cells (VSMCs) are pathological processes contributing to this disorder. Here, based on previous high-throughput sequencing data from vein grafts, miR-29a-3p and its target, the role of Ten-eleven translocation methylcytosinedioxygenase 1 (TET1) in phenotypic transformation of VSMCs induced by mechanical stretch was investigated. Vein grafts were generated by using the "cuff" technique in rats. Deep transcriptome sequencing revealed that the expression of TET1 was significantly decreased, a process confirmed by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analysis. MicroRNA-seq showed that miR-29a-3p was significantly up-regulated, targeting TET1 as predicted by Targetscan. Bioinformatics analysis indicated that the co-expressed genes with TET1 might modulate VSMC contraction. Venous VSMCs exposed to 10%-1.25 Hz cyclic stretch by using the Flexcell system were used to simulate arterial mechanical conditions in vitro. RT-qPCR revealed that mechanical stretch increased the expression of miR-29a-3p at 3 h. Western blot analysis showed that TET1 was significantly decreased, switching contractile VSMCs to cells with a synthetic phenotype. miR-29a-3p mimics (MI) and inhibitor (IN) transfection confirmed the negative impact of miR-29a-3p on TET1. Taken together, results from this investigation demonstrate that mechanical stretch modulates venous VSMC phenotypic transformation via the mediation of the miR-29a-3p/TET1 signaling pathway. miR-29a-3p may have potential clinical implications in the pathogenesis of remodeling of vein graft restenosis.

Inhalation of Ultrafine Zinc Particles Impaired Cardiovascular Functions in Hypertension-Induced Heart Failure Rats With Preserved Ejection Fraction

Although it is possible for inhalation of ultrafine particles to impair human health, its effect is not clear in patients with HFpEF. This study investigated cardiac and hemodynamic changes in hypertension-induced rats of HFpEF after inhaling ultrafine zinc particles for a while. Multiple experimental measurements were carried out in DSS rats fed with high salt (HS) and low salt (LS) diets as well as HS diet with the inhalation of ultrafine zinc particles (defined as HP). Cardiac strain and strain rate were quantified by the speckle tracking echocardiography. The pressure and flow waves were recorded in the carotid artery and abdominal aorta and analyzed by the models of Windkessel and Womersley types. HS and HP rats were found to show lower strains on endocardium and epicardium than LS rats. The inhalation of ultrafine zinc particles further reduced the strain in the longitudinal direction on the endocardium of rats with HFpEF, but had relatively small effects on the epicardium. The inhalation of ultrafine zinc particles resulted in the increase of systemic resistance and the decrease of total vascular compliance as well as the increased PWV and induced more severe vascular stiffening in rats with HFpEF. In summary, the inhalation of ultrafine zinc particles deteriorated local myocardial dysfunctions in the LV and the hemodynamic environment in peripheral arteries in rats of HFpEF. This study is of importance to understand the mechanisms of cardiovascular impairments owing to air pollution.

Ultrasound assessment of tensile stress in carotid arteries of healthy human subjects with varying age

Background

Arterial remodeling is thought to reflect the adaptation of the vessel wall to mechanical and hemodynamic stimuli and contributes to the progression of cardiovascular and cerebrovascular diseases. Tensile stress (TS) is one of the mechanical properties of the artery wall. The purpose of this study was to investigate the tensile stress change (TS) of carotid artery with varying viscoelasticity in healthy subjects within two groups of different ages.

Methods

Forty-five subjects were recruited and randomly assigned into the group at the age above 50 years and below 50 years. The carotid arteries were examined by ultrasonography, using the techniques of shear wave elastography (SWE), shear wave dispersion (SWD) and radiofrequency (RF) -based ultrasound. The following values, including elastic modulus (SWER) and viscous index (SWDR), as well as the peak and mean TS of the left and right carotid arteries (L-PTS, R-PTS, L-MTS and R-MTS) were measured. The correlations between SWER, SWDR and tensile stress were evaluated.

Results

The SWE_R and SWD_R of carotid arteries are lower in the subjects ≥50 years old than the subjects younger than 50 years (SWE_R, 10.29 ± 9.57 kPa VS 17.24 ± 14.07 kPa; SWD_R, 11.99 ± 3.51 (m/s)/kHz VS 13.97 ± 3.71 (m/s)/kHz, P < 0.05). The R-PTS was lower in the group with younger age (P < 0.05). Pearson correlation analysis showed that SWE_R of carotid artery was positively correlated with the parameters of tensile stress, R-PTS, R-MTS, L-PTS and L-MTS(r = 0.218, r = 0.359, r = 0.209 and r = 0.369, respectively, P < 0.05). However, SWD_R of carotid arteries was not significantly associated with TS.

Conclusion

Ultrasonic shear wave imaging could be used to quantitatively assess carotid viscoelasticity. The carotid TS was related to its elasticity while little related to its viscosity, suggesting that mechanical properties of the arterial wall might be better revealed.

Trial registration

Date of our trial registration: 2018-06-11. Registered with the official website of China Clinical Trial Registration Center (ChiCTR1800016590)