Frequency-Dependent Phenotype Modulation of Vascular Smooth Muscle Cells under Cyclic Mechanical Strain

Effect of Mechanical Stimuli on the Phenotypic Plasticity of Induced Pluripotent Stem-Cell-Derived Vascular Smooth Muscle Cells in a 3D Hydrogel

Introduction: Vascular smooth muscle cells (VSMCs) play a pivotal role in vascular homeostasis, with dysregulation leading to vascular complications. Human-induced pluripotent stem-cell (hiPSC)-derived VSMCs offer prospects for personalized disease modeling and regenerative strategies. Current research lacks comparative studies on the impact of three-dimensional (3D) substrate properties under cyclic strain on phenotypic adaptation in hiPSC-derived VSMCs. Here, we aim to investigate the impact of intrinsic substrate properties, such as the hydrogel's elastic modulus and cross-linking density in a 3D static and dynamic environment, on the phenotypical adaptation of human mural cells derived from hiPSC-derived organoids (ODMCs), compared to aortic VSMCs. Methods and results: ODMCs were cultured in two-dimensional (2D) conditions with synthetic or contractile differentiation medium or in 3D Gelatin Methacryloyl (GelMa) substrates with varying degrees of functionalization and percentages to modulate Young's modulus and cross-linking density. Cells in 3D substrates were exposed to cyclic, unidirectional strain. Phenotype characterization was conducted using specific markers through immunofluorescence and gene expression analysis. Under static 2D culture, ODMCs derived from hiPSCs exhibited a VSMC phenotype, expressing key mural markers, and demonstrated a level of phenotypic plasticity similar to primary human VSMCs. In static 3D culture, a substrate with a higher Young's modulus and cross-linking density promoted a contractile phenotype in ODMCs and VSMCs. Dynamic stimulation in the 3D substrate promoted a switch toward a contractile phenotype in both cell types. Conclusion: Our study demonstrates phenotypic plasticity of human ODMCs in response to 2D biological and 3D mechanical stimuli that equals that of primary human VSMCs. These findings may contribute to the advancement of tailored approaches for vascular disease modeling and regenerative strategies.

Controlled and Synchronised Vascular Regeneration upon the Implantation of Iloprost- and Cationic Amphiphilic Drugs-Conjugated Tissue-Engineered Vascular Grafts into the Ovine Carotid Artery: A Proteomics-Empowered Study

Implementation of small-diameter tissue-engineered vascular grafts (TEVGs) into clinical practice is still delayed due to the frequent complications, including thrombosis, aneurysms, neointimal hyperplasia, calcification, atherosclerosis, and infection. Here, we conjugated a vasodilator/platelet inhibitor, iloprost, and an antimicrobial cationic amphiphilic drug, 1,5-bis-(4-tetradecyl-1,4-diazoniabicyclo [2.2.2]octan-1-yl) pentane tetrabromide, to the luminal surface of electrospun poly(ε-caprolactone) (PCL) TEVGs for preventing thrombosis and infection, additionally enveloped such TEVGs into the PCL sheath to preclude aneurysms, and implanted PCL^Ilo/CAD TEVGs into the ovine carotid artery (n = 12) for 6 months. The primary patency was 50% (6/12 animals). TEVGs were completely replaced with the vascular tissue, free from aneurysms, calcification, atherosclerosis and infection, completely endothelialised, and had clearly distinguishable medial and adventitial layers. Comparative proteomic profiling of TEVGs and contralateral carotid arteries found that TEVGs lacked contractile vascular smooth muscle cell markers, basement membrane components, and proteins mediating antioxidant defense, concurrently showing the protein signatures of upregulated protein synthesis, folding and assembly, enhanced energy metabolism, and macrophage-driven inflammation. Collectively, these results suggested a synchronised replacement of PCL with a newly formed vascular tissue but insufficient compliance of PCL^Ilo/CAD TEVGs, demanding their testing in the muscular artery position or stimulation of vascular smooth muscle cell specification after the implantation.

Soft pneumatic actuators for mimicking multi-axial femoropopliteal artery mechanobiology

Tissue biomanufacturing aims to produce lab-grown stem cell grafts and biomimetic drug testing platforms but remains limited in its ability to recapitulate native tissue mechanics. The emerging field of soft robotics aims to emulate dynamic physiological locomotion, representing an ideal approach to recapitulate physiologically complex mechanical stimuli and enhance patient-specific tissue maturation. The kneecap's femoropopliteal artery (FPA) represents a highly flexible tissue across multiple axes during blood flow, walking, standing, and crouching positions, and these complex biomechanics are implicated in the FPA's frequent presentation of peripheral artery disease. We developed a soft pneumatically actuated (SPA) cell culture platform to investigate how patient-specific FPA mechanics affect lab-grown arterial tissues. Silicone hyperelastomers were screened for flexibility and biocompatibility, then additively manufactured into SPAs using a simulation-based design workflow to mimic normal and diseased FPA extensions in radial, angular, and longitudinal dimensions. SPA culture platforms were seeded with mesenchymal stem cells, connected to a pneumatic controller, and provided with 24-hour multi-axial exercise schedules to demonstrate the effect of dynamic conditioning on cell alignment, collagen production, and muscle differentiation without additional growth factors. Soft robotic bioreactors are promising platforms for recapitulating patient-, disease-, and lifestyle-specific mechanobiology for understanding disease, treatment simulations, and lab-grown tissue grafts.

Effect of pulsatile stretch on unfolded protein response in a new model of the pulmonary hypertensive vascular wall

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by hypoxemia and arterial remodeling. Dynamic stretch and recoil of the arterial wall during pulsation (in normal conduit arteries, stretch 20% above diastolic diameter) maintains homeostasis; a static arterial wall is associated with remodeling. PPHN is diagnosed by echocardiography as decreased pulmonary artery wall displacement during systole, causing decreased pulmonary arterial pressure acceleration time in a stiff artery.

We hypothesized that a ‘normal’ amplitude of pulsatile stretch is protective against ER stress, while the loss of stretch is a trigger for hypoxia-induced stress responses. Using a novel in vitro model of pulmonary arterial myocytes subject to repetitive stretch-relaxation cycles within a normoxic or hypoxic environment, we examined the relative impact of hypoxia (pulmonary circuit during unresolved PPHN) and cyclic mechanical stretch (diminished in PPHN) on myocyte homeostasis, specifically on signaling proteins for autophagy and endoplasmic reticulum (ER) stress.

Stretch induced autophagosome abundance under electron microscopy. Hypoxia, in presence or absence of pulsatile stretch, decreased unfolded protein response (UPR) hallmark BIP (GRP78) in contractile phenotype pulmonary arterial myocytes. Inositol requiring enzyme-1 α (IRE1α) was not activated; but hypoxia induced eif2α phosphorylation, increasing expression of ATF4 (activating transcription factor-4). This was sensitive to inhibition by autophagy inhibitor bafilomycin A1.

We conclude that in the pulmonary circuit, hypoxia induces one arm of the UPR pathway and causes ER stress. Pulsatile stretch ameliorates the hypoxic UPR response, and while increasing presence of autophagosomes, does not activate canonical autophagy signaling pathways. We propose that simultaneous application of hypoxia and graded levels of cyclic stretch can be used to distinguish myocyte signaling in the deformable pulmonary artery of early PPHN, versus the inflexible late stage PPHN artery.

Three-dimensional printing for cardiovascular diseases: from anatomical modeling to dynamic functionality

Three-dimensional (3D) printing is widely used in medicine. Most research remains focused on forming rigid anatomical models, but moving from static models to dynamic functionality could greatly aid preoperative surgical planning. This work reviews literature on dynamic 3D heart models made of flexible materials for use with a mock circulatory system. Such models allow simulation of surgical procedures under mock physiological conditions, and are; therefore, potentially very useful to clinical practice. For example, anatomical models of mitral regurgitation could provide a better display of lesion area, while dynamic 3D models could further simulate in vitro hemodynamics. Dynamic 3D models could also be used in setting standards for certain parameters for function evaluation, such as flow reserve fraction in coronary heart disease. As a bridge between medical image and clinical aid, 3D printing is now gradually changing the traditional pattern of diagnosis and treatment.

Biomechanical signal communication in vascular smooth muscle cells

Biomechanical stresses are closely associated with cardiovascular development and diseases. In vivo, vascular smooth muscle cells are constantly stimulated by biomechanical factors caused by increased blood pressure leading to the non-specific activation of cell transmembrane proteins. Thus, various intracellular signal molecules are simultaneously activated via signaling cascades, which are closely related to alterations in the differentiation, phenotype, inflammation, migration, pyroptosis, calcification, proliferation, and apoptosis of vascular smooth muscle cells. Meanwhile, mechanical stress-induced miRNAs and epigenetics modification on vascular smooth muscle cells play critical roles as well. Eventually, the overall pathophysiology of the cells is altered, resulting in the development of many major clinical diseases, including hypertension, atherosclerosis, grafted venous atherosclerosis, and aneurysm, among others. In this paper, important advances in mechanical signal communication in vascular smooth muscle cells are reviewed.

Restoring Blood Pressure in Hypertensive Mice Fails to Fully Reverse Vascular Stiffness

Background

Hypertension is a well-established driver of vascular remodeling and stiffening. The goal of this study was to evaluate whether restoring normal blood pressure (BP) fully restores vascular stiffness toward that of normotensive controls.

Methods

C57Bl6/J male mice received angiotensin II (angII; 1 μg/kg/min) via infusion pump for 8 weeks (hypertension group: HH), angII for 4 weeks (hypertension group: H4), angII for 4 weeks followed by 4 weeks of recovery (reversal group: HN), or sham treatment (normotensive group: NN). BP, heart rate, and pulse wave velocity (PWV) were measured longitudinally. At the end of the study period, aortas were harvested for testing of vasoreactivity, passive mechanical properties, and vessel structure.

Results

The HH group exhibited a sustained increase in BP and PWV over the 8-week period (p < 0.01). In the HN group, BP and PWV increased during the 4-week angII infusion, and, though BP was restored during the 4-week recovery, PWV exhibited only partial restoration (p < 0.05). Heart rate was similar in all cohorts. Compared to NN controls, both HH and HN groups had significantly increased wall thickness (p < 0.05 HH vs. NN, p < 0.01 HN vs. NN), mucosal extracellular matrix accumulation (p < 0.0001 HH vs. NN, p < 0.05 HN vs. NN), and intralamellar distance (p < 0.001 HH vs. NN, p < 0.01 HN vs. NN). Both intact and decellularized vessels were noted to have significantly higher passive stiffness in the HH and H4 cohorts than in NN controls (p < 0.0001). However, in the HN cohort, intact vessels were only modestly stiffer than those of NN controls, and decellularized HN vessels were identical to those from the NN controls. Compared to NN controls, the HH and HN cohorts exhibited significantly diminished phenylephrine-induced contraction (p < 0.0001) and endothelium-dependent vasodilation (p < 0.05).

Conclusion

Hypertension causes a significant increase in in vivo aortic stiffness that is only partially reversible after BP normalization. Although hypertension does lead to matrix stiffening, restoration of BP restores matrix mechanics to levels similar to those of normotensive controls. Nevertheless, endothelial and vascular smooth muscle cell dysfunction persist after restoration of normotension. This dysfunction is, in part, responsible for augmented PWV after restoration of BP.

Incrementing the Frequency of Dynamic Strain on SMC-Cellularised Collagen-Based Scaffolds Affects Extracellular Matrix Remodeling and Mechanical Properties

Notwithstanding the efforts injected in vascular tissue engineering in the past 30 years, the clinical translation of engineered artery constructs is far from being successful. One common approach to improve artery regeneration is the use of cyclic mechanical stimuli to guide cellular remodeling. However, there is a lack of information on the effect of cyclic strain on cells within a 3D environment. To this end, this work explored the effect of gradual increase in stimulation frequency on the response of human umbilical artery smooth muscle cells (HUASMCs) embedded in a 3D collagen matrix. The results demonstrate that, with an applied strain of 5%, the gradual increase of frequency from 0.1 to 1 Hz improved collagen remodeling by HUASMCs compared to samples constantly stimulated at 1 Hz. The expression of collagen, elastin and matrix metalloproteinase-2 (MMP-2) genes was similar at 7 days for gradual and 1 Hz samples which showed lower amounts than static counterparts. Interestingly the mechanical properties of the constructs, specifically the amplitude of the time constants and the elastic equilibrium modulus, were enhanced by gradual increase of frequency. Taken together, these results show an increase in collagen remodeling by the HUASMCs overtime under incremental cyclic mechanical strain. This work suggests that only the in-depth investigation of the effects of stimulation parameters on the behavior of vSMC under cyclic strain in a 3D environment could lead to the design of optimized control strategies for enhanced vascular tissue generation and maturation in bioreactors.

Application of laser scanning cytometry in vascular smooth muscle remodeling

Pulmonary artery hyperplasia is the result of proliferation of the pulmonary arterial smooth muscles (PASM). Hypoxia-induced PASM proliferation in the fetus and the newborn is the primary cause of persistent pulmonary hypertension of the newborn (PPHN). This study was performed to characterize the utility of the Laser Scanning Cytometry (LSC) method in elucidating arterial cytoskeletal remodeling in an in vitro model of PPHN. The aim was to demonstrate the following: (a) LSC is a valid method for the analysis of nuclear and cytosolic fluorescence and (b) the cumulative effects of mechanical stretch together with hypoxia promote reactive oxygen species (ROS) formation. The molecular events in response to hypoxia and the mechanical overload of the pulmonary circuit were demonstrated in vitro by subjecting hypoxic cultured primary PASM or human airway smooth muscles (hASM) to repetitive stretch-relaxation cycles at rates comparable to dynamic stretch in vivo. The altered cytoskeleton in the form of filamentous to globular actin (F:G actin) ratio was imaged and quantified at the cellular level by LSC as an endpoint. LSC can remove the nuclear G-actin fluorescence from the total G-actin fluorescence. Pulsatile stretch was found to significantly increase the total endogenous ROS and superoxide anion release in normoxic and hypoxic conditions in primary PASM fibers. The effect of stretch was predominant in increasing superoxide anion release, only under hypoxic conditions. These findings, obtained by LSC in vitro are amenable to validation in any in vivo model of interest. The in vitro model is clinically relevant to human pulmonary vascular remodeling.

Cyclic Mechanical Stretch Up-regulates Hepatoma-Derived Growth Factor Expression in Cultured Rat Aortic Smooth Muscle Cells

Hepatoma-derived growth factor (HDGF) is a potent mitogen for vascular smooth muscle cells (SMCs) during embryogenesis and injury repair of vessel walls. Whether mechanical stimuli modulate HDGF expression remains unknown. The present study aimed at investigating whether cyclic mechanical stretch plays a regulatory role in HDGF expression and regenerative cytokine production in aortic SMCs. A SMC cell line was grown on a silicone-based elastomer chamber with extracellular matrix coatings (either type I collagen or fibronectin) and received cyclic and uniaxial mechanical stretches with 10% deformation at frequency 1 Hz. Morphological observation showed that fibronectin coating provided better cell adhesion and spreading and that consecutive 6 h of cyclic mechanical stretch remarkably induced reorientation and realignment of SMCs. Western blotting detection demonstrated that continuous mechanical stimuli elicited up-regulation of HDGF and proliferative cell nuclear antigen, a cell proliferative marker. Signal kinetic profiling study indicated that cyclic mechanical stretch induced signaling activity in RhoA/ROCK and PI3K/Akt cascades. Kinase inhibition study further showed that blockade of PI3K activity suppressed the stretch-induced tumor necrosis factor-α (TNF-α), whereas RhoA/ROCK inhibition significantly blunted the interleukin-6 (IL-6) production and HDGF overexpression. Moreover, siRNA-mediated HDGF gene silencing significantly suppressed constitutive expression of IL-6, but not TNF-α, in SMCs. These findings support the role of HDGF in maintaining vascular expression of IL-6, which has been regarded a crucial regenerative factor for acute vascular injury. In conclusion, cyclic mechanical stretch may maintain constitutive expression of HDGF in vascular walls and be regarded an important biophysical regulator in vascular regeneration.

Computational Fluid Dynamics and Additive Manufacturing to Diagnose and Treat Cardiovascular Disease

Noninvasive engineering models are now being used for diagnosing and planning the treatment of cardiovascular disease. Techniques in computational modeling and additive manufacturing have matured concurrently, and results from simulations can inform and enable the design and optimization of therapeutic devices and treatment strategies. The emerging synergy between large-scale simulations and 3D printing is having a two-fold benefit: first, 3D printing can be used to validate the complex simulations, and second, the flow models can be used to improve treatment planning for cardiovascular disease. In this review, we summarize and discuss recent methods and findings for leveraging advances in both additive manufacturing and patient-specific computational modeling, with an emphasis on new directions in these fields and remaining open questions.

Deriving vascular smooth muscle cells from mesenchymal stromal cells: Evolving differentiation strategies and current understanding of their mechanisms

Vascular smooth muscle cells (VSMCs) play essential roles in regulating blood vessel form and function. Regeneration of functional vascular smooth muscle tissue to repair vascular diseases is an area of intense research in tissue engineering and regenerative medicine. For functional vascular smooth muscle tissue regeneration to become a practical therapy over the next decade, the field will need to have access to VSMC sources that are effective, robust and safe. While pluripotent stem cells hold good future promise to this end, more immediate translation is expected to come from approaches that generate functional VSMCs from adult sources of multipotent adipose-derived and bone marrow-derived mesenchymal stromal cells (ASCs and BMSCs). The research to this end is extensive and is dominated by studies relating to classical biochemical signalling molecules used to induce differentiation of ASCs and BMSCs. However, prolonged use of the biochemical induction factors is costly and can cause potential endotoxin contamination in the culture. Over recent years several non-traditional differentiation approaches have been devised to mimic defined aspects of the native micro-environment in which VSMCs reside to contribute to the differentiation of VSMC-like cells from ASCs and BMSCs. In this review, the promises and limitations of several non-traditional culture approaches (e.g., co-culture, biomechanical, and biomaterial stimuli) targeting VSMC differentiation are discussed. The extensive crosstalk between the underlying signalling cascades are delineated and put into a translational context. It is expected that this review will not only provide significant insight into VSMC differentiation strategies for vascular smooth muscle tissue engineering applications, but will also highlight the fundamental importance of engineering the cellular microenvironment on multiple scales (with consideration of different combinatorial pathways) in order to direct cell differentiation fate and obtain cells of a desired and stable phenotype. These strategies may ultimately be applied to different sources of stem cells in the future for a range of biomaterial and tissue engineering disciplines.

Effects of shear stress on endothelial cells: go with the flow

Haemodynamic forces influence the functional properties of vascular endothelium. Endothelial cells (ECs) have a variety of receptors, which sense flow and transmit mechanical signals through mechanosensitive signalling pathways to recipient molecules that lead to phenotypic and functional changes. Arterial architecture varies greatly exhibiting bifurcations, branch points and curved regions, which are exposed to various flow patterns. Clinical studies showed that atherosclerotic plaques develop preferentially at arterial branches and curvatures, that is in the regions exposed to disturbed flow and shear stress. In the atheroprone regions, the endothelium has a proinflammatory phenotype associated with low nitric oxide production, reduced barrier function and increased proadhesive, procoagulant and proproliferative properties. Atheroresistant regions are exposed to laminar flow and high shear stress that induce prosurvival antioxidant signals and maintain the quiescent phenotype in ECs. Indeed, various flow patterns contribute to phenotypic and functional heterogeneity of arterial endothelium whose response to proatherogenic stimuli is differentiated. This may explain the preferential development of endothelial dysfunction in arterial sites with disturbed flow.

Unraveling the role of mechanical stimulation on smooth muscle cells: A comparative study between 2D and 3D models

A thorough understanding of cell response to combined culture configuration and mechanical cues is of paramount importance in vascular tissue engineering applications. Herein, we investigated and compared the response of vascular smooth muscle cells (vSMCs) cultured in different culture environments (2D cell monolayers and 3D cellularized collagen-based gels) in combination with mechanical stimulation (7% uniaxial cyclic strain, 1 Hz) for 2 and 5 days. When cyclic strain was applied, two different responses, in terms of cell orientation and expression of contractile-phenotype proteins, were observed in 2D and 3D models. Specifically, in 2D configuration, cyclic strain caused ∼50% of cell population to align nearly perpendicular (80-90 degrees) to the strain direction, while not influencing the contractile-phenotype protein expression, as compared to the 2D static controls. Conversely, the application of uniaxial strain to 3D constructs induced a ∼60% cell alignment almost parallel (0-10 degrees) to the strain direction. Moreover, 3D mechanical stimulation applied for 5 days induced a twofold increase of SM α-actin level and a 14-fold increase of calponin expression as compared to 3D static controls. Altogether these findings provide a new insight into the potential to drive cell behavior by modulating the extracellular matrix and the biomechanical environment. Biotechnol. Bioeng. 2016;113: 2254-2263. © 2016 Wiley Periodicals, Inc.

Simultaneous Increases in Proliferation and Apoptosis of Vascular Smooth Muscle Cells Accelerate Diabetic Mouse Venous Atherosclerosis

Aims

This study was designed to demonstrate simultaneous increases in proliferation and apoptosis of vascular smooth muscle cells (VSMCs) leading to accelerated vein graft remodeling and to explore the underlying mechanisms.

Methods

Vein grafts were performed in non-diabetic and diabetic mice. The cultured quiescent VSMCs were subjected to mechanical stretch stress (SS) and/or advanced glycosylation end products (AGEs). Harvested vein grafts and treated VSMCs were used to detect cell proliferation, apoptosis, mitogen-activated protein kinases (MAPKs) activation and SM-α-actin expression.

Results

Significantly thicker vessel walls and greater increases in proliferation and apoptosis were observed in diabetic vein grafts than those in non-diabetic. Both SS and AGEs were found to induce different activation of three members of MAPKs and simultaneous increases in proliferation and apoptosis of VSMCs, and combined treatment with both had a synergistic effect. VSMCs with strong SM-α-actin expression represented more activated JNKs or p38MAPK, and cell apoptosis, while the cells with weak SM-α-actin expression demonstrated preferential activation of ERKs and cell proliferation. In contrast, inhibition of MAPKs signals triggered significant decreases in VSMC proliferation, and apoptosis. Treatment of the cells with RNA interference of receptor of AGEs (RAGE) also resulted in significant decreases in both proliferation and apoptosis.

Conclusions

Increased pressure-induced SS triggers simultaneous increases in proliferation and apoptosis of VSMCs in the vein grafts leading to vein arterializations, which can be synergistically accelerated by high glucose-induced AGEs resulting in vein graft atherosclerosis. Either SS or AGEs and their combination induce simultaneous increases in proliferation and apoptosis of VSMCs via different activation of three members of MAPKs resulting from different VSMC subtypes classified by SM-α-actin expression levels.

Mesenchymal stromal cells for sphincter regeneration

Stress urinary incontinence (SUI), defined as the involuntary loss of considerable amounts of urine during increased abdominal pressure (exertion, effort, sneezing, coughing, etc.), is a severe problem to the individuals affected and a significant medical, social and economic challenge. SUI is associated with pelvic floor debility, absence of detrusor contraction, or a loss of control over the sphincter muscle apparatus. The pathology includes an increasing loss of muscle cells, replacement of muscular tissue with fibrous tissue, and general aging associated processes of the sphincter complex. When current therapies fail to cure or improve SUI, application of regeneration-competent cells may be an alternative therapeutic option. Here we discuss different aspects of the biology of mesenchymal stromal cells, which are relevant to their clinical applications and for regenerating the sphincter complex. However, there are reports in favor of and against cell-based therapies. We therefore summarize the potential and the risks of cell-based therapies for the treatment of SUI.

Magnitude-dependent proliferation and contractility modulation of human bladder smooth muscle cells under physiological stretch

PURPOSE

The purpose of this study was to describe and test a kind of stretch pattern which is based on modified BOSE BioDynamic system to produce optimum physiological stretch during bladder cycle. Moreover, we aimed to emphasize the effects of physiological stretch's amplitude upon proliferation and contractility of human bladder smooth muscle cells (HBSMCs).

METHODS

HBSMCs were seeded onto silicone membrane and subjected to stretch simulating bladder cycle at the range of stretches and time according to customized software on modified BOSE BioDynamic bioreactor. Morphological changes were assessed using immunofluorescence and confocal laser scanning microscope. Cell proliferation and cell viability were determined by BrdU incorporation assay and Cell Counting Kit-8, respectively. Contractility of the cells was determined using collagen gel contraction assay. RT-PCR was used to assess phenotypic and contractility markers.

RESULTS

HBSMCs were found to show morphologically spindle-shaped and orientation at various elongations in the modified bioreactor. Stretch-induced proliferation and viability depended on the magnitude of stretch, and stretches also regulate contractility and contraction markers in a magnitude-dependent manner.

CONCLUSION

We described and tested a kind of stretch pattern which delivers physiological stretch implemented during bladder cycle. The findings also showed that mechanical stretch can promote magnitude-dependent morphological, proliferative and contractile modulation of HBSMCs in vitro.

Impact of cyclic stretch on induced elastogenesis within collagenous conduits

In vitro tissue engineering of vascular conduits requires a synergy between several external factors, including biochemical supplementation and mechanotranductive stimulation. The goal of this study was to improve adult human vascular smooth muscle cell orientation and elastic matrix synthesis within 3D tubular collagen gel constructs. We used a combination of elastogenic factors (EFs) previously tested in our lab, along with cyclic circumferential strains at low amplitude (2.5%) delivered at a range of frequencies (0.5, 1.5, and 3 Hz). After 21 days of culture, the constructs were analyzed for elastic matrix outcomes, activity of matrix metalloproteinases (MMPs)-2 and -9, cell densities and phenotype, and mechanical properties of constructs. While cell densities remained unaffected by the addition of stretch, contractile phenotypic markers were elevated in all stretched constructs relative to control. Constructs cultured with EFs stretched at 1.5 Hz exhibited the maximum elastin mRNA expression and total matrix elastin (over sixfold vs. the static EFs control). MMP-2 content was comparable in all treatment conditions, but MMP-9 levels were elevated at the higher frequencies (1.5 and 3 Hz). Minimal circumferential orientation was achieved and the mechanical properties remained comparable among the treatment conditions. Overall, constructs treated with EFs and stretched at 1.5 Hz exhibited the most elastogenic outcomes.

The role of SIRT6 in the differentiation of vascular smooth muscle cells in response to cyclic strain

Vascular smooth muscle cells (VSMCs) may switch their phenotype between a quiescent contractile phenotype and a synthetic phenotype in response to cyclic strain, and this switch may contribute to hypertension, atherosclerosis, and restenosis. SIRT 6 is a member of the sirtuin family, and plays an important role in different cell processes, including differentiation. We hypothesized that cyclic strain modulates the differentiation of VSMCs via a transforming growth factor-β1 (TGF-β1)-Smad-SIRT6 pathway. VSMCs were subjected to cyclic strain using a Flexercell strain unit. It was demonstrated that the strain stimulated the secretion of TGF-β1 into the supernatant of VSMCs. After exposed to the strain, the expressions of contractile phenotype markers, including smooth muscle protein 22 alpha, alpha-actin, and calponin, and phosphorylated Smad2, phosphorylated Smad5, SIRT6 and c-fos were up-regulated in VSMCs by western blot and immunofluorescence. And the expression of intercellular-adhesion molecule-1 (ICAM-1) was also increased detected by flow cytometry. The strained-induced up-regulation of SIRT6 was blocked by a TGF-β1 neutralizing antibody. Furthermore, the effects of strain on VSMCs were abrogated by SIRT6-specific siRNA transfection via the suppression c-fos and ICAM-1. These results suggest that SIRT6 may play a critical role in the regulation of VSMC differentiation in response to the cyclic strain.

Perivascular cells in blood vessel regeneration

Vascular engineering seeks to design and construct functional blood vessels comprising endothelial cells (ECs) and perivascular cells (PCs), with the ultimate goal of clinical translation. While EC behavior has been extensively investigated, PCs play an equally significant role in the development of novel regenerative strategies, providing functionality and stability to vessels. The two major classes of PCs are vascular smooth muscle cells (vSMCs) and pericytes; vSMCs can be further sub-classified as either contractile or synthetic. The inclusion of these cell types is crucial for successful regeneration of blood vessels. Furthermore, understanding distinctions between vSMCs and pericytes will enable improved therapeutics in a tissue-specific manner. Here we focus on the approaches and challenges facing the use of PCs in vascular regeneration, including their characteristics, stem cell sources, and interactions with ECs. Finally, we discuss biochemical and microRNA (miR) regulators of PC behavior and engineering approaches that mimic various cues affecting PC function.

The effect of mechanical strain on soft (cardiovascular) and hard (bone) tissues: common pathways for different biological outcomes

Mechanical stress plays a pivotal role in developing and maintaining tissues functionalities. Cells are constantly subjected to strain and compressive forces that are sensed by specialized membrane mechanosensors and converted in biochemical signals able to differently influence cellular behavior in terms of surviving, differentiation and extracellular matrix remodeling. This review focuses on the effects of mechanical strain on soft and hard tissues. Unexpectedly, different cells share almost the same membrane mechanosensors and the relative intracellular pathways, but to ultimately obtain very different biological effects. The events occurring in cardiovascular and bone tissues are treated in details, showing that integrins, cadherins, growth factor receptors and ions channels specifically expressed in the different tissues are the major actors of the sight. However, MAPkinases and RhoGTPases are mainly involved in the biochemical intracellular signaling directed to nuclear modifications.

Cyclic stretch-induced thrombin generation by rat vascular smooth muscle cells is mediated by the integrin αvβ3 pathway

AIMS

Vascular smooth muscle cell (VSMC) phenotypic modulation plays a pivotal role in atherothrombotic diseases. Thrombin generation at the surface of VSMCs and activation of integrin mechanotransduction pathways represent potential mechanisms. Here, we examine whether mechanical stretch increases thrombin generation on cultured rat aortic VSMCs.

METHODS AND RESULTS

The integrin α(v)β(3) antagonist peptide (cRGDPV) dose-dependently decreased thrombin generation without stretch. Static stretch (5%, 1 Hz) failed to modify the thrombin-forming capacity of VSMCs, whereas 10% cyclic stretch during 60 and 360 min enhanced integrin α(v)β(3) expression and thrombin generation at the surface of VSMCs by 30% without inducing apoptosis. Cyclic stretch also stimulated Src phosphorylation, cleavage of talin, and binding of prothrombin to VSMCs. Upregulation of α(v)β(3) expression, Src phosphorylation, and enhanced thrombin generation by cyclic stretch were abolished by cRGDPV and silencing RNA (siRNA) against α(v) as well as by selective inhibition of integrin α(v)β(3) inside-out signalling by a talin-siRNA. Complete abolition of stretch-induced VSMC-supported thrombin generation by the RGT peptide, which disrupts the interaction of Src with the β(3) cytoplasmic tail, demonstrates the link between outside-in pathways involving β(3)-Src interaction and thrombin activity dependent on inside-out signalling.

CONCLUSION

These data show that the contribution of cyclic stretch to VSMC-supported thrombin generation is driven by the integrin α(v)β(3) signalling pathway and suggest a role for pulsatility-induced intramural thrombin in VSMC-dependent vascular remodelling.

Mechanical stretching for tissue engineering: two-dimensional and three-dimensional constructs

Mechanical cell stretching may be an attractive strategy for the tissue engineering of mechanically functional tissues. It has been demonstrated that cell growth and differentiation can be guided by cell stretch with minimal help from soluble factors and engineered tissues that are mechanically stretched in bioreactors may have superior organization, functionality, and strength compared with unstretched counterparts. This review explores recent studies on cell stretching in both two-dimensional (2D) and three-dimensional (3D) setups focusing on the applications of stretch stimulation as a tool for controlling cell orientation, growth, gene expression, lineage commitment, and differentiation and for achieving successful tissue engineering of mechanically functional tissues, including cardiac, muscle, vasculature, ligament, tendon, bone, and so on. Custom stretching devices and lab-specific mechanical bioreactors are described with a discussion on capabilities and limitations. While stretch mechanotransduction pathways have been examined using 2D stretch, studying such pathways in physiologically relevant 3D environments may be required to understand how cells direct tissue development under stretch. Cell stretch study using 3D milieus may also help to develop tissue-specific stretch regimens optimized with biochemical feedback, which once developed will provide optimal tissue engineering protocols.

Cyclic strain improves strength and function of a collagen-based tissue-engineered vascular media

Tissue-engineered blood vessels may provide a solution to the lack of suitable blood vessels for coronary and peripheral vessel bypass grafting. Cyclic strain can be used to provide a more physiological environment that may result in tissue that more closely resembles native artery. In this study, cyclic strain is applied to a collagen-based, tissue-engineered vascular medium. An increased culture time was used to allow the tissue to adhere to the silastic sleeve and to eliminate longitudinal compaction. Cyclic strain improved tissue strength through increased collagen content as well as some radial tissue compaction. Mechanical stimulation promoted a more contractile phenotype and led to a greater contractile response to the vasoconstrictor endothelin-1.

Molecular regulation of contractile smooth muscle cell phenotype: implications for vascular tissue engineering

The molecular regulation of smooth muscle cell (SMC) behavior is reviewed, with particular emphasis on stimuli that promote the contractile phenotype. SMCs can shift reversibly along a continuum from a quiescent, contractile phenotype to a synthetic phenotype, which is characterized by proliferation and extracellular matrix (ECM) synthesis. This phenotypic plasticity can be harnessed for tissue engineering. Cultured synthetic SMCs have been used to engineer smooth muscle tissues with organized ECM and cell populations. However, returning SMCs to a contractile phenotype remains a key challenge. This review will integrate recent work on how soluble signaling factors, ECM, mechanical stimulation, and other cells contribute to the regulation of contractile SMC phenotype. The signal transduction pathways and mechanisms of gene expression induced by these stimuli are beginning to be elucidated and provide useful information for the quantitative analysis of SMC phenotype in engineered tissues. Progress in the development of tissue-engineered scaffold systems that implement biochemical, mechanical, or novel polymer fabrication approaches to promote contractile phenotype will also be reviewed. The application of an improved molecular understanding of SMC biology will facilitate the design of more potent cell-instructive scaffold systems to regulate SMC behavior.

Stretch-induced stress fiber remodeling and the activations of JNK and ERK depend on mechanical strain rate, but not FAK

BACKGROUND

Cells within tissues are subjected to mechanical forces caused by extracellular matrix deformation. Cells sense and dynamically respond to stretching of the matrix by reorienting their actin stress fibers and by activating intracellular signaling proteins, including focal adhesion kinase (FAK) and the mitogen-activated proteins kinases (MAPKs). Theoretical analyses predict that stress fibers can relax perturbations in tension depending on the rate of matrix strain. Thus, we hypothesized stress fiber organization and MAPK activities are altered to an extent dependent on stretch frequency.

PRINCIPAL FINDINGS

Bovine aortic endothelial cells and human osteosarcoma cells expressing GFP-actin were cultured on elastic membranes and subjected to various patterns of stretch. Cyclic stretching resulted in strain rate-dependent increases in stress fiber alignment, cell retraction, and the phosphorylation of the MAPKs JNK, ERK and p38. Transient step changes in strain rate caused proportional transient changes in the levels of JNK and ERK phosphorylations without affecting stress fiber organization. Disrupting stress fiber contractile function with cytochalasin D or Y27632 decreased the levels of JNK and ERK phosphorylation. Previous studies indicate that FAK is required for stretch-induced cell alignment and MAPK activations. However, cyclic uniaxial stretching induced stress fiber alignment and the phosphorylation of JNK, ERK and p38 to comparable levels in FAK-null and FAK-expressing mouse embryonic fibroblasts.

CONCLUSIONS

These results indicate that cyclic stretch-induced stress fiber alignment, cell retraction, and MAPK activations occur as a consequence of perturbations in fiber strain. These findings thus shed new light into the roles of stress fiber relaxation and reorganization in maintenance of tensional homeostasis in a dynamic mechanical environment.

Atheromas feel the pressure: biomechanical stress and atherosclerosis

Atherosclerosis, a chronic vascular disease, is the underlying cause of over half the deaths in the United States each year. Variations in local vascular hemodynamics predispose select sites in the vasculature to atherosclerosis, and the atherosclerotic lesions, in turn alter the biomechanical functioning of the local microenvironment, the consequences of which are not well understood on a molecular level. Further progress in the field of atherosclerosis will require an understanding of the relationship between biomechanics, the tissue microenvironment, and the cellular and molecular response to these factors. This review summarizes this field, particularly within the context of the vascular smooth muscle cell.

Schlafen 3 induction by cyclic strain regulates intestinal epithelial differentiation

The intestinal epithelium is subjected to repetitive deformation during normal gut function by peristalsis and villous motility. In vitro, cyclic strain promotes intestinal epithelial proliferation and induces an absorptive phenotype characterized by increased dipeptidyl dipeptidase (DPPIV) expression. Schlafen 3 is a novel gene recently associated with cellular differentiation. We sought to evaluate whether Schlafen 3 mediates the effects of strain on the differentiation of intestinal epithelial cell (IEC)-6 in the absence or presence of cyclic strain. Strain increased Schlafen 3 mRNA and protein. In cells transfected with a control-nontargeting siRNA, strain increased DPPIV-specific activity. However, Schlafen 3 reduction by siRNA decreased basal DPPIV and prevented any stimulation of DPPIV activity by strain. Schlafen 3 reduction also prevented DPPIV induction by sodium butyrate (1 mM) or transforming growth factor (TGF)-beta (0.1 ng/ml), two unrelated differentiating stimuli. However, Schlafen-3 reduction by siRNA did not prevent the mitogenic effect of strain or that of EGF. Blocking Src and phosphatidyl inositol (PI3)-kinase prevented strain induction of Schlafen 3, but Schlafen 3 induction required activation of p38 but not ERK. These results suggest that cyclic strain induces an absorptive phenotype characterized by increased DPPIV activity via Src-, p38-, and PI3-kinase-dependent induction of Schlafen 3 in rat IEC-6 cells on collagen, whereas Schlafen 3 may also be a key factor in the induction of intestinal epithelial differentiation by other stimuli such as sodium butyrate or TGF-beta. The induction of Schlafen 3 or its human homologs may modulate intestinal epithelial differentiation and preserve the gut mucosa during normal gut function.

A novel seamless elastic scaffold for vascular tissue engineering

Tissue-engineered vascular grafts have been investigated as a substitute for prosthetic vascular grafts. The current scaffolds have several limitations due to weak mechanical properties in withstanding the pressure of blood vessel. A gel-spinning molding device including three-separate drivers that make a cylindrical shaft turn on its axis, orbit, and concurrently move up and down was developed for preparing seamless fibrous tubular scaffolds for vascular grafts. A seamless double-layered tubular scaffold, which was composed of an outer fibrous network and inner porous layer, was fabricated by using the device for the spinning of poly(L-lactide-co-caprolactone) (PLCL, 50:50) solution as a gel state on a rotating cylindrical shaft that had been dip-coated with the mixture of PLCL solution and NaCl particles. A scaffold that had an inner layer fabricated with 30% salts, below 20 mum in salt size, and more than 100 microm in thickness, was found to be optimal from a blood leakage test. The burst pressures of the scaffolds were more than 900 mmHg. The scaffolds exhibited 550-670% elongation-at-break. The measured circumferential and longitudinal tensile strengths of the scaffolds were 3.62 +/- 0.68 and 2.64 +/- 0.41 MPa, respectively. The suture retention strength of the scaffold was measured to be 7.68 +/- 0.75 N. These mechanically strong and elastic properties of the newly developed scaffolds provide an important basis for blood vessel tissue engineering.

Cell-shape regulation of smooth muscle cell proliferation

Vascular smooth muscle cells (SMCs) play an important role in vascular remodeling. Heterogeneity and phenotypic changes in SMCs are usually accompanied by a morphological difference, i.e., elongated/spindle-like versus spread-out or epithelioid/rhomboid cell shapes. However, it is not known whether the cell shape directly regulates SMC proliferation, and what the underlying mechanisms are. In this study, microgrooves and micropatterned matrix islands were used to engineer the cell shape and investigate the associated biophysical and biological mechanisms. Compared to spread-out SMCs on nonpatterned surfaces, SMCs on micropatterned surfaces demonstrated elongated morphology, significantly lower cell and nucleus shape indexes, less spreading, a lower proliferation rate, and a similar response (but to a lesser extent) to platelet-derived growth factor, transforming growth factor-beta, and mechanical stretching. DNA microarray profiling revealed a lower expression of neuron-derived orphan receptor-1 (NOR-1) in elongated SMCs. Knocking down NOR-1 suppressed DNA synthesis in SMCs, suggesting that NOR-1 is a mediator of cell elongation effects. Regulation of DNA synthesis in SMCs by the cell shape alone and a decrease in DNA synthesis in the case of small cell spreading area were achieved by micropatterning SMCs on matrix islands of different shapes and spreading areas. Changes in the cell shape also affected the nucleus shape, whereas variations in the cell spreading area modulated the nucleus volume, indicating a possible link between nucleus morphology (both shape and volume) and DNA synthesis. The findings of this investigation provide insight into cell shape effects on cell structure and proliferation, and have direct implications for vascular pathophysiology.

TRPV4 channels mediate cyclic strain-induced endothelial cell reorientation through integrin-to-integrin signaling

Cyclic mechanical strain produced by pulsatile blood flow regulates the orientation of endothelial cells lining blood vessels and influences critical processes such as angiogenesis. Mechanical stimulation of stretch-activated calcium channels is known to mediate this reorientation response; however, the molecular basis remains unknown. Here, we show that cyclically stretching capillary endothelial cells adherent to flexible extracellular matrix substrates activates mechanosensitive TRPV4 (transient receptor potential vanilloid 4) ion channels that, in turn, stimulate phosphatidylinositol 3-kinase-dependent activation and binding of additional beta1 integrin receptors, which promotes cytoskeletal remodeling and cell reorientation. Inhibition of integrin activation using blocking antibodies and knock down of TRPV4 channels using specific small interfering RNA suppress strain-induced capillary cell reorientation. Thus, mechanical forces that physically deform extracellular matrix may guide capillary cell reorientation through a strain-dependent "integrin-to-integrin" signaling mechanism mediated by force-induced activation of mechanically gated TRPV4 ion channels on the cell surface.

Cellular and molecular effects of mechanical stretch on vascular cells and cardiac myocytes

Cells in the cardiovascular system are permanently subjected to mechanical forces due to the pulsatile nature of blood flow and shear stress, created by the beating heart. These haemodynamic forces play an important role in the regulation of vascular development, remodelling, wound healing and atherosclerotic lesion formation. Mechanical stretch can modulate several different cellular functions in VSMCs (vascular smooth muscle cells). These functions include, but are not limited to, cell alignment and differentiation, migration, survival or apoptosis, vascular remodelling, and autocrine and paracrine functions. Laminar shear stress exerts anti-apoptotic, anti-atherosclerotic and antithrombotic effects on ECs (endothelial cells). Mechanical stretch of cardiac myocytes can modulate growth, apoptosis, electric remodelling, alterations in gene expression, and autocrine and paracrine effects. The aim of the present review is primarily to summarize the cellular and molecular effects of mechanical stretch on vascular cells and cardiac myocytes, emphasizing the molecular mechanisms underlying the regulation. Knowledge of the impact of mechanical stretch on the cardiovascular system is vital to the understanding of the pathogenesis of cardiovascular diseases, and is also crucial to provide new insights into the prevention and therapy of cardiovascular diseases.

An analysis of the strain field in biaxial Flexcell membranes for different waveforms and frequencies

Mechanical stimuli have been shown to affect cell behaviour in terms of proliferation, apoptosis, and protein expression. In terms of cardiovascular diseases, for example, endothelial and smooth muscle cells exposed to an abnormal strain environment have been associated with atherosclerosis and in-stent restenosis. The FX-4000™ system (Flexercell® Tension Plus System, Flexcell Corporation, McKeesport, Pennsylvania, USA) is an in-vitro system that is widely used to strain cells in order to evaluate their response to strain. The precision, accuracy, and repeatability of the strains controlled by the system are therefore crucial to analyse and interpret the results confidently. The aim of this study was to investigate the mechanical behaviour of the FX-4000™ Flexercell® six-well-plate silicon membranes for static and dynamic cyclic strains by measuring the maximum peak strain and analysing the change in the membrane deformation after cyclic strain for 0 h, 24 h, and 48 h at different strain amplitudes and frequencies. The results of the tests conducted demonstrate notable differences between the measured strains of the membranes in comparison with both the inputs and the outputs of the Flexcell® software. The calibration method used by Flexcell® International assumes that the strain values determined for a given vacuum pressure on the silicone membranes are reliable for different waveforms and frequencies. The data reported here clearly indicate that this is not the case. The results indicate that a unique calibration pressure—strain curve must be determined for each test given the viscoelastic nature of the Flexcell system. A new method to calibrate the machine in house was applied using new pressure—strain equations. This new calibration method has been presented and should enable researchers using the Flexcell® machine to set up their cell experiments more accurately.

Role of Rac and Rho-GDI alpha in the frequency-dependent expression of h1-calponin in vascular smooth muscle cells under cyclic mechanical strain

Phenotype transformation of vascular smooth muscle cells (VSMCs) has been reported to be directly influenced by the frequency of mechanical strain. This study explored the effects of different frequencies of mechanical strain on expression of phenotype marker h1-calponin and the possible mechanism. VSMCs were subjected to cyclic strains of 10% elongation at 1 and 2 Hz for 24 h by using a Flexercell strain unit. The protein expression of h1-calponin was assessed by Western blotting and the possible protein kinases involved were evaluated by their specific inhibitor or targeted siRNA 'knock-down.' The results showed that cyclic strains modulated the expressions of h1-calponin, phospho-p38, Rac and Rho-guanine nucleotide dissociation inhibitor alpha (Rho-GDI alpha) in nonlinear frequency-dependent manners. This nonlinear frequency-dependent change of h1-calponin expression could be blocked by a specific p38 inhibitor, SB202190. The changed expression of phospho-p38 induced by the frequencies of cyclic strain was reversed by targeted siRNA 'knock-down' of Rac, while enhanced by targeted siRNA 'knock-down' of Rho-GDI alpha. These results suggest that the frequency-dependent expression of h1-calponin under cyclic strain is mediated at least partly by the regulation of Rac and Rho-GDI alpha expression on the activation of p38 pathway.

Effects of serum deprivation on the mechanical properties of adherent vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) function plays a key role in regulating the development and progression of vascular lesions. Among the more significant phenomena that occur during the development of these lesions is the phenotypic switching of VSMCs from a contractile to a synthetic state. A better understanding of the concurrent changes to VSMC mechanical properties that occur with phenotypic shifts can help to elucidate the role of VSMC mechanics in the development of vascular diseases. In the current study, the mechanical properties of adherent cultured rat aortic VSMCs were assessed by atomic force microscopy. Serum starvation was used to induce a phenotypic shift in vitro. It was concluded that serum starvation led to a statistically significant increase in apparent elastic modulus after 5 days, as well as a statistically significant decrease in hysteresis after culture for 3 days. If this trend of VSMC mechanical properties changing concurrently with phenotypic shifts were to hold true in vivo, such changes could affect the processes of mechanotransduction and/or arterial mechanical properties, thereby contributing to the progression of vascular disease.

The early- and late stages in phenotypic modulation of vascular smooth muscle cells: differential roles for lysophosphatidic acid

Lysophosphatidic acid (LPA) has been implicated as causative in phenotypic modulation (PM) of cultured vascular smooth muscle cells (VSMC) in their transition to the dedifferentiated phenotype. We evaluated the contribution of the three major LPA receptors, LPA1 and LPA2 GPCR and PPARgamma, on PM of VSMC. Expression of differentiated VSMC-specific marker genes, including smooth muscle alpha-actin, smooth muscle myosin heavy chain, calponin, SM-22alpha, and h-caldesmon, was measured by quantitative real-time PCR in VSMC cultures and aortic rings kept in serum-free chemically defined medium or serum- or LPA-containing medium using wild-type C57BL/6, LPA1, LPA2, and LPA1&2 receptor knockout mice. Within hours after cells were deprived of physiological cues, the expression of VSMC marker genes, regardless of genotype, rapidly decreased. This early PM was neither prevented by IGF-I, inhibitors of p38, ERK1/2, or PPARgamma nor significantly accelerated by LPA or serum. To elucidate the mechanism of PM in vivo, carotid artery ligation with/without replacement of blood with Krebs solution was used to evaluate contributions of blood flow and pressure. Early PM in the common carotid was induced by depressurization regardless of the presence/absence of blood, but eliminating blood flow while maintaining blood pressure or after sham surgery elicited no early PM. The present results indicate that LPA, serum, dissociation of VSMC, IGF-I, p38, ERK1/2, LPA1, and LPA2 are not causative factors of early PM of VSMC. Tensile stress generated by blood pressure may be the fundamental signal maintaining the fully differentiated phenotype of VSMC.

Role of cyclic strain frequency in regulating the alignment of vascular smooth muscle cells in vitro

The arterial system is subjected to cyclic strain because of periodic alterations in blood pressure, but the effects of frequency of cyclic strain on arterial smooth muscle cells (SMCs) remain unclear. Here, we investigated the potential role of the cyclic strain frequency in regulating SMC alignment using an in vitro model. Aortic SMCs were subject to cyclic strain at one elongation but at various frequencies using a Flexercell Tension Plus system. It was found that the angle information entropy, the activation of integrin-beta1, p38 MAPK, and F/G actin ratio of filaments were all changed in a frequency-dependent manner, which was consistent with SMC alignment under cyclic strain with various frequencies. A treatment with anti-integrin-beta1 antibody, SB202190, or cytochalasin D inhibited the cyclic strain frequency-dependent SMC alignment. These observations suggested that the frequency of cyclic strain plays a role in regulating the alignment of vascular SMCs in an intact actin filament-dependent manner, and cyclic strain at 1.25 Hz was the most effective frequency influencing SMC alignment. Furthermore, integrin-beta1 and p38 MAPK possibly mediated cyclic strain frequency-dependent SMC alignment.