Integrin receptors on aortic smooth muscle cells mediate adhesion to fibronectin, laminin, and collagen

Single-cell RNA sequencing reveals the vascular smooth muscle cell phenotypic landscape in aortic aneurysm

BACKGROUND AND OBJECTIVES

Phenotypic switching in vascular smooth muscle cells (VSMCs) has been linked to aortic aneurysm, but the phenotypic landscape in aortic aneurysm is poorly understood. The present study aimed to analyse the phenotypic landscape, phenotypic differentiation trajectory, and potential functions of various VSMCs phenotypes in aortic aneurysm.

METHODS

Single-cell sequencing data of 12 aortic aneurysm samples and 5 normal aorta samples (obtained from GSE166676 and GSE155468) were integrated by the R package Harmony. VSMCs were identified according to the expression levels of ACTA2 and MYH11. VSMCs clustering was determined by the R package 'Seurat'. Cell annotation was determined by the R package 'singleR' and background knowledge of VSMCs phenotypic switching. The secretion of collagen, proteinases, and chemokines by each VSMCs phenotype was assessed. Cell‒cell junctions and cell-matrix junctions were also scored by examining the expression of adhesion genes. Trajectory analysis was performed by the R package 'Monocle2'. qPCR was used to quantify VSMCs markers. RNA fluorescence in situ hybridization (RNA FISH) was performed to determine the spatial localization of vital VSMCs phenotypes in aortic aneurysms.

RESULTS

A total of 7150 VSMCs were categorize into 6 phenotypes: contractile VSMCs, fibroblast-like VSMCs, T-cell-like VSMCs, adipocyte-like VSMCs, macrophage-like VSMCs, and mesenchymal-like VSMCs. The proportions of T-cell-like VSMCs, adipocyte-like VSMCs, macrophage-like VSMCs, and mesenchymal-like VSMCs were significantly increased in aortic aneurysm. Fibroblast-like VSMCs secreted abundant amounts of collagens. T-cell-like VSMCs and macrophage-like VSMCs were characterized by high chemokine levels and proinflammatory effects. Adipocyte-like VSMCs and mesenchymal-like VSMCs were associated with high proteinase levels. RNA FISH validated the presence of T-cell-like VSMCs and macrophage-like VSMCs in the tunica media and the presence of mesenchymal-like VSMCs in the tunica media and tunica adventitia.

CONCLUSION

A variety of VSMCs phenotypes are involved in the formation of aortic aneurysm. T-cell-like VSMCs, macrophage-like VSMCs, and mesenchymal-like VSMCs play pivotal roles in this process. Video Abstract.

How vascular smooth muscle cell phenotype switching contributes to vascular disease

Vascular smooth muscle cells (VSMCs) are the most abundant cell in vessels. Earlier experiments have found that VSMCs possess high plasticity. Vascular injury stimulates VSMCs to switch into a dedifferentiated type, also known as synthetic VSMCs, with a high migration and proliferation capacity for repairing vascular injury. In recent years, largely owing to rapid technological advances in single-cell sequencing and cell-lineage tracing techniques, multiple VSMCs phenotypes have been uncovered in vascular aging, atherosclerosis (AS), aortic aneurysm (AA), etc. These VSMCs all down-regulate contractile proteins such as α-SMA and calponin1, and obtain specific markers and similar cellular functions of osteoblast, fibroblast, macrophage, and mesenchymal cells. This highly plastic phenotype transformation is regulated by a complex network consisting of circulating plasma substances, transcription factors, growth factors, inflammatory factors, non-coding RNAs, integrin family, and Notch pathway. This review focuses on phenotypic characteristics, molecular profile and the functional role of VSMCs phenotype landscape; the molecular mechanism regulating VSMCs phenotype switching; and the contribution of VSMCs phenotype switching to vascular aging, AS, and AA. Video Abstract.

Thrombospondins in human aortic aneurysms

Thrombospondins are a family of matricellular proteins with a multimeric structure that is known to be involved in several biological and pathological processes. Their relationship with vascular disorders has raised special interest recently. Aortic aneurysms are related to the impairment of vascular remodeling, in which extracellular matrix proteins seem to play an important role. Thus, research in thrombospondins, and their potential role in aneurysm development is progressively gaining importance. Nevertheless, studies showing thrombospondin dysregulation in human samples are still scarce. Although studies performed in vitro and in vivo models are essential to understand the molecular mechanisms and pathways underlying the disorder, descriptive studies in human samples are also necessary to ascertain their real value as biomarkers and/or novel therapeutic targets. The present article reviews the latest findings regarding the role of thrombospondins in aortic aneurysm development, paying particular attention to the studies performed in human samples.

Nanocasting of fibrous morphology on a substrate for long-term propagation of human induced pluripotent stem cells

Human-induced pluripotent stem cells (hiPSCs) can be self-renewed for many generations on nanofibrous substrates. Herein, a casting method is developed to replicate the nanofibrous morphology into a thin layer of polymethylsiloxane (PDMS). The template is obtained by electrospinning and chemical crosslinking of gelatin nanofibers on a glass slide. The replicas of the template are surface-functionalized by gelatin and used for propagation of hiPSCs over tenth generations. The performance of the propagated hiPSCs is checked by immunofluorescence imaging, flowcytometry, and RT-PCR, confirming the utility of the method. The results are also compared with those obtained using electrospun nanofiber substrates. Inherently, the PDMS replicas is of low stiffness and can be reproduced easily. Compared to other patterning techniques, casting is more flexible and cost-effective, suggesting that this method might find applications in cell-based assays that rely on stringent consideration of both substrate stiffness and surface morphology.

Targeting smooth muscle cell phenotypic switching in vascular disease

Objective

The phenotypic plasticity of vascular smooth muscle cells (VSMCs) is central to vessel growth and remodeling, but also contributes to cardiovascular pathologies. New technologies including fate mapping, single cell transcriptomics, and genetic and pharmacologic inhibitors have provided fundamental new insights into the biology of VSMC. The goal of this review is to summarize the mechanisms underlying VSMC phenotypic modulation and how these might be targeted for therapeutic benefit.

Methods

We summarize findings from extensive literature searches to highlight recent discoveries in the mechanisms underlying VSMC phenotypic switching with particular relevance to intimal hyperplasia. PubMed was searched for publications between January 2001 and December 2020. Search terms included VSMCs, restenosis, intimal hyperplasia, phenotypic switching or modulation, and drug-eluting stents. We sought to highlight druggable pathways as well as recent landmark studies in phenotypic modulation.

Results

Lineage tracing methods have determined that a small number of mature VSMCs dedifferentiate to give rise to oligoclonal lesions in intimal hyperplasia and atherosclerosis. In atherosclerosis and aneurysm, single cell transcriptomics reveal a striking diversity of phenotypes that can arise from these VSMCs. Mechanistic studies continue to identify new pathways that influence VSMC phenotypic plasticity. We review the mechanisms by which the current drug-eluting stent agents prevent restenosis and note remaining challenges in peripheral and diabetic revascularization for which new approaches would be beneficial. We summarize findings on new epigenetic (DNA methylation/TET methylcytosine dioxygenase 2, histone deacetylation, bromodomain proteins), transcriptional (Hippo/Yes-associated protein, peroxisome proliferator-activity receptor-gamma, Notch), and β3-integrin-mediated mechanisms that influence VSMC phenotypic modulation. Pharmacologic and genetic targeting of these pathways with agents including ascorbic acid, histone deacetylase or bromodomain inhibitors, thiazolidinediones, and integrin inhibitors suggests potential therapeutic value in the setting of intimal hyperplasia.

Conclusions

Understanding the molecular mechanisms that underlie the remarkable plasticity of VSMCs may lead to novel approaches to treat and prevent cardiovascular disease and restenosis.

Use of MALDI Mass Spectrometry Imaging to Identify Proteomic Signatures in Aortic Aneurysms after Endovascular Repair

Endovascular repair (EVAR) has become the standard procedure in treating thoracic (TAA) or abdominal aortic aneurysms (AAA). Not entirely free of complications, a persisting perfusion of the aneurysm after EVAR, called Endoleak (EL), leads to reintervention and risk of secondary rupture. How the aortic wall responds to the implantation of a stentgraft and EL is mostly uncertain. We present a pilot study to identify peptide signatures and gain new insights in pathophysiological alterations of the aortic wall after EVAR using matrix-assisted laser desorption or ionization mass spectrometry imaging (MALDI-MSI). In course of or accompanying an open aortic repair, tissue sections from 15 patients (TAA = 5, AAA = 5, EVAR = 5) were collected. Regions of interest (tunica media and tunica adventitia) were defined and univariate (receiver operating characteristic analysis) statistical analysis for subgroup comparison was used. This proof-of-concept study demonstrates that MALDI-MSI is feasible to identify discriminatory peptide signatures separating TAA, AAA and EVAR. Decreased intensity distributions for actin, tropomyosin, and troponin after EVAR suggest impaired contractility in vascular smooth muscle cells. Furthermore, inability to provide energy caused by impaired respiratory chain function and continuous degradation of extracellular matrix components (collagen) might support aortic wall destabilization. In case of EL after EVAR, this mechanism may result in a weakened aortic wall with lacking ability to react on reinstating pulsatile blood flow.

Vascular aging, the vascular cytoskeleton and aortic stiffness

Vascular aging, aortic stiffness and hypertension are mechanistically interrelated. The perspective presented here will focus mainly on the molecular mechanisms of age-associated increases in the stiffness of the vascular smooth muscle cell (VSMC). This review will highlight the mechanisms by which the VSMC contributes to disorders of vascular aging. Distinct functional sub-components of the vascular cell and the molecular mechanisms of the protein-protein interactions, signaling mechanisms and intracellular trafficking processes in the setting of the aging aorta will be detailed.

Insights on the Pathogenesis of Aneurysm through the Study of Hereditary Aortopathies

Thoracic aortic aneurysms (TAA) are permanent and localized dilations of the aorta that predispose patients to a life-threatening risk of aortic dissection or rupture. The identification of pathogenic variants that cause hereditary forms of TAA has delineated fundamental molecular processes required to maintain aortic homeostasis. Vascular smooth muscle cells (VSMCs) elaborate and remodel the extracellular matrix (ECM) in response to mechanical and biochemical cues from their environment. Causal variants for hereditary forms of aneurysm compromise the function of gene products involved in the transmission or interpretation of these signals, initiating processes that eventually lead to degeneration and mechanical failure of the vessel. These include mutations that interfere with transduction of stimuli from the matrix to the actin-myosin cytoskeleton through integrins, and those that impair signaling pathways activated by transforming growth factor-β (TGF-β). In this review, we summarize the features of the healthy aortic wall, the major pathways involved in the modulation of VSMC phenotypes, and the basic molecular functions impaired by TAA-associated mutations. We also discuss how the heterogeneity and balance of adaptive and maladaptive responses to the initial genetic insult might contribute to disease.

Efficient Isolation and Enrichment of Mesenchymal Stem Cells from Human Embryonic Stem Cells by Utilizing the Interaction between Integrin α5β1 and Fibronectin

Human pluripotent stem cells (hPSCs) are a potent source of clinically relevant mesenchymal stem cells (MSCs) that confer functional and structural benefits in cell therapy and tissue regeneration. Obtaining sufficient numbers of MSCs in a short period of time and enhancing the differentiation potential of MSCs can be offered the potential to improve the regenerative activity of MSCs therapy. In addition, the underlying processes in the isolation and derivation of MSCs from hPSCs are still poorly understood and controlled. To overcome these clinical needs, an efficient and simplified technique on the isolation of MSCs from spontaneously differentiated human embryonic stem cells (hESCs) via integrin α5β1 (fibronectin (FN) receptor)-to-FN interactions (hESC-FN-MSCs) is successfully developed. It is demonstrated that hESC-FN-MSCs exhibit a typical MSC surface phenotype, cellular morphology, with the whole transcriptome similar to conventional adult MSCs; but show higher proliferative capacity, more efficient trilineage differentiation, enhanced cytokine secretion, and attenuated cellular senescence. In addition, the therapeutic potential and regenerative capacity of the isolated hESC-FN-MSCs are confirmed by in vitro and in vivo multilineage differentiation. This novel method will be useful in the generation of abundant amounts of clinically relevant MSCs for stem cell therapeutics and regenerative medicine.

Current challenges and future trends in manufacturing small diameter artificial vascular grafts in bioreactors

Cardiovascular diseases are a leading cause of death. Vascular surgery is mainly used to solve this problem. However, the generation of a functional and suitable substitute for small diameter (< 6 mm) displacement is challengeable. Moreover, synthetic prostheses, made of polyethylene terephthalate and extended polytetrafluoroethylene show have shown insufficient performance. Therefore, the challenges dominating the use of autografts have prevented their efficient use. Tissue engineering is highlighted in regenerative medicine perhaps in aiming to address the issue of end-stage organ failure. While organs and complex tissues require the vascular supply to support the graft survival and render the bioartificial organ role, vascular tissue engineering has shown to be a hopeful method for cell implantation by the production of tissues in vitro. Bioreactors are a salient point in vascular tissue engineering due to the capability for reproducible and controlled variations showing a new horizon in blood vessel substitution. This review strives to display the overview of current concepts in the development of small-diameter by using bioreactors. In this work, we show a critical look at different factors for developing small-diameter and give suggestions for future studies.

Reduced stiffness and augmented traction force in type 2 diabetic coronary microvascular smooth muscle

Type 2 diabetic (T2DM) coronary resistance microvessels (CRMs) undergo inward hypertrophic remodeling associated with reduced stiffness and reduced coronary blood flow in both mice and pig models. Since reduced stiffness does not appear to be due to functional changes in the extracellular matrix, this study tested the hypothesis that decreased CRM stiffness in T2DM is due to reduced vascular smooth muscle cell (VSMC) stiffness, which impacts the traction force generated by VSMCs. Atomic force microscopy (AFM) and traction force microscopy (TFM) were conducted on primary low-passage CRM VSMCs from normal Db/db and T2DM db/db mice in addition to low-passage normal and T2DM deidentified human coronary VSMCs. Elastic modulus was reduced in T2DM mouse and human coronary VSMCs compared with normal (mouse: Db/db 6.84 ± 0.34 kPa vs. db/db 4.70 ± 0.19 kPa, P < 0.0001; human: normal 3.59 ± 0.38 kPa vs. T2DM 2.61 ± 0.35 kPa, P = 0.05). Both mouse and human T2DM coronary microvascular VSMCs were less adhesive to fibronectin compared with normal. T2DM db/db coronary VSMCs generated enhanced traction force by TFM (control 692 ± 67 Pa vs. db/db 1,507 ± 207 Pa; P < 0.01). Immunoblot analysis showed that T2DM human coronary VSMCs expressed reduced β₁-integrin and elevated β₃-integrin (control 1.00 ± 0.06 vs. T2DM 0.62 ± 0.14, P < 0.05 and control 1.00 ± 0.49 vs. T2DM 3.39 ± 1.05, P = 0.06, respectively). These data show that T2DM coronary VSMCs are less stiff and less adhesive to fibronectin but are able to generate enhanced force, corroborating previously published computational findings that decreasing cellular stiffness increases the cells' ability to generate higher traction force.NEW & NOTEWORTHY We show here that a potential causative factor for reduced diabetic coronary microvascular stiffness is the direct reduction in coronary vascular smooth muscle cell stiffness. These cells were also able to generate enhanced traction force, validating previously published computational models. Collectively, these data show that smooth muscle cell stiffness can be a contributor to overall tissue stiffness in the coronary microcirculation, and this may be a novel area of interest for therapeutic targets.

Microstructure of early embryonic aortic arch and its reversibility following mechanically altered hemodynamic load release

In the embryonic heart, blood flow is distributed through a bilaterally paired artery system composed of the aortic arches (AAs). The purpose of this study is to establish an understanding of the governing mechanism of microstructural maturation of the AA matrix and its reversibility, toward the desired macroscopic vessel lumen diameter and thickness for healthy, abnormal, and in ovo repaired abnormal mechanical loading. While matrix-remodeling mechanisms were significantly different for normal versus conotruncal banding (CTB), both led to an increase in vessel lumen. Correlated with right-sided flow increase at Hamburger & Hamilton stages 21, intermittent load switching between collagen I and III with elastin and collagen-IV defines the normal process. However, decreases in collagen I, elastin, vascular endothelial growth factor-A, and fibrillin-1 in CTB were recovered almost fully following the CTB-release model, primarily because of the pressure load changes. The complex temporal changes in matrix proteins are illustrated through a predictive finite-element model based on elastin and collagen load-sharing mechanism to achieve lumen area increase and thickness increase resulting from wall shear stress and tissue strain, respectively. The effect of embryonic timing in cardiac interventions on AA microstructure was established where abnormal mechanical loading was selectively restored at the key stage of development. Recovery of the normal mechanical loading via early fetal intervention resulted in delayed microstructural maturation. Temporal elastin increase, correlated with wall shear stress, is required for continuous lumen area growth.NEW & NOTEWORTHY The present study undertakes comparative analyses of the mechanistic differences of the arterial matrix microstructure and dynamics in the three fundamental processes of control, conotruncal banded, and released conotruncal band in avian embryo. Among other findings, this study provides specific evidence on the restorative role of elastin during the early lumen growth process. During vascular development, a novel intermittent load-switching mechanism between elastin and collagen, triggered by a step increase in wall shear stress, governs the chronic vessel lumen cross-sectional area increase. Mimicking the fetal cardiovascular interventions currently performed in humans, the early release of the abnormal mechanical load rescues the arterial microstructure with time lag.

Extracellular matrix, regional heterogeneity of the aorta, and aortic aneurysm

Aortic aneurysm is an asymptomatic disease with dire outcomes if undiagnosed. Aortic aneurysm rupture is a significant cause of death worldwide. To date, surgical repair or endovascular repair (EVAR) is the only effective treatment for aortic aneurysm, as no pharmacological treatment has been found effective. Aortic aneurysm, a focal dilation of the aorta, can be formed in the thoracic (TAA) or the abdominal (AAA) region; however, our understanding as to what determines the site of aneurysm formation remains quite limited. The extracellular matrix (ECM) is the noncellular component of the aortic wall, that in addition to providing structural support, regulates bioavailability of an array of growth factors and cytokines, thereby influencing cell function and behavior that ultimately determine physiological or pathological remodeling of the aortic wall. Here, we provide an overview of the ECM proteins that have been reported to be involved in aortic aneurysm formation in humans or animal models, and the experimental models for TAA and AAA and the link to ECM manipulations. We also provide a comparative analysis, where data available, between TAA and AAA, and how aberrant ECM proteolysis versus disrupted synthesis may determine the site of aneurysm formation.

A review of aneurysm formation, swelling in blood vessel, in the aorta, examines distinctions between two forms of the condition and the role of proteins in the extracellular matrix which surrounds cells of the arterial wall. Rupture of aneurysms in the aorta, the body’s main artery, is a major cause of death. Researchers led by Zamaneh Kassiri at the University of Alberta, Edmonton, Canada, emphasize that aneurysms in the thoracic and abdominal regions of the aorta are distinct conditions with crucial differences in their causes. Disrupted production and assembly of the extracellular matrix and its proteins may underlie thoracic aneurysm formation. Factors triggering the degradation of extracellular matrix proteins may be more significant in abdominal aneurysms. Understanding the differing molecular mechanisms involved could help address the current lack of effective drug treatments for these dangerous conditions.

PFN2a, a new partner of RARα in the cytoplasm

Retinoic acid receptors (RARs) are classically considered as nuclear ligand-dependent regulators of transcription. Here we highlighted a novel face of the RARα subtype: RARα is present in low amounts in the cytoplasm of mouse embryonic fibroblasts (MEFs) where it interacts with profilin2a (PFN2A), a small actin-binding protein involved in filaments polymerization. The interaction involves the N-terminal proline-rich motif (PRM) of RARα and the SH3-like domain of PFN2a. When increased in the cytoplasm, RARα competes with other PFN2a-binding proteins bearing PRMs and involved in actin filaments elongation. Consequently, the actin filament network is altered and MEFs adhesion is decreased. This novel role opens novel avenues for the understanding of pathologies characterized by increased levels of cytoplasmic RARα.

Eukaryotic elongation factor 2 kinase upregulates the expression of proteins implicated in cell migration and cancer cell metastasis

Eukaryotic elongation factor 2 kinase (eEF2K) negatively regulates the elongation phase of mRNA translation and hence protein synthesis. Increasing evidence indicates that eEF2K plays an important role in the survival and migration of cancer cells and in tumor progression. As demonstrated by two-dimensional wound-healing and three-dimensional transwell invasion assays, knocking down or inhibiting eEF2K in cancer cells impairs migration and invasion of cancer cells. Conversely, exogenous expression of eEF2K or knocking down eEF2 (the substrate of eEF2K) accelerates wound healing and invasion. Importantly, using LC-HDMS^E analysis, we identify 150 proteins whose expression is decreased and 73 proteins which are increased upon knocking down eEF2K in human lung carcinoma cells. Of interest, 34 downregulated proteins are integrins and other proteins implicated in cell migration, suggesting that inhibiting eEF2K may help prevent cancer cell mobility and metastasis. Interestingly, eEF2K promotes the association of integrin mRNAs with polysomes, providing a mechanism by which eEF2K may enhance their cellular levels. Consistent with this, genetic knock down or pharmacological inhibition of eEF2K reduces the protein expression levels of integrins. Notably, pharmacological or genetic inhibition of eEF2K almost completely blocked tumor growth and effectively prevented the spread of tumor cells in vivo. High levels of eEF2K expression were associated with invasive carcinoma and metastatic tumors. These data provide the evidence that eEF2K is a new potential therapeutic target for preventing tumor metastasis.

Nanotopography-Induced Structural Anisotropy and Sarcomere Development in Human Cardiomyocytes Derived from Induced Pluripotent Stem Cells

Understanding the phenotypic development of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is a prerequisite to advancing regenerative cardiac therapy, disease modeling, and drug screening applications. Lack of consistent hiPSC-CM in vitro data can be largely attributed to the inability of conventional culture methods to mimic the structural, biochemical, and mechanical aspects of the myocardial niche accurately. Here, we present a nanogrid culture array comprised of nanogrooved topographies, with groove widths ranging from 350 to 2000 nm, to study the effect of different nanoscale structures on the structural development of hiPSC-CMs in vitro. Nanotopographies were designed to have a biomimetic interface, based on observations of the oriented myocardial extracellular matrix (ECM) fibers found in vivo. Nanotopographic substrates were integrated with a self-assembling chimeric peptide containing the Arg-Gly-Asp (RGD) cell adhesion motif. Using this platform, cell adhesion to peptide-coated substrates was found to be comparable to that of conventional fibronectin-coated surfaces. Cardiomyocyte organization and structural development were found to be dependent on the nanotopographical feature size in a biphasic manner, with improved development achieved on grooves in the 700-1000 nm range. These findings highlight the capability of surface-functionalized, bioinspired substrates to influence cardiomyocyte development, and the capacity for such platforms to serve as a versatile assay for investigating the role of topographical guidance cues on cell behavior. Such substrates could potentially create more physiologically relevant in vitro cardiac tissues for future drug screening and disease modeling studies.

Expression of Integrin •5•1 and the Relationship to Collagen and Elastin Content in Human Suprarenal and Infrarenal Aortas

The infrarenal aorta is especially prone to the development of aneurysm, suggesting an intrinsic structural and molecular difference in different parts of the aorta. Previous study from this laboratory has implicated a potential role of integrin a5b1 in maintaining aortic integrity. The aim of this study was to investigate the expression of integrin a5b1 and the relationship to collagen and elastin content between 2 different aortic segments. In this study, the variation of smooth muscle cells and the localization of integrin a5b1 in the suprarenal and infrarenal aorta tissues removed from organ donors were studied immunohistochemically. The biochemical analysis for matrix proteins and integrin a5b1 protein was done by Western Blot on the corresponding tissues. All interested protein content was normalized to the smooth muscle a-actin protein. No significant difference of smooth muscle cells density between the 2 segments of aortas was observed. Integrin a5b1 was localized in the outer layer of all aortic media. The authors found that the ratio of collagen/elastin in infrarenal aortas was significantly increased 2-fold because elastin content in infrarenal aortas decreased 49% as compared with suprarenal aortas. Integrin a5b1 content relative to its specific ligand — collagen—did not differ between these 2 different aortic segments. These results suggest that the infrarenal aorta differed biochemically from the suprarenal aorta. A decrease in infrarenal elastin without a corresponding decrease in collagen and integrin a5b1 may affect the compliance and integrity of the distal aorta. These intrinsic anatomic differences may be important in the susceptibility of the infrarenal aortas to aneurysm formation.

Collagen Promotes Higher Adhesion, Survival and Proliferation of Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) can differentiate into several cell types and are desirable candidates for cell therapy and tissue engineering. However, due to poor cell survival, proliferation and differentiation in the patient, the therapy outcomes have not been satisfactory. Although several studies have been done to understand the conditions that promote proliferation, differentiation and migration of MSC in vitro and in vivo, still there is no clear understanding on the effect of non-cellular bio molecules. Of the many factors that influence the cell behavior, the immediate cell microenvironment plays a major role. In this context, we studied the effect of extracellular matrix (ECM) proteins in controlling cell survival, proliferation, migration and directed MSC differentiation. We found that collagen promoted cell proliferation, cell survival under stress and promoted high cell adhesion to the cell culture surface. Increased osteogenic differentiation accompanied by high active RHOA (Ras homology gene family member A) levels was exhibited by MSC cultured on collagen. In conclusion, our study shows that collagen will be a suitable matrix for large scale production of MSC with high survival rate and to obtain high osteogenic differentiation for therapy.

Simple surface engineering of polydimethylsiloxane with polydopamine for stabilized mesenchymal stem cell adhesion and multipotency

Polydimethylsiloxane (PDMS) has been extensively exploited to study stem cell physiology in the field of mechanobiology and microfluidic chips due to their transparency, low cost and ease of fabrication. However, its intrinsic high hydrophobicity renders a surface incompatible for prolonged cell adhesion and proliferation. Plasma-treated or protein-coated PDMS shows some improvement but these strategies are often short-lived with either cell aggregates formation or cell sheet dissociation. Recently, chemical functionalization of PDMS surfaces has proved to be able to stabilize long-term culture but the chemicals and procedures involved are not user- and eco-friendly. Herein, we aim to tailor greener and biocompatible PDMS surfaces by developing a one-step bio-inspired polydopamine coating strategy to stabilize long-term bone marrow stromal cell culture on PDMS substrates. Characterization of the polydopamine-coated PDMS surfaces has revealed changes in surface wettability and presence of hydroxyl and secondary amines as compared to uncoated surfaces. These changes in PDMS surface profile contribute to the stability in BMSCs adhesion, proliferation and multipotency. This simple methodology can significantly enhance the biocompatibility of PDMS-based microfluidic devices for long-term cell analysis or mechanobiological studies.

Nanomechanics of Cells and Biomaterials Studied by Atomic Force Microscopy

The behavior and mechanical properties of cells are strongly dependent on the biochemical and biomechanical properties of their microenvironment. Thus, understanding the mechanical properties of cells, extracellular matrices, and biomaterials is key to understanding cell function and to develop new materials with tailored mechanical properties for tissue engineering and regenerative medicine applications. Atomic force microscopy (AFM) has emerged as an indispensable technique for measuring the mechanical properties of biomaterials and cells with high spatial resolution and force sensitivity within physiologically relevant environments and timescales in the kPa to GPa elastic modulus range. The growing interest in this field of bionanomechanics has been accompanied by an expanding array of models to describe the complexity of indentation of hierarchical biological samples. Furthermore, the integration of AFM with optical microscopy techniques has further opened the door to a wide range of mechanotransduction studies. In recent years, new multidimensional and multiharmonic AFM approaches for mapping mechanical properties have been developed, which allow the rapid determination of, for example, cell elasticity. This Progress Report provides an introduction and practical guide to making AFM-based nanomechanical measurements of cells and surfaces for tissue engineering applications.

Role of Nonmuscle Myosin II in Migration of Wharton's Jelly-Derived Mesenchymal Stem Cells

It is the promise of regeneration and therapeutic applications that has sparked an interest in mesenchymal stem cells (MSCs). Following infusion, MSCs migrate to sites of injury or inflammation by virtue of their homing property. To exert optimal clinical benefits, systemically delivered MSCs need to migrate efficiently and in adequate numbers to pathological areas in vivo. However, underlying molecular mechanisms responsible for MSC migration are still not well understood. The Wharton's jelly (WJ) of the umbilical cord is an attractive source of MSCs for stem cell therapy because of its abundant availability and painless collection. In this study, we attempted to identify the role of nonmuscle myosin II (NMII), if any, in the migration of WJ-derived MSCs (WJ-MSCs). Expression of NMII isoforms, NMIIA, and NMIIB was observed both at RNA and protein levels in WJ-MSCs. Inhibition of NMII or its regulator ROCK, by pharmacological inhibitors, resulted in significant reduction in the migration of WJ-MSCs as confirmed by the scratch migration assay and time-lapse microscopy. Next, trying to dissect the role of each NMII isoform in migration of WJ-MSCs, we found that siRNA-mediated downregulation of NMIIA, but not NMIIB expression, led to cells failing to retract their trailing edge and losing cell-cell cohesiveness, while exhibiting a nondirectional migratory pathway. Migration, moreover, is also dependent on optimal affinity adhesion, which would allow rapid attachment and release of cells and, hence, can be influenced by extracellular matrix (ECM) and adhesion molecules. We demonstrated that inhibition of NMII and more specifically NMIIA resulted in increased gene expression of ECM and adhesion molecules, which possibly led to stronger adhesions and, hence, decreased migration. Therefore, these data suggest that NMII acts as a regulator of cell migration and adhesion in WJ-MSCs.

Quantification of extracellular matrix proteins from a rat lung scaffold to provide a molecular readout for tissue engineering

The use of extracellular matrix (ECM) scaffolds, derived from decellularized tissues for engineered organ generation, holds enormous potential in the field of regenerative medicine. To support organ engineering efforts, we developed a targeted proteomics method to extract and quantify extracellular matrix components from tissues. Our method provides more complete and accurate protein characterization than traditional approaches. This is accomplished through the analysis of both the chaotrope-soluble and -insoluble protein fractions and using recombinantly generated stable isotope labeled peptides for endogenous protein quantification. Using this approach, we have generated 74 peptides, representing 56 proteins to quantify protein in native (nondecellularized) and decellularized lung matrices. We have focused on proteins of the ECM and additional intracellular proteins that are challenging to remove during the decellularization procedure. Results indicate that the acellular lung scaffold is predominantly composed of structural collagens, with the majority of these proteins found in the insoluble ECM, a fraction that is often discarded using widely accepted proteomic methods. The decellularization procedure removes over 98% of intracellular proteins evaluated and retains, to varying degrees, proteoglycans and glycoproteins of the ECM. Accurate characterization of ECM proteins from tissue samples will help advance organ engineering efforts by generating a molecular readout that can be correlated with functional outcome to drive the next generation of engineered organs.

Smooth muscle cell functionality on collagen immobilized polycaprolactone nanowire surfaces

Inhibition of smooth muscle cell (SMC) proliferation and preservation of a differentiated state are important aspects in the management, avoidance and progression of vascular diseases. An understanding of the interaction between SMCs and the biomaterial involved is essential for a successful implant. In this study, we have developed collagen immobilized nanostructured surfaces with controlled arrays of high aspect ratio nanowires for the growth and maintenance of human aortic SMCs. The nanowire surfaces were fabricated from polycaprolactone and were immobilized with collagen. The objective of this study is to reveal how SMCs interact with collagen immobilized nanostructures. The results indicate significantly higher cellular adhesion on nanostructured and collagen immobilized surfaces; however, SMCs on nanostructured surfaces exhibit a more elongated phenotype. The reduction of MTT was significantly lower on nanowire (NW) and collagen immobilized NW (colNW) surfaces, suggesting that SMCs on nanostructured surfaces may be differentiated and slowly dividing. Scanning electron microscopy results reveal that SMCs on nanostructured surfaces are more elongated and that cells are interacting with the nano-features on the surface. After providing differentiation cues, heavy chain myosin and calponin, specific to a contractile SMC phenotype, are upregulated on collagen immobilized surfaces. These results suggest that nanotopography affects cell adhesion, proliferation, as well as cell elongation, while collagen immobilized surfaces greatly affect cell differentiation.

Surface chemical modification of poly(dimethylsiloxane) for the enhanced adhesion and proliferation of mesenchymal stem cells

The surface chemistry of materials has an interactive influence on cell behavior. The optimal adhesion of mammalian cells is critical in determining the cell viability and proliferation on substrate surfaces. Because of the inherent high hydrophobicity of a poly(dimethylsiloxane) (PDMS) surface, cell culture on these surfaces is unfavorable, causing cells to eventually dislodge from the surface. Although physically adsorbed matrix proteins can promote initial cell adhesion, this effect is usually short-lived. Here, (3-aminopropyl)triethoxy silane (APTES) and cross-linker glutaraldehyde (GA) chemistry was employed to immobilize either fibronectin (FN) or collagen type 1 (C1) on PDMS. The efficiency of these surfaces to support the adhesion and viability of mesenchymal stem cells (MSCs) was analyzed. The hydrophobicity of the native PDMS decreased significantly with the mentioned surface functionalization. The adhesion of MSCs was mostly favorable on chemically modified PDMS surfaces with APTES + GA + protein. Additionally, the spreading area of MSCs was significantly higher on APTES + GA + C1 surfaces than on other unmodified/modified PDMS surfaces with C1 adsorption. However, there were no significant differences in the MSC spreading area on the unmodified/modified PDMS surfaces with FN adsorption. Furthermore, there was a significant increase in cell proliferation on the PDMS surface with APTES + GA + protein functionalization as compared to the PDMS surface with protein adsorption only. Therefore, the covalent surface chemical modification of PDMS with APTES + GA + protein could offer a more biocompatible platform for the enhanced adhesion and proliferation of MSCs. Similar strategies can be applied for other substrates and cell lines by appropriate combinations of self-assembly monolayers (SAMs) and extracellular matrix proteins.

Evaluating extracellular matrix influence on adherent cell signaling by cold trypsin phosphorylation-specific flow cytometry

BACKGROUND

Tissue microenvironments comprise different extracellular matrix (ECM) proteins that regulate cellular responsiveness to growth factors. In vitro culture of adherent cells on ECM-coated substrata is commonly used to study microenvironmental influence on specific cell signaling responses. Phosphorylation-specific flow cytometry can be utilized to quantify intracellular phosphorylation-dependent signaling events in single cells. However this approach necessitates trypsinization of adherent cells to accommodate flow cytometric analysis. Trypsin is a potent activator of cell signaling and can obscure signal transduction events induced by other factors.

RESULTS

To address this we developed a cold trypsin-phosphorylation-specific flow cytometry protocol, where adherent cells are prepared for flow cytometric analysis on ice (~0°C), a temperature where trypsin retains activity but where intracellular kinases are inactive. We show that this straightforward approach can be used to quantify intracellular pERK levels in single adherent primary human vascular smooth muscle cells grown on different ECM.

CONCLUSIONS

Exploiting the limited temperature dependence of trypsin facilitated development of a generally applicable phosphorylation-specific flow cytometry method for analysis of adherent cell types including primary patient derived cells. We demonstrate the utility of cold trypsin-phosphorylation-specific flow cytometry analysis of cell signaling to measure microenvironmental influence in single adherent cells.

Formation of composite polyacrylamide and silicone substrates for independent control of stiffness and strain

Cells that line major tissues in the body such as blood vessels, lungs and gastrointestinal tract experience deformation from mechanical strain with our heartbeat, breathing, and other daily activities. Tissues also remodel in both development and disease, changing their mechanical properties. Taken together, cells can experience vastly different mechanical cues resulting from the combination of these interdependent stimuli. To date, most studies of cellular mechanotransduction have been limited to assays in which variations in substrate stiffness and strain were not combined. Here, we address this technological gap by implementing a method that can simultaneously tune both substrate stiffness and mechanical strain. Substrate stiffness is controlled with different monomer and crosslinker ratios during polyacrylamide gel polymerization, and strain is transferred from the underlying silicone platform when stretched. We demonstrate this platform with polyacrylamide gels with elastic moduli at 6 kPa and 20 kPa in combination with two different silicone formulations. The gels remain attached with up to 50% applied strains. To validate strain transfer through the gels into cells, we employ particle-tracking methods and observe strain transmission via cell morphological changes.

Aortic aneurysm generation in mice with targeted deletion of integrin-linked kinase in vascular smooth muscle cells

RATIONALE

Integrin-linked kinase (ILK) is located at focal adhesions and links the extracellular matrix (ECM) to the actin cytoskeleton via β1- and β3-integrins. ILK plays a role in the activation of kinases including protein kinase B/Akt and glycogen synthase kinase 3β and regulates cell proliferation, motility, and survival.

OBJECTIVE

To determine the function of ILK in vascular smooth muscle cells (SMCs) in vivo.

METHODS AND RESULTS

SM22Cre(+)Ilk(Fl/Fl) conditional mutant mice were generated in which the Ilk gene was selectively ablated in SMCs. SM22Cre(+)Ilk(Fl/Fl) conditional mutant mice survive to birth but die in the perinatal period exhibiting multiple vascular pathologies including aneurysmal dilatation of the aorta and patent ductus arteriosus (PDA). Defects in morphogenetic development of the aorta were observed as early as E12.5 in SM22Cre(+)Ilk(Fl/Fl) mutant embryos. By late gestation (E16.5 to 18.5), striking expansion of the thoracic aorta was observed in ILK mutant embryos. Histological analyses revealed that the structural organization of the arterial tunica media is severely disrupted with profound derangements in SMC morphology, cell-cell, and cell-matrix relationships, including disruption of the elastic lamellae. ILK deletion in primary aortic SMCs results in alterations of RhoA/cytoskeletal signaling transduced through aberrant localization of myocardin-related transcription factor (MRTF)-A repressing the transcription and expression of SMC genes, which are required for the maintenance of the contractile SMC phenotype.

CONCLUSIONS

These data identify a molecular pathway linking ILK signaling to the contractile SMC gene program. Activation of this pathway is required for morphogenetic development of the aorta and ductus arteriosus during embryonic and postnatal survival.

Surface modifications of photocrosslinked biodegradable elastomers and their influence on smooth muscle cell adhesion and proliferation

Photocrosslinked, biodegradable elastomers based on aliphatic polyesters have many desirable features as scaffolds for smooth muscle tissue engineering. However, they lack cell adhesion motifs. To address this shortcoming, two different modification procedures were studied utilizing a high and a low crosslink density elastomer: base etching and the incorporation of acryloyl-poly(ethylene glycol) (PEG)-Gly-Arg-Gly-Asp-Ser (GRGDS) into the elastomer network during photocrosslinking. Base etching improved surface hydrophilicity without altering surface topography, but did not improve bovine aortic smooth muscle cell adhesion. Incorporation of PEG-GRGDS into the elastomer network significantly improved cell adhesion for both high and low crosslink density elastomers, with a greater effect with the higher crosslink density elastomer. Incorporation of GRGDS into the high crosslink density elastomer also enhanced smooth muscle cell proliferation, while proliferation on the low crosslink density unmodified, base etched, and PEG-GRGDS incorporated elastomers was significantly greater than on the high crosslink density unmodified and base etched elastomer.

Biomimetic control of vascular smooth muscle cell morphology and phenotype for functional tissue-engineered small-diameter blood vessels

Small-diameter blood vessel substitutes are urgently needed for patients requiring replacements of their coronary and below-the-knee vessels and for better arteriovenous dialysis shunts. Circulatory diseases, especially those arising from atherosclerosis, are the predominant cause of mortality and morbidity in the developed world. Current therapies include the use of autologous vessels or synthetic materials as vessel replacements. The limited availability of healthy vessels for use as bypass grafts and the failure of purely synthetic materials in small-diameter sites necessitate the development of a biological substitute. Tissue engineering is such an approach and has achieved promising results, but reconstruction of a functional vascular tunica media, with circumferentially oriented contractile smooth muscle cells (SMCs) and extracellular matrix, appropriate mechanical properties, and vasoactivity has yet to be demonstrated. This review focuses on strategies to effect the switch of SMC phenotype from synthetic to contractile, which is regarded as crucial for the engineering of a functional vascular media. The synthetic SMC phenotype is desired initially for cell proliferation and tissue remodeling, but the contractile phenotype is then necessary for sufficient vasoactivity and inhibition of neointima formation. The factors governing the switch to a more contractile phenotype with in vitro culture are reviewed.

Growth inhibition and differentiation of cultured smooth muscle cells depend on cellular crossbridges across the tubular lumen of type I collagen matrix honeycombs

Although rabbit vascular smooth muscle cells (SMCs) showed a differentiated phenotype in three-dimensional type I collagen matrices (honeycombs, diameter of pores=200-500 microm), mouse vascular SMCs proliferated in honeycombs having the same pore size. Here we investigated the relationship between pore sizes of honeycombs and differentiation of SMCs using various pore sizes of honeycombs. Rabbit SMCs (length: 200+/-32 microm) and mouse SMCs (49+/-10 microm) formed crossbridges in honeycombs with 200-300 microm and less than 200 microm of pores, respectively. Both SMCs spread on the inner wall but did not form crossbridges in honeycombs with larger pores. [(3)H]Thymidine incorporation and cell number of both SMCs were decreased when the crossbridges were formed in honeycombs. Because proliferation inhibition and crossbridge formation were observed in the culture of rabbit and mouse SMCs using 200-300 microm and less than 200 microm pore sized honeycombs, respectively, these data suggested that forming crossbridges was important for the inhibition of proliferation of SMCs. Rabbit SMCs differentiation was accompanied by the expression of caldesmon heavy chain when cultured in honeycombs having less than 300 microm pores. Proliferation of mouse SMCs stopped in honeycombs having less than 200 microm pores, but caldesmon heavy chain was not detected despite the expression of its mRNA. Proliferation of SMCs stopped on plates when cells reached confluent state, however, caldesmon heavy chain was not expressed. These data suggested that an appropriate structure and suitable honeycomb pore size are important for the differentiation of SMCs.

Small-diameter human vessel wall engineered from bone marrow-derived mesenchymal stem cells (hMSCs)

Using biodegradable scaffold and a biomimetic perfusion system, our lab has successfully engineered small-diameter vessel grafts using endothelial cells (ECs) and smooth muscle cells (SMCs) obtained from vessels in various species. However, translating this technique into humans has presented tremendous obstacles due to species and age differences. SMCs from elderly persons have limited proliferative capacity and a reduction in collagen production, which impair the mechanical strength of engineered vessels. As an alternative cell source, adult human bone marrow-derived mesenchymal stem cells (hMSCs) were studied for their ability to differentiate into SMCs in culture plates as well as in a bioreactor system. In the former setting, immunofluorescence staining showed that MSCs, after induction for 14 days, expressed smooth muscle alpha-actin (SMA) and calponin, early and mid-SMC phenotypic markers, respectively. In the latter setting, vessel walls were constructed with MSC-derived SMCs. Various factors (i.e., matrix proteins, soluble factors, and cyclic strain) in the engineering system were further investigated for their effects on hMSC cell proliferation and differentiation into SMCs. Based on a screening of multiple factors, the engineering system was optimized by dividing the vessel culture into proliferation and differentiation phases. The vessel walls engineered under the optimized conditions were examined histologically and molecularly, and found to be substantially similar to native vessels. In conclusion, bone marrow-derived hMSCs can serve as a new cell source of SMCs in vessel engineering. Optimization of the culture conditions to drive SMC differentiation and matrix production significantly improved the quality of the hMSC-derived engineered vessel wall.

Platelets as targets of snake venom metalloproteinases

For centuries snake venoms have been known to interfere with haemostasis and this is now known basically due either to toxins activating/inhibiting clotting factors, having effects on blood vessels or interfering with platelet function. In this short review, the interaction of one major group of toxins, the snake venom metalloproteinases, with platelets is considered. This is relevant for understanding the mechanism of haemorrhage induced by these toxins.

AGE-related cross-linking of collagen is associated with aortic wall matrix stiffness in the pathogenesis of drug-induced diabetes in rats

Diabetes mellitus is major risk factor for cardiovascular disease, and atherosclerosis accounts for most of the morbidity and mortality of diabetic patients. To examine the effects of diabetes on the vessel wall, we examined the association of collagen cross-linking in relation to matrix stiffness of the descending aorta in streptozotocin-induced diabetic rats. The matrix stiffness of the vessel was determined by measuring the tensile properties of the tissue. Seven weeks following the establishment of diabetes, both control and diabetic rats were killed and the descending aortas were excised and analyzed. The findings from biomechanical analysis indicated a significant increase in maximum load (26%), stress (22%), Young's modulus of elasticity (60%), and toughness (32%) in diabetic aortas compared to control. In contrast, the maximum strain of the diabetic rat aorta was significantly reduced by 20% compared to control rats, suggesting stiffening of the blood vessel. The results from biochemical analysis showed that the amount of total collagen increased by 21% in diabetic tissues compared to the control. The sequential extractions of collagen showed that the diabetic specimens yielded 34% more neutral salt-soluble collagen (NSC) than the control. The amount of pepsin-soluble collagen was 31% less in diabetic tissues than in the control group, whereas the amount of insoluble collagen (ISC) increased by 56%. A significant accumulation in advanced glycation end products (AGEs) were seen in pepsin- and collagenase-soluble collagen in diabetic vessel. Furthermore, the altered biomechanical properties of the vessel wall were strongly correlated with the biochemistry of collagen. Overall, these results provide evidence that the diabetic state is associated with the changes in collagen biochemistry and in the biomechanics of the blood vessel.

Pre-procedural expression of Mac-1 and LFA-1 on leukocytes for prediction of late restenosis and their possible correlation with advanced coronary artery disease

BACKGROUND

The activation status of the inflammatory system has been suggested to play an important role in predicting restenosis. Activation of leukocyte adhesion molecules occur after coronary intervention and the level of activation correlates to restenosis. However, little is known about the specific role of adhesion molecules before intervention. The purpose of this study concerned the search for differences in the expression level of selected adhesion molecules to identify suitable tools for the pre-procedural identification of restenosis patients prior to angioplasty.

METHODS

Blood samples of 31 patients undergoing elective coronary angiography were obtained just before intervention. Seven healthy volunteers were also enrolled. Surface expression of leukocyte adhesion molecules Mac-1 (CD11b/CD18), LFA-1 (CD11a/CD18), L-Selectin (CD62L), ICAM-1 (CD54), and MHC-II (HLA-DR) were assessed by flow cytometry. Patients with a successful angioplasty received a follow-up angiography after six months.

RESULTS

According to the clinical and angiographic data, patients were divided into four groups: control (N = 14), no restenosis (N = 11), restenosis (N = 4), and advanced coronary artery disease (CAD, N = 9). The restenosis group and the advanced CAD group showed higher expression of Mac-1 and LFA-1 on monocytes and neutrophils compared to the other groups. Using the pre-procedural expression levels, patients with restenosis could be predicted by discriminant analysis with CD11a, CD11b, and CD18 (average recognition index = 95.5%).

CONCLUSIONS

The data of this pilot study indicate that pre-procedural activation status of CD11a and CD11b may play a role in the subsequent development of restenosis. Moreover, CD11a, CD11b, and CD18 may be helpful as indicators for the progression of CAD.

Statins regulate alpha2beta1-integrin expression and collagen I-dependent functions in human vascular smooth muscle cells

HMG-CoA reductase inhibitors have direct vascular effects that contribute to plaque stability. In the current study, the authors demonstrate that the HMG-CoA reductase inhibitors atorvastatin and pravastatin augment the adhesion of human (HSMCs) and rat aortic smooth muscle cells (RASMCs) to collagen I via induction of alpha2beta1-integrin receptors. Atorvastatin (0.1 microM ) increased the adhesion of HSMCs to collagen I up to 2-fold (p < 0.01) and pravastatin (1.0 microM ) up to 1.8-fold (p < 0.01) after treatment of at least 24 h. This increase in adhesion was concentration dependent and was observed for treatment periods from 16 to 72 h. Inhibition of isoprenoid synthesis with mevalonate and geranyl-geraniol prevented the statin-induced effect on human and rat smooth muscle cells. Flow cytometry revealed an increased expression of alpha2- and beta1-integrins after treatment with atorvastatin (0.1 microM ) at 24 and 48 h. Atorvastatin increased levels of beta1-integrin mRNA after 12- and 24-h treatment in HSMCs, which was inhibited by mevalonate. Furthermore, atorvastatin (0.1 microM ) and pravastatin (1.0 microM ) inhibited chemotaxis of HSMCs on collagen I, which was also reversed by mevalonate treatment. In contrast, inhibition of beta1-integrins with a specific antibody nearly doubled (p < 0.01) the rate of chemotaxis. These data indicate that the chemotactic activity in HSMCs is inhibited in part by up-regulation of alpha2beta1-integrin receptors. The current study indicates that HMG-CoA reductase inhibitors increase cell-matrix interaction with collagen I via induction of alpha2beta1-integrins and increased adhesion to collagen I.

Hypoxia activates beta(1)-integrin via ERK 1/2 and p38 MAP kinase in human vascular smooth muscle cells

Hypoxia plays an important role in vascular remodeling and directly affects vascular smooth muscle cell (VSMC) functions. VSMC adhesion participates in changes of vascular structure; however, little is known about VSMC adhesion under hypoxic conditions. It was the aim of the present study to investigate the effects of hypoxia on adhesion mechanisms in human VSMCs. Compared to normoxic cells, hypoxia (1% O(2), 24h) significantly increased adhesion of VSMCs to collagen I by 30.2% and fibronectin by 58.0%. This effect was completely inhibited in the presence of the pharmacological ERK 1/2 mitogen-activated protein kinase (MAPK) pathway inhibitor PD98059 (30 microM) or the p38 MAPK inhibitor SB203580 (1 microM). Basal adhesion of normoxic cells was not affected by pretreatment with PD98059 and SB203580. Hypoxia induced a time-dependent activation of ERK 1/2 and p38 MAPK activation in human VSMCs, which were completely abolished by PD98059 or SB203580, respectively. Since adhesion of VSMCs to fibronectin and collagen I involves beta(1)-integrin receptors, we used a blocking antibody against beta(1)-integrin (P5D2) to examine potential effects of hypoxia on beta(1)-integrins. P5D2 significantly reduced VSMC adhesion to fibronectin and collagen I in normoxia and hypoxia in a comparable manner; however, beta(1)-integrin protein or mRNA levels were not affected by hypoxia. As evidenced by flow cytometry, hypoxia induced a activation of beta(1)-integrins by exposing an conformationally sensitive epitope on the beta(1)-subunit. These results demonstrate that hypoxia enhances adhesion of VSMC on extracellular matrix proteins by activating beta(1)-integrin.

Smooth muscle cell adhesion to tissue engineering scaffolds

Synthetic polyesters of lactic and glycolic acid, and the extracellular matrix molecule collagen are among the most widely-utilized scaffolding materials in tissue engineering. However, the mechanism of cell adhesion to these tissue engineering scaffolds has not been extensively studied. In this paper, the mechanism of adhesion of smooth muscle cells to these materials was investigated. Vitronectin was found to be the predominant matrix protein adsorbed from serum-containing medium onto polyglycolic acid, poly(lactic co-glycolic) acid, and collagen two-dimensional films and three-dimensional scaffolds. Fibronectin adsorbed to both materials as well, although to a much lower density. Smooth muscle cell adhesion was mediated through specific integrin receptors interacting with these adsorbed proteins, as evidenced by both immunostaining and blocking studies. The receptors involved in adhesion included the alpha(v)beta5 to vitronectin, the alpha5beta1 to fibronectin and the alpha2beta1 to collagen I. Identification of the specific receptors used to adhere to these polymers clarifies why smooth muscle tissue development differs on these scaffolds, and may allow one to design tissue formation by controlling the surface chemistry of tissue engineering scaffolds.

Type VIII collagen stimulates smooth muscle cell migration and matrix metalloproteinase synthesis after arterial injury

Type VIII collagen is a matrix protein expressed in a number of tissues undergoing active remodeling, including injured arteries during neointimal formation and in human atherosclerotic plaques; however, very little is known about its function. We have investigated whether the type VIII collagen stimulates smooth muscle cell (SMC) migration and invasion by binding to integrin receptors and up-regulating matrix metalloproteinase (MMP) production. SMCs attached to plates coated with type VIII collagen in a dose-dependent manner, with maximal attachment occurring with coating solutions containing 25 microgram/ml collagen. Type VIII collagen at 100 microgram/ml stimulated an 83-fold increase in the migration of SMCs in a chemotaxis chamber. Antibodies against beta1 integrin receptors prevented attachment and migration of SMCs. Antibodies against alpha1 or alpha2 integrins reduced attachment of SMCs to type VIII collagen by 29% and 77%, respectively. We found that SMCs grown from the rat neointima, but not medial SMCs, increased their production of MMP-2 and -9 on adherence to type VIII collagen. This suggests that there is an important difference in phenotype between intimal and medial SMCs and that intimal SMCs have distinct matrix-dependent signaling mechanisms. Our findings suggest that type VIII collagen deposited in vascular lesions functions to promote SMC attachment and chemotaxis, and signals through integrin receptors to stimulate MMP synthesis, all of which are important mechanisms used in cell migration and invasion.

Regulation of smooth muscle cell migration and integrin expression by the Gax transcription factor

Homeobox transcription factors specify body plan by regulating differentiation, proliferation, and migration at a cellular level. The homeobox transcription factor Gax is expressed in quiescent vascular smooth muscle cells (VSMCs), and its expression is downregulated by vascular injury or other conditions that lead to VSMC proliferation. Previous investigations demonstrate that Gax may regulate VSMC proliferation by upregulating the cyclin-dependent kinase (cdk) inhibitor p21. Here we examined whether Gax influences VSMC migration, a key feature in the development of stenotic lesions after balloon injury. Transduction of a Gax cDNA inhibited the migratory response of VSMCs toward PDGF-BB, basic fibroblast growth factor, or hepatocyte growth factor/scatter factor. Gax expression also inhibited migration of NIH.3T3 fibroblasts and embryonic fibroblasts lacking p53. Gax was unable to inhibit the migration of fibroblasts lacking p21, but this effect could be restored in these cells by providing exogenous p21 or by overexpressing another cdk inhibitor, p16. Flow cytometric analysis implicated a Gax-mediated downregulation of alpha(v)beta(3) and alpha(v)beta(5) integrin expression in VSMCs as a potential cause for reduced cell motility. Gax specifically downregulated beta(3) and beta(5) in VSMCs in culture and after acute vascular injury in vivo. Repression of integrin expression was also found in NIH 3T3 cells and p53 knockout fibroblasts, but not in p21-knockout fibroblasts, unless these cells express exogenous p21 or p16. These data suggest that cycle progression, integrin expression, and cell migration can be regulated in VSMCs by the homeobox gene product Gax.

Engineered smooth muscle tissues: regulating cell phenotype with the scaffold

Culturing cells on three-dimensional, biodegradable scaffolds may create tissues suitable either for reconstructive surgery applications or as novel in vitro model systems. In this study, we have tested the hypothesis that the phenotype of smooth muscle cells (SMCs) in three-dimensional, engineered tissues is regulated by the chemistry of the scaffold material. Specifically, we have directly compared cell growth and patterns of extracellular matrix (ECM) (e.g. , elastin and collagen) gene expression on two types of synthetic polymer scaffolds and type I collagen scaffolds. The growth rates of SMCs on the synthetic polymer scaffolds were significantly higher than on type I collagen sponges. The rate of elastin production by SMCs on polyglycolic acid (PGA) scaffolds was 3.5 +/- 1.1-fold higher than that on type I collagen sponges on Day 11 of culture. In contrast, the collagen production rate on type I collagen sponges was 3.3 +/- 1.1-fold higher than that on PGA scaffolds. This scaffold-dependent switching between elastin and collagen gene expression was confirmed by Northern blot analysis. The finding that the scaffold chemistry regulates the phenotype of SMCs independent of the scaffold physical form was confirmed by culturing SMCs on two-dimensional films of the scaffold materials. It is likely that cells adhere to these scaffolds via different ligands, as the major protein adsorbed from the serum onto synthetic polymers was vitronectin, whereas fibronectin and vitronectin were present at high density on type I collagen sponges. In summary, this study demonstrates that three-dimensional smooth muscle-like tissues can be created by culturing SMCs on three-dimensional scaffolds, and that the phenotype of the SMCs is strongly regulated by the scaffold chemistry. These engineered tissues provide novel, three-dimensional models to study cellular interaction with ECM in vitro.

The role of vascular smooth muscle cell integrins in the compaction and mechanical strengthening of a tissue-engineered blood vessel

Vascular smooth muscle cells (VSMC) influence vessel structure and function during normal development, and in disease states. VSMC interactions with extracellular matrix, via cell surface integrins, play an important role in these processes. A greater understanding of the molecular basis of these interactions is also critical to advances in the field of cardiovascular tissue engineering. This study examined the role of VSMC integrins in the spontaneous compaction and eventual strengthening of a rudimentary tissue-engineered blood vessel (TEBV) consisting of a fibrillar type I collagen network populated by human aortic smooth muscle cells. Using integrin subunit-specific antibodies, we demonstrated that anti-beta1 (Mab13 and P4C10) and anti-alpha2 (P1E6) antibodies that inhibit aortic smooth muscle cell (AoSMC) adhesion to collagen, also significantly inhibit TEBV compaction during the 24-hour period following TEBV construction. However, no difference in the tensile stress of antibody-treated and control TEBVs was observed at this time point. In contrast, 72 hours after construction, the inhibitory effect of anti-integrin antibodies on compaction had been overcome but tensile stress was decreased in TEBVs treated with anti-alpha2/anti-beta1 antibodies when compared to controls. These data provide evidence linking VSMC integrins, specifically the alpha2beta1 integrin, with the initial compaction, as well as, the postcompaction strengthening of the TEBV.

Prevention of arterial structural alterations with verapamil and trandolapril and consequences for mechanical properties in spontaneously hypertensive rats

We compared the chronic effects in spontaneously hypertensive rats (SHR) of low doses of an angiotensin converting enzyme inhibitor, trandolapril, a Ca2+ channel antagonist, verapamil, and their combination (trandolapril-verapamil), on arterial mechanical properties, arterial wall hypertrophy and extracellular matrix proteins. Four-week-old SHR were randomly allocated to oral treatment with verapamil (50 mg kg(-1) day(-1)), trandolapril (0.3 mg kg(-1) day(-1)), the combination of verapamil (50 mg kg(-1) day(-1)) plus trandolapril (0.3 mg kg(-1) day(-1)), or placebo for 4 months. A group of Wistar Kyoto (WKY) control rats received placebo for the same period of time. At the end of the treatment, mean blood pressure was lower in verapamil-trandolapril than in trandolapril SHR, but remained higher than in WKY. Verapamil had no effects on blood pressure. Equivalent reduction in aortic wall hypertrophy was obtained in all treated SHR. Trandolapril and verapamil-trandolapril combination produced a significant reduction of aortic collagen density compared with placebo SHR. Carotid total fibronectin, EIIIA fibronectin isoform and alpha5beta1 integrin, were higher in the media of placebo SHR than in WKY. EIIIA fibronectin isoform and alpha5beta1 integrin were reduced in verapamil-SHR compared with placebo-SHR and normalized in trandolapril and verapamil-trandolapril-SHR compared with WKY. SHR-placebo and SHR treated with either verapamil or trandolapril as single-drug treatment showed a 4-fold increase in total fibronectin compared to the WKY. Only SHR treated with verapamil-trandolapril combination had total fibronectin not significantly different from that of WKY. Carotid arterial distensibility increased only in verapamil-trandolapril treated rats. Multivariate analysis showed arterial distensibility to be negatively correlated to mean blood pressure (P < 0.0001) and total fibronectin (P < 0.01). In conclusion, chronic treatment with the verapamil-trandolapril combination significantly improved in vivo arterial distensibility in SHR. The most important effects of the combination on arterial mechanics compared to those of verapamil or trandolapril alone may have been the consequence of its stronger action on arterial pressure, arterial wall hypertrophy and total fibronectin density. However we suggest that, in addition to the structural effects, complete normalization of blood pressure is necessary to obtain normal arterial distensibility.

The extracellular matrix in balloon arterial injury: a novel target for restenosis prevention

The role of the extracellular matrix (ECM) in the pathobiology of restenosis has not been fully appreciated. Recent discoveries have shown the ECM to be a complex, heterogeneous structure whose components are dynamically altered in response to vascular injury. This report reviews the structure and function of vascular ECM and the importance of the matrix in modulating the vascular response to arterial injury such as balloon angioplasty and atherosclerosis.

Vitronectin regulates smooth muscle contractility via alphav and beta1 integrin

Previous work from this laboratory has established a method for maintaining physiological contractility of dissociated avian smooth muscle in a defined medium at low density. The present report emphasizes the dramatic potency of serum to alter smooth muscle phenotype and induce a loss of contractility. Vitronectin, a molecule purified from plasma, mimicked these effects of serum via an integrin that is RGD-sensitive. Studies utilizing blocking antibodies against vitronectin demonstrated that the presence of this specific adhesion molecule was necessary for the serum-induced loss of contractility. Based on the actions of function-blocking antibodies and RGD-containing peptides, the integrin alphavbeta1 appears to be the primary receptor involved in vitronectin's ability to induce phenotypic transformation in amniotic smooth muscle. The influence of vitronectin on smooth muscle contractility is particularly relevant, because this molecule is abundant in whole blood and plasma (approx. 400 microg/ml). The results suggest that smooth muscle needs to be continually protected from normal blood constituents in vivo. The implications of these results for smooth muscle-related diseases like atherosclerosis, restenosis and Kaposi's sarcoma are discussed.

The inhibition of vascular smooth muscle cell migration by peptide and antibody antagonists of the alphavbeta3 integrin complex is reversed by activated calcium/calmodulin- dependent protein kinase II

The migration of vascular smooth muscle cells (VSMCs) is thought to play a key role in the pathogenesis of many vascular diseases and is regulated by soluble growth factors/ chemoattractants as well as interactions with the extracellular matrix. We have studied the effects of antibodies to rat beta3 and human alphavbeta3 integrins on the migration of VSMCs. Both integrin antibodies as well as cyclic RGD peptides that bind to the vitronectin receptors alphavbeta3 and alphavbeta5 significantly inhibited PDGF-directed migration. This resulted in a reduction in the accumulation of inositol (1,4,5) trisphosphate and the activation of calcium/calmodulin-dependent protein kinase II (CamKII), an important regulatory event in VSMC migration identified previously. PDGF-directed VSMC migration in the presence of the anti-integrin antibodies and cyclic RGD peptides was restored when intracellular CamKII activity was elevated by either raising intracellular calcium levels with the ionophore, ionomycin, or infecting with a replication-defective recombinant adenovirus expressing a constitutively activated CamKII cDNA (AdCMV.CKIID3). Rescue of rat VSMCs was also observed in stably transfected cell lines expressing constitutively activated but not wild-type CamKII. These observations identify a key intermediate in the regulation of VSMC migration by outside-in signaling from the integrin alphavbeta3.

Platelet-derived growth factor and extracellular matrix proteins provide a synergistic stimulus for human vascular smooth muscle cell migration

PURPOSE

Smooth muscle cell (SMC) migration contributes significantly to the hyperplastic response that follows arterial injury. In vitro studies have shown that a number of growth factors and extracellular matrix (ECM) proteins individually stimulate vascular SMC migration. However, after arterial injury, SMCs exist in a complex environment in which they are exposed to many of these proteins simultaneously. The response of SMCs to multiple simultaneous stimuli may differ significantly from their response to any single individual stimulus. In this study, we evaluated the chemotactic response of human vascular SMCs to various combinations of growth factors and ECM proteins.

METHODS

Human saphenous vein SMCs were used for all experiments. Using a 4-hour modified Boyden-chamber assay, we evaluated the effect on SMC chemotaxis of combinations of one of three growth factors (platelet-derived growth factor [PDGF]-AB, basic fibroblast growth factor [bFGF], or epidermal growth factor [EGF]), and one of four ECM proteins (fibronectin, laminin, or collagen type I or IV). A standard fluorimetric assay was used to assess changes in intracellular calcium ([Ca2+]i) in response to the various combinations of growth factors and ECM proteins.

RESULTS

A simple additive effect was seen between ECM proteins and bFGF or EGF. However, when SMCs were simultaneously exposed to PDGF and ECM proteins, we observed a synergistic increase in chemotaxis. This synergy was evident for all concentrations of collagen type I and IV but only with higher concentrations of fibronectin and laminin. We evaluated whether intracellular calcium may be the signaling pathway through which this synergistic effect is mediated. Although ECM proteins alone did not stimulate a rise in [Ca2+]i, ECM proteins enhanced the early peak in [Ca2+]i induced by PDGF.

CONCLUSION

These data show that PDGF acts synergistically with the ECM proteins to promote SMC migration; this effect appears to be specific for PDGF and was not observed with other growth factors. The mechanism responsible for this phenomenon may be a synergistic increase in [Ca2+]i in SMCs simultaneously exposed to both proteins.

Dietary coenzyme Q10 supplementation alters platelet size and inhibits human vitronectin (CD51/CD61) receptor expression

Improved cardiovascular morbidity and mortality have been observed in several clinical studies of dietary supplementation with coenzyme Q10 (CoQ10, ubiquinone). Several mechanisms have been proposed to explain the effects of CoQ10, but a comprehensive explanation of its cardioprotective properties is still lacking. One attractive theory links ubiquinone with the inhibition of platelets. The effect of CoQ10 intake on platelet size and surface antigens was examined in human volunteers. Study participants received 100 mg of CoQ10 twice daily in addition to their usual diet for 20 days. Receptor expression was measured by flow cytometry with monoclonal murine anti-human antibodies CD9 (p24), CD42B (Ib), CD41b (IIb), CD61 (IIIa), CD41a (IIb/IIIa), CD49b (VLA-2), CD62p (P selectin), CD31 (PECAM-1), and CD51/CD61 (vitronectin). An increase of total serum CoQ10 level (from 0.6 +/- 0.1 to 1.8 +/- 0.3 micrograms/ml; p < 0.001) was found at protocol termination. Fluorescence intensity was higher for the large platelets when compared with the whole platelet population. Significant inhibition of vitronectin-receptor expression was observed consistently throughout ubiquinone treatment. Reduction of platelet size was observed at the end of CoQ10 supplementation. Inhibition of the platelet vitronectin receptor and a reduction of the platelet size are direct evidence of a link between dietary CoQ10 intake and platelets. These findings may not be fully explained by the known antioxidant and bioenergetic properties of CoQ10. Diminished vitronectin-receptor expression and reduced platelet size resulting from CoQ10 therapy may contribute to the observed clinical benefits in patients with cardiovascular diseases.