Adhesion and function of human endothelial cells co-cultured on smooth muscle cells

Endothelial Cells Increase Mesenchymal Stem Cell Differentiation in Scaffold-Free 3D Vascular Tissue

In this study, we present a versatile, scaffold-free approach to create ring-shaped engineered vascular tissue segments using human mesenchymal stem cell-derived smooth muscle cells (hMSC-SMCs) and endothelial cells (ECs). We hypothesized that incorporation of ECs would increase hMSC-SMC differentiation without compromising tissue ring strength or fusion to form tissue tubes. Undifferentiated hMSCs and ECs were co-seeded into custom ring-shaped agarose wells using four different concentrations of ECs: 0%, 10%, 20%, and 30%. Co-seeded EC and hMSC rings were cultured in SMC differentiation medium for a total of 22 days. Tissue rings were then harvested for histology, Western blotting, wire myography, and uniaxial tensile testing to examine their structural and functional properties. Differentiated hMSC tissue rings comprising 20% and 30% ECs exhibited significantly greater SMC contractile protein expression, endothelin-1 (ET-1)-meditated contraction, and force at failure compared with the 0% EC rings. On average, the 0%, 10%, 20%, and 30% EC rings exhibited a contractile force of 0.745 ± 0.117, 0.830 ± 0.358, 1.31 ± 0.353, and 1.67 ± 0.351 mN (mean ± standard deviation [SD]) in response to ET-1, respectively. Additionally, the mean maximum force at failure for the 0%, 10%, 20%, and 30% EC rings was 88.5 ± 36. , 121 ± 59.1, 147 ± 43.1, and 206 ±  0.8 mN (mean ± SD), respectively. Based on these results, 30% EC rings were fused together to form tissue-engineered blood vessels (TEBVs) and compared with 0% EC TEBV controls. The addition of 30% ECs in TEBVs did not affect ring fusion but did result in significantly greater SMC protein expression (calponin and smoothelin). In summary, co-seeding hMSCs with ECs to form tissue rings resulted in greater contraction, strength, and hMSC-SMC differentiation compared with hMSCs alone and indicates a method to create a functional 3D human vascular cell coculture model.

Endothelial-Smooth Muscle Cell Interactions in a Shear-Exposed Intimal Hyperplasia on-a-Dish Model to Evaluate Therapeutic Strategies

Intimal hyperplasia (IH) represents a major challenge following cardiovascular interventions. While mechanisms are poorly understood, the inefficient preventive methods incentivize the search for novel therapies. A vessel-on-a-dish platform is presented, consisting of direct-contact cocultures with human primary endothelial cells (ECs) and smooth muscle cells (SMCs) exposed to both laminar pulsatile and disturbed flow on an orbital shaker. With contractile SMCs sitting below a confluent EC layer, a model that successfully replicates the architecture of a quiescent vessel wall is created. In the novel IH model, ECs are seeded on synthetic SMCs at low density, mimicking reendothelization after vascular injury. Over 3 days of coculture, ECs transition from a network conformation to confluent 2D islands, as promoted by pulsatile flow, resulting in a "defected" EC monolayer. In defected regions, SMCs incorporated plasma fibronectin into fibers, increased proliferation, and formed multilayers, similarly to IH in vivo. These phenomena are inhibited under confluent EC layers, supporting therapeutic approaches that focus on endothelial regeneration rather than inhibiting proliferation, as illustrated in a proof-of-concept experiment with Paclitaxel. Thus, this in vitro system offers a new tool to study EC-SMC communication in IH pathophysiology, while providing an easy-to-use translational disease model platform for low-cost and high-content therapeutic development.

Bionic Microbubble Neutrophil Composite for Inflammation-Responsive Atherosclerotic Vulnerable Plaque Pluripotent Intervention

Rupture or erosion of inflammatory atherosclerotic vulnerable plaque is essential to acute coronary events, while the target intervene of vulnerable plaque is very challenging, due to the relatively small volume, high hemodynamic shear stress, and multifactorial nature of the lesion foci. Herein, we utilize the biological functionality of neutrophil and the versatility of microbubble in the acoustic field, to form Neu-balloon through CD11b antibody binding. The Neu-balloon inherits the advantage of neutrophils on firming the endothelium adhesion even at shear stress up to 16 dyne/cm2 and also maintains the acoustic enhancement property from the microbubble, to accumulate at atherosclerotic lesions under acoustic in an atherosclerotic Apo E-/- mice model. Interestingly, Neo-balloon also has high and broad drug loading capacity, which enables the delivery of indocyanine green and miR-126a-5p into vulnerable plagues in vivo. Overall, the bionic Neu-balloon holds great potential to boost on-demand drug transportation into plaques in vivo.

Co-culture of smooth muscle cells and endothelial cells on three-dimensional bioprinted polycaprolactone scaffolds for cavernosal tissue engineering

PURPOSE

In vitro evaluation of polycaprolactone (PCL) scaffolds fabricated by a three-dimensional (3D) printing technique for tissue engineering applications in the corpus cavernosum.

MATERIALS AND METHODS

PCL scaffolds were fabricated by use of a 3 D bioprinting system. The 3D-printed scaffolds had interconnected structures for cell ingrowth. Human aortic smooth muscle cells (haSMCs) were seeded on the scaffold and cultured for 5 days, and then human umbilical vein endothelial cells (HUVECs) were also added on the scaffolds and co-cultured with haSMCs for up to 7 days. The ability of these scaffolds to support the growth of HUVECs and haSMCs was investigated in vitro. 3 D strand-deposited scaffolds were characterized by scanning electron microscopy (SEM) images and porosity measurement.

RESULTS

SEM images showed the surface of the PCL scaffolds to be well covered by HUVECs and haSMCs. Immunofluorescent staining of α-flk1 and α-smooth muscle actin on the HUVECs and haSMCs seeded scaffolds confirmed that the cells remained viable and proliferated throughout the time course of the culture.

CONCLUSION

3 D bioprinting of a PCL scaffold is feasible for co-culturing of HUVECs and haSMCs. This was a preliminary study to investigate the possibility of fabrication of tissue-engineered corpus cavernosum.

Metabolism of vascular smooth muscle cells in vascular diseases

Vascular smooth muscle cells (VSMCs) are the fundamental component of the medial layer of arteries and are essential for arterial physiology and pathology. It is becoming increasingly clear that VSMCs can alter their metabolism to fulfill the bioenergetic and biosynthetic requirements. During vascular injury, VSMCs switch from a quiescent "contractile" phenotype to a highly migratory and proliferative "synthetic" phenotype. Recent studies have found that the phenotype switching of VSMCs is driven by a metabolic switch. Metabolic pathways, including aerobic glycolysis, fatty acid oxidation, and amino acid metabolism, have distinct, indispensable roles in normal and dysfunctional vasculature. VSMCs metabolism is also related to the metabolism of endothelial cells. In the present review, we present a brief overview of VSMCs metabolism and how it regulates the progression of several vascular diseases, including atherosclerosis, systemic hypertension, diabetes, pulmonary hypertension, vascular calcification, and aneurysms, and the effect of the risk factors for vascular disease (aging, cigarette smoking, and excessive alcohol drinking) on VSMC metabolism to clarify the role of VSMCs metabolism in the key pathological process.

Construction of vascular graft with circumferentially oriented microchannels for improving artery regeneration

Design and fabrication of scaffolds with three-dimensional (3D) topological cues inducing regeneration of the neo-tissue comparable to native one remains a major challenge in both scientific and clinical fields. Here, we developed a well-designed vascular graft with 3D highly interconnected and circumferentially oriented microchannels by using the sacrificial sugar microfiber leaching method. The microchannels structure was capable of promoting the migration, oriented arrangement, elongation, and the contractile phenotype expression of vascular smooth muscle cells (VSMCs) in vitro. After implantation into the rat aorta defect model, the microchannels in vascular grafts simultaneously improved the infiltration and aligned arrangement of VSMCs and the oriented deposition of extracellular matrix (ECM), as well as the recruitment and polarization of macrophages. These positive results also provided protection and support for ECs growth, and ultimately accelerated the endothelialization. Our research provides a new strategy for the fabrication of grafts with the capability of inducing arterial regeneration, which could be further extended to apply in preparing other kinds of oriented scaffolds aiming to guide oriented tissue in situ regeneration.

Tirofiban Promotes the Proliferation of Human Umbilical Vein Endothelial Cells In Vitro Via Enhanced Vascular Endothelial Growth Factor Expression

BACKGROUND

In the design and development of small-caliber artificial blood vessels, endothelialization is a key issue, but it is not well understood at present. Some studies have used vascular endothelial growth factor (VEGF) sustained-release methods to promote endothelial cell proliferation. However, this method is not ideal. This study has used drugs to induce endothelial cells to produce VEGF. This method in turn functions to promote cell proliferation and promote the endothelialization of artificial blood vessels. This study aimed to investigate the effect of the antiplatelet drug tirofiban on endothelial cell proliferation in vitro.

METHODS

In this study, human umbilical vein endothelial cells (HUVECs) were used to determine the effect of tirofiban-stimulated cell proliferation. Analysis of cell proliferation, assayed by the Cell Counting Kit-8 assay, showed that the number of cells was increasingly higher than in the absence of tirofiban. It was also observed that heparin enhanced the tirofiban effect. The cell VEGF expression at different time points after tirofiban addition was detected by western blot analysis.

RESULTS

The absorbance values of the experimental (1 μg/mL tirofiban) and the control groups (0 tirofiban) were 1.74 (SD, 0.03) and 1.51 (SD, 0.07) (P < .001), respectively, after 4 days of culture under the same conditions. The amount of VEGF produced by HUVECs gradually increased after treatment with tirofiban, reached a peak at 2 hours, and was 1.3-fold greater than the control group (P = .034). Compared with the tirofiban-only group, the absorbance value of the tirofiban and 10 μg/mL of heparin group was significantly increased (P < .001).

CONCLUSIONS

Tirofiban promoted the proliferation of HUVECs by promoting the synthesis of VEGF in HUVECs. Heparin enhanced tirofiban activity in promoting HUVEC proliferation.

Stiffness of Aligned Fibers Regulates the Phenotypic Expression of Vascular Smooth Muscle Cells

Electrospun uniaxially aligned ultrafine fibers show great promise in constructing vascular grafts mimicking the anisotropic architecture of native blood vessels. However, understanding how the stiffness of aligned fibers would impose influences on the functionality of vascular cells has yet to be explored. The present study aimed to explore the stiffness effects of electrospun aligned fibrous substrates (AFSs) on phenotypic modulation in vascular smooth muscle cells (SMCs). A stable jet coaxial electrospinning (SJCES) method was employed to generate highly aligned ultrafine fibers of poly(l-lactide- co-caprolactone)/poly(l-lactic acid) (PLCL/PLLA) in shell-core configuration with a remarkably varying stiffness region from 0.09 to 13.18 N/mm. We found that increasing AFS stiffness had no significant influence on the cellular shape and orientation along the fiber direction with the cultured human umbilical artery SMCs (huaSMCs) but inhibited the cell adhesion rate, promoted cell proliferation and migration, and especially enhanced the F-actin fiber assembly in the huaSMCs. Notably, higher fiber stiffness resulted in significant downregulation of contractile markers like alpha-smooth muscle actin (α-SMA), smooth muscle myosin heavy chain, calponin, and desmin, whereas upregulated the gene expression of pathosis-associated osteopontin ( OPN) in the huaSMCs. These results allude to the phenotype of huaSMCs on stiffer AFSs being miserably modulated into a proliferative and pathological state. Consequently, it adversely affected the proliferation and migration behavior of human umbilical vein endothelial cells as well. Moreover, stiffer AFSs also revealed to incur significant upregulation of inflammatory gene expression, such as interleukin-6 ( IL-6), monocyte chemoattractant protein-1 ( MCP-1), and intercellular adhesion molecule-1 ( ICAM-1), in the huaSMCs. This study stresses that although electrospun aligned fibers are capable of modulating native-like oriented cell morphology and even desired phenotype realization or transition, they might not always direct cells into correct functionality. The integrated fiber stiffness underlying is thereby a critical parameter to consider in engineering structurally anisotropic tissue-engineered vascular grafts to ultimately achieve long-term patency.

Optimizing endothelial cell functionalization for cell therapy of vascular proliferative disease using a direct contact co-culture system

Increased susceptibility to thrombosis, neoatherosclerosis, and restenosis due to incomplete regrowth of the protective endothelial layer remains a critical limitation of the interventional strategies currently used clinically to relieve atherosclerotic obstruction. Rapid recovery of endothelium holds promise for both preventing the thrombotic events and reducing post-angioplasty restenosis, providing the rationale for developing cell delivery strategies for accelerating arterial reendothelialization. The successful translation of experimental cell therapies into clinically viable treatment modalities for restoring vascular endothelium critically depends on identifying strategies for enhancing the functionality of endothelial cells (EC) derived from high cardiovascular risk patients, the target group for the majority of angioplasty procedures. Enhancing EC-associated nitric oxide (NO) synthesis by inducing overexpression of NO synthase (NOS) has shown promise as a way of increasing paracrine activity and restoring function of EC. In the present study, we developed a direct contact co-culture approach compatible with highly labile effectors, such as NO, and applied it for determining the effect of EC functionalization via NOS gene transfer on the growth of co-cultured arterial smooth muscle cells (A10 cell line) exhibiting the defining characteristics of neointimal cells. Bovine aortic endothelial cells magnetically transduced with inducible NOS-encoding adenovirus (Ad) formulated in zinc oleate-based magnetic nanoparticles (MNP[_iNOSAd]) strongly suppressed growth of proliferating A10 and attenuated the stimulatory effect of a potent mitogen, platelet-derived growth factor (PDGF-BB), whereas EC functionalization with free _iNOSAd or MNP formulated with a different isoform of the enzyme, endothelial NOS, was associated with lower levels of NO synthesis and less pronounced antiproliferative activity toward co-cultured A10 cells. These results show feasibility of applying magnetically facilitated gene transfer to potentiate therapeutically relevant effects of EC for targeted cell therapy of restenosis. The direct contact co-culture methodology provides a sensitive and reliable tool with potential utility for a variety of biomedical applications.

Bioinspired 3D Multilayered Shape Memory Scaffold with a Hierarchically Changeable Micropatterned Surface for Efficient Vascularization

How to achieve three-dimensional (3D) cell alignment and subsequent prompt tissue regeneration remains a great challenge. Here, inspired by the interior 3D architecture of native arteries, we develop a new 3D multilayered shape memory vascular scaffold with a hierarchically changeable micropatterned surface for vascularization. The shape memory function renders the implantation of the scaffold safe and convenient via minimally invasive surgery. By co-culturing endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) on the 3D multilayered structure, the inner monolayer, which has a square micropatterned surface, can promote EC adhesion and migration, resulting in a rapid endothelialization, and the outer multilayers, which have rectangular micropatterned surfaces, can induce a circumferential alignment of VSMCs. After implantation in the cervical artery of a New Zealand rabbit for 120 days, the graft developed a high capacity for modulating cellular 3D alignment, to generate a neonatal functional blood vessel with an endothelium layer in the inner layer and multilevel VSMC circumferential alignments in the outer layers.

A planar model of the vessel wall from cellularized-collagen scaffolds: focus on cell–matrix interactions in mono-, bi- and tri-culture models

An easy to prepare and manipulate model of the vascular wall in a planar shape to investigate physiological and pathological processes of vascular tissues.

Three-Dimensional Coculture Model to Analyze the Cross Talk Between Endothelial and Smooth Muscle Cells

The response of blood vessels to physiological and pathological stimuli partly depends on the cross talk between endothelial cells (EC) lining the luminal side and smooth muscle cells (SMC) building the inner part of the vascular wall. Thus, the in vitro analysis of the pathophysiology of blood vessels requires coculture systems of EC and SMC. We have developed and validated a modified three-dimensional sandwich coculture (3D SW-CC) of EC and SMC using open μ-Slides with a thin glass bottom allowing direct imaging. The culture dish comprises an intermediate plate to minimize the meniscus resulting in homogenous cell distribution. Human umbilical artery SMC were sandwiched between coatings of rat tail collagen I. Following SMC quiescence, human umbilical vein EC were seeded on top of SMC and cultivated until confluence. By day 7, EC had formed a confluent monolayer and continuous vascular endothelial (VE)-cadherin-positive cell/cell contacts. Below, spindle-shaped SMC had formed parallel bundles and showed increased calponin expression compared to day 1. EC and SMC were interspaced by a matrix consisting of laminin, collagen IV, and perlecan. Basal messenger RNA (mRNA) expression levels of E-selectin, angiopoietin-1, calponin, and intercellular adhesion molecule 1 (ICAM-1) of the 3D SW-CC was comparable to that of a freshly isolated mouse inferior vena cava. Addition of tumor necrosis factor alpha (TNF α) to the 3D SW-CC induced E-selectin and ICAM-1 mRNA and protein induction, comparable to the EC and SMC monolayers. In contrast, the addition of activated platelets induced a significantly delayed but more pronounced activation in the 3D SW-CC compared to EC and SMC monolayers. Thus, this 3D SW-CC permits analyzing the cross talk between EC and SMC that mediate cellular quiescence as well as the response to complex activation signals.

Bottom-up fabrication of artery-mimicking tubular co-cultures in collagen-based microchannel scaffolds

We developed a robust bottom-up approach to construct open-ended, tubular co-culture constructs that simulate the human vascular morphology and microenvironment. By design, these three-dimensional artificial vessels mimic the basic architecture of an artery: a collagen-rich extracellular matrix (as the tunica externa), smooth muscle cells (SMCs) (as the tunica media), and an endothelial cell (EC) lining (as the tunica interna). A versatile needle-based fabrication technique was employed to achieve controllable arterial layouts within a PDMS-hosted collagen microchannel scaffold (330 ± 10 μm in diameter): (direct co-culture) a SMC/EC bilayer to follow the structure of an arteriole-like segment; and (encapsulated co-culture) a lateral SMC multilayer covered by an EC monolayer lining to simulate the architecture of a larger artery. Optical and fluorescence microscopy images clearly evidenced the progressive cell elongation and sprouting behavior of SMCs and ECs along the collagen gel contour and within the gel matrix under static co-culture conditions. The progressive cell growth patterns effectively led to the formation of a tubular co-culture with an internal endothelial lining expressing prominent CD31 (cluster of differentiation 31) intercellular junction markers. During a 4-day static maturation period, the artery constructs showed modest alteration in the luminal diameters (i.e. less than 10% changes from the initial measurements). This argues in favor of stable and predictable arterial architecture achieved via the proposed fabrication protocols. Both co-culture models showed a high glucose metabolic rate during the initial proliferation phase, followed by a temporary quiescent (and thus, mature) stage. These proof-of-concept models with a controllable architecture create an important foundation for advanced vessel manipulations such as the integration of relevant physiological functionality or remodeling into a vascular disease-mimicking tissue.

Dual-Microstructured Porous, Anisotropic Film for Biomimicking of Endothelial Basement Membrane

Human endothelial basement membrane (BM) plays a pivotal role in vascular development and homeostasis. Here, a bioresponsive film with dual-microstructured geometries was engineered to mimic the structural roles of the endothelial BM in developing vessels, for vascular tissue engineering (TE) application. Flexible poly(ε-caprolactone) (PCL) thin film was fabricated with microscale anisotropic ridges/grooves and through-holes using a combination of uniaxial thermal stretching and direct laser perforation, respectively. Through optimizing the interhole distance, human mesenchymal stem cells (MSCs) cultured on the PCL film's ridges/grooves obtained an intact cell alignment efficiency. With prolonged culturing for 8 days, these cells formed aligned cell multilayers as found in native tunica media. By coculturing human umbilical vein endothelial cells (HUVECs) on the opposite side of the film, HUVECs were observed to build up transmural interdigitation cell-cell contact with MSCs via the through-holes, leading to a rapid endothelialization on the PCL film surface. Furthermore, vascular tissue construction based on the PCL film showed enhanced bioactivity with an elevated total nitric oxide level as compared to single MSCs or HUVECs culturing and indirect MSCs/HUVECs coculturing systems. These results suggested that the dual-microstructured porous and anisotropic film could simulate the structural roles of endothelial BM for vascular reconstruction, with aligned stromal cell multilayers, rapid endothelialization, and direct cell-cell interaction between the engineered stromal and endothelial components. This study has implications of recapitulating endothelial BM architecture for the de novo design of vascular TE scaffolds.

Experimental study on the construction of small three-dimensional tissue engineered grafts of electrospun poly-ε-caprolactone

Studies on three-dimensional tissue engineered graft (3DTEG) have attracted great interest among researchers as they present a means to meet the pressing clinical demand for tissue engineering scaffolds. To explore the feasibility of 3DTEG, high porosity poly-ε-caprolactone (PCL) was obtained via the co-electrospinning of polyethylene glycol and PCL, and used to construct small-diameter poly-ε-caprolactone-lysine (PCL-LYS-H) scaffolds, whereby heparin was anchored to the scaffold surface by lysine groups. A variety of small-diameter 3DTEG models were constructed with different PCL layers and the mechanical properties of the resulting constructs were evaluated in order to select the best model for 3DTEGs. Bone marrow mononuclear cells were induced and differentiated to endothelial cells (ECs) and smooth muscle cells (SMCs). A 3DTEG (labeled '10-4%') was successfully produced by the dynamic co-culture of ECs on the PCL-LYS-H scaffolds and SMCs on PCL. The fluorescently labeled cells on the 3DTEG were subsequently observed by laser confocal microscopy, which showed that the ECs and SMCs were embedded in the 3DTEG. Nitric oxide and endothelial nitric oxide synthase assays showed that the ECs behaved normally in the 3DTEG. This study consequently provides a new thread to produce small-diameter tissue engineered grafts, with excellent mechanical properties, that are perfusable to vasculature and functional cells.

Micropatterned coculture of vascular endothelial and smooth muscle cells on layered electrospun fibrous mats toward blood vessel engineering

A major challenge in vascular engineering is the establishment of proper microenvironment to guide the spatial organization, growth, and extracellular matrix (ECM) productions of cells found in blood vessels. In the current study, micropatterned fibrous mats with distinct ridges and grooves of different width were created to load smooth muscle cells (SMCs), which were assembled by stacking on vascular endothelial cell (EC)-loaded flat fibrous mats to mimic the in vivo-like organized structure of blood vessels. SMCs were mainly distributed in the ridges, and aligned fibers in the patterned regions led to the formation of elongated cell bodies, intense actin filaments, and expressions of collagen I and α-smooth muscle actin in a parallel direction with fibers. ECs spread over the flat fibrous mats and expressed collagen IV and laminin with a cobblestone-like feature. A z-stack scanning of fluorescently stained fibrous mats indicated that SMCs effectively infiltrated into fibrous scaffolds at the depth of around 200 μm. Compared with SMCs cultured alone, the coculture with ECs enhanced the proliferation, infiltration, and cytoskeleton elongation of SMCs on patterned fibrous mats. Although the coculture of SMCs made no significant difference in the EC growth, the coculture system on patterned fibrous scaffolds promoted ECM productions of both ECs and SMCs. Thus, this patterned fibrous configuration not only offers a promising technology in the design of tissue engineering scaffolds to construct blood vessels with durable mechanical properties, but also provides a platform for patterned coculture to investigate cell-matrix and cell-cell interactions in highly organized tissues.

Paeonol Inhibits Proliferation of Vascular Smooth Muscle Cells Stimulated by High Glucose via Ras-Raf-ERK1/2 Signaling Pathway in Coculture Model

Paeonol (Pae) has been previously reported to protect against atherosclerosis (AS) by inhibiting vascular smooth muscle cell (VSMC) proliferation or vascular endothelial cell (VEC) injury. But studies lack how VSMCs and VECs interact when Pae plays a role. The current study was based on a coculture model of VSMCs and VECs to investigate the protective mechanisms of Pae on atherosclerosis (AS) by determining the secretory function of VECs and proliferation of VSMCs focusing on the Ras-Raf-ERK1/2 signaling pathway. VECs were stimulated by high glucose. Our data showed that high concentration (35.5 mM) of glucose induced damage in VECs. Injury of VECs stimulated VSMC proliferation in the coculture model. Pae (120  μ M) decreased vascular endothelial growth factor (VEGF) and platelet derivative growth factor B (PDGF-B) release from VECs and inhibited overexpression of Ras, P-Raf, and P-ERK proteins in VSMCs. The results indicate that diabetes modulates the inflammatory response in VECs to stimulate VSMC proliferation and promote the development of AS. Pae was beneficial by inhibiting the inflammatory effects of VECs on VSMC proliferation. This study suggests the inhibitory mechanism of Pae due to the inhibition of VEGF and PDGF-B secretion in VECs and Ras-Raf-ERK1/2 signaling pathway in VSMCs.

Endothelialization of electrospun polycaprolactone (PCL) small caliber vascular grafts spun from different polymer blends

Small caliber vascular grafts represent a challenge to material scientists. In contrast to large caliber grafts, prostheses with diameter <6 mm, lead to increased hemodynamic disturbances and thrombogenic complications. Thus, endothelialization of small caliber grafts should create a compatible interface for hemodynamic processes. The purpose of our study was to compare different compositions of electrospun scaffolds with conventional ePTFE grafts with an inner diameter of 4 mm as well as different pre-coatings to create an optimized physiological interface for endothelialization. Polycaprolactone, polylactide, and polyethylenglycol (PCL/PLA and PCL/PLA/PEG) electrospun grafts and ePTFE grafts were pre-coated with blood, gelatine or fibronectin and seeded with endothelial cells from the human term placenta. Best results were obtained with fibronectin-coated PCL/PLA/PEG grafts. Here, the number of attached viable cells was 78-81% higher than on fibronectin pre-treated ePTFE grafts. Cells attached to PCL/PLA/PEG grafts appeared in physiological cobblestone morphology. Viability analysis showed a high cell viability of more than 98%. Fibronectin-coated PCL/PLA/PEG grafts may be a promising improvement to conventionally used ePTFE grafts.

Wall shear stress effects on endothelial-endothelial and endothelial-smooth muscle cell interactions in tissue engineered models of the vascular wall

Vascular functions are affected by wall shear stresses (WSS) applied on the endothelial cells (EC), as well as by the interactions of the EC with the adjacent smooth muscle cells (SMC). The present study was designed to investigate the effects of WSS on the endothelial interactions with its surroundings. For this purpose we developed and constructed two co-culture models of EC and SMC, and compared their response to that of a single monolayer of cultured EC. In one co-culture model the EC were cultured on the SMC, whereas in the other model the EC and SMC were cultured on the opposite sides of a membrane. We studied EC-matrix interactions through focal adhesion kinase morphology, EC-EC interactions through VE-Cadherin expression and morphology, and EC-SMC interactions through the expression of Cx43 and Cx37. In the absence of WSS the SMC presence reduced EC-EC connectivity but produced EC-SMC connections using both connexins. The exposure to WSS produced discontinuity in the EC-EC connections, with a weaker effect in the co-culture models. In the EC monolayer, WSS exposure (12 and 4 dyne/cm² for 30 min) increased the EC-EC interaction using both connexins. WSS exposure of 12 dyne/cm² did not affect the EC-SMC interactions, whereas WSS of 4 dyne/cm² elevated the amount of Cx43 and reduced the amount of Cx37, with a different magnitude between the models. The reduced endothelium connectivity suggests that the presence of SMC reduces the sealing properties of the endothelium, showing a more inflammatory phenotype while the distance between the two cell types reduced their interactions. These results demonstrate that EC-SMC interactions affect EC phenotype and change the EC response to WSS. Furthermore, the interactions formed between the EC and SMC demonstrate that the 1-side model can simulate better the arterioles, while the 2-side model provides better simulation of larger arteries.

Late-outgrowth endothelial progenitors from patients with coronary artery disease: endothelialization of confluent stromal cell layers

Patients with coronary artery disease (CAD) are the primary candidates to receive small-diameter tissue-engineered blood vessels (TEBVs). Peripheral blood derived endothelial progenitor cells (EPCs) from CAD patients (CAD EPCs) represent a minimally invasive source of autologous cells for TEBV endothelialization. We have previously shown that human CAD EPCs are highly proliferative and express many of the hallmarks of mature and healthy endothelial cells; however, their behavior on stromal cells that comprise the media of TEBVs has not yet been evaluated. Primary CAD EPCs or control human aortic endothelial cells (HAECs) were seeded over confluent, quiescent layers of human smooth muscle cells (SMCs) using a direct co-culture model. The percent coverage, adhesion strength, alignment under flow and generation of flow-induced nitric oxide of the seeded CAD EPCs were compared to that of HAECs. The integrin-binding profile of CAD EPCs was also evaluated over a layer of confluent, quiescent SMCs. Direct comparison of our CAD EPC results to analogous co-culture studies with cord blood EPCs show that both types of blood-derived EPCs are viable options for endothelialization of TEBVs.

Influence of mesenchymal stem cells on the response of endothelial cells to laminar flow and shear stress

The interactions between endothelial cells (ECs) and smooth muscle cells (SMCs) in a complex hemodynamic environment play an important role in the control of blood vessel function. Since autologous SMCs are not readily available for the tissue engineering of a blood vessel substitute, a substitute for SMCs, such as human adult bone marrow-derived mesenchymal stem cells (MSCs), is needed. The objective of this study was to use a three-dimensional coculture model of the blood vessel wall, comprised of ECs and MSCs, to determine how the presence of MSCs affects EC function. Two vascular coculture models with an EC monolayer were created using type I collagen. All models were exposed to steady laminar flow with a shear stress of 15 dyn/cm(2) for up to 48 h. ECs in both the MSC and SMC coculture models expressed up-regulated EC-specific markers compared to the EC-only control model. The most dramatic difference observed between the two coculture models was in the experiments assessing monocyte adhesion. Here, fewer monocytes bound after laminar shear compared to static conditions; however, the number of bound monocytes was much lower for the EC-MSC coculture model than the EC-SMC coculture model for both static and shear conditions. These results suggest the feasibility of developing a tissue-engineered blood vessel substitute using MSCs as a substitute for SMCs.

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

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

Endothelial control of vasodilation: integration of myoendothelial microdomain signalling and modulation by epoxyeicosatrienoic acids

Endothelium-derived epoxyeicosatrienoic acids (EETs) are fatty acid epoxides that play an important role in the control of vascular tone in selected coronary, renal, carotid, cerebral and skeletal muscle arteries. Vasodilation due to endothelium-dependent smooth muscle hyperpolarization (EDH) has been suggested to involve EETs as a transferable endothelium-derived hyperpolarizing factor. However, this activity may also be due to EETs interacting with the components of other primary EDH-mediated vasodilator mechanisms. Indeed, the transfer of hyperpolarization initiated in the endothelium to the adjacent smooth muscle via gap junction connexins occurs separately or synergistically with the release of K(+) ions at discrete myoendothelial microdomain signalling sites. The net effects of such activity are smooth muscle hyperpolarization, closure of voltage-dependent Ca(2+) channels, phospholipase C deactivation and vasodilation. The spatially localized and key components of the microdomain signalling complex are the inositol 1,4,5-trisphosphate receptor-mediated endoplasmic reticulum Ca(2+) store, Ca(2+)-activated K(+) (KCa), transient receptor potential (TRP) and inward-rectifying K(+) channels, gap junctions and the smooth muscle Na(+)/K(+)-ATPase. Of these, TRP channels and connexins are key endothelial effector targets modulated by EETs. In an integrated manner, endogenous EETs enhance extracellular Ca(2+) influx (thereby amplifying and prolonging KCa-mediated endothelial hyperpolarization) and also facilitate the conduction of this hyperpolarization to spatially remote vessel regions. The contribution of EETs and the receptor and channel subtypes involved in EDH-related microdomain signalling, as a candidate for a universal EDH-mediated vasodilator mechanism, vary with vascular bed, species, development and disease and thus represent potentially selective targets for modulating specific artery function.

The Effect of Stress-Induced Senescence on Aging Human Cord Blood-Derived Endothelial Cells

PURPOSE

We sought to determine the effect of stress-induced senescence on the permeability to albumin of aging endothelial progenitor cells.

METHODS

Human umbilical cord blood derived endothelial cells (hCB-ECs) and human aortic endothelial cells (HAECs) were treated with 200 μM H₂O₂ and permeability to FITC-bovine serum albumin was measured. Some samples were subsequently treated with 100μM 8-pCPT-2'-O-Me-cAMP, a cAMP analog that activates the Epac1-Rap1 pathway. Cell proliferation was measured with the EdU assay. Phase contrast, and immunofluorescence images were taken to observe morphological changes in cells after exposure to H₂O₂.

RESULTS

hCB-ECs exposed to H₂O₂ exhibited a significant increase in permeability, but their response differed from the HAECs. Low passage hCB-ECs had a permeability increase of about 82% (p<0.01) compared to aged cells which had a permeability increase of about 37% (p<0.05). This increase in permeability was reduced by treating the cells with 100 μM 8-pCPT-2'-O-Me-cAMP. The younger cells exhibited a significant decrease in proliferation after being subjected to various concentrations of H₂O₂ whereas the aged cells exhibited a more gradual decrease in the percent of cells in S-phase. These changes also correlated with changes in cell morphology and junction staining. When placed back in the original media, the morphology and permeability of the hCB-ECs returned to the control condition, while the HAECs did not.

CONCLUSIONS

The permeability of low and high passage hCB-ECs and HAECs initially increases in response to oxidative stress. hCB-ECs, but not HAECs, were able to recover from the stress 24 hours later. Early passage hCB-ECs were more susceptible to exogenous H₂O₂ than late passage hCB-ECs. The increase in permeability of hCB-ECs to H₂O₂ also correlated with decreased cell proliferation and changes in cell junctions.

Comparison of mixed and lamellar coculture spatial arrangements for tissue engineering capillary networks in vitro

Coculture of endothelial cells (ECs) and smooth muscle cells (SMCs) in vitro can yield confluent monolayers or EC networks. Factors influencing this transition are not known. In this study, we examined whether the spatial arrangement of EC-SMC cocultures affected EC migration, network morphology, and angiogenic protein secretion. Human umbilical cord blood-derived ECs (hCB-ECs) were grown in coculture with human aortic SMCs in either a mixed or lamellar spatial geometry and analyzed over a culture period of 12 days. The hCB-ECs cultured on SMCs in a mixed system had higher cell speeds, shorter persistence times, and lower random motility coefficients than ECs in a lamellar system. By day 12 of coculture, mixed systems demonstrated greater anastomoses and capillary loop formation than lamellar systems as evidenced by a higher number of branch points, angle of curvature between branch points, and percentage of imaged area covered by networks. The network morphology was more uniform in the mixed systems than the lamellar systems with fewer EC clusters present after several days in culture. Proliferation of hCB-ECs was higher for mixed cocultures during the first 24 h of coculture, and then declined dramatically suggesting that proliferation only contributed to network formation during the early stages of coculture. Proteome assay results show reduced solution levels, but no change in intracellular levels of angiogenic proteins in lamellar systems compared to mixed systems. These data suggest that mixing ECs and SMCs together favors the formation of EC networks to a greater extent than a lamellar arrangement in which ECs form a cell layer above a confluent, quiescent layer of SMCs.

Effect of cellular senescence on the albumin permeability of blood-derived endothelial cells

In this study, we tested the hypotheses that endothelial cells (ECs) derived from human umbilical cord blood (hCB-ECs) exhibit low permeability, which increases as hCB-ECs age and undergo senescence, and that the change in the permeability of hCB-ECs is due to changes in tight junction protein localization and the activity of exchange protein activated by cAMP (Epac)1. Albumin permeability across low-passage hCB-EC monolayers on Transwell membranes was 10 times lower than for human aortic ECs (HAECs) (P < 0.01) but similar to in vivo values in arteries. Expression of the tight junction protein occludin and tyrosine phosphorylation of occludin were less in hCB-ECs than in HAECs (P < 0.05). More hCB-ECs than HAECs underwent mitosis (P < 0.01). hCB-ECs that underwent >44 population doublings since isolation had a significantly higher permeability than hCB-ECs that underwent <31 population doublings (P < 0.05). This age-related increase in hCB-EC permeability was associated with an increase in tyrosine phosphorylation of occludin (P < 0.01); permeability and occludin phosphorylation were reduced by treatment with 2 μM resveratrol. Tyrosine phosphorylation of occludin and cell age influence the permeability of hCB-ECs, whereas levels of EC proliferation and expression of tight junction proteins did not explain the differences between hCB-EC and HAEC permeability. The elevated permeability in late passage hCB-ECs was reduced by 25-40% by elevation of membrane-associated cAMP and activation of the Epac1 pathway. Given the similarity to in vivo permeability to albumin and the high proliferation potential, hCB-ECs may be a suitable in vitro model to study transport-related pathologies and cell aging.

Serotonin passes through myoendothelial gap junctions to promote pulmonary arterial smooth muscle cell differentiation

Myoendothelial gap junctional signaling mediates pulmonary arterial endothelial cell (PAEC)-induced activation of latent TGF-β and differentiation of cocultured pulmonary arterial smooth muscle cells (PASMCs), but the nature of the signal passing from PAECs to PASMCs through the gap junctions is unknown. Because PAECs but not PASMCs synthesize serotonin, and serotonin can pass through gap junctions, we hypothesized that the monoamine is the intercellular signal. We aimed to determine whether PAEC-derived serotonin mediates PAEC-induced myoendothelial gap junction-dependent activation of TGF-β signaling and differentiation of PASMCs. Rat PAECs and PASMCs were monocultured or cocultured with (touch) or without (no-touch) direct cell-cell contact. In all cases, tryptophan hydroxylase 1 (Tph1) transcripts were expressed predominantly in PAECs. Serotonin was detected by immunostaining in both PAECs and PASMCs in PAEC/PASMC touch coculture but was not found in PASMCs in either PAEC/PASMC no-touch coculture or in PASMC/PASMC touch coculture. Furthermore, inhibition of gap junctions but not of the serotonin transporter in PAEC/PASMC touch coculture prevented serotonin transfer from PAECs to PASMCs. Inhibition of serotonin synthesis pharmacologically or by small interfering RNAs to Tph1 in PAECs inhibited the PAEC-induced activation of TGF-β signaling and differentiation of PASMCs. We concluded that serotonin synthesized by PAECs is transferred through myoendothelial gap junctions into PASMCs, where it activates TGF-β signaling and induces a more differentiated phenotype. This finding suggests a novel role of gap junction-mediated intercellular serotonin signaling in regulation of PASMC phenotype.

Development of an endothelial-smooth muscle cell coculture model using phenotype-controlled smooth muscle cells

A coculture of endothelial cells (ECs) and smooth muscle cells (SMCs), which mimics cellular interactions appearing in vivo, has been performed in studies on the relationship between atherogenesis and fluid shear stress conditions. Although healthy arteries in vivo consist of contractile phenotype SMCs, cultured cells used in many studies normally exhibit a synthetic phenotype. Here, we developed an EC-SMC coculture model to investigate the interactions between ECs and contractile SMCs, and examined the effect of shear stress applied to ECs on SMC phenotypes. Cultured human umbilical artery SMCs were differentiated into contractile states by arresting cell growth using a serum-free medium. Western blotting confirmed that SMC expression of contractile protein markers, α-smooth muscle actin (SMA) and calponin, increased to levels similar to those observed in arterial cells. After coculturing contractile SMCs with ECs separated by a collagen gel layer, the expression of α-SMA decreased under static conditions, indicating that the SMC phenotype tended to be synthetic by coculturing with ECs, but shear stress applied to cocultured ECs maintained the level of α-SMA expression in SMCs. The coculture model constructed in the present study will be a useful tool to investigate interactions between ECs and contractile SMCs under shear conditions.

Myoendothelial gap junctional signaling induces differentiation of pulmonary arterial smooth muscle cells

Myoendothelial gap junctions are involved in regulating systemic arterial smooth muscle cell phenotype and function, but their role in the regulation of pulmonary arterial smooth muscle cell (PASMC) phenotype is unknown. We therefore investigated in cocultured pulmonary arterial endothelial cells (PAECs) and PASMCs whether myoendothelial gap junctional signaling played a role in PAEC-dependent regulation of PASMC phenotype. Rat PAECs and PASMCs were cocultured on opposite sides of a porous Transwell membrane that permitted formation of heterotypic cell-cell contacts. Immunostaining showed expression of the gap junctional protein connexin 43 (Cx43) on projections extending into the membrane from both cell types. Dye transfer exhibited functional gap junctional communication from PAECs to PASMCs. PASMCs cocultured with PAECs had a more contractile-like phenotype (spindle shape and increased expression of the contractile proteins myosin heavy chain, H1-calponin, and α-smooth muscle cell-actin) than PASMCs cocultured with PASMCs or cocultured without direct contact with PAECs. Transforming growth factor (TGF)-β1 signaling was activated in PASMCs cocultured with PAECs, and the PASMC differentiation was inhibited by TGF-β type I receptor blockade. Inhibition of gap junctional communication pharmacologically or by knock down of Cx43 in PAECs blocked TGF-β signaling and PASMC differentiation. These results implicate myoendothelial gap junctions as a gateway for PAEC-derived signals required for maintaining TGF-β-dependent PASMC differentiation. This study identifies an alternative pathway to paracrine signaling to convey regulatory signals from PAECs to PASMCs and raises the possibility that dysregulation of this direct interaction is involved in the pathogenesis of hypertensive pulmonary vascular remodeling.

Biomechanical effects of flow and coculture on human aortic and cord blood-derived endothelial cells

Human endothelial cells derived from umbilical cord blood (hCB-ECs) represent a promising cell source for endothelialization of tissue engineered blood vessels. hCB-ECs cultured directly above human aortic smooth muscle cells (SMCs), which model native and tissue engineered blood vessels, produce a confluent endothelium that responds to flow like normal human aortic endothelial cells (HAECs). The objective of this study was to quantify the elastic modulus of hCB-ECs cocultured with SMCs under static and flow conditions using atomic force microscopy (AFM). Cytoskeleton structures were assessed by AFM cell surface imaging and immunofluorescence of F-actin. The elastic moduli of hCB-ECs and HAECs were similar and significantly smaller than the value for SMCs in monoculture under static conditions (p<0.05). In coculture, hCB-ECs and HAECs became significantly stiffer with moduli 160-180% larger than their corresponding values in monoculture. While the moduli of hCB-ECs and HAECs almost doubled in monoculture and flow condition, their corresponding values in coculture declined after exposure to flow. Both the number and diameter of cortical stress fiber per cell width increased in coculture and/or flow conditions, whereas the subcortical stress fiber density throughout the cell interior increased by a smaller amount. These findings indicate that changes to biomechanical properties in coculture and/or exposure to flow are correlated with changes in the cortical stress fiber density. For ECs, fluid shear stress appeared to have greater effect on the elastic modulus than the presence of SMCs and changes to the elastic modulus in coculture may be due to EC-SMC communication.

The biocompatibility of titanium cardiovascular devices seeded with autologous blood-derived endothelial progenitor cells: EPC-seeded antithrombotic Ti implants

Implantable and extracorporeal cardiovascular devices are commonly made from titanium (Ti) (e.g. Ti-coated Nitinol stents and mechanical circulatory assist devices). Endothelializing the blood-contacting Ti surfaces of these devices would provide them with an antithrombogenic coating that mimics the native lining of blood vessels and the heart. We evaluated the viability and adherence of peripheral blood-derived porcine endothelial progenitor cells (EPCs), seeded onto thin Ti layers on glass slides under static conditions and after exposure to fluid shear stresses. EPCs attached and grew to confluence on Ti in serum-free medium, without preadsorption of proteins. After attachment to Ti for 15 min, less than 5% of the cells detached at a shear stress of 100 dyne / cm(2). Confluent monolayers of EPCs on smooth Ti surfaces (Rq of 10 nm), exposed to 15 or 100 dyne/cm(2) for 48 h, aligned and elongated in the direction of flow and produced nitric oxide dependent on the level of shear stress. EPC-coated Ti surfaces had dramatically reduced platelet adhesion when compared to uncoated Ti surfaces. These results indicate that peripheral blood-derived EPCs adhere and function normally on Ti surfaces. Therefore EPCs may be used to seed cardiovascular devices prior to implantation to ameliorate platelet activation and thrombus formation.

Hepatic stellate cell-mediated three-dimensional hepatocyte and endothelial cell triculture model

Hepatic stellate cells (HSCs) form a functional unit with endothelia and hepatocytes in the liver to play a pivotal role in heterotypic cellular communication. To investigate this role of HSCs, it is of great benefit to establish a triculture model that forms the functional unit from proximal layers of hepatocytes, HSCs, and endothelial cells (ECs). Here, we established a three-dimensional triculture model, using a microporous membrane to create the functional unit. HSC behavior was controlled by the membrane pore size, which was critical for achieving proximal cell layers. With a specific pore size, the HSCs intercalated between layers of hepatocytes and ECs, due to the limitation on HSC behavior. When only cytoplasmic processes of quiescent HSCs were adjacent to ECs, while the HSC bodies remained on the side of the hepatocytes, the ECs changed morphologically and were capable of long-term survival. We confirmed that HSCs mediated the communication between hepatocytes and ECs in terms of EC morphogenesis. This triculture model allows us to investigate the roles of HSCs as both facilitators and integrators of cell-cell communication between hepatocytes and ECs, and is useful for investigating heterotypic cellular communication in vitro.

Endothelial Cell Vascular Smooth Muscle Cell Co-Culture Assay For High Throughput Screening Assays For Discovery of Anti-Angiogenesis Agents and Other Therapeutic Molecules

Drug development for many diseases would be aided greatly by accurate in vitro model systems that replicate key elements of in vivo physiology. The recent development of co-culture systems of endothelial cells and vascular smooth muscle cells can be extended to high throughput systems for the identification of compounds for angiogenesis, vascular repair and hypertension. In this review, the various co-culture systems are reviewed and biological interactions between endothelial cells and vascular smooth muscle cells are discussed. Key considerations in the design of high throughput systems are presented and selected examples are discussed.

Porcine endothelial cells cocultured with smooth muscle cells became procoagulant in vitro

Endothelial cell (EC) seeding represents a promising approach to provide a nonthrombogenic surface on vascular grafts. In this study, we used a porcine EC/smooth muscle cell (SMC) coculture model that was previously developed to examine the efficacy of EC seeding. Expression of tissue factor (TF), a primary initiator in the coagulation cascade, and TF activity were used as indicators of thrombogenicity. Using immunostaining, primary cultures of porcine EC showed a low level of TF expression, but a highly heterogeneous distribution pattern with 14% of ECs expressing TF. Quiescent primary cultures of porcine SMCs displayed a high level of TF expression and a uniform pattern of staining. When we used a two-stage amidolytic assay, TF activity of ECs cultured alone was very low, whereas that of SMCs was high. ECs cocultured with SMCs initially showed low TF activity, but TF activity of cocultures increased significantly 7-8 days after EC seeding. The increased TF activity was not due to the activation of nuclear factor kappa-B on ECs and SMCs, as immunostaining for p65 indicated that nuclear factor kappa-B was localized in the cytoplasm in an inactive form in both ECs and SMCs. Rather, increased TF activity appeared to be due to the elevated reactive oxygen species levels and contraction of the coculture, thereby compromising the integrity of EC monolayer and exposing TF on SMCs. The incubation of cocultures with N-acetyl-cysteine (2 mM), an antioxidant, inhibited contraction, suggesting involvement of reactive oxygen species in regulating the contraction. The results obtained from this study provide useful information for understanding thrombosis in tissue-engineered vascular grafts.

Human umbilical cord blood-derived endothelial cells reendothelialize vein grafts and prevent thrombosis

OBJECTIVE

To accelerate vein graft reendothelialization and reduce vein graft thrombosis by infusing human umbilical cord blood-derived endothelial cells (hCB-ECs) because loss of endothelium contributes to vein graft thrombosis and neointimal hyperplasia.

METHODS AND RESULTS

Under steady flow conditions in vitro, hCB-ECs adhered to smooth muscle cells 2.5 to 13 times more than ECs derived from peripheral blood or human aorta (P<0.05). Compared with peripheral blood and human aorta ECs, hCB-ECs had 1.4-fold more cell surface α(5)β(1) integrin heterodimers per cell (P<0.05) and proliferated on fibronectin 4- to 10-fold more rapidly (P<0.05). Therefore, we used hCB-ECs to enhance reendothelialization of carotid interposition vein grafts implanted in NOD.CB17-Prkdc(scid)/J mice. Two weeks postoperatively, vein grafts from hCB-EC-treated mice demonstrated approximately 55% reendothelialization and no luminal thrombosis. In contrast, vein grafts from sham-treated mice demonstrated luminal thrombosis in 75% of specimens (P<0.05) and only approximately 14% reendothelialization. In vein grafts from hCB-EC-treated mice, 33±10% of the endothelium was of human origin, as judged by human major histocompatibility class I expression.

CONCLUSIONS

The hCB-ECs adhere to smooth muscle cells under flow conditions in vitro, accelerate vein graft reendothelialization in vivo, and prevent vein graft thrombosis. Thus, hCB-ECs offer novel therapeutic possibilities for vein graft disease.

Scaffold-free in vitro arterial mimetics: the importance of smooth muscle-endothelium contact

We have developed an in vitro endothelial cell (EC)-smooth muscle cell (SMC) coculture platform that can mimic either the healthy or diseased state of blood vessels. Transforming growth factor-beta1 (TGF-beta1) and heparin were introduced to the SMC cultures to upregulate the SMC differentiation markers, alpha-smooth muscle actin (alpha-SMA) and calponin (homotypic model). Interestingly, seeding of near-confluent concentrations of ECs on the SMCs (heterotypic model) induced higher levels of alpha-SMA and calponin expression in the SMC cultures than did the addition of heparin and TGF-beta1 alone. The expression levels increased further on pretreating the SMCs with TGF-beta1 and heparin before adding a near-confluent monolayer of ECs. In contrast, seeding of sparse concentrations of ECs forced the SMCs into a more hyperplastic state as determined by alpha-SMA and calponin expression. This study highlights the importance of both soluble factors and EC seeding densities when considering culture conditions; in vivo SMCs are in close proximity with and interact with a monolayer of ECs. Our study suggests that this architecture is important for healthy vascular tissue function. In addition, it shows that disruption of this architecture can be used to mimic diseased states. As the EC-SMC coculture model can mimic either a diseased or a healthy blood vessel it may be useful as a test bed for evaluating cardiovascular therapeutics.

Direct-contact co-culture between smooth muscle and endothelial cells inhibits TNF-alpha-mediated endothelial cell activation

We used a direct-contact endothelial cell-smooth muscle cell (EC-SMC) co-culture to examine whether quiescent SMCs regulate the EC inflammatory response to tumor necrosis factor (TNF)-alpha. ECs were cultured under static and physiological flow conditions. Compared with TNF-alpha-treated ECs in monoculture, TNF-alpha-treated ECs in co-culture had less NF-kappaB nuclear translocation; less intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin surface protein expression; no change in TNF receptor expression, but greater Kruppel-like factor 2 (KLF2) gene expression. After flow preconditioning for 24 h at 15 dyne/cm(2), and exposure of ECs to flow and TNF-alpha for 4.5 h, ECs in co-culture had less ICAM-1, VCAM-1, and E-selectin surface protein expression. Exposure to flow greatly increased KLF2 gene expression levels in both EC cultures; as a result, ECs in co-culture and monoculture had similar levels of post-flow KLF2 gene expression. The reduced levels of TNF-alpha-induced adhesion molecule expression in co-culture required the presence of quiescent SMCs; adhesion to decellularized extracellular matrix (ECM) or co-culture with fibroblasts produced only a modest reduction in EC adhesion molecule expression. Furthermore, co-culture of quiescent SMCs and ECs on the opposite side of a 10-microm-thick porous membrane did not alter the TNF-alpha-mediated ICAM-1 surface protein expression. Although the ECM produced by SMCs plays some role in reducing TNF-alpha-mediated inflammation, these results suggest that the direct contact between ECs and quiescent SMCs is required to inhibit TNF-alpha-mediated activation.

Characterization of umbilical cord blood-derived late outgrowth endothelial progenitor cells exposed to laminar shear stress

Endothelial progenitor cells isolated from umbilical cord blood (CB-EPCs) represent a promising source of endothelial cells for synthetic vascular grafts and tissue-engineered blood vessels since they are readily attainable, can be easily isolated, and possess a high proliferation potential. The objective of this study was to compare the functional behavior of late outgrowth CB-EPCs with human aortic endothelial cells (HAECs). CB-EPCs and HAECs were cultured on either smooth muscle cells in a coculture model of a tissue-engineered blood vessels or fibronectin adsorbed to Teflon-AF-coated glass slides. Late outgrowth CB-EPCs expressed endothelial cell-specific markers and were negative for the monocytic marker CD14. CB-EPCs have higher proliferation rates than HAECs, but are slightly smaller in size. CB-EPCs remained adherent under supraphysiological shear stresses, oriented and elongated in the direction of flow, and expressed similar numbers of alpha(5)beta(1) and alpha(v)beta(3) integrins and antithrombotic genes compared to HAECs. There were some differences in mRNA levels of E-selectin and vascular cell adhesion molecule 1 between CB-EPCs and HAECs; however, protein levels were similar on the two cell types, and CB-EPCs did not support adhesion of monocytes in the absence of tumor necrosis factor-alpha stimulation. Although CB-EPCs expressed significantly less endothelial nitric oxide synthase protein after exposure to flow than HAECs, nitric oxide levels induced by flow were not significantly different. These results suggest that late outgrowth CB-EPCs are functionally similar to HAECs under flow conditions and are a promising cell source for cardiovascular therapies.

Microcirculation within grooved substrates regulates cell positioning and cell docking inside microfluidic channels

Immobilization of cells inside microfluidic devices is a promising approach for enabling studies related to drug screening and cell biology. Despite extensive studies in using grooved substrates for immobilizing cells inside channels, a systematic study of the effects of various parameters that influence cell docking and retention within grooved substrates has not been performed. We demonstrate using computational simulations that the fluid dynamic environment within microgrooves significantly varies with groove width, generating microcirculation areas in smaller microgrooves. Wall shear stress simulation predicted that shear stresses were in the opposite direction in smaller grooves (25 and 50 microm wide) in comparison to those in wider grooves (75 and 100 microm wide). To validate the simulations, cells were seeded within microfluidic devices, where microgrooves of different widths were aligned perpendicularly to the direction of the flow. Experimental results showed that, as predicted, the inversion of the local direction of shear stress within the smaller grooves resulted in alignment of cells on two opposite sides of the grooves under the same flow conditions. Also, the amplitude of shear stress within microgrooved channels significantly influenced cell retainment in the channels. Therefore, our studies suggest that microscale shear stresses greatly influence cellular docking, immobilization, and retention in fluidic systems and should be considered for the design of cell-based microdevices.

Smooth muscle cell rigidity and extracellular matrix organization influence endothelial cell spreading and adhesion formation in coculture

Efforts to develop functional tissue-engineered blood vessels have focused on improving the strength and mechanical properties of the vessel wall, while the functional status of the endothelium within these vessels has received less attention. Endothelial cell (EC) function is influenced by interactions between its basal surface and the underlying extracellular matrix. In this study, we utilized a coculture model of a tissue-engineered blood vessel to evaluate EC attachment, spreading, and adhesion formation to the extracellular matrix on the surface of quiescent smooth muscle cells (SMCs). ECs attached to and spread on SMCs primarily through the alpha(5)beta(1)-integrin complex, whereas ECs used either alpha(5)beta(1)- or alpha(v)beta(3)-integrin to spread on fibronectin (FN) adsorbed to plastic. ECs in coculture lacked focal adhesions, but EC alpha(5)beta(1)-integrin bound to fibrillar FN on the SMC surface, promoting rapid fibrillar adhesion formation. As assessed by both Western blot analysis and quantitative real-time RT-PCR, coculture suppressed the expression of focal adhesion proteins and mRNA, whereas tensin protein and mRNA expression were elevated. When attached to polyacrylamide gels with similar elastic moduli as SMCs, focal adhesion formation and the rate of cell spreading increased relative to ECs in coculture. Thus, the elastic properties are only one factor contributing to EC spreading and focal adhesion formation in coculture. The results suggest that the softness of the SMCs and the fibrillar organization of FN inhibit focal adhesions and reduce cell spreading while promoting fibrillar adhesion formation. These changes in the type of adhesions may alter EC signaling pathways in tissue-engineered blood vessels.