Complimentary endothelial cell/smooth muscle cell co-culture systems with alternate smooth muscle cell phenotypes

Current Advances in 3D Dynamic Cell Culture Systems

The traditional two-dimensional (2D) cell culture methods have a long history of mimicking in vivo cell growth. However, these methods cannot fully represent physiological conditions, which lack two major indexes of the in vivo environment; one is a three-dimensional 3D cell environment, and the other is mechanical stimulation; therefore, they are incapable of replicating the essential cellular communications between cell to cell, cell to the extracellular matrix, and cellular responses to dynamic mechanical stimulation in a physiological condition of body movement and blood flow. To solve these problems and challenges, 3D cell carriers have been gradually developed to provide a 3D matrix-like structure for cell attachment, proliferation, differentiation, and communication in static and dynamic culture conditions. 3D cell carriers in dynamic culture systems could primarily provide different mechanical stimulations which further mimic the real in vivo microenvironment. In this review, the current advances in 3D dynamic cell culture approaches have been introduced, with their advantages and disadvantages being discussed in comparison to traditional 2D cell culture in static conditions.

Fabrication of a mimetic vascular graft using melt spinning with tailorable fiber parameters

Smooth muscle cells play a pivotal role in maintaining blood pressure and remodeling of the extracellular matrix. These cells have a characteristic spindle shape and are aligned in the radial direction to aid in the constriction of any artery. Tissue engineered grafts have the potential to recreate this alignment and offer a viable alternative to non-resorbable or autologous grafts. Specifically, with melt spinning small diameter fibers can be created that can align circumferentially on the scaffolds. In this study, a set of simplified equations were formulated to predict the final fiber parameters. Smooth muscle cell alignment was monitored on the fabricated scaffolds. Finally, a co-culture of smooth muscle cells in direct contact with endothelial cells was performed to assess the influence of the smooth muscle cell alignment on the morphology of the endothelial cells. The results show that the equations were able to accurately predict the fiber diameter, distance and angle. Primary vascular smooth muscle cells aligned according to the fiber direction mimicking the native orientation. The co-culture with endothelial cells showed that the aligned smooth muscle cells did not have an influence on the morphology of the endothelial cells. In conclusion, we formulated a series of equations that can predict the fiber parameters during melt spinning. Furthermore, the method described here can create a vascular graft with smooth muscle cells aligned circumferentially that morphologically mimics the native orientation.

Orthogonal co-cultivation of smooth muscle cell and endothelial cell layers to construct in vivo-like vasculature

Development of a three-dimensional (3D) vascular co-cultivation system is one of the major challenges to provide an advanced analytical platform for studying blood vessel related diseases. To date, however, the in vivo-like vessel system has not been fully realized due to the difficulty of co-cultivation of the cells with orthogonal alignment. In this study, we report the utilization of microfabrication technology to construct biomimetic 3D co-cultured vasculature. First, microwrinkle patterns whose direction was perpendicular to the axis of a circular microfluidic channel were fabricated, and vascular smooth muscle cells (VSMCs) were cultured inside the microchannel, leading to an in vivo-like circumferential VSMC layer. Then, human umbilical vein endothelial cells (HUVECs) were co-cultured on the circumferentially aligned VSMC, and the success of double layer formation of HUVEC-VSMC in the circular microchannel could be monitored. After HUVEC cultivation, we applied shear flow in order to induce the orientation of HUVEC parallel to the axis, and the analysis of orientation angle and spreading area of HUVECs indicated that they were changed by shear stress to be aligned to the direction of flow. Thus, the HUVEC and VSMC layer could be aligned with a distinct direction. The expression level of VE-Cadherin located at the boundary of HUVECs implies in vivo-like vascular behavior. The proposed in vitro microfluidic vascular assay platform would be valuable for studying vascular diseases with high reliability due to in vivo-likeness.

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.

A bilayer small diameter in vitro vascular model for evaluation of drug induced vascular injury

In pre-clinical safety studies, drug-induced vascular injury (DIVI) is defined as an adverse response to a drug characterized by degenerative and hyperplastic changes of endothelial cells and vascular smooth muscle cells. Inflammation may also be seen, along with extravasation of red blood cells into the smooth muscle layer (i.e., hemorrhage). Drugs that cause DIVI are often discontinued from development after considerable cost has occurred. An in vitro vascular model has been developed using endothelial and smooth muscle cells in co-culture across a porous membrane mimicking the internal elastic lamina. Arterial flow rates of perfusion media within the endothelial chamber of the model induce physiologic endothelial cell alignment. Pilot testing with a drug known to cause DIVI induced extravasation of red blood cells into the smooth muscle layer in all devices with no extravasation seen in control devices. This engineered vascular model offers the potential to evaluate candidate drugs for DIVI early in the discovery process. The physiologic flow within the co-culture model also makes it candidate for a wide variety of vascular biology investigations.

Hydraulic Conductivity of Smooth Muscle Cell-Initiated Arterial Cocultures

The purpose of the study was to examine the effects of arterial coculture conditions on the transport properties of several in vitro endothelial cell (EC)-smooth muscle cell (SMC)-porous filter constructs in which SMC were grown to confluence first and then EC were inoculated. This order of culturing simulates the environment of a blood vessel wall after endothelial layer damage due to stenting, vascular grafting or other vascular wall insult. For all coculture configurations examined, we observed that hydraulic conductivity (L(p)) values were significantly higher than predicted by a resistances-in-series (RIS) model accounting for the L(p) of EC and SMC measured separately. The greatest increases were observed when EC were plated directly on top of a confluent SMC layer without an intervening filter, presumably mediated by direct EC-SMC contacts that were observed under confocal microscopy. The results are the opposite of a previous study that showed L(p) was significantly reduced compared to an RIS model when EC were grown to confluency first. The physiological, pathophysiological and tissue engineering implications of these results are discussed.

Regulation of vascular smooth muscle cell phenotype in three-dimensional coculture system by Jagged1-selective Notch3 signaling

The modulation of vascular smooth muscle cell (VSMC) phenotype is an essential element to fabricate engineered conduits of clinical relevance. In vivo, owing to their close proximity, endothelial cells (ECs) play a role in VSMC phenotype switching. Although considerable progress has been made in vascular tissue engineering, significant knowledge gaps exist on how the contractile VSMC phenotype is induced at the conclusion of the tissue fabrication process. The objectives of this study were as follows: (1) to establish ligand presentation modes on transcriptional activation of VSMC-specific genes, (2) to develop a three-dimensional (3D) coculture model using human coronary artery smooth muscle cells (HCASMCs) and human coronary artery endothelial cells (HCAECs) on porous synthetic scaffolds and, (3) to investigate EC-mediated Notch signaling in 3D cultures and the induction of the HCASMC contractile phenotype. Whereas transcriptional activation of VSMC-specific genes was not induced by presenting soluble Jagged1 and Jagged1 bound to protein G beads, a direct link between HCAEC-bound Jagged1 and HCASMC differentiation genes was observed. Our 3D culture results showed that HCASMCs seeded to scaffolds and cultured for up to 16 days readily attached, infiltrated the scaffold, proliferated, and formed dense confluent layers. HCAECs, seeded on top of an HCASMC layer, formed a distinct, separate monolayer with cell-type partitioning, suggesting that HCAEC growth was contact inhibited. While we observed EC monolayer formation with 200,000 HCAECs/scaffold, seeding 400,000 HCAECs/scaffold revealed the formation of cord-like structures akin to angiogenesis. Western blot analyses showed that 3D coculture induced an upregulation of Notch3 receptor in HCASMCs and its ligand Jagged1 in HCAECs. This was accompanied by a corresponding induction of the contractile HCASMC phenotype as demonstrated by increased expression of smooth muscle-α-actin (SM-α-actin) and calponin. Knockdown of Jagged1 with siRNA showed a reduction in SM-α-actin and calponin in cocultures, identifying a link between Jagged1 and the expression of contractile proteins in 3D cocultures. We therefore conclude that the Notch3 signaling pathway is an important regulator of VSMC phenotype and could be targeted when fabricating engineered vascular tissues.

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.

Hydraulic conductivity of endothelial cell-initiated arterial cocultures

This study describes cocultures of arterial smooth muscle cells (SMCs) and endothelial cells (ECs) and the influences of their heterotypic interactions on hydraulic conductivity (L p ), an important transport property. A unique feature of these cocultures is that ECs were first grown to confluence and then SMCs were inoculated. Bovine aortic smooth muscle cells and bovine aortic endothelial cells (BAECs) were cocultured on Transwell Permeable Supports, and then exposed to a pressure-driven transmural flow. L p across each culture was measured using a bubble tracking apparatus that determined water flux (J v ). Our results indicate that arterial L p is significantly modulated by EC-SMC proximity, and serum content in culture. The L p of cocultures was also compared to the predictions of a resistances-in-series model to distinguish the contributions of heterotypic interactions between SMCs and ECs. Conditions that lead to significantly reduced coculture L p , compared to BAEC monoculture controls, have been uncovered and the lowest L p in the literature for an in vitro system are reported. In addition, VE-cadherin immunostaining of intact BAEC monolayers in each culture configuration reveals that EC-SMC proximity on a porous membrane has a dramatic influence on EC morphology patterns. The cocultures with the lowest L p have ECs with significantly elongated morphology. Confocal imaging indicates that there are no direct EC-SMC contacts in coculture.

P-selectin glycoprotein ligand-1 forms dimeric interactions with E-selectin but monomeric interactions with L-selectin on cell surfaces

Interactions of selectins with cell surface glycoconjugates mediate the first step of the adhesion and signaling cascade that recruits circulating leukocytes to sites of infection or injury. P-selectin dimerizes on the surface of endothelial cells and forms dimeric bonds with P-selectin glycoprotein ligand-1 (PSGL-1), a homodimeric sialomucin on leukocytes. It is not known whether leukocyte L-selectin or endothelial cell E-selectin are monomeric or oligomeric. Here we used the micropipette technique to analyze two-dimensional binding of monomeric or dimeric L- and E-selectin with monomeric or dimeric PSGL-1. Adhesion frequency analysis demonstrated that E-selectin on human aortic endothelial cells supported dimeric interactions with dimeric PSGL-1 and monomeric interactions with monomeric PSGL-1. In contrast, L-selectin on human neutrophils supported monomeric interactions with dimeric or monomeric PSGL-1. Our work provides a new method to analyze oligomeric cross-junctional molecular binding at the interface of two interacting cells.

Characterization of the human smooth muscle cell secretome for regenerative medicine

Smooth muscle cells (SMC) play a central role in maintaining the structural and functional integrity of muscle tissue. Little is known about the early in vitro events that guide the assembly of 'bioartificial tissue' (constructs) and recapitulate the key aspects of smooth muscle differentiation and development before surgical implantation. Biomimetic approaches have been proposed that enable the identification of in vitro processes which allow standardized manufacturing, thus improving both product quality and the consistency of patient outcomes. One essential element of this approach is the description of the SMC secretome, that is, the soluble and deposited factors produced within the three-dimensional (3D) extracellular matrix (ECM) microenvironment. In this study, we utilized autologous SMC from multiple tissue types that were expanded ex vivo and generated with a rigorous focus on operational phenotype and genetic stability. The objective of this study was to characterize the spatiotemporal dynamics of the first week of organoid maturation using a well-defined in vitro-like, 3D-engineered scale model of our validated manufacturing process. Functional proteomics was used to identify the topological properties of the networks of interacting proteins that were derived from the SMC secretome, revealing overlapping central nodes related to SMC differentiation and proliferation, actin cytoskeleton regulation, and balanced ECM accumulation. The critical functions defined by the Ingenuity Pathway Analysis included cell signaling, cellular movement and proliferation, and cellular and organismal development. The results confirm the phenotypic and functional similarity of the SMC generated by our platform technology at the molecular level. Furthermore, these data validate the biomimetic approaches that have been established to maintain manufacturing consistency.

Quantitative study of the dynamic tumor-endothelial cell interactions through an integrated microfluidic coculture system

The interaction between tumor and endothelial cells is crucial to cancer metastasis and angiogenesis. We developed a novel microfluidic device to assess the cell-cell interaction quantitatively at the single cell resolution. This integrated chip offers 16 coculture experiments in parallel with controllable microenvironments to study interactions between cells dynamically. We applied this approach to model the tumor invasion using Hela cells and human umbilical vein endothelial cells (HUVECs) and monitored the migration of both. We observed the retreatment of HUVECs upon the approach of Hela cells during coculture, indicating that the interaction between two cells was mediated by soluble factors. This interaction was further analyzed through quantitatively processing the phase-contrast microscopic time-lapse images of each individual coculture chamber. We also confirmed this paracrine effect by varying the frequency of medium change. This microfluidic technique is highly controllable, contamination free, fully automatic, and inexpensive. This approach not only offers a unique way to quantitatively study the interaction between cells but also provides accurate spatial-temporal tunability of microenvironments for cell coculture. We believe this method, intrinsically high-throughput and quantitative, will greatly facilitate the study of cell-cell interactions and communications.

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

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

Endothelial cells negatively modulate reactive oxygen species generation in vascular smooth muscle cells: role of thioredoxin

In intact vessels, endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) act as an integrated system, possibly through reactive oxygen species (ROS). Using a coculture system we tested whether ECs modulate VSMC redox status by regulating activity of NAD(P)H oxidase and antioxidants. VSMC production of O(2)(*-), H(2)O(2), and NO was assessed using fluoroprobes and amplex-red. NAD(P)H oxidase subunit expression and oxidase activity were determined by Western blotting and chemiluminescence, respectively. Expression of thioredoxin, SOD, growth signaling pathways (PCNA, p21cip1, CDK4, ERK1/2, p38MAPK) was evaluated by immunoblotting. Thioredoxin activity was assessed by the insulin disulfide reduction assay. In cocultured conditions, VSMC ROS production was reduced by approximately 50% without changes in NAD(P)H oxidase expression/activity versus monoculture (P<0.05). This was associated with decreased cell growth (P<0.05). Expression of Cu/Zn SOD and thioredoxin was increased in coculture versus monoculture VSMCs (P<0.01). Pretreatment of ECs with L-NAME (NOS inhibitor), NS-398 (Cox2 inhibitor), and HET0016 (20-HETE inhibitor) did not influence VSMC ROS formation, whereas CDNB, thioredoxin reductase inhibitor, abolished ROS modulating effects of ECs. These findings indicate that in a coculture system recapitulating intact vessels, ECs negatively regulate ROS production in VSMCs through thioredoxin upregulation. Functionally this is associated with growth inhibition. The modulatory actions of ECs are independent of NOS/NO, Cox2, and HETE and do not involve NAD(P)H oxidase. Our data identify novel mechanisms whereby ECs protect against VSMC oxidative stress, a process that may be important in maintaining vascular integrity.