Endothelial colony-forming cells show a mature transcriptional response to shear stress. In Vitro Cell Dev Biol Anim. 2012;48:21-29. [PMID: 22101679 DOI: 10.1007/s11626-011-9470-z]

Intraluminal pressure triggers a rapid and persistent reinforcement of endothelial barriers

In response to mechanical cues, endothelial cells elicit highly sensitive cellular response pathways that contribute to the regulation of the physiology and disorders of the vascular system. However, it remains relatively unexplored how endothelial tissues process and integrate the intraluminal pressure, and in turn regulate the permeation flow across the vessel wall. Leveraging a tissue engineering approach to create microvessels (MVs), we measured real-time permeation flow induced by intraluminal pressures ranging from 0.1 to 2.0 kPa. Our findings reveal that mechanically stimulated MVs strengthen their barrier function within seconds of exposure to pressures below 1 kPa, with this enhanced barrier function persisting for 30 minutes. We demonstrate that this barrier reinforcement is linked to the closure of paracellular gaps. Additionally, we observe that it is associated with, and depends on, actin cytoskeleton reorganization, including the accumulation of stress fibers near intercellular junctions and the broadening of adherence junction protein localization. These findings provide insights into the ability of endothelial tissues to regulate interstitial fluid flow in response to sudden increases in blood pressure.

Harnessing the potential of monocytes/macrophages to regenerate tissue-engineered vascular grafts

Cell-free tissue-engineered vascular grafts provide a promising alternative to treat cardiovascular disease, but timely endothelialization is essential for ensuring patency and proper functioning post-implantation. Recent studies from our lab showed that blood cells like monocytes (MCs) and macrophages (Mϕ) may contribute directly to cellularization and regeneration of bioengineered arteries in small and large animal models. While MCs and Mϕ are leucocytes that are part of the innate immune response, they share common developmental origins with endothelial cells (ECs) and are known to play crucial roles during vessel formation (angiogenesis) and vessel repair after inflammation/injury. They are highly plastic cells that polarize into pro-inflammatory and anti-inflammatory phenotypes upon exposure to cytokines and differentiate into other cell types, including EC-like cells, in the presence of appropriate chemical and mechanical stimuli. This review focuses on the developmental origins of MCs and ECs; the role of MCs and Mϕ in vessel repair/regeneration during inflammation/injury; and the role of chemical signalling and mechanical forces in Mϕ inflammation that mediates vascular graft regeneration. We postulate that comprehensive understanding of these mechanisms will better inform the development of strategies to coax MCs/Mϕ into endothelializing the lumen and regenerate the smooth muscle layers of cell-free bioengineered arteries and veins that are designed to treat cardiovascular diseases and perhaps the native vasculature as well.

Origin and flow-mediated remodeling of the murine and human extraembryonic circulation systems

The transduction of mechanical stimuli produced by blood flow is an important regulator of vascular development. The vitelline and umbilico-placental circulations are extraembryonic vascular systems that are required for proper embryonic development in mammalian embryos. The morphogenesis of the extraembryonic vasculature and the cardiovascular system of the embryo are hemodynamically and molecularly connected. Here we provide an overview of the establishment of the murine and human vitelline and umbilico-placental vascular systems and how blood flow influences various steps in their development. A deeper comprehension of extraembryonic vessel development may aid the establishment of stem-cell based embryo models and provide novel insights to understanding pregnancy complications related to the umbilical cord and placenta.

Endothelial tissue remodeling induced by intraluminal pressure enhances paracellular solute transport

The endothelial layers of the microvasculature regulate the transport of solutes to the surrounding tissues. It remains unclear how this barrier function is affected by blood flow-induced intraluminal pressure. Using a 3D microvessel model, we compare the transport of macromolecules through endothelial tissues at mechanical rest or with intraluminal pressure, and correlate these data with electron microscopy of endothelial junctions. On application of an intraluminal pressure of 100 Pa, we demonstrate that the flow through the tissue increases by 2.35 times. This increase is associated with a 25% expansion of microvessel diameter, which leads to tissue remodeling and thinning of the paracellular junctions. We recapitulate these data with the deformable monopore model, in which the increase in paracellular transport is explained by the augmentation of the diffusion rate across thinned junctions under mechanical stress. We therefore suggest that the deformation of microvasculatures contributes to regulate their barrier function.

Novel Strategies in the Early Detection and Treatment of Endothelial Cell-Specific Mitochondrial Dysfunction in Coronary Artery Disease

Although elevated cholesterol and other recognised cardiovascular risk factors are important in the development of coronary artery disease (CAD) and heart attack, the susceptibility of humans to this fatal process is distinct from other animals. Mitochondrial dysfunction of cells in the arterial wall, particularly the endothelium, has been strongly implicated in the pathogenesis of CAD. In this manuscript, we review the established evidence and mechanisms in detail and explore the potential opportunities arising from analysing mitochondrial function in patient-derived cells such as endothelial colony-forming cells easily cultured from venous blood. We discuss how emerging technology and knowledge may allow us to measure mitochondrial dysfunction as a potential biomarker for diagnosis and risk management. We also discuss the "pros and cons" of animal models of atherosclerosis, and how patient-derived cell models may provide opportunities to develop novel therapies relevant for humans. Finally, we review several targets that potentially alleviate mitochondrial dysfunction working both via direct and indirect mechanisms and evaluate the effect of several classes of compounds in the cardiovascular context.

The vicious circle of UHRF1 down-regulation and KEAP1/NRF2/HO-1 pathway impairment promotes oxidative stress-induced endothelial cell apoptosis in diabetes

BACKGROUND

Oxidative stress is recognized as a key factor in the induction of endothelial dysfunction in diabetes. However, the specific mechanisms have not been fully elucidated. We herein hypothesized that ubiquitin-like containing PHD and RING finger domains 1 (UHRF1) might have a role in oxidative stress-induced endothelial cell (EC) apoptosis in diabetes.

METHODS

Western blot, qPCR, wound healing assay, apoptosis assay, reactive oxygen species (ROS) detection, dual-luciferase reporter assay, methylation-specific PCR, bisulfite sequencing PCR and chromatin immunoprecipitation assay were performed.

RESULTS

UHRF1 expression levels were significantly decreased in endothelial colony-forming cells derived from peripheral blood of participants with type 2 diabetes compared with individuals without diabetes. ECs treated with high glucose, palmitate or hydrogen peroxide in vitro also exhibited decreased UHRF1 protein levels. Silencing of UHRF1 led to decreased migration ability and increased apoptosis and ROS production in ECs, which might be related to impaired Kelch-like ECH-associated protein 1 (KEAP1)/nuclear factor erythroid 2-related factor 2 (NRF2)/haeme oxygenase-1 pathway. Mechanistically, UHRF1 is closely implicated in epigenetic regulation of chromatin modification status at KEAP1 genomic locus via histone acetylation. NRF2 down-regulation in turn inhibits UHRF1 protein level, which might be due to increased ROS generation.

CONCLUSION

Diabetes-induced oxidative stress can mediate down-regulation of UHRF1, which enhances ROS production by regulating KEAP1/p-NRF2 pathway through histone acetylation and might also form a self-perpetuating feedback loop with KEAP1/p-NRF2 to further promote oxidative stress-induced apoptosis of ECs in diabetes.

Peripheral blood derived endothelial colony forming cells as suitable cell source for pre-endothelialization of arterial vascular grafts under dynamic flow conditions

In regenerative medicine, autologous peripheral blood derived endothelial colony forming cells (PB-derived ECFC) represent a promising source of endothelial cells (EC) for pre-endothelialization of arterial tissue engineered vascular grafts (TEVG) since they are readily attainable, can easily be isolated and possess a high proliferation potential. The aim of this study was to compare the phenotype of PB-derived ECFC with arterial and venous model cells such as human aortic endothelial cells (HAEC) and human umbilical vein endothelial cells (HUVEC) under dynamic cell culture conditions to find a suitable cell source of EC for pre-endothelialization. In this study PB-derived ECFC were cultivated over 24 h under a high pulsatile shear stress (20 dyn/cm², 1 Hz) and subsequently analyzed. ECFC oriented and elongated in the direction of flow and expressed similar anti-thrombotic and endothelial differentiation markers compared to HAEC. There were significant differences observable in gene expression levels of CD31, CD34 and NOTCH4 between ECFC and HUVEC. These results therefore suggest an arterial phenotype for PB-derived ECFC both under static and flow conditions, and this was supported by NOTCH4 protein expression profiles. ECFC also significantly up-regulated gene expression levels of anti-thrombotic genes such as krueppel-like factor 2, endothelial nitric oxide synthase 3 and thrombomodulin under shear stress cultivation as compared to static conditions. Dynamically cultured PB-derived ECFC therefore may be a promising cell source for pre-endothelialization of arterial TEVGs.

Patient Endothelial Colony-Forming Cells to Model Coronary Artery Disease Susceptibility and Unravel the Role of Dysregulated Mitochondrial Redox Signalling

Mechanisms involved in the individual susceptibility to atherosclerotic coronary artery disease (CAD) beyond traditional risk factors are poorly understood. Here, we describe the utility of cultured patient-derived endothelial colony-forming cells (ECFCs) in examining novel mechanisms of CAD susceptibility, particularly the role of dysregulated redox signalling. ECFCs were selectively cultured from peripheral blood mononuclear cells from 828 patients from the BioHEART-CT cohort, each with corresponding demographic, clinical and CT coronary angiographic imaging data. Spontaneous growth occurred in 178 (21.5%) patients and was more common in patients with hypertension (OR 1.45 (95% CI 1.03-2.02), p = 0.031), and less likely in patients with obesity (OR 0.62 [95% CI 0.40-0.95], p = 0.027) or obstructive CAD (stenosis > 50%) (OR 0.60 [95% CI 0.38-0.95], p = 0.027). ECFCs from patients with CAD had higher mitochondrial production of superoxide (O₂^--MitoSOX assay). The latter was strongly correlated with the severity of CAD as measured by either coronary artery calcium score (R² = 0.46; p = 0.0051) or Gensini Score (R² = 0.67; p = 0.0002). Patient-derived ECFCs were successfully cultured in 3D culture pulsatile mini-vessels. Patient-derived ECFCs can provide a novel resource for discovering mechanisms of CAD disease susceptibility, particularly in relation to mitochondrial redox signalling.

Specific arterio-venous transcriptomic and ncRNA-RNA interactions in human umbilical endothelial cells: A meta-analysis

Whether arterial-venous differences of primary endothelial cells commonly used for vascular research are preserved in vitro remains under debate. To address this issue, a meta-analysis of Affymetrix transcriptomic data sets from human umbilical artery (HUAECs) and vein (HUVEC) endothelial cells was performed. The meta-analysis showed 2,742 transcripts differentially expressed (false discovery rate <0.05), of which 78% were downregulated in HUVECs. Comparisons with RNA-seq data sets showed high levels of agreement and correlation (p < 0.0001), identifying 84 arterial-venous identity markers. Functional analysis revealed enrichment of key vascular processes in HUAECs/HUVECs, including nitric oxide- (NO) and hypoxia-related genes, as well as differences in miRNA- and ncRNA-mRNA interaction profiles. A proof of concept of these findings in primary cells exposed to hypoxia in vitro and in vivo confirmed the arterial-venous differences in NO-related genes and miRNAs. Altogether, these data defined a cross-platform arterial-venous transcript profile for cultured HUAEC-HUVEC and support a preserved identity involving key vascular pathways post-transcriptionally regulated in vitro.

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Transcriptional differences among HUAEC and HUVEC are preserved in culture

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These differences occur even after correcting for experimental conditions

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The heterogenous regulation affects NO- and hypoxia-related genes

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Cell-specific ncRNA/mRNA interactions are found

miR-25-5p regulates endothelial progenitor cell differentiation in response to shear stress through targeting ABCA1

The importance of flow shear stress (SS) on the differentiation of endothelial progenitor cells (EPCs) has been demonstrated in various studies. Cholesterol retention and microRNA regulation have been also proposed as relevant factors involved in this process, though evidence regarding their regulatory roles in the differentiation of EPCs is currently lacking. In the present study on high shear stress (HSS)-induced differentiation of EPCs, we investigated the importance of ATP-binding cassette transporter 1 (ABCA1), an important regulator in cholesterol efflux, and miR-25-5p, a potential regulator of endothelial reconstruction. We first revealed an inverse correlation between miR-25-5p and ABCA1 expression levels in EPCs under HSS treatment; their direct interaction was subsequently validated by a dual-luciferase reporter assay. Further studies using flow cytometry and quantitative polymerase chain reaction demonstrated that both miR-25-5p overexpression and ABCA1 inhibition led to elevated levels of specific markers of endothelial cells, with concomitant downregulation of smooth muscle cell markers. Finally, knockdown of ABCA1 in EPCs significantly promoted tube formation, which confirmed our conjecture. Our current results suggest that miR-25-5p might regulate the differentiation of EPCs partially through targeting ABCA1, and such a mechanism might account for HSS-induced differentiation of EPCs.

A pre-conditioning protocol of peripheral blood derived endothelial colony forming cells for endothelialization of tissue engineered constructs

In regenerative medicine, autologous endothelial colony forming cells (ECFCs) bear the greatest potential to be used for surface endothelialization of tissue engineered constructs, as they are easily attainable and possess a high proliferation rate. The aim of this study was to develop a standardized pre-conditioning protocol under dynamic conditions simulating the physiology of human circulation to improve the formation of a flow resistant monolayer of ECFCs and to enhance the antithrombogenicity of the endothelial cells. The main focus of the study was to consequently compare the cellular behavior under a steady laminar flow against a pulsatile flow. Mononuclear cells were isolated out of peripheral blood (PB) buffy coats and plated on uncoated tissue culture flasks in anticipation of guidelines for Advanced Therapy Medicinal Products. ECFCs were identified by typical surface markers such as CD31, CD146 and VE-Cadherin. To explore the effects of dynamic cultivation, ECFCs and human umbilical vein endothelial cells were comparatively cultured under either laminar or pulsatile (1 Hz) flow conditions with different grades of shear stress (5 dyn/cm²versus 20 dyn/cm²). High shear stress of 20 dyn/cm² led to a significant upregulation of the antithrombotic gene marker thrombomodulin in both cell types, but only ECFCs orientated and elongated significantly after shear stress application forming a confluent endothelial cell layer. The work therefore documents a suitable protocol to pre-condition PB-derived ECFCs for sustainable endothelialization of blood contacting surfaces and provides essential knowledge for future cultivations in bioreactor systems.

Mechanoresponse of stem cells for vascular repair

Stem cells have shown great potential in vascular repair. Numerous evidence indicates that mechanical forces such as shear stress and cyclic strain can regulate the adhesion, proliferation, migration, and differentiation of stem cells via serious signaling pathways. The enrichment and differentiation of stem cells play an important role in the angiogenesis and maintenance of vascular homeostasis. In normal tissues, blood flow directly affects the microenvironment of vascular endothelial cells (ECs); in pathological status, the abnormal interactions between blood flow and vessels contribute to the injury of vessels. Next, the altered mechanical forces are transduced into cells by mechanosensors to trigger the reformation of vessels. This process occurs when signaling pathways related to EC differentiation are initiated. Hence, a deep understanding of the responses of stem cells to mechanical stresses and the underlying mechanisms involved in this process is essential for clinical translation. In this the review, we provide an overview of the role of stem cells in vascular repair, outline the performance of stem cells under the mechanical stress stimulation, and describe the related signaling pathways.

Layer-specific cell differentiation in bi-layered vascular grafts under flow perfusion

Bioengineered grafts have the potential to overcome the limitations of autologous and non-resorbable synthetic vessels as vascular substitutes. However, one of the challenges in creating these living grafts is to induce and maintain multiple cell phenotypes with a biomimetic organization. Our biomimetic grafts with heterotypic design hold promises for functional neovessel regeneration by guiding the layered cellular and tissue organization into a native-like structure. In this study, a perfusable two-compartment bioreactor chamber was designed for the further maturation of these vascular grafts, with a compartmentalized exposure of the graft's luminal and outer layer to cell-specific media. We used the system for a co-culture of endothelial colony forming cells and multipotent mesenchymal stromal cells (MSCs) in the vascular grafts, produced by combining electrospinning and melt electrowriting. It was demonstrated that the targeted cell phenotypes (i.e. endothelial cells (ECs) and vascular smooth muscle cells (vSMCs), respectively) could be induced and maintained during flow perfusion. The confluent luminal layer of ECs showed flow responsiveness, as indicated by the upregulation of COX-2, KLF2, and eNOS, as well as through stress fiber remodeling and cell elongation. In the outer layer, the circumferentially oriented, multi-layered structure of MSCs could be successfully differentiated into vSM-like cells using TGFβ, as indicated by the upregulation of αSMA, calponin, collagen IV, and (tropo)elastin, without affecting the endothelial monolayer. The cellular layers inhibited diffusion between the outer and the inner medium reservoirs. This implies tightly sealed cellular layers in the constructs, resulting in truly separated bioreactor compartments, ensuring the exposure of the inner endothelium and the outer smooth muscle-like layer to cell-specific media. In conclusion, using this system, we successfully induced layer-specific cell differentiation with a native-like cell organization. This co-culture system enables the creation of biomimetic neovessels, and as such can be exploited to investigate and improve bioengineered vascular grafts.

Static spatial growth restriction micropatterning of endothelial colony forming cells influences their morphology and gene expression

BACKGROUND

Endothelialization of small diameter synthetic vascular grafts is a potential solution to the thrombosis and intimal hyperplasia that plague current devices. Endothelial colony forming cells, which are blood-derived and similar to mature endothelial cells, are a potential cell source. Anisotropic spatial growth restriction micropatterning has been previously shown to affect the morphology and function of mature endothelial cells in a manner similar to unidirectional fluid shear stress. To date, endothelial colony forming cells have not been successfully micropatterned. This study addresses the hypothesis that micropatterning of endothelial colony forming cells will induce morphological elongation, cytoskeletal alignment, and changes in immunogenic and thrombogenic-related gene expression.

METHODS

Spatially growth restrictive test surfaces with 25 μm-wide lanes alternating between collagen-I and a blocking polymer were created using microfluidics. Case-matched endothelial colony forming cells and control mature carotid endothelial cells were statically cultured on either micropatterned or non-patterned surfaces. Cell elongation was quantified using shape index. Using confocal microscopy, cytoskeletal alignment was visualized and density and apoptotic rate were determined. Gene expression was measured using quantitative PCR to measure KLF-2, eNOS, VCAM-1, and vWF.

RESULTS

Endothelial colony forming cells were successfully micropatterned for up to 50 hours. Micropatterned cells displayed elongation and actin alignment. Micropatterning increased the packing densities of both cell types, but did not affect apoptotic rate, which was lower in endothelial colony forming cells. KLF-2 gene expression was increased in micropatterned relative to non-patterned endothelial colony forming cells after 50 hours. No significant differences were seen in the other genes tested.

CONCLUSIONS

Endothelial colony forming cells can be durably micropatterned using spatial growth restriction. Micropatterning has a significant effect on the gross and subcellular morphologies of both cell types. Further study is required to fully understand the effect of micropatterning on endothelial colony forming cell gene expression.

Characterization of the hemodynamic wall shear stresses in human umbilical vessels from normal and intrauterine growth restricted pregnancies

Significant reductions in blood flow and umbilical diameters were reported in pregnancies affected by intrauterine growth restriction (IUGR) from placental insufficiency. However, it is not known if IUGR umbilical blood vessels experience different hemodynamic wall shear stresses (WSS) compared to normal umbilical vessels. As WSS is known to influence vasoactivity and vascular growth and remodeling, which can regulate flow rates, it is important to study this parameter. In this study, we aim to characterize umbilical vascular WSS environment in normal and IUGR pregnancies, and evaluate correlation between WSS and vascular diameter, and gestational age. Twenty-two normal and 21 IUGR pregnancies were assessed via ultrasound between the 27th and 39th gestational week. IUGR was defined as estimated fetal weight and/or abdominal circumference below the 10th centile, with no improvement during the remainder of the pregnancy. Vascular diameter was determined by 3D ultrasound scans and image segmentation. Umbilical artery (UA) WSS was computed via computational flow simulations, while umbilical vein (UV) WSS was computed via the Poiseuille equation. Univariate multiple regression analysis was used to test for the differences between normal and IUGR cohort. UV volumetric flow rate, UA and UV diameters were significantly lower in IUGR fetuses, but flow velocities and WSS trends in UA and UV were very similar between normal and IUGR groups. In both groups, UV WSS showed a significant negative correlation with diameter, but UA WSS had no correlation with diameter, suggesting a constancy of WSS environment and the existence of WSS homeostasis in UA, but not in UV. Despite having reduced flow rate and vascular sizes, IUGR UAs had hemodynamic mechanical stress environments and trends that were similar to those in normal pregnancies. This suggested that endothelial dysfunction or abnormal mechanosensing was unlikely to be the cause of small vessels in IUGR umbilical cords.

Shear stress: An essential driver of endothelial progenitor cells

The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo. EPCs have been proposed as a promising agent to induce reendothelialization of injured arteries, neovascularization of ischemic tissues, and endothelialization or vascularization of bioartificial constructs. A number of preconditioning approaches have been suggested to improve the regenerative potential of EPCs, including the use of biophysical stimuli such as shear stress. However, in spite of well-defined influence of shear stress on mature endothelial cells (ECs), articles summarizing how it affects EPCs are lacking. Here we discuss the impact of shear stress on homing, paracrine effects, and differentiation of EPCs. Unidirectional laminar shear stress significantly promotes homing of circulating EPCs to endothelial injury sites, induces anti-thrombotic and anti-atherosclerotic phenotype of EPCs, increases their capability to form capillary-like tubes in vitro, and enhances differentiation of EPCs into mature ECs in a dose-dependent manner. These effects are mediated by VEGFR2, Tie2, Notch, and β1/3 integrin signaling and can be abrogated by means of complementary siRNA/shRNA or selective pharmacological inhibitors of the respective proteins. Although the testing of sheared EPCs for vascular tissue engineering or regenerative medicine applications is still an unaccomplished task, favorable effects of unidirectional laminar shear stress on EPCs suggest its usefulness for their preconditioning.

Whole-Transcriptome Sequencing: a Powerful Tool for Vascular Tissue Engineering and Endothelial Mechanobiology

Among applicable high-throughput techniques in cardiovascular biology, whole-transcriptome sequencing is of particular use. By utilizing RNA that is isolated from virtually all cells and tissues, the entire transcriptome can be evaluated. In comparison with other high-throughput approaches, RNA sequencing is characterized by a relatively low-cost and large data output, which permits a comprehensive analysis of spatiotemporal variation in the gene expression profile. Both shear stress and cyclic strain exert hemodynamic force upon the arterial endothelium and are considered to be crucial determinants of endothelial physiology. Laminar blood flow results in a high shear stress that promotes atheroresistant endothelial phenotype, while a turbulent, oscillatory flow yields a pathologically low shear stress that disturbs endothelial homeostasis, making respective arterial segments prone to atherosclerosis. Severe atherosclerosis significantly impairs blood supply to the organs and frequently requires bypass surgery or an arterial replacement surgery that requires tissue-engineered vascular grafts. To provide insight into patterns of gene expression in endothelial cells in native or bioartificial arteries under different biomechanical conditions, this article discusses applications of whole-transcriptome sequencing in endothelial mechanobiology and vascular tissue engineering.

Impaired functional capacity of fetal endothelial cells in preeclampsia

Objectives

Preeclampsia is one of the main contributers to maternal and fetal morbidity and mortality during pregnancy. A history of preeclampsia puts mother and offspring at an increased cardiovascular risk in later life. We hypothesized that at the time of birth functional impairments of fetal endothelial cells can be detected in pregnancies complicated by preeclampsia and that a therapeutic intervention using 1,25 (OH)₂ vitamin D₃ can reverse the adverse effects of preeclampsia on cell function.

Methods

Human umbilical vein endothelial cells (HUVEC) were isolated from umbilical cords obtained from preeclamptic (N = 12) and uncomplicated pregnancies (N = 13, control). Placental villous tissue fragments from uncomplicated term pregnancies were incubated in explant culture for 48 h at 2% (hypoxia), 8% or 21% O₂. Explant conditioned media (CM) was collected and pooled according to oxygen level. We compared the ability of preeclampsia vs. control HUVEC to migrate, proliferate, and form tubule-like networks in a Matrigel assay, in the presence/absence of CM and 1,25(OH)₂ vitamin D₃.

Results

HUVEC from preeclamptic pregnancies showed reduced migration (P = 0.04) and tubule formation (P = 0.04), but no change in proliferation (P = 0.16) compared to healthy pregnancies. Placental villous explant CM derived from 2% O₂ incubations significantly reduced HUVEC migration, when compared to non-CM (P = 0.04). Vitamin D₃ improved HUVEC function in neither of the groups. There was no significant difference in VEGF gene expression between healthy and preeclamptic pregnancies and no effect of Vitamin D₃ on VEGF expression.

Conclusions

Reduced functional abilities of fetal endothelial cells from preeclamptic pregnancies suggests that disease pathways, possibly originating from the dysfunctional placenta, negatively impact fetal endothelium. The neutral effect of 1,25(OH)₂ vitamin D₃ contrasts with previous findings that vitamin D rescues the poor migration, proliferation and tubule formation exhibited by cord blood fetal endothelial progenitor cells from preeclamptic pregnancies. Further investigations to distinguish pathways by which offspring exposed to preeclampsia are at risk for cardiovascular disease are needed.

Dynamic Perfusion Culture of Human Outgrowth Endothelial Progenitor Cells on Demineralized Bone Matrix In Vitro

Background

The aim of this study was to investigate the proliferation, differentiation, and tube formation of human outgrowth endothelial progenitor cells (OECs) cultured with porous demineralized bone matrix (DBM) under a dynamic perfusion system in vitro.

Material/Methods

OECs were isolated, expanded, characterized, eGFP-transfected and seeded on DBM scaffold and cultured under static or dynamic perfusion conditions, and continuously observed under fluorescence microscope. DBM scaffolds were harvested on day six for RT-PCR and western blot assay to analyze the mRNA and protein expression level of CD34, VE-cadherin, and VEGF. Scanning electron microscope (SEM) was used to observe the tube formation of OECs seeded on DBM scaffolds.

Results

The results showed the cell density of OECs on DBM was higher when exposed to shear stress generated by a dynamic perfusion system. Shear stress also markedly increased the expression level of VE-cadherin and VEGF and decreased the expression of CD34, at both mRNA and protein levels. SEM showed that the shear-stressed OECs formed tube-like structures inside the pores of DBM scaffolds.

Conclusions

A dynamic perfusion system can be used as an innovative method for the rapid vascularization in tissue engineering, which can accelerate the proliferation and differentiation of OECs and the vascularization of implanted scaffolds.

In Vitro Endothelialization of Biodegradable Vascular Grafts Via Endothelial Progenitor Cell Seeding and Maturation in a Tubular Perfusion System Bioreactor

A critical challenge to the success of biodegradable vascular grafts is the establishment of a healthy endothelium. To establish this monolayer of endothelial cells (ECs), a variety of techniques have been developed, including cell seeding. Vascular grafts may be seeded with relevant cell types and allowed to mature before implantation. Due to the low proliferative ability of adult ECs and issues with donor site morbidity, there has been increasing interest in using endothelial progenitor cells (EPCs) for vascular healing procedures. In this work, we combined the proliferative and differentiation capabilities of a commercial cell line of early EPCs with an established bioreactor system to support the maturation of cell-seeded vascular grafts. All components of the vascular graft and bioreactor setup are commercially available and allow for complete customization of the scaffold and culturing system. This bioreactor setup enables the control of flow through the graft, imparting fluid shear stress on EPCs and affecting cellular proliferation and differentiation. Grafts cultured with EPCs in the bioreactor system demonstrated greatly increased cell populations and neotissue formation compared with grafts seeded and cultured in a static system. Increased expression of markers for mature endothelial tissues were also observed in bioreactor-cultured EPC-seeded grafts. These findings suggest the distinct advantages of a customizable bioreactor setup for the proliferation and maturation of EPCs. Such a strategy may be beneficial for utilizing EPCs in vascular tissue engineering applications.

Gestational diabetes induces alterations of sirtuins in fetal endothelial cells

BACKGROUND

Gestational diabetes (GDM) has long-term consequences for the offspring. Sirtuins (SIRTs) are associated with vascular and metabolic functions. We studied the impact of GDM on SIRT activity and expression in fetal endothelial colony-forming cells (ECFCs) and human umbilical vein endothelial cells (HUVECs) from pregnancies complicated by GDM.

METHODS

ECFCs and HUVECs were isolated from cord and cord blood of 10 uncomplicated pregnancies (NPs) and 10 GDM pregnancies. Nicotinamidadenindinukleotid (NAD(+)) concentration, SIRT1 and SIRT3 activity, transcription levels of SIRT1, SIRT3, and SIRT4, and protein levels of SIRT1, SIRT3, and SIRT4 were determined in vitro with or without SIRT activators resveratrol (RSV) and paeonol.

RESULTS

Fetal ECFCs from GDM pregnancies showed a decreased NAD(+) concentration, reduced SIRT1 and SIRT3 activity, and lower transcription levels of SIRT1, SIRT3, and SIRT4. HUVECs from GDM pregnancies had decreased NAD(+) concentrations and transcription levels of SIRT1 and SIRT4. RSV markedly enhanced the expression and activity of SIRTs in ECFCs and HUVECs, while paeonol was active only in ECFCs.

CONCLUSION

A reduction of SIRT activity and expression in fetal endothelial cells provides potential mechanistic insights into the pathophysiology of long-term cardiovascular complications observed in the offspring of GDM pregnancies. SIRT activators can increase SIRT activity in ECFCs, which opens perspectives for new therapeutic targets.

Environmental Influences on Endothelial to Mesenchymal Transition in Developing Implanted Cardiovascular Tissue-Engineered Grafts

Tissue-engineered grafts for cardiovascular structures experience biochemical stimuli and mechanical forces that influence tissue development after implantation such as the immunological response, oxidative stress, hemodynamic shear stress, and mechanical strain. Endothelial cells are a cell source of major interest in vascular tissue engineering because of their ability to form a luminal antithrombotic monolayer. In addition, through their ability to undergo endothelial to mesenchymal transition (EndMT), endothelial cells may yield a cell type capable of increased production and remodeling of the extracellular matrix (ECM). ECM is of major importance to the mechanical function of all cardiovascular structures. Tissue engineering approaches may employ EndMT to recapitulate, in part, the embryonic development of cardiovascular structures. Improved understanding of how the environment of an implanted graft could influence EndMT in endothelial cells may lead to novel tissue engineering strategies. This review presents an overview of biochemical and mechanical stimuli capable of influencing EndMT, discusses the influence of these stimuli as found in the direct environment of cardiovascular grafts, and discusses approaches to employ EndMT in tissue-engineered constructs.

Role of the fetoplacental endothelium in fetal growth restriction with abnormal umbilical artery Doppler velocimetry

Growth-restricted fetuses with absent or reversed end-diastolic velocities in the umbilical artery are at substantially increased risk for adverse perinatal and long-term outcome, even in comparison to growth-restricted fetuses with preserved end-diastolic velocities. Translational studies show that this Doppler velocimetry correlates with fetoplacental blood flow, with absent or reversed end-diastolic velocities signifying abnormally elevated resistance within the placental vasculature. The fetoplacental vasculature is unique in that it is not subject to autonomic regulation, unlike other vascular beds. Instead, humoral mediators, many of which are synthesized by local endothelial cells, regulate placental vascular resistance. Existing data demonstrate that in growth-restricted pregnancies complicated by absent or reversed umbilical artery end-diastolic velocities, an imbalance in production of these vasoactive substances occurs, favoring vasoconstriction. Morphologically, placentas from these pregnancies also demonstrate impaired angiogenesis, whereby vessels within the terminal villi are sparsely branched, abnormally thin, and elongated. This structural deviation from normal placental angiogenesis restricts blood flow and further contributes to elevated fetoplacental vascular resistance. Although considerable work has been done in the field of fetoplacental vascular development and function, much remains unknown about the mechanisms underlying impaired development and function of the human fetoplacental vasculature, especially in the context of severe fetal growth restriction with absent or reversed umbilical artery end-diastolic velocities. Fetoplacental endothelial cells are key regulators of angiogenesis and vasomotor tone. A thorough understanding of their role in placental vascular biology carries the significant potential of discovering clinically relevant and innovative approaches to prevention and treatment of fetal growth restriction with compromised umbilical artery end-diastolic velocities.

RETRACTED ARTICLE: High Pulsatility Flow Promotes Vascular Fibrosis by Triggering Endothelial EndMT and Fibroblast Activation

Vascular fibrosis, the formation of excess fibrous tissue on the blood vessel wall, is characterized by unmitigated proliferation of fibroblasts or myofibroblast-like cells exhibiting α-smooth-muscle-actin in vessel lumen and other vascular layers. It likely contributes to vascular unresponsiveness to conventional therapies. This paper demonstrates a new flow-induced vascular fibrosis mechanism. Using our developed flow system which simulates the effect of vessel stiffening and generates unidirectional high pulsatility flow (HPF) with the mean shear flow at a physiological level, we have shown that HPF caused vascular endothelial dysfunction. Herein, we further explored the role of HPF in vascular fibrosis through endothelial-to-mesenchymal transdifferentiation (EndMT). Pulmonary arterial endothelial cells (ECs) were exposed to steady flow and HPF, which have the same physiological mean fluid shear but different in flow pulsatility. Cells were analyzed after being conditioned with flows for 24 or 48 h. HPF was found to induce EndMT of cells after 48 h stimulation; cells demonstrated drastically decreased expression in EC marker CD31, as well as increased transforming growth factor β, α-SMA, and collagen type-I, in both gene and protein expression profiles. Using the flow media from HPF-conditioned endothelial culture to cultivate arterial adventitial fibroblasts (AdvFBs) and ECs respectively, we found that the conditioned media respectively enhanced migration, proliferation and α-SMA expression of AdvFBs, and induced EndMT of ECs. It was further revealed that cells exposed to HPF exhibited much higher percentage of caspase-positive cells compared to those exposed to steady flow. Apoptotic cells together with remaining, caspase-negative cells suggested the presence of apoptosis-resistant dysfunctional ECs which likely underwent EndMT process and perpetuated fibrosis throughout vascular tissues. Therefore, our results indicate that prolonged HPF stimuli induce vascular fibrosis through triggering EndMT and EC-mediated AdvFB activation and migration, which follows initial endothelial inflammation, dysfunction and apoptosis.

Transcriptional profiling reveals crosstalk between mesenchymal stem cells and endothelial cells promoting prevascularization by reciprocal mechanisms

Mesenchymal stem cells (MSCs) show great promise in blood vessel restoration and vascularization enhancement in many therapeutic situations. Typically, the co-implantation of MSCs with vascular endothelial cells (ECs) is effective for the induction of functional vascularization in vivo, indicating its potential applications in regenerative medicine. The effects of MSCs-ECs-induced vascularization can be modeled in vitro, providing simplified models for understanding their underlying communication. In this article, a contact coculture model in vitro and an RNA-seq approach were employed to reveal the active crosstalk between MSCs and ECs within a short time period at both morphological and transcriptional levels. The RNA-seq results suggested that angiogenic genes were significantly induced upon coculture, and this prevascularization commitment might require the NF-κB signaling. NF-κB blocking and interleukin (IL) neutralization experiments demonstrated that MSCs potentially secreted IL factors including IL1β and IL6 to modulate NF-κB signaling and downstream chemokines during coculture. Conversely, RNA-seq results indicated that the MSCs were regulated by the coculture environment to a smooth muscle commitment within this short period, which largely induced myocardin, the myogenic co-transcriptional factor. These findings demonstrate the mutual molecular mechanism of MSCs-ECs-induced prevascularization commitment in a quick response.

Regulation of EPCs: The Gateway to Blood Vessel Formation

Endothelial progenitor cells (EPCs) are primitive endothelial precursors which are known to functionally contribute to the pathogenesis of disease. To date a number of distinct subtypes of these cells have been described, with differing maturation status, cellular phenotype, and function. Although there is much debate on which subtype constitutes the true EPC population, all subtypes have endothelial characteristics and contribute to neovascularisation. Vasculogenesis, the process by which EPCs contribute to blood vessel formation, can be dysregulated in disease with overabundant vasculogenesis in the context of solid tumours, leading to tumour growth and metastasis, and conversely insufficient vasculogenesis can be present in an ischemic environment. Importantly, it is widely known that transcription factors tightly regulate cellular phenotype and function by controlling the expression of particular target genes and in turn regulating specific signalling pathways. This suggests that transcriptional regulators may be potential therapeutic targets to control EPC function. Herein, we discuss the observed EPC subtypes described in the literature and review recent studies describing the role of a number of transcriptional families in the regulation of EPC phenotype and function in normal and pathological conditions.

Vitamin D antagonizes negative effects of preeclampsia on fetal endothelial colony forming cell number and function

CONTEXT

Endothelial dysfunction is a primary feature of preeclampsia, a pregnancy complication associated with an increased future cardiovascular risk for mother and offspring. Endothelial colony forming cells (ECFC) are endothelial progenitor cells that participate in vasculogenesis and endothelial repair.

OBJECTIVE

We hypothesized that the number and functional properties of fetal cord blood-derived ECFCs are reduced in preeclampsia compared to uncomplicated pregnancy (controls), and asked if adverse effects of preeclampsia on ECFC function are reversed by 1,25 (OH)2 vitamin D3.

DESIGN, SETTING, PATIENTS

This was a nested, case-control study. Forty women with uncomplicated pregnancy and 33 women with PE were recruited at Magee-Womens Hospital (USA) or at Hannover Medical School (Germany).

MAIN OUTCOME MEASURES

Time to ECFC colony appearance in culture, and number of colonies formed, were determined. Functional abilities of ECFCs were assessed in vitro by tubule formation in Matrigel assay, migration, and proliferation. ECFC function was tested in the presence or absence of 1,25 (OH)2 vitamin D3, and after vitamin D receptor (VDR) or VEGF signaling blockade.

RESULTS

The number of cord ECFC colonies was lower (P = 0.04) in preeclampsia compared to controls. ECFCs from preeclampsia showed reduced proliferation (P<0.0001), formed fewer tubules (P = 0.02), and migrated less (P = 0.049) than control. Vitamin D3 significantly improved preeclampsia ECFC functional properties. VDR- or VEGF blockade reduced tubule formation, partially restorable by vitamin D3.

CONCLUSION

Fetal ECFCs from preeclamptic pregnancies are reduced in number and dysfunctional. Vitamin D3 had rescuing effects. This may have implications for the increased cardiovascular risk associated with preeclampsia.

Vitamin D prevents endothelial progenitor cell dysfunction induced by sera from women with preeclampsia or conditioned media from hypoxic placenta

CONTEXT

Placenta-derived circulating factors contribute to the maternal endothelial dysfunction underlying preeclampsia. Endothelial colony forming cells (ECFC), a sub-population of endothelial progenitor cells (EPCs), are thought to be involved in vasculogenesis and endothelial repair. Low vitamin D concentrations are associated with an increased risk for preeclampsia.

OBJECTIVE

We hypothesized that the function of human fetal ECFCs in culture would be suppressed by exposure to preeclampsia-related factors--preeclampsia serum or hypoxic placental conditioned medium--in a fashion reversed by vitamin D.

DESIGN, SETTING, PATIENTS

ECFCs were isolated from cord blood of uncomplicated pregnancies and expanded in culture. Uncomplicated pregnancy villous placenta in explant culture were exposed to either 2% (hypoxic), 8% (normoxic) or 21% (hyperoxic) O2 for 48 h, after which the conditioned media (CM) was collected.

OUTCOME MEASURES

ECFC tubule formation (Matrigel assay) and migration were examined in the presence of either maternal serum from preeclampsia cases or uncomplicated pregnancy controls, or pooled CM, in the presence or absence of 1,25(OH)2 vitamin D3.

RESULTS

1,25(OH)2 vitamin D3 reversed the adverse effects of preeclampsia serum or CM from hypoxic placenta on ECFCs capillary-tube formation and migration. Silencing of VDR expression by VDR siRNA, VDR blockade, or VEGF pathway blockade reduced ECFC functional abilities. Effects of VDR or VEGF blockade were partially prevented by vitamin D.

CONCLUSION

Vitamin D promotes the capillary-like tubule formation and migration of ECFCs in culture, minimizing the negative effects of exposure to preeclampsia-related factors. Further evaluation of the role of vitamin D in ECFC regulation and preeclampsia is warranted.

Uterine vasculature remodeling in human pregnancy involves functional macrochimerism by endothelial colony forming cells of fetal origin

The potency of adult-derived circulating progenitor endothelial colony forming cells (ECFCs) is drastically surpassed by their fetal counterparts. Human pregnancy is associated with robust intensification of blood flow and vascular expansion in the uterus, crucial for placental perfusion and fetal supply. Here, we investigate whether fetal ECFCs transmigrate to maternal bloodstream and home to locations of maternal vasculogenesis, primarily the pregnant uterus. In the first instance, endothelial-like cells, originating from mouse fetuses expressing paternal eGFP, were identified within uterine endothelia. Subsequently, LacZ or enhanced green fluorescent protein (eGFP)-labeled human fetal ECFCs, transplanted into immunodeficient (NOD/SCID) fetuses on D15.5 pregnancy, showed similar integration into the mouse uterus by term. Mature endothelial controls (human umbilical vein endothelial cells), similarly introduced, were unequivocally absent. In humans, SRY was detected in 6 of 12 myometrial microvessels obtained from women delivering male babies. The copy number was calculated at 175 [IQR 149-471] fetal cells per millimeter square endothelium, constituting 12.5% of maternal vessel lumina. Cross-sections of similar human vessels, hybridized for Y-chromosome, positively identified endothelial-associated fetal cells. It appears that through ECFC donation, fetuses assist maternal uterine vascular expansion in pregnancy, potentiating placental perfusion and consequently their own fetal supply. In addition to fetal growth, this cellular mechanism holds implications for materno-fetal immune interactions and long-term maternal vascular health.

Endothelial heterogeneity in the umbilico-placental unit: DNA methylation as an innuendo of epigenetic diversity

The endothelium is a multifunctional heterogeneous tissue playing a key role in the physiology of every organ. To accomplish this role the endothelium presents a phenotypic diversity that is early prompted during vascular development, allowing it to cope with specific requirements in a time- and site-specific manner. During the last decade several reports show that endothelial diversity is also present in the umbilico-placental vasculature, with differences between macro- and microvascular vessels as well as arterial and venous endothelium. This diversity is evidenced in vitro as a higher angiogenic capacity in the microcirculation; or disparity in the levels of several molecules that control endothelial function (i.e., receptor for growth factors, vasoactive mediators, and adhesion molecules) which frequently are differentially expressed between arterial and venous endothelium. Emerging evidence suggests that endothelial diversity would be prominently driven by epigenetic mechanisms which also control the basal expression of endothelial-specific genes. This review outlines evidence for endothelial diversity since early stages of vascular development and how this heterogeneity is expressed in the umbilico-placental vasculature. Furthermore a brief picture of epigenetic mechanisms and their role on endothelial physiology emphasizing new data on umbilical and placental endothelial cells is presented. Unraveling the role of epigenetic mechanisms on long term endothelial physiology and its functional diversity would contribute to develop more accurate therapeutic interventions. Altogether these data show that micro- versus macro-vascular, or artery versus vein comparisons are an oversimplification of the complexity occurring in the endothelium at different levels, and the necessity for the future research to establish the precise source of cells which are under study.

Instruction of circulating endothelial progenitors in vitro towards specialized blood-brain barrier and arterial phenotypes

OBJECTIVE

The vascular system is adapted to specific functions in different tissues and organs. Vascular endothelial cells are important elements of this adaptation, leading to the concept of 'specialized endothelial cells'. The phenotype of these cells is highly dependent on their specific microenvironment and when isolated and cultured, they lose their specific features after few passages, making models using such cells poorly predictive and irreproducible. We propose a new source of specialized endothelial cells based on cord blood circulating endothelial progenitors (EPCs). As prototype examples, we evaluated the capacity of EPCs to acquire properties characteristic of cerebral microvascular endothelial cells (blood-brain barrier (BBB)) or of arterial endothelial cells, in specific inducing culture conditions.

APPROACH AND RESULTS

First, we demonstrated that EPC-derived endothelial cells (EPDCs) co-cultured with astrocytes acquired several BBB phenotypic characteristics, such as restricted paracellular diffusion of hydrophilic solutes and the expression of tight junction proteins. Second, we observed that culture of the same EPDCs in a high concentration of VEGF resulted, through activation of Notch signaling, in an increase of expression of most arterial endothelial markers.

CONCLUSIONS

We have thus demonstrated that in vitro culture of early passage human cord blood EPDCs under specific conditions can induce phenotypic changes towards BBB or arterial phenotypes, indicating that these EPDCs maintain enough plasticity to acquire characteristics of a variety of specialized phenotypes. We propose that this property of EPDCs might be exploited for producing specialized endothelial cells in culture to be used for drug testing and predictive in vitro assays.

Endothelial outgrowth cells: function and performance in vascular grafts

The clinical need for vascular grafts continues to grow. Tissue engineering strategies have been employed to develop vascular grafts for patients lacking sufficient autologous vessels for grafting. Restoring a functional endothelium on the graft lumen has been shown to greatly improve the long-term patency of small-diameter grafts. However, obtaining an autologous source of endothelial cells for in vitro endothelialization is invasive and often not a viable option. Endothelial outgrowth cells (EOCs), derived from circulating progenitor cells in peripheral blood, provide an alternative cell source for engineering an autologous endothelium. This review aims at highlighting the role of EOCs in the regulation of processes that are central to vascular graft performance. To characterize EOC performance in vascular grafts, this review identifies the characteristics of EOCs, defines functional performance criteria for EOCs in vascular grafts, and summarizes the existing work in developing vascular grafts with EOCs.

Shear stress regulates late EPC differentiation via mechanosensitive molecule-mediated cytoskeletal rearrangement

Background

Previous studies have demonstrated that endothelial progenitor cells (EPCs), in particular late EPCs, play important roles in endothelial maintenance and repair. Recent evidence has revealed shear stress as a key regulator for EPC differentiation. However, the underlying mechanisms regulating the shear stress–induced EPC differentiation have not been understood completely. The present study was undertaken to further investigate the effects of shear stress on the late EPC differentiation, and to elucidate the signal mechanism involved.

Methodology/Principal Finding

In vitro and in vivo assays revealed that cytoskeletal remodeling was involved in the shear stress-upregulated expression of endothelial markers vWF and CD31 in late EPCs, with subsequently increased in vivo reendothelialization after arterial injury. Moreover, shear stress activated several mechanosensitive molecules including integrin β₁, Ras, ERK1/2, paxillin and FAK, which were all involved in both cytoskeletal rearrangement and cell differentiation in response to shear stress in late EPCs.

Conclusions/Significance

Shear stress is a key regulator for late EPC differentiation into endothelial cells, which is important for vascular repair, and the cytoskeletal rearrangement mediated by the activation of the cascade of integrin β₁, Ras, ERK1/2, paxillin and FAK is crucial in this process.

Restitutio ad integrum: a dream or a real possibility?

The subject of organ regeneration has attracted substantial investigative attention and has been extensively reviewed. Therefore, I shall focus on several only recently emerged issues and on those aspects of stem cell-mediated regeneration which, although are important in my opinion, have nevertheless evaded the radar of scientific pursuit. Specifically, I shall describe the recent work on the prominence of local lineage-restricted stem cells, as opposed to the bone marrow-derived or circulating ones, in regeneration. This will be followed by an attempt to re-interpret a bulk of published data on the beneficial effects of cell therapy with the focus on the secretome of stem cells. Multiple factors that conspire to cause insufficient or failed regeneration in adult mammals will be screened with emphasis placed on the mechanical forces, senescence and exhaustion, each leading to phenotypical switch and/or stem cell incompetence. Finally, I shall enumerate several potential pathways to induce or restore stem cell competence. Although a significant amount of work has been performed in the non-renal field, I would hope that some of the mechanisms and concepts discussed herein will eventually trickle into kidney regeneration.

Dynamic shear stress regulation of inflammatory and thrombotic pathways in baboon endothelial outgrowth cells

Endothelial outgrowth cells (EOCs) have garnered much attention as a potential autologous endothelial source for vascular implants or in tissue engineering applications due to their ease of isolation and proliferative ability; however, how these cells respond to different hemodynamic cues is ill-defined. This study investigates the inflammatory and thrombotic response of baboon EOCs (BaEOCs) to four hemodynamic conditions using the cone and plate shear apparatus: steady, laminar shear stress (SS); pulsatile, nonreversing laminar shear stress (PS); oscillatory, laminar shear stress (OS); and net positive, pulsatile, reversing laminar shear stress (RS). In summary, endothelial nitric oxide synthase (eNOS) mRNA was significantly upregulated by SS compared to OS. No differences were found in the mRNA levels of the inflammatory markers intercellular adhesion molecule-1 (ICAM-1), E-selectin, and vascular cell adhesion molecule-1 (VCAM-1) between the shear conditions; however, OS significantly increased the number of monocytes bound when compared to SS. Next, SS increased the anti-thrombogenic mRNA levels of CD39, thrombomodulin, and endothelial protein-C receptor (EPCR) compared to OS. SS also significantly increased CD39 and EPCR mRNA levels compared to RS. Finally, no significant differences were detected when comparing pro-thrombotic tissue factor mRNA or its activity levels. These results indicate that shear stress can have beneficial (SS) or adverse (OS, RS) effects on the inflammatory or thrombotic potential of EOCs. Further, these results suggest SS hemodynamic preconditioning may be optimal in increasing the efficacy of a vascular implant or in tissue-engineered applications that have incorporated EOCs.

Endothelial cells (ECs) for vascular tissue engineering: venous ECs are less thrombogenic than arterial ECs

Primary endothelial cells (ECs) are the preferred cellular source for luminal seeding of tissue-engineered (TE) vascular grafts. Research into the potential of ECs for vascular TE has focused particularly on venous rather than arterial ECs. In this study we evaluated the functional characteristics of arterial and venous ECs, relevant for vascular TE. Porcine ECs were isolated from femoral artery (PFAECs) and vein (PFVECs). The proliferation rate was comparable for both EC sources, whereas migration, determined through a wound-healing assay, was less profound for PFVECs. EC adhesion was lower for PFVECs on collagen I, measured after 10 min of arterial shear stress. Gene expression was analysed by qRT-PCR for ECs cultured under static conditions and after exposure to arterial shear stress and revealed differences in gene expression, with lower expression of EphrinB2 and VCAM-1 and higher levels of vWF and COUP-TFII in PFVECs than in PFAECs. PFVECs exhibited diminished platelet adhesion under flow and cell-based thrombin generation was delayed for PFVECs, indicating diminished tissue factor (TF) activity. After stimulation, prostacyclin secretion, but not nitric oxide (NO), was lower in PFVECs. Our data support the use of venous ECs for TE because of their beneficial antithrombogenic profile.

Biomechanics of early cardiac development

Biomechanics affect early cardiac development, from looping to the development of chambers and valves. Hemodynamic forces are essential for proper cardiac development, and their disruption leads to congenital heart defects. A wealth of information already exists on early cardiac adaptations to hemodynamic loading, and new technologies, including high-resolution imaging modalities and computational modeling, are enabling a more thorough understanding of relationships between hemodynamics and cardiac development. Imaging and modeling approaches, used in combination with biological data on cell behavior and adaptation, are paving the road for new discoveries on links between biomechanics and biology and their effect on cardiac development and fetal programming.