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Find video protocols related to scientific articles indexed in Pubmed.
Quantification of blood flow and topology in developing vascular networks.
PLoS ONE
PUBLISHED: 01-01-2014
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Since fluid dynamics plays a critical role in vascular remodeling, quantification of the hemodynamics is crucial to gain more insight into this complex process. Better understanding of vascular development can improve prediction of the process, and may eventually even be used to influence the vascular structure. In this study, a methodology to quantify hemodynamics and network structure of developing vascular networks is described. The hemodynamic parameters and topology are derived from detailed local blood flow velocities, obtained by in vivo micro-PIV measurements. The use of such detailed flow measurements is shown to be essential, as blood vessels with a similar diameter can have a large variation in flow rate. Measurements are performed in the yolk sacs of seven chicken embryos at two developmental stages between HH 13+ and 17+. A large range of flow velocities (1 µm/s to 1 mm/s) is measured in blood vessels with diameters in the range of 25-500 µm. The quality of the data sets is investigated by verifying the flow balances in the branching points. This shows that the quality of the data sets of the seven embryos is comparable for all stages observed, and the data is suitable for further analysis with known accuracy. When comparing two subsequently characterized networks of the same embryo, vascular remodeling is observed in all seven networks. However, the character of remodeling in the seven embryos differs and can be non-intuitive, which confirms the necessity of quantification. To illustrate the potential of the data, we present a preliminary quantitative study of key network topology parameters and we compare these with theoretical design rules.
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Endothelial colony-forming cells show a mature transcriptional response to shear stress.
In Vitro Cell. Dev. Biol. Anim.
PUBLISHED: 09-16-2011
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Endothelial progenitor cells (EPC) play a central role in endothelial maintenance and repair. Endothelial colony-forming cells (ECFC) form a subpopulation of EPC. ECFC are readily attainable, can be easily isolated, possess a high proliferation potential, and are therefore a promising source of endothelial cells (EC) for future cardiovascular therapeutic applications. The extent to which these cells respond to shear stress as adult vascular EC remains to be elucidated. Here, we study the transcriptional response of ECFC induced by shear stress and compare it with the response of mature arterial and venous cells. ECFC, as well as human umbilical vein EC (HUVEC) and human umbilical artery EC (HUAEC), were subjected to low (0.5 Pa) and high (2.5 Pa) shear stress. The endothelial differentiation phenotype and transcriptional responses were analyzed using immunocytochemistry and quantitative polymerase chain reaction (Q-PCR). Performing absolute quantification of copy numbers by Q-PCR allows comparing the responses of cell types relative to each other. Our data show that isolated ECFC resemble mature EC in cobblestone morphology and endothelial marker expression. Absolute Q-PCR quantification revealed that although being truly endothelial, ECFC do not fully resemble HUVEC or HUAEC in the expression of specific differentiation markers. When subjected to shear stress, ECFC show a mature response to fluid flow, comparable to that of HUVEC and HUAEC. The capacity of endothelial progenitors to respond to fluid flow in a similar manner to HUVEC and HUAEC highlights the universal response of EC to fluid shear stress, independently of their endothelial differentiation status. This property supports the use of these cells as an EC source for tissue engineering applications.
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Primary cilia as biomechanical sensors in regulating endothelial function.
Differentiation
PUBLISHED: 09-13-2011
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Depending on the pattern of blood flow to which they are exposed and their proliferative status, vascular endothelial cells can present a primary cilium into the flow compartment of a blood vessel. The cilium modifies the response of endothelial cells to biomechanical forces. Shear stress, which is the drag force exerted by blood flow, is best studied in this respect. Here we review the structural composition of the endothelial cilia and the current status of knowledge about the relation between the presence of primary cilia on endothelial cells and the shear stress to which they are exposed.
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Role for primary cilia as flow detectors in the cardiovascular system.
Int Rev Cell Mol Biol
PUBLISHED: 08-31-2011
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The cardiovascular system is exposed to biochemical and biomechanical signals. Various sensors for these signals have been described and they contribute to cardiovascular development, maintenance of vessel integrity during adult life, and to pathogenesis. In the past 10years, primary cilia, membrane-covered, rod-like cellular protrusions, were discovered on multiple cell types of the cardiovascular system. Primary cilia are sensory organelles involved in several key (developmental) signaling pathways and in chemo- and mechanosensing on a myriad of cell types. In the embryonic and adult cardiovascular system, they have been demonstrated to function as shear stress sensors on endothelial cells and could act as strain sensors on smooth muscle cells and cardiomyocytes and as chemosensors on fibroblasts. This review will cover their occurrence and elaborate on established and possible functions of primary cilia in the cardiovascular system.
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Tgf?/Alk5 signaling is required for shear stress induced klf2 expression in embryonic endothelial cells.
Dev. Dyn.
PUBLISHED: 04-14-2011
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Endothelial cells (EC) translate biomechanical forces into functional and phenotypic responses that play important roles in cardiac development. Specifically, EC in areas of high shear stress, i.e., in the cardiac outflow tract and atrioventricular canal, are characterized by high expression of Krüppel-like factor 2 (Klf2) and by transforming growth factor-beta (Tgf?)-driven endothelial-to-mesenchymal transition. Extraembryonic venous obstruction (venous clip model) results in congenital heart malformations, and venous clip-induced alterations in shear stress-related gene expression are suggestive for an increase in cardiac shear stress. Here, we study the effects of shear stress on Klf2 expression and Tgf?-associated signaling in embryonic EC in vivo using the venous clip model and in vitro by subjecting cultured EC to fluid flow. Cellular responses were assessed by analysis of Klf2, Tgf? ligands, and their downstream signaling targets. Results show that, in embryonic EC, shear stress activates Tgf?/Alk5 signaling and that induction of Klf2 is an Alk5 dependent process.
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Lack of primary cilia primes shear-induced endothelial-to-mesenchymal transition.
Circ. Res.
PUBLISHED: 03-10-2011
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Primary cilia are cellular protrusions that serve as mechanosensors for fluid flow. In endothelial cells (ECs), they function by transducing local blood flow information into functional responses, such as nitric oxide production and initiation of gene expression. Cilia are present on ECs in areas of low or disturbed flow and absent in areas of high flow. In the embryonic heart, high-flow regime applies to the endocardial cushion area, and the absence of cilia here coincides with the process of endothelial-to-mesenchymal transition (EndoMT).
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The mechanosensory role of primary cilia in vascular hypertension.
Int J Vasc Med
PUBLISHED: 01-12-2011
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Local regulation of vascular tone plays an important role in cardiovascular control of blood pressure. Aside from chemical or hormonal regulations, this local homeostasis is highly regulated by fluid-shear stress. It was previously unclear how vascular endothelial cells were able to sense fluid-shear stress. The cellular functions of mechanosensory cilia within vascular system have emerged recently. In particular, hypertension is insidious and remains a continuous problem that evolves during the course of polycystic kidney disease (PKD). The basic and clinical perspectives on primary cilia are discussed with regard to the pathogenesis of hypertension in PKD.
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Prenatal exposure to apoE deficiency and postnatal hypercholesterolemia are associated with altered cell-specific lysine methyltransferase and histone methylation patterns in the vasculature.
Am. J. Pathol.
PUBLISHED: 12-24-2009
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We recently demonstrated that neointima formation of adult heterozygous apolipoprotein E (apoE(+/-)) offspring from hypercholesterolemic apoE(-/-) mothers was significantly increased as compared with genetically identical apoE(+/-) offspring from normocholesterolemic wild-type mothers. Since atherosclerosis is the consequence of a complex microenvironment and local cellular interactions, the effects of in utero programming and type of postnatal diet on epigenetic histone modifications in the vasculature were studied in both groups of offspring. An immunohistochemical approach was used to detect cell-specific histone methylation modifications and expression of accompanying lysine methyltransferases in the carotid arteries. Differences in histone triple-methylation modifications in vascular endothelial and smooth muscle cells revealed that the offspring from apoE(-/-) mothers had significantly different responses to a high cholesterol diet when compared with offspring from wild-type mothers. Our results suggest that both in utero programming and postnatal hypercholesterolemia affect epigenetic patterning in the vasculature, thereby providing novel insights regarding initiation and progression of vascular disease in adults.
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Tapered microfluidic chip for the study of biochemical and mechanical response at subcellular level of endothelial cells to shear flow.
Lab Chip
PUBLISHED: 02-27-2009
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A lab-on-a-chip application for the investigation of biochemical and mechanical response of individual endothelial cells to different fluid dynamical conditions is presented. A microfluidic flow chamber design with a tapered geometry that creates a pre-defined, homogeneous shear stress gradient on the cell layer is described and characterized. A non-intrusive, non-tactile measurement method based on micro-PIV is used for the determination of the topography and shear stress distribution over individual cells with subcellular resolution. The cellular gene expression is measured simultaneously with the shape and shear stress distribution of the cell. With this set-up the response of the cells on different pre-defined shear stress levels is investigated without the influence of variations in repetitive experiments. Results are shown on cultured endothelial cells related to the promoter activity of the shear-responsive transcription factor KLF2 driving the marker gene for green fluorescent protein.
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Accurate blood flow measurements: are artificial tracers necessary?
PLoS ONE
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Imaging-based blood flow measurement techniques, such as particle image velocimetry, have become an important tool in cardiovascular research. They provide quantitative information about blood flow, which benefits applications ranging from developmental biology to tumor perfusion studies. Studies using these methods can be classified based on whether they use artificial tracers or red blood cells to visualize the fluid motion. We here present the first direct comparison in vivo of both methods. For high magnification cases, the experiments using red blood cells strongly underestimate the flow (up to 50% in the present case), as compared to the tracer results. For medium magnification cases, the results from both methods are indistinguishable as they give the same underestimation of the real velocities (approximately 33%, based on in vitro reference measurements). These results suggest that flow characteristics reported in literature cannot be compared without a careful evaluation of the imaging characteristics. A method to predict the expected flow averaging behavior for a particular facility is presented.
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Shear induced collateral artery growth modulated by endoglin but not by ALK1.
J. Cell. Mol. Med.
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Transforming growth factor-beta (TGF-?) stimulates both ischaemia induced angiogenesis and shear stress induced arteriogenesis by signalling through different receptors. How these receptors are involved in both these processes of blood flow recovery is not entirely clear. In this study the role of TGF-? receptors 1 and endoglin is assessed in neovascularization in mice. Unilateral femoral artery ligation was performed in mice heterozygous for either endoglin or ALK1 and in littermate controls. Compared with littermate controls, blood flow recovery, monitored by laser Doppler perfusion imaging, was significantly hampered by maximal 40% in endoglin heterozygous mice and by maximal 49% in ALK1 heterozygous mice. Collateral artery size was significantly reduced in endoglin heterozygous mice compared with controls but not in ALK1 heterozygous mice. Capillary density in ischaemic calf muscles was unaffected, but capillaries from endoglin and ALK1 heterozygous mice were significantly larger when compared with controls. To provide mechanistic evidence for the differential role of endoglin and ALK1 in shear induced or ischaemia induced neovascularization, murine endothelial cells were exposed to shear stress in vitro. This induced increased levels of endoglin mRNA but not ALK1. In this study it is demonstrated that both endoglin and ALK1 facilitate blood flow recovery. Importantly, endoglin contributes to both shear induced collateral artery growth and to ischaemia induced angiogenesis, whereas ALK1 is only involved in ischaemia induced angiogenesis.
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TGF-? signaling in endothelial-to-mesenchymal transition: the role of shear stress and primary cilia.
Sci Signal
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Endothelial-to-mesenchymal transition (EndoMT) is an instrumental step in the development of valves in the embryonic heart. This process is driven by activation of transforming growth factor-? (TGF-?) signaling and is characterized by the loss of endothelial and gain of mesenchymal phenotype, and by delamination of cells from the surface into the underlying endocardial cushion matrix. The endothelial cells (ECs) overlying the cushions are typically exposed to high blood flow and concomitant shear stress and do not have a primary cilium. Here, we show that shear stress activates TGF-?-Alk5 signaling in ECs, which is necessary for EndoMT in the cushions. Moreover, we show that the absence of a primary cilium is critically important for this transition process.
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What is Visualize?

JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.

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We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.

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In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.