Name: incorporating pericytes into an endothelial cell bead sprouting assay
Uploaded: 2018-02-16T15:00:00
Description: Watch this Scientific Journal Video about Incorporating Pericytes into an Endothelial Cell Bead Sprouting Assay at JoVE.com

We thank Drs. Victoria Bautch and Joshua Boucher for helpful discussions and advice on optimizing standard bead sprouting assay conditions and a sprouting assay staining protocol.&#160;S.H.A. was supported in part by a grant from the National Institute of General Medical Sciences under award 5T32 GM007092.

Day 1:
1. Transient Transfection of Endothelial Cells
<ol>
	<li>If desired, perform a transient transfection of Human Umbilical Vein Endothelial Cells (HUVEC) using gene-regulatory oligonucleotides (e.g. micro-RNAs or small interfering RNA (siRNA)) and the appropriate lipofectamine reagent according to manufacturer&#39;s instructions. 
	NOTE: This protocol has had great success performing reverse transfections with custom siRNA sequences and a commercial transf...

<ol>
	<li>Hanahan, D., Folkman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patterns+and+emerging+mechanisms+of+the+angiogenic+switch+during+tumorigenesis.">Patterns and emerging mechanisms of the angiogenic switch during tumorigenesis.</a> Cell. 86 (3), 353-364 (1996).</li><li>Semenza, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Angiogenesis+in+ischemic+and+neoplastic+disorders.">Angiogenesis in ischemic and neoplastic disorders.</a> Annu Rev Med. 54, 17-28 (2003).</li><li>Zhang, Z. G., Chopp, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neurorestorative+therapies+for+stroke:+underlying+mechanisms+and+translation+to+the+clinic.">Neurorestorative therapies for stroke: underlying mechanisms and translation to the clinic.</a> Lancet Neurol. 8 (5), 491-500 (2009).</li><li>Nakatsu, M. N., Hughes, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+optimized+three-dimensional+in+vitro+model+for+the+analysis+of+angiogenesis.">An optimized three-dimensional in vitro model for the analysis of angiogenesis.</a> Methods Enzymol. 443, 65-82 (2008).</li><li>Nehls, V., Drenckhahn, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel,+microcarrier-based+in+vitro+assay+for+rapid+and+reliable+quantification+of+three-dimensional+cell+migration+and+angiogenesis.">A novel, microcarrier-based in vitro assay for rapid and reliable quantification of three-dimensional cell migration and angiogenesis.</a> Microvasc Res. 50 (3), 311-322 (1995).</li><li>Sims, D. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+pericyte--a+review.">The pericyte--a review.</a> Tissue Cell. 18 (2), 153-174 (1986).</li><li>Armulik, A., Genove, G., Betsholtz, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pericytes:+developmental,+physiological,+and+pathological+perspectives,+problems,+and+promises.">Pericytes: developmental, physiological, and pathological perspectives, problems, and promises.</a> Dev Cell. 21 (2), 193-215 (2011).</li><li>Tattersall, I. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+modeling+of+endothelial+interaction+with+macrophages+and+pericytes+demonstrates+Notch+signaling+function+in+the+vascular+microenvironment.">In vitro modeling of endothelial interaction with macrophages and pericytes demonstrates Notch signaling function in the vascular microenvironment.</a> Angiogenesis. 19 (2), 201-215 (2016).</li><li>Jain, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Normalization+of+tumor+vasculature:+an+emerging+concept+in+antiangiogenic+therapy.">Normalization of tumor vasculature: an emerging concept in antiangiogenic therapy.</a> Science. 307 (5706), 58-62 (2005).</li><li>Tahergorabi, Z., Khazaei, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+on+angiogenesis+and+its+assays.">A review on angiogenesis and its assays.</a> Iran J Basic Med Sci. 15 (6), 1110-1126 (2012).</li><li>Popson, S. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interferon-induced+transmembrane+protein+1+regulates+endothelial+lumen+formation+during+angiogenesis.">Interferon-induced transmembrane protein 1 regulates endothelial lumen formation during angiogenesis.</a> Arterioscler Thromb Vasc Biol. 34 (5), 1011-1019 (2014).</li><li>Coultas, L., Chawengsaksophak, K., Rossant, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+cells+and+VEGF+in+vascular+development.">Endothelial cells and VEGF in vascular development.</a> Nature. 438 (7070), 937-945 (2005).</li><li>Newman, A. C., Nakatsu, M. N., Chou, W., Gershon, P. D., Hughes, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+requirement+for+fibroblasts+in+angiogenesis:+fibroblast-derived+matrix+proteins+are+essential+for+endothelial+cell+lumen+formation.">The requirement for fibroblasts in angiogenesis: fibroblast-derived matrix proteins are essential for endothelial cell lumen formation.</a> Mol Biol Cell. 22 (20), 3791-3800 (2011).</li></ol>

This protocol presents a method for characterizing the complex stages and heterotypic cellular interactions of sprouting angiogenesis by enabling the researcher to employ genetic and imaging approaches to conduct thorough mechanistic investigations. When performing the assay, it is essential that efficient endothelial coating of the beads takes place during the bead agitation steps. Poor endothelial coating will be made evident, if the beads do not appear to have a golf ball-like rough surface the next morning prior to g...

Angiogenesis is vital to appropriate embryogenesis and wound healing, and it also plays key roles in numerous diseases including cancer progression1 and coronary artery disease.2,3 Having a better understanding of how angiogenesis occurs during normal development, and how it is reactivated in pathologic contexts, is critical for the development of novel, effective therapeutics. Faithful in vitro models that recapitulate the important stages and cell types involved in angiogenesis in vivo are needed to allow researchers to better characterize the molecular mechanisms driving angiogenesis and make novel discoveries in endothelial regulation.
Nakatsu and Hughes have optimized a sprouting bead assay that they have demonstrated undergoes the many known stages of sprouting angiogenesis.4,5 The purpose of the method presented here is to build upon the assay optimized by Nakatsu and Hughes by incorporating perictyes into the assay, so that the paracrine and juxtracrine roles of mural cells in endothelial cell sprouting can be incorporated in novel angiogenesis studies. Pericytes are mural cells that are defined by their role as cells that maintain close physical contact with endothelial cells due to their being embedded in the vascular basement membrane.6 Pericytes and endothelial cells engage in complex cross-talk via signaling pathways including Notch signaling, Ang-Tie2, PDGFR&#946;, TGFR&#946;, and many others.7,8 Mouse models deficient in these signaling pathways demonstrate poor pericyte coverage of developing vasculature in embryogenesis, leading to poor vascular remodeling and dysfunctional vasculature.7 In addition, the role of pericytes in pathologic angiogenesis is important but oftentimes under-appreciated. For example, a unique feature of tumor vasculature is that the vessels are more immature, leaky, and dysfunctional due to poor pericyte coverage.9 It has been proposed that the presence or absence of pericytes dramatically impacts the phenotype of tumor blood vessels and is an important mediator of responses to antiangiogenic and antitumor therapies.9 Thus, including the role of pericytes in in vitro assays is key to more completely capture the important mechanisms of endothelial regulation.
Although there are many in vitro and ex vivo assays currently employed to study angiogenesis, there are shortcomings to consider in each. Some, such as endothelial proliferation and endothelial migration assays, are overly simplified and focus on one endothelial function in an isolated setting on tissue culture plastic.10 Other assays occur in a more 3 dimensional (3D) setting, such as the Matrigel tube formation assay,10 but these assays are still oversimplified and focus more on the ability of endothelial cells to migrate and form de novo vascular structures, as opposed to sprouting from pre-existing vasculature. Furthermore, none of these assays incorporate mural cell types. There are ex vivo models such as the ring aorta assay that do incorporate pericytes present in the host organ, but genetic manipulation of these models is much more challenging due to the necessity of generating knockout or transgenic mouse models of the pathways of interest. The bead sprouting assay is ideal because it models endothelial sprouting, proliferation, migration, and even anastomosis and lumen formation in a 3D matrix.4 The assay faithfully allows for mechanistic assessment of the many different stages of sprouting, while still allowing for direct genetic modification of either the endothelial cells or pericytes in a more controlled setting. The fibrin clots containing the sprouting beads can be easily fixed, stained, and imaged at different stages of sprouting; these sprouts can also be placed in a live imaging chamber to perform real-time imaging of sprouting. The methodology presented here is ideal for studying basic mechanisms of angiogenesis through in depth phenotyping and thorough analysis of the pathways activated during angiogenesis.

<table>
	<tbody>
		<tr>
			<td>Sterile Pipette tips</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Pipettors</td>
			<td>Eppendorf</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Complete EGM2 Media Bullet Kit</td>
			<td>Lonza</td>
			<td>CC-3162</td>
			<td>HUVEC Media</td>
		</tr>
		<tr>
			<td>MEM</td>
			<td>Gibco</td>
			<td>11095114</td>
			<td>10T1/2 Media</td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Gibco</td>
			<td>11965118</td>
			<td>NHLF Media</td>
		</tr>
		<tr>
			<td>Tissue culture-grade PBS</td>
			<td>Gibco</td>
			<td>14190-144</td>
			<td>Magnesium and calcium free</td>
		</tr>
		<tr>
			<td>Accutase</td>
			<td>Life Technologies</td>
			<td>A1110501</td>
			<td>For lifting HUVEC</td>
		</tr>
		<tr>
			<td>Trypsin</td>
			<td>Life Technologies</td>
			<td>15050065</td>
			<td>For lifting 10T 1/2 and NHLF</td>
		</tr>
		<tr>
			<td>Customs siRNAs</td>
			<td>Sigma</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Lipofectamine RNAiMax</td>
			<td>Life Technologies</td>
			<td>13778150</td>
			<td></td>
		</tr>
		<tr>
			<td>HUVEC</td>
			<td>Lonza</td>
			<td>C2517A</td>
			<td></td>
		</tr>
		<tr>
			<td>10T 1/2</td>
			<td>ATCC</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NHLF</td>
			<td>ATCC</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cytodex 3 microcarrier beads</td>
			<td>Sigma</td>
			<td>C3275</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue culture-coated 6 and 10 cm plates</td>
			<td>Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fibrinogen from bovine plasma</td>
			<td>Sigma</td>
			<td>F8630</td>
			<td></td>
		</tr>
		<tr>
			<td>Thrombin</td>
			<td>Sigma</td>
			<td>t9549</td>
			<td></td>
		</tr>
		<tr>
			<td>Aprotinin</td>
			<td>Sigma</td>
			<td>a3428</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon Round-Bottom Tubes</td>
			<td>Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue culture incubator and hood</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>24-well glass bottom plates</td>
			<td>MatTek</td>
			<td>P24G1.513F</td>
			<td>Glass-bottom plates are needed only if the sprouts are going to be imaged. If not, tissue culture plastic is also acceptable.</td>
		</tr>
		<tr>
			<td>Sterile Filtration Device</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

incorporating pericytes into an endothelial cell bead sprouting assay

Angiogenesis is the growth of new vessels from pre-existing vasculature and is an important component of many biological processes, including embryogenesis and development, wound healing, tumor growth and metastasis, and ocular and cardiovascular diseases. Effective in vitro models that recapitulate the biology of angiogenesis are needed to appropriately study this process and identify mechanisms of regulation that can be ultimately targeted for novel therapeutic strategies. The bead angiogenesis assay has been previously demonstrated to recapitulate the multiple stages of endothelial sprouting in vitro. However, a limitation of this assay is a lack of endothelial &#8211; mural cell interactions, which are key to the molecular and phenotypic regulation of endothelial cell function in vivo. The protocol given here presents a methodology for the incorporation of mural cells into the bead angiogenesis assay and demonstrates a tight association of endothelial cells and pericytes during sprouting in vitro. The protocol also details a methodology for effective silencing of target genes using siRNA in endothelial cells for mechanistic studies. Altogether, this protocol provides an in vitro assay that more appropriately models the diverse cell types involved in sprouting angiogenesis, and provides a more physiologically-relevant platform for therapeutic assessment and novel discovery of mechanisms of angiogenesis regulation.

This protocol allows for a tight association of the two cell types in vitro, and the presence of the pericytes complements the occurrence of sprouting (Figure 1A, B). The protocol also enables effective silencing (e.g. via RNA interference) of a gene of interest in a cell type of interest (such as VEGFA specifically in endothelial cells or PDGFR&#946; in pericytes)7,12</su...

Watch this Scientific Journal Video about Incorporating Pericytes into an Endothelial Cell Bead Sprouting Assay at JoVE.com

Incorporating Pericytes into an Endothelial Cell Bead Sprouting Assay

This protocol presents a novel in vitro bead assay that more appropriately models the process of in vivo sprouting angiogenesis by incorporating pericytes. This modification enables the bead assay to more faithfully recapitulate the heterotypic cellular interactions between endothelial cells and mural cells that are critical for angiogenesis.

Angiogenesis is the growth of new vessels from pre-existing vasculature and is an important component of many biological processes, including ...

The overall goal of this assay is to incorporate heterotypic cellular interactions in vitro that encapsulate the complexity of angiogenesis in vivo. This method can help answer key questions in the vascular biology field about the importance of pericyte endothelial cell interactions during angiogenesis. The main advantage of this technique is that it integrates the different stages of sprouting angiogenesis, including proliferation, migration and anastomosis while still permitting the study of endothelial cell pericyte interactions.Begin by reconstituting the microcarrier beads at a six times 10 to the fourth beads per milliliter concentration in PBS, followed by autoclave sterilization of the microcarrier bead suspension. Next, aliquot one milliliter of complete medium into the appropriate number of round-bottom Fluorescence Activated Cell Sorting, or FACS, tubes, and add 20 microliters of room temperature-cooled, autoclave sterilized microcarrier bead suspension to each tube. Add one milliliter of cells to each tube.Agitate tubes and incubate the tubes at 37 degrees Celsius for 2 1/2 to three hours with gentle agitation every 20 minutes. At the end of the incubation, rest the cells in beads at room temperature for five minutes to allow the cells and beads to settle to the bottom of the tubes. Then, use a P1000 pipette to replace 0.5 milliliters of medium from each tube with two times 10 to the fifth pericytes and 0.5 milliliters of complete medium.Agitate the cell-bead suspension, and return the cells to the 37 degrees Celsius incubator with gentle agitation every 20 minutes until the beads have been agitated for a total of four hours. At the end of the incubation, gently agitate the tubes one last time, and immediately transfer the entire two milliliter volume of solution from each tube into individual six centimeter plates. Then, add an additional three milliliters of complete medium to each plate, and incubate the plates at 37 degrees Celsius overnight.The next morning, examine the dishes of microcarrier-coated beads under the microscope at a 20 times magnification to confirm that all of the beads have been sufficiently coated by the endothelial cells. Transfer the plates to a laminar flow hood, and use a P1000 pipette to vigorously aspirate and dispense the coated-bead solutions to detach the cells from the plate bottoms and transfer the supernatants into individual tubes. Allow the beads to settle to the bottoms of the tubes for three minutes.Then use the P1000 pipette to remove as much of the supernatants as possible without disturbing the bead clusters. Re-suspend the beads in one milliliter of complete medium per tube, and allow the beads to settle for 30 to 60 seconds. Use the P1000 pipette to aspirate the supernatant again, and wash the free-floating endothelial cells from the bead suspension with fresh complete medium two more times as just demonstrated.After the third wash, re-suspend the beads in 2.5 milliliters of fibrinogen solution. Add 13 microliters of thrombin solution per well in a 24-well, glass-bottom plate. Then add 0.5 milliliters of the bead fibrinogen solution to each well, taking care to carefully pipette the beads directly into the thrombin, and slowly pipette up and down two to three times to thoroughly mix the solutions.When all of the wells have been seeded, allow the thrombin-fibrinogen solution to preclot in the laminar flow hood for 30 minutes at room temperature. At the end of the incubation, carefully transfer the plate to a 37 degree Celsius incubator for an additional 1.5 to two hours. When the gel has fully solidified, re-suspend normal, human lung fibroblasts at a two times 10 to the fourth cells per milliliter concentration in complete medium, and add one milliliter of fibroblasts to each well.Then return the plate to the cell culture incubator. Strict adherence to the coating protocol will result in cell-coated beads with a rough, golf ball-like appearance, as illustrated in this representative image of sufficiently coated beads that are ready for fibrin gel implantation. Further, this protocol facilitates a tight association of the two cell types in vitro with the presence of the pericytes complementing the occurrence of sprouting.While attempting this procedure, it is important to remember to completely coat the beads with cells during the agitation steps, and to carefully embed the beads in the fibrin gel without introducing bubbles during the gel implantation. Following this procedure, other analyses like mouse studies of angiogenesis can be performed to answer additional questions, such as what is the in vivo relevance of the mechanisms and phenotypes explored in the pericyte beads sprouting assay in vitro? This technique will be useful for researchers in the field of cancer biology and exploring endothelial cell pericyte interactions and functions in a more physiologically relevant in vitro model of angiogenesis.

incorporating-pericytes-into-an-endothelial-cell-bead-sprouting-assay

Research

JoVE Journal

Developmental Biology

Assessment of Endothelial Cell Migration After Exposure to Toxic Chemicals

Exposure to chemical substances (including alkylating chemical warfare agents like sulfur and nitrogen mustards) cause a plethora of clinical symptoms including wound healing disorder. The physiological process of wound healing is highly complex. The formation of granulation tissue is a key step in this process resulting in a preliminary wound closure and providing a network of new capillary blood vessels &#8211; either through vasculogenesis (novel formation) or angiogenesis (sprouting of existing vessels). Both vasculo- and angiogenesis require functional, directed migration of endothelial cells. Thus, investigation of early endothelial cell (EEC) migration is important to understand the pathophysiology of chemical induced wound healing disorders and to potentially identify novel strategies for therapeutic intervention.
We assessed impaired wound healing after alkylating agent exposure and tested potential candidate compounds for treatment. We used a set of techniques outlined in this protocol. A modified Boyden chamber to quantitatively investigate chemokinesis of EEC is described. Moreover, the use of the wound healing assay in combination with track analysis to qualitatively assess migration is illustrated. Finally, we demonstrate the use of the fluorescent dye TMRM for the investigation of mitochondrial membrane potential to identify underlying mechanisms of disturbed cell migration. The following protocol describes basic techniques that have been adapted for the investigation of EEC.

Investigation of early endothelial cell (EEC) migration is important to understand the pathophysiology of certain illnesses and to potentially identify novel strategies for therapeutic intervention. The following protocol describes techniques to assess cell migration that have been adapted for the investigation of EEC.

Exposure to chemical substances (including alkylating chemical warfare agents like sulfur and nitrogen mustards) cause a plethora of clinical symptoms ...

Isolation of Murine Embryonic Hemogenic Endothelial Cells

The specification of hemogenic endothelial cells from embryonic vascular endothelium occurs during brief developmental periods within distinct tissues, and is necessary for the emergence of definitive HSPC from the murine extra embryonic yolk sac, placenta, umbilical vessels, and the embryonic aorta-gonad-mesonephros (AGM) region. The transient nature and small size of this cell population renders its reproducible isolation for careful quantification and experimental applications technically difficult. We have established a fluorescence-activated cell sorting (FACS)-based protocol for simultaneous isolation of hemogenic endothelial cells and HSPC during their peak generation times in the yolk sac and AGM. We demonstrate methods for dissection of yolk sac and AGM tissues from mouse embryos, and we present optimized tissue digestion and antibody conjugation conditions for maximal cell survival prior to identification and retrieval via FACS. Representative FACS analysis plots are shown that identify the hemogenic endothelial cell and HSPC phenotypes, and describe a methylcellulose-based assay for evaluating their blood forming potential on a clonal level.

Hematopoietic stem and progenitor cells (HSPC) derive from specialized (hemogenic) endothelial cells during development, yet little is known about the process by which some endothelial cells specify to become blood forming. We demonstrate a flow-cytometry based method allowing simultaneous isolation of hemogenic endothelial cells and HSPC from murine embryonic tissues.

The specification of hemogenic endothelial cells from embryonic vascular endothelium occurs during brief developmental periods within distinct tissues, ...

A Novel Mammary Fat Pad Transplantation Technique to Visualize the Vessel Generation of Vascular Endothelial Stem Cells

Endothelial cells (ECs) are the fundamental building blocks of the vascular architecture and mediate vascular growth and remodeling to ensure proper vessel development and homeostasis. However, studies on endothelial lineage hierarchy remain elusive due to the lack of tools to gain access as well as to directly evaluate their behavior in vivo. To address this shortcoming, a new tissue model to study angiogenesis using the mammary fat pad has been developed. The mammary gland develops mostly in the postnatal stages, including puberty and pregnancy, during which robust epithelium proliferation is accompanied by extensive vascular remodeling. Mammary fat pads provide space, matrix, and rich angiogenic stimuli from the growing mammary epithelium. Furthermore, mammary fat pads are located outside the peritoneal cavity, making them an easily accessible grafting site for assessing the angiogenic potential of exogenous cells. This work also describes an efficient tracing approach using fluorescent reporter mice to specifically label the targeted population of vascular endothelial stem cells (VESCs) in vivo. This lineage tracing method, coupled with subsequent tissue whole-mount microscopy, enable the direct visualization of targeted cells and their descendants, through which the proliferation capability can be quantified and the differentiation commitment can be fate-mapped. Using these methods, a population of bipotent protein C receptor (Procr) expressing VESCs has recently been identified in multiple vascular systems. Procr+ VESCs, giving rise to both new ECs and pericytes, actively contribute to angiogenesis during development, homeostasis, and injury repair. Overall, this manuscript describes a new mammary fat pad transplantation and in vivo lineage tracing techniques that can be used to evaluate the stem cell properties of VESCs.

This work demonstrates a novel approach to assess the proliferation, differentiation, and vessel-forming potential of vascular endothelial stem cells (VESCs) through mammary fat pad transplantation followed by whole-mount tissue preparation for microscopic observation. A lineage tracing strategy to investigate the behavior of VESCs in vivo is also presented.

Endothelial cells (ECs) are the fundamental building blocks of the vascular architecture and mediate vascular growth and remodeling to ensure proper ...

Isolation of Type I and Type II Pericytes from Mouse Skeletal Muscles

Pericytes are perivascular multipotent cells that show heterogeneity in different organs or even within the same tissue. In skeletal muscles, there are at least two pericyte subpopulations (called type I and type II), which express different molecular markers and have distinct differentiation capabilities. Using NG2-DsRed and Nestin-GFP double-transgenic mice, type I (NG2-DsRed+Nestin-GFP-) and type II (NG2-DsRed+Nestin-GFP+) pericytes have been successfully isolated. However, the availability of these double-transgenic mice prevents the widespread use of this purification method. This work describes an alternative protocol that allows for the easy and simultaneous isolation of type I and type II pericytes from skeletal muscles. This protocol utilizes the fluorescence-activated cell sorting (FACS) technique and targets PDGFR&#946;, rather than NG2, together with the Nestin-GFP signal. Following isolation, type I and type II pericytes show distinct morphologies. In addition, type I and type II pericytes isolated with this new method, like those isolated from the double-transgenic mice, are adipogenic and myogenic, respectively. These results suggest that this protocol can be used to isolate pericyte subpopulations from skeletal muscles and possibly from other tissues.

This work describes a FACS-based protocol that allows for easy and simultaneous isolation of type I and type II pericytes from skeletal muscles.

Pericytes are perivascular multipotent cells that show heterogeneity in different organs or even within the same tissue. In skeletal muscles, there are at ...

Clonal Analysis of Embryonic Hematopoietic Stem Cell Precursors Using Single Cell Index Sorting Combined with Endothelial Cell Niche Co-culture

The ability to study hematopoietic stem cell (HSC) genesis during embryonic development has been limited by the rarity of HSC precursors in the early embryo and the lack of assays that functionally identify the long-term multilineage engraftment potential of individual putative HSC precursors. Here, we describe methodology that enables the isolation and characterization of functionally validated HSC precursors at the single cell level. First, we utilize index sorting to catalog the precise phenotypic parameter of each individually sorted cell, using a combination of phenotypic markers to enrich for HSC precursors with additional markers for experimental analysis. Second, each index-sorted cell is co-cultured with vascular niche stroma from the aorta-gonad-mesonephros (AGM) region, which supports the maturation of non-engrafting HSC precursors to functional HSC with multilineage, long-term engraftment potential in transplantation assays. This methodology enables correlation of phenotypic properties of clonal hemogenic precursors with their functional engraftment potential or other properties such as transcriptional profile, providing a means for the detailed analysis of HSC precursor development at the single cell level.

Here we present methodology for the clonal analysis of hematopoietic stem cell precursors during murine embryonic development. We combine index sorting of single cells from the embryonic aorta-gonad-mesonephros region with endothelial cell co-culture and transplantation to characterize the phenotypic properties and engraftment potential of single hematopoietic precursors.

The ability to study hematopoietic stem cell (HSC) genesis during embryonic development has been limited by the rarity of HSC precursors in the early ...

Probing Cell Mechanics with Bead-Free Optical Tweezers in the Drosophila Embryo

Morphogenesis requires coordination between genetic patterning and mechanical forces to robustly shape the cells and tissues. Hence, a challenge to understand morphogenetic processes is to directly measure cellular forces and mechanical properties in vivo during embryogenesis. Here, we present a setup of optical tweezers coupled to a light sheet microscope, which allows to directly apply forces on cell-cell contacts of the early Drosophila embryo, while imaging at a speed of several frames per second. This technique has the advantage that it does not require the injection of beads into the embryo, usually used as intermediate probes on which optical forces are exerted. We detail step by step the implementation of the setup, and propose tools to extract mechanical information from the experiments. By monitoring the displacements of cell-cell contacts in real time, one can perform tension measurements and investigate cell contacts&#39; rheology.

Probing Cell Mechanics with Bead-Free Optical Tweezers in the Drosophila Embryo

We present a setup of optical tweezers coupled to a light sheet microscope, and its implementation to probe cell mechanics without beads in the Drosophila embryo.

Morphogenesis requires coordination between genetic patterning and mechanical forces to robustly shape the cells and tissues. Hence, a challenge to ...

Microfluidic Assay for the Assessment of Leukocyte Adhesion to Human Induced Pluripotent Stem Cell-derived Endothelial Cells (hiPSC-ECs)

Endothelial cells (ECs) are essential for the regulation of inflammatory responses by either limiting or facilitating leukocyte recruitment into affected tissues via a well-characterized cascade of pro-adhesive receptors which are upregulated on the leukocyte cell surface upon the inflammatory trigger. Inflammatory responses differ between individuals in the population and the genetic background can contribute to these differences. Human induced pluripotent stem cells (hiPSCs) have been shown to be a reliable source of ECs (hiPSC-ECs), thus representing an unlimited source of cells that capture the genetic identity and any genetic variants or mutations of the donor. hiPSC-ECs can therefore be used for modeling inflammatory responses in donor-specific cells. Inflammatory responses can be modeled by determining leukocyte adhesion to the hiPSC-ECs under physiological flow. This step-by-step protocol provides a detailed description of the experimental setup and data analysis for the assessment of inflammatory responses in hiPSC-ECs and the analysis of leukocyte adhesion under physiological flow.

Microfluidic Assay for the Assessment of Leukocyte Adhesion to Human Induced Pluripotent Stem Cell-derived Endothelial Cells hiPSC-ECs

This step-by-step protocol provides a detailed description of the experimental setup and data analysis for the assessment of inflammatory responses in hiPSC-ECs and the analysis of leukocyte adhesion under physiological flow.

Endothelial cells (ECs) are essential for the regulation of inflammatory responses by either limiting or facilitating leukocyte recruitment into affected ...

Efficient Differentiation of Human Pluripotent Stem Cells into Liver Cells

The liver detoxifies harmful substances, secretes vital proteins, and executes key metabolic activities, thus sustaining life. Consequently, liver failure&#8212;which can be caused by chronic alcohol intake, hepatitis, acute poisoning, or other insults&#8212;is a severe condition that can culminate in bleeding, jaundice, coma, and eventually death. However, approaches to treat liver failure, as well as studies of liver function and disease, have been stymied in part by the lack of a plentiful supply of human liver cells. To this end, this protocol details the efficient differentiation of human pluripotent stem cells (hPSCs) into hepatocyte-like cells, guided by a developmental roadmap that describes how liver fate is specified across six consecutive differentiation steps. By manipulating developmental signaling pathways to promote liver differentiation and to explicitly suppress the formation of unwanted cell fates, this method efficiently generates populations of human liver bud progenitors and hepatocyte-like cells by days 6 and 18 of PSC differentiation, respectively. This is achieved through the temporally-precise control of developmental signaling pathways, exerted by small molecules and growth factors in a serum-free culture medium. Differentiation in this system occurs in monolayers and yields hepatocyte-like cells that express characteristic hepatocyte enzymes and have the ability to engraft a mouse model of chronic liver failure. The ability to efficiently generate large numbers of human liver cells in vitro has ramifications for treatment of liver failure, for drug screening, and for mechanistic studies of liver disease.

This protocol details a monolayer, serum-free method to efficiently generate hepatocyte-like cells from human pluripotent stem cells (hPSCs) in 18 days. This entails six steps as hPSCs sequentially differentiate into intermediate cell-types such as the primitive streak, definitive endoderm, posterior foregut and liver bud progenitors before forming hepatocyte-like cells.

The liver detoxifies harmful substances, secretes vital proteins, and executes key metabolic activities, thus sustaining life. Consequently, liver ...

An In Vitro 3D Model and Computational Pipeline to Quantify the Vasculogenic Potential of iPSC-Derived Endothelial Progenitors

Induced pluripotent stem cells (iPSCs) are a patient-specific, proliferative cell source that can differentiate into any somatic cell type. Bipotent endothelial progenitors (EPs), which can differentiate into the cell types necessary to assemble mature, functional vasculature, have been derived from both embryonic and induced pluripotent stem cells. However, these cells have not been rigorously evaluated in three-dimensional environments, and a quantitative measure of their vasculogenic potential remains elusive. Here, the generation and isolation of iPSC-EPs via fluorescent-activated cell sorting are first outlined, followed by a description of the encapsulation and culture of iPSC-EPs in collagen hydrogels. This extracellular matrix (ECM)-mimicking microenvironment encourages a robust vasculogenic response; vascular networks form after a week of culture. The creation of a computational pipeline that utilizes open-source software to quantify this vasculogenic response is delineated. This pipeline is specifically designed to preserve the 3D architecture of the capillary plexus to robustly identify the number of branches, branching points, and the total network length with minimal user input.

Endothelial progenitors derived from induced pluripotent stem cells (iPSC-EPs) have the potential to revolutionize cardiovascular disease treatments and to enable the creation of more faithful cardiovascular disease models. Herein, the encapsulation of iPSC-EPs in three-dimensional (3D) collagen microenvironments and a quantitative analysis of these cells&#8217; vasculogenic potential are described.

Induced pluripotent stem cells (iPSCs) are a patient-specific, proliferative cell source that can differentiate into any somatic cell type. Bipotent ...

Three-dimensional Angiogenesis Assay System using Co-culture Spheroids Formed by Endothelial Colony Forming Cells and Mesenchymal Stem Cells

Studies in the field of angiogenesis have been aggressively growing in the last few decades with the recognition that angiogenesis is a hallmark of more than 50 different pathological conditions, such as rheumatoid arthritis, oculopathy, cardiovascular diseases, and tumor metastasis. During angiogenesis drug development, it is crucial to use in vitro assay systems with appropriate cell types and proper conditions to reflect the physiologic angiogenesis process. To overcome limitations of current in vitro angiogenesis assay systems using mainly endothelial cells, we developed a 3-dimensional (3D) co-culture spheroid sprouting assay system. Co-culture spheroids were produced by two human vascular cell precursors, endothelial colony forming cells (ECFCs) and mesenchymal stem cells (MSCs) with a ratio of 5 to 1. ECFCs+MSCs spheroids were embedded into type I collagen matrix to mimic the in vivo extracellular environment. A real-time cell recorder was utilized to continuously observe the progression of angiogenic sprouting from spheroids for 24 h. Live cell fluorescent labeling technique was also applied to tract the localization of each cell type during sprout formation. Angiogenic potential was quantified by counting the number of sprouts and measuring the cumulative length of sprouts generated from the individual spheroids. Five randomly-selected spheroids were analyzed per experimental group. Comparison experiments demonstrated that ECFCs+MSCs spheroids showed greater sprout number and cumulative sprout length compared with ECFCs-only spheroids. Bevacizumab, an FDA-approved angiogenesis inhibitor, was tested with the newly-developed co-culture spheroid assay system to verify its potential to screen anti-angiogenic drugs. The IC50 value for ECFCs+MSCs spheroids compared to the ECFCs-only spheroids was closer to the effective plasma concentration of bevacizumab obtained from the xenograft tumor mouse model. The present study suggests that the 3D ECFCs+MSCs spheroid angiogenesis assay system is relevant to physiologic angiogenesis, and can predict an effective plasma concentration in advance of animal experiments.

Three-dimensional co-culture spheroid angiogenesis assay system is designed to mimic the physiologic angiogenesis. Co-culture spheroids are formed by two human vascular cell precursors, ECFCs and MSCs, and embedded in collagen gel. The new system is effective for evaluating angiogenic modulators, and provides more relevant information to the in vivo study.

Studies in the field of angiogenesis have been aggressively growing in the last few decades with the recognition that angiogenesis is a hallmark of more ...