This work was supported by grants from the Nederlandse organisatie voor gezondheidsonderzoek en zorginnovatie (ZonMW 446002501), Health Holland (LSHM19057-H040), Leading Fellows Programme Marie Sk&#322;odowska-Curie COFUND, and by the Association Maladie de Rendu-Osler (AMRO).

1. Media preparation and culture of mESC
<ol>
	<li>Prepare conditioned medium +/- (CM+/-) using the supplement 1x Glasgow MEM (G-MEM BHK-21) medium with 10% (vol/vol) heat-inactivated Fetal Bovine Serum (FBS), 0.05 mM &#946;-mercaptoethanol, 1x non-essential amino acids (NEAA 1x), 2 mM L-glutamine, and 1 mM sodium pyruvate.</li>
	<li>Prepare conditioned medium +/+ (CM+/+) using the supplement CM+/- medium with Leukemia Inhibitory Factor (LIF) (1,500 U/mL) and 0.1 mM &#946;-mercaptoethanol.</li>
	<li>Prepare conditioned...

<ol>
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The authors have nothing to disclose.

This protocol describes an unbiased, robust, and reproducible 3D EB-based vascular sprouting assay that is amenable to screening for drugs and genes modulating angiogenesis. This method offers advantages over many widely used two dimensional (2D) assays using endothelial cell cultures such as Human Umbilical Vein Endothelial Cells (HUVECs) to monitor migration (lateral scratch assay or the Boyden chamber assay)22,23&#160;or proliferation (counting cell number, de...

In the past three decades, target-based drug discovery (TDD) has been widely employed in drug discovery by the pharmaceutical industry. TDD incorporates a defined molecular target playing an important role in a disease and relies on the development of relatively simple cell culture systems and readouts for drug screening1. Most typical disease models used in TDD programs include traditional cell culture methods such as cancer cells or immortalized cell lines grown within artificial environments and non-physiological substrates. Although many of these models have provided viable tools for identifying successful drug candidates, the use of such systems can be questionable owing to their poor disease relevance2.
For most diseases, the underlying mechanisms are indeed complex and various cell types, independent signaling pathways, and multiple sets of genes are often found to contribute to a specific disease phenotype. This is also true for inherited diseases where the primary cause is a mutation in one single gene. With the recent advent of human induced pluripotent stem cell (iPSC) technologies and gene editing tools, it is now possible to generate 3D organoids and organ-on-chip disease models that could better recapitulate the in vivo human complexity3,4. The development of such technologies is associated with a resurgence in interest in phenotypic drug discovery (PDD) programs1. PDD can be compared to empirical screening, as they do not rely on knowledge of the identity of a specific drug target or a hypothesis about its role in disease. The PDD approach is now increasingly recognized to strongly contribute to the discovery of first-in-class drugs5. Because the development of human organoid and organ-on-chip technologies is still in its infancy, it is expected that iPSC models (complemented with innovative imaging and machine-learning tools6,7) will provide, in the near future, multiple novel complex cell-based disease models for drug screening and associated PDD programs to overcome the poor productivity of the TDD approach8,9.
While human organoid and organ-on-chip models can provide important insights into disease complexity and to the identification of novel drugs, bringing drugs into new clinical practice also strongly relies on data from animal models to assess their efficacy and safety. Among them, genetically modified mice are certainly the most preferred mammalian models. They have many advantages as they have a relatively short generation time for mammals, have many similar phenotypes to human diseases, and can be easily genetically manipulated. They are therefore extensively used in drug discovery programs10. However, bridging the gap between mice and humans remains an important challenge11. The development of in vitro mouse models equivalent to human organoid and organ-on-chip models could at least partially fill this gap as it will allow direct drug efficacy and safety comparisons between in vivo mouse and in vitro human data.
Here, a vascular sprouting assay in mouse embryoid bodies (EBs) is described. Blood vessels are composed of endothelial cells (inner lining of vessel walls), mural cells (vascular smooth muscle cells&#160;and pericytes)12. This protocol is based on the differentiation of mouse embryonic stem cells (mESCs) into vascularized EBs using hanging droplets that recapitulate de novo endothelial cell and mural cell differentiation13,14. Mouse ESCs can be easily established in culture from isolated day 3.5 mouse blastocysts having different genetic backgrounds15. They also provide possibilities for clonal analysis, lineage tracing, and can be easily genetically manipulated to generate disease models13,16.
As blood vessels nourish all organs, it is not surprising that many diseases if not all, are associated with changes in the microvasculature. In pathological conditions, endothelial cells can adopt an activated state or can become dysfunctional resulting in mural cell death or migration away from blood vessels. These can result in excessive angiogenesis or in vessel rarefaction, can induce abnormal blood flow and defective blood vessel barrier leading to immune cell extravasation, and inflammation12,17,18,19. Research for the development of drugs modulating blood vessels is, therefore&#160;high, and multiple molecular players and concepts have already been identified for therapeutic targeting. In this context, the protocol described is particularly suitable for building disease models and for drug testing as it recapitulates key features of in vivo sprouting angiogenesis, including endothelial tip and stalk cell selection, endothelial cell migration and proliferation, endothelial cell guidance, tube formation, and mural cell recruitment. It also shows similarities with recently described 3D vascular assays based on human iPSC technologies20.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2-mercaptoethanol</td>
			<td>Milipore, Merck</td>
			<td>805740</td>
			<td>Biohazard: adequate safety instructions should be taken when handling</td>
		</tr>
		<tr>
			<td>Agar Noble</td>
			<td>Difco, BD Pharmigen</td>
			<td>214220</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluo 555 goat anti rat IgG</td>
			<td>Life technologies</td>
			<td>A21434</td>
			<td></td>
		</tr>
		<tr>
			<td>APC conjugated rat anti-mouse PECAM-1 antibody (clone MEC13.3)</td>
			<td>BD Biosciences</td>
			<td>551262</td>
			<td></td>
		</tr>
		<tr>
			<td>APC Rat IgG2a &#954; Isotype Control (Clone&#160; R35-95)</td>
			<td>BD Biosciences</td>
			<td>553932</td>
			<td></td>
		</tr>
		<tr>
			<td>Axiovert 25 inverted phase contrast tissue culture microscope</td>
			<td>ZEISS</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Basic Fibroblast Growth Factor-2 (bFGF)</td>
			<td>Peprotech</td>
			<td>450-33</td>
			<td></td>
		</tr>
		<tr>
			<td>Benchtop Centrifuge, Allegra X-15R</td>
			<td>Beckman Coulter</td>
			<td>392932</td>
			<td></td>
		</tr>
		<tr>
			<td>Biosafety cabinet BioVanguard (Green Line)</td>
			<td>Telstar</td>
			<td>133H401001</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>Sigma-Aldrich</td>
			<td>A9418</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell counting chamber, Buerker, 0.100mm</td>
			<td>Marienfeld</td>
			<td>640211</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell culture dishes 60 x 15mm</td>
			<td>Corning</td>
			<td>353802</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell culture dishes, 35 x 10 mm</td>
			<td>Corning</td>
			<td>353801</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell culture plates 12-well</td>
			<td>Corning</td>
			<td>3512</td>
			<td></td>
		</tr>
		<tr>
			<td>CFX96 Touch Real-Time PCR Detection System</td>
			<td>Biorad</td>
			<td>1855196</td>
			<td></td>
		</tr>
		<tr>
			<td>Chicken serum</td>
			<td>Sigma-Aldrich</td>
			<td>C5405</td>
			<td></td>
		</tr>
		<tr>
			<td>CHIR-99021 (CT99021) HCl</td>
			<td>Selleckchem</td>
			<td>S2924</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagen I, High Concentration, Rat Tail, 100mg</td>
			<td>Corning</td>
			<td>354249</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase A</td>
			<td>Roche</td>
			<td>10103586001</td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal Laser Scanning Microscope, TCS SP5</td>
			<td>Leica</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cover glasses, 24 &#215; 50 mm</td>
			<td>Vwr</td>
			<td>631-0146</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPT &#947;&#8209;secretase inhibitor</td>
			<td>Sigma Aldrich</td>
			<td>D5942</td>
			<td></td>
		</tr>
		<tr>
			<td>DC101 anti mouse VEGFR-2 Clone</td>
			<td>BioXcell</td>
			<td>BP0060</td>
			<td></td>
		</tr>
		<tr>
			<td>DC101 isotype rat IgG1</td>
			<td>BioXcell</td>
			<td>BP0290</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide (DMSO)</td>
			<td>Sigma-Aldrich</td>
			<td>D2438-5X</td>
			<td>Biohazard: adequate safety instructions should be taken when handling</td>
		</tr>
		<tr>
			<td>DPBS (10x), no calcium, no magnesium</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>14200067</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA 40 mM</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>15575-038</td>
			<td></td>
		</tr>
		<tr>
			<td>Embryonic stem-cell Fetal Bovine Serum</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>16141-079</td>
			<td>Should be lot-tested for maximum ES cell viability and growth. Heat inactivate at 60&#176;C and store at &#8722;20 &#176;C for up to 1 year</td>
		</tr>
		<tr>
			<td>Eppendorf Microcentrifuge 5415R</td>
			<td>Eppendorf AG</td>
			<td>&#160;Z605212</td>
			<td></td>
		</tr>
		<tr>
			<td>Erythropoietin, human (hEPO), 250 U (2.5 &#181;g) (1 mL)</td>
			<td>Roche</td>
			<td>11120166001</td>
			<td></td>
		</tr>
		<tr>
			<td>ESGRO Recombinant Mouse LIF Protein (10&#8311; units&#160;&#160;1 mL)</td>
			<td>Milipore, Merck</td>
			<td>ESG1107</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon tubes 15 mL</td>
			<td>Greiner Bio-One</td>
			<td>188271</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon tubes 50 mL</td>
			<td>Greiner Bio-0ne</td>
			<td>227270</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter tip ,clear ,sterile F.Gilson, P-200</td>
			<td>Greiner Bio-One</td>
			<td>739288</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter tip ,clear ,sterile F.Gilson, P10</td>
			<td>Greiner Bio-One</td>
			<td>771288</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter tip ,clear ,sterile F.Gilson, P1000</td>
			<td>Greiner Bio-One</td>
			<td>740288</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC conjugated anti-&#945; Smooth Muscle Actin (SMA) (clone 1A4)</td>
			<td>Sigma Aldrich</td>
			<td>F3777</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC conjugated rat anti-mouse CD45 (clone 30-F11)</td>
			<td>Biolegend</td>
			<td>103107</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC Rat IgG2b, &#954; Isotype Ctrl Antibody (clone RTK4530)</td>
			<td>Biolegend</td>
			<td>400605</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorscent mounting media</td>
			<td>DAKO</td>
			<td>S3023</td>
			<td></td>
		</tr>
		<tr>
			<td>Gascompress</td>
			<td>Cutisoft</td>
			<td>45846</td>
			<td></td>
		</tr>
		<tr>
			<td>Gauze Cutisoft 10 x 10 cm</td>
			<td>Bsn Medical</td>
			<td>45844_00</td>
			<td></td>
		</tr>
		<tr>
			<td>Gel blotting paper, Grade GB003</td>
			<td>Whatman</td>
			<td>WHA10547922</td>
			<td></td>
		</tr>
		<tr>
			<td>Gelatin solution, type B</td>
			<td>Sigma-Aldrich</td>
			<td>G1393-100 ml</td>
			<td></td>
		</tr>
		<tr>
			<td>Glasgow&#39;s MEM (GMEM)</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>21710082</td>
			<td></td>
		</tr>
		<tr>
			<td>IHC Zinc Fixative</td>
			<td>BD Pharmigen</td>
			<td>550523</td>
			<td></td>
		</tr>
		<tr>
			<td>IncuSafe CO2 Incubator</td>
			<td>PHCBi</td>
			<td>MCO-170AICUV-PE</td>
			<td></td>
		</tr>
		<tr>
			<td>Interleukin-6, human (hIL-6)</td>
			<td>Roche</td>
			<td>11138600001</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Glutamine 200 mM</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>25030-024</td>
			<td></td>
		</tr>
		<tr>
			<td>MEM Non-Essential Amino Acids Solution (100x)</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>11140035</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope slide box</td>
			<td>Kartell Labware</td>
			<td>278</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope slide, Starfrost</td>
			<td>Knittel glass</td>
			<td>VS113711FKB.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Cdh5_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00110467</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Eng_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00148981</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Epha4_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00093576</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Ephb2_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00154014</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Flt1_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00096292</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Flt4_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00099064</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Gapdh_3_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT01658692</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Kdr_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00097020</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Notch1_1_SG QuantiTect Primer</td>
			<td>Qiagen</td>
			<td>QT00156982</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Nr2f2_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00153104</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Pecam1_1_SG QuantiTect Primer</td>
			<td>Qiagen</td>
			<td>QT01052044</td>
			<td></td>
		</tr>
		<tr>
			<td>Mm_Tek_1_SG QuantiTect Primer Assay</td>
			<td>Qiagen</td>
			<td>QT00114576</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse (ICR) Inactivated Embryonic Fibroblasts&#160; (2 M)</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>A24903</td>
			<td>Store vials in liquid nitrogen (195.79 &#176;C) indefinitely</td>
		</tr>
		<tr>
			<td>Mouse embryonic stem cell line 7AC5/EYFP (ATCC SCRC-1033)</td>
			<td>ATCC</td>
			<td>SCRC-1033</td>
			<td>Generated by Dr A Nagy, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Ave, Toronto, Ontario, M5G 1X5, Canada. [Hadjantonakis, A. K., et al. Mechanisms of Development. 76 (1&#8211;2), 79&#8211;90 (1998)].</td>
		</tr>
		<tr>
			<td>Mouse embryonic stem cell lines Acvrl1 +/- and Acvrl1 +/+</td>
			<td></td>
			<td></td>
			<td>Generated at Leiden University Medical Centre [Thalgott, J.H. et al. Circulation. 138 (23), 2698&#8211;2712 (2018)].</td>
		</tr>
		<tr>
			<td>Mouse embryonic stem cells line E14</td>
			<td></td>
			<td></td>
			<td>Provided by M Letarte laboratory and generated according to Cho, S. K., et al. Blood. 98 (13), 3635&#8211;3642 (2001).</td>
		</tr>
		<tr>
			<td>Mouse embryonic stem cells line R1 (ATCC SCRC-1011)</td>
			<td>ATCC</td>
			<td>SCRC-1011</td>
			<td>Generated by Dr A Nagy, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Ave, Toronto, Ontario, M5G 1X5, Canada. [Nagy, A., et al. Procedings of the National Academy of Sciences of the United States of America. 90 (18), 8424&#8211;8428 (1993)].</td>
		</tr>
		<tr>
			<td>Mouse embryonic stem cells line Z/Red (strain 129/Ola)</td>
			<td></td>
			<td></td>
			<td>Generated by Dr A Nagy, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Ave, Toronto, Ontario, M5G 1X5, Canada [Vintersten, K., et al. Genesis. 40 (4), 241&#8211;246 (2004)].</td>
		</tr>
		<tr>
			<td>NanoDrop 1000 UV/VIS Spectrophotometer</td>
			<td>Thermo Fischer Scientific</td>
			<td>ND-1000</td>
			<td></td>
		</tr>
		<tr>
			<td>PD0325901</td>
			<td>Selleckchem</td>
			<td>S1036</td>
			<td></td>
		</tr>
		<tr>
			<td>PDGF-BB, Recombinant Human</td>
			<td>Peprotech</td>
			<td>100-14B</td>
			<td></td>
		</tr>
		<tr>
			<td>Pecam-1 antibody, Rat Anti-Mouse</td>
			<td>BD Biosciences</td>
			<td>550274</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-streptomycin (10,000 U/mL)</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri dish, PS, 94/16 mm, standard ,with vents, sterile</td>
			<td>Greiner Bio-One</td>
			<td>633181</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipetboy acu 2</td>
			<td>Integra-Biosciences</td>
			<td>155 019</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipetman G Multichannel P8 x 200G</td>
			<td>Gilson</td>
			<td>F144072</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipetman G Starter Kit, 4 Pipette Kit, P2G, P20G, P200G, P1000G</td>
			<td>Gilson</td>
			<td>F167360</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Human BMP-4 Protein</td>
			<td>R&#38;D Systems</td>
			<td>314-BP</td>
			<td></td>
		</tr>
		<tr>
			<td>RNeasy Plus mini Kit</td>
			<td>QIAGEN</td>
			<td>74134</td>
			<td></td>
		</tr>
		<tr>
			<td>Serological pipettes, 10 mL</td>
			<td>Greiner Bio-One</td>
			<td>607 180</td>
			<td></td>
		</tr>
		<tr>
			<td>Serological pipettes, 25 mL</td>
			<td>Greiner Bio-One</td>
			<td>760 180</td>
			<td></td>
		</tr>
		<tr>
			<td>Serological pipettes, 5 mL</td>
			<td>Greiner Bio-One</td>
			<td>606 180</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide (NaOH)</td>
			<td>Merck</td>
			<td>106498</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyruvate 100 mM</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>11360039</td>
			<td></td>
		</tr>
		<tr>
			<td>Test tubes 5ml round-bottom with cell-strainer cap</td>
			<td>Corning</td>
			<td>352235</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermal cycler, T100</td>
			<td>Biorad</td>
			<td>1861096</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100 (BioXtra)</td>
			<td>Sigma Aldrich</td>
			<td>T9284</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan Blue Solution, 0.4%</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>15250061</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin (2.5%)</td>
			<td>Gibco, Thermofisher scientific</td>
			<td>15090046</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum Filter/Storage Bottle System, 500 mL</td>
			<td>Corning</td>
			<td>430758</td>
			<td></td>
		</tr>
		<tr>
			<td>VEGFA165 , recombinant murine</td>
			<td>Peprotech</td>
			<td>450-32</td>
			<td></td>
		</tr>
		<tr>
			<td>Water, Sterile</td>
			<td>Fresenius-Kabi</td>
			<td>B230531</td>
			<td></td>
		</tr>
		<tr>
			<td>Waterbath, Lab-Line Digital</td>
			<td>Thermo Fischer Scientific</td>
			<td>18052A</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vitro three-dimensional sprouting assay of angiogenesis using mouse embryonic stem cells for vascular disease modeling and drug testing

Recent advances in induced pluripotent stem cells (iPSC) and gene editing technologies enable the development of novel human cell-based disease models for phenotypic drug discovery (PDD) programs. Although these novel devices could predict the safety and efficacy of investigational drugs in humans more accurately, their development to the clinic still strongly rely on mammalian data, notably the use of mouse disease models. In parallel to human organoid or organ-on-chip disease models, the development of relevant in vitro mouse models is therefore an unmet need for evaluating direct drug efficacy and safety comparisons between species and in vivo and in vitro conditions. Here, a vascular sprouting assay that utilizes mouse embryonic stem cells differentiated into embryoid bodies (EBs) is described. Vascularized EBs cultured onto 3D-collagen gel develop new blood vessels that expand, a process called sprouting angiogenesis. This model recapitulates key features of in vivo sprouting angiogenesis-formation of blood vessels from a pre-existing vascular network-including endothelial tip cell selection, endothelial cell migration and proliferation, cell guidance, tube formation, and mural cell recruitment. It is amenable to screening for drugs and genes modulating angiogenesis and shows similarities with recently described three-dimensional (3D) vascular assays based on human iPSC technologies.

The protocol overview of the blood vessel sprouting assay is shown in Figure 1. Nine-day-old EBs derived from three independent 129/Ola mESC lines (Z/Red, R1, and E14) were enzymatically dissociated into single cells using collagenase A. Cells were stained for PECAM-1 and analyzed by Fluorescence-activated cell sorting (FACS) as described. All the cell lines exhibited robust endothelial differentiation, and no differences in their ability to differentiate into endothelial cells were observed...

Watch this Scientific Journal Video about In Vitro Three-Dimensional Sprouting Assay of Angiogenesis Using Mouse Embryonic Stem Cells for Vascular Disease Modeling and Drug Testing at JoVE.com

In Vitro Three-Dimensional Sprouting Assay of Angiogenesis Using Mouse Embryonic Stem Cells for Vascular Disease Modeling and Drug Testing

This assay utilizes mouse embryonic stem cells differentiated into embryoid bodies cultured in 3D-collagen gel to analyze the biological processes that control sprouting angiogenesis in vitro. The technique can be applied for testing drugs, modeling diseases, and for studying specific genes in the context of deletions that are embryonically lethal.

In Vitro Three-Dimensional Sprouting Assay of Angiogenesis Using Mouse Embryonic Stem Cells for Vascular Disease Modeling and Drug Testing

Recent advances in induced pluripotent stem cells (iPSC) and gene editing technologies enable the development of novel human cell-based disease models for ...

This protocol describes an in vitro sprouting angiogenesis assay that recapitulates many features of the formation of blood vessels and can be used for testing drugs. This method is easy to implement in a lab, robust, and scalable. It has many similarities with assays using human endothelial cells and microspheres.This model robustly mimics the phenotype showing defective endothelial tip cell selection and orientated endothelial cell migration that leads to pathological angiogenesis. The work can provide insights into the mechanisms regulating sprouting angiogenesis, the key genes, and the signaling pathways involved, notably by performing genetic screening The main challenge is maintaining the quality or pluripotency of mouse embryonic stem cells in culture. Regularly checking the pluripotency stages and morphology of the cell lines is important.It is also important to perform a karyotyping of the cell lines as they tend to culture to lose or gain chromosomes. Begin by coating one well of the six well cell culture plate with 500 microliters of 0.1%gelatin solution and place it in a carbon dioxide incubator for 30 minutes. Then wash the gelatin coated plates with PBS and add 500 microliters of freshly prepared CM plus minus medium.To obtain a pure population of mouse embryonic stem cells or mESCs, trypsinize the cell culture plate with 10x TVP buffer for 30 seconds at room temperature. Then resuspend the cells in one milliliter of mesoderm differentiation medium before transferring them to the gelatin coated six well plate for 30 minutes to allow the mouse embryonic fibroblasts to attach while the mESCs stay in suspension. Transfer the cell suspension to a 15 milliliter tube before counting live cells using a Neubauer hemocytometer in Trypan blue dye.Then centrifuge the cells at 200 times G for five minutes at room temperature. Remove the supernatant and resuspend the cell pellet in an appropriate volume of mesoderm differentiation medium. Prepare four 94 millimeter low attachment polystyrene dishes by adding 15 milliliters of sterile water to the bottom.After transferring the cell suspension into a sterile plastic reservoir, load four positions of a multi-channel pipette with 22 microliters of cell suspension per channel. Lift and place the inverted lid of the 94 millimeter dish on the clean surface of the flow cabinet with the inner side facing upwards. Deposit 40 drops of the cell suspension on the inner surface of each lid and carefully invert the lid without disturbance to place it back on the dish, so that the drops face the water.Incubate the dishes in a carbon dioxide incubator for four days, considering this as differentiation day zero. After four days of incubation, collect the hanging drops in a 15 milliliter conical tube using a P1000 pipette. Let EB sediment in the tube before removing the supernatant.Resuspend the EBs in three milliliters of 2x vascular differentiation medium before transferring and uniformly distributing EB suspension in a 60 millimeter agar-coated dish. Incubate the dishes in a carbon dioxide incubator until day nine with a medium refresh every two days. Prepare a 35 millimeter culture dish by adding one milliliter of the sprouting medium to its bottom.To induce gelation, incubate the dish at 37 degrees Celsius for five minutes. Collect nine day old EBs from one agar dish in a 15 milliliter conical tube and remove the supernatant. Resuspend the EBs in two milliliters of cold sprouting medium to transfer to the culture dish coated with the first layer of sprouting medium.Distribute the EBs all over the plate, ensuring they are at an equal distance from each other. The first sprout formation should be evident after incubation for around 24 to 48 hours. On day 12, use a spatula to carefully transfer the collagen gel containing EBs to a glass slide.Remove the excess liquid with a pipette and dehydrate the gel by placing a gauze sheet of nylon linen and absorbent filter cards on top of the gel. Apply pressure with a weight of 250 grams for two minutes. Then remove the nylon papers to allow the slides to air dry for 30 minutes at room temperature.After drying, fix the EBs using zinc solution overnight at four degrees Celsius. On the next day, remove the fixative before washing the slides five times with PBS. Permeabilize the EBs and PBS containing 0.1%Triton X-100.After 15 minutes, remove the permeabilization solution to wash the slides five times with PBS for five minutes. Incubate the EBs in the blocking buffer for one hour at room temperature and wash with PBS for five minutes. Then add the primary antibody diluted in the blocking buffer and incubate at four degrees Celsius overnight.Then incubate the slides with Goat anti-Rat Alexa 555 secondary antibody in a blocking buffer for two hours at room temperature. After incubation, wash the slides three times with PBS for five minutes and one time with water before mounting them for microscopy. The 3D sprouting angiogenesis assay was carried out on three EBs with two drugs, DC101 and DAPT.Both compounds progressively blocked the angiogenesis in the EB model with increasing concentrations. The various concentrations of drugs in EBs showed that high doses of DC101 inhibit the number and length of the vessel sprouts. DAPT had opposite effects at the dose of one micromole per liter.DAPT strongly increased the number of endothelial tip cells per vessel sprouts having a misguidance phenotype even at low doses, compared to DC101. Defective vessel sprouting was observed in hereditary hemorrhagic telangiectasia EBs from ACVRL1 control and ACVRL1 heterozygous genotypes with numerous misguidance phenotypes sprouting at random angles relative to the parent vessels. Mixtures of a wild-type mESC line at a one-to-one ratio with an unlabeled mESC wild-type line, led to an equal contribution to the leading endothelial tip cells.Microscopic analysis of this representative chimeric EB was conducted to identify the genotypic origin of the leading endothelial tip cells. To quantify mural cell coverage of the vessel sprout, EBs were fixed and stained for endothelial cell markers, PECAM, and mural cell marker, alpha smooth muscle actin. A high magnification image revealed that one individual vessel sprout was surrounded by mural cells.The binary transformation was performed after color channel separation and the ratio of PECAM positive vessels covered by alpha SMA positive mural cells was quantified. The genetic background of the embryonic stem cell line is also a key factor the researchers must consider as some lines sprout better than others. This method can be used to perform genetic screening using RNAi approaches or a bank of mouse embryonic stem cells harboring gene mutations.

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2.6K Views.  Leiden University Medical Center. This protocol describes an in vitro sprouting angiogenesis assay that recapitulates many features of the formation of blood vessels and can be used for testing drugs. This method is easy to implement in a lab, robust, and scalable. It has many similarities with assays using human endothelial cells and microspheres.This model robustly mimics the phenotype showing defective endothelial tip cell selection and orientated endothelial cell migration that leads to pathological angiogenesis. T...