The authors would like to thank Nora Lakes for proofreading. Research reported in this manuscript was supported by the National Heart, Lung, and Blood Institute, under Award Number R01 HL117952 (E.B.), part of the National Institutes of Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Venous+malformation:+update+on+aetiopathogenesis,+diagnosis+and+management.">Venous malformation: update on aetiopathogenesis, diagnosis and management.</a> Phlebology: The Journal of Venous Disease. 25 (5), 224-235 (2010).</li><li>Limaye, N., 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=Somatic+mutations+in+angiopoietin+receptor+gene+TEK+cause+solitary+and+multiple+sporadic+venous+malformations.">Somatic mutations in angiopoietin receptor gene TEK cause solitary and multiple sporadic venous malformations.</a> Nature Genetics. 41 (1), 118-124 (2009).</li><li>Castel, P., 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=Somatic+PIK3CA+mutations+as+a+driver+of+sporadic+venous+malformations.">Somatic PIK3CA mutations as a driver of sporadic venous malformations.</a> Science Translational Medicine. 8 (332), 42 (2016).</li><li>Limaye, N., 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=Somatic+Activating+PIK3CA+Mutations+Cause+Venous+Malformation.">Somatic Activating PIK3CA Mutations Cause Venous Malformation.</a> The American Journal of Human Genetics. 97 (6), 914-921 (2015).</li><li>Castillo, S. D., 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=Somatic+activating+mutations+in+Pik3ca+cause+sporadic+venous+malformations+in+mice+and+humans.">Somatic activating mutations in Pik3ca cause sporadic venous malformations in mice and humans.</a> Science Translational Medicine. 8 (332), 43 (2016).</li><li>Stratman, A. N., 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=Endothelial+cell+lumen+and+vascular+guidance+tunnel+formation+requires+MT1-MMP-dependent+proteolysis+in+3-dimensional+collagen+matrices.">Endothelial cell lumen and vascular guidance tunnel formation requires MT1-MMP-dependent proteolysis in 3-dimensional collagen matrices.</a> Blood. 114 (2), 237-247 (2009).</li><li>Okada, S., Vaeteewoottacharn, K., Kariya, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+Highly+Immunocompromised+Mice+for+the+Establishment+of+Patient-Derived+Xenograft+(PDX)+Models.">Application of Highly Immunocompromised Mice for the Establishment of Patient-Derived Xenograft (PDX) Models.</a> Cells. 8 (8), 889 (2019).</li><li>Byrne, A. T., 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=Interrogating+open+issues+in+cancer+precision+medicine+with+patient-derived+xenografts.">Interrogating open issues in cancer precision medicine with patient-derived xenografts.</a> Nature Reviews Cancer. 17 (4), 254-268 (2017).</li><li>Allen, P., Melero-Martin, J., Bischoff, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Type+I+collagen,+fibrin+and+PuraMatrix+matrices+provide+permissive+environments+for+human+endothelial+and+mesenchymal+progenitor+cells+to+form+neovascular+networks.">Type I collagen, fibrin and PuraMatrix matrices provide permissive environments for human endothelial and mesenchymal progenitor cells to form neovascular networks.</a> Journal of Tissue Engineering and Regenerative Medicine. 5 (4), 74 (2011).</li><li>Allen, P., Kang, K. T., Bischoff, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+onset+of+perfused+blood+vessels+after+implantation+of+ECFCs+and+MPCs+in+collagen,+PuraMatrix+and+fibrin+provisional+matrices.">Rapid onset of perfused blood vessels after implantation of ECFCs and MPCs in collagen, PuraMatrix and fibrin provisional matrices.</a> Journal of Tissue Engineering and Regenerative. 9 (5), 632-636 (2015).</li><li>Nowak-Sliwinska, P., 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=Consensus+guidelines+for+the+use+and+interpretation+of+angiogenesis+assays.">Consensus guidelines for the use and interpretation of angiogenesis assays.</a> Angiogenesis. 21 (3), 425 (2018).</li><li>Roh, Y. N., 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=The+results+of+surgical+treatment+for+patients+with+venous+malformations.">The results of surgical treatment for patients with venous malformations.</a> Annals of Vascular Surgery. 26 (5), 665-673 (2012).</li><li>Marler, J. J., Mulliken, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+management+of+hemangiomas+and+vascular+malformations.">Current management of hemangiomas and vascular malformations.</a> Clinics in Plastic Surgery. 32 (1), 99-116 (2005).</li><li>Goines, J., 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=A+xenograft+model+for+venous+malformation.">A xenograft model for venous malformation.</a> Angiogenesis. 21 (4), 725-735 (2018).</li><li>Li, X., 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=Ponatinib+Combined+With+Rapamycin+Causes+Regression+of+Murine+Venous+Malformation.">Ponatinib Combined With Rapamycin Causes Regression of Murine Venous Malformation.</a> Arteriosclerosis, thrombosis, and vascular biology. 39 (3), 496-512 (2019).</li><li>Le Cras, T. D., 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=Constitutively+active+PIK3CA+mutations+are+expressed+by+lymphatic+and+vascular+endothelial+cells+in+capillary+lymphatic+venous+malformation.">Constitutively active PIK3CA mutations are expressed by lymphatic and vascular endothelial cells in capillary lymphatic venous malformation.</a> Angiogenesis. , 1-18 (2020).</li><li>Boscolo, E., 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=Rapamycin+improves+TIE2-mutated+venous+malformation+in+murine+model+and+human+subjects.">Rapamycin improves TIE2-mutated venous malformation in murine model and human subjects.</a> Journal of Clinical Investigation. 125 (9), 3491-3504 (2015).</li></ol>

The authors have no conflicts-of-interests to disclose.

Here, we describe a method to generate a patient-derived xenograft model of VM. This murine model presents an excellent system that allows researchers to gain a deeper understanding of pathological lumen enlargement and will be instrumental in developing more effective and targeted therapies for the treatment of VM. This can be easily adapted to investigate other types of vascular anomalies such as capillary lymphatic venous malformation16. There are several steps that are crucial for the successful generation of reproducible vascular lesions. First, the patient-derived endothelial cells must be pure (without the presence of other cell types) and growing exponentially at the time of injection. Contaminating fibroblast or other mesenchymal non-EC can be easily recognized by elongated morphology. On rare occasion, it is possible that even after purification using anti-CD31 antibody conjugated magnetic beads, a small number of non-EC remain in the culture. These cultures require further purification with endothelial specific cell surface markers. As an alternative approach, single cell clonal expansion of endothelial cells is possible. This would reinsure the homogeneity of mutant-EC as all of the cells within one culture would derive from one single cell. However, this approach is not recommended for VM-derived EC as cells tend to top their proliferation capabilities and convert into a senescent phenotype after 9&#8210;10 passages. It is critical to use cells between passages 3&#8210;8 for xenograft experiments and to not passage cells the day before the injection.
The xenograft model can be modified to investigate other vascular anomalies carrying different activating mutations. Moreover, as patient tissue samples are difficult to access for some laboratories, the xenograft model can be adapted by using EC, such as human umbilical cord blood endothelial cells (HUVEC), genetically engineered to express the mutation/s known to cause dysfunctional vascular growth15,17.
The number of cells recommended for the injection in the xenograft is 2.5 x 106 cells/200 &#181;L of BMEM. However, if the cell number is insufficient it is possible to either reduce the number of injections per animal to one or to reduce the injection volume to a minimum of 100 &#181;L. For the latter, it is however important to maintain the cell density ratio e.g., 1.25 x 106 cells/100 &#181;L BMEM. When working with BMEM, all the steps must be performed on ice to avoid solidification of the cell suspension before injection. During injection, it is important and that the needle is inserted at an angle of 45&#176; directly under the skin and away from the muscle tissue, as injecting into muscle impedes lesion reproducibility and makes the lesion dissection difficult. A total of two injections can be performed on each mouse&#8212;one on the right and one on the left side of each animal. The second injection in the same mouse can serve as a technical replicate. More injections on the back are not recommended as lesions grow over time and might interfere with each other. For statistical analysis in pre-clinical studies comparing xenograft plugs of treated versus untreated (vehicle only) mice, we recommend the use of a minimum of 5 animals (10 xenograft plugs) per study group. If available, the second injection could alternatively be used as a &#8216;internal control&#8217; using non-mutant EC. We have used primary non-mutant EC, such as HUVEC, as a control and have shown that these cells formed a negligible number of small channels14,15. Furthermore, in these HUVEC control lesion plugs, we have noticed infiltration of murine-derived vascular channels into the plug after day 9. If the experimental design requires longer incubation times, these infiltrating channels can be easily excluded from analysis by staining for a human-specific marker such as human-specific CD31 antibody or Ulex europaeus agglutinin I (UEA-I) that does not cross react with mouse.
To ensure that the lesion does not become a burden to animal health and wellbeing it is important to observe lesion size, record mouse weight daily, and pay attention to any side complications such as bleeding and bruising. If the lesion volume exceeds 500 mm3, the experiment has to be terminated.
When vascular lesions are enlarged and perfused, extreme attention must be paid during dissection to avoid rupturing the lesion. It is important to avoid touching the lesion plug with dissection tools and leave excessive surrounding tissue (such as skin) attached to the plug. This prevents collapse of the vascular structures within the xenograft plug which would interfere with accurate analysis.
Finally, to maintain consistency, it is important that the initial histological analysis begins in the center of the plug (about 50&#8210;70 &#181;m into the tissue) rather than the border regions where anastomosing mouse vasculature might be present. It is highly recommended to stain the tissue sections with a human-specific EC marker, such as UEA-I&#160;or an alternative human-specific antibody which will not cross-react with mouse, in order to confirm that vascular structures are formed by human-derived EC rather than invading mouse EC.

Defects in the development of the vasculature are the underlying cause of many diseases including venous malformation (VM). VM is a congenital disease characterized by abnormal morphogenesis and expansion of veins1. Important studies on VM tissue and endothelial cells (EC) have identified gain-of-function mutations in two genes: TEK, which encodes the tyrosine kinase receptor TIE2, and PIK3CA, which encodes the p110&#945; (catalytic subunit) isoform of PI3-kinase (PI3K)2,3,4,5. These somatic mutations result in ligand-independent hyper-activation of key angiogenic/growth signaling pathways, including PI3K/AKT, thereby resulting in dilated ectatic veins3. Despite these important genetic discoveries, the subsequent cellular and molecular mechanisms triggering abnormal angiogenesis and the formation of enlarged vascular channels are still not fully understood.
During normal and pathological angiogenesis, new vessels sprout from a pre-existing vascular network and EC undergo a sequence of important cellular processes including proliferation, migration, extracellular matrix (ECM) remodeling and lumen formation6. Two- and three- dimensional (2D/3D) in vitro cultures of EC are important tools to investigate each of these cellular properties individually. Nevertheless, there is a clear demand for a mouse model recapitulating pathological vessel enlargement within the host microenvironment while providing an efficient platform for preclinical evaluation of targeted drugs for translational research.
Up to date, a transgenic murine model of VM associated with TIE2 gain-of-function mutations has not been reported. Current transgenic VM mouse models rely on the ubiquitous or tissue-restricted expression of the activating mutation PIK3CA p.H1047R3,5. These transgenic animals provide significant insight into whole-body or tissue-specific effects of this hotspot PIK3CA mutation. The limitation of these models is the formation of a highly pathological vascular network resulting in early lethality. Thus, these mouse models do not fully reflect the sporadic occurrence of mutational events and localized nature of VM pathology.
On the contrary, patient-derived xenograft models are based on the transplantation or injection of pathological tissue or cells derived from patients into immunodeficient mice7. Xenograft models are a powerful tool to broaden knowledge about disease development and discovery of novel therapeutic agents8. In addition, using patient-derived cells allows scientists to recapitulate mutation heterogeneity to study the spectrum of patient phenotypes.
Here, we describe a protocol where patient-derived VM EC which express a mutant constitutively-active form of TIE2 and/or PIK3CA are injected subcutaneously in the back of athymic nude mice. Injected vascular cells are suspended in an ECM framework in order to promote angiogenesis as described in previous vascular xenograft models9,10,11. These VM EC undergo significant morphogenesis and generate enlarged, perfused pathological vessels in the absence of supporting cells. The described xenograft model of VM provides an efficient platform for preclinical evaluation of targeted drugs for their ability to inhibit uncontrolled lumen expansion.

<table>
	<tbody>
		<tr>
			<td>Athymic nude mice, (Foxn1-nu); 5-6 weeks, males</td>
			<td>Envigo</td>
			<td>069(nu)/070(nu/+)</td>
			<td>Subcutaneous injection</td>
		</tr>
		<tr>
			<td>Biotinylated Ulex europeaus Agglutinin-I (UEA-I)</td>
			<td>Vector Laboratories</td>
			<td>B-1065</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Bottle top filter (500 ml; 0.2 &#181;M)</td>
			<td>Thermo Fisher</td>
			<td>974106</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>BSA</td>
			<td>A7906-50MG</td>
			<td>Cell culture; Histological analysis</td>
		</tr>
		<tr>
			<td>Calcium cloride dihydrate (CaCl2.2H2O)</td>
			<td>Sigma</td>
			<td>C7902-500G</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Caliper</td>
			<td>Electron Microscopy Sciences</td>
			<td>50996491</td>
			<td>Lesion plug measurment</td>
		</tr>
		<tr>
			<td>CD31-conjugated magnetic beads (Dynabeads)</td>
			<td>Life Technologies</td>
			<td>11155D</td>
			<td>EC separation</td>
		</tr>
		<tr>
			<td>Cell strainer (100 &#956;M)</td>
			<td>Greiner</td>
			<td>542000</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Collagenase A</td>
			<td>Roche</td>
			<td>10103578001</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Conical Tube; polypropylene (15 mL)</td>
			<td>Greiner</td>
			<td>07 000 241</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Conical Tube; polypropylene (50 mL)</td>
			<td>Greiner</td>
			<td>07 000 239</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Coplin staining jar</td>
			<td>Ted Pella</td>
			<td>21029</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Coverglass (50 X 22 mm)</td>
			<td>Fisher Scientific</td>
			<td>12545E</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>DAB: 3,3&#39;Diaminobenzidine Reagent (ImmPACT DAB)</td>
			<td>Vector Laboratories</td>
			<td>SK-4105</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modification of Eagle&#39;s Medium (DMEM)</td>
			<td>Corning</td>
			<td>10-027-CV</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>DynaMag-2</td>
			<td>Life Technologies</td>
			<td>12321D</td>
			<td>EC separation</td>
		</tr>
		<tr>
			<td>Ear punch</td>
			<td>VWR</td>
			<td>10806-286</td>
			<td>Subcutaneous injection</td>
		</tr>
		<tr>
			<td>EDTA (0.5M, pH 8.0)</td>
			<td>Life Technologies</td>
			<td>15575-020</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Endothelial Cell Growth Medium-2 (EGM2) Bulletkit (basal medium and supplements)</td>
			<td>Lonza</td>
			<td>CC-3162</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Eosin Y (alcohol-based)</td>
			<td>Thermo Scientific</td>
			<td>71211</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Decon Labs</td>
			<td>2716</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (FBS) , HyClone</td>
			<td>GE Healthcare</td>
			<td>SH30910.03</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Filter tip 1,250 &#956;L</td>
			<td>MidSci</td>
			<td>AV1250-H</td>
			<td>Multiple steps</td>
		</tr>
		<tr>
			<td>Filter tip 20 &#956;L</td>
			<td>VWR</td>
			<td>10017-064</td>
			<td>Multiple steps</td>
		</tr>
		<tr>
			<td>Filter tip 200 &#956;L</td>
			<td>VWR</td>
			<td>10017-068</td>
			<td>Multiple steps</td>
		</tr>
		<tr>
			<td>Formalin buffered solution (10%)</td>
			<td>Sigma</td>
			<td>F04586</td>
			<td>Lesion plug dissection</td>
		</tr>
		<tr>
			<td>Hemacytometer (INCYTO; Disposable)</td>
			<td>SKC FILMS</td>
			<td>DHCN015</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Hematoxylin</td>
			<td>Vector Hematoxylin</td>
			<td>H-3401</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Human plasma fibronectin purified protein (1mg/mL)</td>
			<td>Sigma</td>
			<td>FC010-10MG</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Hydrogen Peroxide solution (30% w/w)</td>
			<td>Sigma</td>
			<td>H1009</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>ImageJ Software</td>
			<td></td>
			<td></td>
			<td>Analysis</td>
		</tr>
		<tr>
			<td>Isoflurane, USP</td>
			<td>Akorn Animal Health</td>
			<td>59399-106-01</td>
			<td>Subcutaneous injection</td>
		</tr>
		<tr>
			<td>magnesium sulfate heptahydrate (MgSO4.7H2O)</td>
			<td>Sigma</td>
			<td>M1880-500G</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Basement Membrane Matrix (Phenol Red-Free; LDEV-free)</td>
			<td>Corning</td>
			<td>356237</td>
			<td>Subcutaneous injection</td>
		</tr>
		<tr>
			<td>Microcentrifuge tube (1.5 mL)</td>
			<td>VWR</td>
			<td>87003-294</td>
			<td>EC separation</td>
		</tr>
		<tr>
			<td>Microscope Slide Superfrost (75mm X 25mm)</td>
			<td>Fisher Scientific</td>
			<td>1255015-CS</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Needles, 26G x 5/8 inch Sub-Q sterile needles</td>
			<td>Becton Dickinson (BD)</td>
			<td>BD305115</td>
			<td>Subcutaneous injection</td>
		</tr>
		<tr>
			<td>Normal horse serum</td>
			<td>Vector Laboratories</td>
			<td>S-2000</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin-L-Glutamine (100X)</td>
			<td>Corning</td>
			<td>30-009-CI</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Permanent mounting medium (VectaMount)</td>
			<td>Vector Laboratories</td>
			<td>H-5000</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Pestle Size C, Plain</td>
			<td>Thomas Scientific</td>
			<td>3431F55</td>
			<td>EC isolation</td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline (PBS)</td>
			<td>Fisher Scientific</td>
			<td>BP3994</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Scale</td>
			<td>VWR</td>
			<td>65500-202</td>
			<td>Subcutaneous injection</td>
		</tr>
		<tr>
			<td>Serological pipettes (10 ml)</td>
			<td>VWR</td>
			<td>89130-898</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Serological pipettes (5ml)</td>
			<td>VWR</td>
			<td>89130-896</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Sodium carbonate (Na2CO3)</td>
			<td>Sigma</td>
			<td>223530</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Streptavidin, Horseradish Peroxidase, Concentrate, for IHC</td>
			<td>Vector Laboratories</td>
			<td>SA-5004</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Syringe (60ml)</td>
			<td>BD Biosciences</td>
			<td>309653</td>
			<td>Cel culture</td>
		</tr>
		<tr>
			<td>SYRINGE FILTER (0.2 &#181;M)</td>
			<td>Corning</td>
			<td>431219</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Syringes (1 mL with Luer Lock)</td>
			<td>Becton Dickinson (BD)</td>
			<td>BD-309628</td>
			<td>Subcutaneous injection</td>
		</tr>
		<tr>
			<td>Tissue culture-treated plate (100 X 20 mm)</td>
			<td>Greiner</td>
			<td>664160</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Tissue culture-treated plate (145X20 mm)</td>
			<td>Greiner</td>
			<td>639160</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Tissue culture-treated plates (60 X 15) mm</td>
			<td>Eppendorf</td>
			<td>30701119</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Tris-base (Trizma base)</td>
			<td>Sigma</td>
			<td>T6066</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Trypan Blue Solution (0.4 %)</td>
			<td>Life Technologies</td>
			<td>15250061</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Trypsin EDTA, 1X (0.05% Trypsin/0.53mM EDTA)</td>
			<td>Corning</td>
			<td>25-052-Cl</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Tween-20</td>
			<td>Biorad</td>
			<td>170-6531</td>
			<td>Histological anlaysis</td>
		</tr>
		<tr>
			<td>Wheaton bottle</td>
			<td>VWR</td>
			<td>16159-798</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Xylenes</td>
			<td>Fisher Scientific</td>
			<td>X3P-1GAL</td>
			<td>Histological anlaysis</td>
		</tr>
	</tbody>
</table>

a patient-derived xenograft model for venous malformation

Venous malformation (VM) is a vascular anomaly that arises from impaired development of the venous network resulting in dilated and often dysfunctional veins. The purpose of this article is to carefully describe the establishment of a murine xenograft model that mimics human VM and is able to reflect patient heterogeneity. Hyper-activating non-inherited (somatic) TEK (TIE2) and PIK3CA mutations in endothelial cells (EC) have been identified as the main drivers of pathological vessel enlargement in VM. The following protocol describes the isolation, purification and expansion of patient-derived EC expressing mutant TIE2 and/or PIK3CA. These EC are injected subcutaneously into the back of immunodeficient athymic mice to generate ectatic vascular channels. Lesions generated with TIE2 or PIK3CA-mutant EC are visibly vascularized within 7&#8210;9 days of injection and recapitulate histopathological features of VM patient tissue. This VM xenograft model provides a reliable platform to investigate the cellular and molecular mechanisms driving VM formation and expansion. In addition, this model will be instrumental for translational studies testing the efficacy of novel drug candidates in preventing the abnormal vessel enlargement seen in human VM.

This protocol describes the process of generating a murine xenograft model of VM based on the subcutaneous injection of patient-derived EC into the back of immunodeficient nude mice. Endothelial cell colonies can be harvested within 4 weeks after initial cell isolation from VM tissue or lesional blood (Figure 1A,B). The day after injection, the xenograft lesion plug covers a surface area of approximately 80&#8210;100 mm2. In our hands, lesion plugs with TIE2/PIK3CA-mutant EC are visibly vascularized and perfused within 7&#8210;9 days from injection 14,15 (Figure 1C-E). However, the extent of lesion growth is variable and reflects on patient and sample heterogeneity.
Lesion plugs closely recapitulate the histopathological features of human VM tissue: enlarged vascular channels lined by a thin layer of endothelial cells (Figure 1F&#8210;H). These vascular structures typically contain erythrocytes, confirming functional anastomoses with the host mouse vasculature (Figure 1F&#8210;H). Immunohistochemical staining using the human specific lectin UEA-I can confirm that cells lining vascular lesions are derived from human implanted cells rather than mouse vasculature (Figure 1H).&#160;A scheme summarizing the steps from VM-EC isolation to dissection of lesion plug is presented in&#160;Figure 2.&#160;
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61501/61501fig01.jpg" /> 
Figure 1: Representative results. 
(A) Representative image of primary mixed cell culture three weeks after isolation from VM tissue before EC selection. Typical endothelial cell colony (EC) and contaminating fibroblast (FB). (B) Image of a purified (CD31 bead-selection) endothelial cell culture from VM patient-derived tissue. Scale bar = 200 &#181;m. (C) The lesion will form a spherical structure. Vascularization is visible due to blueish color through the skin of nude mice. (D) Dashed lines show how lesion size is recoded by measuring the length (L) and the width (W) using a caliper. (E) Photo of visibly vascularized, xenograft lesion explant at day 9. Scale bar = 1 cm. (F) Representative image of a lesion plug section. The x-plane pattern in which five high power field images are taken for quantification are indicated by white dashed boxes. Scale bar = 1000 &#181;m. (G&#8210;H) Representative images of VM lesion plug sections. (G) Hematoxylin and Eosin staining and (H) immunohistochemistry of human specific lectin UEA-I. Scale bar = 100 &#181;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61501/61501fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61501/61501fig02.jpg" /> 
Figure 2: Schematic of the workflow to generate a patient-derived xenograft of VM. 
(A) Endothelial cells isolated from patient VM lesion solid tissue or lesional blood are plated and, when 80% confluency is reached, are selected by anti CD31-conjugated immunomagnetic beads and expanded. (B) For subcutaneous injection of EC, on day 0, skin on the backside of the mouse is pinched using forefinger and thumb to create a tent-like structure. Lesions are measured at day 1 and then every other day (red arrows) using a caliper through experimental day 9. Lesions are dissected and processed for histological analysis. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61501/61501fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about A Patient-Derived Xenograft Model for Venous Malformation at JoVE.com

A Patient-Derived Xenograft Model for Venous Malformation

We present a detailed protocol to generate a murine xenograft model of venous malformation. This model is based on the subcutaneous injection of patient-derived endothelial cells containing hyper-activating TIE2 and/or PIK3CA gene mutations. Xenograft lesions closely recapitulate the histopathological features of VM patient tissue.

Venous malformation (VM) is a vascular anomaly that arises from impaired development of the venous network resulting in dilated and often dysfunctional ...

a-patient-derived-xenograft-model-for-venous-malformation

Nanyang Technological University

Research

JoVE Journal

Developmental Biology

5.2K Views.  Cincinnati Children's Hospital Medical Center. We present a detailed protocol to generate a murine xenograft model of venous malformation. This model is based on the subcutaneous injection of patient-derived endothelial cells containing hyper-activating TIE2 and/or PIK3CA gene mutations. Xenograft lesions closely recapitulate the histopathological features of VM patient tissue.

Video: A Patient-Derived Xenograft Model for Venous Malformation

Establishment of a Clinically Relevant Ex Vivo Mock Cataract Surgery Model for Investigating Epithelial Wound Repair in a Native Microenvironment

The major impediment to understanding how an epithelial tissue executes wound repair is the limited availability of models in which it is possible to follow and manipulate the wound response ex vivo in an environment that closely mimics that of epithelial tissue injury in vivo. This issue was addressed by creating a clinically relevant epithelial ex vivo injury-repair model based on cataract surgery. In this culture model, the response of the lens epithelium to wounding can be followed live in the cells&#8217; native microenvironment, and the molecular mediators of wound repair easily manipulated during the repair process. To prepare the cultures, lenses are removed from the eye and a small incision is made in the anterior of the lens from which the inner mass of lens fiber cells is removed. This procedure creates a circular wound on the posterior lens capsule, the thick basement membrane that surrounds the lens. This wound area where the fiber cells were attached is located just adjacent to a continuous monolayer of lens epithelial cells that remains linked to the lens capsule during the surgical procedure. The wounded epithelium, the cell type from which fiber cells are derived during development, responds to the injury of fiber cell removal by moving collectively across the wound area, led by a population of vimentin-rich repair cells whose mesenchymal progenitors are endogenous to the lens1. These properties are typical of a normal epithelial wound healing response. In this model, as in vivo, wound repair is dependent on signals supplied by the endogenous environment that is uniquely maintained in this ex vivo culture system, providing an ideal opportunity for discovery of the mechanisms that regulate repair of an epithelium following wounding.

Establishment of a Clinically Relevant Ex Vivo Mock Cataract Surgery Model for Investigating Epithelial Wound Repair in a Native Microenvironment

Described here is the establishment of a clinically relevant ex vivo mock cataract surgery model that can be used to investigate mechanisms of the injury response of epithelial tissues within their native microenvironment.

The major impediment to understanding how an epithelial tissue executes wound repair is the limited availability of models in which it is possible to ...

A Novel Culture Model for Human Pluripotent Stem Cell Propagation on Gelatin in Placenta-conditioned Media

The propagation of human pluripotent stem cells (hPSCs) in conditioned medium derived from human cells in feeder-free culture conditions has been of interest. Nevertheless, an ideal humanized ex vivo feeder-free propagation method for hPSCs has not been developed; currently, additional exogenous substrates including basic fibroblast growth factor (bFGF), a master hPSC-sustaining factor, is added to all of culture media and synthetic substrata such as Matrigel or laminin are used in all feeder-free cultures. Recently, our group developed a simple and efficient protocol for the propagation of hPSCs using only conditioned media derived from the human placenta on a gelatin-coated dish without additional exogenous supplementation or synthetic substrata specific to hPSCs. This protocol has not been reported previously and might enable researchers to propagate hPSCs efficiently in humanized culture conditions. Additionally, this model obviates hPSC contamination risks by animal products such as viruses or unknown proteins. Furthermore, this system facilitates easy mass production of hPSCs using the gelatin coating, which is simple to handle, dramatically decreases the overall costs of ex vivo hPSC maintenance.

This protocol provides a simple and efficient way to propagate human pluripotent stem cells (hPSCs) using only conditioned media derived from the human placenta in a gelatin-coated dish without additional exogenous supplementation or hPSC-specific synthetic substrata.

The propagation of human pluripotent stem cells (hPSCs) in conditioned medium derived from human cells in feeder-free culture conditions has been of ...

Microinjection for Transgenesis and Genome Editing in Threespine Sticklebacks

The threespine stickleback fish has emerged as a powerful system to study the genetic basis of a wide variety of morphological, physiological, and behavioral phenotypes. The remarkably diverse phenotypes that have evolved as marine populations adapt to countless freshwater environments, combined with the ability to cross marine and freshwater forms, provide a rare vertebrate system in which genetics can be used to map genomic regions controlling evolved traits. Excellent genomic resources are now available, facilitating molecular genetic dissection of evolved changes. While mapping experiments generate lists of interesting candidate genes, functional genetic manipulations are required to test the roles of these genes. Gene regulation can be studied with transgenic reporter plasmids and BACs integrated into the genome using the Tol2 transposase system. Functions of specific candidate genes and cis-regulatory elements can be assessed by inducing targeted mutations with TALEN and CRISPR/Cas9 genome editing reagents. All methods require introducing nucleic acids into fertilized one-cell stickleback embryos, a task made challenging by the thick chorion of stickleback embryos and the relatively small and thin blastomere. Here, a detailed protocol for microinjection of nucleic acids into stickleback embryos is described for transgenic and genome editing applications to study gene expression and function, as well as techniques to assess the success of transgenesis and recover stable lines.

Transgenic manipulations and genome editing are critical for functionally testing the roles of genes and cis-regulatory elements. Here a detailed microinjection protocol for the generation of genomic modifications (including Tol2-mediated fluorescent reporter transgene constructs, TALENs, and CRISPRs) is presented for the emergent model fish, the threespine stickleback.

The threespine stickleback fish has emerged as a powerful system to study the genetic basis of a wide variety of morphological, physiological, and ...

Culture of Murine Embryonic Metatarsals: A Physiological Model of Endochondral Ossification

The fundamental process of endochondral ossification is under tight regulation in the healthy individual so as to prevent disturbed development and/or longitudinal bone growth. As such, it is imperative that we further our understanding of the underpinning molecular mechanisms involved in such disorders so as to provide advances towards human and animal patient benefit. The mouse metatarsal organ explant culture is a highly physiological ex vivo model for studying endochondral ossification and bone growth as the growth rate of the bones in culture mimic that observed in vivo. Uniquely, the metatarsal organ culture allows the examination of chondrocytes in different phases of chondrogenesis and maintains cell-cell and cell-matrix interactions, therefore providing conditions closer to the in vivo situation than cells in monolayer or 3D culture. This protocol describes in detail the intricate dissection of embryonic metatarsals from the hind limb of E15 murine embryos and the subsequent analyses that can be performed in order to examine endochondral ossification and longitudinal bone growth.

We present a protocol to dissect and culture embryonic day 15 (E15) murine metatarsal bones. This highly physiological ex vivo model of endochondral ossification provides conditions closer to the in vivo situation than cells in monolayer or 3D culture and is a vital tool for investigating bone growth and development.

The fundamental process of endochondral ossification is under tight regulation in the healthy individual so as to prevent disturbed development and/or ...

Drug Treatment and In Vivo Imaging of Osteoblast-Osteoclast Interactions in a Medaka Fish Osteoporosis Model

Bone-forming osteoblasts interact with bone-resorbing osteoclasts to coordinate the turnover of bone matrix and to control skeletal homeostasis. Medaka and zebrafish larvae are widely used to analyze the behavior of bone cells during bone formation, degeneration, and repair. Their optical clarity allows the visualization of fluorescently labeled bone cells and fluorescent dyes bound to the mineralized skeletal matrix. Our lab has generated transgenic medaka fish that express the osteoclast-inducing factor Receptor Activator of Nuclear-factor &#954;B Ligand (RANKL) under the control of a heat&#160;shock-inducible promoter. Ectopic expression of RANKL results in the excess formation of activated osteoclasts, which can be visualized in reporter lines with nlGFP expression under the control of the cathepsin K (ctsk) promoter. RANKL induction and ectopic osteoclast formation leads to severe osteoporosis-like phenotypes. Compound transgenic medaka lines that express ctsk:nlGFP in osteoclasts, as well as mCherry under the control of the osterix (osx) promoter in premature osteoblasts, can be used to study the interaction of both cell types. This facilitates the in vivo observation of cellular behavior under conditions of bone degeneration and repair. Here, we describe the use of this system to test a drug commonly used in human osteoporosis therapy and describe a protocol for live imaging. The medaka model complements studies in cell culture and mice, and offers a novel system for the in vivo analysis of drug action in the skeletal system.

Drug Treatment and In Vivo Imaging of Osteoblast-Osteoclast Interactions in a Medaka Fish Osteoporosis Model

Small laboratory fish have become popular models for bone research on the mechanisms underlying human bone disorders and for the screening of bone-modulating drugs. In this report, we describe a protocol to assess the effect of alendronate on bone cells in medaka larvae with osteoporotic lesions.

Bone-forming osteoblasts interact with bone-resorbing osteoclasts to coordinate the turnover of bone matrix and to control skeletal homeostasis. Medaka ...

Rapid Isolation of BMPR-IB+ Adipose-Derived Stromal Cells for Use in a Calvarial Defect Healing Model

Invasive cancers, major injuries, and infection can cause bone defects that are too large to be reconstructed with preexisting bone from the patient's own body. The ability to grow bone de novo using a patient's own cells would allow bony defects to be filled with adequate tissue without the morbidity of harvesting native bone. There is interest in the use of adipose-derived stromal cells (ASCs) as a source for tissue engineering because these are obtained from an abundant source: the patient's own adipose tissue. However, ASCs are a heterogeneous population and some subpopulations may be more effective in this application than others. Isolation of the most osteogenic population of ASCs could improve the efficiency and effectiveness of a bone engineering process. In this protocol, ASCs are obtained from subcutaneous fat tissue from a human donor. The subpopulation of ASCs expressing the marker BMPR-IB is isolated using FACS. These cells are then applied to an in vivo calvarial defect healing assay and are found to have improved osteogenic regenerative potential compared with unsorted cells.

Adipose-derived stromal cells may be useful for engineering new tissue from a patient's own cells. We present a protocol for the isolation of a subpopulation of human adipose-derived stromal cells (ASCs) with increased osteogenic potential, followed by application of the cells in an in vivo calvarial healing assay.

Invasive cancers, major injuries, and infection can cause bone defects that are too large to be reconstructed with preexisting bone from the patient's own ...

A Seminiferous Tubule Squash Technique for the Cytological Analysis of Spermatogenesis Using the Mouse Model

Meiotic progression in males is a process that requires the concerted action of a number of highly regulated cellular events. Errors occurring during meiosis can lead to infertility, pregnancy loss or genetic defects. Commencing at the onset of puberty and continuing throughout adulthood, continuous semi-synchronous waves of spermatocytes undergo spermatogenesis and ultimately form haploid sperm. The first wave of mouse spermatocytes undergoing meiotic initiation appear at day 10 post-partum (10 dpp) and are released into the lumen of seminiferous tubules as mature sperm at 35 dpp. Therefore, it is advantageous to utilize mice within this developmental time-window in order to obtain highly enriched populations of interest. Analysis of rare cell stages is more difficult in older mice due to the contribution of successive spermatogenic waves, which increase the diversity of the cellular populations within the tubules. The method described here is an easily implemented technique for the cytological evaluation of the cells found within the seminiferous tubules of mice, including spermatogonia, spermatocytes, and spermatids. The tubule squash technique maintains the integrity of isolated male germ cells and allows examination of cellular structures that are not easily visualized with other techniques. To demonstrate the possible applications of this tubule squash technique, spindle assembly was monitored in spermatocytes progressing through the prophase to metaphase I transition (G2/MI transition). In addition, centrosome duplication, meiotic sex chromosome inactivation (MSCI), and chromosome bouquet formation were assessed as examples of the cytological structures that can be observed using this tubule squash method. This technique can be used to pinpoint specific defects during spermatogenesis that are caused by mutation or exogenous perturbation, and thus, contributes to our molecular understanding of spermatogenesis.

The goal of this tubule squash technique is to rapidly assess cytological features of developing mouse spermatocytes while preserving cellular integrity. This method allows for the study of all stages of spermatogenesis, and can be easily implemented alongside other biochemical and molecular biological approaches for the study of mouse meiosis.

Meiotic progression in males is a process that requires the concerted action of a number of highly regulated cellular events. Errors occurring during ...

Partial Lobular Hepatectomy: A Surgical Model for Morphologic Liver Regeneration

Morphological organ regeneration following acute tissue loss is common among lower vertebrates, but is rarely observed in mammalian postnatal life. Adult liver regeneration after 70% partial hepatectomy results in hepatocyte hypertrophy with some replication in remaining lobes with restoration of metabolic activity, but with permanent loss of the injured lobe&#39;s morphology and architecture. Here, we detail a new surgical method in the neonate that leaves a physiologic environment conducive to regeneration. This model involves amputation of the left lobe apex and a subsequent conservative management regimen, and lacks the necessity for ligation of major liver vessels or chemical injury, leaving a physiologic environment where regeneration may occur. We extend this protocol to amputations on juvenile (P7-14) mice, during which the injured liver transitions from organ regeneration to compensatory growth by hypertrophy. The presented, brief 30 min protocol provides a framework to study the mechanisms of regeneration, its age-associated decline in mammals, and the characterization of putative hepatic stem or progenitors.

Here, we present a new method for partial resection of the left hepatic lobe in neonatal (day 0) mice. This new protocol is suitable for studying acute liver injury and injury response in the neonatal setting.

Morphological organ regeneration following acute tissue loss is common among lower vertebrates, but is rarely observed in mammalian postnatal life. Adult ...

Whole-mount Confocal Microscopy for Adult Ear Skin: A Model System to Study Neuro-vascular Branching Morphogenesis and Immune Cell Distribution

Here, we present a protocol of a whole-mount adult ear skin imaging technique to study comprehensive three-dimensional neuro-vascular branching morphogenesis and patterning, as well as immune cell distribution at a cellular level. The analysis of peripheral nerve and blood vessel anatomical structures in adult tissues provides some insights into the understanding of functional neuro-vascular wiring and neuro-vascular degeneration in pathological conditions such as wound healing. As a highly informative model system, we have focused our studies on adult ear skin, which is readily accessible for dissection. Our simple and reproducible protocol provides an accurate depiction of the cellular components in the entire skin, such as peripheral nerves (sensory axons, sympathetic axons, and Schwann cells), blood vessels (endothelial cells and vascular smooth muscle cells), and inflammatory cells. We believe this protocol will pave the way to investigate morphological abnormalities in peripheral nerves and blood vessels as well as the inflammation in the adult ear skin under different pathological conditions.

Here, we describe a high resolution whole-mount imaging method in the entire adult mouse ear skin, which enables us to visualize branching morphogenesis and patterning of peripheral nerves and blood vessels, as well as immune cell distribution.

Here, we present a protocol of a whole-mount adult ear skin imaging technique to study comprehensive three-dimensional neuro-vascular branching ...

A Mouse Distraction Osteogenesis Model

Distraction osteogenesis (DO) is a surgical procedure that involves skeletal tissue regeneration without cell transplantation. A DO model consists of the following three phases: the latency phase after osteotomy and placement of the external distractor; the distraction phase, wherein the separated bone ends are gradually and continuously distracted; and the consolidation phase. This custom-made distractor used for DO is comprised of two incomplete acrylic resin rings and an expansion screw. The process was initiated by making a mold with silicone impression material and then creating the custom-made distractor. Dental resin was poured into the formwork made of silicone impression material, and it was allowed to polymerize to create the incomplete resin rings required for the custom-made distractor. These rings were fixed with an expansion screw using transparent resin. The custom-made distractor created via this approach was attached to the tibia of mice. The tibia was fixed to the device using one pair of 25 G needles proximally, one pair of 27 G needles distally, and acrylic resin. After a latency period of 5 days, distraction was initiated at a rate of 0.2 mm/12 h. The lengthening was continued for 8 days, resulting in a total gap of 3.2 mm. The mice were sacrificed 4 weeks after distraction. Bone formation in the distraction gap was confirmed using both radiography and histology.

We present a mouse tibial distraction osteogenesis model developed using a custom-made distractor. The use of a mouse as an analysis target is advantageous for advancing research.

Distraction osteogenesis (DO) is a surgical procedure that involves skeletal tissue regeneration without cell transplantation. A DO model consists of the ...