The authors are most grateful to the medical and surgical retina colleagues, nurses and whole staff of the Diabetic Unit and Vitreoretinal Surgery Unit at the Department of Ophthalmology, Helsinki University Hospital for actively participating in the recruitment of patients. We thank Biomedicum Molecular Imaging Unit for imaging facilities. We thank Anastasiya Chernenko for excellent technical assistance. This study was supported by grants from the Academy of Finland (KL), University of Helsinki (KL), Sigrid Juselius Foundation (KL), K. Albin Johansson Foundation (KL), Finnish Cancer Institute (KL), Karolinska Institutet (KL), Finnish Eye Foundation (SL), Eye and Tissue Bank Foundation (SL), Mary and Georg C. Ehrnrooth Foundation (SL), and HUCH Clinical Research Grants (TYH2018127 after TYH2016230, SL), Diabetes Research Foundation (SL, KL, AK, EG) as well as the Doctoral Programme in Biomedicine (EG).

This research was approved by the Institutional Review Board and Ethical committee of Helsinki University Hospital. Signed informed consent was obtained from each patient.
1. Preparation of Solutions, Media and Equipment
<ol>
	<li>Prepare the following equipment prior to collection of the fibrovascular tissue (FT) to ensure rapid processing.
	<ol>
		<li>Sterile-autoclave two microdissection tweezers.</li>
		<li>Prepare 1x phosphate-buffered saline (PBS) by dissolving 1 pre-weighed PBS tablet (0.14 M NaCl, 0.0027 M KCl, 0.010 M PO4-3) in 900 mL of deionized water and stir to dissolve. Adjust the water volume up to 1 L and sterile-autoclave the ready solution. Store at RT.</li>
		<li>Gather the above mentioned solution and equipment in a basket, together with a single-use sterile scalpel, a sterile 6-cm cell culture dish and five sterile 12-well cell culture plates.</li>
	</ol>
	</li>
	<li>Prepare a 6 mg/mL fibrinogen solution in Hanks Balanced Salt Solution (HBSS) by dissolving 30 mg of plasminogen-depleted human fibrinogen into 5 mL of HBSS, using a 50 mL tube immersed into a water bath at 37 &#176;C, for at least 1 h. 
	NOTE: This solution can be kept in the water bath (37 &#176;C) for 7 h&#160;(maximum 10 h) before use.</li>
	<li>Prepare the ex vivo culture medium by adding 5% fetal calf serum (FCS) or 5% human serum, 0.4% endothelial cell growth supplement, 10 ng/mL recombinant human epidermal growth factor, 1 &#956;g/mL hydrocortisone, and 50 &#956;g/mL gentamycin to commercially available endothelial cell growth medium and keep in water bath at 37 &#176;C until use. Store at 4 &#176;C for up to a month.</li>
</ol>
2. Fibrovascular Tissue Dissection
<ol>
	<li>Collect the fibrovascular tissue (FT) that has been excised from human subjects undergoing trans-conjunctival microincision vitreoretinal surgery, by 23 or 20 gauge three-port pars plana vitrectomy as part of the vitreoretinal surgical management of PDR. 
	NOTE: The FT is excised using segmentation and delamination, cut if needed with microscissors, and removed from the vitreous cavity with intraocular end-gripping microforceps by experienced vitreoretinal surgeon. Extreme care needs to be taken to remove intact, undamaged FT without causing damage to ocular structures including the optic nerve or temporal vascular arcade where the pathological neovascular tissue is most commonly located. The size of the excised tissue is variable, usually ranging between 3 and 50 mm2.</li>
	<li>Keep the FT in a 6 cm cell culture dish or 1.5 mL tube containing 1 mL of sterile PBS placed on wet ice, and transfer it immediately to research laboratory for processing. 
	NOTE: It is essential that the research unit (lab facilities) are physically close to the hospital operating room (OR) to minimize the transfer times of the small excised FT. In this case the transfer takes less than 5 minutes and the explants are embedded within fibrin usually in 1 - 1.5 h&#160;(maximum 2 h) after surgical removal. The impact of longer transfer times on the 3D culture would need to be tested.</li>
	<li>Place the FT in a 6-cm cell culture dish containing 1 mL of PBS at room temperature (RT, 25 &#176;C) and acquire images of the tissue using an inverted epifluorescence microscope with a 5x objective. 
	NOTE: Images are acquired for qualitative assessment and documentation. It will be possible to observe the tissue size, density and general composition (e.g., vascular structures).</li>
	<li>Cut the FT into ~1 mm2 pieces under an upright dissection stereomicroscope, using a sterile scalpel and microdissection tweezers. Hold the tissue, well submerged in PBS, in place using a microdissection tweezer, and perform clear cuts using a sterile scalpel. Avoid tearing FT, as this would alter the native fibrovascular structures.</li>
	<li>Place each individual piece into a well of a 12-well cell culture plate containing 1 mL of sterile PBS. 
	NOTE: If needed, gently spread the FT onto the plate, using microdissection tweezers, prior to performing cuts.</li>
</ol>
3. Casting Upright Fibrin Gel Droplets for the Characterization of Native FT and Ex Vivo Culture
<ol>
	<li>Sterile-filter the ready fibrinogen solution prepared in step 1.2 with a 0.22 &#956;m filter mounted into a 10 mL syringe.</li>
	<li>Prepare aliquots of the fibrinogen solution (25 &#956;L per 1.5 mL tube) and keep at RT. Prepare an aliquot for fibrin gel/every FT piece obtained after the dissection, and a couple of extra aliquots for testing the fibrin gel formation.</li>
	<li>Prepare a solution of HBSS containing 4 units/mL of thrombin and 400 &#956;g/mL of aprotinin, called hereafter TA solution, and keep at RT. Prepare as much TA solution as needed, depending on the number of pieces obtained after dissection (25 &#956;L of TA solution is used for each FT/fibrin gel), and an extra amount (e.g., 250 &#956;L) for testing the fibrin gel formation and ensuring that enough solution is available throughout casting of the fibrin gel droplets. 
	NOTE: Thrombin is required for fibrin polymerization while aprotinin is added to prevent degradation of the fibrin gel by cellular proteases expressed by the FTs13,14.</li>
	<li>Test the timing of fibrin gel formation: add 25 &#956;L of TA solution to the aliquoted 25 &#956;L fibrinogen solution prepared in step 3.2 and, using another pipette set to 50 &#956;L, mix in the tube by pipetting and dispense into a 6 cm cell culture dish, forming an upright droplet. 
	NOTE: The fibrin gel formation should take place in ~1 min. If this takes over 1.5 min, the concentration of thrombin in the TA solution prepared in step 3.3 can be increased by adding more thrombin stock solution. One tenth of the initially used volume of thrombin stock solution can be added, repeatedly, until the fibrin gel formation occurs within 1.5 min. The time of fibrin gel formation is critical for the three dimensionality of the culture, as quick gel formation (within 1.5 minutes) prevents the FT piece from sinking to the bottom of the fibrin gel, and thus coming in contact with the 2D plastic surface of the cell culture plate, which can lead to 2D cell adhesion and outgrowth.</li>
	<li>Place one FT piece at the center of one well of a 24-well plate using a sterile tweezer and remove any excess PBS by pipetting with a 0.5-10 &#956;L pipette to avoid suction force on the FT. In the case the tissue sticks to the tweezer, use an additional tweezer to aid the placement of the tissue piece on the plate. 
	NOTE: FT/fibrin gels can also be cast on 48-well plate to reduce the usage of reagents. However, this is more challenging as the space is more limited and fibrin will spread if it comes into contact with the well wall.</li>
	<li>Add 25 &#956;L of TA solution to the 25 &#956;L fibrinogen solution aliquoted in step 3.2, and using another pipette set to 50 &#956;L mix in the tube by pipetting. Dispense onto the FT piece placed on the plate well, and pipette up and down 2- 3 times in order to include the FT piece within the upright droplet, providing a 3D surrounding matrix to the FT. 
	NOTE: Ensure that the FT is not aspirated during pipetting and that no air bubbles are formed. Ensure also that mixing, dispensation and pipetting are performed quickly as the fibrin gel will form within 1.5 min, as tested in step 3.4. If casting fibrin gels on 48-well plate, use instead 20 &#956;L of fibrinogen solution and 20 &#956;L of TA solution.</li>
	<li>Repeat steps 3.5 and 3.6 for all the FT pieces.</li>
	<li>Allow the fibrin gels to solidify by incubating the plates in a cell culture incubator at 37 &#176;C in a humidified atmosphere with 5% CO2.</li>
	<li>After 0.5-1 h, check that the fibrin gel is completely formed by carefully tilting the plate. Proceed to step 3.10 when the gel does not move as the plate is tilted, indicating that the fibrin gel formation is complete.</li>
	<li>Overlay the FT/fibrin gels with ex vivo culture medium (600 &#956;L/well in 24-well plate or 300 &#956;L/well in 48-well plate) supplemented with 100 &#956;g/mL aprotinin. Pipette the medium gently by drop-wise dispensation. 
	NOTE: Here, aprotinin is used to prevent degradation of the fibrin gel by cellular proteases expressed by the FTs13,14. The ex vivo culture medium can additionally be supplemented with recombinant growth factors, such as VEGFA, VEGFC, bFGF, TGF&#946; (see Table of Materials)11.</li>
	<li>Place the FT ex vivo culture plate back into the 37 &#176;C, 5% CO2 cell culture incubator and culture for the desired time period (e.g., 2- 18 days, longer culture periods will need to be tested). Replace 50% of the medium with fresh ex vivo culture medium every three days.</li>
</ol>
4. &#8220;In Matrix&#8221; Imaging
<ol>
	<li>Acquire images of the FT ex vivo cultures on the same day (day 0) and at set intervals (e.g., every other day), using an inverted epifluorescence microscope, in order to follow the 3D growth. 
	NOTE: The images obtained can be used for the quantification of the FT outgrowth as the total length of two perpendicular diameters across the explant11.</li>
</ol>
5. Native FT and Ex Vivo Culture End-Point
NOTE: The FT/fibrin gels can be cultured ex vivo for the desired time period (FT ex vivo cultures) or fixed on the same day (native FT) for native FT characterization11.
<ol>
	<li>Fix the native FT or the FT ex vivo cultures by replacing the culture medium with 1 mL/well of 4% paraformaldehyde in PBS solution, for 1 h&#160;at RT. For the native FT/fibrin gels, fix 0.5-1 h after addition of the ex vivo culture medium (if the fibrin gels have not been soaked in medium, fixation will damage them). 
	NOTE: Perform this step in fume hood as paraformaldehyde is corrosive, toxic and carcinogenic.</li>
	<li>Rinse the FT/fibrin gels with three 5 min washes in PBS (2 mL/well).</li>
	<li>Replace the PBS with 2 mL/well of PBS containing 0.02% sodium azide and store the fixed fibrin gels at 4 &#176;C until further processing. Seal the plates with paraffin film to ensure that the FT/fibrin gels do not dry in storage. 
	NOTE: Perform this step in fume hood as sodium azide is toxic.</li>
</ol>
6. Whole-Mount Immunofluorescence Staining
NOTE: This protocol lasts 5 days and can be interrupted with overnight incubations where indicated. Do not let the fibrin gels dry at any point. All steps are performed at RT unless otherwise indicated.
<ol>
	<li>Prepare the following solutions before starting the staining protocol.
	<ol>
		<li>Post-fixation solution: prepare 50:50 acetone:methanol solution by mixing equal amounts of acetone and methanol (e.g., 50 mL). Store at -20 &#176;C. Prepare this solution latest on the day before the staining. This solution can be stored back at -20 &#176;C and be used for subsequent stainings. 
		NOTE: Prepare this solution in fume hood as acetone and methanol are flammable and hazardous to health.</li>
		<li>Blocking solution: prepare a 15% fetal bovine serum (FBS), 0.3% octyl phenol ethoxylate solution in PBS by first adding 15% FBS to PBS. Add octyl phenol ethoxylate and stir to dissolve. Store at 4 &#176;C. 
		NOTE: This solution can be prepared in large amount in advance, stored in 15 mL aliquotes at -20 &#176;C and thawed before use, on the day when the staining protocol is started. Use a freshly prepared or freshly thawed aliquote for each staining protocol.</li>
		<li>Washing solution: Prepare 1 L of PBS supplemented with 0.45% octyl phenol ethoxylate by adding 4.5 mL of octyl phenol ethoxylate to 995.5 mL of PBS. Stir to dissolve. Store at RT.</li>
	</ol>
	</li>
	<li>Lift the droplets carefully from the plate by using a stainless steel square-edged spatula. Detach the droplet first from the edges before lifting the center, and transfer to a well of 12-well plate containing 1 mL of PBS. 
	NOTE: Perform post-fixation, washes and blocking steps in this plate format.</li>
	<li>Post-fix the droplets with 1 mL of ice-cold 50:50 acetone:methanol solution for ~1 min (the border of the droplets will turn white). 
	NOTE: Perform this step in fume hood as acetone and methanol are hazardous to health.</li>
	<li>Rinse with 3 - 5 washes in 2 mL of PBS (the droplets will sink in the PBS solution when rehydration is complete). 
	NOTE: Avoid touching the droplets with the pipette tip as, after post-fixation, they are sticky to plastic. Throughout the protocol, avoid aspirating post-fix, antibody, blocking and washing solutions by suction, as this may damage or completely destroy the droplets. Instead, tilt the plate and carefully remove solutions using a 500-5,000 &#956;L pipette.</li>
	<li>Centrifuge the blocking solution for 15 min at 21,000 x g and 4 &#176;C in order to remove debris. 
	NOTE: The solution can be aliquoted in 1.5 mL tubes for centrifugation. The unused solution can be stored at 4 &#176;C and used for all relevant subsequent steps.</li>
	<li>Incubate the droplets in 500 &#956;L blocking solution for 2 h at RT. 
	NOTE: To reduce the volume of blocking solution used, the plate can be tilted on a support and as little as 300 &#956;L of solution/droplet can be used.</li>
	<li>Prepare the primary antibody mixture (at least 30 &#956;L/droplet) at appropriate dilution in blocking solution and centrifuge for 15 min at 21,000 x g and 4 &#176;C.</li>
	<li>Transfer the droplets into round (U)-bottom 96-well plate by using a round-edged spatula, and incubate with at least 30 &#956;L/droplet of the primary antibody mixture overnight at 4 &#176;C.</li>
	<li>On the following day, transfer the droplets into 12-well plate containing 2 mL of washing solution/well, rinse with three 5 min washes first and then with nine 30 min washes. Leave the last wash (2 mL) overnight at 4 &#176;C.</li>
	<li>On the following day, rinse three times with PBS and transfer the droplets into round (U)-bottom 96-well plate.</li>
	<li>During the washes, prepare the appropriate fluorophore-conjugated secondary antibody mixture (diluted 1:500, at least 30 &#956;L/droplet) in blocking solution and centrifuge for 15 min at 21,000 x g and 4 &#176;C.</li>
	<li>Transfer the droplets into a round (U)-bottom 96-well plate by using a round-edged spatula and incubate with at least 30 &#956;L of the secondary antibody mixture, for 4 h&#160;at RT, protected from light. 
	NOTE: Perform all subsequent incubations and washing steps protected from light.</li>
	<li>Transfer the droplets into 12-well plate containing 2 mL of washing solution/well using a round-edged spatula, rinse with three 5 min washes first and then with four 30 min washes. Leave the last wash (2 mL) overnight at 4 &#176;C.</li>
	<li>On the following day, rinse the gels with five 30 min washes and then three times with PBS. Leave the last wash (2 mL) overnight at 4 &#176;C.</li>
	<li>On the following day, transfer the droplets into a round (U)-bottom 96-well plate by using a round-edged spatula and counterstain nuclei by incubating with 10 &#956;g/mL Hoechst nuclear stain (at least 30 &#956;L/droplet) for 30 minutes at RT. 
	NOTE: Mounting medium supplemented with 4&#39;,6-diamidino-2-phenylindole (DAPI) for nuclei counterstaining can alternatively be used. In which case, this step and step 6.16 are skipped, proceeding directly to step 6.17.</li>
	<li>Transfer the droplets into 12-well plate containing 2 mL of PBS/well using a round-edged spatula and rinse three times with PBS.</li>
	<li>Mount the droplets onto microscope slide as follows:
	<ol>
		<li>Apply a narrow layer of quick-hardening mounting medium on the edges of a square-shaped 22 mm x 22 mm coverglass and let dry for ~1 minute. Perform this step for each drop individually, to avoid excessive hardening of the mounting medium. 
		NOTE: Perform this step in fume hood as the quick-hardening mounting medium is hazardous to health.</li>
		<li>Rinse the droplet by dipping in a well of a 12-well plate containing 2 mL of deionized water and transfer onto a microscope slide, using a round-edged spatula. Remove excess water by using a small piece of absorbent paper.</li>
		<li>Dispense 15 &#956;L of non-hardening antifade mounting medium onto the droplet. 
		NOTE: Alternatively, if Hoechst nuclear stain has not been used, mounting medium containing 4&#39;,6-diamidino-2-phenylindole (DAPI) can be used.</li>
		<li>Gently position the cover glass, with the quick-hardening mounting medium facing the microscopic slide, over the droplet and let settle. 
		NOTE: The quick-hardening medium will stick to the microscopic slide and keep the droplet in place.</li>
	</ol>
	</li>
	<li>Repeat step 6.17&#160;for all droplets. Mount two droplets on each microscope slide.</li>
	<li>Let the slides air-dry at RT for ~2 h and store at 4 &#176;C overnight. Ensure that the slides are positioned horizontally and protected from light.</li>
	<li>Image the stained native or end-point FT ex vivo cultures using a confocal microscope or an upright epifluorescence microscope equipped with an optical sectioning function and 20x or 40x objective. Use tile function to capture a greater area of the tissue at once.</li>
</ol>

<ol>
	<li>Cho, N. H., 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=IDF+Diabetes+Atlas:+Global+estimates+of+diabetes+prevalence+for+2017+and+projections+for+2045.">IDF Diabetes Atlas: Global estimates of diabetes prevalence for 2017 and projections for 2045.</a> Diabetes Research and Clinical Practice. 138, 271-281 (2018).</li><li>Liew, G., Wong, V. W., Ho, I. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mini+Review:+Changes+in+the+Incidence+of+and+Progression+to+Proliferative+and+Sight-Threatening+Diabetic+Retinopathy+Over+the+Last+30+Years.">Mini Review: Changes in the Incidence of and Progression to Proliferative and Sight-Threatening Diabetic Retinopathy Over the Last 30 Years.</a> Ophthalmic Epidemiology. 24 (2), 73-80 (2017).</li><li>Loukovaara, S., 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=Indications+of+lymphatic+endothelial+differentiation+and+endothelial+progenitor+cell+activation+in+the+pathology+of+proliferative+diabetic+retinopathy.">Indications of lymphatic endothelial differentiation and endothelial progenitor cell activation in the pathology of proliferative diabetic retinopathy.</a> Acta Ophthalmologica. 93 (6), 512-523 (2015).</li><li>Stitt, A. 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=The+progress+in+understanding+and+treatment+of+diabetic+retinopathy.">The progress in understanding and treatment of diabetic retinopathy.</a> Progress in Retinal and Eye Research. 51, 156-186 (2016).</li><li>Duh, E. J., Sun, J. K., Stitt, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diabetic+retinopathy:+current+understanding,+mechanisms,+and+treatment+strategies.">Diabetic retinopathy: current understanding, mechanisms, and treatment strategies.</a> JCI Insight. 2 (14), (2017).</li><li>Gross, J. G., 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=Five-Year+Outcomes+of+Panretinal+Photocoagulation+vs+Intravitreous+Ranibizumab+for+Proliferative+Diabetic+Retinopathy:+A+Randomized+Clinical+Trial.">Five-Year Outcomes of Panretinal Photocoagulation vs Intravitreous Ranibizumab for Proliferative Diabetic Retinopathy: A Randomized Clinical Trial.</a> JAMA Ophthalmology. 136 (10), 1138-1148 (2018).</li><li>Robinson, R., Barathi, V. A., Chaurasia, S. S., Wong, T. Y., Kern, T. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Update+on+animal+models+of+diabetic+retinopathy:+from+molecular+approaches+to+mice+and+higher+mammals.">Update on animal models of diabetic retinopathy: from molecular approaches to mice and higher mammals.</a> Disease Models, Mechanisms. 5 (4), 444-456 (2012).</li><li>Villacampa, P., Haurigot, V., Bosch, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proliferative+retinopathies:+animal+models+and+therapeutic+opportunities.">Proliferative retinopathies: animal models and therapeutic opportunities.</a> Current Neurovascular Research. 12 (2), 189-198 (2015).</li><li>Cox, T. R., Erler, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remodeling+and+homeostasis+of+the+extracellular+matrix:+implications+for+fibrotic+diseases+and+cancer.">Remodeling and homeostasis of the extracellular matrix: implications for fibrotic diseases and cancer.</a> Disease Models, Mechanisms. 4 (2), 165-178 (2011).</li><li>Sharma, 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=Surgical+treatment+for+diabetic+vitreoretinal+diseases:+a+review.">Surgical treatment for diabetic vitreoretinal diseases: a review.</a> Clinical, Experimental Ophthalmology. 44 (4), 340-354 (2016).</li><li>Gucciardo, 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=The+microenvironment+of+proliferative+diabetic+retinopathy+supports+lymphatic+neovascularization.">The microenvironment of proliferative diabetic retinopathy supports lymphatic neovascularization.</a> The Journal of Pathology. 245 (2), 172-185 (2018).</li><li>Rezzola, S., 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=3D+endothelial+cell+spheroid/human+vitreous+humor+assay+for+the+characterization+of+anti-angiogenic+inhibitors+for+the+treatment+of+proliferative+diabetic+retinopathy.">3D endothelial cell spheroid/human vitreous humor assay for the characterization of anti-angiogenic inhibitors for the treatment of proliferative diabetic retinopathy.</a> Angiogenesis. 20 (4), 629-640 (2017).</li><li>Pepper, M. S., Montesano, R., Mandriota, S. J., Orci, L., Vassalli, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Angiogenesis:+a+paradigm+for+balanced+extracellular+proteolysis+during+cell+migration+and+morphogenesis.">Angiogenesis: a paradigm for balanced extracellular proteolysis during cell migration and morphogenesis.</a> Enzyme, Protein. 49 (1-3), 138-162 (1996).</li><li>Lafleur, M. A., Handsley, M. M., Knauper, V., Murphy, G., Edwards, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+tubulogenesis+within+fibrin+gels+specifically+requires+the+activity+of+membrane-type-matrix+metalloproteinases+(MT-MMPs).">Endothelial tubulogenesis within fibrin gels specifically requires the activity of membrane-type-matrix metalloproteinases (MT-MMPs).</a> Journal of Cell Science. 115 (Pt 17), 3427-3438 (2002).</li><li>Loukovaara, S., 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=Quantitative+Proteomics+Analysis+of+Vitreous+Humor+from+Diabetic+Retinopathy+Patients.">Quantitative Proteomics Analysis of Vitreous Humor from Diabetic Retinopathy Patients.</a> Journal of Proteome Research. 14 (12), 5131-5143 (2015).</li><li>Abu El-Asrar, A. M., Struyf, S., Opdenakker, G., Van Damme, J., Geboes, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+stem+cell+factor/c-kit+signaling+pathway+components+in+diabetic+fibrovascular+epiretinal+membranes.">Expression of stem cell factor/c-kit signaling pathway components in diabetic fibrovascular epiretinal membranes.</a> Molecular Vision. 16, 1098-1107 (2010).</li><li>Loukovaara, S., 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=Ang-2+upregulation+correlates+with+increased+levels+of+MMP-9,+VEGF,+EPO+and+TGFbeta1+in+diabetic+eyes+undergoing+vitrectomy.">Ang-2 upregulation correlates with increased levels of MMP-9, VEGF, EPO and TGFbeta1 in diabetic eyes undergoing vitrectomy.</a> Acta Ophthalmologica. 91 (6), 531-539 (2013).</li><li>Sugiyama, 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=EphA2+cleavage+by+MT1-MMP+triggers+single+cancer+cell+invasion+via+homotypic+cell+repulsion.">EphA2 cleavage by MT1-MMP triggers single cancer cell invasion via homotypic cell repulsion.</a> Journal of Cell Biology. 201 (3), 467-484 (2013).</li><li>Tatti, O., 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=MMP16+Mediates+a+Proteolytic+Switch+to+Promote+Cell-Cell+Adhesion,+Collagen+Alignment,+and+Lymphatic+Invasion+in+Melanoma.">MMP16 Mediates a Proteolytic Switch to Promote Cell-Cell Adhesion, Collagen Alignment, and Lymphatic Invasion in Melanoma.</a> Cancer Research. 75 (10), 2083-2094 (2015).</li><li>Zudaire, E., Gambardella, L., Kurcz, C., Vermeren, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+computational+tool+for+quantitative+analysis+of+vascular+networks.">A computational tool for quantitative analysis of vascular networks.</a> PLoS One. 6 (11), e27385 (2011).</li><li>Senger, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+framework+for+angiogenesis:+a+complex+web+of+interactions+between+extravasated+plasma+proteins+and+endothelial+cell+proteins+induced+by+angiogenic+cytokines.">Molecular framework for angiogenesis: a complex web of interactions between extravasated plasma proteins and endothelial cell proteins induced by angiogenic cytokines.</a> American Journal of Pathology. 149 (1), 1-7 (1996).</li><li>Senger, D. R., Davis, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Angiogenesis.">Angiogenesis.</a> Cold Spring Harbor Perspectives in Biology. 3 (8), a005090 (2011).</li><li>Bishop, P. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+macromolecules+and+supramolecular+organisation+of+the+vitreous+gel.">Structural macromolecules and supramolecular organisation of the vitreous gel.</a> Progress in Retinal and Eye Research. 19 (3), 323-344 (2000).</li><li>Marmorstein, A. D., Marmorstein, L. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+challenge+of+modeling+macular+degeneration+in+mice.">The challenge of modeling macular degeneration in mice.</a> Trends in Genetics. 23 (5), 225-231 (2007).</li><li>Kim, L. 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=Characterization+of+cells+from+patient-derived+fibrovascular+membranes+in+proliferative+diabetic+retinopathy.">Characterization of cells from patient-derived fibrovascular membranes in proliferative diabetic retinopathy.</a> Molecular Vision. 21, 673-687 (2015).</li><li>Avery, R. L., 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=Intravitreal+bevacizumab+(Avastin)+in+the+treatment+of+proliferative+diabetic+retinopathy.">Intravitreal bevacizumab (Avastin) in the treatment of proliferative diabetic retinopathy.</a> Ophthalmology. 113 (10), e1691-e1615 (2006).</li><li>Zhao, L. Q., Zhu, H., Zhao, P. Q., Hu, Y. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+systematic+review+and+meta-analysis+of+clinical+outcomes+of+vitrectomy+with+or+without+intravitreal+bevacizumab+pretreatment+for+severe+diabetic+retinopathy.">A systematic review and meta-analysis of clinical outcomes of vitrectomy with or without intravitreal bevacizumab pretreatment for severe diabetic retinopathy.</a> The British Journal of Ophthalmology. 95 (9), 1216-1222 (2011).</li><li>Carrion, B., Janson, I. A., Kong, Y. P., Putnam, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+safe+and+efficient+method+to+retrieve+mesenchymal+stem+cells+from+three-dimensional+fibrin+gels.">A safe and efficient method to retrieve mesenchymal stem cells from three-dimensional fibrin gels.</a> Tissue Engineering. Part C, Methods. 20 (3), 252-263 (2014).</li></ol>

The authors have nothing to disclose.

Considering the importance of relevant tissue microenvironment for reliable functional cell and molecular mechanistic results, it is imperative to find appropriate experimental models that provide this tissue environment. The herein described ex vivo PDR culture model for the fibrin-embedded FTs allows the investigation of the mechanisms of PDR pathophysiology in the native, complex and multicellular context of the PDR clinical samples.
Critical steps within the protocol are the prope...

DR is a serious ocular complication of diabetes, a disease that has reached enormous proportions in the last three decades1. Twenty years after diagnosis, virtually every patient with type 1 diabetes and 60% of patients with type 2 diabetes present signs of retinopathy, making diabetes per se one of the leading causes of blindness in working age adults2. According to the level of microvascular degeneration and ischemic damage, DR is classified into non-proliferative DR (non-PDR) and proliferative DR (PDR). The end-stage disease, PDR, is characterized by ischemia- and inflammation-induced neovascularization and fibrotic responses at the vitreoretinal interface. In untreated conditions, these processes will lead to blindness due to vitreous hemorrhage, retinal fibrosis, tractional retinal detachment, and neovascular glaucoma3,4. Despite recent advances, current treatment options target only DR stages, including diabetic macular edema and PDR, when retinal damage has already ensued. Moreover, a great proportion of DR patients does not benefit from current treatment armamentarium, indicating an urgent need for improved therapies4,5,6.
Multiple other in vivo disease/developmental models and diabetic animal models have been developed to date, but none of them recapitulates the full range of pathologic features observed in human PDR7,8. Moreover, increasing evidence indicates that treatment responses are tightly connected to the ECM composition as well as the spatial arrangement and interaction between the cellular and acellular microenvironment9. We, therefore, set out to develop a clinically relevant model of human PDR by utilizing the FT pathological material that is commonly excised from eyes undergoing vitrectomy as part of the surgical management of PDR10.
This manuscript describes the protocol for the 3D ex vivo culture and characterization of the surgically-excised, PDR patient-derived pathological FT. The method described here has been used in a recent publication that demonstrated successful deconstruction of the native 3D PDR tissue landscape, and recapitulation of features of PDR pathophysiology including angiogenic and fibrotic responses of the abnormal vascular structures11. This model also revealed novel features that cannot be easily appreciated from thin histological sections, such as spatially confined apoptosis and proliferation as well as vascular islet formation11. Vitreous fluid has been successfully used by others on 3D endothelial spheroid cultures to evaluate its angiogenic potential and the efficacy of angiostatic molecules12. When combined with an in vitro 3D lymphatic endothelial cell (LEC) spheroid sprouting assay using PDR vitreous as stimulant, our model revealed the contribution of both soluble vitreal factors as well as local cues within the neovascular tissue to the as yet poorly understood LEC involvement in PDR pathophysiology3,11. In the management of PDR, vitreoretinal surgery is a routinely performed yet challenging procedure. As surgical instrumentations and techniques are seeing continuous advancement and sophistication, timely and conservative removal of fibrovascular proliferative specimen not only improves vision outcome but also provides invaluable tissue material for the investigation of PDR pathophysiology and treatment responses in the complex translational aspects of the live human tissue microenvironment.

<table>
	<tbody>
		<tr>
			<td>Material</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Microforceps</td>
			<td>Medicon</td>
			<td>07.60.03</td>
			<td>Used for handling the FTs</td>
		</tr>
		<tr>
			<td>Disposable Scalpels - Sterile</td>
			<td>Swann-Morton</td>
			<td>0513</td>
			<td>Used for FT dissection</td>
		</tr>
		<tr>
			<td>Culture dish, vented, 28 ml (60mm)</td>
			<td>Greiner Bio-One</td>
			<td>391-3210</td>
			<td>Used for dissection and for testing fibrin gel formation</td>
		</tr>
		<tr>
			<td>Cell culture plates, 12-well</td>
			<td>Greiner Bio-One</td>
			<td>392-0049</td>
			<td>Used for FT dissection and whole-mount immunofluorescence</td>
		</tr>
		<tr>
			<td>Reagent/centrifuge tube with screw cap, 15 mL</td>
			<td>Greiner Bio-One</td>
			<td>391-3477</td>
			<td></td>
		</tr>
		<tr>
			<td>Reagent/centrifuge tube with screw cap, 50 mL</td>
			<td>Greiner Bio-One</td>
			<td>525-0384</td>
			<td></td>
		</tr>
		<tr>
			<td>Millex-GV Syringe Filter Unit, 0.22&#160;&#181;m, PVDF</td>
			<td>Millipore</td>
			<td>SLGV033RS</td>
			<td>Used to sterile-filter the fibrinogen solution</td>
		</tr>
		<tr>
			<td>Syringe, 10 mL</td>
			<td>Braun</td>
			<td>4606108V</td>
			<td>Used to sterile-filter the fibrinogen solution</td>
		</tr>
		<tr>
			<td>Polypropylene Microcentrifuge Tubes, 1.5 mL</td>
			<td>Fisher</td>
			<td>FB74031</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell-Culture Treated Multidishes, 24-well</td>
			<td>Nunc</td>
			<td>142475</td>
			<td>Used for casting the FT/fibrin gels for native FT characterization and ex vivo culture</td>
		</tr>
		<tr>
			<td>Cell culture plates, 96-well, U-bottom</td>
			<td>Greiner Bio-One</td>
			<td>392-0019</td>
			<td>Used for whole-mount immunofluorescence</td>
		</tr>
		<tr>
			<td>Round/Flat Spatulas, Stainless Steel</td>
			<td>VWR</td>
			<td>82027-528</td>
			<td>Used for whole-mount immunofluorescence</td>
		</tr>
		<tr>
			<td>Coverslips 22x22mm #1</td>
			<td>Menzel/Fisher</td>
			<td>15727582</td>
			<td>Used for mounting</td>
		</tr>
		<tr>
			<td>Microscope slides</td>
			<td>Fisher</td>
			<td>Kindler K102</td>
			<td>Used for mounting</td>
		</tr>
		<tr>
			<td>Absorbent paper</td>
			<td>VWR</td>
			<td>115-0202</td>
			<td>Used for mounting</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Reagents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PBS tablets</td>
			<td>Medicago</td>
			<td>09-9400-100</td>
			<td>Used for preparing 1x PBS</td>
		</tr>
		<tr>
			<td>Fibrinogen, Plasminogen-Depleted, Human Plasma</td>
			<td>Calbiochem</td>
			<td>341578</td>
			<td></td>
		</tr>
		<tr>
			<td>Hanks Balanced Salt Solution</td>
			<td>Sigma-Aldrich</td>
			<td>H9394-500ML</td>
			<td>Used for preparing the fibrinogen and TA solution</td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>Gibco</td>
			<td>10270106</td>
			<td>Used for preparing the blocking solution</td>
		</tr>
		<tr>
			<td>Human Serum</td>
			<td>Sigma-Aldrich</td>
			<td>H4522</td>
			<td>Aliquoted in -20 &#176;C, thaw before preparing the ex vivo culture media</td>
		</tr>
		<tr>
			<td>Gentamicin Sulfate 10mg/ml</td>
			<td>Biowest</td>
			<td>L0011-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Endothelial cell media MV Kit</td>
			<td>Promocell</td>
			<td>C-22120</td>
			<td>Contains 500 ml of Endothelial Cell Growth Medium MV, 25 mL of fetal calf serum, 2 mL of endothelial cell growth supplement,&#160; 500 &#956;L of recombinant human epidermal growth factor (10 &#956;g/ mL) and 500 &#956;L of hydrocortisone (1 g/ mL)</td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>Sigma-Aldrich</td>
			<td>S2002</td>
			<td>Used for storage of the native and ex vivo cultured FTs. TOXIC: wear protective gloves and/or clothing, and eye and/or face protection. Use in fume hood.</td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>Sigma-Aldrich</td>
			<td>32201-2.5L-M</td>
			<td>Used to prepare the post-fixation solution. HARMFUL: wear protective gloves and/or clothing. Use in fume hood.</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Sigma-Aldrich</td>
			<td>32213</td>
			<td>Used to prepare the post-fixation solution. TOXIC: wear protective gloves and/or clothing. Use in fume hood.</td>
		</tr>
		<tr>
			<td>Triton X-100 (octyl phenol ethoxylate)</td>
			<td>Sigma-Aldrich</td>
			<td>T9284</td>
			<td>Used for whole-mount immunofluorescence. HARMFUL: wear protective gloves and/or clothing.</td>
		</tr>
		<tr>
			<td>Hoechst 33342, 20mM</td>
			<td>Life Technologies</td>
			<td>62249</td>
			<td>For nuclei counterstaining. HARMFUL: wear protective gloves and/or clothing, and eye and/or face protection.</td>
		</tr>
		<tr>
			<td>VECTASHIELD Antifade Mounting Medium</td>
			<td>Vector Laboratories</td>
			<td>H-1000</td>
			<td>Wear protective gloves and/or clothing, and eye protection. Use in fume hood.</td>
		</tr>
		<tr>
			<td>VECTASHIELD Antifade Mounting Medium with DAPI</td>
			<td>Vector Laboratories</td>
			<td>H-1200</td>
			<td>Mounting medium with nuclei counterstaining. Wear protective gloves and/or clothing, and eye protection. Use in fume hood.</td>
		</tr>
		<tr>
			<td>Eukitt Quick-hardening mounting medium</td>
			<td>Sigma-Aldrich</td>
			<td>03989-100ml</td>
			<td>TOXIC: Wear protective gloves and/or clothing, and eye protection. Use in fume hood.</td>
		</tr>
		<tr>
			<td>Thrombin from bovine plasma, lyophilized powder</td>
			<td>Sigma-Aldrich</td>
			<td>T9549-500UN&#160;</td>
			<td>Dissolve at 100 units/ mL, aliquote and store at -20 &#176;C, avoid repeated freeze/ thaw</td>
		</tr>
		<tr>
			<td>Aprotinin from bovine lung, lyophilized powder</td>
			<td>Sigma</td>
			<td>A3428</td>
			<td>Dissolve at 50 mg/ mL, aliquote and store at -20 &#176;C, avoid repeated freeze/ thaw</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Growth factors</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant human VEGFA</td>
			<td>R&#38;D Systems</td>
			<td>293-VE-010</td>
			<td>50 ng/ mL final concentration</td>
		</tr>
		<tr>
			<td>Recombinant human VEGFC</td>
			<td>R&#38;D Systems</td>
			<td>752-VC-025</td>
			<td>200 ng/ mL final concentration</td>
		</tr>
		<tr>
			<td>Recombinant human TGF&#946;</td>
			<td>Millipore</td>
			<td>GF346</td>
			<td>1 ng/ mL final concentration</td>
		</tr>
		<tr>
			<td>Recombinant human bFGF</td>
			<td>Millipore</td>
			<td>01-106</td>
			<td>50 ng/ mL final concentration</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Primary antibodies</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>CD31 (JC70A)</td>
			<td>Dako</td>
			<td>M0823</td>
			<td>Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab</td>
		</tr>
		<tr>
			<td>CD34 (QBEND10)</td>
			<td>Dako</td>
			<td>M716501-2</td>
			<td>Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab</td>
		</tr>
		<tr>
			<td>CD45 (2B11+PD7/26)</td>
			<td>Dako</td>
			<td>M070129-2</td>
			<td>Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab</td>
		</tr>
		<tr>
			<td>CD68</td>
			<td>ImmunoWay</td>
			<td>RLM3161</td>
			<td>Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab</td>
		</tr>
		<tr>
			<td>Cleaved caspase-3 (5A1E)</td>
			<td>Cell Signalling</td>
			<td>9664</td>
			<td>Used at 1:200 dilution, Goat anti Rabbit Alexa 594 Secondary Ab</td>
		</tr>
		<tr>
			<td>ERG (EP111)</td>
			<td>Dako</td>
			<td>M731429-2</td>
			<td>Used at 1:100 dilution, Goat anti Rabbit Alexa 594 Secondary Ab</td>
		</tr>
		<tr>
			<td>GFAP</td>
			<td>Dako</td>
			<td>Z0334</td>
			<td>Used at 1:100 dilution, Goat anti Rabbit Alexa 594 Secondary Ab</td>
		</tr>
		<tr>
			<td>Ki67</td>
			<td>Leica Microsystems</td>
			<td>NCL-Ki67p</td>
			<td>Used at 1:1500 dilution, Goat anti Rabbit Alexa 594 Secondary Ab</td>
		</tr>
		<tr>
			<td>Lyve1</td>
			<td>R&#38;D Systems</td>
			<td>AF2089</td>
			<td>Used at 1:100 dilution, Donkey anti Goat Alexa 568 Secondary Ab</td>
		</tr>
		<tr>
			<td>NG2</td>
			<td>Millipore</td>
			<td>AB5320</td>
			<td>Used at 1:100 dilution, Goat anti Rabbit Alexa 594 Secondary Ab</td>
		</tr>
		<tr>
			<td>Prox1</td>
			<td>ReliaTech</td>
			<td>102-PA32</td>
			<td>Used at 1:200 dilution, Goat anti Rabbit Alexa 568 Secondary Ab</td>
		</tr>
		<tr>
			<td>Prox1</td>
			<td>R&#38;D Systems</td>
			<td>AF2727</td>
			<td>Used at 1:40 dilution, Chicken anti Goat Alexa 594 Secondary Ab</td>
		</tr>
		<tr>
			<td>VEGFR3 (9D9F9)</td>
			<td>Millipore</td>
			<td>MAB3757</td>
			<td>Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab</td>
		</tr>
		<tr>
			<td>&#945;-SMA (1A4)</td>
			<td>Sigma</td>
			<td>C6198</td>
			<td>Used at 1:400 dilution, Cy3 conjugated</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Secondary antibodies</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor488 Donkey Anti-Mouse IgG</td>
			<td>Life Technologies</td>
			<td>A-21202</td>
			<td>Used at 1:500 dilution</td>
		</tr>
		<tr>
			<td>Alexa Fluor594 Goat Anti-Rabbit IgG</td>
			<td>Invitrogen</td>
			<td>A-11012</td>
			<td>Used at 1:500 dilution</td>
		</tr>
		<tr>
			<td>Alexa Fluor568 Donkey anti-Goat IgG</td>
			<td>Thermo Scientific</td>
			<td>A-11057</td>
			<td>Used at 1:500 dilution</td>
		</tr>
		<tr>
			<td>Alexa Fluor568 Goat anti-Rabbit IgG</td>
			<td>Thermo Scientific</td>
			<td>A-11036</td>
			<td>Used at 1:500 dilution</td>
		</tr>
		<tr>
			<td>Alexa Fluor594 Chicken Anti-Goat IgG</td>
			<td>Molecular Probes</td>
			<td>A-21468</td>
			<td>Used at 1:500 dilution</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Microscopes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Axiovert 200 inverted epifluorescence microscope</td>
			<td>Zeiss</td>
			<td></td>
			<td>For imaging of the fresh and fibrin-embedded FT</td>
		</tr>
		<tr>
			<td>SZX9 upright dissection stereomicroscope</td>
			<td>Olympus</td>
			<td></td>
			<td>For FT dissection</td>
		</tr>
		<tr>
			<td>LSM 780 confocal microscope</td>
			<td>Zeiss</td>
			<td></td>
			<td>For imaging of whole-mount immunostained FT</td>
		</tr>
		<tr>
			<td>AxioImager.Z1 upright epifluorescence microscope with Apotome</td>
			<td>Zeiss</td>
			<td></td>
			<td>For imaging of whole-mount immunostained FT</td>
		</tr>
	</tbody>
</table>

an ex vivo tissue culture model for fibrovascular complications in proliferative diabetic retinopathy

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and one of the leading causes of blindness in working-age adults. No current animal models of diabetes and oxygen-induced retinopathy develop the full-range progressive changes manifested in human proliferative diabetic retinopathy (PDR). Therefore, understanding of the disease pathogenesis and pathophysiology has relied largely on the use of histological sections and vitreous samples in approaches that only provide steady-state information on the involved pathogenic factors. Increasing evidence indicates that dynamic cell-cell and cell-extracellular matrix (ECM) interactions in the context of three-dimensional (3D) microenvironments are essential for the mechanistic and functional studies towards the development of new treatment strategies. Therefore, we hypothesized that the pathological fibrovascular tissue surgically excised from eyes with PDR could be utilized to reliably unravel the cellular and molecular mechanisms of this devastating disease and to test the potential for novel clinical interventions. Towards this end, we developed a novel method for 3D ex vivo culture of surgically-excised patient-derived fibrovascular tissue (FT), which will serve as a relevant model of human PDR pathophysiology. The FTs are dissected into explants and embedded in fibrin matrix for ex vivo culture and 3D characterization. Whole-mount immunofluorescence of the native FTs and end-point cultures allows thorough investigation of tissue composition and multicellular processes, highlighting the importance of 3D tissue-level characterization for uncovering relevant features of PDR pathophysiology. This model will allow the simultaneous assessment of molecular mechanisms, cellular/tissue processes and treatment responses in the complex context of dynamic biochemical and physical interactions within the PDR tissue architecture and microenvironment. Since this model recapitulates PDR pathophysiology, it will also be amenable for testing or developing new treatments.

Deeper understanding of the PDR fibrovascular tissue properties and protein expression has relied mainly on vitreous samples and thin histological FT sections3,15,16,17. To develop a method for thorough investigation of the 3D tissue organization and multicellular physiopathological processes of PDR, we set out to utilize the surgically excised, patient-derived ...

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An Ex Vivo Tissue Culture Model for Fibrovascular Complications in Proliferative Diabetic Retinopathy

Here, we present a protocol to study the pathophysiology of proliferative diabetic retinopathy by using patient-derived, surgically-excised, fibrovascular tissues for three-dimensional native tissue characterization and ex vivo culture. This ex vivo culture model is also amenable for testing or developing new treatments.

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and one of the leading causes of blindness in working-age adults. No ...

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JoVE Journal

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7.7K Views.  University of Helsinki. Here, we present a protocol to study the pathophysiology of proliferative diabetic retinopathy by using patient-derived, surgically-excised, fibrovascular tissues for three-dimensional native tissue characterization and ex vivo culture. This ex vivo culture model is also amenable for testing or developing new treatments.

Video: An Ex Vivo Tissue Culture Model for Fibrovascular Complications in Proliferative Diabetic Retinopathy

Ex Vivo Culture of Patient Tissue &amp; Examination of Gene Delivery

This video describes the use of patient tissue as an ex vivo model for the study of gene delivery. Fresh patient tissue obtained at the time of surgery is sliced and maintained in culture. The ex vivo model system allows for the physical delivery of genes into intact patient tissue and gene expression is analysed by bioluminescence imaging using the IVIS detection system. The bioluminescent detection system demonstrates rapid and accurate quantification of gene expression within individual slices without the need for tissue sacrifice. This slice tissue culture system may be used in a variety of tissue types including normal and malignant tissue and allows us to study the effects of the heterogeneous nature of intact tissue and the high degree of variability between individual patients. This model system could be used in certain situations as an alternative to animal models and as a complementary preclinical mode prior to entering clinical trial.

Ex Vivo Culture of Patient Tissue &amp; Examination of Gene Delivery

This article describes the culture of patient tissue slices for gene delivery studies and subsequent analysis of gene expression using IVIS bioluminescence imaging.

This video describes the use of patient tissue as an ex vivo model for the study of gene delivery.  Fresh patient tissue obtained at the time of surgery ...

Ex Vivo Infection of Live Tissue with Oncolytic Viruses

Oncolytic Viruses (OVs) are novel therapeutics that selectively replicate in and kill tumor cells1. Several clinical trials evaluating the effectiveness of a variety of oncolytic platforms including HSV, Reovirus, and Vaccinia OVs as treatment for cancer are currently underway2-5. One key characteristic of oncolytic viruses is that they can be genetically modified to express reporter transgenes which makes it possible to visualize the infection of tissues by microscopy or bio-luminescence imaging6,7. This offers a unique advantage since it is possible to infect tissues from patients ex vivo prior to therapy in order to ascertain the likelihood of successful oncolytic virotherapy8. To this end, it is critical to appropriately sample tissue to compensate for tissue heterogeneity and assess tissue viability, particularly prior to infection9. It is also important to follow viral replication using reporter transgenes if expressed by the oncolytic platform as well as by direct titration of tissues following homogenization in order to discriminate between abortive and productive infection. The object of this protocol is to address these issues and herein describes 1. The sampling and preparation of tumor tissue for cell culture 2. The assessment of tissue viability using the metabolic dye alamar blue 3. Ex vivo infection of cultured tissues with vaccinia virus expressing either GFP or firefly luciferase 4. Detection of transgene expression by fluorescence microscopy or using an In Vivo Imaging System (IVIS) 5. Quantification of virus by plaque assay. This comprehensive method presents several advantages including ease of tissue processing, compensation for tissue heterogeneity, control of tissue viability, and discrimination between abortive infection and bone fide viral replication.

Ex Vivo Infection of Live Tissue with Oncolytic Viruses

Oncolytic viruses are promising for cancer therapeutics. The ability to ascertain the infectability of live tissue specimens obtained from patients prior to treatment is a unique advantage of this therapeutic approach. This protocol describes how to process tissues for ex vivo infection with oncolytic virus and subsequent viral quantification.

Oncolytic Viruses (OVs) are novel therapeutics that selectively replicate in and kill tumor cells1. Several clinical trials evaluating the effectiveness ...

An Ex vivo Model to Study Hormone Action in the Human Breast

The study of hormone action in the human breast has been hampered by lack of adequate model systems. Upon in vitro culture, primary mammary epithelial cells tend to lose hormone receptor expression. Widely used hormone receptor positive breast cancer cell lines are of limited relevance to the in vivo situation. Here, we describe an ex vivo model to study hormone action in the human breast. Fresh human breast tissue specimens from surgical discard material such as reduction mammoplasties or mammectomies are mechanically and enzymatically digested to obtain tissue fragments containing ducts and lobules and multiple stromal cell types. These tissue microstructures kept in basal medium without growth factors preserve their intercellular contacts, the tissue architecture, and remain hormone responsive for several days. They are readily processed for RNA and protein extraction, histological analysis or stored in freezing medium. Fluorescence activated cell sorting (FACS) can be used to enrich for specific cell populations. This protocol provides a straightforward, standard approach for translational studies with highly complex, varied human specimens.

An Ex vivo Model to Study Hormone Action in the Human Breast

We have developed a novel ex vivo model to study hormone action in the human breast. It is based on tissue microstructures isolated from surgical breast tissue specimens which preserve tissue architecture, intercellular interactions, and paracrine signaling.

The study of hormone action in the human breast has been hampered by lack of adequate model systems. Upon in vitro culture, primary mammary epithelial ...

Human Dupuytren's Ex Vivo Culture for the Study of Myofibroblasts and Extracellular Matrix Interactions

Organ fibrosis or &#8220;scarring&#8221; is known to account for a high death toll due to the extensive amount of disorders and organs affected (from cirrhosis to cardiovascular diseases). There is no effective treatment and the in vitro tools available do not mimic the in vivo situation rendering the progress of the out of control wound healing process still enigmatic.
To date, 2D and 3D cultures of fibroblasts derived from DD patients are the main experimental models available. Primary cell cultures have many limitations; the fibroblasts derived from DD are altered by the culture conditions, lack cellular context and interactions, which are crucial for the development of fibrosis and weakly represent the derived tissue. Real-time PCR analysis of fibroblasts derived from control and DD samples show that little difference is detectable. 3D cultures of fibroblasts include addition of extracellular matrix that alters the native conditions of these cells. 
As a way to characterize the fibrotic, proliferative properties of these resection specimens we have developed a 3D culture system, using intact human resections of the nodule part of the cord. The system is based on transwell plates with an attached nitrocellulose membrane that allows contact of the tissue with the medium but not with the plastic, thus, preventing the alteration of the tissue. No collagen gel or other extracellular matrix protein substrate is required. The tissue resection specimens maintain their viability and proliferative properties for 7 days. This is the first &#8220;organ&#8221; culture system that allows human resection specimens from DD patients to be grown ex vivo and functionally tested, recapitulating the in vivo situation.

Human Dupuytren&#039;s Ex Vivo Culture for the Study of Myofibroblasts and Extracellular Matrix Interactions

Dupuytren&#8217;s disease (DD) is a fibroproliferative disease of the palm of the hand. Here, we present a protocol to culture resection specimens from DD in a three-dimensional (3D) culture system. Such short-term culture system allows preservation of the 3D structure and molecular properties of the fibrotic tissue.

Organ fibrosis or &#8220;scarring&#8221; is known to account for a high death toll due to the extensive amount of disorders and organs affected (from ...

Breast Milk Enhances Growth of Enteroids: An Ex Vivo Model of Cell Proliferation

Human small intestinal enteroids are derived from the crypts and when grown in a stem cell niche contain all of the epithelial cell types. The ability to establish human enteroid ex vivo culture systems are important to model intestinal pathophysiology and to study the particular cellular responses involved. In recent years, enteroids from mice and humans are being cultured, passaged, and banked away for future use in several laboratories across the world. This enteroid platform can be used to test the effects of various treatments and drugs and what effects are exerted on different cell types in the intestine. Here, a protocol for establishing primary stem cell-derived small intestinal enteroids derived from neonatal mice and premature human intestine is provided. Moreover, this enteroid culture system was utilized to test the effects of species-specific breast milk. Mouse breast milk can be obtained efficiently using a modified human breast pump and expressed mouse milk can then be used for further research experiments. We now demonstrate the effects of expressed mouse, human, and donor breast milk on the growth and proliferation of enteroids derived from neonatal mice or premature human small intestine.

Breast Milk Enhances Growth of Enteroids: An Ex Vivo Model of Cell Proliferation

This protocol describes how to establish an enteroid culture system from neonatal mouse or premature human intestine as well as an efficient method to collect milk from mice.

Human small intestinal enteroids are derived from the crypts and when grown in a stem cell niche contain all of the epithelial cell types. The ability to ...

A Small Animal Model of Ex Vivo Normothermic Liver Perfusion

There is a significant shortage of liver allografts available for transplantation, and in response the donor criteria have been expanded. As a result, normothermic ex vivo liver perfusion (NEVLP) has been introduced as a method to evaluate and modify organ function. NEVLP has many advantages in comparison to hypothermic and subnormothermic perfusion including reduced preservation injury, restoration of normal organ function under physiologic conditions, assessment of organ performance, and as a platform for organ repair, remodeling, and modification. Both murine and porcine NEVLP models have been described. We demonstrate a rat model of NEVLP and use this model to show one of its important applications &#8212; the use of a therapeutic molecule added to liver perfusate. Catalase is an endogenous reactive oxygen species (ROS) scavenger and has been demonstrated to decrease ischemia-reperfusion in the eye, brain, and lung. Pegylation has been shown to target catalase to the endothelium. Here, we added pegylated-catalase (PEG-CAT) to the base perfusate and demonstrated its ability to mitigate liver preservation injury. An advantage of our rodent NEVLP model is that it is inexpensive in comparison to larger animal models. A limitation of this study is that it does not currently include post-perfusion liver transplantation. Therefore, prediction of the function of the organ post-transplantation cannot be made with certainty. However, the rat liver transplant model is well established and certainly could be used in conjunction with this model. In conclusion, we have demonstrated an inexpensive, simple, easily replicable NEVLP model using rats. Applications of this model can include testing novel perfusates and perfusate additives, testing software designed for organ evaluation, and experiments designed to repair organs.

A Small Animal Model of Ex Vivo Normothermic Liver Perfusion

There is a significant liver donor shortage, and criteria for liver donors have been expanded. Normothermic ex vivo liver perfusion (NEVLP) has been developed to evaluate and modify organ function. This study demonstrates a rat model of NEVLP and tests the ability of pegylated-catalase, to mitigate liver preservation injury.

There is a significant shortage of liver allografts available for transplantation, and in response the donor criteria have been expanded. As a result, ...

Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System

Since its invention in the late 19th century, the Langendorff ex vivo heart perfusion system continues to be a relevant tool for studying a broad spectrum of physiological, biochemical, morphological, and pharmacological parameters in centrally denervated hearts. Here, we describe a setup for the modulation of the intracardiac autonomic nervous system and the assessment of its influence on basic electrophysiology, arrhythmogenesis, and cyclic adenosine monophosphate (cAMP) dynamics. The intracardiac autonomic nervous system is modulated by the mechanical dissection of atrial fat pads-in which murine ganglia are located mainly&#8212;or by the usage of global as well as targeted pharmacological interventions. An octapolar electrophysiological catheter is introduced into the right atrium and the right ventricle, and epicardial-placed multi-electrode arrays (MEA) for high-resolution mapping are used to determine cardiac electrophysiology and arrhythmogenesis. F&#246;rster resonance energy transfer (FRET) imaging is performed for the real-time monitoring of cAMP levels in different cardiac regions. Neuromorphology is studied by means of antibody-based staining of whole hearts using neuronal markers to guide the identification and modulation of specific targets of the intracardiac autonomic nervous system in the performed studies. The ex vivo Langendorff setup allows for a high number of reproducible experiments in a short time. Nevertheless, the partly open nature of the setup (e.g., during MEA measurements) makes constant temperature control difficult and should be kept to a minimum. This described method makes it possible to analyze and modulate the intracardiac autonomic nervous system in decentralized hearts.

Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System

Here, we present a protocol for the modulation of the intracardiac autonomic nervous system and the assessment of its influence on basic electrophysiology, arrhythmogenesis, and cAMP dynamics using an ex vivo Langendorff setup.

Since its invention in the late 19th century, the Langendorff ex vivo heart perfusion system continues to be a relevant tool for studying a broad spectrum ...

Ex Vivo Corneal Organ Culture Model for Wound Healing Studies

The cornea has been used extensively as a model system to study wound healing. The ability to generate and utilize primary mammalian cells in two dimensional (2D) and three dimensional (3D) culture has generated a wealth of information not only about corneal biology but also about wound healing, myofibroblast biology, and scarring in general. The goal of the protocol is an assay system for quantifying myofibroblast development, which characterizes scarring. We demonstrate a corneal organ culture ex vivo model using pig eyes. In this anterior keratectomy wound, corneas still in the globe are wounded with a circular blade called a trephine. A plug of approximately 1/3 of the anterior cornea is removed including the epithelium, the basement membrane, and the anterior part of the stroma. After wounding, corneas are cut from the globe, mounted on a collagen/agar base, and cultured for two weeks in supplemented-serum free medium with stabilized vitamin C to augment cell proliferation and extracellular matrix secretion by resident fibroblasts. Activation of myofibroblasts in the anterior stroma is evident in the healed cornea. This model can be used to assay wound closure, the development of myofibroblasts and fibrotic markers, and for toxicology studies. In addition, the effects of small molecule inhibitors as well as lipid-mediated siRNA transfection for gene knockdown can be tested in this system.

A protocol for an ex vivo corneal organ culture model useful for wound healing studies is described. This model system can be used to assess the effects of agents to promote regenerative healing or drug toxicity in an organized 3D multicellular environment.

The cornea has been used extensively as a model system to study wound healing. The ability to generate and utilize primary mammalian cells in two ...

Preclinical Model of Hind Limb Ischemia in Diabetic Rabbits

Peripheral vascular disease is a widespread clinical problem that affects millions of patients worldwide. A major consequence of peripheral vascular disease is the development of ischemia. In severe cases, patients can develop critical limb ischemia in which they experience constant pain and an increased risk of limb amputation. Current therapies for peripheral ischemia include bypass surgery or percutaneous interventions such as angioplasty with stenting or atherectomy to restore blood flow. However, these treatments often fail to the continued progression of vascular disease or restenosis or are contraindicated due to the overall poor health of the patient. A promising potential approach to treat peripheral ischemia involves the induction of therapeutic neovascularization to allow the patient to develop collateral vasculature. This newly formed network alleviates peripheral ischemia by restoring perfusion to the affected area. The most frequently employed preclinical model for peripheral ischemia utilizes the creation of hind limb ischemia in healthy rabbits through femoral artery ligation. In the past, however, there has been a strong disconnect between the success of preclinical studies and the failure of clinical trials regarding treatments for peripheral ischemia. Healthy animals typically have robust vascular regeneration in response to surgically induced ischemia, in contrast to the reduced vascularity and regeneration in patients with chronic peripheral ischemia. Here, we describe an optimized animal model for peripheral ischemia in rabbits that includes hyperlipidemia and diabetes. This model has reduced collateral formation and blood pressure recovery in comparison to a model with a higher cholesterol diet. Thus, the model may provide better correlation with human patients with compromised angiogenesis from the common co-morbidities that accompany peripheral vascular disease.

We describe a surgical procedure used to induce peripheral ischemia in rabbits with hyperlipidemia and diabetes. This surgery acts as a preclinical model for conditions experienced in peripheral artery disease in patients. Angiography is also described as a means to measure the extent of introduced ischemia and recovery of perfusion.

Peripheral vascular disease is a widespread clinical problem that affects millions of patients worldwide. A major consequence of peripheral vascular ...

Murine Precision-Cut Liver Slices as an Ex Vivo Model of Liver Biology

Understanding the mechanisms of liver injury, hepatic fibrosis, and cirrhosis that underlie chronic liver diseases (i.e., viral hepatitis, non-alcoholic fatty liver disease, metabolic liver disease, and liver cancer) requires experimental manipulation of animal models and in vitro cell cultures. Both techniques have limitations, such as the requirement of large numbers of animals for in vivo manipulation. However, in vitro cell cultures do not reproduce the structure and function of the multicellular hepatic environment. The use of precision-cut liver slices is a technique in which uniform slices of viable mouse liver are maintained in laboratory tissue culture for experimental manipulation. This technique occupies an experimental niche that exists between animal studies and in vitro cell culture methods. The presented protocol describes a straightforward and reliable method to isolate and culture precision-cut liver slices from mice. As an application of this technique, ex vivo liver slices are treated with bile acids to simulate cholestatic liver injury and ultimately assess the mechanisms of hepatic fibrogenesis.

This protocol provides a simple and reliable method for the production of viable precision-cut liver slices from mice. The ex vivo tissue samples can be maintained under laboratory tissue culture conditions for multiple days, providing a flexible model to examine liver pathobiology.

Understanding the mechanisms of liver injury, hepatic fibrosis, and cirrhosis that underlie chronic liver diseases (i.e., viral hepatitis, non-alcoholic ...