Name: trypsin digest protocol to analyze the retinal vasculature of a mouse model
Uploaded: 2013-06-13T13:00:00
Description: Watch this Scientific Journal Video about Trypsin Digest Protocol to Analyze the Retinal Vasculature of a Mouse Model at JoVE.com

This work was partially supported by the NIH RO1-EY019951 (AAF), Illinois Society for Prevention of Blindness (JCC, AAF), unrestricted funds to the Department of Ophthalmology from Research to Prevent Blindness (RPB), NY and RPB Medical Student Fellowship Grant (JCC).

1. Retinal Preparation
<ol>
 <li>Enucleate the mouse eye. Using one hand, open the eye lids so that the eye is visible. With the other hand, using a curved forceps (curved facing upwards), apply pressure on superior and inferior aspects of the orbit until the globe protrudes. Gently close forceps at the posterior aspect of the eye and lift in a continuous motion to enucleate the eye.</li>
 <li>Fix eye with 10% neutral buffered formalin for at least 24 hr.</li>
 <li>Place eye in PBS solution in a small Petri dish.</li>
...

<ol>
	<li>Kuwabara, T., Cogan, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+of+retinal+vascular+patterns.+I.+Normal+architecture.">Studies of retinal vascular patterns. I. Normal architecture.</a> Arch. Ophthalmol. 64, 904-911 (1960).</li><li>Kuwabara, T., Cogan, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retinal+vascular+patterns.+VII.+Acellular+change.">Retinal vascular patterns. VII. Acellular change.</a> Invest. Ophthalmol. 4, 1049-1064 (1965).</li><li>Bell, W. R., Green, W. R., Goldberg, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histopathologic+and+trypsin+digestion+studies+of+the+retina+in+incontinentia+pigmenti.">Histopathologic and trypsin digestion studies of the retina in incontinentia pigmenti.</a> Ophthalmology. 115, 893-897 (2008).</li><li>Danis, R. P., Wallow, I. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HRP/trypsin+technique+for+studies+of+the+retinal+vasculature.">HRP/trypsin technique for studies of the retinal vasculature.</a> Invest. Ophthalmol. Vis. Sci. 27, 434-437 (1986).</li><li>Kim, S. H., Chu, Y. K., Kwon, O. W., McCune, S. A., Davidorf, F. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphologic+studies+of+the+retina+in+a+new+diabetic+model;+SHR/N:Mcc-cp+rat.">Morphologic studies of the retina in a new diabetic model; SHR/N:Mcc-cp rat.</a> Yonsei Med. J. 39, 453-462 (1998).</li><li>Cuthbertson, R. A., Mandel, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anatomy+of+the+mouse+retina.+Endothelial+cell-pericyte+ratio+and+capillary+distribution.">Anatomy of the mouse retina. Endothelial cell-pericyte ratio and capillary distribution.</a> Invest. Ophthalmol. Vis. Sci. 27, 1659-1664 (1986).</li><li>Laver, N. M., Robison, W. G., Pfeffer, B. 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Endothelial cell-pericyte ratio.</a> Ophthalmic Res. 21, 106-111 (1989).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+30.">Chapter 30.</a> Diabetic Retinopathy. , (2005).</li><li>Rosenblatt, B., Benson, W. E., Yannoff, M., Duker, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+6.19+Diabetic+Retinopathy.">Chapter 6.19 Diabetic Retinopathy.</a> Ophthalmology. , (2008).</li><li>Friedenwald, J. 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+new+approach+to+some+problems+of+retinal+vascular+disease.">A new approach to some problems of retinal vascular disease.</a> Am. J. Ophthalmol. 32, 487-498 (1949).</li><li>Podesta, F., 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=Bax+is+increased+in+the+retina+of+diabetic+subjects+and+is+associated+with+pericyte+apoptosis+in+vivo+and+in+vitro.">Bax is increased in the retina of diabetic subjects and is associated with pericyte apoptosis in vivo and in vitro.</a> Am. J. Pathol. 156 (10), 1025-1032 (2000).</li><li>Dagher, Z., 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=Studies+of+rat+and+human+retinas+predict+a+role+for+the+polyol+pathway+in+human+diabetic+retinopathy.">Studies of rat and human retinas predict a role for the polyol pathway in human diabetic retinopathy.</a> Diabetes. 53, 2404-2411 (2004).</li><li>Puro, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retinovascular+physiology+and+pathophysiology:+new+experimental+approach/new+insights.">Retinovascular physiology and pathophysiology: new experimental approach/new insights.</a> Prog. Retin. Eye Res. 31, 258-270 (2012).</li><li>Roy, S., Nasser, S., Yee, M., Graves, D. T., Roy, 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+long-term+siRNA+strategy+regulates+fibronectin+overexpression+and+improves+vascular+lesions+in+retinas+of+diabetic+rats.">A long-term siRNA strategy regulates fibronectin overexpression and improves vascular lesions in retinas of diabetic rats.</a> Mol. Vis. 17, 3166-3174 (2011).</li><li>Li, Q., 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=Diabetic+eNOS-knockout+mice+develop+accelerated+retinopathy.">Diabetic eNOS-knockout mice develop accelerated retinopathy.</a> Invest. Ophthalmol. Vis. Sci. 51, 5240-5246 (2010).</li><li>Connor, K. M., 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=Quantification+of+oxygen-induced+retinopathy+in+the+mouse:+a+model+of+vessel+loss,+vessel+regrowth+and+pathological+angiogenesis.">Quantification of oxygen-induced retinopathy in the mouse: a model of vessel loss, vessel regrowth and pathological angiogenesis.</a> Nature Protocols. 4, 1565-1573 (2009).</li></ol>

Trypsin digest is a standard method to assess the vasculature of the retina. Unfortunately, it is technically challenging and can result in high rate of specimen loss if not performed correctly. Furthermore, the procedure is especially difficult in mice, which can limit the application of this technique in the commonly used genetic animal models of eye diseases. This paper provides guidance on how to perform the procedure effectively and consistently in mouse eyes.
There are several critical s...

Visualizing the vasculature of the retina is an extremely important approach to dissect the mechanisms of various eye diseases such as diabetic retinopathy. It allows one to assess the earliest vascular abnormalities, including microaneurysms, capillary degeneration, and pericyte loss 8,9 . To date, there have been several techniques developed to analyze the retinal vasculature. Perfusion of various dyes has been used to highlight the vessels, but all have shared similar limitations. Injection rarely highlights the entire retinal vasculature unless given at a high pressure, which risks rupturing and damaging the vessels 1. Immunostaining of vascular endothelium with fluorophore-labeled G isolectin B4 (Alexa Fluor 594 conjugated; I21413; Invitrogen; 1:100 dilution) and retinal flat mounts can highlight the overall architecture of the vessels, but without detailed visualization of capillaries, basement membranes and pericytes. It was noted by Friedenwald that vessels can be highlighted by staining flat-mounts of retina with periodic acid-Schiff (PAS) or hematoxylin and eosin (H&amp;E) staining 10. However, staining was non-specific to the vessels and highlighted the non-vascular tissue as well, making it difficult to differentiate the vessels. In the 1960s, Cogan and Kuwabara developed the trypsin digest technique that made it easier to visualize the retinal vasculature by digesting the nonvascular components of the retina 1. Since that time, the trypsin digest has become the gold standard method in analyzing the vasculature of the retina 2-5. However, it is important to note that other alternative techniques to isolate the vasculature have been described. The use of osmotic lysis has been used to isolate the vasculature and allow biochemical studies of the tissue 11,12, but the procedure has not been used as a primary method for anatomical study. The tissue print method has been used to isolate large segments of microvasculature and allows the ability to study the electrotonic architecture of the vasculature 13. In theory, this technique could also be used to study anatomical changes, as the quality of the vessels is high. However, it is only able to isolate segments of the entire vasculature network. Although these methods cannot replace trypsin digest, it is important to note that they have different advantages and shortcomings and are complementary in this regard.
The trypsin digest method is technically challenging and is difficult to perform consistently 6,7. Furthermore, it has been noted that trypsin digest is especially difficult on a mouse model, particularly if one desires to preserve the overall vascular architecture of the retina 6,7. Challenges include (1) over-digestion of the retina that causes loss of both the vasculature as well as non-vascular tissue, (2) under-digestion, requiring extensive mechanical dissection which could in turn lead to damage of the vessel bed, (3) poor separation of the non-vascular tissue from the vasculature leading to non-specific staining. Several manuscripts have highlighted these challenges, but none have provided a detailed and consistent protocol to overcome them 14,15. This manuscript will introduce a step-by-step methodology detailing the technique to perform the trypsin digest on mouse and rat retinas with specific tips on handling the particularly difficult steps. A schematic overview is shown in Figure 1.

<table border="1">
	<tbody>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>REAGENTS</td>
		</tr>
		<tr>
			<td>10% neutral buffered formalin</td>
			<td>Fischer Scientific</td>
			<td>SF100-4</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Trypsin (1:250)</td>
			<td>Amresco</td>
			<td>0458-50G</td>
			<td>Make 3% trypsin in 0.1 M Tris</td>
		</tr>
		<tr>
			<td>TRIZMA base</td>
			<td>Sigma</td>
			<td>T1503-1KG</td>
			<td>Create 0.1 M Tris Buffer (pH 7.8 @ 37 &deg;C)</td>
		</tr>
		<tr>
			<td>TRIZMA</td>
			<td>Sigma</td>
			<td>T3253-500G</td>
		</tr>
		<tr>
			<td>Steritop sterile vacuum bottle</td>
			<td>Millipore</td>
			<td>SCGPS05RE</td>
			<td>Create filtered water</td>
		</tr>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>EQUIPMENT</td>
		</tr>
		<tr>
			<td>Dissecting microscope</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Any microscope that allows good visualization of the retina is adequate. (10x is sufficient with working distance of 24 mm)</td>
		</tr>
		<tr>
			<td>Straight scissors</td>
			<td>Fine Science Tools</td>
			<td>15024-10</td>
			<td>Cutting edge: 8 mm; Tip diameter: 0.2 mm; 10 cm</td>
		</tr>
		<tr>
			<td>Straight Forceps (Inox)</td>
			<td>Dumont #5</td>
			<td>11252-20</td>
			<td>Biologie tip; 0.05 x 0.02 mm; 11 cm</td>
		</tr>
		<tr>
			<td>Curved Forcepts (Dumostar)</td>
			<td>Dumont #7</td>
			<td>11297-10</td>
			<td>Biologie tip; 0.07 x 0.04 mm; 11.5 cm</td>
		</tr>
		<tr>
			<td>Dubnoff Metabolic Shaker Incubator</td>
			<td>Precision Scientific</td>
			<td>BDG59442</td>
			<td>Shaker optional</td>
		</tr>
		<tr>
			<td>24-well dish</td>
			<td>Falcon</td>
			<td>353047</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Microscope Slides</td>
			<td>VWR</td>
			<td>82027-132</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>

trypsin digest protocol to analyze the retinal vasculature of a mouse model

Trypsin digest is the gold standard method to analyze the retinal vasculature 1-5. It allows visualization of the entire network of complex three-dimensional retinal blood vessels and capillaries by creating a two-dimensional flat-mount of the interconnected vascular channels after digestion of the non-vascular components of the retina. This allows one to study various pathologic vascular changes, such as microaneurysms, capillary degeneration, and abnormal endothelial to pericyte ratios. However, the method is technically challenging, especially in mice, which have become the most widely available animal model to study the retina because of the ease of genetic manipulations 6,7. In the mouse eye, it is particularly difficult to completely remove the non-vascular components while maintaining the overall architecture of the retinal blood vessels. To date, there is a dearth of literature that describes the trypsin digest technique in detail in the mouse. This manuscript provides a detailed step-by-step methodology of the trypsin digest in mouse retina, while also providing tips on troubleshooting difficult steps.

The final product of a successful procedure is a flat-mount of the entire network of the mouse retinal vasculature, with the architecture maintained, stained with either PAS/hematoxylin or H&amp;E, as shown in Figures 2-4. Clear differentiation of endothelial cells and pericytes can be seen as shown in Figure 3. In the retina, the nuclei of endothelial cells are oval or elongated and lie entirely within the vessel wall. Pericyte nuclei are small, spherical, stain densely and generally ha...

Watch this Scientific Journal Video about Trypsin Digest Protocol to Analyze the Retinal Vasculature of a Mouse Model at JoVE.com

Trypsin Digest Protocol to Analyze the Retinal Vasculature of a Mouse Model

Trypsin digest is one of the most commonly used methods to analyze retinal vasculature. This manuscript describes the method in detail, including key alterations to optimize the technique and remove the non-vascular tissue while preserving the overall architecture of the vessels.

Trypsin digest is the gold standard method to analyze the retinal vasculature 1-5. It allows visualization of the entire network of complex ...

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