We thank the Unit for Laboratory Animal Medicine of the University of Michigan for their help with animal feeding and breeding. This study is supported by NIH RO1 HL138139, NIH RO1 HL153710 to&#160;J. Zhang, NIH RO1 HL109946, RO1 HL134569 to Y.E. Chen, and the American Heart Association grant 20POST35110064 to G. Zhao.

The animal protocols were approved by the University of Michigan Institutional Animal Care and Use Committee (PRO00010092). Male and female C57BL/6J wild-type (WT) mice, ~7 weeks of age, were used for the experiments.
1. Animal preparation
<ol>
	<li>Feed the mice with the standard chow diet (see Table of Materials) before and after the surgery. 
	&#8203;NOTE: Different strains and ages of mice can be used. However, age ranging from 5.5-12 week-old is re...

<ol>
	<li>Kent, K. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+practice:+Abdominal+aortic+aneurysms.">Clinical practice: Abdominal aortic aneurysms.</a> The New England Journal of Medicine. 371 (22), 2101-2108 (2014).</li><li>Karthikesalingam, 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=Mortality+from+ruptured+abdominal+aortic+aneurysms:+Clinical+lessons+from+a+comparison+of+outcomes+in+England+and+the+USA.">Mortality from ruptured abdominal aortic aneurysms: Clinical lessons from a comparison of outcomes in England and the USA.</a> Lancet. 383 (9921), 963-969 (2014).</li><li>Noel, A. 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=Ruptured+abdominal+aortic+aneurysms:+The+excessive+mortality+rate+of+conventional+repair.">Ruptured abdominal aortic aneurysms: The excessive mortality rate of conventional repair.</a> Journal of Vascular Surgery. 34 (1), 41-46 (2001).</li><li>Lederle, F. 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=Rupture+rate+of+large+abdominal+aortic+aneurysms+in+patients+refusing+or+unfit+for+elective+repair.">Rupture rate of large abdominal aortic aneurysms in patients refusing or unfit for elective repair.</a> JAMA. 287 (22), 2968-2972 (2002).</li><li>Kochanek, K. D., Xu, J., Murphy, S. L., Minino, A. M., Kung, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deaths:+Final+data+for+2009.">Deaths: Final data for 2009.</a> National Vital Statistics Reports. 60 (3), 1 (2011).</li><li>Daugherty, A., Cassis, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+abdominal+aortic+aneurysm+formation.">Mechanisms of abdominal aortic aneurysm formation.</a> Current Atherosclerosis Reports. 4 (3), 222-227 (2002).</li><li>Quintana, R. A., Taylor, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+mechanisms+of+aortic+aneurysm+formation.">Cellular mechanisms of aortic aneurysm formation.</a> Circulation Research. 124 (4), 607-618 (2019).</li><li>Kuivaniemi, H., Ryer, E. J., Elmore, J. R., Tromp, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+pathogenesis+of+abdominal+aortic+aneurysms.">Understanding the pathogenesis of abdominal aortic aneurysms.</a> Expert Review of Cardiovascular Therapy. 13 (9), 975-987 (2015).</li><li>Trollope, A., Moxon, J. V., Moran, C. S., Golledge, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Animal+models+of+abdominal+aortic+aneurysm+and+their+role+in+furthering+management+of+human+disease.">Animal models of abdominal aortic aneurysm and their role in furthering management of human disease.</a> Cardiovascular Pathology. 20 (2), 114-123 (2011).</li><li>Patelis, 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=Animal+models+in+the+research+of+abdominal+aortic+aneurysms+development.">Animal models in the research of abdominal aortic aneurysms development.</a> Physiological Research. 66 (6), 899-915 (2017).</li><li>Senemaud, 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=Translational+relevance+and+recent+advances+of+animal+models+of+abdominal+aortic+aneurysm.">Translational relevance and recent advances of animal models of abdominal aortic aneurysm.</a> Arteriosclerosis, Thrombosis, and Vascular Biology. 37 (3), 401-410 (2017).</li><li>Lysgaard Poulsen, J., Stubbe, J., Lindholt, 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=Animal+models+used+to+explore+abdominal+aortic+aneurysms:+A+systematic+review.">Animal models used to explore abdominal aortic aneurysms: A systematic review.</a> European Journal of Vascular and Endovascular Surgery. 52 (4), 487-499 (2016).</li><li>Tsui, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+models+of+abdominal+aortic+aneurysms.">Experimental models of abdominal aortic aneurysms.</a> Open Cardiovascular Medicine Journal. 4, 221-230 (2010).</li><li>Manning, M. W., Cassi, L. A., Huang, J., Szilvassy, S. J., Daugherty, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Abdominal+aortic+aneurysms:+Fresh+insights+from+a+novel+animal+model+of+the+disease.">Abdominal aortic aneurysms: Fresh insights from a novel animal model of the disease.</a> Vascular Medicine. 7 (1), 45-54 (2002).</li><li>Chiou, A. C., Chiu, B., Pearce, W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Murine+aortic+aneurysm+produced+by+periarterial+application+of+calcium+chloride.">Murine aortic aneurysm produced by periarterial application of calcium chloride.</a> Journal of Surgical Research. 99 (2), 371-376 (2001).</li><li>Allaire, E., Guettier, C., Bruneval, P., Plissonnier, D., Michel, 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=Cell-free+arterial+grafts:+Morphologic+characteristics+of+aortic+isografts,+allografts,+and+xenografts+in+rats.">Cell-free arterial grafts: Morphologic characteristics of aortic isografts, allografts, and xenografts in rats.</a> Journal of Vascular Surgery. 19 (3), 446-456 (1994).</li><li>Anidjar, 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=Elastase-induced+experimental+aneurysms+in+rats.">Elastase-induced experimental aneurysms in rats.</a> Circulation. 82 (3), 973-981 (1990).</li><li>Sun, 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=Mast+cells+modulate+the+pathogenesis+of+elastase-induced+abdominal+aortic+aneurysms+in+mice.">Mast cells modulate the pathogenesis of elastase-induced abdominal aortic aneurysms in mice.</a> Journal of Clinical Investigation. 117 (11), 3359-3368 (2007).</li><li>Bhamidipati, C. 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=Development+of+a+novel+murine+model+of+aortic+aneurysms+using+peri-adventitial+elastase.">Development of a novel murine model of aortic aneurysms using peri-adventitial elastase.</a> Surgery. 152 (2), 238-246 (2012).</li><li>Pyo, R., 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=Targeted+gene+disruption+of+matrix+metalloproteinase-9+(gelatinase+B)+suppresses+development+of+experimental+abdominal+aortic+aneurysms.">Targeted gene disruption of matrix metalloproteinase-9 (gelatinase B) suppresses development of experimental abdominal aortic aneurysms.</a> Journal of Clinical Investigation. 105 (11), 1641-1649 (2000).</li><li>Tanaka, A., Hasegawa, T., Chen, Z., Okita, Y., Okada, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+rat+model+of+abdominal+aortic+aneurysm+using+a+combination+of+intraluminal+elastase+infusion+and+extraluminal+calcium+chloride+exposure.">A novel rat model of abdominal aortic aneurysm using a combination of intraluminal elastase infusion and extraluminal calcium chloride exposure.</a> Journal of Vascular Surgery. 50 (6), 1423-1432 (2009).</li><li>Busch, 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=Four+surgical+modifications+to+the+classic+elastase+perfusion+aneurysm+model+enable+haemodynamic+alterations+and+extended+elastase+perfusion.">Four surgical modifications to the classic elastase perfusion aneurysm model enable haemodynamic alterations and extended elastase perfusion.</a> European Journal of Vascular and Endovascular Surgery. 56 (1), 102-109 (2018).</li><li>Liang, 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=KLF11+protects+against+venous+thrombosis+via+suppressing+tissue+factor+expression.">KLF11 protects against venous thrombosis via suppressing tissue factor expression.</a> Thrombosis and Haemostasis. , (2021).</li><li>Marinov, G. R., 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=Can+the+infusion+of+elastase+in+the+abdominal+aorta+of+the+Yucatan+miniature+swine+consistently+produce+experimental+aneurysms.">Can the infusion of elastase in the abdominal aorta of the Yucatan miniature swine consistently produce experimental aneurysms.</a> Journal of Investigative Surgery. 10 (3), 129-150 (1997).</li><li>Shannon, A. 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=Porcine+model+of+infrarenal+abdominal+aortic+aneurysm.">Porcine model of infrarenal abdominal aortic aneurysm.</a> Journal of Visualized Experiments. (153), e60169 (2019).</li></ol>

The authors have nothing to disclose.

The elastase-induced AAA model was first reported by Anidjar et al. using rats in 199017. A variety of modified versions have been introduced in the past thirty years, along with significant improvement in the surgical techniques19,20,21,22. Hundreds of institutes use elastase-induced AAA models as the second most used rodent experimental model for AAA studies<sup class=...

Abdominal aortic aneurysm (AAA) is defined as a segmental dilatation of the abdominal aorta with at least a 50% increase of vessel diameter1. AAA is potentially fatal, as the rupture can result in an extremely high mortality rate, even with intervention2,3,4. It has been reported that AAA is responsible for approximately 13,000 deaths annually in the USA, which makes it the 10th leading cause of death1,5.
The pathogenesis of AAA is not yet wholly understood6,7,8. To investigate the molecular mechanism of AAA and test potential therapeutic targets, several experimental AAA models have been established9,10. Rodent models of AAA include elastase, calcium chloride, angiotensin II and xenograft models, among which the elastase-induced AAA model is the second most used model10,11,12,13,14,15,16,17. This model involves direct infusion or application of porcine pancreatic elastase (PPE) to the infrarenal segment of the aorta. The penetration of elastase into the medial layer of the aorta will cause degradation of elastic lamellae and infiltration of inflammatory cells, leading to the loss of aortic wall integrity and subsequent dilation of abdominal aorta7,18. The elastase-induced AAA model was first reported by Anidjar et al. in 1990 using rats, in which an isolated segment of the aorta was perfused with elastase17. Later in 2012, a modified model using a periadventitial application of PPE was reported by Bhamidipati et al.19. Nowadays, most surgeries for the elastase-induced AAA model are inspired by Bhamidipati&#39;s group and are performed with the external application rather than intraluminal perfusion of PPE. Although the external application has less requirement on fine surgical skills, the incidence rate of AAA is relatively lower and size somewhat smaller than that of intraluminal perfusion11,19.
Although widely used in AAA studies, the elastase-induced AAA model possesses certain limitations. One caveat of this model is the inevitable variations of how the surgery is performed, which can lead to the issue of reproducibility. For example, the difference may exist in the surgical procedure regarding how the infrarenal segment of the aorta is isolated and which part of the segment is selected for PPE application among different laboratories. The enzymatic activity of PPE and the time duration of PPE incubation can also vary. These, however, are all essential determinants that affect the eventual AAA formation rate and aneurysm diameter.The variation of these critical determinants makes data comparison of AAA studies from different groups using this model very difficult. Therefore, a standardized surgical procedure is needed as a tool to get comparable results from various institutions.
This article describes a standardized surgical protocol for the elastase-induced AAA model through direct application of PPE to the adventitia of infrarenal abdominal aorta in mice. Details about surgical material and procedures essential for successful and robust generation of AAA in mice using this model will also be discussed.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>6-0 non-absorbable monofilament suture</td>
			<td>Pro Advantage</td>
			<td>P420697</td>
			<td></td>
		</tr>
		<tr>
			<td>Carprofen</td>
			<td>Zoetis Inc.</td>
			<td>NDC: 54771-8507</td>
			<td></td>
		</tr>
		<tr>
			<td>Chow Diet</td>
			<td>LabDiet</td>
			<td>3005659-220</td>
			<td>PicoLab 5L0D</td>
		</tr>
		<tr>
			<td>Cotton Applicator</td>
			<td>Dynarex</td>
			<td>4303</td>
			<td></td>
		</tr>
		<tr>
			<td>Cotton Pad</td>
			<td>Rael</td>
			<td>UPC: 810027130969</td>
			<td></td>
		</tr>
		<tr>
			<td>GraphPad Prism 8</td>
			<td>GraphPad Software Inc.</td>
			<td></td>
			<td>Version 8.4.3</td>
		</tr>
		<tr>
			<td>Grarfe Forceps</td>
			<td>Fine Science Tools</td>
			<td>11051-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Halsted Mosquito Hemostats</td>
			<td>Fine Science Tools</td>
			<td>13009-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Ketamine</td>
			<td>Par Pharmaceutical</td>
			<td>NDC: 42023-0115-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Nitrile gloves</td>
			<td>Fisherbrand</td>
			<td>19-130-1597</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>Thermo Fisher</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr>
			<td>Porcine pancreatic elastase</td>
			<td>Sigma-Aldrich</td>
			<td>E1250-100MG</td>
			<td></td>
		</tr>
		<tr>
			<td>Scissors</td>
			<td>Fine Science Tools</td>
			<td>14068-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile 0.9% saline solution</td>
			<td>Baxter</td>
			<td>2B1324X</td>
			<td></td>
		</tr>
		<tr>
			<td>Xylazine</td>
			<td>Akorn</td>
			<td>NDC: 59399-110-20</td>
			<td></td>
		</tr>
	</tbody>
</table>

mouse abdominal aortic aneurysm model induced by perivascular application of elastase

Abdominal aortic aneurysm (AAA), although primarily asymptomatic, is potentially life-threatening as the rupture of AAA usually has a devastating outcome. Currently, there are several distinct experimental models of AAA, each emphasizing a different aspect in the pathogenesis of AAA. The elastase-induced AAA model is the second most used rodent AAA model. This model involves direct infusion or application of porcine pancreatic elastase (PPE) to the infrarenal segment of the aorta. Due to technical challenges, most elastase-induced AAA model nowadays is performed with the external application rather than an intraluminal infusion of PPE. The infiltration of elastase will cause degradation of elastic lamellae in the medial layers, resulting in the loss of aortic wall integrity and subsequent dilation of the abdominal aorta. However, one disadvantage of the elastase-induced AAA model is the inevitable variation of how the surgery is performed. Specifically, the surgical technique of isolating the infrarenal segment of the aorta, the material used for aorta wrapping and PPE incubation, the enzymatic activity of PPE, and the time duration of PPE application can all be important determinants that affect the eventual AAA formation rate and aneurysm diameter. Notably, the difference in these factors from different studies on AAA can lead to reproducibility issues. This article describes a detailed surgical process of the elastase-induced AAA model through direct application of PPE to the adventitia of the infrarenal abdominal aorta in the mouse. Following this procedure, a stable AAA formation rate of around 80% in male and female mice is achievable. The consistency and reproducibility of AAA studies using an elastase-induced AAA model can be significantly enhanced by establishing a standard surgical procedure.

A total of twenty-three 7-week-old wild-type (WT) mice, including 12 females and 11 males, were operated following the presented protocol. The survival rate was 100% (surgical mortality excluded). Maximal abdominal aorta diameter was measured by a caliper.
AAA was defined as dilating the abdominal aorta with a 50% vessel diameter increase. Therefore, a 50% increase in the maximal abdominal aorta diameter was selected as the cut-off point for successful AAA induction. Based upon this criterion,...

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Mouse Abdominal Aortic Aneurysm Model Induced by Perivascular Application of Elastase

The present protocol describes a standardized surgical method for the elastase-induced AAA model through the direct application of elastase to the adventitia of infrarenal abdominal aorta in mice.

Abdominal aortic aneurysm (AAA), although primarily asymptomatic, is potentially life-threatening as the rupture of AAA usually has a devastating outcome. ...

This is a standardized protocol for elastase induced abdominal aortic aneurysm, which would greatly enhance the reproducibility and the consistency of studies using this model. This technique has a consistent induction rate of abdominal aortic aneurysm. It also owns the advantage of low expenses and short operation time, which will result in stronger statistical power and the reproducibility.You need to ensure the connective tissues covering the aorta were removed so that the elastase will have a better chance of penetration, but be careful not to damage the vessels. To begin, administer five milligrams per kilograms of carprofen subcutaneously, 30 minutes before the induction of anesthesia. Test the anesthetized mouse for the lack of toe pinch response before skin incision.Make a 2.5 centimeter longitudinal incision on the skin, along the midline of the middle and lower abdomen. Gently pull up the underlying muscle and make a 2.5 centimeter longitudinal incision along linea alba. Use wetted cotton tipped applicators to move the intestines and stomach to the right side of the mouse, and access the abdominal cavity.Use forceps to gently remove the connective tissue covering the abdominal aorta and inferior vena cava. Use forceps to gently dissect the backside of the abdominal aorta and inferior vena cava from the underlying muscles. Place a piece of four centimeters by four millimeters glove stripe through the backside of the abdominal aorta and inferior vena cava, and straighten the stripe.Place the stripe approximately 0.5 centimeters away from the right renal artery. Above the stripe, place a piece of three centimeters by two millimeters cotton pad through the backside of the abdominal aorta and inferior vena cava. Then, straighten the cotton pad.To incubate the elastase, use a pipette to drop 30 microliters of porcine pancreatic elastase onto the aorta segment above the cotton pad. Wrap the cotton pad and stripe around the aorta and inferior vena cava. Rinse a piece of 10 centimeters by 10 centimeters gauze with sterile 0.9%saline and place it on the abdomen.After 30 minutes, remove the stripe and cotton pad with forceps. Irrigate the aorta and abdominal cavity with 500 microliters of sterile 0.9%saline. Use gauze to absorb the remaining saline.Re-approximate the muscle layers with a running 6-0 non-absorbable monofilament suture. Then, close the skin with three to four interrupted at 6-0 non-absorbable monofilament sutures. The incidence rate of developing an abdominal aortic aneurysm on postoperative day 14 was 91.7%for female animals, while the incidence rate for male animals was 72.7%Among the 19 animals in which abdominal aortic aneurysm was developed, a 1.7 fold and 1.6 fold increase of maximum abdominal aortic diameter was observed, in females and males respectively, compared to non-surgery controls.Representative images of the aorta from non-surgery and surgery groups on a post-operative day 14 are displayed. This technique served as a potential tool to help dissect the pathophysiology of triple A and help for the discovery of new potential therapeutic targets.

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4.8K Views.  University of Michigan, Ann Arbor. This is a standardized protocol for elastase induced abdominal aortic aneurysm, which would greatly enhance the reproducibility and the consistency of studies using this model. This technique has a consistent induction rate of abdominal aortic aneurysm. It also owns the advantage of low expenses and short operation time, which will result in stronger statistical power and the reproducibility.You need to ensure the connective tissues covering the aorta were removed so that the elastase ...