Murine model of surgically induced acute aortic dissection type A

Abstract

Objectives: This study aimed at developing a murine model of surgically induced acute aortic dissection type A for investigation of the formation and progression of acute aortic dissection and to test whether this system could be used for biomarker discovery.

Methods: Adult fibrillin-1 deficient, Fbn1(C1039G/+) mice and wild-type mice were anesthetized, ventilated, and the ascending aorta exposed via hemisternotomy. We hypothesized that acute aortic dissection could be induced either by injecting autologous blood into the aortic wall or by injury to the wall with aortic clamping. Echocardiography was done preoperatively, and serum samples were collected before and 30 minutes after the operation and analyzed by enzyme-linked immunosorbent assay.

Results: Echocardiography revealed larger aortic root diameters in Fbn1(C1039G/+) compared with wild-type mice (P = .001). Histologic examination showed that aortic clamp injury but not injection of blood leads to large intimal tears, disruption of aortic wall structures, and localized dissection of the aortic media in Fbn1(C1039G/+) mice. Acute aortic dissection developed in 4 of 5 Fbn1(C1039G/+) mice versus 0 of 5 wild-type mice after aortic clamping (P < .01). Elastin staining showed higher elastic fiber fragmentation and disarray in Fbn1(C1039G/+) compared with wild-type mice. Enzyme-linked immunosorbent assay analysis revealed elevated circulating transforming growth factor beta1 concentrations after induction of acute aortic dissection in Fbn1(C1039G/+) mice (P = .02, 150 +/- 61 ng/mL vs 456 +/- 97 ng/mL), but not in wild-type or sham-operated mice.

Conclusions: Aortic clamp injury can induce AAD in Fbn1(C1039G/+), but not in wild-type mice. This murine model of surgically induced acute aortic dissection is highly reproducible and nonlethal in the short term. Using this system, we revealed that circulating transforming growth factor beta1 is a promising biomarker for acute aortic dissection.

Figure 1

(A) Intraoperative view through the dissecting microscope (Microsurgery Instruments Inc., Bellaire, TX) showing the surgical approach through an upper partial sternotomy and the opened pericardium in a Fbn1^C1039G/+ mouse. The ascending aorta (tip of the arrow) was partially clamped with a microsurgical needleholder. (B) Macroscopic view of the ascending aorta 30 minutes after the aortic clamp injury in the Fbn1^C1039G/+ mouse. The aortic dissection was induced by clamping in the middle part of the ascending aorta (*). After the clamp injury, the hematoma and partially the dissection extended towards the aortic root and the distal ascending aorta (arrows). Ao=ascending aorta; Cr=cranial; RV=right ventricle.

Figure 2

Histological sections of the ascending aorta stained with hematoxylin and eosin. (A) Aortic section in a wild-type mouse after the aortic clamp injury which led to transmural tears (arrows) and periadventitial hematoma, however no aortic media dissection occurred. (B-D) In contrast, the clamp injury in Fbn1^C1039G/+ mice resulted in large intimal tears, disruption and break-up of the aortic medial layer with subsequent localized dissection and blood within the aortic media (arrows). WT=wild-type, Lu=lumen of the vessel.

Figure 3

Verhoeff-van Gieson (VVG; elastin) stained sections of the ascending aorta in Fbn1^C1039G/+ mice. (A–D) The aortic clamp injury led to extensive intimal tears, disruption of elastic fibers and localized dissection with blood within the aortic medial layer (arrows). Lu=lumen of the vessel.

Figure 4

Verhoeff-van Gieson (VVG; elastin) stained sections of the ascending aorta in Fbn1^C1039G/+ mice at 1 month, 4 months and 9 months of age. Histological sections show progressive fragmentation and disarray of elastic fibers (arrows), and increased matrix deposition within the aortic media over time. While severe structural aortic wall changes already exist in 4 month old Fbn1^C1039G/+ mice, these lesions translate into progressive aortic root dilatation with increasing age and subsequently a predisposition for developing aortic dissection. Lu=lumen of the vessel.

Figure 5

Circulating TGFβ1 serum concentrations in Fbn1^C1039G/+ and age-matched wild-type mice before (pre-clamping) and 30 minutes after (post-clamping) the aortic clamp injury. Circulating TGFβ1 levels significantly increased after inducing the AAD in Fbn1^C1039G/+ mice (P=0.02), but not in wild-type mice and sham operated litters. The graph shows each data point (square), mean values (rhombus) and SEM.