ILT tissue is vulnerable against fatigue failure and shows significant decreasing strength with respect to the number of load cycles. Hence, after a reasonable time of pulsating loading ILT's strength is far below its ultimate strength, and when compared with stress predictions from finite element (FE) studies, this indicates the likelihood of fatigue failure in vivo. Failure within the ILT could propagate towards the weakened vessel wall behind it and could initialize AAA failure thereafter.

Granzyme B (GZMB) is a serine protease that is abundantly expressed in advanced human atherosclerotic lesions and may contribute to plaque instability. Perforin is a pore-forming protein that facilitates GZMB internalization and the induction of apoptosis. Recently a perforin-independent, extracellular role for GZMB has been proposed. In the current study , the role of GZMB in abdominal aortic aneurysm (AAA) was assessed. Apolipoprotein E (APOE)and APOE ؊/؊ ؋ perforin ؊/؊ double knockout (GDKO, PDKO) mice were generated to test whether GZMB exerted a causative role in aneurysm formation. To induce aneurysm, mice were given angiotensin II (1000 ng/kg/min) for 28 days. GZMB was found to be abundant in both murine and human AAA specimens. GZMB deficiency was associated with a decrease in AAA and increased survival compared with APOE-KO and PDKO mice. Although AAA rupture was observed frequently in APOE-KO (46.7%; n ‫؍‬ 15) and PDKO (43.3%; n ‫؍‬ 16) mice, rupture was rarely observed in GDKO (7.1%; n ‫؍‬ 14) mice. APOE-KO mice exhibited reduced fibrillin-1 staining compared with GDKO mice, whereas in vitro protease assays demonstrated that fibrillin-1 is a substrate of GZMB. As perforin deficiency did not affect the outcome, our results suggest that GZMB contributes to AAA pathogenesis via a perforin-independent mechanism involving extracellular matrix degradation and subsequent loss of vessel An aneurysm is a permanent focal dilatation of an artery that is associated with progressive weakening of the vessel wall. Approximately 80% of all aortic aneurysms occur in the abdominal region.1 Abdominal aortic aneurysm (AAA) is an increasingly common and frequently fatal clinical condition, responsible for more than 15,000 deaths per year in the United States.1 The most significant risk factors for AAA are male gender, cigarette smoking, age, family history, and atherosclerotic disease.2,3 The incidence of AAA measuring 2.9 to 4.9 cm in diameter ranges from 1.3% in men 45 to 54 years of age to 12.5% in men 75 to 84 years of age. In women, prevalence ranges from 0% to 5.2% in the same age groups. 2Rupture occurs in approximately 20% of AAA exceeding 5 cm in diameter but is expected in over 50% of AAA greater than 7 cm. 2

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Our results suggest a role for abnormal necrotic, inflamed, proteolytic adipose tissue to the adjacent aneurysmal aortic wall in ongoing vascular damage.

The results support participation of MCs in the pathogenesis of AAA, particularly regarding neovascularization of aortic wall.