Abstract 17136: MicroRNA-181b Inhibition Stabilises Abdominal Aortic Aneurysms by Promoting Collagen Accumulation and Elastin Deposition

Abstract

Increased matrix metalloproteinase (MMP) activity, and related collagen and elastin degradation as a result of macrophage accumulation, are key characteristics of abdominal aortic aneurysm (AAA) progression and rupture. Accordingly targeting MMPs or promoting expression of the endogenous tissue inhibitor of metalloproteinases (TIMPs), may represent novel therapeutic strategies to prevent AAA progression and rupture. To closely mimic human AAA, we used an angiotensin II (AngII)-infused, high fat-fed apolipoprotein E knockout mouse model. Sudden death due to aortic dissection/rupture, was significantly increased (30%, p<0.001, n=20) in TIMP3 KO mice compared to wild-type controls, supporting a protective role for TIMP3 in AAA progression. Moreover Q-PCR revealed that microRNA (miR)-181b, a validated repressor of TIMP3 protein expression, was up-regulated 22-fold (n=6, p<0.001) in human AAA compared to non-aneurysmal sites. In vitro, miR181b inhibition increased macrophage TIMP3 protein expression 3-fold (n=4, p<0.05), highlighting miR181b inhibition as a potential approach to retard AAA progression. Indeed using a miR181b inhibitor, AAA development and inflammation was retarded in AngII-infused high fat-fed ApoE KO mice. This effect was characterised by a 56% reduction in macrophage content (n=5, p<0.05), augmented collagen content 1.9-fold (n=5, p<0.05) and collagen fibre thickness (+24%, p<0.05) in AAAs compared to scrambled-miR control animals. AAA elastin content was also increased (1.5-fold, n=5, p<0.05) in miR181b inhibitor treated mice versus controls. Collagen accumulation was TIMP-3 dependent as miR-181b inhibition did not affect collagen levels in TIMP-3 KO mice. However elastin content remained elevated in miR-181b inhibitor treated TIMP3 KO mice (2-fold, n=6, p=0.001), suggesting a TIMP-3 independent mechanism. In vitro miR181b inhibition in smooth muscle cells revealed a 2.5-fold increase in elastin production (n=3, p<0.05), supporting a direct role for miR-181b in elastin regulation. Collectively our data show that miR181b inhibition stabilises AAA through a dual beneficial effect, by promoting collagen preservation via TIMP3 modulation, and through directly increasing elastin production and deposition.