Abstract Body: Background and Objective:Thoracic aortic aneurysm (TAA) is an asymptomatic, life-threatening disease with high mortality greater than 80% after rupture. The assembly of cytoskeletal structural proteins, e.g. Filamin A (FLNA) with extracellular matrix (ECM), which helps in maintaining aortic structural integrity and function, is highly disrupted in TAA. Besides surgical interventions, no medical therapies are available to blunt TAA progression and rupture. miR-146a, a short non-coding microRNA, is well known to regulate inflammatory and auto-immune processes under cardiovascular diseases. Increased miR-146a has been observed in plasma and dissected aortic tissue of TAA patients. In this study, we examined the effect of miR-146a deficiency on TAA rupture in mice induced by Lysyl oxidase inhibitor, β-aminopropionitrile (BAPN).
Methods and Results: 3-week-old male and female C57BL/6J miR146a wild type (WT) or deficient (KO) [n=12-18/group] mice were administered with either vehicle or BAPN (0.5% wt/vol) in drinking water for 28 days. TAA was examined by in vivo ultrasound aortic lumen measurements and ex vivo aortic external width measurements. Mortality by TAA rupture was calculated. BAPN administration promoted TAA development equivalently in both WT and KO male [WT=67%,12/18; KO=62%,8/13] and female [WT=75%,9/12; KO=50%,8/16] mice compared to control. miR-146a deficiency significantly protected mice from BAPN-induced TAA rupture (Male-WT=33%,6/18; KO=0%,0/13; Female-WT=33%,4/12; KO=0%,0/16; P<0.05) and improved survival rate (P<0.05). Histological analyses showed a strong increase in adventitial collagen in miR-146a KO mice administered with BAPN compared to WT-BAPN. In silico target prediction identified miR-146a binding sites in the cytoskeletal structural protein FLNA 3’UTR. Western blot and immunohistochemical analyses revealed a strong reduction of FLNA protein in WT-BAPN mice especially in the SMC-rich aortic medial layer, whereas miR-146a deficiency prevented BAPN-induced loss of aortic FLNA protein. Immunofluorescence staining of FLNA and F-actin on aortic SMCs transfected with miR-146a mimetics showed a strong and significant suppression of FLNA associated with disorganized F-actin compared to control.
Conclusion: Our findings suggest that miR-146a deficiency significantly protects mice from BAPN-induced TAA rupture, which is associated with preserved cytoskeletal structural protein FLNA in SMC-rich medial layer and adventitial collagen in the aorta.