Abstract Aims Marfan syndrome is one of the most common inherited disorders of connective tissue caused by fibrillin-1 mutations, characterized by enhanced transcription factor AP-1 DNA binding activity and subsequently abnormally increased expression and activity of matrix-metalloproteinases (MMPs). We aimed to establish a novel adeno-associated virus (AAV)-based strategy for long-term expression of an AP-1 neutralizing RNA hairpin (hp) decoy oligonucleotide (dON) in the aorta to prevent aortic elastolysis in a murine model of Marfan syndrome. Methods and results Using fibrillin-1 hypomorphic mice (mgR/mgR), aortic grafts from young (9 weeks old) donor mgR/mgR mice were transduced ex vivo with AAV vectors and implanted as infrarenal aortic interposition grafts in mgR/mgR mice. Grafts were explanted after 30 days. For in vitro studies, isolated primary aortic smooth muscle cells (SMCs) from mgR/mgR mice were used. Elastica-van-Giesson staining visualized elastolysis, reactive oxygen species (ROS) production was assessed using dihydroethidine staining. RNA F.I.S.H. verified AP-1 hp dON generation in the ex vivo transduced aortic tissue. MMP expression and activity were assessed by western blotting and immunoprecipitation combined with zymography. Transduction resulted in stable therapeutic dON expression in endothelial and SMCs. MMP expression and activity, ROS formation as well as expression of monocyte chemoattractant protein-1 were significantly reduced. Monocyte graft infiltration declined and the integrity of the elastin architecture was maintained. RNAseq analysis confirmed the beneficial effect of AP-1 neutralization on the pro-inflammatory environment in SMCs. Conclusion This novel approach protects from deterioration of aortic stability by sustained delivery of nucleic acids-based therapeutics and further elucidated how to interfere with the mechanism of elastolysis.