PROJECT SUMMARY: Thoracic aortic aneurysm (TAA) represents a major cause of morbidity and mortality in the United States and continues to be a difficult management problem for cardiovascular surgeons. This disease process weakens the vessel wall and leads to dilation that often progresses to rupture. Currently no effective medical therapy exists. The primary focus of this laboratory is defining novel targets for non-surgical treatment of TAAs. We have developed a model of TAA in mice and established primary aortic cell cultures to study the underlying mechanisms of pathology. These models not only recapitulate the structural hallmarks of clinical TAA, but also replicate the changes in biochemical mediators in ways that are consistent with what is observed in human disease. As such, this study aims to verify the hypothesis that regulation of key molecular pathways inhibits aneurysm formation. The three molecules under investigation are: the membrane type-1 matrix metalloproteinase (MT1- MMP), Furin, and miR-133a. MT1-MMP is elevated in TAA tissue and required for development of aneurysm. MT1-MMP degrades the vascular wall, activates other enzymes, and alters cellular phenotype. TAAs do not form in mice deficient of MT1-MMP (heterozygous knockout). Furin, an activator of multiple enzymes including MT1-MMP, is elevated in TAA. This molecule has been implicated in a vast range of diseases and our data consistently suggest a role in aneurysm progression. The small non-coding RNA, miR-133a, represses both MT1-MMP and Furin. miR-133a is reduced in TAA tissue. When miR-133a is administered to mice, TAAs do not form. Cellular location of these three molecules is altered in TAA. Endocytosis (internalization), exocytosis (secretion), and vesicle trafficking (intracellular transport), all modify the above molecules' access to substrates and likely play an obligate role in aneurysm development. This study will utilize a device that facilitates cell-type specific expression of nucleic acid vectors in the thoracic aorta of mice. These vectors will directly regulate (increase/decrease/localize) the abundance and functionality of the three molecules under investigation. Our approach is therefore a combinatorial one that both enhances rigor and maximizes therapeutic effect. This investigation will define novel and clinically applicable modalities for therapeutic intervention in TAA.