Thoracic Aortic Aneurysm Development Is Dependent on Membrane Type-1 Matrix Metalloproteinase Activity and Abundance

Thoracic aortic aneurysm (TAA) results from dysregulated remodeling of the extracellular matrix mediated by matrix metalloproteinase (MMP) activity. Previous studies identified elevated membrane type-1 MMP (MT1-MMP) abundance and activity during TAA development and suggested aortic fibroblasts as a potential key source. Herein, we extended our understanding of the role of MT1-MMP during TAA development using various MT1-MMP transgenic mouse strains. MT1-MMP deficient (MT1-MMP^+/-) mice exhibited reduced MT1-MMP abundance, activity, and collagen volume fraction following TAA induction, concomitant with reduced aortic dilatation. TAA tissue from wild-type and MT1-MMP^+/- mice showed a similar reduction in thin collagen fibers, while the MT1-MMP^+/- mice displayed no change in thick collagen fibers. The role of fibroblast-derived MT1-MMP was examined using a conditional fibroblast-specific tamoxifen-inducible MT1-MMP knockout strain (FbMT1KO). TAA-induced changes in aortic diameter and MT1-MMP abundance were attenuated in FbMT1KO mice. Using aortic fibroblasts isolated from multiple mouse strains expressing different levels of MT1-MMP, a significant correlation between MT1-MMP abundance and TGF-β activation was observed. Importantly, treatment with MT1-MMP activity-neutralizing antibody or TGF-β neutralizing antibody resulted in the attenuation aortic dilatation. Together, these findings suggest that fibroblast-derived MT1-MMP is required for TAA development, in part through its ability to induce TGF-β signaling.