PROJECT SUMMARY Vascular Ehlers-Danlos syndrome (EDS Type IV, vEDS) is a variant of Ehlers-Danlos syndrome (EDS)—a family of connective tissue disorders with 13 defined subtypes—that is caused by mutations in the COL3A1 gene. These mutations result in reduced collagen III in the vascular ECM and typically leads to aortic dissection and aneurysm, resulting in vessel rupture. In vEDS and other EDS variants there is evidence that ECM content, protein structure, and mechanical properties are altered. Vascular endothelial cells (ECs) sense and respond to ECM composition and mechanical properties, and pathologic changes to ECM, including increased stiffness, can induce effector signaling that results in increased vascular permeability and secretion of factors such as vascular endothelial growth factor and nitric oxide. Such changes in EC phenotype and function, broadly referred to as endothelial dysfunction and can contribute to vascular diseases, such as in aneurysm formation. I hypothesize that mutations in the COL3A1 gene alter ECM mechanical properties, as a result of protein content and structural changes in the ECM, which leads to EC dysfunction and results in weakened vasculature. I will address this hypothesis with three aims using a combination of in vitro and in vivo methods. In Aim 1, I will address the impact of COL3A1 mutations on ECM composition and mechanical properties using cell-derived matrix (CDM) from vEDS patient-derived cells in vitro to determine how mutations in COL3A1 alter elastic and viscoelastic properties of ECM. In Aim 2, I will address how changes in mechanical properties of vEDS CDM relates to vascular EC phenotype and function. I will analyze endothelial cell response to vEDS CDM with varying stiffness to decouple ECM protein content and mechanics to define specific mechanisms by which pathologic CDM influences endothelial cell phenotype and vascular barrier function. In Aim 3, I will address the impact of both endothelial dysfunction and changes in ECM mechanical properties on disease progression in vivo. I will use an established mouse model of vEDS to investigate both endothelial cell phenotype and ECM mechanics in addition to vascular rupture events and overall tissue fragility to probe the link between changes in EC phenotype and aortic mechanical failure. This proposed work will identify how compromised ECM mechanical properties impact vEDS disease manifestation through the probing of endothelial cell signaling pathways related to vascular function, inflammation, and mechanotransduction. A better understanding of these pathways will lead to new routes of treatment for vEDS patients – of which there are none currently approved by the FDA. Further, these mechanisms of failure are likely more broadly relevant for aneurysm formation and progression in general (not just in vEDS patients) and may be of help for furthering research of identifying, treating, and preventing aneurysms.