PROJECT SUMMARY
Aneurysms, which are defined as a 50% increase in the diameter of a blood vessel, are an important cause of
death worldwide. Aortic aneurysms (AAs) are the most common type and they are divided into two groups:
thoracic (TAAs) and abdominal (AAAs). All aneurysms share similar histopathologic features of elastic fiber
fragmentation, disorganization and loss of smooth muscle cells (SMCs) and accumulation of collagen and
proteoglycans, however, TAAs and AAAs differ in their pathogenesis. While TAAs have a strong genetic
predilection, AAAs are considered of atherothrombotic origin. Regardless of type, there is currently no directed
medical therapy for AAs, which progressively enlarge over time, increasing the risk of vessel rupture and fatal
hemorrhage. Therefore, there is an urgent need to understand the pathogenesis of AAs to devise targeted
therapeutic strategies. A single gene mutation is identified in nearly 20% of individuals with TAAs and the genes
identified to date largely belong to three functional groups: 1) extracellular matrix (ECM) organization, 2)
transforming growth factor b signaling and 3) SMC contractility, which underscores the importance of the interplay
between the cell, signaling and the ECM in the pathogenesis of AAs. SMCs have been the focus of investigation
in AA pathogenesis, however it is increasingly recognized that endothelial cells (ECs) play a role through
endothelial dysfunction. We and others identified mutations in lysyl oxidase (LOX), a gene that encodes an
enzyme important for collagen and elastin crosslinking, as a cause of inherited TAAs in humans. Mice
homozygous for a Lox mutation identified in humans die perinatally of aneurysm rupture similar to mice lacking
LOX, therefore it is challenging to study AA pathogenesis and progression using these models. Our collaborator,
Dr. Philip Trackman at the Forsyth Institute, generated a conditional Lox mouse model, which when bred to mice
carrying Cre recombinase in certain cell types will lead to deletion or loss of LOX from that cell type. Dr. Trackman
generously shared this mouse model with us and we have bred to mice expressing Cre recombinase in ECs,
SMCs as well as specific SMCs of the ascending aorta, which are derived from two developmental origins. Our
preliminary data show increased proliferation markers in the ascending aorta where aneurysms are present. This
observation led us to hypothesize that loss of LOX leads to a phenotypic change in the cell from a differentiated
phenotype to a proliferative phenotype contributing to aneurysmal disease. This hypothesis will be explored in
this application. Results generated from the proposed studies will not only further our understanding of the role
LOX plays in arterial development and maintenance, but they will also help identify new pathways that may be
leveraged to develop targeted therapeutic strategies for aneurysmal disease.