NOS3 and aortic aneurysm: The importance of preserving endothelial quiescence has been well-illustrated: loss of endothelial nitric oxide synthase accelerates murine atherosclerosis and aortic aneurysm formation (12), while endothelial-specific MAPK1/2 (ERK1/2) knockout in mice has a catastrophic impact, with hypertension, decreased endothelial nitric oxide synthase expression, increased endothelin-1 expression, and death within 5 weeks (13).