Notch signaling in aortic valve development and disease

Abstract

Bicuspid aortic valve (BAV) is the most common type of cardiac malformation with an estimated prevalence of 1 % in the population. BAV results in significant morbidity usually during adulthood due to its association with aortic valve calcification and ascending aortic aneurysms. Mutations in the signaling and transcriptional regulator, NOTCH1, are a cause of bicuspid aortic valve in non-syndromic autosomal dominant human pedigrees. The Notch signaling pathway is critical for multiple cellular processes during both development and disease and is expressed in the developing and adult aortic valve consistent with the cardiac phenotypes identified in affected family members. Recent work has begun to elucidate the molecular mechanisms underlying the link between Notch1 signaling and the development of BAV and valve calcification. Using in vitro approaches, loss of Notch signaling has been shown to contribute to aortic valve calcification via Runx2-, Sox9-, and Bmp2-dependent mechanisms. In addition, Notch1 signaling has been shown to be responsive to nitric oxide signaling during this disease process. A new highly penetrant mouse model of aortic valve disease using Notch1 haploinsufficient mice that are backcrossed in an endothelial nitric oxide synthase (Nos3)-null background was generated. Notch1 and Nos3 compound mutant mice (Notch1+/-;Nos3-/-) display a nearly 100 % incidence of aortic valve malformations, most commonly BAV. The aortic valves of adult mutant mice are thickened and have associated stenosis and regurgitation. Based upon the initial discovery of NOTCH1 mutations in humans with aortic valve disease, subsequent studies have provided significant molecular insights into BAV-associated diseases.