Abstract 3445: Notch1 Represses Bmp-Dependent Aortic Valve Calcification in a Cell-Autonomous Manner

Calcific aortic stenosis is the third leading cause of adult heart disease and the most common form of acquired valvular disease in developed countries. However, the molecular pathways leading to calcification are poorly understood. We recently reported two families in which heterozygous mutations in NOTCH1 that resulted in premature stop codons caused bicuspid aortic valve and severe calcification of the aortic valve. Notch1 is a part of a highly conserved signaling pathway involved in cell fate decisions, cell differentiation, and cardiac valve formation. We found that mice heterozygous-null for Notch1 had over four-fold more aortic valve calcification compared to age and sex matched littermates (p<0.03). To determine what cell type is involved in the Notch1 related calcification, Notch1+/− bone-marrow was transplanted into wild-type mice. Six months after transplant, there was no difference in the amount of aortic valve calcification between the recipients of Notch1+/− bone-marrow versus recipients of control bone-marrow. In contrast, cultured sheep aortic valve interstitial cells (AVICs) treated with a chemical inhibitor of Notch signaling developed over five-fold more calcification (p<0.03). We found that expression of Bmp2, which has been implicated in human aortic valve disease, was 3-fold higher in aortic valve leaflets of Notch1+/− mice compared to wild type littermates (p<0.02). Furthermore, AVICs treated with the Notch inhibitor had increased Bmp2 protein levels and siRNA-mediated knock-down of Bmp2 expression in the AVICs blocked the calcification process induced by Notch inhibition. These findings suggest that Notch1 signaling within aortic valve cells is required for repression of Bmp2-dependent calcification pathways and may provide novel approaches to inhibit the progression of calcific aortic stenosis.