Dissertation Date: Thursday, July 17, 2025
Bicuspid aortic valve (BAV) is a common congenital cardiovascular defect characterized by formation of two, rather than three, cusps. Approximately 50% of BAV patients prematurely develop calcification and aortic stenosis (AS), while the remaining subset of patients exhibits normal aortic valve function throughout life. Despite this, the factors that contribute to early onset AS in a subset of BAV patients are unknown. Our objective is to determine the contributions of BAV-specific structure, function, and mechanical stress to the temporal activation of pro-calcific signaling within the bicuspid valve. To better understand mechanical stress (i.e. wall shear stress and von Mises stress) in a pre-calcific setting, we performed fluid-structure interaction (FSI) simulations in a young adult (23-year-old) patient with BAV and compared with an age- and sex- matched normal aortic valve control patient. Simulations revealed that the most profound perturbations in mechanical stress occurred in regions of the valve cusps most prone to calcium deposition. To further understand how these perturbations in BAV may influence premature calcification in BAV, we employed a murine model of BAV that mimics human disease. We investigated the temporal progression of structure, tissue morphology, function, and gene expression changes leading up to the onset of calcification. Additionally, we associated these findings with BAV-specific mechanical stress using FSI simulations in BAV mice. In our hands, Nfatc1enCre(+);Notch1fl/fl mice develop Type 1 BAV with a raphe conjoining the right and left coronary cusps and develop mild to severe AS by 5 weeks. At 10 weeks, BAV mice develop thicker cusps and increased total cusp volume as quantified by 3D reconstruction. At 10 weeks, a subset of BAV mice develop chondrocyte-like morphological changes at the attachment region, but in the absence of calcification. This is more prevalent at 18 weeks in BAV mice and accompanied by calcium deposition as detected by alizarin red staining. Spatial transcriptomics performed on BAV mice (n=3 control, n=5 BAV) at 18 weeks further identified regionalized upregulation of early calcific markers at the attachment region in BAV, including Spp1, when compared to tricuspid aortic valve genotype controls. Preliminary FSI simulations reveal increased von Mises stress at the attachment region where early-stage calcium deposition occurs in BAV mice, further suggesting a potential role in initiating calcification. This work further substantiates our hypothesis that BAV- induced mechanical stimuli could be driving premature calcification in BAV.
