Abstract 679: Modeling Thoracic Aortic Aneurysm of Bicuspid Aortic Valve Patients with Induced Pluripotent Stem Cells Reveals Distinct Phenotypes of Smooth Muscle Cells from Different LIneages

Abstract

Ascending aortic aneurysm occurs in 35%-68% patients with bicuspid aortic valves (BAV), which is more frequently than it does in patients with normal trileaflet aortic valves (TAV). In contrast to recurrent aneurysms of the ascending aorta, descending aortic aneurysms is very rare in patients with BAV. Vascular Smooth Muscle Cells (SMCs) make up the media of the aortic walls, and their contractile properties help sustain vessel tone. Interestingly, ascending aorta is populated by SMCs arising from neural crest and descending aorta by SMCs from paraxial mesoderm. An intriguing hypothesis is that the distinct susceptibility of aneurysm in the ascending and descending aorta in patients with BAV is due in part to disparities in SMC embryonic origins. To prove our hypothesis, we used an induced Pluripotent Stem Cells (iPS) model system to generate SMCs from neural crest and paraxial mesoderm. Firstly, iPSCs were established from a patient with BAV and ascending thoracic aortic aneurysm (BAV/TAA) and two control patients with normal aorta and TAV. The iPSCs pluripotency was verified by standard stem cell markers and teratoma formation. Neural crest stem cells (NCSCs) were differentiated from iPSCs and expressed neural crest markers, including P75, HNK1, AP2 and Sox9. In parallel, paraxial mesoderm cells (PMCs) were differentiated from iPSCs and expressed specific markers, including TCF15, TBX6, Meox1 and Pax1. The SMCs differentiated from both lineages had expression of SMC markers including MYH11, CNN1, ACTA2, SM22α. Interestingly, SMCs derived from BAV-NCSCs had significantly decreased in MYH11 and ACTA2 gene expression and impaired contractile property by gel contraction assay compared to SMCs derived from control-NCSCs. However, SMCs from BAV-PMCs had similar level of expression of MYH11 and ACTA2, and strong contractile activity with Carbacol treatment compared to SMCs derived from control PMCs. In conclusion, the iPS model system revealed decreased expression of contractile proteins and impairment of contractility in SMCs derived from NCSCs in BAV patient, but not in the SMCs derived from paraxial mesoderm cells. The high susceptibility of aneurysm in the ascending aorta in patients with BAV might be partly due to embryonic origin of the SMCs.