Abstract 15539: Single-cell Analysis of Aortic Tissues From Patients With Marfan Syndrome Reveals Changes in Smooth Muscle Cell Differentiation

Background: Thoracic aortic aneurysms associated with Marfan syndrome (MFS) carry a high risk of mortality; however, the molecular and cellular processes leading to aortopathy in this population remain poorly understood. We aimed to use single-cell RNA (scRNA) sequencing to define the non-immune cell populations present within the aortic wall in MFS, hypothesizing that these would differ from those of non-aneurysmal control tissue. Methods: We performed scRNA sequencing of ascending aortic aneurysm tissues from MFS patients (n=3) undergoing aneurysm repair and of age-matched, non-aneurysmal control tissue from cardiac transplant donors and recipients (n=4). The Seurat package in R was used for analysis. Differentially expressed genes were identified using edgeR. Results: Eighteen non-immune cell clusters were identified, with conserved gene expression of the largest of the clusters consistent with smooth muscle cells (SMCs; n=6), fibroblasts (n=3), and endothelial cells (n=3). The SMCs and fibroblasts exhibited graded changes in their expression of contractile and extracellular matrix protein genes, supportive of a phenotypic continuum. Additionally, we identified differences in the proportions of non-immune cells in MFS tissues compared to controls. In control tissues, the most common non-immune cells expressed markers of contractile SMC maturity including CNN1 , MYH11 , and SMTN . In contrast, the largest clusters in MFS tissue were most closely related to SMCs on correlation analysis, but displayed increased expression of cyclin genes as well as immune, endothelial, and fibroblast genes indicative of de-differentiated, proliferative SMCs. Additionally, expression of genes associated with SMC phenotypic maturity, including MYH11 and MYOCD , were significantly downregulated in several of the MFS SMC clusters. Conclusion: Our data demonstrate a phenotypic continuum between fibroblasts and SMCs, with aortas from patients with MFS exhibiting an increased proportion of de-differentiated, proliferative SMCs compared to controls. Additionally, markers of SMC maturity were downregulated in SMCs in MFS compared to controls. This may be due to disruption of signaling pathways that promote differentiation.