Distinct transcriptomic patterns in bicuspid aortic valve aortopathy suggest a unique mechanism of ascending aortic aneurysm progression

Objective: To compare RNA-sequencing-derived transcriptomic profiles of thoracic aortic aneurysm tissue from individuals with bicuspid versus trileaflet aortic valves. Methods: Human ascending aortic tissue was collected from patients undergoing cardiac surgery at a single institution between January 2021 and December 2022 with bicuspid aortic valves (BAV) and trileaflet aortic valves (TAV) with (-A) and without (-N) thoracic aortic aneurysm. TAV-N tissue was collected from heart transplant donors. The decision to perform ascending aortic replacement was at surgeon discretion following ACC/AHA guidelines. Bulk RNA was extracted from the aortic wall, and Illumina RNA Sequencing performed. Differential gene expression analysis, enrichment analyses, network analysis, and deconvolution single cell-mapping were performed in R. Cell-type specificity of differentially expressed genes was determined using an established Aorta single cell RNA sequencing matrix. Results: Tissue samples from 60 patients were included: 4 TAV-N, 16 BAV-N, 28 BAV-A, and 12 TAV-A. Average absolute aortic diameter was 5.1 +/- 0.38 cm for BAV-A and 5.3 +/- 0.44 cm for TAV-A, as measured on pre-operative CT. Gene ontology analyses of differentially expressed genes revealed enrichment of genes associated with extracellular matrix (ECM) organization, cellular receptor interactions and vascular smooth muscle cell (VSMC) function in BAV-A and BAV-N. In contrast, analysis of TAV-A versus TAV-N showed enrichment in genes associated with immune and inflammatory processes. Cell-type specificity analysis revealed a downregulation of genes associated with ECM components, cell signaling, and ECM remodeling in mesenchymal cells, VSMCs, and matrix fibroblasts specifically in BAV-A versus BAV-N. Conclusions: The transcriptome changes observed in aneurysmal aortas of BAV and TAV patients are distinct, suggesting mechanistic differences contributing to aneurysm development and progression. The observed differences in gene expression between the non-aneurysmal aortas may signify a predisposition to aneurysm development unique to BAV aortopathy.