Big data analytics and scRNA-seq in human aortic aneurysms and dissections: role of endothelial MerTK.

Rationale: Aortic aneurysms and dissections (AAD) cause more than 10,000 deaths in the United States each year. However, there are no medications that can effectively prevent the pathogenesis of AAD. MER proto-oncogene tyrosine kinase (MerTK) is a key receptor for efferocytosis, a process for the clearance of apoptotic cells. Here, we mainly focused on ascending aortic aneurysms and dissections (AAAD) and investigated the role of endothelial MerTK in AAAD progression. Methods: Single-cell RNA sequencing (scRNA-seq) analysis in human AAAD samples and RNA-seq big data analytics, combined with our unique MerTK^flox/flox/Tie2^Cre mouse model with MerTK deficiency in endothelial cells (ECs), were applied to define the role of endothelial MerTK in AAAD. Results: Through comparative analyses of scRNA-seq in human AAAD (communications of ECs with other cells) and comprehensive big data analytics including about 600,000 cross analyses, we found that the expression of endothelial MerTK is significantly inhibited in human AAAD, resulting in decreased ability of ECs to engulf antigen presenting cells, phagocytes, leukocytes, blood cells and myeloid cells. Our in vivo data showed a significantly higher incidence of AAAD in MerTK ^flox/flox/Tie2^Cre mice compared to that of their littermate controls of MerTK ^flox/flox mice (100% vs. 11.1%). MerTK deficiency in ECs induces both endothelial dysfunction and SMC phenotypic alterations, subsequently promoting AAAD development. Conclusions: Our findings indicate that endothelial MerTK impairment and subsequent endothelial dysfunction and SMC phenotypic alterations represent novel mechanisms promoting AAAD.