Protective Role of Endothelial Fibulin-4 in Valvulo-Arterial Integrity

Background Homeostasis of the vessel wall is cooperatively maintained by endothelial cells (ECs), smooth muscle cells, and adventitial fibroblasts. The genetic deletion of fibulin-4 ( ) in smooth muscle cells ( ) leads to the formation of thoracic aortic aneurysms with the disruption of elastic fibers. Although is expressed in the entire vessel wall, its function in ECs and relevance to the maintenance of valvulo-arterial integrity are not fully understood. Methods and Results Gene silencing of was conducted on human aortic ECs to evaluate morphological changes and gene expression profile. double knockout ( ) mice in ECs and smooth muscle cells were generated and subjected to histological analysis, echocardiography, Western blotting, RNA sequencing, and immunostaining. An evaluation of the thoracic aortic aneurysm phenotype and screening of altered signaling pathways were performed. Knockdown of in human aortic ECs induced mesenchymal cell-like changes with the upregulation of mesenchymal genes, including and . mice showed the exacerbation of thoracic aortic aneurysms when compared with those of and upregulated Thbs1, a mechanical stress-responsive molecule, throughout the aorta. mice also showed progressive aortic valve thickening with collagen deposition from postnatal day 14, as well as turbulent flow in the ascending aorta. Furthermore, RNA sequencing and immunostaining of the aortic valve revealed the upregulation of genes involved in endothelial-to-mesenchymal transition, inflammatory response, and tissue fibrosis in valves and the presence of activated valve interstitial cells. Conclusions The current study uncovers the pivotal role of endothelial fibulin-4 in the maintenance of valvulo-arterial integrity, which influences thoracic aortic aneurysm progression.