[Engulfment of senescent erythrocytes by endothelial cells promotes endothelial-to-mesenchymal transition]

Endothelial cells, as non-professional phagocytes, play a role in clearing senescent red blood cells (RBCs). This study explores the phenotypic differentiation of endothelial cells following the phagocytosis of senescent RBCs. A hypertensive mouse model was established via implantation of an angiotensin II (Ang II) micro-osmotic pump. RBCs were isolated from these mice, and an in vitro endothelial cell-RBC phagocytosis model was developed. Mito-FerroGreen and Liperfluo fluorescent probes were employed to measure mitochondrial free iron and lipid peroxidation levels, respectively. Quantitative proteomics analyzed the expression of differentially expressed proteins in endothelial cells before and after phagocytosing senescent RBCs. Results showed that, with increasing blood pressure, RBCs from the Ang II group exhibited typical aging characteristics compared to the control group, including swelling and the appearance of echinocytes, along with a significant decrease in the expression of integrin-associated protein (CD47). Following phagocytosis of senescent RBCs, endothelial cells exhibited increased mitochondrial free iron and lipid peroxidation. Quantitative proteomics analysis revealed upregulation of proteins involved in fatty acid, carbohydrate metabolism, and mesenchymal cytoskeleton in endothelial cells. Moreover, immunoblotting results showed decreased expression levels of vascular endothelial cadherin (VE-cadherin) and platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), while mesenchymal markers such as α-smooth muscle actin (α-SMA) and fibroblast-specific protein 1 (FSP-1) were significantly upregulated. These findings suggest that Ang II-induced RBC senescence promotes their phagocytosis by endothelial cells, which in turn facilitates the transition of endothelial cells into mesenchymal cells.