SEC62-dependent ER-phagy contributes to apelin-13/APJ-induced monocyte-vascular endothelial cell adhesion in atherosclerosis pathogenesis

The monocyte adhesion to vascular endothelial cells constitutes a key step in atherosclerosis pathogenesis. We previously found that ROS-autophagy pathway participated in the monocyte-endothelial cell adhesion induced by angiotensin domain type 1 receptor-associated proteins (APJ) and its endogenous ligand apelin-13. In this study, we investigated what specific type of autophagy apelin-13 regulated in this process. By conducting full-scale transcriptomic analysis in apelin-13-treated human umbilical vein endothelial cells (HUVECs), we found that the transcription levels of ER-phagy receptor protein SEC62 were significantly elevated. Importantly, SEC62 was also upregulated in human atherosclerotic lesions. Thus, we investigated the effects of SEC62-dependent ER-phagy on apelin-13-induced monocyte-endothelial cell adhesion and atherosclerosis pathogenesis. We demonstrated that Apelin-13 (0.001−1 μM) dose-dependently upregulated SEC62 expression thereby inducing ER-phagy in HUVECs. This effect was reversed by autophagy inhibitor 3MA (10 mM) and endoplasmic reticulum stress inhibitor salubrinal (10 μM). The siRNA-Sec62, 3MA (10 mM), and salubrinal (10 μM) all inhibited apelin-13-induced monocyte-endothelial cells adhesion, whereas vascular endothelial cells specific SEC62 deletion alleviated atherosclerotic plaques area, intercellular adhesion molecules expression and lesional macrophages in apelin-13-treated APOE^−/− mice with high-fat and high-cholesterol diet. Moreover, we demonstrated that ubiquitin-like modification of ALDH1L1 was involved in SEC62-dependent ER-phagy in apelin-13-treated HUVECs: apelin-13 upregulated small ubiquitin-like protein UBL4A, which mediated the ubiquitination-like modification of ALDH1L1 at 812-lysine site. This, in turn, promoted insertion of ALDH1L1 into ER membrane and led to SEC62-dependent ER-phagy. We showed that siRNA-UBL4A, siRNA-ALDH1L1, siRNA-ASNA1, and the mutant of 812 lysine site of ALDH1L1 all decreased apelin-13-induced monocyte-endothelial cell adhesion. We conclude that apelin-13 induces SEC62-dependent ER-phagy to promote monocyte-endothelial cell adhesion and atherosclerosis. This study reveals new mechanisms underlying atherosclerosis and identifies a potential therapeutic target.