Aberrant proliferation of vascular smooth muscle cells (VSMC) is a critical contributor to the pathogenesis of atherosclerosis (AS). Our previous studies have demonstrated that apelin‐13/APJ confers a proliferative response in VSMC, however, its underlying mechanism remains elusive. In this study, we aimed to investigate the role of mitophagy in apelin‐13‐induced VSMC proliferation and atherosclerotic lesions in apolipoprotein E knockout (ApoE‐/‐) mice. Apelin‐13 enhances human aortic VSMC proliferation and proliferative regulator proliferating cell nuclear antigen expression in dose and time‐dependent manner, while is abolished by APJ antagonist F13A. We observe the engulfment of damage mitochondria by autophagosomes (mitophagy) of human aortic VSMC in apelin‐13 stimulation. Mechanistically, apelin‐13 increases p‐AMPKα and promotes mitophagic activity such as the LC3I to LC3II ratio, the increase of Beclin‐1 level and the decrease of p62 level. Importantly, the expressions of PINK1, Parkin, VDAC1, and Tom20 are induced by apelin‐13. Conversely, blockade of APJ by F13A abolishes these stimulatory effects. Human aortic VSMC transfected with AMPKα, PINK1, or Parkin and subjected to apelin‐13 impairs mitophagy and prevents proliferation. Additional, apelin‐13 not only increases the expression of Drp1 but also reduces the expressions of Mfn1, Mfn2, and OPA1. Remarkably, the mitochondrial division inhibitor‐1(Mdivi‐1), the pharmacological inhibition of Drp1, attenuates human aortic VSMC proliferation. Treatment of ApoE‐/‐ mice with apelin‐13 accelerates atherosclerotic lesions, increases p‐AMPKα and mitophagy in aortic wall in vivo. Finally, PINK1‐/‐ mutant mice with apelin‐13 attenuates atherosclerotic lesions along with defective in mitophagy. PINK1/Parkin‐mediated mitophagy promotes apelin‐13‐evoked human aortic VSMC proliferation by activating p‐AMPKα and exacerbates the progression of atherosclerotic lesions.

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APJ is a G protein‐coupled receptor and its endogenous ligand is apelin. Studies have shown that apelin/APJ system is widely distributed in the body, especially highly expressed in the vascular endothelial cells (ECs). Numerous reports have demonstrated that apelin/APJ system plays an important role in the regulation of ECs function. Our lab has demonstrated that apelin‐13 is able to promote adhesion of monocyte‐human umbilical vein EC via 14‐3‐3, and reactive oxygen species‐autophagy signaling pathways. In this review, we concentrate on the regulatory mechanism of apelin/APJ system in EC, including promotion of proliferation, migration, and angiogenesis. Moreover, we also analyze the role of apelin/APJ on endothelial dysfunction‐related diseases including atherosclerosis, diabetes, hypertension, and myocardial infarction. Finally, we summarize the most commonly used agonists and antagonists of APJ. Therefore, apelin/APJ system is expected to be a therapeutic target for the treatment of endothelial dysfunction‐related diseases.

Apelin is an endogenous ligand of seven‐transmembrane G‐protein‐coupled receptor APJ. Apelin and APJ are distributed in various tissues, including the heart, lung, liver, kidney, and gastrointestinal tract and even in tumor tissues. Studies show that apelin messenger RNA is widely expressed in gastrointestinal (GI) tissues, including stomach and small intestine, which is closely correlated with GI function. Thus, the apelin/APJ system may exert a broad range of activities in the digestive system. In this paper, we review the role of the apelin/APJ system in the digestive system in physiological conditions, such as gastric acid secretion, control of appetite and food intake, cell proliferation, cholecystokinin secretion and histamine release, gut–brain axis, GI motility, and others. In pathological conditions, the apelin/APJ system plays an important role in the healing process of stress gastric injury, the clinical features and prognosis of patients with gastric cancers, the reduction of inflammatory response to enteritis and pancreatitis, the mediation of liver fibrogenesis, the promotion of liver damage, the inhibition of liver regeneration, the contribution of splanchnic neovascularization in portal hypertension, the treatment of colon cancer, and GI oxidative damage. Overall, the apelin/APJ system plays diversified functions and regulatory roles in digestive physiology and pathology. Further exploration of the relationship between the apelin/APJ system and the digestive system will help to find new and effective drugs for treating and alleviating the pain of digestive diseases.

APJ, an orphan G protein-coupled receptor, is first identified through homology cloning in 1993. Apelin is endogenous ligand of APJ extracted from bovine stomach tissue in 1998. Apelin/APJ system is widely expressed in many kinds of cells such as endothelial cells, cardiomyocytes, especially vascular smooth muscle cell. Vascular smooth muscle cell (VSMC), an integral part of the vascular wall, takes part in many normal physiological processes. Our experiment firstly finds that apelin/APJ system enhances VSMC proliferation by ERK1/2-cyclin D1 signal pathway. Accumulating studies also show that apelin/APJ system plays a pivotal role in mediating the function of VSMC. In this paper, we review the exact role of apelin/APJ system in VSMC, including induction of proliferation and migration, enhance of contraction and relaxation, inhibition of calcification. Furthermore, we discuss the role of apelin/APJ system in vascular diseases, such as atherosclerosis, hypertension, and chronic kidney disease (CKD) from the point of VSMC. Above all, apelin/APJ system is a promising target for managing vascular disease.