APLN and atherosclerosis: It promotes vascular smooth muscle cell proliferation,73 and loss of the apelin receptor protects against the development of atherosclerosis in the apolipoprotein E knockout mouse.74 However, loss of apelin promotes atherosclerosis in this model and apelin treatment reduces angiotensin II-induced atherosclerosis43 and enhances atherosclerotic plaque stability.75 The reasons for these discrepancies are unclear, and to date, there is no evidence for ligand-independent signalling at the apelin receptor in this setting.