摘要METRNL is a recently identified secreted protein with emerging functions.This study is to find major cellular source of circulating METRNL and to determine METRNL novel function.Here,we show METRNL is abundant in human and mouse vascular endothelium and released by endothelial cells using endoplasmic reticulum-Golgi apparatus pathway.By creating endothelial cell-specific Metml knockout mice,combined with bone marrow transplantation to produce bone marrow-specific deletion of Metrnl,we demonstrate that most of circulating METRNL(approximately 75％)originates from the endothelial cells.Both endothelial and circulating METRNL decrease in atherosclerosis mice and pa-tients.By generating endothelial cell-specific Metml knockout in apolipoprotein E-deficient mice,com-bined with bone marrow-specific deletion of Metrnl in apolipoprotein E-deficient mice,we further demonstrate that endothelial METRNL deficiency accelerates atherosclerosis.Mechanically,endothelial METRNL deficiency causes vascular endothelial dysfunction including vasodilation impairment via reducing eNOS phosphorylation at Ser1177 and inflammation activation via enhancing NFKB pathway,which promotes the susceptibility of atherosclerosis.Exogenous METRNL rescues METRNL deficiency induced endothelial dysfunction.These findings reveal that METRNL is a new endothelial substance not only determining the circulating METRNL level but also regulating endothelial function for vascular health and disease.METRNL is a therapeutic target against endothelial dysfunction and atherosclerosis.