Objectives— A low level of high-density lipoprotein (HDL) in plasma has been recognized as an aspect of metabolic syndrome and as a crucial risk factor of cardiovascular events. However, the physiological regulation of plasma HDL levels has not been completely defined. Current studies aim to reveal the contribution of angiopoietin-like protein3 (angptl3), previously known as a plasma suppressor of lipoprotein lipase, to HDL metabolism.

Methods and Results— Angptl3-deficient mice showed low plasma HDL cholesterol and HDL phospholipid (PL), and which were increased by ANGPTL3 supplementation via adenovirus. In vitro, ANGPTL3 inhibited the phospholipase activity of endothelial lipase (EL), which hydrolyzes HDL-PL and hence decreases plasma HDL levels, through a putative heparin-binding site in the N-terminal domain of ANGPTL3. Post-heparin plasma in Angptl3-knockout mice had higher phospholipase activity than did that in wild-type mice, suggesting that the activity of endogenous EL is elevated in Angptl3-deficient mice. Furthermore, we established an ELISA system for human ANGPTL3 and found that plasma ANGPTL3 levels significantly correlated with plasma HDL cholesterol and HDL-PL levels in human subjects.

Conclusions— Angptl3 acts as an inhibitor of EL and may be involved in the regulation of plasma HDL cholesterol and HDL-PL levels in humans and rodents.