Abstract 498: Decreased High-Density Lipoprotein Cholesterol Levels and Macrophage Cholesterol Efflux Capacity in Mice Lacking Proprotein Convertase Subtilisin/Kexin Type 9
Background: Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates low-density lipoprotein cholesterol catabolism and has been proposed as a promising therapeutic target for lowering low-density lipoprotein cholesterol levels in hypercholesterolemia patients. Several studies have shown that PCSK9 influences HDL cholesterol levels, however the molecular mechanism and potential consequence of targeting PCSK9 needs further study.
Methods and Results: We isolated serum from Pcsk9 knockout (KO) mice to determine HDL cholesterol levels, HDL subunits and macrophage cholesterol efflux capacity. HDL cholesterol levels in Pcsk9 KO mice were significantly decreased in both sexes fed a normal chow and an atherogenic diet. HDL subunits were separated by gradient gel electrophoresis and HDL proteins were identified by mass spectrometry. Apolipoprotein E (APOE) was found in large HDL subunits in C57BL6/J (B6) mice, while it was absent in Pcsk9 KO mice. We found that Pcsk9 KO mice have decreased levels of serum APOE and increased LDLR in livers. We demonstrated that LDLR regulates serum APOE level by measuring this in mice containing gain- and loss-of-function in LDLR. APOE levels were decreased in Pcsk9 KO and human LDLR overexpressing transgenic mice, and increased in mouse containing non-functional LDLR. We tested the hypothesis that absence of APOE in HDL of Pcsk9 KO mice decreases macrophage cholesterol efflux capacity. Decreased fluorescently-labeled cholesterol efflux of Pcsk9 KO serum was demonstrated using both human THP-1 and mouse J774A.1 macrophage foam cells in vitro. We isolated hearts from Pcsk9 KO mice fed an atherogenic diet for 10 weeks until 34 weeks of age and determined atherosclerosis susceptibility by measuring atherosclerotic lesion size. The average volume of atherosclerotic lesions in the first 120 um of the ascending aorta was not significantly different between B6 and Pcsk9 KO mice.
Conclusion: PCSK9 plays a critical role in regulating not only LDL, but also HDL in mice. The results demonstrate that increased LDLR level in Pcsk9 KO mouse liver likely decreases APOE in large HDL, which impairs macrophage cholesterol efflux capacity of Pcsk9 KO mouse serum.
- Proprotein Convertase Subtilisin/Kexin Type 9
- High-density Lipoprotein Cholesterol
- Macrophage Cholesterol Efflux
- © 2012 by American Heart Association, Inc.