Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) regulates the cell-surface localization of LDL receptors in hepatocytes and is associated with LDL and lipoprotein(a) [Lp(a)] uptake, reducing blood concentrations. However, the connection be-tween PCSK9 and HDL is unclear. Here, we investi-gated the association of plasma PCSK9 with HDL subpopulations and examined the effects of PCSK9 on the atheroprotective function of HDL. We exam-ined the association of PCSK9 with HDL in apoB-depleted plasma by ELISA, native PAGE, and immu-noblotting. Our analyses showed that upon apoB-depletion, total circulating PCSK9 levels were 32% of those observed in normolipidemic plasma, and only 6% of PCSK9 in the apoB-depleted plasma, including both the mature and furin-cleaved forms, was associated with HDL. We also show human re-combinant PCSK9 abolished the capacity of recon-stituted HDL to reduce the formation of ROS in endothelial cells, while a PCSK9-blocking antibody enhanced the capacity of human HDL (in apoB-depleted plasma) to reduce ROS formation in endo-thelial cells and promote endothelial cell migration. Overall, our findings suggest that PCSK9 is only minimally associated with HDL particles, but PCSK9 in apoB-depleted plasma can affect the atheropro-tective properties of HDL related to preservation of endothelial function. This study contributes to the elucidation of the pathophysiological role of plasma PCSK9 and highlights further the anti-atherosclerotic effect of PCSK9 inhibition.
