Annie Demers1, Samaneh Samami1, Benjamin Lauzier1, Christine Des Rosiers1, Emilienne Tudor Ngo Sock1, Huy Ong1, Gaetan Mayer2. 1. From the Laboratory of Molecular Cell Biology (A.D., S.S., E.T.N.S., G.M.) and Laboratory of Metabolomic (C.D.R.), Montreal Heart Institute, Montréal, Québec, Canada; Université de Nantes, L'institut du thorax, Inserm UMR 1087 / CNRS UMR 6291, Nantes, France (B.L.); and Faculty of Pharmacy (H.O.), Université de Montréal, Department of Pharmacology, Faculty of Medicine (S.S., E.T.N.S., G.M.), Department of Nutrition, Faculty of Medicine (C.D.R.), and Department of Medicine (G.M.), Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada. 2. From the Laboratory of Molecular Cell Biology (A.D., S.S., E.T.N.S., G.M.) and Laboratory of Metabolomic (C.D.R.), Montreal Heart Institute, Montréal, Québec, Canada; Université de Nantes, L'institut du thorax, Inserm UMR 1087 / CNRS UMR 6291, Nantes, France (B.L.); and Faculty of Pharmacy (H.O.), Université de Montréal, Department of Pharmacology, Faculty of Medicine (S.S., E.T.N.S., G.M.), Department of Nutrition, Faculty of Medicine (C.D.R.), and Department of Medicine (G.M.), Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada. gaetan.mayer@icm-mhi.org.
Abstract
OBJECTIVE: Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes the degradation of the low-density lipoprotein receptor thereby elevating plasma low-density lipoprotein cholesterol levels and the risk of coronary heart disease. Thus, the use of PCSK9 inhibitors holds great promise to prevent heart disease. Previous work found that PCSK9 is involved in triglyceride metabolism, independently of its action on low-density lipoprotein receptor, and that other yet unidentified receptors could mediate this effect. Therefore, we assessed whether PCSK9 enhances the degradation of CD36, a major receptor involved in transport of long-chain fatty acids and triglyceride storage. APPROACH AND RESULTS: Overexpressed or recombinant PCSK9 induced CD36 degradation in cell lines and primary adipocytes and reduced the uptake of the palmitate analog Bodipy FL C16 and oxidized low-density lipoprotein in 3T3-L1 adipocytes and hepatic HepG2 cells, respectively. Surface plasmon resonance, coimmunoprecipitation, confocal immunofluorescence microscopy, and protein degradation pathway inhibitors revealed that PCSK9 directly interacts with CD36 and targets the receptor to lysosomes through a mechanism involving the proteasome. Importantly, the level of CD36 protein was increased by >3-fold upon small interfering RNA knockdown of endogenous PCSK9 in hepatic cells and similarly increased in the liver and visceral adipose tissue of Pcsk9(-/-) mice. In Pcsk9(-/-) mice, increased hepatic CD36 was correlated with an amplified uptake of fatty acid and accumulation of triglycerides and lipid droplets. CONCLUSIONS: Our results demonstrate an important role of PCSK9 in modulating the function of CD36 and triglyceride metabolism. PCSK9-mediated CD36 degradation may serve to limit fatty acid uptake and triglyceride accumulation in tissues, such as the liver.
OBJECTIVE: Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes the degradation of the low-density lipoprotein receptor thereby elevating plasma low-density lipoprotein cholesterol levels and the risk of coronary heart disease. Thus, the use of PCSK9 inhibitors holds great promise to prevent heart disease. Previous work found that PCSK9 is involved in triglyceride metabolism, independently of its action on low-density lipoprotein receptor, and that other yet unidentified receptors could mediate this effect. Therefore, we assessed whether PCSK9 enhances the degradation of CD36, a major receptor involved in transport of long-chain fatty acids and triglyceride storage. APPROACH AND RESULTS: Overexpressed or recombinant PCSK9 induced CD36 degradation in cell lines and primary adipocytes and reduced the uptake of the palmitate analog Bodipy FL C16 and oxidized low-density lipoprotein in 3T3-L1 adipocytes and hepatic HepG2 cells, respectively. Surface plasmon resonance, coimmunoprecipitation, confocal immunofluorescence microscopy, and protein degradation pathway inhibitors revealed that PCSK9 directly interacts with CD36 and targets the receptor to lysosomes through a mechanism involving the proteasome. Importantly, the level of CD36 protein was increased by >3-fold upon small interfering RNA knockdown of endogenous PCSK9 in hepatic cells and similarly increased in the liver and visceral adipose tissue of Pcsk9(-/-) mice. In Pcsk9(-/-) mice, increased hepatic CD36 was correlated with an amplified uptake of fatty acid and accumulation of triglycerides and lipid droplets. CONCLUSIONS: Our results demonstrate an important role of PCSK9 in modulating the function of CD36 and triglyceride metabolism. PCSK9-mediated CD36 degradation may serve to limit fatty acid uptake and triglyceride accumulation in tissues, such as the liver.
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