title: Apolipoproteins C-I and C-III inhibit lipoprotein lipase activity by displacement of the enzyme from lipid droplets.
abstract: Apolipoproteins (apo) C-I and C-III are known to inhibit lipoprotein lipase (LPL) activity, but the molecular mechanisms for this remain obscure. We present evidence that either apoC-I or apoC-III, when bound to triglyceride-rich lipoproteins, prevent binding of LPL to the lipid/water interface. This results in decreased lipolytic activity of the enzyme. Site-directed mutagenesis revealed that hydrophobic amino acid residues centrally located in the apoC-III molecule are critical for attachment to lipid emulsion particles and consequently inhibition of LPL activity. Triglyceride-rich lipoproteins stabilize LPL and protect the enzyme from inactivating factors such as angiopoietin-like protein 4 (angptl4). The addition of either apoC-I or apoC-III to triglyceride-rich particles severely diminished their protective effect on LPL and rendered the enzyme more susceptible to inactivation by angptl4. These observations were seen using chylomicrons as well as the synthetic lipid emulsion Intralipid. In the presence of the LPL activator protein apoC-II, more of apoC-I or apoC-III was needed for displacement of LPL from the lipid/water interface. In conclusion, we show that apoC-I and apoC-III inhibit lipolysis by displacing LPL from lipid emulsion particles. We also propose a role for these apolipoproteins in the irreversible inactivation of LPL by factors such as angptl4.
authors.affiliation: Department of Medical Biosciences/Physiological Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Mikael
authors.initials: M
authors.lastname: Larsson
authors.affiliation: Department of Medical Biosciences/Physiological Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Evelina
authors.initials: E
authors.lastname: Vorrsjö
authors.affiliation: Centre for Cardiovascular Genetics, Institute of Cardiovascular Science, University College London, 5 University Street, London WC1E 6JF, United Kingdom.
authors.forename: Philippa
authors.initials: P
authors.lastname: Talmud
authors.affiliation: Department of Chemistry, Tallinn University of Technology, Tallinn 12618, Estonia.
authors.forename: Aivar
authors.initials: A
authors.lastname: Lookene
authors.affiliation: Department of Medical Biosciences/Physiological Chemistry, Umeå University, SE-901 87 Umeå, Sweden. Electronic address: gunilla.olivecrona@medbio.umu.se.
authors.forename: Gunilla
authors.initials: G
authors.lastname: Olivecrona
mesh_terms: D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000818:Animals; D053302:Apolipoprotein C-I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D053305:Apolipoprotein C-III / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002417:Cattle; D004655:Emulsions; D006801:Humans; D008066:Lipolysis / Q000502:physiology; D008071:Lipoprotein Lipase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D014280:Triglycerides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: C474772:ANGPTL4 protein, human; C505803:APOC1 protein, human; D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins; D053302:Apolipoprotein C-I; D053305:Apolipoprotein C-III; D004655:Emulsions; D014280:Triglycerides; C548261:LPL protein, human; D008071:Lipoprotein Lipase
keywords: Apolipoprotein C-I; Apolipoprotein C-III; Apolipoproteins; Dyslipidemia; Lipolysis; Lipoprotein; Lipoprotein Lipase; Lipoprotein Metabolism; Triglyceride