title: Apolipoprotein A-V-heparin interactions: implications for plasma lipoprotein metabolism.
abstract: Transgenic and gene disruption experiments in mice have revealed that apolipoprotein (apo) A-V is a potent regulator of plasma triglyceride (TG) levels. To investigate the molecular basis of apoA-V function, the ability of isolated recombinant apoA-V to modulate lipoprotein lipase (LPL) activity was examined in vitro. With three distinct lipid substrate particles, including very low-density lipoprotein (VLDL), a TG/phospholipid emulsion, or dimyristoylphosphatidylcholine liposomes, apoA-V had little effect on LPL activity. In the absence or presence apolipoprotein C-II, apoA-V marginally inhibited LPL activity. On the other hand, apoA-V-dimyristoylphosphatidylcholine disc particles bound to heparin-Sepharose and were specifically eluted upon application of a linear gradient of NaCl. The interaction of apoA-V with sulfated glycosaminoglycans was further studied by surface plasmon resonance spectroscopy. ApoA-V showed strong binding to heparin-coated chips, and binding was competed by free heparin. ApoA-V enrichment enhanced binding of apoC-II-deficient chylomicrons and VLDL to heparin-coated chips. When LPL was first bound to the heparin-coated chip, apoA-V-enriched chylomicrons showed binding. Finally, human pre- and post-heparin plasma samples were subjected to immunoblot analysis with anti-apoA-V IgG. No differences in the amount of apoA-V present were detected. Taken together, the results show that apoA-V lipid complexes bind heparin and, when present on TG-rich lipoprotein particles, may promote their association with cell surface heparan sulfate proteoglycans. Through such interactions, apoA-V may indirectly affect LPL activity, possibly explaining its inverse correlation with plasma TG levels.
authors.affiliation: Department of Medical Biosciences/Physiological Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Aivar
authors.initials: A
authors.lastname: Lookene
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Beckstead
authors.forename: Solveig
authors.initials: S
authors.lastname: Nilsson
authors.forename: Gunilla
authors.initials: G
authors.lastname: Olivecrona
authors.forename: Robert O
authors.initials: RO
authors.lastname: Ryan
mesh_terms: D000818:Animals; D000072040:Apolipoprotein A-V; D053305:Apolipoprotein C-III; D001053:Apolipoproteins / Q000378:metabolism*; D001054:Apolipoproteins A; D001056:Apolipoproteins C / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism; D002417:Cattle; D015243:Cholesterol, VLDL / Q000378:metabolism*; D002846:Chromatography, Affinity; D004134:Dimyristoylphosphatidylcholine / Q000378:metabolism; D004789:Enzyme Activation; D006493:Heparin / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008071:Lipoprotein Lipase / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D012685:Sepharose; D020349:Surface Plasmon Resonance; D014280:Triglycerides / Q000378:metabolism
chemical_list: C437704:APOA5 protein, human; D000072040:Apolipoprotein A-V; D053305:Apolipoprotein C-III; D001053:Apolipoproteins; D001054:Apolipoproteins A; D001056:Apolipoproteins C; D001798:Blood Proteins; D015243:Cholesterol, VLDL; D008081:Liposomes; D014280:Triglycerides; D006493:Heparin; D012685:Sepharose; D008071:Lipoprotein Lipase; D004134:Dimyristoylphosphatidylcholine