title: ATP binding cassette A1 (ABCA1) mediates microparticle formation during high-density lipoprotein (HDL) biogenesis.
abstract: Micro-particles (MP) are secreted by various cells. Their biological roles in health and in disease remain unknown. Here we describe formation of MP in the process of ABCA1-dependent cholesterol efflux in different cell types.
  
  
  
  The ATP-binding cassette transporter, subfamily A, member 1 (ABCA1) is the rate-limiting step in the biogenesis of high-density lipoproteins (HDL). We have found that ABCA1 and apoA-I contribute to the formation of MP. Using cell-based systems with overexpression and selective inactivation of ABCA1, pharmacological blockade and modulation of membrane cholesterol content, we characterized MP release from various cell lines. We studied MP release in BHK cells stably expressing ABCA1 under mifepristone control, human THP-1 macrophages and HepG2 cells without, or with incubation with human apoA-I.
  
  
  
  ABCA1 mediates the production of MPs containing cholesterol. This was also confirmed in primary human monocyte-derived macrophages (MDMs). Adding apoA-I markedly increases MP release from cells. Inhibition of ABCA1 with probucol or decreasing plasma membrane cholesterol with methyl-β cyclodextrin (CDX) markedly reduced MP release and nascent HDL formation. MPs do not contain apoA-I, but contain flotilin-2, a marker of plasma membrane, and CD63, an exosome marker. MPs exhibit considerable size heterogeneity (50-250 nm).
  
  
  
  We show that MPs are lipoprotein-sized structures created by the ABCA1 transporter, and contribute approximately 30% of ABCA1-and apoA-I mediated cholesterol efflux. In addition, we found that MPs release from cells consists, in part, of exosomes and depends on the same pathway used for HDL biogenesis.
authors.affiliation: Research Institute of the McGill University Health Center, Montreal, Canada.
authors.forename: Anouar
authors.initials: A
authors.lastname: Hafiane
authors.affiliation: Research Institute of the McGill University Health Center, Montreal, Canada. Electronic address: Jacques.genest@mcgill.ca.
authors.forename: Jacques
authors.initials: J
authors.lastname: Genest
mesh_terms: D064286:ATP Binding Cassette Transporter 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D055252:Cell-Derived Microparticles / Q000187:drug effects / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism; D006224:Cricetinae; D055354:Exosomes / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D008075:Lipoproteins, HDL / Q000096:biosynthesis*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D010316:Particle Size; D011341:Probucol / Q000494:pharmacology; D060149:Tetraspanin 30 / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: C577836:ABCA1 protein, human; C505693:APOA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D016632:Apolipoprotein A-I; C554586:CD63 protein, human; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D060149:Tetraspanin 30; D047392:beta-Cyclodextrins; C106354:flotillins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol; D011341:Probucol
keywords: ABCA1; Apolipoprotein apoA-I; CD63; Cholesterol efflux; Flotillin-2; HDL; Microparticles