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Cytotoxic cellular cholesterol is selectively removed by apoA-I via ABCA1

  • Ginny Kellner-Weibel
    Correspondence
    Corresponding author. Tel.: +1-215-590-0595; fax: +1-215-590-0583.
    Affiliations
    Division of Gasteroenterology and Nutrition, Abramson Research Center, Suite 302, The Children’s Hospital of Philadelphia, University of Pennsylvania School of Medicine, 3615 Civic Center Blvd., Philadelphia, PA 19104-8651, USA
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  • Steven J. Luke
    Affiliations
    Division of Gasteroenterology and Nutrition, Abramson Research Center, Suite 302, The Children’s Hospital of Philadelphia, University of Pennsylvania School of Medicine, 3615 Civic Center Blvd., Philadelphia, PA 19104-8651, USA
    Search for articles by this author
  • George H. Rothblat
    Affiliations
    Division of Gasteroenterology and Nutrition, Abramson Research Center, Suite 302, The Children’s Hospital of Philadelphia, University of Pennsylvania School of Medicine, 3615 Civic Center Blvd., Philadelphia, PA 19104-8651, USA
    Search for articles by this author

      Abstract

      Excess intracellular free cholesterol (FC) is cytotoxic. This study examines prevention of FC-induced cytotoxicity in J774 macrophage foam cells by incubation with apolipoprotein AI (apoA-I). J774 were cholesterol enriched using acetylated low-density lipoprotein and FC/phospholipid (PL) dispersions. Treatment with an acyl coenzyme-A:cholesterol acyltransferase (ACAT) inhibitor, in the absence of extracellular acceptors, produced hydrolysis of stored esterified cholesterol (EC) and FC-induced cytotoxicity. Incubation of cells with ACAT inhibitor plus apoA-I resulted in FC efflux (0.39±0.02%/h) along with a reduction in cytotoxicity (26.30±5.80%), measured by adenine release. Small unilamellar vesicles (SUV) caused greater FC efflux (0.53±0.02%/h, P=0.001), but a modest reduction in cytotoxicity (8.40±2.70%, P=0.008). Co-incubation of ACAT inhibitor plus the cholesterol transport inhibitor U18666A or the antioxidant Probucol reduced efflux to apoA-I, but not to SUV. Pre-treatment of J774 foam cells with CTP-cAMP upregulates hormone sensitive lipase (HSL) and further upregulates ATP binding cassette A1 (ABCA1). Using mouse serum as a cholesterol acceptor, CTP-cAMP caused greater protection against FC-induced cytotoxicity compared to cells without pre-treatment, suggesting a role of ABCA1 in removal of cytotoxic FC. We conclude that a cytotoxic pool of FC is located in the plasma membrane, is readily available for efflux to apoA-I, and removal of cytotoxic cholesterol may involve ABCA1.

      Abbreviations:

      FC (unesterified (free) cholesterol), EC (esterified cholesterol), ACAT (acyl CoA:cholesterol acyltransferase), PBS (phosphate buffered saline), BSA (bovine serum albumin), acLDL (acetylated LDL), PL (phospholipid), SUV (small unilamellar vesicles), ABCA1 (ATP binding cassette A1), SR-BI (scavenger receptor BI), CME (cholesteryl methyl ether)

      Keywords

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