Targeted inactivation of hepatic Abca1 causes profound hypoalphalipoproteinemia and kidney hypercatabolism of apoA-I
Jenelle M. Timmins, … , Nobuyo Maeda, John S. Parks
Jenelle M. Timmins, … , Nobuyo Maeda, John S. Parks
Published May 2, 2005
Citation Information: J Clin Invest. 2005;115(5):1333-1342. https://doi.org/10.1172/JCI23915.
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Article Cardiology

Targeted inactivation of hepatic Abca1 causes profound hypoalphalipoproteinemia and kidney hypercatabolism of apoA-I

Abstract

Patients with Tangier disease exhibit extremely low plasma HDL concentrations resulting from mutations in the ATP-binding cassette, sub-family A, member 1 (ABCA1) protein. ABCA1 controls the rate-limiting step in HDL particle assembly by mediating efflux of cholesterol and phospholipid from cells to lipid-free apoA-I, which forms nascent HDL particles. ABCA1 is widely expressed; however, the specific tissues involved in HDL biogenesis are unknown. To determine the role of the liver in HDL biogenesis, we generated mice with targeted deletion of the second nucleotide-binding domain of Abca1 in liver only (Abca1–L/–L). Abca1–L/–L mice had total plasma and HDL cholesterol concentrations that were 19% and 17% those of wild-type littermates, respectively. In vivo catabolism of HDL apoA-I from wild-type mice or human lipid-free apoA-I was 2-fold higher in Abca1–L/–L mice compared with controls due to a 2-fold increase in the catabolism of apoA-I by the kidney, with no change in liver catabolism. We conclude that in chow-fed mice, the liver is the single most important source of plasma HDL. Furthermore, hepatic, but not extrahepatic, Abca1 is critical in maintaining the circulation of mature HDL particles by direct lipidation of hepatic lipid-poor apoA-I, slowing its catabolism by the kidney and prolonging its plasma residence time.

Authors

Jenelle M. Timmins, Ji-Young Lee, Elena Boudyguina, Kimberly D. Kluckman, Liam R. Brunham, Anny Mulya, Abraham K. Gebre, Jonathan M. Coutinho, Perry L. Colvin, Thomas L. Smith, Michael R. Hayden, Nobuyo Maeda, John S. Parks

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Figure 1

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Targeting strategy and genotypic analysis of liver-specific Abca1-knocko...
Targeting strategy and genotypic analysis of liver-specific Abca1-knockout mice. (A) Schematic of 3′ region (exons 44–49) of Abca1 gene showing wild-type (top), floxed (middle), and knockout (bottom) Abca1 alleles. Three loxP sites, 2 flanking the neomycin (Neo) resistance gene and 1 in intron 46, are shown as arrowheads. Arrows below the floxed allele indicate relative position of primers used for PCR screen of alleles. The size of the EcoRV (RV) fragment is shown above each allele, and the relative location of the probe used for Southern blot analysis is shown above the wild-type allele (Probe A). Cre recombinase–mediated elimination of exons 45 and 46 will delete the second ATP-binding cassette, resulting in a knockout allele. Restriction sites: Bg2, Bgl II; E, EcoRI; H, HindIII; S, SacI. (B) Southern blot analysis of liver (L) and kidney (K) genomic DNA from mice that inherited both the Cre and wild-type or floxed Abca1 alleles. DNA was digested with EcoRV and hybridized with probe A. –L denotes a liver-specific knockout allele. (C) Quantitative real-time PCR analysis of RNA isolated from liver and kidney. Relative fold change compared with a wild-type (+/+) liver sample was calculated using the 2–ØØCT method (42). (D) Western blot analysis of liver membranes isolated from 3 mice of the indicated Abca1 genotypes. (E) Multi-tissue Southern blot of genomic DNA from the indicated tissues from a wild-type and liver-specific knockout (–L/–L) mouse.