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Pathway of biogenesis of apolipoprotein E-containing HDL in vivo with the participation of ABCA1 and LCAT.

ABSTRACT: We have investigated the ability of apoE (apolipoprotein E) to participate in the biogenesis of HDL (high-density lipoprotein) particles in vivo using adenovirus-mediated gene transfer in apoA-I-/- (apolipoprotein A-I) or ABCA1-/- (ATP-binding cassette A1) mice. Infection of apoA-I-/- mice with 2x10(9) pfu (plaque-forming units) of an apoE4-expressing adenovirus increased both HDL and the triacylglycerol-rich VLDL (very-low-density lipoprotein)/IDL (intermediate-density lipoprotein)/LDL (low-density lipoprotein) fraction and generated discoidal HDL particles. ABCA1-/- mice treated similarly failed to form HDL particles, suggesting that ABCA1 is essential for the generation of apoE-containing HDL. Combined infection of apoA-I-/- mice with a mixture of adenoviruses expressing both apoE4 (2x10(9) pfu) and human LCAT (lecithin:cholesterol acyltransferase) (5x10(8) pfu) cleared the triacylglycerol-rich lipoproteins, increased HDL and converted the discoidal HDL into spherical HDL. Similarly, co-infection of apoE-/- mice with apoE4 and human LCAT corrected the hypercholesterolaemia and generated spherical particles, suggesting that LCAT is essential for the maturation of apoE-containing HDL. Overall, the findings indicate that apoE has a dual functionality. In addition to its documented functions in the clearance of triacylglycerol-rich lipoproteins, it participates in the biogenesis of HDL-sized apoE-containing particles. HDL particles generated by this pathway may account at least for some of the atheroprotective functions of apoE.

SUBMITTER: Kypreos KE

PROVIDER: S-EPMC1874240 | biostudies-other | 2007 Apr

REPOSITORIES: biostudies-other

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Project description:ATP-binding cassette transporter A1 (ABCA1) is a major reverse cholesterol transporter and plays critical role in the formation of brain high-density lipoprotein (HDL) cholesterol. Apolipoprotein E (ApoE) is the most abundant apolipoprotein and transports cholesterol into cells in brain. ABCA1 and ApoE are upregulated by liver-X receptors. Activation of liver-X receptors has neurorestorative benefit for stroke. The current study investigates whether ABCA1/ApoE/HDL pathway mediates GW3965, a synthetic dual liver-X receptor agonist, induced neurorestoration after stroke.Middle-aged male specific brain ABCA1-deficient (ABCA1-B/-B) and floxed-control (ABCA1fl/fl) mice were subjected to distal middle-cerebral artery occlusion (dMCAo) and gavaged with saline or GW3965 (10 mg/kg) or intracerebral infusion of artificial cerebrospinal fluid or human plasma HDL3 in ABCA1-B/-B stroke mice, starting 24 hours after dMCAo and daily until euthanization 14 days after dMCAo.No differences in the blood level of total cholesterol and triglyceride and lesion volume were found among the groups. Compared with ABCA1fl/fl ischemic mice, ABCA1-B/-B ischemic mice exhibited impairment functional outcome and decreased ABCA1/ApoE expression and decreased gray/white matter densities in the ischemic boundary zone 14 days after dMCAo. GW3965 treatment of ABCA1fl/fl ischemic mice led to increased brain ABCA1/ApoE expression, concomitantly to increased blood HDL, gray/white matter densities and oligodendrocyte progenitor cell numbers in the ischemic boundary zone, as well as improved functional outcome 14 days after dMCAo. GW3965 treatment had negligible beneficial effects in ABCA1-B/-B ischemic mice. However, intracerebral infusion of human plasma HDL3 significantly attenuated ABCA1-B/-B-induced deficits. In vitro, GW3965 treatment (5 ?M) increased ABCA1/synaptophysin level and neurite/axonal outgrowth in primary cortical neurons derived from ABCA1fl/fl embryos, but not in neurons derived from ABCA1-B/-B embryos. HDL treatment (80 ?g/mL) attenuated the reduction of neurite/axonal outgrowth in neurons derived from ABCA1-B/-B embryos.ABCA1/ApoE/HDL pathway, at least partially, contributes to GW3965-induced neurorestoration after stroke.

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Pathway of biogenesis of apolipoprotein E-containing HDL in vivo with the participation of ABCA1 and LCAT.

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