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The aim of this study was to correlate the lipid content and size of discoidal reconstituted HDL particles with their ability to promote cellular cholesterol efflux. Homogeneous discoidal rHDL particles containing apoA-I and POPC, with diameters of 7.8, 9.6, 10.8, 12.5, and 17.0 nm, were prepared by the cholate dialysis technique. Cholesterol efflux to rHDL was evaluated in pathway-specific cell models for ABCA1-, ABCG1-, and SR-BI-mediated efflux. ABCA1-mediated efflux was efficiently promoted by the 7.8 nm rHDL containing 82 POPC molecules per particle. This rHDL also promoted ABCG1, but not SR-BI, cholesterol efflux. All large and lipid-rich rHDLs, with a diameter of ≥9.6 nm and a phospholipid content of ≥202 molecules per particle, promoted both SR-BI- and ABCG1-mediated efflux. Our results indicated that the ABCA1-mediated cell cholesterol efflux can be efficiently driven not only by monomolecular lipid free/poor apoA-I but also by a small discoidal phospholipid-containing particle resembling plasma pre-β1 HDL. This same particle also promotes ABCG1- but not SR-BI-mediated efflux. These results help to clarify the role of plasma pre-β1 HDL in reverse cholesterol transport. [ABSTRACT FROM AUTHOR]

Apolipoprotein-E (apoE) plays an important role in neuronal lipid transport and is thought to stabilize microtubules by preventing tau hyperphosphorylation. ApoE is also associated with insoluble amyloid detected in Alzheimer disease brain lesions. The apoE C-terminal shares several physicochemical features with α-synuclein, another neuronal apolipoprotein-like protein. α-Synuclein is phosphorylated by protein kinase CK2 (CK2) at an atypical PSDIE motif in vivo and in vitro. We identified a similar PSD/IE motif in apoE and therefore investigated its potential phosphorylation by CK2 in vitro. When a [32P]-labeling approach was used, CK2 readily phosphorylated purified human apoE as well as recombinant forms of human apoE3 and apoE4. Using liquid chromatography mass spectrometry techniques, we mapped the major apoE CK2 phosphorylation site to Ser296 within the apoE PSD/E motif. We also found that apoE potently activated CK2 as demonstrated by increased CK2β subunit autophosphorylation and by increased phosphorylation of tau when the latter was added to the kinase reaction mixtures. Other proteins such as apolipoprotein A-I and albumin did not effectively activate CK2. The phosphorylation of apoE by CK2 as well as the activation of CK2 by apoE may be relevant in vivo where apoE, CK2, and tau are co-localized with additional CK2 targets on neuronal microtubules. [ABSTRACT FROM AUTHOR]

Investigates whether incorporation of 7-ketocholesterol (7K) into membranes resulted in the impairment of cholesterol efflux studied from lipoprotein-loaded THP-1 cells, from plasma membrane vesicles obtained from these cells and from artificial, protein-free liposomes. Inhibition of cholesterol efflux by 7K; High density lipoprotein apolipoprotein receptors.

Examines the kinetics of cholesterol efflux to delipidated apoliproprotein A-1. Mathematical model involving two independent pathways of cholesterol efflux; Effect of the oxysterol 7-ketocholesterol on the initial efflux; Characterization of the cholesterol efflux pathways.