Abstract
Apolipoproteins (apo)A-I and A-II are major proteins of human HDL. The cycling of apoA-I between lipid-poor and lipid-rich forms of HDL plays a key role in the transport of cholesterol by these particles. ApoA-II resides only in part of HDL particles, and little is known about its role in HDL metabolism. Our study investigates the redistribution of apoA-II after HDL remodelling induced by exogenous phospholipids (PL). During incubation with egg yolk lecithin (EYL) liposomes, human HDL became PL-enriched and free cholesterol (FC)-depleted, and lost small amounts of apoA-I and apoA-II. The loss of FC and apolipoproteins correlated with the rise of PL content in HDL. Agarose gel electrophoresis demonstrated the appearance of new pre-beta mobility fractions containing apoA-I and apoA-II in liposomes and HDL mixtures. Two-dimensional nondenaturing 2-27% PAGE has shown that the pre-beta mobility fraction that appeared at initial liposome-PL/HDL-PL ratio 5:1 consisted of two distinct heterogeneous subpopulations of particles containing either apoA-I or apoA-II. Our study provides evidence that during HDL conversion mediated by PL apoA-II dissociated from HDL particles yielding apoA-II-specific pre-beta mobility particles. This observation supports the hypothesis that apoA-II in plasma, like apoA-I, may cycle between lipid-poor and lipid-rich forms of HDL.
Highlights
ApolipoproteinsA-I and A-II are major proteins of human HDL
Our experiments demonstrated that the interaction of HDL with liposomes evokes dissociation of apoA-II from HDL and yields apoA-II-specific lipid-protein particles migrating with pre-b mobility during agarose gel electrophoresis
The formation of new lipoprotein fraction migrating with pre-b mobility in agarose gel electrophoresis following the incubation of ultracentrifuged human HDL with egg yolk lecithin (EYL) liposomes was demonstrated by Sudan Black B staining (Fig. 1A), autoradiography (Fig. 2), and immunodetection of apoA-I and apoA-II (Fig. 1B)
Summary
The cycling of apoA-I between lipidpoor and lipid-rich forms of HDL plays a key role in the transport of cholesterol by these particles. Two-dimensional nondenaturing 2–27% PAGE has shown that the pre-b mobility fraction that appeared at initial liposome-PL/HDL-PL ratio 5:1 consisted of two distinct heterogeneous subpopulations of particles containing either apoA-I or apoA-II. Our study provides evidence that during HDL conversion mediated by PL apoA-II dissociated from HDL particles yielding apoA-II-specific pre-b mobility particles. This observation supports the hypothesis that apoA-II in plasma, like apoA-I, may cycle between lipid-poor and lipid-rich forms of HDL.—Wróblewska, M., B. Phospholipids mediated conversion of HDLs generates specific apoA-II pre-b mobility particles.
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