Phospholipids mediated conversion of high density lipoproteins generates specific apo A-II pre-beta mobility particles

Malgorzata Wróblewska, Barbara Kortas-Stempak, Andrzej Szutowicz, and Tadeusz Badzio

Department of Laboratory Medicine, Medical University of Gdansk, Gdansk

Corresponding Author: wroblew{at}amg.gda.pl

Apolipoproteins (apo) A-I and A-II are major proteins of human HDL. The cycling of apo A-I between lipid-poor and lipid-rich forms of HDL plays a key role in the transport of cholesterol by these particles. Apo A-II resides only in part of HDL particles and little is known about its role in HDL metabolism. Our study investigates the redistribution of apo A-II after HDL remodelling induced by exogenous phospholipids (PL). During incubation with egg yolk lecithin liposomes human HDL became PL-enriched, free cholesterol (FC)-depleted and lost small amounts of both apo A-I and apo A-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 both apo A-I and apo A-II in liposomes and HDL mixtures. Two-dimensional non-denaturing 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 apo A-I or apo A-II. Our study provides evidence, that during HDL conversion mediated by phospholipids apo A-II dissociated from HDL particles yielding apo A-II specific pre-beta mobility particles. This observation supports the hypothesis that apo A-II in plasma, like apo A-I, may cycle between lipid-poor and lipid-rich forms of HDL.

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