THE EFFECT OF HIGH-DENSITY-LIPOPROTEIN PHOSPHOLIPID ACYL-CHAIN COMPOSITION ON THE EFFLUX OF CELLULAR FREE-CHOLESTEROL
THE EFFECT OF HIGH-DENSITY-LIPOPROTEIN PHOSPHOLIPID ACYL-CHAIN COMPOSITION ON THE EFFLUX OF CELLULAR FREE-CHOLESTEROL
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DOI：
10.1074/jbc.270.11.5882
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发表时间：
1995-03-17
影响因子：
4.8
通讯作者：
PHILLIPS, MC
中科院分区：
文献类型：
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作者：
DAVIDSON, WS;GILLOTTE, KL;PHILLIPS, MC
高密度脂蛋白（HDL）磷脂（PL）脂肪酸酰基链组成已被提出影响HDL参与逆向胆固醇转运第一步的能力。为了研究PL脂肪酸链长度和不饱和程度对这一过程的影响，我们用载脂蛋白A-I和含有14 - 18个碳的脂肪酸链的PL合成了重组HDL （rHDL）颗粒，这些脂肪酸链在一条或两条链上都是完全饱和或不饱和的。这些颗粒的结构特征以及它们促进游离（未酯化）胆固醇（FC）从培养细胞中流出的能力。盘状rHDL颗粒是均匀的，具有相似的流体动力学直径（10.4 +/- 1.0 nm），表明apoA-I形成了具有各种PL的类似大小的圆盘。构象稳定性表明，apoA-I的构象在不同的颗粒中存在差异。这些构象对apoA-I的影响与PL流动性对两亲性卢螺旋段与FL酰基链相互作用的影响是一致的。差示扫描量热法表明，rHDL - PL在37℃时的物理状态随酰基链长度和不饱和程度的不同而变化；测定了凝胶态和液晶态PL粒子的FC射流效率。rHDL接受细胞FC的能力取决于rHDL中PL的物理状态。液晶PL形成了最有效的FC受体颗粒，其最大流出速度（V-max）为每小时释放细胞总FC的12-14%。凝胶相PL形成了低效的rHDL受体，其V-max约为3%/h。当使用小鼠l细胞或大鼠Fu5AH肝癌细胞作为FC供体时，发现了类似的FC外排效率等级。此外，这种层次结构被发现是由于PL的特性，而不是由于可变的apoA-I构象，因为由相同PL制成的无蛋白小单层囊泡具有相似的相对外排能力。一般来说，给定rHDL颗粒接受细胞FC的能力与rHDL PL酰基链长度和不饱和程度有关；氟酰基链长度的减少和链不饱和的增加倾向于产生更有效的氟酰基受体颗粒。这些结果表明，含有高度流体表面的rHDL受体颗粒比含有高度组织化的脂质表面且限制FL酰基链迁移的rHDL受体颗粒以更快的速度隔离从细胞膜扩散的FC分子，这一信息为理解脂质含量在HDL结构和功能多样性中的作用奠定了基础。
High density lipoprotein (HDL) phospholipid (PL) fatty acyl chain composition has been proposed to affect the ability of HDL to participate in the first step of reverse cholesterol transport. To examine the effects of PL fatty acid chain length and degree of unsaturation in this process, reconstituted HDL (rHDL) particles were made with human apolipoprotein (apo) A-I and PL containing fatty acid chains from 14 to 18 carbons in length, which were either fully saturated or unsaturated in one or both chains. These particles were characterized structurally and for their ability to promote free (unesterified) cholesterol (FC) efflux from cells growing in culture, The discoidal rHDL particles were homogeneous and exhibited similar hydrodynamic diameters (10.4 +/- 1.0 nm) indicating that apoA-I forms similarly sized discs with a variety of PL. Measurements of particle surface charge, apoA-I alpha-helix content, and conformational stability indicated that the conformation of apoA-I varies among the particles. These conformational effects on apoA-I are consistent with the PL fluidity influencing the interaction between the amphipathic Lu-helical segments and FL acyl chains. Differential scanning calorimetry demonstrated that the physical state of the rHDL PL at 37 degrees C varied according to acyl chain length and degree of unsaturation; the FC efflux efficiencies for particles with PL in either the gel or liquid crystal states were determined. The ability of the rHDL to accept cellular FC depended on the physical state of the PL in the rHDL. Liquid crystal PL formed the most efficient FC acceptor particles exhibiting a maximal efflux velocity (V-max) of 12-14% release of total cellular FC per h. Gel-phase PL formed inefficient rHDL acceptors with a V-max of about 3%/h. A similar hierarchy of FC efflux efficiency was noted when either mouse L-cells or rat Fu5AH hepatoma cells were used as the FC donors. Furthermore, this hierarchy was found to be due to the characteristics of the PL and not due to variable apoA-I conformation because protein-free, small unilamellar vesicles made with the same PL exhibited similar relative efflux capabilities. Generally, the ability of a given rHDL particle to accept cellular FC was related to rHDL PL acyl chain length and degree of unsaturation; decreases in FL acyl chain length and increases in chain unsaturation tended to result in more efficient FC acceptor particles. These results suggest that rHDL acceptor particles that contain highly fluid surfaces sequester FC molecules that have diffused from the cell plasma membrane at a significantly faster rate than those containing highly organized lipid surfaces with restricted FL acyl chain mobility, This information forms a basis for understanding the role of lipid content in the structural and functional diversity of HDL.