Molecular Basis of Intracellular Cholesterol Homeostasis and Genration of HDL

1）ABCA 1被反应中产生的二酰基甘油激活的RKCa磷酸化，以补充被apoA-I去除的鞘磷脂，以产生HDL。该反应通常在能够产生HDL的螺旋载脂蛋白以及模拟载脂蛋白的两亲性螺旋的模型肽中观察到。2)与ABCA 1高度同源的人ABCA 7介导HDL的产生，当在HEK 293中表达时，其以与ABCA 1相似的方式被载脂蛋白稳定。3)细胞胆固醇向HDL的释放由两种不同的机制介导：非特异性交换和载脂蛋白/ABCA 1介导的途径。后一反应通过使用仅识别无脂质apoA-I的抗apoA-I单克隆抗体来研究。该抗体抑制胆固醇释放反应的ABCA 1依赖性部分。ABCA 1依赖的HDL仅以其蛋白质部分而非脂质部分与细胞结合。因此，apoA-I从HDL解离并与细胞相互作用以产生新的HDL。

1)ABCA1 is phosphorylated by RKCa activated by diacylglycerol generated in the reactions to replenish sphingomyelin that is removed by apoA-I to generate HDL. This reaction is generally observed with helical apolipoproteins that are capable of generating HDL, as well as the model peptides mimicking amphiphilic helices of apolipoprotein. 2)Human ABCA7 that is highly homologous to ABCA1mediates generation of HDL is stabilized by apolipoproteins in a similar manner to that of ABCA1 when expressed in HEK293. 3)Release of cellular cholesterol to HDL is mediated by two distinct mechanism ; non-specific exchange and an apolipoprotein/ABCA1 mediated pathway. The latter reaction was investigated by using an anti-apoA-I monoclonal antibody that recognizes only lipid free apoA-I. This antibody inhibited the ABCA1-dependent part of the cholesterol release reaction. The ABCA1-dependent HDL abiding to cells is only its protein moiety but not the lipid part. Thus, apoA-I dissociates from HDL and interacts with the cells to generate new HDL.