Ishikawa Y, Nishide T, Sasaki N, Shirai K, Saito Y, Yoshida S
Second Department of Internal Medicine, School of Medicine, Chiba University, Japan.
Atherosclerosis. 1989 Nov;80(1):1-7. doi: 10.1016/0021-9150(89)90061-0.
Phospholipid associated with LDL (LDL-phospholipid) has been suggested to affect metabolism of LDL in arterial smooth muscle cells. However, the metabolism of LDL-phosphatidylcholine in these cells has not been well clarified. We compared the metabolic pathway of LDL-phosphatidylcholine with that of cholesteryl ester associated with LDL (LDL-cholesteryl ester) in rabbit arterial smooth muscle cells by incubating the cells in the absence or presence of chloroquine, an inhibitor of lysosomal function. When the cells were incubated with LDL-[3H]cholesterol linoleate in the absence of chloroquine, 26.6 and 51.4% of incorporated radioactivity was found as cholesteryl ester in the lysosome-rich and microsome-rich fractions, respectively. When the cells were incubated in the presence of 50 microM chloroquine, the radioactivity found as cholesteryl ester in the lysosome-rich fraction increased to 45.5% while that in microsome-rich fraction decreased to 21.4%, indicating that LDL-cholesteryl ester accumulated in lysosomes as a consequence of inhibition of lysosomal function. When the cells were incubated with LDL-[14C]linoleoyl phosphatidylcholine in the absence of chloroquine, 25.1% of incorporated radioactivity was found as phosphatidylcholine in the lysosome-rich fraction and 24.8% in the cytosol-rich fraction. When the cells were incubated in the presence of chloroquine, phosphatidylcholine-associated radioactivity found in the lysosome-rich and cytosol-rich fractions changed only to 28.8% and 26.1%, respectively, showing that LDL-phosphatidylcholine did not accumulate in lysosomes when lysosomal function was inhibited. In conclusion, these data indicate that LDL-phosphatidylcholine, in contrast to LDL-cholesteryl ester, is not only hydrolyzed in lysosomes, but also at other subcellular sites.
与低密度脂蛋白相关的磷脂（低密度脂蛋白 - 磷脂）被认为会影响动脉平滑肌细胞中低密度脂蛋白的代谢。然而，这些细胞中低密度脂蛋白 - 磷脂酰胆碱的代谢尚未得到很好的阐明。我们通过在有无溶酶体功能抑制剂氯喹的情况下培养兔动脉平滑肌细胞，比较了低密度脂蛋白 - 磷脂酰胆碱与低密度脂蛋白相关胆固醇酯（低密度脂蛋白 - 胆固醇酯）在这些细胞中的代谢途径。当细胞在无氯喹的情况下与低密度脂蛋白 - [³H]胆固醇亚油酸酯一起孵育时，分别在富含溶酶体和富含微粒体的组分中发现26.6%和51.4%的掺入放射性以胆固醇酯的形式存在。当细胞在50微摩尔氯喹存在下孵育时，富含溶酶体组分中以胆固醇酯形式存在的放射性增加到45.5%，而富含微粒体组分中的放射性降低到21.4%，这表明由于溶酶体功能受到抑制，低密度脂蛋白 - 胆固醇酯在溶酶体中积累。当细胞在无氯喹的情况下与低密度脂蛋白 - [¹⁴C]亚油酰磷脂酰胆碱一起孵育时，在富含溶酶体的组分中发现25.1%的掺入放射性以磷脂酰胆碱的形式存在，在富含胞质溶胶的组分中为24.8%。当细胞在氯喹存在下孵育时，在富含溶酶体和富含胞质溶胶的组分中发现的与磷脂酰胆碱相关的放射性仅分别变为28.8%和26.1%，这表明当溶酶体功能受到抑制时，低密度脂蛋白 - 磷脂酰胆碱不会在溶酶体中积累。总之，这些数据表明，与低密度脂蛋白 - 胆固醇酯相比，低密度脂蛋白 - 磷脂酰胆碱不仅在溶酶体中水解，还在其他亚细胞位点水解。
