Effects of LDL on SMC Proliferation and Intracellular Signalings

为了阐明家族性高胆固醇血症（FH）患者低密度脂蛋白（LDL）对培养的平滑肌细胞（SMC）的影响机制，研究了细胞增殖、Ca2+运动和膜结构，以及肝素和硫酸糖胺聚糖的抗增殖作用。与对照组（不含LDL）相比，FH-LDL以浓度依赖性的方式刺激细胞生长和Ca^<2+>摄取。与对照组相比，甲基化LDL不具有结合LDL受体的能力，但其增殖和Ca2+摄取仍显著增加。但甲基化降低了约60%的增幅。在脂质组成分析中，暴露于FH-LDL使SMC膜中游离胆固醇含量升高。在结构分析中，与对照组相比，FH-LDL引起双层膜内和双层膜间结构的肿胀，这与质膜游离胆固醇升高的变化有很好的相关性。肝素或硫代糖胺聚糖通过降低质膜游离胆固醇抑制细胞增殖。我们认为FH-LDL可能通过不依赖LDL受体的途径增加细胞膜内游离胆固醇的组成，改变细胞膜结构，从而影响Ca2+通道功能。

To elucidate the mechanism of low-density lipoprotein (LDL) from familial hypercholesterolemic (FH) human subjects on the cultured smooth muscle cell (SMC), cell proliferation, Ca2+ movements and membrane structure were examined, along with the antiproliferative action of heparin or sulfated glycosaminoglycans. Cell growth as well as Ca^<2+> uptake was stimulated in a concentration-dependent fashion with FH-LDL compared to control (without LDL). With methylated LDL, which had no capacity to bind LDL receptor, the proliferation and Ca2+ uptake were still significantly increased compared to control. But the about 60% of increase over control was reduced by methylation. In analysis of lipid composition, the exposure to FH-LDL elevated free cholesterol contents in SMC membrane. In structural analysis, FH-LDL brought the swelling in the intrabilayr and interbilayr structure compared to control, which well correlated with change in the increase in free cholesterol in plasma membrane. Heparin or sulfated glycosaminoglycans inhibited the cell proliferation with reduction of free cholesterol in plasma membrane. We concluded that FH-LDL might increase the free cholesterol composition in plasma membrane through LDL receptor-independent pathway, and that change structure of membrane, which affect Ca2+ channel function.