Role of Plant Sterol and Sterolin in Macrophages and T Lynphocytes

已知ABCG5或ABCG8基因突变会导致植物类固醇血症，表现为动脉粥样硬化早发。然而，植物类固醇血症动脉粥样硬化形成的确切机制尚未阐明。在这项研究中，我们研究了ABCG5和ABCG8在巨噬细胞中的基因表达，以及类固醇诱导巨噬细胞产生细胞因子。人巨噬细胞、小鼠腹膜巨噬细胞、J774。本研究以AL细胞和RAW264.7细胞为研究对象。巨噬细胞不表达ABCG5和ABCG8，即使胆固醇负荷或LXR激动剂对细胞的刺激也不能导致ABCG5和ABCG8的表达。用低浓度(16微米)和高浓度(160微米)的胆固醇、谷甾醇或油菜籽甾醇负载细胞，检测细胞产生的细胞因子。当低浓度的谷甾醇负载RAW264.7细胞时，谷甾醇可诱导细胞因子在脂多糖刺激下略有增加。在内毒素刺激的高固醇负荷下，胆固醇诱导两种细胞产生显著的细胞因子增加。AL细胞和RAW264.7细胞，谷甾醇和油菜籽甾醇减少细胞因子的产生。由于东京大学动物设施的事故，我们无法进行充分的动物实验，但初步研究发现，双基因敲除小鼠的血浆总胆固醇水平和细胞因子水平可能低于apoE缺陷小鼠。这些结果表明，巨噬细胞在植物类固醇血症的动脉粥样硬化形成中不起主要作用。通过这项研究，我们发现ABCG5基因在肝脏和肠道中的剪接不同，这表明斯特林1在肝脏和肠道中的行为可能不同。

It has been known that the gene mutations in ABCG5 or ABCG8 result in phytosterolemia which is characterized with the premature atherosclerosis. However, the precise mechanism underlying in the atherogenesis in phytosterolemia has not been elucidated. In this study, we evaluated gene expressions of ABCG5 and ABCG8 in macrophages, and sterol-induced cytokine production in macrophages. Human macrophages, mouse peritoneal macrophages, J774. Al cells and RAW264.7 cells were utilized in this study. Neither ABCG5 nor ABCG8 were expressed in macrophages; even the cholesterol loading or stimulation with LXR agonist to the cells did not result in the expressions. The cells were loaded with cholesterol, sitosterol or campesterol in low (16 uM) and high (160 uM) concentrations, and cytokines production from the cells were examined. When the sterols were loaded to RAW264.7 cells in low concentration, sitosterol induced slight increase in cytokines in case they were stimulated with LPS. In high sterol loading with LPS stimulation, cholesterol induced prominent increase in cytokine production in both J774. Al cells and RAW264.7 cells, while sitosterol and campesterol reduced the production of cytokines. Due to the accidents of the animal facility of the Tokyo University, we could not perform sufficient animal experiments; however, the preliminary study revealed that the plasma total cholesterol levels and cytokine levels in the double knock out mice in apoE and sterolins might be lower than those of apoE deficient mice. These results indicate that the macrophages would not the main player in the atherogenesis of phytosterolemia. Through this study, we found that the splicing of ABCG5 cDNA in the liver is different from that in the intestine, which suggests that the sterolin 1 in the liver would behave differently from that in the intestine.