泡沫细胞形成过程中酰基CoA:胆固醇酰基转移酶1活性改变及其机制研究

目的　研究人单核细胞系在分化为巨噬细胞及转化为泡沫细胞过程中酰基CoA :胆固醇酰基转移酶 1(ACAT1)活性的改变及其机制。方法　体外培养人THP 1单核细胞系 ,由佛波酯作用使其分化为巨噬细胞 ,后者再由氧化低密度脂蛋白 (Ox LDL)进一步作用转变为泡沫细胞。此过程中以放射性同位素标记底物法检测ACAT1活性的变化 ,并用Westernblot法检测ACAT1蛋白的表达及RT PCR法检测ACAT1mRNA的水平。结果　在单核细胞分化为巨噬细胞的过程中ACAT1活性升高了 2倍 ,差异具有显著性 (P <0 0 5 ) ,酶蛋白及mRNA水平呈现类似变化趋势 ,在进一步转化为泡沫细胞过程中 ,ACAT1活性、酶蛋白及mRNA仍处于较高水平 ,但与巨噬细胞相比差异无显著性。结论　单核细胞分化为巨噬细胞的过程中ACAT1转录水平的上调导致酶蛋白量合成增加 ,从而使ACAT1活性也大为增强 ,而Ox LDL对ACAT1活性影响则不明显。

The mechanisms of increased activity of acyl coenzyme A:cholesteryl acyltransferase1 in monocyte/macrophage derived foam cells

Objective To explore the mechanisms of increased activity of the acyl coenzyme A: cholesteryl acyltransferase 1 (ACAT1) during the formation of foam cells. Methods The THP-1 human monocytic leukemia cell line (THP-1) was chosen in our study. The differentiation of THP-1 cells into macrophages (MP) was induced by using phorbol esters. The MP cells were then incubated with oxidized LDL (Ox-LDL) to generate foam cells (FC). The ACAT1 enzyme activity, protein mass and mRNA levels were determined in all three groups respectively. The ACAT1 activity was measured by quantifying the incorporation of 1- 14 C] oleoyl CoA into cholesteryl esters. The ACAT1 protein and mRNA levels were detected by Western blotting and RT-PCR. Results The ACAT1 activity was significantly increased during the differenciation of monocytes into macrophages (P<0.05) as well as in lipid-laden foam cells. Accordingly, the ACAT1 protein mass and ACAT1 mRNA level were also found to be significantly increased. In contrast, there were no significant differences between macrophages and foam cells (P>0.05). Conclusions The upregulation of ACAT1 gene expression during the differentiation of monocytes into macrophages could increase ACAT1 protein synthesis dramatically, which may be closely related to the increased ACAT1 activity. We found very little effect of Ox-LDL on modifying ACAT1 activity.