Objective: To explore the effects of oleic acid and palmitic acid on lipid deposition and mTOR/S6K1/SREBP-1c pathways in HepG2 cells. Methods: The model of steatosis was established with induction of oleic acid and palmitic acid and was intervened by rapamycin. The changes in lipid droplets were observed after staining the cells with oil Red O. Intracellular triglyceride (TG) contents in cells were measured by TG kit. mTOR, S6K1, and SREBP-1c mRNA expression levels were detected using QRT-PCR. Western blot was used to determine protein expression levels of mTOR, S6K1 and SREBP-1c. Results: Both fatty acids increased lipid droplets in HepG2 cells. Fatty degeneration with elevated TG occurred with significant changes in oleic acid group lipids. Rapamycin alleviated lipid deposition caused by oleic acid and palmitic acid and inhibited their induction of increased expression of mTOR, S6K1, and SREBP-1c. QRT-PCR and Western blot results showed that mRNA and protein expressions of mTOR, S6K1, and SREBP-1c in oleic acid and palmitic acid group were significantly higher than the control group (P < 0.05). The increase was more pronounced in the palmitic acid group (P < 0.05); however, after rapamycin intervention, the expression of mRNA and protein in the three groups were significantly lower (P < 0.05), and the change in palmitic acid group was more pronounced (P < 0.05). Conclusion: Oleic acid and palmitic acid can induce lipid deposition in HepG2 cells and increase expression of every component of mTOR/S6K1/SREBP-1c pathway; however, Oleic acid-induced lipid deposition is more pronounced, and the mTOR, S6K1, and SREBP-1c pathway change is more obvious in palmitic acid. Rapamycin has high potent inhibitory effect on palmitic acid-induced lipid deposition. These results specify that lipid synthesis involved in the mTOR/S6K1/SREBP-1c pathways are mainly associated to palmitic acid in HepG2 cells, whereas other signaling pathway may mediate oleic acid-induced lipid synthesis.
目的： 探讨油酸及软脂酸对HepG2细胞脂质沉积及雷帕霉素靶蛋白（mTOR）/蛋白核糖体S6蛋白激酶1（S6K1）/固醇调节元件结合蛋白1c（SREBP-1c）通路的影响。 方法： 采用油酸和软脂酸诱导建立肝细胞脂肪变性模型，并利用雷帕霉素干预处理。油红O染色观察细胞内脂滴变化；甘油三酯（TG）试剂盒检测细胞内TG含量；实时荧光定量PCR检测mTOR、S6K1、SREBP-1c mRNA的表达；Western blot检测mTOR、p-S6（Thr389）、SREBP-1c蛋白表达水平。用单因素方差分析或t检验进行统计学分析。 结果： 油酸及软脂酸均可导致HepG2细胞内脂滴增多，发生TG升高的脂肪变性，以油酸组脂变更明显，雷帕霉素均可减轻因油酸及软脂酸导致的脂质沉积及抑制它们诱导的mTOR、S6K1和SREBP-1c表达增加。实时荧光定量PCR和Western blot结果显示油酸及软脂酸组mTOR、S6K1、SREBP-1c的mRNA和蛋白表达均较对照组明显升高（P < 0.05），软脂酸组升高更明显（P < 0.05）；雷帕霉素干预后，三组mRNA和蛋白质表达明显降低（P < 0.05），软脂酸组的改变更明显（P < 0.05）。 结论： 油酸和软脂酸均可引起HepG2细胞脂质沉积及mTOR/S6K1/SREBP-1c通路中各成分表达增加；但油酸诱发的脂质沉积更明显，而软脂酸引起mTOR/S6K1/SREBP-1c通路变化更明显，且雷帕霉素对软脂酸引起的脂质沉积更具有抑制作用。提示在HepG2细胞中，mTOR/S6K1/SREBP-1c通路参与的脂质合成主要与软脂酸相关，而油酸诱导的脂质合成可能主要由其他信号通路介导。.
Keywords: Oleic acid; Palmitic acid; Rapamycin; Steatosis.