Guangdong Provincial Key Laboratory of Food, Nutrition and Health, Department of Nutrition, School of Public Health, Sun Yat-sen University, China.
Department of Cardiology, Affiliated NanHai Hospital of Southern Medical University, China.
J Toxicol Sci. 2019;44(7):481-491. doi: 10.2131/jts.44.481.
Bisphenol A (BPA), an environmental chemical to which humans are commonly exposed, has been shown to increase cholesterol level but the molecular mechanism is not clear. Since cholesterol biosynthesis plays an important role in elevating cholesterol level, the aim of the present study is to explore the effects of BPA on cholesterol biosynthesis in HepG2 cells and its possible mechanisms. HepG2 cells were treated with different concentrations of BPA for 24 hr, the total cholesterol level and the activity of 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) were measured using commercial enzymatic assay kits, and the mRNA and protein expression levels of sterol regulatory element binding protein-2(SREBP-2) and HMGCR were analyzed by qPCR, Western blotting and immunofluorescence, respectively. After treating HepG2 cells with different concentrations (0.1 nM~10 µM) of BPA for 24 hr, we found that BPA at the environmentally relevant concentrations of 1 nM and 10 nM significantly increased the total cholesterol content, the activity and expression of HMGCR in HepG2 cells, but at 100 nM, 1 µM and 10 µM doses, BPA had no stimulatory effect on cholesterol biosynthesis. The whole dose-response relationship follows non-monotonic dose responses, such as an inverted U-shape. Using human SREBP-2 small interfering RNA, we further discovered that the stimulatory effects of BPA on cholesterol biosynthesis and HMGCR expression could be prevented by blockade of the SREBP-2 pathway. This study provides important implications for understanding the potential lipotoxicity of BPA exposure, and it also indicates that low-dose BPA induces hepatic cholesterol biosynthesis through upregulating the SREBP-2/HMGCR signaling pathway.
双酚 A（BPA）是一种环境化学物质，人类通常会接触到它，已被证明会增加胆固醇水平，但分子机制尚不清楚。由于胆固醇生物合成在升高胆固醇水平方面起着重要作用，因此本研究旨在探讨 BPA 对 HepG2 细胞中胆固醇生物合成的影响及其可能的机制。用不同浓度的 BPA 处理 HepG2 细胞 24 小时，使用商业酶法测定试剂盒测定总胆固醇水平和 3-羟-3-甲基戊二酰基辅酶 A 还原酶（HMGCR）的活性，并用 qPCR、Western blot 和免疫荧光分别分析固醇调节元件结合蛋白-2（SREBP-2）和 HMGCR 的 mRNA 和蛋白表达水平。用不同浓度（0.1 nM~10 µM）的 BPA 处理 HepG2 细胞 24 小时后，我们发现 BPA 在环境相关浓度 1 nM 和 10 nM 时显著增加了 HepG2 细胞中的总胆固醇含量、HMGCR 的活性和表达，但在 100 nM、1 µM 和 10 µM 剂量时，BPA 对胆固醇生物合成没有刺激作用。整个剂量反应关系呈现出非单调的剂量反应，如倒 U 形。使用人 SREBP-2 小干扰 RNA，我们进一步发现，BPA 对胆固醇生物合成和 HMGCR 表达的刺激作用可以通过阻断 SREBP-2 途径来预防。这项研究为理解 BPA 暴露的潜在脂毒性提供了重要意义，也表明低剂量 BPA 通过上调 SREBP-2/HMGCR 信号通路诱导肝内胆固醇生物合成。
