Unidad de Hepatología Experimental, Centro de investigación, Hospital Universitario La Fe, Valencia, Spain.
Chem Biol Interact. 2010 Mar 30;184(3):376-87. doi: 10.1016/j.cbi.2010.01.008. Epub 2010 Jan 15.
Steatosis is the first step in the development of non-alcoholic fatty liver disease (NAFLD). However, the mechanisms involved in its pathogenesis are not fully understood. Many nuclear receptors (NRs) involved in energy homeostasis and biotransformation constitute a network connecting fatty acids, cholesterol and xenobiotic metabolisms; therefore, multiple NRs and their ligands may play a prominent role in liver fat metabolism and accumulation. In this study we have attempted to gain insight into the relevance of the NR superfamily in NAFLD by investigating the steatogenic potential of 76 different NR ligands in fatty acid overloaded human hepatocytes and hepatoma cells. Moreover, we have determined the mRNA expression level of 24 NRs to correlate the steatogenic potential of the ligands with the expression of their associated NRs in the cultured cells. Our results demonstrate that 18% of the examined NR ligands enhanced lipid accumulation in human hepatocytes and/or hepatoma cells. Among them, ligands of PPARgamma (e.g., thiazolidinediones), LXR (paxilline and 24(S),25-epoxycholesterol), PXR (hyperforin), CAR (3alpha,5alpha-androstenol), ERalpha (tamoxifen), FXR (Z-guggulsterone), VDR (25-hydroxyvitamin D3) and particular retinoids and farnesoids showed a significant pro-steatotic effect. The mRNA level of most of the NRs examined was well preserved in human hepatocytes, but HepG2 showed a deranged profile, where many of the receptors had a marginal or negligible level of expression in comparison with the human liver. By comparing the steatogenic effect of NR ligands with the NR expression levels, we conclude that LXR, PXR, RAR and PPARgamma ligands likely induce fat accumulation by a NR-dependent mechanism. Indeed, over-expression of PXR in HepG2 cells enhanced the steatogenic effect of hyperforin and rifampicin. However, the accumulation of fat induced by other ligands did not correlate with the expression of their associated NR. Our results also suggest that human hepatocytes cultured with free fatty acids offer a highly valuable in vitro system to investigate the pathogenesis and therapeutics of the human fatty liver.
脂肪变性是非酒精性脂肪性肝病 (NAFLD) 发展的第一步。然而，其发病机制中涉及的机制尚不完全清楚。许多参与能量平衡和生物转化的核受体 (NR) 构成了连接脂肪酸、胆固醇和异生物质代谢的网络；因此，多种 NR 和它们的配体可能在肝脏脂肪代谢和积累中发挥重要作用。在这项研究中，我们试图通过研究 76 种不同的 NR 配体在脂肪酸超负荷的人肝细胞和肝癌细胞中的生脂潜力，来深入了解 NR 超家族在 NAFLD 中的相关性。此外，我们还测定了 24 种 NR 的 mRNA 表达水平，以将配体的生脂潜力与培养细胞中相关 NR 的表达相关联。我们的结果表明，在所检查的 NR 配体中，有 18%增强了人肝细胞和/或肝癌细胞中的脂质积累。其中，PPARγ 的配体（如噻唑烷二酮）、LXR（paxilline 和 24(S),25-环氧胆固醇）、PXR（hyperforin）、CAR（3α,5α-雄甾醇）、ERα（他莫昔芬）、FXR（Z-育亨宾）、VDR（25-羟维生素 D3）和特定的类视黄醇和法尼醇显示出显著的促脂作用。大多数检查的 NR 的 mRNA 水平在人肝细胞中得到很好的保存，但 HepG2 显示出紊乱的特征，其中许多受体的表达水平与人类肝脏相比微不足道或可以忽略不计。通过比较 NR 配体的生脂作用与 NR 表达水平，我们得出结论，LXR、PXR、RAR 和 PPARγ 配体可能通过 NR 依赖的机制诱导脂肪堆积。事实上，在 HepG2 细胞中过表达 PXR 增强了 hyperforin 和 rifampicin 的生脂作用。然而，其他配体诱导的脂肪堆积与它们相关的 NR 的表达无关。我们的结果还表明，用游离脂肪酸培养的人肝细胞提供了一个非常有价值的体外系统，可用于研究人类脂肪肝的发病机制和治疗方法。
