Division of Liver Diseases, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
Dis Model Mech. 2013 Sep;6(5):1213-26. doi: 10.1242/dmm.012195. Epub 2013 Jun 20.
Secretory pathway dysfunction and lipid accumulation (steatosis) are the two most common responses of hepatocytes to ethanol exposure and are major factors in the pathophysiology of alcoholic liver disease (ALD). However, the mechanisms by which ethanol elicits these cellular responses are not fully understood. Recent data indicates that activation of the unfolded protein response (UPR) in response to secretory pathway dysfunction can cause steatosis. Here, we examined the relationship between alcohol metabolism, oxidative stress, secretory pathway stress and steatosis using zebrafish larvae. We found that ethanol was immediately internalized and metabolized by larvae, such that the internal ethanol concentration in 4-day-old larvae equilibrated to 160 mM after 1 hour of exposure to 350 mM ethanol, with an average ethanol metabolism rate of 56 μmol/larva/hour over 32 hours. Blocking alcohol dehydrogenase 1 (Adh1) and cytochrome P450 2E1 (Cyp2e1), the major enzymes that metabolize ethanol, prevented alcohol-induced steatosis and reduced induction of the UPR in the liver. Thus, we conclude that ethanol metabolism causes ALD in zebrafish. Oxidative stress generated by Cyp2e1-mediated ethanol metabolism is proposed to be a major culprit in ALD pathology. We found that production of reactive oxygen species (ROS) increased in larvae exposed to ethanol, whereas inhibition of the zebrafish CYP2E1 homolog or administration of antioxidants reduced ROS levels. Importantly, these treatments also blocked ethanol-induced steatosis and reduced UPR activation, whereas hydrogen peroxide (H2O2) acted as a pro-oxidant that synergized with low doses of ethanol to induce the UPR. Collectively, these data demonstrate that ethanol metabolism and oxidative stress are conserved mechanisms required for the development of steatosis and hepatic dysfunction in ALD, and that these processes contribute to ethanol-induced UPR activation and secretory pathway stress in hepatocytes.
分泌途径功能障碍和脂质积累（脂肪变性）是肝细胞对乙醇暴露的两种最常见反应，也是酒精性肝病（ALD）发病机制的主要因素。然而，乙醇引发这些细胞反应的机制尚未完全阐明。最近的数据表明，对分泌途径功能障碍的未折叠蛋白反应（UPR）的激活可导致脂肪变性。在这里，我们使用斑马鱼幼虫研究了酒精代谢、氧化应激、分泌途径应激与脂肪变性之间的关系。我们发现，乙醇可被幼虫立即内化和代谢，以致于在暴露于 350mM 乙醇 1 小时后，4 天大的幼虫的内部乙醇浓度平衡至 160mM，平均乙醇代谢率为 56μmol/幼虫/小时，持续 32 小时。阻断主要代谢乙醇的醇脱氢酶 1（Adh1）和细胞色素 P450 2E1（Cyp2e1）可防止乙醇诱导的脂肪变性并减少肝脏中 UPR 的诱导。因此，我们得出结论，乙醇代谢会导致斑马鱼发生 ALD。Cyp2e1 介导的乙醇代谢产生的氧化应激被认为是 ALD 病理的主要罪魁祸首。我们发现，暴露于乙醇的幼虫中活性氧（ROS）的产生增加，而抑制斑马鱼 CYP2E1 同源物或给予抗氧化剂可降低 ROS 水平。重要的是，这些处理还阻断了乙醇诱导的脂肪变性和 UPR 激活，而过氧化氢（H2O2）则作为一种促氧化剂，与低剂量的乙醇协同作用诱导 UPR。总的来说，这些数据表明，乙醇代谢和氧化应激是 ALD 中脂肪变性和肝功能障碍发展的保守机制，这些过程有助于乙醇诱导的 UPR 激活和肝细胞分泌途径应激。
