两项研究：肝病防护转录因子FOXO3

　　

生物通报道：来自堪萨斯大学的研究者在最新一期American Journal of Pathology杂志上分别发表了两项研究成果，表明转录因子FOXO3能够预防丙型肝炎和酒精引起的肝脏损伤。他们认为，对FOXO3通路的调整，能够为由HCV-酒精引起的肝脏损伤提供一种潜在的治疗方法。

最新一期的American Journal of Pathology杂志上刊出了两篇关于肝病防护转录因子FOXO3的论文。其中一项研究表明，转录因子FOXO3能够保护肝脏免受酒精引起的肝脏损伤。研究者确定，酒精引起小鼠FOXO3缺乏从而导致类似人酒精性肝炎一样的严重的肝脏损伤。他们进一步发现，尽管丙型肝炎病毒（HCV）和酒精能独立激活FOXO3因子，但它们组合在一起能够抑制FOXO3，降低细胞保护基因的表达，加重肝脏损伤。

堪萨斯大学医学中心内科系的医学博士Steven A. Weinman称，“已经有新的证据表明，FOXO转录因子家族在肝脏的代谢、抗氧化和细胞死亡反应中起了关键作用。FOXO在损伤过程中所起的作用非常复杂，因为FOXO转录程序能够被细胞保护，或者有细胞毒素，关于这两种现象的证据充分的例子非常多。”

根据这些新的证据，Weinman医生的团队，在三周时间里，用酒精喂养FOXO3缺乏的小鼠。这些小鼠中有1/3得了严重的脂肪肝（肝细胞的脂肪浸润）、中性粒细胞浸润和细胞坏死，这跟在酒精性肝炎病人中观察到的症状一样。在一些小鼠中，肝脏转氨酶（ALT）水平，与对照组相比，增加了十倍。

研究者在HCV小鼠模型（转基因的HCV/Sod 2+/-）中使用酒精，也引起了严重的肝脏损伤。这些动物表现ALT上升，ICAM-1的表达增加、切冬酶3裂解、严重脂肪肝、小叶性肝炎和肝细胞气球样变性。在这些小鼠中，肝脏损伤的程度与线粒体抗氧化酶超氧化物歧化酶（SOD2）有关（SOD2也被认为在保护肝脏免受酒精损伤的过程中起作用）。与其它类型的小鼠细胞核位置的FOXO3相比，酒精处理的HCV/Sod 2+/-小鼠，其细胞溶质的FOXO3表现出一个较大浓度。

Weinman继续称，“对于酒精性肝病，目前还没有解决的重要问题之一是，为什么饮酒的包括酗酒的人中只有少数人患上肝病。在多数人中，肝脏对酒精具有有效的保护机制。我们的结果表明，FOXO3是一种新的酒精防护因子，能够被HCV-酒精组合破坏。因此我们认为，FOXO3通路的调整，对于由HCV-酒精引起的肝脏损伤是一种潜在的治疗方法。”

在细胞培养中，HCV或者酒精都能单独引起FOXO3转录活性的一个增加。然而，Weinman及其同事发现，尽管这两种针对FOXO3的压力刺激产生的效应是类似的，但是其作用机制是不同的。例如，尽管HCV活化与FOXO3从细胞溶质到细胞核的迁移有关，但是酒精能够引起转录激活，而细胞核-细胞溶质的比率没有一个明显变化。另外发现的一个差异是，HCV而不是酒精，能够引起一个依赖miRNA的SOD2转化抑制。

Weinman称，HCV感染和酒精暴露，似乎共同作用产生效应，它们组合所产生的效应与它们单独作用所产生的效应不同，这是一项“新的和意想不到” 的发现。通过HCV和酒精的结合抑制FOXO3，一部分归因于出核转运和一个降低的蛋白质半衰期，这两种现象并没有在HCV或者酒精单独起作用的情况中出现。Weinman推断，“这些结果表明，FOXO3是一种新的酒精防护因子，能够被HCV-酒精组合破坏。”

发表在同一期American Journal of Pathology杂志中的另外一项相关研究成果也来自堪萨斯大学医学中心，是由药理学、毒理学和治疗学系的博士Wen-Xing Ding医生带领的另外一支研究团队。他们报道称，FOXO3保护肝脏免受酒精诱导的严重脂肪肝和肝损伤。这项研究表明，FOXO3对于自噬——一种细胞降解途径，通过移除受伤的线粒体，保护酒精引起的肝脏损伤——的激活是必需的。急性酒精处理的FOXO3缺乏小鼠，较野生型小鼠，发生了更严重的肝脏损伤，这是因为自噬相关基因的表达降低。

Ding医生称：“我们的研究，是一个急性的酒精模型，而Weinman医生实验室的研究是一个慢性的酒精喂养模型。然而，这两项研究都证明，FOXO3是防护性的。因此，这些结果表明，FOXO3是一种重要的通用机制，这种机制通过激活正常肝脏用来抵抗酒精毒性效应的多个细胞防护功能来发挥作用。”（生物通：王英）

生物通推荐两篇原文摘要：
Hepatitis C and Alcohol Exacerbate Liver Injury by Suppression of FOXO3
Abstract：Hepatitis C virus (HCV) infection exacerbates alcoholic liver injury by mechanisms that include enhanced oxidative stress. The forkhead box transcription factor FOXO3 is an important component of the antioxidant stress response that can be altered by HCV. To test whether FOXO3 is protective for alcoholic liver injury, we fed alcohol to FOXO3−/− mice. After 3 weeks, one third of these mice developed severe hepatic steatosis, neutrophilic infiltration, and >10-fold alanine aminotransferase (ALT) elevations. In cell culture, either alcohol or HCV infection alone increased FOXO3 transcriptional activity and expression of target genes, but the combination of HCV and alcohol together caused loss of nuclear FOXO3 and decreased its transcriptional activity. This was accompanied by increased phosphorylation of FOXO3. Mice expressing HCV structural proteins on a background of reduced expression of superoxide dismutase 2 (SOD2; Sod2+/−) also had increased liver sensitivity to alcohol, with elevated ALT, steatosis, and lobular inflammation. Elevated ALT was associated with an alcohol-induced decrease in SOD2 and redistribution of FOXO3 to the cytosol. These results demonstrate that FOXO3 functions as a protective factor preventing alcoholic liver injury. The combination of HCV and alcohol, but not either condition alone, inactivates FOXO3, causing a decrease in expression of its target genes and an increase in liver injury. Modulation of the FOXO3 pathway is a potential therapeutic approach for HCV-alcohol–induced liver injury.
Critical Role of FoxO3a in Alcohol-Induced Autophagy and Hepatotoxicity
Abstract：Autophagy is a lysosomal degradation process that degrades long-lived cellular proteins and damaged organelles as a critical cell survival mechanism in response to stress. We recently reported that acute ethanol induces autophagy, which then reduces ethanol-induced liver injury. However, the mechanisms by which ethanol induces autophagy are not known. In the present study, ethanol treatment significantly increased both mRNA and protein levels of various essential autophagy-related genes in primary cultured mouse hepatocytes and in mouse liver. Both nuclear translocation of FoxO3a and expression of FoxO3a target genes were increased in ethanol-treated primary hepatocytes and mouse liver. Overexpression of a dominant negative form of FoxO3a inhibited ethanol-induced autophagy-related gene expression and enhanced ethanol-induced cell death in primary hepatocytes, which suggests that FoxO3a is a key factor in regulating ethanol-induced autophagy and cell survival. Resveratrol, a well-known SIRT1 agonist, further enhanced ethanol-induced expression of autophagy-related genes, likely via increased deacetylation of FoxO3a. Moreover, acute ethanol–treated Foxo3a−/− mice exhibited decreased autophagy-related gene expression, but enhanced steatosis and liver injury, compared with wild-type mice. FoxO3a thus plays a critical role in ethanol-induced autophagy in mouse liver. Modulating the FoxO3a autophagy pathway may offer novel therapeutic approaches for treating alcoholic liver pathogenesis.