Insulin Regulation of Hepatic Function via Zone-Specific Transcriptional Programs

非酒精性脂肪性肝病(NAFLD)在我们的社会中已经达到了流行的程度，而我们的 对这种疾病的发病机制的了解仍处于初步阶段7.临床研究表明 胰岛素抵抗与非酒精性脂肪肝发生发展的关系 发生在发育过程中的甘油三酯、胆固醇和胆汁酸代谢的变化 对于NAFLD来说，清楚地了解胰岛素是如何调节这些过程是必要的。到目前为止，对 胰岛素在肝脏中的作用是在假设所有肝细胞都相同的情况下进行的。这 假设是从实际出发的，因为我们能够分离和分析不同的肝细胞群 个人的数量是有限的。然而，肝细胞在它们执行的代谢功能方面明显不同，它们的 对不同侮辱的敏感性10.例如，静脉周围的肝细胞是胆汁的主要部位 酸的合成和甘油三酯在NAFLD 11，12中最常见的积累位置。在这里，我们将确定 胰岛素如何调节静脉周围肝细胞的基因表达以维持动态平衡。 我们的小说，未发表的初步数据揭示了一个显著的区域特定转录的例子 胰岛素的调节作用。我们发现胰岛素仅在静脉周围肝细胞中抑制Cyp8b1。Cyp8b1 编码唯一能催化胆汁酸12A-羟基化的酶13；12A-羟化胆汁酸 增加肝脏胆固醇，促进进展为非酒精性脂肪性肝炎(NASH)14-16。在 在缺乏胰岛素的情况下，静脉周围肝细胞中Cyp8b1的抑制与12A- 羟化胆汁酸，肝脏胆固醇升高，以及严重炎症。NAFLD的事实是 人类的进展也与12A-羟基胆汁酸和肝脏的增加有关 胆固醇，以及炎症标志着非酒精性脂肪性肝炎的发展，这是一种 严重和进行性疾病，突出研究这一途径的重要性17-19。基于这些 和其他初步数据，我们假设胰岛素调节主链b-连环蛋白的活性。 仅在静脉周围肝细胞20中激活的转录调节因子，以维持正常的脂质 动态平衡和预防炎症。为了验证这一假设，我们的目标是(1)定义胰岛素调节的细胞 利用单核序列分析肝脏转录程序；以及(2)剖析b-连环蛋白在肝脏中的作用。 对胰岛素产生转录和生理反应。我们预计胰岛素可以重新编程 静脉周围肝细胞通过调节b-连环蛋白驱动转录，这是正常所必需的 动态平衡。这样的结果可能最终导致开发出精确的干预措施，从而逆转 胰岛素抵抗对周围静脉肝细胞的影响，预防NASH。

Non-alcoholic fatty liver disease (NAFLD) has reached epidemic proportions in our society, and yet our understanding of the pathogenesis of this disorder remains rudimentary 7. Clinical studies show a close correlation between insulin resistance and the development and progression of NAFLD 8,9. To understand mechanistically the changes in triglyceride, cholesterol, and bile acid metabolism that occur with the development of NAFLD, a clear understanding of how insulin regulates these processes is necessary. Until now, studies of insulin action in the liver have been done with the assumption that all hepatocytes are equivalent. This assumption was made out of practicality, as our ability to isolate and analyze different populations of hepatocytes individually was limited. Yet, hepatocytes clearly vary in terms of the metabolic functions they perform, and their susceptibility to different insults 10. For example, the perivenous hepatocytes are the predominant site of bile acid synthesis and the most common site of triglyceride accumulation in NAFLD 11,12. Here, we will determine how insulin modulates gene expression in the perivenous hepatocytes to maintain homeostasis. Our novel, unpublished preliminary data reveal a striking example of zone-specific transcriptional regulation by insulin. We find that insulin suppresses Cyp8b1 only in the perivenous hepatocytes. Cyp8b1 encodes the sole enzyme capable of catalyzing the 12a-hydroxylation of bile acids 13; 12a-hydroxylated bile acids increase hepatic cholesterol and promote the progression to non-alcoholic steatohepatitis (NASH) 14-16. In the absence of insulin, the de-repression of Cyp8b1 in the perivenous hepatocytes is associated with increased 12a- hydroxylated bile acids, increased hepatic cholesterol, and severe inflammation. The fact that NAFLD progression in humans is also associated with an increase in 12a-hydroxylated bile acids and hepatic cholesterol, and the fact that inflammation marks the development of non-alcoholic steatohepatitis, a more severe and progressive form of disease, highlight the importance of studying this pathway 17-19. Based on these and other preliminary data, we hypothesize that insulin modulates the activity of b-catenin, a master transcriptional regulator that is activated only in the perivenous hepatocytes 20, to maintain normal lipid homeostasis and prevent inflammation. To test this hypothesis, we aim to (1) define the insulin-regulated cellular transcriptional programs in the liver using single-nuclei sequencing; and (2) dissect the role of b-catenin in producing the transcriptional and physiological response to insulin. We expect that insulin can reprogram the perivenous hepatocytes by modulating b-catenin driven transcription, and that this is required for normal homeostasis. Such results may ultimately lead to the development of precise interventions that reverse the effects of insulin resistance in the perivenous hepatocytes, preventing NASH.