Elucidating the role of the FXR-PTEN-PI3K-AKT-mTOR axis in liver progenitor cell-driven liver regeneration

慢性肝病是美国死亡和发病的主要原因之一，有550万人 患有这些疾病的人。目前，肝移植是治疗终末期疾病的唯一有效方法。 肝脏疾病；然而，供体肝脏的短缺使这种疗法极其有限。增强先天功能 晚期肝病的肝再生是一种有吸引力的治疗选择。为了开发这样一种疗法， 了解肝脏再生的分子机制是至关重要的，尤其是在病变的肝脏中。vt.在.的基础上 肝损伤时，肝细胞增殖产生更多的肝细胞，恢复失去的肝脏质量，维持肝功能。 然而，当肝细胞增殖受损时，这是在晚期肝病中观察到的现象， 或者当发生大量肝细胞坏死时，肝祖细胞(LPC)被激活，这些LPC扩张 并能够分化为肝细胞。疾病严重程度与LPC数之间的相关性 慢性肝病患者提示病变肝脏中存在LPC激活，但激活程度较低。 分化为肝细胞。此外，LPCS还分泌促炎、促纤维化的细胞因子，这些细胞因子可以 使炎症持续存在，并导致随后的纤维化。因此，增强先天LPC驱动的肝脏 再生有望通过产生更多有功能的肝细胞对肝脏患者产生有益的影响。 同时减少炎症和纤维化。尽管如此，LPC的分子基础-- 驱动的肝脏再生仍然知之甚少。我们的长期目标是完全描绘出分子 LPC驱动的肝脏再生的机制。为了实现这一目标，在上一个赠款周期中，我们 阐明骨形态发生蛋白(BMP)信号在LPC驱动的肝再生中的关键作用； 这次续期拨款申请，我们建议确定核受体法尼醇X受体(FXR)是如何 调节LPC驱动的肝脏再生。我们已经建立了斑马鱼和小鼠肝损伤模型 LPC驱动的肝脏再生。使用斑马鱼模型，我们进行了化学筛选，发现 用合成的FXR激动剂GW4064治疗会损害LPC驱动的再生。考虑到有益的影响 FXR激动剂治疗肝脏脂肪变性、纤维化和肝细胞驱动的肝再生及其多重临床研究进展 在对激动剂的试验中，它们对LPC驱动的肝再生的负面影响是意想不到和令人惊讶的， 证明广泛的机械性调查是合理的。根据我们的初步发现，我们假设FXR 激活通过抑制PI3K-AKT-mTOR通路来损害LPC驱动的肝再生。我们将对此进行测试 通过阐明FXR激活和抑制对LPC驱动的肝再生的影响提出假说(AIM 1)和确定PTEN-PI3K-AKT-mTOR轴在再生过程中的作用(目标2)。 拟议工作的成功完成不仅将显著推进机械化 了解病变肝脏中的肝再生，但也支持更谨慎地使用FXR 用于治疗晚期肝病患者的激动剂。

Chronic liver diseases are among the leading causes of mortality and morbidity in the U.S., with 5.5 million people suffering from these diseases. Currently, liver transplantation is the only definitive treatment for end-stage liver diseases; however, the shortage of donor livers makes this therapy extremely limited. Augmenting innate liver regeneration in advanced liver diseases is an attractive therapeutic alternative. To develop such a therapy, it is crucial to understand the molecular mechanisms of liver regeneration, particularly in the diseased liver. Upon liver injury, hepatocytes proliferate to yield more hepatocytes to restore lost liver mass and maintain liver function. However, when hepatocyte proliferation is compromised, a phenomenon observed in advanced liver diseases, or when massive hepatocyte necrosis occurs, liver progenitor cells (LPCs) are activated and these LPCs expand and are able to differentiate into hepatocytes. A correlation between disease severity and LPC numbers in patients with chronic liver diseases suggests the occurrence of LPC activation in the diseased livers but its poor differentiation into hepatocytes. In addition, LPCs secrete pro-inflammatory, pro-fibrogenic cytokines that can perpetuate inflammation and contribute to subsequent fibrosis. Thus, augmenting innate LPC-driven liver regeneration is expected to have beneficial effects in liver patients by generating more functional hepatocytes and by concomitantly reducing inflammation and fibrosis. Despite this significance, the molecular basis of LPC- driven liver regeneration remains poorly understood. Our long-term goal is to completely delineate the molecular mechanisms underlying LPC-driven liver regeneration. In pursuit of this goal, during the previous grant cycle, we elucidated the crucial role of bone morphogenetic protein (BMP) signaling in LPC-driven liver regeneration; in this renewal grant application, we propose to determine how the nuclear receptor farnesoid X receptor (FXR) regulates LPC-driven liver regeneration. We have established both zebrafish and mouse liver injury models for LPC-driven liver regeneration. Using the zebrafish model, we performed chemical screening and discovered that treatment with a synthetic FXR agonist, GW4064, impaired LPC-driven regeneration. Given the beneficial effects of FXR agonists on hepatic steatosis, fibrosis, and hepatocyte-driven liver regeneration and the multiple clinical trials of the agonists, their negative effect on LPC-driven liver regeneration is unexpected and surprising, justifying an extensive mechanistic investigation. Based on our preliminary findings, we hypothesize that FXR activation impairs LPC-driven liver regeneration by repressing the PI3K-AKT-mTOR pathway. We will test this hypothesis by elucidating the effects of FXR activation and suppression on LPC-driven liver regeneration (Aim 1) and by determining the role of the PTEN-PI3K-AKT-mTOR axis in the regeneration process (Aim 2). Successful accomplishment of the proposed work will not only significantly advance the mechanistic understanding of liver regeneration in diseased livers, but also support a more cautionary administration of FXR agonists for treating patients with advanced liver diseases.