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率和发病率的主要原因之一，550万 患有这些疾病的人。目前，肝移植是终末期肝癌的唯一确定性治疗方法。 肝脏疾病;然而，供体肝脏的短缺使得这种治疗非常有限。增强先天性 晚期肝病的肝再生是一种有吸引力的治疗选择。为了开发这种疗法， 了解肝脏再生的分子机制，特别是在患病肝脏中，是至关重要的。后 肝损伤时，肝细胞增殖以产生更多的肝细胞，以恢复失去的肝质量并维持肝功能。 然而，当肝细胞增殖受到损害时，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）被激活并且这些LPC扩增 并且能够分化成肝细胞。水稻病害严重度与LPC数的相关性研究 慢性肝病患者提示病肝中存在LPC激活，但其激活程度低， 分化成肝细胞。此外，LPCs分泌促炎、促纤维化细胞因子， 使炎症持续并导致随后的纤维化。因此，增强先天LPC驱动的肝脏 通过产生更多的功能性肝细胞， 并同时减少炎症和纤维化。尽管如此，LPC的分子基础- 驱动的肝再生仍然知之甚少。我们的长期目标是完全描绘出 LPC驱动肝再生的潜在机制。为了实现这一目标，在上一个赠款周期，我们 阐明了骨形态发生蛋白（BMP）信号在LPC驱动的肝再生中的关键作用; 在这项更新拨款申请中，我们建议确定核受体法尼醇X受体（FXR） 调节LPC驱动的肝再生。我们建立了斑马鱼和小鼠肝损伤模型， LPC驱动的肝再生。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GW 4064处理，损害LPC驱动的再生。鉴于其有益的效果 FXR激动剂对肝脂肪变性、纤维化和肝细胞驱动的肝再生的作用，以及多个临床 激动剂的试验，它们对LPC驱动的肝再生的负面影响是出乎意料和令人惊讶的， 证明了广泛的机械研究的合理性。根据我们的初步发现，我们假设FXR 活化通过抑制PI 3 K-AKT-mTOR途径损害LPC驱动的肝再生。我们将测试这个 通过阐明FXR激活和抑制对LPC驱动的肝再生的影响， 1)以及通过确定PTEN-PI 3 K-AKT-mTOR轴在再生过程中的作用（目的2）。 成功完成拟议的工作不仅将大大推进机械化， 了解病变肝脏的肝再生，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.