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 万人患有慢性肝病 患有这些疾病的人。目前，肝移植是终末期唯一确定的治疗方法 肝脏疾病；然而，供体肝脏的短缺使得这种疗法极其有限。增强先天 晚期肝病的肝再生是一种有吸引力的治疗选择。为了开发这样的疗法， 了解肝再生的分子机制至关重要，特别是在患病的肝脏中。之上 肝损伤时，肝细胞增殖产生更多肝细胞，以恢复损失的肝脏质量并维持肝功能。 然而，当肝细胞增殖受到损害时，这是在晚期肝脏疾病中观察到的现象， 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扩张 并能分化为肝细胞。疾病严重程度与 LPC 数量之间的相关性 慢性肝病患者提示病变肝脏中存在LPC活化，但其活性较差 分化为肝细胞。此外，LPC 还分泌促炎、促纤维化细胞因子， 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功能性肝细胞对肝脏患者产生有益影响 并同时减少炎症和纤维化。尽管有这样的意义，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分子 LPC 驱动肝再生的机制。为了实现这一目标，在上一个资助周期中，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 在这次续签拨款申请中，我们建议确定核受体法尼醇X受体（FXR）如何 调节 LPC 驱动的肝脏再生。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 使用合成 FXR 激动剂 GW4064 治疗会损害 LPC 驱动的再生。鉴于有益效果 FXR 激动剂对肝脂肪变性、纤维化和肝细胞驱动的肝再生的影响以及多种临床研究 激动剂的试验表明，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， 证明广泛的机械研究是合理的。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，提出了这一假设（目标 1) 并确定 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着推进机械化 了解患病肝脏的肝再生，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.