The role of the HNF4alpha transcription network in the maintenance of key hepatocyte functions during acute liver failure

大量肝细胞损失导致急性肝衰竭（ALF），这是一种在世界范围内具有高死亡率的医疗紧急情况。在这种不利的条件下，剩余的肝细胞和活化的肝祖细胞（LPC）的基本肝功能的性能对于患者的生存至关重要。作为主要的肝转录因子，HNF 4 α在剩余肝细胞和LPC中的表达对于维持ALF中的关键肝功能至关重要。迄今为止，在严重疾病条件下调节HNF 4 α的详细机制，如大量肝细胞损失和严重炎症，在很大程度上仍然未知。我们最近的研究表明，激活素通过上调LPC中HNF 4 α的表达来诱导凝血因子的表达，从而决定ALF的临床结果。此外，HNF 4 α与靶基因增强子的结合需要先锋因子FOXA 2来保持肝细胞和LPC中染色质的可接近性。基于这些新的见解，我们提出了以下假设：（1）在先驱因子FOXA 2的支持下，HNF 4与其他转录因子如C/EBPalpha协同作用，在肝细胞中形成转录网络，调节生理需求的关键功能基因。(2)当严重炎症抑制肝细胞中HNF 4 α表达时，FOXA 2与转录因子如RAR协调调节关键功能基因。(3)在伴有MHN的ALF中，在FOXA 2激活的LPC的支持下，启动了HNF 4主导的转录网络，以在没有肝细胞的区域中接管关键的肝细胞功能。为了证实这些假设，原代肝细胞和LPC以及细胞系将用于体外分子生物学研究。转录因子在ALF中的作用和潜在机制将在ALF患者、对乙酰氨基酚和LPS联合D-半乳糖胺治疗的小鼠和甲硝唑治疗的斑马鱼体内进行研究。阐明肝细胞大量丧失后维持基本肝功能的确切分子机制将增强我们对ALF的理解，并为治疗干预提供新的靶点。

Massive hepatocyte loss results in acute liver failure (ALF), a medical emergency with high mortality worldwide. In such a detrimental condition, performance of essential liver functions by the remaining hepatocytes and activated liver progenitor cells (LPC) is crucial for the survival of patients. As a master hepatic transcription factor, HNF4alpha expression in the remaining hepatocytes and LPC is essential to maintain key liver functions in ALF. To date, the detailed mechanism regulating HNF4alpha under severe disease conditions, such as massive hepatocyte loss and severe inflammation, remains largely unknown. Our recent studies showed that activin induces coagulation factor expression by upregulating HNF4alpha expression in LPC, and thus determines the clinical outcome of ALF. In addition, the binding of HNF4alpha to target genes’ enhancers requires pioneer factor FOXA2 to keep chromatin accessible in both hepatocytes and LPC. Based on these new insights, we propose to investigate the following hypotheses: (1) Supported by pioneer factor FOXA2, HNF4 synergizes with additional transcription factors such as C/EBPalpha to form a transcriptional network in hepatocytes that regulates key functional genes for physiological demand. (2) When severe inflammation inhibits HNF4alpha expression in hepatocytes, FOXA2 coordinates with transcription factors such as RAR to regulate key functional genes. (3) In ALF with MHN, supported by FOXA2 activated LPC initiate an HNF4-dominated transcriptional network to take over key hepatocyte functions in areas in the absence of hepatocytes. To confirm these hypotheses, primary hepatocytes and LPC as well as cell lines will be used for molecular biological investigation in vitro. The role and potential mechanisms of transcription factors in ALF will be examined in vivo in ALF patients, acetaminophen- and LPS combined with D-galactosamine-treated mice and metronidazole-treated zebrafish. Clarification of the exact molecular mechanisms maintaining essential liver functions following massive hepatocyte loss will enhance our understanding of ALF and provide novel targets for therapeutic intervention.