Hepatic stellate cell plasticity and maladaptive fibrogenic memory in chronic liver disease

项目摘要 慢性肝病患者肝星状细胞可塑性和适应不良性纤维化记忆 与慢性肝病相关的纤维化影响着全球数亿患者。肝星状 肝细胞（HSC）又代表肝纤维化的主要细胞驱动因素。一个关键的未解之谜是为什么 HSC激活以促进组织修复，以应对急性肝损伤，但过度激活以产生旺盛的 细胞外基质对反复肝损伤的反应，导致纤维化。这种行为转变的核心是 HSC记住先前损伤事件的机制，以便不同地响应，即过度激活， 当暴露于再次损伤时。最近的研究，包括我们的研究（Wang et al. Dev Cell 2019），强烈支持 表观基因组，特别是DNA甲基化模式作为发育和组织中细胞记忆的载体 损伤本研究的目的是阐明表观基因组，特别是DNA甲基化模式 编码这种适应不良的细胞记忆，并在再损伤后放大HSC的纤维化反应。这项建议 建立在单细胞技术和我们优化的低输入染色质分析的最新进展之上 广泛测量HSC基因表达和表观基因组变化在体内的一种新的小鼠模型， 纤维性记忆在我们的纤维化记忆模型中，HSC在纤维化消退后完全失活， 它们的转录组与未损伤的HSC无法区分，然而表观基因组变化持续存在于 染色质可及性的变化。作为对再损伤的反应，来自退化肝脏的HSC过度活化， 由独特的转录网络（WT 1，TEAD 1，TBX 20和PBX 1）驱动，这些转录网络在经历初始阶段的HSC中没有发现。 损伤使用之前在我们的Dev Cell论文中生成的Uhrf 1 floxed小鼠特异性去除Uhrf 1， DNA甲基化机制的关键组成部分，在HSC中，我们发现这些小鼠表现出增强的 纤维性记忆对再损伤的反应我们的中心假设是，通过记忆先前的伤害， 表观遗传变化改变HSC的可塑性，并增强其对再损伤的反应。我们将解决 这一假设有三个相互关联但又不同的具体目标：1）定义控制 2）确定UHRF 1和DNA甲基化组如何控制HSC中的纤维化记忆; 3）揭示在再损伤中驱动HSC的适应不良反应的新的调节节点。这一创新 利用尖端基因组学技术和独特的动物模型的方法是重要的，因为它将 通过揭示纤维化记忆的表观遗传基础，产生对星状细胞生物学的基本新见解， 特定基因和转录网络对纤维化记忆和肝纤维化的贡献，以及 在肝病患者中保守的纤维化驱动因子可以导致潜在的治疗靶点。

PROJECT SUMMARY Hepatic stellate cell plasticity and maladaptive fibrogenic memory in chronic liver disease Fibrosis associated with chronic liver disease affects hundreds of millions of patients worldwide. Hepatic stellate cells (HSCs), in turn, represent the main cellular driver of hepatic fibrosis. A key unanswered question is why HSCs activate to facilitate tissue repair in response to acute liver injury but hyperactivate to produce exuberant extracellular matrix in response to repeated liver injury, leading to fibrosis. Central to this behavior switch is a mechanism for HSCs to remember previous injury episodes in order to respond differently, i.e. hyperactivate, when exposed to re-injury. Recent studies, including ours (Wang et al. Dev Cell 2019), strongly support the epigenome and in particular DNA methylation patterns as the carrier of cell memory in development and in tissue injury. The objective of this research is to clarify how the epigenome and specifically DNA methylation patterns encode this maladaptive cell memory and amplify HSC’s fibrogenic response following re-injury. This proposal builds upon recent advances in single cell technology and low-input chromatin profiling which we optimized extensively to measure HSC gene expression and epigenomic changes in vivo in a novel mouse model of fibrogenic memory. In our fibrogenic memory model, HSCs completely deactivate following fibrosis regression, with their transcriptome indistinguishable from uninjured HSCs, however epigenomic changes persist in the form of chromatin accessibility changes. In response to re-injury, HSCs from regressed liver hyperactivate and are driven by unique transcriptional networks (WT1, TEAD1, TBX20, and PBX1) not found in HSCs undergoing initial injury. Using the Uhrf1 floxed mice generated previously in our Dev Cell paper to specifically remove Uhrf1, a critical component of the DNA methylation machinery, in HSCs, we found that these mice display augmented fibrogenic memory in response to re-injury. Our central hypothesis is that memory of previous injury through epigenetic changes modify HSC plasticity and amplify their activation in response to re-injury. We will address this hypothesis in three interrelated, but distinct specific aims:1) Define the regulatory elements controlling fibrogenic memory in HSCs; 2) Determine how UHRF1 and the DNA methylome control fibrogenic memory in HSCs; 3) Uncover novel regulatory nodes driving HSC’s maladaptive response in re-injury. This innovative approach leveraging cutting-edge genomics technology and unique animal models is significant because it will yield fundamental new insights into stellate cell biology by uncovering the epigenetic basis of fibrogenic memory, the contribution of specific genes and transcriptional networks to fibrogenic memory and hepatic fibrosis, and conserved fibrogenic drivers in liver disease patients that can lead to potential therapeutic targets.