The NRF2-FBP1 crossregulatory loop and the control of healthy and diseased liver metabolism

项目概要/摘要 果糖二磷酸磷酸酶 (FBP1) 是糖异生 (GNG) 中的限速酶，而 由 NFE2L2 基因 (NRF2) 编码的核因子红细胞相关因子 2 是一种转录因子，以前 被确定为抗氧化防御反应的主要激活剂。 NRF2 还激活 许多代谢基因，尤其是肝脏中的基因。我们发现Nrf2Act-HEP小鼠，其中NRF2被选择性激活 在肝细胞中，以及禁食的 Fbp1ΔHEP 小鼠（其中肝细胞中 FBP1 被条件性删除）表现出类似的结果 代谢表型，包括低血糖、肝肿大、肝脂肪变性和高甘油三酯血症， 胰岛素过量的个体和缺乏葡萄糖或碳水化合物的 FBP1 缺陷者也表现出这种症状 孩子们。鉴于这些相似之处，我们询问 NRF2 和 FBP1 是否参与生化串扰。 令人惊讶的是，我们发现 NRF2 的肝脏激活会诱导 FBP1 降解，这是由 NRF2 介导的 EGF 和 PDGF 表达，通过自分泌信号机制导致 ERK1/2 MAP 激活 磷酸化 FBP1 丝氨酸 271 并触发其泛素化和蛋白酶体降解的激酶。 更令人惊讶的是，发现 FBP1 表达导致 AKT 抑制，从而缓解抑制作用 GSK3 同工酶的磷酸化，磷酸化嵌入 NRF2 分子内的降解决定子 从而诱导其泛素依赖性蛋白水解。这些发现使我们推测 NRF2-FBP1 交叉调节环是肝脏代谢和体内平衡的关键调节因子，其功能异常可导致 促进肝脏损伤和癌症。我们计划通过三个具体目标来检验这一假设：1）。调查 FBP1 通过激活 GSK3 或增强 GSK3 来诱导门静脉周围肝细胞中 NRF2 降解的假设 NRF2 的招募； 2）。确定 NRF2 激活是否改变肝脏分区并有助于 FBP1消融引起的代谢缺陷； 3）。研究 NRF2 诱导的 FBP1 降解还是 NRF2 诱导的降解 上调控制从慢性代谢应激到肝细胞癌的进展。追求这些 我们通过新的小鼠模型、细胞生物学研究和高度创新的 Seq-Scope 技术来实现目标 为单个肝细胞的高内涵空间转录组和蛋白质组分析而开发，将回答几个问题 具有普遍重要性的关键问题： 1). FBP1 通过哪些非酶促机制发挥作用？ 除了经过充分研究的 GNG 参与之外，它对肝脏代谢还有广泛的影响吗？ 2）。 NRF2的作用是什么 FBP1 缺乏引起的代谢改变？ 3）。先前描述的 FBP1- 的作用是什么？ 醛缩酶 B 在 AKT 抑制和 GSK3 诱导的 NRF2 降解中的相互作用？和 4)。 AKT的作用是什么 代谢缺陷的激活和致癌转化的易感性增加 FBP1 缺乏肝脏？

Project Summary/Abstract Fructose bisphosphate phosphatase (FBP1) is the rate-limiting enzyme in gluconeogenesis (GNG), whereas nuclear factor erythroid-related factor 2 encoded by the NFE2L2 gene (NRF2) is a transcription factor, previously identified as the master activator of the antioxidant defense response. NRF2 also activates the transcription of many metabolic genes, especially in liver. We found that Nrf2Act-HEP mice, in which NRF2 was selectively activated in hepatocytes, and fasted Fbp1ΔHEP mice, in which FBP1 was conditionally deleted in hepatocytes, exhibit similar metabolic phenotypes, including hypoglycemia, hepatomegaly, hepatosteatosis and hypertriglyceridemia, which are also manifested by insulin overdosed individuals and glucose- or carbohydrate-deprived FBP1-deficient children. Given these similarities, we asked whether NRF2 and FBP1 engage in biochemical crosstalk. Surprisingly, we found that hepatic activation of NRF2 induces FBP1 degradation, mediated by NRF2 induced EGF and PDGF expression, which through an autocrine signaling mechanism led to activation of ERK1/2 MAP kinases that phosphorylated FBP1 at serine 271 and triggered its ubiquitination and proteasomal degradation. Even more surprising was the finding that FBP1 expression led to inhibition of AKT, thereby relieving inhibitory phosphorylation of GSK3 isozymes, which phosphorylate a degron embedded within the NRF2 molecule and thereby induce its ubiquitin-dependent proteolysis. These findings led us to hypothesize that the NRF2-FBP1 crossregulatory loop is a key regulator of liver metabolism and homeostasis, whose aberrant function can promote liver damage and cancer. We plan to test this hypothesis through three specific aims: 1). Investigate the hypothesis that FBP1 induces NRF2 degradation in periportal hepatocytes by activating GSK3 or enhancing its recruitment to NRF2; 2). Determine whether NRF2 activation alters liver zonation and contributes to the metabolic defects caused by FBP1 ablation; 3). Investigate whether NRF2-induced FBP1 degradation or NRF2 upregulation control the progression from chronic metabolic stress to hepatocellular carcinoma. Pursuing these aims via new mouse models, cell biological studies and highly innovative Seq-Scope technology, which we had developed for high-content spatial transcriptomic and proteomic profiling of single liver cells, will answer several critical questions of general importance: 1). What are the non-enzymatic mechanisms through which FBP1 has a broad effect on liver metabolism beyond its well-studied involvement in GNG? 2). What is the role of NRF2 in the metabolic alterations caused by FBP1 deficiency? 3). What is the role of a previously described FBP1- aldolase B interaction in AKT inhibition and GSK3-induced NRF2 degradation? and 4). What is the role of AKT activation in the metabolic defects and increased susceptibility to oncogenic transformation exhibited by the FBP1-deficient liver?