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

项目摘要/摘要 果糖二磷酸磷酸酶(FBP1)是糖异生过程中的限速酶，而 核因子红系相关因子2由NFE2L2基因(NRF2)编码，是一种转录因子，以前 被认为是抗氧化剂防御反应的主要激活剂。NRF2还激活了转录 很多代谢基因，特别是在肝脏中。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Fbp1的ΔHEp小鼠，其中Fbp1在肝细胞中有条件地删除，表现出类似的 代谢表型，包括低血糖、肝肿大、肝骨病和高甘油三酯血症， 还表现为胰岛素过量和葡萄糖或碳水化合物缺乏的FBP1缺陷 孩子们。鉴于这些相似之处，我们询问NRF2和FBP1是否参与了生化串扰。 令人惊讶的是，我们发现肝脏激活NRF2诱导FBP1降解，这是由NRF2诱导的 EGF和PDGF的表达通过自分泌信号机制导致ERK1/2 MAP的激活 使丝氨酸271处的FBP1磷酸化并触发其泛素化和蛋白酶体降解的激酶。 更令人惊讶的是，FBP1的表达导致了对AKT的抑制，从而解除了抑制 GSK3同工酶的磷酸化，它磷酸化嵌入NRF2分子中的降解子和 从而诱导其泛素依赖的蛋白分解。这些发现使我们假设NRF2-FBP1 交叉调节环是肝脏代谢和动态平衡的关键调节因子，其异常功能可 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说：1)。调查 FBP1通过激活GSK3或增强GSK3诱导门脉周围肝细胞NRF2降解的假设 它招募到NRF2；2)。确定NRF2激活是否改变肝脏分区并导致 FBP1消融引起的代谢缺陷；调查NRF2诱导的FBP1降解还是NRF2 上调控制从慢性代谢应激到肝细胞癌的进展。追求这些 旨在通过新的小鼠模型、细胞生物学研究和高度创新的序列显微镜技术，我们拥有 为单个肝细胞的高含量空间转录和蛋白质组学分析而开发，将回答以下几个问题 具有普遍重要性的关键问题：1)。FBP1的非酶机制是什么？ 对肝脏代谢的广泛影响超出了对GNG的充分研究？2)。NRF2在其中的作用是什么？ 3)FBP1缺乏引起的代谢改变。前面描述的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 表现出代谢缺陷的激活和对致癌转化的敏感性增加 FBP1基因缺陷的肝脏？

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?