Unravelling the importance of Iron Regulatory Proteins for Granulopoiesis

过去几年的研究揭示了代谢对造血系统中干细胞行为和谱系规范的控制至关重要。虽然大部分焦点都集中在中间代谢和能量代谢上，但铁等微量元素在造血细胞命运决定中的作用仍不清楚。在哺乳动物中，细胞铁稳态是由铁调节蛋白(IRP)-1和-2在转录后调控的，它们控制着细胞中编码关键铁代谢蛋白的mrna的命运。我们已经建立了一种新的小鼠模型，使整个身体的IRP功能急性中断，并发现IRP是维持成年期中性粒细胞生理水平所必需的。对造血系统的彻底分析揭示了骨髓中性粒细胞分化的明显缺陷，祖细胞的积累不能正常地向粒细胞谱系发展，反而产生了看似“不成熟”的中性粒细胞。基于体内互惠骨髓移植实验和离体细胞培养模型，我们可以证明IRPs以细胞内在方式支持中性粒细胞分化。这些结果揭示了IRPs在成人造血中以前未被认识到的作用。我们现在建议定义irp缺陷中性粒细胞的功能和分子特征，并研究irp如何精确地支持正常的中性粒细胞生成。我们将首先评估缺乏IRP表达的“未成熟”中性粒细胞的形态和检测关键功能。同时，我们将分析中性粒细胞分化不同阶段造血细胞的转录组。结合基因/功能富集聚类方法，这将有助于我们描述哪些细胞途径主要受IRP缺乏的影响，从而对IRP的中性粒细胞功能具有潜在的重要意义。然后，我们将使用体外和体内基因治疗的基因拯救实验来确定哪些候选途径将IRP功能与中性粒细胞生成联系起来。通过这项工作，我们希望揭示细胞中中央稳态控制系统的新方面，并增强我们对代谢在造血中的作用的理解。

Research in the past few years uncovered the critical importance of metabolism for the control of stem cell behavior and lineage specification in the hematopoietic system. While much of the focus has been on intermediary and energy metabolism, the role of trace elements such as iron in hematopoietic cell fate decisions remains ill understood. In mammals, cellular iron homeostasis is orchestrated posttranscriptionally by the iron regulatory proteins (IRP)-1 and -2, which control the fate of mRNAs encoding key iron metabolism proteins in the cell. We have generated a novel mouse model enabling acute disruption of IRP function in the entire body, and discovered that IRPs are required for maintaining physiological levels of neutrophils during adulthood. A thorough analysis of the hematopoietic system revealed marked defects in neutrophil differentiation in the bone marrow, with accumulation of progenitor cells that fail to progress normally towards the granulocytic lineage and instead give rise to seemingly “immature” neutrophils. Based on reciprocal bone marrow transplantation experiments in vivo and an ex vivo cell culture model, we could demonstrate that IRPs support neutrophil differentiation in a cell intrinsic manner. These results uncover a previously unrecognized role for the IRPs in adult hematopoiesis. We now propose to define the functional and molecular characteristics of IRP-deficient neutrophils, and investigate how precisely the IRPs support normal neutropoiesis. We will first assess the morphology and assay key functions of “immature” neutrophils lacking IRP expression. In parallel, we will profile the transcriptome of hematopoietic cells at different stages of neutrophil differentiation. Combined with gene/functional enrichment clustering approaches, this will help us delineate which cellular pathways are primarily affected in IRP deficiency and thus potentially important for the neutropoietic functions of the IRPs. We will then use gene rescue experiments ex vivo and in vivo gene therapy to determine which of the candidate pathways links IRP function to neutropoiesis. With this work we wish to unveil new facets of a central homeostatic control system in the cell and enhance our understanding of the role of metabolism in hematopoiesis.