Fine-tuning of Hematopoiesis by the Mirn23a/b MiRNA Clusters

 描述（由申请人提供）：获得性血细胞减少症是一种或多种血细胞类型大大减少的血液疾病。了解造血干细胞和祖细胞（HSPC）的发育对于开发新的血细胞减少症治疗至关重要。信号转导通路和转录因子网络协调造血。然而，刺激这些途径以增加血液发育伴随着促进血液恶性肿瘤的风险。miRNA被描述为基因表达的微调器，因为它们通常下调其靶点不到50%。我们推测，通过靶向信号或转录网络中的多个基因，miRNAs对细胞分化有重要影响。然而，我们假设调节miRNA的表达，由于其对单个靶点的适度影响，促进恶性肿瘤的风险较低。使用过表达和shRNA实验，我们已经发表了编码3个前体miRNA的miRNA簇mirn 23 a，调节造血祖细胞向免疫细胞命运的特化，以及从胚胎干细胞向HSPC的发育。为了进一步研究miRNA对造血的调节，我们产生了mirn 23 a-/-小鼠。这些小鼠由于来自同源mirn 23 B基因的补偿而存活;然而，mirn 23 a/B miRNAs的亚型表达导致骨髓和脾脏中B细胞增加，单核细胞/粒细胞减少。免疫细胞群的这些变化似乎是由于对骨髓祖细胞群的影响。初步证据表明，mirn 23 a/B miRNAs影响淋巴和髓系祖细胞上游多能祖细胞（MPP）中转录因子的表达。Mirn 23 a调节PI 3 K/ Akt途径和BMP/ Smad途径，其具有影响造血祖细胞中转录因子平衡的潜力。在这个项目中，我们将检查缺乏mirn 23 a和mirn 23 b基因的小鼠的造血功能。我们假设mirn 23 a/B miRNAs作为细胞信号通路的变阻器，控制成年HSPCs的发育和功能。该项目的完成将确定mirn 23 a/B miRNAs在成人HSPC发育和维持中的作用，以及确定mirn 23 a/B表达是否是造血过程中协调PI 3 K/ Akt和BMP/ Smad活性的新机制。重要的是，结果将证明mirn 23 a/B miRNAs是否是造血分化的调节因子，可以作为血细胞减少症治疗的靶点。与目前的细胞因子方案或使用细胞因子模拟物相比，靶向miRNA可能具有更低的促进恶性肿瘤的风险。脱离细胞因子刺激的标准方法可能是治疗血细胞减少症问题的创新方法，这将比频繁的静脉内细胞因子注射更方便，并且降低了有害副作用的风险。

 DESCRIPTION (provided by applicant): Acquired cytopenias are blood disorders in which one or more blood cell types are greatly reduced. Understanding hematopoietic stem and progenitor cell (HSPC) development is critical for the development of new cytopenia treatments. Signal transduction pathways and networks of transcription factors orchestrate hematopoiesis. However, agonizing these pathways to increase blood development comes with the risk of promoting hematological malignancies. MiRNAs have been described as fine-tuners of gene expression as they typically downregulate their targets by less than 50%. We hypothesize that through targeting multiple genes in a signaling or transcriptional network miRNAs have major effects on cell differentiation. However we postulate that modulating miRNA expression will carry lower risk of promoting malignancy due to their modest effects on individual targets. Using overexpression and shRNA experiments, we have published that the miRNA cluster mirn23a, which codes for 3 pre-miRNAs, regulates specification of hematopoietic progenitors to immune cell fates, as well as the development of HSPCs from embryonic stem cells. To further investigate miRNA regulation of hematopoiesis, we generated mirn23a-/- mice. These mice are viable due to compensation from the homologous mirn23b gene; however, the hypomorphic expression of mirn23a/b miRNAs results in increased B cells, and decreased monocytes/granulocytes in the bone marrow and spleen. These changes in immune cell populations appear to be due to effects on bone marrow progenitor populations. Preliminary evidence suggests that mirn23a/b miRNAs affect transcription factor expression in the multipotential progenitor (MPP) upstream of lymphoid and myeloid progenitors. Mirn23a modulates both the PI3K/ Akt pathway, and BMP/ Smad pathways, which has the potential to influence the balance of transcription factors in hematopoietic progenitors. In this project we wil examine hematopoiesis in mice lacking both the mirn23a, and mirn23b genes. We hypothesize that the mirn23a/b miRNAs act as a rheostat for cell signaling pathways, which control the development and function of adult HSPCs. The completion of this project will define the role of the mirn23a/b miRNAs in adult HSPC development and maintenance, as well as determine whether mirn23a/b expression is a novel mechanism for coordinating PI3K/ Akt, and BMP/ Smad activity during hematopoiesis. Importantly results will demonstrate whether the mirn23a/b miRNAs are regulators of hematopoietic differentiation that could be pursued as targets for cytopenia therapy. Targeting miRNAs may carry less risk of promoting malignancies than current cytokine regimens or use of cytokine mimetics. Breaking away from the standard approach of cytokine stimulation could be an innovative approach to the problem of treating cytopenias, which would be more convenient than frequent intravenous cytokine injections, and have reduced risk of harmful side effects.