Role of Gab1 and Gab2 in Stress Erythropoiesis

描述（由申请方提供）：骨髓稳态红细胞生成主要是稳态的，以恒定速率产生红细胞，以替代通过正常转换损失的红细胞。然而，在胚胎发生过程中和对贫血应激的反应中，新的红细胞必须以加速的速率产生。该过程称为应激红细胞生成，其利用表型上不同于稳态红系祖细胞的应激祖细胞的特化群体。在这里显示的初步数据中，我们首次证明了支架蛋白Gab 1和Gab 2在应激红细胞生成中的重要作用。支架蛋白通过整合来自各种外部信号的信息并将这些信息转化为适当的生物反应来形成信号枢纽。然而，由于这些支架的高度复杂性，Gab 1和Gab 2促进不同生物功能的机制仍然难以捉摸。我们在这里证明，虽然Gab 1和Gab 2是高度相关的，它们在应激红细胞生成中的功能是非代偿性的。此外，我们已经开发了一种新的应激红细胞生成的离体模型，其中连续可移植的应激红系干细胞经历特化和扩增，最终产生应激BFU-E。使用这种方法，我们已经表明，Gab 1在应激红系干细胞的应激BFU-E的分化中起着至关重要的作用，正如Gab-deficient细胞不能上调CD 71和Ter 119所证明的那样。我们还提供了证据表明，Gab 2在促进应激红系祖细胞的增殖和/或存活中起着至关重要的作用。本文提出的研究将确定这些相关支架在应激红细胞生成中促进非冗余功能的分子机制。为此，我们提出三个具体目标。在目标1中，我们将检验这样的假设：Gab 1募集Shp 2促进细胞膜上持续的Erk激活，从而促进应激BFU-E从应激干细胞分化。在目标2中，我们将检验Gab 2在Stat 3的激活中起重要作用的假设， Pu.1表达的上调，从而防止过早分化并促进分化应激红系祖细胞的存活。最后，在目标3中，我们将测试Gab 1和Gab 2在人应激红系祖细胞的离体扩增中起重要作用的假设。这些研究将提供重要的洞察力的分子机制，管理应激红系祖细胞在急性需要的时候快速扩增，并将在确定新的药理学目标，以及开发新的细胞为基础的治疗急性和慢性贫血的疗法至关重要。 公共卫生相关性：遗传性贫血是人类最常见的单基因遗传病之一，与慢性病或老年性贫血以及化疗或放疗引起的治疗性贫血一起，是严重的公共卫生问题。应激性红细胞生成是响应急性需要而替换丢失的红细胞的过程。我们已经确定了新的信号通路，这在应激红细胞生成中发挥核心作用，通过促进分化和生存的一个专门的人口的应激红系祖细胞。本文提出的研究旨在确定调节这些功能的分子机制。了解控制应激祖细胞扩张的信号通路将是开发基于细胞的治疗方法以对抗慢性和急性贫血的关键一步。

DESCRIPTION (provided by applicant): Bone marrow steady state erythropoiesis is primarily homeostatic, producing erythrocytes at a constant rate to replace the erythrocytes lost through normal turnover. However, during embryogenesis and in response to anemic stress, new erythrocytes must be produced at an accelerated rate. This process, termed stress erythropoiesis, utilizes a specialized population of stress progenitors that are phenotypically distinct from steady state erythroid progenitors. In preliminary data shown here we demonstrate, for the first time, an essential role for the scaffold proteins, Gab1 and Gab2, in stress erythropoiesis. Scaffold proteins form signaling hubs by integrating the information from a variety of external signals and transforming this information into the appropriate biological response. However, due to the high level of complexity of these scaffolds, the mechanisms by which Gab1 and Gab2 promote distinct biological functions have remained elusive. We demonstrate here that, while Gab1 and Gab2 are highly related, their functions in stress erythropoiesis are non-compensatory. Furthermore, we have developed a novel ex vivo model of stress erythropoiesis in which serially transplantable stress erythroid stem cells undergo specification and expansion, ultimately giving rise to stress BFU-E. Using this approach, we have shown that Gab1 plays an essential role in the differentiation of stress BFU-E from stress erythroid stem cells, as demonstrated by the inability of Gab-deficient cells to upregulate CD71 and Ter119. We also provide evidence that Gab2 plays an essential role in promoting the proliferation and/or survival of stress erythroid progenitors. The studies proposed here will determine the molecular mechanism by which these related scaffolds promote non-redundant functions in stress erythropoiesis. Toward that end, we propose three specific aims. In aim 1, we will test the hypothesis that Recruitment of Shp2 by Gab1 promotes sustained Erk activation at the cell membrane, thus promoting the differentiation of stress BFU-E from stress stem cells. In aim 2, we will test the hypothesis that Gab2 plays an essential role in the activation of Stat3 and the upregulation of Pu.1 expression, thus preventing premature differentiation and promoting survival of differentiating stress erythroid progenitors. Finally, in aim 3 we will test the hypothsis that Gab1 and Gab2 play essential roles in the ex vivo expansion of human stress erythroid progenitors. These studies will provide significant insight into the molecular mechanisms governing the rapid expansion of stress erythroid progenitor cells during times of acute need, and will be essential in the identification of new pharmacological targets as well as the development of novel cell-based therapies for the treatment of acute and chronic anemia. PUBLIC HEALTH RELEVANCE: Hereditary anemias are amongst the most common monogenic traits in man. These diseases, together with anemia from chronic disease or old age, as well as treatment-induced anemia as accompanies chemotherapy or radiation therapy, are significant public health problems. Stress erythropoiesis is the process of replacing lost red blood cells in response to acute need. We have identified novel signaling pathways, which play a central role in stress erythropoiesis, by promoting the differentiation and survival of a specialized population of stress erythroid progenitor cells. The studies proposed herein aim to identify the molecular mechanisms by which these functions are regulated. Understanding the signaling pathways that govern the expansion of stress progenitors will be a critical step in the development of cell-based therapies for combating chronic and acute anemia.