Effects of Aging on Lymphoid Biased Hematopoietic Stem Cells

 描述（由申请人提供）：造血干细胞（HSC）区室是异质的，包括淋巴偏向（Ly-HSC）和骨髓偏向（My-HSC）亚群。已经假设Ly-HSC的数量随着年龄的增长而下降，这解释了为什么淋巴细胞生成在老年人中减弱。然而，这种观点是基于评估干细胞频率。当计算HSC数量时，很明显My-HSC的总数随着年龄的增长而增加，并且这些是骨髓中存在的主要干细胞群。然而，同样明显的是，Ly-HSC的总数也随着年龄的增长而增加。为什么淋巴细胞生成会随着年龄的增长而下降，尽管Ly-HSC的数量不会减少？该提案将测试内在Ly-HSC缺陷与其环境变化相结合的假设。在目标1中，我们将为从年轻和老年小鼠中分离的Ly-HSC和My-HSC生成强大的全转录组数据库，并使用消减方法，识别两者共同或仅限于一个或另一个HSC子集的基因表达变化。这些数据集将为后续实验提供理论基础，这些实验确定衰老如何影响Ly-HSC与My-HSC中的增殖，自我更新和DNA修复等关键功能。慢性炎症随着年龄的增长而增加，并已被证明会影响HSC的增殖，分化和自我更新。目的2将使用体内和体外模型来验证炎症介质对Ly-HSC和My-HSC具有选择性作用的假设。使用目标1中生成的数据库，我们将鉴定Ly-HSC和My-HSC上表达的细胞因子受体，并使用我们开发的干细胞集落测定法测试其配体如何影响每个HSC亚群的生长和分化。我们还将检验Ly-HSC和My-HSC由于它们激活NF-κ B B和表达NF-κ B B调节基因的水平不同而不同地处理炎症信号的假设。刺激老年人淋巴细胞生成的能力可能具有重要的翻译意义。我们已经观察到，用胰岛素样生长因子-I（IGF-I）（一种天然存在的激素，其产量随年龄增长而下降）治疗老年小鼠可以扩大HSC数量，并将Ly-HSC/My-HSC比率恢复到年轻动物中的水平。目的3中的实验将评估从IGF-I处理的小鼠收获的Ly-HSC中的基因表达模式，并使用目的1和2中定义的方法，确定来自IGF-I处理的小鼠的Ly-HSC是否已经再生。总之，拟议的研究将提供有关衰老如何影响HSC亚群的新信息，以及对药物干预刺激老年人淋巴细胞生成的潜力的临床前见解。

 DESCRIPTION (provided by applicant): The hematopoietic stem cell (HSC) compartment is heterogeneous and includes lymphoid biased (Ly-HSCs) and myeloid biased (My-HSCs) subpopulations. It has been assumed that the number of Ly-HSCs declines with age and that this explains why lymphopoiesis is attenuated in the elderly. However, this view is based on assessing stem cell frequency. When HSC numbers are calculated, it is clear that the total number of My- HSCs increases with age and these are the predominant stem cell population present in the bone marrow. However, it is also evident that the total number of Ly-HSCs also increases with age. Why does lymphopoiesis decline with age despite the fact that Ly-HSCs do not decrease in number? This proposal will test the hypothesis that intrinsic Ly-HSC defects combined with alterations in their environment are responsible. In Aim 1, we will generate robust, whole transcriptome databases for Ly-HSCs and My-HSCs isolated from young and old mice and, using subtractive approaches, identify changes in gene expression common to both or restricted to one or the other HSC subset. These data sets will provide the rationale for subsequent experiments that determine how aging affects such key functions as proliferation, self-renewal, and DNA repair in Ly-HSCs versus My-HSCs. Chronic inflammation increases with age and has been shown to affect the proliferation, differentiation, and self-renewal of HSCs. Aim 2 will use both in vivo and in vitro models to test the hypothesis that inflammatory mediators have selective effects on Ly-HSCs and My-HSCs. Using the databases generated in Aim 1, we will identify cytokine receptors expressed on Ly-HSCs and My-HSCs and test how their ligands affect the growth and differentiation of each HSC subset using a stem cell colony assay we have developed. We will also test the hypothesis that Ly-HSCs and My-HSCs differentially process inflammatory signals due to differences in the level at which they activate NF-B and express NF-B regulated genes. The ability to stimulate lymphopoiesis in the elderly could have important translational implications. We have observed that treatment of old mice with Insulin-Like Growth Factor-I (IGF-I), a naturally occurring hormone whose production declines with age, can expand HSC numbers and restore the Ly-HSC/My-HSC ratio to that in young animals. Experiments in Aim 3 will assess the pattern of gene expression in Ly-HSCs harvested from the IGF-I treated mice and, using approaches defined in Aims 1 and 2, determine if the Ly-HSCs from IGF-I treated mice have been rejuvenated. Taken together, the proposed studies will provide new information about how aging impacts HSC subpopulations and pre-clinical insights into the potential of pharmacologic interventions to stimulate lymphopoiesis in the elderly.