Characterization of Age-Related Changes in Stem Cell Behavior

描述（由申请人提供）：组织干细胞在整个生命过程中提供器官和组织的维持和再生，干细胞促进组织稳态的能力取决于它们产生新干细胞（自我更新）的独特能力，以及专门的细胞类型（分化）。干细胞是在离散的、特殊的微环境中发现的，在那里它们暴露于不同的系统和局部信号中，这些信号与细胞内在因素相结合，以调节干细胞的行为。随着年龄的增长，许多内在和外在的变化会导致干细胞行为的改变，导致组织维持和再生的减少。这个实验室已经开发了黑腹果蝇作为一个系统来探索衰老对干细胞和生态位的影响。在果蝇的睾丸中，干细胞围绕并接触顶端中枢，这是一群表达自我更新因子Unpaired （Upd）的体细胞，它激活邻近干细胞中的JAK-STAT通路，以指定自我更新和维持。在这项资助的前几年，研究表明衰老会导致中心细胞中upd表达的减少。实验室最近的研究表明，IGF-II mRNA结合蛋白（Imp）可以抵消内嵌sirna，从而稳定中枢细胞中的upd RNA。然而，Imp在老年男性中枢细胞中的表达下降，类似于upd，这是由于异慢性microRNA let-7靶向Imp。因此，在缺乏Imp的情况下，upd mRNA变得不受保护，容易降解，导致与年龄相关的生态位功能丧失。Imp和let-7也在生殖细胞中表达，尽管水平较低，而let-7在年轻动物的中肠中表达，而不是老年动物。因此，本研究将建立在先前研究结果的基础上，解决以下具体目标：具体目标1)表征Imp在生殖细胞和种系衰老中的作用。2)研究let-7在肠道干细胞生态位中的作用。3)揭示睾丸和肠道衰老过程中let-7表达变化的机制。有报道表明let-7家族mirna可能靶向哺乳动物Imp同源物（Igf2bps1-3）。鉴于let-7家族在衰老、干细胞、癌症和代谢中的广泛作用，let-7对Imp的调节可能是许多生理过程中重要的保守机制。除了提供对组织稳态的见解外，关注干细胞年龄相关变化及其特定微环境的研究将有助于识别和克服老年患者组织干细胞操作中的独特障碍，并促进再生医学技术的发展，以治疗与衰老相关的疾病。

DESCRIPTION (provided by applicant): Tissue stem cells provide for the maintenance and regeneration of organs and tissues throughout life, and the ability of stem cells to contribute to tissue homeostasis depends on their unique ability to generate new stem cells (self-renewal), as well as specialized cell types (differentiation). Stem cells are found in discrete, specialized microenvironments (niches) where they are exposed to diverse systemic and local signals that are integrated with cell intrinsic factors to regulate stem cell behavior. Numerous intrinsic and extrinsic changes occur with age that result in altered stem cell behavior, leading to reduced tissue maintenance and regeneration. This lab has developed Drosophila melanogaster as a system to probe the effects of aging on stem cells and the niche. In the Drosophila testis, stem cells surround and contact the apical hub, a cluster of somatic cells that express the self-renewal factor Unpaired (Upd), which activates the JAK-STAT pathway in adjacent stem cells to specify self-renewal and maintenance. In previous years of this grant, it was shown that aging results in a decrease in upd expression in hub cells. Recent work by the lab has revealed that IGF-II mRNA binding protein (Imp) counteracts endo siRNAs to stabilize upd RNA in hub cells. However, Imp expression decreases in hub cells of older males, similar to upd, which is due to targeting of Imp by the heterochronic microRNA let-7. Therefore, in the absence of Imp, upd mRNA becomes unprotected and susceptible to degradation, leading age-related loss of niche function. Imp and let-7 are also expressed in germ cells, albeit at lower levels, and let-7 is expressed in the midgut of young, but not old, animals. Therefore, this proposal will build upon previous findings by addressing the following Specific Aims: Specific Aim 1) To characterize the role of Imp in germ cells and germline aging. Specific Aim 2) To characterize a role for let-7 in the intestinal stem cell niche. Specific Aim 3) To uncover the mechanism by which let-7 expression changes during aging in the testis and intestine. Reports have indicated that the let-7 family of miRNAs likely target mammalian Imp homologs (Igf2bps1-3). Given the broad role of the let-7 family in aging, stem cells, cancer and metabolism, the regulation of Imp by let-7 is likely an important, conserved mechanism in numerous physiological processes. In addition to providing insights into tissue homeostasis, studies focusing on age-related changes in stem cells and their specialized microenvironments will help to identify and overcome unique hurdles in the manipulation of tissue stem cells derived from older patients and to facilitate the development of techniques for regenerative medicine to treat aging-related diseases.