Redox Signaling and Stem Cell Function

描述(申请人提供)：成体干细胞的活性必须被精确地控制和调整，以适应生物体的要求。潜在的调控机制还不是很清楚，但可以在遗传上易驯化的果蝇肠道干细胞(ISCs)中进行研究。两个申请者的实验室产生的初步数据表明，细胞应激和组织损伤可以显著增加ISCs的增殖活性。值得注意的是，这种ISCs的激活需要伴随着细胞氧化还原状态的降低。基于氧化还原对干细胞和祖细胞功能的调节以前已经被假设，但这种效应的遗传和机制基础仍然不清楚。这项建议所基于的初步数据表明，Nrf2转录因子发挥了关键作用，以前主要与抗氧化和解毒计划有关。当ISCs处于应激状态时，Nrf2的功能受到抑制，允许活性氧物种(ROS)浓度升高，从而促进这些细胞的增殖能力。Nrf2在应激和组织损伤中的下调是干细胞所特有的，与大多数其他体细胞类型中所描述的Nrf2的应激依赖激活形成鲜明对比。这种仅限于干细胞的独特的Nrf2信号系统的发现提出了一些有趣的问题，并为定向操纵干细胞功能提供了机会。本项目将探索Nrf2在ISCs中的独特调控和作用。几条实验路线将探索压力信号如何影响Nrf2来调节ISC的增殖。单独的实验将检验这一假设，即Nrf2和氧化还原控制是调节干细胞活动的普遍机制，这不仅需要传递对直接细胞破坏性压力的反应，还需要介导内分泌分化信号的影响。最后，我们将探讨氧化还原变化能够以如此深刻的方式改变干细胞功能的机制。为实现后一目标，将进行实验，以确定控制干细胞活动的相关氧化还原信号分子。这项提案中描述的工作将提供对基于氧化还原的机制的机械理解，这些机制控制干细胞功能，从而控制组织动态平衡。目标是测试Nrf2活性决定了ISCs减少的、不活跃的状态的模型，在这种状态下，它们受到保护，不受氧化应激的影响，但不能参与再生过程。通过胁迫或有丝分裂信号下调Nrf2的功能，然后诱导一种氧化状态，使再生得以进行。这一模型的验证将证实并从机制上解释长期存在的干细胞和祖细胞调控理论，并可能为操纵干细胞行为的策略和目标提供建议，例如在细胞移植范例或干细胞疾病的治疗中。 公共卫生相关性：躯体干细胞对组织维持和再生至关重要。控制它们的再生能力和增殖活性对于维持组织内环境的稳定是至关重要的。该项目研究氧化还原信号作为干细胞调节的中心组成部分。

DESCRIPTION (provided by applicant): The activity of adult somatic stem cells has to be precisely controlled and adjusted to the organism's requirements. The underlying regulatory mechanisms are not well understood, but can be studied in the genetically tractable Drosophila intestinal stem cells (ISCs). Preliminary data generated in the laboratories of the two applicants have shown that cell stress and tissue damage can significantly increase the proliferative activity of ISCs. Strikingly, this activation of ISCs requires a concomitant decrease in cellular redox state. Redox based regulation of stem and progenitor cell function has been postulated before, but the genetic and mechanistic basis for this effect remains obscure. The preliminary data on which this proposal is based indicate a key role of the Nrf2 transcription factor, which has previously been mostly associated with antioxidant and detoxification programs. Upon stress exposure of ISCs, Nrf2 function is repressed, permitting the concentration of reactive oxygen species (ROS) to rise, and promoting proliferative competence of these cells. The down regulation of Nrf2 in response to stress and tissues injury is unique to stem cells and contrasts sharply with stress dependent activation of Nrf2 described in most other somatic cell types. The discovery of this unique Nrf2 signaling system that is restricted to stem cells raises interesting questions and offers opportunities for the targeted manipulation of stem cell function. This project will explore the distinctive regulation and the effects of Nrf2 in ISCs. Several lines of experimentation will explore how stress signaling affects Nrf2 to regulate ISC proliferation. Separate experiments will test the hypothesis that Nrf2 and redox control are universal mechanisms regulating stem cell activity, which are not only required to convey the response to direct cell damaging stress, but also to mediate the effects of endocrine differentiation signals. Finally, the mechanisms by which redox changes can alter stem cell function in such profound ways will be explored. For this latter aim experiments will be conducted to identify relevant redox sensing signaling molecules that control stem cell activity. The work described in this proposal will provide a mechanistic understanding of the redox-based mechanisms that control stem cell function and consequently tissue homeostasis. The goal is to test the model that Nrf2 activity determines a reduced, inactive state of ISCs, in which they are protected from oxidative stress, but cannot engage in regenerative processes. Down regulation of Nrf2 function by stress or mitogenic signaling then induces an oxidized state that allows regeneration to proceed. Validation of this model will confirm and mechanistically explain long standing theories on stem and progenitor cell regulation and may suggest strategies and targets for the manipulation of stem cell behavior, for example in cell transplantation paradigms or in the treatment of stem cell diseases. PUBLIC HEALTH RELEVANCE: Somatic stem cells are critical for tissue maintenance and regeneration. Controlling their regenerative capacity and proliferative activity is of fundamental importance for the maintenance of tissue homeostasis. This project investigates redox signaling as a central component of stem cell regulation.