Redox Signaling and Stem Cell Function

描述（由申请人提供）：成体干细胞的活性必须精确控制和调整以适应生物体的要求。潜在的调控机制还没有很好地理解，但可以在遗传上易处理的果蝇肠道干细胞（ISCs）中进行研究。在两个申请人的实验室中产生的初步数据显示，细胞应激和组织损伤可以显著增加ISC的增殖活性。引人注目的是，ISCs的这种激活需要伴随细胞氧化还原状态的降低。基于氧化还原的干细胞和祖细胞功能的调节以前已经被假定，但这种作用的遗传和机制基础仍然不清楚。该提议所基于的初步数据表明Nrf2转录因子的关键作用，该转录因子以前主要与抗氧化剂和解毒程序相关。在ISCs的应激暴露后，Nrf2功能被抑制，允许活性氧（ROS）的浓度升高，并促进这些细胞的增殖能力。响应于应激和组织损伤的Nrf2的下调是干细胞特有的，并且与大多数其他体细胞类型中描述的Nrf2的应激依赖性活化形成鲜明对比。发现这种仅限于干细胞的独特Nrf2信号系统提出了有趣的问题，并为靶向操纵干细胞功能提供了机会。本项目将探讨Nrf2在ISCs中的独特调节和作用。几条实验线将探索应激信号如何影响Nrf2调节ISC增殖。单独的实验将测试Nrf2和氧化还原控制是调节干细胞活性的通用机制的假设，其不仅需要传递对直接细胞损伤应激的响应，而且还需要介导内分泌分化信号的作用。最后，氧化还原变化可以改变干细胞功能的机制，在这种深刻的方式将进行探讨。对于后一个目标，将进行实验以鉴定控制干细胞活性的相关氧化还原传感信号分子。本提案中描述的工作将提供对控制干细胞功能和组织稳态的基于氧化还原的机制的机械理解。我们的目标是测试Nrf2活性决定ISCs减少的非活性状态的模型，在这种状态下，它们受到氧化应激的保护，但不能参与再生过程。通过应激或促有丝分裂信号传导下调Nrf2功能然后诱导允许再生进行的氧化状态。该模型的验证将证实并机械地解释关于干细胞和祖细胞调节的长期存在的理论，并且可以建议用于操纵干细胞行为的策略和靶点，例如在细胞移植范例中或在干细胞疾病的治疗中。

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.