Latexin function in the maintenance and regeneration of the hematopoietic system

项目总结 这项研究的长期目标是开发新的策略来减轻和保护辐射引起的 增强造血干细胞的分子机制及其对造血损伤的影响 细胞(HSC)自我更新和存活。放射治疗通常不仅会导致急性造血 抑制还会对骨髓(BM)造成长期损伤。迄今为止，还没有开发出有效的治疗方法。 来预防或治疗这些病理性后果。提高HSC存活率并维持其基因组 辐射后的完整性对于保存HSC的自我更新功能和防止 放射性骨髓损伤。然而，调控HSC存活和自我更新的分子机制 没有很好地定义。HSC的数量和功能显示了自然变异和潜在的遗传多样性 是调节HSC功能的一个重要机制，但在很大程度上还不为人所知。莱克辛(LXN)是 先前被确认为第一个干细胞调节基因，其自然变异对 不同品系小鼠的HSC群体大小。在初步研究中，结构性基因消融方法 以确定LXN在正常和辐射应激条件下的HSCs和造血中的作用。 结果表明，LXN失活对HSCs和造血祖细胞(HPC)具有保护作用。 诱导细胞死亡，从而减轻急性造血抑制，并赋予生存优势。 此外，LXN基因敲除小鼠在单独或分割后不会发生血液系统恶性肿瘤。 辐射剂量。从机制上讲，体内LXN失活可增加HSC的自我更新和存活率。在 在分子水平上，我们发表的和初步的工作表明，核糖体蛋白亚基3(RPS3)是一个新的 LXN结合蛋白，LXN过表达抑制RPS3活性，从而增强辐射敏感性和 毒性。此外，人HSCs/HPC数量与LXN表达水平呈负相关， 提示LXN在人体造血调控中具有潜在的作用。这些发现导致了假设 LXN维持体内平衡HSC和造血及抑制LXN功能的保护作用 辐射通过RPS3依赖的生存途径引起的造血损伤。具体目标是：1) 确定LXN失活促进HSC存活和自我更新的细胞机制 提供辐射防护，2)确定LXN失活增强LXN-RPS3-的分子机制- 核因子-kB的生存途径；3)确定LXN在减轻人造血细胞毒性中的作用 不受辐射伤害。这项研究将促进对一种关键但未被研究的机制的理解 参与HSC功能的天然调节和自我更新。通过使用鼠标和人体模型系统 和最先进的分子和基因组技术，拟议的研究结果可能有助于 基于机制的新治疗策略的发展，以防止辐射诱导的骨髓损伤， 这对接受癌症治疗和骨髓移植的患者可能是有益的。

PROJECT SUMMARY The long-term goal of this study is to develop new strategies to mitigate and protect radiation-induced hematopoietic injury by delineating the molecular mechanisms responsible for enhancing hematopoietic stem cells (HSC) self-renewal and survival. Radiation therapy commonly results in not only acute hematopoietic suppression but also long-term bone marrow (BM) injury. To date, no effective treatment has been developed to prevent or treat these pathological consequences. Enhancing HSC survival and maintaining their genomic integrity upon radiation are crucial for preservation of HSC self-renewal function and for protection against radiation-induced BM injury. However, the molecular mechanisms for regulating HSC survival and self-renewal are not well defined. HSC number and function demonstrate natural variations, and underlying genetic diversity is an important, yet largely unknown, mechanism involved in the regulation of HSC function. Latexin (Lxn) was previously identified as the first stem cell regulatory gene whose natural variation negatively contributes to the HSC population size in different mouse strains. In preliminary studies, constitutive gene ablation approaches were developed to define the role of Lxn in HSCs and hematopoiesis in normal and radiation stress conditions. Results showed that Lxn inactivation protects HSCs and hematopoietic progenitor cells (HPCs) from radiation- induced cell death, thus mitigating acute hematopoietic suppression and conferring a survival advantage. Moreover, Lxn knockout mice do not develop hematological malignancies following single or fractionated dosages of radiation. Mechanistically, Lxn inactivation in vivo increases HSC self-renewal and survival. At the molecular level, our published and preliminary work showed that ribosomal protein subunit 3 (Rps3) is a novel Lxn-binding protein, and Lxn overexpression inhibits Rps3 activity, thus enhancing radiation sensitivity and toxicity. In addition, the number of human HSCs/HPCs negatively correlates with Lxn expression level, indicating the potential role of Lxn in regulating human hematopoiesis. These findings lead to the hypothesis that Lxn maintains homeostatic HSC and hematopoiesis and inhibition of Lxn function protects against radiation-induced hematopoietic injury via Rps3-dependent prosurvival pathways. Specific aims are to: 1) determine the cellular mechanisms by which Lxn inactivation enhances HSC survival and self-renewal and confers radioprotection, 2) identify the molecular mechanisms by which Lxn inactivation enhances Lxn-Rps3- NF-kB prosurvival pathway, and 3) determine the role of Lxn in mitigating human hematopoietic cell toxicity from radiation injury. This research will advance understanding of a critical but understudied mechanism involved in the natural regulator of HSC function and self-renewal. By using mouse and human model systems and state-of-the-art molecular and genomic techniques, findings from the proposed study may facilitate to the development of novel mechanism-based therapeutic strategy to protect against radiation-induced BM injury, which could be beneficial for the patients receiving cancer therapy and BM transplantation.