Erythropoiesis - Injury and Recovery

描述(申请人提供)：我们每秒从骨髓合成和释放200多万个红细胞，以维持循环稳定水平。这种大量的红细胞生成系统使其成为一个对正常生理功能至关重要的过程，但也是一个对直接伤害(如辐射)极其敏感的过程。辐射损伤为研究红系损伤、恢复和调节机制提供了一个独特的模型，并允许更深入地理解作为一个动态过程的红细胞生成。这项建议的总体目标是更好地了解异种毒性暴露后红系血统损伤和恢复的机制，如亚致死剂量辐射所模拟的那样。通过传统的集落分析和一种新的多光谱成像流式细胞仪(MIFC)分析获得的初步数据表明，红系祖细胞和前体细胞在4Grey照射后48小时严重耗尽，然后在照射后5天开始迅速增加。目的1研究将进一步明确红系祖细胞和红系前体细胞对辐射的不同敏感性和恢复的时间进程，并探索亚致死性辐射损伤后红系丢失的潜在凋亡机制。有趣的是，初步研究结果表明，晚期红系祖细胞(CFU-E)可以独立于更未成熟的(BFU-E)祖细胞恢复。基于这些数据，晚期红系祖细胞被假设为在一种修改的应激性红细胞生成反应中增殖，这是辐射后红系恢复波的原因。因此，目标2将研究在传统的应激红系反应中重要的内源性化合物，如促红细胞生成素(EPO)、干细胞因子(SCF)和糖皮质激素的作用，以及它们各自在红系辐射恢复过程中刺激CFU-E细胞增殖的信号通路。最后，目标3将通过确定外源性给予细胞因子如促红细胞生成素和干细胞因子是否可以减少损伤并促进红系血统的恢复，将目标1中潜在的损伤机制与目标2中的恢复机制结合起来。总体而言，这些实验将通过研究其对辐射的潜在敏感性和损伤后恢复反应的机制，提供对正常造血的更全面的了解。这些研究最终将导致新的治疗方法，以保护和缓解造血系统免受辐射和化疗等碎裂因素的影响。

DESCRIPTION (provided by applicant): We synthesize and release more than 2 million red blood cells per second from our bone marrow to maintain circulating steady-state levels. This massive output of the erythropoietic system makes it a process that is essential for normal physiological function but also one that is exquisitely sensitive to direct injury such as radiation. Radiation injury provides a unique model for study of erythroid lineage injury, recovery, and regulation mechanisms and allows for a more thorough understanding of erythropoiesis as a dynamic process. The overall aim of this proposal is to better understand the mechanisms of injury and recovery of the erythroid lineage following xenotoxic exposure as modeled by sublethal radiation. Preliminary data obtained through traditional colony assays in combination with a novel multispectral imaging flow cytometry (MIFC) analysis indicate that erythroid progenitors and precursors are severely depleted at 48 hours post 4 Grey irradiation followed by a rapid increase beginning at 5 days post- irradiation. Aim 1 studies will further define the time course of differential radiosensitivity and recovery of erythroid progenitor and precursor populations as well as explore potential apoptotic mechanisms underlying erythroid loss following sublethal radiation injury. Interestingly, preliminary findings suggest that late-stage erythroid progenitors (CFU-E) may recover independent of more immature (BFU-E) progenitors. Based on these data, late-stage erythroid progenitors are hypothesized to proliferate in a modified stress erythropoiesis response that is responsible for the wave of erythroid recovery post-radiation. Therefore, Aim 2 will investigate the role of endogenous compounds important in the traditional stress erythroid response, such as erythropoietin (EPO), stem cell factor (SCF), and glucocorticoids, and their respective signaling pathways on the stimulation and subsequent proliferation of CFU-E cells during the recovery of the erythroid lineage from radiation. Finally, Aim 3 will combine proposed mechanisms underlying injury in Aim 1 and recovery in Aim 2 by determining if exogenous administration of cytokines such as EPO and SCF can reduce injury and enhance recovery of the erythroid lineage. Overall, these experiments will provide a more thorough understanding of normal hematopoiesis by investigating both its underlying sensitivity to radiation and the mechanisms of its recovery response following injury. These studies will ultimately lead to new treatments to protect and mitigate the hematopoietic system from clastogenic agents such as radiation and chemotherapy.