亚精胺激活自噬降低电离辐射诱导的造血干细胞衰老及其机制

HSC senescence induced by ionizing radiation(IR) is the main cause for residual bone marrow suppression, previous study showed that spermidine could alleviate aging-related diseases by activating autophagy. Our preliminary data showed that hematopoietic stem cell(HSC) coculture with spermidine in vitro could rescue the IR-induced HSC proliferation inhibition and clonogenicity function defect. These findings suggested that spermidine showed promising prospect against irradiation-induced hematopoietic syndrome and accelerating restoration of hematopoiesis. To investigate whether spermidine could alleviate IR-induced HSC senescence and long-term bone marrow suppression, the C57 mice were fed spermidine before or after radiation, and the properties of HSC (self-renewal, pluripotency, differentiation) and HSC senescence associated makers were measured. To further explore the mechanisms for spermidine in protecting the HSC against IR, radiation damage in the hematopoietic system of a conditional autophagy defect mouse model(Atg7f/f;Mx1-Cre)were examined, this study try to find out whether spermidine could induce sustained autophagy activation in HSC, and if activation of the autophagy mitigates radiation injury by DNA damage repair pathways and removing ROS, and by regulating HSC self-renewal transcription factor and decreasing the expression of p38 and p53. We hypothesized that induction of autophagy by spermidine could protect HSCs against irradiation and maintain their multipotential status. The purpose of this study is to investigate the role of spermidine in alleviating HSC aging and long-term bone marrow suppression during exposure to IR and the potential mechanisms, and to provide a new way to protect the hematopoietic system from nuclear radiation exposure.

研究发现电离辐射（IR）诱导造血干细胞（HSC）衰老是辐射引起的骨髓长期抑制的重要机制，而亚精胺可以通过激活自噬缓解多种衰老相关疾病。我们前期发现HSC体外孵育亚精胺可以减轻IR导致的HSC多系增殖能力和自我更新能力降低。提示亚精胺对IR损伤的HSC功能有修复作用。本项研究拟利用体内和体外HSC辐射损伤模型，观察亚精胺是否会持续激活HSC中自噬水平，降低HSC中ROS和DNA损伤，调节HSC自我更新转录因子表达，降低HSC中β-gal和p16的表达，缓解IR诱导的HSC衰老，减轻IR导致的长期骨髓损伤。为确认亚精胺通过调节自噬缓解造血辐射损伤，利用条件性敲除小鼠诱导自噬基因Atg7在造血系统中特异性敲除进行验证，进一步检测下游p53，p38表达，阐明亚精胺缓解HSC衰老的机制。本项目的研究将阐明亚精胺在缓解IR诱导的HSC衰老中的作用及其作用机制，为辐射导致的骨髓持久性抑制的防治提供依据。

造血系统对辐射最为敏感，辐射暴露后会导致造血细胞的凋亡和衰老。目前没有有效的保护剂或治疗药。亚精胺属于多胺家族，具有抗氧化，抗炎、抗衰老等多种生物学活性。抗衰老作用与其诱导自噬能力有关。预实验结果显示亚精胺可以缓解辐射诱导的HSC集落形成能力和自我更新能力降低。为了研究亚精胺对造血干细胞辐射损伤的保护作用及其机制，我们进行了相关的体内外实验。亚精胺对小鼠骨髓细胞体外照射后的急性期损伤有一定缓解作用，对造血干细胞功能具有保护作用。体内实验中，亚精胺可以减少全身照射引起的小鼠造血干细胞和祖细胞比例降低，增加造血干细胞分化，缓解受照小鼠造血干细胞功能抑制，但是小鼠骨髓细胞竞争性移植实验结果显示对造血干细胞重建能力损伤没有保护作用。探讨亚精胺保护造血系统功能的机制研究，发现亚精胺降低辐射诱导的小鼠造血干细胞氧化应激水平，未发现亚精胺与自噬基因表达有相关性。本项研究显示亚精胺通过降低ROS水平，保护造血干细胞的数量和功能。但是在本实验条件下，未发现亚精胺通过Atg7基因激活自噬保护造血细胞损伤。研究结果为后续研究提供参考。