Epidermal growth factor mitigates radiation-induced hematopoietic failure

描述(申请人提供)：造血衰竭是急性放射病的主要死因。不幸的是，几乎没有有效的治疗方法来减轻辐射对造血系统的损害。我们假设，骨髓微环境中的细胞，特别是内皮细胞(ECs)，调节辐射损伤后的造血再生。作为检验这一假说的一种手段，我们在Tie2内皮细胞(Tie2Cre；Bak-/-；BaxF1/-小鼠)中产生了缺失固有的凋亡介质Bak和Bax的小鼠(Tie2Cre；Bak-/-；BaxF1/-小鼠)，并发现Tie2内皮细胞中Bak和Bax缺失的小鼠可以免受致死剂量的辐射照射，而在Tie2内皮细胞中保留1个Bax等位基因的小鼠仍然对辐射高度敏感。我们对受辐射保护的Tie2Cre；Bak-/-；BaxF1/-小鼠的骨髓血清进行了细胞因子阵列分析，并鉴定出几种分泌蛋白，与辐射敏感小鼠相比，在辐射保护小鼠中显著上调。发现的一种蛋白质是表皮生长因子(EGF)，这是一种未知的造血干细胞(HSCs)生长因子，但受辐射保护的小鼠骨髓血清中的浓度是对照组小鼠的18倍。因此，我们在初步研究中测试了在受辐射的小鼠骨髓造血干细胞培养中添加EGF是否能减轻对造血干细胞或祖细胞的辐射损伤。我们的初步结果表明，EGF能显著促进体外培养的HSCs和祖细胞在照射后的恢复。此外，我们发现，全身照射(TBI)后对小鼠全身应用EGF可显著提高小鼠的存活率，与受照射的对照组小鼠相比。基于这些初步结果，我们假设EGF是急性放射病的候选缓释剂，特别是急性辐射损伤后继而发生的造血衰竭。为了验证我们的假设，我们提出了以下具体目标：1)确定全身应用EGF是否能加速辐射损伤后小鼠的造血恢复并提高其存活率。2)确定EGF减轻辐射对造血干细胞损伤的细胞和信号机制。3)确定EGF能否促进恒河猴全身照射后的造血恢复。我们在这项建议中的广泛目标是提供一种新的、可翻译的和有效的放射诱导的造血损伤缓解剂。除了对急性放射损伤有潜在的缓解作用外，EF还具有潜在的双重治疗作用，可以促进接受骨髓抑制化疗和/或放射治疗的患者以及接受脐血移植的患者的造血恢复，在这些患者中，血液恢复经常被推迟。

DESCRIPTION (provided by applicant): Hematopoietic failure is the major cause of death in Acute Radiation Sickness. Unfortunately, few therapies exist that are effective at mitigating radiation-induced damage to the hematopoietic system. We hypothesized that cells within the bone marrow microenvironment, specifically endothelial cells (ECs), regulate hematopoietic regeneration following radiation injury. As a means to test this hypothesis, we generated mice bearing deletion of the intrinsic mediators of apoptosis, Bak and Bax, within Tie2+ endothelial cells (Tie2Cre;Bak-/-;BaxFl/- mice) and found that mice with deletion of Bak and Bax in Tie2+ ECs were radioprotected from lethal dose irradiation, whereas mice retaining 1 allele of Bax in Tie2+ ECs remained highly radiosensitive. We performed a cytokine array analysis of bone marrow serum from radioprotected Tie2Cre;Bak-/-;BaxFl/- mice and identified several secreted proteins which were significantly upregulated in radioprotected mice compared to radiosensitive mice. One protein identified was epidermal growth factor (EGF), which is not known to be a growth factor for hematopoietic stem cells (HSCs), but was 18-fold increased in concentration in the BM serum of radioprotected mice compared to control mice. We therefore tested in preliminary studies whether the addition of EGF to cultures of irradiated murine BM HSCs caused the mitigation of radiation injury to HSCs or progenitor cells. Our preliminary results indicate that EGF promotes a significant increase in the recovery of HSCs and progenitor cells in vitro following irradiation. Furthermore, we found that systemic administration of EGF to mice following total body irradiation (TBI) caused a significant increase in mice survival compared to irradiated, control mice. Based on these preliminary results, we hypothesize that EGF is a candidate mitigator of acute radiation sickness and specifically the hematopoietic failure which ensues following acute radiation injury. In order to test our hypothesis, we propose the following Specific Aims: 1) Determine whether systemic administration of EGF can accelerate hematopoietic recovery and improve the survival of mice following radiation injury. 2) Determine the cellular and signaling mechanisms through which EGF mitigates radiation damage to hematopoietic stem cells. 3) Determine whether EGF treatment can improve hematopoietic recovery in rhesus macaques following total body irradiation. Our broad objective in this proposal is to deliver a novel, translatable and potent mitigator of radiation-induced hematopoietic injury. In addition to its potential role as a mitigator of acute radiation injury, EF also has potential dual use as a therapeutic to accelerate hematopoietic recovery in patients receiving myelosuppressive chemotherapy and/or radiotherapy and those undergoing human cord blood transplantation, in which hematologic recovery is frequently delayed.