Radiation-Induced Paneth Cell Dysfunction

大规模辐射事故引起的公众辐射暴露是全球日益关注的问题。急性 辐射综合征(ARS)与高发病率和死亡率有关，但没有FDA批准 胃肠道(GI)ARS的治疗。因此，描绘辐射背后的机制 制定有针对性的医疗对策(MCM)是一项高度优先的任务。胃肠道黏膜免疫 系统对电离辐射很敏感，粘膜免疫功能障碍是主要原因 在ARS发病机制中的作用。这一领域的空白是辐射通过的精确机制 损伤粘膜免疫系统和免疫功能障碍介导的肠道微生物区系和 多器官损伤(MOI)的定义并不明确。我们研究的长期目标是确定辐射- 敏感的免疫特异性通路和测试和开发针对免疫功能障碍的新型MCM 辐射暴露。内毒素血症和全身性炎症是与 急性呼吸窘迫综合征的发病率和死亡率。临床和实验证据表明，肠道生物失调 (有益物种枯竭，致病细菌增加，多样性减少)是 出现内毒素血症、全身性炎症和MOI。A-防御素是分泌的抗菌肽。 来自潘氏细胞，高度专业化的肠道上皮细胞，以维持微生物区系的动态平衡。 人Paneth细胞产生两种α-防御素--防御素5(HD5)和防御素6(HD6)。我们的初步数据显示 小鼠肠道电离辐射1)耗尽Paneth细胞a-防御素，2)减少粘膜TCF4 MRNA，3)改变微生物区系组成，4)破坏上皮屏障，5)继发的粘膜 炎症反应、内毒素血症和全身炎症。重要的是，HD5在 照射后24小时的饮食可减轻肠道微生物区系改变、肠道屏障功能障碍和内毒素血症。 这些发现形成了科学前提(图1)，并支持了中心假设，即HD5缓解了 通过逆转肠道微生物区系的失调和上皮屏障功能障碍，导致GI-ARS缓解 内毒素血症和全身性炎症。我们将通过确定1)电离来检验这一假设 辐射下调肠道Paneth细胞Wnt信号，2)TCF4下调介导 辐射诱导的α-防御素耗竭和随后的生物失调，3)α-防御素的补充逆转 辐射诱导的肠道微生物区系失调，4)辐射诱导的微生物区系失调导致肠道屏障功能障碍， 内毒素血症和全身炎症，5)HD5缓解胃肠道感染的最低和最有效剂量。 ARS，6)HD5逆转GI-ARS的暴露后(+24-96小时)有效性的理想时间窗口，以及 7)提高致死剂量辐射存活率的HD5治疗模式。 。

Public exposure to radiation due to large-scale radiation incidents is a rising global concern. Acute radiation syndrome (ARS) is associated with high morbidity and mortality, but no FDA-approved therapeutics for gastrointestinal (GI) ARS. Therefore, delineating the mechanisms underlying radiation injury to develop targeted medical countermeasures (MCM) is a high priority. The GI mucosal immune system is susceptible to ionizing radiation, and dysfunctional mucosal immunity is a major contributing factor in the pathogenesis of ARS. The gap in this field is that the precise mechanisms by which radiation impairs the mucosal immune system and immune dysfunction-mediated dysbiosis of gut microbiota and multi-organ injury (MOI) are poorly defined. The long-term goal of our research is to identify the radiation- sensitive immune-specific pathways and test and develop novel immune dysfunction-targeted MCM for radiation exposure. Endotoxemia and systemic inflammation are common conditions associated with morbidity and mortality in ARS. Clinical and experimental evidence indicates that intestinal dysbiosis (depleted beneficial species, increased pathobionts, and decreased diversity) is a prerequisite for developing endotoxemia, systemic inflammation, and MOI. a-Defensins are antibacterial peptides secreted from Paneth cells, the highly specialized intestinal epithelial cells, to maintain microbiota homeostasis. Human Paneth cells produce two a-defensins - defensin 5 (HD5) and 6 (HD6). Our preliminary data show that ionizing radiation in mouse intestine 1) depletes Paneth cell a-defensins, 2) reduces mucosal Tcf4 mRNA, 3) alters microbiota composition, 4) disrupts epithelial barrier, and 5) consequent mucosal inflammatory response, endotoxemia, and systemic inflammation. Importantly, HD5 administered in the diet at 24 h post-irradiation mitigates altered gut microbiota, gut barrier dysfunction, and endotoxemia. These findings form the scientific premise (FIG 1) and support the central hypothesis that “HD5 mitigates GI-ARS by reversing dysbiosis of gut microbiota and epithelial barrier dysfunction, leading to mitigation of endotoxemia and systemic inflammation.” We will test this hypothesis by determining that 1) Ionizing radiation downregulates Wnt signaling in intestinal Paneth cells, 2) TCF4 down-regulation mediates radiation-induced a-defensin depletion and consequent dysbiosis, 3) a-Defensin supplementation reverses radiation-induced dysbiosis of gut microbiota, 4) Radiation-induced dysbiosis drives gut barrier dysfunction, endotoxemia, and systemic inflammation, 5) the lowest and most effective dose of HD5 in mitigating GI- ARS, 6) the ideal time window for post-exposure (+24-96 h) effectiveness of HD5 to reverse GI-ARS, and 7) the HD5 treatment paradigm to increase the survival rates from lethal dose radiation. .