Radiation-Induced Paneth Cell Dysfunction

大规模辐射事件造成的公众辐射暴露是一个日益令人关切的全球问题。急性 放射综合征（ARS）与高发病率和死亡率相关，但FDA尚未批准 胃肠道（GI）ARS的治疗剂。因此，描绘辐射的机制 制定有针对性的医疗对策（MCM）是一个高度优先事项。胃肠道黏膜免疫 系统易受电离辐射影响，粘膜免疫功能障碍是主要原因 ARS发病机制中的一个因素。这一领域的差距在于， 损害粘膜免疫系统和免疫功能障碍介导的肠道微生物群的生态失调， 多器官损伤（MOI）定义不明确。我们研究的长期目标是确定辐射- 敏感的免疫特异性途径，并测试和开发新的免疫功能障碍靶向MCM， 辐射暴露内毒素血症和全身性炎症是与内毒素血症相关的常见病症。 发病率和死亡率。临床和实验证据表明，肠道生态失调 （耗尽有益物种，增加致病菌，减少多样性）是一个先决条件， 发展为内毒素血症、全身炎症和MOI。α-防御素是一种分泌型抗菌肽 来自潘氏细胞，高度特化的肠上皮细胞，以维持微生物群的稳态。 人潘氏细胞产生两种α-防御素-防御素5（HD 5）和6（HD 6）。我们的初步数据显示 电离辐射在小鼠肠道中1）耗尽潘氏细胞α-防御素，2）降低粘膜Tcf 4 mRNA，3）改变微生物群组成，4）破坏上皮屏障，和5）随后的粘膜 炎症反应、内毒素血症和全身性炎症。重要的是，HD 5在 辐照后24小时的饮食减轻了改变的肠道微生物群、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），并支持中心假设，即“HD 5减轻了 通过逆转肠道微生物群的生态失调和上皮屏障功能障碍， 内毒素血症和全身炎症。”我们将通过确定1）电离 辐射下调肠道潘氏细胞中的Wnt信号，2）TCF 4下调介导 辐射诱导的α-防御素耗竭和随后的生态失调，3）α-防御素补充逆转 辐射诱导的肠道微生物群的生态失调，4）辐射诱导的生态失调驱动肠道屏障功能障碍， 内毒素血症和全身性炎症，5）最低和最有效剂量的HD 5在减轻GI- ARS，6）HD 5逆转GI-ARS的暴露后（+24-96 h）有效性的理想时间窗，以及 7)HD 5治疗模式，以增加从致死剂量辐射的存活率。 .

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. .