FS4-Radiation/Microbiome/HD5/A muciniphila study

<em><strong>Introduction:</strong></em> The mechanism underlying radiation-induced gut microbiota dysbiosis is undefined. This study examined the effect of radiation on the intestinal Paneth cell α-defensin expression and its impact on microbiota composition and mucosal tissue injury and evaluated the radio-mitigative effect of human α-defensin 5 (HD5). <em><strong>Methods:</strong></em> Adult mice were subjected to total body irradiation, and Paneth cell α-defensin expression was evaluated by measuring α-defensin mRNA by RT-PCR and α-defensin peptide levels by mass spectrometry. Vascular-to-luminal flux of FITC-inulin was measured to evaluate intestinal mucosal permeability and endotoxemia by measuring plasma lipopolysaccharide. HD5 was administered in a liquid diet 24 hours before or after irradiation. Gut microbiota was analyzed by 16S rRNA sequencing. Intestinal epithelial junctions were analyzed by immunofluorescence confocal microscopy and mucosal inflammatory response by cytokine expression. Systemic inflammation was evaluated by measuring plasma cytokine levels. <em><strong>Results:</strong></em> Ionizing radiation reduced the Paneth cell α-defensin expression and depleted α-defensin peptides in the intestinal lumen. α-Defensin down-regulation was associated with the time-dependent alteration of gut microbiota composition, increased gut permeability, and endotoxemia. Administration of human α-defensin 5 (HD5) in the diet 24 hours before irradiation (prophylactic) significantly blocked radiation-induced gut microbiota dysbiosis, disruption of intestinal epithelial tight junction and adherens junction, mucosal barrier dysfunction, and mucosal inflammatory response. HD5, administered 24 hours after irradiation (treatment), reversed radiation-induced microbiota dysbiosis, tight junction and adherens junction disruption, and barrier dysfunction. Furthermore, HD5 treatment also prevents and reverses radiation-induced endotoxemia and systemic inflammation. <em><strong>Conclusions:</strong></em> These data demonstrate that radiation induces Paneth cell dysfunction in the intestine, and HD5 feeding prevents and mitigates radiation-induced intestinal mucosal injury, endotoxemia, and systemic inflammation.

<em><strong>引言：</strong></em> 辐射诱导的肠道菌群失调（gut microbiota dysbiosis）的潜在作用机制尚未明确。本研究探讨了辐射对肠道潘氏细胞（Paneth cell）α-防御素（α-defensin）表达的影响，及其对菌群组成、黏膜组织损伤的作用，并评估了人α-防御素5（human α-defensin 5, HD5）的辐射防护与缓解效果。
<em><strong>方法：</strong></em> 选取成年小鼠进行全身照射（total body irradiation），通过逆转录聚合酶链式反应（RT-PCR）检测α-防御素mRNA水平、质谱法（mass spectrometry）测定α-防御素肽类物质的含量，以评估潘氏细胞α-防御素的表达情况。通过测定FITC-菊粉（FITC-inulin）的血管-管腔通量以评估肠道黏膜通透性，并通过检测血浆脂多糖（lipopolysaccharide）水平判断内毒素血症（endotoxemia）。于照射前24小时或照射后24小时，通过流质饮食给予HD5。采用16S rRNA测序（16S rRNA sequencing）技术分析肠道菌群组成。通过免疫荧光共聚焦显微镜（immunofluorescence confocal microscopy）观察肠道上皮连接结构，并通过细胞因子表达水平评估黏膜炎症反应；通过检测血浆细胞因子水平评估全身性炎症反应。
<em><strong>结果：</strong></em> 电离辐射（ionizing radiation）可降低潘氏细胞α-防御素的表达，并耗竭肠道腔内的α-防御素肽类物质。α-防御素的下调与肠道菌群组成的时间依赖性改变、肠道通透性升高及内毒素血症密切相关。于照射前24小时通过饮食给予HD5的预防性给药方案，可显著阻断辐射诱导的肠道菌群失调、肠道上皮紧密连接（tight junction）与黏附连接（adherens junction）破坏、黏膜屏障功能障碍及黏膜炎症反应。于照射后24小时给予HD5的治疗性给药方案，则可逆转辐射诱导的菌群失调、紧密连接与黏附连接破坏及屏障功能障碍。此外，HD5治疗还可预防并逆转辐射诱导的内毒素血症与全身性炎症反应。
<em><strong>结论：</strong></em> 本研究数据表明，辐射可引发肠道潘氏细胞功能异常，而HD5饮食干预可预防并缓解辐射诱导的肠道黏膜损伤、内毒素血症及全身性炎症反应。