PAI-1-Dependent Endothelial Cell Death Determines Severity of Radiation-Induced Intestinal Injury

Normal tissue toxicity still remains a dose-limiting factor in clinical radiation therapy. Recently, plasminogen activator inhibitor type 1 (SERPINE1/PAI-1) was reported as an essential mediator of late radiation-induced intestinal injury. However, it is not clear whether PAI-1 plays a role in acute radiation-induced intestinal damage and we hypothesized that PAI-1 may play a role in the endothelium radiosensitivity. In vivo, in a model of radiation enteropathy in PAI-1 −/− mice, apoptosis of radiosensitive compartments, epithelial and microvascular endothelium was quantified. In vitro, the role of PAI-1 in the radiation-induced endothelial cells (ECs) death was investigated. The level of apoptotic ECs is lower in PAI-1 −/− compared with Wt mice after irradiation. This is associated with a conserved microvascular density and consequently with a better mucosal integrity in PAI-1 −/− mice. In vitro, irradiation rapidly stimulates PAI-1 expression in ECs and radiation sensitivity is increased in ECs that stably overexpress PAI-1, whereas PAI-1 knockdown increases EC survival after irradiation. Moreover, ECs prepared from PAI-1 −/− mice are more resistant to radiation-induced cell death than Wt ECs and this is associated with activation of the Akt pathway. This study demonstrates that PAI-1 plays a key role in radiation-induced EC death in the intestine and suggests that this contributes strongly to the progression of radiation-induced intestinal injury.正常组织毒性仍是临床放射治疗中的剂量限制性因素。近期有研究报道，1型纤溶酶原激活物抑制剂（SERPINE1/PAI-1）是晚期放射性肠损伤的关键介导因子。然而，目前尚不清楚PAI-1是否参与急性放射性肠损伤，因此本研究假设PAI-1可能在内皮细胞辐射敏感性中发挥作用。体内实验方面，我们在PAI-1基因敲除（PAI-1−/−）小鼠的放射性肠病模型中，对辐射敏感区域（上皮细胞与微血管内皮细胞）的凋亡水平进行了定量检测。体外实验则探究了PAI-1在辐射诱导的内皮细胞（Endothelial Cells, ECs）死亡中的作用。辐照后，PAI-1−/−小鼠体内的凋亡内皮细胞水平较野生型（Wild Type, Wt）小鼠更低，该现象与PAI-1−/−小鼠体内维持的微血管密度相关，进而使其黏膜完整性更佳。体外实验中，辐照可快速诱导内皮细胞的PAI-1表达；稳定过表达PAI-1的内皮细胞辐射敏感性增强，而敲低PAI-1则可提升辐照后内皮细胞的存活率。此外，从PAI-1−/−小鼠中分离的内皮细胞较野生型内皮细胞更耐受辐射诱导的细胞死亡，这一现象与Akt通路的激活相关。本研究证实，PAI-1在肠道内辐射诱导的内皮细胞死亡中发挥关键作用，并提示该作用可显著促进放射性肠损伤的进展。