电离辐射触发血管内皮细胞FKN/CX3CR1通路调控小胶质细胞M2表型转化在放射性脑损伤中的作用

The mechanism of Radiation induced brain injury (RIB) is still remained not clear, but the neuro- inflammation and vascular injury are considered to be the main factors. Our preliminary studies suggested, radiation-induced microglial activation is a major source of neuro-inflammation. Previous study indicated that activation of microglial cells could Chemotaxis to injury area, and then the phenotype changed into the phagocytosis of M2, and swallowing damaged endothelial cells or products, which have the effect of anti-inflammatory. These indicated that phenotype transformation of microglia is a key role for neuro-inflammation. Our previous study also indicated: irradiation caused vascular endothelial cell to form senescence-like phenotype via DSB/NEMO/NF-κB signal pathway in vitro, and then the activated microglia chemotaxis to damaged blood vessel, chemotactic factor FKN was then released from endothelial cell. The specific receptor CX3CR1 was expressed in microglial cells in brain tissues, but the specific mechanism is not clear. Therefore, we puts forward the research hypothesis: the NF- κB signaling pathway was activiated in vascular endothelial cells post-irradiation and FKN was released, then it combined with microglial cell surface CX3CR1 receptors, which could promote microglia switch to the M2 polarization, with the anti-inflammatory effects, thereby reducing the RIB. These provide a new research clue for the treatment of RIB.

放射性脑损伤（RIB）的机制目前尚不明确，神经炎症和血管损伤被认为是主要因素。我们的前期研究提示，小胶质细胞激活是神经炎症的主要根源，有研究显示：激活的小胶质细胞向脑损伤区域移动，同时转化为具有吞噬功能的M2表型，进而吞噬受损的内皮细胞或产物，发挥抗炎作用。这给我们提示：小胶质细胞的表型转化是决定神经炎症走向的关键环节。我们也发现：血管内皮细胞照射后通过DSB/NF-κB信号通路产生衰老表型，诱导激活的小胶质细胞趋化到受损血管边，而NF-κB信号活化可以释放趋化因子FKN，特异性受体CX3CR1表达于小胶质细胞，CX3CR1可以触发细胞吞噬作用。因此，提出研究假设：电离辐射后血管内皮细胞NF-κB信号通路激活，释放FKN与小胶质细胞表面CX3CR1受体结合，促进其向M2型转化，发挥抗炎作用，从而减轻RIB，为RIB的治疗提供新的研究依据和理论基础。

颅脑放射治疗是头颈部的原发肿瘤、转移性肿瘤等疾病的重要局部治疗方式。然而，50-90%的患者放疗后表现出进行性的认知功能障碍：包括学习、记忆、注意力和执行功能即放射性脑损伤（RIBI）。RIBI病理表现可为水肿、脱髓鞘及坏死，目前RIBI的发生机制尚不明确，有研究表明其与小胶质细胞激活释放炎症因子和血管损伤密切相关。本研究通过10 Gy全脑照射成功建立小鼠放射性脑损伤模型，通过免疫荧光双染Iba-1（小胶质细胞标志物）和CD34（血管标志物）动态观察发现，小鼠全脑照射后海马区血管周围小胶质细胞数量增多，并向血管趋化；并通过体外细胞迁移实验和血管内皮细胞（ECs）/小胶质细胞（BV2）共培养实验进一步表明，10 Gy电离辐射可通过ECs促进BV2发生M2表型转化并向血管迁移，且与NF-κB通路激活分泌趋化因子FKN相关，而颅内小胶质细胞特异性表达FKN受体CX3CR1；本研究应用外源性FKN预处理BV2细胞发现，FKN可促进照射后BV2细胞表达M2型相关分子，抑制促炎因子释放并增强BV2细胞吞噬功能。同时体内实验论证小鼠侧脑室注射FKN慢病毒上调FKN表达，可促进小鼠10 Gy全脑照射后海马区M2表型相关分子的表达，改善全脑照射后炎症微环境并促进损伤修复；并且Morris水迷宫实验表明上调FKN可缓解小鼠10 Gy全脑照射对其学习及记忆功能的损害；最后通过构建CX3CR1ko基因小鼠以及Sh-CX3CR1慢病毒敲低BV2细胞CX3CR1的表达，进一步证实调控FKN/CX3CR1轴可促进照射后小胶质细胞发生M2表型转化，减缓小鼠全脑照射后认知功能的损伤。 .综上研究结果表明，电离辐射通过NF-κB通路促进ECs分泌趋化因子FKN，募集BV2细胞并与BV2细胞表面CX3CR1受体结合，促进其向M2型转化，增强BV2细胞吞噬功能，发挥其抗炎作用，从而减轻RIBI病理损伤，促进RIBI后神经认知功能修复。本研究发现FKN/CX3CR1轴在RIBI中发挥重要作用，靶向调控FKN/CX3R1轴是治疗RIBI的重要策略。