调控IRF3介导小胶质细胞向M2方向极化改善放射性脑损伤的机制研究

Preliminary data and literatures indicated that radiation activated microglia have two phenotype, pro-inflammatory M1 and anti-inflammatory M2. Modulation of the phenotypic variation from M1 to M2 will be potential therapeutic stratergy for radiation induced brain injury(RI). However, when and how to modulate the transformation remains unknown. IRF3 is an ideal target to promote M2 phenotype, for it can suppress secrection of inflammatory factors, yet enhance the production of anti-inflammatory cytokines. We aim to firstly confirm the temporal change of microglia phenotype. By using IRF3-/-cells and gene knockout animal model, we will further study the level of pro-inflammatory and anti-inflammatory cytokines secreted by microglia, as well as its phagocytosis ability. Remyelination and axon regeneration would be examined to evaluate the effect of modulation of microglia phenotype variation from M1 to M2 in RI. The study would provide evidence for targeting phenotype variation of microglia as the further treatment strategy of RI.

我们前期数据提示放射后小胶质细胞（MG）存在损伤性M1（表现为分泌炎症因子，同时吞噬力下降致有害代谢物蓄积加重损伤）和保护性M2（分泌抑炎因子同时吞噬力升高）两种表型，调控M1向M2方向极化是潜在治疗策略，但何时进行调控，怎样调控值得进一步研究。转录因子IRF3具有抑制MG分泌炎症因子同时促进抗炎因子分泌的特性，是使MG向M2极化的理想调控靶点。本课题拟：①研究放射后 M1/M2表型变化，明确极化表型时相及调控切入点；②通过IRF3 -/-细胞及基因敲除动物，探讨上调IRF3后MG分泌因子谱及吞噬能力变化，证实上调IRF3后MG表型由M1向M2转变，并研究其信号机制；③上调IRF3使MG向M2方向极化，抑制MG分泌炎症递质，提高MG吞噬力，通过神经元共培养、髓鞘形成共培养，轴突和髓鞘染色及神经元损伤病理检查，阐明上调IRF3促进M2极化改善脑损伤的机制，为放射性脑损伤的治疗提供新的突破口。

文献及前期实验数据提示放射后小胶质细胞（MG）存在损伤性M1（表现为分泌炎症因子，同时吞噬力下降致有害代谢物蓄积加重损伤）和保护性M2（分泌抑炎因子同时吞噬力升高）两种表型，调控M1向M2方向极化是潜在治疗策略，但何时进行调控，怎样调控值得进一步研究。本课题证实放射后小胶质细胞出现由P2X7介导的M1型转化，除受到放射线直接作用外，还受到血脑屏障破坏局部微环境改变后血管毒性物质渗出的持续激活作用，该过程可由TREM2介导。本课题证实 TREM2 在离体及在体放射性脑损伤模型中均有表达，且照射后呈现下降的表达趋势；确定了过表达 TREM2 在小胶质细胞离体照射损伤模型中，抑制促炎因子的作用，抑制炎症反应；发现照射后TREM2 表达降低，小胶质细胞激活增多，并出现在照射后损伤的微血管周围，呈现血管趋向性。而外源性给予Trem2可提高照射动物的生存率，逆转少突祖细胞的损伤，提示Trem2在放射性脑损伤发生发展中的重要功能，可能为放射性脑损伤的治疗提供新的突破口。