Induction of an Inflammatory Loop by Interleukin-1β and Tumor Necrosis Factor-α Involves NF-kB and STAT-1 in Differentiated Human Neuroprogenitor Cells

Proinflammatory cytokines secreted from microglia are known to induce a secondary immune response in astrocytes leading to an inflammatory loop. Cytokines also interfere with neurogenesis during aging and in neurodegenerative diseases. The present study examined the mechanism of induction of inflammatory mediators at the transcriptional level in human differentiated neuroprogenitor cells (NPCs). Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) induced the expression of cytokines and chemokines in differentiated human NPCs as shown by an immune pathway-specific array. Network motif (NM) analysis of these genes revealed 118 three-node NMs, suggesting complex interactions between inflammatory mediators and transcription factors. Immunofluorescent staining showed increases in the levels of IL-8 and CXCL10 proteins in neurons and glial cells. Findings from Taqman low density array suggested the synergistic actions of IL-1β and TNF-α in the induction of a majority of inflammatory genes by a mechanism involving NF-kB and STAT-1. Nuclear localization of these transcription factors in differentiated NPCs was observed following exposure to IL-1α and TNF-α. Further studies on CXCL10, a chemokine known to be elevated in the Alzheimer's brain, showed that TNF-α is a stronger inducer of CXCL10 promoter when compared to IL-1β. The synergy between these cytokines was lost when ISRE or kB elements in CXCL10 promoter were mutated. Our findings suggest that the activation of inflammatory pathways in neurons and astrocytes through transcription factors including NF-kB and STAT-1 play important roles in neuroglial interactions and in sustaining the vicious cycle of inflammatory response.已知小胶质细胞分泌的促炎细胞因子可诱导星形胶质细胞产生继发性免疫应答，进而形成炎症环路。细胞因子还会在衰老及神经退行性疾病过程中干扰神经发生。本研究针对人类分化型神经前体细胞（neuroprogenitor cells, NPCs）中炎症介质诱导过程的转录水平调控机制展开了探究。经免疫通路特异性基因芯片检测证实，白细胞介素-1β（Interleukin-1β, IL-1β）与肿瘤坏死因子-α（tumor necrosis factor-α, TNF-α）可诱导人类分化型NPCs表达细胞因子及趋化因子。对上述基因的网络基序（network motif, NM）分析共筛选得到118个三节点网络基序，提示炎症介质与转录因子间存在复杂的相互作用。免疫荧光染色结果显示，神经元与胶质细胞内IL-8及CXCL10蛋白水平均有所升高。Taqman低密度基因芯片的分析结果表明，IL-1β与TNF-α可通过涉及核因子κB（NF-κB）及信号转导与转录激活因子1（STAT-1）的分子机制，协同诱导绝大多数炎症基因的表达。在暴露于IL-1α与TNF-α后，分化型NPCs内可观察到上述转录因子发生核定位。针对阿尔茨海默病患者脑组织中表达上调的趋化因子CXCL10开展的进一步研究显示，相较于IL-1β，TNF-α对CXCL10启动子的激活效果更强。当CXCL10启动子上的干扰素刺激应答元件（ISRE）与κB元件发生突变后，这两种细胞因子间的协同效应便会消失。本研究结果提示，通过包括NF-κB及STAT-1在内的转录因子激活神经元与星形胶质细胞内的炎症通路，在神经胶质相互作用及维持炎症应答恶性循环的过程中发挥了重要作用。