FOXO3a Inhibits TNF-α-and IL-1β-Induced Astrocyte Proliferation:Implication for Reactive Astrogliosis

反应性星形胶质细胞增生是神经退行性疾病的特征性病理性改变之一。炎性细胞因子,如TNF-α和IL-1β,已被证实在神经退行性疾病中介导反应性星形胶质细胞增生,尽管其分子机制仍不清楚。本研究探讨严重反应性星形胶质细胞增生的一个主要方面——转录因子FOXO3a在星形胶质细胞增生中的作用。本研究通过Ki67和BrdU免疫染色证实TNF-α和IL-1β促进星形胶质细胞增生。本研究进一步发现细胞因子介导的星形胶质细胞增生伴有FOXO3a磷酸化的增加和核表达的下降。颅内注射TNF-α和IL-1β导致星形胶质细胞增生和肥大,这与星形胶质细胞中的Foxo3a核表达下降有关。为了确定Foxo3a在星形胶质细胞增生中的作用,在腺病毒中过表达野生型Foxo3a,引起p27Kip1及Gadd45α上调,且显著抑制细胞因子介导的星形胶质细胞增生。与之相反,负显性型FOXO3a的过表达使p27Kip1降低,下调Cyclin D1,促进星形胶质细胞增生。同样,Foxo3a敲除小鼠中分离的星形胶质细胞表现出更高的增生趋势。颅内注射细胞因子后,Foxo3a敲除小鼠在体内表现出严重的星形胶质细胞增生。综上所述,FOXO3a在促炎因子刺激时对于遏制星形胶质细胞增生发挥重要作用,FOXO3a功能的缺失可能是严重反应性星形胶质细胞增生中星形胶质细胞增生的原因。了解FOXO3a在反应性星形胶质细胞增生中的关键调节作用可能为神经炎症提供一个新的治疗靶点。

Reactive astrogliosis is one of the pathological hallmarks of neurodegenerative diseases. Inflammatory cytokines, such as TNF-α and II.-1β, have been shown to mediate the reactive astrogliosis in neurodegenerative diseases; however, the molecular mechanism remains unclear. In this study, we investigated the role of transcription factor FOXO3a on astrocyte proliferation, one primary aspect of severe reactive astrogliosis. Our results confirmed that TNF-α and IL-1β increased astrocyte proliferation, as determined by Ki67 and BrdU immunostaining. Furthermore, we found that cytokine-mediated astrocyte proliferation was accompanied by an increase of the phosphorylation and reduced nuclear expression of FOXO3a. Intracranial injection of TNF-α and IL-1β induced astrocyte proliferation and hypertrophy, which was associated with reduced nuclear expression of Foxo3a in astrocytes. To determine the function of FOXO3α in astrocyte proliferation, wild type FOXO3a was overexpressed with adenovirus, which subsequently upregulated p27Kipl and Gadd45α,and significantly inhibited cytokine-induced astrocyte proliferation. In contrast, overexpression of dominant negative FOXO3a decreased p27Kipl, upregulated cyclin D1 and promoted astrocyte proliferation. Along the same line, astrocytes isolated from Foxo3a-null mice have higher prolif- erative potential. In response to intracranial injection of cytokines, Foxo3a-null mice manifested severe astrogliosis in vivo. In conclusion, FOXO3a is important in restraining astroeyte proliferation during proinflammatory cytokine stimulation and loss of function of FOXO3a may be responsible for the proliferation of astrocytes in the severe form of reactive astrogliosis. Understanding the key regulatory role of FOXOSa in reactive astrogliosis may provide a novel therapeutic target during neuroinflammation. 2011 Wiley-Liss, Inc.