Department of Cell Biology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States of America.
PLoS One. 2013;8(2):e56891. doi: 10.1371/journal.pone.0056891. Epub 2013 Feb 14.
Astrocytes are essential for proper central nervous system (CNS) function and are intricately involved in neuroinflammation. Despite evidence that immune-activated astrocytes contribute to many CNS pathologies, little is known about the inflammatory pathways controlling gene expression. Our laboratory identified altered levels of tissue inhibitor of metalloproteinase (TIMP)-1 in brain lysates from human immunodeficiency virus (HIV)-1 infected patients, compared to age-matched controls, and interleukin (IL)-1β as a key regulator of astrocyte TIMP-1. Additionally, CCAAT enhancer binding protein (C/EBP)β levels are elevated in brain specimens from HIV-1 patients and the transcription factor contributes to astrocyte TIMP-1 expression. In this report we sought to identify key signaling pathways necessary for IL-1β-mediated astrocyte TIMP-1 expression and their interaction with C/EBPβ. Primary human astrocytes were cultured and treated with mitogen activated protein kinase-selective small molecule inhibitors, and IL-1β. TIMP-1 and C/EBPβ mRNA and protein expression were evaluated at 12 and 24 h post-treatment, respectively. TIMP-1 promoter-driven luciferase plasmids were used to evaluate TIMP-1 promoter activity in inhibitor-treated astrocytes. These data show that extracellular regulated kinase (ERK) 1/2-selective inhibitors block IL-1β-induced astrocyte TIMP-1 expression, but did not decrease C/EBPβ expression in parallel. The p38 kinase (p38K) inhibitors partially blocked both IL-1β-induced astrocyte TIMP-1 expression and C/EBPβ expression. The ERK1/2-selective inhibitor abrogated IL-1β-mediated increases in TIMP-1 promoter activity. Our data demonstrate that ERK1/2 activation is critical for IL-1β-mediated astrocyte TIMP-1 expression. ERK1/2-selective inhibition may elicit a compensatory response in the form of enhanced IL-1β-mediated astrocyte C/EBPβ expression, or, alternatively, ERK1/2 signaling may function to moderate IL-1β-mediated astrocyte C/EBPβ expression. Furthermore, p38K activation contributes to IL-1β-induced astrocyte TIMP-1 and C/EBPβ expression. These data suggest that ERK1/2 signals downstream of C/EBPβ to facilitate IL-1β-induced astrocyte TIMP-1 expression. Astrocyte ERK1/2 and p38K signaling may serve as therapeutic targets for manipulating CNS TIMP-1 and C/EBPβ levels, respectively.
星形胶质细胞对于中枢神经系统（CNS）的正常功能至关重要，并且它们与神经炎症密切相关。尽管有证据表明免疫激活的星形胶质细胞有助于许多 CNS 病理，但对于控制基因表达的炎症途径知之甚少。我们的实验室发现，与年龄匹配的对照组相比，人类免疫缺陷病毒（HIV）-1 感染患者的脑匀浆中组织抑制剂金属蛋白酶（TIMP）-1 的水平发生了改变，白细胞介素（IL）-1β是星形胶质细胞 TIMP-1 的关键调节因子。此外，HIV-1 患者的脑标本中 CCAAT 增强子结合蛋白（C/EBP）β水平升高，转录因子有助于星形胶质细胞 TIMP-1 的表达。在本报告中，我们试图确定 IL-1β 介导的星形胶质细胞 TIMP-1 表达所需的关键信号通路及其与 C/EBPβ 的相互作用。原代人星形胶质细胞培养并接受丝裂原激活蛋白激酶选择性小分子抑制剂和 IL-1β处理。分别在处理后 12 和 24 小时评估 TIMP-1 和 C/EBPβ mRNA 和蛋白表达。使用 TIMP-1 启动子驱动的荧光素酶质粒评估抑制剂处理的星形胶质细胞中的 TIMP-1 启动子活性。这些数据表明，细胞外调节激酶（ERK）1/2 选择性抑制剂可阻断 IL-1β诱导的星形胶质细胞 TIMP-1 表达，但不能平行降低 C/EBPβ 的表达。p38 激酶（p38K）抑制剂部分阻断了 IL-1β诱导的星形胶质细胞 TIMP-1 表达和 C/EBPβ 的表达。ERK1/2 选择性抑制剂消除了 IL-1β 介导的 TIMP-1 启动子活性的增加。我们的数据表明，ERK1/2 的激活对于 IL-1β 介导的星形胶质细胞 TIMP-1 表达至关重要。ERK1/2 选择性抑制可能以增强 IL-1β 介导的星形胶质细胞 C/EBPβ 表达的形式引起代偿性反应，或者 ERK1/2 信号可能起到调节 IL-1β 介导的星形胶质细胞 C/EBPβ 表达的作用。此外，p38K 的激活有助于 IL-1β 诱导的星形胶质细胞 TIMP-1 和 C/EBPβ 的表达。这些数据表明，ERK1/2 信号下游的 C/EBPβ 促进了 IL-1β 诱导的星形胶质细胞 TIMP-1 表达。星形胶质细胞 ERK1/2 和 p38K 信号可能分别作为操纵 CNS TIMP-1 和 C/EBPβ 水平的治疗靶点。
