Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
Stem Cells Dev. 2011 Feb;20(2):313-26. doi: 10.1089/scd.2009.0529. Epub 2010 Aug 31.
Neurogenesis involves the proliferation of multipotent neuroepithelial stem cells followed by differentiation into lineage-restricted neural precursor cells (NPCs) during the embryonic period. Interestingly, these progenitor cells express robust levels of the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor that regulates expression of genes important for growth regulation, and xenobiotic metabolism. Upon binding 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a pervasive environmental contaminant and potent AhR ligand, AhR, is activated and disrupts gene expression patterns to produce cellular toxicity. Because of its widespread distribution in the brain during critical proliferative phases of neurogenesis, it is conceivable that AhR participates in NPC expansion. Therefore, this study tested the hypothesis that AhR activation by TCDD disrupts signaling events that regulate NPC proliferation. The C17.2 NPC line served as a model system to (1) assess whether NPCs are targets for TCDD-induced neurotoxicity and (2) characterize the effects of TCDD on NPC proliferation. We demonstrated that C17.2 NPCs express an intact AhR signaling pathway that becomes transcriptionally active after TCDD exposure. (3)H-thymidine and alamar blue reduction assays indicated that TCDD suppresses NPC proliferation in a concentration-dependent manner without the loss of cell viability. Cell cycle distribution analysis by flow cytometry revealed that TCDD-induced growth arrest results from an impaired G1 to S cell cycle transition. Moreover, TCDD exposure altered p27( kip1) and cyclin D1 cell cycle regulatory protein expression levels consistent with a G1 phase arrest. Initial studies in primary NPCs isolated from the ventral forebrain of embryonic mice demonstrated that TCDD reduced cell proliferation through a G1 phase arrest, corroborating our findings in the C17.2 cell line. Together, these observations suggest that the inappropriate or sustained activation of AhR by TCDD during neurogenesis can interfere with signaling pathways that regulate neuroepithelial stem cell/NPC proliferation, which could adversely impact final cell number in the brain and lead to functional impairments.
神经发生涉及多能神经上皮干细胞的增殖，随后在胚胎期分化为谱系受限的神经前体细胞（NPCs）。有趣的是，这些祖细胞表达高水平的芳香烃受体（AhR），这是一种配体激活的转录因子，调节生长调节和外源性代谢基因的表达。当结合 2,3,7,8-四氯二苯并-p-二恶英（TCDD）时，一种普遍存在的环境污染物和有效的 AhR 配体，AhR 被激活并破坏基因表达模式以产生细胞毒性。由于其在神经发生的关键增殖阶段广泛分布于大脑中，因此可以想象 AhR 参与 NPC 的扩增。因此，本研究检验了 TCDD 激活 AhR 破坏调节 NPC 增殖的信号事件的假设。C17.2 NPC 系作为模型系统用于：（1）评估 NPC 是否是 TCDD 诱导的神经毒性的靶标；（2）描述 TCDD 对 NPC 增殖的影响。我们证明 C17.2 NPC 表达完整的 AhR 信号通路，该通路在 TCDD 暴露后转录激活。（3）H-胸腺嘧啶和 alamar blue 还原测定表明，TCDD 以浓度依赖的方式抑制 NPC 增殖，而不降低细胞活力。通过流式细胞术进行的细胞周期分布分析表明，TCDD 诱导的生长停滞是由于 G1 到 S 细胞周期过渡受损所致。此外，TCDD 暴露改变了 p27（kip1）和细胞周期调节蛋白 cyclin D1 的表达水平，与 G1 期停滞一致。从胚胎小鼠腹侧前脑分离的原代 NPC 中的初步研究表明，TCDD 通过 G1 期停滞减少细胞增殖，与我们在 C17.2 细胞系中的发现一致。总之，这些观察结果表明，在神经发生过程中，TCDD 对 AhR 的不适当或持续激活可能会干扰调节神经上皮干细胞/NPC 增殖的信号通路，从而对大脑中的最终细胞数量产生不利影响，并导致功能障碍。
