Collins Loretta L, Williamson Mary A, Thompson Bryan D, Dever Daniel P, Gasiewicz Thomas A, Opanashuk Lisa A
Department of Environmental Medicine, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14642, USA.
Toxicol Sci. 2008 May;103(1):125-36. doi: 10.1093/toxsci/kfn017. Epub 2008 Jan 27.
The widespread environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been linked to developmental neurotoxicity associated with abnormal cerebellar maturation in both humans and rodents. TCDD mediates toxicity via binding to the aryl hydrocarbon receptor (AhR), a transcription factor that regulates the expression of xenobiotic metabolizing enzymes and growth regulatory molecules. Our previous studies demonstrated that cerebellar granule neuron precursor cells (GNPs) express transcriptionally active AhR during critical developmental periods. TCDD exposure also impaired GNP proliferation and survival in vitro. Therefore, this study tested the hypothesis that TCDD exposure disrupts cerebellar development by interfering with GNP differentiation. In vivo experiments indicated that TCDD exposure on postnatal day (PND) 6 resulted in increased expression of a mitotic marker and increased thickness of the external granule layer (EGL) on PND10. Expression of the early differentiation marker TAG-1 was also more pronounced in postmitotic, premigratory granule neurons of the EGL, and increased apoptosis of GNPs was observed. On PND21, expression of the late GNP differentiation marker GABA(A alpha 6) receptor (GABAR(A alpha 6)) and total estimated cell numbers were both reduced following exposure on PND6. Studies in unexposed adult AhR(-/-) mice revealed lower GABAR(A alpha 6) levels and DNA content. In vitro studies showed elevated expression of the early differentiation marker p27/Kip1 and the GABAR(A alpha 6) in GNPs following TCDD exposure, and the expression patterns of proteins related to granule cell neurite outgrowth, beta III-tubulin and polysialic acid neural cell adhesion molecule, were consistent with enhanced neuroblast differentiation. Together, our data suggest that TCDD disrupts a normal physiological role of AhR, resulting in compromised GNP maturation and neuroblast survival, which impacts final cell number in the cerebellum.
广泛存在的环境污染物2,3,7,8-四氯二苯并对二恶英（TCDD）已被证明与人类和啮齿动物小脑成熟异常相关的发育性神经毒性有关。TCDD通过与芳烃受体（AhR）结合介导毒性，AhR是一种转录因子，可调节外源性代谢酶和生长调节分子的表达。我们之前的研究表明，小脑颗粒神经元前体细胞（GNPs）在关键发育时期表达转录活性AhR。TCDD暴露也会损害体外GNPs的增殖和存活。因此，本研究检验了TCDD暴露通过干扰GNPs分化而破坏小脑发育的假说。体内实验表明，出生后第6天（PND6）暴露于TCDD会导致有丝分裂标记物表达增加以及PND10时外颗粒层（EGL）厚度增加。早期分化标记物TAG-1在EGL有丝分裂后、迁移前颗粒神经元中的表达也更明显，并且观察到GNPs凋亡增加。在PND21时，PND6暴露后晚期GNP分化标记物GABA(Aα6)受体（GABAR(Aα6)）的表达和总估计细胞数均减少。对未暴露的成年AhR(-/-)小鼠的研究显示GABAR(Aα6)水平和DNA含量较低。体外研究表明，TCDD暴露后GNPs中早期分化标记物p27/Kip1和GABAR(Aα6)的表达升高，并且与颗粒细胞神经突生长相关的蛋白质βIII-微管蛋白和多唾液酸神经细胞粘附分子的表达模式与神经母细胞分化增强一致。总之，我们的数据表明TCDD破坏了AhR的正常生理作用，导致GNPs成熟受损和神经母细胞存活受影响，进而影响小脑的最终细胞数量。
