Huang Ping, Ceccatelli Sandra, Hoegberg Pi, Sten Shi Tie Jun, Håkansson Helen, Rannug Agneta
Division of Work Environment Toxicology, Institute of Environmental Medicine, Karolinska Institutet, S-171 77 Stockholm, Sweden.
Toxicol Appl Pharmacol. 2003 Nov 1;192(3):262-74. doi: 10.1016/s0041-008x(03)00296-5.
The 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) is a highly toxic, widespread environmental contaminant. Most of the toxic damage caused by TCDD is considered to be secondary to the binding of TCDD to the aryl hydrocarbon receptor, the AH receptor (AHR). TCDD is known to affect the vitamin A homeostasis. The effects of TCDD on body weight and on the expressions of AHR-associated genes may be modulated by the retinoid system. Therefore, we investigated the regulation pattern of expression of the AHR associated genes after TCDD exposure in wild-type 129/SV/C57BL/6 mice and in mice deficient in cellular retinol-binding protein type I (CRBP-I) of the same mixed genetic background. A single oral dose of TCDD (50 or 250 mug/kg) was administrated by gavage. Different brain areas, including cortex, hypothalamus, cerebellum, and olfactory bulb, as well as pituitary and liver, were dissected from CRBP-I knockout homozygous mice (-/-) and wild-type mice (+/+) killed at two time points (7 or 28 days after treatment). Compared with vehicle-treated controls, the relative levels of cytochrome P450 1A1 (CYP1A1) mRNA and protein expression in TCDD-treated animals were dramatically increased in mice of both CRBP-I genotypes (-/-, +/+). CYP1A1 mRNA levels increased up to 1400-fold in the pituitary, 110-fold in the brain, and up to 1600-fold in the liver. A general observation was that the relative induction of CYP1A1 and AHR transcription after TCDD dosing was highest in the +/+ mice. A high TCDD-induced aryl hydrocarbon receptor repressor (AHRR) mRNA expression was observed in the liver and in brain tissues. Interestingly, however, mice that lacked the CRBP-I protein (-/-) were found to have a significantly higher basal expression of AHRR gene in the pituitary compared to the wild-type (CRBP-I +/+) mice and in accordance a less pronounced induction of CYP1A1 and AHR was observed in the pituitary of the -/- mice. Immunohistochemical double staining analyses of the expression pattern of CYP1A1 and AHRR proteins in the pituitary revealed a colocalization of these two proteins. We conclude that the vitamin A homeostasis seems to have some influence to the TCDD-induced activation of AHR-regulated gene transcription in the brain and pituitary of the adult mouse.
2,3,7,8-四氯二苯并对二噁英（2,3,7,8-TCDD）是一种毒性极强、广泛存在的环境污染物。TCDD造成的大多数毒性损害被认为是TCDD与芳烃受体即AH受体（AHR）结合的继发结果。已知TCDD会影响维生素A的体内平衡。TCDD对体重以及AHR相关基因表达的影响可能会受到类视黄醇系统的调节。因此，我们研究了在野生型129/SV/C57BL/6小鼠以及具有相同混合遗传背景的细胞视黄醇结合蛋白I（CRBP-I）缺陷型小鼠中，TCDD暴露后AHR相关基因的表达调控模式。通过灌胃给予单次口服剂量的TCDD（50或250μg/kg）。在两个时间点（处理后7天或28天）处死CRBP-I基因敲除纯合小鼠（-/-）和野生型小鼠（+/+），并解剖不同的脑区，包括皮质、下丘脑、小脑和嗅球，以及垂体和肝脏。与溶剂处理的对照组相比，在两种CRBP-I基因型（-/-、+/+）的小鼠中，TCDD处理组动物体内细胞色素P450 1A1（CYP1A1）mRNA和蛋白表达的相对水平均显著增加。CYP1A1 mRNA水平在垂体中增加高达1400倍，在脑中增加110倍，在肝脏中增加高达1600倍。一个普遍的观察结果是，TCDD给药后，+/+小鼠中CYP1A1和AHR转录的相对诱导程度最高。在肝脏和脑组织中观察到高TCDD诱导的芳烃受体阻遏蛋白（AHRR）mRNA表达。然而，有趣的是，与野生型（CRBP-I +/+）小鼠相比，缺乏CRBP-I蛋白的小鼠（-/-）在垂体中AHRR基因的基础表达显著更高，并且相应地，在-/-小鼠的垂体中观察到CYP1A1和AHR的诱导作用不太明显。垂体中CYP1A1和AHRR蛋白表达模式的免疫组织化学双重染色分析显示这两种蛋白共定位。我们得出结论，维生素A的体内平衡似乎对成年小鼠脑和垂体中TCDD诱导的AHR调节基因转录激活有一定影响。
