Baba Kazunobu, Okada Kazushi, Kinoshita Tsutomu, Imaoka Susumu
Department of Bioscience, Nanobiotechnology Research Center, School of Science and Technology, Kwansei Gakuin University, Sanda, Japan.
Toxicol Sci. 2009 Apr;108(2):344-55. doi: 10.1093/toxsci/kfp025. Epub 2009 Feb 13.
Bisphenol A (BPA) is being recognized as an endocrine-disrupting chemical (EDC). Recently, several reports indicated that BPA affects the central nervous system (CNS) during embryonic development. However, the molecular mechanism of BPA in the CNS is not well known. Here, we show that BPA affected Notch signaling by inhibiting the activity of the Notch intracellular domain (NICD) cleavage-related enzyme, gamma-secretase (gamma-secretase), at the neurula stage of the Xenopus laevis. BPA caused various morphologic aberrations including scoliosis, eye dysplasia, and loss of pigments in the X. laevis tadpole. These abnormalities were seen whenever BPA was used at the neurula stage. In addition, the expression levels of several marker mRNAs at the neurula stage were investigated by RT-PCR, and we found that the mRNAs expression of ectodermal marker, Pax6, CNS marker, Sox2, and neural crest marker, FoxD3, were decreased by treatment with BPA. These genes contribute to the neural differentiation at the neurula stage, and also the downstream factors of Notch signaling. Injection of NICD but not a Notch ligand, delta 1, rescued the abnormalities caused by BPA. We subsequently assayed the inhibition of the activities of NICD cleavage-related enzymes, tumor necrosis factor alpha converting enzyme, and gamma-secretase, by BPA and found that BPA inhibited the gamma-secretase activity. Furthermore, we expressed presenilin, a main component of gamma-secretase, in Escherichia coli and found the direct binding of BPA with presenilin. These results suggest that BPA affected the neural differentiation by inhibiting gamma-secretase activity, leading to neurodevelopmental abnormalities.
双酚A（BPA）被认为是一种内分泌干扰化学物质（EDC）。最近，有几份报告表明，BPA在胚胎发育过程中会影响中枢神经系统（CNS）。然而，BPA在中枢神经系统中的分子机制尚不清楚。在此，我们表明，在非洲爪蟾的神经胚阶段，BPA通过抑制Notch细胞内结构域（NICD）裂解相关酶γ-分泌酶（γ-分泌酶）的活性来影响Notch信号通路。BPA导致了各种形态畸变，包括脊柱侧凸、眼睛发育异常和非洲爪蟾蝌蚪色素缺失。只要在神经胚阶段使用BPA，就会出现这些异常。此外，通过逆转录聚合酶链反应（RT-PCR）研究了神经胚阶段几种标记mRNA的表达水平，我们发现，用BPA处理后，外胚层标记物Pax6、中枢神经系统标记物Sox2和神经嵴标记物FoxD3的mRNA表达均降低。这些基因有助于神经胚阶段的神经分化，也是Notch信号通路的下游因子。注射NICD而非Notch配体delta 1可挽救由BPA引起的异常。我们随后检测了BPA对NICD裂解相关酶、肿瘤坏死因子α转换酶和γ-分泌酶活性的抑制作用，发现BPA抑制了γ-分泌酶的活性。此外，我们在大肠杆菌中表达了γ-分泌酶的主要成分早老素，并发现BPA与早老素直接结合。这些结果表明，BPA通过抑制γ-分泌酶活性影响神经分化，导致神经发育异常。
