Ho Pei I, Ashline David, Dhitavat Sirikarnt, Ortiz Daniela, Collins Scott C, Shea Thomas B, Rogers Eugene
Center for Cellular Neurobiology and Neurodegeneration Research, University of Massachusetts-Lowell, Lowell, MA 01854, USA.
Neurobiol Dis. 2003 Oct;14(1):32-42. doi: 10.1016/s0969-9961(03)00070-6.
Clinical studies suggest a relationship between folate deficiency and neurological and disorders including Alzheimer's disease (AD). To investigate mechanisms underlying this association, we examined the consequences of folate deprivation on neuronal cultures. Culturing embryonic cortical neurons and differentiated SH-SY-5Y human neuroblastoma cells in folate-free medium induced neurodegenerative changes characteristic of those observed in AD, including increased cytosolic calcium, reactive oxygen species (ROS), phospho-tau and apoptosis. In accord with clinical studies, generation of the neurotoxic amino acid homocysteine (HC) was likely to contribute to these phenomena, since (1) a significant increase in HC was detected following folate deprivation, (2) addition of the inhibitor of HC formation, 3-deazaadenosine, both prevented HC formation and eliminated the increase in ROS that normally accompanied folate deprivation, (3) direct addition of HC in the presence of folate induced the neurotoxic effects that accompanied folate deprivation, and (4) an antagonist of NMDA channels that blocks HC-induced calcium influx also blocked calcium influx following folate deprivation. Folate deprivation decreased the reduced form of glutathione, indicating a depletion of oxidative buffering capacity. This line of reasoning was supported by an increase in glutathione and reduction in ROS following supplementation of folate-deprived cultures with the cell-permeant glutathione precursor, N-acetyl-L-cysteine, or vitamin E. Folate deprivation potentiated ROS and apoptosis induced by amyloid-beta, while folate supplementation at higher concentrations prevented generation of ROS by amyloid-beta, suggesting that folate levels modulate the extent of amyloid-beta neurotoxicity. These findings underscore the importance of folate metabolism in neuronal homeostasis and suggest that folate deficiency may augment AD neuropathology by increasing ROS and excitotoxicity via HC generation.
临床研究表明叶酸缺乏与包括阿尔茨海默病（AD）在内的神经和精神障碍之间存在关联。为了研究这种关联背后的机制，我们检测了叶酸缺乏对神经元培养物的影响。在无叶酸培养基中培养胚胎皮质神经元和分化的SH-SY-5Y人神经母细胞瘤细胞会诱导出AD中观察到的特征性神经退行性变化，包括细胞溶质钙增加、活性氧（ROS）、磷酸化tau蛋白增加和细胞凋亡。与临床研究一致，神经毒性氨基酸同型半胱氨酸（HC）的产生可能导致了这些现象，因为：（1）叶酸缺乏后检测到HC显著增加；（2）添加HC形成抑制剂3-去氮腺苷可防止HC形成，并消除通常伴随叶酸缺乏的ROS增加；（3）在有叶酸存在的情况下直接添加HC会诱导出伴随叶酸缺乏的神经毒性作用；（4）一种阻断HC诱导的钙内流的NMDA通道拮抗剂也能阻断叶酸缺乏后的钙内流。叶酸缺乏会降低谷胱甘肽的还原形式，表明氧化缓冲能力耗尽。用细胞可渗透的谷胱甘肽前体N-乙酰-L-半胱氨酸或维生素E补充叶酸缺乏的培养物后，谷胱甘肽增加且ROS减少，支持了这一推理思路。叶酸缺乏增强了淀粉样β蛋白诱导的ROS和细胞凋亡，而较高浓度的叶酸补充可防止淀粉样β蛋白产生ROS，这表明叶酸水平调节淀粉样β蛋白神经毒性的程度。这些发现强调了叶酸代谢在神经元稳态中的重要性，并表明叶酸缺乏可能通过增加ROS和经由HC产生的兴奋性毒性来加剧AD神经病理学。
