Gu Wei, Fukuda Tomohiko, Isaji Tomoya, Hang Qinglei, Lee Ho-hsun, Sakai Seiichiro, Morise Jyoji, Mitoma Junya, Higashi Hideyoshi, Taniguchi Naoyuki, Yawo Hiromu, Oka Shogo, Gu Jianguo
From the Division of Regulatory Glycobiology and.
the Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, 980-8577.
J Biol Chem. 2015 Jul 10;290(28):17566-75. doi: 10.1074/jbc.M114.579938. Epub 2015 May 15.
Core fucosylation is catalyzed by α1,6-fucosyltransferase (FUT8), which transfers a fucose residue to the innermost GlcNAc residue via α1,6-linkage on N-glycans in mammals. We previously reported that Fut8-knock-out (Fut8(-/-)) mice showed a schizophrenia-like phenotype and a decrease in working memory. To understand the underlying molecular mechanism, we analyzed early form long term potentiation (E-LTP), which is closely related to learning and memory in the hippocampus. The scale of E-LTP induced by high frequency stimulation was significantly decreased in Fut8(-/-) mice. Tetraethylammonium-induced LTP showed no significant differences, suggesting that the decline in E-LTP was caused by postsynaptic events. Unexpectedly, the phosphorylation levels of calcium/calmodulin-dependent protein kinase II (CaMKII), an important mediator of learning and memory in postsynapses, were greatly increased in Fut8(-/-) mice. The expression levels of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) in the postsynaptic density were enhanced in Fut8(-/-) mice, although there were no significant differences in the total expression levels, implicating that AMPARs without core fucosylation might exist in an active state. The activation of AMPARs was further confirmed by Fura-2 calcium imaging using primary cultured neurons. Taken together, loss of core fucosylation on AMPARs enhanced their heteromerization, which increase sensitivity for postsynaptic depolarization and persistently activate N-methyl-d-aspartate receptors as well as Ca(2+) influx and CaMKII and then impair LTP.
核心岩藻糖基化由α1,6-岩藻糖基转移酶（FUT8）催化，该酶通过α1,6-连接将岩藻糖残基转移至哺乳动物N-聚糖最内侧的N-乙酰葡糖胺残基上。我们之前报道，Fut8基因敲除（Fut8(-/-)）小鼠表现出精神分裂症样表型且工作记忆减退。为了解潜在的分子机制，我们分析了早期形式的长时程增强（E-LTP），其与海马体中的学习和记忆密切相关。高频刺激诱导的E-LTP幅度在Fut8(-/-)小鼠中显著降低。四乙铵诱导的LTP无显著差异，提示E-LTP的下降是由突触后事件引起的。出乎意料的是，突触后学习和记忆的重要介质钙/钙调蛋白依赖性蛋白激酶II（CaMKII）的磷酸化水平在Fut8(-/-)小鼠中大幅升高。尽管总表达水平无显著差异，但Fut8(-/-)小鼠突触后致密部中α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体（AMPARs）的表达水平增强，这意味着未进行核心岩藻糖基化的AMPARs可能处于激活状态。使用原代培养神经元进行的Fura-2钙成像进一步证实了AMPARs的激活。综上所述，AMPARs上核心岩藻糖基化的缺失增强了它们的异聚化，这增加了对突触后去极化的敏感性，并持续激活N-甲基-D-天冬氨酸受体以及Ca(2+)内流和CaMKII，进而损害LTP。
