Minami Akira, Meguro Yuko, Ishibashi Sayaka, Ishii Ami, Shiratori Mako, Sai Saki, Horii Yuuki, Shimizu Hirotaka, Fukumoto Hokuto, Shimba Sumika, Taguchi Risa, Takahashi Tadanobu, Otsubo Tadamune, Ikeda Kiyoshi, Suzuki Takashi
From the Department of Biochemistry, School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan and.
Department of Organic Chemistry, School of Pharmaceutical Sciences, Hiroshima International University, 5-1-1 Hirokoshingai, Kure-shi, Hiroshima 737-0112, Japan.
J Biol Chem. 2017 Apr 7;292(14):5645-5654. doi: 10.1074/jbc.M116.764357. Epub 2017 Feb 17.
Sialidase cleaves sialic acids on the extracellular cell surface as well as inside the cell and is necessary for normal long-term potentiation (LTP) at mossy fiber-CA3 pyramidal cell synapses and for hippocampus-dependent spatial memory. Here, we investigated in detail the role of sialidase in memory processing. Sialidase activity measured with 4-methylumbelliferyl-α-d--acetylneuraminic acid (4MU-Neu5Ac) or 5-bromo-4-chloroindol-3-yl-α-d--acetylneuraminic acid (X-Neu5Ac) and Fast Red Violet LB was increased by high-K-induced membrane depolarization. Sialidase activity was also increased by chemical LTP induction with forskolin and activation of BDNF signaling, non-NMDA receptors, or NMDA receptors. The increase in sialidase activity with neural excitation appears to be caused not by secreted sialidase or by an increase in sialidase expression but by a change in the subcellular localization of sialidase. Astrocytes as well as neurons are also involved in the neural activity-dependent increase in sialidase activity. Sialidase activity visualized with a benzothiazolylphenol-based sialic acid derivative (BTP3-Neu5Ac), a highly sensitive histochemical imaging probe for sialidase activity, at the CA3 stratum lucidum of rat acute hippocampal slices was immediately increased in response to LTP-inducible high-frequency stimulation on a time scale of seconds. To obtain direct evidence for sialic acid removal on the extracellular cell surface during neural excitation, the extracellular free sialic acid level in the hippocampus was monitored using microdialysis. The free sialic acid level was increased by high-K-induced membrane depolarization. Desialylation also occurred during hippocampus-dependent memory formation in a contextual fear-conditioning paradigm. Our results show that neural activity-dependent desialylation by sialidase may be involved in hippocampal memory processing.
唾液酸酶可切割细胞外表面以及细胞内的唾液酸，对于苔藓纤维 - CA3 锥体细胞突触处的正常长期增强（LTP）以及海马体依赖的空间记忆是必需的。在此，我们详细研究了唾液酸酶在记忆处理中的作用。用 4 - 甲基伞形酮基 -α - d - 乙酰神经氨酸（4MU - Neu5Ac）或 5 - 溴 - 4 - 氯吲哚 - 3 - 基 -α - d - 乙酰神经氨酸（X - Neu5Ac）以及固红紫 LB 测定的唾液酸酶活性，会因高钾诱导的膜去极化而增加。用福司可林进行化学 LTP 诱导以及激活脑源性神经营养因子（BDNF）信号通路、非 NMDA 受体或 NMDA 受体也会增加唾液酸酶活性。神经兴奋时唾液酸酶活性的增加似乎不是由分泌的唾液酸酶或唾液酸酶表达增加引起的，而是由唾液酸酶亚细胞定位的变化导致的。星形胶质细胞以及神经元也参与了神经活动依赖的唾液酸酶活性增加。用基于苯并噻唑基苯酚的唾液酸衍生物（BTP3 - Neu5Ac）（一种用于唾液酸酶活性的高灵敏度组织化学成像探针）在大鼠急性海马切片的 CA3 透明层可视化的唾液酸酶活性，在数秒的时间尺度上，响应 LTP 诱导的高频刺激会立即增加。为了获得神经兴奋期间细胞外表面唾液酸去除的直接证据，使用微透析监测海马体中的细胞外游离唾液酸水平。高钾诱导的膜去极化会使游离唾液酸水平升高。在情境恐惧条件化范式的海马体依赖记忆形成过程中也会发生去唾液酸化。我们的结果表明，唾液酸酶介导的神经活动依赖去唾液酸化可能参与海马体记忆处理。
