Dey P M, Polunas M A, Philbert M A, Reuhl K R
Department of Pharmacology and Toxicology, Rutgers College of Pharmacy, Piscatawy, NJ 08854-0789, USA.
Neurotoxicology. 1997;18(3):633-43.
Proper structuring of neural connections in the hippocampus is mediated by cell adhesion molecules, membrane-linked proteins involved in cell recognition and stabilization of cytoarchitecture. Modulated expression of the neural cell adhesion molecule (NCAM) at the synapse permits plasticity required for both learning and memory. Polysialylation of NCAM, particularly the synapse-specific 180 kDa isoform (NCAM180), allows hippocampal neurons to alter their neuronal connections during learning acquisition and memory consolidation in mature brain. These activity-dependent changes in NCAM expression represent a sensitive target for neurotoxicity. Trimethyltin (TMT), a potent hippocampal neurotoxicant, alters total NCAM expression in whole mouse hippocampus and impairs learning in rodents. To investigate the expression of polysialylated NCAM following TMT administration, Swiss-Webster mice were injected (i.p.) with 2.0 or 3.0 mg TMT/kg and sacrificed 6 hrs to 7 days later. Immunocytochemical staining for polysialylated NCAM (PSA-NCAM) revealed marked reduction of staining of hippocampal dentate granule cells 6-72 hours after TMT treatment. Partial recovery of hippocampal polysialylated NCAM was observed after 7 days. Immunoblot data indicated that loss of PSA-NCAM expression paralleled reductions seen in NCAM180 and markers of cytoskeletal integrity. Assays for proteolytic activity in hippocampus revealed rapid, reversible protease activation which correlated temporally with the reduction of NCAM180 and PSA-NCAM. Proteolytic degradation following hippocampal injury may serve to disrupt NCAM-mediated adhesion. Protracted loss of polysialylated NCAM in dentate gyrus following injury may serve as a useful marker in toxicant-induced learning disorders.
海马体中神经连接的正确构建由细胞黏附分子介导，这些分子是参与细胞识别和细胞结构稳定的膜联蛋白。神经细胞黏附分子（NCAM）在突触处的表达调节允许学习和记忆所需的可塑性。NCAM的多唾液酸化，特别是突触特异性180 kDa异构体（NCAM180），使成熟大脑中海马神经元在学习获取和记忆巩固过程中能够改变其神经连接。这些依赖于活动的NCAM表达变化是神经毒性的一个敏感靶点。三甲基锡（TMT）是一种强效的海马体神经毒素，可改变整个小鼠海马体中NCAM的总表达，并损害啮齿动物的学习能力。为了研究TMT给药后多唾液酸化NCAM的表达，给瑞士韦伯斯特小鼠腹腔注射2.0或3.0 mg TMT/kg，并在6小时至7天后处死。对多唾液酸化NCAM（PSA-NCAM）的免疫细胞化学染色显示，TMT处理后6至72小时海马齿状颗粒细胞的染色明显减少。7天后观察到海马多唾液酸化NCAM部分恢复。免疫印迹数据表明，PSA-NCAM表达的丧失与NCAM180和细胞骨架完整性标志物的减少平行。海马体中蛋白水解活性的测定显示蛋白酶迅速、可逆地激活，这在时间上与NCAM180和PSA-NCAM的减少相关。海马损伤后的蛋白水解降解可能会破坏NCAM介导的黏附。损伤后齿状回中多唾液酸化NCAM的长期丧失可能是毒物诱导的学习障碍的一个有用标志物。
