Proteolytic degradation of glutamate decarboxylase mediates disinhibition of hippocampal CA3 pyramidal cells in cathepsin D‐deficient mice
Proteolytic degradation of glutamate decarboxylase mediates disinhibition of hippocampal CA3 pyramidal cells in cathepsin D‐deficient mice
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DOI：
10.1111/j.1471-4159.2005.03250.x
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发表时间：
2005-08
影响因子：
4.7
通讯作者：
Tokiko Shimizu;Yoshinori Hayashi;R. Yamasaki;J. Yamada;Jian Zhang;K. Ukai;M. Koike;K. Mine;K. von Figura;C. Peters;P. Saftig;T. Fukuda;Y. Uchiyama;H. Nakanishi
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文献类型：
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作者：
Tokiko Shimizu;Yoshinori Hayashi;R. Yamasaki;J. Yamada;Jian Zhang;K. Ukai;M. Koike;K. Mine;K. von Figura;C. Peters;P. Saftig;T. Fukuda;Y. Uchiyama;H. Nakanishi
神经元蜡样质脂褐质沉积症（NCL）的癫痫发作机制虽然具有重要的临床意义，但目前仍知之甚少。在本研究中，我们试图阐明组织蛋白酶D缺陷（CD-/-）小鼠癫痫发作的机制，这些小鼠表现出一种新型的溶酶体贮积病，其表型类似于晚期婴儿NCL。在从纳塔尔后第24天（P）的CD-/-小鼠制备的海马切片中，记录了CA 3锥体细胞的自发爆发放电。在P24，刺激苔藓纤维后IPSP的平均振幅显著小于野生型小鼠，这通过高效液相色谱法（HPLC）测定的海马中γ-氨基丁酸（GABA）含量水平降低得到证实。在这个阶段，发现激活的小胶质细胞聚集在CD-/-小鼠海马CA 3区的锥体细胞层中。然而，通过计算谷氨酸脱羧酶（GAD）67免疫反应性胞体的数量估计，在P24时CD-/-小鼠CA 3子区中GABA能中间神经元的数密度没有显著变化。在P24时CD-/-小鼠的海马和皮质中，一些GABA能中间神经元显示出极高的GAD 67体细胞颗粒免疫反应性，表明GAD 67的溶酶体蓄积。在CD-/-小鼠中，即使在P24，邻接海马CA 3锥体细胞的体周区的轴突终末中的GAD 67水平也没有显著变化，而在P24后CD-/-小鼠的海马和皮质中的GAD 67的总蛋白水平由于降解而显著降低。此外，重组人GAD 65/67被从野生型和CD-/-小鼠的全脑制备的溶酶体组分快速消化。这些观察结果强烈表明，GABA含量的减少，可能是由于GAD 67的溶酶体降解和其降解形式的溶酶体蓄积，是导致CD-/-小鼠海马CA 3区GABA能中间神经元功能障碍的原因。
Although of clinical importance, little is known about the mechanism of seizure in neuronal ceroid lipofuscinosis (NCL). In the present study, we have attempted to elucidate the mechanism underlying the seizure of cathepsin D‐deficient (CD–/–) mice that show a novel type of lysosomal storage disease with a phenotype resembling late infantile NCL. In hippocampal slices prepared from CD–/– mice at post‐natal day (P)24, spontaneous burst discharges were recorded from CA3 pyramidal cells. At P24, the mean amplitude of IPSPs after stimulation of the mossy fibres was significantly smaller than that of wild‐type mice, which was substantiated by the decreased level of γ‐aminobutyric acid (GABA) contents in the hippocampus measured by high‐performance liquid chromatography (HPLC). At this stage, activated microglia were found to accumulate in the pyramidal cell layer of the hippocampal CA3 subfield of CD–/– mice. However, there was no significant change in the numerical density of GABAergic interneurons in the CA3 subfield of CD–/– mice at P24, estimated by counting the number of glutamate decarboxylase (GAD) 67‐immunoreactive somata. In the hippocampus and the cortex of CD–/– mice at P24, some GABAergic interneurons displayed extremely high somatic granular immunoreactivites for GAD67, suggesting the lysosomal accumulation of GAD67. GAD67 levels in axon terminals abutting on to perisomatic regions of hippocampal CA3 pyramidal cells was not significantly changed in CD–/– mice even at P24, whereas the total protein levels of GAD67 in both the hippocampus and the cortex of CD–/– mice after P24 were significantly decreased as a result of degradation. Furthermore, the recombinant human GAD65/67 was rapidly digested by the lysosomal fraction prepared from the whole brain of wild‐type and CD–/– mice. These observations strongly suggest that the reduction of GABA contents, presumably because of lysosomal degradation of GAD67 and lysosomal accumulation of its degraded forms, are responsible for the dysfunction of GABAergic interneurons in the hippocampal CA3 subfield of CD–/– mice.