Lane Meredith C, Jackson Joshua G, Krizman Elizabeth N, Rothstein Jeffery D, Porter Brenda E, Robinson Michael B
Department of Pediatrics, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, PA 19104, USA.
Department of Neurology and Neuroscience, Johns Hopkins University, Brain Sciences Institute, Baltimore, MD 21205, USA.
Neurochem Int. 2014 Jul;73:152-8. doi: 10.1016/j.neuint.2013.11.013. Epub 2013 Dec 12.
Excitatory amino acid carrier 1 (EAAC1 also called EAAT3) is a Na(+)-dependent glutamate transporter expressed by both glutamatergic and GABAergic neurons. It provides precursors for the syntheses of glutathione and GABA and contributes to the clearance of synaptically released glutamate. Mice deleted of EAAC1 are more susceptible to neurodegeneration in models of ischemia, Parkinson's disease, and aging. Antisense knock-down of EAAC1 causes an absence seizure-like phenotype. Additionally, EAAC1 expression increases after chemonvulsant-induced seizures in rodent models and in tissue specimens from patients with refractory epilepsy. The goal of the present study was to determine if the absence of EAAC1 affects the sensitivity of mice to seizure-induced cell death. A chemoconvulsant dose of pilocarpine was administered to EAAC1(-/-) mice and to wild-type controls. Although EAAC1(-/-) mice experienced increased latency to seizure onset, no significant differences in behavioral seizure severity or mortality were observed. We examined EAAC1 immunofluorescence 24h after pilocarpine administration and confirmed that pilocarpine causes an increase in EAAC1 protein. Forty-eight hours after induction of seizures, cell death was measured in hippocampus and in cortex using Fluoro-Jade C. Surprisingly, there was ∼2-fold more cell death in area CA1 of wild-type mice than in the corresponding regions of the EAAC1(-/-) mice. Together, these studies indicate that absence of EAAC1 results in either a decrease in pilocarpine-induced seizures that is not detectable by behavioral criteria (surprising, since EAAC1 provides glutamate for GABA synthesis), or that the absence of EAAC1 results in less pilocarpine/seizure-induced cell death, possible explanations as discussed.
兴奋性氨基酸载体1（EAAC1，也称为EAAT3）是一种钠离子依赖性谷氨酸转运体，由谷氨酸能神经元和γ-氨基丁酸能神经元共同表达。它为谷胱甘肽和γ-氨基丁酸的合成提供前体，并有助于清除突触释放的谷氨酸。EAAC1基因敲除的小鼠在缺血、帕金森病和衰老模型中更容易发生神经退行性变。EAAC1的反义敲低会导致失神发作样表型。此外，在啮齿动物模型和难治性癫痫患者的组织标本中，化学惊厥剂诱导的癫痫发作后EAAC1表达增加。本研究的目的是确定EAAC1的缺失是否会影响小鼠对癫痫诱导的细胞死亡的敏感性。向EAAC1基因敲除小鼠和野生型对照小鼠注射化学惊厥剂量的毛果芸香碱。虽然EAAC1基因敲除小鼠癫痫发作的潜伏期延长，但在行为性癫痫严重程度或死亡率方面未观察到显著差异。我们在注射毛果芸香碱24小时后检测了EAAC1免疫荧光，并证实毛果芸香碱可导致EAAC1蛋白增加。癫痫发作诱导48小时后，使用Fluoro-Jade C检测海马体和皮质中的细胞死亡情况。令人惊讶的是，野生型小鼠CA1区的细胞死亡比EAAC1基因敲除小鼠相应区域多约2倍。总之，这些研究表明，EAAC1的缺失要么导致毛果芸香碱诱导的癫痫发作减少，而这在行为标准上无法检测到（令人惊讶，因为EAAC1为γ-氨基丁酸合成提供谷氨酸），要么EAAC1的缺失导致毛果芸香碱/癫痫诱导的细胞死亡减少，具体解释如前所述。
