Cell selective conditional null mutations of serine racemase demonstrate a predominate localization in cortical glutamatergic neurons.
Cell selective conditional null mutations of serine racemase demonstrate a predominate localization in cortical glutamatergic neurons.
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DOI：
10.1007/s10571-012-9808-4
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发表时间：
2012-05
影响因子：
4
通讯作者：
Coyle JT
中科院分区：
文献类型：
--
作者：
Benneyworth MA;Li Y;Basu AC;Bolshakov VY;Coyle JT
D-丝氨酸由丝氨酸消旋酶 (SR) 合成，是 N-甲基-D-天冬氨酸受体 (NMDAR) 的共激动剂。了解 D-丝氨酸信号传导功能的关键是确定负责其合成和释放的位点。为了量化星形胶质细胞和神经元对 SR 和 D-丝氨酸定位的贡献，我们使用重组 DNA 技术来实现星形胶质细胞 (aSRCKO) 和前脑谷氨酸能神经元 (nSRCKO) 中 SR 表达的细胞类型选择性抑制。大多数 SR 在神经元中表达：通过蛋白质印迹定量，nSRCKO 大脑皮层和海马中 SR 表达减少约 65%，但 aSRCKO 中仅减少约 15%。相比之下，nSRCKO仅与HPLC定量的D-丝氨酸水平适度降低相关，而aSRCKO小鼠中的D-丝氨酸水平不受影响。 nSRCKO 中 SR 的肝脏表达增加了 35%，表明外周 SR 在维持脑 D-丝氨酸中发挥作用。对 Schaffer 侧支 CA1 锥体神经元突触的长时程增强 (LTP) 的电生理学研究显示，aSRCKO 小鼠与野生型小鼠相比没有变化。 nSRCKO 小鼠中，单次强直刺激诱导的 LTP 减少了近 70%。此外，在 nSRCKO 小鼠中，由 NMDA 受体介导而非 AMPA 受体介导的微型兴奋性突触后电流显着减少。我们的研究结果表明，在前脑中，D-丝氨酸似乎是 NMDA 受体的内源性共激动剂，SR 主要在谷氨酸能神经元中表达，并且谷氨酸和 D-丝氨酸的共同释放是突触后 NMDA 受体的最佳激活所必需的。
D-Serine, which is synthesized by the enzyme serine racemase (SR), is a co-agonist at the N-methyl-D-aspartate receptor (NMDAR). Crucial to an understanding of the signaling functions of D-serine is defining the sites responsible for its synthesis and release. In order to quantify the contributions of astrocytes and neurons to SR and D-serine localization, we used recombinant DNA techniques to effect cell type selective suppression of SR expression in astrocytes (aSRCKO) and in forebrain glutamatergic neurons (nSRCKO). The majority of SR is expressed in neurons: SR expression was reduced by ~65% in nSRCKO cerebral cortex and hippocampus, but only ~15% in aSRCKO as quantified by western blots. In contrast, nSRCKO is associated with only modest decreases in D-serine levels as quantified by HPLC, whereas D-serine levels were unaffected in aSRCKO mice. Liver expression of SR was increased by 35% in the nSRCKO, suggesting a role for peripheral SR in the maintenance of brain D-serine. Electrophysiologic studies of long-term potentiation (LTP) at the Schaffer collateral–CA1 pyramidal neuron synapse revealed no alterations in the aSRCKO mice versus wild-type. LTP induced by a single tetanic stimulus was reduced by nearly 70% in the nSRCKO mice. Furthermore, the mini-excitatory post-synaptic currents mediated by NMDA receptors but not by AMPA receptors were significantly reduced in nSRCKO mice. Our findings indicate that in forebrain, where D-serine appears to be the endogenous co-agonist at NMDA receptors, SR is predominantly expressed in glutamatergic neurons, and co-release of glutamate and D-serine is required for optimal activation of post-synaptic NMDA receptors.