Hardingham Giles E, Bading Hilmar
Department of Preclinical Veterinary Sciences, Royal (Dick) School of Veterinary Studies, Edinburgh University, Summerhall, EH9 1QH, Edinburgh, UK.
Biochim Biophys Acta. 2002 Nov 4;1600(1-2):148-53. doi: 10.1016/s1570-9639(02)00455-7.
Electrical activation of hippocampal neurons can cause calcium influx through different entry sites which may specify nuclear signalling and induction of gene transcription and downstream physiological outputs. Genomic responses initiated by NMDA receptors (NMDARs) are critically dependent on whether synaptically or extrasynaptically located receptors are stimulated; calcium flux through synaptic NMDARs activates CREB whereas flux through extrasynaptic NMDARs triggers a CREB shut-off signal. Here we investigated the possibility that the coupling of extrasynaptic NMDARs to the CREB shut-off pathway is regulated during in vitro development. Cultured hippocampal neurons were analyzed after 7 or 12 days of in vitro culturing. We found that synaptic NMDAR activity induced CREB phosphorylation at day in vitro (DIV) 7 and DIV 12. In contrast, the extrasynaptic NMDAR-dependent CREB shut-off signal is developmentally regulated. At DIV 12 extrasynaptic NMDAR activation shuts down CREB and overrides the CREB-activating signal triggered by synaptic NMDAR activation. In contrast, at DIV 7 this shut off signal is absent; both synaptic and extrasynaptic NMDARs activate CREB function. Developmental changes in NMDAR signaling have been proposed to contribute to the emergence of glutamate excitotoxicity, which causes apoptosis or necrosis depending on the severity of the insult. Since CREB regulates a number of pro-survival genes, the emergence of this shut-off around DIV 7 may contribute to the increase in susceptibility of neurons to glutamate-induced neuropathology in vitro and in vivo during post-natal development.
海马神经元的电激活可导致钙离子通过不同的进入位点内流，这可能会明确核信号传导以及基因转录和下游生理输出的诱导。由N-甲基-D-天冬氨酸受体（NMDARs）引发的基因组反应严重依赖于突触或突触外定位的受体是否受到刺激；通过突触NMDARs的钙通量激活CREB，而通过突触外NMDARs的钙通量触发CREB关闭信号。在这里，我们研究了在体外发育过程中突触外NMDARs与CREB关闭途径的偶联是否受到调节的可能性。在体外培养7天或12天后对培养的海马神经元进行分析。我们发现，在体外培养第7天和第12天，突触NMDAR活性诱导CREB磷酸化。相比之下，突触外NMDAR依赖的CREB关闭信号受到发育调节。在体外培养第12天，突触外NMDAR激活会关闭CREB，并覆盖由突触NMDAR激活触发的CREB激活信号。相比之下，在体外培养第7天，这种关闭信号不存在；突触和突触外NMDARs均激活CREB功能。有人提出，NMDAR信号传导的发育变化会导致谷氨酸兴奋性毒性的出现，谷氨酸兴奋性毒性会根据损伤的严重程度导致细胞凋亡或坏死。由于CREB调节许多促生存基因，在体外培养第7天左右这种关闭信号的出现可能有助于神经元在出生后发育过程中在体外和体内对谷氨酸诱导的神经病理学易感性的增加。
