Neuronal and glial responses in the brain under hypoxic stress

二酰甘油激酶(DGK)通过调节脂质信使二酰甘油的水平，在细胞的病理生理反应中发挥关键作用。在DGK同工酶中，DGKζ定位于神经元等多种细胞的细胞核。我们先前报道，短暂性前脑缺血20min后，DGKζ在海马CA1区锥体神经元中从胞核移位到胞浆。在这项研究中，我们研究了DGKζ易位的潜在机制，使用暴露于缺氧-葡萄糖剥夺的海马片来模拟脑缺血模型。缺氧20min后，CA1区锥体细胞DGKζ免疫阳性反应逐渐由胞核向胞浆转化，复氧后未见胞核表达。有趣的是，DGKζ在缺氧10min时在胞核内检测到，而在随后60min复氧诱导DGKζ完全胞浆易位。形态计量学分析显示，DGKζ胞浆易位与核萎缩相关，表明神经元早期变性过程。在OGD条件下，这种转位可被NMDAR抑制剂阻断，并被NMDAR激活所诱导。胞外Ca(2)的螯合作用阻断了OGD条件下的细胞外钙转运。这些结果表明，DGKζ胞浆易位是由NMDAR激活和随后的细胞外Ca(2)内流触发的。此外，在缺氧条件下抑制PKC活性导致约1/3的神经元DGKζ核滞留，提示PKC活性部分调节DGKζ胞浆易位。这些发现为进一步研究海马神经元谷氨酸兴奋性毒性机制提供了线索。

Diacylglycerol kinase (DGK) plays a key role in pathophysiological cellular responses by regulating the levels of a lipid messenger diacylglycerol. Of DGK isozymes, DGKζ localizes to the nucleus in various cells such as neurons. We previously reported that DGKζ translocates from the nucleus to the cytoplasm in hippocampal CA1 pyramidal neurons after 20 min of transient forebrain ischemia. In this study, we examined the underlying mechanism of DGKζ translocation using hippocampal slices exposed to oxygen-glucose deprivation (OGD) to simulate an ischemic model of the brain. DGKζ-immunoreactivity gradually changed from the nucleus to the cytoplasm in CA1 pyramidal neurons after 20 min of OGD and was never detected in the nucleus after reoxygenation. Intriguingly, DGKζ was detected in the nucleus at 10 min OGD whereas the following 60 min reoxygenation induced complete cytoplasmic translocation of DGKζ. Morphometric analysis revealed that DGKζ cytoplasmic translocation correlated with nuclear shrinkage indicative of an early process of neuronal degeneration. The translocation under OGD conditions was blocked by NMDA receptor (NMDAR) inhibitor, and was induced by activation of NMDAR. Chelation of the extracellular Ca(2+) blocked the translocation under OGD conditions. These results show that DGKζ cytoplasmic translocation is triggered by activation of NMDAR with subsequent extracellular Ca(2+) influx. Furthermore, inhibition of PKC activity under OGD conditions led to nuclear retention of DGKζ in about one-third of the neurons, suggesting that PKC activity partially regulates DGKζ cytoplasmic translocation. These findings provide clues to guide further investigation of glutamate excitotoxicity mechanisms in hippocampal neurons.