NMDA receptor-mediated Ca 2+ inXux triggers nucleocytoplasmictranslocation of diacylglycerol kinase ζ under oxygen-glucose deprivation conditions, an in vitro model of ischemia, in rat hippocampal slices
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.
"Knockdown of DGKz results in enhanced expression of cyclins and phosphorylated pRB, together with increased apoptotic marker expression and DNA fragmentation in hippocampal neurons after kainate-induced seizures (Okada et al., 2012). With regard to the time scales of this phenomenon, it should be mentioned that, in dissociated cultured neurons, cytoplasmic translocation of DGKz is observed after several hours of glutamate stimulation (Okada et al., 2012), whereas it occurs after 20 min of hypoxia in the animal model (Ali et al., 2004), or within 1 h under OGD–reperfusion conditions in hippocampal slice culture (Suzuki et al., 2012). This time scale difference may be ascribed to the distinct environmental conditions surrounding neurons: in primary neuron culture systems, neurons are principally dissociated from each other and have no intimate contact with glial cells, whereas neurons retain physiological interactions with glial cells in the brain in vivo and in slice culture. "
[Show abstract][Hide abstract] ABSTRACT: Eukaryotic cells have evolved to possess a distinct subcellular compartment, the nucleus, separated from the cytoplasm in a manner that allows the precise operation of the chromatin, thereby permitting controlled access to the regulatory elements in the DNA for transcription and replication. In the cytoplasm, genetic information contained in the DNA sequence is translated into proteins, including enzymes that catalyze various reactions, such as metabolic processes, energy control, and responses to changing environments. One mechanism that regulates these events involves phosphoinositide turnover signaling, which generates a lipid second messenger, diacylglycerol (DG). Since DG acts as a potent activator of several signaling molecules, it should be tightly regulated to keep cellular responsiveness within a physiological range. DG kinase (DGK) metabolizes DG by phosphorylating it to generate phosphatidic acid, thus serving as a critical regulator of DG signaling. Phosphoinositide turnover is employed differentially in the nucleus and the cytoplasm. A member of the DGK family, DGKζ, localizes to the nucleus in various cell types and is considered to regulate nuclear DG signaling. Recent studies have provided evidence that DGKζ shuttles between the nucleus and the cytoplasm in neurons under pathophysiological conditions. Transport of a signal regulator between the nucleus and the cytoplasm should be a critical function for maintaining basic processes in the nucleus, such as cell cycle regulation and gene expression, and to ensure communication between nuclear processes and cytoplasmic functions. In this review, a series of studies on nucleocytoplasmic translocation of DGKζ have been summarized, and the functional implications of this phenomenon in postmitotic neurons and cancer cells under stress conditions are discussed.
"Cell death in neurons occurs under ischemic conditions in the brain. Suzuki et al. (2012) used a rat hippocampal acute slice model employing oxygen–glucose deprivation as a model of ischemia to investigate nuclear to cytoplasmic translocation of diacylglycerol kinase f (DGKf), a key molecule in the regulation of cellular physiology. Using immunohistochemical staining, they observed that DGKf underwent nuclear to cytoplasmic translocation in CA1 pyramidal neurons following 20 min of oxygen–glucose deprivation and did not return to the nucleus following reoxygenation . "
[Show abstract][Hide abstract] ABSTRACT: The year 2012 was another exciting year for Histochemistry and Cell Biology. Innovations in immunohistochemical techniques and microscopy-based imaging have provided the means for advances in the field of cell biology. Over 130 manuscripts were published in the journal during 2012, representing methodological advancements, pathobiology of disease, and cell and tissue biology. This annual review of the manuscripts published in the previous year in Histochemistry and Cell Biology serves as an abbreviated reference for the readership to quickly peruse and discern trends in the field over the past year. The review has been broadly divided into multiple sections encompassing topics such as method advancements, subcellular components, extracellular matrix, and organ systems. We hope that the creation of this subdivision will serve to guide the reader to a specific topic of interest, while simultaneously providing a concise and easily accessible encapsulation of other topics in the broad area of Histochemistry and Cell Biology.
"To date, we have raised specific antibodies against DGKs and examined unique expression patterns of respective isozymes in rat brain under pathophysiological conditions (Hozumi et al. 2003; Goto et al. 2007; Nakano, Iseki, et al. 2009; Saino-Saito et al. 2011; Hozumi and Goto 2012; Suzuki et al. 2012). However, little is known about the nature and morphological aspects of DGKs in the retina, which is also of neuroectodermal origin. "
[Show abstract][Hide abstract] ABSTRACT: Recent studies have revealed that phosphoinositide (PI) signaling molecules are expressed in mammalian retinas, suggesting their importance in its signal transduction. We previously showed that diacylglycerol kinase (DGK) isozymes are expressed in distinct patterns in rat retina at the mRNA level. However, little is known about the nature and morphological aspects of DGKs in the retina. For this study, we performed immunohistochemical analyses to investigate in the retina the expression and localization of DGK isozymes at the protein level. Here, we show that both DGKβ and DGKι localize in the outer plexiform layer, within which photoreceptor cells make contact with bipolar and horizontal cells. These isozymes exhibit distinct subcellular localization patterns: DGKι localizes to the synaptic area of bipolar cells in a punctate manner, whereas DGKβ distributes diffusely in the subsynaptic and dendritic regions of bipolar and horizontal cells. However, punctate labeling for DGKϵ is evident in the outer limiting membrane. DGKζ and DGKα localize predominantly to the nucleus of ganglion cells. These findings show distinct expression and localization of DGK isozymes in the retina, suggesting a different role of each isozyme.
Journal of Histochemistry and Cytochemistry 03/2013; 61(6). DOI:10.1369/0022155413483574 · 1.96 Impact Factor
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