BackgroundDiacylglycerol (DG) kinase (DGK) phosphorylates DG to produce phosphatidic acid (PA). Of the 10 subtypes of mammalian DGKs, DGKβ is a membrane-localized subtype and abundantly expressed in the cerebral cortex, hippocampus, and caudate-putamen. However, its physiological roles in neurons and higher brain function have not been elucidated.Methodology/Principal FindingsWe, therefore, developed DGKβ KO mice using the Sleeping Beauty transposon system, and found that its long-term potentiation in the hippocampal CA1 region was reduced, causing impairment of cognitive functions including spatial and long-term memories in Y-maze and Morris water-maze tests. The primary cultured hippocampal neurons from KO mice had less branches and spines compared to the wild type. This morphological impairment was rescued by overexpression of DGKβ. In addition, overexpression of DGKβ in SH-SY5Y cells or primary cultured mouse hippocampal neurons resulted in branch- and spine-formation, while a splice variant form of DGKβ, which has kinase activity but loses membrane localization, did not induce branches and spines. In the cells overexpressing DGKβ but not the splice variant form, DGK product, PA, was increased and the substrate, DG, was decreased on the plasma membrane. Importantly, lower spine density and abnormality of PA and DG contents in the CA1 region of the KO mice were confirmed.Conclusions/SignificanceThese results demonstrate that membrane-localized DGKβ regulates spine formation by regulation of lipids, contributing to the maintenance of neural networks in synaptic transmission of cognitive processes including memory.

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BackgroundDiacylglycerol kinase (DGK) is an enzyme that phosphorylates diacylglycerol (DG) to produce phosphatidic acid (PA). DGKβ is widely distributed in the central nervous system, such as the olfactory bulb, cerebral cortex, striatum, and hippocampus. Recent studies reported that the splice variant at the COOH-terminal of DGKβ was related to bipolar disorder, but its detailed mechanism is still unknown.Methodology/Principal FindingsIn the present study, we performed behavioral tests using DGKβ knockout (KO) mice to investigate the effects of DGKβ deficits on psychomotor behavior. DGKβ KO mice exhibited some behavioral abnormalities, such as hyperactivity, reduced anxiety, and reduced depression. Additionally, hyperactivity and reduced anxiety were attenuated by the administration of the mood stabilizer, lithium, but not haloperidol, diazepam, or imipramine. Moreover, DGKβ KO mice showed impairment in Akt-glycogen synthesis kinase (GSK) 3β signaling and cortical spine formation.Conclusions/SignificanceThese findings suggest that DGKβ KO mice exhibit lithium-sensitive behavioral abnormalities that are, at least in part, due to the impairment of Akt-GSK3β signaling and cortical spine formation.

In terms of mental illnesses, depression has an enormous influence in society. Major symptoms of depression are a "depressed mood" and "loss of interest and joy." Despite recent advances in the knowledge related to brain development and function, the mechanisms underlying the pathogenesis of depression remain unclear.The endoplasmic reticulum is a principal site for protein synthesis, folding, and calcium signaling.1) It is highly sensitive to alterations in calcium homeostasis and perturbations in its environment. A condition that impaired the function of the endoplasmic reticulum, collectively designated "endoplasmic reticulum stress," can lead to an accumulation of unfolded proteins in the endoplasmic reticulum lumen.2) In response to endoplasmic reticulum stress, cells have developed a self-protective signal pathway termed the unfolded protein response (UPR), leading to induction of molecular chaperones such as 78 kDa glucose-regulated protein (GRP78) and 94 kDa glucose-regulated protein (GRP94), translational attenuation, and endoplasmic reticulum associated degradation.3) However, if the damage is excessive, the UPR ultimately activates an apoptotic pathway such as CCAAT/enhancer binding protein (C/EBP)-homologous protein (CHOP) activation. 4)Recently, GRP78 and GRP94 have been found in the temporal cortex of subjects with major depressive disorder who died by suicide.5) Furthermore, in a rodent depression model, endoplasmic reticulum stress-related proteins were increased and these were attenuated by an antidepressant.6) Recently, we have reported that restraint stress increases in the expression of endoplasmic reticulum stress-related genes in the mouse brain.7) These findings indicate that endoplasmic reticulum stress may have some roles in the pathogenesis of depression.Luteolin is a common flavonoid that exists in many types of plants such as Apium graveolens L. var. dulce, 8)Petroselium crispum, 9) and Capsicum annuum L. var.'grossum.' 10) It has various pharmacological activities such as antioxidant, 11) anticancer action, 12) memory-improving, 13) and anxiolytic 14) activities, suggesting that luteolin could penetrate easily into the brain. 15) In this study, we investigated the antidepressant effects of luteolin from the green pepper leaf, as well as its mechanism, using cell death assay induced by endoplasmic reticulum stress in human neuroblastoma (SH-SY5Y) cells and animal models of depression. MATERIALS AND METHODS Purification of LuteolinLuteolin aglycon (luteolin) was provided by Theravalues (Tokyo, Japan). The purity of luteolin was 80%. In the experiments, it was dissolved in phosphate buffered saline contained 1% dimethyl sulfoxide (DMSO) or suspended in the 0.5% carboxymethylcellulose (Wako, Osaka, Japan).Cell Culture SH-SY5Y cells were purchased from the European Collection of Cell Culture (Wiltshire, U.K.) and maintained in Dulbecco's modified Eagle's medium (SigmaAldrich, St. Louis, MO, U.S.A.) containing 10% fetal bovine serum (VALEANT, Costa Mesa, CA, U.S.A.), 100 units/ml of penici...

Recently, neurotrophic factors and cytokines have been shown to be associated in psychiatric disorders, such as schizophrenia, bipolar disorder, and depression. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family, serves as a neurotrophic molecular and plays a significant role in the brain. We generated mice in which HB-EGF activity is disrupted specifically in the ventral forebrain. These knockout mice showed (a) behavioral abnormalities similar to those described in psychiatric disorders, which were ameliorated by typical or atypical antipsychotics, (b) altered dopamine and serotonin levels in the brain, (c) decreases in spine density in neurons of the prefrontal cortex, (d) reductions in the protein levels of the NR1 subunit of the N-methyl-D-aspartate (NMDA) receptor and post-synaptic protein-95 (PSD-95), (e) decreases in the EGF receptor, and in the calcium/calmodulin-dependent protein kinase II (CaMK II) signal cascade. These results suggest the alterations affecting HB-EGF signaling could comprise a contributing factor in psychiatric disorder.

BackgroundDiacylglycerol kinase (DGK) is an enzyme that phosphorylates diacylglycerol to produce phosphatidic acid. DGKβ is one of the subtypes of the DGK family and regulates many intracellular signaling pathways in the central nervous system. Previously, we demonstrated that DGKβ knockout (KO) mice showed various dysfunctions of higher brain function, such as cognitive impairment (with lower spine density), hyperactivity, reduced anxiety, and careless behavior. In the present study, we conducted further tests on DGKβ KO mice in order to investigate the function of DGKβ in the central nervous system, especially in the pathophysiology of attention deficit hyperactivity disorder (ADHD).Methodology/Principal FindingsDGKβ KO mice showed attention-deficit behavior in the object-based attention test and it was ameliorated by methylphenidate (MPH, 30 mg/kg, i.p.). In the open field test, DGKβ KO mice displayed a decreased response to the locomotor stimulating effects of MPH (30 mg/kg, i.p.), but showed a similar response to an N-methyl-d-aspartate (NMDA) receptor antagonist, MK-801 (0.3 mg/kg, i.p.), when compared to WT mice. Examination of the phosphorylation of extracellular signal-regulated kinase (ERK), which is involved in regulation of locomotor activity, indicated that ERK1/2 activation induced by MPH treatment was defective in the striatum of DGKβ KO mice.Conclusions/SignificanceThese findings suggest that DGKβ KO mice showed attention-deficit and hyperactive phenotype, similar to ADHD. Furthermore, the hyporesponsiveness of DGKβ KO mice to MPH was due to dysregulation of ERK phosphorylation, and that DGKβ has a pivotal involvement in ERK regulation in the striatum.

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