Essential Role of Neuron-Enriched Diacylglycerol Kinase (DGK), DGKβ in Neurite Spine Formation, Contributing to Cognitive Function

Abstract

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.

The Roles of Diacylglycerol Kinases in the Central Nervous System: Review of Genetic Studies in Mice

“…expression (25). These results suggest that DGKb plays an important role in synaptic formations, which is consistent with another study (59).…”

“…DGKb KO mice were generated by Shirai et al in 2010 (25). Based on their behavioral analysis, DGKb KO mice exhibit cognitive impairment, manialike behavior, and increased seizure susceptibility (25,32,55).…”

“…Based on their behavioral analysis, DGKb KO mice exhibit cognitive impairment, manialike behavior, and increased seizure susceptibility (25,32,55). DGKb has been reported to show unique membrane localization and its expression levels in rat brains rapidly increases after postnatal day 14 (56,57), when synaptic formation is progressing.…”

“…To date, several overexpression or knockout (KO)mice have been generated by many research groups: DGKaKO (23), cardiacspecific overexpression of DGKa (24), DGKbKO (25), DGKdKO (26), DGKe KO (27), DGKzKO (28), and DGKiKO mice (29). From the phenotypes of these DGKKO mice, each DGK has been shown to play an important roles in regulating various neuronal functions such as cognitive functions (25,30,31) , mood (32), and resistance to excitatory stimuli (33 -35).…”

Fragile X Mental Retardation Protein (FMRP) controls diacylglycerol kinase activity in neurons

“…Dgkκ is a member of the DGK isozymes, master regulators of the balance between DAG and PA signaling (31). Several DGKs have been shown to be involved in structural and synaptic plasticity control (33)(34)(35)(36), but no data were available on Dgkκ neuronal function. We identified that the absence of FMRP leads to the deregulation of mGluRIdependent DGK activity, causing perturbations in the balance between its substrate, DAG, and its product, PA.…”