Precise Regulation of the Basal PKCγ Activity by DGKγ Is Crucial for Motor Coordination

Design, Synthesis, and Evaluation of 11C-Labeled 3-Acetyl-Indole Derivatives as a Novel Positron Emission Tomography Imaging Agent for Diacylglycerol Kinase Gamma (DGKγ) in Brain

Diacylglycerol kinase gamma (DGKγ) is a subtype of DGK enzyme, which catalyzes ATP-dependent conversion of diacylglycerol to phosphatidic acid. DGKγ, localized in the brain, plays an important role in the central nervous system. However, its function has not been widely investigated. Positron emission tomography (PET) imaging of DGKγ validates target engagement of therapeutic DGKγ inhibitors and investigates DGKγ levels under normal and disease conditions. In this study, we designed and synthesized a series of 3-acetyl indole derivatives as candidates for PET imaging agents for DGKγ. Among the synthesized compounds, 2-((3-acetyl-1-(6-methoxypyridin-3-yl)-2-methyl-1H-indol-5-yl)oxy)-N-methylacetamide (9) exhibited potent inhibitory activity (IC50 = 30 nM) against DGKγ and desirable physicochemical properties allowing efficient blood-brain barrier penetration and low levels of undesirable nonspecific binding. The radiolabeling of 9 followed by PET imaging of wild-type and DGKγ-deficient mice and rats indicated that [11C]9 ([11C]T-278) specifically binds to DGKγ and yields a high signal-to-noise ratio for DGKγ in rodent brains.

Cellular expression and subcellular localization of diacylglycerol kinase γ in rat brain

Gq protein-coupled receptors lead to activation of phospholipase C, which triggers phosphoinositide signaling. Diacylglycerol (DG) is one of the phosphoinositide metabolites and serves as a second messenger. Diacylglycerol kinase (DGK) phosphorylates DG to produce another second messenger phosphatidic acid. Of the DGK family, DGKγ is predominantly expressed in the brain at the mRNA level. Recent studies have shown the expression of DGKγ in vascular endothelial cells and adrenal medullary cells at the protein level, although its detailed cellular expression pattern and subcellular localization in the brain remain to be determined. In the present study, we addressed this point using specific DGKγ antibody. DGKγ was expressed in both projection neurons and interneurons in the cerebral cortex, hippocampal formation, and cerebellum. In cerebellar Purkinje cells, DGKγ was distributed to the soma and dendrites. Fractionation study revealed that DGKγ was enriched in the internal membranes containing the endoplasmic reticulum and Golgi complex. In immunoelectron microscopy, DGKγ was localized throughout the smooth endoplasmic reticulum system. These findings suggest that DGKγ shows unique cellular expression pattern in the brain and distinct subcellular localization different from other DGK isozymes.

Motor Dyscoordination and Alteration of Functional Correlation Between DGKγ and PKCγ in Senescence-Accelerated Mouse Prone 8 (SAMP8)

Senescence-accelerated mouse prone 8 (SAMP8) is an animal model of age-related central nervous system (CNS) disorders. Although SAMP8 shows deficits in learning, memory, and emotion, its motor coordination has not been clarified. We have recently reported that DGKγ-regulated PKCγ activity is important for cerebellar motor coordination. However, involvement of the functional correlation between the kinases in age-related motor dyscoordination still remains unknown. Therefore, we have investigated the motor coordination in SAMP8 and involvement of the functional correlation between DGKγ and PKCγ in the age-related motor dyscoordination. Although 6 weeks old SAMP8 showed equivalent motor coordination with control mice (SAMR1) in the rotarod test, 24 weeks old SAMP8 exhibited significantly less latency in the rotarod test and more frequent slips in the beam test compared to the age-matched SAMR1. Furthermore, 24 weeks old SAMP8 showed the higher locomotor activity in open field test and Y-maze test. Western blotting revealed that DGKγ expression decreased in the cerebellum of 24 weeks old SAMP8, while PKCγ was upregulated. These results suggest that SAMP8 is a useful model of age-related motor dysfunction and that the DGKγ-regulated PKCγ activity is involved in the age-related motor dyscoordination.