Diacylglycerol Kinase Epsilon Modulates Rapid Kindling Epileptogenesis

Abstract

Summary:Purpose: Diacylglycerol kinase epsilon (DGK ) regulates seizure susceptibility and long-term potentiation through arachidonoyl-inositol lipid signaling. We studied the significance of arachidonoyl-diacylglycerol (20:4 DAG) in epileptogenesis in DGK -deficient mice undergoing rapid kindling epileptogenesis.Methods: Tripolar electrode units were implanted in right dorsal hippocampi of male DGK +/+ and DGK −/− mice. Ten days after surgery, kindling was achieved by stimulating 6 times daily for 4 days with a subconvulsive electrical stimulation (10-s train of 50-Hz biphasic pulses, 75-200 μA amplitude) at 30-min intervals. After 1 week, mice were rekindled. EEGs were recorded and analyzed to characterize epileptogenic events as spikes, sharp waves, or abnormal amplitudes and rhythms. Right hippocampi were analyzed by histology [Timm's staining, neuropeptide Y (NPY) and glial fibrillary acidic protein immunoreactivity], and for DNA fragmentation (TUNEL).Results: DGK −/− mice had significantly fewer motor seizure and epileptic events compared with DGK +/+ mice from the second day of stimulation. These differences were maintained during rekindling. DGK −/− mice also exhibited lowamplitude spike-wave complexes, short spreading depression, and predominant lower-frequency (1-4 Hz) bands throughout stimulation, whereas DGK +/+ mice exhibited increased highfrequency bands (4-8 Hz; 8-15 Hz) from the second day of stimulation, as determined by power spectral analysis. DGK −/− mice displayed no sprouting in the supragranular area or NPY inmunoreactivity in the hilus and had weak astrocyte reactivation in all hippocampal areas. No TUNEL-positive cells were detected in any group of mice.Conclusions: DGK modulates kindling epileptogenesis through inositol lipid signaling. Because arachidonatecontaining diacylglycerol phosphorylation to phosphatidic acid is selectively blocked in DGK −/− mice, we postulate that the shortage of arachidonoyl-moiety inositol lipids and/or the messengers derived thereof is a key signaling event in epileptogenesis. Key Words: Diacylglycerol kinase-Kindling epileptogenesis-Inositol lipid signaling-Hippocampus.Partial complex seizure with secondary generalized seizure is one of the semiologic characteristics of mesial temporal lobe epilepsy (MTLE). In most cases, MTLE progresses with severe recurrence of seizures, becomes refractory to antiepileptic drugs (AEDs), and is related to certain mental and learning disabilities and psychosocial problems (1).Abnormal electrophysiologic responses through different mechanisms (abnormal excitation, enhanced synchronization, less frequency adaptation, diminutions of feedforward inhibition, abnormal burst, and paroxysmal firing) were found in hippocampal regions from patients who had MTLE (2). Excitatory glutamatergic signaling is one of the mechanisms proposed to trigger paroxysm shift depolarization (PSD), characterized as spikes that correlate with Accepted August 18, 2005. Address correspondence and reprint requests to Dr. N. G. Bazan at LSU Neuroscience ...

Molecular properties of diacylglycerol kinase-epsilon in relation to function

“…DGKe KO mice demonstrated a rapid behavioural recovery following brain stimulation and showed a lack of morphological changes in hippocampal glial cells, including the absence of hypertrophied cell bodies or elongated cell processes that were seen in WT mice (Musto and Bazan, 2006). Thus, DGKe appears to regulate seizure susceptibility and LTP via its involvement in PI signalling (Bazan, 2005;Musto and Bazan, 2006;Rodriguez de Turco et al, 2001;Bazan, 2001).…”

“…The observed resistance to seizures and attenuation of LTP in DGKe KO mice make DGKe an attractive target for studying epilepsy (Rodriguez de Turco et al, 2001). Similarly, other studies using DGKe KO mice have linked DGKe to hippocampal plasticitymediated kindling and epileptogenesis (Musto and Bazan, 2006). DGKe KO mice demonstrated a rapid behavioural recovery following brain stimulation and showed a lack of morphological changes in hippocampal glial cells, including the absence of hypertrophied cell bodies or elongated cell processes that were seen in WT mice (Musto and Bazan, 2006).…”

“…Thus DGKe may also be involved in another function to increase enrichment of arachidonoyl content during the conversion of PA to PI (Milne et al, 2008) which we are currently investigating. shown to reduce levels of free arachidonic acid, 20:4-DAG, and 20:4-PI(4,5)P 2 in response to electroconvulsive shock (Lukiw et al, 2005;Musto and Bazan, 2006;Bazan, 2005). These lipids serve several important biological functions and their dysregulation is implicated in a range of diseased states.…”

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

“…As discussed, DGKb, DGKd, or DGKz deficiency (which is noted in a later chapter) exacerbated seizure phenotypes, but DGKe KO mice showed a higher resistance to seizures induced by electroconvulsive shock (27,34). DGKe is the only DGK to exhibit high selectivity for arachidonatecontaining substrates (13).…”

Expression and Localization of Type II Diacylglycerol Kinase Isozymes δ and η in the Developing Mouse Brain

“…expressed in the Purkinje cells of the cerebellum, pyramidal cells of the hippocampus and mitral cells of the olfactory bulb, is also associated with epilepsy (Musto and Bazan 2006;Rodriguez de Turco et al 2001). Because the brain expression pattern of DGKε is different from that of DGKδ (Figs.…”