Transient P2X7 Receptor Antagonism Produces Lasting Reductions in Spontaneous Seizures and Gliosis in Experimental Temporal Lobe Epilepsy

Abstract

Neuroinflammation is thought to contribute to the pathogenesis and maintenance of temporal lobe epilepsy, but the underlying cell and molecular mechanisms are not fully understood. The P2X7 receptor is an ionotropic receptor predominantly expressed on the surface of microglia, although neuronal expression has also been reported. The receptor is activated by the release of ATP from intracellular sources that occurs during neurodegeneration, leading to microglial activation and inflammasome-mediated interleukin 1␤ release that contributes to neuroinflammation.UsingareportermouseinwhichgreenfluorescentproteinisinducedinresponsetothetranscriptionofP2rx7,weshowthat expression of the receptor is selectively increased in CA1 pyramidal and dentate granule neurons, as well as in microglia in mice that developed epilepsy after intra-amygdala kainic acid-induced status epilepticus. P2X7 receptor levels were increased in hippocampal subfields in the mice and in resected hippocampus from patients with pharmacoresistant temporal lobe epilepsy. Cells transcribing P2rx7 in hippocampal slices from epileptic mice displayed enhanced agonist-evoked P2X7 receptor currents, and synaptosomes from these animals showed increased P2X7 receptor levels and altered calcium responses. A 5 d treatment of epileptic mice with systemic injections of the centrally available, potent, and specific P2X7 receptor antagonist JNJ-47965567 (30 mg/kg) significantly reduced spontaneous seizures during continuous video-EEG monitoring that persisted beyond the time of drug presence in the brain. Hippocampal sections from JNJ-47965567-treated animals obtained Ͼ5 d after treatment ceased displayed strongly reduced microgliosis and astrogliosis. The present study suggests that targeting the P2X7 receptor has anticonvulsant and possibly disease-modifying effects in experimental epilepsy.

Silencing of P2X7R by RNA interference in the hippocampus can attenuate morphological and behavioral impact of pilocarpine-induced epilepsy

“…Previous studies have shown that P2X7R antagonists trigger anticonvulsant effect, reducing electrographic and behavioral seizures, microglia activation, decrease IL-1β production and prevent cell damage resulting from seizures [14,15,33,38,41,42]. Studies using P2X7R (Pfizer) [46] knockout mice also show reduction in the severity of seizures compared to wild-type mice [33].…”

“…In microglia, P2X7R activation is associated with the inflammatory response in the central nervous system through cytokines production and release, especially interleukin-1β (IL-1β), interleukin-18 (IL-18), tumor necrosis factor (TNF-α), signaling through nuclear factor kappa B (NF-kB), nitric oxide synthase (NOS) activation, free radical production, and proapoptotic transcription factor formation [6, 7, 9, 10, 14, 15, 17-19, 21, 57]. The P2X7R activation in astrocytes has been related to inflammatory response and facilitation of glutamate release [7,9,12,13,15,18,19,21,23,57,58]. Neuronal death in pilocarpine model occurs by different mechanisms [59].…”

“…The kinins along with the cytokines may affect the junction of blood vessel epithelial cells and reduce the integrity of the tight junctions in endothelial cells walls, leading to a dysfunction of the blood brain barrier and consequently increasing the vascular permeability and accumulation of extracellular fluid [63,70,79,80]. There are a number of studies showing robust evidence that IL-1β released following seizures may be pro-convulsant in experimental models of epilepsy [6,14,15,76,81]. According to our results, P2X7R can modulate the mechanisms involved in edema since the reduction in the expression of these receptors by siRNA prevented the edema in hippocampal subareas as hilus, dentate gyrus suprapyramidal, CA1, and CA3 of rats underwent to pilocarpine-induced SE.…”

“…The activation of P2X7R with Bz-ATP (P2X7R agonist) causes microglial activation, enhances TNF-α immunoreactivity, reduces astrocytes, and intensifies seizures expression [19,[38][39][40]. Conversely, P2X7R blockage promotes anticonvulsant effects and reduces electroencephalographic and behavioral seizures, IL-1β production, microglial activation, recruitment and infiltration of neutrophils into the frontoparietal cortex, and damage resulting from seizure [14,15,33,38,[41][42][43][44]. Surprisingly, P2X7R antagonists have been described to exacerbate seizures and enhance cell death in the hippocampal CA3 subfield in the pilocarpine and intraamygdala kainic acid models, but do not change behavioral pattern in the intraperitoneal kainic acid and picrotoxin models of epilepsy [39,41,45].…”

Interleukin-1 receptor (IL-1R) mediates epilepsy-induced sleep disruption

“…IL-1 may enhance seizures by facilitating LTP in the hippocampus; however, it is also suggested that as the dosage is increased, IL-1 performs the opposite role and suppresses LTP [29, 30]. A recently published paper further describes that the pathogenesis and maintenance of temporal lobe epilepsies are attributed to the activation of P2X7 receptors by the release of ATP during neurodegeneration, which activates the microglia to release IL-1β [31]. In contrast, the anticonvulsant role of IL-1β has also been suggested in BLA-kindling rats, as evidenced by the decrease in seizures after ICV injection of IL-1β [18].…”