Increased Expression and Cellular Localization of P2X7R in Cortical Lesions of Patients With Focal Cortical Dysplasia

Abstract

Focal cortical dysplasias (FCDs) are major brain malformations that commonly lead to medically intractable epilepsy. The purinergic ionotropic P2X7 receptor (P2X7R) is an atypical P2X subtype that gates calcium and sodium ions. Previous animal studies have suggested that P2X7R is a contributing factor in epileptogenesis. This study aimed to define the distribution and expression of P2X7R in 35 FCD patient-surgical-resection specimens relative to autopsy control samples (n = 8). Immunohistochemical colocalization assays revealed that P2X7R was primarily expressed in neurons, astrocytes, and microglia. In FCD samples, P2X7R protein levels were increased in abnormal cell types such as dysmorphic neurons and balloon cells, which are characteristic of FCD. By real-time PCR and Western blotting, P2X7R mRNA and protein expression levels were elevated in FCD patient samples vs control samples; P2X7R expression was also higher in FCDII vs FCDIa patient samples. Because interleukin-1β is a downstream factor of the P2X7R signaling pathway, we determined that there was also moderate-to-strong interleukin-1β expression in the dysmorphic neurons, balloon cells, and microglia in FCD patient lesions. These results indicate that increasing P2X7R levels may contribute to the pathogenesis of human FCD and that P2X7R represents a potential anti-epileptogenic target.

Review: Neuroinflammatory pathways as treatment targets and biomarker candidates in epilepsy: emerging evidence from preclinical and clinical studies

“…Experimental data have been corroborated by neuropathological evidence of IL‐1R/TLR signalling activation in brain specimens resected at surgery from patients with drug‐resistant epilepsy . Thus, IL‐1β/ILR1 and HMGB1/TLR4 axes, and their key signalling molecules, have been studied by immunohistochemistry and biochemical methods in low‐grade epilepsy‐associated glioneuronal tumours (GNT) (ganglioglioma, dysembryoplastic neuroepithelial tumours) , malformations of cortical development (focal cortical dysplasia, tuberous sclerosis) , temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS) and Rasmussen's encephalitis . Interestingly, the number of IL‐1β‐ and IL‐1R1‐positive neurons in GNTs was positively correlated with the frequency of seizures, whereas the number of IL‐1ra‐positive neurons and astrocytes was negatively correlated with the duration of epilepsy prior to surgery , therefore establishing a potential pathogenic link between IL‐R1/TLR4 signalling activation and lesion's epileptogenicity.…”

Neuroinflammatory targets and treatments for epilepsy validated in experimental models

“…Increased P2X7 receptor levels were observed in hippocampus resected from patients with pharmacoresistant temporal lobe epilepsy, as well as in patients with focal cortical dysplasia. 37,38 Moreover, twice-daily 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. Of interest, the spontaneous seizure rate did not return to baseline during a relatively short monitoring after drug washout.…”

“…Intracellular recordings and analysis of synaptoneurosomes indicated enhanced agonist‐evoked and altered calcium responses in hippocampal neurons from epileptic mice. Increased P2X7 receptor levels were observed in hippocampus resected from patients with pharmacoresistant temporal lobe epilepsy, as well as in patients with focal cortical dysplasia . Moreover, twice‐daily 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.…”

Evaluation of the Anticonvulsant Effect of Brilliant Blue G, a Selective P2X7 Receptor Antagonist, in the iv PTZ-, Maximal Electroshock-, and 6 Hz-Induced Seizure Tests in Mice

“…Their increased expression was noted in some abnormal cells characteristic for this disorder, i.e., in dysmorphic cells and balloon cells. Moreover overexpression of P2X7 receptor in surgically resected cortical lesions of these patients was connected with higher expression of interleukin β1, a downstream factor of the P2X7 receptor signaling pathway [ 35 ].…”

“…Results of many studies show that anticonvulsant and antiepileptic activity of some P2X7 receptor antagonists observed in animal models of epilepsy (i.e., kindling model, kainic acid and pilocarpine models) might arise from their anti-inflammatory action [ 20 , 35 ]. The lack of anticonvulsant action of BBG in the present study may not be surprising, as there is no inflammation in used acute seizure models.…”