Differences in mRNA expression of neuroinflammation-related genes in the temporal lobe of patients with drug-resistant focal epilepsy.

OBJECTIVES

Approximately one-third of epilepsy patients will not achieve seizure freedom with current antiseizure medications, and the identification of novel treatment targets is needed. We characterized alterations in neuroinflammation-related mRNA levels to aid in the identification of possible molecular mediators of DRTLE and discuss the potential for immunomodulatory therapies in this condition.

METHODS

Temporal lobe samples from DRTLE and postmortem controls without neurological conditions were obtained. RT-qPCR of 60 genes of interest was performed on BioMark Fluidigm custom-made gene expression integrated fluidic circuits (IFC) and cycle threshold values were obtained and analyzed using the 2 - ∆ ∆ C T method. Correlation with various clinical parameters was assessed. Immunohistochemistry was performed on a subset of seven cases and four controls.

RESULTS

Temporal lobe tissue from 17 DRTLE patients (age: 46.3 ± 12.8 years; female: 35.3%) and 12 controls (age: 56.1 ± 6.1 years; female: 33.3%) were analyzed. Compared to controls, TNF and CCL3 were upregulated 52.7 (p < .0002) and 68.9 (p < .0001)-fold, respectively. C3 was increased by 5.9-fold (p < .0001). IL1B and IL18 were increased 6.4 (p < .0001) and 5.2 (p < .0001) times, respectively. Microglial markers TMEM119 and P2RY12 had a 7.1 (p < .0001) and 5.9 (p < .0001)-fold increase, respectively, with overall lower but significant increases in general mononuclear cell-associated mRNA. There was only low-level or no upregulation of T cell and B cell associated mRNA. No correlation between mRNA alterations and clinical parameters was found. On immunohistochemistry, TMEM119 protein expression was noted in resected brain tissue from DRTLE but was largely absent from controls, consistent with the mRNA results.

SIGNIFICANCE: Given the cross-sectional study design, causality cannot be determined. However, this study suggests that proinflammatory mechanisms may play a role in the pathogenesis of the ongoing epileptic state in DRTLE. In particular, complement, inflammasome, and microglial/mononuclear cell-mediated inflammatory processes had the most significant elevations in mRNA, while B and T cell associated mRNA were less altered.