Abstracts

Rationale:
Focal cortical dysplasias (FCD) are a group of localized cortical malformations responsible for focal epileptic seizures, which are highly refractory to current antiepileptic drugs. Emerging data have identified that an increased proportion of patients with FCD have mutations in the mTOR pathway. Many of these mutations are somatic and result in mosaicism in the brain, which has led to difficulties in understanding the functional consequences of these mutations. Therefore, experimental models of epilepsy-associated FCD are needed to develop effective treatments. Recent data suggests an involvement of inflammatory processes in resected tissue from FCD patients. Whether this inflammatory response is triggered by recurrent seizures or represents an intrinsic feature of FCD is unclear. The goal of the present study was to extend the characterization, by mass cytometry, of a mouse model of epilepsy-associated FCD to investigate the immune cell profiling and assessment of central and peripheral immune activation and infiltration.

Methods:
We have evaluated a mouse model of epilepsy-associated FCD using in utero electroporation of mutations into the embryonic brain. Two cohorts of animals were generated: A sham control group, injected with and empty plasmid and an FCD group, injected with a mutated Rheb plasmid. Presence of seizures in this model was evaluated in a group housing video-EEG wireless telemetry platform. For immune cell profiling characterization, once animals were epileptic (~3 months old), we used mass cytometry, a high dimensional analog of flow cytometry involving mass spectrometry-based analysis of single cells bound with metal-tagged antibodies.

Results:
The model recapitulates the human pathophysiology of FCD. The abnormalities caused by mTOR activity upregulation led to focal cortical disorganization. Additionally, the model showed spontaneous and recurrent seizures starting at postnatal day 20 that closely resemble the dysplastic pathologies. Using mass cytometry, the immune cell profiling characterization showed no significant changes in the percentage of resident or infiltrating cell populations in ipsilateral brain compared with sham controls. However, there was a significant increased expression of activation markers (CD68, CD11c, CD86) and significant decreased expression of CD172a and anti-inflammatory (CD206) markers in FCD ipsilateral brain, particularly in microglia. The contralateral brain in the FCD cases showed general decrease in expression of activation markers and neutrophil infiltration compared with sham controls.

Conclusions:
In our study, microglia seem to be highly phagocytic and activated in the FCD model. This indicates that microglial activation might play an important role in the pathogenesis of epilepsy-associated FCD by maintaining chronic inflammatory responses. There is a clear need to investigate these mechanisms concerning the role of neuroinflammation in epilepsy and FCD to evaluate the need for immunomodulatory therapies for seizure prevention.

Funding: UCB Biopharma-sponsored