Abstracts

Rationale: The leading cause of focal pediatric epilepsy (FPE) is malformation of cortical development with the most common diagnosis being focal cortical dysplasia (FCD). While some genetic causes of FCD have been identified, the etiology of epilepsy remains largely unknown. Another common cause of FPE is tuberous sclerosis complex (TSC). Unlike FCD, the cause of TSC is known to be mutation in TSC1 or TSC2; part of the mammalian target of rapamycin (mTOR) pathway. The mTOR pathway is a potent regulator of cellular metabolism and signaling. Since some gene mutations identified in FCD are mTOR pathway genes, we hypothesise that focal pediatric epilepsy may have a common metabolic signature. As control, we use samples from patients with Rasmussen encephalitis (RE), a disease with unilateral inflammation of the cerebral cortex causing epilepsy. Using an unbiased transcriptomics-metabolomics screen in human surgical samples, we compared differentially expressed genes (DEGs) and metabolites (DEMs) to identify a common metabolic pathway in focal pediatric epilepsy.

Methods: Fresh-frozen surgically-resected epileptogenic tissue was collected from 40 pediatric patients with FCD, 9 with TSC, and 4 with RE. Control tissue was obtained from 10 samples of perilesional areas in patients with FCD. RNA was extracted and sequenced on Illumina HiSeq 2x150bp, single index platform with polyA selection library prep. Standard HISAT2-FeatureCounts-DESeq2 pipeline was conducted to generate DEGs. For the untargeted metabolomics, frozen tissues were extracted in 70% methanol solution. Metabolites were run on a ZIC-pHILIC column on a Q-Exactive Orbitrap LC/MS. Metabolomics data were analysed using CompoundDiscoverer and TraceFinder to generate DEMs.

Results: Out of all the DEGs, we identified 851 (10.29%) shared genes. Gene ontology analysis revealed that shared pathogenic pathways included inflammation and immune response, regulation of actin cytoskeleton, NF-kappaB signaling, and the PI3K-AKT signaling. Interestingly, both the NF-kappaB and the PI3K-AKT signaling interact closely with the mTOR pathway. Targeted examination of these shared genes showed some interesting metabolic signatures such as implication of mitochondrial complex I (NDUFA10), carnitine metabolism (PANK2), lactate transporter (SLC16A1), and lysine catabolism (AASS). These transcriptomic changes are accompanied by the correlated changes in metabolite levels. Specifically, we observed increased levels of 2-aminoadipate, a lysine catabolism product, in all three diseases. 2-aminoadipate appears to be a pro-convulsant and cytotoxic metabolite; which can induce spontaneous epileptic activity in in vitro brain slice preparation.

Conclusions: In our screen of FCD, TSC, and RE; we have identified a common metabolic signature of focal pediatric epilepsy. Lysine catabolism appears to be upregulated in all three diseases; leading to an increased generation of 2-aminoadipate. 2-aminoadipate may have a pro-convulsant effect; thus targeting the generation of this toxic byproduct may be a novel strategy for therapeutics in focal pediatric epilepsy.

Funding: Please list any funding that was received in support of this abstract.: This study was supported by CURE, NIH/NINDS NS104428-01 and institutional funds (Brown University).