Beyond Impaired GABAergic Signaling: Inflammation and Metabolic Dysfunction in Genetic Epilepsy Induced by GABRG2...

Although the mechanisms underlying genetic epilepsies associated with mutations in the γ-aminobutyric acid type A receptor γ2 subunit gene (GABRG2) have been extensively investigated, prior studies primarily focused on the functional alterations of mutant ion channels. Emerging evidence has indicated that neuroinflammation and metabolic disturbances are involved in acquired epilepsies. To further investigate the potential involvement of these mechanisms in genetic epilepsies, we generated a transgenic zebrafish line, Tg(hGABRG2^I107T), harboring the GABRG2(I107T) mutation associated with developmental and epileptic encephalopathies. The Tg(hGABRG2^I107T) zebrafish exhibited spontaneous seizure-like behaviors and hyperexcitability as demonstrated by electrophysiological recordings and elevated c-fos transcript levels. Total γ2 subunit expression increased and its cell membrane localization was reduced. These zebrafish also displayed disrupted neuronal marker expression and abnormal synaptic ultrastructure, indicative of an excitatory/inhibitory imbalance. Transcriptome analysis revealed that differentially expressed genes in the brain were enriched in the endoplasmic reticulum (ER) protein processing, metabolic pathway, and TGF-β signaling pathway. Pro-inflammatory factors were upregulated, while genes involved in the tricarboxylic acid (TCA) cycle were downregulated. Similarly, HEK293T cells transfected with the mutant γ2(I107T) exhibited significant reductions in TCA-related gene expression, ATP levels, and mitochondrial density. In addition to impairing receptor trafficking, the γ2(I107T) mutation may induce ER stress, and disrupt inflammatory and metabolic pathways, thereby leading to an imbalance of excitatory/inhibitory neurotransmission and potentially contributing to the pathogenesis of genetic epilepsy. Pharmacological intervention with dexamethasone and INCB3344, a C-C chemokine receptor type 2 antagonist, ameliorated seizure-like behavior in Tg(hGABRG2^I107T) zebrafish, further supporting the causal role of neuroinflammation in epileptogenesis in genetic epilepsy.