Status Epilepticus Alters the Function of Brain-Derived Extracellular Vesicles

Epilepsy is a neurological disorder characterised by recurrent spontaneous seizures. Approximately 30% of patients are unable to achieve adequate seizure control with available medications, highlighting the need to better understand disease mechanisms and develop improved treatments. Mesial temporal lobe epilepsy (MTLE) is a common subtype of treatment-resistant epilepsy. Patients with MTLE often have experienced a prior neurological insult, such as a traumatic brain injury, or status epilepticus (SE), that is believed to contribute to epileptogenic changes that lead to MTLE. However, the molecular mechanisms underlying epileptogenesis remain incompletely understood. Extracellular vesicles (EVs) are small membrane-bound particles released by cells that are important for intercellular communication. Recent studies identified altered microRNA (miRNA) content in brain-derived EVs (BDEVs) in models of MTLE, but whether BDEV function is altered has not been explored. Using the pilocarpine mouse model of MTLE, we examined the effects of SE on the function and miRNA cargo of hippocampal BDEVs during the epileptogenic period. BDEVs were isolated from hippocampi of control and pilocarpine-treated mice 24 h after SE. To assess functional changes, we compared gene expression in N2a neuronal-like cells and BV2 microglial-like cells exposed to control BDEVs (CON-BDEVs) or BDEVs collected after SE (SE-BDEVs). SE-BDEVs induced distinct transcriptional changes in N2a cells including alterations in the expression of genes related to TGF-β signalling, amino acid regulation of mTORC1 and neurotransmitter signalling. In BV2 cells, SE-BDEVs increased the expression of genes associated with inflammatory cytokine release. Analysis of BDEV miRNA content revealed multiple differentially expressed miRNAs between SE- and CON-BDEVs, with predicted targets overlapping with genes uniquely altered by SE-BDEVs. Notably, SE-induced miRNA changes were still observed 10 days post-SE, indicating sustained modulation of BDEV cargo. These findings identify SE-induced alterations in both the function and miRNA composition of hippocampal BDEVs, suggesting that BDEVs may contribute to epileptogenesis in MTLE.