Abstracts

Rationale: Angelman syndrome (AS) is associated with epilepsy, abnormal electroencephalographic (EEG) activity, and increased vulnerability to febrile seizures (FS). Deletions in the maternally imprinted UBE3A gene, encoding ubiquitin protein ligase E3A (UBE3A) is a common cause of AS and a number of AS phenotypes are identified in the Ube3a maternal deletion rat model, including lower temperature threshold to FS. It is not known if loss of neuronal Ube3a alters the response to FS-induced neuroinflammation and if there is a long-term impact on the AS epilepsy phenotype. We examined neuroinflammatory markers after induction of FS in the AS rat model and evaluated long term alterations in EEG and epileptiform activity following FS.

Methods: EEGs were recorded from WT and AS rat pups placed under a heat lamp to raise core body temperature to induce prolonged and repeated hyperthermia-induced seizures (complex FS; cFS). Control groups were handled similarly but maintained at normothermic temperatures. EEGs were analyzed offline for epileptiform activity and delta power (an AS EEG biomarker). Brain tissue was collected from cFS rat pups 1- or 6- days post-FS to determine levels of the neuroinflammatory markers interleukin 1β (IL1-β), glial fibrillary acidic protein (GFAP), nuclear receptor NR42A, and ionized calcium binding adapter molecule 1 (IBA1) using western blotting. A subset of rat pups exposed to cFS were treated with the anti-inflammatory corticosteroid dexamethasone (DEX), once daily for three days at the end of the cFS.

Results: vEEGs revealed that AS rat pups exhibited seizures at lower temperatures and a greater number of seizures during hyperthermia compared to WT littermates (p < 0.01). One month following cFS, the WT cFS group had myoclonic seizures and the AS NT group exhibited myoclonic seizures at a similar frequency, while the AS cFS group showed a significantly higher number of myoclonic seizures (p < 0.01) with increased EEG delta power (p < 0.05) compared to all groups. AS cFS rats treated with DEX had fewer myoclonic seizures compared to untreated AS cFS group (p < 0.05). One day after cFS, both WT and AS cortical tissue exhibited high levels of IBA-1 and NR4A2 (p < 0.01 compared to NT), however only cortex from the AS cFS group maintained significantly high levels of IBA-1 6 days after cFS (p < 0.05), whereas IBA-1 returned to NT levels in the WT cFS group (p >0.05).

Conclusions: Our findings suggest that AS rat pups are more susceptible to FS compared to WT rats and that there are long-term FS effects on seizures and the biomarker, EEG delta power in AS rats. The acute effects of FS on the neuroinflammatory response may provide a substrate for epileptogenesis in AS. Establishing a causal link will be important to determine if anti-inflammatory therapy can modulate long term consequences of early life FS in AS.

Funding: Foundation for Angelman Syndrome Therapeutics