Seizure is one of the common comorbidities in Alzheimer's disease (AD). Seizures in AD have been shown to occur more often with early-onset disease, particularly when there is a familial presenilin I (PS1) mutation or abnormal expression of amyloid precursor protein (APP). AD patients with seizures have been associated with a faster decline in cognitive functions. However, it remains unclear how seizures exacerbate neurodegeneration in AD. Here, we showed that, using a kainic acid-induced acute seizure model, mitochondrial function is enhanced and the reactive oxygen species (ROS) are reduced in the brain of wild-type (WT) mice but not in an AD mouse model, APP/PS1 mice. These data suggest a lack of protective mechanism following seizures in APP/PS1 mice. Mechanistically, we found that an E3 ubiquitin ligase, the neural precursor cell-expressed developmentally downregulated protein 4-like (Nedd4-2), is elevated but stays dephosphorylated in APP/PS1 mice upon seizure inductions. Immunocytochemistry and sub-cellular fractionation experiments demonstrate an interaction between Nedd4-2 and mitochondria. Unbiased proteomics analysis suggests that Nedd4-2 regulates the expression of multiple mitochondrial proteins including one of the key mitochondrial outer membrane proteins, Mitofusin 2 (MFN2). Upon seizure induction, Nedd4-2 exhibits elevated interaction with mitochondria and downregulates MFN2 in APP/PS1 mice but not in WT mice. These data suggest that seizures aggravate mitochondrial dysfunction in AD, and Nedd4-2, which acts as a negative mitochondrial regulator, contributes to this effect. Altogether, our findings illustrate a potential mechanism by which seizures exacerbate neurodegeneration in AD and suggest Nedd4-2 as a novel therapeutic target for AD patients with comorbid seizures.
Wang et al. (Wed,) studied this question.