Abstracts

Rationale: Epilepsy is one of the most prevalent pediatric neurological disorders, and can be comorbid with autism. An example of this interaction occurs in Fragile X Syndrome (FXS), in which Fragile X Mental Retardation Protein (FMRP) is silenced, manifesting with autistic behavior, seizures, and altered synaptic plasticity. The mammalian Target of Rapamycin (mTOR) pathway has also been shown to be dysregulated in FXS. We have recently shown that early-life seizures result in later-life epilepsy and autism, with mTOR upregulation playing a critical role, as treatment with rapamycin blocks these consequences (Talos et al, 2012). In addition, we recently reported that early-life seizures increase dendritic spine density, similar to that observed in FXS (Lippman Bell et al, 2010 AES abstract). Given that FMRP and mTOR regulate each other, we evaluated neonatal seizure-induced changes in FMRP in cortical tissue from epilepsy patients and cortical and hippocampal tissue in rats following hypoxia-induced seizures (HS). Methods: Seizures were induced in P10 rats by global hypoxia. Brains were collected 1, 3, and 24h post-HS and from age-matched littermates. Fresh, frozen tissue was collected from 7-14 year old patients with refractory seizures and focal cortical dysplasia (FCD), who underwent surgical resection, and compared to autopsy age-matched controls. Western blots were run and probed for phospho (Ser499) and total FMRP. Data was expressed as a percent of control of either phospho/total (p/t) or total FMRP normalized to actin (for rat) or adult control (for human). Results: In rat hippocampus 1h after seizures, FMRP expression and p/t ratio began to trend upwards by 10% and 15% respectively, compared to controls (p= 0.2 for total FMRP, p=0.1 for p/t; n=13 con, 13 HS). By 24h post-HS, total FMRP expression significantly increased by 20% (p=0.03, n=16 con, 13 HS). In the cortex, p/t FMRP trended towards 20% and 15% decreases at 1 and 24h post-HS, respectively (p=0.1 for both, n=3/group at 1h, 11 con and 8 HS at 24h), with no change in total FMRP. Phosho and total FMRP appeared unchanged 3h post-HS in hippocampus and cortex (n=5 con, 3 HS). In cortical tissue from human epilepsy (n=2) and FCD (n=3) cases, seizures also appear to dysregulate FMRP, showing an increase in total FMRP 83% and 53% above age-matched controls (n=2), respectively. In contrast, p/t FMRP in epilepsy and FCD tissue decreases by 58% and 42%, respectively, from age-matched controls. Conclusions: These results show altered FMRP expression and phosphorylation in human and rat tissue after seizures. When phosphorylated, FMRP stalls translation of many synaptic proteins, including itself. FMRP is dephosphorylated in an activity-dependent manner by p70S6 kinase, activity of which is also altered post-HS (Talos et al, 2012). Many proteins regulated by FMRP modulate important signaling pathways involved in synaptic plasticity, and thus potentially in cognitive function. Therefore, we conclude that early-life seizures disrupt the FMRP pathway, and that this can contribute to later-life cognitive dysfunction and epileptogenesis.