Abstracts

Rationale: Autism spectrum disorders (ASDs) nicely illustrate the bidirectional comorbidity between epilepsy and neuropsychiatric dysfunction. Maternally inherited duplications and triplications of 15q11-13 (termed "Dup15" and "Idic15" respectively) represent the most common copy number variant in autism. One gene within this chromosomal segment, Ube3a, is expressed exclusively from the maternal allele in neurons and functions as an E3 ubiquitin ligase as well as a transcriptional coregulator. We have shown previously that transgenic mice with one additional copy of Ube3a ("Ube3a1x") modeling Dup15 are largely indistinguishable from wild-type counterparts, whereas "Ube3a2x" mice with two extra copies modeling Idic15 display multiple core features of autistic behavior, nicely recapitulating gene dosage effects observed in humans. Epilepsy is an important comorbidity in 15q duplication syndromes as well as other forms of autism, and has been shown to amplify autistic endophenotypes through unknown mechanisms. Methods: Mice were examined either three hours following a single seizure or 24 hours following 5-10 repeated seizures, elicited through intraperitoneal pentylenetetrazole (PTZ) injections. Hippocampi were dissected for biochemical measures via immunoblotting and mRNA quantified via qRT-PCR. A three-chamber social interaction task measured autism-related social impairment. Experiments were approved by the BIDMC Institutional Animal Care and Use Committee (IACUC). Results: Wild-type mice (males, FVB) displayed a loss of social preference in the three-chamber social interaction task following ten daily PTZ-induced seizures, and this was associated with significantly increased hippocampal phospho-AKT levels and reduced levels of the phosphatidylinositol 3-phosphatase PTEN mRNA, a major negative regulator of PIP3 levels and Akt phosphorylation. PTEN mRNA was also reciprocally regulated by Ube3a dosage: maternal Ube3a knockout mice displayed higher, whereas Ube3a2x mice had lower levels of PTEN mRNA. The application of repeated seizures to Ube3a1x mice impaired social behavior, decreased PTEN mRNA, and increased phospho-AKT. Conclusions: Our results suggest that increases of Ube3a protein in Idic15 may diminish sociability in part through decreases of PTEN. PTEN heterozygosity is found in a subset of patients with autism and comorbid macrocephaly, and genetic deletion of PTEN in mice induces an autism phenotype. Ongoing experiments aim to: i) examine whether Ube3a is necessary for seizure-induced repression of PTEN, ii) implicate specific hippocampal sub-regions in seizure-induced impairments in social behavior (e.g., dentate gyrus versus CA3), iii) identify molecular mechanisms by which seizures repress PTEN expression through Ube3a, and iv) correlate changes in PTEN expression and AKT phosphorylation with changes in PIP3 levels.