Abstracts

Rationale: Infantile Spasms (IS) constitute a devastating childhood epilepsy syndrome, characterized by neonatal spasms, chronic seizures throughout life, and developmental delays. Effective treatments are largely lacking because the pathophysiologic changes that cause IS are poorly defined. A significant barrier is the lack of animal models. We have generated two new genetic mutant mouse models that show characteristics of IS and suggest a central role for deregulation of β-catenin and its associated pathways.Methods: To generate mice with conditional knockout of adenomatous polyposis coli protein (APC cKO), we used CamKII-Cre recombinase-mediated homologous recombination to delete floxed APC in neurons during synaptic differentiation (Mohn et al., 2014). To generate β-catenin conditional overexpression mice (β-cat cOE), we used CamKII-Cre to delete the floxed degradation domain in β-cat. Littermates, negative for Cre, were used as controls in all experiments. The mice were assessed using multi-disciplinary approaches including behavioral spasms in neonates, EEG recordings in neonates and adults, whole-cell recordings of synaptic activity, immunoblotting, and synaptic spine density analysis.Results: Both APC cKO and β-cat cOE mice exhibit characteristics associated with IS, as well as cognitive impairments and autism-like behaviors, known co-morbidities of IS. APC is the major negative regulator of β-cat levels in the canonical Wnt signaling pathway. β-cat, in turn, has dual roles in the N-cadherin synaptic adhesion complex and the canonical Wnt pathway; both are critical for normal brain circuit formation and function. Neonatal APC cKO and β-cat cOE mice display spasms (increased high amplitude spontaneous movements) and spend more time on their side, compared with control littermates. At adult ages, both mutant mouse models exhibit spontaneous seizures. EEG recordings show abnormal cortical circuit activity and seizures in neonatal and adult APC cKOs. Cortical hyperexcitability is further indicated by increased spontaneous and evoked excitatory electrical activity, as well as increased synaptic spine density, in cortical layer 5 pyramidal neurons. At the molecular level, there are increases in β-cat protein, canonical Wnt target gene expression, and β-cat association with N-cadherin, indicative of altered synaptic stability and plasticity.Conclusions: Our APC cKO and β-cat cOE mice recapitulate key features of human IS. Our findings strongly link deregulation of β-cat networks to IS. Intriguingly, several genes implicated in human IS, including FoxG1, ARX, TSC1/2 and Magi-2/S-SCAM (Paciorkowski et al., 2011), are predicted to affect β-cat synaptic scaffolds and the canonical Wnt pathway. We propose a novel molecular etiology of IS that is centered on aberrant β-cat networks. Defining new molecular targets is essential for developing novel and effective therapeutic interventions to ameliorate this devastating condition. This work is funded by CURE.