Exaggerated translation causes synaptic and behavioural aberrations associated with autism

Autism spectrum disorders (ASDs) are an early onset, heterogeneous group of heritable neuropsychiatric disorders with symptoms that include deficits in social interaction skills, impaired communication abilities, and ritualistic-like repetitive behaviours. One of the hypotheses for a commonmolecular mechanism underlying ASDs is altered translational control resulting in exaggerated protein synthesis. Genetic variants in chromosome 4q, which contains theEIF4E locus,have beendescribed inpatientswithautism. Importantly, a rare single nucleotide polymorphism has been identified in autism that is associated with increased promoter activity in the EIF4E gene. Here we show that genetically increasing the levels of eukaryotic translation initiation factor 4E (eIF4E) inmice results in exaggerated cap-dependent translation and aberrant behaviours reminiscent of autism, including repetitive and perseverative behaviours and social interaction deficits. Moreover, these autistic-like behaviours are accompanied by synaptic pathophysiology in themedial prefrontal cortex, striatumandhippocampus. The autistic-like behaviours displayed by the eIF4E-transgenic mice are corrected by intracerebroventricular infusions of the capdependent translation inhibitor 4EGI-1. Our findings demonstrate a causal relationship between exaggerated cap-dependent translation, synaptic dysfunction and aberrant behaviours associated with autism. eIF4E-transgenic mice (bT-Eif4e) exhibited increased levels of eIF4E across brain regions (Fig. 1a) without compensatory changes in levels of other translational control proteins (Fig. 1b). We investigated whether eIF4E was bound preferentially to either eIF4E-binding protein (4E-BP) or eIF4G, which repress and promote, respectively, the initiation of cap-dependent translation. We found significantly higher levels of eIF4E–eIF4G interactions in the brains of eIF4Etransgenic mice (Fig. 1c and Supplementary Fig. 1a), with no alterations in the interaction between eIF4E and 4E-BP (Fig. 1c, left, and Supplementary Fig. 1a). To confirm that the increased eIF4E–eIF4G interactions resulted in increased protein synthesis, we infused puromycin into the lateral ventricle of cannulated mice and labelled newly synthesized proteins using SUnSET, and observed increased de novo cap-dependent translation (Fig. 1d and Supplementary Fig. 1b–g). Overall, our results indicate that overexpression of eIF4E results in exaggerated cap-dependent translation in the brains of eIF4E-transgenic mice. We then determined whether eIF4E-transgenic mice display repetitive and perseverative behaviours, which are behavioural domains required for ASD diagnosis. eIF4E-transgenic mice exhibited repetitive digging behaviour in the marble-burying test and increased selfgrooming compared with wild-type littermate controls (Fig. 2a, b). eIF4E-transgenic mice also displayed cognitive inflexibility in both a water-based Y-maze task and a modified version of the Morris water maze. Learning ability in the acquisition and memory phases of these tasks was intact; however, in the reversal phases, eIF4E-transgenic mice were impaired in locating the new platform positions (Fig. 2c, d and Supplementary Fig. 2e–h). We tested an additional form of behavioural inflexibility by examining the eIF4E-transgenicmice for extinction of cued fear conditioning and found that they did not exhibit a significant reduction in freezing responses after extinction training (Fig. 2e). These experiments suggest that excessive cap-dependent translation in the brain affects the ability to suppress previously codified response patterns and the ability to form new behavioural strategies in response to changed environmental circumstances. Abnormalities in social interaction skills are another behavioural defect displayed by individuals with ASDs. In tests to examine social behaviour, the eIF4E-transgenic mice did not show a preference for a nonspecific stranger versus a new, inanimate object (Fig. 2f, g). Moreover, eIF4E-transgenic mice exhibited diminished reciprocal interactions with a freely moving stranger mouse (Fig. 2h), further evidence of deficits in social behaviour. The deficits in social behaviour of the eIF4E-transgenic mice are unlikely to be caused by a generalized increase in anxiety (Supplementary Fig. 2c, d, j). Moreover, the eIF4Etransgenicmice exhibitedmild hyperactivity (Supplementary Fig. 2a, b), but no impairments in motor coordination, motor learning and sensorimotor gating (Supplementary Fig. 2i, k, l). Taken together, our behavioural analysis of the eIF4E-transgenic mice indicates that increased cap-dependent translation in the brain results in a distinct pattern of behavioural abnormalities consistent with ASDs. Previous studies suggest that ASD symptoms such as cognitive inflexibility and deficits in social behaviour are generated by abnormalities in prefrontal and/or striatal circuits. Consistent with this idea, the medial prefrontal cortex (PFC) is implicated in the modulation of social behaviours and social skills, whereasmotor, social and communication impairments in boys with ASDs are associated with anatomical abnormalities in the striatum.Therefore,wenext examined whether the eIF4E-transgenic mice exhibited specific synaptic pathophysiologies in the medial PFC and striatum. In the eIF4E-transgenic mice, examination of spontaneous synaptic ‘mini’ events in layers 2/3 of acute medial PFC slices revealed an increase in the frequency but not amplitude of excitatory events (miniature excitatory postsynaptic currents (mEPSCs); Fig. 3a), and an increase in the amplitude, but not frequency, of inhibitory events (miniature inhibitory postsynaptic currents (mIPSCs); Fig. 3b). No changes were observed in layer 5 (Supplementary Fig. 3a, b). Thus, our data suggest an enhancement of excitatory input and postsynaptic sensitivity for inhibitory events onto layer 2/3 pyramidal neurons, consistentwith the hypothesis that autismmay arise froman imbalance between excitatory and inhibitory synaptic transmission. To determine whether the increased frequency of spontaneous mEPSCs might result from an enhanced number of synaptic contacts, we imaged dendritic spines using two-photon laser-scanning