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Longitudinal Behavioural Study of Shank3 KO Mice Combined with Rnaseq Analyses Reveals New Candidate Modifier Genes for Autism
Autism Spectrum disorders (ASD) are neurodevelopmental conditions affecting more than 1% of the population. Diagnosis is based on two main criteria: alteration of social communication and interaction as well as repetitive and stereotyped behaviours (DSM-5). Among the ASD-risk genes, SHANK3 encodes a scaffolding protein at the postsynaptic density (PSD) of glutamatergic synapses. A meta-analysis of SHANK mutations in ASD estimated that 1-2% of patients with ASD and intellectual disability (ID) are carrying a de novo deleterious mutation in SHANK3. SHANK3 is also deleted in the vast majority of the patients with Phelan-McDermid syndrome (PMS). Many patients carrying a mutation in SHANK3 or diagnosed with PMS show a worsening of the phenotype in adolescence or early adulthood (i.e. a behavioural decline). Several laboratories have generated mouse models lacking Shank3 to understand the biological role of this protein, but none of these studies analysed the progression of the phenotype during development.
Objectives:
In the present study, we tested whether a mouse model mutated in Shank3, namely Shank3Δex11 displayed a worsening of the phenotype when aging. We therefore studied the stability of the phenotype in this mouse model by following the same individuals in adulthood, over their first year of life.
Methods:
The Shank3Δex11 mouse model carries a deletion of exon 11, involved in the SH3 domain (Src homology 3 domain). We characterised the same individuals at 3, 8 and 12 months of age. We tested homozygous wild-type, heterozygous and homozygous knock-out littermates of both sexes. We focused on locomotion/exploration, social and stereotyped behaviours at the three times points. We conducted comparisons between genotypes at each times point, but also within genotypes over the three time points. At twelve months of age, the brain from each animal was extracted and dissected. RNA sequencing was performed on four brain regions: cortex, hippocampus, striatum and cerebellum.
Results:
At 3 months of age, the Shank3-KO mice displayed a significant decrease in locomotion, a significant increase in self-grooming, but mild impairments in social interactions in comparison with wild-type littermates.
Between 3,8 and 12 months of age, 7 out of 12 males and 4 out of 12 female Shank3-KO mice displayed a worsening of the phenotype, with a drastic increase in self-grooming. Interestingly, 4 males and 5 females Shank3-KO mice with a lower level of grooming at 3 months remained stable at 1 year. RNA sequencing data already revealed several genes differentially expressed between wild-type littermate and Shank3-KO mice. These results point at some biological pathways that could be influenced by the absence of Shank3. Further data on the comparison between the RNA level and the level of grooming will be presented.
Conclusions:
These data showed that some Shank3Δex11 mutant individual mice displayed a worsening of the phenotype, reminiscent to what is observed in patients carrying a mutation in Shank3. These inter-individual variations remain to be better understood in order to identify spontaneous compensations. This should provide new pathways for innovative knowledge-based treatments.