30950
Role of the Gut Microbiome in Autism-Related Behaviors
Phelan-McDermid syndrome (PMS) is a neurodevelopmental disorder caused by haploinsufficiency of the Shank3 gene. Patients with this mutation are also commonly diagnosed with autism spectrum disorder (ASD). In fact, PMS has been identified as one of the most frequent monogenic causes of ASD. In clinical populations there is marked heterogeneity in the severity of the PMS phenotype, while these differences may be due to variety in the mutations involved, it is important to consider potential contributing environmental influences. Interestingly, a significant subset of patients with ASD present with gastrointestinal disturbances, and sequencing of the gut microbiota has shown significant alterations in the bacterial makeup of stool from patients with ASD. Additionally, there is a large body of evidence linking the composition of the gut microbiome to brain development and behavior. To this end, we investigated changes in gut microbiome and metabolites as well as effects of microbiome depletion in a recently developed Shank3 mouse model with exons 4-22 deleted (SHANK3∆4-22) resulting in knockout of all detectable SHANK3 isoforms.
Objectives:
To examine the effect of Shank3 deletion on the microbiome and metabolome as well as assessing the effects of the lack of a diverse gut microbiome on autism-like behaviors in the SHANK3∆4-22 model.
Methods:
Heterozygous SHANK3∆4-22 breeders produced (Wt), heterozygous and homozygous KO offspring. Offspring (both males and females) were weaned on postnatal day (PND) 21 and split into two treatment groups – control drinking water and antibiotic depletion (Abx). The Abx group received a cocktail of broad spectrum non-absorbable antibiotics (Bacitracin 0.5mg/ml, Neomycin 2mg/ml, Vancomycin 0.2mg/ml, Pimaricin 1.2ug/ml) via their home cage drinking water, while the control groups received untreated water. When animals reached PND60 they were subjected to behavioral tests including three-chambered social interaction, marble burying and open field. After behavioral assessment animals were culled and brains were collected for molecular analysis and cecal contents for 16S rRNA sequencing and metabolomic profiling.
Results:
Cecal content analysis demonstrated marked differences in microbiome composition at the phylum and class level between SHANK3∆4-22 KO and Wt controls. Additionally, SHANK3∆4-22 KO mice were found to have an altered cecal metabolic profile as shown by increased levels of a number of amino acids including phenylalanine and methionine, as well as decreases in levels of several short-chain fatty acids. Behaviorally, SHANK3 ∆4-22 Het & SHANK3∆4-22 KO mice demonstrated decreased social interaction compared to Wt in the three-chambered social interaction paradigm and this deficit was exacerbated by microbiome depletion.
Conclusions:
Mice constitutively lacking the Shank3 gene demonstrate alterations in the content of their gut flora and the resultant metabolome even when diet and environment are controlled. Additionally, the autistic-like behaviors seen in SHANK3 ∆4-22 mutant mice are influenced by alterations to the endogenous flora. Taken together, these studies suggest a gene x microbiome interaction may be contributing to the phenotype of PMS. Although these findings are preliminary, they raise the possibility that interventions targeted at normalizing the gut flora and metabolome may have translational potential in PMS or other causes of ASD.