Abstract

Investigating Role of Gut-derived Acetate in A Mouse Model of Autism Spectrum Disorder

Background:  Mounting evidence demonstrates a role for the gut microbiome in Autism Spectrum Disorder (ASD), with signaling via microbially produced metabolites being one potential mechanism. In particular the  short chain fatty acids (SCFA) such as acetate have received attention for their ability to influence brain and behavior. In order to investigate this, here we combine antibiotic (Abx) depletion of the microbiome with acetate replenishment in a genetic model of ASD – deletion of the Shank3 gene (Shank3KO).  This gene x microbiome model allows interrogation of shifts in both microbiome and metabolome composition on brain and behavior in a model of ASD. Moreover, to begin assessing the clinical relevance of findings from the mouse model, we also carried out targeted serum SCFA metabolomic analysis in human Phelan McDermid (PMS) patients who are hemizygous for the Shank3 gene.

Methods: Shank3KO mice and wild-type (Wt) littermates were divided into control, Abx depletion, acetate replenishment and acetate + Abx groups at weaning. On postnatal day 60, animals were subjected to behavioral testing using three-chambered social interaction and open field. Caecal content was collected for 16S sequencing and metabolomic profiling and medial prefrontal cortex (mPFC) taken for gene expression profiling as well as western blot analysis. Serum from male and female PMS patients and their control counterparts was collected for targeted SCFA analysis.

Results: Shank3KO in mice causes baseline alterations in microbiome composition at the phylum and class levels as well as altered levels of SCFAs including acetate – effects that were exacerbated by Abx treatment. Behaviorally, control KO mice demonstrated decreased social interaction, a deficit exacerbated following Abx treatment. RNA-sequencing showed marked changes in gene expression related to epigenetic regulation and synaptic plasticity in Abx+KO mice compared to Wt, while western blot analysis demonstrated imbalance between histone acetylation and methylation in mPFC Abx+KO mice. Treatment of KO animals with acetate or Abx + acetate reversed the social deficits reported accompanied by changes to acetylation of specific histone marks. Human PMS patients were found to have sex specific alterations in SCFA levels including acetate, which correlated with clinical behavioral measures.

Conclusions: Our rodent data identified an altered gut microbiome and acetate levels in the Shank3KO model which can be targeted to reverse core social deficits possibly via epigenetic mechanisms. Clinical data corroborate findings of altered gut derived metabolites in PMS and add sex differences as a variable for further investigation.