The influence of dietary zinc treatment on the gut microbiome of a mouse model of autism

Abstract

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterised by impairments in social interactions and increased stereotypical repetitive behaviour. The high prevalence of gastrointestinal problems in people with ASD may relate to an underlying imbalance (dysbiosis) in the gut microbial community, though the extent of the microbial involvement in ASD remains unclear. Shank3 gene mutations adversely affect brain synapse structure and are implicated in ~1% of autism cases. Zinc is a key element required for SHANK proteins, in a mouse model of ASD based on a Shank3B-/- mutation, a high zinc diet shows promise in reversing ASD-like behaviours as well as deficiencies in brain synapse structure. The intent of this research is to determine the effect of dietary zinc on the Shank3B-/- mouse gut microbiome. Specifically, this research aims to: (1) determine the gut microbial composition in Shank3B-/- mice that have been subjected to different dietary zinc treatments; (2) establish the functional profiles of these gut microbes. Gut tissue (ileum, caecum, colon) and faecal samples were collected for Shank3B-/- and wild type Shank3B+/+ mice. DNA was extracted and bacterial 16S rRNA genes amplified by PCR for subsequent sequencing using Illumina MiSeq. A subset of the faecal samples was also sequenced using shotgun metagenomics to explore the functional potential of these gut microbes. The 16S rRNA gene amplicon sequencing revealed that the dominant bacterial phyla were Firmicutes, Bacteroidetes and Verrucomicrobia, with notable genera including the mucin degrader Akkermansia and ‘Homeothermaceae’ (family S24-7), a widely found homoeothermic gut microbe. At the overall community level, the mouse gut microbiota did not exhibit major changes in composition among treatment groups. Instead, the majority of the gut microbiota variation was attributed to cage type effects. However, there were major differences between treatment groups based on the abundances of membrane transporter and various zinc metalloenzyme-associated genes. This suggests that dietary zinc treatment and genetic background contribute to functional changes in the gut microbiota. This thesis describes the first characterisation of the gut microbiota in Shank3B-/- mice, witin the overall framework of a research programme striving to find a treatment for people with ASD who require it and seek treatment.