The autism-associated Neuroligin-3 R451C mutation alters mucus density and the spatial distribution of bacteria in the mouse gastrointestinal tract

The intestinal mucus layer protects the host from invading pathogens and is essential for maintaining a healthy mucosal microbial community. Alterations in the mucus layer and composition of mucus-residing microbiota in people diagnosed with Autism Spectrum Disorder (ASD; autism) may contribute to dysbiosis and gastrointestinal (GI) dysfunction. Although microbial dysbiosis based on sequencing data is frequently reported in autism, spatial profiling of microbes adjacent to the mucosa is needed to identify changes in bacterial subtypes in close contact with host tissues. Here, we analysed the spatial distribution of the MUC-2 protein using immunofluorescence as well as total bacteria, Bacteroidetes, Firmicutes phyla and Akkermansia muciniphila (A. muciniphila) using fluorescent in situ hybridization in mice expressing the autism-associated R451C mutation in the Neuroligin-3 (Nlgn3) gene. We show that the Nlgn3 R451C mutation increases mucus density adjacent to the distal ileal epithelium in mice. The relative density of total bacteria, Firmicutes and A. muciniphila was increased whereas the density of Bacteroidetes was decreased closer to the epithelium in Nlgn3R451C mice. In summary, this study suggests that increased mucus density could contribute to mucosal microbial dysbiosis in ASD.