Fecal microbiota transplantation and <i>Akkermansia muciniphila</i> restore neurodevelopment and behavior <i>via</i> the gut-brain axis in autism-like zebrafish

Effective therapies for Autism Spectrum Disorder (ASD) are currently limited, and the functional connections between gut microbiota and brain development are not fully elucidated. Using the Katnal2 mutant zebrafish as an ASD-like model, we evaluated whether fecal microbiota transplantation (FMT) from wild-type donors or supplementation with the probiotic Akkermansia muciniphila (A. muciniphila) could ameliorate neurodevelopmental deficits. Assessments included developmental phenotypes, behavior, microbial profiling, neurotransmitter-related gene expression, and short-chain fatty acid (SCFA) signaling in conventionally reared (CR) and germ-free (GF) fish. FMT from wild-type donors and A. muciniphila supplementation significantly improved hatching rates, growth parameters, heart rate, and locomotor activity in Katnal2 mutants, whereas microbiota from Katnal2 mutants induced analogous deficits in wild-type recipients. A. muciniphila successfully colonized the gut, reshaped microbial communities, and reduced anxiety-like behaviors. Mechanistically, A. muciniphila upregulates genes involved in dopamine (th), serotonin (tph1a), and gamma-aminobutyric acid (GABA) synthesis, downregulates the serotonin receptor htr3a, and enhances expression of the SCFA receptor ffar2, independently of total SCFA levels. Correlation analyses linked key developmental, behavioral, and transcriptional changes to altered microbial genera in a sample-specific manner, highlighting compositionally driven neuromodulatory effects of genetic and probiotic interventions. Thus, microbiota-targeted intervention with A. muciniphila rescues neurodevelopmental impairments in ASD models by remodeling the gut-brain axis, supporting its translational potential.