Melatonin ameliorates autistic-like behaviors by restoring gut microbiota-derived tryptophan metabolites

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social deficits and repetitive stereotyped behavior. Disrupted microbiota‒gut‒brain axis (MGBA) signaling contributes to the pathology of ASD and cognitive disability. Melatonin (MT), a naturally occurring compound, has shown potential in ameliorating core symptoms of ASD and mitigating gut microbiota dysbiosis, yet the underlying mechanism is poorly understood. This study aimed to investigate whether exogenous melatonin improves behavioral deficits in valproic acid (VPA)-exposed male offspring rats, and the modulation of gut microbiota-derived tryptophan metabolites. In prenatal VPA-induced model rats, microbial diversity and construction was analyzed through metagenomic sequencing, targeted-metabolomics and transcriptomics were conducted to explore related metabolic pathways and molecular profiles. We identified 7 gut bacterial genus causally associated to ASD: Faecali-bacterium, Lachnospiraceae, Ruminococcaceae, Butyricimonas, and Bacteroides exhibited protection, whereas Erysipelotrichaceae and Clostridia enhanced risk. The exacerbation of Erysipelotrichaceae and Clostridia by VPA versus restoration of Faecalibacterium, Butyricimonas, Bacteroides and Bifidobacterium by melatonin, which are known to participate in tryptophan metabolism. Correspondingly, systemic metabolomics pointed to melatonin’s restoration of tryptophan metabolic disorders (IDO1-kynurenine, TPH1/2-serotonin-melatonin, and Indole-3-propionic acid (IPA)) induced by VPA, paralleled the rectification of microglial reactivity, synaptic proteins, dendritic morphology, and hippocampal neurogenesis. These molecular profiles were further integrated by transcriptomics, highlighted tryptophan-derived neurotransmitters and neuroactive ligand-receptor interaction, contributing to enhanced social and cognitive behaviors under melatonin intervention. Based on multi-omic analysis, our findings underscore key bacteria and metabolites contributing to neurological and immune dysfunction in VPA-exposed rats, providing novel targets for possible therapeutics of melatonin.