Modulation of anxiety-like behavior in galactooligosaccharide-fed mice: A potential role for bacterial tryptophan metabolites and reduced microglial reactivity

• Published in: Brain, behavior, and immunity behavior, and immunity, 2024-10, Vol.121, p.229-243
• Main Authors: Spencer, Kyle D., Bline, Heather, Chen, Helen J., Verosky, Branden G., Hilt, Miranda E., Jaggers, Robert M., Gur, Tamar L., Mathé, Ewy A., Bailey, Michael T.
• Format: Article
• Language: English
• Subjects: Animals; Anxiety - metabolism; Behavior, Animal - drug effects; Chemokine CCL2 - metabolism; Colon - metabolism; Gastrointestinal Microbiome - drug effects; Gastrointestinal Microbiome - physiology; Male; Mice; Mice, Inbred C57BL; Microglia - metabolism; Oligosaccharides - administration & dosage; Oligosaccharides - metabolism; Oligosaccharides - pharmacology; Prebiotics - administration & dosage; Prefrontal Cortex - metabolism; Tryptophan - metabolism; Tumor Necrosis Factor-alpha - metabolism
• ISSN: 0889-1591; 1090-2139; 1090-2139
• DOI: 10.1016/j.bbi.2024.07.024

•Prebiotic galactooligosaccharide significantly reduced anxiety-like behavior as well as brain cytokine and chemokine gene expression.•Prebiotic galactooligosaccharide also increased colonic Akkermansia and Lachnospiraceae_UCG.006 relative abundances and altered the colonic and serum metabolomes.•The abundance of the bacterial metabolite methyl-indole-3-acetate (methyl-IAA) in the serum was directly correlated with anxiety-like behavior in mice given prebiotic galactooligosaccharide.•Administering methyl-IAA reduced brain cytokine gene expression and anxiety-like behavior.•A pathway is proposed wherein prebiotic galactooligosaccharide increases the abundance of bacteria, such as Akkermansia and Lachnospiraceae spp, that metabolize dietary tryptophan to produce indole-derivatives that reduce microglial activity and anxiety-like behavior. Prebiotic galactooligosaccharides (GOS) reduce anxiety-like behaviors in mice and humans. However, the biological pathways behind these behavioral changes are not well understood. To begin to study these pathways, we utilized C57BL/6 mice that were fed a standard diet with or without GOS supplementation for 3 weeks prior to testing on the open field. After behavioral testing, colonic contents and serum were collected for bacteriome (16S rRNA gene sequencing, colonic contents only) and metabolome (UPLC-MS, colonic contents and serum data) analyses. As expected, GOS significantly reduced anxiety-like behavior (i.e., increased time in the center) and decreased cytokine gene expression (Tnfa and Ccl2) in the prefrontal cortex. Notably, time in the center of the open field was significantly correlated with serum methyl-indole-3-acetic acid (methyl-IAA). This metabolite is a methylated form of indole-3-acetic acid (IAA) that is derived from bacterial metabolism of tryptophan. Sequencing analyses showed that GOS significantly increased Lachnospiraceae UCG006 and Akkermansia; these taxa are known to metabolize both GOS and tryptophan. To determine the extent to which methyl-IAA can affect anxiety-like behavior, mice were intraperitoneally injected with methyl-IAA. Mice given methyl-IAA had a reduction in anxiety-like behavior in the open field, along with lower Tnfa in the prefrontal cortex. Methyl-IAA was also found to reduce TNF-α (as well as CCL2) production by LPS-stimulated BV2 microglia. Together, these data support a novel pathway through which GOS reduces anxiety-like behaviors in mice and suggests that the bacterial metabo