The Metabolomic Mind: Microbial Metabolite Programming of Microglia.

Background: The gut microbiota is increasingly recognized as a critical regulator of brain function, influencing neurodevelopment, brain physiology, and disease vulnerability in part through its interactions with microglia, the resident immune cells of the central nervous system. Microbial metabolites, beginning prenatally and persisting throughout the lifespan, modulate fundamental aspects of microglial biology.

Summary: Microglia from germ-free mice exhibit persistent immaturity, altered energy metabolism, and blunted inflammatory responses, which can be partially reversed by microbial colonization or supplementation with specific bacterial metabolites. Short-chain fatty acids, tryptophan-derived indoles, and secondary bile acids have emerged as key microbial mediators that regulate microglial development, metabolism, and immune function, whereas certain inflammatory metabolites, such as trimethylamine n-oxide, disrupt microglial homeostasis, and worsen neurodegeneration.

Key Messages: These findings reveal distinct metabolite-driven pathways linking microbial composition to microglial phenotypes, positioning the microbiome as a potential key influencer of neurodevelopmental trajectories and the pathophysiology of psychiatric and neurological disorders. Despite recent advances, major knowledge gaps persist in understanding the precise molecular intermediaries and mechanisms through which metabolite signaling to microglia shapes susceptibility or resilience to brain-based disorders. Understanding both the bacterial metabolomic landscape and its collective impact on microglial programming holds substantial therapeutic promise, offering avenues to target microbial metabolite production or administer them directly to modulate disease susceptibility.