The gut-immune-brain axis in CNS tumors: Causal roles of microbiota and inflammatory proteins unveiled by Mendelian randomization and single-cell transcriptomics.

There is a growing number of research suggesting that there is an association between gut microbiota and central nervous system (CNS) tumor. However, the causal relationships and the mediation effects of inflammatory proteins in the associations are unclear. We extracted genetic variants associated with gut microbiota, inflammatory proteins, and 4 subtypes of CNS tumors from published genome-wide association studies and performed a Mendelian randomization analysis to identify potential causal effects. The inverse variance weighted method was used as the main method. Mediation analysis and single-cell RNA-seq analysis were performed to explore the mediation effects and the expression in cells. This study identified 73 gut microbial taxa and 11 inflammatory proteins that were significantly associated with CNS tumors. The inflammatory proteins may act as intermediate mediators in the potential causal association between gut microbiota and 4 CNS tumor subtypes. Mediation analysis suggested that CX3CL1 may partially mediate the relationship between gut microbiota and Glioblastoma, while Eotaxin, CSF-1, IL-15RA and the other 5 cytokines may serve as subtype-specific potential mediators for the remaining 3 tumor types. Our research supports a hypothesized "gut-immune-brain" axis that may mediate the effects of gut microbiota on different CNS tumor subtypes, with distinct immune proteins implicated for each. These findings strongly suggest potential targets for microbiome therapy and immune therapy, though the underlying mechanistic links require experimental validation.