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The microbiome protects against septic hyperinflammation and bacterial proliferation in a zebrafish model of blood infection with E.coli and mycobacteria

ABSTRACT: The microbiome is an important immune regulator, but the mechanisms by which commensal microbes shape systemic host defense during bloodstream infection remain poorly defined and commonly used pre-clinical models have practical, ethical and scientific limitations. Here, we establish a gnotobiotic zebrafish larval model to investigate microbiome-dependent protection against systemic blood infection by E. coli bacteria, an important cause of early onset neonatal sepsis and nontuberculous mycobacteria to investigate the contribution of Toll-like receptor 2 (TLR2) in the defense responses. Germ-free (GF) and conventionalized (CONVD) larvae derived from the same clutches were systemically infected with E. coli, revealing that microbiome colonization significantly reduces early mortality. RNA-seq revealed a conserved core immune activation program in both GF and CONVD larvae, but the absence of a microbiome was associated with a broader transcriptional response and stronger repression of metabolic pathways, suggesting that commensal microbes buffer infection-induced metabolic suppression. Extending this framework to nontuberculous mycobacteria, we performed systemic infections with fluorescent Mycobacterium marinum and M. avium in tlr2 wild-type and mutant larvae under GF and CONVD conditions. While survival was largely unchanged, imaging-based quantification demonstrated increased bacterial proliferation in tlr2 mutants and in GF larvae, with microbiome-mediated restriction of bacterial burden evident in wild-type but not tlr2-deficient hosts. Together, these data show that microbiome colonization buffers septic outcomes by reshaping systemic inflammatory and metabolic programs, and identify TLR2 as a key node linking microbial colonization to effective host defense during nontuberculous mycobacterial infection

ORGANISM(S): Danio rerio

PROVIDER: GSE325739 | GEO | 2026/03/24

REPOSITORIES: GEO

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Project description:Background: Toll-like receptor 2 (TLR2) plays a pivotal role in innate immunity and has recently emerged as a criti-cal regulator of host-microbiome interactions. However, how TLR2 influences host transcriptional responses to colonized microbiome and microbial community dynamics remains largely unclear. Germ free (GF) and conven-tionalized zebrafish (Danio rerio) model provides a valuable system to study microbiome functions. Results: RNAseq analysis revealed that transcriptomic alterations resulted from tlr2 mutation were more extensive in the presence of the microbiome than under the GF condition, indicating that tlr2 mutation has a more pro-nounced impact on host transcriptional responses when microbial signals are present. KEGG enrichment analyses showed an enhanced host response to the energy metabolism in the presence of microbial stimuli resulting from tlr2 deficiency. In addition, microbiome colonization elicited a broader transcriptional response in tlr2 wild-type larvae than in the mutants, highlighting the essential role of tlr2 in regulating host transcriptomic programs in re-sponse to microbial signals. In terms of how tlr2 influences microbial composition, 16S rRNA gene sequencing showed that tlr2 mutants exhibited higher microbial diversity during early development, whereas adult microbial diversity was highest in wild-type males, indicating a developmental stage- and sex-specific restructuring of the gut microbiome. For larvae at the genus level, tlr2 mutant larvae showed increased Chryseobacterium and Flecto-bacillus but reduced Gracilibacteria abundance relative to wild-type controls. For adult gut samples, the relative abundance of Cetobacterium was lower, while genera such as Romboutsia, Aeromonas and Pseudarthrobacter were more abundant in tlr2 wild-type male group compared to other groups. Predicted functional analyses revealed that tlr2 deficiency induced complex alterations in microbial metabolic pathways, with distinct pathway enrichments observed between larval and adult stages. Conclusions: TLR2 not only modulates host transcriptional responses to microbial colonization but also shapes gut microbial diversity, composition, and metabolic potential. Our findings highlight the critical role of TLR2 in orchestrating immunometabolic homeostasis and provide new insights into its broader function in maintaining host-microbiota symbiosis across developmental stages.

Project description:Mechanisms through which the microbiome communicates with the systemic immune system remain unclear. We have identified a family of microbiome Bacteroidota-derived lipopeptides – the serine-glycine (S/G) lipids, and specifically L654 – that are TLR2 ligands, access the systemic circulation, and potentially link the microbiome and systemic innate immunity. We have previously postulated that L654 and the S/G lipids regulate systemic innate immunity by entering the systemic circulation and mediating weak TLR2 interactions that maintain “normal” levels of innate immune signaling feedback inhibitors. In proof-of-concept studies, we reported that increasing systemic L654 levels in mice by administering exogenous L654 intravenously significantly diminishes systemic innate immune responses and attenuates murine autoimmunity. In the present study, our goal was to confirm the role of the microbiome in mediating this mode of immunoregulation by decreasing the microbiome-based production of S/G lipids. We now report that decreasing microbiome Bacteroidota in mice using a specific oral antibiotic/rest protocol reduces fecal and plasma S/G lipids levels and significantly enhances systemic innate immune responses. Replenishing systemic levels of S/G lipids after antibiotic treatment through exogenous administration of L654 returns innate immune responses to normal levels, confirming the regulatory role of S/G lipids in this mode of microbiome regulation. Finally, RNAseq analysis of splenic monocytes derived from antibiotic-treated and control mice prior to ex vivo stimulation demonstrates that the antibiotic/rest protocol and the concomitant decrease in microbiome S/G lipids and Bacteroidota has significant downregulatory effects on normal homeostatic pro-inflammatory pathways. These effects are also associated with downregulation of specific proinflammatory pathway inhibitors, which may suggest a potential mechanism underlying the enhancement in ex vivo innate immune stimulated responses of these monocytes. Overall, our results suggest that S/G lipids are microbiome-derived bacterial factors capable of regulating systemic innate immunity and as such are manipulatable targets with therapeutic potential for enhancing or decreasing innate immunity in the context of infectious, malignant, and autoimmune diseases.

Project description:Mechanisms through which the microbiome communicates with the systemic immune system remain unclear. We have identified a family of microbiome Bacteroidota-derived lipopeptides – the serine-glycine (S/G) lipids, and specifically L654 – that are TLR2 ligands, access the systemic circulation, and potentially link the microbiome and systemic innate immunity. We have previously postulated that L654 and the S/G lipids regulate systemic innate immunity by entering the systemic circulation and mediating weak TLR2 interactions that maintain “normal” levels of innate immune signaling feedback inhibitors. In proof-of-concept studies, we reported that increasing systemic L654 levels in mice by administering exogenous L654 intravenously significantly diminishes systemic innate immune responses and attenuates murine autoimmunity. In the present study, our goal was to confirm the role of the microbiome in mediating this mode of immunoregulation by decreasing the microbiome-based production of S/G lipids. We now report that decreasing microbiome Bacteroidota in mice using a specific oral antibiotic/rest protocol reduces fecal and plasma S/G lipids levels and significantly enhances systemic innate immune responses. Replenishing systemic levels of S/G lipids after antibiotic treatment through exogenous administration of L654 returns innate immune responses to normal levels, confirming the regulatory role of S/G lipids in this mode of microbiome regulation. Finally, RNAseq analysis of splenic monocytes derived from antibiotic-treated and control mice with or without exogenous L654 prior to ex vivo stimulation demonstrates that the antibiotic/rest protocol and the concomitant decrease in microbiome S/G lipids and Bacteroidota has significant downregulatory effects on normal homeostatic pro-inflammatory pathways. These effects are also associated with downregulation of specific proinflammatory pathway inhibitors, which may suggest a potential mechanism underlying the enhancement in ex vivo innate immune stimulated responses of these monocytes. Overall, our results suggest that S/G lipids are microbiome-derived bacterial factors capable of regulating systemic innate immunity and as such are manipulatable targets with therapeutic potential for enhancing or decreasing innate immunity in the context of infectious, malignant, and autoimmune diseases.

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The microbiome protects against septic hyperinflammation and bacterial proliferation in a zebrafish model of blood infection with E.coli and mycobacteria

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