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Depletion and Reconstitution of Macrophages in Mice
Published on: August 1, 2012
The gut microbial metabolite trimethylamine N-oxide aggravates GVHD by inducing M1 macrophage polarization in mice
Kunpeng Wu1, Yan Yuan1, Huihui Yu1
1Department of Hematology, Huashan Hospital, Fudan University, Shanghai, China; and.
Abstract:
The diversity of the human microbiome heralds the difference of the impact that gut microbial metabolites exert on allogenic graft-versus-host (GVH) disease (GVHD), even though short-chain fatty acids and indole were demonstrated to reduce its severity. In this study, we dissected the role of choline-metabolized trimethylamine N-oxide (TMAO) in the GVHD process. Either TMAO or a high-choline diet enhanced the allogenic GVH reaction, whereas the analog of choline, 3,3-dimethyl-1-butanol reversed TMAO-induced GVHD severity. Interestingly, TMAO-induced alloreactive T-cell proliferation and differentiation into T-helper (Th) subtypes was seen in GVHD mice but not in in vitro cultures. We thus investigated the role of macrophage polarization, which was absent from the in vitro culture system. F4/80+CD11b+CD16/32+ M1 macrophage and signature genes, IL-1β, IL-6, TNF-α, CXCL9, and CXCL10, were increased in TMAO-induced GVHD tissues and in TMAO-cultured bone marrow-derived macrophages (BMDMs). Inhibition of the NLRP3 inflammasome reversed TMAO-stimulated M1 features, indicating that NLRP3 is the key proteolytic activator involved in the macrophage's response to TMAO stimulation. Consistently, mitochondrial reactive oxygen species and enhanced NF-κB nuclear relocalization were investigated in TMAO-stimulated BMDMs. In vivo depletion of NLRP3 in GVHD recipients not only blocked M1 polarization but also reversed GVHD severity in the presence of TMAO treatment. In conclusion, our data revealed that TMAO-induced GVHD progression resulted from Th1 and Th17 differentiation, which is mediated by the polarized M1 macrophage requiring NLRP3 inflammasome activation. It provides the link among the host choline diet, microbial metabolites, and GVH reaction, shedding light on alleviating GVHD by controlling choline intake.
Insights
Trimethylamine N-oxide (TMAO), a metabolite from choline, exacerbates graft-versus-host disease (GVHD) by promoting M1 macrophage polarization and T-cell differentiation. Inhibiting NLRP3 inflammasome activation can reverse this TMAO-induced GVHD severity.
Area of Science:
- Immunology
- Microbiome Research
- Transplantation Science
Background:
- Gut microbial metabolites significantly influence graft-versus-host disease (GVHD) severity.
- While some metabolites like short-chain fatty acids and indole reduce GVHD, the role of others, such as trimethylamine N-oxide (TMAO), remains less understood.
- TMAO is derived from dietary choline metabolism by gut microbes.
Purpose of the Study:
- To investigate the specific role of the choline-metabolized product, TMAO, in the pathogenesis of allogenic graft-versus-host disease (GVHD).
- To elucidate the underlying mechanisms by which TMAO influences immune responses in GVHD.
- To identify potential therapeutic targets for mitigating TMAO-induced GVHD.
Main Methods:
- Studies were conducted in mouse models of GVHD, comparing the effects of TMAO administration and high-choline diets.
- In vitro and in vivo experiments assessed T-cell proliferation and differentiation, macrophage polarization (M1 phenotype), and the involvement of the NLRP3 inflammasome.
- Key molecular pathways, including mitochondrial reactive oxygen species and NF-κB signaling, were investigated in TMAO-stimulated macrophages.
Main Results:
- Both TMAO and a high-choline diet significantly enhanced the allogenic GVH reaction.
- TMAO promoted T-helper (Th) 1 and Th17 cell differentiation, a process dependent on M1 macrophage polarization.
- The NLRP3 inflammasome was identified as a critical mediator of TMAO-induced M1 macrophage activation, with its inhibition reversing GVHD severity.
Conclusions:
- TMAO derived from dietary choline metabolism plays a crucial role in exacerbating GVHD.
- The mechanism involves TMAO-induced M1 macrophage polarization via NLRP3 inflammasome activation, leading to Th1/Th17 cell differentiation.
- Targeting the NLRP3 inflammasome or controlling choline intake presents a potential strategy for alleviating GVHD.
