Gut microbial metabolites sulfonolipids mediate high fat diet-induced intestinal inflammation

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High fat diets (HFDs) alter both host inflammatory responses and gut microbial metabolites. While these metabolites have been hypothesized to mediate host intestinal inflammation, an existing gap is how to pinpoint the functional and responsible metabolites from an extremely complicated metabolites pool that contains numerous unknown chemicals. We seek to discover such functional metabolites and establish their role in modulating HFDs-induced intestinal inflammation. In our preliminary study, we first established a mouse model that displayed HFDsinduced intestinal inflammation. We next performed comparative metagenomic analysis of the gut microbiome collected from aforementioned mice, leading to identification of a genus, Alistipes, which was significantly increased during HFDs-induced inflammation. Alistipes is isolated primarily from clinical samples and shows emerging implications to inflammation, motivating us to investigate the potential links between Alistipes metabolites and the observed intestinal inflammation of our mouse model. Thus, we developed complementary metabolomics and genome mining approaches: metabolomic analysis of the mice fecal and serum samples directly displayed metabolic changes while genome mining revealed unique patterns of biosynthetic gene clusters that encode the metabolites of interests. Indeed, the cross-validation of these two approaches led to the discovery of a class of rare lipids, sulfonolipids (SLs) which were significantly increased in the HFDs-fed mice samples. The potential biosynthetic genes of these SLs were also accumulated in the HFDs-fed mice samples. The pure SLs were subsequently isolated, with the chemical structures elucidated by NMR. We then tested sulfobacin A, a major member of the isolated SLs, and it indeed induced macrophage RAW264.7 inflammatory responses by RT-PCR and ELISA analyses. All these preliminary data suggest that gut microbial metabolites SLs mediate HFDsinduced intestinal inflammation. Intriguingly, SLs structurally mimic human endogenous sphingolipids (SPs), with the latter known to mediate inflammation. In addition, a genus of gut microbiota, bacteroides, also produces SPs but not SLs. The bacteroidesderived SPs were recently shown to enter hosts’ metabolism and are critical for maintaining intestinal homeostasis and symbiosis. Taken together, this raises an interesting hypothesis that SLs may directly induce inflammation, but also may modulate inflammation by affecting intestinal homeostasis of SLs and SPs. Thus, we are now set up to unambiguously establish, both in vitro and in vivo, the role of SLs in mediating HFDsinduced intestinal inflammation, with an emphasis on the potential relationship between SLs and SPs. This goal will be achieved through completion of the following Specific Aims (SA). SA 1: Characterizing the HFDs-associated expression of microbial SLs, microbial SPs and host endogenous SPs. SA 2: Investigate the activities and relationship of SLs and SPs in mediating intestinal inflammation, using both invitro assays and in vivo germ-free mouse models. in vitro and in vivo, the role of SLs in mediating HFDs-induced intestinal inflammation, with an emphasis on the potential relationship between SLs and SPs. This goal will be achieved through completion of the following Specific Aims (SA).