Dietary-fat-induced taurocholic acid promotes pathobiont expansion and colitis in Il10-/- mice

Abstract

The composite human microbiome of Western populations has probably changed over the past century, brought on by new environmental triggers that often have a negative impact on human health. Here we show that consumption of a diet high in saturated (milk-derived) fat, but not polyunsaturated (safflower oil) fat, changes the conditions for microbial assemblage and promotes the expansion of a low-abundance, sulphite-reducing pathobiont, Bilophila wadsworthia. This was associated with a pro-inflammatory T helper type 1 (T(H)1) immune response and increased incidence of colitis in genetically susceptible Il10(−/−), but not wild-type mice. These effects are mediated by milk-derived-fat-promoted taurine conjugation of hepatic bile acids, which increases the availability of organic sulphur used by sulphite-reducing microorganisms like B. wadsworthia. When mice were fed a low-fat diet supplemented with taurocholic acid, but not with glycocholic acid, for example, a bloom of B. wadsworthia and development of colitis were observed in Il10(−/−) mice. Together these data show that dietary fats, by promoting changes in host bile acid composition, can markedly alter conditions for gut microbial assemblage, resulting in dysbiosis that can perturb immune homeostasis. The data provide a plausible mechanistic basis by which Western-type diets high in certain saturated fats might increase the prevalence of complex immune-mediated diseases like inflammatory bowel disease in genetically susceptible hosts.

Figure 1. Saturated MF-induced colitis is associated with bloom of Bilophila wadsworthia (Bw) in IL10^−/− mice

a,g Samples from SPF C57BL/6 (n=6/group), and b–g, SPF IL10^−/− mice fed MF, PUFA or LF for 24 weeks (n=20/group). a, Phyla representation shown for LF, PUFA, and MF with means ± S.E.M. *P<.05 compared to LF, ^#P<.05 compared to PUFA and LF. b, Gross incidence of colitis. c, Representative colon lengths (top) and H&E staining of distal colon (bottom). Scale bars, 400µm. d, Blinded histological colitis scores. e, Distal colonic mucosal cytokines determined by ELISA. f, PCoA plot of the UNIFRAC metric matrix. g, Q-PCR of cecal content dsrA (normalized to LF diet).

Figure 2. Bw monoassociation in germ-free (GF) IL10^−/− mice can only be established with consumption of MF diet, resulting in a T_H1 immune response and development of colitis

a–c, Samples from GF IL10^−/− mice ± monoassociation with 10⁸ CFU Bw maintained on LF, PUFA, or MF for 5 weeks (n=5/group). a, CFU counts of cultured cecal-derived Bw. b, Blinded histological colitis scores. c, IFNγ production by CD4⁺ T cells in mesenteric lymph nodes (MLN). d, IFNγ production by MLNs from GF C57BL/6 and IL10^−/− mice colonized with either Bw or L. murinus (Lacto) and restimulated ex vivo with pure culture lysate from the respective bacterium. e, In vitro CD4⁺ T cell differentiation assay. (Left) IL12p40 produced by dendritic cells (DCs) challenged with pure lysates from Bw, Lacto, or Alistipes (Alist). Data represents pooled values from MLN DCs and splenic DCs in the presence of RA/TGFβ. (Right) IFNγ production by CD4⁺ T cells stimulated with supernatants from the bacteria-challenged DC’s. Data shown represents 1 out of 2 assays, performed in triplicate.

Figure 3. Induction of taurocholic bile acid (TC) following consumption of MF promotes bloom of Bw both in vitro and in SPF IL10^−/− mice resulting in colitis

a, TC content of gall bladder aspirates from IL10^−/− mice consuming LF, PUFA or MF for 5 weeks. b, Growth curve of Bw in media containing gall bladder aspirates. c–g, Samples from SPF IL10^−/− mice gavaged with PBS, TC, or glycocholic acid (GC) daily for 21 days while maintained on LF diet (n=8/group). c, Phyla representation with bloom of Bw in the TC group with means ± S.E.M. *P<.05 compared to PBS and GC. d, Relative abundance of dsrA in cecal contents (by qPCR and normalized to LF diet). e, Blinded histological colitis scores, and f, H&E staining of distal colon. Scale bars, 400µm g, IFNγ production in MLNs.

Figure 4. Monoassociation with Bw in GF IL10^−/− is successful only if accompanied by TC gavage

a–c, Samples from GF IL10^−/− mice fed LF ± monoassociation with Bw followed by daily gavage with PBS, GC, or TC for 21 days (n=5/group). a, Robust Bw growth when re-isolated from cecal content of TC-fed GF mice (black film in TC plate indicates H₂S production), and CFU counts of cecal-derived Bw. b, Blinded histological colitis scores. c, IFNγ production in MLN CD4⁺ T cells determined by intracellular staining. d, Proposed experimental model.