A Large Polysaccharide Produced by Helicobacter hepaticus Induces an Anti-inflammatory Gene Signature in Macrophages

Abstract

Interactions between the host and its microbiota are of mutual benefit and promote health. Complex molecular pathways underlie this dialog, but the identity of microbe-derived molecules that mediate the mutualistic state remains elusive. Helicobacter hepaticus is a member of the mouse intestinal microbiota that is tolerated by the host. In the absence of an intact IL-10 signaling, H. hepaticus induces an IL-23-driven inflammatory response in the intestine. Here we investigate the interactions between H. hepaticus and host immune cells that may promote mutualism, and the microbe-derived molecule(s) involved. Our results show that H. hepaticus triggers early IL-10 induction in intestinal macrophages and produces a large soluble polysaccharide that activates a specific MSK/CREB-dependent anti-inflammatory and repair gene signature via the receptor TLR2. These data identify a host-bacterial interaction that promotes mutualistic mechanisms at the intestinal interface. Further understanding of this pathway may provide novel prevention and treatment strategies for inflammatory bowel disease.

Keywords: CREB; Helicobacter hepaticus; MSK1/2; TLR2; anti-inflammatory gene signature; host-microbe interactions; inflammatory bowel disease; macrophage; mutualism; polysaccharide.

Graphical abstract

Figure 1

H. hepaticus Induces IL-10 in Gut-Resident Macrophages (A–D) SPF WT mice were infected with Helicobacter hepaticus (Hh) for 3 or 5 days. (A) Experimental design. (B and C) FACS analysis of caecum and colon LPL after 3 days of infection with Hh. (B) Frequency of resident macrophages among total CD45⁺ cells. (C) Frequency of IL-10^high cells among resident macrophages, using an anti-mouse IL-10 antibody or its isotype control. (D) Expression level of Il10, Il6, and Tnf mRNA in caecum or colon tissue after 3 or 5 days of infection with Hh. Each symbol represents an individual mouse (two to three independent experiments). Mann-Whitney test (B and C) or one-way ANOVA and Tukey’s multiple comparisons test (D), p < 0.05. See also Figure S1.

Figure 2

H. hepaticus Produces a Large Soluble Polysaccharide-Inducing IL-10 Production in Macrophages (A–G) M-CSF-differentiated BMDMs were stimulated for 3 hr with different culture fractions of H. hepaticus. (A) mRNA and protein induction of the cytokines IL-10 and IL-6 after stimulation with control medium (TSB), H. hepaticus whole bacteria (Hh), or H. hepaticus-filtered cultured supernatant (SNHh). (B–D) Induction of (B) IL-10, (C) IL-6, and (D) IL-10/IL-6 ratio after 3 hr stimulation with SNHh treated with enzymes and heat (SNHht), SNHht fractionated by size (SNHht > 30 kDa and SNHht < 30 kDa), and LPS UP. (E) Induction of IL-10 after stimulation with TSBt or SNHht, treated with buffer (−) or sodium metaperiodate (+, NaIO₄). Stimulation with TSBt ± NaIO₄ and LPS ST is used as a positive control for IL-10 production by BMDMs. (F) Induction of IL-10 after stimulation with TSBt, LPS ST, SNHht, or SNHht depleted using increasing concentrations of ConA-lectin beads (0.8%, 1.5%, 3%, and 6% v/v). (G) Induction of IL-10 and IL-6 after stimulation with SNHht crude polysaccharide fraction extracted by a cold-ethanol precipitation method (CPHht). Data from three independent experiments. Mann-Whitney test, p < 0.05. Mean ± SD. LPS UP, LPS ultrapure from E. coli O111:B4; LPS ST, LPS standard from E. coli O55:B5. See also Figure S2.

Figure 3

SNHht Is Sufficient to Induce IL-10 In Vivo (A) Frequency of IL-10^high cells among resident macrophages from caecum and colon LPL. SPF WT mice were infected with Hh or orally gavaged with TSBt or SNHht for 3 days. (B and C) Il10, Il6, and Tnf mRNA expression levels in the peritoneal cell fraction after 2 days (B) or Il10 and Il6 mRNA transcripts after 6 hr (C) challenge. Ligands (TSBt and SNHht, 200 μL; LPS UP and Pam3, 50 μg) were injected into the intraperitoneal cavity of SPF WT mice. Each symbol represents an individual mouse (two to three independent experiments). Pam3, Pam3CSK4. Mann-Whitney test, p < 0.05. See also Figure S3.

Figure 4

SNHht Signals through TLR2 and MyD88 to Induce IL-10 (A) Induction of IL-10 production in different knockout C57BL/6 BMDMs stimulated for 3 hr with SNHht normalized to WT BMDMs (three independent experiments). Two-way ANOVA and Bonferroni’s multiple comparisons test, p < 0.05. Ifnar, interferon-a/b receptor; Mr, mannose receptor; Sra, scavenger receptor A. (B) Il10 mRNA and protein induction in different knockout BMDMs stimulated for 3 hr with SNHht (one of three independent experiments). One-way ANOVA and Tukey’s multiple comparisons test, p < 0.05. (C) Induction of IL-10 production in WT and Tlr2^−/− BMDMs stimulated for 3 hr with TSBt, SNHht, CPHht (SNHht crude polysaccharide fraction), LPS UP (TLR4 ligand), or Pam3 (TLR2/1) (one of three independent experiments). Two-way ANOVA and Sidak’s multiple comparisons test, p < 0.05. (D) Induction of IL-10 production in WT BMDMs pre-treated for 2 hr with a blocking antibody specifically inhibiting TLR2 signaling (monoclonal α-mTLR2-IgG) or its isotype control before stimulation for 3 hr with TSBt, SNHht, Pam2 (TLR2/6), Pam3, or LPS UP (three independent experiments). Two-way ANOVA and Sidak’s multiple comparisons test, p < 0.05. (E) Western blot showing the phosphorylation of ERK1/2 and p38 and the total ERK1/2 and p38 protein amounts in WT and Tlr2^−/− BMDMs after stimulation with TSBt, SNHht, Pam3, or LPS UP for 15 min, 30 min, and 3 hr. Mean ± SD. See also Figure S4.

Figure 5

Differential Regulation of Transcription by SNHht and Pam3 (A–F) Microarray analysis performed on M-CSF BMDMs differentiated from 5 WT mice and stimulated for 3 hr. (A) Principle components analysis (PCA) of transcriptional profiles (empirical Bayes normalized expression values from LIMMA) across three conditions (TSBt, Pam3, and SNHht, n = 5/condition, 16,692 probes). (B) Hierarchical clustering heatmap (Manhattan distance with Ward clustering of empirical Bayes normalized expression values) of the union of differentially expressed probes between any condition-condition contrast (i.e., TSBt versus Pam3, TSBt versus SNHht, or Pam3 versus SNHht) (n = 172 probes, n = 146 genes). Probes were assigned to clusters using k-means clustering (k = 4) and cluster assignments are annotated as colors to the left of the heatmap. The number of probes assigned to each cluster were: cluster 1 = 75, cluster 2 = 10, cluster 3 = 68, and cluster 4 = 19. (C) Scatterplot displaying the relationship between log2 (fold changes) for each gene shown in (B) obtained when comparing either Pam3 (x axis) or SNHht (y axis) with the TSBt control condition. Colors represent the cluster assignments. (D and E) Transcription factor (TF) motif enrichment analysis among genes assigned to (D) cluster 4 (i.e., specifically induced by SNHht) and (D) cluster 1 (i.e., specifically induced by Pam3). Motif names correspond to Transfac motif identifiers derived from the Molecular Signatures Database (MSigDB). Motifs significantly overrepresented at an adjusted p < 0.05 (permutation test) are shown. (F) mRNA levels of CREB (Il10, Fosb, Egr3, Rcan1) and NF-κB (Il6, Ccl5, Cd40, Icam1) target genes were validated by qRT-PCR.

Figure 6

SNHht Stimulates CREB Phosphorylation and Induction of an Anti-inflammatory and Repair Gene Signature in Macrophages (A) Western blot showing the phosphorylation of CREB1 S133 and RelA S536 and the total CREB1 and RelA protein amounts in WT and Tlr2^−/− BMDMs after 30 min stimulation with TSBt, SNHht, Pam3, or LPS UP. β-actin used as a loading control. (B) mRNA levels of Il10, Fosb, and Egr3 genes in BMDMs from conditional vav-cre CREB^WT and CREB^{S133A KI} mice after 1 hr stimulation with TSBt, Hh, SNHht, or Pam3. (C) Induction of IL-10, IL-6, and TNFα; IL-10/IL-6; and IL-10/TNFα protein ratios in BMDMs from conditional vav-cre CREB^WT and CREB^{S133A KI} mice after 10 hr stimulation with TSBt, Hh, SNHht, or Pam3. One of three independent experiments. Two-way ANOVA and Sidak’s and/or Tukey’s multiple comparisons tests, p < 0.05. (D) mRNA levels of Il10, Fosb, Egr3, Rcan1, Il6, Tnf, and Cd40 genes in caecum total tissue from WT mice gavaged with TSBt or SNHht for 2 days. Each symbol represents an individual mouse (two independent experiments). Mann-Whitney test, p < 0.05. Mean ± SD. See also Figure S5.

Figure 7

MSK1/2 Is Essential to the Anti-inflammatory Properties of SNHht (A) Western blot showing the phosphorylation of CREB1 S133 and MSK1 T581 and the total CREB1 and MSK1 protein amounts in WT and Msk1/2^−/− BMDMs after 30 min stimulation with TSBt, SNHht, Pam3, or LPS UP. (B) mRNA levels of Il10, Fosb, and Egr3 genes in BMDMs from WT or Msk1/2^−/− mice after 1 hr stimulation. (C) Induction of IL-10, IL-6, and TNFα; IL-10/IL-6; and IL-10/TNFα protein ratios in BMDMs from WT or Msk1/2^−/− mice after 10 hr stimulation. One of three independent experiments. Two-way ANOVA and Sidak’s and/or Tukey’s multiple comparisons tests, p < 0.05. Mean ± SD. See also Figure S6.