Auricularia auricula's Exopolysaccharide Mitigates DSS-Induced Colitis Through Dectin-1-Mediated Immunomodulation and Microbiota Remodeling

Abstract

Background/Objectives: Ulcerative colitis (UC) is characterized by the interplay between immune responses and dysbiosis in disease development. Aiming to provide additional insights into disease development and potential treatment strategies, the present study investigates the local effect of oral treatment with polysaccharides obtained from Auricularia auricula's submerged culture in an experimental model of DSS-induced colitis and its impact on lesion resolution. Methods: The structure and monosaccharide composition of Auricularia polysaccharides were characterized through Nuclear Magnetic Resonance (NMR). To evaluate the effect of this polysaccharide on the murine model, wild-type and Dectin-1 knockout mice were treated or not with the exopolysaccharide (EPS) while under DSS consumption. During the experimental period, feces samples were collected to evaluate microbial shifts during disease development, and, finally, the colonic tissue was analyzed to assess the inflammatory process and cytokine production. Results: The EPS composition showed a polymeric mixture of glucans and fucogalactomannans. The treatment of the wild-type DSS-induced colitis group improved the inflammatory response by increasing gut-homeostatic cytokines, such as interleukin-10 (IL-10) and tumor necrosis factor-alpha (TNF-α). The Dectin-1 KO mice group did not show the same enhancement after EPS treatment. The microbiome analysis revealed a difference in the genotype, and the treatment modified the DSS microbiome modulation, with nine and four ASVs in WT and Dectin-1 KO mice, respectively. Conclusions: The EPS treatment demonstrated therapeutic potential in treating inflammatory intestinal diseases by modulating cytokine secretion and microbiota composition, which is dependent on the Dectin-1 receptor's carbohydrate recognition.

Keywords: microbiome; mushroom polysaccharide; prebiotics; ulcerative colitis.

Figure 1

(A) ¹³C NMR spectrum of polysaccharides from Auricularia auricula (500 MHz, DMSO at 70 °C). (B) ¹ H NMR spectrum (500 MHz, DMSO at 70 °C) (D), with an amplified insert of the anomeric region. (C) HSQC_edit spectra, with amplified inserts of aromatic and aliphatic region (500 MHz, DMSO at 70 °C).

Figure 2

Effect of A. auricula polysaccharide on the mice’s body weight (g) and colon length (cm) according to the treatment (●) not treated, (◼) DSS 2%-induced-colites, (▲) treated with EPS, and (▼) treated with EPS and DSS 2%-induced-colites. (A) body weight curve of c57BL6/J wild-type mice through the experimental period; (B) body weight curve of c57BL6/J and Dectin-1 KO mice throughout the experimental period; (C) Graphical representation of colon length measured with ImageJ 1.53t. Mixed-effects analysis, where p < 0.05 compared to the control group; (D) Photograph showing the mice’s intestinal length. * p < 0.05; ** p < 0.005; and **** p < 0.0001; and compared to the group treated with EPS, one-way ANOVA and Tukey’s test.

Figure 3

Quantifying cytokines measured in the colon of wild-type and Dectin-1 KO mice, given DSS 2% and treated/or not with Auricularia exopolysaccharide, according to the treatment (●) not treated, (◼) DSS 2%-induced-colites, (▲) treated with EPS, and (▼) treated with EPS and DSS 2%-induced-colites. (A,B) TNFα, (C,D) IL-10, (E,F) IL-23. Data are expressed as mean ± SD, compared to the DSS 2% group, where * p < 0.05; ** p < 0.005; and *** p < 0.001; and compared to the group treated with EPS, where # p < 0.05, one-way ANOVA and Tukey’s test.

Figure 4

Quantifying cytokines measured in the colon of wild-type and Dectin-1 KO mice, given DSS 2% and treated/or not with Auricularia exopolysaccharide, according to the treatment (●) not treated, (◼) DSS 2%-induced-colites, (▲) treated with EPS, and (▼) treated with EPS and DSS 2%-induced-colites. (A,B) IFN-ɣ, (C,D) IL-13, (E,F) IL-17A. Data are expressed as mean ± SD, compared to the DSS 2% group, where * p < 0.05; ** p < 0.005; and **** p < 0.0001; and compared to the group treated with EPS, where # p < 0.05, and ### p < 0.001, one-way ANOVA and Tukey’s test.

Figure 5

Principal coordinate analysis of beta diversity on WT control mice, as assessed by Bray–Curtis, Jaccard, weighted UniFrac, and unweighted UniFrac distances. Black squares and gray circles indicate the control group; black circles and red circles indicate the groups with DSS-induced colitis; black triangle and blue circle indicate the EPS treated group, and black diamond and green circle indicate the EPS treated group with DSS-induced colitis. Each point represents a single mouse sample, and lines are drawn to connect samples from the same mouse over time.

Figure 6

Principal coordinate analysis of beta diversity on Dectin-1 KO mice, as assessed by Bray–Curtis, Jaccard, weighted UniFrac, and unweighted UniFrac distances. Black squares and gray circles indicate the control group; black circles and red circles indicate the groups with DSS-induced colitis; black triangle and blue circle indicate the EPS treated group, and black diamond and green circle indicate the EPS treated group with DSS-induced colitis. Each point represents a single-mouse sample, and lines are drawn to connect samples from the same mouse over time.

Figure 7

Heatmap showing the ASVs that are differentially abundant between the genotypes, regardless of treatment status. G0—healthy wild-type mice; G1—DSS-induced colitis wild-type mice; G2—EPS-treated wild-type mice, and G3—EPS treated and DSS-induced colitis wild-type mice. The color scale indicates the CLR transformed counts.

Figure 8

Heatmap showing the ASVs that are differentially abundant for each treatment combination. G0—healthy Dectin-1 KO mice; G1—DSS-induced-colitis Dectin-1 KO mice; G2—EPS-treated Dectin-1 KO mice and G3—EPS treated and DSS-induced-colitis Dectin-1 KO mice. The row annotation indicates in which treatment/genotype combination the ASV was modulated. DSS_WT and DSS_KO—effects of DSS treatment on WT and KO genotypes, EPS_WT and EPS_KO—effects of EPS treatment on WT and KO genotypes, INT_WT and INT_KO—effects of the interaction of DSS and EPS treatments. The color scale indicates the CLR transformed counts.