DOP115 Exophiala dermatitidis aggravates colitis through the Syk-CARD9 signaling pathway
Authors: Sun M , Ju J , Luo M , Zeng L , Xu H , Li Z , Wang Y 
Published: January 2025

Abstract

Background
As a small but important part of the intestinal microbiota, there is more and more research about the involvement of the fungal community (mycobiota) in the occurrence and development of Crohn's disease (CD)1. In the previous study of our research group, the increased relative abundance of Exophiala dermatitidis (E. dermatitidis) has been found in the gut of patients with Crohn’s disease (CD) and active CD2. The caspase recruitment domain family member 9 (CARD9), important for antifungal defense3, is strongly associated with CD4. In this study, we aimed to investigate the potential effects and mechanisms of E. dermatitidis on intestinal inflammation.

Methods
To determine the effects of E. dermatitidis on intestinal inflammation, we generated Card9-knockout (KO) (Card9-/-) mice and constructed a dextran sulfate sodium (DSS)-induced colitis model colonized by E. dermatitidis. Flow cytometry was performed to analyze the proportions of myeloid cells and CX3CR1+ macrophages in the lamina propria (LP) of the colon. The molecular mechanism of E. dermatitidis on intestinal inflammation was studied by various biochemical methods.

Results
Compared with the mice with DSS-induced colitis only (WT-DSS group), the DSS-treated mice colonized by E. dermatitidis (WT-DSS + Ed group) showed a significant weight loss (Figure B), a worsening of disease activity (Figure C), a shorter length of the large intestine (Figure D), and more severe intestinal inflammation characterized by increased inflammatory cell infiltration and crypt destruction in the histological examination of colon hematoxylin and eosin (H&E) staining (Figure E). To further investigate whether E. dermatitis-mediated inflammation was dependent on the CARD9 signaling pathway, we constructed Card9-/- mice and treated the DSS mice with E. dermatitidis gavage (KO-DSS + Ed group) (Figure A). Compared with the mice from the WT-DSS + Ed group, the CARD9 deletion could help ameliorate the E. dermatitidis-aggravated (Figure B-F). In addition, a higher percentage of CX3CR1+ macrophages in the mice from the WT-DSS + Ed group and a lower percentage in the mice from the KO-DSS + Ed group were found in the LP of the colon via flow cytometry (Figure G). Moreover, we revealed the crucial role of the Mincle-Syk-CARD9-nuclear factor kappa-B (NF-κB) signaling pathway in the inflammatory immune responses to E. dermatitidis (Figure H-I).

Conclusion
E. dermatitidis aggravates the DSS-induced colitis in mice through the Mincle-Syk-CARD9-NF-κB pathway with the participation of CX3CR1+ macrophages (Figure J), providing a novel therapeutic strategy for CD targeting specific intestinal fungi.

References
1.Sokol H, Leducq V, Aschard H, et al. Fungal microbiota dysbiosis in IBD. Gut 2017;66:1039-1048.
2.Zeng L, Feng Z, Zhuo M, et al. Fecal fungal microbiota alterations associated with clinical phenotypes in Crohn's disease in southwest China. PeerJ 2022;10:e14260.
3.Hu A, Hu Z, Zou H, et al. CARD9 in host immunity to fungal, bacterial, viral, and parasitic infections: An update. Frontiers In Microbiology 2022;13:1021837.
4.Franke A, McGovern DPB, Barrett JC, et al. Genome-wide meta-analysis increases to 71 the number of confirmed Crohn's disease susceptibility loci. Nature Genetics 2010;42:1118-1125.