Transcriptomic analysis to study interactions between murine host and fungal commensal Candida albicans upon its gastrointestinal colonization
Candida albicans is a ubiquitous fungus in the human gut microbiome as well as a prevalent cause of opportunistic mucosal and systemic disease.  There is currently little understanding, however, as to how crosstalk between C. albicans and the host regulates colonization of this key niche.  Here, we performed expression profiling on ileal and colonic tissues in germ-free mice colonized with C. albicans to define the global response to this fungus.  We reveal that Duox2 and Duoxa2, encoding dual NADPH oxidase activity, are upregulated in both the ileum and colon, and that induction requires the C. albicans yeast-hyphal transition and hyphal-specific toxin candidalysin.  Hosts lacking the IL-17 receptor failed to upregulate Duox2/Duoxa2 in response to C. albicans, while addition of IL-17A to colonoids induced these genes together with the concomitant production of hydrogen peroxide. To directly define the role of Duox2/Duoxa2 in fungal colonization, antibiotic-treated mice lacking intestinal DUOX2 activity were evaluated for C. albicans colonization and host responses.  Surprisingly, loss of DUOX2 function reduced fungal colonization at extended time points (>17 days colonization) and increased the proportion of hyphal cells in the gut.  IL-17A levels were also elevated in C. albicans-colonized mice lacking functional DUOX2 highlighting cross-regulation between DUOX2 on this cytokine.  Together, these experiments reveal novel links between fungal cells, candidalysin and the host IL-17-DUOX2 axis, and that a complex interplay between these factors regulates C. albicans filamentation and colonization in the gut. Overall design: A group (n=5, 3F,2M) of germ-free mice were colonized with WT-SC5314 strain of Candida albicans for 7 and 21 days. Distal ileum and colon tissues were harvested at 7 days and 21 days post colonization in addition to a control group of non-colonized mice. Bulk RNA sequencing was carried out from these tissues to study any changes in the host gene expression upon C. albicans colonization of the murine gastrointestinal tract.