DIVERSITY LOSS DRIVES EARLY COLITIS IN A HIGH GENETIC RISK CROHN’S DISEASE MURINE MODEL

Abstract Genetic predisposition and the gut microbiome both contribute to Crohn’s disease (CD) pathogenesis. However, individuals can be discordant between their CD genetic risk and disease presence. Our lab hypothesizes that these discordant individuals may harbor microbiomes that are especially CD-promoting or CD-protective. To test this hypothesis, we have been collecting fecal specimens from multigenerational CD families, regardless of CD diagnosis, and categorized a select sample from 12 subjects into 4 groups based on CD status and polygenic risk score (PRS): CD+/high PRS, CD+/low PRS, CD-/high PRS, and CD-/low PRS. Samples were gavaged into 64 germ-free IL-10-/- 129S6/SvEvTac mice. Disease activity index (DAI, based on a combination of weight loss, stool consistency and fecal blood) was scored over 23 days. 16S rRNA sequences from mouse pellets were used to analyze microbiome features longitudinally. Mice receiving CD+/high PRS microbiota developed rapid colitis, before gradual recovery; all other human-inoculated groups maintained low DAI throughout. In the CD+/high PRS group, alpha diversity was low early and increased during colitis recovery, inversely correlating with DAI. In contrast, all donor groups from CD+/low PRS donors exhibited relatively higher baseline alpha diversity which remained stable. Of note, mice gavaged with CD -/high PRS inocula were among the highest in alpha diversity across timepoints. The microbiome of the CD+/high PRS group was characterized by an increased number of differentially abundant taxa between early and late timepoints, followed by the CD+/low PRS group, and then the CD- group. Increases in Escherichia-Shigella and Enterococcus after day 11 in the experiment were noted consistently in the CD+/high PRS inocula, which may be related to the temporal differences in DAI. These findings demonstrate the influence of CD genetic risk on the gut microbiome, as well as in differential disease activity. Our findings along with further research in this pre-clinical model may further identify targets for treating clinical CD. Figure 1:Testing of taxonomic abundance (ANCOM-BC) identifies those enriched at early (days 0–11) or late (days 12–23) timepoints. Only differentially abundant taxa found in all 3 inocula of a treatment group were considered. Taxa with less than 3% abundance were filtered out. The greatest number of differentially abundant taxa were found in the CD+/high risk group. The least number of differences were found in the CD-/high risk group. Marked increases in Escherichia-Shigella, Enterococcus, and Akkermansia were noted consistently in the CD+/high risk inocula, which may be related to the temporal differences in DAI.Figure 2:Faith’s Phylogenetic Diversity over time. Inocula from the CD+/high risk group were typified by lower alpha diversity compared to the other 3 inocula. Inocula from the CD-/high risk group consistently had higher alpha diversity. The largest variation in diversity was seen among the CD-/low risk samples.