Fmo5 plays a sex-specific role in goblet cell maturation and mucus barrier formation

The intestine plays a key role in metabolism, nutrient and water absorption, and provides both physical and immunological defense against dietary and luminal antigens. The protective mucosal lining in the intestine is a critical component of intestinal barrier that when compromised, can lead to increased permeability, a defining characteristic of inflammatory bowel disease (IBD), among other intestinal diseases. Here, we define a new role for the flavin-containing monooxygenase (FMO) family of enzymes in maintaining a healthy intestinal epithelium.

Using Caenorhabditis elegans we measure intestinal barrier function, actin expression, and intestinal damage response. In mice, we utilize an intestine-specific, tamoxifen- inducible knockout model of the mammalian homolog of Cefmo-2 , Fmo5, and assess histology, mucus barrier thickness, and goblet cell physiology. We also treat mice with the ER chaperone Tauroursodeoxycholic acid (TUDCA).

In nematodes, we find Cefmo-2 is necessary and sufficient for intestinal barrier function, intestinal actin expression, and is induced by intestinal damage. In mice, we find striking changes to the intestine within two weeks following Fmo5 disruption. Alterations include sex-dependent changes in colon epithelial histology, goblet cell localization, and mucus barrier formation. These changes are significantly more severe in female mice, mirroring differences observed in IBD patients. Furthermore, we find increased protein folding stress in Fmo5 knockout animals and successfully rescue the severe female phenotype with addition of a chemical ER chaperone.

Together, our results identify a highly conserved and novel role for Fmo5 in the mammalian intestine and support a key role for Fmo5 in maintenance of ER/protein homeostasis and proper mucus barrier formation.