Goblet cell-expressed microprotein FXYD3 determines gut homeostasis by maintaining mucus barrier integrity

The intestinal mucus layer produced by goblet cells is a critical component of innate immunity. The key host factors and regulatory mechanisms controlling goblet cell function in mucus layer formation remain poorly understood. This study identifies a function for the microprotein FXYD domain-containing transport regulator 3 (FXYD3) in goblet cells in regulating mucus layer formation to maintain intestinal homeostasis. Deficiency of FXYD3 in mouse intestinal epithelial cellsresults in a damaged mucus barrier, leading to microbiota dysbiosis and increased susceptibility to colitis. Mechanistically, FXYD3 interacts with endoplasmic reticulum Ca2+-ATPase SERCA2 to enhances its pump activity. FXYD3 deficiency causes defects in ER Ca2+ homeostasis and mucin glycosylation, impairing mucus layer integrity. Furthermore, metabolites of gut microbiota, propionate and butyrate promoteFXYD3 expression. In ulcerative colitis (UC) patients, FXYD3 expression is significantly downregulated and correlats with disease severity. These findings indicat FXYD3 is a key mediator of host-microbiota interactions for intestinal health.