DISTINCT MUCIN PROFILES CORRELATE WITH INFLAMMATION IN ULCERATIVE COLITIS

In the human gut, goblet cells produce the mucin proteins MUC2 and MUC5B. In addition to goblet cells, all epithelial cells harbor mucins anchored to their apical membrane. These secreted and adherent mucins create a barrier to maintain gut homeostasis. Dysfunction of mucins can lead to increased susceptibility to infection, inflammation, and contribute to the pathology of inflammatory bowel disease (IBD). Previous studies have indicated that IBD patients, particularly those with ulcerative colitis, have reduced numbers of goblet cells, altered mucin glycosylation and more permeable mucus compared to healthy individuals. We set out to generate a comprehensive analysis of mucins and glycosyltransferases in IBD in the context of inflammation.

We analyzed bulk RNAseq data from rectal mucosal biopsies from 206 control non-IBD individuals and new-onset patients with ulcerative colitis. Ulcerative colitis patients were classified based on the level of inflammation as determined by calprotectin levels and histological severity score during diagnostic colonoscopy. RNAseq revealed that ulcerative colitis patients had increased levels of adherent mucins MUC1, MUC4, and MUC13 and these mucins were elevated with increasing histological severity. We also found that ulcerative colitis patients had decreasing levels of MUC3A and MUC20 with increasing levels of inflammation. No changes were observed in other adherent mucins such as MUC12, MUC16, MUC17 or MUC19. In terms of secreted mucins, we found that histological severity scores of 2 and 3 were associated with increased MUC2, MUC5B and MUC5AC. We confirmed the levels of MUC5B and MUC5AC protein by immunostaining colonic tissue from healthy individuals and ulcerative colitis patients with varying levels of inflammation. To determine if host-derived cytokines could shift the mucin profiles, we examined the mucin profiles of intestinal organoids derived from healthy individuals and ulcerative colitis patients after passaging. Interestingly, only MUC4 was significantly elevated in ulcerative colitis organoids; suggesting that other components absent in the organoid cultures were responsible for elevating mucins. To identify which cytokines could be involved, we examined mucin expression in organoids after incubation with INFy, IL-17A, IL-22 and TNF. We found that only IL-22 shifted the mucin profile and increased MUC1, MUC4, MUC13 and MUC5B in treated organoids. Finally, we found decreased levels of glycosyltransferases GALNT3, GALNT5, GALNT7, GALNT12, B4GALT4, B4GALT5, B3GNT2, B3GNT3, B3GALT5, B3GNT7, B3GNT8, and ST6GALNAC1, and increased levels of ST3GAL1 and ST3GAL2 in ulcerative colitis patients; suggesting that the mucins are not properly glycosylated.

These data point to a causative link between inflammatory cytokines and mucin profiles in IBD patients.