A21 ROLE OF SIALIC ACID O-ACETYLATION IN MAINTAINING MUCUS INTEGRITY AND HOMEOSTASIS OF THE COLONIC MUCOSA

Abstract Background The mucus network provides innate immune defense to protect our gastrointestinal tract from pathogens, and promote homeostasis with resident microbiota. This is constituted by the mucin MUC2 (Muc2 in mouse), which ~80% complex O-linked glycans weight. Sialic acid (Sia) a key capping monosaccharide on O-glycans has recently been linked preserving integrity. Sia can undergo enzymatic modifications including addition of O-acetyl groups. 9-O-acetyltransferase CasD1 responsible for 9-OAc variants. Functionally, OAc-modification known inhibit microbial sialidase activities may preserve Sia’s protective roles mucins. However, extent these OAc human murine Mucin-2, how they influence function unclear. Purpose: To determine whether O-acetylation colonic regulates integrity, host-microbe interactions, colitis susceptibility. Method We used viral-derived probes that target specific OAc-Sia analogues sections feces mouse colon tissues visualize their spatial arrangement interaction situ. For glycomics, were quantitated purified Muc2 HPLC-MS after derivatization 4,5-dimethyl-1,2-diaminobenzamine (DMBA). released via non-reductive ammonia-catalyzed β-elimination analyzed mass spectrometry. vivo work, we generated intestinal epithelial cell-specific Casd1 KO mice (Casd1flox/flox;VillinCre or IEC Casd1-/- mice) Sialidase quantified supernatants fecal materials WT mutants using fluorogenic substrate 4-MU-NeuNAc. Colitis susceptibility was monitored 1.5% w/v Dextran Sodium Sulfate (DSS). Result(s) found Sias both heavily O-acetylated, ~75% ~45% having 9-OAc-based modification humans respectively, distributed throughout niche barrier layers viable healthy knockdown confirmed staining, western blot protein lysates mucins, sialylomics. encapsulation appeared overall intact regardless status. showed heightened DSS colitis, thinning vs littermates challenge. Consistent role inhibition, loss associated increased as assessed 4 MU signal littermate mice. O-glycomics also reduction number sialylated O-glycan structures upon Sia. Conclusion(s) appears important maintaining aspects Sia-dependent protecting inflammatory insult. Please acknowledge all funding agencies checking applicable boxes below: CCC Disclosure Interest None Declared