Thesis Defence: Development of a novel model of conditional Casd1 deficiency to investigate the role of Sialic acid O-acetylation in colon homeostasis
December 10 at 9:00 am - 1:00 pm
Simin Jafaripour, supervised by Dr. Kirk Bergstrom, will defend their thesis titled “Development of a novel model of conditional Casd1 deficiency to investigate the role of Sialic acid O-acetylation in colon homeostasis” in partial fulfillment of the requirements for the degree of Master of Science in Biology.
An abstract for Simin Jafaripour’s thesis is included below.
Defences are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.
ABSTRACT
The O-glycosylated intestinal mucus network—made up of polymers of the MUC2 mucin— provides innate immune defense to protect our gastrointestinal tract from microbial insult. Sialic acid (Sia) is a key capping monosaccharide on complex O-glycans which has recently been linked to preserving mucus integrity. Sia is extensively modified by O-acetyl (OAc) groups at the C-4, -7, -8, and/or -9 positions. However, the extent and role of these OAc modifications on mucus is unclear. We hypothesized that Sia’s protective functions on gut mucus are regulated through its O-acetylation. To understand the biologic roles of OAc-Sia in vivo, we generated intestinal epithelial cell-specific Casd1 KO mice (Casd1flox/flox; VillinCre or IEC Casd1-/- mice) and analyzed their mucins and phenotypes vs. WT littermates. IEC Casd1-/- mice were viable and healthy with knockdown confirmed by lack of 9-OAc signals on tissue sections and via western blot of protein lysates and mucins. Notably, sialomics on extracted Muc2 showed loss of gut epithelial Casd1 impaired O-acetylation at the C-7, -8, and -9 positions. Consistent with the known role of OAc Sia in sialidase inhibition, loss of OAc Sia was associated with increased sialidase activities as assessed by heightened fluorogenic substrate 4-MU-Neu5Ac in fecal supernatants in IEC Casd1-/- vs. WT mice. Paradoxically, we observed increased Sia (Neu5Ac) on Muc2 from IEC Casd1-/- mice, where O-glycomics revealed a unique population of O-glycans in the absence of Casd1 activity. This, in turn, could explain why mucus barrier function appeared intact regardless of 9-OAc status. IEC Casd1-/- mice showed slightly heightened susceptibility to 1.5% w/v Dextran Sodium Sulfate (DSS) colitis, linked to thinning of the mucus in IEC Casd1-/- vs. WT littermates. Unexpectedly, we observed a unique genetic phenotype in our model, namely a reversion of the floxed locus into a WT locus which led to discordant genotypes and phenotypes. Taken together, this suggests there is strong genetic pressure to preserve Casd1 activity as it governs the majority of OAc-Sia modifications on Muc2 in mice, which may be necessary for a fully adaptive sialome on mucus to mediate protection in response to mucosal challenge.
