Thesis Defence: Role of alpha 2,6-linked sialylated galactose on intestinal epithelial glycans in regulating sex-specific mucus-microbe interactions and protection from colitis

Mackenzie Melvin, supervised by Dr. Kirk Bergstrom, will defend their thesis titled “Role of alpha 2,6-linked sialylated galactose on intestinal epithelial glycans in regulating sex-specific mucus-microbe interactions and protection from colitis” in partial fulfillment of the requirements for the degree of Master of Science in Biochemistry & Molecular Biology.

An abstract for Mackenzie Melvin’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.

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ABSTRACT

The colon produces copious amounts of mucus that is composed of large, carbohydrate-rich molecules decorated with diverse sugars. Sialic acid (Sia) is a protective sugar that has been shown to be implicated in mucus functions by preserving its integrity and acting as a nutrient source for bacteria. The addition of Sia to mucus, known as sialylation, can occur via different linkages, where one of the most observed is an α2,6 linkage to galactose (Gal). The addition of α2,6-linked Sia to these structures is mediated by beta-galactoside alpha-2,6-sialyltransferase 1 (ST6Gal1), which has been well-studied in the context of the immune system. The role of α2,6-linked Sia in gut health and preventing disease is poorly defined, and data looking at sex-specificity and sialylation is limited, with most studies not considering sex a contributing factor. The goal of this study was to determine if the loss of α2,6-linked Sia has an impact on the gut mucus and its bacteria, and if there is any relationship between sex and disease susceptibility. To address these questions, we derived a mouse line that conditionally lacks ST6Gal1 in the gut epithelium using CreLox Technology to target Siaα2,6Gal sialylation. Lectin staining revealed a loss of α2,6-linked Sia signal in the colon crypts of intestinal epithelial cell (IEC) St6gal1-/- mice, indicating that ST6Gal1 is the sole contributor of Siaα2,6Gal in the colon. Sialomic and glycomic analyses revealed genotype- and sex-specific differences, showing that a loss of α2,6-linked Sia impacts the composition of gut mucus. There were significant sex- and genotype-specific differences when looking at microbiota profiles assessed through 16S rRNA profiling, indicating an impact of ST6Gal1 on colonic microbial ecology. Treatment with dextran sodium sulfate revealed a mildly worsened clinical score and disease overall in male vs. female IEC St6gal1-/- mice compared to St6gal1f/f littermates. Further, the Citrobacter rodentium infection model highlighted worsened infection in female IEC St6gal1-/- mice, with bacterial lipopolysaccharide staining and pathology suggesting a more widespread and heightened infection. Collectively, this study expands the current knowledge surrounding the physiological role of ST6Gal1 in vivo and its sex-specific impact on gut homeostasis and mucus sialylation.