UC Davis

Human Milk Oligosaccharides (HMOs) are the third most abundant solid component in human breast milk, consisting of hundreds of unique structures. HMOs are indigestible by the infant but have shown to be very beneficial to the infant’s development, making them an intriguing constituent. However, due to the lack of standards, reliable methods for quantitation, and complexity of performing large scale analysis, there are limits to our general knowledge of their abundances and functions. This dissertation focuses on the development and implication of mass spectrometry-based methods to characterize and quantitate HMOs to address unanswered questions in the field. Chapter 1 provides an overview of HMO structures and the functions they collectively play in infant development. Chapter 2 details the development of a comprehensive library and a high-throughput method that allowed for accurate quantitation of HMOs using high resolution mass spectrometry. Optimized methods were applied to breast milk samples collected from over 2000 mothers from 19 geographically diverse sites to investigate how HMO profiles vary across the globe. The results revealed significant phenotypic variations in the mother’s milk and secretor status globally. Chapter 3 reports discovery of several oligosaccharides, inclusive of 8 HMOs, found in amniotic fluid. This chapter detailed the methodologies from sample preparation to data analysis and was applied to a cohort of over 500 mothers, making it the most comprehensive study of amniotic fluid to date. Analysis revealed compositional changes in HMO profiles across gestation. Chapter 4 studies demonstrated that select HMOs, including linkage-specific sialylated structures, can act as decoys to prevent SARS-Cov2 infection. This study also investigated the mechanism of binding between the spike protein and the ACE2 receptor on the cell surface. The results detailed here exemplify the important role that cell surface glycosylation plays in host-pathogen interactions.