The importance of protein glycosylation: a glycoscope into the reproductive process

The aim of this thesis is to enhance our understanding of the role of glycosylation in the reproductive process in both male and female tracts from both a glycomics and glycoproteomics perspective. Within the scope of this thesis, protein macro-glycosylation (at the cellular/tissue level) was investigated by analysis of aberrant glycosylation in STZ- and high glucosamine -induced diabetic ovarian tissues of mice. The two diabetic models shared a relative decrease in protein N-linked oligomannose, and a decrease in sialylated, structures compared to non-diabetic mice. We are the first to report changes occurring in the glycan biosynthesis pathway in diabetes of any reproductive organ. The same level of analysis (macro-glycosylation) was investigated as a means of differentiating active sperm from inactive sperm. Active sperm were generated via two isolation protocols, namely Percoll density gradient centrifugation and "swim-up" collection and compared with inactive sperm. The most significant result was seen in the large individual biological variation within each donor's sperm populations. On the other hand, the micro-glycosylation (at the single glycoprotein level) focused on two functionally relevant reproductive proteins, namely: endometrial MUC1 and seminal Cluster of Differentiation 52 (CD52). MUC1 on the surface of mouse oviduct and uterine tissues exhibited no significant difference in O-glycan structures at the time of window of implantation (WOI) or in diabetes, although the carbohydrate/protein abundance increased on MUC1 on the uterine lining in the WOI. CD52 has a proposed immune-suppressive function in semen, but only lymphocyte CD52 has been fully characterized from the point of view of activity. Lymphocyte CD52 initiates immunosuppression by binding to the sialic acid-binding immunoglobulin-like lectin-10 (Siglec-10) receptor on activated T cells. As a prelude to understanding the role of CD52 glycosylation in reproduction we comprehensively defined the glycan structures on lymphocyte CD52. Sialylation was essential for the immunosuppression and enabled the identification of the most immune suppressive CD52 glycoforms. Overall, this thesis provides support for the inherent contribution of protein glycosylation, on a macro and micro level, in the process of reproduction in both male and female.