Effects of glycodelins on functional competence of spermatozoa

Glycodelin is a glycoprotein with 4 known glycoforms, namely glycodelin-S, glycodelin-A, glycodelin-F and glycodelin-C. The glycoforms are present in the female reproductive tract which the spermatozoa must pass through before fertilizing the oocyte. Thus the spermatozoa interact with each of these glycoforms in succession. The glycoforms have different effects on sperm function. Glycodelin-S in the seminal plasma suppresses albumin-induced cholesterol efflux from the spermatozoa and thereby regulates the initiation of capacitation. Glycodelin-A in the oviductal fluid suppresses extracellular signal-regulated kinase making the spermatozoa more sensitive to zona pellucida-induced acrosome reaction. Follicular fluid glycodelin-F suppresses progesterone-induced acrosome reaction and prevents premature acrosome reaction. Glycodelin-A and glycodelin-F also inhibit spermatozoa–zona pellucida binding by interacting with sperm surface fucosyltransferase-5, which also binds to zona pellucida glycoproteins. The physiological implication of this phenomenon remains to be determined. The inhibitory activities of glycodelin-A and glycodelin-F on spermatozoa–zona pellucida binding is removed by glycodelin-C in the cumulus matrix. Glycodelin-C not only displaces sperm-bound glycodelin-A and glycodelin-F, it also enhances spermatozoa–zona pellucida binding. These different biological activities of the glycodelin isoforms are determined by glycosylation of the proteins. Deglycosylation abolishes the binding and therefore the action of the glycodelins on spermatozoa. Knowledge of the mechanism of actions of glycodelins may enable development of novel strategies for fertility regulation.