Epididymal St3gal2-mediated α2,3-sialylation regulates murine sperm motility and correlates with N-glycan alterations in human asthenozoospermia.

Sialic acid residues on the sperm surface play crucial roles in sperm maturation, capacitation, and sperm-oocyte interactions. Here, we investigated the dynamic regulation of α2,3-sialylation on the sperm membrane during epididymal maturation in mice, with a focus on the sialyltransferase St3gal2. St3gal2 is highly expressed in the caput epididymis and mediates the progressive accumulation of α2,3-linked sialic acid on the murine sperm surface during epididymal transit. Enzymatic removal of surface α2,3-sialic acid significantly reduced mouse sperm progressive motility, whereas co-incubation of desialylated mouse sperm with conditioned medium from St3gal2-overexpressing COS-7 cells restored both surface α2,3-sialylation and motility, establishing a direct functional link between St3gal2 activity and sperm movement. To extend these findings to human reproductive pathology, we performed systematic N-glycomic profiling of sperm membrane proteins from healthy donors (PR ≥ 32%, n = 18) and asthenozoospermic donors (PR < 32%, n = 15) by MALDI-MS. α2,3-Sialylated N-glycans were positively correlated with progressive motility and significantly reduced in asthenozoospermic sperm, while fucosylated N-glycans were significantly elevated in asthenozoospermia. α2,6-Sialylated N-glycans showed no significant difference between groups and no significant association with progressive motility. Lectin-based flow cytometry independently confirmed increased surface fucosylation and decreased surface α2,3-sialylation in asthenozoospermic sperm. Together, these findings establish a causal role for St3gal2-mediated α2,3-sialylation in murine sperm motility and reveal a characteristic N-glycan imbalance - reduced α2,3-sialylation and elevated fucosylation - associated with human asthenozoospermia, identifying the sperm surface glycocalyx as a potential target for therapeutic intervention in motility-related male infertility.