Epididymal epithelial cells facilitate NEU1 loading to modulate sperm α-2,6 sialylation, enhance maturation and motility.

BACKGROUND: Male infertility is a prevalent reproductive disorder worldwide, with decreased sperm quality-particularly reduced motility and fertilization capacity-being one of its common causes. Sperm maturation is a complex process involving multiple molecular mechanisms, the specific pathways regulating sperm motility remain unclear and require further investigation. Among these mechanisms, sialylation serves as an important glycosylation modification during sperm maturation and capacitation, playing a crucial role in these processes. Nonetheless, the specific function of Neuraminidase-1 (NEU1), a kind of sialidase, in sperm maturation and function remains poorly understood. This study aims to investigate the origin and function of NEU1 in sperm, as well as its impact on sperm motility and fertilization potential, providing new insights into its role in male infertility. METHODS: A combination of computational prediction and experimental validation was used to assess the expression profile of sialylation-related enzymes in the male reproductive tract, identifying NEU1 as a candidate for further investigation. Immunofluorescence, Western blotting, and flow cytometry were performed to analyze the expression pattern of NEU1 in human and murine sperm. Functional studies were conducted by inhibiting NEU1 activity to examine its effects on sperm motility and fertilization capacity. Additionally, NEU1 expression was compared between asthenozoospermic and normozoospermic individuals, and in vitro fertilization (IVF) assays were performed to evaluate its role in fertilization. Furthermore, a murine model was used to explore the origin of NEU1 during sperm maturation, particularly focusing on whether it is secreted and transferred onto sperm by epididymal epithelial cells. RESULTS: This study demonstrated that NEU1 is highly expressed in both human and murine sperm, and its expression level is closely associated with sperm motility and fertilization capacity. Sperm with higher motility exhibited significantly elevated NEU1 expression, which positively correlated with sperm kinematic parameters such as velocity and linearity. Inhibition of NEU1 activity resulted in a marked decline in sperm motility and fertilization potential. Furthermore, NEU1 is secreted by epididymal epithelial cells and subsequently transferred to the sperm surface. It regulates α-2,6 sialylation, thereby influencing sperm maturation, energy metabolism, and capacitation. IVF assays further confirmed a significant correlation between NEU1 expression and fertilization success. CONCLUSION: This study identifies NEU1 as a key regulatory enzyme on the sperm surface, directly influencing sperm motility and fertilization capacity. NEU1 is secreted by epididymal epithelial cells and transferred onto sperm, mediating sialylation modifications and regulating sperm capacitation and metabolic processes. These findings provide novel insights into the functional role of sialidases in sperm maturation and function, offering potential biomarkers and therapeutic targets for the diagnosis and treatment of male infertility.