Sialic Acids and Tetraspanins: An Insight into their Potential as Indicators of Human Sperm Quality

Since routine sperm analysis cannot detect molecular-level defects, efforts continue to find additional markers for selecting the "highest quality" sperm. This study analyzes ejaculates from normozoospermic and non-normozoospermic men, including teratozoospermics (T), asthenoteratozoospermics (AT), and oligoasthenoteratozoospermics (OAT), by two approaches. The first is distribution of sialic acid residues, molecules critical for sperm migration and survival in female reproductive tract, using lectins with distinct binding specificities (SNA I, MAL I, WGA). The second is the localization of membrane proteins, tetraspanins (CD9, CD63, CD81, CD151), which are involved in regulation of numerous cellular processes. Flow cytometry showed no significant differences in overall lectin positivity between diagnostic groups. However, in relation to sperm viability based on propidium iodide (PI) staining, SNA I binding was significantly higher in PI-low sperm across all groups. MAL I labeling increased in PI-intermediate and PI-high sperm, particularly in T and OAT ejaculates. WGA positivity decreased in the viable sperm of non-normozoospermic groups. Immunofluorescence analysis revealed tetraspanins in a subset of spermatozoa in both groups, most frequently in the acrosome and/or equatorial region, the primary site of sperm-egg fusion. Our results suggest that lectin-staining combined with PI could provide valuable insights into sperm status. SNA I and MAL I-based analysis could support early detection of potentially poor-quality sperm, that is, negative selection.