ZAN, IZUMO1, and TMEM95 Protein Domains Identify the Physiological Status of the Sperm

Infertility is a growing concern, which has led to an increase in the use of assisted reproductive techniques, involving in vitro sperm capacitation. Nonetheless, the optimal capacitation time remains a matter of debate, and it is unknown whether it has an impact on the localization of key membrane proteins.

This study aimed to evaluate the distribution and dynamics of membrane protein domains zonadhesin (ZAN), izumo sperm-egg fusion 1 (IZUMO1), and transmembrane protein 95 (TMEM95) in sperm following 1 and 4 h of in vitro capacitation and subsequent induction of the acrosome reaction.

Sperm from 16 humans under five physiological conditions were used: noncapacitation, 1- and 4 h in vitro capacitation, and acrosome reaction induction. Immunolocalization of ZAN, IZUMO1, and TMEM95 was assessed using confocal microscopy.

The univariate and multivariate statistical analysis revealed a clear relationship between physiological conditions and protein dynamics. In particular, noncapacitated spermatozoa were characterized by an absence of ZAN and TMEM95. Whereas, regardless of the capacitation time (1 h vs. 4 h), there was an increase in the key protein presence with ZAN and IZUMO1 in the acrosomal region and TMEM95 in the equatorial region. After induction of acrosome reaction, IZUMO1 was relocated to the equatorial region.

Here we illustrate the potential to quantify physiological differences among human spermatozoa by a multibiomarker approach. However, no evidence supports that capacitation time influences ZAN, IZUMO1, and TMEM95 distribution.