Aquaporins 2, 3, 4, 7, 8, and 11 in feline spermatozoa: relations to semen quality, osmotolerance and freezability.

Aquaporins (AQPs) play a critical role in maintaining the osmotic equilibrium necessary for sperm function and survival in changing environment. This study aimed to characterize the expression and localization of AQP2, -3, -4, -7, -8, and -11 in domestic cat spermatozoa and to evaluate their relationship with fresh semen quality, osmotic stress response, and cryotolerance. Semen samples from 5 adult males were analyzed using immunocytochemistry (localization) and from the other 15 individuals were analyzed using Western blot (correlations with semen quality, osmotic stress response, and freezability). All examined AQPs were identified, primarily localized to the sperm tail, and AQP11 additionally in the acrosomal region. AQP7 showed variable staining patterns, with strong immunoreactivity in cytoplasmic droplets and spermatozoa with the Dag-like defect. Correlation analysis revealed that AQP8 abundance was positively associated with normal morphology and was significantly higher in spermatozoa with high hyperosmotic survival, but lower in good freezing group. AQP2 abundance was significantly higher in young males compared to adults and correlated positively with midpiece defects. Specific AQPs were also linked to movement patterns (ALH, LIN) and acrosomal integrity; notably, AQP7 was negatively correlated, and AQP11 positively with acrosomal damage. These results demonstrate that AQPs are widely expressed in feline spermatozoa and are significantly associated with sperm morphology, movement characteristics, acrosome integrity, and cryopreservation success. In particular, AQP8 may serve as a potential biomarker for sperm cryotolerance in the domestic cat, but further studies on larger number of individuals are required.