New Approaches to Define The Functional Competency of Human Sperm Subpopulations and Its Relationship to Semen Quality

BACKGROUND: This study aimed at comparing a comprehensive set of functional and structural sperm characteristics be- tween sperm motility fractions and correlating results to the standard semen parameters. By grouping related variables, our objective was to establish the predictive power of semen parameters and whether they accurately reflect the function- ality of sperm motility fractions or merely a small set of parameters within individual fractions. MATERIALS AND METHODS: In this non-invasive experimental study, donor semen samples (n=55) were separated via double density gradient centrifugation, isolating a high (HM) and low motile (LM) sperm fraction. Fractions were evaluated for percentage vitality, chromatin integrity, mature spermatozoa, motility and kinematic parameters, hyper- activation, positive reactive oxygen species, intact mitochondrial membrane potential (MMP) and acrosome reaction. RESULTS: HM fractions had significantly (P<0.001) enhanced percentages of induced acrosome reaction (HM, 55.6 ± 14.3%, LM, 25.0 ± 16.5%), motility and kinematic parameters, hyperactivation, vitality (HM, 70.4 ± 9.7%, LM, 47.9 ± 10.3%), mitochondrial membrane intactness (HM, 67.2 ± 10.4%, LM, 44.7 ± 15.0%) and mature spermatozoa (HM, 83.4 ± 10.0%, LM, 64.6 ± 8.2%) with intact chromatin (HM, 80.5 ± 8.1%, LM, 71.3 ± 8.0%). Various sperm mor- phology abnormalities correlated with LM fractions’ grouped motility parameters (range, 0.46 to 0.51; range -0.4 to -0.75), whereas combined semen traits of total motility, progressive motility, viscosity and mucus penetration (MPT) correlated with HM fractions’ grouped motility parameters (range, 0.44 to 0.84). CONCLUSION: Collectively, total and progressive motility, viscosity and MPT may represent a reliable grouping of semen parameters for predicting the quality of HM sperm fractions. Separating the same donor semen samples into two signifi- cantly diverse motility sperm fractions could be a potential model in mimicking the qualities of fertile and sub-fertile males’ sperm populations and used for future research on the improvement of sperm subpopulations from males with different fertility statuses.