Mammalian sperm hyperactivation regulates navigation via physical boundaries and promotes pseudo-chemotaxis

Area of Science:

• Reproductive Biology
• Biophysics
• Microfluidics

Background:

• Mammalian sperm require precise navigation within the female reproductive tract for fertilization.
• Sperm hyperactivation, a change in flagellar beating, is crucial for fertilization in vivo.
• Understanding sperm navigation mechanisms is vital for reproductive health research.

Purpose of the Study:

• To investigate how sperm hyperactivation influences sperm navigation in microfluidic environments.
• To elucidate the role of physical boundaries and sperm-motility changes in sperm guidance.
• To explore the phenomenon of "pseudo-chemotaxis" in sperm.

Main Methods:

• Utilized high-aspect ratio microfluidic reservoirs to observe bovine sperm motion.
• Employed theoretical and computational modeling to analyze sperm-wall interactions.
• Administered pharmacological agonists to induce and study sperm hyperactivation.

Main Results:

• Sperm hyperactivation significantly modulates sperm-sidewall interactions and navigation.
• Hyperactivated sperm showed reduced swimming along sidewalls once intrinsic curvature exceeded a critical value.
• Nonthermal fluctuations in curvature near the critical value induced "Run-Stop" motion.
• Hyperactivation led to "pseudo-chemotaxis," with sperm preferring areas of higher agonist concentration.

Conclusions:

• Sperm hyperactivation is a critical factor in modulating sperm navigation through physical boundaries.
• The study reveals a novel mechanism of sperm guidance influenced by motility changes and microenvironmental cues.
• Findings contribute to understanding sperm behavior and may inform fertility treatments.