Coupling biochemistry and hydrodynamics captures hyperactivated sperm motility in a simple flagellar model

Area of Science:

• Biophysics
• Reproductive Biology
• Computational Biology

Background:

• Sperm hyperactivation, essential for egg fertilization, involves characteristic asymmetrical flagellar waveforms and increased bend amplitude.
• Calcium (Ca(2+)) dynamics are critically involved in initiating and sustaining hyperactivated motility.

Purpose of the Study:

• To develop an integrative model linking CatSper channel-mediated Ca(2+) dynamics to a mechanical model of sperm flagellar movement.
• To investigate how Ca(2+) concentration and flagellar elasticity influence sperm swimming patterns and hyperactivation.

Main Methods:

• Coupling a model of Ca(2+) dynamics through the CatSper channel with a 3-D mechanical model of an idealized sperm flagellum.
• Incorporating passive stiffness and active bending moments dependent on local Ca(2+) concentration, with an asymmetry to simulate the axoneme's response.
• Simulating sperm movement in a viscous, incompressible fluid.

Main Results:

• The model successfully captures the transition from activated to hyperactivated motility by including asymmetry in bending moments.
• Simulated swimming velocities of the model flagellum show good agreement with experimental data for hyperactivated mouse sperm.
• Analysis revealed the significant impact of flagellar elastic properties and Ca(2+) dynamics on overall swimming patterns.

Conclusions:

• The integrative model provides a robust framework for understanding the biophysical mechanisms underlying sperm hyperactivation.
• This computational approach offers insights into the complex interplay between calcium signaling and flagellar mechanics in sperm motility.
• The model's predictive accuracy supports its utility in studying factors affecting sperm function and fertilization efficiency.