Dynamics of the axon plasma membrane skeleton

Area of Science:

• Biophysics
• Cell Biology
• Computational Neuroscience

Background:

• The axon plasma membrane skeleton (APMS) forms an orthotropic network of actin rings and spectrin filaments.
• APMS is known to enhance axon structural stability, but its role in axon deformation remains unclear.

Purpose of the Study:

• To investigate the mechanical response of the APMS to extensional forces.
• To understand the contribution of spectrin unfolding and actin-spectrin interactions to axon deformation.

Main Methods:

• Development of a coarse-grain molecular dynamics model of the APMS.
• Simulation of the network under uniaxial extension at various rates.
• Analysis of force-extension curves and spectrin repeat unfolding dynamics.

Main Results:

• The force-extension curve is initially linear and rate-dependent, with spectrin unfolding occurring even at low extensions.
• Unsynchronized spectrin unfolding prevents a synchronized force drop, unlike single spectrin tetramers.
• At higher extension rates, actin-spectrin dissociation leads to network softening and eventual severing.

Conclusions:

• The APMS exhibits complex mechanical behavior under tension, characterized by spectrin unfolding and potential network softening.
• The integrity of actin-spectrin links is crucial for maintaining APMS resistance to deformation.
• The findings provide insights into the biomechanical properties of axons and their response to physical stress.