Microtubule Polymerization and Cross-Link Dynamics Explain Axonal Stiffness and Damage

Area of Science:

• Neuroscience
• Biophysics
• Computational Biology

Background:

• Axonal damage is a key indicator of traumatic brain injury.
• The precise mechanisms underlying axonal damage remain incompletely understood.

Purpose of the Study:

• To develop a dynamic computational model of the axon to investigate the evolution of axonal damage under physical forces.
• To elucidate the interplay between microtubule dynamics, cross-link behavior, and mechanical forces in causing axonal failure.

Main Methods:

• A mechanistic, dynamic model of the axon was created, featuring polymerizing/depolymerizing microtubules and dynamic cross-links.
• Simulations explored axonal response to varying stretch and stretch rates, analyzing force, stiffness, and damage.
• Cross-link attachment probability was governed by thermal fluctuations, while detachment increased with applied physical forces.

Main Results:

• Slow loading resulted in gradual damage accumulation driven by cross-link dynamics and reduction.
• Fast loading led to rapid stretch and immediate rupture risk, dominated by cross-link deformation.
• Microtubule dynamics influenced axonal stiffness but not damage evolution at failure-relevant timescales.

Conclusions:

• Axonal failure mechanisms are emergent properties of microtubule polymerization, cross-link dynamics, and applied physical forces.
• The model provides insights into how molecular mechanisms dictate the timeline and severity of axon damage after brain impacts.