Modeling molecular mechanisms in the axon.

Area of Science:

• Biophysics
• Computational Biology
• Cell Biology

Background:

• Axons exhibit dynamic mechanical properties like stiffness and viscosity.
• The molecular basis for these emergent cellular properties is not well understood.

Purpose of the Study:

• To develop a computational mechanics model of axons.
• To investigate how molecular-level events, specifically microtubule crosslinking, give rise to macroscopic axonal mechanical properties.
• To explore the roles of passive and active crosslinking mechanisms in axon mechanics and elongation.

Main Methods:

• Developed a discrete computational model of axons, representing microtubules and their crosslinking.
• Simulated passive crosslinking (varying density and dynamics) and active crosslinking (involving dynein motors).
• Analyzed the impact of crosslink density, detachment, and reattachment times on axonal stiffness, viscosity, and internal stress.

Main Results:

• Axonal stiffness and viscosity increase linearly with crosslink density.
• These mechanical properties are highly sensitive to the timing of crosslink detachment and reattachment.
• Active crosslinking, utilizing dynein motors, was shown to generate internal stresses and actively drive axon elongation.

Conclusions:

• The computational model successfully links molecular-level crosslinking to emergent cellular-level mechanical properties of axons.
• Crosslink dynamics are critical determinants of axonal mechanical behavior.
• Active crosslinking provides a mechanism for generating internal stress and driving axon growth, with implications for understanding both normal physiology and pathology.