Investigating circular dorsal ruffles through varying substrate stiffness and mathematical modeling

Area of Science:

• Cell Biology
• Biophysics
• Mechanobiology

Background:

• Circular dorsal ruffles (CDRs) are transient, actin-rich structures on stimulated cells.
• The formation dynamics and mechanisms of CDRs remain largely unknown.
• CDRs are associated with the disappearance of nearby stress fibers.

Purpose of the Study:

• To investigate the effect of substrate stiffness on CDR formation and dynamics.
• To elucidate the underlying molecular mechanisms linking substrate stiffness to CDRs.

Main Methods:

• NIH 3T3 fibroblasts were cultured on substrates with stiffness ranging from 20 kPa to 1800 kPa.
• Experimental observations of CDRs were correlated with substrate stiffness.
• A mathematical model of signaling pathways (Rac-Rho antagonism) was developed to explain observed phenomena.

Main Results:

• Increased substrate stiffness significantly prolonged the lifetime of CDRs.
• A model indicated that stiffness enhances mDia1-nucleated stress fiber formation via Rho activation.
• This leads to increased G-actin availability, prolonging Arp2/3-nucleated CDR formation via Rac activation.
• Negative feedback mechanisms explain CDR actin propagation as an excitable wave.

Conclusions:

• Substrate stiffness is a critical regulator of CDR formation and lifetime.
• The Rac-Rho signaling axis mediates the mechanosensitive regulation of CDR dynamics.
• CDRs exhibit excitable wave-like propagation, influenced by actin dynamics and feedback mechanisms.