Polarized actin structural dynamics in response to cyclic uniaxial stretch

Area of Science:

• Cell Biology
• Biophysics
• Mechanobiology

Background:

• Endothelial cell (EC) alignment to physical cues like flow or stretch is crucial for anti-inflammatory functions.
• The precise mechanisms governing polarized structural adaptation of ECs to mechanical stimuli are not fully understood.

Purpose of the Study:

• To investigate if early actin edge ruffling, a factor in cell polarization, is a prerequisite for stress fiber (SF) reorientation under cyclic uniaxial stretch.
• To elucidate the relationship between edge dynamics and cytoskeletal remodeling in response to mechanical stress.

Main Methods:

• Time-lapse microscopy of endothelial cells expressing EGFP-actin.
• Application of cyclic uniaxial and equibiaxial stretch.
• Pharmacological inhibition of Rho-kinase and Arp2/3 complex.
• Assessment of p21-activated kinase (PAK) localization.

Main Results:

• Cyclic stretch initially increased non-directional edge ruffling, followed by polarized ruffling perpendicular to the stretch axis.
• Rho-kinase inhibition shifted both ruffling and SF alignment parallel to the stretch axis.
• Arp2/3 inhibition affected cell elongation and polarized dynamics but not SF reorientation extent.
• PAK inhibition did not prevent SF reorientation, indicating it's not critical for this process.

Conclusions:

• Directional edge ruffling is not the primary driver of stress fiber reorientation in ECs subjected to stretch.
• Edge ruffling and stress fiber reorientation are coincident events, not causally linked, in response to mechanical stretch.
• These findings refine our understanding of endothelial cell mechanotransduction pathways.