Nascent Focal Adhesions Are Responsible for the Generation of Strong Propulsive Forces in Migrating Fibroblasts

TLDR

Fibroblast migration relies on complex mechanical interactions with the substrate, yet the contribution of focal adhesions to force transduction remains unclear. The study aims to determine how focal adhesions mediate traction forces by mapping stress patterns in GFP‑zyxin–expressing fibroblasts. Traction stress was mapped by imaging GFP‑zyxin–labeled focal adhesions in migrating fibroblasts. The analysis revealed that small, faint adhesions at the leading edge generate strong propulsive forces, whereas large, mature adhesions exert weaker traction, an inverse relationship unique to the leading edge that diminishes as adhesions mature and shift from force transmission to passive anchorage.

Abstract

Fibroblast migration involves complex mechanical interactions with the underlying substrate. Although tight substrate contact at focal adhesions has been studied for decades, the role of focal adhesions in force transduction remains unclear. To address this question, we have mapped traction stress generated by fibroblasts expressing green fluorescent protein (GFP)-zyxin. Surprisingly, the overall distribution of focal adhesions only partially resembles the distribution of traction stress. In addition, detailed analysis reveals that the faint, small adhesions near the leading edge transmit strong propulsive tractions, whereas large, bright, mature focal adhesions exert weaker forces. This inverse relationship is unique to the leading edge of motile cells, and is not observed in the trailing edge or in stationary cells. Furthermore, time-lapse analysis indicates that traction forces decrease soon after the appearance of focal adhesions, whereas the size and zyxin concentration increase. As focal adhesions mature, changes in structure, protein content, or phosphorylation may cause the focal adhesion to change its function from the transmission of strong propulsive forces, to a passive anchorage device for maintaining a spread cell morphology.