Mapping the relationship between integrin activation, focal adhesion organization and mechanotransduction in fibroblasts

Abstract: Cells can sense and respond to mechanical forces through a process called mechanotransduction. It is controlled by the mechanical cues, originated from the cell's microenvironment, and occurs via a complex, step-wise process. In this process, a cascade of events occurs, where the forces are essentially sensed by integrins and transmitted through filamentous actin (F-actin). The downstream events lead to the activation of transcriptional factors, which in turn impact the cellular response. YAP is a transcriptional coregulator, involved in cell proliferation. It is controlled by the canonical Hippo signaling pathway together with the mechanotransduction pathway. The effect of the latter is less studied and the exact process is yet unknown. This thesis focuses on further investigations of the mechanotransduction pathway and its influence on YAP activation in fibroblasts. Different microenvironments were modulated by modifying the fibronectin (FN) coating, which controls the amount of integrin activation and consequently affects the FA morphology together with the organization of F-actin. The organizational degree of F-actin in focal adhesions (FA) and morphological FA properties were compared to the YAP response. The results revealed that YAP activation is increased proportionally to the FN concentration, correlating to F-actin data. However, the lowest FN concentration caused a non-matching increase of activation. The findings propose that the YAP response might to some extent be determined by integrin activation. However, it has yet been impossible to decouple the effect of the Hippo signaling.