Fibronectin (Fn) is an extracellular matrix protein that orchestrates complex cell adhesion and signaling through cell surface integrin receptors during tissue development, remodeling, and disease, such as fibrosis. Fn is sensitive to mechanical forces in its tandem type III repeats, resulting in extensive molecular enlongation. As such, it has long been hypothesized that cell- and tissue-derived forces may activate an “integrin switch” within the critical integrin-binding ninth and 10th type III repeats—conferring differential integrin-binding specificity, leading to differential cell responses. Yet, no direct evidence exists to prove the hypothesis nor demonstrate the physiological existence of the switch. We report direct experimental evidence for the Fn integrin switch both in vitro and ex vivo using a scFv engineered to detect the transient, force-induced conformational change, representing an opportunity for detection and targeting of early molecular signatures of cell contractile forces in tissue repair and disease.

Cells communicate with the extracellular matrix (ECM) protein fibronectin (Fn) through integrin receptors on the cell surface. Controlling integrin-Fn interactions offers a promising approach to directing cell behavior, such as adhesion, migration, and differentiation, as well as coordinated tissue behaviors such as morphogenesis and wound healing. Several different groups have developed recombinant fragments of Fn that can control epithelial to mesenchymal transition, sequester growth factors, and promote bone and wound healing. It is thought that these physiological responses are, in part, due to specific integrin engagement. Furthermore, it has been postulated that the integrin-binding domain of Fn is a mechanically sensitive switch that drives binding of one integrin heterodimer over another. Although computational simulations have predicted the mechano-switch hypothesis and recent evidence supports the existence of varying strain states of Fn , experimental evidence of the Fn integrin switch is still lacking. Evidence of the integrin mechano-switch will enable the development of new Fn-based peptides in tissue engineering and wound healing, as well as deepen our understanding of ECM pathologies, such as fibrosis.

Highlights d Angiomotin is required for vascular expansion d Angiomotin is an important component of the integrin adhesome d Angiomotin relays mechanical signals from the integrins to the cytoskeleton