Matrix stiffness increases energy efficiency of endothelial cells.

To form blood vessels, endothelial cells rearrange their cytoskeleton, generate traction stresses, migrate, and proliferate, all of which require energy. Despite these energetic costs, stiffening of the extracellular matrix promotes tumor angiogenesis and increases cell contractility. However, the interplay between extracellular matrix, cell contractility, and cellular energetics remains mechanistically unclear. Here, we utilized polyacrylamide substrates with various stiffnesses, a real-time biosensor of ATP, and traction force microscopy to show that endothelial cells exhibit increasing traction forces and energy usage trend as substrate stiffness increases. Inhibition of cytoskeleton reorganization via ROCK inhibition resulted in decreased cellular energy efficiency, and an opposite trend was found when cells were treated with manganese to promote integrin affinity. Altogether, our data reveal a link between matrix stiffness, cell contractility, and cell energetics, suggesting that endothelial cells on stiffer substrates can better convert intracellular energy into cellular traction forces. Given the critical role of cellular metabolism in cell function, our study also suggests that not only energy production but also the efficiency of its use plays a vital role in regulating cell behaviors and may help explain how increased matrix stiffness promotes angiogenesis.