β1 integrin is a sensor of blood flow direction

The ability of endothelial cells (EC) to sense blood flow direction is a critical determinant of vascular health and disease. Unidirectional flow induces EC alignment and vascular homeostasis, whereas bidirectional flow has pathophysiological effects. EC express several mechanoreceptors that can respond to fluid flow (shear stress) but the mechanism for sensing the direction of shearing force is poorly understood. We observed using in vitro flow systems and magnetic tweezers that β1 integrin is a key sensor of force direction because it is activated by unidirectional but not bidirectional shearing forces. Consistently, β1 integrin was essential for Ca2+ signalling and cell alignment in response to unidirectional but not bidirectional shear stress. β1 integrin activation by unidirectional force was amplified in EC that were pre-sheared in the same direction, indicating that alignment and β1 integrin activity has a feedforward interaction which is a hallmark of system stability. En face staining and EC-specific genetic deletion studies of the murine aorta revealed that β1 integrin is activated and is essential for EC alignment at sites of unidirectional flow but is not activated at sites of bidirectional flow. In summary, β1 integrin sensing of unidirectional force is a key mechanism for decoding blood flow mechanics to promote vascular homeostasis.