Interplay of actin nematodynamics and anisotropic tension controls endothelial mechanics

Blood vessels expand and contract actively, while continuously experiencing dynamic external stresses from the blood flow. The mechanical response of the vessel wall is that of a composite material: its mechanical properties depend on a diverse set of cellular mechanical components, which change dynamically as cells respond to external stress. Mapping the relationship between these underlying cellular processes and emergent tissue mechanics is an on-going challenge, in particular in endothelial cells. Here we use a microstretcher mimicking the native environment of blood vessels to assess both the mechanics and cellular dynamics of an endothelial tube in response to a physiological increase in luminal pressure. The characterization of the instantaneous monolayer elasticity reveals a strain-stiffening, actin-dependent and substrate-responsive behavior. In response to a maintained pressure increase, the tissue displays a fluid-like expansion, accompanied by the reorientation of cell shape and of actin fibers. This actin-driven reorientation depends on focal adhesions and adherens junctions, two key mechanosensors. We introduce a mechanical model coupling actin fiber nematodynamics with active and elastic tension generation by actin fibers in the endothelium, which recapitulates the response to pressure of endothelial tubes.