Fig. 1: Endothelial tubes exhibit actin-dependent elasticity under luminal pressure.

a, Optical coherence tomography images of the vessel cross-section showing an increase in radius during pressure increase. Scale bar, 50 μm. b, Schematic of laser ablation showing the two directions of ablation: longitudinal (L) and circumferential (C) (i). Fluorescence images of LifeAct-endothelial cells showing the endothelial actin network pre- and post-longitudinal ablation (the area of ablation is denoted in yellow), showing a rapid opening of the wound, which is characteristic of high tissue tension in the circumferential direction. Scale bar, 20 μm. b, Initial recoil velocity post-ablation for monolayers cultured on a 6 mg ml⁻¹ collagen gel, showing an increase between the control (150 Pa) and stretched (650 Pa) channels, but only in the circumferential direction (ii). Ablations were performed in the minutes following the pressure increase for the stretched condition (n = 3). c, Channel diameter as a function of the luminal pressure (points) for monolayers cultured on a 2 mg ml⁻¹ (yellow, n = 3) and 6 mg ml⁻¹ (red) collagen gel, obtained either continuously with live imaging (chain of dots, n = 3) or at the beginning and end of pressure application (paired dots, n = 18), with the fitted analytical curves obtained from the strain-stiffening model (solid lines) (i). c, Inferred Young’s moduli of the endothelial tissue for the two collagen concentrations. For the 6 mg ml⁻¹ concentration (red), data from the continuous measurement (right, n = 3) and the discrete two-point measurement (left, n = 18), matching the curves in b(ii), are separated for clarity (ii). d, Endothelium stained for VE-cadherin, phalloidin and vinculin for two collagen concentrations (i): 2 mg ml⁻¹ (top) and 6 mg ml⁻¹ (bottom). Fluorescence intensity of the actin stress fibres (normalized by the mean cell intensity) as a function of collagen concentration (n = 5 (2 mg ml^–1) and n = 6 (6 mg ml^–1)) (ii). e, Channel diameter as a function of luminal pressure for control monolayers (yellow, n = 3) and monolayers treated with cytochalasin D (green, n = 3) and EDTA (blue, n = 2), cultured on a 2 mg ml⁻¹ collagen gel (i). Inferred Young’s moduli of control (n = 3) and endothelia treated with cytochalasin D (n = 3) and EDTA (n = 2), cultured on a 2 mg ml⁻¹ collagen gel (ii). f, Channel diameter as a function of time just after treatment with cytochalasin D (at t = 0), for monolayers cultured on a 6 mg ml⁻¹ collagen gel (n = 7) (i). Channel diameter as a function of luminal pressure for control monolayers (red, n = 18) and monolayers treated with cytochalasin D (green, n = 9) and EDTA (blue, n = 12), cultured on a 6 mg ml⁻¹ collagen gel ((ii) and (iii)). Inferred Young’s moduli of control (n = 18) and endothelia treated with cytochalasin D (n = 9) and EDTA (n = 12), cultured on a 6 mg ml⁻¹ collagen gel (iv).

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