Title:
Vascular Mechanobiology: Endothelial Cell Responses to Fluid Shear Stress

Kimiko Yamamoto
Laboratory of System Physiology, Department of Biomedical Engineering,
Graduate School of Medicine, University of Tokyo , Tokyo , Japan

Abstract:
Endothelial cells (ECs) alter their functions in response to hemodynamic shear stress, and although their responses play important roles in vascular tone control, angiogenesis, and atherogenesis, how ECs recognize shear stress and transmit signals into the cell interior is poorly understood. Our previous studies demonstrated that calcium signaling is crucial to shear-stress mechanotransduction. Shear stress evokes a rapid, dose-dependent increase in intracellular calcium concentration caused by an influx of extracellular calcium via ATP-operated P2X4 ion channels. P2X4 activation requires the presence of endogenous ATP released by ECs, but the mechanism of the ATP release remains unknown. To analyze the dynamics of ATP release, we visualized ATP release at the cell surface by using cell-surface attached luciferase and a CCD camera. When exposed to shear stress, cultured ECs simultaneously released ATP in both, a highly concentrated, localized manner and a diffuse manner. The hot spots of ATP release occurred at caveolin-1-rich regions of the cell membrane and were blocked by caveolin-1 knockdown with siRNA, indicating involvement of caveolae in the localized ATP release. Immediately after this localized ATP release, an increase in intracellular calcium concentration and subsequent calcium wave occurred at the same site as the localized ATP release, suggesting that the ATP released at caveolae activates nearby P2X4 ion channels, which triggers shear stress calcium signaling in ECs. Our study in P2X4 -knockout mice revealed that the absence of shear stress calcium signaling leads to a reduction in endothelial NO production and impairs control of blood pressure, flow-induced vasodilation, and flow-mediated vascular remodeling in vivo.

References:
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