Response of lymphatic endothelial cells to combined spatial and temporal variations in fluid flow.

One-way valves within lymphatic vessels are required for the efficient drainage of lymphatic fluids. Fluid flow is proposed to be a key cue in regulating both the formation and maintenance of lymphatic valves. However, to our knowledge, no previous study has systematically examined the response of LECs to the complex combination of spatially and temporally varying fluid flows that occur at lymphatic valves in vivo. We built an in vitro microfluidic device that reproduces key aspects of the flow environment found at lymphatic valves. Using this device, we found that a combination of spatially and temporally varying wall shear stresses (WSSs) led to upregulated transcription of PROX1 and FOXC2. In addition, we observed that combined spatial and temporal variations in WSS-modulated Ca 2+ signaling and led to increased cellular levels of NFATc1. These observations suggest that the physical cues generated by the flow environment present within lymphatic valves may act to activate key regulatory pathways that contribute to valve maintenance.