Microfluidic Devices for Quantifying the Role of Soluble Gradients in Early Angiogenesis - Mechanical and Chemical Signaling in Angiogenesis - page 55

a

b

C

Fig. 6 Human umbilical vein endothelial cells (HUVECs) extend filopodia with a directional
bias if cultured under a gradient above a threshold magnitude. Representative fluorescent
micrographs, nulclei = blue, actin cytoskeleton = red, of HUVECs in the a absence or
b presence of a VEGF gradient of magnitude 14 ng/mL/mm and of direction indicated by the
thick white arrow. We define filopodia, indicated by fine white arrows, as protrusions from the
cell membrane of length [ 3 lm and width \ 1 lm. To assess possible directional bias in
extensions, each cell is divided through its centroid into sections facing higher and lower
concentrations of VEGF. c Number of filopodia per cell facing each direction under different
linear concentration profiles of VEGF. Means are of n [ 70 cells ±standard deviation.
Statistically significant, p \ 0.001. Originally published in [ 30 ]. Reproduced by permission of
The Royal Society of Chemistry, http://dx.doi.org/10.1039/B719788H

substrates to enable a multifactorial study of VEGF gradients and cell-surface
interactions.
The importance of analyzing gradient steepness and average concentration as
separate inputs is further emphasized by studies of filopodia extension in 2D [ 30 ].
Cytoskeletal remodeling is a prerequisite for chemotaxis, so cytoskeletal asymmetry
is expected under conditions that induce chemotaxis. Similar to the results discussed
above, a gradient steepness of 14 ng/mL/mm was sufficient to induce asymmetry in