Inhibition effects of spermidine on VEGF-induced endothelial cell sprouting. A. HUVEC spheroids embedded in three-dimensional collagen gel were treated with VEGF (50 ng/ml), 200 nM TAT peptides and 10 μM spermidine as indicated. Spheroids were analyzed after 24 h with 10× magnification and the cumulative sprout length was quantified using image analysis. Shown is a representative of three similar experiments (mean ± SEM; n = 4-5 spheroids per treatment; **, p ≤ 0.01). B. Representative images show HUVEC spheroids after 24 h incubation with the indicated treatments taken with 10× magnification. C. HUVEC spheroid assay performed as in A, but with TCPTP siRNA -treated HUVEC (mean ± SEM; n = 4-5 spheroids per treatment; *, p ≤ 0.05). D. qRT-PCR quantitation of the TCPTP knockdown in HUVECs used in C.