Ptn stimulates spheroid sprouting of HRMVECs. a Representative images of spheroid sprouting. Ptn, 20 ng/ml; VEGF, 5 ng/ml. Bar 100 μl. b Quantification of endothelial sprouts. The average length of sprouts per spheroid was quantified. The assay was independently performed three times with similar outcomes. One representative experiment is shown. n = 7 wells. ±SEM, ***p < 0.001, ****p < 0.0001, versus control, t test.