Effects of VEGF and TNF-α on tip cell differentiation and effects of VEGF on glycolysis and mitochondrial respiration. VEGF (25 ng/ml) treatment of HUVEC cultures increased relative tip cell numbers (a) and increased mRNA expression levels of 5 out of 8 tip cell-specific genes (b) at 24 h after treatment. Reduced percentage of tip cells (c) and reduced mRNA expression levels of 7 out of 8 tip cell-specific genes (d) were found in HUVEC cultures at 24 h after treatment with TNF-α (10 ng/ml). HUVEC cultures treated with VEGF showed induced mitochondrial respiration (e) and glycolysis (f). VEGF induced mitochondrial respiration (g) and glycolysis (h) in tip cells at 24 h after treatment. OCR and ECAR measurements were represented as fold change compared to control basal OCR and ECAR levels, respectively. Results are shown as means ± SEM of experiments with HUVECs of at least 3 donors. *P < 0.05, **P < 0.01, and ***P < 0.001 as compared to control (Unpaired Student’s t-test).