Figure 4. NGF increases VEGF expression via the TrkA receptor and is mediated by the activation of ERK1/2 and AKT signaling. Müller cells were treated with 100 ng/ml of nerve growth factor (NGF) with or without 20 nM K252a (TrkA inhibitor), 10 µM U0126 (extracellular signal-regulated kinases 1/2 (ERK1/2) pathway inhibitor), or 10 µM LY294002 (phosphatidylinositol 3-kinase (PI3K)/AKT inhibitor) for 12 or 24 h. The vascular endothelial growth factor (VEGF) protein level in the supernatants was detected with enzyme-linked immunosorbent assay (ELISA). The TrkA, ERK1/2, and PI3K/AKT inhibitors decreased the ability of NGF to promote VEGF expression to some extent. n=6, * p<0.05, ** p<0.01, *** p<0.001.