Figure 2. Effect of nerve growth factor on the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) and mitogen activated protein kinase (MAPK)/extracellular signal-regulated kinase (Erk) signaling pathways in human corneal epithelial cells. A: Human corneal epithelial cells (HCECs) were incubated in defined keratinocyte serum-free medium (K-SFM) without growth factors for 24 h before nerve growth factor (NGF) stimulation and then treated with NGF at 25 ng/ml for different periods. B: HCECs were treated with different concentrations of NGF for 60 min. A total of 50 μg cell lysates were analyzed for expression of the indicated genes by immunoblotting analysis. Tyr674/675 phospho-TrkA indicates the NGF signaling activity. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was used as a loading control. For both A and B, results are representative of three independent experiments. Experiments were performed in triplicate.