Neurotrophic factors in the human cornea

PURPOSE. To investigate neurotrophic growth factors and corresponding recep tors in human and rabbit corneal epithelium and stroma. METHODS. Transcription of nerve growth factor (NGF), neurotrophin 3 (NT-3), NT-4, brain-derived neurotrophic factor (BDNF), glial cell line- derived n eurotrophic factor (GDNF), and receptors Trk A-E, was investigated by rever se transcription-polymerase chain reaction. DNA dot blot analysis allowed t o estimate transcription levels. Single cell proliferation assays were perf ormed using recombinant NGF, BDNF, and GDNF. Mitogen-activated protein kina se signal transduction was investigated with Western blot analysis using an tibodies against-activated and total extracellular signal-regulated kinase (ERK) 1/2 and the jun N-terminal protein kinase (JNK) 1/2. RESULTS. Transcription of NGF, NT-3, BDNF, and Trk A, Trk B, Trk C, and Trk E receptors was detected in both ex vivo and cultured epithelium and strom a. Transcription of NT-4 was only detected in epithelium and transcription of GDNF only in stroma. Levels of transcription were higher for NT-3, NT-4, and the Trk receptors and lower for NGF, BDNF, and GDNF. NGF and GDNF stim ulated both epithelial colony formation and proliferation, whereas BDNF onl y enhanced colony formation. Stromal proliferation was enhanced in serum-fr ee medium. In epithelium, predominantly ERK 1 was activated by NGF, GDNF, a nd BDNF. In stromal cells NGF and GDNF stimulated phosphorylation of ERK 1 and JNK 1. CONCLUSIONS. Neurotrophic factors and tyrosine kinase receptors are transcr ibed in the human cornea. GDNF and NGF stimulate corneal epithelial prolife ration, and the effect of the latter might be mediated by activation of ERK 1. Neurotrophic factors have very specific effects on phosphorylation of E RK and JNK in epithelial and stromal cells. The differential expression of NT-4 and GDNF suggests a regulatory function within the cytokine network of the cornea.