Purpose: Glaucoma is the number one cause of preventable blindness in the United States. The lamina cribrosa (LC) region of the optic nerve head (ONH) is a major site of injury in glaucomatous optic neuropathy. Neurotrophins (NTs), which include NGF, BDNF, NT-3, and NT-4, are growth factors involved in the development and support of neurons and in non-neuronal interactions. Cells within the human LC express high affinity tyrosine kinase receptors (Trks) for NTs. The purpose of this study was to determine if exogenous NTs cause (a) phosphorylation of Trk receptors in LC cells and ONH astrocytes and (b) cell proliferation and/or secretion of NTs by LC cells and ONH astrocytes. Methods: Trk phosphorylation in response to exogenous NGF, BDNF, NT-3, and NT-4 treatment was studied in LC cells and ONH astrocytes using immunoprecipitation and Western blotting. Cell number was assayed following treatment with exogenous NTs or the Trk phosphorylation inhibitor compound K-252a. Secretion of NTs following exogenous administration of NTs was determined using immunoassays. Results: LC cells and ONH astrocytes express Trk receptors that are phosphorylated in response to exogenous NTs. Autocrine/paracrine signaling was also evident by Trk phosphorylation in the absence of exogenous NT treatment. ONH astrocyte cell number increased following exogenous treatment with each NT. LC cell number increased following exogenous NGF or NT-3 treatment only. Treatment with the Trk phosphorylation inhibitor K-252a decreased both LC and ONH astrocyte cell number. Exogenous NT treatment increased the secretion of NGF by LC cells and ONH astrocytes. BDNF secretion by LC cells and ONH astrocytes was decreased by exogenous NT treatment. Conclusions: LC cells and ONH astrocytes express functional Trk receptors that can be activated in response to exogenous NTs. The activation of Trk receptors expressed by LC cells and ONH astrocytes in the absence of exogenous NT treatment suggests autocrine/paracrine NT signaling may occur within the ONH. Neurotrophin signaling in LC cells and ONH astrocytes may regulate cell number and/or NT secretion within the LC region of the ONH.
|Number of pages||8|
|State||Published - 19 Apr 2004|