Effect of exogenous neurotrophins on Trk receptor phosphorylation, cell proliferation, and neurotrophin secretion by cells isolated from the human lamina cribrosa.
OBJECTIVE
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.
Lambert
Wendi S
WS
Department of Cell Biology and Genetics, University of North Texas Health Science Center at Fort Worth, Fort Worth, TX, USA. wlambert@chg.duhs.duke.edu
Clark
Abbot F
AF
Wordinger
Robert J
RJ
D000199:Actins / Q000378:metabolism; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D015153:Blotting, Western; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism; D002227:Carbazoles / Q000494:pharmacology; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D003094:Collagen / Q000378:metabolism; D004549:Elastin / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006801:Humans; D026121:Indole Alkaloids; D020932:Nerve Growth Factor / Q000378:metabolism; D009414:Nerve Growth Factors / Q000378:metabolism* / Q000494:pharmacology*; D019006:Neural Cell Adhesion Molecules / Q000378:metabolism; D009898:Optic Disk / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*
D000199:Actins; D019208:Brain-Derived Neurotrophic Factor; D002227:Carbazoles; D004791:Enzyme Inhibitors; D005904:Glial Fibrillary Acidic Protein; D026121:Indole Alkaloids; D009414:Nerve Growth Factors; D019006:Neural Cell Adhesion Molecules; D003094:Collagen; D004549:Elastin; D020932:Nerve Growth Factor; C049985:staurosporine aglycone; D020794:Receptor Protein-Tyrosine Kinases