Neurotrophic effect of a novel TrkB agonist on retinal ganglion cells.
OBJECTIVE
Retinal ganglion cells (RGCs) die in glaucoma and virtually all optic neuropathies. Recently, novel tropomyosin-related kinase B (TrkB) monoclonal antibodies have been shown to activate TrkB receptors and exert neuroprotective and neurotrophic effects. In the present study, the authors examined the ability of one of them, 29D7, to elicit RGC survival and neurite growth both in culture and in vivo.


METHODS
RGCs from postnatal day (P)3 to P4 Sprague-Dawley rats were isolated by sequential immunopanning using a monoclonal antibody to Thy1. RGCs were cultured in serum-free defined medium in 96-well plates. RGC viability was assessed after 1 to 3 days by MTT assay. Activation of TrkB and downstream signaling molecules was confirmed by Western blot analysis. Intravitreal injections of 29D7 were performed after optic nerve axotomy, and subsequent RGC survival was quantified using beta-III tubulin immunostaining. Regeneration was assessed using retrograde fluorogold tracing in an optic nerve-peripheral nerve graft model.


RESULTS
Similar to brain-derived neurotrophic factor (BDNF), the 29D7 antibody strongly promoted RGC survival and neurite growth in vitro compared with medium alone or control IgG. Forskolin, which weakly supported RGC survival on its own, potentiated the effect of 29D7. Intravitreal injection of 29D7 enhanced RGC survival but not regeneration in vivo 2 weeks after optic nerve injury.


CONCLUSIONS
Together, these findings demonstrate the potential for antibody-mediated TrkB agonism as a potential therapeutic approach to enhance RGC survival after optic nerve injury. Further studies are needed to elucidate the mechanistic differences between this TrkB agonist and BDNF.
Hu
Ying
Y
Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA.
Cho
Seongeun
S
Goldberg
Jeffrey L
JL
D000818:Animals; D000831:Animals, Newborn; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D019771:Axotomy; D015415:Biomarkers / Q000378:metabolism; D015153:Blotting, Western; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology; D002452:Cell Count; D002469:Cell Separation; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016501:Neurites / Q000502:physiology; D009900:Optic Nerve / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020813:Receptor, trkB / Q000819:agonists*; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000502:physiology
D000911:Antibodies, Monoclonal; D015415:Biomarkers; D019208:Brain-Derived Neurotrophic Factor; D005576:Colforsin; D019869:Phosphatidylinositol 3-Kinases; D020813:Receptor, trkB; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases