title: A splice variant of trkB and brain-derived neurotrophic factor are co-expressed in retinal pigmented epithelial cells and promote differentiated characteristics.
abstract: There is evidence suggesting reciprocal trophic interactions between photoreceptors and the retinal pigmented epithelium (RPE), but the factors involved have not been identified. In this study, we investigated the hypothesis that one or more known neurotrophic factors act upon the RPE. Cultured human and freshly isolated bovine RPE cells demonstrated saturable specific binding for [125I]labeled BDNF, NT-4/5 and NT-3 with little specific binding for CNTF and none for NGF. Cross-competition experiments showed that BDNF is the preferred ligand and cross-linking of [125I]BDNF resulted in a doublet at 160 kd that was increased in RPE cells incubated in all-trans retinoic acid. There was basal phosphorylation of a 145 kd protein recognized by an anti-trk antibody that was increased in RPE cells pulsed with BDNF. RT-PCR with primers spanning the transmembrane domain demonstrated that RPE cells express trkB mRNA lacking a region homologous to exon 9 of chicken trkB, a splice variant that has been demonstrated to preferentially interact with BDNF. Northern blots demonstrated that cultured RPE cells also express mRNA for BDNF. BDNF did not stimulate proliferation or increase survival of RPE cells in serum-free medium, but promoted a differentiated morphology and increased the expression of cellular retinaldehyde binding protein, a marker of the differentiated state in RPE cells. An RPE cell line that spontaneously shows differentiated features showed a high level of BDNF mRNA. These data demonstrate that RPE cells express a short splice variant of trkB whose activation correlates with expression of differentiated characteristics and the cells themselves are capable of producing a ligand for the receptors. Signaling through trkB could play a role in differentiation of RPE cells during development and maintenance of the differentiated state in adult RPE.
authors.affiliation: Department of Ophthalmology, Johns Hopkins University School of Medicine, 600 N. Wolfe Street, Baltimore, MD 21287-9277, USA.
authors.forename: S F
authors.initials: SF
authors.lastname: Hackett
authors.forename: Z
authors.initials: Z
authors.lastname: Friedman
authors.forename: J
authors.initials: J
authors.lastname: Freund
authors.forename: C
authors.initials: C
authors.lastname: Schoenfeld
authors.forename: R
authors.initials: R
authors.lastname: Curtis
authors.forename: P S
authors.initials: PS
authors.lastname: DiStefano
authors.forename: P A
authors.initials: PA
authors.lastname: Campochiaro
mesh_terms: D000818:Animals; D001483:Base Sequence; D019208:Brain-Derived Neurotrophic Factor / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D004274:DNA, Recombinant; D015870:Gene Expression / Q000502:physiology*; D014644:Genetic Variation / Q000235:genetics*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors / Q000494:pharmacology; D010641:Phenotype; D010766:Phosphorylation; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D020801:Receptor, Ciliary Neurotrophic Factor; D017475:Receptors, Nerve Growth Factor / Q000235:genetics* / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D016895:Culture Media, Serum-Free; D004274:DNA, Recombinant; D009414:Nerve Growth Factors; D020801:Receptor, Ciliary Neurotrophic Factor; D017475:Receptors, Nerve Growth Factor; D014443:Tyrosine; D020794:Receptor Protein-Tyrosine Kinases