title: Neurotrophic factors cause activation of intracellular signaling pathways in Müller cells and other cells of the inner retina, but not photoreceptors.
abstract: OBJECTIVE
  Intravitreal injection of brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), or basic fibroblast growth factor (FGF2) promotes survival of photoreceptors exposed to various types of insults, but it is not known if these survival-promoting effects occur by direct action of the factors on photoreceptors or indirectly through the activation of other cells. In this study, the authors have sought to address this issue by determining which cells in the retina show evidence of activated intracellular signaling pathways acutely and at longer time points after intravitreal injection of these agents.
  
  
  METHODS
  Retinas were removed from C57BL/6J mice at 1, 6, or 24 hours after intravitreal injection of 1 microg of human BDNF, rat CNTF, human FGF2, or human transforming growth factor-alpha (TGFalpha), and immunohistochemically stained for phosphorylated extracellular signal-regulated kinase (pERK), phosphorylated cAMP responsive element binding protein (pCREB), or c-fos. Retinal organ cultures were incubated with 10 ng/ml of BDNF, CNTF, FGF2, or TGFalpha for 10 or 30 minutes or 1, 3, or 6 hours and then immunohistochemically stained for pERK, pCREB, or c-fos.
  
  
  RESULTS
  Intravitreal injection of BDNF, CNTF, or FGF2 resulted in a rapid increase in pERK immunoreactivity in Müller cells and a rapid increase in c-fos immunoreactivity in Müller, amacrine, and ganglion cells. Immunoreactivity for pERK and c-fos returned to baseline in all retinal cells at 6 or 24 hours after injection, but there was increased staining for glial fibrillary acidic protein (GFAP) in Müller cells at these time points. At no time after injection was there any staining for pERK or c-fos in photoreceptors. Similarly, retinal explants treated with FGF2, BDNF, or CNTF showed increased staining for pCREB, pERK, and c-fos in cells of the inner retina, but not photoreceptors.
  
  
  CONCLUSIONS
  These data support the hypothesis that BDNF, CNTF, and FGF2 exert their effects on photoreceptors by acting indirectly through activation of Müller cells and perhaps other nonphotoreceptor cells.
authors.affiliation: Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Wahlin
authors.forename: P A
authors.initials: PA
authors.lastname: Campochiaro
authors.forename: D J
authors.initials: DJ
authors.lastname: Zack
authors.forename: R
authors.initials: R
authors.lastname: Adler
mesh_terms: D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology*; D020934:Ciliary Neurotrophic Factor / Q000494:pharmacology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D019084:Fluorescent Antibody Technique, Indirect; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D007267:Injections; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009457:Neuroglia / Q000187:drug effects* / Q000378:metabolism; D009924:Organ Culture Techniques; D020419:Photoreceptor Cells, Vertebrate / Q000187:drug effects*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014822:Vitreous Body
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D020934:Ciliary Neurotrophic Factor; D017362:Cyclic AMP Response Element-Binding Protein; D005904:Glial Fibrillary Acidic Protein; D016760:Proto-Oncogene Proteins c-fos; D016222:Fibroblast Growth Factor 2; D020928:Mitogen-Activated Protein Kinases