title: Inhibition of fibroblast growth factor receptor 1 endocytosis promotes axonal branching of adult sensory neurons.
abstract: Fibroblast growth factors (FGFs) promote axon growth during development and regeneration of the nervous system. Among the four types of FGF receptors (FGFRs), FGFR1 is expressed in adult sensory neurons of dorsal root ganglia (DRG), and overexpression of FGFR1 promotes FGF-2-induced elongative axon growth in vitro. Ligand-induced activation of FGFR1 is followed by endocytosis and lysosomal degradation, which leads to the termination of receptor signaling. We previously reported that the lysosomal inhibitor leupeptin enhances FGF-2-induced elongative axon growth of adult DRG neurons overexpressing FGFR1. To better understand the role of subcellular localization of FGFR1 in axon growth, we analyzed the effects of inhibition of endocytosis of FGFR1 on FGF-2-induced neurite outgrowth in PC12 pheochromocytoma cells and adult DRG neurons. The endocytosis inhibitors methyl-β-cyclodextrin (MβCD) and chlorpromazine enhanced surface localization of FGFR1 in PC12 cells and DRG neurons. Furthermore, MβCD and chlorpromazine increased FGF-2-induced neurite outgrowth of PC12 cells and axonal branching of adult DRG neurons overexpressing FGFR1, whereas MβCD inhibited FGF-2-induced axonal elongation. Analysis of the signaling pathways involved in axon morphology revealed that FGF-2-induced phosphorylation of extracellular signal-regulated kinase (ERK) and Akt was increased by inhibition of FGFR1 endocytosis. Together, our results imply that inhibition of FGFR1 endocytosis by MβCD or chlorpromazine promotes FGF-2-induced axonal branching. The results of this study confirm that internalization of FGFR1 controls axon growth and morphology of adult sensory neurons via selective activation of intracellular signaling pathways.
authors.affiliation: Division of Neuroanatomy, Innsbruck Medical University, Muellerstrasse 59, A-6020 Innsbruck, Austria.
authors.forename: B
authors.initials: B
authors.lastname: Hausott
authors.forename: A
authors.initials: A
authors.lastname: Rietzler
authors.forename: N
authors.initials: N
authors.lastname: Vallant
authors.forename: M
authors.initials: M
authors.lastname: Auer
authors.forename: I
authors.initials: I
authors.lastname: Haller
authors.forename: S
authors.initials: S
authors.lastname: Perkhofer
authors.forename: L
authors.initials: L
authors.lastname: Klimaschewski
mesh_terms: D000375:Aging; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001369:Axons / Q000187:drug effects / Q000378:metabolism*; D015153:Blotting, Western; D002746:Chlorpromazine / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D005727:Ganglia, Spinal / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D018613:Microscopy, Confocal; D055495:Neurogenesis / Q000187:drug effects / Q000502:physiology*; D016716:PC12 Cells; D051381:Rats; D051496:Receptor, Fibroblast Growth Factor, Type 1 / Q000378:metabolism*; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D018492:Dopamine Antagonists; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; C496350:Fgfr1 protein, rat; D051496:Receptor, Fibroblast Growth Factor, Type 1; D002746:Chlorpromazine