Glial cell line-derived neurotrophic factor requires transforming growth factor-beta for exerting its full neurotrophic potential on peripheral and CNS neurons.
Numerous studies have suggested that glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic molecule. We show now on a variety of cultured neurons including peripheral autonomic, sensory, and CNS dopaminergic neurons that GDNF is not trophically active unless supplemented with TGF-beta. Immunoneutralization of endogenous TGF-beta provided by serum or TGF-beta-secreting cells, as e.g., neurons, in culture abolishes the neurotrophic effect of GDNF. The dose-response relationship required for the synergistic effect of GDNF and TGF-beta identifies 60 pg/ml of either factor combined with 2 ng/ml of the other factor as the EC50. GDNF/TGF-beta signaling employs activation of phosphatidylinositol-3 (PI-3) kinase as an intermediate step as shown by the effect of the specific PI-3 kinase inhibitor wortmannin. The synergistic action of GDNF and TGF-beta involves protection of glycosylphosphatidylinositol (GPI)-linked receptors as shown by the restoration of their trophic effects after phosphatidylinositol-specific phospholipase C-mediated hydrolysis of GPI-anchored GDNF family receptor alpha. The biological significance of the trophic synergism of GDNF and TGF-beta is underscored by colocalization of the receptors for TGF-beta and GDNF on all investigated GDNF-responsive neuron populations in vivo. Moreover, the in vivo relevance of the TGF-beta/GDNF synergism is highlighted by the co-storage of TGF-beta and GDNF in secretory vesicles of a model neuron, the chromaffin cell, and their activity-dependent release. Our results broaden the definition of a neurotrophic factor by incorporating the possibility that two factors that lack a neurotrophic activity when acting separately become neurotrophic when acting in concert. Moreover, our data may have a substantial impact on the treatment of neurodegenerative diseases.
Krieglstein
K
K
Department of Neuroanatomy, University of Heidelberg, D-69120 Heidelberg, Germany.
Henheik
P
P
Farkas
L
L
Jaszai
J
J
Galter
D
D
Krohn
K
K
Unsicker
K
K
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D019439:Chromaffin Cells / Q000166:cytology / Q000187:drug effects; D004298:Dopamine / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D005333:Fetus / Q000166:cytology; D015870:Gene Expression / Q000502:physiology; D051100:Glial Cell Line-Derived Neurotrophic Factor; D017261:Glycosylphosphatidylinositols / Q000502:physiology; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects*; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000494:pharmacology*; D018696:Neuroprotective Agents / Q000032:analysis / Q000494:pharmacology*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000494:pharmacology; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; C495041:Gdnf protein, rat; D051100:Glial Cell Line-Derived Neurotrophic Factor; D017261:Glycosylphosphatidylinositols; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D018696:Neuroprotective Agents; D016212:Transforming Growth Factor beta; D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D004298:Dopamine; D000077191:Wortmannin