Programmed cell death in the developing inner ear is balanced by nerve growth factor and insulin-like growth factor I.
Nerve growth factor induces cell death in organotypic cultures of otic vesicle explants. This cell death has a restricted pattern that reproduces the in vivo pattern of apoptosis occurring during inner ear development. In this study, we show that binding of nerve growth factor to its low affinity p75 neurotrophin receptor is essential to achieve the apoptotic response. Blockage of binding to p75 receptor neutralized nerve-growth-factor-induced cell death, as measured by immunoassays detecting the presence of cytosolic oligonucleosomes and by TUNEL assay to visualize DNA fragmentation. Nerve growth factor also induced a number of cell-death-related intracellular events including ceramide generation, caspase activation and poly-(ADP ribose) polymerase cleavage. Again, p75 receptor blockade completely abolished all of these effects. Concerning the intracellular pathway, ceramide increase depended on initiator caspases, whereas its actions depended on both initiator and effector caspases, as shown by using site-specific caspase inhibitors. Conversely, insulin-like growth factor I, which promotes cell growth and survival in the inner ear, abolished apoptosis induced by nerve growth factor. Insulin-like growth factor cytoprotective actions were accomplished, at least in part, by decreasing endogenous ceramide levels and activating Akt. Taken together, these results strongly suggest that regulation of nerve-growth-factor-induced apoptosis in the otocysts occurs via p75 receptor binding and is strictly controlled by the interaction with survival signalling pathways.
Frago
Laura M
LM
Instituto de Investigaciones Biomédicas "Alberto Sols", Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Arturo Duperier 4, 28029 Madrid, Spain.
Cañón
Susana
S
de la Rosa
Enrique J
EJ
León
Yolanda
Y
Varela-Nieto
Isabel
I
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D020169:Caspases / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002518:Ceramides / Q000378:metabolism; D002642:Chick Embryo; D053938:DNA Fragmentation / Q000187:drug effects / Q000502:physiology; D004347:Drug Interactions / Q000502:physiology; D007758:Ear, Inner / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000494:pharmacology; D020932:Nerve Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D009924:Organ Culture Techniques; D011065:Poly(ADP-ribose) Polymerases / Q000187:drug effects / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D020800:Receptor, Nerve Growth Factor / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D002518:Ceramides; D004791:Enzyme Inhibitors; D011518:Proto-Oncogene Proteins; D020800:Receptor, Nerve Growth Factor; D007334:Insulin-Like Growth Factor I; D020932:Nerve Growth Factor; D011065:Poly(ADP-ribose) Polymerases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020169:Caspases