TGF-beta-induced apoptosis of cerebellar granule neurons is prevented by depolarization.
The regulation of programmed cell death in the developing nervous system involves target-derived survival factors, afferent synaptic activity, and hormone- and cytokine-dependent signaling. Cultured immature cerebellar granule neurons die by apoptosis within several days in vitro unless maintained in depolarizing (high) concentrations of potassium (25 mM K+). Here we report that transforming growth factors (TGF)-beta1, -beta2, and -beta3 accelerate apoptosis of these neurons when maintained in physiological (low) K+ medium (5mM K+) as assessed by measures of viability, quantitative DNA fragmentation, and nuclear morphology. TGF-beta-induced apoptosis of these neurons is not blocked by CNTF and LIF, cytokines that enhance neuronal survival when applied alone, or by IGF-I, which prevents apoptosis upon potassium withdrawal. In contrast, neurons that differentiate in high K+ medium for several days in vitro acquire resistance to TGF-beta-mediated cell death. Granule neurons maintained in either low or high K+ medium produce latent, but not bioactive, TGF-beta1 and -beta2. Because neutralizing TGF-beta antibodies fail to augment survival of low K+ neurons, the cerebellar neurons are apparently unable to activate latent TGF-beta. Thus, apoptosis of low K+ neurons is not attributable to endogenous production of TGF-beta. Taken together, our data suggest that TGF-beta may limit the expansion of postmitotic neuronal precursor populations by promoting their apoptosis but may support survival of those neurons that have maturated, differentiated, and established supportive synaptic connectivity.
de Luca
A
A
Section of Clinical Immunology, Department of Internal Medicine, University Hospital, Zürich, Switzerland.
Weller
M
M
Fontana
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A
D000818:Animals; D017209:Apoptosis; D002470:Cell Survival / Q000187:drug effects; D016922:Cellular Senescence; D002531:Cerebellum / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D003470:Culture Media; D016207:Cytokines / Q000494:pharmacology; D004594:Electrophysiology; D006801:Humans; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011994:Recombinant Proteins; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000494:pharmacology* / Q000502:physiology
D003470:Culture Media; D016207:Cytokines; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D011188:Potassium