Abstract
Neuronal apoptosis contributes to the progression of neurodegenerative disease. Primary cerebellar granule neurons are an established in vitro model for investigating neuronal death. After removal of serum and depolarizing potassium, granule neurons undergo apoptosis via a mechanism that requires intrinsic (mitochondrial) death signals; however, the role of extrinsic (death receptor-mediated) signals is presently unclear. Here, we investigate involvement of death receptor signaling in granule neuron apoptosis by expressing adenoviral, AU1-tagged, dominant-negative Fas-associated death domain (Ad-AU1-deltaFADD). Ad-AU1-deltaFADD decreased apoptosis of granule neurons from 65 +/- 5 to 27 +/- 2% (n = 7, p < 0.01). Unexpectedly, immunocytochemical staining for AU1 revealed that <5% of granule neurons expressed deltaFADD. In contrast, deltaFADD was expressed in >95% of calbindin-positive Purkinje neurons ( approximately 2% of the cerebellar culture). Granule neurons in proximity to deltaFADD-expressing Purkinje cells demonstrated markedly increased survival. Both granule and Purkinje neurons expressed insulin-like growth factor-I (IGF-I) receptors, and deltaFADD-mediated survival of granule neurons was inhibited by an IGF-I receptor blocking antibody. These results demonstrate that the selective suppression of death receptor signaling in Purkinje neurons is sufficient to rescue neighboring granule neurons that depend on Purkinje cell-derived IGF-I. Thus, the extrinsic death pathway has a profound but indirect effect on the survival of cerebellar granule neurons.
Highlights
Cognate death receptors (e.g. Fas) [3]
When granule neuron apoptosis was carefully analyzed on a field-by-field basis, it was evident that the protection observed with ⌬Fas-associated death domain protein (FADD) was not uniformly distributed throughout the cell culture (Fig. 1B)
We investigated a role for the extrinsic death pathway in the apoptotic cell death of primary cerebellar granule neurons subjected to trophic factor withdrawal
Summary
24546 –24553, 2002 Printed in U.S.A. Suppression of Death Receptor Signaling in Cerebellar Purkinje Neurons Protects Neighboring Granule Neurons from Apoptosis via an Insulin-like Growth Factor I-dependent Mechanism*. Both granule and Purkinje neurons expressed insulin-like growth factor-I (IGF-I) receptors, and ⌬FADD-mediated survival of granule neurons was inhibited by an IGF-I receptor blocking antibody These results demonstrate that the selective suppression of death receptor signaling in Purkinje neurons is sufficient to rescue neighboring granule neurons that depend on Purkinje cell-derived IGF-I. We examined the involvement of death receptor signaling in cerebellar granule neuron apoptosis by expressing a dominant-negative mutant of FADD (⌬FADD) in primary cultures of cerebellar granule neurons using adenoviral vectors. The ⌬FADD-mediated survival of granule neurons was dependent on their proximity to ⌬FADD-expressing Purkinje cells and required Purkinje cell-derived IGF-I These data indicate that the extrinsic death pathway significantly, but indirectly, influences the survival of cerebellar granule neurons
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