The Journal of Neuroscience, April 1, 2002, 22(7):2637-2649
Caspase Inhibitors Attenuate 1-Methyl-4-Phenylpyridinium Toxicity
in Primary Cultures of Mesencephalic Dopaminergic Neurons
James
Bilsland1,
Sophie
Roy2,
Steve
Xanthoudakis2,
Donald W.
Nicholson2,
Yongxin
Han2,
Erich
Grimm2,
Franz
Hefti1, and
Sarah J.
Harper1
1 Merck, Sharp and Dohme Neuroscience Research Centre,
Terlings Park, Harlow, Essex, CM20 2QR, United Kingdom, and
2 Merck-Frosst Centre for Therapeutic Research, Pointe
Claire-Duval, Quebec, H9R 4P8, Canada
Parkinson's disease is characterized by a loss of dopaminergic
nigrostriatal neurons. This neuronal loss is mimicked by the neurotoxin
1-methyl-4-phenylpyridinium (MPP+).
MPP+ toxicity is mediated through inhibition of
mitochondrial complex I, decreasing ATP production, and upregulation of
oxygen radicals. There is evidence that the cell death induced by
MPP+ is apoptotic and that inhibition of caspases
may be neuroprotective. In primary cultures of rat mesencephalic
dopaminergic neurons, MPP+ treatment decreased the
number of surviving dopaminergic neurons in the cultures and the
ability of the neurons to take up [3H]dopamine
([3H]DA). Caspase inhibition using the
broad-spectrum inhibitor
benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk)
spared MPP+-treated dopaminergic neurons and
increased somatic size. There was a partial restoration of neurite
length in zVAD-fmk-treated cultures, but little restoration of
[3H]DA uptake. Peptide inhibitors of caspases 2, 3, and 9, but not of caspase 1, caused significant neuroprotection. Two
novel caspase inhibitors were tested for neuroprotection, a broad
spectrum inhibitor and a selective caspase 3 inhibitor; both inhibitors
increased survival to >90% of control. No neuroprotection was
observed with an inactive control compound. MPP+
treatment caused chromatin condensation in dopaminergic neurons and
increased expression of activated caspase 3. Inhibition of caspases
with either zVAD-fmk or a selective caspase 3 inhibitor decreased the
number of apoptotic profiles, but not expression of the active caspase.
We conclude that MPP+ toxicity in primary
dopaminergic neurons involves activation of a pathway terminating in
caspase 3 activation, but that other mechanisms may underlie the
neurite loss.
Key words:
Parkinson's disease; apoptosis; MPP+; caspase; neuroprotection; dopaminergic neurons
Copyright © 2002 Society for Neuroscience 0270-6474/02/2272637-13$05.00/0