Reassessment of Caspase Inhibition to Augment Grafted Dopamine Neuron Survival
Abstract:One experimental therapy for Parkinson’s disease (PD) is the transplantation of embryonic ventral mesencephalic tissue. Unfortunately, up to 95% of grafted neurons die, many via apoptosis. Activated caspases play a key role in execution of the apoptotic pathway; therefore, exposure to caspase inhibitors may provide an effective intervention strategy for protection against apoptotic cell death. In the present study we examined the efficacy of two different caspase inhibitors, caspase-1 inhibitor Ac-YVAD-CMK and caspase-3 inhibitor Ac-DEVD-CMK, to augment mesencephalic tyrosine hydroxylase-immunoreactive (TH-ir) neuron survival in culture and following implantation into the denervated striatum of rats. We report that treatment with Ac-YVAD-CMK provided partial but nonsignificant protection for TH-ir neurons against serum withdrawal in mesencephalic cultures plated at low density, while neither caspase inhibitor promoted TH-ir neuron survival in higher density cultures, simulating graft density. We demonstrate that plating procedures (full well vs. microislands) and cell density directly affect the degree of insult experienced by TH-ir neurons following serum withdrawal. This varying degree of insult directly impacts whether caspase inhibition will augment TH-ir neuron survival. Our grafting experiments demonstrate that Ac-YVAD-CMK does not augment grafted TH-ir neuron survival when added to mesencephalic cell suspensions prior to grafting or to mesencephalic reaggregates for 3 days in vitro prior to transplantation. These experiments provide further evidence of the failure of these caspase inhibitors to augment TH-ir neuron survival. Furthermore, we suggest that cell culture paradigms used to model grafting paradigms must more closely approximate the cell densities of mesencephalic grafts to effectively screen potential augmentative treatments.
Document Type: Research Article
Affiliations: Department of Neurological Sciences, Research Center for Brain Repair, Rush University Medical Center, Chicago, IL 60612
Publication date: January 1, 2004
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