This study investigated the effect of a knockout of the caspase 2 gene on the sensitivity of murine nigral dopaminergic neurons to 1-methyl-4-1,2,3,6-tetrahydropyridine (MPTP)-induced toxicity. Female wild type (WT), heterozygous caspase 2 NL (HET) and homozygous caspase 2 null (NL) mice were treated with cumulative dosages of 0, 10, 15 or 20. mg/kg MPTP free base. Without MPTP treatment, one week later dopamine (DA) levels were not significantly different in HET or NL versus WT mice. Twenty mg/kg MPTP reduced striatal DA in WT and HET (p < 0.01) but not NL mice. This same MPTP dosage regimen also induced a significantly greater decrease in tyrosine hydroxylase immunopositive (TH+) protein in striata of WT compared to NL mice (p < 0.001). Subsequently, WT and NL mice were treated daily with 20. mg/kg MPTP for 3. days and 25. mg/kg MPTP for 2 additional days, and TH+ neurons in the substantia nigra (SN) were estimated using unbiased stereology. When compared to untreated WT, the numbers of TH+ neurons were significantly lower in the SN of untreated NL mice (p < 0.05). Treatment with the MPTP regimen significantly reduced TH+ neurons in WT mice but not NL mice. In primary mesencephalic cultures both the cell bodies and the neuronal processes of TH immunopositive (TH+) neurons from NL embryos were significantly (p < 0.001) more resistant to 10 μM MPP+ compared to WT. Following MPP+ treatment, features of apoptotic cell death were also significantly (p < 0.001) more prevalent in nuclei of TH+ neurons in cultures prepared from WT versus NL mouse pups. These results suggest that caspase 2 may play a role in modulating the MPTP-induced damage to the nigrostriatal dopaminergic system.
Bibliographical noteFunding Information:
This work was supported by grants from the Merit Review Medical Research Program of the Department of Veterans Affairs (WWM) and from the NIH ( AG07218 , AG19316 ) (BH). The technical assistance of Elisa Figueroa, Nancy Lopez and Jacqueline Alcala is gratefully acknowledged. Thanks also to Dr. James Roberts (Department of Pharmacology, UTHSCSA and Trinity University, San Antonio) for the use of his microscope and to David Price for his assistance in learning to perform unbiased stereology. The authors also thank Dr. Martin Javors (Department of Psychiatry, UTHSCSA) whose laboratory performed the MPP+ assays. Dr. Carol Troy (Columbia University) kindly provided the caspase 2 null mice.
- Caspase 2
- Cell death
- Parkinson's disease
- Tyrosine hydroxylase