Loss of caspase-2-dependent apoptosis induces autophagy after mitochondrial oxidative stress in primary cultures of young adult cortical neurons.

Mitochondrial dysfunctions have been associated with neuronal apoptosis and are characteristic of neurodegenerative conditions. Caspases play a central role in apoptosis; however, their involvement in mitochondrial dysfunction-induced neuronal apoptosis remains elusive. In the present report using rotenone, a complex I inhibitor that causes mitochondrial dysfunction, we determined the initiator caspase and its role in cell death in primary cultures of cortical neurons from young adult mice (1-2 months old). By pretreating the cells with a cell-permeable, biotinylated pan-caspase inhibitor that irreversibly binds to and traps the active caspase, we identified caspase-2 as an initiator caspase activated in rotenone-treated primary neurons. Loss of caspase-2 inhibited rotenone-induced apoptosis; however, these neurons underwent a delayed cell death by necrosis. We further found that caspase-2 acts upstream of mitochondria to mediate rotenone-induced apoptosis in neurons. The loss of caspase-2 significantly inhibited rotenone-induced activation of Bid and Bax and the release of cytochrome c and apoptosis inducing factor from mitochondria. Rotenone-induced downstream activation of caspase-3 and caspase-9 were also inhibited in the neurons lacking caspase-2. Autophagy was enhanced in caspase-2 knock-out neurons after rotenone treatment, and this response was important in prolonging neuronal survival. In summary, the present study identifies a novel function of caspase-2 in mitochondrial oxidative stress-induced apoptosis in neurons cultured from young adult mice.

Macrophage-mediated GDNF delivery protects against dopaminergic neurodegeneration: a therapeutic strategy for Parkinson's disease.

Glial cell line-derived neurotrophic factor (GDNF) has emerged as the most potent neuroprotective agent tested in experimental models for the treatment of Parkinson's disease (PD). However, its use is hindered by difficulties in delivery to the brain due to the presence of the blood-brain barrier (BBB). In order to circumvent this problem, we took advantage of the fact that bone marrow stem cell-derived macrophages are able to pass the BBB and home to sites of neuronal degeneration. Here, we report the development of a method for brain delivery of GDNF by genetically modified macrophages. Bone marrow stem cells were transduced ex vivo with lentivirus expressing a GDNF gene driven by a synthetic macrophage-specific promoter and then transplanted into recipient mice. Eight weeks after transplantation, the mice were injected with the neurotoxin, MPTP, for 7 days to induce dopaminergic neurodegeneration. Macrophage-mediated GDNF treatment dramatically ameliorated MPTP-induced degeneration of tyrosine hydroxylase (TH)-positive neurons of the substantia nigra and TH(+) terminals in the striatum, stimulated axon regeneration, and reversed hypoactivity in the open field test. These results indicate that macrophage-mediated GDNF delivery is a promising strategy for developing a neuroprotective therapy for PD.

Functional evaluation of therapeutic response for a mouse model of medulloblastoma.

Medulloblastoma is an aggressive childhood cerebellar tumor. We recently reported a mouse model with conditional deletion of Patched1 gene that recapitulates many characteristics of the human medulloblastoma. Qualitative symptoms observed in the mouse model include irregular stride length, impaired cranial nerve function and decreased motor coordination and performance. In our current study, several quantitative behavioral assays including a mouse rotarod, a forced air challenge, a screen inversion test, a horizontal wire test, and stride length analysis were evaluated to determine the most sensitive and cost-effective functional assay for impaired neuromotor behavior associated with disease progression. Magnetic resonance imaging (MRI) was used to confirm and monitor tumor growth and as an anatomical biomarker for therapeutic response. Wild type mice or medulloblastoma-prone, conditional Patched1 knockout mice were observed by behavioral assays and MRI from postnatal weeks 3-6. Bortezomib treatment was administered during this period and therapeutic response was assessed using cerebellar volumes at the end of treatment. Of the behavioral tests assessed in this study, stride length analysis was best able to detect differences between tumor-prone mice and wild type mice as early as postnatal day 37 (P=0.003). Significant differences between stride lengths of bortezomib treated and control tumor-bearing mice could be detected as early as postnatal day 42 (P=0.020). Cerebellar volumes measured by MRI at the end of treatment validated the therapeutic effects seen by behavioral tests (P=0.03). These findings suggest that stride length analysis may serve as one of the more sensitive and cost-effective method for assessing new therapeutic compounds in this and other preclinical model of brain tumors.

Chemokines in the MPTP model of Parkinson's disease: absence of CCL2 and its receptor CCR2 does not protect against striatal neurodegeneration.

Recent studies have invoked inflammation as a major contributor to the pathogenesis of Parkinson's disease (PD). We determined the role of members of the chemokine system, key inflammatory mediators, in PD pathogenesis. In the MPTP model of murine PD, several chemokines, including CC chemokine ligand 2 (CCL2, Monocyte Chemoattractant Protein-1) and CCL3 (Macrophage Inflammatory Protein-1alpha), were upregulated in the striatum and the ventral midbrain. Astrocytes were the predominant source of CCL2 and CCL3 in the striatum and the substantia nigra, and dopaminergic neurons in the substantia nigra constitutively expressed these two chemokines. MPTP treatment resulted in decreased CCL2 expression and increased CCL3 expression in the surviving dopaminergic neurons. Because we found that CCL2 induced production of TNF-alpha in microglial cells, a cytokine known to play a detrimental role in PD, we anticipated that deletion of the genes encoding CCL2 and CCR2, its major receptor, would confer a protective phenotype. However, MPTP-induced striatal dopamine depletion was comparable in double knockout and wild-type mice. Our results demonstrate that chemokines such as CCL2 are induced following MPTP treatment, but that at least within the context of this PD model, the absence of CCL2 and CCR2 does not protect against striatal dopamine loss.

Dietary restriction does not protect the nigrostriatal dopaminergic pathway of older animals from low-dose MPTP-induced neurotoxicity.

To determine whether reduced caloric intake affects the susceptibility of nigrostriatal dopamine (DA) neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity, 1-year-old male C57BL6 mice were offered food ad libitum or were given only 60% of the normal dietary intake. After 3 months, both groups were treated with low cumulative doses of 0, 10, 15, or 20 mg/kg MPTP. One week later, the striata were collected and DA, dihydroxyphenylalanine (DOPAC), and norepinephrine (NE) were measured. Treatment with MPTP had no effect on striatal NE but produced a dose-related depletion of DA and DOPAC in both the ad libitum-fed and the dietary-restricted mice. The MPTP-induced depletions of DA and DOPAC were not ameliorated in the dietary-restricted versus the ad libitum-fed mice. Baseline DA levels and those observed after treatment with the 15-mg/kg dose of MPTP were lower in the dietary-restricted mice compared with the ad libitum-fed mice. Overall, these results suggest that, at least in 1-year-old mice, dietary restriction for 3 months does not protect nigral DA nerve terminals from low toxic dosages of MPTP.

A knockout of the caspase 2 gene produces increased resistance of the nigrostriatal dopaminergic pathway to MPTP-induced toxicity.

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.