Faculty Bibliography

Protein bound and free 3-nitrotyrosine (3NT) levels are elevated in neurodegenerative diseases and have been used as evidence for peroxynitrite generation. Intrastriatal injection of free 3NT causes dopaminergic neuron injury and represents a new mouse model of Parkinson's disease (PD). We are investigating the nature of free 3NT neurotoxicity. In primary ventral midbrain cultures, free 3NT damaged dopaminergic neurons, while adjacent non-dopaminergic neurons were unaffected. Combined treatment with free 3NT and subtoxic amounts of dopamine caused extensive death of non-dopaminergic forebrain neurons in culture. Free 3NT alone directly inhibited mitochondrial complex I, decreased ATP, sensitized neurons to mitochondrial depolarization, and increased superoxide production. Subtoxic concentrations of rotenone (instead of free 3NT) caused similar results. Additionally, free 3NT and dopamine combined increased extraneuronal hydrogen peroxide and decreased intraneuronal glutathione levels more than dopamine alone. Oxidative and bioenergetic processes have been proposed to contribute to neurodegeneration in PD. As free 3NT is a compound that is increased in PD, damages dopamine neurons in vivo and in vitro and has detrimental effects on neuronal bioenergetics, it is possible that free 3NT is an endogenous contributing factor to neuronal loss, in addition to being a marker of oxidative and nitrative processes.

Huntington's disease (HD) is a hereditary neurodegenerative disease that leads to striatal degeneration and a severe movement disorder. We used a transgenic mouse model of HD (the R6/2 line with approximately 150 glutamine repeats) to test a new therapy for this disease. We treated HD mice with metformin, a widely used anti-diabetes drug, in the drinking water (0, 2 or 5mg/ml) starting at 5 weeks of age. Metformin treatment significantly prolonged the survival time of male HD mice at the 2mg/ml dose (20.1% increase in lifespan) without affecting fasting blood glucose levels. This dose of metformin also decreased hind limb clasping time in 11-week-old mice. The higher dose did not prolong survival, and neither dose of metformin was effective in female HD mice. Collectively, our results suggest that metformin may be worth further investigation in additional HD models.

We have developed a simple and sensitive assay to quantify neuron-specific death in primary cell cultures that represents a significant improvement over more commonly used methods including manual cell counting and lactate dehydrogenase release. This new method selectively detects neuronal death by combining immunolabeling for a neuron-specific marker with the ease, sensitivity, and speed of an enzyme-linked fluorescence assay. Using microtubule associated protein 2 (MAP2) as a neuron-specific marker, we assessed glutamate-receptor mediated neurotoxicity in neuron-enriched cultures and in mixed neuronal/glial cultures established from mouse forebrain and compared these results to neuronal death measured by lactate dehydrogenase (LDH) release. We were able to achieve statistically significant differences in toxicity between intermediately toxic concentrations of glutamate (30, 50, and 100 microM) with the MAP2 assay, while we were not able to discriminate among these concentrations with the LDH assay. We were also able to measure hydrogen peroxide-induced neuronal death, and demonstrate neuroprotection by antioxidant addition. This new assay is easily adaptable to high-throughput in vitro screens of neurodegeneration and of neuroprotective therapies.