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Oligodendrocyte progenitors are highly sensitive to oxidative insults. Among the factors postulated to contribute to this susceptibility are high levels of intracellular iron and low antioxidant content. During ischemia, the neurotransmitter dopamine (DA) is released and may contribute to oxidative stress and oligodendrocyte injury in the hypomyelinating disorder, periventricular leucomalacia (PVL). In this thesis, I investigated the role of iron in DA-induced toxicity in primary cultures of oligodendrocyte progenitors, and assessed the contribution of the antioxidant defenses (glutathione (GSH), glutathione peroxidase (GPx) and superoxide dismutase (SOD)) and other survival factors (heat shock proteins and the protein kinase Akt) in determining the response of the cells to DA. / Addition of iron to cultures increased DA-induced expression of the stress protein heme oxygenase-1 (HO-1), and toxicity as assessed by mitochondrial activity, cellular release of lactate dehydrogenase, nuclear condensation and caspase-3 activation. In contrast, an iron chelator reduced these events. Furthermore, DA induced accumulation of superoxide, which was also reduced by the iron chelator. Surprisingly, a mimetic of the superoxide detoxifying enzyme, SOD potentiated DA toxicity, suggesting that generation of hydrogen peroxide via superoxide dismutation may be contributing to toxicity. Both a mimetic of the peroxide-scavenging enzyme, GPx and a GSH analog blocked DA-induced superoxide accumulation, HO-1 expression and caspase-3 activation. In addition, the GPx mimetic blocked caspase-3 activation induced by the combination of DA with iron. In contrast, an inhibitor of glutathione synthesis potentiated DA-induced HO-1 expression and cell death. / Finally, in further examining the cellular defense mechanisms, I found that various heat shock proteins increased in expression levels during oligodendroglial differentiation, however only heat shock protein-90 (HSP-90) was detected in oligodendrocyte progenitors. An HSP-90 inhibitor decreased activated Akt levels, induced caspase-3 activation, increased nuclear condensation, reduced oligodendrocyte progenitor viability, and potentiated DA-induced apoptosis. In addition, an Akt inhibitor alone exacerbated DA toxicity and in combination with the HSP-90 inhibitor caused synergistic potentiation of DA toxicity by enhancing caspase-3 activation. / In conclusion, elevated levels of iron, superoxide, deficient detoxification of peroxides by glutathione peroxidase and inadequate defense by glutathione contribute to the susceptibility of oligodendrocyte progenitors to DA-induced toxicity. On the other hand, HSP-90 alone or in concert with Akt play important roles in oligodendrocyte progenitors survival following an insult that produces oxidative stress.

No description available.

Major depressive disorder (MDD) and suicide have been associated with elevated indices of oxidative damage in the brain, as well as white matter pathology including reduced myelination by oligodendrocytes. Oligodendrocytes highly populate white matter and are inherently susceptible to oxidative damage. Pathology of white matter oligodendrocytes has been reported to occur in brain regions that process behaviors that are disrupted in MDD and that may contribute to suicidal behavior. The present study was designed to determine whether oligodendrocyte pathology related to oxidative damage extends to brain areas outside of those that are traditionally considered to contribute to the psychopathology of MDD and suicide. Relative telomere lengths and the gene expression of five antioxidant-related genes, SOD1, SOD2, GPX1, CAT, and AGPS were measured in oligodendrocytes laser captured from two non-limbic brain areas: occipital cortical white matter and the brainstem locus coeruleus. Postmortem brain tissues were obtained from brain donors that died by suicide and had an active MDD at the time of death, and from psychiatrically normal control donors. Relative telomere lengths were significantly reduced in oligodendrocytes of both brain regions in MDD donors as compared to control donors. Three antioxidant-related genes (SOD1, SOD2, GPX1) were significantly reduced and one was significantly elevated (AGPS) in oligodendrocytes from both brain regions in MDD as compared to control donors. These findings suggest that oligodendrocyte pathology in MDD and suicide is widespread in the brain and not restricted to brain areas commonly associated with depression psychopathology.