The Role of Zinc in Neuronal Injury and Death in an Oxygen-Glucose Deprivation Model of Ischemic Stroke

STORK, CHRISTIAN J., Ph.D., March 2011, Molecular and Cellular Biology The Role of Zinc in Neuronal Injury and Death in an Oxygen-Glucose Deprivation Model of Ischemic Stroke (183 pp.) Director of Dissertation: Yang V. Li Stroke injury is a devastating medical condition in which less than 3% of victims can even meet the qualifications to receive the one FDA-approved treatment, tissue plasminogen activator (tPA). The dominant theory to describe how cerebral ischemia damages the brain is centered on excessive Ca influx into ischemic neurons where a resultant “Ca-overload” triggers neuron death and overall injury. Directed by this theory, dozens of potential stroke therapeutics designed to prevent Ca-overload have been developed and tested in clinical trials, showing mixed results. Much of the evidence that has provided experimental support for the theory of Ca-overload has been made where Ca was identified on the basis of detection with fluorescent Ca indicators. Zn also accumulates in neurons under ischemic conditions. In the current work results are presented that demonstrated Zn accumulation in ischemic neurons comprised the majority of the signal from a popular fluorescent Ca indicator, showing how the Zn transient in ischemia could be readily interpreted as support for Ca-overload. Moreover, the Zn accumulation with ischemia was shown to correlate significantly with neuronal injury. And, prevention of the Zn accumulation prevented the development of damage from simulated ischemic injury. 4 The source of the ischemically-evolved Zn was determined to be of intracellular origin, and results of the investigation to localize sites of intracellular Zn storage are presented in the present work. Under basal conditions, primary cultured cells from the rat cerebral cortex showed labile Zn within mitochondria, the Golgi apparatus, and the endoplasmic reticulum. Zn localized in the endoplasmic reticulum was found to be released by thapsigargin and IP3. To further investigate ischemic Zn liberation and characterize the specific effects of this event independent from that of Ca-overload, the respective effects of Ca and Zn were tested to compare their relative toxicity, and the relative neuroprotection afforded by treatments targeting each ion in ischemia. As shown in this study, the induced elevation of Zn resulted in significantly greater neuronal injury compared to the induced elevation of Ca. Further, preventing Zn accumulation under ischemic conditions was highly protective for both 10 min and 30 min insult; whereas preventing Ca influx showed a protective effect for up to only 10 min of simulated ischemia. The collective work presented here shows how Zn can be misconstrued as Ca under ischemic conditions. It demonstrated that the Zn-mediated damage was of greater consequence than the Ca-mediated damage. Collectively, these data support Zn accumulation to be a more significant causal factor of the neuronal injury and death resultant from simulated ischemia. These findings have implications that are relevant to ischemic stroke and to the development of therapeutic interventions for ischemic stroke. 5 Approved: _____________________________________________________________ Yang V. Li Associate Professor of Neuroscience