Stroke is the third leading cause of death in the United States and the leading cause of adult disability. With the aging of the population, the number of stroke patients in the US is likely to grow. Current models describing excitotoxic injury, such as during ischemia and reperfusion (I/R) injury, center on the concept of calcium (Ca2+) ion accumulation leading to cell death. Oxidative damage due to the presence of radical oxygen species (ROS) and cross-talk between Ca2+ and ROS is the essential step in the molecular biology of ischemia/reperfusion. However, experimental treatments targeting Ca2+ homeostasis and ROS generation (e.g. Ca2+ channel blockers and ROS scavengers) have not been very successful in reducing the volume or severity of neuronal damage. Accumulating evidence suggests that another divalent ion zinc (Zn2+) is also involved in excitotoxic neuronal death after head trauma, epilepsy, cerebral ischemia and reperfusion. The Overall Hypothesis behind the proposed research is that acute neural injury in I/R is associated with an increase in intracellular Zn2+ or Zn2+ overload that could be the precursor for cell death or subsequent brain degeneration.
The specific aim 1 of this proposal will test the hypothesis that Zn2+ elevation plays a major role in oxidative damage of neuron by facilitating ROS generation, and that ROS mediated neuronal damages in simulated ischemia by oxygen-glucose deprivation (OGD) and reperfusion are largely Zn2+-dependent. We will evaluate the specific contributions made by Ca2+ and Zn2+ towards ROS generation during OGD and reperfusion, and to characterize the relationship between increases of intracellular Zn2+ and corresponding development of cell death. The significance of this aim is to decipher and differentiate Zn2+-caused and Ca2+-caused events in ROS generation, so that specific therapeutic interventions can be designed to target the relevant ion.
In specific aim 2 we will test the hypothesis that Zn2+-mediated neuronal injury depends on its interaction with ROS. Specifically, during the OGD, the dysfunctional mitochondria triggers ROS production and subsequently aggravate Zn2+ accumulation;the elevated Zn2+ then amplifies ROS production, by activating NADPH oxidase, in reperfusion. The mechanisms and time course of Zn2+ accumulation in relation to ROS generation during the course of OGD/reperfusion will be explored.
In specific aim 3, we will determine the source of Zn2+ accumulation upon acute brain injury, and to study the Zn2+ release from intracellular storages such as mitochondria, endoplasmic reticulum, Golgi apparatus and lysosomes. The release of Zn2+ from the storages may contribute to early Zn2+ accumulation and subsequent mitochondrial dysfunction. The long-term goal of the project is to elucidate novel regulatory mechanisms for neuronal injury and to identify new therapeutic modalities or rehabilitation strategies to prevent or attenuate neurodegenerative disorders after acute brain injury.
Neurological disorders associated with traumatic brain injury, ischemic stroke, hypoxia, and excitotoxicity represent a long-standing public health problem. Thus, the ability to identify the cellular and molecular mechanism specific to the acute neural injury that may initiate neurodegeneration is of clinical importance. We will determine the role of zinc (Zn2+) or Zn2+ dyshomeostasis in the neural injury. Therefore, the proposed studies address an important aspect of the mechanisms/pathophysiology of neurological disorders that need to be examined in greater detail.