NO-Induced Neurotoxicity and Apoptotic Cell Shrinkage

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DESCRIPTION (provided by applicant): Excessive stimulation of glutamate receptors of the NMDA sub-type result in the activation of nitric oxide synthase (NOS), the generation of nitric oxide (NO), and neuronal cell death. The apoptotic signaling pathway by which NO exerts its neurotoxic effects remains poorly understood. Events such as protein nitrosylation, mitochondrial dysfunction and activation of stress-activated p38 mitogen activated protein (MAP) kinase have been proposed to act as downstream effectors of NO-induced neurotoxicity. Affected neurons are thought to die by apoptosis, a form of cell death that involves the activation of cell death proteases, known as caspases. However, caspase inhibition often only delays neuronal cell death. Thus cell death determining events, upstream of casr ase activation, are likely to contribute to the commitment to cell death. Cell shrinkage is a universal event of all apoptotic cell death and involves the efflux of intracellular K+ ions. The molecular mechanism that drives K+ efflux during apoptosis is unclear. The purpose of this project will be to explore the possibility whether activation of outward voltage-gated K+ channels and subsequent cell shrinkage and mitochondrial injury via a pathway mediated by free Zn+ may constitute early events that commit neurons irreversibly to NO-induced neurotoxicity. To pursue these goals, primary cerebrocortical neurons will be analyzed using approaches such as time-lapse deconvolution microscopy, whole cell patch-clamp recording, transient transfections, biochemistry, and cell-free systems of apoptosis with isolated mitochondria. Among the specific questions that will be addressed in this project are: (1) Does NO provoke K+ efflux, enhancement of voltage-gated K+ channels, and apoptotic cell shrinkage? (2) Does stress-activated p38 MAP kinase regulate the activity of voltage-gated potassium channels and cell shrinkage? (3) Does NO provoke Zn2+ release from metallothionein (MT) which in turn results in mitochondrial damage, generation of reactive oxygen species, and p38 MAP kinase phosphorylation? Because NO plays an important role in a wide range of neurodegenerative diseases including stroke, Parkinson's disease, Alzheimer's disease, multiple sclerosis, epilepsy, and AIDS dementia, results obtained from this project could provide broad implications for the development of new therapeutic drugs to mitigate or even prevent neuronal cell loss during neurodegeneration.