Glycogen synthase kinase-3beta (GSKbeta) is a key component of numerous cell signaling cascades, affecting many fundamental cellular functions associated with neural plasticity. Furthermore, GSK3beta is being recognized as an important mediator of apoptosis, a process of cell death that may contribute to neuronal loss following brain injury due to cerebral ischemia, and in certain types of neurodegenerative diseases. GSK3beta is known to exist in at least three cellular compartments, the cytosol, the nucleus and mitochondria. The activities of GSK3beta in these three compartments was measured in SHSY5Y cells following activation of proapoptotic signaling with thapsigargin, an agent which causes endoplasmic reticulum (ER) stress. Neuronal death in cerebral ischemia is believed to be due to increased intracellular calcium from ER stress. Thapsigargin treatment selectively increased GSK3b activity in the nucleus and the mitochondria, but cytosolic GSK3beta activity was not increased. To test if other apoptotic stimuli could also activate nuclear and mitochondrial GSK3beta, cells were treated with camptothecin, an agent that causes genotoxic stress. Camptothecin also activated GSK3beta in the nucleus and mitochondria, but not in the cytosol. The selective activation of GSK3beta in the nuclear and mitochondrial compartments is likely a major factor in the proapoptotic actions of GSK3beta. The goal of Specific Aim 1 is to examine if nuclear GSK plays a role in apoptosis and test the effects of modulating nuclear GSK3beta on two transcription factors, camp response element binding protein (CREB) and heat shock factor-1 (HSF1), which are critical for maintaining neural plasticity and cell survival, and whose actions are known to be impaired by increased GSK3beta activity. The goal of Specific Aim 2 is to selectively modulate the activity of mitochondrial GSK3beta, and test if increased mitochondria GSK3beta contributes to apoptotic signaling and inhibits the activity of the key metabolic enzyme pyruvate dehydrogenase, and impairs mitochondrial function. The goal of Specific Aim 3 is to test if GSK3beta plays a deleterious role in the generation of neuronal damage following NMDA treatment and in a model of transient focal cerebral ischemia, and if inhibition of GSK3beta has the potential to provide significant therapeutic neuronal protection from both insults. Overall, these aims will identify the mechanisms by which GSK3beta activity is regulated and the relative contributions of distinct pools of GSK3beta in impairing neural plasticity.
