GSK3B AS A TARGET FOR PRO-NEURONAL SURVIVAL IN CNS NEURONS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cell death that follows traumatic CNS injuries contributes to permanent neurological deficits in trauma survivors. In spinal cord injury (SCI), axonal damage may result in denervation-induced neuronal apoptosis in cerebrocortical neurons. Therefore, prevention of SCI-induced neuronal death in the cortex may be required for the successful repair of the spinal cord damage. Glycogen Synthase Kinase 3b (GSK3b) is a protein kinase that is involved in neuronal apoptosis induced by trophic support withdrawal. This implicates GSK3b as a potential target for the neuroprotective interventions. In healthy neurons, the high basal activity of GSK3b is limited by inhibition through Akt-mediated phosphorylation at the serine 9 residue (pSer9). In addition, recently published studies with PI's contribution revealed that basal or BDNF-stimulated ERK1/2 signaling activity inhibited the pro-apoptotic action of GSK3b in the absence of serine 9 phosphorylation. This suggests a novel pro-survival mechanism that controls neuronal GSK3b. This is further supported by our preliminary data indicating that moderate stimulation of glutamate NMDA receptors inhibited GSK3b-mediated apoptosis in pSer9-independent and ERK1/2-dependent manner. Furthermore, we found that GSK3b is directly phosphorylated by ERK1/2 in vitro at a site that is distinct from Ser9. Therefore, in addition to Ser9 phosphorylation, GSK3b may be regulated by other mechanisms. In addition, the full control over GSK-mediated cell death may require both pSer9-dependent and independent pathways. Consequently, we hypothesize that the anti-apoptotic mechanisms activated by neurotrophins or glutamate include ERK1/2-mediated inhibition of GSK3b. Furthermore, we propose that this inhibition is by the direct phosphorylation at a residue different than Ser9. We plan to further address this possibility through the studies organized into following specific aims: (i) dissection of the molecular mechanism employed by ERK1/2 to inhibit GSK3b, (ii) identification of functional consequences of pSer9-independent regulation of GSK3b by ERK1/2, and (iii) testing the generality of ERK1/2-mediated regulation of GSK3b activity. We propose to use primary cultures of rat cortical neurons as a main system to address these issues. We would also like to validate the key observation done in cultures by in vivo experimentation using rat pups. This research is aimed on identification of novel signaling mechanisms that support neuronal survival in the cerebral cortex. Therefore, it may provide potential targets for neuroprotective therapies in SCI and neurodegenerative disorders.