Involvement of the Glycogen Synthase Kinase-3 Signaling Pathway in TBI Pathology and Neurocognitive Outcome Pramod K. Dash1*, Daniel Johnson1, Jordan Clark1, Sara A. Orsi1, Min Zhang1, Jing Zhao 1 , Raymond J. Grill2, Anthony N. Moore1, Shibani Pati3 1 Department of Neurobiology and Anatomy, The University of Texas Health Science Center at Houston, Houston, Texas, United States of America, 2 Department of Integrated Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas, United States of America, 3 Center for Translational Injury Research, The University of Texas Health Science Center at Houston, Houston, Texas, United States of America Abstract Background: Traumatic brain injury (TBI) sets in motion cascades of biochemical changes that result in delayed cell death and altered neuronal architecture. Studies have demonstrated that inhibition of glycogen synthase kinase-3 (GSK-3) effectively reduces apoptosis following a number of stimuli. The Wnt family of proteins, and growth factors are two major factors that regulate GSK-3 activity. In the absence of stimuli, GSK-3 is constitutively active and is complexed with Axin, adenomatous polyposis coli (APC), and casein kinase Ia (CK1a) and phosphorylates ß-Catenin leading to its degradation. Binding of Wnt to Frizzled receptors causes the translocation of GSK-3 to the plasma membrane, where it phosphorylates and inactivates the Frizzled co-receptor lipoprotein-related protein 6 (LRP6). Furthermore, the translocation of GSK-3 reduces ß-Catenin phosphorylation and degradation, leading to ß-Catenin accumulation and gene expression. Growth factors activate Akt, which in turn inhibits GSK-3 activity by direct phosphorylation, leading to a reduction in apoptosis. Methodology/Principal Findings: Using a rodent model, we found that TBI caused a rapid, but transient, increase in LRP6 phosphorylation that is followed by a modest decrease in ß-Catenin phosphorylation. Phospho-GSK-3b immunoreactivity was found to increase three days post injury, a time point at which increased Akt activity following TBI has been observed. Lithium influences several neurochemical cascades, including inhibiting GSK-3. When the efficacy of daily lithium was assessed, reduced hippocampal neuronal cell loss and learning and memory improvements were observed. These influences were partially mimicked by administration of the GSK-3-selective inhibitor SB-216763, as this drug resulted in improved motor function, but only a modest improvement in memory retention and no overt neuroprotection. Conclusion/Significance: Taken together, our findings suggest that selective inhibition of GSK-3 may offer partial cognitive improvement. As a broad spectrum inhibitor of GSK-3, lithium offers neuroprotection and robust cognitive improvement, supporting its clinical testing as a treatment for TBI. Citation: Dash PK, Johnson D, Clark J, Orsi SA, Zhang M, et al. (2011) Involvement of the Glycogen Synthase Kinase-3 Signaling Pathway in TBI Pathology and Neurocognitive Outcome. PLoS ONE 6(9): e24648. doi:10.1371/journal.pone.0024648 Editor: Pascale Chavis, Inserm U901, France Received February 23, 2011; Accepted August 17, 2011; Published September 15, 2011 Copyright: 2011 Dash et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This research was made possible by funding support from the Department of Defense (W81XWH-08-2-0134 and W81XWH-08-2-0150). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: P.Dash@uth.tmc.edu Introduction Both clinical and experimental studies have shown that the pathophysiology of traumatic brain injury (TBI) is complex and involves both primary and secondary injuries. Primary pathologies develop extremely rapidly after the traumatic event, and are typically not amenable to pharmacological interventions. In addition to causing immediate physical damage to the brain, the primary injury sets in motion cascades of molecular, cellular, genomic and metabolic processes that result in secondary injury [1,2]. Secondary injury encompasses a number of pathological processes such as neuronal cell death and changes in neuronal architecture that can continue to evolve over time [3–6]. The hippocampus, a structure critically involved in learning and memory, is highly vulnerable to insults to the brain. Studies have shown that apoptotic loss of hippocampal neurons continues for days-to-weeks after the initial injury [7,8], an effect thought to contribute to the learning and memory impairments observed following experimental TBI and in persons with brain trauma. Glycogen synthase kinase3 (GSK-3) was originally identified as a regulator of glycogen metabolism. Its role has been expanded to include regulation of protein synthesis, cell proliferation, cell differentiation, microtubule dynamics, cell motility and apoptosis [9]. GSK-3 activity has been linked to neuronal death triggered by a number of stimuli such as prion proteins, p53-induced apoptosis and amyloid-beta toxicity [10–12]. Consistent with a role of GSK- 3 activity in apoptosis, selective small molecular inhibitors of GSK- 3b protect cells in response to these and other pro-apoptotic stimuli. Wnt and Akt (also called protein kinase B) are two major signaling pathways that have been shown to regulate GSK-3 PLoS ONE | www.plosone.org 1 September 2011 | Volume 6 | Issue 9 | e24648