Traumatic brain injury: novel targets for potential therapies

Traumatic brain injury (TBI) induces severe neurological damage leading to significant deficits in learning and memory and poor quality of life. It is a pathology that involves a variety of molecular and physiological responses, and in order to find an effective treatment these responses need to be addressed in a comprehensive manner. This study involves several approaches that aim to investigate specific proteins, molecular pathways, as well as cellular responses to brain injury. Cytosolic PSD-95 interactor (cypin), a guanine deaminase, regulates dendritic spine reemergence and promotes neuronal survival in an in vitro N-methyl-D-aspartate (NMDA) induced injury model of TBI. In this study, we identify novel small molecule activators, H9 and G5, and an inhibitor, B9, of cypin and show neuroprotective potential of cypin activators in vitro and in vivo in mice subjected to controlled cortical impact (CCI) injury. Hippocampal neurons pretreated with H9 or G5 display preserved physiology and survival after injury, phenotypes that are lost in cultures pretreated with B9 or when cypin is knocked down. Secondly, we expanded our scope and focused on the role of the PI3K/Akt/mTORC1 pathway in brain injury. We show that exposure to sublethal levels of NMDA does not alter phosphorylation of Akt, S6, and GSK3β at two and twenty-four hours following injury. Electrophysiological recordings show that NMDA-induced injury causes a significant decrease in spontaneous excitatory postsynaptic currents at both two and twenty-four hours, and this phenotype can be prevented by inhibiting mTORC1 or GSK3β, but not Akt. Additionally, inhibition of mTORC1 or GSK3β promotes neuronal survival following NMDA-induced injury. Thus, NMDA-induced excitotoxicity involves a mechanism that requires the permissive activity of mTORC1 and GSK3β, demonstrating the importance of these kinases in the neuronal response to injury. Finally, we investigated the role of microglia, the resident immune cells in the central nervous system, in brain injury using a combination of two-photon imaging, electrophysiology, and genetic tools. We show that ATP-induced outward current in microglia, which has been implicated in microglial chemotaxis in response to injury, is largely dependent on P2Y12R activation and mediated by G-proteins. Similarly, P2Y12R-coupled outward current is also evoked in response to laser-induced single neuron injury. Taken together, we progress our understanding of the complexity of brain injury using a multidimensional approach and propose new therapeutic targets for further investigation.Ph.D.Includes bibliographical referencesby Przemyslaw Swiatkowsk