Preserving Inhibitory Cortical Networks Following TBI: Attenuating Excitation Using Inhibitors of Glycolysis

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Project summary Traumatic brain injuries (TBI) are the leading cause of death and disability in children and the aged. Cognitive and motor dysfunction, as well as post-traumatic epilepsy (PTE), often occurs following TBI. There are limited therapeutic options for TBI, none of which have proven to be efficacious in improving neurological outcomes across diverse groups of TBI patients. Therefore, developing new therapeutic tools based on mechanistic rationale are critical to finding treatments to improve patient outcome following TBI. Recently, we reported that the controlled cortical impact (CCI) model of TBI resulted in a significant loss of parvalbumin-positive inhibitory interneurons in the cortex. Parvalbumin-positive interneurons provide a bulk of cortical inhibition which constrains neuronal activity. When parvalbumin-positive interneurons were lost following TBI, uncontrolled glutamatergic activity was seen along with increased excitatory and decreased inhibitory synaptic inputs. Based on these findings, we set out to develop approaches to preserve interneurons following TBI. Based on published data showing areas of increased glycolytic activity in the brain following TBI, and known linkages between glycolysis and neuronal activity, we set out to determine if inhibiting glycolysis following TBI would attenuate loss of parvalbumin interneurons. We hypothesized that TBI leads to glycolysis-dependent increases in excitatory neuron activity. This would lead to hyper-activation of inhibitory interneurons and their subsequent excitotoxic cell death. We propose to interrupt glycolysis to attenuate excitatory neuronal activity following TBI. Using 2-deoxyglucose (2DG), an inhibitor of hexokinase (the rate-limiting enzyme of glycolysis), we have begun to test this hypothesis. Our preliminary data suggests that 2DG can acutely attenuate cortical hyperexcitability in brain slices 2-4 weeks following TBI and that in vivo treatment with 2DG following TBI attenuates both network hyperexcitability and parvalbumin-positive cell loss. Our preliminary data also suggests that 2DG attenuates excitatory, but not inhibitory, neuron excitability. Here we propose to further these studies by demonstrating that 2DG reduces parvalbumin-positive interneuron cell death and reduces changes in synaptic communication in the cortex following injury. We also propose to test the hypothesis that inhibition of glycolysis attenuates excitatory, but not inhibitory, cell excitability. Furthermore, we aim to determine whether there is differential expression of glycolytic and related proteins in excitatory neurons vs. inhibitory interneurons via single-cell qPCR. This aspect of the proposal is both high-risk and high-reward. Our studies will determine if 2DG is able to preserve interneurons following TBI, will begin to establish 2DG's mechanism of action, and will potentially demonstrate a novel form of cell type-specific coupling of metabolic and electrical activity. Based on these studies, we will be better able to manipulate neuronal excitability with cell type-specific metabolic disruption and to design therapeutic strategies to reduce TBI-associated pathology.