EPIGENETIC FACTORS AND CORTICAL MAP PLASTICITY IN THE MODEL OF TBI

TBI is a major health issue with life-long deficits in behavior & cognition, and its repetitive incidence may cause early-onset dementia. Occurrence of TBI is considered a potential risk factor for the development of Alzheimer disease later in life. TBI can induce a wide range of neurological impairments. Some of the health effects may appear immediately after the injury and other symptoms may not emerge for days or weeks. The neurological consequences of TBI are likely caused by dysfunctional neuronal circuits; however, due to the complexity of brain trauma no clear neurophysiological and signaling targets have been revealed to date. How the balance between excitation and inhibition is maintained within a healthy neural circuit and disrupted after TBI injury remains to be answered. Changes in this balance may lead to an abnormal pattern of neuronal activity that impacts activity-dependent molecular and epigenetic mechanisms. In fact, major neurological diseases such as epilepsy, anxiety disorder, schizophrenia, autism and Down syndrome, are linked to a disruption of this balance. We hypothesize that TBI leads to a specific set of epigenetic modifications and a shift in the inhibitory and excitatory balance caused by strengthening of inhibitory circuits caused by injury with accompanying vasculature damage sets brakes on the ability of the neocortex to recover. Therefore, better understanding of the time course of these two injuries can shed a novel light on their roles in TBI suggesting treatment and treatment window opportunities to reduce TBI cognitive deficits.Consequently, pharmacological attenuation of cortical excitation/inhibition balance after TBI should facilitate functional restoration of cortical plasticity and vasculature in mature cortex. Using 2-photon imaging and electrophysiological techniques, we continue to determine the balance between inhibition and excitation in the context of synaptic and structural plasticity in sensory barrel cortex following TBI. Our present assessment of network activity by two-photon calcium imaging in combination with whole-cell electrophysiological recordings suggest desynchronization of neocortical activity following TBI with an impaired inhibition underling hyperactivity/hypoactivity of excitatory neurons. Based on combined imaging and electrophysiological recording we plan to identify molecular players that underlie changes in network/synaptic activity leading to mechanistic targets for future drug interventions underlying TBI pathophysiology. Our ongoing studies are focused on mapping chromatin modifications following CCI injury in sensory cortex.Since some HDAC inhibitors and fluoxetine may compete for the same targets, we propose to use these compounds to reverse epigenetic modifications and changes in barrel cortex circuitry occurring in response to TBI. Implementing chromatin immunoprecipitation (ChIP) assays, significant gene-specific histone posttranslational modifications were observed 24 hours after TBI. In comparison to naïve control, TBI mice (ipsilateral cortex) showed significant decrease in acetylation of histone H3 in the promoter regions of genes crucial for learning and memory mechanisms. Enhanced pCREB binding in promoters of another set of genes was found in TBI ipsilateral cortex as compared to sham. To extend these epigenetic findings to genome-wide level, we are in the process of developing experimental protocols including sample preparation for ChIPSeq (that combines ChIP with massively parallel sequencing) as well as bioinformatic tools and pipelines for the ChIPSeq data storage, statistical analysis and following functional studies to narrow down potential signaling pathways and genes underlying TBI pathophysiology.