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Theses Doctoral

Reducing the Societal Costs of Traumatic Brain Injury: Astrocyte-Based Therapeutics and Functional Injury Tolerance of the Living Brain

Kang, Woo Hyeun

Approximately 1.7 million traumatic brain injuries (TBI) occur annually in the United States, with an annual estimated societal cost of at least $76.5 billion. Addressing the growing TBI epidemic will require a multi pronged approach: developing novel treatment strategies and enhancing existing preventative measures. The specific aims of this thesis are: (1) to modulate astrocyte activation as a potential therapeutic strategy post TBI, (2) to determine the relationship between tissue deformation and alterations in electrophysiological function in the living brain, and (3) to investigate underlying mechanisms of functional changes post TBI by utilizing stretchable microelectrode arrays (SMEAs). In response to disease or injury, astrocytes become activated in a process called reactive astrogliosis. Activated astrocytes generate harmful radicals that exacerbate brain damage and can hinder regeneration of damaged neural circuits by secreting neuro developmental inhibitors and glycosaminoglycans (GAGs). Since mechanically-activated astrocytes upregulate GAG production, delivery of GFP-TAT, a mock therapeutic protein conjugated to the cell-penetrating peptide TAT, increased significantly after activation. A TAT-conjugated peptide JNK inhibitor was delivered to activated astrocytes and significantly reduced activation. These results suggest a potentially new, targeted therapeutic utilizing TAT for preventing astrocyte activation with the possibility of limiting off-target, negative side effects. While modulating astrocyte activation is a promising treatment strategy for TBI, effective therapeutic treatments are still lacking. Preventing TBI, by developing more effective safety systems, remains crucial. We determined functional tolerance criteria for the hippocampus and cortex based on alterations in electrophysiological function in response to controlled mechanical stimuli. Organotypic hippocampal and cortical slice cultures were mechanically injured at tissue strains and strain rates relevant to TBI, and changes in electrophysiological function were quantified. Most changes in electrophysiological function were dependent on strain and strain rate in a complex, nonlinear manner. Our results provide functional data that can be incorporated into finite element (FE) models to improve their biofidelity of accident and collision reconstructions. TBI causes alterations in macroscopic function and behavior, which can be characterized by alterations in electrophysiological function in vitro. We utilized a novel in vitro platform for TBI research, the SMEA, to investigate the effects of TBI on pharmacologically induced, long lasting network synchronization in the hippocampus. Mechanical stimulation of organotypic hippocampal slice cultures significantly disrupted this network synchronization 24 hours after injury. Our results suggest that the ability of the hippocampal neuronal network to develop and sustain network synchronization was disrupted after mechanical injury, while also demonstrating the utility of the SMEA for TBI research. Herein, we identified a novel therapeutic strategy for treating the deleterious effects of astrocyte activation post-TBI. We also developed tolerance criteria relating mechanical injury parameters to electrophysiological function, an important step in developing more accurate computational simulations of TBI. Equipping FE models with new information on the functional response of the living brain will enhance their biofidelity, potentially leading to improved safety systems while reducing development costs. Finally, we utilized a novel in vitro TBI research platform, the SMEA, to investigate the effects of TBI on long-lasting network synchronization in the hippocampus. Compared to more labor intensive in vivo approaches, the ability of the SMEA to efficiently test TBI hypotheses within a single organotypic slice culture over extended durations could increase the speed of drug discovery through high-content screening. This multi-pronged approach is necessary to address the growing public health concern of TBI.

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More Information

Academic Units
Biomedical Engineering
Thesis Advisors
Morrison, Barclay
Degree
Ph.D., Columbia University
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