Date of Award

2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Bioengineering

First Advisor

David F. Meaney

Abstract

Traumatic brain injury (TBI) is a major and costly epidemic in the United States and around the world. There are little treatment options and currently no cure. Past research aimed at treating neurons as a therapeutic target have not been successful treatments clinically. Recent interest has turned to another cell type, the astrocyte, as a potential therapeutic target. In this dissertation, we expand upon past findings by further exploring the role of astrocytes and astrocytic signaling in TBI in vivo. Creating a new mild TBI model based on human mild TBI biomechanics, we produced behavioral deficits and histopathological changes similar to mild human TBI. We modified and applied the new TBI model to see if the in vitro astrocytic response to mild mechanical injury could be reproduced in vivo. By imaging the intracellular calcium in cortical astrocytes after mechanical impact in vivo with a 2-photon microscope, we found that mild mechanical injury produced a strong intercellular calcium wave originating from the site of injury. Drug applications to determine the mechanism of calcium wave showed that ATP signaling, and not gap junction coupling among the astrocytes, was responsible for this immediate effect of mild mechanical injury. Next we tested two transgenic animals, each with a different aspect of inhibited astrocyte signaling to determine the effect on TBI recovery. The first transgenic line, VIPP, had an over expression of IP3 phosphatase and was able to reduce the injury induced intercellular calcium wave in astrocytes. Reducing IP3 signaling specifically in astrocytes led to a worse behavioral outcome in a more severe TBI model and no significant difference in the mild TBI model. The second transgenic line, dnSNARE, was used to study the role of inhibited vesicular release from astrocytes. Reducing gliotransmission in this manner improved outcome in both the severe and the mild TBI models. In both cases, baseline behavior did not differ from wildtype littermates suggesting that targeting either pathway may have limited side effects. Histopathologies revealed significant reduction of astrogliosis in both VIPP and dnSNARE injured mice compared to WT. Together these results suggest that injury level can affect the effectiveness of a particular pathway as a therapeutic target and that overall targeting gliotransmission is an effective strategy.

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