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Degree

Doctor of Philosophy, Ohio State University, Pharmacy, 2008.

Abstract

Huntington's disease (HD) is a hereditary neurodegenerative disease caused by a polyglutamine expansion (>39 repeats) in the huntingtin protein. HD causes loss of striatal neurons and patients develop progressive chorea, rigidity, and lack of motor coordination. We have cultured forebrain neurons from both the R6/2 transgenic mouse line (expressing an N-terminal fragment of human huntingtin with ~150 glutamines) and the YAC72 line (expressing full-length human huntingtin with 72 glutamines) to study the effect of mutant huntingtin expression on AMPA/kainate receptor-mediated neuronal signaling and cell death. Using a sensitive and selective neuronal cell death assay our lab recently developed, we found that R6/2 neurons, but not YAC72 neurons, are significantly more vulnerable to glutamate and kainate-mediated neuronal death compared to wildtype (WT) control neurons. Since calcium is a key mediator of glutamate receptor-mediated neuronal death, we measured calcium levels in response to kainate. Kainate-induced (30 second) neuronal calcium responses were significantly greater in R6/2 neurons compared to WT neurons; however, this increased sensitivity to kainate was not seen in YAC72 neurons. When we used a low-affinity fluorescent calcium indicator to monitor longer (15 minute) exposures to kainate, we revealed a subset (~20%) of neurons that exhibit very large increases in calcium. However, there were few notable differences between kainate-mediated calcium responses in HD and WT neurons under these recording conditions. Similarly, kainate-induced mitochondrial depolarization and ATP decreases were comparable in HD and WT neurons. Collectively, our results suggest that mutant huntingtin expression in young cultured neurons does not profoundly affect AMPA/kainate receptor mediated signaling. This is in contrast to the reports of robust modulation of NMDA receptor-mediated signaling and death in HD transgenic neurons. While we have focused on the short-term effect (weeks) of mutant huntingtin expression on AMPA/kainate receptor signaling, we do not know the cumulative effect of mutant huntingtin expression on both NMDA and AMPA/kainate receptor-mediated signaling over the decades of disease progression in HD patients. Whether the relatively modest potentiation of AMPA/kainate receptors that we discovered, along with previously reported effects on NMDA receptors, contribute to neuronal dysfunction in HD patients remains to be determined.

Subject Headings

Pharmacology

Keywords

excitotoxicity; calcium; huntingtin; kainate; glutamate; mitochondria

Committee / Advisors

Kari Hoyt, PhD (Advisor)
Lane Wallace, PhD (Committee Member)
Lakhu Keshvara, PhD (Committee Member)
Karl Obrietan, PhD (Committee Member)
Peng Wang, PhD (Committee Member)

Pages

205p.

Document number: osu1213361299
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1213361299

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