The molecular pathogenesis of Huntington's disease : the role of molecular chaperones and methods of modulation of polyglutamine-induced aggregate formation and cell death

• Main Author: Carmichael, J.
• Published: University of Cambridge 2002
• Subjects: 616.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597295

The aim of my project was to investigate whether overexpression of specific heat shock proteins and treatment with pharmacological agents could modify intracellular aggregate formation and influence cell death. I used a cell culture of Huntington's disease in which the mutant huntingtin protein containing 53 or 74 glutamine repeats was transiently expressed together with the heat shock protein of interest and I quantified the effect on aggregate formation and cell death. I used molecular chaperones from mammalian, bacterial and yeast origin belonging to different chaperone families and with different mechanisms of action. I also tested the effects of treatment with LiCl and GSK-3b inhibitors on polyglutamine-induced aggregation and cell death. The key findings of my study were: 1. Overexpression of human heat shock protein 70, the bacterial chaperone complex GroEL/GroES, bacterial chaperones derived from GroEL and the yeast heat shock protein 104 significantly reduced polyglutamine-induced aggregate formation and cell death. These results also cast light on the molecular mechanisms of action of specific chaperone constructs. 2. Overexpression of the human heat shock protein Hdj-2 led to increased polyglutamine-induced aggregate formation without having any significant effect on cell death. 3. In the cell culture model of Huntington's disease, the drug Lithium chloride (LiCl) at concentrations mimicking those found in extracellular fluid in patients treated with this drug, significantly reduced both polyglutamine-induced aggregate formation and cell death. I identified for the first time that LiCl activates a pro-survival pathway through reduced degradation of b-catenin leading to increased transcription via the transcription factor Tcf. Furthermore I found that overexpression of mutant huntingtin reduced the leves of b-catenin, suggesting a novel potential mechanism for mutant huntingtin-mediated toxicity.