Investigation of Heat shock Factor 1 as a Therapeutic Target for Huntington s Disease

Increased life expectancy in the developed world has resulted in a greater incidence of age-related neurodegenerative disorders such as Alzheimer?s disease and Parkinson?s disease, which already impose a significant health, social and economic burden on families, communities and the country as a whole. Insight into the cause of these diseases has arisen through the study of rare genetic forms of Alzheimer?s and Parkinson?s disease as well as from inherited disorders like Huntington?s disease. The underlying mutations cause disease related proteins to misfold and adopt abnormal shapes allowing them to interact with themselves or other proteins in a detrimental manner. These aberrant interactions result in the malfunction and death of brain cells. Treatments that will slow or halt the progression of these ?protein-folding? diseases do not exist.
All cells must ensure that as every protein is made, it is folded into the correct shape or conformation. Cells use ?chaperones? to fold proteins and if this is repeatedly unsuccessful, misfolded proteins are broken down or degraded. If this natural process to remove misfolded proteins becomes overwhelmed, as in the presence of a disease-related aggregation-prone protein, misfolded proteins accumulate and clump together as protein aggregates. The capacity of cells to maintain correctly folded proteins diminishes with age, resulting in an increasing susceptibility to protein-folding disease in the elderly.
Strategies that might decrease the propensity of an aggregation-prone protein to misfold include increasing either the protein folding or protein degradation capacity of the cell. One possible approach is to harness the cells? natural defence against insults that cause proteins to misfold e.g. heat or toxic chemicals. This ?heat shock response? leads to the immediate increase in levels of many chaperones known as heat shock proteins and is switched on by heat shock factor 1 (HSF1). We have recently gained access to a drug that can cross the blood brain barrier and activate HSF1 in brain cells. We are also generating mouse models in which we can induce the presence of an activated form of HSF1 in brain. We shall use these complementary approaches understand the heat shock response in brain cells and to test whether activation of HSF1 can alleviate disease-related phenotypes in a mouse model of Huntington?s disease. This work will allow us to determine whether the activation of HSF1 should be pursued as a target for therapeutic development for Huntington?s disease and other neurodegenerative disorders.

Within the aging populations of the developed world the health, social and economic burden of neurodegenerative disease is already substantial and expected to increase. The occurrence of the most common neurodegenerative disorders: Alzheimer?s disease (AD), Parkinson?s disease (PD) and amyotrophic lateral sclerosis (ALS) is largely sporadic, however, rare familial cases of these diseases, together with inherited monogenic disorders such as Huntington?s disease (HD) have provided clues to their aetiology. In AD, PD, ALS and HD, mutations result in the propensity of disease-associated proteins to misfold, form a-sheet structures and become ?aggregation-prone? properties for which they have been named ?protein-folding? diseases. In all cases, disease-modifying therapies do not exist.
All cells maintain protein-folding homeostasis through integrated protein-folding and clearance networks and pathways. Molecular chaperones direct the folding of newly synthesised and damaged proteins and those that cannot be successfully folded into their native conformation are degraded through the ubiquitin proteasome system (UPS) or cleared by lysosome-mediated autophagy. In the presence of an aggregation-prone protein, the mechanisms that maintain protein folding homeostasis become overwhelmed resulting in misfolding and aggregation. The capacity to maintain protein folding homeostasis diminishes with age, resulting in an increasing susceptibility to protein folding disease in the elderly.
Strategies that might decrease the propensity of an aggregation-prone protein to misfold include increasing either the protein folding or protein degradation capacity of the cell. One possible approach is to induce the cellular stress response. Conditions of cellular stress including elevated temperature and oxidative damage activate the heat shock response which results in the immediate induction of heat shock proteins that encode molecular chaperones and other proteins important for the recovery from stress induced protein damage. Heat shock factor 1 (HSF1) is the master regulator of the heat shock response and can be activated pharmacologically by inhibition of Hsp90. We shall use complimentary approaches: exposure to elevated temperature, administration of a brain penetrant Hsp90 inhibitor and the generation of mice expressing an inducible form of activated HSF1 to define the neuronal heat shock response in vivo and to determine whether activation of HSF1 can alleviate disease-related phenotypes in a mouse model of HD. Thereby, we shall validate whether HSF1 activation is a rational therapeutic target for HD, and by extension, other protein-folding neurodegenerative disorders.