Activation of the heat shock response by sulfhydryl-reactive chemoprotective agents

Context: Disturbances in the protein homeostasis are major contributors to the complex biological processes that accompany ageing and age-associated pathologies, and also occur during conditions of stress. To protect the proteome, eukaryotic organisms have evolved highly efficient mechanisms. Most prominent are the heat shock response and the phase 2 response that are controlled by transcription factors heat shock factor 1 (HSF1) and nuclear factor-erythroid 2-related factor 2 (Nrf2), respectively. There is a growing interest in the discovery and development of small molecule-inducers of these systems for prevention and treatment of chronic degenerative conditions associated with ageing. Induction of the heat shock response and the phase 2 response leads to upregulation of large networks of cytoprotective proteins that detect and counteract the potentially deleterious consequences of thermal, oxidative and electrophilic stress, and promote survival. Furthermore, both pathways are involved in multiple interactions that link homeostatic metabolism with stress biology, and ultimately play crucial roles in determining health and life span.

Small molecule activators of Nrf2 have a common chemical signature, that of sulfhydryl reactivity. Emerging evidence suggests that sulfhydryl-reactive molecules also activate the heat shock response. Curiously, anti-inflammatory activity is a consistent property of Nrf2 inducers, indicating that suppression of inflammation is a central aspect of their chemoprotective actions. However, this property is only partially Nrf2-dependent. Interestingly, HSF1 activation has anti-inflammatory effects and is required for protection during inflammatory responses.

Aims and Objectives: We hypothesize that the cytoprotective and anti-inflammatory activities of sulfhydryl-reactive chemoprotective agents are mediated through activation of two distinct transcription factors, i.e., Nrf2 and HSF1, through a common chemical signal, that of sulfhydryl reactivity. The specific aims of the proposed study are:

1. To establish which classes of sulfhydryl-reactive chemoprotective agents upregulate HSF1-mediated gene expression.
2. To elucidate the importance of sulfhydryl reactivity in the activation of transcription factor HSF1.
3. To define the relative roles of transcription factors HSF1 and Nrf2 in protection against pro-inflammatory stimuli.

Potential applications and benefits: The burden of chronic degenerative conditions on our society is expected to continue to increase, largely due to ageing of the population. Whereas no satisfactory solutions are yet available, it is timely to think about implementing prevention measures that harness the intrinsic cytoprotective mechanisms of the cell. Exploiting the ability of small molecules, many of which are present in the human diet and therefore of presumed low toxicity, to upregulate intracellular defenses, is an exciting area for future development. If, as hypothesized, redox regulation and transcription factor cysteine modifications are central to both the phase 2 response and heat shock response, the development of such "dual" activators will be ideal for simultaneously manipulating these pathways and achieving synergistic protective effects.

Context: The heat shock response and the phase 2 response represent two highly conserved mechanisms that determine the ability of cells and organisms to adapt and survive under conditions of stress. Both pathways do not normally operate at maximal capacity, but can be induced by small-molecule chemoprotective agents. Induction results in enhanced transcription of a battery of cytoprotective genes under the control of transcription factors heat shock factor 1 (HSF1) and nuclear factor-erythroid 2-related factor 2 (Nrf2). Small molecule activators of Nrf2 have a common chemical signature, that of sulfhydryl reactivity. They react with cysteine residues of the sensor protein Keap1, leading to Nrf2 activation. Emerging evidence suggests that sulfhydryl-reactive molecules also induce the heat shock response. Anti-inflammatory activity is a consistent property of Nrf2 activators, indicating that suppression of inflammation is a central aspect of their chemoprotective actions. However, this property is only partially Nrf2-dependent. Critically, HSF1 activation has anti-inflammatory effects.

Aims and Objectives: To test the hypothesis that the cytoprotective and anti-inflammatory activities of sulfhydryl-reactive chemoprotective agents are mediated by activation of Nrf2 and HSF1, through a common chemical signal, that of sulfhydryl reactivity. To establish whether activation of HSF1 is a common property of sulfhydryl-reactive chemoprotective agents. To elucidate the importance of sulfhydryl reactivity in activation of HSF1. To define the individual roles of HSF1 and Nrf2 in protection against pro-inflammatory stimuli.

Potential applications and benefits: The proposed studies will establish whether activation of HSF1 mediates the Nrf2-independent portion of the anti-inflammatory activity of sulfhydryl-reactive inducers and will provide essential mechanistic understanding for the development of such molecules as chemoprotective agents to improve human health.

The findings from this work will benefit academic research groups working in the field of the heat shock response, the phase 2 response, and those interested in chemoprotection, including researchers working in the areas of ageing and neuroscience. In addition, the pharmaceutical industry will be interested in this project as it involves small molecules that could be potentially developed as pharmaceutical agents and, most importantly, the precise identification of their molecular targets and their mechanism(s) of action. Because the heat shock response and the phase 2 response are involved in multiple interactions that link homeostatic metabolism with stress biology, and ultimately play crucial roles in determining health and life span, our findings will also have an impact on those scientists that study the intricate details of gene-environment interactions.

To make an impact, we will make every effort to publish in peer-reviewed journals and present our findings at scientific conferences. In addition, we will participate in workshop and networking events organized by BioDundee and Scottish Enterprise to link with biotechnology companies specializing in small molecule discovery to use our findings to leverage the greatest advantage to the UK economy. The University of Dundee Research and Innovation Services have well-established links with the pharmaceutical industry, which will ensure timely transition of our findings.

In addition to academics and scientists, the development of this project will impact the general public. As an RC UK Academic Fellow, I have already been involved in projects (e.g., "Light Up the Lab") in which I have presented my work to the 5th and 6th form pupils in local secondary schools, at the schools themselves during their regular classes, as well as in the course of a science exhibition at the Dundee Science Centre, and also have had groups of students spending time in my lab to receive hands-on-experience and appreciation for every day scientific research. All of these activities have been highly successful, and based on the feedback received from the pupils, I have been strongly encouraged to continue my involvement in public engagement. In terms of the wider community, the project will give our staff valuable training and experience in communicating their findings at both scientific and lay levels, which can only have positive benefits. I envision this interaction will occur throughout the project.