Induction of heat-shock proteins (Hsp), such as via Hsp90 inhibition, is being investigated as a treatment option for neurodegenerative diseases such as Alzheimer's disease (AD). We have demonstrated that a central nervous system-permeable Hsp90 inhibitor, OS-20, shows potent efficacy for ameliorating memory deficit in various acute and chronic AD mouse models. Further, we have found that the synaptic effect of OS- 20 is largely dependent on heat-shock transcription factor, HSF1, a major stress-responsive transcriptional factor. HSF1 induces transcriptions of genes that have heat shock elements (HSE) upon stress (e.g., heat shock and oxidative stress) and protect cells from cell death. HSF1 function has been most studied in relation to cancer. However, its function in neurons remains largely unknown. We recently found that activation of HSF1 by OS-20 increased hippocampal levels of brain-derived neurotrophic factor (BDNF), a critical factor for neuroprotection and learning/memory. Thus, activation of HSF1 by Hsp90 inhibition likely increases neuroprotection, in part, by inducing BDNF. What remains unknown is how HSF1 controls transcription of the BDNF gene. Nine promoters control BDNF gene transcription, leading to different effects in neural functions and behavior. Much is known about BDNF promoter regulation by neuronal activity such as via cAMP- response element-binding protein (CREB). By contrast, limited information is available for BDNF promoter regulation for resilience upon cellular stress. Our sequence search identified 12 putative HSEs in most of the BDNF promoters. Interestingly, some HSEs are located in proximity to cAMP-response element-binding protein (CREB) sites. These findings led us to hypothesize that HSF1 mediates OS-20- or stress-induced BDNF transcription by activating specific BDNF promoters, interacting with CREB pathways. Our idea of HSF1 controlling BDNF induction and its interaction with CREB is novel. Our goal is to test this hypothesis, by determining HSF1 controls of promoter-specific BDNF transcription upon Hsp90 inhibition (Aim 1) and its interplay with CREB (Aim 2).
In Aim 1, we will determine HSF1 kinetics, HSF1 binding to individual BDNF promoters, and promoter-specific BDNF transcription induced by OS-20 treatment and shock stress both in vitro (cultured neuron) and in vivo (mice).
In Aim 2, we will investigate the interplay of HSF1 and CREB in regulating BDNF transcription. We will assess their temporal and spatial regulation of BDNF promoter activity under OS-20 treatment or stress both in vitro and in vivo. We will also identify gene populations bound to HSF1 and CREB by using comparative ChIP-sequencing analysis and those activated by OS-20 by using RNA- sequencing. Successful outcomes will elucidate transcriptional mechanisms of HSF1 and validate HSF1- promoter interaction as an important and novel AD therapeutic target. This study is significant because the verified HSE sites will be targets for developing drugs that directly activate the HSE sites to induce BDNF and for identifying any defects at the promoter sites for AD susceptibility (e.g. SNPs, epigenetic controls).
Brain-derived neurotrophic factor is a critical factor for neuronal survival and synaptic plasticity. This research will provide important information about how heat-shock transcription factor (HSF)1 regulates promoter-specific BDNF transcriptions, verifying the heat-shock elements in the BDNF promoters. Successful validation of this major heat-shock transcription factor may identify potential targets useful in future therapeutic design and biomarkers for neurodegenerative diseases.