Different members of the HSP multigene family have been implicated the inhibition of ischemia- induced protein damage, abrogation of protein misfolding/aggregation, and prevention of mitochondrial dysfunction. However, the precise cellular mechanisms remain partially understood and effective strategies for their coordinated recruitment are poorly defined. Robust upregulation of HSP synthesis requires repression of tight basal repression (control) and full activation of the Heat Shock Factor 1 (HSF1) by a highly conserved process triggered by diverse stimuli under stressful conditions. In Preliminary Studies, we have developed a transgenic mouse model carrying a constitutively active HSF1 (caHSF1) transactivator that conveniently circumvents these stress-inducible requirements and provides us the robust versatility to up-regulate global HSP expression in the intact heart. The main objectives of this research application are to definitively address the cellular mechanisms that up-regulation of HSPs by caHSF1 decreases post-ischemic LV dysfunction and improves myocardial salvage. Specifically, we wish to characterize if HSF1-dependent modulation of the cytosolic/unfolded protein response (cyUPR) prevents mitochondrial dysfunction and improves post-ischemic cardiac metabolism. The specific hypothesis, to be tested, is that tissue-specific constitutively active heat shock factor 1 (caHSF1) expression represents a novel chaperone-dependent pathway for preserving mitochondrial permeability transition and cellular protection. The following three specific aims are designed to test this hypothesis:
Aim 1 : Determine the precise levels of tissue-specific HSP expression required to decrease protein aggregation and to achieve ischemic protection after moderate to severe ischemic challenges ex vivo.
Aim 2 : Characterize the tissue-specific HSP overexpression for changes in cardiac metabolism and myocardial oxygen consumption under basal and ischemic conditions ex vivo.
This aim will address if the chaperone-dependent effects of HSPs directly affects mitochondrial respiration and energy production.
Aim 3 : Characterize the cellular mechanisms by which conditional HSP overexpression prevents mitochondrial permeability transition (MPT) opening. Conditional strategies are ideally suited for testing the efficacy of interventions to aforementioned clinical outcomes (e.g., myocardial infarction, cardiac arrhythmias, contractile dysfunction). In this proposal, our preclinical studies will address several timely and novel questions related to the elapsed times needed to establish the biological plausibility for therapeutic intervention at the functional, biochemical, molecular and cellular levels. Accordingly, we propose that a conditional caHSF1 animal model permits more rigorous assessment of the mechanisms of ischemic protection on a time scale between intervention and clinical outcomes. Given the burgeoning epidemic of ischemia-related heart failure, there is increased urgency to establish proof-of-principle novel strategies whose administration at the time of acute myocardial infarction might reduce post-ischemic left ventricular dysfunction and favorably improve long-term outcomes, such as heart failure and cardiac sudden death.
7. Potential Impact on Veterans' Health Heart attacks and strokes account for the first and third leading causes of mortality and morbidity in the United States, respectively. Heart failure from either inherited or acquired conditions claims 500,000 lives annually and costs ~$30 billion dollars in the US alone. Ischemic heart disease-the most common acquired heart disease in both men and women- has a higher prevalence in veterans of both sexes due to higher rates of obesity and cigarette use than the general population. This research proposal seeks to understand the mechanisms of cellular protection with the ultimate goal for disease prevention in the high-risk veteran population. If successful, such beneficial outcomes may improve the health of veterans with acute ischemic syndromes during cardiac transplantation, coronary bypass surgery, and other acquired cardiac conditions.