Dissecting the Protective Role of Cardiac Hsp90ß Ablation/Inhibition - PROJECT SUMMARY Dysfunctions are observed at multiple cellular and subcellular levels in heart diseases. However, current therapeutics are designed to tackle a single subcellular disease mechanism or molecular target. Our long term goal is to develop strategies to correct several pathways simultaneously, which can ultimately improve clinical outcomes. In this regard, Hsp90β is a desirable target, as it can affect many downstream signaling pathways. However, the role of Hsp90β in cardiac function is not clear due to a lack of viable ablation animal models. To this end, we generated a cardiac-specific inducible Hsp90β knockout (Hsp90βCM-/-) mice and to our surprise, their hearts were protected from myocardial infarction induced by ischemia/reperfusion (I/R) injury, which is paradoxical to its known pro-survival role. Furthermore, this protection is specific to Hsp90β as Hsp90αCM-/- hearts were not protected. These findings suggest that specific Hsp90β inhibition may be a good therapeutic strategy for I/R injury. Thus, our main goal in this application is to carefully examine the protective role of cardiac Hsp90β and dissect the Hsp90β specific interactome to identify the underlying mechanisms. Based on our previous publications and existing pilot data, we hypothesize that removal of cardiac Hsp90β confers cardioprotection, partly by preserving mitochondrial membrane integrity. In this R01 application, we will address this hypothesis in three independent but related aims. In Aim 1, we will thoroughly examine if our new Hsp90βCM-/- hearts are protected from ischemic insult at young (3 months) or old (12 months) age. We will examine the potential pro-death role of cardiac Hsp90β in sensitizing the opening of mitochondrial permeability transition pore and necrotic cell death upon I/R injury. In Aim 2, with our previous knowledge on the role of Hsp90β/HCLS1-associated protein X-1 (HAX-1) interaction in mitochondrial membrane protection, we will map out the minimal binding domains and test the feasibility of using this mimetic peptide to confer protection only in the mitochondria. In Aim 3, we will furthermore examine the effect of Hsp90 ablation in chronic cardiac diseases. We also aim to identify the gene dosage effect of Hsp90 on cardiac function by using Hsp90αCM-/-, Hsp90αCM-/- βCM+/- and Hsp90αCM+/-βCM-/- mice as well. We will perform interactome analysis for both Hsp90α and Hsp90β in human patient hearts to identify isoform-specific interactome and their shift during cardiac diseases. Lastly, we have developed a prediction tool for binding interface for Hsp90 substrates. We will combine the use of this prediction tool and mimetic peptide to identify novel Hsp90 isoform specific binding partners in the heart. By the completion of this study, we expect to gain important insight on how to specifically study particular Hsp90α or Hsp90β complex and evaluate the potential therapeutic application in the future.
