Nearly 5 million Americans have heart failure, with 400,000 new cases diagnosed annually. Most treatment is aimed at stemming the downward spiral of heart failure, but despite vigorous attempts to dissect the underlying mechanisms, much remains to be understood. The heat shock proteins (HSP) are a ubiquitous family of endogenous, protective proteins with high sequence conservation across species. Previously, we observed that the cardioprotective HSP60, normally a mitochondrial and cytosolic protein, is abnormally localized in the plasma membrane in the failing human heart. We have determined that acute hypoxic injury in rat cardiac myocytes precipitates translocation of cytosolic HSP60 to the plasma membrane. Cytosolic HSP60 complexes with the pro-apoptotic bax in the normal heart, and reduction in HSP60 will precipitate myocyte apoptosis. Our central hypothesis is that membrane localization of HSP60 mediates cardiac myocyte damage and cell death. We specifically hypothesize that cellular stress/injury causes phosphorylation/myristoylation of cytosolic HSP60 resulting in HSP60 translocating to the plasma membrane, We will address this hypothesis with three Specific Aims: 1. Determine the Mechanism of Translocation of HSP60 to the Plasma Membrane with Stress. Identify modifications of HSP60 that account for change in cellular localization with injury, and pinpoint signaling pathways involved in the observed modifications. 2. Determine the Function of Membrane Localization of HSP60 with Stress - HSP60 translocates from the cytoplasm to the plasma membrane with stress. We hypothesize that the presence of HSP60 in the membrane is detrimental to the heart, and will test this by expressing mutated HSP60 with altered localization in myocytes. We will also identify membrane proteins that interact with HSP60. 3. Define the Mechanism of the HSP60/bax Interaction - HSP60 and bax form a complex in the cytosol. We postulate that this interaction between HSP60 and bax is important for preventing apoptosis. The underlying mechanism of regulation of this interaction is unknown, and will be identified in the planned experiments. In the planned work, we will study a novel aspect of HSP60 function - its translocation with stress/injury from the cytosol to the plasma membrane, and the effect of this migration on cardiac cell function and viability. The key issue is whether the movement of HSP60 to the plasma membrane is a cause vs. a consequence of injury. These experiments will help delineate whether movement of HSP60 the membrane alone will precipitate cell death, and whether preventing movement will prevent cell death. The long-term goal of this research initiative is to further understand the mechanisms underlying heart failure's progression. ? ?
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