This proposal addresses a paradigm shift: that extracellular heat shock proteins (HSP) are pro-inflammatory and pro-apoptotic. HSPs prevent or ameliorate injury; however, there is evidence of a pro-inflammatory side to these proteins. Extracellular HSP60 is activates the innate immune system via the toll-like receptors (TLR), leading to the production of cytokines. Antibodies to HSPs are found in the population, and more prevalent in those with cardiovascular disease, as is the presence of HSP60 in the plasma. Induction of the heat shock response with expression of HSPs in the setting of a pre-existing inflammatory injury, results not in protection, but in cell death. We hypothesize that extracellular HSP60 can function as an inducer of inflammation in the cardiovascular system, and that inflammation can paradoxically inhibit the HSP response to injury, or convert the induction of the heat shock response from protective to harmful. We will address this in 3 Specific Aims: 1. Define the role of HSP60 in cardiac inflammation- HSP60 is a ligand forTLR-4 and can activate the innate immune system resulting in the production of cytokines. In adult cardiac myocytes, we will characterize the binding of HSP60, define the pro-apoptotic effect of HSP60 and as well as its effect on cytokine production. 2. Determine how repetitive injury interacts with the heat shock response to convert it from protective to pro-apoptotic- Sequential injury by an inflammatory stimulus followed by a HSP inducing injury results in apoptosis rather than protection. We have found that inflammatory stimuli, including TNF-alpha and HSP60, induce apoptosis, and when followed by heat shock, greatly increase apoptosis. Thus, HSP60 can prime the cardiovascular system for injury. Experiments will study the effect of TNF-alpha followed by heat shock, determine how this disproportionately increases injury, and how HSP60 causes apoptosis. 3. Identify the mechanism (s) leading to increased HSP60 in the failing heart. We hypothesize that HSF-1, a transcription factor for HSPs, is inactivated in heart failure by ERK1 and GSK3, and that increased HSP60 expression is driven by NFKB. In turn, extracellular HSP60 in heart failure causes inflammation and activation of NFKB. Work will address HSF-1 modification and function, and control of HSP expression. The long term goal of the Pi's research is to understand the role of heat shock proteins in cardiac injury, and thus, to achieve further insights into how to prevent as well as treat cardiac injury.
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