Ischemic heart disease (IHD) is a leading cause of death among veterans. Myocardial infarction (MI) is a serious outcome of IHD, and is generally attributable to the detrimental effects of myocardial ischemia/reperfusion (I/R) injury. Cardiac inflammation and extracellular matrix deposition (scar formation) are essential events in the cardiac remodeling post-MI. Therapeutic approaches targeting these events may hold promise for patients with MI. This proposal investigates the therapeutic potential of ubiquitin (UB; a small molecular weight protein typically associated with tagging proteins for proteasomal degradation) in myocardial remodeling following myocardial ischemia and I/R injury. The proposal is based on our novel observations that exogenous UB plays a protective role in ?- adrenergic receptor-stimulated myocardial remodeling. In human THP1 leukemia cells, CXCR4 is identified as a receptor for extracellular UB. Our preliminary data using - i) isolated heart model of global ischemia/reperfusion (I/R; Langendorff model); and ii) in vivo myocardial I/R injury in mice now suggest a protective role of exogenous UB in myocardial remodeling following I/R injury. UB treatment decreased infarct size, reduced cardiac inflammatory response and improved heart function 3 days post-I/R. In vitro, UB treatment inhibited migration of neutrophils, and enhanced phagocytic activity of macrophages. In adult cardiac fibroblasts, UB treatment activated ERK1/2, and increased expression of vascular endothelial growth factor-A (VEGF-A). UB co-immunoprecipitated with CXCR4, and CXCR4 antagonism negated the effects of extracellular UB on ERK1/2 activation and VEGF-A expression. UB treatment augmented ?-smooth muscle actin (a marker for myofibroblast differentiation) expression and collagen gel contractile activity of fibroblasts, while decreasing migration of fibroblasts into the wound area and inhibiting FBS-stimulated cell proliferation. These observations led us to hypothesize that exogenous UB, most likely acting via CXCR4, modulates cardiac inflammatory response and extracellular matrix biology by affecting phenotype and/or function of neutrophils, macrophages and fibroblasts, thereby playing a cardioprotective role in myocardial remodeling following ischemia and I/R injury.
Aim 1 will investigate, in vivo, the therapeutic potential of exogenous UB in myocardial remodeling following myocardial ischemia and I/R injury.
Aim 2 will examine, in vivo, the role of CXCR4 in modulation of cardioprotective effects of exogenous UB using CXCR4 antagonist, UB mutants and cell type-specific CXCR4 knockout mice.
Aim 3 will investigate the cellular and molecular mechanisms by which exogenous UB affects cardiac inflammatory response and extracellular matrix biology to coordinate post-I/R cardioprotective response. The Innovation of this project lies in the investigation of therapeutic potential of exogenous UB in myocardial remodeling following myocardial ischemia and I/R injury (clinically relevant model). The proposed studies investigating the role of exogenous UB in cardiac inflammation and extracellular matrix biology may uncover novel strategies for the treatment of IHD.
Heart attack, a leading cause of death among veterans, causes damage to the heart and compromises heart function. Therapies aimed to preserve heart function have been somewhat effective, however, development of new therapeutic approaches is needed to improve the outcome of patients suffering from heart attack. Using a mouse model, this project explores the therapeutic potential of ubiquitin (a naturally occurring small molecular weight protein; found in all eukaryotic cells) following heart attack, which may lead to the development of new and cost effective strategies for the treatment of heart attack.