Background-Inflammation plays a key role in the pathophysiology of myocardial ischemia/reperfusion (I/R) injury; however, the mechanism by which myocardial I/R induces inflammation remains unclear. Recent evidence indicates that a sterile inflammatory response triggered by tissue damage is mediated through a multiple-protein complex called the inflammasome. Therefore, we hypothesized that the inflammasome is an initial sensor for danger signal(s) in myocardial I/R injury. Methods and Results-We demonstrate that inflammasome activation in cardiac fibroblasts, but not in cardiomyocytes, is crucially involved in the initial inflammatory response after myocardial I/R injury. We found that inflammasomes are formed by I/R and that its subsequent activation of inflammasomes leads to interleukin-1␤ production, resulting in inflammatory responses such as inflammatory cell infiltration and cytokine expression in the heart. In mice deficient for apoptosis-associated speck-like adaptor protein and caspase-1, these inflammatory responses and subsequent injuries, including infarct development and myocardial fibrosis and dysfunction, were markedly diminished. Bone marrow transplantation experiments with apoptosis-associated speck-like adaptor protein-deficient mice revealed that inflammasome activation in bone marrow cells and myocardial resident cells such as cardiomyocytes or cardiac fibroblasts plays an important role in myocardial I/R injury. In vitro experiments revealed that hypoxia/reoxygenation stimulated inflammasome activation in cardiac fibroblasts, but not in cardiomyocytes, and that hypoxia/reoxygenation-induced activation was mediated through reactive oxygen species production and potassium efflux. Conclusions-Our results demonstrate the molecular basis for the initial inflammatory response after I/R and suggest that the inflammasome is a potential novel therapeutic target for preventing myocardial I/R injury. (Circulation. 2011;123:594-604.)Key Words: cytokine Ⅲ heart Ⅲ hypoxia Ⅲ inflammation Ⅲ leukocyte I ncreasing evidence indicates that inflammation is involved in the pathophysiology of myocardial ischemia/reperfusion (I/R) injury. 1 One prominent and early mediator for inflammation in I/R injury is interleukin-1␤ (IL-1␤). 2,3 I/R induces IL-1␤ expression in the heart, and the inhibition of IL-1␤ prevents myocardial injury after I/R, 3 suggesting that the deleterious effects of myocardial I/R are mediated, at least in part, by IL-1␤. In the generation of IL-1␤, pro-IL-1␤, an inactive precursor, undergoes proteolysis by the converting enzyme caspase-1. Caspase-1 is activated within a cytosolic multiprotein complex, the inflammasome. The inflammasome contains cytoplasmic receptors of the NACHT leucine-rich-repeat protein family that are associated with the apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), which in turn recruits and activates caspase-1. 4,5 Increasing evidence indicates that several sterile inflammatory responses triggered by tissue damage are mediated by th...

Abstract-Myocardial infarction (MI) is accompanied by inflammatory responses that lead to the recruitment of leukocytes and subsequent myocardial damage, healing, and scar formation. Because monocyte chemoattractant protein-1 (MCP-1) (also known as CCL2) regulates monocytic inflammatory responses, we investigated the effect of cardiac MCP-1 overexpression on left ventricular (LV) dysfunction and remodeling in a murine MI model. Transgenic mice expressing the mouse JE-MCP-1 gene under the control of the ␣-cardiac myosin heavy chain promoter (MHC/MCP-1 mice) were used for this purpose. MHC/MCP-1 mice had reduced infarct area and scar formation and improved LV dysfunction after MI. These mice also showed induction of macrophage infiltration and neovascularization; however, few bone marrow-derived endothelial cells were detected in MHC/MCP-1 mice whose bone marrow was replaced with that of Tie2/LacZ transgenic mice. Flow cytometry analysis showed no increase in endothelial progenitor cells (CD34 ϩ /Flk-1 ϩ cells) in MHC/MCP-1 mice. Marked myocardial interleukin (IL)-6 secretion, STAT3 activation, and LV hypertrophy were observed after MI in MHC/MCP-1 mice. Furthermore, cardiac myofibroblasts accumulated after MI in MHC/MCP-1 mice. In vitro experiments revealed that a combination of IL-6 with MCP-1 synergistically stimulated and sustained STAT3 activation in cardiomyocytes. MCP-1, IL-6, and hypoxia directly promoted the differentiation of cardiac fibroblasts into myofibroblasts. Our results suggest that cardiac overexpression of MCP-1 induced macrophage infiltration, neovascularization, myocardial IL-6 secretion, and accumulation of cardiac myofibroblasts, thereby resulting in the prevention of LV dysfunction and remodeling after MI. They also provide a new insight into the role of cardiac MCP-1 in the pathophysiology of MI. Key Words: cytokines Ⅲ heart failure Ⅲ hypertrophy Ⅲ inflammation Ⅲ myocardial infarction M yocardial infarction (MI) is accompanied by inflammatory responses that lead to the recruitment of leukocytes and subsequent myocardial damage, healing, and scar formation. 1 Recruitment and activation of monocytes/macrophages in the infarcted myocardium have been shown to contribute importantly to the processes that occur after MI. The activated macrophages lead to the release of cytokines and proteinases, which can induce further inflammation and left ventricular (LV) remodeling. Meanwhile, recent evidence indicates that some endothelial progenitor cells (EPCs) are derived from monocytic lineage cells and participate in neovascularization in ischemic tissues. [2][3][4] Moreover, monocytic-derived EPCs secrete a large amount of angiogenic factors such as the vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF), 4 thereby suggesting that monocytes/macrophages could improve LV dysfunction and remodeling after MI.Chemokines are a family of potent chemotactic cytokines that regulate locomotion and trafficking of leukocytes in basal and inflammatory processes; however, it has been rece...

Background-Inflammatory cytokines such as interleukin (IL)-1␤ and IL-18 play an important role in the development of atherosclerosis and restenosis. Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is an adaptor protein that regulates caspase-1-dependent IL-1␤ and IL-18 generation; however, the role of ASC in vascular injury remains undefined. Here, we investigated the contribution of ASC to neointimal formation after vascular injury in ASC-deficient (ASC Ϫ/Ϫ ) mice. Methods and Results-Wire-mediated vascular injury was produced in the femoral artery of ASC Ϫ/Ϫ and wild-type mice. Immunohistochemical analysis revealed that ASC was markedly expressed at the site of vascular injury. Neointimal formation was significantly attenuated in ASC Ϫ/Ϫ mice after injury. IL-1␤ and IL-18 were expressed in the neointimal lesion in wild-type mice but showed decreased expression in the lesion of ASC Ϫ/Ϫ mice. To investigate the contribution of bone marrow-derived cells, we developed bone marrow-transplanted mice and found that neointimal formation was significantly decreased in wild-type mice in which bone marrow was replaced with ASC Ϫ/Ϫ bone marrow cells. Furthermore, in vitro experiments showed that the proliferation activity of ASC Ϫ/Ϫ vascular smooth muscle cells was not impaired. Conclusions-These findings suggest that bone marrow-derived ASC is critical for neointimal formation after vascular injury and identify ASC as a novel therapeutic target for atherosclerosis and restenosis. (Circulation. 2008;117: 3079-3087.)