Hajime Morimoto

Inflammasome Activation of Cardiac Fibroblasts Is Essential for Myocardial Ischemia/Reperfusion Injury

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&bgr; 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.

Cardiac Overexpression of Monocyte Chemoattractant Protein-1 in Transgenic Mice Prevents Cardiac Dysfunction and Remodeling After Myocardial Infarction

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 α-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+/Flk-1+ 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.

Critical Role of Bone Marrow Apoptosis-Associated Speck-Like Protein, an Inflammasome Adaptor Molecule, in Neointimal Formation After Vascular Injury in Mice

Background— Inflammatory cytokines such as interleukin (IL)-1β 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-1β 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−/−) mice. Methods and Results— Wire-mediated vascular injury was produced in the femoral artery of ASC−/− 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−/− mice after injury. IL-1β and IL-18 were expressed in the neointimal lesion in wild-type mice but showed decreased expression in the lesion of ASC−/− 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−/− bone marrow cells. Furthermore, in vitro experiments showed that the proliferation activity of ASC−/− 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.

M-CSF Accelerates Neointimal Formation in the Early Phase After Vascular Injury in Mice. The Critical Role of the SDF-1-CXCR4 System

Objective—Since the macrophage colony-stimulating factor (M-CSF) has been shown to stimulate differentiation and proliferation of monocyte/macrophage lineage and to be involved in the process of neointimal formation after vascular injury, we tested the effects of M-CSF on the recruitment of bone marrow–derived progenitor cells in neointimal formation after vascular injury in mice. Methods and Results—Wire-mediated vascular injury was produced in the femoral artery of C57BL/6 mice. Recombinant human M-CSF [500 &mgr;g/(kg·day)] or saline (control) was administered for 10 consecutive days, starting 4 days before the injury. Treatment with M-CSF accelerated neointimal formation in the early phase after injury, and this neointimal lesion mainly consisted of bone marrow–derived cells. M-CSF treatment had no effect on the mobilization of endothelial progenitor cells (EPCs: CD34+/Flk-1+) and reendothelialization after injury. The stromal cell-derived factor-1 (SDF-1) was markedly expressed in the neointima and media after injury, whereas CXCR4+ cells were observed in the neointima. Further, a novel CXCR4 antagonist, AMD3100, significantly attenuated the M-CSF–induced neointimal formation. Conclusions—These findings suggest that M-CSF accelerated neointimal formation after vascular injury via the SDF-1–CXCR4 system, and the inhibition of this system has therapeutic potential for the treatment of cardiovascular diseases.

MCP-1 induces cardioprotection against ischaemia/reperfusion injury: role of reactive oxygen species

AIMS Monocyte chemoattractant protein-1 (MCP-1: CCL2) has been demonstrated to be involved in the pathophysiology of ischaemic heart disease; however, the precise role of MCP-1 in ischaemia/reperfusion (I/R) injury is controversial. Here, we investigated the role of cardiac MCP-1 expression on left ventricular (LV) dysfunction after global I/R in Langendorff-perfused hearts isolated from transgenic mice expressing the mouse JE-MCP-1 gene under the control of the alpha-cardiac myosin heavy chain promoter (MHC/MCP-1 mice). METHODS AND RESULTS In vitro experiments showed that MCP-1 prevented the apoptosis of murine neonatal cardiomyocytes after hypoxia/reoxygenation. I/R significantly increased the mRNA expression of MCP-1 in the Langendorff-perfused hearts of wild-type mice. Cardiac MCP-1 overexpression in the MHC/MCP-1 mice improved LV dysfunction after I/R without affecting coronary flow; in particular, it ameliorated LV diastolic pressure after reperfusion. This improvement was independent of both sarcolemmal and mitochondrial K(ATP) channels. Cardiac MCP-1 overexpression prevented superoxide generation in the I/R hearts, and these hearts showed decreased expression of the NADPH oxidase family proteins Nox1, gp91phox, and Nox3 compared with the hearts of wild-type mice. Further, superoxide dismutase activity in the hearts of MHC/MCP-1 mice was significantly increased compared with that in the hearts of wild-type mice. CONCLUSION These findings suggest that cardiac MCP-1 prevented LV dysfunction after global I/R through a reactive oxygen species-dependent but K(ATP) channel-independent pathway; this provides new insight into the beneficial role of MCP-1 in the pathophysiology of ischaemic heart diseases.

Bone marrow CXCR4 induction by cultivation enhances therapeutic angiogenesis

AIMS The chemokine stromal cell-derived factor-1 (SDF-1) and its receptor (CXCR4, CXC chemokine receptor 4) play a critical role in the process of post-natal neovascularization. Here, we investigated the role of CXCR4(+) bone marrow cells (BMCs) in neovascularization in a murine hindlimb ischaemia model. METHODS AND RESULTS We found that the expression of CXCR4 in BMCs was specifically upregulated by cultivation; therefore, we used freshly isolated BMCs and cultivated BMCs, designated as BMC(Fr) and BMC(Cul), respectively. The increased CXCR4 expression corresponded to the migratory capacity in response to SDF-1 alpha. Real-time reverse transcription-polymerase chain reaction and immunohistochemical analyses revealed that SDF-1 alpha expression was significantly increased in the ischaemic limbs of mice. Blood flow perfusion and capillary density were significantly accelerated in mice implanted with BMC(Cul) as compared with those in mice implanted with BMC(Fr). The stimulatory effect of BMC(Cul) on neovascularization was significantly impaired when BMC(Cul) derived from CXCR4(+/-) mice were implanted. The implanted BMC(Cul) showed high retention in the ischaemic limbs. Further, the implantation of BMC(Cul) significantly increased the expression of interleukin (IL)-1 beta and vascular endothelial growth factor-A in the ischaemic limbs. CONCLUSION The upregulation of CXCR4 expression by cultivation may serve as a useful source of BMCs for accelerating therapeutic angiogenesis in ischaemic cardiovascular diseases.

Critical role of Th17 cells in inflammation and neovascularization after ischaemia

AIMS Increasing evidence suggests that CD4(+) T cells contribute to neovascularization in ischaemic tissue. However, the T cell subset responsible for neovascularization after ischaemia remains to be determined. Here, we investigated the role of Th17 cells secreting interleukin (IL)-17, a newly identified subset of CD4(+) T cells, in the neovascularization after murine hindlimb ischaemia. METHODS AND RESULTS Unilateral hindlimb ischaemia was produced in wild-type (WT) C57BL/6 mice. Depletion of CD4(+) T cells resulted in significantly reduced blood flow perfusion in the ischaemic limbs. The expression of IL-17 and retinoic acid receptor-related orphan receptor γt (RORγt) was up-regulated in the ischaemic limbs. IL-17-deficient mice showed a significant reduction in blood flow perfusion, inflammatory cell infiltration, and production of angiogenic cytokines in the ischaemic limbs compared with WT mice. In bone marrow transplantation experiments, the absence of IL-17 specifically in bone marrow cells diminished the neovascularization after ischaemia. Furthermore, IL-17-deficient CD4(+) T cells transferred into the ischaemic limbs of T cell-deficient athymic nude mice evoked a significantly limited neovascularization compared with WT CD4(+) T cells. CONCLUSION These findings identify Th17 cells as a new angiogenic T cell subset and provide new insight into the mechanism by which T cells promote neovascularization after ischaemia.