Takanori Hayasaki

Targeted Deletion of CC Chemokine Receptor 2 Attenuates Left Ventricular Remodeling after Experimental Myocardial Infarction

A key component of cardiac remodeling after acute myocardial infarction (MI) is the inflammatory response, which modulates cardiac tissue repair. The purpose of this study was to investigate the relationship between the monocytic inflammatory response and left ventricular remodeling after MI using mice deficient in CC chemokine receptor 2 (CCR2), the primary receptor for the critical regulator of CC chemokine ligand 2. Immunohistochemical analysis revealed rapid infiltration of macrophages into infarcted tissue within 7 days in wild-type (WT) mice. However, this process was greatly impaired in CCR2-deficient (CCR2(-/-)) mice. Echocardiography demonstrated beneficial effects of CCR2 deficiency on left ventricular remodeling at 7 and 28 days after MI. In situ zymography showed augmented gelatinolytic activity in WT mice within 7 days after MI, whereas gelatinolytic activity was barely detectable in CCR2(-/-) mice. Moreover, the distribution of gelatinolytic activity in serial sections was very similar to the distribution of macrophages rather than neutrophils. Expression of matrix metalloproteinases and tumor necrosis factor-alpha mRNAs was up-regulated in infarcted regions from WT mice compared to CCR2(-/-) mice at 3 days after MI. Direct inhibition of CCR2 functional pathway might contribute to the attenuation of left ventricular remodeling after MI.

Targeted Deletion of Class A Macrophage Scavenger Receptor Increases the Risk of Cardiac Rupture After Experimental Myocardial Infarction

Background— Class A macrophage scavenger receptor (SR-A) is a macrophage-restricted multifunctional molecule that optimizes the inflammatory response by modulation of the activity of inflammatory cytokines. This study was conducted with SR-A–deficient (SR-A−/−) mice to evaluate the relationship between SR-A and cardiac remodeling after myocardial infarction. Methods and Results— Experimental myocardial infarction (MI) was produced by ligation of the left coronary artery in SR-A−/− and wild-type (WT) male mice. The number of mice that died within 4 weeks after MI was significantly greater in SR-A−/− mice than in WT mice (P=0.03). Importantly, death caused by cardiac rupture within 1 week after MI was 31% (17 of 54 mice) in SR-A−/− mice and 12% (6 of 51 mice) in WT mice (P=0.01). In situ zymography demonstrated augmented gelatinolytic activity in the infarcted myocardium in SR-A−/− mice compared with WT mice. Real-time reverse transcription–polymerase chain reaction at day 3 after MI showed that the expression of matrix metalloproteinase-9 mRNA increased significantly in the infarcted myocardium in SR-A−/− mice compared with WT mice. Furthermore, SR-A−/− mice showed augmented expression of tumor necrosis factor-α and reduction of interleukin-10 in the infarcted myocardium at day 3 after MI. In vitro experiments also demonstrated increased tumor necrosis factor-α and decreased interleukin-10 expression in activated SR-A−/− macrophages. Conclusions— The present findings suggest that SR-A deficiency might cause impairment of infarct remodeling that results in cardiac rupture via insufficient production of interleukin-10 and enhanced expression of tumor necrosis factor-α and of matrix metalloproteinase-9. SR-A might contribute to the prevention of cardiac rupture after MI.

Pioglitazone, a peroxisome proliferator-activated receptor-γ agonist, attenuates myocardial ischemia–reperfusion injury in mice with metabolic disorders

Although considerable attention has focused on obesity, insulin resistance and abnormal lipid metabolism as coronary risk factors, it remains unclear how these pathogenic factors affect the inflammatory response after myocardial ischemia-reperfusion. This study was conducted to evaluate whether these metabolic disorders exacerbate myocardial ischemia-reperfusion injury, and to determine if ischemia-reperfusion injury could be modified with the thiazolidinedione, pioglitazone. Experiments were performed in KK-A(y) and C57BL/6J mice subjected to 40 min of ischemia followed by reperfusion. Infiltration of inflammatory cells in ischemic myocardium, and infarct size 3 days after reperfusion were significantly higher in KK-A(y) than C57BL/6J mice (p<0.05 and p<0.001, respectively). Furthermore, expression of chemokines, inflammatory cytokines and extracellular matrix proteins in ischemic myocardium was significantly higher in KK-A(y) than C57BL/6J mice 1 day after reperfusion. Pioglitazone treatment of KK-A(y) mice for 14 days significantly reduced the accumulation of inflammatory cells in ischemic myocardium, and infarct size 3 days after reperfusion compared to vehicle treatment (p<0.05 and p<0.05, respectively). Pioglitazone also attenuated expression of chemokines, inflammatory cytokines and extracellular matrix proteins in ischemic myocardium 1 day after reperfusion. In vitro experiments demonstrated that tumor necrosis factor-alpha (TNF-alpha) was significantly higher in cultured peritoneal macrophages from KK-A(y) than C57BL/6J mice, and pioglitazone significantly reduced TNF-alpha in macrophages from both types of mice. These findings suggest that metabolic disorders exacerbate ischemia-reperfusion injury as a result of overexpression of inflammatory mediators, and this effect might be improved, in part by the anti-inflammatory effects of pioglitazone.

MCP-1/CCR2 signalling pathway regulates hyperoxia-induced acute lung injury via nitric oxide production

To clarify the role of the monocyte chemoattractant protein‐1 (MCP‐1)/C–C chemokine receptor 2 (CCR2) signalling pathway in hyperoxia‐induced acute lung injury, CCR2‐deficient (CCR2−/−) and wild‐type (CCR2+/+) mice were exposed to 85% O2 for up to 6 days. At day 3, body weight significantly decreased and total protein concentration in bronchoalveolar lavage fluid (BALF) was higher in CCR2−/− mice compared with CCR2+/+ mice. Cumulative survivals were significantly lower in CCR2−/− mice than in CCR2+/+ mice. However, the two groups showed no significant differences in both histological changes and number of macrophages in BALF. Real‐time reverse transcriptase‐polymerase chain reaction revealed increased mRNA levels of MCP‐1, interleukin‐1β thioredoxin‐1, and inducible nitric oxide synthase (iNOS) in lung tissues in CCR2−/− mice compared with CCR2+/+ mice. Increased iNOS mRNA levels in alveolar macrophages exposed to 85% O2 for 48 h in vivo or in vitro were significantly higher in CCR2−/− mice than in CCR2+/+ mice. These results suggest that the MCP‐1/CCR2 signalling pathway is protective against hyperoxia‐induced tissue injury by suppressing induction of iNOS and consequent production of reactive oxygen species by activated alveolar macrophages.