Background-Toll-like receptors (TLRs) are members of the interleukin-1 receptor family and are involved in the responsiveness to pathogen-associated molecular patterns. Recent studies have demonstrated that TLRs are activated by endogenous signals, such as heat shock proteins and oxidative stress, which may contribute to congestive heart failure.Oxidative stress is one of the major factors in doxorubicin (Dox)-induced cardiac dysfunction. Thus, we hypothesized that TLRs contribute to the pathogenesis of Dox-induced cardiac dysfunction. Methods and Results-Cardiac dysfunction was induced by a single injection of Dox (20 mg/kg IP) into wild-type (WT) mice and TLR-2-knockout (KO) mice. Five days after Dox injection, left ventricular dimension at end-diastole was smaller and fractional shortening was higher in KO mice compared with WT mice (PϽ0.01). Nuclear factor-B activation and production of proinflammatory cytokines after Dox were suppressed in KO mice compared with WT mice (PϽ0.01). The numbers of TUNEL-positive nuclei and Dox-induced caspase-3 activation were less in KO mice than in WT mice (PϽ0.01). Survival rate was significantly higher in KO mice than in WT mice 10 days after Dox injection (46% vs 11%, PϽ0.05). Conclusions-These findings suggest that TLR-2 may play a role in the regulation of inflammatory and apoptotic mediators in the heart after Dox administration.
Background-Protease-activated receptor-1 (PAR-1) is the high-affinity receptor for the coagulation protease thrombin. It is expressed by a variety of cell types in the heart, including cardiomyocytes and cardiac fibroblasts. We have shown that tissue factor (TF) and thrombin contribute to infarct size after cardiac ischemia-reperfusion (I/R) injury. Moreover, in vitro studies have shown that PAR-1 signaling induces hypertrophy of cardiomyocytes and proliferation of cardiac fibroblasts. The purpose of the present study was to investigate the role of PAR-1 in infarction, cardiac remodeling, and hypertrophy after I/R injury. In addition, we analyzed the effect of overexpression of PAR-1 on cardiomyocytes. Methods and Results-We found that PAR-1 deficiency reduced dilation of the left ventricle and reduced impairment of left ventricular function 2 weeks after I/R injury. Activation of ERK1/2 was increased in injured PAR-1 Ϫ/Ϫ mice compared with wild-type mice; however, PAR-1 deficiency did not affect infarct size. Cardiomyocyte-specific overexpression of PAR-1 in mice induced eccentric hypertrophy (increased left ventricular dimension and normal left ventricular wall thickness) and dilated cardiomyopathy. Deletion of the TF gene in cardiomyocytes reduced the eccentric hypertrophy in mice overexpressing PAR-1.Conclusions-Our results demonstrate that PAR-1 contributes to cardiac remodeling and hypertrophy. Moreover, overexpression of PAR-1 on cardiomyocytes induced eccentric hypertrophy. Inhibition of PAR-1 after myocardial infarction may represent a novel therapy to reduce hypertrophy and heart failure in humans.
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