Abstract 316: Role of an Inflammasome Adaptor Molecule ASC (Apoptosis-associated Speck-like Protein Containing a Caspase Recruitment Domain) in Myocardial Ischemia-Reperfusion Injury

Abstract

Inflammatory responses play a key role in the pathophysiology of myocardial ischemia-reperfusion (I/R) injury. ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) is an adaptor protein that forms “inflammasome” whose activation leads to caspase-1-dependent interleukin (IL)-1β generation and subsequent inflammatory responses; however, the role of ASC in myocardial I/R injury remains unclear. Baseline left ventricular (LV) function was unaltered in ASC-deficient (ASC −/− ) mice. ASC −/− (n=42) and wild-type control (WT) (n=42) mice were subjected to 30 min LAD occlusion, followed by reperfusion. ASC −/− mice showed reduced infarct area (infarct area/area at risk: 18.7% vs. 28.6% at 48 h, p< 0.01) and scar formation (scar/LV area: 9.7% vs. 14.6% at 14 days, p< 0.01) after myocardial I/R. Echocardiography showed improved LV dysfunction (%FS: 35.2 vs. 28.4 at 7 days, p< 0.01; 34.0 vs. 25.7 at 14 days, p< 0.01) and dimensions (LVEDD [mm]: 3.88 vs. 4.21 at 7 days, p< 0.01; 3.99 vs. 4.43 at 14 days, p< 0.01) in the ASC −/− mice after myocardial I/R. Immunohistochemistry revealed that infiltration of macrophages (Mac3) and neutrophils (Gr-1) was markedly decreased in the injured myocardium of the ASC −/− mice (48 hr [/mm 2 ]: 1226 vs. 884, p< 0.01; 782 vs. 554, p< 0.01, respectively); however, there was no difference of neovascularization (CD31) in the ischemic area. Double immunofluorescent staining showed that ASC expression was clearly observed in the infiltrated macrophages and neutrophils in the injured myocardium. Real-time RT-PCR analysis demonstrated that the myocardial expression of inflammatory cytokines, such as IL-1β, IL-6, and MCP-1, after I/R were significantly decreased in the ASC −/− mice, compared to that in the WT mice. Further, in vitro experiments showed that LPS-induced production of these inflammatory cytokines in the ASC −/− bone marrow cells was significantly decreased. These findings demonstrate that ASC deficiency prevents inflammatory cell infiltration and cytokine expression, thereby resulting in the improvement of LV dysfunction and remodeling after myocardial I/R injury, and suggest that ASC is a novel therapeutic target for myocardial I/R injury.