Abstract 5053: Deficiency of ASC (Apoptosis-associated Speck-like Protein Containing a Caspase Recruitment Domain) in Bone Marrow Cells Improved Myocardial Ischemia-Reperfusion Injury in Mice
Background: Inflammatory responses play a key role in the pathophysiology of myocardial ischemia-reperfusion (I/R) injury. ASC 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 to be determined.
Methods and Results: ASC deficient (ASC−/−) and wild-type (WT) mice were subjected to 30 min LAD occlusion, followed by reperfusion. ASC−/− mice showed improved LV dysfunction (%FS: 34.0% vs. 25.7% at 14 days p<0.01), reduced infarct area/area at risk (IA/AAR: 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. Immunostaining revealed decreased infiltration of macrophages (Mac3) and neutrophils (Gr-1), but not neovascularization (CD31), in the injured myocardium of the ASC−/− mice. Real-time RT-PCR and ELISA analyses demonstrated that the myocardial mRNA and protein expression of inflammatory cytokines, such as IL-1β, IL-6, and MCP-1, after I/R were significantly decreased in the ASC−/− mice. Further, improved myocardial I/R injury was also observed in the caspase-1−/− mice, compared with WT mice (IA/AAR: 20.2% vs. 28.6% at 48 h, p<0.05). Since double immunostaining revealed that ASC was expressed in the infiltrated macrophages and neutrophils, bone marrow-transplanted (BMT) mice were prepared. The IA/AAR was significantly decreased in the BMTASC−/−→WT mice, compared with BMTWT→WT (IA/AAR: 17.8% vs. 27.9% at 48 h, p<0.01). Further, in vitro experiments showed that LPS-induced production of inflammatory cytokines such as IL-1β, IL-6, and MCP-1 in the ASC−/− -bone marrow cells was significantly decreased compared, with that in the WT-bone marrow cells.
Conclusion: ASC deficiency improved myocardial I/R injury via inflammatory cell infiltration and cytokine expression. These results suggest that ASC is a novel therapeutic target for myocardial I/R injury.