Abstract 1175: Critical Role of Bone Marrow ASC (Apoptosis-associated Speck-like Protein Containing a CARD) in Neointimal Formation After Vascular Injury in Mice
Background: ASC is an adaptor protein that forms inflammasome complex and regulates caspase-1-dependent interleukin (IL)-1β and IL-18 generation; however, the role of ASC in the pathophysiology of cardiovascular diseases 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 (WT: C57BL/6) mice. Immunohistochemical analysis revealed that ASC was markedly expressed in the infiltrated macrophages in the neointima. Histological analysis revealed that neointimal formation was significantly reduced in ASC−/− mice as compared to that in the WT mice (I/M ratio, p = 0.007). IL-1β and IL-18 were clearly expressed in the neointimal lesion of the WT mice but showed decreased expression in the lesion of ASC−/− mice. However, TUNEL staining showed no significant difference in apoptotic cells of the media between these mice. Further, no significant differences were observed in early reendothelialization (CD31) and the number of macrophages (F4/80) and smooth muscle cells (SMCs: αSMA) per unit of the neointima. Flow cytometry analysis also showed no difference in the number of peripheral CD34+/Flk-1+ cells (EPCs) after injury. To determine the contribution of bone marrow cells, we developed 3 types of bone marrow transplantation (BMTWild+Wild, BMTWild+ASC−/−, and BMTASC−/− → Wild) mice. The neointimal formation in BMTASC−/−+Wild mice mice was remarkably reduced as compared to that in BMTWild+Wild (I/M ratio, p = 0.0003) and BMTWild+ASC−/− mice (p = 0.015), indicating that bone marrow ASC is critical for neointimal formation. In vitro experiments showed that the lipopolysaccharide-induced production of inflammatory cytokines such as IL-1β, IL-6, MCP-1, and IFN-γ, but not TNF-α, in ASC−/− bone marrow cells was significantly decreased. Further, serum-stimulated proliferation activity and MAP kinase (ERK1/2 and p38) activation of ASC−/− SMCs were not impaired.
Conclusions: These findings suggest that bone marrow-derived ASC is critical for the neointimal formation after vascular injury and identify ASC as a novel therapeutic target for cardiovascular diseases.