The Role of Syk in Inflammatory Response of Human Abdominal Aortic Aneurysm Tissue

Objective: Inflammatory response is central to pathogenesis of abdominal aortic aneurysm (AAA). Recently, we reported that Syk, a signaling molecule in inflammatory cells, promotes AAA development in a mouse model. In this study, we aimed to investigate the role of Syk in human AAA pathogenesis. Materials and Methods: We obtained human AAA wall samples during open surgical aortic repair at Kurume University Hospital. Immunohistochemical analyses of AAA samples were performed for Syk activation and cell type markers. Ex vivo culture of human AAA tissue was utilized to evaluate the effect of P505-15, a Syk inhibitor, on secretions of interleukin-6 (IL-6) and matrix metalloproteinases (MMPs). Results: Immunohistochemical analysis showed infiltration of B cells, T cells, and macrophages in AAA samples. Syk activation was localized mainly in B cells and part of macrophages. AAA tissue in culture secreted IL-6, MMP-9, and MMP-2 without any stimulation. The unstimulated secretions of IL-6, MMP-9, and MMP-2 were insensitive to P505-15. Secretions of IL-6 and MMP-9 were enhanced by exogenous normal human immunoglobulin G (IgG), which was suppressed by P505-15, whereas secretion of MMP-2 was insensitive to IgG or P505-15. Conclusion: These results demonstrate an important role of Syk for IgG-dependent inflammatory response in human AAA.