Abstract 1008: Inflammatory Cytokines Mobilize Bone Marrow Cells to Vascular Wall, Resulting in Neointimal Formation through Their Inflammatory Effects
Background: Recent studies suggest that bone marrow cells contribute to neointimal formation after vascular injury. In many factors to relate with bone marrow cell mobilization, local inflammation induced by cytokines is possible to derive bone marrow cells to vascular wall, resulting thickened neointima. However, the relationship between the inflammatory reactions and bone marrow cell invasion has not been clarified. Here we performed vascular injury model using TNF-alpha or IL-6, which are inflammatory cytokine, knockout mice (KO) to investigate the involvement of inflammation on bone marrow cells mobilization in the process of neointimal formation.
Method and Results: We insert a large wire (0.38 mm in a diameter) into the femoral arteries of 6 – 8 week-old male balb/c (WT) and TNF-alpha or IL-6 KO mice. Animals were sacrificed at 1 and 4 weeks, and immunohiistochemistry using alpha-smooth muscle actin, macrophage, myeloperoxidase and hematopoietic stem cell marker (CD45, 34) antibodies was performed. TUNEL staining was performed to detect apoptotic cells. Morphometric analysis for intima/media ratio and semiquantification of macrophage and myeloperoxidase were also examined. In morphometric analysis at 4 weeks after the injury, intima/media ratio was significantly smaller in KO (TNF-alpha 1.52±0.15, IL-6 1.89±0.26) than in WT (2.99±0.24, p<0.05, respectively). The number of inflammatory cells such as neutrophils, macrophages and apoptotic cells in neointima were much less in both KO than in WT. In imunohistochmistry using CD34 at 1 week, positive cells possibly containing bone marrow derived cells, were hardly observed in both KO, but some were observed in WT in neointima and a part of them were positive for alpha-smooth muscle actin. At 4 weeks. CD34 positive cells were not observed in both groups. Furthermore, re-endothelialization appeared earlier in both KO than in WT. Moreover, in IL-6 KO, Stat-3 signal was markedly inhibited.
Conclusion: Mobilization of CD34 positive cells was less observed under less inflammatory circumstances induced by TNF-alpha or IL-6 KO mice. Inflammatory cytokines involved in neointimal formation after vascular injury, possible through their inflammatory effects to induce bone marrow cells.