Interleukin-1β induces fibroblast growth factor 2 expression and subsequently promotes endothelial progenitor cell angiogenesis in chondrocytes

Arthritis is a process of chronic inflammation that results in joint damage. IL (interleukin)-1 beta is an inflammatory cytokine that acts as a key mediator of cartilage degradation, and is abundantly expressed in arthritis. Neovascularization is one of the pathological characteristics of arthritis. However, the role of IL-1 beta in the angiogenesis of chondrocytes remains unknown. In the present study, we demonstrate that stimulating chondrocytes (ATDC5) with IL-1 beta increased the expression of FGF (fibroblast growth factor)-2, a potent angiogenic inducer, and then promoted EPC (endothelial progenitor cell) tube formation and migration. In addition, FGF-2-neutralizing antibody abolished ATDC5-conditional medium-mediated angiogenesis in vitro, as well as its angiogenic effects in the CAM (chick chorioallantoic membrane) assay and Matrigel plug nude mice model in vivo. IHC (immunohistochemistry) staining from a CIA (collagen-induced arthritis) mouse model also demonstrates that arthritis increased the expression of IL-1 beta and FGF-2, as well as EPC homing in articular cartilage. Moreover, IL-1 beta-induced FGF-2 expression via IL-1RI (type-1 IL-1 receptor), ROS (reactive oxygen species) generation, AMPK (AMP-activated protein kinase), p38 and NF-kappa B (nuclear factor kappa B) pathway has been demonstrated. On the basis of these findings, we conclude that IL-1 beta promotes FGF-2 expression in chondrocytes through the ROS/AMPK/p38/NF-kappa B signalling pathway and subsequently increases EPC angiogenesis. Therefore IL-1 beta serves as a link between inflammation and angiogenesis during arthritis.