Background Interleukin 18 (IL-18) is a novel mediator of angiogenesis in rheumatoid arthritis (RA).
Objective To examine the role of IL-18 in RA angiogenesis and the signalling mechanisms involved.
Methods Human dermal microvascular endothelial cell (HMVEC) chemotaxis, capillary morphogenesis assays and Matrigel plug angiogenesis assays were performed in vivo using IL-18 with or without signalling inhibitors. A novel model of angiogenesis was devised using dye-tagged HMVECs to study their homing into RA and normal (NL) synovial tissues (STs) engrafted in severe combined immunodeficient (SCID) mice.
Results IL-18-mediated angiogenesis depended on Src and Jnk, as the inhibitors of Src and Jnk blocked IL-18-induced HMVEC chemotaxis, tube formation and angiogenesis in Matrigel plugs. However, inhibitors of Janus kinase 2, p38, MEK, phosphatidylinositol-3-kinase and neutralising antibodies to vascular endothelial growth factor or stromal derived factor-1α did not alter IL-18-induced HMVEC migration. These results were confirmed with Jnk or Src sense or antisense oligodeoxynucleotides. Moreover, IL-18 induced phosphorylation of Src and Jnk in HMVECs. As proof of principle, IL-18 null mice had a significantly decreased angiogenesis compared with wild-type mice in Matrigel plug angiogenesis assays in vivo. IL-18 markedly enhanced mature HMVEC homing to human RA ST compared with NL ST in SCID mice, confirming the role of IL-18-induced angiogenesis in RA ST in vivo.
Conclusion Targeting IL-18 or its signalling intermediates may prove to be a potentially novel therapeutic strategy for angiogenesis-dependent diseases, such as RA.
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Funding This study was supported by funds from the Veterans' Administration Research Service (AEK) and the Frederick G L Huetwell and William D Robinson Professorship (AEK). Additional support included funds from National Institute of Health grants AI40987 (AEK), HL58695 (AEK), AR48267 (AEK), HL094017 (BJR) and AR052482 (MAA).
Competing interests None
Provenance and peer review Not commissioned; externally peer reviewed.