Interleukin-6 promotes destabilized angiogenesis by modulating angiopoietin expression in rheumatoid arthritis
Kayakabe K et al. – IL–6 not only enhances VEGF expression but also inhibits angiopoietin (Ang)–1 signalling by directly down–regulating Ang–1 expression and up–regulating Ang–2, an antagonist of Ang–1. These synergistic effects may play a critical role in destabilized angiogenesis in RA.Methods
- Synovial fibroblasts derived from RA patients (RASFs) and human umbilical vein endothelial cells (HUVECs) were co–cultured for 6 days with or without recombinant IL–6, VEGF or Ang–1.
- HUVECs were stained with anti–CD31 antibody and their growth was determined by quantifying the CD31–positive area.
- SFs were collected from RA (n=25) and OA (n=7) patients.
- In the co–culture system, IL–6 and VEGF significantly enhanced HUVEC growth to a similar extent.
- However, the morphology of proliferating cells was distinct between IL–6– and VEGF–stimulated HUVEC.
- HUVEC stimulated with IL–6 exhibited small, loose clusters surrounded by dispersed single cells, suggesting destabilized angiogenesis by IL–6.
- In the supernatants, IL–6 up–regulated VEGF compared with controls and Ang–2, while it down–regulated Ang–1.
- In contrast, down–regulation of Ang–1 was not observed with VEGF stimulation.
- Consistent with the destabilized morphology, stimulation with IL–6 decreased cell surface expression of vascular endothelial cadherin (VE–cadherin) on HUVEC, presumably by inducing internalization.
- Interestingly, adding recombinant Ang–1 partially inhibited IL–6–induced morphological changes in HUVEC including a destabilized morphology with small, loose clusters and internalization of VE–cadherin.
- In SFs from RA patients, VEGF was negatively correlated with Ang–1 (r = –0.559, P = 0.004).