Angiogenesis in bone and osteogenesis appear to be closely linked, suggesting the existence of molecular crosstalk between pro-angiogenic molecules and osteoblasts. The pro-angiogenic molecules vascular endothelial growth factor (VEGF) with its receptors Flt-1, Flk-1 and fibroblast growth factor (FGF)-2 play a crucial role in born formation, an early and critical event in the pathogenesis of rheumatoid arthritis (RA). Interleukin (IL)-35 is demonstrated to be an anti-inflammatory cytokine in RA. However, the mechanisms involved are not fully understood. This study aims to investigate whether IL-35 has an impact on angiogenesis in osteoblasts and its related signalling pathway in RA.
The effects of IL-35 on osteoblasts proliferation, apoptosis and pro-angiogenic molecules mRNA and protein were examined using osteoblast-like MC3T3E1 cells in vitro. The effects of IL-35 on proliferation and apoptosis were examined using cell counting kit-8 (CCK-8) assay and flow cytometry, respectively. Pro-angiogenic molecules expression were assessed by real time PCR and ELISA, respectively. The signalling pathway between IL-35, bone formation, angiogenesis and signalling pathway was also investigated.
IL-35 promoted osteoblasts proliferation and inhibited apoptosis in a dose-dependent manner in vitro. IL-35 increased basal and TNF-α induced pro-angiogenic molecules expression by osteoblasts. Blocking the Th17/IL-17 signalling pathway with plumbagin inhibited the pro-angiogenic effects of IL-35 in osteoblasts.
These results suggested that IL-35 promotes bone formation and angiogenesis by fostering osteoblasts proliferation, inhibiting apoptosis and upregulating pro-angiogenic molecules through Th17/IL-17 related-signalling pathway. Our findings extend the current understanding of mechanisms modulating bone formation and angiogenesis in RA.