Figure 1.

Pluripotent stem cells (PSC) in the bone marrow give rise to haemangioblasts (HA), with the potential to differentiate into either haematopoietic stem cells (HSC) or endothelial cell precursors (EPC; green). Mobilisation of EPC from the bone marrow is upregulated by many factors, including vascular endothelial growth factor (VEGF), erythropoietin, angiopoietin-1, and colony-stimulating factors such as granulocyte-macrophage colony-stimulating factor (GM-CSF). In rheumatoid arthritis (RA), these cells appear to traffic to RA synovium at an enhanced rate, incorporating into blood vessels and giving rise to increased vascularity – thereby reducing the potential for revascularisation of ischaemic areas. Angiogenesis in the synovium is also VEGF dependent. As a consequence, circulating EPC numbers are reduced in RA and may lead to increased cardiovascular mortality.