Figure 1.

Effect of Oxygen Levels on Angiogenesis after Fracture. After bone fracture, lactate, produced by aerobic metabolism, stabilizes HIF1α and leads to up-regulation of VEGF. In hypoxic conditions endothelial cells (ECs, round circles) respond to VEGF, proliferate and form tubes. However, collagen (red bars) does not assemble and the vascular sprouts disintegrate. In the presence of oxygen, the collagen forms cross-links and the basement membrane stabilizes the newly formed angiogenic sprouts and angiogenesis proceeds (red lines). In hyperoxic conditions this process is amplified and angiogenesis is more robust.