Critical Roles of Reactive Oxygen Species in Age-Related Impairment in Ischemia-Induced Neovascularization by Regulating Stem and Progenitor Cell Function

Figure 2

Schematic diagram of bone marrow microenvironment (Niche). Stem cells with self-renewal capacity reside in the hypoxic niche where the levels of reactive oxygen species (ROS) are low. Proliferation and differentiation of stem cells occur at the oxygenic niche where higher levels of ROS promote cell differentiation. During ischemia, hypoxic expansion upregulates transcription factor and hypoxia inducible factor-1α (HIF-1α), increasing the levels of vascular endothelial growth factor (VEGF) expression in the bone marrow. Meanwhile, there is an increase in NADPH oxidase- (Nox-) mediated ROS production. With aging, stem cells loss their self-renewal ability and displayed a skewed differentiation pattern (for details please see text).