Keap1-Nrf2 signaling pathway in angiogenesis and vascular diseases.

The transcription factor, nuclear factor E2-related factor 2 (Nrf2), is highly sensitive to oxidative burst products, including reactive oxygen species (ROS) and reactive nitrogen species. In the cell nucleus, Nrf2 activates various antioxidant genes by binding to the antioxidant response elements. As an adapter for cullin 3/ring-box 1, kelch-like ECH-associated protein 1 (Keap1) ubiquitinates and degrades Nrf2 under physiological conditions. Conversely, with the aggravation of oxidative stress, Keap1-Nrf2 interaction could be much more easily dissociated. ROS play a key role in regulating the redox signaling pathway and affect the vasculature in a dose-dependent manner. Long-term production or high concentration of ROS are harmful to the vascular system, while moderate ROS can promote angiogenesis and tissue regeneration. Furthermore, appropriate regulation of oxidative stress mediated via the Keap1-Nrf2 pathway would be beneficial in various diseases associated with abnormal angiogenesis, including diabetes and cancers. Nrf2 deficiency has also been shown to result in significantly impaired survival, proliferation, and angiogenic capacity of endothelial cells in a hind limb ischemia model. Thus, this review will briefly summarize the underlying molecular mechanisms of Keap1-Nrf2 pathway in regulating oxidative stress and also help elucidate the critical role of Keap1-Nrf2 in angiogenesis under physiological and pathological conditions.