Mechanisms of Oxygen Sensing and Hypoxic Increase in Replicative Lifespan

Public Deposited

The response to reduced levels of oxygen (hypoxia) is essential for embryonic development by promoting the proper formation of vascular networks. Conversely, hypoxia also promotes the development of pathophysiological processes such as pulmonary hypertension and cancer. The main mediator of responses to hypoxia within the cell is the transcription factor hypoxia-inducible factor (HIF). Defining the mechanism(s) that regulate HIF activation, and understanding the consequences of activating HIF, are essential to understand how hypoxia mediates proper development, as well as the promotion of pulmonary hypertension and cancer. Mitochondrial electron transport is required for cellular oxygen sensing. However, it is unknown which mitochondrial function, respiration or the generation of reactive oxygen species (ROS), necessary for mitochondrial oxygen sensing. This thesis demonstrates that cells deficient in the mitochondrial complex III subunit cytochrome b, which are respiratory incompetent, increase ROS and activate HIF. RNAi of the complex III subunit Rieske iron sulfur protein in the cytochrome b null cells abolished ROS generation at the Qo site of complex III and hypoxic activation of HIF. Treatment with antioxidants maintained hydroxylation of HIF-1α protein thereby preventing its activation during hypoxia. These results provide genetic evidence that the Qo site of complex III is required for oxygen sensing by releasing ROS that inhibit HIF-1α hydroxylation, thereby stabilizing and activating the HIF-1α protein. Physiological hypoxia extends the replicative lifespan of human cells in culture. Increased replicative lifespan contributes to the progression of cancer and it may influence the development of pulmonary hypertension. The hypoxic extension of replicative lifespan is ablated by a dominant negative HIF. HIF is sufficient to induce telomerase reverse transcriptase mRNA, telomerase activity, and extend replicative lifespan. Furthermore, the down-regulation of the von-Hippel Lindau (pVHL) tumor suppressor protein by RNA interference increases HIF and extends replicative lifespan under normoxia. These findings provide genetic evidence that hypoxia utilizes mitochondrial ROS as signaling molecules to activate HIF dependent extension of replicative lifespan, further linking HIF activation to diseases associated with increased replicative lifespan. Furthermore, they provide the first association of an increase in ROS with an increase in replicative lifespan

Last modified
  • 08/01/2018
Date created
Resource type
Rights statement