A Comprehensive Review on Environmental and Microenvironmental Oxygen Sensing Pathways Mediated by Hypoxia-Inducible Factors (HIFs)

Oxygen deficiency, referred to as hypoxia, can be divided into two categories of environmental (exogenous) which is sensitized by respiratory cells, and microenvironmental (endogenous) responses by other cells in the body, like cancer cells. Cell responses to oxygen fluctuations are mediated by hypoxia-inducible factors (HIFs). Lung is known as the first organ that encounters the exogenous and environmental oxygen after breathing. However, data are limited for HIF respiratory pathways of environmental oxygen sensing inside the lung cells. Thus, we evaluated the role of both HIF-1 and HIF-2 isoforms in environmental hypoxia sensation by pulmonary vascular and bronchial cells. Then, we introduced the role of HIFs in microenvironmental and endogenous oxygen sensation in tissues and cells other than respiratory cells as well as all of involved molecular mechanisms in those non-lung cells and tissues. Next, a detailed emphasize was put on the strict role of HIF molecule in tumor cells and cancer stem cells.