We have suggested that hypoxia-inducible factor 2α (HIF-2α), a paralog of HIF-1 and HIF-3α, is a key factor in IPF development by inhibiting lung repair or regeneration [54,55,56]; this is evidenced by its elevated expression in pulmonary fibroblasts from IPF patients, in contrast to its absence in the epithelial cell epithelium [45]. The gene discussed is EPAS1; the disease is idiopathic pulmonary fibrosis.