Notably, HIF-1α and HIF-2α can oppose each other during intestinal inflammation: for example, epithelial cell HIF-1α helps maintain intestinal barrier functions during colitis (4, 40, 41), whereas HIF-2α worsens colitis by promoting tumor necrosis factor alpha (TNFα) production in epithelial cells (12). The gene discussed is TNF; the disease is colitis.