ADH1C Down-Regulation Is a Key Hypoxia Response in Colon Epithelium

Insights into how normal epithelial cells adapt to microenvironmental perturbations may reveal molecular vulnerabilities that become obscured later in carcinogenesis, and hypoxia is common in colorectal cancer (CRC). Although colon mucosa exists in a state of physiological hypoxia and is susceptible to ischemic injury, normal colon epithelial adaptive responses to changes in oxygenation are largely uncharacterized. In this study, human colon organoids (colonoids) were subjected to sustained hypoxia in vitro with characterization of consequent phenotypes and transcriptional changes. Hypoxia tolerance in human colonoids resulted in robust down-regulation of alcohol dehydrogenase 1C (ADH1C), which was also validated in archival tissue from patients with ischemic colitis. ADH1C transcripts revealed a nonuniform expression pattern in normal colon epithelium, with enrichment in transit-amplifying and progenitor epithelial cells. Ectopic expression of ADH1C in colonoids subjected to hypoxia increased reactive oxygen species and reduced NADPH compared with those in normoxia, suggesting that hypoxia-induced ADH1C down-regulation facilitates neutralization of reactive oxygen species. Hypoxia-induced ADH1C down-regulation also showed reduced transit-amplifying cell signatures and increased expression of regeneration-associated stem cell marker FGFBP1. Finally, ADH1C-low CRC showed significant enrichment for hypoxia-associated colon epithelial signatures compared with ADH1C-high CRC. Taken together, these results establish ADH1C as a mediator of colon epithelial hypoxia responses and epithelial identity with relevance to human CRC.