ADH1C downregulation is a key hypoxia response in colon epithelium
Defining how normal epithelial cells adapt to microenvironmental perturbations may reveal molecular vulnerabilities obscured later in carcinogenesis. Although the colon is susceptible to hypoxic injury and hypoxia is common in colorectal cancer (CRC), the insight into how non-neoplastic colon epithelium responds to hypoxia is lacking. To discover these mechanisms, 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 downregulation of alcohol dehydrogenase 1C (ADH1C), previously associated with poor prognosis and metabolic reprogramming in CRC. In normal crypts, ADH1C transcripts localized to transit amplifying (TA) and progenitor epithelial cells, and colon epithelial ADH1C downregulation was validated in archival tissue from patients with acute ischemic colitis, a form of hypoxic injury. Hypoxia induced PHGDH (the first and rate-limiting step in the serine synthesis pathway, SSP) in colonoids in an ADH1C-dependent manner, and the SSP contributed to neutralization of hypoxia-induced reactive oxygen species (ROS) in colonoids. Hypoxia-induced ADH1C downregulation was also associated with reduced TA 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. Taken together, these results establish ADH1C as a mediator of colon epithelial hypoxia responses, metabolic reprogramming, and epithelial identity with relevance to human CRC. Overall design: RNA-seq for 4 differed colon epithelial organoid lines grown under either abient oxygen concentration or at 0.2% oxygene for one week. RNA-seq as paired end sequencing. RNA-seq for 3samples of ischemic colitis. Regions with ischemia compared to normal regions in the same patients.