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Background and Aims The Cancer Genome Atlas (TCGA) project has identified HER2 mutations or amplification in 7% of colon cancers. In addition to HER2 mutations, colon cancer patients also possess co-occurring mutations in genes such as APC. Here, we investigated the role of HER2 and APC mutations on the crypt-villus architecture of the intestinal epithelium, localization of secretory cells, and expression of intestinal stem cell markers. Methods We generated a HER2 transgenic mouse (HER2V777L Tg) possessing an activating mutation commonly found in colorectal cancer patients, HER2V777L, using transcription activator-like effector nucleases–based gene editing technology. We expressed the HER2V777L transgene in mouse small intestine and colon using Lgr5-Cre and Villin-Cre recombinases. In addition, we analyzed Lgr5-Cre; APCmin; HER2V777L Tg mice by morphologic and gene expression assays on intestinal sections and organoids derived from the epithelium. Results HER2V777L expression resulted in hypertrophic crypt formation with expanded zones of proliferation. Proximal intestinal villi showed increased abundance of multiple differentiated lineages including extensive intermediate cell differentiation, as evidenced by MUC2/MMP7 co-immunofluorescence and transmission electron microscopy. HER2V777L expression in the context of APC loss resulted in further enhancement and expansion of the proliferative crypt compartment. Conclusions We established an epithelial intrinsic role for HER2V777L on enhanced cellular proliferation. Additionally, we determined that HER2 and APC mutations, when combined, promote enhanced proliferation of intestinal crypts., Graphical abstract Model of HER2 and APC mutations on the intestinal epithelium. HER2V777L expression conferred hypertrophic crypt formation characterized by increased intestinal stem cells and promoted intermediate cells formation along the villus. HER2V777L expression, in the context of APC loss, induced hyperproliferation of the crypt compartment.

Loss of differentiated cells to tissue damage is a hallmark of many diseases. In slow-turnover tissues, long-lived differentiated cells can re-enter the cell cycle or transdifferentiate to another cell type to promote repair. Here, we show that in a high-turnover tissue, severe damage to the differentiated compartment induces progenitors to transiently acquire a unique transcriptional and morphological postmitotic state. We highlight this in an acute villus injury model in the mouse intestine, where we identified a population of progenitor-derived cells that covered injured villi. These atrophy-induced villus epithelial cells (aVECs) were enriched for fetal markers but were differentiated and lineage committed. We further established a role for aVECs in maintaining barrier integrity through the activation of yes-associated protein (YAP). Notably, loss of YAP activity led to impaired villus regeneration. Thus, we define a key repair mechanism involving the activation of a fetal-like program during injury-induced differentiation, a process we term "adaptive differentiation."

The colonic epithelium can undergo multiple rounds of damage and repair, often in response to excessive inflammation. The responsive stem cell that mediates this process is unclear, in part because of a lack of in vitro models that recapitulate key epithelial changes that occur in vivo during damage and repair. Here, we identify a Hopx+ colitis-associated regenerative stem cell (CARSC) population that functionally contributes to mucosal repair in mouse models of colitis. Hopx+ CARSCs, enriched for fetal-like markers, transiently arose from hypertrophic crypts known to facilitate regeneration. Importantly, we established a long-term, self-organizing two-dimensional (2D) epithelial monolayer system to model the regenerative properties and responses of Hopx+ CARSCs. This system can reenact the “homeostasis-injury-regeneration” cycles of epithelial alterations that occur in vivo. Using this system, we found that hypoxia and endoplasmic reticulum stress, insults commonly present in inflammatory bowel diseases, mediated the cyclic switch of cellular status in this process.

Two biological activities of butyrate in the colon (suppression of proliferation of colonic epithelial stem cells and inflammation) correlate with inhibition of histone deacetylases. Cellular and biochemical studies of molecules similar in structure to butyrate, but different in molecular details (functional groups, chain-length, deuteration, oxidation level, fluorination, or degree of unsaturation) demonstrated that these activities were sensitive to molecular structure, and were compatible with the hypothesis that butyrate acts by binding to the Zn2+ in the catalytic site of histone deacetylases. Structure-activity relationships drawn from a set of 36 compounds offer a starting point for the design of new compounds targeting the inhibition of histone deacetylases. The observation that butyrate was more potent than other short-chain fatty acids is compatible with the hypothesis that crypts evolved (at least in part), to separate stem cells at the base of crypts from butyrate produced by commensal bacteria.