The intestinal epithelium exhibits a rapid and efficient regenerative response to injury. Emerging evidence supports a model where plasticity of differentiated cells, particularly those in the secretory lineages, contributes to epithelial regeneration upon ablation of injury-sensitive stem cells. However, such facultative stem cell activity is rare within secretory populations. Here, we ask whether specific functional properties predict facultative stem cell activity. We utilize in vivo labeling combined with ex vivo organoid formation assays to evaluate how cell age and autophagic state contribute to facultative stem cell activity within secretory lineages. Strikingly, we find that cell age (time elapsed since cell cycle exit) does not correlate with secretory cell plasticity. Instead, high autophagic vesicle content predicts plasticity and resistance to DNA damaging injury independently of cell lineage. Our findings indicate that autophagic status prior to injury serves as a lineageagnostic marker for the prospective identification of facultative stem cells.

Calorie restriction can enhance the regenerative capacity of the injured intestinal epithelium. Among other metabolic changes, calorie restriction can activate the autophagy pathway. While independent studies have attributed the regenerative benefit of calorie restriction to downregulation of mTORC1, it is not known whether autophagy itself is required for the regenerative benefit of calorie restriction. We used mouse and organoid models with autophagy gene deletion to evaluate the contribution of autophagy to intestinal epithelial regeneration following calorie restriction. In the absence of injury, mice with intestinal epithelial-specific deletion of autophagy gene Atg7 (Atg7ΔIEC) exhibit weight loss and histological changes similar to wildtype mice following calorie restriction. Conversely, calorie restricted Atg7ΔIEC mice displayed a significant reduction in regenerative crypt foci following irradiation compared to calorie restricted wildtype mice. Targeted analyses of tissue metabolites in calorie restricted mice revealed an association between calorie restriction and reduced glycocholic acid (GCA) in wildtype but not Atg7ΔIEC mice. To evaluate whether GCA can directly modulate epithelial stem cell self-renewal, we performed enteroid formation assays with or without GCA. Wildtype enteroids exhibited reduced enteroid formation efficiency in response to GCA treatment, suggesting that reduced availability of GCA during calorie restriction may be one mechanism by which calorie restriction favors epithelial regeneration in a manner dependent upon epithelial autophagy. Taken together, our data support the premise that intestinal epithelial Atg7 is required for the regenerative benefit of calorie restriction, due in part to its role in modulating luminal GCA with direct effects on epithelial stem cell self-renewal.

The METTL3-METTL14 methyltransferase complex adds N6-methyladenosine (m6A) to mRNA with profound impacts on cell fate. Studies delete METTL3 or METTL14 interchangeably to define the role of m6A in target tissues despite a lack of data confirming that these deletions are equivalent. Intestinal epithelial METTL14 deletion triggers stem cell death in the colon with no overt phenotype in the small intestine. The effect of METTL3 deletion in the same tissues remains unknown. We report that intestinal epithelial METTL3 deletion caused unexpected severe defects in the small intestine, including crypt and villus atrophy associated with cellular senescence and death in the crypt transit amplifying zone. Ribosome profiling and m6A-sequencing demonstrated downregulated translation of hundreds of unique methylated transcripts, including genes essential to growth factor signal transduction, such as Kras. Our study suggests that METTL3 is essential for small intestinal homeostasis via enhanced translation of growth factor signaling in crypt transit amplifying cells.

SummaryThe intestinal epithelium exhibits a rapid and efficient regenerative response to injury. Emerging evidence supports a model where plasticity of differentiated cells, particularly those in the secretory lineages, contributes to epithelial regeneration upon ablation of injury-sensitive stem cells. However, such facultative stem cell activity is rare within secretory populations. Here we ask whether specific functional properties predict facultative stem cell activity. We utilize in vivo labeling combined with ex vivo organoid formation assays to evaluate how cell age and autophagic state contribute to facultative stem cell activity within secretory lineages. Strikingly, we find that cell age (time elapsed since cell cycle exit) does not correlate with secretory cell plasticity. Instead, high autophagic activity predicts plasticity and resistance to DNA damaging injury independently of cell lineage. Our findings indicate that autophagic status prior to injury serves as a lineageagnostic marker for the prospective identification of facultative stem cells.