The small intestinal epithelium self-renews every four or five days. Intestinal stem cells (Lgr5 crypt base columnar cells (CBCs)) sustain this renewal and reside between terminally differentiated Paneth cells at the bottom of the intestinal crypt. Whereas the signalling requirements for maintaining stem cell function and crypt homeostasis have been well studied, little is known about how metabolism contributes to epithelial homeostasis. Here we show that freshly isolated Lgr5 CBCs and Paneth cells from the mouse small intestine display different metabolic programs. Compared to Paneth cells, Lgr5 CBCs display high mitochondrial activity. Inhibition of mitochondrial activity in Lgr5 CBCs or inhibition of glycolysis in Paneth cells strongly affects stem cell function, as indicated by impaired organoid formation. In addition, Paneth cells support stem cell function by providing lactate to sustain the enhanced mitochondrial oxidative phosphorylation in the Lgr5 CBCs. Mechanistically, we show that oxidative phosphorylation stimulates p38 MAPK activation by mitochondrial reactive oxygen species signalling, thereby establishing the mature crypt phenotype. Together, our results reveal a critical role for the metabolic identity of Lgr5 CBCs and Paneth cells in supporting optimal stem cell function, and we identify mitochondria and reactive oxygen species signalling as a driving force of cellular differentiation.

Differential signalling of the WNT and Notch pathways regulates proliferation and differentiation of Lgr5 + cryptbased columnar cells (CBCs) into all cell lineages of the intestine. We have recently shown that high mitochondrial activity in CBCs is key in maintaining stem cell function. Interestingly, while high mitochondrial activity drives CBCs, it is reduced in the adjacent secretory Paneth cells (PCs). This observation implies that during differentiation towards PCs, CBCs undergo a metabolic rewiring involving downregulation of mitochondrial number and activity, through a hitherto unknown mechanism. Here we demonstrate, using intestinal organoids that FoxO transcription factors and Notch signalling functionally interact in determining CBC cell fate. In agreement with the organoid data, combined Foxo1 and 3 deletion in mice increases PC number in the intestine. Importantly, we show that FOXO and Notch signalling converge onto regulation of mitochondrial fission, which in turn provokes stem cell differentiation into the secretory types; Goblet cells and PCs. Finally, mapping intestinal stem cell differentiation based on pseudotime computation of scRNA-seq data further supports the role of FOXO, Notch and mitochondria in determining secretory differentiation. This shows that mitochondria is not only a discriminatory hallmark of CBCs and PCs, but that its status actively determines lineage commitment during differentiation. Together, our work describes a new signalling-metabolic axis in stem cell differentiation and highlights the importance of mitochondria in determining cell fate.

FOXO transcription factors are regulators of cellular homeostasis and putative tumor suppressors, yet the role of FOXO in cancer progression remains to be determined. The data on FOXO function, particularly for epithelial cancers, are fragmentary and come from studies that focused on isolated aspects of cancer. To clarify the role of FOXO in epithelial cancer progression, we characterized the effects of inducible FOXO activation and loss in a mouse model of metastatic invasive lobular carcinoma. Strikingly, either activation or loss of FOXO function suppressed tumor growth and metastasis. We show that the multitude of cellular processes critically affected by FOXO function include proliferation, survival, redox homeostasis, and PI3K signaling, all of which must be carefully balanced for tumor cells to thrive. FOXO proteins are not solely tumor suppressors, but also support tumor growth and metastasis by regulating a multitude of cellular processes essential for tumorigenesis. .