SUN-646 A Novel Population of FOXO1-Expressing Cells in the Stomach Controls Cell Plasticity by Regulating the Cyclin CCNE1

Abstract

A promising new therapy for type 1 diabetes is the reprogramming of gut enteroendocrine cells into cells that produce insulin. The mechanism by which gut epithelial cells are converted into cells that make insulin remains unknown. We have previously found that elimination of Foxo1 in neurogenin3 (Ngn3)-expressing cells of the intestine generates glucose-sensing, insulin-producing cells that are capable of reversing streptozotocin-induced diabetes. Others have reported that stomach cells have a similar property when made to express β-cell factors Ngn3, Pdx1, and MafA. Using mice bearing a Foxo1-GFP knock-in allele, we traced Foxo1-expressing cells in the gut to subpopulations of Ngn3+, as well as acid-secreting parietal stomach cells. To study these cells, we established a 2D co-culture method in which primary stomach cells are isolated from mice and cultured with embryonic fibroblasts. Deletion of Foxo1 in this system generated cells immunoreactive for insulin and C-peptide. Interestingly, Foxo1 ablation also altered the abundance of other gastric cell populations, including more parietal cells and decreased expression of stem cell marker, Lgr5. Tissue-specific elimination of Foxo1 in vivo in either Ngn3+ or parietal cells also resulted in the appearance of insulin+ cells, increased parietal cells, and reduced Lgr5 mRNA. To determine how Foxo1 regulated these changes, we used cells isolated from reporter mice that change from red to green after genetic recombination to collect Foxo1-deleted primary stomach cells using FACS. While the mRNA levels of many known Foxo1 targets did not change, cyclin E1 (CCNE1), which regulates G1 to S-phase progression of the cell cycle, was significantly decreased. Conversely, primary stomach cells overexpressing Foxo1 had increased levels of CCNE1. Finally, using ChIP-seq, we found that Foxo1 binds directly to the CCNE promoter in a nutrient-dependent manner. In summary, we show that Foxo1 is expressed in a subpopulation of stomach parietal cells and that it regulates their function through the cell cycle regulator, CCNE1.