Finally, the presence of glucagon-producing cells in organoids following FOXO1 inhibition is also consistent with the generalized de-repression of a pancreatic progenitor-type cell. The approach described here could be used to efficiently generate large quantities of insulin-producing cells for transplantation. 1 diabetes treatment. Efforts to generate surrogate insulin-producing cells that could serve as a permanent cure of the disease have been underway for nearly two decades, and progress has been made toward the generation of pancreatic hormone-producing cells from either embryonic stem Philanthotoxin 74 dihydrochloride or induced pluripotent stem cells (iPS)1C3. However, cells thus generated are often polyhormonal, and they are characterized by an indifferent response to glucose, unless transplanted into mice, where they acquire undetermined factors required for their functional maturation2,4. Although terminally differentiated -cells are only present in the pancreas, endocrine progenitors with comparable features to pancreatic endocrine progenitors are also found in the intestine, the site of the bodys largest endocrine system5. The enteroendocrine Philanthotoxin 74 dihydrochloride system is comprised of many different cell types, some of which are shared in common with the endocrine pancreas (e.g., somatostatin- and ghrelin-producing cells), and some of which are organ-specific5. We have shown in previous work that genetic inactivation of Foxo1a in mice results in the expansion of the enteroendocrine Neurogenin3 (Neurog3)-positive progenitor cell pool, and the appearance of functional insulin-producing cells that express all markers of mature pancreatic -cells, secrete insulin in response to physiologic and pharmacologic cues, and can readily regenerate to alleviate diabetes caused by the -cell toxin streptozotocin6. These data did not arise in a vacuum; rather, they are a part of a burgeoning body of evidence indicating that enteric and pancreatic endocrine cells can convert into different subtypes7, possibly through a Philanthotoxin 74 dihydrochloride dedifferentiation process8C10. In contrast to the mouse, little is known about the effect of FOXO1 on endocrine differentiation in human gut, especially whether FOXO1 loss-of-function can alter the fate of enteroendocrine cells toward the insulin-producing lineage11. The present study was undertaken to assess the human relevance of the observation that deleting Foxo1 can promote the insulin-producing fate in experimental animals6, as a necessary preliminary step toward the therapeutic application of these observations to diabetic patients. We report here that FOXO1 expression defines endocrine progenitor and serotonin-positive cells in the human gut. Using gut organoid differentiation12 of human iPS cells, we show that FOXO1 inhibition in FOXO1-expressing cells results in their conversion into insulin-positive cells that express markers of mature pancreatic -cells. Further, we show that these cells secrete C-peptide in response to Philanthotoxin 74 dihydrochloride glucose, arginine, and KCl. These data provide the required proof of principle to attempt to engineer insulin-producing cells from human gut organoid cultures, or to pursue direct FOXO1 inhibition in the human gut as approaches to type 1 diabetes treatment. Results Survey of FOXO1 localization in human gut We used fluorescence immunohistochemistry MAPKK1 to survey FOXO1 localization in the human gut (Fig. 1). FOXO1-expressing cells were most abundant near the bottom of crypts; 60% of Philanthotoxin 74 dihydrochloride FOXO1-positive cells were located between positions 0 to +9 relative to the crypt bottom in duodenum and colon, with lower frequencies at positions more distal than +10, and in jejunum and ileum (Fig. 2aCd). mRNA levels correlated with the abundance of FOXO1-immunoreactive cells (Fig. 2e). Intestinal lineage marker analysis indicated that FOXO1 expression was virtually restricted to CHROMOGRANIN A (CGA)-positive endocrine cells (Fig. 1aCd). 95.3 1.8 % of FOXO1-positive cells were CGA-positive, whereas 61.8 3.8% of CGA-positive cells had immunoreactivity with FOXO1 in three human duodenal specimens. FOXO1-positive crypt cells were OLFACTOMEDIN4 (OLFM4)-unfavorable (Fig. 1e), indicating that they are unlikely to be intestinal stem cells13. They were, however, immunoreactive with EPHB3, a pro-endocrine marker in pancreas14 that localizes to columnar cells at the crypt base and Paneth cells (Fig. 1c)15. These findings are consistent with FOXO1-positive crypt cells being endocrine progenitors. But attempts to characterize these cells with NEUROG3 antibodiesCa marker of pancreatic16,17 and intestinal18 endocrine progenitorsCfailed. We found that >80% of FOXO1-positive cells in villi were immunoreactive with serotonin antibodies and 85 11% of serotonin (5HT)-positive cells were FOXO1-positive (Fig. 1h). Interestingly, pancreatic -cells also make serotonin19. In addition, FOXO1-immunoreactive cells showed reactivity with prohormone convertases (PC) 1/3 and 2 (Ref.20,21), as.