Reprogrammed Stomach Tissue as a Renewable Source of Functional β Cells for Blood Glucose Regulation

Abstract

The gastrointestinal (GI) epithelium is a highly regenerative tissue with the potential to provide a renewable source of insulin(+) cells after undergoing cellular reprogramming. Here, we show that cells of the antral stomach have a previously unappreciated propensity for conversion into functional insulin-secreting cells. Native antral endocrine cells share a surprising degree of transcriptional similarity with pancreatic β cells, and expression of β cell reprogramming factors in vivo converts antral cells efficiently into insulin(+) cells with close molecular and functional similarity to β cells. Induced GI insulin(+) cells can suppress hyperglycemia in a diabetic mouse model for at least 6 months and regenerate rapidly after ablation. Reprogramming of antral stomach cells assembled into bioengineered mini-organs in vitro yielded transplantable units that also suppressed hyperglycemia in diabetic mice, highlighting the potential for development of engineered stomach tissues as a renewable source of functional β cells for glycemic control.

Figure 1. NPM Factors Efficiently Reprogram Gastrointestinal Endocrine Cells to Insulin⁺ Cells with the Highest Induction Efficiency in Antral Stomach

(A) Diagram of the triple-cross transgenic mouse line, referred to as NRT (Ngn3-Cre; Rosa-floxed-rtTA; Teto-NMPcherry). Ngn3-cre is used to target inducible expression of the NPM factors (Ngn3, Pdx1, and Mafa) into the enteroendocrine cells of the antral stomach and the intestine. Black bars in Teto-NPMcherry indicate 2A peptides used to mediate polycistronic expression. (B–G) Doxycycline treatment of NRT animals yielded many insulin⁺cherry⁺ cells from the antral stomach (B), the duodenum (C), and the colon (D), among other GI regions. Quantitation showed a higher induction efficiency of insulin⁺ cells in antrum compared with duodenum (du), ileum (IL), and colon (Co) (E, n = 3 animals, p = 0.0026). Antrum tissue also has higher insulin content (F, n = 3 animals, p = 0.0046). Using FACS-purified cherry⁺ cells, the expression level of transgenes in the endocrine population was found to be comparable (G), n = 3 animals). Scale bar, 100 μm. Yellow arrows indicate insulin⁺cherry⁺ cells; white arrowheads indicate insulin⁻cherry⁺ cells. See also Figure S1.

Figure 2. Induced Insulin⁺ Cells from the GI Tract Can Reverse Hyperglycemia Long-Term and Regenerate Rapidly

(A) Glucose monitoring of hyperglycemic NRT animals over 6 months. Streptozotocin (STZ) was used to ablate endogenous pancreatic β cells and create hyperglycemia. Doxycycline (Dox) was administered continuously from week 1 onward (red line). Compared with persistent hyperglycemia and death of control animals (–Dox group, black squares), Dox treatment led to long-term suppression of hyperglycemia (+Dox group, red circles). A second round of STZ ablation was conducted at week 10 to evaluate the regenerative capacity of this experimental system. The ensuing hyperglycemia was suppressed again by week 13. Pancreatectomy was performed on week 19 to remove ~80% of the pancreas. No significant effect on blood glucose levels was observed. (B–D) Dox treatment and induction of insulin⁺ cells led to significant improvement in the survival of hyperglycemic NRT animals (B, n = 12 animals in each group). Glucose tolerance tests showed near-normal responses for Dox-treated animals (C, n = 4 animals in each group). The blood insulin levels of the induced animals are comparable with that of wild-type animals and significantly higher than non-induced animals (D, n = 4 animals in each group, p < 0.001). (E) Immunohistochemistry showed before and after induction of insulin⁺ cells (first and second panel, respectively). STZ treatment was used at week 11 to ablate the induced insulin⁺ cells from the GI tract (third panel). Insulin⁺ cells were regenerated rapidly 3 weeks later (last panel). Ki67 staining labels the proliferating stem/progenitor cell compartment at the base of the glands. Scale bar, 100 μm. All quantitative data presented as mean ± SD. Statistical significance was evaluated with the Student’s t test (***p < 0.001). See also Figures S2 and S3.

Figure 3. Induced Insulin⁺ Cells from the Antral Stomach More Closely Resemble β Cells Molecularly and Functionally

(A) Immunohistochemistry showed that induced insulin⁺ cells from the antrum express β cell genes Nkx6.1, Nkx2.2, and Prohormone convertase 2 (PC2), which are largely absent from duodenum and colon insulin⁺ cells. In contrast, Prohormone convertase 1/3 (PC1/3), glucose transporter 2 (Glut2), and c-peptide (c-ppt) are expressed commonly in antral, duodenal, and colonic insulin⁺ cells. Arrows indicate antral insulin⁺ that are PC2⁺, Nkx2.2⁺, and Nkx6.1⁺. Scale bar, 50 μm. (B) Glucose stimulated insulin secretion (GSIS) in vitro. Antral tissues have significantly higher glucose responsiveness, defined as fold increase of insulin release at high versus low glucose conditions, compared with duodenal and colonic tissues (n = 8, p < 0.001). (C and D) The antidiabetic drug Glibenclamide (Glib) stimulated insulin release from the antral insulin⁺ cells whereas Diazoxide (Dzx), a suppressor of insulin release, reduced antral insulin secretion (C, n = 4). In contrast, duodenal and colonic insulin⁺ cells do not respond to Glib or Dzx (C). Antral insulin⁺ cells also respond to Exendin-4 (Ex4) with enhanced insulin secretion at high glucose levels whereas duodenal and colonic cells do not respond to Exendin (D, n = 4). All quantitative data presented as mean ± SD. Statistical significance was evaluated with the Student’s t test (*p < 0.05, **p < 0.01, and ***p < 0.001). See also Figure S4.

Figure 4. Enteroendocrine Cells of the Antral Stomach Share Substantial Transcriptional Similarity with Pancreatic β Cells

(A) Immunohistochemistry showing distribution of GFP⁺ in the GI tract of the Ngn3-GFP mouse line. The GFP⁺ cells include both relatively immature (GFP⁺Chromogranin⁻) and more mature enteroendocrine cells (GFP⁺Chromogranin⁺). Scale bar, 50 μm. (B and C) Ngn3-GFP⁺ cells were purified by FACS from antrum, duodenum, and colon (B). Scatterplots of transcriptome comparisons between pancreatic β cells and the GI enteroendocrine populations (C). Antral enteroendocrine cells show a greater similarity with β cells. (D and E) Analysis of 2,398 β cell-enriched genes showed a general trend of elevated expression in antral enteroendocrine cells compared with duodenal and colonic enteroendocrine cells (D). In particular, antral enteroendocrine cells share a group of genes (group 2) with β cells (D) that are enriched for factors important in β cell development and function (E). Quantitative data presented as mean ± SD. Statistical significance was evaluated with the Student’s t test (*p < 0.05, **p < 0.01, and ***p < 0.001). (F) Immunohistochemistry showed that Nkx6.1 is present in a population of Chga⁺ enteroendocrine cells in the antrum, but not expressed in duodenum or colon (top, arrows). Nkx2.2 is expressed in a majority of Chga⁺ enteroendocrine cells in the antrum and a minority of Chga⁺ cells in the duodenum and colon (F, bottom, arrows). Scale bar, 50 μm. See also Figure S5.

Figure 5. The Intestine-Specific Cell Fate Regulator Cdx2 Can Inhibit β Cell Conversion

(A) Duodenal and colonic insulin⁺ cells express Cdx2, the master regulator of intestine cell fate whereas antral stomach cells do not express Cdx2 before or after induction in NRT animals. Scale bar, 50 μm. (B–D) Epithelial organoids were established from antral tissues of double-transgenic Rosa-rtTA;Teto-NPMcherry (Rosa-NPM) animals and infected with either control adenovirus expressing Cherry (pAd-cherry) or adenovirus expressing Cdx2 and Cherry (pAd-Cdx2.cherry) (B and C). Dox treatment was subsequently used to induce β cell conversion in these antral organoids. qPCR analysis showed that ectopic Cdx2 suppressed the expression of multiple β cell genes (D, n = 3). Scale bar, 100 μm. (E–G) Duodenal organoids were established from Cdx2^fl/+ and Cdx2^fl/fl animals (E, left and right, respectively). Infection with an adenovirus co-expressing both NPM factors and the Cre recombinase led to simultaneous deletion of floxed Cdx2 allele and expression of NPM factors (E). Complete removal of Cdx2 was observed in majority of Cdx2^fl/fl duodenal cells by immunohistochemistry and qPCR analysis (E and F) and led to enhanced expression of multiple β cell genes from the duodenal organoids (G, n = 3). Scale bar, 100 μm. Quantitative data presented as mean ± SD. Statistical significance was evaluated with the Student’s t test (*p < 0.05, **p < 0.01, and ***p < 0.001). See also Figure S6.

Figure 6. Construction of Bioengineered Stomach and Intestine Mini-organs to Produce Insulin⁺ Cells

(A–K) Schematic diagram of engineering stomach and intestine mini-organs (A). Gastric or intestinal units were isolated from the antrum or duodenum of CAG-NPM (Cag-rtTA∷TetO-NPMcherry) animals (B and I) and loaded onto polyglycolic acid scaffolds (C and J). The scaffolds were placed inside the omental flap of recipient immune-deficient NSG animals. 4 weeks later, an engineered stomach (E. St) or intestine (E. Int) sphere formed (D and K, circled tissue). Scale bars represent 400 μm (B and I) and 6 μm (C and J). (E–R) In engineered stomach and intestine spheres where reconstitution of epithelium was successful, Dox treatment led to induction of many insulin⁺ cells (E and L). The induction efficiency is higher for stomach tissues (P, n = 3). Stomach tissues also have higher insulin content (Q, n = 3). The majority of insulin⁺ cells from engineered stomach express Nkx6.1, PC1/3, and Glut2 (F, G, H, and R) whereas insulin⁺ cells from engineered intestine lack Nkx6.1 and have reduced PC1/3 expression (M, N, O, and R). Quantitation presented as mean ± SD. Statistical significance was evaluated with the Student’s t test (**p < 0.01 and ***p < 0.001). See also Figure S7.

Figure 7. Transplanted Stomach Mini-organs Can Reverse Hyperglycemia in Diabetic Mice

(A) Diagram of the experimental design. STZ treatment was used to ablate endogenous β cells in NSG animals transplanted with 4-week-old stomach spheres, followed by continuous Dox treatment of induce insulin⁺ cells. At the end of the experiment, the engineered stomachs were removed surgically. (B–D) STZ treatment led to rapid hyperglycemia that persists in the absence of treatment (−Dox group, n = 6, black squares) (B). After Dox treatment, a group of five animals showed prolonged suppression of hyperglycemia (G1 animals, n = 5, red squares), whereas another group of animals remained hyperglycemic (G2 animals, n = 17, blue squares) (B). After 6 weeks, the engineered stomach spheres were removed from the G1 animals, which led to their reversal back to hyperglycemia (B). G1 animals showed improved response in glucose tolerance test (C, n = 4) and substantially higher blood insulin levels (D, n = 4) compared with G2 animals or control STZ-treated animals without Dox induction. Wilde-type control animals in (C) (green squares) are non-STZ-treated animals with intact pancreatic β cell mass. Quantitative data presented as mean ± SEM. Statistical significance was evaluated with the Student’s t test (***p < 0.001). (E–G) Sox9⁺ and Ki67⁺ cells are present in the engineered stomach after 4-week Dox treatment (E and F), indicating persistence of stem/progenitor cells. PEcam⁺ blood vessels are closely associated with insulin⁺ cells inside the engineered stomach sphere (G). Scale bars, 100 μm. Blue channel, DAPI. See also Figure S7.