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Glucagon-like peptide 1 (GLP-1) can increase pancreatic β-cells, and α-cells could be a source for new β-cell generation. We investigated whether GLP-1 increases β-cells through α-cell transdifferentiation. New β-cells originating from non-β-cells were significantly increased in recombinant adenovirus expressing GLP-1 (rAd-GLP-1)-treated RIP-CreER;R26-YFP mice. Proliferating α-cells were increased in islets of rAd-GLP-1-treated mice and αTC1 clone 9 (αTC1-9) cells treated with exendin-4, a GLP-1 receptor agonist. Insulin+glucagon+ cells were significantly increased by rAd-GLP-1 or exendin-4 treatment in vivo and in vitro. Lineage tracing to label the glucagon-producing α-cells showed a higher proportion of regenerated β-cells from α-cells in rAd-GLP-1-treated Glucagon-rtTA;Tet-O-Cre;R26-YFP mice than rAd producing β-galactosidase-treated mice. In addition, exendin-4 increased the expression and secretion of fibroblast growth factor 21 (FGF21) in αTC1-9 cells and β-cell-ablated islets. FGF21 treatment of β-cell-ablated islets increased the expression of pancreatic and duodenal homeobox-1 and neurogenin-3 and significantly increased insulin+glucagon+ cells. Generation of insulin+glucagon+ cells by exendin-4 was significantly reduced in islets transfected with FGF21 small interfering RNA or islets of FGF21 knockout mice. Generation of insulin+ cells by rAd-GLP-1 treatment was significantly reduced in FGF21 knockout mice compared with wild-type mice. We suggest that GLP-1 has an important role in α-cell transdifferentiation to generate new β-cells, which might be mediated, in part, by FGF21 induction. [ABSTRACT FROM AUTHOR]

GAD is a pancreatic β-cell autoantigen in humans and nonobese diabetic (NOD) mice. Modulation of GAD expression in pancreatic β-cells has been suggested to be associated with the development of autoimmune diabetes. Hormonal changes through environmental stimuli are considered to influence the expression of the disease. We determined whether steroid hormones would modulate the expression of GAD in pancreatic β-cells. We treated NOD mouse β-cells (MIN6N8a cells) with various steroids, including testosterone, estradiol, progesterone, and cortisol, and examined the expression of GAD67 mRNA. We found that only cortisol enhanced the expression of GAD67, whereas the other steroid hormones had no effect. When we treated MIN6N8a cells with a synthetic glucocorticoid, dexamethasone, we found that GAD67 mRNA expression was stimulated in a dose- and time-dependent manner. Cells treated with 100 nmol/l dexamethasone for 6 h showed a 10-fold increase in the expression of GAD67 mRNA and an increase in GAD67 protein. The upregulation of GAD67 expression in β-cells by dexamethasone was found to be due to the transcriptional activation of the GAD67 promoter. We then examined whether dexamethasone would influence the development of diabetes in NOD mice. Injection of dexamethasone into neonatal NOD mice resulted in a significant increase in the expression of GAD67 mRNA in pancreatic β-cells and the development of insulitis and diabetes. We conclude that glucocorticoid hormones can modulate GAD expression by the transcriptional activation of the GAD promoter and may influence the development of autoimmune diabetes in NOD mice. [ABSTRACT FROM AUTHOR]

Stem or progenitor cells are a potential source of insulin-producing cells, if methods can be found to reliably manipulate their differentiation. Glucagon-like peptide-1 (GLP-1) and its analog, exendin-4, axe known to induce differentiation of insulin-producing pancreatic β cells from different types of stem and progenitor cells. We previously found that when nonobese diabetic (NOD) mice were given a single intravenous injection of a recombinant adenovirus expressing GLP-1 (rAd-GLP-1), insulin-positive cells were detected not only in the pancreas, but also in the intestine. The present study investigated methods to promote the differentiation of intestinal stem cells to insulin-producing cells. An increased number of insulin-stained cells were observed in the intestine of NOD mice when rAd-GLP-1 was locally administered by intra-intestinal injection, as compared with systemic administration of rAd-GLP-1, suggesting that the intestinal stem cell pool might be a good source for differentiation into insulin-producing cells. Neurogenin (ngn)-3 is a transcription factor that responds to Notch signaling, and the expression of ngn-3 determines endocrine differentiation. When we examined the expression of ngn-3 and insulin by immunohistochemical staining in rAd-GLP-l-treated NOD mice, we detected expression of ngn-3 at 1 week after virus injection and insulin at 2 weeks after virus injection. As Notch signaling inhibits ngn-3 expression, we treated a segment of the small intestine (jejunum) from 8-week-old NOD mice with the Notch inhibitor, γ-secretase inhibitor, and exendin-4 alone or in combination and examined insulin mRNA expression. Treatment with a combination of γ-secretase inhibitor and exendin-4 showed additive effects on insulin mRNA expression as compared with treatment with either compound alone. We conclude that differentiation of intestinal stem cells into insulin-producing cells by exendin-4 in adult mice is mediated by ngn-3 expression and promoted by inhibition of Notch signaling. [ABSTRACT FROM AUTHOR]

GAD is a pancreatic beta-cell autoantigen in humans and nonobese diabetic (NOD) mice. Modulation of GAD expression in pancreatic beta-cells has been suggested to be associated with the development of autoimmune diabetes. Hormonal changes through environmental stimuli are considered to influence the expression of the disease. We determined whether steroid hormones would modulate the expression of GAD in pancreatic beta-cells. We treated NOD mouse beta-cells (MIN6N8a cells) with various steroids, including testosterone, estradiol, progesterone, and cortisol, and examined the expression of GAD67 mRNA. We found that only cortisol enhanced the expression of GAD67, whereas the other steroid hormones had no effect. When we treated MIN6N8a cells with a synthetic glucocorticoid, dexamethasone, we found that GAD67 mRNA expression was stimulated in a dose- and time-dependent manner. Cells treated with 100 nmol/l dexamethasone for 6 h showed a 10-fold increase in the expression of GAD67 mRNA and an increase in GAD67 protein. The upregulation of GAD67 expression in beta-cells by dexamethasone was found to be due to the transcriptional activation of the GAD67 promoter. We then examined whether dexamethasone would influence the development of diabetes in NOD mice. Injection of dexamethasone into neonatal NOD mice resulted in a significant increase in the expression of GAD67 mRNA in pancreatic beta-cells and the development of insulitis and diabetes. We conclude that glucocorticoid hormones can modulate GAD expression by the transcriptional activation of the GAD promoter and may influence the development of autoimmune diabetes in NOD mice.