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Autophagy is known to play a pivotal role in β-cell function. While the lifelong inhibition of autophagy through Atg7 deletion in β cells has been demonstrated to lead to impaired glucose tolerance together with β-cell dysfunction, the temporal association between autophagy inhibition and β-cell dysfunction remains unclear. To address such questions, inducible β-cell-specific Atg7-knockout (iβAtg7 KO ) mice were generated, and autophagy inhibition was induced for two different time durations. Whereas 2 weeks of Atg7 ablation was sufficient to induce autophagy deficiency, confirmed by the accumulation of p62, iβAtg7 KO mice exhibited normal glucose tolerance. In contrast, prolonged autophagy deficiency for 6 weeks resulted in glucose intolerance together with impaired insulin secretion. Direct mRNA sequencing and pathway analysis revealed that the gene set associated with insulin secretion was downregulated only after the 6-week prolonged autophagy inhibition. Furthermore, we identified a novel gene, Sprr1a, which was expressed at more than 50-fold higher levels during both the 2-week and 6-week autophagy inhibition. These findings suggest that autophagy insufficiency cumulatively leads to β-cell failure after a certain interval, accompanied by stepwise alterations of gene expression patterns., Competing Interests: Declaration of competing interest This work was supported by grants from the Japan Society for the Promotion of Science (JSPS) KAKENHI (No. 19K22642 to T.M., No. 19K18014 to L.S., and No. 20H03735 to H.W.), the joint research program of the Institute for Molecular and Cellular Regulation, Gunma University (No. 17002 to T.M., and No. 20004 to M.H.), MSD Life Science Foundation, and the Japan Foundation for Applied Enzymology (to L.S.). The authors declare that they have no potential conflicts of interest that might bias their work., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Autophagy in β cells has been demonstrated to play a pivotal role in cellular homeostasis and the progression of glucose intolerance. Although autophagic activity is affected by metabolic stress both in vivo and in vitro, it remains unclear as to what extent the autophagic status in each β cell is different from its neighboring cells. To address this question, GFP-LC3 reporter mice, which can visualize the autophagic status of each β cell as green-fluorescent puncta, were crossed with obese diabetic db/db mice. Imaging of green-fluorescent puncta in the islets of GFP-LC3 mice revealed that β cells are a heterogeneous population, as the density of GFP-LC3 puncta in each cell was variable. Furthermore, the variability was greater in GFP-LC3; db/db mice than in non-diabetic GFP-LC3; db/+ mice. Furthermore, when GFP-LC3 mice were treated with a low dose of S961, which antagonizes insulin signaling without inducing overt hyperglycemia, the number of β cells with a high density of GFP puncta was increased, suggesting that insulin resistance affects autophagic status independently of glucose profiles. These results suggest that pancreatic β cells under metabolic stress are heterogeneous regarding their autophagic status, which provides insights into the cellular dynamics of each β cell rather than the whole β-cell population., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background & Aims: The usefulness of low-carbohydrate diet (LCD) for Japanese patients with type 2 diabetes mellitus (T2DM) has not been fully investigated. Therefore, we compared the effectiveness and safety of LCD with calorie restricted diet (CRD)., Methods: This prospective, randomized, open-label, comparative study included 66 T2DM patients with HbA1c >7.5% even after receiving repeated education programs on CRD. They were randomly allocated to either the 130g/day LCD group (n = 33) or CRD group (n = 33). Patients received personal nutrition education of CRD or LCD for 30 min at baseline, 1, 2, 4, and 6 months. Patients of the CRD group were advised to maintain the intake of calories and balance of macronutrients (28× ideal body weight calories per day). Patients of the LCD group were advised to maintain the intake of 130 g/day carbohydrate without other specific restrictions. Several parameters were assessed at baseline and 6 months after each intervention. The primary endpoint was a change in HbA1c level from baseline to the end of the study., Results: At baseline, BMI and HbA1c were 26.5 (24.6-30.1) and 8.3 (8.0-9.3), and 26.7 (25.0-30.0) kg/m 2 and 8.0 (7.6-8.9) %, in the CRD and LCD, respectively. At the end of the study, HbA1c decreased by -0.65 (-1.53 to -0.10) % in the LCD group, compared with 0.00 (-0.68 to 0.40) % in the CRD group (p < 0.01). Also, the decrease in BMI in the LCD group [-0.58 (-1.51 to -0.16) kg/m 2 ] exceeded that observed in the CRD group (p = 0.03)., Conclusions: Our study demonstrated that 6-month 130 g/day LCD reduced HbA1c and BMI in poorly controlled Japanese patients with T2DM. LCD is a potentially useful nutrition therapy for Japanese patients who cannot adhere to CRD. This trial was registered at http://www.umin.ac.jp/english/ (University Hospital Medical Information Network: study ID number 000010663)., (Copyright © 2016 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.)

Autophagy is a tightly regulated self-digestion system. As in other cell types, autophagy plays an essential role in the homeostasis of pancreatic beta cells. However, the mechanisms involved in the deterioration of beta cell function caused by autophagic failure have not yet been fully elucidated. To gain insight into its mechanisms, we compared the protein expression of islets from beta cell-specific Atg7-deficient mice (Atg7(Δβ-cell) mice) and their controls (Atg7(f/f) mice). Liquid chromatography/mass spectrometry after 1-dimensional electrophoresis identified the increased expression of ERp57/GRP58 in islets isolated from Atg7(Δβ-cell) mice compared with those from Atg7(f/f) mice. The expression level of ERp57 was also elevated in rat insulinoma INS-1 cells by inducible knock-down of the atg7-gene. In Atg7 knock-down INS-1 cells, the suppression of ERp57 expression by siRNA resulted in an increase in the level of cleaved Caspase-3 protein and a decrease in the number of live cells. Furthermore, cell cycle analyses demonstrated that the suppressed expression of ERp57 increased the sub-G1 population. These data reveal that increased expression of ERp57 may contribute to the protection from beta cell death caused by autophagic failure., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Exercise enhances insulin sensitivity in skeletal muscle, but the underlying mechanism remains obscure. Recent data suggest that alternatively activated M2 macrophages enhance insulin sensitivity in insulin target organs such as adipose tissue and liver. Therefore, the aim of this study was to determine the role of anti-inflammatory M2 macrophages in exercise-induced enhancement of insulin sensitivity in skeletal muscle. C57BL6J mice underwent a single bout of treadmill running (20 m/min, 90 min). Twenty-four hours later, ex vivo insulin-stimulated 2-deoxy glucose uptake was found to be increased in plantaris muscle. This change was associated with increased number of CD163-expressing macrophages (i.e. M2-polarized macrophages) in skeletal muscle. Systemic depletion of macrophages by pretreatment of mice with clodronate-containing liposome abrogated both CD163-positive macrophage accumulation in skeletal muscle as well as the enhancement of insulin sensitivity after exercise, without affecting insulin-induced phosphorylation of Akt and AS160 or exercise-induced GLUT4 expression. These results suggest that accumulation of M2-polarized macrophages is involved in exercise-induced enhancement of insulin sensitivity in mouse skeletal muscle, independently of the phosphorylation of Akt and AS160 and expression of GLUT4., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Dipeptidyl peptidase-4 (DPP-4) inhibitors improve glycemic control in patients with type 2 diabetes primarily by increasing plasma active glucagon-like peptide-1 (GLP-1) levels. While various combination therapies based on DPP-4 inhibitors have been proposed for treatment of type 2 diabetes, the effects of combination therapy of DPP-4 inhibitors and alpha-glucosidase inhibitors on β-cell function are less characterized. We evaluated the effects of long-term treatment with vildagliptin, a DPP-4 inhibitor, on metabolic parameters and β-cell function, in combination with miglitol, an alpha-glucosidase inhibitor, in diet-controlled db/db mice. In this study, 6-week-old male db/db mice were provided with standard chow twice a day for 6 weeks. Meal tolerance tests and glucose tolerance tests showed that the combination therapy of vildagliptin with miglitol, but not each alone, suppressed postprandial glycemic excursion, enhanced postprandial active GLP-1 levels and prevented deterioration of glucose tolerance in the db/db mice. The combination treatment did not alter β-cell mass, but resulted in preserved expression of glucose transporter 2, Zinc transporter 8 and MafA and reduced the number of α cells. These results suggest that the combination of vildagliptin and miglitol prevents the development of overt diabetes in diet-controlled pre-diabetic db/db mice by normalizing postprandial glucose and incretin response, and by preserving β-cell structure and the expression of factors essential for β-cell function., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The aim of this study was to investigate the role of insulin receptor substrate-2 (IRS-2) mediated signal in macrophages on the accumulation of macrophages in the vascular wall. Mice transplanted with IRS-2(-/-) bone marrow, a model of myeloid cell restricted defect of IRS-2, showed accumulation of monocyte chemoattractant protein-1-expressing macrophages in the vascular wall. Experiments using cultured peritoneal macrophages showed that IRS-2-mediated signal pathway stimulated by physiological concentrations of insulin, not by IL-4, contributed to the suppression of monocyte chemoattractant protein-1 expression induced by lipopolysaccharide. Our data indicated that IRS-2 deficiency in macrophages enhanced their accumulation in the vascular wall accompanied by increased expression of proinflammatory mediators in macrophages. These results suggest a role for insulin resistance in macrophages in early atherosclerogenesis., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Glucagon-like peptide-1 is a hormone secreted by L cells of the small intestine and stimulates glucose-dependent insulin response. Glucagon-like peptide-1 receptor agonists such as exendin-4 are currently used in type 2 diabetes, and considered to have beneficial effects on the cardiovascular system. To further elucidate the effect of glucagon-like peptide-1 receptor agonists on cardiovascular diseases, we investigated the effects of exendin-4 on intimal thickening after endothelial injury. Under continuous infusion of exendin-4 at 24 nmol/kg/day, C57BL/6 mice were subjected to endothelial denudation injury of the femoral artery. Treatment of mice with exendin-4 reduced neointimal formation at 4weeks after arterial injury without altering body weight or various metabolic parameters. In addition, in vitro studies of isolated murine, rat and human aortic vascular smooth muscle cells showed the expression of GLP-1 receptor. The addition of 10nM exendin-4 to cultured smooth muscle cells significantly reduced their proliferation induced by platelet-derived growth factor. Our results suggested that exendin-4 reduced intimal thickening after vascular injury at least in part by the suppression of platelet-derived growth factor-induced smooth muscle cells proliferation., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Recent studies have suggested that free fatty acids stimulate autophagy of pancreatic beta cells. The aim of this study was to verify the free fatty acids (FFA)-induced autophagy and investigate its molecular mechanism. As reported previously, palmitate strongly enhanced the conversion of light chain (LC)3-I to LC3-II, a marker of activation of autophagy in INS-1 beta cells. Palmitate-induced conversion of LC3-I to LC3-II was also observed in neuron-, muscle-, and liver-derived cells. In addition, palmitate induced the formation of typical autophagosomes and autolysosomes and enhanced the degradation rate of long-lived proteins. These results confirmed that palmitate activates autophagic flux in most of the cells. While FFAs reportedly activate several signal transduction pathways in beta cells, palmitate-induced autophagy was blocked by a JNK inhibitor. Although enhanced oxidative stress and endoplasmic reticulum (ER) stress are suspected to mediate FFA-induced activation of JNK1, the induction of autophagy was not associated with changes in molecular markers related to oxidative and endoplasmic reticulum stresses. On the other hand, phosphorylation of double stranded RNA-dependent protein kinase (PKR) paralleled JNK1 activation. Considered together, our study suggested that FFA stimulated functional autophagy possibly through the PKR-JNK1 pathway independent of ER or oxidative stress., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Epidemiological studies suggest that insulin resistance is an independent risk factor for cardiovascular disease. However, there is little information on the role of insulin resistance in atherosclerogenesis independent of LDL cholesterol level. The aim of this study was to investigate the impact of systemic insulin resistance on monocyte adhesion to endothelial cells and atherosclerotic lesions independent of LDL cholesterol level. KKAy mice are obese mice with spontaneous diabetes and insulin resistance, and normal levels of LDL cholesterol. In parallel with systemic insulin resistance, decreased insulin signal, and the increased expression of monocyte chemoattractant protein-1 (MCP-1) were noted in macrophages isolated from KKAy mice. These mice showed enhanced monocyte adhesion to the endothelial cells of the thoracic artery. Furthermore, these mice showed expanded atherosclerotic lesions when fed high cholesterol diet. Our data indicate that insulin resistance promotes the atherosclerogenesis independent of LDL cholesterol level. Decreased insulin signaling in macrophages associated with systemic insulin resistance could be involved, at least in part, in this pathological process., (Copyright (c) 2010 Elsevier Inc. All rights reserved.)

Beta-cell proliferation is regulated by various metabolic demands including peripheral insulin resistance, obesity, and hyperglycemia. In addition to enhancement of glucose-induced insulin secretion, agonists for glucagon-like peptide-1 receptor (GLP-1R) stimulate proliferation and inhibit apoptosis of beta-cells, thereby probably preserve beta-cell mass. To evaluate the beta-cell preserving actions of GLP-1R agonists, we assessed the acute and chronic effects of exendin-4 on beta-cell proliferation, mass and glucose tolerance in C57BL/6J mice under various conditions. Short-term administration of high-dose exendin-4 transiently stimulated beta-cell proliferation. Comparative transcriptomic analysis showed upregulation of IGF-1 receptor and its downstream effectors in islets. Treatment of mice with exendin-4 daily for 4 weeks (long-term administration) and feeding high-fat diet resulted in significant inhibition of weight gain and improvement of glucose tolerance with reduced insulin secretion and beta-cell mass. These findings suggest that long-term GLP-1 treatment results in insulin sensitization of peripheral organs, rather than enhancement of beta-cell proliferation and function, particularly when animals are fed high-fat diet. Thus, the effects of exendin-4 on glucose tolerance, insulin secretion, and beta-cell proliferation largely depend on treatment dose, duration of treatment and meal contents. While GLP-1 enhances proliferation of beta-cells in some diabetic mice models, our results suggest that GLP-1 stimulates beta-cell growth only when expansion of beta-cell mass is required to meet metabolic demands.

The inability to increase of islet mass adequately to compensate for the demand of insulin due to insulin resistance is an important pathophysiological feature of type 2 diabetes. Previous studies suggested a relationship between pancreatic beta-cell mass and islet vascularization, although no evidence has confirmed this association in response to insulin resistance. Vascular endothelial growth factor-A (VEGF-A) in islets is essential for maintaining normal islet blood vessels. Here, insulin resistance was induced in mice carrying a beta-cell-specific VEGF-A gene mutation (RIP-Cre:Vegf(fl/fl)) by 20-week feeding of high-fat diet as a model of impaired islet vascularization. These mice showed only a modest decrease in glucose tolerance, compared with control mice. In addition, although the endothelial cell area in the islets of high-fat-fed RIP-Cre:Vegf(fl/fl) mice remained diminished, the pancreatic beta-cell area was modestly more than in high-fat-fed control mice. Thus, normal islet vascularization does not seem to be essential for expansion of beta cell mass in response to insulin resistance.

Alpha-smooth muscle actin-positive endothelial cells have not been found in adult aortic endothelium except valve leaflets. Here, using en face immunostaining method, we identified alpha-smooth muscle actin-positive endothelial cells in the luminal surface of rat, mouse and human thoracic aortas. These cells express both endothelial markers and definite smooth muscle cell markers and were only occasionally observed in thoracic aorta of wild type mice and rats. Their density did not increase with aging. Given that alpha-smooth muscle actin-positive endothelial cells express low level of vascular endothelial-cadherin that is important for the maintenance of cell contact, these cells were frequently detected in the thoracic aorta of 5-week-old apolipoprotein-E deficient mice. In 20- to 24-week-old apolipoprotein-E deficient mice, marked accumulation of alpha-smooth muscle actin-positive endothelial cells was observed especially in the luminal surface of atheromatous plaques. Our findings indicate the existence of alpha-smooth muscle actin-positive endothelial cells in adult aortic endothelium and the possible association with progression of atherosclerosis.

The pancreas is derived from a pool of multipotent progenitor cells (MPCs) that co-express Pdx-1 and Ptf1a. To more precisely define how the individual and combined loss of Pdx-1 and Ptf1a affects pancreatic MPC specification and differentiation we derived and studied mice bearing a novel Ptf1a(YFP) allele. While the expression of Pdx-1 and Ptf1a in pancreatic MPCs coincides between E9.5 and 12.5 the developmental phenotypes of Pdx-1 null and Pdx-1; Ptf1a double null mice are indistinguishable, and an early pancreatic bud is formed in both cases. This finding indicates that Pdx-1 is required in the foregut endoderm prior to Ptf1a for pancreatic MPC specification. We also found that Ptf1a is neither required for specification of Ngn3-positive endocrine progenitors nor differentiation of mature beta-cells. In the absence of Pdx-1 Ngn3-positive cells were not observed after E9.5. Thus, in contrast to the deletion of Ptf1a, the loss of Pdx-1 precludes the sustained Ngn3-based derivation of endocrine progenitors from pancreatic MPCs. Taken together, these studies indicate that Pdx-1 and Ptf1a have distinct but interdependent functions during pancreatic MPC specification.

It is well known that activating protein-1 (AP-1) is involved in a variety of cellular functions such as proliferation, differentiation, apoptosis, and oncogenesis. AP-1 is a dimer complex consisting of different subunits, and c-Jun is known to be one of its major components. In addition, it has been shown that mice lacking c-Jun are embryonic lethal and that c-Jun is essential for liver and heart development. However, the role of c-Jun in the pancreas is not well known. The aim of this study was to examine the possible role of c-Jun in the pancreas. First, c-Jun was strongly expressed in pancreatic duct-like structures at an embryonic stage, while a lower level of expression was observed in some part of the adult pancreas, implying that c-Jun might play a role during pancreas development. Second, to address this point, we generated pancreas-specific c-Jun knock-out mice (Ptf1a-Cre; c-Jun(flox/flox) mice) by crossing Ptf1a-Cre knock-in mice with c-Jun floxed mice. Ptf1a is a pancreatic transcription factor and its expression is confined to pancreatic stem/progenitor cells, which give rise to all three types of pancreatic tissue: endocrine, exocrine, and duct. Contrary to our expectation, however, there was no morphological difference in the pancreas between Ptf1a-Cre; c-Jun(flox/flox) and control mice. In addition, there was no difference in body weight, pancreas weight, and the expression of various pancreas-related factors (insulin, glucagon, cytokeratin, and amylase) between the two groups. Furthermore, there was no difference in glucose tolerance between Ptf1a-Cre; c-Jun(flox/flox) and control mice. Taken together, although we cannot exclude the possibility that c-Jun ablation is compensated by some unknown factors, c-Jun appears to be dispensable for pancreas development at least after ptf1a gene promoter is activated.

It is well known that pancreatic and duodenal homeobox gene-1 (PDX-1) plays a crucial role in beta-cell differentiation, and maintaining mature beta-cell function. Thus, it is important to understand how pdx-1 gene is regulated under various pathophysiological conditions in vivo. In this study, to non-invasively and quantitatively monitor pdx-1 promoter activity in vivo, we constructed a pdx-1 promoter-SEAP-IRES-GFP reporter plasmid. In this construct, the -4.6kb pdx-1 promoter region sufficient for driving beta-cell-selective PDX-1 expression was inserted to the upstream of the secreted alkaline phosphatase (SEAP) reporter gene. It is noted here that the pdx-1 promoter-mediated SEAP activity can be distinguished from endogenous alkaline phosphatase activity. First, we transfected the construct in mouse beta-cell line MIN6 and human hepatocellular carcinoma cell line HepG2. SEAP activity was readily detected in the media of MIN6 cells, but not in HepG2 cells. These results indicate that this construct specifically reports beta-cell-specific pdx-1 promoter activity in a cell culture system. Based on these in vitro findings, we next generated transgenic mice using the same construct. SEAP activity was readily detected in serum of the transgenic mice, but not in their littermate mice. Furthermore, SEAP activity was detected in protein extract from the transgenic pancreas and slightly from the transgenic duodenum, but not from the liver, and brain. These results indicate that serum SEAP activity likely represents in vivo pdx-1 promoter activity. This transgenic mouse model would be useful to non-invasively monitor in vivo pdx-1 promoter activity and to screen new molecules which regulate PDX-1 expression.

The aim of this study was to investigate the effect of fluctuations in blood glucose levels on atherogenesis. Apolipoprotein (apo) E-deficient mice fed maltose twice daily were used as a model of repetitive postprandial glucose spikes. We investigated the number of macrophages adherent to the endothelium and the area of fibrotic arteriosclerotic lesions, with and without administration of miglitol, an alpha-glucosidase inhibitor. Macrophage adhesion to endothelial cells in thoracic aorta was quantitated by the en face method for optimal observation of endothelial surface after immunohistochemical staining for Mac-2. The area of arteriosclerotic lesions was measured in elastica van Giesson-stained proximal aorta. The number of adherent macrophages increased at 1 week after commencement of maltose feeding and the size of arteriosclerotic lesion increased at 5 weeks after such feeding. These increases were prevented by simultaneous use of miglitol. Our data demonstrated that glucose fluctuations accelerate atherogenesis. This was independent of changes in serum cholesterol level in vivo. Reduction of glucose fluctuation by alpha-glucosidase inhibitor efficiently controlled the progression of atherosclerosis.

Epidemiological studies demonstrated the importance of postprandial hyperglycemia on the progression of atherosclerosis. However, whether treatment of postprandial hyperglycemia by insulin or insulin secretagogues has a beneficial effect on atherosclerosis has not been elucidated. To elucidate the effects of reduction of postprandial rise of blood glucose by insulin and nateglinide on monocyte adhesion to endothelial cells, we used non-obese type 2 diabetic Goto-Kakizaki (GK) rats fed twice daily, as a model of repetitive postprandial hyperglycemia. We investigated the effects of insulin injection and nateglinide administration just before each meal for 12 weeks on monocyte adhesion to endothelial cells. By setting the doses of insulin and nateglinide, both treatment significantly reduced postprandial hyperglycemia without significant reduction of HbA1c. Nateglinide also reduced serum insulin level just after 1 h meal. Both nateglinide and insulin therapy reduced the number of monocytes adherent to the aortic endothelial layer. Nateglinide, but not insulin, reduced intimal thickness of the thoracic aorta. While increased serum insulin level might be regarded as a factor responsible for the progression of atherosclerosis, our data showed that treatment with pre-meal insulin or nateglinide, which reduces postprandial hyperglycemia, reduced monocyte adhesion to endothelial cells.

The unique, well-demarcated expression domain of Pdx1 within the posterior foregut suggests that investigating its transcriptional regulation will provide insight into mechanisms that regionally pattern the endoderm. Previous phylogenetic comparison identified conserved noncoding regions that stimulate transcriptional activity selectively in cultured pancreatic beta cells. Characterization of these regulatory elements is helping to dissect the transcription factor networks that operate within beta cells, which is important for understanding the etiology of beta cell dysfunction and diabetes, as well as for developing methods to produce beta cells in vitro for cell-based therapies. We recently reported that deletion of three proximally located conserved areas (Area I-II-III) from the endogenous Pdx1 locus resulted in severely reduced expression of Pdx1 in the pancreas, and a milder decrease in other foregut tissues. Here, we report transgene-based complementation experiments on Pdx1 null mice, which reveal that the proximal promoter/enhancer region, including Area I-II-III, rescues the pancreatic defects caused by Pdx1 deficiency, but only weakly promotes expression of Pdx1 in the postnatal stomach and duodenum. These results reveal a role for distal cis-regulatory elements in achieving the correct level of extra-pancreatic Pdx1 expression, which is necessary for the production of duodenal GIP cells and stomach gastrin cells.

Nkx family members are essential for normal development of many different tissues such as the heart, lungs, thyroid, prostate, and CNS. Here, we describe the endodermal expression pattern of three Nkx6 family genes of which two shows conserved expression in the early pancreatic epithelium. In chicken, Nkx6.1 expression is not restricted to the presumptive pancreatic area but is more broadly expressed in the endoderm. In mice, expression of Nkx6.1 is restricted to the pancreatic epithelium. In both mice and chicken, Nkx6.2 and Pdx1 are expressed in very similar domains, identifying Nkx6.2 as a novel marker of pancreas endoderm. Additionally, our results show that Nkx6.3 is expressed transiently in pancreatic endoderm in chicken but not mouse embryos. At later stages, Nkx6.3 is found in the caudal stomach and rostral duodenum in both species. Finally, we demonstrate that Pdx1 is required for Nkx6.1 but not Nkx6.2 expression in mice and that ectopic Pdx1 can induce Nkx6.1 but not Nkx6.2 or Nkx6.3 expression in anterior chicken endoderm. These results demonstrate that Nkx6.1 lies downstream of Pdx1 in a genetic pathway and that Pdx1 is required and sufficient for Nkx6.1 expression in the early foregut endoderm.

Normal islet formation and function depends on the action of various growth factors operating in pre- and postnatal development; however, the specific physiological function of each factor is largely unknown. Loss-of-function analyses in mice have provided little information so far, perhaps due to functional redundancies of the growth factors acting on the pancreas. The present study focuses on the role of the transcription factor STAT3 in insulin-producing cells. STAT3 is one of the potential downstream mediators for multiple growth factors acting on the pancreatic beta-cells, including betacellulin, hepatocyte growth factor, growth hormone, and heparin-binding EGF-like growth factor. To elucidate its role in the beta-cells, the STAT3 gene was disrupted in insulin-producing cells in mice (STAT3-insKO), using a cre-mediated gene recombination approach. Unexpectedly, STAT3-insKO mice exhibited an increase in appetite and obesity at 8 weeks of age or older. The mice showed partial leptin resistance, suggesting that expression of the RIP (rat insulin promoter)-cre transgene in hypothalamus partially inhibited the appetite-regulating system. Intraperitoneal glucose tolerance tests, performed in non-obese 5-week-old mice, showed that the STAT3-insKO mice were glucose intolerant. Islet perifusion experiments further revealed a deficiency in early-phase insulin secretion. Whereas islet insulin content or islet mass was not affected, expression levels of GLUT2, SUR1, and VEGF-A were significantly reduced in STAT3-insKO islets. Interestingly, STAT3-insKO mice displayed impaired islet morphology: alpha-cells were frequently seen in central regions of islets. Our present observations demonstrate a unique role of STAT3 in maintaining glucose-mediated early-phase insulin secretion and normal islet morphology.