STAT5 activity in pancreatic beta-cells influences the severity of diabetes in animal models of type 1 and 2 diabetes

STATs, promising targets for the treatment of autoimmune and inflammatory diseases

Cytokines play a crucial role in the pathophysiology of autoimmune and inflammatory diseases, with over 50 cytokines undergoing signal transduction through the Signal Transducers and Activators of Transcription (STAT) signaling pathway. Recent studies have solidly confirmed the pivotal role of STATs in autoimmune and inflammatory diseases. Therefore, this review provides a detailed summary of the immunological functions of STATs, focusing on exploring their mechanisms in various autoimmune and inflammatory diseases. Additionally, with the rapid advancement of structural biology in the field of drug discovery, many STAT inhibitors have been identified using structure-based drug design strategies. In this review, we also examine the structures of STAT proteins and compile the latest research on STAT inhibitors currently being tested in animal models and clinical trials for the treatment of immunological diseases, which emphasizes the feasibility of STATs as promising therapeutic targets and provides insights into the design of the next generation of STAT inhibitors.

Modulatory role of prolactin in type 1 diabetes

Objectives

Patients with type 1 diabetes mellitus have been reported to have elevated prolactin levels and a possible relationship between prolactin levels and the development of the disease has been proposed. However, some studies show that prolactin mediates beneficial functions in beta cells. Therefore, we review information on the roles of prolactin in type 1 diabetes mellitus.

Content

Here we summarize the functions of prolactin in the immune system and in pancreatic beta cells, in addition, we describe studies related to PRL levels, its regulation and alterations of secretion in patients with type 1 diabetes mellitus.

Summary

Studies in murine models have shown that prolactin protects beta cells from apoptosis, stimulates their proliferation and promotes pancreatic islet revascularization. In addition, some studies in patients with type 1 diabetes mellitus have shown that elevated prolactin levels correlate with better disease control.

Outlook

Prolactin treatment appears to be a promising strategy to improve beta-cell vascularization and proliferation in transplantation and immunotherapies.

STAT5A modulated EndMT via upregulation of ELTD1 expression in diabetic nephropathy

Diabetic nephropathy (DN), one of microvascular complications of diabetes mellitus, results in renal dysfunction and end-stage renal disease. Recently, endothelial-to-mesenchymal transition (EndMT) was reported to mediate glomerular endothelial dysfunction, thus participating in the progress of fibrosis in DN. As a special type of epithelial-to-mesenchymal transition, EndMT and epithelial-to-mesenchymal transition may share corporate modulators. It was reported that EGF, Latrophilin And Seven Transmembrane Domain Containing 1 (ELTD1) and signal transducer and activator of transcription 5A (STAT5A) participate in epithelial-to-mesenchymal transition in some situations. In this work, we proposed that STAT5A participated in high glucose-mediated EndMT via modulation of ELTD1 levels in DN. Our data indicated that hyperglycemia/high glucose-induced ELTD1 and EndMT in DN rats and hyperglycemic human glomerular endothelial cells (HGECs). Also, high glucose mediated STAT5A nuclear translocation in HGECs. Moreover, high glucose-mediated EndMT was reversed by ELTD1 silencing. Further, STAT5A was found to be elevated in DN rats and hyperglycemic HGECs. The effect of high glucose-mediated increase of ELTD1 expression and EndMT was reversed by STAT5A silencing in vitro. Further, STAT5A overexpression enhanced ELTD1 levels and EndMT, which was inhibited by si-ELTD1. ChIP and luciferase assay represented that STAT5A directly regulated ELTD1 transcription. STAT5A directly regulated ELTD1 transcription, thus participating in high glucose-mediated EndMT in glomeruli of DN. This article is protected by copyright. All rights reserved.

Erythropoietin exposure of isolated pancreatic islets accelerates their revascularization after transplantation

AIMS

The exposure of isolated pancreatic islets to pro-angiogenic factors prior to their transplantation represents a promising strategy to accelerate the revascularization of the grafts. It has been shown that erythropoietin (EPO), a glycoprotein regulating erythropoiesis, also induces angiogenesis. Therefore, we hypothesized that EPO exposure of isolated islets improves their posttransplant revascularization.

METHODS

Flow cytometric, immunohistochemical and quantitative real-time (qRT)-PCR analyses were performed to study the effect of EPO on the viability, cellular composition and gene expression of isolated islets. Moreover, islets expressing a mitochondrial or cytosolic H₂O₂ sensor were used to determine reactive oxygen species (ROS) levels. The dorsal skinfold chamber model in combination with intravital fluorescence microscopy was used to analyze the revascularization of transplanted islets.

RESULTS

We found that the exposure of isolated islets to EPO (3 units/mL) for 24 h does not affect the viability and the production of ROS when compared to vehicle-treated and freshly isolated islets. However, the exposure of islets to EPO increased the number of CD31-positive cells and enhanced the gene expression of insulin and vascular endothelial growth factor (VEGF)-A. The revascularization of the EPO-cultivated islets was accelerated within the initial phase after transplantation when compared to both controls.

CONCLUSION

These findings indicate that the exposure of isolated islets to EPO may be a promising approach to improve clinical islet transplantation.

Genetic variants in glutamate cysteine ligase confer protection against type 2 diabetes

Oxidative stress contributes to the pathogenesis of type 2 diabetes (T2D). This study investigated whether single nucleotide polymorphisms (SNPs) at genes encoding glutamate cysteine ligase catalytic (rs12524494, rs17883901, rs606548, rs636933, rs648595, rs761142 at GCLC) and modifier (rs2301022, rs3827715, rs7517826, rs41303970 at GCLM) subunits are associated with susceptibility to type 2 diabetes. 2096 unrelated Russian subjects were enrolled for the study. Genotyping was done with the use of the MassArray System. Plasma levels of reactive oxygen species (ROS) and glutathione in the study subjects were analyzed by fluorometric and colorimetric assays, respectively.The present study found, for the first time, an association of SNP rs41303970 in the GCLM gene with a decreased risk of T2D (P = 0.034, Q = 0.17). Minor alleles such as rs12524494-G GCLC gene (P = 0.026, Q = 0.17) and rs3827715-C GCLM gene (P = 0.03, Q = 0.17) were also associated with reduced risk for T2D. Protective effects of variant alleles such as rs12524494-G at GCLC (P = 0.02, Q = 0.26) and rs41303970-A GCLM (P = 0.013, Q = 0.25) against the risk of T2D were seen solely in nonsmokers. As compared with healthy controls, diabetic patients had markedly increased levels of ROS and decreased levels of total GSH in plasma. Interestingly, fasting blood glucose level positively correlated with oxidized glutathione concentration (r_s = 0.208, P = 0.01). Three SNPs rs17883901, rs636933, rs648595 at GCLC and one rs2301022 at GCLM were associated with decreased levels of ROS, while SNPs rs7517826, rs41303970 at GCLM were associated with increased levels of total GSH in plasma. Single nucleotide polymorphisms in genes encoding glutamate cysteine ligase subunits confer protection against type 2 diabetes and their effects are mediated through increased levels of glutathione.

Bacteriophage-mediated manipulation of the gut microbiome – promises and presents limitations

Gut microbiome (GM) composition and function are linked to human health and disease, and routes for manipulating the GM have become an area of intense research. Due to its high treatment efficacy, the use of fecal microbiota transplantation (FMT) is generally accepted as a promising experimental treatment for patients suffering from GM imbalances (dysbiosis), e.g. caused by recurrent Clostridioides difficile infections (rCDI). Mounting evidence suggests that bacteriophages (phages) play a key role in successful FMT treatment by restoring the dysbiotic bacterial GM. As a refinement to FMT, removing the bacterial component of donor feces by sterile filtration, also referred to as fecal virome transplantation (FVT), decreases the risk of invasive infections caused by bacteria. However, eukaryotic viruses and prophage-encoded virulence factors remain a safety issue. Recent in vivo studies show how cascading effects are initiated when phage communities are transferred to the gut by e.g. FVT, which leads to changes in the GM composition, host metabolome, and improve host health such as alleviating symptoms of obesity and type-2-diabetes (T2D). In this review, we discuss the promises and limitations of FVT along with the perspectives of using FVT to treat various diseases associated with GM dysbiosis.

Serotonin Regulates Adult β-Cell Mass by Stimulating Perinatal β-Cell Proliferation

A sufficient β-cell mass is crucial for preventing diabetes, and perinatal β-cell proliferation is important in determining the adult β-cell mass. However, it is not yet known how perinatal β-cell proliferation is regulated. Here, we report that serotonin regulates β-cell proliferation through serotonin receptor 2B (HTR2B) in an autocrine/paracrine manner during the perinatal period. In β-cell-specific Tph1 knockout (Tph1 βKO) mice, perinatal β-cell proliferation was reduced along with the loss of serotonin production in β-cells. Adult Tph1 βKO mice exhibited glucose intolerance with decreased β-cell mass. Disruption of Htr2b in β-cells also resulted in decreased perinatal β-cell proliferation and glucose intolerance in adulthood. Growth hormone (GH) was found to induce serotonin production in β-cells through activation of STAT5 during the perinatal period. Thus, our results indicate that GH-GH receptor-STAT5-serotonin-HTR2B signaling plays a critical role in determining the β-cell mass by regulating perinatal β-cell proliferation, and defects in this pathway affect metabolic phenotypes in adults.

Impaired endocrine-metabolic homeostasis: underlying mechanism of its induction by unbalanced diet

To characterize the intrinsic mechanism by which sucrose induces β-cell dysfunction. Normal rats received for 3 weeks a standard diet supplemented with 10% sucrose in the drinking water (high sucrose (HS)) with/out an antioxidant agent (R/S α-lipoic acid). We measured plasma glucose, insulin, triglyceride, leptin, and lipid peroxidation levels; homeostasis model assessment (HOMA)-insulin resistance (HOMA-IR) and HOMA for β-cell function (HOMA-β) indexes were also determined. Insulin secretion, β-cell apoptosis, intracellular insulin and leptin mediators, and oxidative stress (OS) markers were also measured in islets isolated from each experimental group. HS rats had increased plasma triglyceride, insulin, leptin, and lipid peroxidation (OS marker) levels associated with an insulin-resistant state. Their islets developed an initial compensatory increase in glucose-induced insulin secretion and mRNA and protein levels of β-cell apoptotic markers. They also showed a significant decrease in mRNA and protein levels of insulin and leptin signaling pathway mediators. Uncoupling protein 2 (UCP2), peroxisome proliferator-activated receptor (PPAR)-α and -δ mRNA and protein levels were increased whereas mRNA levels of Sirtuin-1 (Sirt-1), glutathione peroxidase, and catalase were significantly lower in these animals. Development of all these endocrine-metabolic abnormalities was prevented by co-administration of R/S α-lipoic acid together with sucrose. OS may be actively involved in the mechanism by which unbalanced/unhealthy diet induces β-cell dysfunction. Since metabolic-endocrine dysfunctions recorded in HS rats resembled those measured in human pre-diabetes, knowledge of its molecular mechanism could help to develop appropriate strategies to prevent the progression of this metabolic state toward type 2 diabetes (T2D).

JAK/STAT - Emerging Players in Metabolism

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is crucial for transducing signals from a variety of metabolically relevant hormones and cytokines including growth hormone, leptin, erythropoietin, IL4, IL6 and IFNγ. A growing body of evidence suggests that this pathway is dysregulated in the context of obesity and metabolic disease. Recent development of animal models has been instrumental in identifying the role of JAK/STAT signaling in the peripheral metabolic organs including adipose, liver, muscle, pancreas, and the immune system. In this review we summarize current knowledge about the function of JAK/STAT proteins in the regulation of metabolism, and highlight new potential therapeutic targets for the treatment of obesity and diabetes.

The role of growth hormone receptor in β cell function

Growth hormone (GH) exerts numerous effects on tissues through binding to its receptor, GHR, which resides on cell membranes in many different organs and tissues. Endocrine pancreatic β cells are the only source of insulin secretion in response to metabolic demand, thereby regulating blood glucose and maintaining metabolic homeostasis. β cell dysfunction is the main composition of diabetes mellitus. Numerous studies have provided strong evidence that GHR signaling plays an independent role in β cell function. In this review, we focus on the role of GHR signaling in β cell actions and the underlying molecular mechanisms.

Regulation of malonyl-CoA-acyl carrier protein transacylase network in umbilical cord blood affected by intrauterine hyperglycemia

Background

Gestational diabetes mellitus (GDM) has been shown to be associated with high risk of diabetes in offspring. However, the mechanisms involved in the insulin resistance in offspring are still unclear. Mitochondrial dysfunction is related with insulin resistance. In mitochondria, malonyl-CoA-acyl carrier protein transacylase (MCAT) is the key enzyme of mitochondrial fatty acid synthesis and is estimated to contribute to insulin resistance. In this study, we aimed to examine the role of MCAT and its network in the umbilical cord blood in GDM-induced offspring insulin resistance.

Methods

We isolated lymphocytes from umbilical cord vein blood in 6 GDM patients and 6 controls and examined the differences of RNA by RNA sequencing. qRT-PCR and western blot were used to measure mRNA and protein changes. Bisulfite genomic sequencing PCR was applied to detect DNA methylation.

Results

We found more than 400 genes were differentially regulated in the lymphocytes of umbilical cord blood from GDM patients and these genes were mainly enriched in immune system and endocrine system, which relate to mitochondrial dysfunction and insulin resistance. MCAT closely related with PTPN1 (Protein Tyrosine Phosphatase, Non-Receptor Type1) and STAT5A (Signal Transducer And Activator of Transcription 5A), which were all increased in umbilical cord blood from GDM patients. Increase in MCAT may be due to decreased MCAT DNA methylation.

Conclusion

MCAT and its network with PTPN1, STAT5A are regulated in umbilical cord blood affected by maternal intrauterine hyperglycemia.

Suppressor of cytokine signaling 2 (SOCS2) deletion protects against multiple low dose streptozotocin-induced type 1 diabetes in adult male mice

BACKGROUND

Diabetes type 1 is characterized by the failure of beta cells to produce insulin. Suppressor of cytokine signaling (SOCS) proteins are important regulators of the Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway. Previous studies have shown that GH can prevent the development of type I diabetes in mice and that SOCS2 deficiency mimics a state of increased GH sensitivity.

METHODOLOGY

The elevated sensitivity of SOCS2-/- mice to GH and possibly to PRL was the rationale to analyze the effects of multiple low dose streptozotocin (MLDSTZ)-induced diabetes in SOCS2-/- mice.

RESULTS

We show that 6-month-old SOCS2-/- mice, but not 2-month-old mice, were less sensitive to MLDSTZ-induced diabetes, compared to controls. MLDSTZ treatment induced glucose intolerance in both SOCS2+/+ and SOCS2-/- mice, as shown by glucose tolerance tests, with SOCS2+/+ mice showing a more marked intolerance, compared to SOCS2-/- mice. Furthermore, insulin tolerance tests showed that the SOCS2-/- mice have an improved hypoglycemic response to exogenous insulin, compared to SOCS2+/+ mice. Moreover, in isolated islets, lipotoxic effects on insulin release could partly be overcome by ligands, which bind to GH or PRL receptors.

CONCLUSION

Knockdown of SOCS2 makes mice less sensitive to MLDSTZ. These results are consistent with the proposal that elimination of SOCS2 in pancreatic islets creates a state of β-cell hypersensitivity to GH/PRL that mimics events in pregnancy, and which is protective against MLDSTZ-induced type I diabetes in mice. SOCS2-dependent control of β-cell survival may be of relevance to islet regeneration and survival in transplantation.

Single-Cell Mass Cytometry Analysis of the Human Endocrine Pancreas

The human endocrine pancreas consists of multiple cell types and plays a critical role in glucose homeostasis. Here, we apply mass cytometry technology to measure all major islet hormones, proliferative markers, and readouts of signaling pathways involved in proliferation at single-cell resolution. Using this innovative technology, we simultaneously examined baseline proliferation levels of all endocrine cell types from birth through adulthood, as well as in response to the mitogen harmine. High-dimensional analysis of our marker protein expression revealed three major clusters of beta cells within individuals. Proliferating beta cells are confined to two of the clusters.

Integrative Genomics Outlines a Biphasic Glucose Response and a ChREBP-RORγ Axis Regulating Proliferation in β Cells

Glucose is an important inducer of insulin secretion, but it also stimulates long-term adaptive changes in gene expression that can either promote or antagonize the proliferative potential and function of β cells. Here, we have generated time-resolved profiles of enhancer and transcriptional activity in response to glucose in the INS-1E pancreatic β cell line. Our data outline a biphasic response with a first transcriptional wave during which metabolic genes are activated, and a second wave where cell-cycle genes are activated and β cell identity genes are repressed. The glucose-sensing transcription factor ChREBP directly activates first wave enhancers, whereas repression and activation of second wave enhancers are indirect. By integrating motif enrichment within late-regulated enhancers with expression profiles of the associated transcription factors, we have identified multiple putative regulators of the second wave. These include RORγ, the activity of which is important for glucose-induced proliferation of both INS-1E and primary rat β cells.

Suppression of STAT5b in pancreatic cancer cells leads to attenuated gemcitabine chemoresistance, adhesion and invasion

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal solid malignancies, and there is an urgent need for new therapeutic strategies based on the molecular biology of PDAC. Signal transducers and activators of transcription 5 (STAT5) are known to be activated in a variety of malignancies and involved in tumor proliferation, apoptosis, and invasion, whereas the expression and biological role of STAT5b in PDAC are less clearly defined. In the present study, we examined the expression and role of STAT5b in human pancreatic cancer cell lines. Expressions of STAT5b mRNA and protein were detected in eight kinds of pancreatic cancer cells. Confocal microscopy and western blot analysis indicated that STAT5b is localized in both cytoplasm and nuclei. Immunoprecipitation analysis revealed tyrosine phosphorylation of STAT5b in pancreatic cancer cells. These results indicate that STAT5b in pancreatic cancer cells is constitutively activated. STAT5b shRNA clones in PANC-1 cells, which express relatively high levels of STAT5b, exhibited reduced chemoresistance against gemcitabine, adhesion and invasion compared to sham. On the other hand, AsPC-1 and BxPC3 cells, which express relatively low levels of STAT5b, exhibited reduced chemoresistance compared to PANC-1 cells. Moreover, STAT5b overexpression clones in AsPC-1 cells exhibited increased chemoresistance compared to sham. STAT5b shRNA clones in PANC-1 cells were more sensitive to the proapoptotic actions of gemcitabine, as evidenced by PARP and cleaved caspase-3 activation. Gemcitabine also significantly reduced Bcl-xL levels in the STAT5b shRNA-expressing cells. We also investigated the clinicopathological characteristics of STAT5b expression of PDAC. Although a significant correlation between STAT5b expression and overall survival rates was not observed, a significant correlation with main pancreatic duct invasion was observed. These findings suggest that STAT5b confers gemcitabine chemoresistance and promotes cell adherence and invasiveness in pancreatic cancer cells. Targeting STAT5b may lead to novel therapeutic strategies for PDAC.

Augmented Stat5 Signaling Bypasses Multiple Impediments to Lactogen-Mediated Proliferation in Human β-Cells

Pregnancy in rodents is associated with a two- to threefold increase in β-cell mass, which is attributable to large increases in β-cell proliferation, complimented by increases in β-cell size, survival, and function and mediated mainly by the lactogenic hormones prolactin (PRL) and placental lactogens. In humans, however, β-cell mass does not increase as dramatically during pregnancy, and PRL fails to activate proliferation in human islets in vitro. To determine why, we explored the human PRL-prolactin receptor (hPRLR)-Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5)-cyclin-cdk signaling cascade in human β-cells. Surprisingly, adult human β-cells express little or no PRLR. As expected, restoration of the hPRLR in human β-cells rescued JAK2-STAT5 signaling in response to PRL. However, rescuing hPRLR-STAT5 signaling nevertheless failed to confer proliferative ability on adult human β-cells in response to PRL. Surprisingly, mouse (but not human) Stat5a overexpression led to upregulation of cyclins D1-3 and cdk4, as well as their nuclear translocation, all of which are associated with β-cell cycle entry. Collectively, the findings show that human β-cells fail to proliferate in response to PRL for multiple reasons, one of which is a paucity of functional PRL receptors, and that murine Stat5 overexpression is able to bypass these impediments.

Islet insulin content and release are increased in male mice with elevated endogenous GH and IGF-I, without evidence of systemic insulin resistance or alterations in β-cell mass

It is clear that elevations in circulating GH can lead to an increase in insulin levels. This increase in insulin may be due to GH-mediated insulin resistance and enhanced lipolysis. However, there is also in vitro and in vivo evidence that GH acts directly to increase β-cell proliferation and insulin production. Our laboratory recently developed an animal model with elevated endogenous GH levels associated with a small (25%), but significant, increase in IGF-I (HiGH mice). As expected, insulin levels were elevated in HiGH mice; however, whole body insulin sensitivity was not altered and glucose tolerance was improved. This metabolic phenotype suggests that modest elevations in circulating GH and IGF-I may enhance β-cell mass and/or function, in the absence of systemic insulin resistance, thus improving glucose homeostasis.

OBJECTIVE

To determine if β-cell mass and/or function is altered in HiGH mice.

DESIGN

Male HiGH mice and their littermate controls were fed a low-fat or high-fat diet. Body composition and circulating metabolic endpoints were monitored overtime. The pancreas was recovered and processed for assessment of β-cell mass or in vitro basal and glucose-stimulated insulin secretion.

RESULTS

HiGH mice showed elevated circulating insulin and normal glucose levels, while non-esterified FFA levels and triglycerides were reduced or normal, depending on diet and age. β-cell mass did not differ between HiGH and control mice, within diet. However, islets from HiGH mice contained and released more insulin under basal conditions, as compared to control islets, while the relative glucose-stimulated insulin release did not differ.

CONCLUSIONS

Taken together, these results suggest moderate elevations in circulating GH and IGF-I can directly increase basal insulin secretion without impacting β-cell mass, independent of changes in whole body insulin sensitivity and hyperlipidemia.

The beneficial effect of growth hormone treatment on islet mass in streptozotocin-treated mice

BACKGROUND

Type 1 diabetes is an autoimmune disease, characterized by a loss of pancreatic β-cell mass and function, which results in dramatic reductions in insulin secretion and circulating insulin levels. Patients with type 1 diabetes are traditionally treated with insulin injections and insulin pumps ex vivo or undergo transplantation. Growth hormone (GH) has been shown to be involved in β-cell function and survival in culture.

METHODS

Twelve-week-old female C57BL/6 mice were treated with streptozotocin and monitored for their weight and blood glucose levels. Fourteen days post-initial injection, these mice were separated into two groups at random. One group was treated with GH while the other treated with vehicle for up to 3 weeks. These mice were compared with mice not treated with streptozotocin.

RESULTS

Under our experimental conditions, we observed that mice treated with GH had larger islets and higher serum insulin levels than streptozotocin-treated mice treated with saline (0.288 vs. 0.073 ng/mL, p < 0.01).

CONCLUSIONS

Our data demonstrate that GH may rescue islets and therefore may possess therapeutic potential in the treatment of type 1 diabetes, although consideration should be made regarding GH's effect on insulin resistance.

Human β-cell proliferation and intracellular signaling: part 3

This is the third in a series of Perspectives on intracellular signaling pathways coupled to proliferation in pancreatic β-cells. We contrast the large knowledge base in rodent β-cells with the more limited human database. With the increasing incidence of type 1 diabetes and the recognition that type 2 diabetes is also due in part to a deficiency of functioning β-cells, there is great urgency to identify therapeutic approaches to expand human β-cell numbers. Therapeutic approaches might include stem cell differentiation, transdifferentiation, or expansion of cadaver islets or residual endogenous β-cells. In these Perspectives, we focus on β-cell proliferation. Past Perspectives reviewed fundamental cell cycle regulation and its upstream regulation by insulin/IGF signaling via phosphatidylinositol-3 kinase/mammalian target of rapamycin signaling, glucose, glycogen synthase kinase-3 and liver kinase B1, protein kinase Cζ, calcium-calcineurin-nuclear factor of activated T cells, epidermal growth factor/platelet-derived growth factor family members, Wnt/β-catenin, leptin, and estrogen and progesterone. Here, we emphasize Janus kinase/signal transducers and activators of transcription, Ras/Raf/extracellular signal-related kinase, cadherins and integrins, G-protein-coupled receptors, and transforming growth factor β signaling. We hope these three Perspectives will serve to introduce these pathways to new researchers and will encourage additional investigators to focus on understanding how to harness key intracellular signaling pathways for therapeutic human β-cell regeneration for diabetes.

Impaired islet function in commonly used transgenic mouse lines due to human growth hormone minigene expression

The human growth hormone (hGH) minigene is frequently used in the derivation of transgenic mouse lines to enhance transgene expression. Although this minigene is present in the transgenes as a secondcistron, and thus not thought to be expressed, we found that three commonly used lines, Pdx1-Cre(Late), RIP-Cre, and MIP-GFP, each expressed significant amounts of hGH in pancreatic islets. Locally secreted hGH binds to prolactin receptors on β cells, activates STAT5 signaling, and induces pregnancy-like changes in gene expression, thereby augmenting pancreatic β cell mass and insulin content. In addition, islets of Pdx1-Cre(Late) mice have lower GLUT2 expression and reduced glucose-induced insulin release and are protected against the β cell toxin streptozotocin. These findings may be important when interpreting results obtained when these and other hGH minigene-containing transgenic mice are used.

Regulation of pancreatic islet beta-cell mass by growth factor and hormone signaling

Dysfunction and destruction of pancreatic islet beta cells is a hallmark of diabetes. Better understanding of cellular signals in beta cells will allow development of therapeutic strategies for diabetes, such as preservation and expansion of beta-cell mass and improvement of beta-cell function. During the past several decades, the number of studies analyzing the molecular mechanisms, including growth factor/hormone signaling pathways that impact islet beta-cell mass and function, has increased exponentially. Notably, somatolactogenic hormones including growth hormone (GH), prolactin (PRL), and insulin-like growth factor-1 (IGF-1) and their receptors (GHR, PRLR, and IGF-1R) are critically involved in beta-cell growth, survival, differentiation, and insulin secretion. In this chapter, we focus more narrowly on GH, PRL, and IGF-1 signaling, and GH-IGF-1 cross talk. We also discuss how these signaling aspects contribute to the regulation of beta-cell proliferation and apoptosis. In particular, our novel findings of GH-induced formation of GHR-JAK2-IGF-1R protein complex and synergistic effects of GH and IGF-1 on beta-cell signaling, proliferation, and antiapoptosis lead to a new concept that IGF-1R may serve as a proximal component of GH/GHR signaling.

Growth hormone prevents the development of autoimmune diabetes

Evidence supports a relationship between the neuroendocrine and the immune systems. Data from mice that overexpress or are deficient in growth hormone (GH) indicate that GH stimulates T and B-cell proliferation and Ig synthesis, and enhances maturation of myeloid progenitor cells. The effect of GH on autoimmune pathologies has nonetheless been little studied. Using a murine model of type 1 diabetes, a T-cell-mediated autoimmune disease characterized by immune cell infiltration of pancreatic islets and destruction of insulin-producing β-cells, we observed that sustained GH expression reduced prodromal disease symptoms and eliminated progression to overt diabetes. The effect involves several GH-mediated mechanisms; GH altered the cytokine environment, triggered anti-inflammatory macrophage (M2) polarization, maintained activity of the suppressor T-cell population, and limited Th17 cell plasticity. In addition, GH reduced apoptosis and/or increased the proliferative rate of β-cells. These results support a role for GH in immune response regulation and identify a unique target for therapeutic intervention in type 1 diabetes.

Gender-specific transcriptomic response to environmental exposure in Flemish adults

Flanders, Belgium, is one of the most densely populated areas in Europe. The Flemish Environment and Health Survey (2002-2006) aimed at determining exposure to pollutants of neonates, adolescents, and older adults and to assess associated biological and health effects. This study investigated genome wide gene expression changes associated with a range of environmental pollutants, including cadmium, lead, PCBs, dioxin, hexachlorobenzene, p,p'-DDE, benzene, and PAHs. Gene expression levels were measured in peripheral blood cells of 20 adults with relatively high and 20 adults with relatively low combined internal exposure levels, all non-smokers aged 50-65. Pearson correlation was used to analyze associations between pollutants and gene expression levels, separately for both genders. Pollutant- and gender-specific correlation analysis results were obtained. For organochlorine pollutants, analysis within genders revealed that genes were predominantly regulated in opposite directions in males and females. Significantly modulated pathways were found to be associated with each of the exposure biomarkers measured. Pathways and/or genes related to estrogen and STAT5 signaling were correlated to organochlorine exposures in both genders. Our work demonstrates that gene expression in peripheral blood is influenced by environmental pollutants. In particular, gender-specific changes are associated with organochlorine pollutants, including gender-specific modulation of endocrine related pathways and genes. These pathways and genes have previously been linked to endocrine disruption related disorders, which in turn have been associated with organochlorine exposure. Based on our results, we recommend that males and females be considered separately when analyzing gene expression changes associated with exposures that may include chemicals with endocrine disrupting properties.

Finding type 2 diabetes causal single nucleotide polymorphism combinations and functional modules from genome-wide association data

Background

Due to the low statistical power of individual markers from a genome-wide association study (GWAS), detecting causal single nucleotide polymorphisms (SNPs) for complex diseases is a challenge. SNP combinations are suggested to compensate for the low statistical power of individual markers, but SNP combinations from GWAS generate high computational complexity.

Methods

We aim to detect type 2 diabetes (T2D) causal SNP combinations from a GWAS dataset with optimal filtration and to discover the biological meaning of the detected SNP combinations. Optimal filtration can enhance the statistical power of SNP combinations by comparing the error rates of SNP combinations from various Bonferroni thresholds and p-value range-based thresholds combined with linkage disequilibrium (LD) pruning. T2D causal SNP combinations are selected using random forests with variable selection from an optimal SNP dataset. T2D causal SNP combinations and genome-wide SNPs are mapped into functional modules using expanded gene set enrichment analysis (GSEA) considering pathway, transcription factor (TF)-target, miRNA-target, gene ontology, and protein complex functional modules. The prediction error rates are measured for SNP sets from functional module-based filtration that selects SNPs within functional modules from genome-wide SNPs based expanded GSEA.

Results

A T2D causal SNP combination containing 101 SNPs from the Wellcome Trust Case Control Consortium (WTCCC) GWAS dataset are selected using optimal filtration criteria, with an error rate of 10.25%. Matching 101 SNPs with known T2D genes and functional modules reveals the relationships between T2D and SNP combinations. The prediction error rates of SNP sets from functional module-based filtration record no significance compared to the prediction error rates of randomly selected SNP sets and T2D causal SNP combinations from optimal filtration.

Conclusions

We propose a detection method for complex disease causal SNP combinations from an optimal SNP dataset by using random forests with variable selection. Mapping the biological meanings of detected SNP combinations can help uncover complex disease mechanisms.

STAT5b as molecular target in pancreatic cancer--inhibition of tumor growth, angiogenesis, and metastases

The prognosis of patients suffering from pancreatic cancer is still poor and novel therapeutic options are urgently needed. Recently, the transcription factor signal transducer and activator of transcription 5b (STAT5b) was associated with tumor progression in human solid cancer. Hence, we assessed whether STAT5b might serve as an anticancer target in ductal pancreatic adenocarcinoma (DPAC). We found that nuclear expression of STAT5b can be detected in approximately 50% of DPAC. Blockade of STAT5b by stable shRNA-mediated knockdown showed no effects on tumor cell growth in vitro. However, inhibition of tumor cell motility was found even in response to stimulation with epidermal growth factor or interleukin-6. These findings were paralleled by a reduction of prometastatic and proangiogenic factors in vitro. Subsequent in vivo experiments revealed a strong growth inhibition on STAT5b blockade in subcutaneous and orthotopic models. These findings were paralleled by impaired tumor angiogenesis in vivo. In contrast to the subcutaneous model, the orthotopic model revealed a strong reduction of tumor cell proliferation that emphasizes the meaning of assessing targets in an appropriate microenvironment. Taken together, our results suggest that STAT5b might be a potential novel target for human DPAC.

Over-expression of Stat5b confers protection against diabetes in the non-obese diabetic (NOD) mice via up-regulation of CD4(+)CD25(+) regulatory T cells

The signal transducers and activators of transcription (STAT) family of proteins play a critical role in cytokine signaling required for fine tuning of immune regulation. Previous reports showed that a mutation (L327M) in the Stat5b protein leads to aberrant cytokine signaling in the NOD mice. To further elaborate the role of Stat5b in diabetes, we established a NOD transgenic mouse that over-expresses the wild type Stat5b gene. The incidences of spontaneous diabetes as well as cyclophosphamide-induced diabetes were significantly reduced and delayed in the Stat5b transgenic NOD mice compared to their littermate controls. The total cell numbers of CD4(+) T cells and especially CD8(+) T cells in the spleen and pancreatic lymph node were increased in the Stat5b transgenic NOD mice. Consistent with these findings, CD4(+) and CD8(+) T cells from the Stat5b transgenic NOD mice showed a higher proliferation capacity and up-regulation of multiple cytokines including IL-2, IFN-γ, TNF-α and IL-10 as well as anti-apoptotic gene Bcl-xl. Furthermore, the number and proportion of CD4(+)CD25(+) regulatory T cells were significantly increased in transgenic mice although in vitro suppression ability of the regulatory T-cells was not affected by the transgene. Our results suggest that Stat5b confers protection against diabetes in the NOD mice by regulating the numbers and function of multiple immune cell types, especially by up-regulating CD4(+)CD25(+) regulatory T cells.

Lactogens protect rodent and human beta cells against glucolipotoxicity-induced cell death through Janus kinase-2 (JAK2)/signal transducer and activator of transcription-5 (STAT5) signalling

AIMS/HYPOTHESIS

A leading cause of type 2 diabetes is a reduction in functional beta cell mass partly due to increased beta cell death, triggered by stressors such as glucolipotoxicity (GLT). This study evaluates the hypothesis that lactogens can protect beta cells against GLT and examines the mechanism behind the pro-survival effect.

METHODS

The effect of exogenous treatment or endogenous expression of lactogens on GLT-induced beta cell death was examined in INS-1 cells, and in rodent and human islets. The mechanism behind the pro-survival effect of lactogens was determined using an inhibitor, siRNAs, a dominant negative (DN) mutant, and Cre-lox-mediated gene deletion analysis.

RESULTS

Lactogens significantly protect INS-1 and primary rodent beta cells against GLT-induced cell death. The pro-survival effect of lactogens in rodent beta cells is mediated through activation of the Janus kinase-2 (JAK2)/signal transducer and activator of transcription-5 (STAT5) signalling pathway. Lactogen-induced increase in the anti-apoptotic B cell lymphoma-extra large (BCLXL) protein is required to mediate its pro-survival effects in both INS-1 cells and primary rodent beta cells. Most importantly, lactogens significantly protect human beta cells against GLT-induced cell death, and their pro-survival effect is also mediated through the JAK2/STAT5 pathway.

CONCLUSIONS/INTERPRETATION

These studies, together with previous work, clearly demonstrate the pro-survival nature of lactogens and identify the JAK2/STAT5 pathway as an important mediator of this effect in both rodent and human beta cells. Future studies will determine the effectiveness of this peptide in vivo in the pathophysiology of type 2 diabetes.

Identification of a redox-sensitive switch within the JAK2 catalytic domain

Four cysteine residues (Cys866, Cys917, Cys1094, and Cys1105) have direct roles in cooperatively regulating Janus kinase 2 (JAK2) catalytic activity. Additional site-directed mutagenesis experiments now provide evidence that two of these residues (Cys866 and Cys917) act together as a redox-sensitive switch, allowing JAK2's catalytic activity to be directly regulated by the redox state of the cell. We created several variants of the truncated JAK2 (GST/(NΔ661)rJAK2), which incorporated cysteine-to-serine or cysteine-to-alanine mutations. The catalytic activities of these mutant enzymes were evaluated by in vitro autokinase assays and by in situ autophosphorylation and transphosphorylation assays. Cysteine-to-alanine mutagenesis revealed that the mechanistic role of Cys866 and Cys917 is functionally distinct from that of Cys1094 and Cys1105. Most notable is the observation that the robust activity of the CC866,917AA mutant is unaltered by pretreatment with dithiothreitol or o-iodosobenzoate, unlike all other JAK2 variants previously examined. This work provides the first direct evidence for a cysteine-based redox-sensitive switch that regulates JAK2 catalytic activity. The presence of this redox-sensitive switch predicts that reactive oxygen species can impair the cell's response to JAK-coupled cytokines under conditions of oxidative stress, which we confirm in a murine pancreatic β-islet cell line.

Enhanced exercise-induced muscle damage and muscle protein degradation in streptozotocin-induced type 2 diabetic rats

Aims/Introduction:  The effects of 5-day voluntary exercise on muscle damage and muscle protein degradation were investigated in a streptozotocin-induced rat model of moderately glycemic, uncontrolled, type 2 diabetes.

MATERIALS AND METHODS

  In the preliminary experiment, an oral glucose tolerance (1.0 g/kg) test was carried out to confirm the development of diabetes 3 days after streptozotocin treatment (30 mg/kg). In the genuine experiment, rats were divided into four groups: (i) non-diabetic rats without exercise (controls); (ii) non-diabetic rats with exercise; (iii) diabetic rats without exercise; and (iv) diabetic rats with exercise. After 5 days of voluntary wheel running exercise, blood and 24-h urine were collected, and levels of serum creatine kinase, a marker of muscle damage, and 24-h urinary excretion of muscle degradation products were determined.

RESULTS

  Type 2 diabetic rats with insulin deficiency that exercised had higher serum creatine kinase and greater urinary excretions of creatinine, urea nitrogen and 3-methylhistidine compared with both type 2 diabetic rats with insulin deficiency and non-diabetic rats that did not exercise. However, there were no differences in serum creatine kinase and urinary excretions of creatinine, urea nitrogen and 3-methylhistidine between non-diabetic rats that did and did not exercise.

CONCLUSIONS

  These findings suggest that muscle damage is induced and muscle protein degradation are enhanced by chronic moderate exercise in moderately glycemic uncontrolled type 2 diabetic rats with insulin deficiency at an intensity level of exercise that does not affect muscle damage and muscle protein degradation in non-diabetic rats. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00130.x, 2011).

Growth hormone receptor regulates β cell hyperplasia and glucose-stimulated insulin secretion in obese mice

Insulin, growth hormone (GH), and insulin-like growth factor-1 (IGF-1) play key roles in the regulation of β cell growth and function. Although β cells express the GH receptor, the direct effects of GH on β cells remain largely unknown. Here we have employed a rat insulin II promoter-driven (RIP-driven) Cre recombinase to disrupt the GH receptor in β cells (βGHRKO). βGHRKO mice fed a standard chow diet exhibited impaired glucose-stimulated insulin secretion but had no changes in β cell mass. When challenged with a high-fat diet, βGHRKO mice showed evidence of a β cell secretory defect, with further deterioration of glucose homeostasis indicated by their altered glucose tolerance and blunted glucose-stimulated insulin secretion. Interestingly, βGHRKO mice were impaired in β cell hyperplasia in response to a high-fat diet, with decreased β cell proliferation and overall reduced β cell mass. Therefore, GH receptor plays critical roles in glucose-stimulated insulin secretion and β cell compensation in response to a high-fat diet.

Sensitized phenotypic screening identifies gene dosage sensitive region on chromosome 11 that predisposes to disease in mice

The identification of susceptibility genes for human disease is a major goal of current biomedical research. Both sequence and structural variation have emerged as major genetic sources of phenotypic variability and growing evidence points to copy number variation as a particularly important source of susceptibility for disease. Here we propose and validate a strategy to identify genes in which changes in dosage alter susceptibility to disease-relevant phenotypes in the mouse. Our approach relies on sensitized phenotypic screening of megabase-sized chromosomal deletion and deficiency lines carrying altered copy numbers of ∼30 linked genes. This approach offers several advantages as a method to systematically identify genes involved in disease susceptibility. To examine the feasibility of such a screen, we performed sensitized phenotyping in five therapeutic areas (metabolic syndrome, immune dysfunction, atherosclerosis, cancer and behaviour) of a 0.8 Mb reciprocal chromosomal duplication and deficiency on chromosome 11 containing 27 genes. Gene dosage in the region significantly affected risk for high-fat diet-induced metabolic syndrome, antigen-induced immune hypersensitivity, ApoE-induced atherosclerosis, and home cage activity. Follow up studies on individual gene knockouts for two candidates in the region showed that copy number variation in Stat5 was responsible for the phenotypic variation in antigen-induced immune hypersensitivity and metabolic syndrome. These data demonstrate the power of sensitized phenotypic screening of segmental aneuploidy lines to identify disease susceptibility genes.

Effect of catch-up growth after food restriction on the entero-insular axis in rats

BACKGROUND

Catch-up growth after food restriction (CUGFR) is characterized by a significant change in food intake which could theoretically lead to the change in glucagon-like peptide-1 (GLP-1) secretion that consequently results in altered functions of pancreatic islets.

METHODS

Experimental rats were divided into two groups. Rats in CUGFR group were put on food-restriction for 4 weeks, and then allowed full access to food for 0, 2, 4 weeks respectively while rats in the control group were offered ad libitum access to food. Plasma glucose, insulin and GLP-1 level during OGTT were measured in all the rats. Moreover, morphology of intestinal mucosa, number of L cells, beta cell mass, incretin effect and the expression of GLP-1 receptor (GLP-1R) gene in the islets were also determined.

RESULTS

The size of pancreatic islets, insulin concentration, plasma GLP-1 concentration, incretin effect, villus height-to-crypt depth ratio and L cells were all significantly decreased in CUGFR group at the end of a 4-week food-restriction period as compared with the controls. Insulin concentration and the villus height-to-crypt depth ratio were increased and finally exceeded the level of the control group over a 4-week catch-up period. Nevertheless, at the conclusion of the study, islet size, L cells number, plasma GLP-1 concentration and incretin effect increased but failed to reach the levels of the controls.

CONCLUSION

CUGFR decreases incretin effect and disturbs the entero-insular axis partially by decreasing GLP-1 concentration, which might be responsible for the increased risk of metabolic disorder during CUGFR.

Cyclin D2 protein stability is regulated in pancreatic beta-cells

The molecular determinants of beta-cell mass expansion remain poorly understood. Cyclin D2 is the major D-type cyclin expressed in beta-cells, essential for adult beta-cell growth. We hypothesized that cyclin D2 could be actively regulated in beta-cells, which could allow mitogenic stimuli to influence beta-cell expansion. Cyclin D2 protein was sharply increased after partial pancreatectomy, but cyclin D2 mRNA was unchanged, suggesting posttranscriptional regulatory mechanisms influence cyclin D2 expression in beta-cells. Consistent with this hypothesis, cyclin D2 protein stability is powerfully regulated in fibroblasts. Threonine 280 of cyclin D2 is phosphorylated, and this residue critically limits D2 stability. We derived transgenic (tg) mice with threonine 280 of cyclin D2 mutated to alanine (T280A) or wild-type cyclin D2 under the control of the insulin promoter. Cyclin D2 T280A protein was expressed at much higher levels than wild-type cyclin D2 protein in beta-cells, despite equivalent expression of tg mRNAs. Cyclin D2 T280A tg mice exhibited a constitutively nuclear cyclin D2 localization in beta-cells, and increased cyclin D2 stability in islets. Interestingly, threonine 280-mutant cyclin D2 tg mice had greatly reduced beta-cell apoptosis, with suppressed expression of proapoptotic genes. Suppressed beta-cell apoptosis in threonine 280-mutant cyclin D2 tg mice resulted in greatly increased beta-cell area in aged mice. Taken together, these data indicate that cyclin D2 is regulated by protein stability in pancreatic beta-cells, that signals that act upon threonine 280 limit cyclin D2 stability in beta-cells, and that threonine 280-mutant cyclin D2 overexpression prolongs beta-cell survival and augments beta-cell mass expansion.

Regulation of beta cell replication

Beta cell mass, at any given time, is governed by cell differentiation, neogenesis, increased or decreased cell size (cell hypertrophy or atrophy), cell death (apoptosis), and beta cell proliferation. Nutrients, hormones and growth factors coupled with their signalling intermediates have been suggested to play a role in beta cell mass regulation. In addition, genetic mouse model studies have indicated that cyclins and cyclin-dependent kinases that determine cell cycle progression are involved in beta cell replication, and more recently, menin in association with cyclin-dependent kinase inhibitors has been demonstrated to be important in beta cell growth. In this review, we consider and highlight some aspects of cell cycle regulation in relation to beta cell replication. The role of cell cycle regulation in beta cell replication is mostly from studies in rodent models, but whether these findings can be extended to human beta cells remains to be shown.

The interplay of prolactin and the glucocorticoids in the regulation of beta-cell gene expression, fatty acid oxidation, and glucose-stimulated insulin secretion: implications for carbohydrate metabolism in pregnancy

Carbohydrate metabolism in pregnancy reflects the balance between counterregulatory hormones, which induce insulin resistance, and lactogenic hormones, which stimulate beta-cell proliferation and insulin production. Here we explored the interactions of prolactin (PRL) and glucocorticoids in the regulation of beta-cell gene expression, fatty acid oxidation, and glucose-stimulated insulin secretion (GSIS). In rat insulinoma cells, rat PRL caused 30-50% (P < 0.001) reductions in Forkhead box O (FoxO)-1, peroxisome proliferator activator receptor (PPAR)-gamma coactivator-1alpha (PGC-1alpha), PPARalpha, and carnitine palmitoyltransferase 1 (CPT-1) mRNAs and increased Glut-2 mRNA and GSIS; conversely, dexamethasone (DEX) up-regulated FoxO1, PGC1alpha, PPARalpha, CPT-1, and uncoupling protein 2 (UCP-2) mRNAs in insulinoma cells and inhibited GSIS. Hydrocortisone had similar effects. The effects of DEX were attenuated by coincubation of cells with PRL. In primary rat islets, PRL reduced FoxO1, PPARalpha, and CPT-1 mRNAs, whereas DEX increased FoxO1, PGC1alpha, and UCP-2 mRNAs. The effects of PRL on gene expression were mimicked by constitutive overexpression of signal transducer and activator of transcription-5b. PRL induced signal transducer and activator of transcription-5 binding to a consensus sequence in the rat FoxO1 promoter, reduced nuclear FoxO1 protein levels, and induced its phosphorylation and cytoplasmic redistribution. DEX increased beta-cell fatty acid oxidation and reduced fatty acid esterification; these effects were attenuated by PRL. Thus, lactogens and glucocorticoids have opposing effects on a number of beta-cell genes including FoxO1, PGC1alpha, PPARalpha, CPT-1, and UCP-2 and differentially regulate beta-cell Glut-2 expression, fatty acid oxidation, and GSIS. These observations suggest new mechanisms by which lactogens may preserve beta-cell mass and function and maternal glucose tolerance despite the doubling of maternal cortisol concentrations in late gestation.

STAT5 activity in pancreatic β-cells

Signal transducer and activator of transcription (STAT)5A and -5B are latent transcription factors activated by cytokines and hormones of the cytokine family. In pancreatic insulin-secreting β-cells, STAT5A and -5B are activated primarily by prolactin and growth hormone stimulation and are important mediators of the potent stimulation of proliferation and insulin production caused by these hormones. STAT5A and -5B are both expressed in β-cells and control the expression of a number of mRNAs implicated in cell replication control, insulin biosynthesis and secretion. In addition to STAT5A and -5B being transcriptional activators, they may also repress gene transcription. By these means, STAT5 proteins increase the levels of anti-apoptotic transcripts in β-cells and repress expression of pro-apoptotic genes. This review focuses on the anti-apoptotic role of STAT5 signaling, providing a mechanism for β-cell resistance to pro-apoptotic cytokines, Type 1 diabetes mellitus and obesity-associated β-cell stress. It is clear from studies of STAT5 signaling in pancreatic β-cells that STAT5 is important for postnatal β-cell compensatory growth (as in pregnancy or obesity) and in the defense against β-cell stress factors.

The role of FoxO in the regulation of metabolism

Forkhead proteins, and FoxO1 in particular, play a significant role in regulating whole body energy metabolism. Glucose homeostasis is achieved by adjusting endogenous glucose production as well as glucose uptake by peripheral tissues in response to insulin. In the fasted state, the liver is primarily responsible for maintaining glucose levels, with FoxO1 playing a key role in promoting the expression of gluconeogenic enzymes. Following feeding, pancreatic beta cells secrete insulin, which promotes the uptake of glucose by peripheral tissues including skeletal muscle and adipose tissue, and can in part suppress gluconeogenic enzyme expression in the liver. In addition to directly regulating metabolism, FoxO1 also plays a role in the formation of both adipose tissue and skeletal muscle, two major organs that are critical for maintaining energy homeostasis. The importance of FoxO1 in energy homeostasis is particularly striking under conditions of metabolic dysfunction or insulin resistance. In obese or diabetic states, FoxO1-dependent gene expression promotes some of the deleterious characteristics associated with these conditions, including hyperglycemia and glucose intolerance. In addition, the increase in pancreatic beta cell mass that normally occurs in response to a rise in insulin demand is blunted by nuclear FoxO1 expression. However, under these same pathophysiological conditions, FoxO1 expression may help drive the expression of genes involved in combating oxidative stress, thereby preserving cellular function. FoxO1 may also be involved in promoting the switch from carbohydrate to fatty acid as the major energy source during starvation.

The transcription factors Stat5a/b are not required for islet development but modulate pancreatic beta-cell physiology upon aging

In insulinoma cell lines proliferation and insulin gene transcription are stimulated by growth hormone and prolactin, which convey their signals through the transcription factors Stat5a and 5b (referred to as Stat5). However, the contribution of Stat5 to the physiology of beta-cells in vivo could not be assessed directly since Stat5-null mice die perinataly. To explore the physiological role of Stat5 in the mouse, the corresponding gene locus targeted with loxP sites was inactivated in beta-cells using two lines of Cre recombinase expressing transgenic mice. While the RIP-Cre transgene is active in pancreatic beta-cells and the hypothalamus, the Pdx1-Cre transgene is active in precursor cells of the endocrine and exocrine pancreas. Mice carrying two floxed Stat5alleles and a RIP-Cre transgene developed mild obesity, were hyperglycemic and exhibited impaired glucose tolerance. Since RIP-Cre transgenic mice by themselves display some glucose intolerance, the significance of these data is unclear. In contrast, mice, in which the Stat5 locus had been deleted with the Pdx1-Cre transgene, developed functional islets and were glucose tolerant. Mild glucose intolerance occurred with age. We conclude that Stat5 is not essential for islet development but may modulate beta-cell function.