Promote Beta Cell Research Articles

2066-P: Dyrk1a Antisense Oligonucleotides Conjugated to GLP-1R Agonist Promote Pancreatic Beta-Cell Proliferation

Loss of functional beta cell mass is a major contributor to the pathogenesis of both type 1 and type 2 diabetes. Enhancing proliferation of existing beta cells in the pancreatic islet is one of the promising approaches for restoring functional beta cell mass. Increasing evidence indicates inhibition of dual specificity tyrosine-phosphorylation-regulated kinase 1A (Dyrk1a) stimulates beta cell proliferation. However, to date DYRK1a small molecule inhibitors have not been therapeutically viable due to their ability to increase proliferation in peripheral tissues. Previously we demonstrated that generation 2.5 antisense oligonucleotides (ASO) conjugated to a glucagon like peptide 1 receptor (GLP-1R) agonist can specifically target the pancreatic beta cell. When compared to control ASO treated isolated islets, islets administered a GLP-1/Dyrk1a ASO conjugate reduces DYRK1a mRNA and protein expression and significantly increases Ki67 mRNA, a cell proliferation marker, in a dose-response manner in vitro. Furthermore, combination treatment of a GLP-1/Dyrk1a ASO conjugate and the small molecule TGF-β inhibitor Ly364947, can synergistically increase Ki67 mRNA expression, cell cycle progression markers cyclin D1, cyclin E2, Cdk1, Cdk4 mRNAs and beta cell markers Pdx1 and Glut2 mRNAs when compared to a DYRK1a conjugated ASO or Ly364947 alone. Administration of a Dyrk1a conjugated ASO to wild type and db/db mice reduced Dyrk1a mRNA and increased Ki67 mRNA expression in islets when compared to a control ASO. Cell cycle markers cyclin D2, cyclin E2 and Cdk1 mRNAs are also significantly upregulated. In conclusion, a GLP-1/Dyrk1a ASO conjugate can specifically inhibit beta cell Dyrk1a mRNA expression and promote beta cell proliferation, suggesting that this may be an important approach for the treatment of type 1 and type 2 diabetes. Disclosure W. Fu: Employee; Self; Ionis Pharmaceuticals, Inc. R. Lee: Employee; Self; Ionis Pharmaceuticals, Inc. E.C. Pirie: Employee; Self; Ionis Pharmaceuticals, Inc. T. Prakash: None. S. Murray: Employee; Self; Ionis Pharmaceuticals. A. Powers: Employee; Self; Ionis Pharmaceuticals, Inc. Stock/Shareholder; Self; Ionis Pharmaceuticals, Inc. A.E. Mullick: None. R.M. Crooke: Employee; Self; Ionis Pharmaceuticals, Inc. Employee; Spouse/Partner; Ionis Pharmaceuticals, Inc.

Luseogliflozin increases beta cell proliferation through humoral factors that activate an insulin receptor- and IGF-1 receptor-independent pathway.

Sodium-glucose cotransporter 2 (SGLT2) inhibitors, which prevent the renal reabsorption of glucose, decrease blood glucose levels in an insulin-independent manner. We previously reported creating a mouse model of systemic inhibition of target receptors for both insulin and IGF-1 by treating animals with OSI-906, a dual insulin/IGF-1 receptor inhibitor, for 7days. The OSI-906-treated mice exhibited an increased beta cell mass, hepatic steatosis and adipose tissue atrophy, accompanied by hyperglycaemia and hyperinsulinaemia. In the present study, we investigated the effects of an SGLT2 inhibitor, luseogliflozin, on these changes in OSI-906-treated mice. We treated C57BL/6J male mice either with vehicle, luseogliflozin, OSI-906 or OSI-906 plus luseogliflozin for 7days, and phenotyping was performed to determine beta cell mass and proliferation. Subsequently, we tested whether serum-derived factors have an effect on beta cell proliferation in genetically engineered beta cells, mouse islets or human islets. SGLT2 inhibition with luseogliflozin significantly ameliorated hyperglycaemia, but not hyperinsulinaemia, in the OSI-906-treated mice. Liver steatosis and adipose tissue atrophy induced by OSI-906 were not altered by treatment with luseogliflozin. Beta cell mass and proliferation were further increased by SGLT2 inhibition with luseogliflozin in the OSI-906-treated mice. Luseogliflozin upregulated gene expression related to the forkhead box M1 (FoxM1)/polo-like kinase 1 (PLK1)/centromere protein A (CENP-A) pathway in the islets of OSI-906-treated mice. The increase in beta cell proliferation was recapitulated in a co-culture of Irs2 knockout and Insr/IR knockout (βIRKO) beta cells with serum from both luseogliflozin- and OSI-906-treated mice, but not after SGLT2 inhibition in beta cells. Circulating factors in both luseogliflozin- and OSI-906-treated mice promoted beta cell proliferation in both mouse islets and cadaveric human islets. These results suggest that luseogliflozin can increase beta cell proliferation through the activation of the FoxM1/PLK1/CENP-A pathway via humoral factors that act in an insulin/IGF-1 receptor-independent manner.

Vitamin D and Diabetes Mellitus

Through its regulatory effects on pancreatic beta cells and immune cells, vitamin D demonstrates the ability to positively influence insulin sensitivity, enhance insulin secretion, decrease systematic inflammation and promote beta cell longevity. These effects cumulatively link vitamin D to diabetes mellitus (DM) and therefore imply that this steroid hormone (vitamin D) may play a role in the prevention or even treatment of the diabetes. Evidence from research has already established an inverse relationship between vitamin D and diabetes mellitus. Therefore, the aim of this review is to discuss the influencing role of vitamin D in the prevention of type 1 and 2 diabetes mellitus and to briefly present supporting evidence on the relationship between types 1 and 2 diabetes and vitamin D.

Prevalence of leukocytes in type 2 diabetic patients in Erbil City

Background: Diabetes mellitus (DM) has become a global health concern affecting children, youth, and adults. Type 2 DM (T2DM) is considered an inflammatory disease as inflammation can trigger the insulin signaling, assumingly by promoting beta cell death. Objectives: This comparative study has been conducted on white blood cells in diabetic patients to examine the relationship between inflammation and blood glucose levels. Methods: Blood samples from both males and females were obtained randomly and measured at Rizgary Teaching Hospital and Media Laboratory in Erbil City during October 2015 till March 2016. Blood glucose levels and different types of leukocytes were measured in T2DM patients and compared with nondiabetic patients. Results: The results showed an increment in the percentage of monocytes and neutrophils in diabetic females and a decrement in the percentage of lymphocytes as compared to controls, in contrast to diabetic males where an increment in the percentage of monocytes and lymphocytes was found. Conclusions: It has been proven by this study that leucocyte count is elevated in diabetic patients, in reference to the hyperactivated immune system in such people. However, the results revealed that the inflammatory system showed a significant difference between diabetic and nondiabetic people, reflecting on the importance of such system in the response of a body to the lack of control over blood glucose.

Sufu- and Spop-mediated downregulation of Hedgehog signaling promotes beta cell differentiation through organ-specific niche signals

Human embryonic stem cell-derived beta cells offer a promising cell-based therapy for diabetes. However, efficient stem cell to beta cell differentiation has proven difficult, possibly due to the lack of cross-talk with the appropriate mesenchymal niche. To define organ-specific niche signals, we isolated pancreatic and gastrointestinal stromal cells, and analyzed their gene expression during development. Our genetic studies reveal the importance of tightly regulated Hedgehog signaling in the pancreatic mesenchyme: inactivation of mesenchymal signaling leads to annular pancreas, whereas stroma-specific activation of signaling via loss of Hedgehog regulators, Sufu and Spop, impairs pancreatic growth and beta cell genesis. Genetic rescue and transcriptome analyses show that these Sufu and Spop knockout defects occur through Gli2-mediated activation of gastrointestinal stromal signals such as Wnt ligands. Importantly, inhibition of Wnt signaling in organoid and human stem cell cultures significantly promotes insulin-producing cell generation, altogether revealing the requirement for organ-specific regulation of stromal niche signals.

Phlda3 regulates beta cell survival during stress

The loss of functional beta cell mass characterises all forms of diabetes. Beta cells are highly susceptible to stress, including cytokine, endoplasmic reticulum (ER) and oxidative stress. This study examined the role of pleckstrin homology-like, domain family A, member 3 (Phlda3) in beta cell survival under stress conditions and the regulatory basis. We found that the mRNA levels of Phlda3 were markedly upregulated in vivo in the islets of diabetic humans and mice. In vitro, exposure of MIN6 cells or islets to cytokines, palmitate, thapsigargin or ribose upregulated Phlda3 mRNA and protein levels, concurrent with the induction of ER stress (Ddit3 and Trb3) and antioxidant (Hmox1) genes. Furthermore, H2O2 treatment markedly increased PHLDA3 immunostaining in human islets. Phlda3 expression was differentially regulated by adaptive (Xbp1) and apoptotic (Ddit3) unfolded protein response (UPR) mediators. siRNA-mediated knockdown of Xbp1 inhibited the induction of Phlda3 by cytokines and palmitate, whereas knockdown of Ddit3 upregulated Phlda3. Moreover, knockdown of Phlda3 potentiated cytokine-induced apoptosis in association with upregulation of inflammatory genes (iNos, IL1β and IκBα) and NFκB phosphorylation and downregulation of antioxidant (Gpx1 and Srxn1) and adaptive UPR (Xbp1, Hspa5 and Fkbp11) genes. Knockdown of Phlda3 also potentiated apoptosis under oxidative stress conditions induced by ribose treatment. These findings suggest that Phlda3 is crucial for beta cell survival under stress conditions. Phlda3 regulates the cytokine, oxidative and ER stress responses in beta cells via the repression of inflammatory gene expression and the maintenance of antioxidant and adaptive UPR gene expression. Phlda3 may promote beta cell survival in diabetes.

CREB Promotes Beta Cell Gene Expression by Targeting Its Coactivators to Tissue-Specific Enhancers.

CREB mediates effects of cyclic AMP on cellular gene expression. Ubiquitous CREB target genes are induced following recruitment of CREB and its coactivators to promoter proximal binding sites. We found that CREB stimulates the expression of pancreatic beta cell-specific genes by targeting CBP/p300 to promoter-distal enhancer regions. Subsequent increases in histone acetylation facilitate recruitment of the coactivators CRTC2 and BRD4, leading to release of RNA polymerase II over the target gene body. Indeed, CREB-induced hyperacetylation of chromatin over superenhancers promoted beta cell-restricted gene expression, which is sensitive to inhibitors of CBP/p300 and BRD4 activity. Neurod1 appears critical in establishing nucleosome-free regions for recruitment of CREB to beta cell-specific enhancers. Deletion of a CREB-Neurod1-bound enhancer within the Lrrc10b-Syt7 superenhancer disrupted the expression of both genes and decreased beta cell function. Our results demonstrate how cross talk between signal-dependent and lineage-determining factors promotes the expression of cell-type-specific gene programs in response to extracellular cues.

Articles of Significant Interest in This Issue

This article refers to:MafB Is Important for Pancreatic β-Cell Maintenance under a MafA-Deficient ConditionCREB Promotes Beta Cell Gene Expression by Targeting Its Coactivators to Tissue-Specific Enhancers

363-OR: ChREBP-Beta Controls Both Proliferation and Cell Death of Pancreatic Beta Cells

Glucose is a key physiological driver of adaptive beta cell mass expansion, promoting beta cell proliferation both in vitro and in vivo. Carbohydrate response element binding protein β (ChREBPβ) is upregulated in response to glucose and is required for glucose-stimulated beta cell proliferation. To study the role of ChREBPβ in beta cells, we knocked out (KO) or overexpressed (OE) ChREBPβ in mouse pancreatic beta cells using Cre LoxP approaches with either MIP-CreERT (induced by tamoxifen at 3 months of age), or the RIP-Cre model which leads to recombination specifically in β cells, early during embryogenesis (E9). We performed intraperitoneal glucose tolerance tests (IPGTTs) and assessed pancreata for proliferation (Ki67), cell death (TUNEL) and beta cell mass in the 4 mouse models. ChREBPβ MIP-CreERT KO mice displayed impaired glucose tolerance, with an increase of 25.3 ± 7.9% (N=3-4, P<0.05) in the area under the curve (AUC) of IPGTT. Heterozygous or complete Chrebpβ KOs in the RIP-Cre model resulted in an increase in the AUC of IPGTT compared with control littermates (20.1 ± 13.7% and 56 ± 7.1%, respectively; n=2-4). Beta cells from isolated ChREBPβ KO islets had 60.4 ± 17.4% less proliferation compared to control islets in 6 mM glucose, and 22.9 ± 2.4% (P<0.05, N=5) less in 20 mM glucose. Inducible OE of ChREBPβ resulted in 97.7 ± 6% increase in AUC of IPGTT (N=3, p<0.01) and fasting blood glucose levels were increased by 89 ± 13.2% (P<0.01). Similarly, when ChREBPβ was OE early in the embryogenesis of β cells, we observed AUC for GTT was increased by 2.4 ± 0.5 fold compared to non-Cre expressing litter mates (N=5, p<0.05). In both mouse models, the OE of ChREBPβ resulted in β cell death as assessed by TUNEL along with increased in Ki67 staining. Remarkably, the RIP-Cre mice had almost no remaining β cells at 4 months of age and were overtly diabetic. Taken these data together, we propose a molecular regulatory mechanism where ChREBPβ controls both beta cell proliferation and cell death depending on its abundance. Disclosure L.S. Katz: None. G. Brill: None. M.A. Herman: None. D. Scott: None. Funding National Institutes of Health

Bromodomain inhibition instructs macrophages to promote beta cell proliferation and suppress autoimmune diabetes

Abstract A hallmark of autoimmune type 1 diabetes (T1D) is the decline of beta cell mass. Any regimen to promote beta cell expansion will have a great therapeutic promise. We have previously demonstrated that an epigenetic inhibitor targeting BET proteins (I-BET) promotes beta cell proliferation in an animal model of T1D. However, the underlying mechanisms remains unknown. Using both gain-of and loss-of function assays, we demonstrate that macrophages play an indispensable role in I-BET-elicited beta cell proliferation. In vivo ablation of macrophages significantly abolishes, while the supplementation of I-BET preconditioned macrophages enhances, I-BET induced beta cell proliferation. On a molecular level, elevated production of platelet-derived growth factor (PDGF) in I-BET treated macrophages mobilizes PDGFR signaling in beta cells. In summary, these findings reveal a novel strategy to expand beta cells by harnessing macrophages.

Cellular proliferation in mouse and human pancreatic islets is regulated by serpin B13 inhibition and downstream targeting of E-cadherin by cathepsin L.

We previously reported that exposure to antibodies neutralising serpin B13, a protease inhibitor expressed in exocrine pancreatic ducts, promotes beta cell proliferation, underscoring the importance of a functional relationship between exocrine and endocrine pancreas. The aim of the present study was to identify the molecular events that link inhibition of serpin B13 to islet cell proliferation. We used an in vitro culture system consisting of isolated pancreatic islets, an extract of pancreatic ductal epithelium and a monoclonal antibody (mAb) to serpin B13 or IgG isotype control. In vivo studies involved treatment of mice with these mAbs. The catalytic activity of cathepsin L (CatL), a cysteine protease target of serpin B13, was augmented in the pancreas of mice injected with serpin B13 mAb. Furthermore, the addition of serpin B13 mAb to the islets, together with the pancreatic ductal epithelium lysate, caused CatL-dependent cleavage of E-cadherin and concomitant upregulation of REG genes, ultimately leading to beta cell proliferation. Direct blockade of E-cadherin with mAb also markedly enhanced REG gene induction, while chemical inhibition of β-catenin, a binding target of E-cadherin, prevented the serpin B13 mAb-induced upregulation of REG genes. Our work implicates the CatL-E-cadherin-REG pathway in the regulation of islet cell proliferation in response to signals generated in exocrine pancreatic tissue and demonstrates that protease activity may promote adaptive changes in the islets. Microarray data that support the findings of this study have been deposited in Gene Expression Omnibus (GEO) with the accession no. GSE125151.

The transcription factor STAT6 plays a critical role in promoting beta cell viability and is depleted in islets of individuals with type 1 diabetes

Aims/hypothesisIn type 1 diabetes, selective beta cell loss occurs within the inflamed milieu of insulitic islets. This milieu is generated via the enhanced secretion of proinflammatory cytokines and by the loss of anti-inflammatory molecules such as IL-4 and IL-13. While the actions of proinflammatory cytokines have been well-studied in beta cells, the effects of their anti-inflammatory counterparts have received relatively little attention and we have addressed this.MethodsClonal beta cells, isolated human islets and pancreas sections from control individuals and those with type 1 diabetes were employed. Gene expression was measured using targeted gene arrays and by quantitative RT-PCR. Protein expression was monitored in cell extracts by western blotting and in tissue sections by immunocytochemistry. Target proteins were knocked down selectively with interference RNA.ResultsCytoprotection achieved with IL-4 and IL-13 is mediated by the early activation of signal transducer and activator of transcription 6 (STAT6) in beta cells, leading to the upregulation of anti-apoptotic proteins, including myeloid leukaemia-1 (MCL-1) and B cell lymphoma-extra large (BCLXL). We also report the induction of signal regulatory protein-α (SIRPα), and find that knockdown of SIRPα is associated with reduced beta cell viability. These anti-apoptotic proteins and their attendant cytoprotective effects are lost following siRNA-mediated knockdown of STAT6 in beta cells. Importantly, analysis of human pancreas sections revealed that STAT6 is markedly depleted in the beta cells of individuals with type 1 diabetes, implying the loss of cytoprotective responses.Conclusions/interpretationSelective loss of STAT6 may contribute to beta cell demise during the progression of type 1 diabetes.

Innate immune priming of insulin secretion.

Increasing evidence suggests a role for the immune system to finely tune metabolic homeostasis. The possibility that the immune system can likewise regulate islet endocrine function has only commenced drawing attention. Islet beta cells are the main producers of insulin and have to dynamically respond to fluctuating insulin demands of the body. While inflammation has long been considered as an important pathogenic feature of diabetes development, pioneer studies have shown that immune cells reside inside pancreatic islets under steady state and that components of the immune system can promote beta cell insulin production. The present review will thus highlight the recent research on specific immune pathways regulating beta cell function discussing the beneficial influence of innate immune cells.

Novel Small Molecule TXNIP Inhibitor Protects Against Diabetes

Loss of functional beta cell mass represents a major factor in the pathogenesis of diabetes. Currently, there are no therapies that halt this process; however, thioredoxin-interacting protein (TXNIP) has recently emerged as a promising therapeutic target. TXNIP was found to be the top glucose-induced gene in a human pancreatic islet microarray, is increased in diabetes, and TXNIP overexpression results in beta cell apoptosis. TXNIP reduction has shown favorable effects in vivo, where whole body TXNIP-deficient and beta cell-specific TXNIP knockout mice have decreased beta cell apoptosis, increased beta cell mass, elevated insulin levels, and are protected from diabetes. We have also shown that pharmacologic TXNIP inhibition, via the anti-hypertensive medication verapamil, was able to mimic the protective effects of genetic TXNIP deletion and reversed overt diabetes in mice. In addition, it has been established that TXNIP downregulation is beneficial in multiple tissues, making it unnecessary and even undesirable to have a beta cell-specific TXNIP inhibitor and suggesting that detrimental off target effects are unlikely. We have since undertaken a high-throughput screen of 300,000 small molecules that has yielded a novel compound, TI-37330, which is more effective than verapamil in inhibiting TXNIP expression. Moreover, TI-37330 protected primary human islets and INS-1 beta cells against glucose- and cytokine-induced TXNIP and beta cell apoptosis. TI-37330 has also shown in vivo potential as it was found to have good pharmacokinetic properties and was well tolerated in healthy mice. In the context of streptozotocin-induced diabetes, oral administration of TI-37330 promoted beta cell survival, prevented diabetes, and even significantly improved overt diabetes. Collectively, these data establish small molecule TXNIP inhibitors, especially TI-37330, as robust candidates for further development. Disclosure L. Thielen: None. J. Chen: None. G. Xu: None. G. Jing: None. T. Grayson: None. S. Jo: None. A. Shalev: None.

Mir-128 Targets Thioredoxin-Interacting Protein 3’UTR and Downregulates Its Expression in Pancreatic Beta Cells

Thioredoxin-interacting protein (TXNIP) expression is induced by glucose, promotes beta cell apoptosis and is essential for glucotoxicity-induced beta cell death, whereas TXNIP deficiency protects against diabetes. Carbohydrate-response element-binding protein (ChREBP/MondoA) is the major transcription factor conferring glucose-induced TXNIP expression. However, we recently discovered that glucose was still able to induce TXNIP in ChREBP knockout mouse islets suggesting the existence of other factors involved in glucose-induced TXNIP regulation. Analyses of the TXNIP 3’UTR revealed several potential miRNA binding sites including miR-93, miR-106b and miR-128. However, using INS-1 beta cells, primary mouse islets and T2D human islets, we found that only miR-128 was downregulated by glucose or diabetes. This suggested that glucose might decrease miR-128 and thereby promote TXNIP expression. In fact, we found overexpression of miR-128 significantly reduced TXNIP mRNA and protein expression whereas inhibition of miR-128 increased beta cell TXNIP expression. Furthermore, luciferase assays using reporter constructs with the wild type TXNIP 3’UTR or a mutated TXNIP 3’UTR confirmed that TXNIP is indeed a direct target of miR-128. Taken together, the results of these studies have identified a novel microRNA directly targeting TXNIP and revealed an alternative, post-transcriptional pathway by which glucose induces TXNIP expression. Disclosure G. Jing: None. J. Chen: None. G. Xu: None. A. Shalev: None.

LRH-1 agonism favours an immune-islet dialogue which protects against diabetes mellitus

Type 1 diabetes mellitus (T1DM) is due to the selective destruction of islet beta cells by immune cells. Current therapies focused on repressing the immune attack or stimulating beta cell regeneration still have limited clinical efficacy. Therefore, it is timely to identify innovative targets to dampen the immune process, while promoting beta cell survival and function. Liver receptor homologue-1 (LRH-1) is a nuclear receptor that represses inflammation in digestive organs, and protects pancreatic islets against apoptosis. Here, we show that BL001, a small LRH-1 agonist, impedes hyperglycemia progression and the immune-dependent inflammation of pancreas in murine models of T1DM, and beta cell apoptosis in islets of type 2 diabetic patients, while increasing beta cell mass and insulin secretion. Thus, we suggest that LRH-1 agonism favors a dialogue between immune and islet cells, which could be druggable to protect against diabetes mellitus.

I scream, you scream, we all scream for irisin

Skeletal muscle may communicate with pancreatic beta cells through irisin, a muscle-derived hormone that promotes beta cell survival and insulin release.

Homology modeling of FFA2 identifies novel agonists that potentiate insulin secretion

Critical aspects of maintaining glucose homeostasis in the face of chronic insulin resistance and type 2 diabetes (T2D) are increased insulin secretion and adaptive expansion of beta cell mass. Nutrient...

Combined Oral Administration of GABA and DPP-4 Inhibitor Prevents Beta Cell Damage and Promotes Beta Cell Regeneration in Mice.

γ-aminobutyric acid (GABA) or glucagon-like peptide-1 based drugs, such as sitagliptin (a dipeptidyl peptidase-4 inhibitor), were shown to induce beta cell regenerative effects in various diabetic mouse models. We propose that their combined administration can bring forth an additive therapeutic effect. We tested this hypothesis in a multiple low-dose streptozotocin (STZ)-induced beta cell injury mouse model (MDSD). Male C57BL/6J mice were assigned randomly into four groups: non-treatment diabetic control, GABA, sitagliptin, or GABA plus sitagliptin. Oral drug administration was initiated 1 week before STZ injection and maintained for 6 weeks. GABA or sitagliptin administration decreased ambient blood glucose levels and improved the glucose excursion rate. This was associated with elevated plasma insulin and reduced plasma glucagon levels. Importantly, combined use of GABA and sitagliptin significantly enhanced these effects as compared with each of the monotherapies. An additive effect on reducing water consumption was also observed. Immunohistochemical analyses revealed that combined GABA and sitagliptin therapy was superior in increasing beta cell mass, associated with increased small-size islet numbers, Ki67+ and PDX-1+ beta cell counts; and reduced Tunel+ beta cell counts. Thus, beta cell proliferation was increased, whereas apoptosis was reduced. We also noticed a suppressive effect of GABA or sitagliptin on alpha cell mass, which was not significantly altered by combining the two agents. Although either GABA or sitagliptin administration delays the onset of MDSD, our study indicates that combined use of them produces superior therapeutic outcomes. This is likely due to an amelioration of beta cell proliferation and a decrease of beta cell apoptosis.

GLP-1 signalling compensates for impaired insulin signalling in regulating beta cell proliferation in βIRKO mice.

We aimed to investigate potential interactions between insulin and glucagon-like peptide (GLP)-1 signalling pathways in the regulation of beta cell-cycle dynamics in vivo, in the context of the therapeutic potential of GLP-1 to modulate impaired beta cell function. Beta cell-specific insulin receptor knockout (βIRKO) mice, which exhibit beta cell dysfunction and an age-dependent decrease in beta cell mass, were treated with the dipeptidyl peptidase-4 inhibitor vildagliptin. Following this, glucose homeostasis and beta cell proliferation were evaluated and underlying molecular mechanisms were investigated. The sustained elevation in circulating GLP-1 levels, caused by treatment of the knockout mice with vildagliptin for 6weeks, significantly improved glucose tolerance secondary to enhanced insulin secretion and proliferation of beta cells. Treating βIRKO beta cell lines with the GLP-1 analogue, exendin-4, promoted Akt phosphorylation and protein expression of cyclins A, D1 and E two- to threefold, in addition to cyclin D2. Pancreases from the vildagliptin-treated βIRKO mice exhibited increased cyclin D1 expression, while cyclin D2 expression was impaired. Activation of GLP-1 signalling compensates for impaired growth factor (insulin) signalling and enhances expression of cyclins to promote beta cell proliferation. Together, these data indicate the potential of GLP-1-related therapies to enhance beta cell proliferation and promote beneficial outcomes in models with dysfunctional beta cells.