Overexpression of c-Myc in beta-cells of transgenic mice causes proliferation and apoptosis, downregulation of insulin gene expression, and diabetes

Do human adipose stem cell-derived artificial insulin-producing cells develop tumorigenic characteristics throughout differentiation?

BACKGROUND

Artificial insulin-producing cells (IPCs) used to treat diabetes mellitus type 1 (DMT1) are naturally hampered by their carcinogenicity. This in vitro study aimed to examine the carcinogenic potential of IPCs produced by the differentiation of human adipose tissue-derived mesenchymal stem cells (hADSCs).

METHODS AND RESULTS

hADSCs were transformed into IPCs by administering insulin-transferrin, selenium (ITS), and nicotinamide in a 14-day differentiation protocol. The cells were transfected with 20 μg of pure Pdx1-pIRES recombinant vector on the tenth day of differentiation. The successful transfection was confirmed by Pdx1 overexpression and GFP fluorescence activity. The differentiated cells' capacity to release insulin and glucose-dependent C-peptide was used to evaluate their functionality. Gene expression was assessed using real-time PCR. Meanwhile, protein expression was investigated using western blotting. The transfected cells exhibited fluorescence activity and Pdx1 overexpression. The differentiated IPCs were able to secrete C-peptide and insulin. The artificial IPCs showed significantly reduced Oct4 and Nanog expression. However, the differentiation process induced a noticeable elevation in tPA expression. The artificial IPCs expressed much lower c-MYC expression compared to undifferentiated hADSCs. The differentiated cells exhibited a significant elevation in Glut2, MMP-2, CD24, P16, and P21 expression.

CONCLUSIONS

The differentiation technique used in this work produced functional beta-like cells devoid of typical markers of stem cells. The synthetic IPCs displayed characteristics of newly generated β-like cells. The artificial IPCs showed no signs of expressing tumor-associated markers. The findings imply that the artificial IPC cells lack tumor characteristics in vitro.

Circulating hsa-miR-320a and its regulatory network in type 1 diabetes mellitus

Introduction

Increasing evidence from human and animal model studies indicates the significant role of microRNAs (miRNAs) in pancreatic beta cell function, insulin signaling, immune responses, and pathogenesis of type 1 diabetes (T1D).

Methods

We aimed, using next-generation sequencing, to screen miRNAs from peripheral blood mononuclear cells of eight independent Kuwaiti-Arab families with T1D affected siblings, consisting of 18 T1D patients and 18 unaffected members, characterized by no parent-to-child inheritance pattern.

Results

Our analysis revealed 20 miRNAs that are differentially expressed in T1D patients compared with healthy controls. Module-based weighted gene co-expression network analysis prioritized key consensus miRNAs in T1D pathogenesis. These included hsa-miR-320a-3p, hsa-miR-139-3p, hsa-miR-200-3p, hsa-miR-99b-5p and hsa-miR-6808-3p. Functional enrichment analysis of differentially expressed miRNAs indicated that PI3K-AKT is one of the key pathways perturbed in T1D. Gene ontology analysis of hub miRNAs also implicated PI3K-AKT, along with mTOR, MAPK, and interleukin signaling pathways, in T1D. Using quantitative RT-PCR, we validated one of the key predicted miRNA-target gene-transcription factor networks in an extended cohort of children with new-onset T1D positive for islet autoantibodies. Our analysis revealed that hsa-miR-320a-3p and its key targets, including PTEN, AKT1, BCL2, FOXO1 and MYC, are dysregulated in T1D, along with their interacting partners namely BLIMP3, GSK3B, CAV1, CXCL3, TGFB, and IL10. Receiver Operating Characteristic analysis highlighted the diagnostic potential of hsa-miR-320a-3p, CAV1, GSK3B and MYC for T1D.

Discussion

Our study presents a novel link between hsa-miR-320a-3p and T1D, and highlights its key regulatory role in the network of mRNA markers and transcription factors involved in T1D pathogenesis.

Endothelial c-Myc knockout disrupts metabolic homeostasis and triggers the development of obesity

Introduction: Obesity is a major risk factor associated with multiple pathological conditions including diabetes and cardiovascular disease. Endothelial dysfunction is an early predictor of obesity. However, little is known regarding how early endothelial changes trigger obesity. In the present work we report a novel endothelial-mediated mechanism essential for regulation of metabolic homeostasis, driven by c-Myc. Methods: We used conditional knockout (EC-Myc KO) and overexpression (EC-Myc OE) mouse models to investigate the endothelial-specific role of c-Myc in metabolic homeostasis during aging and high-fat diet exposure. Body weight and metabolic parameters were collected over time and tissue samples collected at endpoint for biochemical, pathology and RNA-sequencing analysis. Animals exposed to high-fat diet were also evaluated for cardiac dysfunction. Results: In the present study we demonstrate that EC-Myc KO triggers endothelial dysfunction, which precedes progressive increase in body weight during aging, under normal dietary conditions. At endpoint, EC-Myc KO animals showed significant increase in white adipose tissue mass relative to control littermates, which was associated with sex-specific changes in whole body metabolism and increase in systemic leptin. Overexpression of endothelial c-Myc attenuated diet-induced obesity and visceral fat accumulation and prevented the development of glucose intolerance and cardiac dysfunction. Transcriptome analysis of skeletal muscle suggests that the protective effects promoted by endothelial c-Myc overexpression are associated with the expression of genes known to increase weight loss, energy expenditure and glucose tolerance. Conclusion: Our results show a novel important role for endothelial c-Myc in regulating metabolic homeostasis and suggests its potential targeting in preventing obesity and associated complications such as diabetes type-2 and cardiovascular dysfunction.

Pancreatic β-Cell Identity Change through the Lens of Single-Cell Omics Research

The main hallmark in the development of both type 1 and type 2 diabetes is a decline in functional β-cell mass. This decline is predominantly attributed to β-cell death, although recent findings suggest that the loss of β-cell identity may also contribute to β-cell dysfunction. This phenomenon is characterized by a reduced expression of key markers associated with β-cell identity. This review delves into the insights gained from single-cell omics research specifically focused on β-cell identity. It highlights how single-cell omics based studies have uncovered an unexpected level of heterogeneity among β-cells and have facilitated the identification of distinct β-cell subpopulations through the discovery of cell surface markers, transcriptional regulators, the upregulation of stress-related genes, and alterations in chromatin activity. Furthermore, specific subsets of β-cells have been identified in diabetes, such as displaying an immature, dedifferentiated gene signature, expressing significantly lower insulin mRNA levels, and expressing increased β-cell precursor markers. Additionally, single-cell omics has increased insight into the detrimental effects of diabetes-associated conditions, including endoplasmic reticulum stress, oxidative stress, and inflammation, on β-cell identity. Lastly, this review outlines the factors that may influence the identification of β-cell subpopulations when designing and performing a single-cell omics experiment.

Role of human Kallistatin in glucose and energy homeostasis in mice

OBJECTIVE

Kallistatin (KST), also known as SERPIN A4, is a circulating, broadly acting human plasma protein with pleiotropic properties. Clinical studies in humans revealed reduced KST levels in obesity. The exact role of KST in glucose and energy homeostasis in the setting of insulin resistance and type 2 diabetes is currently unknown.

METHODS

Kallistatin mRNA expression in human subcutaneous white adipose tissue (sWAT) of 47 people with overweight to obesity of the clinical trial "Comparison of Low Fat and Low Carbohydrate Diets With Respect to Weight Loss and Metabolic Effects (B-SMART)" was measured. Moreover, we studied transgenic mice systemically overexpressing human KST (hKST-TG) and wild type littermate control mice (WT) under normal chow (NCD) and high-fat diet (HFD) conditions.

RESULTS

In sWAT of people with overweight to obesity, KST mRNA increased after diet-induced weight loss. On NCD, we did not observe differences between hKST-TG and WT mice. Under HFD conditions, body weight, body fat and liver fat content did not differ between genotypes. Yet, during intraperitoneal glucose tolerance tests (ipGTT) insulin excursions and HOMA-IR were lower in hKST-TG (4.42 ± 0.87 AU, WT vs. 2.20 ± 0.27 AU, hKST-TG, p < 0.05). Hyperinsulinemic euglycemic clamp studies with tracer-labeled glucose infusion confirmed improved insulin sensitivity by higher glucose infusion rates in hKST-TG mice (31.5 ± 1.78 mg/kg/min, hKST-TG vs. 18.1 ± 1.67 mg/kg/min, WT, p < 0.05). Improved insulin sensitivity was driven by reduced hepatic insulin resistance (clamp hepatic glucose output: 7.7 ± 1.9 mg/kg/min, hKST-TG vs 12.2 ± 0.8 mg/kg/min, WT, p < 0.05), providing evidence for direct insulin sensitizing effects of KST for the first time. Insulin sensitivity was differentially affected in skeletal muscle and adipose tissue. Mechanistically, we observed reduced Wnt signaling in the liver but not in skeletal muscle, which may explain the effect.

CONCLUSIONS

KST expression increases after weight loss in sWAT from people with obesity. Furthermore, human KST ameliorates diet-induced hepatic insulin resistance in mice, while differentially affecting skeletal muscle and adipose tissue insulin sensitivity. Thus, KST may be an interesting, yet challenging, therapeutic target for patients with obesity and insulin resistance.

Manipulating Myc for reparative regeneration

The Myc family of proto-oncogenes is a key node for the signal transduction of external pro-proliferative signals to the cellular processes required for development, tissue homoeostasis maintenance, and regeneration across evolution. The tight regulation of Myc synthesis and activity is essential for restricting its oncogenic potential. In this review, we highlight the central role that Myc plays in regeneration across the animal kingdom (from Cnidaria to echinoderms to Chordata) and how Myc could be employed to unlock the regenerative potential of non-regenerative tissues in humans for therapeutic purposes. Mastering the fine balance of harnessing the ability of Myc to promote transcription without triggering oncogenesis may open the door to many exciting opportunities for therapeutic development across a wide array of diseases.

MYC: there is more to it than cancer

MYC is a pleiotropic transcription factor involved in multiple cellular processes. While its mechanism of action and targets are not completely elucidated, it has a fundamental role in cellular proliferation, differentiation, metabolism, ribogenesis, and bone and vascular development. Over 4 decades of research and some 10,000 publications linking it to tumorigenesis (by searching PubMed for "MYC oncogene") have led to MYC becoming a most-wanted target for the treatment of cancer, where many of MYC's physiological functions become co-opted for tumour initiation and maintenance. In this context, an abundance of reviews describes strategies for potentially targeting MYC in the oncology field. However, its multiple roles in different aspects of cellular biology suggest that it may also play a role in many additional diseases, and other publications are indeed linking MYC to pathologies beyond cancer. Here, we review these physiological functions and the current literature linking MYC to non-oncological diseases. The intense efforts towards developing MYC inhibitors as a cancer therapy will potentially have huge implications for the treatment of other diseases. In addition, with a complementary approach, we discuss some diseases and conditions where MYC appears to play a protective role and hence its increased expression or activation could be therapeutic.

Transcriptional activation of the Myc gene by glucose in β-cells requires a ChREBP-dependent 3-D chromatin interaction between the Myc and Pvt1 genes

OBJECTIVE

All forms of diabetes result from insufficient functional β-cell mass. Thus, achieving the therapeutic goal of expanding β-cell mass requires a better mechanistic understanding of how β-cells proliferate. Glucose is a natural β-cell mitogen that mediates its effects in part through the glucose-responsive transcription factor, carbohydrate response element binding protein (ChREBP) and the anabolic transcription factor, MYC. However, mechanistic details by which glucose activates Myc at the transcriptional level are poorly understood.

METHODS

Here, siRNA was used to test the role of ChREBP in the glucose response of MYC, ChIP and ChIPseq to identify potential regulatory binding sites, chromatin conformation capture to identify DNA/DNA interactions, and an adenovirus was constructed to expresses x-dCas9 and an sgRNA that specifically disrupts the recruitment of ChREBP to a specific targeted ChoRE.

RESULTS

We found that ChREBP is essential for glucose-mediated transcriptional induction of Myc, and for increases in Myc mRNA and protein abundance. Further, ChIPseq revealed that the carbohydrate response element (ChoRE) nearest to the Myc transcriptional start site (TSS) is immediately upstream of the gene encoding the lncRNA, Pvt1, 60,000 bp downstream of the Myc gene. Chromatin Conformation Capture (3C) confirmed a glucose-dependent interaction between these two sites. Transduction with an adenovirus expressing x-dCas9 and an sgRNA specifically targeting the highly conserved Pvt1 ChoRE, attenuates ChREBP recruitment, decreases Myc-Pvt1 DNA/DNA interaction, and decreases expression of the Pvt1 and Myc genes in response to glucose. Importantly, isolated and dispersed rat islet cells transduced with the ChoRE-disrupting adenovirus also display specific decreases in ChREBP-dependent, glucose-mediated expression of Pvt1 and Myc, as well as decreased glucose-stimulated β-cell proliferation.

CONCLUSIONS

The mitogenic glucose response of Myc is mediated via glucose-dependent recruitment of ChREBP to the promoter of the Pvt1 gene and subsequent DNA looping with the Myc promoter.

Obesity under the moonlight of c-MYC

The moonlighting protein c-Myc is a master regulator of multiple biological processes including cell proliferation, differentiation, angiogenesis, apoptosis and metabolism. It is constitutively and aberrantly expressed in more than 70% of human cancers. Overwhelming evidence suggests that c-Myc dysregulation is involved in several inflammatory, autoimmune, metabolic and other non-cancerous diseases. In this review, we addressed the role of c-Myc in obesity. Obesity is a systemic disease, accompanied by multi-organ dysfunction apart from white adipose tissue (WAT), such as the liver, the pancreas, and the intestine. c-Myc plays a big diversity of functions regulating cellular proliferation, the maturation of progenitor cells, fatty acids (FAs) metabolism, and extracellular matrix (ECM) remodeling. Moreover, c-Myc drives the expression of a wide range of metabolic genes, modulates the inflammatory response, induces insulin resistance (IR), and contributes to the regulation of intestinal dysbiosis. Altogether, c-Myc is an interesting diagnostic tool and/or therapeutic target in order to mitigate obesity and its consequences.

Myc beyond Cancer: Regulation of Mammalian Tissue Regeneration

Myc is one of the most well-known oncogenes driving tumorigenesis in a wide variety of tissues. From the brain to blood, its deregulation derails physiological pathways that grant the correct functioning of the cell. Its action is carried out at the gene expression level, where Myc governs basically every aspect of transcription. Indeed, in addition to its role as a canonical, chromatin-bound transcription factor, Myc rules RNA polymerase II (RNAPII) transcriptional pause-release, elongation and termination and mRNA capping. For this reason, it is evident that minimal perturbations of Myc function mirror malignant cell behavior and, consistently, a large body of literature mainly focuses on Myc malfunctioning. In healthy cells, Myc controls molecular mechanisms involved in pivotal functions, such as cell cycle (and proliferation thereof), apoptosis, metabolism and cell size, angiogenesis, differentiation and stem cell self-renewal. In this latter regard, Myc has been found to also regulate tissue regeneration, a hot topic in the research fields of aging and regenerative medicine. Indeed, Myc appears to have a role in wound healing, in peripheral nerves and in liver, pancreas and even heart recovery. Herein, we discuss the state of the art of Myc's role in tissue regeneration, giving an overview of its potent action beyond cancer.

Harnessing Human Pluripotent Stem Cell-Derived Pancreatic In Vitro Models for High-Throughput Toxicity Testing and Diabetes Drug Discovery

The long-standing goals in diabetes research are to improve β-cell survival, functionality and increase β-cell mass. Current strategies to manage diabetes progression are still not ideal for sustained maintenance of normoglycemia, thereby increasing demand for the development of novel drugs. Available pancreatic cell lines, cadaveric islets, and their culture methods and formats, either 2D or 3D, allow for multiple avenues of experimental design to address diverse aims in the research setting. More specifically, these pancreatic cells have been employed in toxicity testing, diabetes drug screens, and with careful curation, can be optimized for use in efficient high-throughput screenings (HTS). This has since spearheaded the understanding of disease progression and related mechanisms, as well as the discovery of potential drug candidates which could be the cornerstone for diabetes treatment. This book chapter will touch on the pros and cons of the most widely used pancreatic cells, including the more recent human pluripotent stem cell-derived pancreatic cells, and HTS strategies (cell models, design, readouts) that can be used for the purpose of toxicity testing and diabetes drug discovery.

Maladaptive positive feedback production of ChREBPβ underlies glucotoxic β-cell failure

Preservation and expansion of β-cell mass is a therapeutic goal for diabetes. Here we show that the hyperactive isoform of carbohydrate response-element binding protein (ChREBPβ) is a nuclear effector of hyperglycemic stress occurring in β-cells in response to prolonged glucose exposure, high-fat diet, and diabetes. We show that transient positive feedback induction of ChREBPβ is necessary for adaptive β-cell expansion in response to metabolic challenges. Conversely, chronic excessive β-cell-specific overexpression of ChREBPβ results in loss of β-cell identity, apoptosis, loss of β-cell mass, and diabetes. Furthermore, β-cell "glucolipotoxicity" can be prevented by deletion of ChREBPβ. Moreover, ChREBPβ-mediated cell death is mitigated by overexpression of the alternate CHREBP gene product, ChREBPα, or by activation of the antioxidant Nrf2 pathway in rodent and human β-cells. We conclude that ChREBPβ, whether adaptive or maladaptive, is an important determinant of β-cell fate and a potential target for the preservation of β-cell mass in diabetes.

XBP1 maintains beta cell identity, represses beta-to-alpha cell transdifferentiation and protects against diabetic beta cell failure during metabolic stress in mice

AIMS/HYPOTHESIS

Pancreatic beta cell dedifferentiation, transdifferentiation into other islet cells and apoptosis have been implicated in beta cell failure in type 2 diabetes, although the mechanisms are poorly defined. The endoplasmic reticulum stress response factor X-box binding protein 1 (XBP1) is a major regulator of the unfolded protein response. XBP1 expression is reduced in islets of people with type 2 diabetes, but its role in adult differentiated beta cells is unclear. Here, we assessed the effects of Xbp1 deletion in adult beta cells and tested whether XBP1-mediated unfolded protein response makes a necessary contribution to beta cell compensation in insulin resistance states.

METHODS

Mice with inducible beta cell-specific Xbp1 deletion were studied under normal (chow diet) or metabolic stress (high-fat diet or obesity) conditions. Glucose tolerance, insulin secretion, islet gene expression, alpha cell mass, beta cell mass and apoptosis were assessed. Lineage tracing was used to determine beta cell fate.

RESULTS

Deletion of Xbp1 in adult mouse beta cells led to beta cell dedifferentiation, beta-to-alpha cell transdifferentiation and increased alpha cell mass. Cell lineage-specific analyses revealed that Xbp1 deletion deactivated beta cell identity genes (insulin, Pdx1, Nkx6.1, Beta2, Foxo1) and derepressed beta cell dedifferentiation (Aldh1a3) and alpha cell (glucagon, Arx, Irx2) genes. Xbp1 deletion in beta cells of obese ob/ob or high-fat diet-fed mice triggered diabetes and worsened glucose intolerance by disrupting insulin secretory capacity. Furthermore, Xbp1 deletion increased beta cell apoptosis under metabolic stress conditions by attenuating the antioxidant response.

CONCLUSIONS/INTERPRETATION

These findings indicate that XBP1 maintains beta cell identity, represses beta-to-alpha cell transdifferentiation and is required for beta cell compensation and prevention of diabetes in insulin resistance states.

Physically interacting beta-delta pairs in the regenerating pancreas revealed by single-cell sequencing

Objectives

Until recently, communication between neighboring cells in islets of Langerhans was overlooked by genomic technologies, which require rigorous tissue dissociation into single cells.

Methods

We utilize sorting of physically interacting cells (PICs) with single-cell RNA-sequencing to systematically map cellular interactions in the endocrine pancreas after pancreatectomy.

Results

The pancreas cellular landscape features pancreatectomy associated heterogeneity of beta-cells, including an interaction-specific program between paired beta and delta-cells.

Conclusions

Our analysis suggests that the particular cluster of beta-cells that pairs with delta-cells benefits from stress protection, implying that the interaction between beta- and delta-cells might safeguard against pancreatectomy associated challenges. The work encourages testing the potential relevance of physically-interacting beta-delta-cells also in diabetes mellitus.

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Single-cell RNA-sequencing systematically maps physically interacting endocrine cells in the pancreas.

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The landscape of pancreatectomy associated beta-cell heterogeneity is mapped in a single cell resolution.

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Interaction-specific beta - delta cellular program safeguards beta cells against pancreatectomy-associated stress.

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Physically interacting beta delta pairs were discovered in an injury model and may also be relevant in diabetes.

MYCL-mediated reprogramming expands pancreatic insulin-producing cells

β cells have a limited capacity for regeneration, which predisposes towards diabetes. Here, we show that, of the MYC family members, Mycl plays a key role in proliferation of pancreatic endocrine cells. Genetic ablation of Mycl causes a reduction in the proliferation of pancreatic endocrine cells in neonatal mice. By contrast, the expression of Mycl in adult mice stimulates the proliferation of β and α cells, and the cells persist after withdrawal of Mycl expression. A subset of the expanded α cells give rise to insulin-producing cells after this withdrawal. Transient Mycl expression in vivo is sufficient to normalize the hyperglycaemia of diabetic mice. In vitro expression of Mycl similarly provokes active replication in islet cells, even in those from aged mice. Finally, we show that MYCL stimulates the division of human adult cadaveric islet cells. Our results demonstrate that the induction of Mycl alone expands the functional β-cell population, which may provide a regenerative strategy for β cells.

Deficiency of M-LP/Mpv17L leads to development of β-cell hyperplasia and improved glucose tolerance via activation of the Wnt and TGF-β pathways

M-LP/Mpv17L is a protein that was initially identified during screening of age-dependently expressed genes in mice. We have recently demonstrated that M-LP/Mpv17L-knockout (M-LP/Mpv17L-KO) in human hepatoma cells leads to a reduction of cellular cyclic nucleotide phosphodiesterase (PDE) activity, and that in vitro-synthesized M-LP/Mpv17L possesses PDE activity. These findings suggest that M-LP/Mpv17L functions as an atypical PDE, even though it has none of the well-conserved catalytic region or other structural motifs characteristic of the PDE family. In this study, we found that M-LP/Mpv17L-KO mice developed β-cell hyperplasia and improved glucose tolerance. Deficiency of M-LP/Mpv17L in islets from KO mice at early postnatal stages or siRNA-mediated suppression of M-LP/Mpv17L in rat insulinoma cells led to marked upregulation of lymphoid enhancer binding factor 1 (Lef1) and transcription factor 7 (Tcf7), key nuclear effectors in the Wnt signaling pathway, and some of the factors essential for the development and maintenance of β-cells. Moreover, at the protein level, increases in the levels of phosphorylated β-catenin and glycogen synthase kinase-3β (GSK-3β) were observed, indicating activation of the Wnt and TGF-β signaling pathways. Taken together, these findings suggest that protein kinase A (PKA)-dependent phosphorylations of β-catenin and GSK-3β, the key mediators of the Wnt and/or TGF-β signaling pathways, are the most upstream events triggering β-cell hyperplasia and improved glucose tolerance caused by M-LP/Mpv17L deficiency.

Oxidative Stress Leads to β-Cell Dysfunction Through Loss of β-Cell Identity

Pancreatic β-cell failure is a critical event in the onset of both main types of diabetes mellitus but underlying mechanisms are not fully understood. β-cells have low anti-oxidant capacity, making them more susceptible to oxidative stress. In type 1 diabetes (T1D), reactive oxygen species (ROS) are associated with pro-inflammatory conditions at the onset of the disease. Here, we investigated the effects of hydrogen peroxide-induced oxidative stress on human β-cells. We show that primary human β-cell function is decreased. This reduced function is associated with an ER stress response and the shuttling of FOXO1 to the nucleus. Furthermore, oxidative stress leads to loss of β-cell maturity genes MAFA and PDX1, and to a concomitant increase in progenitor marker expression of SOX9 and HES1. Overall, we propose that oxidative stress-induced β-cell failure may result from partial dedifferentiation. Targeting antioxidant mechanisms may preserve functional β-cell mass in early stages of development of T1D.

Single cell transcriptomics reveal trans-differentiation of pancreatic beta cells following inactivation of the TFIID subunit Taf4

Regulation of gene expression involves a complex and dynamic dialogue between transcription factors, chromatin remodelling and modification complexes and the basal transcription machinery. To address the function of the Taf4 subunit of general transcription factor TFIID in the regulation of insulin signalling, it was inactivated in adult murine pancreatic beta cells. Taf4 inactivation impacted the expression of critical genes involved in beta-cell function leading to increased glycaemia, lowered plasma insulin levels and defective glucose-stimulated insulin secretion. One week after Taf4-loss, single-cell RNA-seq revealed cells with mixed beta cell, alpha and/or delta cell identities as well as a beta cell population trans-differentiating into alpha-like cells. Computational analysis of single-cell RNA-seq defines how known critical beta cell and alpha cell determinants may act in combination with additional transcription factors and the NuRF chromatin remodelling complex to promote beta cell trans-differentiation.

The hepatokine fetuin-A disrupts functional maturation of pancreatic beta cells

AIMS/HYPOTHESIS

Neonatal beta cells carry out a programme of postnatal functional maturation to achieve full glucose responsiveness. A partial loss of the mature phenotype of adult beta cells may contribute to a reduction of functional beta cell mass and accelerate the onset of type 2 diabetes. We previously found that fetuin-A, a hepatokine increasingly secreted by the fatty liver and a determinant of type 2 diabetes, inhibits glucose-stimulated insulin secretion (GSIS) of human islets. Since fetuin-A is a ubiquitous fetal glycoprotein that declines peripartum, we examined here whether fetuin-A interferes with the functional maturity of beta cells.

METHODS

The effects of fetuin-A were assessed during in vitro maturation of porcine neonatal islet cell clusters (NICCs) and in adult human islets. Expression alterations were examined via microarray, RNA sequencing and reverse transcription quantitative real-time PCR (qRT-PCR), proteins were analysed by western blotting and immunostaining, and insulin secretion was quantified in static incubations.

RESULTS

NICC maturation was accompanied by the gain of glucose-responsive insulin secretion (twofold stimulation), backed up by mRNA upregulation of genes governing beta cell identity and function, such as NEUROD1, UCN3, ABCC8 and CASR (Log₂ fold change [Log₂FC] > 1.6). An active TGFβ receptor (TGFBR)-SMAD2/3 pathway facilitates NICC maturation, since the TGFBR inhibitor SB431542 counteracted the upregulation of aforementioned genes and de-repressed ALDOB, a gene disallowed in mature beta cells. In fetuin-A-treated NICCs, upregulation of beta cell markers and the onset of glucose responsiveness were suppressed. Concomitantly, SMAD2/3 phosphorylation was inhibited. Transcriptome analysis confirmed inhibitory effects of fetuin-A and SB431542 on TGFβ-1- and SMAD2/3-regulated transcription. However, contrary to SB431542 and regardless of cMYC upregulation, fetuin-A inhibited beta cell proliferation (0.27 ± 0.08% vs 1.0  ± 0.1% Ki67-positive cells in control NICCs). This effect was sustained by reduced expression (Log₂FC ≤ -2.4) of FOXM1, CENPA, CDK1 or TOP2A. In agreement, the number of insulin-positive cells was lower in fetuin-A-treated NICCs than in control NICCs (14.4 ± 1.2% and 22.3 ± 1.1%, respectively). In adult human islets fetuin-A abolished glucose responsiveness, i.e. 1.7- and 1.1-fold change over 2.8 mmol/l glucose in control- and fetuin-A-cultured islets, respectively. In addition, fetuin-A reduced SMAD2/3 phosphorylation and suppressed expression of proliferative genes. Of note, in non-diabetic humans, plasma fetuin-A was negatively correlated (p = 0.013) with islet beta cell area.

CONCLUSIONS/INTERPRETATION

Our results suggest that the perinatal decline of fetuin-A relieves TGFBR signalling in islets, a process that facilitates functional maturation of neonatal beta cells. Functional maturity remains revocable in later life, and the occurrence of a metabolically unhealthy milieu, such as liver steatosis and elevated plasma fetuin-A, can impair both function and adaptive proliferation of beta cells.

DATA AVAILABILITY

The RNAseq datasets and computer code produced in this study are available in the Gene Expression Omnibus (GEO): GSE144950; https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE144950.

The many lives of Myc in the pancreatic β-cell

Diabetes results from insufficient numbers of functional pancreatic β-cells. Thus, increasing the number of available functional β-cells ex vivo for transplantation, or regenerating them in situ in diabetic patients, is a major focus of diabetes research. The transcription factor, Myc, discovered decades ago lies at the nexus of most, if not all, known proliferative pathways. Based on this, many studies in the 1990s and early 2000s explored the potential of harnessing Myc expression to expand β-cells for diabetes treatment. Nearly all these studies in β-cells used pathophysiological or supraphysiological levels of Myc and reported enhanced β-cell death, dedifferentiation, or the formation of insulinomas if cooverexpressed with Bcl-xL, an inhibitor of apoptosis. This obviously reduced the enthusiasm for Myc as a therapeutic target for β-cell regeneration. However, recent studies indicate that "gentle" induction of Myc expression enhances β-cell replication without induction of cell death or loss of insulin secretion, suggesting that appropriate levels of Myc could have therapeutic potential for β-cell regeneration. Furthermore, although it has been known for decades that Myc is induced by glucose in β-cells, very little is known about how this essential anabolic transcription factor perceives and responds to nutrients and increased insulin demand in vivo. Here we summarize the previous and recent knowledge of Myc in the β-cell, its potential for β-cell regeneration, and its physiological importance for neonatal and adaptive β-cell expansion.

Transcriptional Profiling and Biological Pathway(s) Analysis of Type 2 Diabetes Mellitus in a Pakistani Population

The epidemic of type 2 diabetes mellitus (T2DM) is an important global health concern. Our earlier epidemiological investigation in Pakistan prompted us to conduct a molecular investigation to decipher the differential genetic pathways of this health condition in relation to non-diabetic controls. Our microarray studies of global gene expression were conducted on the Affymetrix platform using Human Genome U133 Plus 2.0 Array along with Ingenuity Pathway Analysis (IPA) to associate the affected genes with their canonical pathways. High-throughput qRT-PCR TaqMan Low Density Array (TLDA) was performed to validate the selected differentially expressed genes of our interest, viz., ARNT, LEPR, MYC, RRAD, CYP2D6, TP53, APOC1, APOC2, CYP1B1, SLC2A13, and SLC33A1 using a small population validation sample (n = 15 cases and their corresponding matched controls). Overall, our small pilot study revealed a discrete gene expression profile in cases compared to controls. The disease pathways included: Insulin Receptor Signaling, Type II Diabetes Mellitus Signaling, Apoptosis Signaling, Aryl Hydrocarbon Receptor Signaling, p53 Signaling, Mitochondrial Dysfunction, Chronic Myeloid Leukemia Signaling, Parkinson's Signaling, Molecular Mechanism of Cancer, and Cell Cycle G1/S Checkpoint Regulation, GABA Receptor Signaling, Neuroinflammation Signaling Pathway, Dopamine Receptor Signaling, Sirtuin Signaling Pathway, Oxidative Phosphorylation, LXR/RXR Activation, and Mitochondrial Dysfunction, strongly consistent with the evidence from epidemiological studies. These gene fingerprints could lead to the development of biomarkers for the identification of subgroups at high risk for future disease well ahead of time, before the actual disease becomes visible.

Hypusine biosynthesis in β cells links polyamine metabolism to facultative cellular proliferation to maintain glucose homeostasis

Deoxyhypusine synthase (DHPS) uses the polyamine spermidine to catalyze the hypusine modification of the mRNA translation factor eIF5A and promotes oncogenesis through poorly defined mechanisms. Because germline deletion of Dhps is embryonically lethal, its role in normal postnatal cellular function in vivo remains unknown. We generated a mouse model that enabled the inducible, postnatal deletion of Dhps specifically in postnatal islet β cells, which function to maintain glucose homeostasis. Removal of Dhps did not have an effect under normal physiologic conditions. However, upon development of insulin resistance, which induces β cell proliferation, Dhps deletion caused alterations in proteins required for mRNA translation and protein secretion, reduced production of the cell cycle molecule cyclin D2, impaired β cell proliferation, and induced overt diabetes. We found that hypusine biosynthesis was downstream of protein kinase C-ζ and was required for c-Myc-induced proliferation. Our studies reveal a requirement for DHPS in β cells to link polyamines to mRNA translation to effect facultative cellular proliferation and glucose homeostasis.

Myc Is Required for Adaptive β-Cell Replication in Young Mice but Is Not Sufficient in One-Year-Old Mice Fed With a High-Fat Diet

Failure to expand pancreatic β-cells in response to metabolic stress leads to excessive workload resulting in β-cell dysfunction, dedifferentiation, death, and development of type 2 diabetes. In this study, we demonstrate that induction of Myc is required for increased pancreatic β-cell replication and expansion during metabolic stress-induced insulin resistance with short-term high-fat diet (HFD) in young mice. β-Cell-specific Myc knockout mice fail to expand adaptively and show impaired glucose tolerance and β-cell dysfunction. Mechanistically, PKCζ, ERK1/2, mTOR, and PP2A are key regulators of the Myc response in this setting. DNA methylation analysis shows hypomethylation of cell cycle genes that are Myc targets in islets from young mice fed with a short-term HFD. Importantly, DNA hypomethylation of Myc response elements does not occur in islets from 1-year-old mice fed with a short-term HFD, impairing both Myc recruitment to cell cycle regulatory genes and β-cell replication. We conclude that Myc is required for metabolic stress-mediated β-cell expansion in young mice, but with aging, Myc upregulation is not sufficient to induce β-cell replication by, at least partially, an epigenetically mediated resistance to Myc action.

miR-17-92 and miR-106b-25 clusters regulate beta cell mitotic checkpoint and insulin secretion in mice

AIMS/HYPOTHESIS

Adult beta cells in the pancreas are the sole source of insulin in the body. Beta cell loss or increased demand for insulin impose metabolic challenges because adult beta cells are generally quiescent and infrequently re-enter the cell division cycle. The aim of this study is to test the hypothesis that a family of proto-oncogene microRNAs that includes miR-17-92 and miR-106b-25 clusters regulates beta cell proliferation or function in the adult endocrine pancreas.

METHODS

To elucidate the role of miR-17-92 and miR-106b-25 clusters in beta cells, we used a conditional miR-17-92/miR-106b-25 knockout mouse model. We employed metabolic assays in vivo and ex vivo, together with advanced microscopy of pancreatic sections, bioinformatics, mass spectrometry and next generation sequencing, to examine potential targets of miR-17-92/miR-106b-25, by which they might regulate beta cell proliferation and function.

RESULTS

We demonstrate that miR-17-92/miR-106b-25 regulate the adult beta cell mitotic checkpoint and that miR-17-92/miR-106b-25 deficiency results in reduction in beta cell mass in vivo. Furthermore, we reveal a critical role for miR-17-92/miR-106b-25 in glucose homeostasis and in controlling insulin secretion. We identify protein kinase A as a new relevant molecular pathway downstream of miR-17-92/miR-106b-25 in control of adult beta cell division and glucose homeostasis.

CONCLUSIONS/INTERPRETATION

The study contributes to the understanding of proto-oncogene miRNAs in the normal, untransformed endocrine pancreas and illustrates new genetic means for regulation of beta cell mitosis and function by non-coding RNAs.

DATA AVAILABILITY

Sequencing data that support the findings of this study have been deposited in GEO with the accession code GSE126516.

Identification of novel diabetes impaired miRNA-transcription factor co-regulatory networks in bone marrow-derived Lin-/VEGF-R2+ endothelial progenitor cells

Endothelial progenitor cells (EPCs) are a group of rare cells that play an important role in the repair of injured vascular endothelial cells and assist in reperfusion of ischemic tissue. Decreased production and/or loss of function of EPCs are associated with diabetic vasculopathy. The molecular mechanisms by which diabetes impairs EPCs remain unclear. We conducted microarray experiments followed by integrative regulatory analysis on cells isolated from Akita diabetic mice (18-weeks after onset of diabetes) and age-matched non-diabetic controls. Two types of cells were isolated from mice bone marrow; Lin⁺ cells and Lin^-/VEGF-R2⁺ EPCs. RNA was hybridized to mouse WG-6 V2 beadchips followed by comprehensive gene network analysis and computational validation of the obtained results. In total, 80 genes were exclusively DE between non-diabetic Lin^-/VEGF-R2⁺ EPCs and diabetic Lin^-/VEGF-R2⁺ EPCs, of which the 3 genes Clcnka, Pik3c2a, and Ptf1a are known to be associated with diabetic complications. Further analysis led to the establishment of a TF-miRNA mediated regulatory network specific to diabetic Lin^-/VEGF-R2⁺ EPCs and to identify 11 central-hub TFs (Tbp, Ahr, Trp53, Gata1, Foxo1, Foxo4, Yy1, Max, Pparg, Myc, Cebpa), and 2 miRNAs (mir-139-5p, mir-709) that might act as putative genomic drivers of diabetic pathogenesis in Lin^-/VEGF-R2⁺ EPCs. Moreover, we identified multiple TF-miRNA co-regulatory network motifs for which we validated their contribution to diabetic Lin^-/VEGF-R2⁺ EPCs in terms of statistical significance and relevance to biological evidence. Our findings suggest that diabetic Lin^-/VEGF-R2⁺ EPCs have specifically altered signature genes and miRNAs that render their capacity to proliferate and differentiate.

Replication confers β cell immaturity

Pancreatic β cells are highly specialized to regulate systemic glucose levels by secreting insulin. In adults, increase in β-cell mass is limited due to brakes on cell replication. In contrast, proliferation is robust in neonatal β cells that are functionally immature as defined by a lower set point for glucose-stimulated insulin secretion. Here we show that β-cell proliferation and immaturity are linked by tuning expression of physiologically relevant, non-oncogenic levels of c-Myc. Adult β cells induced to replicate adopt gene expression and metabolic profiles resembling those of immature neonatal β that proliferate readily. We directly demonstrate that priming insulin-producing cells to enter the cell cycle promotes a functionally immature phenotype. We suggest that there exists a balance between mature functionality and the ability to expand, as the phenotypic state of the β cell reverts to a less functional one in response to proliferative cues.

Adult beta cells, which are highly specialised insulin-secreting cells, rarely replicate. Puri et al. demonstrate that beta cell proliferative capacity is inversely correlated with their functionality and differentiation state, by inducing proliferation of adult cells with ectopic overexpression of the cell cycle regulator c-Myc.

Mechanisms of β-cell dedifferentiation in diabetes: recent findings and future research directions

Like all the cells of an organism, pancreatic β-cells originate from embryonic stem cells through a complex cellular process termed differentiation. Differentiation involves the coordinated and tightly controlled activation/repression of specific effectors and gene clusters in a time-dependent fashion thereby giving rise to particular morphological and functional cellular features. Interestingly, cellular differentiation is not a unidirectional process. Indeed, growing evidence suggests that under certain conditions, mature β-cells can lose, to various degrees, their differentiated phenotype and cellular identity and regress to a less differentiated or a precursor-like state. This concept is termed dedifferentiation and has been proposed, besides cell death, as a contributing factor to the loss of functional β-cell mass in diabetes. β-cell dedifferentiation involves: (1) the downregulation of β-cell-enriched genes, including key transcription factors, insulin, glucose metabolism genes, protein processing and secretory pathway genes; (2) the concomitant upregulation of genes suppressed or expressed at very low levels in normal β-cells, the β-cell forbidden genes; and (3) the likely upregulation of progenitor cell genes. These alterations lead to phenotypic reconfiguration of β-cells and ultimately defective insulin secretion. While the major role of glucotoxicity in β-cell dedifferentiation is well established, the precise mechanisms involved are still under investigation. This review highlights the identified molecular mechanisms implicated in β-cell dedifferentiation including oxidative stress, endoplasmic reticulum (ER) stress, inflammation and hypoxia. It discusses the role of Foxo1, Myc and inhibitor of differentiation proteins and underscores the emerging role of non-coding RNAs. Finally, it proposes a novel hypothesis of β-cell dedifferentiation as a potential adaptive mechanism to escape cell death under stress conditions.

Saxagliptin Induces β-Cell Proliferation through Increasing Stromal Cell-Derived Factor-1α In Vivo and In Vitro

Dipeptidyl peptidase-4 inhibitors, such as saxagliptin, have been reported to have beneficial effects on β-cell function, but the specific underlying mechanism remains unclear. Stromal cell-derived factor-1α (SDF-1α), a chemokine produced in multiple organs, has been considered as a crucial regulator in promoting β-cell survival. Here, we speculate that SDF-1α might mediate the effect of saxagliptin on improving β-cell function. After 12-week saxagliptin treatment in high-fat diet/streptozotocin-induced diabetic rats, significant improvement in pancreas insulin secretion capacity evaluated by hyperglycemia clamp and increased β-cell to α-cell areas ratio were observed. Saxagliptin significantly induced β-cell proliferation and upregulated the expression of proliferation-related factors including c-myc and cyclind D1 determined with western blotting from the isolated islets. The expression/activity of DPP-4 was significantly reduced and paralleled with the restoration of SDF-1α levels in the saxagliptin-treated diabetic rats, subsequently the key WNT-signaling regulators, β-catenin, and AKT were activated. However, the effect of saxagliptin inducing β-cell proliferation was attenuated when we silenced the SDF-1α receptor (CXCR4) with RNAi in INS cell lines. Collectively, our data indicate that SDF-1α mediates the protective effect of saxagliptin on β-cell proliferation, suggesting that DPP-4 inhibitors have the potential role on delaying β-cell failure and SDF-1α could be a therapeutic target of β-cell regeneration.

Definition of a Skp2-c-Myc Pathway to Expand Human Beta-cells

Type 2 diabetes (T2D) is characterized by insulin resistance and reduced functional β-cell mass. Developmental differences, failure of adaptive expansion and loss of β-cells via β-cell death or de-differentiation have emerged as the possible causes of this reduced β-cell mass. We hypothesized that the proliferative response to mitogens of human β-cells from T2D donors is reduced, and that this might contribute to the development and progression of T2D. Here, we demonstrate that the proliferative response of human β-cells from T2D donors in response to cdk6 and cyclin D3 is indeed dramatically impaired. We show that this is accompanied by increased nuclear abundance of the cell cycle inhibitor, p27^kip1. Increasing nuclear abundance of p27^kip1 by adenoviral delivery decreases the proliferative response of β-cells from non-diabetic donors, mimicking T2D β-cells. However, while both p27^kip1 gene silencing and downregulation by Skp2 overexpression increased similarly the proliferative response of human β-cells, only Skp2 was capable of inducing a significant human β-cell expansion. Skp2 was also able to double the proliferative response of T2D β-cells. These studies define c-Myc as a central Skp2 target for the induction of cell cycle entry, expansion and regeneration of human T2D β-cells.

Transcription factor Ets-1 links glucotoxicity to pancreatic beta cell dysfunction through inhibiting PDX-1 expression in rodent models

AIMS/HYPOTHESIS

'Glucotoxicity' is a term used to convey the negative effect of hyperglycaemia on beta cell function; however, the underlying molecular mechanisms that impair insulin secretion and gene expression are poorly defined. Our objective was to define the role of transcription factor v-ets avian erythroblastosis virus E26 oncogene homologue 1 (Ets-1) in beta cell glucotoxicity.

METHODS

Primary islets and Min6 cells were exposed to high glucose and Ets-1 expression was measured. Recombinant adenovirus and transgenic mice were used to upregulate Ets-1 expression in beta cells in vitro and in vivo, and insulin secretion was assessed. The binding activity of H3/H4 histone on the Ets-1 promoter, and that of forkhead box (FOX)A2, FOXO1 and Ets-1 on the Pdx-1 promoter was measured by chromatin immunoprecipitation and quantitative real-time PCR assay.

RESULTS

High glucose induced upregulation of Ets-1 expression and hyperacetylation of histone H3 and H4 at the Ets-1 gene promoter in beta cells. Ets-1 overexpression dramatically suppressed insulin secretion and biosynthesis both in vivo and in vitro. Besides, Ets-1 overexpression increased the activity of FOXO1 but decreased that of FOXA2 binding to the pancreatic and duodenal homeobox 1 (PDX-1) homology region 2 (PH2), resulting in inhibition of Pdx-1 promoter activity and downregulation of PDX-1 expression and activity. In addition, high glucose promoted the interaction of Ets-1 and FOXO1, and the activity of Ets-1 binding to the Pdx-1 promoter. Importantly, PDX-1 overexpression reversed the defect in pancreatic beta cells induced by Ets-1 excess, while knockdown of Ets-1 prevented hyperglycaemia-induced dysfunction of pancreatic beta cells.

CONCLUSIONS/INTERPRETATION

Our observations suggest that Ets-1 links glucotoxicity to pancreatic beta cell dysfunction through inhibiting PDX-1 expression in type 2 diabetes.

JNK1 Deficient Insulin-Producing Cells Are Protected against Interleukin-1β-Induced Apoptosis Associated with Abrogated Myc Expression

The relative contributions of the JNK subtypes in inflammatory β-cell failure and apoptosis are unclear. The JNK protein family consists of JNK1, JNK2, and JNK3 subtypes, encompassing many different isoforms. INS-1 cells express JNK1α1, JNK1α2, JNK1β1, JNK1β2, JNK2α1, JNK2α2, JNK3α1, and JNK3α2 mRNA isoform transcripts translating into 46 and 54 kDa isoform JNK proteins. Utilizing Lentiviral mediated expression of shRNAs against JNK1, JNK2, or JNK3 in insulin-producing INS-1 cells, we investigated the role of individual JNK subtypes in IL-1β-induced β-cell apoptosis. JNK1 knockdown prevented IL-1β-induced INS-1 cell apoptosis associated with decreased 46 kDa isoform JNK protein phosphorylation and attenuated Myc expression. Transient knockdown of Myc also prevented IL-1β-induced apoptosis as well as caspase 3 cleavage. JNK2 shRNA potentiated IL-1β-induced apoptosis and caspase 3 cleavage, whereas JNK3 shRNA did not affect IL-1β-induced β-cell death compared to nonsense shRNA expressing INS-1 cells. In conclusion, JNK1 mediates INS-1 cell death associated with increased Myc expression. These findings underline the importance of differentiated targeting of JNK subtypes in the development of inflammatory β-cell failure and destruction.

Research Resource: A Dual Proteomic Approach Identifies Regulated Islet Proteins During β-Cell Mass Expansion In Vivo

Diabetes is characterized by insulin insufficiency due to a relative paucity of functional β-cell mass. Thus, strategies for increasing β-cell mass in situ are sought-after for therapeutic purposes. Pregnancy is a physiological state capable of inducing robust β-cell mass expansion, however, the mechanisms driving this expansion are not fully understood. Thus, the aim of this study was to characterize pregnancy-induced changes in the islet proteome at the peak of β-cell proliferation in mice. Islets from pregnant and nonpregnant littermates were compared via 2 proteomic strategies. In vivo pulsed stable isotope labeling of amino acids in cell culture was used to monitor de novo protein synthesis during the first 14.5 days of pregnancy. In parallel, protein abundance was determined using ex vivo dimethyl labelling at gestational day 14.5. Comparison of the 2 datasets revealed 170 islet proteins to be up regulated as a response to pregnancy. These included several proteins, not previously associated with pregnancy-induced islet expansion, such as CLIC1, STMN1, MCM6, PPIB, NEDD4, and HLTF. Confirming the validity of our approach, we also identified proteins encoded by genes known to be associated with pregnancy-induced islet expansion, such as CHGB, IGFBP5, MATN2, EHHADH, IVD, and BMP1. Bioinformatic analyses demonstrated enrichment and activation of the biological functions: "protein synthesis" and "proliferation," and predicted the transcription factors HNF4α, MYC, MYCN, E2F1, NFE2L2, and HNF1α as upstream regulators of the observed expressional changes. As the first characterization of the islet-proteome during pregnancy, this study provides novel insight into the mechanisms involved in promoting pregnancy-induced β-cell mass expansion and function.

Integrative enrichment analysis: a new computational method to detect dysregulated pathways in heterogeneous samples

BACKGROUND

Pathway enrichment analysis is a useful tool to study biology and biomedicine, due to its functional screening on well-defined biological procedures rather than separate molecules. The measurement of malfunctions of pathways with a phenotype change, e.g., from normal to diseased, is the key issue when applying enrichment analysis on a pathway. The differentially expressed genes (DEGs) are widely focused in conventional analysis, which is based on the great purity of samples. However, the disease samples are usually heterogeneous, so that, the genes with great differential expression variance (DEVGs) are becoming attractive and important to indicate the specific state of a biological system. In the context of differential expression variance, it is still a challenge to measure the enrichment or status of a pathway. To address this issue, we proposed Integrative Enrichment Analysis (IEA) based on a novel enrichment measurement.

RESULTS

The main competitive ability of IEA is to identify dysregulated pathways containing DEGs and DEVGs simultaneously, which are usually under-scored by other methods. Next, IEA provides two additional assistant approaches to investigate such dysregulated pathways. One is to infer the association among identified dysregulated pathways and expected target pathways by estimating pathway crosstalks. The other one is to recognize subtype-factors as dysregulated pathways associated to particular clinical indices according to the DEVGs' relative expressions rather than conventional raw expressions. Based on a previously established evaluation scheme, we found that, in particular cohorts (i.e., a group of real gene expression datasets from human patients), a few target disease pathways can be significantly high-ranked by IEA, which is more effective than other state-of-the-art methods. Furthermore, we present a proof-of-concept study on Diabetes to indicate: IEA rather than conventional ORA or GSEA can capture the under-estimated dysregulated pathways full of DEVGs and DEGs; these newly identified pathways could be significantly linked to prior-known disease pathways by estimated crosstalks; and many candidate subtype-factors recognized by IEA also have significant relation with the risk of subtypes of genotype-phenotype associations.

CONCLUSIONS

Totally, IEA supplies a new tool to carry on enrichment analysis in the complicate context of clinical application (i.e., heterogeneity of disease), as a necessary complementary and cooperative approach to conventional ones.

Deciphering Signaling Pathway Networks to Understand the Molecular Mechanisms of Metformin Action

A drug exerts its effects typically through a signal transduction cascade, which is non-linear and involves intertwined networks of multiple signaling pathways. Construction of such a signaling pathway network (SPNetwork) can enable identification of novel drug targets and deep understanding of drug action. However, it is challenging to synopsize critical components of these interwoven pathways into one network. To tackle this issue, we developed a novel computational framework, the Drug-specific Signaling Pathway Network (DSPathNet). The DSPathNet amalgamates the prior drug knowledge and drug-induced gene expression via random walk algorithms. Using the drug metformin, we illustrated this framework and obtained one metformin-specific SPNetwork containing 477 nodes and 1,366 edges. To evaluate this network, we performed the gene set enrichment analysis using the disease genes of type 2 diabetes (T2D) and cancer, one T2D genome-wide association study (GWAS) dataset, three cancer GWAS datasets, and one GWAS dataset of cancer patients with T2D on metformin. The results showed that the metformin network was significantly enriched with disease genes for both T2D and cancer, and that the network also included genes that may be associated with metformin-associated cancer survival. Furthermore, from the metformin SPNetwork and common genes to T2D and cancer, we generated a subnetwork to highlight the molecule crosstalk between T2D and cancer. The follow-up network analyses and literature mining revealed that seven genes (CDKN1A, ESR1, MAX, MYC, PPARGC1A, SP1, and STK11) and one novel MYC-centered pathway with CDKN1A, SP1, and STK11 might play important roles in metformin’s antidiabetic and anticancer effects. Some results are supported by previous studies. In summary, our study 1) develops a novel framework to construct drug-specific signal transduction networks; 2) provides insights into the molecular mode of metformin; 3) serves a model for exploring signaling pathways to facilitate understanding of drug action, disease pathogenesis, and identification of drug targets.

A deep understanding of a drug’s mechanisms of actions is essential not only in the discovery of new treatments but also in minimizing adverse effects. Here, we develop a computational framework, the Drug-specific Signaling Pathway Network (DSPathNet), to reconstruct a comprehensive signaling pathway network (SPNetwork) impacted by a particular drug. To illustrate this computational approach, we used metformin, an anti-diabetic drug, as an example. Starting from collecting the metformin-related upstream genes and inferring the metformin-related downstream genes, we built one metformin-specific SPNetwork via random walk based algorithms. Our evaluation of the metformin-specific SPNetwork by using disease genes and genotyping data from genome-wide association studies showed that our DSPathNet approach was efficient to synopsize drug’s key components and their relationship involved in the type 2 diabetes and cancer, even the metformin anticancer activity. This work presents a novel computational framework for constructing individual drug-specific signal transduction networks. Furthermore, its successful application to the drug metformin provides some valuable insights into the mode of metformin action, which will facilitate our understanding of the molecular mechanisms underlying drug treatments, disease pathogenesis, and identification of novel drug targets and repurposed drugs.

A high-throughput chemical screen reveals that harmine-mediated inhibition of DYRK1A increases human pancreatic beta cell replication

Types 1 and 2 diabetes affect some 380 million people worldwide. Both ultimately result from a deficiency of functional pancreatic insulin-producing beta cells. Beta cells proliferate in humans during a brief temporal window beginning around the time of birth, with a peak percentage (∼2%) engaged in the cell cycle in the first year of life. In embryonic life and after early childhood, beta cell replication is barely detectable. Whereas beta cell expansion seems an obvious therapeutic approach to beta cell deficiency, adult human beta cells have proven recalcitrant to such efforts. Hence, there remains an urgent need for antidiabetic therapeutic agents that can induce regeneration and expansion of adult human beta cells in vivo or ex vivo. Here, using a high-throughput small-molecule screen (HTS), we find that analogs of the small molecule harmine function as a new class of human beta cell mitogenic compounds. We also define dual-specificity tyrosine-regulated kinase-1a (DYRK1A) as the likely target of harmine and the nuclear factors of activated T cells (NFAT) family of transcription factors as likely mediators of human beta cell proliferation and differentiation. Using three different mouse and human islet in vivo-based models, we show that harmine is able to induce beta cell proliferation, increase islet mass and improve glycemic control. These observations suggest that harmine analogs may have unique therapeutic promise for human diabetes therapy. Enhancing the potency and beta cell specificity of these compounds are important future challenges.

Interleukin-1/toll-like receptor-induced nuclear factor kappa B signaling participates in intima hyperplasia after carotid artery balloon injury in goto-kakizaki rats: a potential target therapy pathway

The value of restenosis after percutaneous coronary intervention (PCI) is recognized worldwide, especially for diabetic patients. Interleukin-1/Toll-like receptor (IL-1/TLR) signaling is involved in innate and adaptive immune responses, but whether and how the IL-1/TLR-induced nuclear factor kappa B (NFκB) pathway plays key roles in intimal formation is unclear. The underlying mechanism of intima hyperplasia was investigated with a model of carotid balloon injury in Goto-Kakizaki (GK) and Wistar rats and with lipopolysaccharide-stimulated macrophages. Elastic-van Gieson staining showed the medial area peakedon Day 3 post-injury and decreased by Day 7 post-injury in both GK and Wistar rats. The N/M at Day 7 in GK rats was significantly higher than in Wistar rats (p<0.001). The percent of 5-ethynyl-2'-deoxyuridine (EdU) staining-positive cells on Day 3 post-injury was greater than seen on Day 7 post-injury in GK and Wistar rats. The percent of EdU-positive cells on Days 3 and 7 post-injury in Wistar rats was less than that found in GK rats (p<0.01; p<0.05). NFκBp65 immunostaining had increased by Day 7 post-injury. Agilent Whole Genome Oligo Microarray verified that the IL-1/TLR-induced NFκB pathway was activated by carotid balloon injury. TLR4, IL-1 receptor associated kinase, inhibitors α of NFκB, human antigen R, c-Myc (Proto-Oncogene Proteins), EGF-like module-containing mucin-like hormone receptor-like 1 and Interleukin-6 were up-regulated or down-regulated according to immunochemistry, quantitative real-time PCR, Western blotting and Enzyme linked immunosorbent assay. Overall, we conclude that the IL-1/TLR-induced NFκB pathway participates in the intimal hyperplasia after carotid injury in GK and Wistar rats and that GK rats respond more intensely to the inflammation than Wistar rats.

Long-term IKK2/NF-κB signaling in pancreatic β-cells induces immune-mediated diabetes

Type 1 diabetes is a multifactorial inflammatory disease in genetically susceptible individuals characterized by progressive autoimmune destruction of pancreatic β-cells initiated by yet unknown factors. Although animal models of type 1 diabetes have substantially increased our understanding of disease pathogenesis, heterogeneity seen in human patients cannot be reflected by a single model and calls for additional models covering different aspects of human pathophysiology. Inhibitor of κB kinase (IKK)/nuclear factor-κB (NF-κB) signaling is a master regulator of inflammation; however, its role in diabetes pathogenesis is controversially discussed by studies using different inhibition approaches. To investigate the potential diabetogenic effects of NF-κB in β-cells, we generated a gain-of-function model allowing conditional IKK2/NF-κB activation in β-cells. A transgenic mouse model that expresses a constitutively active mutant of human IKK2 dependent on Pdx-1 promoter activity (IKK2-CA(Pdx-1)) spontaneously develops full-blown immune-mediated diabetes with insulitis, hyperglycemia, and hypoinsulinemia. Disease development involves a gene expression program mimicking virus-induced diabetes and allergic inflammatory responses as well as increased major histocompatibility complex class I/II expression by β-cells that could collectively promote diabetes development. Potential novel diabetes candidate genes were also identified. Interestingly, animals successfully recovered from diabetes upon transgene inactivation. Our data give the first direct evidence that β-cell-specific IKK2/NF-κB activation is a potential trigger of immune-mediated diabetes. Moreover, IKK2-CA(Pdx-1) mice provide a novel tool for studying critical checkpoints in diabetes pathogenesis and mechanisms governing β-cell degeneration/regeneration.

Constructing regulatory networks to identify biomarkers for insulin resistance

Insulin resistance (IR) is a physiological condition in which cells fail to respond to the insulin hormone. Despite advances in the diagnosis and treatment of IR, novel molecular targets are still needed to improve the accuracy of diagnosis and the outcomes of therapy. Here, we present a systems approach to identify molecular biomarkers for IR. We downloaded the gene expression profile of IR from the Gene Expression Omnibus (GEO), generated a regulatory network by mapping co-expressed genes to transcription factors (TFs) and calculated the regulatory impact factor of each transcription factor. Finally, we selected a list of potential molecular targets that could be used as therapeutic targets or diagnostic biomarkers, including ETS1, AR, ESR1 and Myc. Our studies identified multiple TFs that could play an important role in the pathogenesis of IR and provided a systems understanding of the potential relationships among these genes. Our study has the potential to aid in the understanding of IR and provides a basis for IR biomarker discovery.

Failure of the adaptive unfolded protein response in islets of obese mice is linked with abnormalities in β-cell gene expression and progression to diabetes

The normal β-cell response to obesity-associated insulin resistance is hypersecretion of insulin. Type 2 diabetes develops in subjects with β-cells that are susceptible to failure. Here, we investigated the time-dependent gene expression changes in islets of diabetes-prone db/db and diabetes-resistant ob/ob mice. The expressions of adaptive unfolded protein response (UPR) genes were progressively induced in islets of ob/ob mice, whereas they declined in diabetic db/db mice. Genes important for β-cell function and maintenance of the islet phenotype were reduced with time in db/db mice, whereas they were preserved in ob/ob mice. Inflammation and antioxidant genes displayed time-dependent upregulation in db/db islets but were unchanged in ob/ob islets. Treatment of db/db mouse islets with the chemical chaperone 4-phenylbutyric acid partially restored the changes in several β-cell function genes and transcription factors but did not affect inflammation or antioxidant gene expression. These data suggest that the maintenance (or suppression) of the adaptive UPR is associated with β-cell compensation (or failure) in obese mice. Inflammation, oxidative stress, and a progressive loss of β-cell differentiation accompany diabetes progression. The ability to maintain the adaptive UPR in islets may protect against the gene expression changes that underlie diabetes development in obese mice.

Role of the saturated nonesterified fatty acid palmitate in beta cell dysfunction

Sustained elevated levels of saturated free fatty acids, such as palmitate, contribute to beta cell dysfunction, a phenomenon aggravated by high glucose levels. The aim of this study was to investigate the mechanisms of palmitate-induced beta cell dysfunction and death, combined or not with high glucose. Protein profiling of INS-1E cells, exposed to 0.5 mmol/L palmitate and combined or not with 25 mmol/L glucose, for 24 h was done by 2D-DIGE, both on full cell lysate and on an enriched endoplasmic reticulum (ER) fraction. Eighty-three differentially expressed proteins (P < 0.05) were identified by MALDI-TOF/TOF mass spectrometry and proteomic results were confirmed by functional assays. 2D-DIGE analysis of whole cell lysates and ER enriched samples revealed a high number of proteins compared to previous reports. Palmitate induced beta cell dysfunction and death via ER stress, hampered insulin maturation, generation of harmful metabolites during triglycerides synthesis and altered intracellular trafficking. In combination with high glucose, palmitate induced increased shunting of excess glucose, increased mitochondrial reactive oxygen species production and an elevation in many transcription-related proteins. This study contributes to a better understanding and revealed novel mechanisms of palmitate-induced beta cell dysfunction and death and may provide new targets for drug discovery.

The molecular mechanisms of pancreatic β-cell glucotoxicity: recent findings and future research directions

It is well established that regular physiological stimulation by glucose plays a crucial role in the maintenance of the β-cell differentiated phenotype. In contrast, prolonged or repeated exposure to elevated glucose concentrations both in vitro and in vivo exerts deleterious or toxic effects on the β-cell phenotype, a concept termed as glucotoxicity. Evidence indicates that the latter may greatly contribute to the pathogenesis of type 2 diabetes. Through the activation of several mechanisms and signaling pathways, high glucose levels exert deleterious effects on β-cell function and survival and thereby, lead to the worsening of the disease over time. While the role of high glucose-induced β-cell overstimulation, oxidative stress, excessive Unfolded Protein Response (UPR) activation, and loss of differentiation in the alteration of the β-cell phenotype is well ascertained, at least in vitro and in animal models of type 2 diabetes, the role of other mechanisms such as inflammation, O-GlcNacylation, PKC activation, and amyloidogenesis requires further confirmation. On the other hand, protein glycation is an emerging mechanism that may play an important role in the glucotoxic deterioration of the β-cell phenotype. Finally, our recent evidence suggests that hypoxia may also be a new mechanism of β-cell glucotoxicity. Deciphering these molecular mechanisms of β-cell glucotoxicity is a mandatory first step toward the development of therapeutic strategies to protect β-cells and improve the functional β-cell mass in type 2 diabetes.

The protective effect of resveratrol on islet insulin secretion and morphology in mice on a high-fat diet

The aim of this study was to investigate the effect of resveratrol on beta cells in male C57BL/6J mice fed a high-fat diet and the possible mechanisms. Male C57BL/6J mice were randomly divided into three groups: normal control (NC) group, high-fat diet (HF) group and high-fat diet and resveratrol treatment (HFR) group (15 in each group). HFR group was fed with high fat diet for 8 weeks and then orally administered resveratrol at 400mg/kg daily. Twenty-four weeks later, the function of insulin secretion in vivo and in vitro was improved robustly in HFR group compared with HF group. The levels of glucose and lipid metabolism, beta cell mass, lipid content, and oxidative stress were lower in HFR group than in HF group. Simultaneously, resveratrol administration promoted the expression of SIRT1 in islets, while the expression of uncoupling protein 2 (UCP2) was restrained. Resveratrol, as well, also had a beneficial effect on the ratios of expressions of Bcl-2/Bax and levels of malondialdehyde/glutathione peroxidase. Resveratrol can protect islets from abnormal insulin secretion and morphological changes induced by a high-fat diet. The effect might be partly related to activated SIRT1 signal pathway, improved oxidative stress induced damage and incidence of apoptosis.

Overexpression of hepatocyte nuclear factor-4α initiates cell cycle entry, but is not sufficient to promote β-cell expansion in human islets

The transcription factor HNF4α (hepatocyte nuclear factor-4α) is required for increased β-cell proliferation during metabolic stress in vivo. We hypothesized that HNF4α could induce proliferation of human β-cells. We employed adenoviral-mediated overexpression of an isoform of HNF4α (HNF4α8) alone, or in combination with cyclin-dependent kinase (Cdk)6 and Cyclin D3, in human islets. Heightened HNF4α8 expression led to a 300-fold increase in the number of β-cells in early S-phase. When we overexpressed HNF4α8 together with Cdk6 and Cyclin D3, β-cell cycle entry was increased even further. However, the punctate manner of bromodeoxyuridine incorporation into HNF4α(High) β-cells indicated an uncoupling of the mechanisms that control the concise timing and execution of each cell cycle phase. Indeed, in HNF4α8-induced bromodeoxyuridine(+,punctate) β-cells we observed signs of dysregulated DNA synthesis, cell cycle arrest, and activation of a double stranded DNA damage-associated cell cycle checkpoint mechanism, leading to the initiation of loss of β-cell lineage fidelity. However, a substantial proportion of β-cells stimulated to enter the cell cycle by Cdk6 and Cyclin D3 alone also exhibited a DNA damage response. HNF4α8 is a mitogenic signal in the human β-cell but is not sufficient for completion of the cell cycle. The DNA damage response is a barrier to efficient β-cell proliferation in vitro, and we suggest its evaluation in all attempts to stimulate β-cell replication as an approach to diabetes treatment.

A simple matter of life and death-the trials of postnatal Beta-cell mass regulation

Pancreatic beta-cells, which secrete the hormone insulin, are the key arbiters of glucose homeostasis. Defective beta-cell numbers and/or function underlie essentially all major forms of diabetes and must be restored if diabetes is to be cured. Thus, the identification of the molecular regulators of beta-cell mass and a better understanding of the processes of beta-cell differentiation and proliferation may provide further insight for the development of new therapeutic targets for diabetes. This review will focus on the principal hormones and nutrients, as well as downstream signalling pathways regulating beta-cell mass in the adult. Furthermore, we will also address more recently appreciated regulators of beta-cell mass, such as microRNAs.

Inhibition of Id1 augments insulin secretion and protects against high-fat diet-induced glucose intolerance

OBJECTIVE

The molecular mechanisms responsible for pancreatic β-cell dysfunction in type 2 diabetes remain unresolved. Increased expression of the helix-loop-helix protein Id1 has been found in islets of diabetic mice and in vitro models of β-cell dysfunction. Here, we investigated the role of Id1 in insulin secretion and glucose homeostasis.

RESEARCH DESIGN AND METHODS

Id1 knockout (Id1(-/-)) and wild-type mice were fed a chow or high-fat diet. Glucose tolerance, insulin tolerance, β-cell mass, insulin secretion, and islet gene expression were assessed. Small interfering RNA (siRNA) was used to silence Id1 in MIN6 cells, and responses to chronic palmitate treatment were assessed.

RESULTS

Id1(-/-) mice exhibited an improved response to glucose challenge and were almost completely protected against glucose intolerance induced by high-fat diet. This was associated with increased insulin levels and enhanced insulin release from isolated islets, whereas energy intake, body weight, fat pad weight, β-cell mass, and insulin action were unchanged. Islets from Id1(-/-) mice displayed reduced stress gene expression and were protected against high-fat diet-induced downregulation of β-cell gene expression (pancreatic duodenal homeobox-1, Beta2, Glut2, pyruvate carboxylase, and Gpr40). In MIN6 cells, siRNA-mediated inhibition of Id1 enhanced insulin secretion after chronic palmitate treatment and protected against palmitate-mediated loss of β-cell gene expression.

CONCLUSIONS

These findings implicate Id1 as a negative regulator of insulin secretion. Id1 expression plays an essential role in the etiology of glucose intolerance, insulin secretory dysfunction, and β-cell dedifferentiation under conditions of increased lipid supply.

cMyc is a principal upstream driver of beta-cell proliferation in rat insulinoma cell lines and is an effective mediator of human beta-cell replication

Adult human β-cells replicate slowly. Also, despite the abundance of rodent β-cell lines, there are no human β-cell lines for diabetes research or therapy. Prior studies in four commonly studied rodent β-cell lines revealed that all four lines displayed an unusual, but strongly reproducible, cell cycle signature: an increase in seven G(1)/S molecules, i.e. cyclins A, D3, and E, and cdk1, -2, -4, and -6. Here, we explore the upstream mechanism(s) that drive these cell cycle changes. Using biochemical, pharmacological and molecular approaches, we surveyed potential upstream mitogenic signaling pathways in Ins 1 and RIN cells. We used both underexpression and overexpression to assess effects on rat and human β-cell proliferation, survival and cell cycle control. Our results indicate that cMyc is: 1) uniquely up-regulated among other candidates; 2) principally responsible for the increase in the seven G(1)/S molecules; and, 3) largely responsible for proliferation in rat β-cell lines. Importantly, cMyc expression in β-cell lines, although some 5- to 7-fold higher than normal rat β-cells, is far below the levels (75- to 150-fold) previously associated with β-cell death and dedifferentiation. Notably, modest overexpression of cMyc is able to drive proliferation without cell death in normal rat and human β-cells. We conclude that cMyc is an important driver of replication in the two most commonly employed rat β-cell lines. These studies reverse the current paradigm in which cMyc overexpression is inevitably associated with β-cell death and dedifferentiation. The cMyc pathway provides potential approaches, targets, and tools for driving and sustaining human β-cell replication.

Redundant role of the cytochrome c-mediated intrinsic apoptotic pathway in pancreatic β-cells

Cytochrome c is one of the central mediators of the mitochondrial or the intrinsic apoptotic pathway. Mice harboring a 'knock-in' mutation of cytochrome c, impairing only its apoptotic function, have permitted studies on the essential role of cytochrome c-mediated apoptosis in various tissue homeostasis. To this end, we examined the role of cytochrome c in pancreatic β-cells under homeostatic conditions and in diabetes models, including those induced by streptozotocin (STZ) and c-Myc. Previous studies have shown that both STZ- and c-Myc-induced β-cell apoptosis is mediated through caspase-3 activation; however, the precise mechanism in these modes of cell death was not characterized. The results of our study show that lack of functional cytochrome c does not affect glucose homeostasis or pancreatic β-cell mass under basal conditions. Moreover, the cytochrome c-mediated intrinsic apoptotic pathway is required for neither STZ- nor c-Myc-induced β-cell death. We also observed that the extrinsic apoptotic pathway mediated through caspase-8 was not essential in c-Myc-induced β-cell destruction. These findings suggest that cytochrome c is not required for STZ-induced β-cell apoptosis and, together with the caspase-8-mediated extrinsic pathway, plays a redundant role in c-Myc-induced β-cell apoptosis.