Recovery from diabetes in mice by beta cell regeneration

Neuronal glucose sensing mechanisms and circuits in the control of insulin and glucagon secretion

Glucose homeostasis is mainly under the control of the pancreatic islet hormones insulin and glucagon, which, respectively, stimulate glucose uptake and utilization by liver, fat, and muscle and glucose production by the liver. The balance between the secretions of these hormones is under the control of blood glucose concentrations. Indeed, pancreatic islet β-cells and α-cells can sense variations in glycemia and respond by an appropriate secretory response. However, the secretory activity of these cells is also under multiple additional metabolic, hormonal, and neuronal signals that combine to ensure the perfect control of glycemia over a lifetime. The central nervous system (CNS), which has an almost absolute requirement for glucose as a source of metabolic energy and thus a vital interest in ensuring that glycemic levels never fall below ∼5 mM, is equipped with populations of neurons responsive to changes in glucose concentrations. These neurons control pancreatic islet cell secretion activity in multiple ways: through both branches of the autonomic nervous system, through the hypothalamic-pituitary-adrenal axis, and by secreting vasopressin (AVP) in the blood at the level of the posterior pituitary. Here, we present the autonomic innervation of the pancreatic islets; the mechanisms of neuron activation by a rise or a fall in glucose concentration; how current viral tracing, chemogenetic, and optogenetic techniques allow integration of specific glucose sensing neurons in defined neuronal circuits that control endocrine pancreas function; and, finally, how genetic screens in mice can untangle the diversity of the hypothalamic mechanisms controlling the response to hypoglycemia.

Moderate beta-cell ablation triggers synergic compensatory mechanisms even in the absence of overt metabolic disruption

Regeneration, the ability to replace injured tissues and organs, is a phenomenon commonly associated with lower vertebrates but is also observed in mammals, in specific tissues. In this study, we investigated the regenerative potential of pancreatic islets following moderate beta-cell loss in mice. Using a rapid model of moderate ablation, we observed a compensatory response characterized by transient inflammation and proliferation signatures, ultimately leading to the recovery of beta-cell identity and function. Interestingly, this proliferative response occurred independently of inflammation, as demonstrated in ablated immunodeficient mice. Furthermore, exposure to high-fat diet stimulated beta-cell proliferation but negatively impacted beta-cell function. In contrast, an equivalent slower ablation model revealed a delayed but similar proliferative response, suggesting proliferation as a common regenerative response. However, high-fat diet failed to promote proliferation in this model, indicating a differential response to metabolic stressors. Overall, our findings shed light on the complex interplay between beta-cell loss, inflammation, and stress in modulating pancreatic islet regeneration. Understanding these mechanisms could pave the way for novel therapeutic strategies based on beta-cell proliferation.

Optogenetic stimulation of vagal nerves for enhanced glucose-stimulated insulin secretion and β cell proliferation

The enhancement of insulin secretion and of the proliferation of pancreatic β cells are promising therapeutic options for diabetes. Signals from the vagal nerve regulate both processes, yet the effectiveness of stimulating the nerve is unclear, owing to a lack of techniques for doing it so selectively and prolongedly. Here we report two optogenetic methods for vagal-nerve stimulation that led to enhanced glucose-stimulated insulin secretion and to β cell proliferation in mice expressing choline acetyltransferase-channelrhodopsin 2. One method involves subdiaphragmatic implantation of an optical fibre for the photostimulation of cholinergic neurons expressing a blue-light-sensitive opsin. The other method, which suppressed streptozotocin-induced hyperglycaemia in the mice, involves the selective activation of vagal fibres by placing blue-light-emitting lanthanide microparticles in the pancreatic ducts of opsin-expressing mice, followed by near-infrared illumination. The two methods show that signals from the vagal nerve, especially from nerve fibres innervating the pancreas, are sufficient to regulate insulin secretion and β cell proliferation.

Acinar to β-like cell conversion through inhibition of focal adhesion kinase

Insufficient functional β-cell mass causes diabetes; however, an effective cell replacement therapy for curing diabetes is currently not available. Reprogramming of acinar cells toward functional insulin-producing cells would offer an abundant and autologous source of insulin-producing cells. Our lineage tracing studies along with transcriptomic characterization demonstrate that treatment of adult mice with a small molecule that specifically inhibits kinase activity of focal adhesion kinase results in trans-differentiation of a subset of peri-islet acinar cells into insulin producing β-like cells. The acinar-derived insulin-producing cells infiltrate the pre-existing endocrine islets, partially restore β-cell mass, and significantly improve glucose homeostasis in diabetic mice. These findings provide evidence that inhibition of the kinase activity of focal adhesion kinase can convert acinar cells into insulin-producing cells and could offer a promising strategy for treating diabetes.

Biochemical pancreatic β-cell lineage reprogramming: Various cell fate shifts

The incidence of pancreatic diseases has been continuously rising in recent years. Thus, research on pancreatic regeneration is becoming more popular. Chronic hyperglycemia is detrimental to pancreatic β-cells, leading to impairment of insulin secretion which is the main hallmark of pancreatic diseases. Obtaining plenty of functional pancreatic β-cells is the most crucial aspect when studying pancreatic biology and treating diabetes. According to the International Diabetes Federation, diabetes has become a global epidemic, with about 3 million people suffering from diabetes worldwide. Hyperglycemia can lead to many dangerous diseases, including amputation, blindness, neuropathy, stroke, and cardiovascular and kidney diseases. Insulin is widely used in the treatment of diabetes; however, innovative approaches are needed in the academic and preclinical stages. A new approach aims at synthesizing patient-specific functional pancreatic β-cells. The present article focuses on how cells from different tissues can be transformed into pancreatic β-cells.

Animal models for type 1 and type 2 diabetes: advantages and limitations

Diabetes mellitus, commonly referred to as diabetes, is a group of metabolic disorders characterized by chronic elevation in blood glucose levels, resulting from inadequate insulin production, defective cellular response to extracellular insulin, and/or impaired glucose metabolism. The two main types that account for most diabetics are type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM), each with their own pathophysiological features. T1D is an autoimmune condition where the body's immune system attacks and destroys the insulin-producing beta cells in the pancreas. This leads to lack of insulin, a vital hormone for regulating blood sugar levels and cellular glucose uptake. As a result, those with T1D depend on lifelong insulin therapy to control their blood glucose level. In contrast, T2DM is characterized by insulin resistance, where the body's cells do not respond effectively to insulin, coupled with a relative insulin deficiency. This form of diabetes is often associated with obesity, sedentary lifestyle, and/or genetic factors, and it is managed with lifestyle changes and oral medications. Animal models play a crucial role in diabetes research. However, given the distinct differences between T1DM and T2DM, it is imperative for researchers to employ specific animal models tailored to each condition for a better understanding of the impaired mechanisms underlying each condition, and for assessing the efficacy of new therapeutics. In this review, we discuss the distinct animal models used in type 1 and type 2 diabetes mellitus research and discuss their strengths and limitations.

Regulation of multiple signaling pathways promotes the consistent expansion of human pancreatic progenitors in defined conditions

The unlimited expansion of human progenitor cells in vitro could unlock many prospects for regenerative medicine. However, it remains an important challenge as it requires the decoupling of the mechanisms supporting progenitor self-renewal and expansion from those mechanisms promoting their differentiation. This study focuses on the expansion of human pluripotent stem (hPS) cell-derived pancreatic progenitors (PP) to advance novel therapies for diabetes. We obtained mechanistic insights into PP expansion requirements and identified conditions for the robust and unlimited expansion of hPS cell-derived PP cells under GMP-compliant conditions through a hypothesis-driven iterative approach. We show that the combined stimulation of specific mitogenic pathways, suppression of retinoic acid signaling, and inhibition of selected branches of the TGFβ and Wnt signaling pathways are necessary for the effective decoupling of PP proliferation from differentiation. This enabled the reproducible, 2000-fold, over 10 passages and 40-45 d, expansion of PDX1+/SOX9+/NKX6-1+ PP cells. Transcriptome analyses confirmed the stabilization of PP identity and the effective suppression of differentiation. Using these conditions, PDX1+/SOX9+/NKX6-1+ PP cells, derived from different, both XY and XX, hPS cell lines, were enriched to nearly 90% homogeneity and expanded with very similar kinetics and efficiency. Furthermore, non-expanded and expanded PP cells, from different hPS cell lines, were differentiated in microwells into homogeneous islet-like clusters (SC-islets) with very similar efficiency. These clusters contained abundant β-cells of comparable functionality as assessed by glucose-stimulated insulin secretion assays. These findings established the signaling requirements to decouple PP proliferation from differentiation and allowed the consistent expansion of hPS cell-derived PP cells. They will enable the establishment of large banks of GMP-produced PP cells derived from diverse hPS cell lines. This approach will streamline SC-islet production for further development of the differentiation process, diabetes research, personalized medicine, and cell therapies.

Hyperglucagonaemia in diabetes: altered amino acid metabolism triggers mTORC1 activation, which drives glucagon production

AIM/HYPOTHESIS

Hyperglycaemia is associated with alpha cell dysfunction, leading to dysregulated glucagon secretion in type 1 and type 2 diabetes; however, the mechanisms involved are still elusive. The nutrient sensor mammalian target of rapamycin complex 1 (mTORC1) plays a major role in the maintenance of alpha cell mass and function. We studied the regulation of alpha cell mTORC1 by nutrients and its role in the development of hyperglucagonaemia in diabetes.

METHODS

Alpha cell mTORC1 activity was assessed by immunostaining for phosphorylation of its downstream target, the ribosomal protein S6, and glucagon, followed by confocal microscopy on pancreatic sections and flow cytometry on dispersed human and mouse islets and the alpha cell line, αTC1-6. Metabolomics and metabolic flux were studied by 13C glucose labelling in 2.8 or 16.7 mmol/l glucose followed by LC-MS analysis. To study the role of mTORC1 in mediating hyperglucagonaemia in diabetes, we generated an inducible alpha cell-specific Rptor knockout in the Akita mouse model of diabetes and tested the effects on glucose tolerance by IPGTT and on glucagon secretion.

RESULTS

mTORC1 activity was increased in alpha cells from diabetic Akita mice in parallel to the development of hyperglycaemia and hyperglucagonaemia (two- to eightfold increase). Acute exposure of mouse and human islets to amino acids stimulated alpha cell mTORC1 (3.5-fold increase), whereas high glucose concentrations inhibited mTORC1 (1.4-fold decrease). The mTORC1 response to glucose was abolished in human and mouse diabetic alpha cells following prolonged islet exposure to high glucose levels, resulting in sustained activation of mTORC1, along with increased glucagon secretion. Metabolomics and metabolic flux analysis showed that exposure to high glucose levels enhanced glycolysis, glucose oxidation and the synthesis of glucose-derived amino acids. In addition, chronic exposure to high glucose levels increased the expression of Slc7a2 and Slc38a4, which encode amino acid transporters, as well as the levels of branched-chain amino acids and methionine cycle metabolites (~1.3-fold increase for both). Finally, conditional Rptor knockout in alpha cells from adult diabetic mice inhibited mTORC1, thereby inhibiting glucagon secretion (~sixfold decrease) and improving diabetes, despite persistent insulin deficiency.

CONCLUSIONS/INTERPRETATION

Alpha cell exposure to hyperglycaemia enhances amino acid synthesis and transport, resulting in sustained activation of mTORC1, thereby increasing glucagon secretion. mTORC1 therefore plays a major role in mediating alpha cell dysfunction in diabetes.

DATA AVAILABILITY

All sequencing data are available from the Gene Expression Omnibus (GEO) repository (accession no. GSE154126; https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE154126 ).

Regeneration of Pancreatic Beta Cells by Modulation of Molecular Targets Using Plant-Derived Compounds: Pharmacological Mechanisms and Clinical Potential

Type 2 diabetes (T2D) is characterized by pancreatic beta-cell dysfunction, increased cell death and loss of beta-cell mass despite chronic treatment. Consequently, there has been growing interest in developing beta cell-centered therapies. Beta-cell regeneration is mediated by augmented beta-cell proliferation, transdifferentiation of other islet cell types to functional beta-like cells or the reprograming of beta-cell progenitors into fully differentiated beta cells. This mediation is orchestrated by beta-cell differentiation transcription factors and the regulation of the cell cycle machinery. This review investigates the beta-cell regenerative potential of antidiabetic plant extracts and phytochemicals. Various preclinical studies, including in vitro, in vivo and ex vivo studies, are highlighted. Further, the potential regenerative mechanisms and the intra and extracellular mediators that are of significance are discussed. Also, the potential of phytochemicals to translate into regenerative therapies for T2D patients is highlighted, and some suggestions regarding future perspectives are made.

A highly sensitive strategy for monitoring real-time proliferation of targeted cell types in vivo

Cell proliferation processes play pivotal roles in timely adaptation to many biological situations. Herein, we establish a highly sensitive and simple strategy by which time-series showing the proliferation of a targeted cell type can be quantitatively monitored in vivo in the same individuals. We generate mice expressing a secreted type of luciferase only in cells producing Cre under the control of the Ki67 promoter. Crossing these with tissue-specific Cre-expressing mice allows us to monitor the proliferation time course of pancreatic β-cells, which are few in number and weakly proliferative, by measuring plasma luciferase activity. Physiological time courses, during obesity development, pregnancy and juvenile growth, as well as diurnal variation, of β-cell proliferation, are clearly detected. Moreover, this strategy can be utilized for highly sensitive ex vivo screening for proliferative factors for targeted cells. Thus, these technologies may contribute to advancements in broad areas of biological and medical research.

Matters arising: Insufficient evidence that pancreatic β cells are derived from adult ductal Neurog3-expressing progenitors

Understanding the origin of pancreatic β cells has profound implications for regenerative therapies in diabetes. For over a century, it was widely held that adult pancreatic duct cells act as endocrine progenitors, but lineage-tracing experiments challenged this dogma. Gribben et al. recently used two existing lineage-tracing models and single-cell RNA sequencing to conclude that adult pancreatic ducts contain endocrine progenitors that differentiate to insulin-expressing β cells at a physiologically important rate. We now offer an alternative interpretation of these experiments. Our data indicate that the two Cre lines that were used directly label adult islet somatostatin-producing ∂ cells, which precludes their use to assess whether β cells originate from duct cells. Furthermore, many labeled ∂ cells, which have an elongated neuron-like shape, were likely misclassified as β cells because insulin-somatostatin coimmunolocalizations were not used. We conclude that most evidence so far indicates that endocrine and exocrine lineage borders are rarely crossed in the adult pancreas.

Determinants and dynamics of pancreatic islet architecture

The islets of Langerhans are highly organized structures that have species-specific, three-dimensional tissue architecture. Islet architecture is critical for proper hormone secretion in response to nutritional stimuli. Islet architecture is disrupted in all types of diabetes mellitus and in cadaveric islets for transplantation during isolation, culture, and perfusion, limiting patient outcomes. Moreover, recapitulating native islet architecture remains a key challenge for in vitro generation of islets from stem cells. In this review, we discuss work that has led to the current understanding of determinants of pancreatic islet architecture, and how this architecture is maintained or disrupted during tissue remodeling in response to normal and pathological metabolic changes. We further discuss both empirical and modeling data that highlight the importance of islet architecture for islet function.

Chronic Intermittent Hypoxia during Sleep Causes Browning of Interscapular Adipose Tissue Accompanied by Local Insulin Resistance in Mice

Obstructive sleep apnea (OSA) is a highly prevalent condition, characterized by intermittent hypoxia (IH), sleep disruption, and altered autonomic nervous system function. OSA has been independently associated with dyslipidemia, insulin resistance, and metabolic syndrome. Brown adipose tissue (BAT) has been suggested as a modulator of systemic glucose tolerance through adaptive thermogenesis. Reductions in BAT mass have been associated with obesity and metabolic syndrome. No studies have systematically characterized the effects of chronic IH on BAT. Thus, we aimed to delineate IH effects on BAT and concomitant metabolic changes. C57BL/6J 8-week-old male mice were randomly assigned to IH during sleep (alternating 90 s cycles of 6.5% F_IO₂ followed by 21% F_IO₂) or normoxia (room air, RA) for 10 weeks. Mice were subjected to glucose tolerance testing and ¹⁸F-FDG PET-MRI towards the end of the exposures followed by BAT tissues analyses for morphological and global transcriptomic changes. Animals exposed to IH were glucose intolerant despite lower total body weight and adiposity. BAT tissues in IH-exposed mice demonstrated characteristic changes associated with "browning"-smaller lipids, increased vascularity, and a trend towards higher protein levels of UCP1. Conversely, mitochondrial DNA content and protein levels of respiratory chain complex III were reduced. Pro-inflammatory macrophages were more abundant in IH-exposed BAT. Transcriptomic analysis revealed increases in fatty acid oxidation and oxidative stress pathways in IH-exposed BAT, along with a reduction in pathways related to myogenesis, hypoxia, and IL-4 anti-inflammatory response. Functionally, IH-exposed BAT demonstrated reduced absorption of glucose on PET scans and reduced phosphorylation of AKT in response to insulin. Current studies provide initial evidence for the presence of a maladaptive response of interscapular BAT in response to chronic IH mimicking OSA, resulting in a paradoxical divergence, namely, BAT browning but tissue-specific and systemic insulin resistance. We postulate that oxidative stress, mitochondrial dysfunction, and inflammation may underlie these dichotomous outcomes in BAT.

Glycemic control releases regenerative potential of pancreatic beta cells blocked by severe hyperglycemia

Diabetogenic ablation of beta cells in mice triggers a regenerative response whereby surviving beta cells proliferate and euglycemia is regained. Here, we identify and characterize heterogeneity in response to beta cell ablation. Efficient beta cell elimination leading to severe hyperglycemia (>28 mmol/L), causes permanent diabetes with failed regeneration despite cell cycle engagement of surviving beta cells. Strikingly, correction of glycemia via insulin, SGLT2 inhibition, or a ketogenic diet for about 3 weeks allows partial regeneration of beta cell mass and recovery from diabetes, demonstrating regenerative potential masked by extreme glucotoxicity. We identify gene expression changes in beta cells exposed to extremely high glucose levels, pointing to metabolic stress and downregulation of key cell cycle genes, suggesting failure of cell cycle completion. These findings reconcile conflicting data on the impact of glucose on beta cell regeneration and identify a glucose threshold converting glycemic load from pro-regenerative to anti-regenerative.

Regenerating islet-derived protein 3 gamma (Reg3g) ameliorates tacrolimus-induced pancreatic β-cell dysfunction in mice by restoring mitochondrial function

BACKGROUND AND PURPOSE

Tacrolimus a first-line medication used after transplantation can induce β-cell dysfunction, causing new-onset diabetes mellitus (NODM). Regenerating islet-derived protein 3 gamma (Reg3g), a member of the pancreatic regenerative gene family, has been reported to improve type 1 diabetes by promoting β-cell regeneration. We aim to investigate the role of Reg3g in reversing tacrolimus-induced β-cell dysfunction and NODM in mice.

EXPERIMENTAL APPROACH

Circulating REG3A (the human homologue of mouse Reg3g) in heart transplantation patients treated with tacrolimus was detected. The glucose-stimulated insulin secretion and mitochondrial functions, including mitochondria membrane potential (MMP), mitochondria calcium, ATP production, oxygen consumption rate and mitochondrial morphology were investigated in β-cells. Additionally, effects of Reg3g on tacrolimus-induced NODM in mice were analysed.

KEY RESULTS

Circulating REG3A level in heart transplantation patients with NODM significantly decreased compared with those without diabetes. Tacrolimus down-regulated Reg3g via inhibiting STAT3-mediated transcription activation. Moreover, Reg3g restored glucose-stimulated insulin secretion suppressed by tacrolimus in β-cells by improving mitochondrial functions, including increased MMP, mitochondria calcium uptake, ATP production, oxygen consumption rate and contributing to an intact mitochondrial morphology. Mechanistically, Reg3g increased accumulation of pSTAT3(Ser727) in mitochondria by activating ERK1/2-STAT3 signalling pathway, leading to restoration of tacrolimus-induced mitochondrial impairment. Reg3g overexpression also effectively mitigated tacrolimus-induced NODM in mice.

CONCLUSION AND IMPLICATIONS

Reg3g can significantly ameliorate tacrolimus-induced β-cell dysfunction by restoring mitochondrial function in a pSTAT3(Ser727)-dependent manner. Our observations identify a novel Reg3g-mediated mechanism that is involved in tacrolimus-induced NODM and establish the novel role of Reg3g in reversing tacrolimus-induced β-cell dysfunction.

Glucagon-receptor-antagonism-mediated β-cell regeneration as an effective anti-diabetic therapy

Type 1 diabetes mellitus (T1D) is a chronic disease with potentially severe complications, and β-cell deficiency underlies this disease. Despite active research, no therapy to date has been able to induce β-cell regeneration in humans. Here, we discover the β-cell regenerative effects of glucagon receptor antibody (anti-GcgR). Treatment with anti-GcgR in mouse models of β-cell deficiency leads to reversal of hyperglycemia, increase in plasma insulin levels, and restoration of β-cell mass. We demonstrate that both β-cell proliferation and α- to β-cell transdifferentiation contribute to anti-GcgR-induced β-cell regeneration. Interestingly, anti-GcgR-induced α-cell hyperplasia can be uncoupled from β-cell regeneration after antibody clearance from the body. Importantly, we are able to show that anti-GcgR-induced β-cell regeneration is also observed in non-human primates. Furthermore, anti-GcgR and anti-CD3 combination therapy reverses diabetes and increases β-cell mass in a mouse model of autoimmune diabetes.

Roles of FoxM1-driven basal β-cell proliferation in maintenance of β-cell mass and glucose tolerance during adulthood

Aims/Introduction

Whether basal β‐cell proliferation during adulthood is involved in maintaining sufficient β‐cell mass, and if so, the molecular mechanism(s) underlying basal β‐cell proliferation remain unclear. FoxM1 is a critical transcription factor which is known to play roles in ‘adaptive’ β‐cell proliferation, which facilitates rapid increases in β‐cell mass in response to increased insulin demands. Therefore, herein we focused on the roles of β‐cell FoxM1 in ‘basal’ β‐cell proliferation under normal conditions and in the maintenance of sufficient β‐cell mass as well as glucose homeostasis during adulthood.

Materials and Methods

FoxM1 deficiency was induced specifically in β‐cells of 8‐week‐old mice, followed by analyzing its short‐ (2 weeks) and long‐ (10 months) term effects on β‐cell proliferation, β‐cell mass, and glucose tolerance.

Results

FoxM1 deficiency suppressed β‐cell proliferation at both ages, indicating critical roles of FoxM1 in basal β‐cell proliferation throughout adulthood. While short‐term FoxM1 deficiency affected neither β‐cell mass nor glucose tolerance, long‐term FoxM1 deficiency suppressed β‐cell mass increases with impaired insulin secretion, thereby worsening glucose tolerance. In contrast, the insulin secretory function was not impaired in islets isolated from mice subjected to long‐term β‐cell FoxM1 deficiency. Therefore, β‐cell mass reduction is the primary cause of impaired insulin secretion and deterioration of glucose tolerance due to long‐term β‐cell FoxM1 deficiency.

Conclusions

Basal low‐level proliferation of β‐cells during adulthood is important for maintaining sufficient β‐cell mass and good glucose tolerance and β‐cell FoxM1 underlies this mechanism. Preserving β‐cell FoxM1 activity may prevent the impairment of glucose tolerance with advancing age.

Txnip deficiency promotes β-cell proliferation in the HFD-induced obesity mouse model

Elucidating the mechanisms of regulation of β-cell proliferation is key to understanding the pathogenesis of diabetes mellitus. Txnip is a tumor suppressor that is upregulated in diabetes and plays an important role in the regulation of insulin sensitivity; however, its potential effect on pancreatic β-cell proliferation remains unclear. Here, we evaluated the role of Txnip in pancreatic β-cell compensatory proliferation by subjecting WT and Txnip knockout (KO) mice to a high-fat diet (HFD). Our results demonstrate that Txnip deficiency improves glucose tolerance and increases insulin sensitivity in HFD-induced obesity. The antidiabetogenic effect of Txnip deficiency was accompanied by increased β-cell proliferation and enhanced β-cell mass expansion. Furthermore, Txnip deficiency modulated the expression of a set of transcription factors with key roles in β-cell proliferation and cell cycle regulation. Txnip KO in HFD mice also led to activated levels of p-PI3K, p-AKT, p-mTOR and p-GSK3β, suggesting that Txnip may act via PI3K/AKT signaling to suppress β-cell proliferation. Thus, our work provides a theoretical basis for Txnip as a new therapeutic target for the treatment of diabetes mellitus.

Membrane tethering of CreER decreases uninduced cell labeling and cytotoxicity while maintaining recombination efficiency

Genetic lineage tracing is indispensable to unraveling the origin, fate, and plasticity of cells. However, the intrinsic leakiness in the CreER-loxP system raises concerns on data interpretation. Here, we reported the generation of a novel dual inducible CreER-loxP system with superior labeling characteristics. This two-component system consists of membrane localized CreER (mCreER: CD8α-FRB-CS-CreER) and TEV protease (mTEVp: CD8α-FKBP-TEVp), which are fusion proteins incorporated with the chemically induced dimerization machinery. Rapamycin and tamoxifen induce sequential dimerization of FKBP and FRB, cleavage of CreER from the membrane, and translocation into the nucleus. The labeling leakiness in Ad293 cells reduced dramatically from more than 70% to less than 5%. This tight labeling feature depends largely on the association of mCreER with HSP90, which conceals the TEV protease cutting site between FRB and CreER and thus preventing uninduced cleavage of the membrane-tethering CreER. Membrane-bound CreER also diminished significantly cytotoxicity. Our studies showed mCreER under the control of the rat insulin promoter increased labeling specificity in MIN6 islet beta-cells. Viability and insulin secretion of MIN6 cells remained intact. Our results demonstrate that this novel system can provide more stringent temporal and spatial control of gene expression and will be useful in cell fate probing.

Hypophosphorylated pRb knock-in mice exhibit hallmarks of aging and vitamin C-preventable diabetes

Despite extensive analysis of pRB phosphorylation in vitro, how this modification influences development and homeostasis in vivo is unclear. Here, we show that homozygous Rb^∆K4 and Rb^∆K7 knock‐in mice, in which either four or all seven phosphorylation sites in the C‐terminal region of pRb, respectively, have been abolished by Ser/Thr‐to‐Ala substitutions, undergo normal embryogenesis and early development, notwithstanding suppressed phosphorylation of additional upstream sites. Whereas Rb^∆K4 mice exhibit telomere attrition but no other abnormalities, Rb^∆K7 mice are smaller and display additional hallmarks of premature aging including infertility, kyphosis, and diabetes, indicating an accumulative effect of blocking pRb phosphorylation. Diabetes in Rb^∆K7 mice is insulin‐sensitive and associated with failure of quiescent pancreatic β‐cells to re‐enter the cell cycle in response to mitogens, resulting in induction of DNA damage response (DDR), senescence‐associated secretory phenotype (SASP), and reduced pancreatic islet mass and circulating insulin level. Pre‐treatment with the epigenetic regulator vitamin C reduces DDR, increases cell cycle re‐entry, improves islet morphology, and attenuates diabetes. These results have direct implications for cell cycle regulation, CDK‐inhibitor therapeutics, diabetes, and longevity.

Circulating Hematopoietic (HSC) and Very-Small Embryonic like (VSEL) Stem Cells in Newly Diagnosed Childhood Diabetes type 1 - Novel Parameters of Beta Cell Destruction/Regeneration Balance and Possible Prognostic Factors of Future Disease Course

Aims/Hypothesis

We aimed to evaluate hematopoietic stem cells (HSC) and very small embryonic-like stem cells (VSEL) mobilization to establish their role in residual beta cell function maintenance and partial remission occurrence in children newly diagnosed with type 1 diabetes.

Methods

We recruited 59 type 1 diabetic patients (aged 6–18 years) monitored for 2 years, and 31 healthy children as a control group. HSC and VSEL levels were assessed at disease onset in PBMC isolated from whole peripheral blood with the use of flow cytometry. An assessment of beta cell function was based on C-peptide secretion. Studied groups were stratified on the basis of VSEL, HSC and/or C-peptide median levels in regard to beta cell function and partial remission.

Results

Patients with higher stimulated C-peptide secretion at disease onset demonstrated lower levels of HSC (p < 0.05), while for VSEL and VSEL/HSC ratio higher values were observed (p < 0.05). Accordingly, after 2 years follow-up, patients with higher C-peptide secretion presented lower initial levels of HSC and higher VSEL/HSC ratio (p < 0.05). Patients with lower values of HSC levels demonstrated a tendency for better partial remission prevalence in the first 3 to 6 months after diagnosis.

Conclusions

These clinical observations indicate a possible significant role of HSC and VSEL in maintaining residual beta cell function in type 1 diabetic patients.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12015-021-10250-7.

Hnf1b-CreER causes efficient recombination of a Rosa26-RFP reporter in duct and islet δ cells

The Hnf1b-CreER^T2 BAC transgenic (Tg(Hnf1b-cre/ERT2)1Jfer) has been used extensively to trace the progeny of pancreatic ducts in developmental, regeneration, or cancer models. Hnf1b-CreER^T2 transgenics have been used to show that the cells that form the embryonic pancreas duct-like plexus are bipotent duct-endocrine progenitors, whereas adult mouse duct cells are not a common source of β cells in various regenerative settings. The interpretation of such genetic lineage tracing studies is critically dependent on a correct understanding of the cell type specificity of recombinase activity with each reporter system. We have reexamined the performance of Hnf1b-CreER^T2 with a Rosa26-RFP reporter transgene. This showed inducible recombination of up to 96% adult duct cells, a much higher efficiency than previously used reporter transgenes. Despite this high duct-cell excision, recombination in α and β cells remained very low, similar to previously used reporters. However, nearly half of somatostatin-expressing δ cells showed reporter activation, which was due to Cre expression in δ cells rather than to duct to δ cell conversions. The high recombination efficiency in duct cells indicates that the Hnf1b-CreER^T2 model can be useful for both ductal fate mapping and genetic inactivation studies. The recombination in δ cells does not modify the interpretation of studies that failed to show duct conversions to other cell types, but needs to be considered if this model is used in studies that aim to modify the plasticity of pancreatic duct cells.

The Potential of Pancreatic Organoids for Diabetes Research and Therapy

The success of clinical transplantation of pancreas or isolated pancreatic islets supports the concept of cell-based cure for diabetes. One limitation is the shortage of cadaver human pancreata. The demand-supply gap could potentially be bridged by harnessing the self-renewal capacity of stem cells. Pluripotent stem cells and adult pancreatic stem cells have been explored as possible cell sources. Recently, a system for long-term culture of proposed adult pancreatic stem cells in a form of organoids was developed. Generated organoids partially mimic the architecture and cell-type composition of pancreatic tissue. Here, we review the attempts over the past decade, to utilize the organoid cell culture principles in order to identify, expand, and differentiate the adult pancreatic stem cells from different compartments of mouse and human pancreata. The development of the culture conditions, effects of specific growth factors and small molecules is discussed. The potential utility of the adult pancreatic stem cells is considered in the context of other cell sources.

Circadian Regulation of the Pancreatic Beta Cell

Beta cell dysfunction is central to the development of type 2 diabetes (T2D). In T2D, environmental and genetic influences can manifest beta cell dysfunction in many ways, including impaired glucose-sensing and secretion coupling mechanisms, insufficient adaptative responses to stress, and aberrant beta cell loss through increased cell death and/or beta cell de-differentiation. In recent years, circadian disruption has emerged as an important environmental risk factor for T2D. In support of this, genetic disruption of the circadian timing system in rodents impairs insulin secretion and triggers diabetes development, lending important evidence that the circadian timing system is intimately connected to, and essential for the regulation of pancreatic beta cell function; however, the role of the circadian timing system in the regulation of beta cell biology is only beginning to be unraveled. Here, we review the recent literature that explores the importance of the pancreatic islet/beta cell circadian clock in the regulation of various aspects of beta cell biology, including transcriptional and functional control of daily cycles of insulin secretion capacity, regulation of postnatal beta cell maturation, and control of the adaptive responses of the beta cell to metabolic stress and acute injury.

Excess of glucocorticoids during late gestation impairs the recovery of offspring's β-cell function after a postnatal injury

Since prenatal glucocorticoids (GC) excess increases the risk of metabolic dysfunctions in the offspring and its effect on β-cell recovery capacity remains unknown we investigated these aspects in offspring from mice treated with dexamethasone (DEX) in the late pregnancy. Half of the pups were treated with streptozotocin (STZ) on the sixth postnatal day (PN). Functional and molecular analyses were performed in male offspring on PN25 and PN225. Prenatal DEX treatment resulted in low birth weight. At PN25, both the STZ-treated offspring developed hyperglycemia and had lower β-cell mass, in parallel with higher α-cell mass and glucose intolerance, with no impact of prenatal DEX on such parameters. At PN225, the β-cell mass was partially recovered in the STZ-treated mice, but they remained glucose-intolerant, irrespective of being insulin sensitive. Prenatal exposition to DEX predisposed adult offspring to sustained hyperglycemia and perturbed islet function (lower insulin and higher glucagon response to glucose) in parallel with exacerbated glucose intolerance. β-cell-specific knockdown of the Hnf4α in mice from the DS group resulted in exacerbated glucose intolerance. We conclude that high GC exposure during the prenatal period exacerbates the metabolic dysfunctions in adult life of mice exposed to STZ early in life, resulting in a lesser ability to recover the islets' function over time. This study alerts to the importance of proper management of exogenous GCs during pregnancy and a healthy postnatal lifestyle since the combination of adverse factors during the prenatal and postnatal period accentuates the predisposition to metabolic disorders in adult life.

Ngn3-Positive Cells Arise from Pancreatic Duct Cells

The production of pancreatic β cells is the most challenging step for curing diabetes using next-generation treatments. Adult pancreatic endocrine cells are thought to be maintained by the self-duplication of differentiated cells, and pancreatic endocrine neogenesis can only be observed when the tissue is severely damaged. Experimentally, this can be performed using a method named partial duct ligation (PDL). As the success rate of PDL surgery is low because of difficulties in identifying the pancreatic duct, we previously proposed a method for fluorescently labeling the duct in live animals. Using this method, we performed PDL on neurogenin3 (Ngn3)-GFP transgenic mice to determine the origin of endocrine precursor cells and evaluate their potential to differentiate into multiple cell types. Ngn3-activated cells, which were marked with GFP, appeared after PDL operation. Because some GFP-positive cells were aligned proximally to the duct, we hypothesized that Ngn3-positive cells arise from the pancreatic duct. Therefore, we next developed an in vitro pancreatic duct culture system using Ngn3-GFP mice and examined whether Ngn3-positive cells emerge from this duct. We observed GFP expressions in ductal organoid cultures. GFP expressions were correlated with Ngn3 expressions and endocrine cell lineage markers. Interestingly, tuft cell markers were also correlated with GFP expressions. Our results demonstrate that in adult mice, Ngn3-positive endocrine precursor cells arise from the pancreatic ducts both in vivo and in vitro experiments indicating that the pancreatic duct could be a potential donor for therapeutic use.

Reduced synchroneity of intra-islet Ca2+ oscillations in vivo in Robo-deficient β cells

The spatial architecture of the islets of Langerhans is hypothesized to facilitate synchronized insulin secretion among β cells, yet testing this in vivo in the intact pancreas is challenging. Robo βKO mice, in which the genes Robo1 and Robo2 are deleted selectively in β cells, provide a unique model of altered islet spatial architecture without loss of β cell differentiation or islet damage from diabetes. Combining Robo βKO mice with intravital microscopy, we show here that Robo βKO islets have reduced synchronized intra-islet Ca2+ oscillations among β cells in vivo. We provide evidence that this loss is not due to a β cell-intrinsic function of Robo, mis-expression or mis-localization of Cx36 gap junctions, or changes in islet vascularization or innervation, suggesting that the islet architecture itself is required for synchronized Ca2+ oscillations. These results have implications for understanding structure-function relationships in the islets during progression to diabetes as well as engineering islets from stem cells.

4-Phenylbutyric acid and rapamycin improved diabetic status in high fat diet/streptozotocin-induced type 2 diabetes through activation of autophagy

An accumulating body of evidence supports the role of autophagy in the pathophysiology of T2DM. Also, abnormal endoplasmic reticulum (ER) stress response that has been implicated as a cause of insulin resistance (IR) could also be affected by the autophagic status in β-cells. The present study was designed to investigate whether autophagy is regulated in T2DM as well as to investigate the modulatory effect of the ER stress inhibitor 4-phenylbutyric acid (4-PBA) and the autophagy inducer rapamycin (Rapa) on the autophagic and diabetic status using type 2 diabetic animal model with IR. Treatment of diabetic rats with either 4-PBA or Rapa improved significantly the states of hyperglycaemia and dyslipidaemia, increased the antioxidant capacity, reduced the levels of lipid peroxidation and ER stress and increased the autophagic flux. The obtained improvements were attributed mainly to the induction of autophagy with subsequent regulation of ER stress-oxidative activation and prevention of β-cell apoptosis.

Biphasic dynamics of beta cell mass in a mouse model of congenital hyperinsulinism: implications for type 2 diabetes

AIMS/HYPOTHESIS

Acute hyperglycaemia stimulates pancreatic beta cell proliferation in the mouse whereas chronic hyperglycaemia appears to be toxic. We hypothesise that this toxic effect is mediated by increased beta cell workload, unrelated to hyperglycaemia per se.

METHODS

To test this hypothesis, we developed a novel mouse model of cell-autonomous increased beta cell glycolytic flux caused by a conditional heterozygous beta cell-specific mutation that activates glucokinase (GCK), mimicking key aspects of the rare human genetic disease GCK-congenital hyperinsulinism.

RESULTS

In the mutant mice, we observed random and fasting hypoglycaemia (random 4.5-5.4 mmol/l and fasting 3.6 mmol/l) that persisted for 15 months. GCK activation led to increased beta cell proliferation as measured by Ki67 expression (2.7% vs 1.5%, mutant and wild-type (WT), respectively, p < 0.01) that resulted in a 62% increase in beta cell mass in young mice. However, by 8 months of age, mutant mice developed impaired glucose tolerance, which was associated with decreased absolute beta cell mass from 2.9 mg at 1.5 months to 1.8 mg at 8 months of age, with preservation of individual beta cell function. Impaired glucose tolerance was further exacerbated by a high-fat/high-sucrose diet (AUC 1796 vs 966 mmol/l × min, mutant and WT, respectively, p < 0.05). Activation of GCK was associated with an increased DNA damage response and an elevated expression of Chop, suggesting metabolic stress as a contributor to beta cell death.

CONCLUSIONS/INTERPRETATION

We propose that increased workload-driven biphasic beta cell dynamics contribute to decreased beta cell function observed in long-standing congenital hyperinsulinism and type 2 diabetes.

Bone marrow-derived mesenchymal stem cells improve rat islet graft revascularization by upregulating ISL1

Revascularization of the islet transplant is a crucial step that defines the success rate of patient recovery. Bone marrow-derived mesenchymal stem cells (BMSCs) have been reported to promote revascularization; however, the underlying cellular mechanism remains unclear. Moreover, our liquid chromatography-tandem mass spectrometry results showed that BMSCs could promote the expression of insulin gene enhancer binding protein-1 (ISL1) in islets. ISL1 is involved in islets proliferation and plays a potential regulatory role in the revascularization of islets. This study identifies the ISL1 protein as a potential modulator in BMSCs-mediated revascularization of islet grafts. We demonstrated that the survival rate and insulin secretion of islets were increased in the presence of BMSCs, indicating that BMSCs promote islet revascularization in a coculture system and rat diabetes model. Interestingly, we also observed that the presence of BMSCs led to an increase in ISL1 and vascular endothelial growth factor A (VEGFA) expression in both islets and the INS-1 rat insulinoma cell line. In silico protein structure modeling indicated that ISL1 is a transcription factor that has four binding sites with VEGFA mRNA. Further results showed that overexpression of ISL1 increased both the abundance of VEGFA transcripts and protein accumulation, while inhibition of ISL1 decreased the abundance of VEGFA. Using a ChIP-qPCR assay, we demonstrated that direct molecular interactions between ISL1 and VEGFA occur in INS-1 cells. Together, these findings reveal that BMSCs promote the expression of ISL1 in islets and lead to an increase in VEGFA in islet grafts. Hence, ISL1 is a potential target to induce early revascularization in islet transplantation.

Pre-existing beta cells but not progenitors contribute to new beta cells in the adult pancreas

It has been suggested that new beta cells can arise from specific populations of adult pancreatic progenitors or facultative stem cells. However, their existence remains controversial, and the conditions under which they would contribute to new beta-cell formation are not clear. Here, we use a suite of mouse models enabling dual-recombinase-mediated genetic tracing to simultaneously fate map insulin-positive and insulin-negative cells in the adult pancreas. We find that the insulin-negative cells, of both endocrine and exocrine origin, do not generate new beta cells in the adult pancreas during homeostasis, pregnancy or injury, including partial pancreatectomy, pancreatic duct ligation or beta-cell ablation with streptozotocin. However, non-beta cells can give rise to insulin-positive cells after extreme genetic ablation of beta cells, consistent with transdifferentiation. Together, our data indicate that pancreatic endocrine and exocrine progenitor cells do not contribute to new beta-cell formation in the adult mouse pancreas under physiological conditions.

Induction of Core Circadian Clock Transcription Factor Bmal1 Enhances β-Cell Function and Protects Against Obesity-Induced Glucose Intolerance

Type 2 diabetes mellitus (T2DM) is characterized by β-cell dysfunction as a result of impaired glucose-stimulated insulin secretion (GSIS). Studies show that β-cell circadian clocks are important regulators of GSIS and glucose homeostasis. These observations raise the question about whether enhancement of the circadian clock in β-cells will confer protection against β-cell dysfunction under diabetogenic conditions. To test this, we used an approach by first generating mice with β-cell-specific inducible overexpression of Bmal1 (core circadian transcription factor; β-Bmal1 ^OV ). We subsequently examined the effects of β-Bmal1 ^OV on the circadian clock, GSIS, islet transcriptome, and glucose metabolism in the context of diet-induced obesity. We also tested the effects of circadian clock-enhancing small-molecule nobiletin on GSIS in mouse and human control and T2DM islets. We report that β-Bmal1 ^OV mice display enhanced islet circadian clock amplitude and augmented in vivo and in vitro GSIS and are protected against obesity-induced glucose intolerance. These effects were associated with increased expression of purported BMAL1-target genes mediating insulin secretion, processing, and lipid metabolism. Furthermore, exposure of isolated islets to nobiletin enhanced β-cell secretory function in a Bmal1-dependent manner. This work suggests therapeutic targeting of the circadian system as a potential strategy to counteract β-cell failure under diabetogenic conditions.

Anti-diabetic effect of a novel oligosaccharide isolated from Rosa canina via modulation of DNA methylation in Streptozotocin-diabetic rats

BACKGROUND

Diabetes mellitus (DM) is a well-known clinical entity with various late complications. There is a surge of research aiming to use the medical herb in the management of DM.

OBJECTIVE

This study aimed to investigate whether the alleviation of DM by an isolated compound from Rosa canina is mediated by DNA methylation in STZ-diabetic rats.

METHODS

Sixty adult Wistar male rats were classified into control, diabetic and treatment groups. Rats were treated with STZ (40 mg/kg), metformin (500 mg/kg), and oligosaccharide fraction (OF; 10, 20 and 30 mg/kg) isolated from Rosa canina. DNA was extracted from the blood and pancreas to determine DNA methylation using the Global DNA Methylation kit. The expressions of DNA methyltransferases (Dnmts), PDX1, Ins1, GCK and PTP1B2 were determined by using qRT-PCR.

RESULTS

The significant blood glucose-lowering potential of OF was associated with a reduced level of global DNA methylation (p < 0.05). The expression levels of Dnmts 1 and 3α increased in the pancreas and blood from diabetic rats compared to control group which declined by OF treatment (p < 0.05). Paradoxically, the expression of Dnmt 3β augmented in the pancreas and blood of OF group compared to diabetic ones (p < 0.05). Besides, the expressions of Pdx1, PTP1B2, Ins1 and GCK increased in OF-treated rats compared to diabetic groups.

CONCLUSION

Results revealed that DNA methylation plays a causal role in the effectiveness of the isolated OF. Furthermore, the possible regenerative potential of oligosaccharide in diabetic rats may have contributed to the modulation of DNA methylation.

The core clock transcription factor BMAL1 drives circadian β-cell proliferation during compensatory regeneration of the endocrine pancreas

Circadian clocks in pancreatic islets participate in the regulation of glucose homeostasis. Here we examined the role of these timekeepers in β-cell regeneration after the massive ablation of β cells by doxycycline-induced expression of diphtheria toxin A (DTA) in Insulin-rtTA/TET-DTA mice. Since we crossed reporter genes expressing α- and β-cell-specific fluorescent proteins into these mice, we could follow the fate of α- and β cells separately. As expected, DTA induction resulted in an acute hyperglycemia, which was accompanied by dramatic changes in gene expression in residual β cells. In contrast, only temporal alterations of gene expression were observed in α cells. Interestingly, β cells entered S phase preferentially during the nocturnal activity phase, indicating that the diurnal rhythm also plays a role in the orchestration of β-cell regeneration. Indeed, in arrhythmic Bmal1-deficient mice, which lack circadian clocks, no compensatory β-cell proliferation was observed, and the β-cell ablation led to aggravated hyperglycemia, hyperglucagonemia, and fatal diabetes.

Glycogen phosphorylase inhibitor, 2,3-bis[(2E)-3-(4-hydroxyphenyl)prop-2-enamido] butanedioic acid (BF142), improves baseline insulin secretion of MIN6 insulinoma cells

Type 2 diabetes mellitus (T2DM), one of the most common metabolic diseases, is characterized by insulin resistance and inadequate insulin secretion of β cells. Glycogen phosphorylase (GP) is the key enzyme in glycogen breakdown, and contributes to hepatic glucose production during fasting or during insulin resistance. Pharmacological GP inhibitors are potential glucose lowering agents, which may be used in T2DM therapy. A natural product isolated from the cultured broth of the fungal strain No. 138354, called 2,3-bis(4-hydroxycinnamoyloxy)glutaric acid (FR258900), was discovered a decade ago. In vivo studies showed that FR258900 significantly reduced blood glucose levels in diabetic mice. We previously showed that GP inhibitors can potently enhance the function of β cells. The purpose of this study was to assess whether an analogue of FR258900 can influence β cell function. BF142 (Meso-Dimethyl 2,3-bis[(E)-3-(4-acetoxyphenyl)prop-2-enamido]butanedioate) treatment activated the glucose-stimulated insulin secretion pathway, as indicated by enhanced glycolysis, increased mitochondrial oxidation, significantly increased ATP production, and elevated calcium influx in MIN6 cells. Furthermore, BF142 induced mTORC1-specific phosphorylation of S6K, increased levels of PDX1 and insulin protein, and increased insulin secretion. Our data suggest that BF142 can influence β cell function and can support the insulin producing ability of β cells.

The MEK Inhibitor Trametinib Suppresses Major Histocompatibility Antigen-mismatched Rejection Following Pancreatic Islet Transplantation

Background.

Potential adverse effects, such as functional impairment of islets, render conventional immunosuppressive drugs unsuitable for use in islet transplantation. In addition, as a single therapy, they cannot prolong islet allograft survival. Here, we investigated the utility of the mitogen-activated protein kinase inhibitor trametinib and asked whether it ameliorates acute rejection of transplanted islets without the need for conventional immunosuppressants.

Methods.

Islets from fully major histocompatibility complex-mismatched BALB/c mice were transplanted into streptozotocin-induced diabetic C57BL/6 mice via the portal vein. These mice received trametinib or vehicle (orally) for 28 days. Isolated islets from BALB/c mice were incubated in vitro with different concentrations of trametinib to determine viability and function.

Results.

Trametinib (0.1 and 0.3 mg/kg) prolonged graft survival significantly (P = 0.0007 and P = 0.005, respectively) when compared with vehicle. Histologic analyses revealed that cellular infiltration of the graft by lymphocytes was inhibited significantly on day 7 (P < 0.05). In addition, trametinib suppressed functional differentiation of naive CD4⁺ T cells in recipients. Expression of mRNA encoding inflammatory cytokines interleukin (IL)-2, tumor necrosis factor α, and interferon γ in recipients treated with trametinib was also inhibited (P < 0.001, P < 0.05, and P < 0.01, respectively). Trametinib also increased production of IL-4 and IL-10 (P < 0.05 and P = 0.20, respectively). In vitro, islets incubated with different concentrations of trametinib exhibited no harmful effects with respect to viability and function.

Conclusions.

Trametinib delayed islet graft rejection by inhibiting functional differentiation of naive CD4⁺ T cells and regulating inflammatory cytokines. Trametinib might be a promising candidate for maintenance immunosuppressive therapy after allogeneic islet transplantation.

The protective effects of human milk-derived peptides on the pancreatic islet biology

Several epidemiological studies support the protective role of breastfeeding in reducing the risk for type 1 diabetes. Human breast milk is the perfect nutrition for infants and contains many complex proteins, lipids and carbohydrates. In this study, we examined the physiological effects of human milk-derived opioid peptides, β-casomorphins (BCM), and compared them with bovine-milk-derived opioid peptides on pancreatic hormone regulation and β-cell regeneration. Exposure of wild-type zebrafish embryos to 50 µg/ml of human BCM-5 and -7 from 3 days post fertilisation until 6 days post fertilisation resulted in an increased insulin domain of expression while exposure to bovine BCM-5 and -7 significantly reduced the insulin domain of expression as analysed by whole-mount in situ hybridisation. These changes may be accounted for by reduced insulin expression or β-cell number and were mitigated by the µ-opioid receptor antagonist, naloxone. The effect of BCM on β-cell regeneration was assessed following ablation of β-cells in Tg (ins: CFP-NTR) zebrafish from 3 days post fertilisation to 4 days post fertilisation, followed by exposure of bovine and human BCM-5 and -7 (50 µg/ml) from 4 days post fertilisation until 7 days post fertilisation. The regenerative capacity of β-cells was not impeded following exposure to human BCM-5 and -7, whereas the capacity of β-cells to regenerate following bovine BCM-5 and -7 exposure was reduced. Our data suggest that human BCM-5 and -7 may promote β-cell development and enable the regeneration of β-cells, while the bovine-milk-derived peptides, BCM-5 and -7, play an opposite role. These data may provide some biological explanation for the protective effect of breastfeeding on the development of type 1 diabetes.

Ternary complex factor regulates pancreatic islet size and blood glucose homeostasis in transgenic mice

A hallmark of diabetes mellitus is the inability of pancreatic β-cells to secrete sufficient amounts of insulin for maintaining normoglycemia. The formation of smaller islets may underlie the development of a diabetic phenotype, as a decreased β-cell mass will produce an insufficient amount of insulin. For a pharmacological intervention it is crucial to identify the proteins determining β-cell mass. Here, we identified the ternary complex factor (TCF) Elk-1 as a regulator of the size of pancreatic islets. Elk-1 mediates, together with a dimer of the serum-response factor (SRF), serum response element-regulated gene transcription. Elk-1 is activated in glucose-treated pancreatic β-cells but the biological functions of this protein in β-cells are so far unknown. Elk-1 and homologous TCF proteins are expressed in islets and insulinoma cells. Gene targeting experiments revealed that the TCF proteins show redundant activities. To solve the problem of functional redundancy of these homologous proteins, we generated conditional transgenic mice expressing a dominant-negative mutant of Elk-1 in pancreatic β-cells. The mutant competes with the wild-type TCFs for DNA and SRF-binding. Expression of the Elk-1 mutant in pancreatic β-cells resulted in the generation of significantly smaller islets and increased caspase-3 activity, indicating that apoptosis was responsible for the reduction of the pancreatic islet size. Glucose tolerance tests revealed that transgenic mice expressing the dominant-negative mutant of Elk-1 in pancreatic β-cells displayed impaired glucose tolerance. Thus, we show here for the first time that TCF controls important functions of pancreatic β-cells in vivo. Elk-1 may be considered as a new therapeutic target for the treatment of diabetes.

Myt Transcription Factors Prevent Stress-Response Gene Overactivation to Enable Postnatal Pancreatic β Cell Proliferation, Function, and Survival

Although cellular stress response is important for maintaining function and survival, overactivation of late-stage stress effectors cause dysfunction and death. We show that the myelin transcription factors (TFs) Myt1 (Nzf2), Myt2 (Myt1l, Nztf1, and Png-1), and Myt3 (St18 and Nzf3) prevent such overactivation in islet β cells. Thus, we found that co-inactivating the Myt TFs in mouse pancreatic progenitors compromised postnatal β cell function, proliferation, and survival, preceded by upregulation of late-stage stress-response genes activating transcription factors (e.g., Atf4) and heat-shock proteins (Hsps). Myt1 binds putative enhancers of Atf4 and Hsps, whose overexpression largely recapitulated the Myt-mutant phenotypes. Moreover, Myt(MYT)-TF levels were upregulated in mouse and human β cells during metabolic stress-induced compensation but downregulated in dysfunctional type 2 diabetic (T2D) human β cells. Lastly, MYT knockdown caused stress-gene overactivation and death in human EndoC-βH1 cells. These findings suggest that Myt TFs are essential restrictors of stress-response overactivity.

Cell therapy for type 1 diabetes

INTRODUCTION

Type 1 diabetes (T1D) is a lifelong condition resulting from autoimmune destruction of insulin-producing β-cells. Islet or whole-pancreas transplantation is limited by the shortage of donors and need for chronic immune suppression. Novel strategies are needed to prevent β-cell loss and to rescue production of endogenous insulin.

AREAS COVERED

This review covers the latest advances in cell-based therapies for the treatment and prevention of T1D. Topics include adoptive transfer of cells with increased immunoregulatory potential for β-cell protection, and β-cell replacement strategies such as generation of insulin-producing β-like cells from unlimited sources.

EXPERT OPINION

Cell therapy provides an opportunity to prevent or reverse T1D. Adoptive transfer of autologous cells having enhanced immunomodulatory properties can suppress autoimmunity and preserve β-cells. Such therapies have been made possible by a combination of genome-editing techniques and transplantation of tolerogenic cells. In-vitro modified autologous hematopoietic stem cells and tolerogenic dendritic cells may protect endogenous and newly generated β-cells from a patient's autoimmune response without hampering immune surveillance for infectious agents and malignant cellular transformations. However, methods to generate cells that meet quality and safety standards for clinical applications require further refinement.

Effects of Different Immunosuppressive Drugs on Incretins in Renal Transplant Patients

BACKGROUND

Immunosuppressive drugs used in transplantation patients, may contribute to the development of post-transplant diabetes mellitus through their possible adverse effects on incretins. We aimed to compare the effects of different immunosuppressive drugs used in renal transplantation patients on glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) levels.

PATIENTS AND METHODS

Forty five subjects were enrolled in the study (cyclosporine-treated 15 and tacrolimus-treated renal transplant patients 15, and healthy volunteers as a control group 15). Oral glucose tolerance test with 75 gr glucose was performed. GLP-1 and GIP levels were measured at 0 (baseline), 30, 60, 90, 120 min using ELISA method.

RESULTS

A statistically significant level of difference was detected in GLP-1 levels at the baseline, 30th and 120th minutes among all three groups (p < 0,001, p = 0,026 and p = 0,022, respectively). Baseline GLP-1 levels in cyclosporine-treated renal transplant patients were higher than in both tacrolimus-treated renal transplant patients (p = 0,016) and control groups (p < 0,001). GLP-1 levels at the 30th minute were higher in tacrolimus-treated renal transplant patients when compared to the cyclosporine-treated renal transplant patients (p = 0,024). GLP-1 levels at the 120th minute were higher in tacrolimus-treated renal transplant patients than the control group (p = 0,024). The areas under the curve of GLP-1 was higher in tacrolimus-treated renal transplant patients when compared to the control group (p = 0,018). GIP levels at 120th was lower in cyclosporine-treated renal transplant patients when compared to control group (p = 0,003).

CONCLUSION

These findings showed a temporally affected incretin hormones in renal transplant patients, a preserved GLP-1 response to an oral glucose load in renal transplant patients on cyclosporine and increased GLP -1 response to an oral glucose load in those on tacrolimus.

Long-term case study of a Wuzhishan miniature pig with diabetes

BACKGROUND

Miniature pigs are attractive animal models for exploring diabetes because they are similar to humans in terms of physiological structure and metabolism. However, little is known about the complications of diabetes in pigs.

METHODS

In this study, a 28-month observation of a Wuzhishan miniature pig with streptozotocin (STZ)-induced (120 mg/kg) diabetes was conducted, to investigate diabetes-related complications and the possibility of self-recovery in miniature pigs. Blood glucose, serum and urinary biochemistry was measured, and histopathologic examinations of eyes, kidney and pancreas were made.

RESULTS

During the observation, diabetic complications of eyes and kidney were observed. The eye complications included bilateral cataracts in the 15th month and degeneration of inner retina and microaneurysm in the 28th month. Kidney complications included glomerular mesangial expansion, focal segmental glomerular sclerosis, and renal tubular epithelial degeneration, but no proteinuria was observed. By 28 months after the application of STZ, with no treatment given, blood glucose had recovered and the number of pancreatic islet beta-cells had increased significantly.

CONCLUSIONS

We showed that the STZ-induced diabetes model in miniature pigs could accurately mimic the pathological changes of human diabetes, and that pancreatic islet beta-cell regeneration did occur in an adult miniature pig, providing a new means for exploring diabetic complications and pancreatic islet beta-cell regeneration.

The use of LCP-Tacrolimus (Envarsus XR) in simultaneous pancreas and kidney (SPK) transplant recipients

BACKGROUND

Extended release LCP-tacrolimus (LCPT) allows once-daily dosing in transplant recipients. The improved bioavailability may be beneficial for simultaneous pancreas-kidney recipients (SPK).

METHODS

This is a study of 39 SPK recipients on standard immediate-release tacrolimus (IR-TAC, n = 21) or LCPT (n = 18). Coefficient of variability (CV = 100∗standard deviation/mean) was calculated to assess drug levels. Hemoglobin A1c (HbA1c), tacrolimus and creatinine levels were measured postoperatively.

RESULTS

There was no difference in tacrolimus CV in the IR-TAC and LCPT groups at 1 month or 3 months postoperatively; however, a greater difference was observed at 1 year (41.0 vs. 33.1%; p = 0.19). There were six episodes of acute rejection in the IR-TAC group compared to zero episodes in the LCPT group (p = 0.01). HbA1c was significantly higher in the IR-TAC group compared to LCPT at 3 (5.5 vs. 4.9%, p = 0.01), 6 (5.6 vs. 4.9%, p = 0.01) and 12 months (5.8 vs. 5.1%, p = 0.07).

CONCLUSIONS

Significantly lower rates of rejection were observed in patients receiving LCPT. The once daily dosing may facilitate medication adherence and result in improved long-term outcomes.

Characterization and anti-diabetic effects of the oligosaccharide fraction isolated from Rosa canina in STZ-Induced diabetic rats

Diabetes mellitus is the most common metabolic disorder characterized by chronic hyperglycemia. There has been a surge of research studies aiming to use natural products in the management of diabetes. The objective of this study was to isolate and characterize the structure and anti-diabetic mechanisms of the main ingredient from Rosa canina. The oligosaccharide was isolated from Rosa canina fruits and characterized by a combination of FTIR, NMR and Mass spectrometry. Wistar rats were divided into negative control, diabetic (type 2), isolated oligosaccharide (IO)-treated diabetic and positive diabetic controls. Oral glucose tolerance, gluconeogenesis and α-glucosidase inhibitory tests as well as immunohistochemistry and quantitative real time-PCR were performed to elucidate the molecular anti-diabetic mechanisms of IO. Structural analyses confirmed the oligosaccharide structure of isolated fraction. Gluconeogenesis and α-glucosidase activity were inhibited by IO in diabetic rats. The oral glucose tolerance test was improved significantly in the group treated with the IO (P < 0.05). Pancreatic β-cells and tissue pathological examination showed a significant improvement after the treatment period. In addition, the expression of Ngn3, Nkx6.1 and insulin increased in oligosaccharide-treated compared to untreated diabetic rats. Owing to the verified anti-diabetic effects and regenerative potential, isolated oligosaccharide could be considered as the promising drug in the management of diabetes.