Regulation of pancreatic beta-cell regeneration in the normoglycemic 60% partial-pancreatectomy mouse

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.

Pancreatic beta-cell mass and function and therapeutic implications of using antidiabetic medications in type 2 diabetes

Nowadays, the focus of diabetes treatment has switched from lowering the glucose level to preserving glycemic homeostasis and slowing the disease progression. The main pathophysiology of both type 1 diabetes and long-standing type 2 diabetes is pancreatic β-cell mass loss and dysfunction. According to recent research, human pancreatic β-cells possess the ability to proliferate in response to elevated insulin demands. It has been demonstrated that in insulin-resistant conditions in humans, such as obesity or pregnancy, the β-cell mass increases. This ability could be helpful in developing novel treatment approaches to restore a functional β-cell mass. Treatment strategies aimed at boosting β-cell function and mass may be a useful tool for managing diabetes mellitus and stopping its progression. This review outlines the processes of β-cell failure and detail the many β-cell abnormalities that manifest in people with diabetes mellitus. We also go over standard techniques for determining the mass and function of β-cells. Lastly, we provide the therapeutic implications of utilizing antidiabetic drugs in controlling the mass and function of 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.

Pancreatic beta cell regenerative potential of Zanthoxylum chalybeum Engl. Aqueous stem bark extract

ETHNOPHARMACOLOGICAL RELEVANCE

Zanthoxylum chalybeum Engl. is endemic to Africa and has been used traditionally to treat diabetes mellitus. Moreover, its pharmacological efficacy has been confirmed experimentally using in vitro and in vivo models of diabetes. However, the effects of Z. chalybeum extracts and its major constituent compounds on beta cell and islet regeneration are not clear. Further, the mechanisms associated with observed antidiabetic effects at the beta cell level are not fully elucidated.

AIM OF THE STUDY

We determined the beta cell regenerative efficacy of Z. chalybeum aqueous stem bark extract, identified the chemical compounds in Z. chalybeum aqueous stem bark extracts and explored their putative mechanisms of action.

MATERIALS AND METHODS

Phytochemical profiling of the Z. chalybeum extract was achieved using ultra high-performance liquid chromatography hyphenated to high-resolution mass spectrometry. Thereafter, molecular interactions of the compounds with beta cell regeneration targets were evaluated via molecular docking. In vitro, effects of the extract on cell viability, proliferation, apoptosis and oxidative stress were investigated in RIN-5F beta cells exposed to palmitate or streptozotocin. In vivo, pancreas tissue sections from streptozotocin-induced diabetic male Wistar rats treated with Z. chalybeum extract were stained for insulin, glucagon, pancreatic duodenal homeobox protein 1 (Pdx-1) and Ki-67.

RESULTS

Based on ligand target and molecular docking interactions diosmin was identified as a dual specificity tyrosine-phosphorylation-regulated kinase 1A (Dyrk1A) inhibitor. In vitro, Z. chalybeum augmented cell viability and cell proliferation while in palmitate-pre-treated cells, the extract significantly increased cell activity after 72 h. In vivo, although morphometric analysis showed decreased islet and beta cell size and density, observation of increased Pdx-1 and Ki-67 immunoreactivity in extract-treated islets suggests that Z. chalybeum extract has mild beta cell regenerative potential mediated by increased cell proliferation.

CONCLUSIONS

Overall, the mitogenic effects observed in vitro, were not robust enough to elicit sufficient recovery of functional beta cell mass in our in vivo model, in the context of a sustained diabetic milieu. However, the identification of diosmin as a potential Dyrk1A inhibitor merits further inquiry into the attendant molecular interactions.

Chronic periodontitis induces the proliferation of pancreatic β-cells to cause hyperinsulinemia in a rat model

BACKGROUND AND OBJECTIVE

The purpose of this study was to determine if chronic periodontitis (CP) may induce hyperinsulinemia and may have the effect of on pancreatic β-cell proliferation in a rat model.

MATERIALS AND METHODS

Twelve male Sprague-Dawley rats were divided into two groups: the CP group and the control group (Con group). The following contents were evaluated: pathological changes in periodontal soft and hard tissues; serum lipopolysaccharide (LPS) level, serum fasting insulin (FINS) level, fasting blood glucose (FBG) level, and homeostasis model assessment (HOMA) β (HOMA-β) index; histopathological examination of islets; immunohistochemistry of insulin and p-Smad2 expression in islets; immunofluorescence of changes in the relative number of β-cells and the number of Ki67-positive β-cells. Western blotting was used to analyze p-Smad2/Smad2 levels. Results were analyzed by two independent samples t tests.

RESULTS

Increased serum LPS level, FINS level, and HOMA-β index were observed in the rats of the CP group; FBG level did not change significantly; histological assessments showed an enlarged islet area, increased insulin content, relatively increased β-cells, increased Ki67-positive β-cells, and decreased p-Smad2 expression in islets in the rats of the CP group.

CONCLUSION

Our study results link CP-induced hyperinsulinemia with changes in islets, such as islet hyperplasia and compensatory β-cell proliferation, by using a CP rat model.

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.

Major β cell-specific functions of NKX2.2 are mediated via the NK2-specific domain

The consolidation of unambiguous cell fate commitment relies on the ability of transcription factors (TFs) to exert tissue-specific regulation of complex genetic networks. However, the mechanisms by which TFs establish such precise control over gene expression have remained elusive-especially in instances in which a single TF operates in two or more discrete cellular systems. In this study, we demonstrate that β cell-specific functions of NKX2.2 are driven by the highly conserved NK2-specific domain (SD). Mutation of the endogenous NKX2.2 SD prevents the developmental progression of β cell precursors into mature, insulin-expressing β cells, resulting in overt neonatal diabetes. Within the adult β cell, the SD stimulates β cell performance through the activation and repression of a subset of NKX2.2-regulated transcripts critical for β cell function. These irregularities in β cell gene expression may be mediated via SD-contingent interactions with components of chromatin remodelers and the nuclear pore complex. However, in stark contrast to these pancreatic phenotypes, the SD is entirely dispensable for the development of NKX2.2-dependent cell types within the CNS. Together, these results reveal a previously undetermined mechanism through which NKX2.2 directs disparate transcriptional programs in the pancreas versus neuroepithelium.

Rab11 is essential to pancreas morphogenesis, lumen formation and endocrine mass

The molecular links between tissue-level morphogenesis and the differentiation of cell lineages in the pancreas remain elusive despite a decade of studies. We previously showed that in pancreas both processes depend on proper lumenogenesis. The Rab GTPase Rab11 is essential for epithelial lumen formation in vitro, however few studies have addressed its functions in vivo and none have tested its requirement in pancreas. Here, we show that Rab11 is critical for proper pancreas development. Co-deletion of the Rab11 isoforms Rab11A and Rab11B in the developing pancreatic epithelium (Rab11pancDKO) results in ∼50% neonatal lethality and surviving adult Rab11^pancDKO mice exhibit defective endocrine function. Loss of both Rab11A and Rab11B in the embryonic pancreas results in morphogenetic defects of the epithelium, including defective lumen formation and lumen interconnection. In contrast to wildtype cells, Rab11pancDKO cells initiate the formation of multiple ectopic lumens, resulting in a failure to coordinate a single apical membrane initiation site (AMIS) between groups of cells. This results in a failure to form ducts with continuous lumens. Here, we show that these defects are due to failures in vesicle trafficking, as apical and junctional components remain trapped within Rab11^pancDKO cells. Together, these observations suggest that Rab11 directly regulates epithelial lumen formation and morphogenesis. Our report links intracellular trafficking to organ morphogenesis in vivo and presents a novel framework for decoding pancreatic development.

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.

SetD7 (Set7/9) is a novel target of PPARγ that promotes the adaptive pancreatic β-cell glycemic response

Loss of functional pancreatic β-cell mass leads to type 2 diabetes (T2D), attributable to modified β-cell-dependent adaptive gene expression patterns. SetD7 is a histone methyltransferase enriched in pancreatic islets that mono- and dimethylates histone-3-lysine-4 (H3K4), promoting euchromatin modifications, and also maintains the regulation of key β-cell function and survival genes. However, the transcriptional regulation of this important epigenetic modifier is unresolved. Here we identified the nuclear hormone receptor peroxisome proliferator-activated receptor-gamma (PPARγ) as a major transcriptional regulator of SetD7 and provide evidence for direct binding and functionality of PPARγ in the SetD7 promoter region. Furthermore, constitutive shRNA-mediated PPARγ knockdown in INS-1 β-cells or pancreas-specific PPARγ deletion in mice led to downregulation of SetD7 expression as well as its nuclear enrichment. The relevance of the SetD7-PPARγ interaction in β-cell adaptation was tested in normoglycemic 60% partial pancreatectomy (Px) and hyperglycemic 90% Px rat models. Whereas a synergistic increase in islet PPARγ and SetD7 expression was observed upon glycemic adaptation post-60% Px, in hyperglycemic 90% Px rats, islet PPARγ, and PPARγ targets SetD7 and Pdx1 were downregulated. PPARγ agonist pioglitazone treatment in 90% Px rats partially restored glucose homeostasis and β-cell mass and enhanced expression of SetD7 and Pdx1. Collectively, these data provide evidence that the SetD7-PPARγ interaction serves as an important element of the adaptive β-cell response.

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.

Debates in Pancreatic Beta Cell Biology: Proliferation Versus Progenitor Differentiation and Transdifferentiation in Restoring β Cell Mass

In all forms of diabetes, β cell mass or function is reduced and therefore the capacity of the pancreatic cells for regeneration or replenishment is a critical need. Diverse lines of research have shown the capacity of endocrine as well as acinar, ductal and centroacinar cells to generate new β cells. Several experimental approaches using injury models, pharmacological or genetic interventions, isolation and in vitro expansion of putative progenitors followed by transplantations or a combination thereof have suggested several pathways for β cell neogenesis or regeneration. The experimental results have also generated controversy related to the limitations and interpretation of the experimental approaches and ultimately their physiological relevance, particularly when considering differences between mouse, the primary animal model, and human. As a result, consensus is lacking regarding the relative importance of islet cell proliferation or progenitor differentiation and transdifferentiation of other pancreatic cell types in generating new β cells. In this review we summarize and evaluate recent experimental approaches and findings related to islet regeneration and address their relevance and potential clinical application in the fight against diabetes.

Mesenchymal stem cells promote pancreatic β-cell regeneration through downregulation of FoxO1 pathway

Background

Mesenchymal stem cells (MSC) are non-haematopoietic, fibroblast-like multipotent stromal cells. In the injured pancreas, these cells are assumed to secrete growth factors and immunomodulatory molecules, which facilitate the regeneration of pre-existing β-cells. However, when MSC are delivered intravenously, their majority is entrapped in the lungs and does not reach the pancreas. Therefore, the aim of this investigation was to compare the regenerative support of hTERT-MSC (human telomerase reverse transcriptase mesenchymal stem cells) via intrapancreatic (IPR) and intravenous route (IVR).

Methods

hTERT-MSC were administered by IPR and IVR to 50% pancreatectomized NMRI nude mice. After eight days, blood glucose level, body weight, and residual pancreatic weight were measured. Proliferating pancreatic β-cells were labelled and identified with bromodeoxyuridine (BrdU) in vivo. The number of residual islets and the frequency of proliferating β-cells were compared in different groups with sequential pancreatic sections. The pancreatic insulin content was evaluated by enzyme-linked immunosorbent assay (ELISA) and the presence of hTERT-MSC with human Alu sequence. Murine gene expression of growth factors, β-cell specific molecules and proinflammatory cytokines were inspected by real-time polymerase chain reaction (RT-PCR) and Western blot.

Results

This study evaluated the regenerative potential of the murine pancreas post-hTERT-MSC administration through the intrapancreatic (IPR) and intravenous route (IVR). Both routes of hTERT-MSC transplantation (IVR and IPR) increased the incorporation of BrdU by pancreatic β-cells compared to control. MSC induced epidermal growth factor (EGF) expression and inhibited proinflammatory cytokines (IFN-γ and TNF-α). FOXA2 and PDX-1 characteristics for pancreatic progenitor cells were activated via AKT/ PDX-1/ FoxO1 signalling pathway.

Conclusion

The infusion of hTERT-MSC after partial pancreatectomy (Px) through the IVR and IPR facilitated the proliferation of autochthonous pancreatic β-cells and provided evidence for a regenerative influence of MSC on the endocrine pancreas. Moderate benefit of IPR over IVR was observed which could be a new treatment option for preventing diabetes mellitus after pancreas surgery.

Supplementary information

The online version contains supplementary material available at at 10.1186/s13287-020-02007-9.

Single-Cell Transcriptome Analysis Dissects the Replicating Process of Pancreatic Beta Cells in Partial Pancreatectomy Model

Heterogeneity of gene expression and rarity of replication hamper molecular analysis of β-cell mass restoration in adult pancreas. Here, we show transcriptional dynamics in β-cell replication process by single-cell RNA sequencing of murine pancreas with or without partial pancreatectomy. We observed heterogeneity of Ins1-expressing β-cells and identified the one cluster as replicating β-cells with high expression of cell proliferation markers Pcna and Mki67. We also recapitulated cell cycle transition accompanied with switching expression of cyclins and E2F transcription factors. Both transient activation of endoplasmic reticulum stress responders like Atf6 and Hspa5 and elevated expression of tumor suppressors like Trp53, Rb1, and Brca1 and DNA damage responders like Atm, Atr, Rad51, Chek1, and Chek2 during the transition to replication associated fine balance of cell cycle progression and protection from DNA damage. Taken together, these results provide a high-resolution map depicting a sophisticated genetic circuit for replication of the β-cells.

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Single cell RNA sequencing dissects a sequence of replication process of beta cells

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ER stress responders are transiently activated in initiation of the proliferation

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Physiological replication accompanied with induced expression of tumor suppressors

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Fine balance of proliferation genes and tumor suppressors is a key of the replication

Current progress in stem cell therapy for type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is the most common chronic autoimmune disease in young patients and is characterized by the loss of pancreatic β cells; as a result, the body becomes insulin deficient and hyperglycemic. Administration or injection of exogenous insulin cannot mimic the endogenous insulin secreted by a healthy pancreas. Pancreas and islet transplantation have emerged as promising treatments for reconstructing the normal regulation of blood glucose in T1DM patients. However, a critical shortage of pancreases and islets derived from human organ donors, complications associated with transplantations, high cost, and limited procedural availability remain bottlenecks in the widespread application of these strategies. Attempts have been directed to accommodate the increasing population of patients with T1DM. Stem cell therapy holds great potential for curing patients with T1DM. With the advent of research on stem cell therapy for various diseases, breakthroughs in stem cell-based therapy for T1DM have been reported. However, many unsolved issues need to be addressed before stem cell therapy will be clinically feasible for diabetic patients. In this review, we discuss the current research advances in strategies to obtain insulin-producing cells (IPCs) from different precursor cells and in stem cell-based therapies for diabetes.

Recent Insights Into Mechanisms of β-Cell Lipo- and Glucolipotoxicity in Type 2 Diabetes

The deleterious effects of chronically elevated free fatty acid (FFA) levels on glucose homeostasis are referred to as lipotoxicity, and the concurrent exposure to high glucose may cause synergistic glucolipotoxicity. Lipo- and glucolipotoxicity have been studied for over 25 years. Here, we review the current evidence supporting the role of pancreatic β-cell lipo- and glucolipotoxicity in type 2 diabetes (T2D), including lipid-based interventions in humans, prospective epidemiological studies, and human genetic findings. In addition to total FFA quantity, the quality of FFAs (saturation and chain length) is a key determinant of lipotoxicity. We discuss in vitro and in vivo experimental models to investigate lipo- and glucolipotoxicity in β-cells and describe experimental pitfalls. Lipo- and glucolipotoxicity adversely affect many steps of the insulin production and secretion process. The molecular mechanisms underpinning lipo- and glucolipotoxic β-cell dysfunction and death comprise endoplasmic reticulum stress, oxidative stress and mitochondrial dysfunction, impaired autophagy, and inflammation. Crosstalk between these stress pathways exists at multiple levels and may aggravate β-cell lipo- and glucolipotoxicity. Lipo- and glucolipotoxicity are therapeutic targets as several drugs impact the underlying stress responses in β-cells, potentially contributing to their glucose-lowering effects in T2D.

Targeted Ablation of Pancreatic β Cells in Medaka

The pancreas plays important roles in the regulation of blood glucose, and is a well-studied organ in mammals because its dysfunction causes serious disorders, such as diabetes mellitus. However, mammals have the limited capacity for tissue regeneration in their organs, including pancreas. Fish may be an attractive model for regeneration studies, as fish exhibit a greater capacity for regeneration than do mammals. To elucidate the regenerative capacity of pancreatic β cells in medaka, we generated transgenic lines, in which β cells can be specifically ablated using the nitroreductase (NTR)/metronidazole (Mtz) system. We examined β-cell regeneration at embryonic-larval stages after specific ablation of β cells, and found that medaka rapidly regenerate β cells. Furthermore, we found that teleost-specific secondary islet have a unique feature in that their size increases in response to β-cell ablation in principal islets.

Lipotoxicity and β Cell Maintenance in Obesity and Type 2 Diabetes

Obesity and diabetes are often associated with lipotoxic conditions in multiple tissues. The insulin-producing β cells are susceptible to elevated lipid levels and the ensuing lipotoxicity. The preservation of β cell mass and function is one of the main goals of diabetes management under these metabolically stressful conditions. However, the adverse effects from the adaptive signaling pathways that β cells use to counteract lipotoxic stress have secondary negative effects in their own right. Antilipotoxic signaling cascades in β cells can contribute to their eventual failure. Such dual roles are seen for many other biological adaptive processes as well.

Functional adenosine triphosphate-sensitive potassium channel is required in high-carbohydrate diet-induced increase in β-cell mass

AIMS/INTRODUCTION

A high-carbohydrate diet is known to increase insulin secretion and induce obesity. However, whether or not a high-carbohydrate diet affects β-cell mass (BCM) has been little investigated.

MATERIALS AND METHODS

Both wild-type (WT) mice and adenosine triphosphate-sensitive potassium channel-deficient (Kir6.2KO) mice were fed normal chow or high-starch (ST) diets for 22 weeks. BCM and the numbers of islets were analyzed by immunohistochemistry, and gene expression levels in islets were investigated by quantitative real-time reverse transcription polymerase chain reaction. MIN6-K8 β-cells were stimulated in solution containing various concentrations of glucose combined with nifedipine and glimepiride, and gene expression was analyzed.

RESULTS

Both WT and Kir6.2KO mice fed ST showed hyperinsulinemia and body weight gain. BCM, the number of islets and the expression levels of cyclinD2 messenger ribonucleic acid were increased in WT mice fed ST compared with those in WT mice fed normal chow. In contrast, no significant difference in BCM, the number of islets or the expression levels of cyclinD2 messenger ribonucleic acid were observed between Kir6.2KO mice fed normal chow and those fed ST. Incubation of MIN6-K8 β-cells in high-glucose media or with glimepiride increased cyclinD2 expression, whereas nifedipine attenuated a high-glucose-induced increase in cyclinD2 expression.

CONCLUSIONS

These results show that a high-starch diet increases BCM in an adenosine triphosphate-sensitive potassium channel-dependent manner, which is mediated through upregulation of cyclinD2 expression.

The role of glucokinase and insulin receptor substrate-2 in the proliferation of pancreatic beta cells induced by short-term high-fat diet feeding in mice

OBJECTIVE

We investigated whether glucokinase and insulin receptor substrate-2 were required for beta cell proliferation induced by short-term high-fat (HF) diet feeding, as has been shown for long-term HF diet.

METHODS

Eight-week-old C57BL/6J mice were exposed to either a standard chow (SC) or HF diet. After 1 week on the diet, histopathological beta cell proliferation and gene expression in isolated islets were examined. Additionally, 8-week-old beta cell-specific glucokinase haploinsufficient (Gck^+/-) and Irs2 knockout (Irs2^-/-) mice were exposed to either an SC or HF diet.

RESULTS

Immunohistochemical analysis revealed that short-term HF diet feeding resulted in a significant increase in BrdU incorporation rate compared with SC consumption in wild-type mice. Western blot analysis demonstrated that Irs2 expression levels did not differ between the two diets. Moreover, there was a significant increase in the BrdU incorporation rate in the HF diet group compared with the SC group in both Gck^+/- and Irs2^-/- mice. Gene expression profiling of isolated islets from mice fed an HF diet for 1 week revealed that the expression levels of downstream genes of Foxm1 were coordinately upregulated. One week of HF diet feeding stimulated beta cell proliferation with Foxm1 upregulation in 48-week-old mice as well as in 8-week-old.

CONCLUSIONS

The mechanism of pancreatic beta cell proliferation induced by short-term HF diet feeding in mice could involve a glucokinase- and Irs2-independent pathway. Our results suggest that the pathways that induce beta cell proliferation in response to short-term HF diet feeding may differ from those in response to sustained HF diet feeding.

The liver surface as a favorable site for islet cell sheet transplantation in type 1 diabetes model mice

INTRODUCTION

Islet transplantation is one of the most promising therapeutic approaches for patients with severe type 1 diabetes mellitus (T1DM). Transplantation of engineered islet cell sheets holds great potential for treating T1DM as it enables the creation of stable neo-islet tissues. However, a large mass of islet cell sheets is required for the subcutaneous transplantation to reverse hyperglycemia in diabetic mice. Here, we investigated whether the liver surface could serve as an alternative site for islet cell sheet transplantation.

METHODS

Dispersed rat islet cells (0.8 × 106 cells) were cultured on laminin-332-coated thermoresponsive culture dishes. After 2 days of cultivation, we harvested the islet cell sheets by lowering the culture temperature using a support membrane with a gelatin gel. We transplanted two recovered islet cell sheets into the subcutaneous space or onto the liver surface of severe combined immunodeficiency (SCID) mice with streptozocin-induced diabetes.

RESULTS

In the liver surface group, the non-fasting blood glucose level decreased rapidly within several days after transplantation. In marked contrast, the hyperglycemia state was maintained in the subcutaneous space transplantation group. The levels of rat C-peptide and insulin in the liver surface group were significantly higher than those in the subcutaneous space group. An immunohistological analysis confirmed that most of the islet cells engrafted on the liver surface were insulin-positive. The CD31-positive endothelial cells formed vascular networks within the neo-islets and in the surrounding tissues. In contrast, viable islet cells were not found in the subcutaneous space group.

CONCLUSIONS

Compared with the subcutaneous space, a relatively small mass of islet cell sheets was enough to achieve normoglycemia in diabetic mice when the liver surface was selected as the transplantation site. Our results demonstrate that the optimization of the transplantation site for islet cell sheets leads to significant improvements in the therapeutic efficiency for T1DM.

Effect of γ-Aminobutyric Acid-Chitosan Nanoparticles on Glucose Homeostasis in Mice

Diabetes mellitus is the most common endocrine disease worldwide; hyperglycemia is a hallmark of this disease. To alleviate the pain caused by diabetes, developing and utilizing effective diabetic drugs to maintain or recover the function of the residual β-cells is an attractive therapeutic approach. γ-aminobutyric acid (GABA) has been shown to have such effects, but it is easy to have reduced GABA activity under physiological conditions. In the present study, GABA-chitosan nanoparticles (GABA-CS NPs) were prepared, and glucose homeostasis, pancreatic β-cell protection, and anti-inflammatory effects of GABA-CS NPs were investigated in vivo. The results showed that blood glucose levels and IL-1β levels in the GABA-CS NP-administered group were both significantly lower, whereas the PDX1 expression was significantly higher than that of the impaired group (p < 0.01). This indicates that GABA-CS NPs can efficiently maintain glucose homeostasis, protect β-cells, and inhibit inflammation. These nanoparticles have the potential to be applied for future diabetes theranostics.

Kinetics of pancreatic tissue proliferation in a polymeric platform in mice

BACKGROUND/OBJECTIVES

Pancreas regenerative capacity after injury is not always sufficient to comply with the body's requirement of digestive enzymes and hormones. We present an alternative system to induce pancreas parenchyma proliferation (exocrine and endocrine components), rather than regeneration or remodeling in normoglycemic mice.

METHODS

Porous discs of polyether-polyurethane were surgically placed adjacent to the native pancreas and removed at days 15, 30 and 45 after implantation. No exogenous growth factors or extracellular matrix components were added to the platform. The synthetic matrix provided a platform that was filled with parenchymal and non-parenchymal pancreas tissue as detected by histological analysis. Immunohistochemistry analysis were performed to identify insulin positive cells in the newly formed tissue. In addition, angiogenic, inflammatory and metabolic parameters were carried out in those mice.

RESULTS

At day 15, the pores of the platform were filled with inflammatory cells, spindled-shaped like fibroblasts, extracellular matrix components, blood vessels and clusters of pancreatic parenchyma (acini, ducts and islet-like structures). At days 30 and 45 the pancreas features remained well organized; its organization resembled that of a native pancreas. Interestingly, besides islet-like structures that showed positive cells to insulin, some ductal cells were also positive for insulin immunostaining. No significant differences in serum glucose and c-peptide concentrations during the experimental period were detected.

CONCLUSIONS

The plain synthetic porous platform (without addition of exogenous molecules) placed adjacent to the native organ exhibits potential to restore and/or expand exocrine (acini, ducts) and endocrine (β-cell mass) components in pancreatic injuries and in high metabolic demand.

Pancreatic β Cell Regeneration as a Possible Therapy for Diabetes

Diabetes is the result of having inadequate supply of functional insulin-producing β cells. Two possible approaches for replenishing the β cells are: (1) replacement by transplanting cadaveric islets or β cells derived from human embryonic stem cells/induced pluripotent stem cells and (2) induction of endogenous regeneration. This review focuses on endogenous regeneration, which can follow two pathways: enhanced replication of existing β cells and formation of new β cells from cells not expressing insulin, either by conversion from a differentiated cell type (transdifferentiation) or differentiation from progenitors (neogenesis). Exciting progress on both pathways suggest that regeneration may have therapeutic promise.

Temporal characterization of β cell-adaptive and -maladaptive mechanisms during chronic high-fat feeding in C57BL/6NTac mice

The onset of type 2 diabetes is characterized by transition from successful to failed insulin secretory compensation to obesity-related insulin resistance and dysmetabolism. Energy-rich diets in rodents are commonly studied models of compensatory increases in both insulin secretion and β cell mass. However, the mechanisms of these adaptive responses are incompletely understood, and it is also unclear why these responses eventually fail. We measured the temporal trends of glucose homeostasis, insulin secretion, β cell morphometry, and islet gene expression in C57BL/6NTac mice fed a 60% high-fat diet (HFD) or control diet for up to 16 weeks. A 2-fold increased hyperinsulinemia was maintained for the first 4 weeks of HFD feeding and then further increased through 16 weeks. β cell mass increased progressively starting at 4 weeks, principally through nonproliferative growth. Insulin sensitivity was not significantly perturbed until 11 weeks of HFD feeding. Over the first 8 weeks, we observed two distinct waves of increased expression of β cell functional and prodifferentiation genes. This was followed by activation of the unfolded protein response at 8 weeks and overt β cell endoplasmic reticulum stress at 12-16 weeks. In summary, β cell adaptation to an HFD in C57BL/6NTac mice entails early insulin hypersecretion and a robust growth phase along with hyperexpression of related genes that begin well before the onset of observed insulin resistance. However, continued HFD exposure results in cessation of gene hyperexpression, β cell functional failure, and endoplasmic reticulum stress. These data point to a complex but not sustainable integration of β cell-adaptive responses to nutrient overabundance, obesity development, and insulin resistance.

Synthetic matrix of polyether-polyurethane as a biological platform for pancreatic regeneration

AIMS

Several alternative cellular approaches using biomaterials to host insulin-producing cells derived from stem cells have been developed to overcome the limitations of type 1 diabetes treatment (exogenous insulin injection). However, none seem to fulfill all requirements needed to induce pancreatic cells successful colonization of the scaffolds. Here, we report a polymeric platform adherent to the native mice pancreas filled with human adipose stem cells (hASCs) that was able to induce growth of pancreatic parenchyma.

MAIN METHODS

Synthetic polyether-polyurethane discs were placed adjacent to pancreas of normoglycemic and streptozotocin-induced diabetic mice. At day 4 post implantation, 1×10⁶ hASCs were injected intra-implant in groups of normoglycemic and diabetic mice. Immunohistochemistry analysis of the implants was performed to identify insulin positive cells in the newly formed tissue. In addition, metabolic, inflammatory and angiogenic parameters were carried out in those mice.

KEY FINDINGS

This study provides evidence of the ability of a biohybrid device to induce the growth of differentiated pancreas parenchyma in both normoglycemic and streptozotocin-induced diabetic mice as detected by histological analysis. Glucose metabolism and body weight of hyperglycemic mice bearing hASCs implants improved.

SIGNIFICANCE

The synthetic porous scaffold bearing hASC cells placed adjacent to the native animal pancreas exhibits the potential to be exploited in future cell-based type 1 diabetes therapies.

Pancreatic β cell identity requires continual repression of non-β cell programs

Loss of β cell identity, the presence of polyhormonal cells, and reprogramming are emerging as important features of β cell dysfunction in patients with type 1 and type 2 diabetes. In this study, we have demonstrated that the transcription factor NKX2.2 is essential for the active maintenance of adult β cell identity as well as function. Deletion of Nkx2.2 in β cells caused rapid onset of a diabetic phenotype in mice that was attributed to loss of insulin and downregulation of many β cell functional genes. Concomitantly, NKX2.2-deficient murine β cells acquired non-β cell endocrine features, resulting in populations of completely reprogrammed cells and bihormonal cells that displayed hybrid endocrine cell morphological characteristics. Molecular analysis in mouse and human islets revealed that NKX2.2 is a conserved master regulatory protein that controls the acquisition and maintenance of a functional, monohormonal β cell identity by directly activating critical β cell genes and actively repressing genes that specify the alternative islet endocrine cell lineages. This study demonstrates the highly volatile nature of the β cell, indicating that acquiring and sustaining β cell identity and function requires not only active maintaining of the expression of genes involved in β cell function, but also continual repression of closely related endocrine gene programs.

A newly developed silymarin nanoformulation as a potential antidiabetic agent in experimental diabetes

Aim: This study aimed to develop a new stable nanoformulation of silymarin (SM) with optimum enhanced oral bioavailability and to evaluate its effect as well as mechanism of action as a superior antidiabetic agent over native SM using streptozotocin-induced diabetic rats. Materials and methods: SM-loaded pluronic nanomicelles (SMnp) were prepared and fully characterized. Biochemical parameters were performed as well as histological, confocal and reverse-transcription polymerase chain reaction studies on pancreatic target tissues. Results & conclusion: SMnp were found to improve significantly the antihyperglycemic, antioxidant and antihyperlipidemic properties as compared with native SM. In addition, SMnp was found to be a more efficient agent over SM in the management of diabetes and its associated complications due to its superior bioavailability in vivo, and the controlled release profile of SM.

[Formula: see text]

Stress-induced adaptive islet cell identity changes

The different forms of diabetes mellitus differ in their pathogenesis but, ultimately, they are all characterized by progressive islet β-cell loss. Restoring the β-cell mass is therefore a major goal for future therapeutic approaches. The number of β-cells found at birth is determined by proliferation and differentiation of pancreatic progenitor cells, and it has been considered to remain mostly unchanged throughout adult life. Recent studies in mice have revealed an unexpected plasticity in islet endocrine cells in response to stress; under certain conditions, islet non-β-cells have the potential to reprogram into insulin producers, thus contributing to restore the β-cell mass. Here, we discuss the latest findings on pancreas and islet cell plasticity upon physiological, pathological and experimental conditions of stress. Understanding the mechanisms involved in cell reprogramming in these models will allow the development of new strategies for the treatment of diabetes, by exploiting the intrinsic regeneration capacity of the pancreas.

Beta Cell Formation in vivo Through Cellular Networking, Integration and Processing (CNIP) in Wild Type Adult Mice

Insulin replacement therapy is essential in type 1 diabetic individuals and is required in ~40-50% of type 2 diabetics during their lifetime. Prior attempts at beta cell regeneration have relied upon pancreatic injury to induce beta cell proliferation, dedifferentiation and activation of the embryonic pathway, or stem cell replacement. We report an alternative method to transform adult non-stem (somatic) cells into pancreatic beta cells. The Cellular Networking, Integration and Processing (CNIP) approach targets cellular mechanisms involved in pancreatic function in the organ’s adult state and utilizes a synergistic mechanism that integrates three important levels of cellular regulation to induce beta cell formation: (i) glucose metabolism, (ii) membrane receptor function, and (iii) gene transcription. The aim of the present study was to induce pancreatic beta cell formation in vivo in adult animals without stem cells and without dedifferentiating cells to recapitulate the embryonic pathway as previously published (1-3). Our results employing CNIP demonstrate that: (i) insulin secreting cells can be generated in adult pancreatic tissue in vivo and circumvent the problem of generating endocrine (glucagon and somatostatin) cells that exert deleterious effects on glucose homeostasis, and (ii) long-term normalization of glucose tolerance and insulin secretion can be achieved in a wild type diabetic mouse model. The CNIP cocktail has the potential to be used as a preventative or therapeutic treatment or cure for both type 1 and type 2 diabetes.

Stem cells versus plasticity in liver and pancreas regeneration

Cell replacement in adult organs can be achieved through stem cell differentiation or the replication or transdifferentiation of existing cells. In the adult liver and pancreas, stem cells have been proposed to replace tissue cells, particularly following injury. Here we review how specialized cell types are produced in the adult liver and pancreas. Based on current evidence, we propose that the plasticity of differentiated cells, rather than stem cells, accounts for tissue repair in both organs.

mTORC1 pathway mediates beta cell compensatory proliferation in 60 % partial-pancreatectomy mice

Beta cell replication is the major component for maintenance of beta cell mass in adult rodents; however, little is known about what is the earliest signals that initiate rodent beta cell proliferation. The mTORC1 pathway integrates signals from growth factors and nutrients and regulates cell growth and survival. Here, we used normoglycemic 60 % partial-pancreatectomy (60 % Px) mouse model to determine whether mTORC1 pathway was required for compensatory beta cell proliferation. C57BL/6 J male mice were subjected to 60 % Px or sham operation, and subsequently treated with either rapamycin or vehicle for 7 days. Metabolic profile, pancreatic beta cell mass, and proliferation were examined, and expression levels of cell cycle regulators were determined. Beta cell proliferation was increased by 2.5-fold, and mTORC1 signaling was activated in islets post-Px. Rapamycin treatment impaired glucose tolerance and glucose stimulating insulin secretion in 60 % Px mice, but did not affect their insulin sensitivity in peripheral tissue. Rapamycin inhibited mTORC1 activity in beta cells, suppressed compensatory beta cell proliferation and growth, and reduced beta cell mass and insulin content in 60 % Px mice. Px caused an increase of the cyclin D2 at protein level and promoted cyclin D2 nuclear localization in an mTOR-dependent manner. Disrupting mTORC1 signaling suppressed cell proliferation and simultaneously diminished cyclin D2 protein abundance in RINm5F cells. Our data demonstrated that mTORC1 plays an essential role in beta cell adaption to significant beta cell mass loss in 60 % Px model and in early compensatory beta cell proliferation via cyclin D2 pathway.

Pancreatic β Cell Mass Death

Type two diabetes (T2D) is a challenging metabolic disorder for which a cure has not yet been found. Its etiology is associated with several phenomena, including significant loss of insulin-producing, beta cell (β cell) mass via progressive programmed cell death and disrupted cellular autophagy. In diabetes, the etiology of β cell death and the role of mitochondria are complex and involve several layers of mechanisms. Understanding the dynamics of those mechanisms could permit researchers to develop an intervention for the progressive loss of β cells. Currently, diabetes research has shifted toward rejuvenation and plasticity technology and away from the simplified approach of hormonal compensation. Diabetes research is currently challenged by questions such as how to enhance cell survival, decrease apoptosis and replenish β cell mass in diabetic patients. In this review, we discuss evidence that β cell development and mass formation are guided by specific signaling systems, particularly hormones, transcription factors, and growth factors, all of which could be manipulated to enhance mass growth. There is also strong evidence that β cells are dynamically active cells, which, under specific conditions such as obesity, can increase in size and subsequently increase insulin secretion. In certain cases of aggressive or advanced forms of T2D, β cells become markedly impaired, and the only alternatives for maintaining glucose homeostasis are through partial or complete cell grafting (the Edmonton protocol). In these cases, the harvesting of an enriched population of viable β cells is required for transplantation. This task necessitates a deep understanding of the pharmacological agents that affect β cell survival, mass, and function. The aim of this review is to initiate discussion about the important signals in pancreatic β cell development and mass formation and to highlight the process by which cell death occurs in diabetes. This review also examines the attempts that have been made to recover or increase cell mass in diabetic patients by using various pharmacological agents.

Intraislet Pancreatic Ducts Can Give Rise to Insulin-Positive Cells

A key question in diabetes research is whether new β-cells can be derived from endogenous, nonendocrine cells. The potential for pancreatic ductal cells to convert into β-cells is a highly debated issue. To date, it remains unclear what anatomical process would result in duct-derived cells coming to exist within preexisting islets. We used a whole-mount technique to directly visualize the pancreatic ductal network in young wild-type mice, young humans, and wild-type and transgenic mice after partial pancreatectomy. Pancreatic ductal networks, originating from the main ductal tree, were found to reside deep within islets in young mice and humans but not in mature mice or humans. These networks were also not present in normal adult mice after partial pancreatectomy, but TGF-β receptor mutant mice demonstrated formation of these intraislet duct structures after partial pancreatectomy. Genetic and viral lineage tracings were used to determine whether endocrine cells were derived from pancreatic ducts. Lineage tracing confirmed that pancreatic ductal cells can typically convert into new β-cells in normal young developing mice as well as in adult TGF-β signaling mutant mice after partial pancreatectomy. Here the direct visual evidence of ducts growing into islets, along with lineage tracing, not only represents strong evidence for duct cells giving rise to β-cells in the postnatal pancreas but also importantly implicates TGF-β signaling in this process.

Diabetes associated with pancreatic diseases

PURPOSE OF REVIEW

A relevant number of patients with pancreatic disorders suffer from secondary diabetes. Recent data have shed light on the link between pancreatic damage and subsequent impairments in glucose homeostasis. Furthermore, epidemiological studies provided insights into the relationship between diabetes and the risk of pancreatic carcinoma or pancreatitis. Pancreaticogenic diabetes requires a tailored therapeutic approach taking into account the individual properties of the available glucose-lowering drugs.

RECENT FINDINGS

We review the available literature concerning diabetes in patients with acute or chronic pancreatitis or pancreatic carcinoma. The relationship between the pancreatic damage and alterations in insulin and glucose homeostasis is summarized as well as the effect of diabetes mellitus on the risk of pancreatic cancer and pancreatitis. Caveats in the treatment of pancreaticogenic diabetes with currently available drugs are being discussed.

SUMMARY

Patients with pancreatic diseases should be screened for diabetes by means of an oral glucose tolerance test. There is a close inverse relationship between pancreatic β-cell loss and postchallenge hyperglycemia. The risk of hypoglycemia may be increased in patients with pancreaticogenic diabetes. Newly diagnosed diabetes may be a harbinger of pancreatic cancer. There is increasing evidence suggesting an increased risk for (pancreatic) cancer and pancreatitis in patients with diabetes mellitus. Further studies on the ideal glucose-lowering treatment of patients with pancreaticogenic diabetes will be required.

Using stem cells to produce insulin

INTRODUCTION

Tremendous progress has been made in generating insulin-producing cells from pluripotent stem cells. The best outcome of the refined protocols became apparent in the first clinical trial announced by ViaCyte, based on the implantation of pancreatic progenitors that would further mature into functional insulin-producing cells inside the patient's body.

AREAS COVERED

Several groups, including ours, have contributed to improve strategies to generate insulin-producing cells. Of note, the latest results have gained a substantial amount of interest as a method to create a potentially functional and limitless supply of β-cell to revert diabetes mellitus. This review analyzes the accomplishments that have taken place over the last few decades, summarizes the state-of-art methods for β-cell replacement therapies based on the differentiation of embryonic stem cells into glucose-responsive and insulin-producing cells in a dish and discusses alternative approaches to obtain new sources of insulin-producing cells.

EXPERT OPINION

Undoubtedly, recent events preface the beginning of a new era in diabetes therapy. However, in our opinion, a number of significant hurdles still stand in the way of clinical application. We believe that the combination of the private and public sectors will accelerate the process of obtaining the desired safe and functional β-cell surrogates.

Biphasic decline of β-cell function with age in euglycemic nonobese diabetic mice parallels diabetes onset

A gradual decline in insulin response is known to precede the onset of type 1 diabetes (T1D). To track age-related changes in the β-cell function of nonobese diabetic (NOD) mice, the most commonly used animal model for T1D, and to establish differences between those who do and do not become hyperglycemic, we performed a long-term longitudinal oral glucose tolerance test (OGTT) study (10-42 weeks) in combination with immunofluorescence imaging of islet morphology and cell proliferation. We observed a clear biphasic decline in insulin secretion (AUC0-30 min ) even in euglycemic animals. A first phase (10-28 weeks) consisted of a relatively rapid decline and paralleled diabetes development in the same cohort of animals. This was followed by a second phase (29-42 weeks) during which insulin secretion declined much slower while no additional animals became diabetic. Blood glucose profiles showed a corresponding, but less pronounced change: the area under the concentration curve (AUC0-150 min ) increased with age, and fit with a bilinear model indicated a rate-change in the trendline around 28 weeks. In control NOD scids, no such changes were observed. Islet morphology also changed with age as islets become surrounded by mononuclear infiltrates, and, in all mice, islets with immune cell infiltration around them showed increased β-cell proliferation. In conclusion, insulin secretion declines in a biphasic manner in all NOD mice. This trend, as well as increased β-cell proliferation, is present even in the NODs that never become diabetic, whereas, it is absent in control NOD scid mice.

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.

Recent progress in studies of factors that elicit pancreatic β-cell expansion

The loss of or decreased functional pancreatic β-cell is a major cause of type 1 and type 2 diabetes. Previous studies have shown that adult β-cells can maintain their ability for a low level of turnover through replication and neogenesis. Thus, a strategy to prevent and treat diabetes would be to enhance the ability of β-cells to increase the mass of functional β-cells. Consequently, much effort has been devoted to identify factors that can effectively induce β-cell expansion. This review focuses on recent reports on small molecules and protein factors that have been shown to promote β-cell expansion.

Therapeutic Approaches for Preserving or Restoring Pancreatic β-Cell Function and Mass

The goal for the treatment of patients with diabetes has today shifted from merely reducing glucose concentrations to preventing the natural decline in β-cell function and delay the progression of disease. Pancreatic β-cell dysfunction and decreased β-cell mass are crucial in the development of diabetes. The β-cell defects are the main pathogenesis in patients with type 1 diabetes and are associated with type 2 diabetes as the disease progresses. Recent studies suggest that human pancreatic β-cells have a capacity for increased proliferation according to increased demands for insulin. In humans, β-cell mass has been shown to increase in patients showing insulin-resistance states such as obesity or in pregnancy. This capacity might be useful for identifying new therapeutic strategies to reestablish a functional β-cell mass. In this context, therapeutic approaches designed to increase β-cell mass might prove a significant way to manage diabetes and prevent its progression. This review describes the various β-cell defects that appear in patients with diabetes and outline the mechanisms of β-cell failure. We also review common methods for assessing β-cell function and mass and methodological limitations in vivo. Finally, we discuss the current therapeutic approaches to improve β-cell function and increase β-cell mass.

You are what you eat, or are you? The challenges of translating high-fat-fed rodents to human obesity and diabetes

Obesity and type 2 diabetes mellitus (T2DM) are rapidly growing worldwide epidemics with major health consequences. Various human-based studies have confirmed that both genetic and environmental factors (particularly high-caloric diets and sedentary lifestyle) greatly contribute to human T2DM. Interactions between obesity, insulin resistance and β-cell dysfunction result in human T2DM, but the mechanisms regulating the interplay among these impairments remain unclear. Rodent models of high-fat diet (HFD)-induced obesity have been used widely to study human obesity and T2DM. With >9000 publications on PubMed over the past decade alone, many aspects of rodent T2DM have been elucidated; however, correlation to human obesity/diabetes remains poor. This review investigates the reasons for this translational discrepancy by critically evaluating rodent HFD models. Dietary modification in rodents appears to have limited translatable benefit for understanding and treating human obesity and diabetes due—at least in part—to divergent dietary compositions, species/strain and gender variability, inconsistent disease penetrance, severity and duration and lack of resemblance to human obesogenic pathophysiology. Therefore future research efforts dedicated to acquiring translationally relevant data—specifically human data, rather than findings based on rodent studies—would accelerate our understanding of disease mechanisms and development of therapeutics for human obesity/T2DM.

Activated FoxM1 attenuates streptozotocin-mediated β-cell death

The forkhead box transcription factor FoxM1, a positive regulator of the cell cycle, is required for β-cell mass expansion postnatally, during pregnancy, and after partial pancreatectomy. Up-regulation of full-length FoxM1, however, is unable to stimulate increases in β-cell mass in unstressed mice or after partial pancreatectomy, probably due to the lack of posttranslational activation. We hypothesized that expression of an activated form of FoxM1 could aid in recovery after β-cell injury. We therefore derived transgenic mice that inducibly express an activated version of FoxM1 in β-cells (RIP-rtTA;TetO-hemagglutinin (HA)-Foxm1(Δ)(NRD) mice). This N-terminally truncated form of FoxM1 bypasses 2 posttranslational controls: exposure of the forkhead DNA binding domain and targeted proteasomal degradation. Transgenic mice were subjected to streptozotocin (STZ)-induced β-cell ablation to test whether activated FoxM1 can promote β-cell regeneration. Mice expressing HA-FoxM1(ΔNRD) displayed decreased ad libitum-fed blood glucose and increased β-cell mass. β-Cell proliferation was actually decreased in RIP-rtTA:TetO-HA-Foxm1(NRD) mice compared with that in RIP-rtTA mice 7 days after STZ treatment. Unexpectedly, β-cell death was decreased 2 days after STZ treatment. RNA sequencing analysis indicated that activated FoxM1 alters the expression of extracellular matrix and immune cell gene profiles, which may protect against STZ-mediated death. These studies highlight a previously underappreciated role for FoxM1 in promoting β-cell survival.

The regulation of pre- and post-maturational plasticity of mammalian islet cell mass

Regeneration of mature cells that produce functional insulin represents a major focus and a challenge of current diabetes research aimed at restoring beta cell mass in patients with most forms of diabetes, as well as in ageing. The capacity to adapt to diverse physiological states during life and the consequent ability to cope with increased metabolic demands in the normal regulation of glucose homeostasis is a distinctive feature of the endocrine pancreas in mammals. Both beta and alpha cells, and presumably other islet cells, are dynamically regulated via nutrient, neural and/or hormonal activation of growth factor signalling and the post-transcriptional modification of a variety of genes or via the microbiome to continually maintain a balance between regeneration (e.g. proliferation, neogenesis) and apoptosis. Here we review key regulators that determine islet cell mass at different ages in mammals. Understanding the chronobiology and the dynamics and age-dependent processes that regulate the relationship between the different cell types in the overall maintenance of an optimally functional islet cell mass could provide important insights into planning therapeutic approaches to counter and/or prevent the development of diabetes.

Automated quantification of pancreatic β-cell mass

β-Cell mass is a parameter commonly measured in studies of islet biology and diabetes. However, the rigorous quantification of pancreatic β-cell mass using conventional histological methods is a time-consuming process. Rapidly evolving virtual slide technology with high-resolution slide scanners and newly developed image analysis tools has the potential to transform β-cell mass measurement. To test the effectiveness and accuracy of this new approach, we assessed pancreata from normal C57Bl/6J mice and from mouse models of β-cell ablation (streptozotocin-treated mice) and β-cell hyperplasia (leptin-deficient mice), using a standardized systematic sampling of pancreatic specimens. Our data indicate that automated analysis of virtual pancreatic slides is highly reliable and yields results consistent with those obtained by conventional morphometric analysis. This new methodology will allow investigators to dramatically reduce the time required for β-cell mass measurement by automating high-resolution image capture and analysis of entire pancreatic sections.

β-Cell proliferation after a partial pancreatectomy is independent of IRS-2 in mice

The glucokinase-induced up-regulation of insulin receptor substrate 2 (IRS-2) plays an important role in β-cell adaptive proliferation in response to high-fat diet-induced insulin resistance. This study aimed to investigate the role of IRS-2 in the proliferation of β-cells after a 60% partial pancreatectomy. IRS-2-deficient (IRS-2(-/-)) mice or wild-type mice were subjected to a pancreatectomy (60% partial pancreatectomy) or a sham operation (Sham). The β-cell proliferation and gene expression profiles of the islets were then assessed. Gene expression in islets from pancreatectomized and Sham C57BL/6J male mice was analyzed using a cDNA microarray analysis. To compare with β-cell proliferation induced by a high-fat diet, Gck(+/-) mice subjected to a pancreatectomy were also analyzed. The IRS-2(-/-) mice exhibited β-cell expansion and a significant increase in β-cell proliferation after the pancreatectomy, compared with the Sham group. Although glucose-stimulated insulin secretion from islets was not impaired, IRS-2(-/-) mice manifested severe hyperglycemia after the pancreatectomy. The expression levels of Aurora kinase B, Cyclin A, and Cyclin B1 in the pancreatectomized islets were also enhanced in the IRS-2(-/-) mice. A gene set enrichment analysis suggested an association between the genes that were up-regulated in the pancreatectomized islets and those involved in M phase progression in the cell cycle. β-Cell proliferation after a pancreatectomy was observed even in the Gck(+/-) mice. In conclusion, IRS-2 was not required for β-cell proliferation but might be needed for functional β-cell mass, after a pancreatectomy. A partial pancreatectomy in mice may be an attractive model for the development of new strategy for exploring the unique nature of β-cell proliferation.

Silymarin induces expression of pancreatic Nkx6.1 transcription factor and β-cells neogenesis in a pancreatectomy model

A physio-pathological feature of diabetes mellitus is a significant reduction of β-pancreatic cells. The growth, differentiation and function maintenance of these cells is directed by transcription factors. Nkx6.1 is a key transcription factor for the differentiation, neogenesis and maintenance of β-pancreatic cells. We reported that silymarin restores normal morphology and endocrine function of damaged pancreatic tissue after alloxan-induced diabetes mellitus in rats. The aim of this study was to analyze the effect of silymarin on Nkx6.1 transcription factor expression and its consequence in β cells neogenesis. Sixty male Wistar rats were partially pancreatectomized and divided into twelve groups. Six groups were treated with silymarin (200 mg/Kg p.o) for periods of 3, 7, 14, 21, 42 and 63 days. Additionally, an unpancreatectomized control group was used. Nkx6.1 and insulin gene expression were assessed by RT-PCR assay in total pancreatic RNA. β-Cell neogenesis was determined by immunoperoxidase assay. Silymarin treated group showed an increase of Nkx6.1 and insulin genic expression. In this group, there was an increment of β-cell neogenesis in comparison to pancreatectomized untreated group. Silymarin treatment produced a rise in serum insulin and serum glucose normalization. These results suggest that silymarin may improve the reduction of β pancreatic cells observed in diabetes mellitus.