Oxygen tension regulates pancreatic beta-cell differentiation through hypoxia-inducible factor 1alpha

Coordination between ECM and cell-cell adhesion regulates the development of islet aggregation, architecture, and functional maturation

Pancreatic islets are three-dimensional cell aggregates consisting of unique cellular composition, cell-to-cell contacts, and interactions with blood vessels. Cell aggregation is essential for islet endocrine function; however, it remains unclear how developing islets establish aggregation. By combining genetic animal models, imaging tools, and gene expression profiling, we demonstrate that islet aggregation is regulated by extracellular matrix signaling and cell-cell adhesion. Islet endocrine cell-specific inactivation of extracellular matrix receptor integrin β1 disrupted blood vessel interactions but promoted cell-cell adhesion and the formation of larger islets. In contrast, ablation of cell-cell adhesion molecule α-catenin promoted blood vessel interactions yet compromised islet clustering. Simultaneous removal of integrin β1 and α-catenin disrupts islet aggregation and the endocrine cell maturation process, demonstrating that establishment of islet aggregates is essential for functional maturation. Our study provides new insights into understanding the fundamental self-organizing mechanism for islet aggregation, architecture, and functional maturation.

Fetal Oxygenation from the 23rd to the 36th Week of Gestation Evaluated through the Umbilical Cord Blood Gas Analysis

The embryo and fetus grow in a hypoxic environment. Intrauterine oxygen levels fluctuate throughout the pregnancy, allowing the oxygen to modulate apparently contradictory functions, such as the expansion of stemness but also differentiation. We have recently demonstrated that in the last weeks of pregnancy, oxygenation progressively increases, but the trend of oxygen levels during the previous weeks remains to be clarified. In the present retrospective study, umbilical venous and arterial oxygen levels, fetal oxygen extraction, oxygen content, CO2, and lactate were evaluated in a cohort of healthy newborns with gestational age < 37 weeks. A progressive decrease in pO2 levels associated with a concomitant increase in pCO2 and reduction in pH has been observed starting from the 23rd week until approximately the 33-34th week of gestation. Over this period, despite the increased hypoxemia, oxygen content remains stable thanks to increasing hemoglobin concentration, which allows the fetus to become more hypoxemic but not more hypoxic. Starting from the 33-34th week, fetal oxygenation increases and ideally continues following the trend recently described in term fetuses. The present study confirms that oxygenation during intrauterine life continues to vary even after placenta development, showing a clear biphasic trend. Fetuses, in fact, from mid-gestation to near-term, become progressively more hypoxemic. However, starting from the 33-34th week, oxygenation progressively increases until birth. In this regard, our data suggest that the placenta is the hub that ensures this variable oxygen availability to the fetus, and we speculate that this biphasic trend is functional for the promotion, in specific tissues and at specific times, of stemness and intrauterine differentiation.

Islets in the body are never flat: transitioning from two-dimensional (2D) monolayer culture to three-dimensional (3D) spheroid for better efficiency in the generation of functional hPSC-derived pancreatic β cells in vitro

Diabetes mellitus (DM), currently affecting more than 537 million people worldwide is a chronic disease characterized by impaired glucose metabolism resulting from a defect in insulin secretion, action, or both due to the loss or dysfunction of pancreatic β cells. Since cadaveric islet transplantation using Edmonton protocol has served as an effective intervention to restore normoglycaemia in T1D patients for months, stem cell-derived β cells have been explored for cell replacement therapy for diabetes. Thus, great effort has been concentrated by scientists on developing in vitro differentiation protocols to realize the therapeutic potential of hPSC-derived β cells. However, most of the 2D traditional monolayer culture could mainly generate insulin-producing β cells with immature phenotype. In the body, pancreatic islets are 3D cell arrangements with complex cell-cell and cell-ECM interactions. Therefore, it is important to consider the spatial organization of the cell in the culture environment. More recently, 3D cell culture platforms have emerged as powerful tools with huge translational potential, particularly for stem cell research. 3D protocols provide a better model to recapitulate not only the in vivo morphology, but also the cell connectivity, polarity, and gene expression mimicking more physiologically the in vivo cell niche. Therefore, the 3D culture constitutes a more relevant model that may help to fill the gap between in vitro and in vivo models. Interestingly, most of the 2D planar methodologies that successfully generated functional hPSC-derived β cells have switched to a 3D arrangement of cells from pancreatic progenitor stage either as suspension clusters or as aggregates, suggesting the effect of 3D on β cell functionality. In this review we highlight the role of dimensionality (2D vs 3D) on the differentiation efficiency for generation of hPSC-derived insulin-producing β cells in vitro. Consequently, how transitioning from 2D monolayer culture to 3D spheroid would provide a better model for an efficient generation of fully functional hPSC-derived β cells mimicking in vivo islet niche for diabetes therapy or drug screening. Video Abstract.

Fetal oxygenation in the last weeks of pregnancy evaluated through the umbilical cord blood gas analysis

Introduction

Embryo and fetus grow and mature over the first trimester of pregnancy in a dynamic hypoxic environment, where placenta development assures an increased oxygen availability. However, it is unclear whether and how oxygenation changes in the later trimesters and, more specifically, in the last weeks of pregnancy.

Methods

Observational study that evaluated the gas analysis of the umbilical cord blood collected from a cohort of healthy newborns with gestational age ≥37 weeks. Umbilical venous and arterial oxygen levels as well as fetal oxygen extraction were calculated to establish whether oxygenation level changes over the last weeks of pregnancy. In addition, fetal lactate, and carbon dioxide production were analyzed to establish whether oxygen oscillations may induce metabolic effects in utero.

Results

This study demonstrates a progressive increase in fetal oxygenation levels from the 37th to the 41st weeks of gestation (mean venous PaO₂ approximately from 20 to 25 mmHg; p < 0.001). This increase is largely attributable to growing umbilical venous PaO₂, regardless of delivery modalities. In neonates born by vaginal delivery, the increased oxygen availability is associated with a modest increase in oxygen extraction, while in neonates born by cesarean section, it is associated with reduced lactate production. Independently from the type of delivery, carbon dioxide production moderately increased. These findings suggest a progressive shift from a prevalent anaerobic metabolism (Warburg effect) towards a growing aerobic metabolism.

Conclusion

This study confirms that fetuses grow in a hypoxic environment that becomes progressively less hypoxic in the last weeks of gestation. The increased oxygen availability seems to favor aerobic metabolic shift during the last weeks of intrauterine life; we hypothesize that this environmental change may have implications for fetal maturation during intrauterine life.

Epigenetic Changes Induced by High Glucose in Human Pancreatic Beta Cells

Epigenetic changes in pancreatic beta cells caused by sustained high blood glucose levels, as seen in prediabetic conditions, may contribute to the etiology of diabetes. To delineate a direct cause and effect relationship between high glucose and epigenetic changes, we cultured human pancreatic beta cells derived from induced pluripotent stem cells and treated them with either high or low glucose, for 14 days. We then used the Arraystar 4x180K HG19 RefSeq Promoter Array to perform whole-genome DNA methylation analysis. A total of 478 gene promoters, out of a total of 23,148 present on the array (2.06%), showed substantial differences in methylation (p < 0.01). Out of these, 285 were hypomethylated, and 193 were hypermethylated in experimental vs. control. Ingenuity Pathway Analysis revealed that the main pathways and networks that were differentially methylated include those involved in many systems, including those related to development, cellular growth, and proliferation. Genes implicated in the etiology of diabetes, including networks involving glucose metabolism, insulin secretion and regulation, and cell cycle regulation, were notably altered. Influence of upstream regulators such as MRTFA, AREG, and NOTCH3 was predicted based on the altered methylation of their downstream targets. The study validated that high glucose levels can directly cause many epigenetic changes in pancreatic beta cells, suggesting that this indeed may be a mechanism involved in the etiology of diabetes.

HIF-2α Preserves Mitochondrial Activity and Glucose Sensing in Compensating β-Cells in Obesity

In obesity, increased mitochondrial metabolism with the accumulation of oxidative stress leads to mitochondrial damage and β-cell dysfunction. In particular, β-cells express antioxidant enzymes at relatively low levels and are highly vulnerable to oxidative stress. Early in the development of obesity, β-cells exhibit increased glucose-stimulated insulin secretion in order to compensate for insulin resistance. This increase in β-cell function under the condition of enhanced metabolic stress suggests that β-cells possess a defense mechanism against increased oxidative damage, which may become insufficient or decline at the onset of type 2 diabetes. Here, we show that metabolic stress induces β-cell hypoxia inducible factor 2α (HIF-2α), which stimulates antioxidant gene expression (e.g., Sod2 and Cat) and protects against mitochondrial reactive oxygen species (ROS) and subsequent mitochondrial damage. Knockdown of HIF-2α in Min6 cells exaggerated chronic high glucose-induced mitochondrial damage and β-cell dysfunction by increasing mitochondrial ROS levels. Moreover, inducible β-cell HIF-2α knockout mice developed more severe β-cell dysfunction and glucose intolerance on a high-fat diet, along with increased ROS levels and decreased islet mitochondrial mass. Our results provide a previously unknown mechanism through which β-cells defend against increased metabolic stress to promote β-cell compensation in obesity.

Vitamin D Receptor-Dependent Protective Effect of Moderate Hypoxia in a Mouse Colitis Model

Although hypoxia is important for maintaining the intestinal barrier, its effect on the barrier during acute colitis and the underlying mechanisms are not fully understood. To explore the influence of hypoxia in dextran sulfate sodium (DSS)-induced colitis mice and the role of hypoxia-inducible factor (HIF) and vitamin D receptor (VDR) in the process. Colitis mice were subjected to hypoxia to detect intestinal barrier function changes. And the mechanisms were explored in vitro. First, compared with colitis mice without hypoxia stimulation, those with hypoxia stimulation showed significantly decreased pathological damage and improved permeability of the intestinal barrier. The expression of tight junction proteins (occludin, ZO-1), HIF-1α as well as VDR was up-regulated in colitis mice with hypoxia stimulation. However, in VDR gene knockout (KO)colitis mice, hypoxia treatment showed no protective effect, suggesting the VDR dependency of this effect. Similarly although hypoxia stimulation could enhance the single-layer epithelial transmembrane electrical resistance in DLD-1 and NCM460 cells, these effects disappeared in VDR-knockdown cells. Furthermore, over-expression of HIF-1α in DLD-1 and NCM460 increased the expression of VDR, whereas HIF-1α-knockdown reduced the VDR expression directly. Chromatin immunoprecipitation and luciferase assays confirmed that HIF-1α can bind to the promoter region of the VDR gene under hypoxia. Finally, compared with their wild-type siblings, VDR-KO mice showed reduced abundance of anaerobic bacteria and SCFA-producing bacteria. Hypoxia was protective against DSS-induced colitis, and VDR is instrumental in it. Furthermore, HIF-1α-VDR mediates the effect of hypoxia on the barrier function. Moreover, intestinal flora may be an important link between hypoxia and VDR.

Adapting Physiology in Functional Human Islet Organogenesis

Generation of three-dimensional (3D)-structured functional human islets is expected to be an alternative cell source for cadaveric human islet transplantation for the treatment of insulin-dependent diabetes. Human pluripotent stem cells (hPSCs), such as human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer infinite resources for newly synthesized human islets. Recent advancements in hPSCs technology have enabled direct differentiation to human islet-like clusters, which can sense glucose and secrete insulin, and those islet clusters can ameliorate diabetes when transplanted into rodents or non-human primates (NHPs). However, the generated hPSC-derived human islet-like clusters are functionally immature compared with primary human islets. There remains a challenge to establish a technology to create fully functional human islets in vitro, which are functionally and transcriptionally indistinguishable from cadaveric human islets. Understanding the complex differentiation and maturation pathway is necessary to generate fully functional human islets for a tremendous supply of high-quality human islets with less batch-to-batch difference for millions of patients. In this review, I summarized the current progress in the generation of 3D-structured human islets from pluripotent stem cells and discussed the importance of adapting physiology for in vitro functional human islet organogenesis and possible improvements with environmental cues.

Optimization of an O2-balanced bioartificial pancreas for type 1 diabetes using statistical design of experiment

A bioartificial pancreas (BAP) encapsulating high pancreatic islets concentration is a promising alternative for type 1 diabetes therapy. However, the main limitation of this approach is O₂ supply, especially until graft neovascularization. Here, we described a methodology to design an optimal O₂-balanced BAP using statistical design of experiment (DoE). A full factorial DoE was first performed to screen two O₂-technologies on their ability to preserve pseudo-islet viability and function under hypoxia and normoxia. Then, response surface methodology was used to define the optimal O₂-carrier and islet seeding concentrations to maximize the number of viable pseudo-islets in the BAP containing an O₂-generator under hypoxia. Monitoring of viability, function and maturation of neonatal pig islets for 15 days in vitro demonstrated the efficiency of the optimal O₂-balanced BAP. The findings should allow the design of a more realistic BAP for humans with high islets concentration by maintaining the O₂ balance in the device.

The response of three-dimensional pancreatic alpha and beta cell co-cultures to oxidative stress

The pancreatic islets of Langerhans have low endogenous antioxidant levels and are thus especially sensitive to oxidative stress, which is known to influence cell survival and behaviour. As bioengineered islets are gaining interest for therapeutic purposes, it is important to understand how their composition can be optimized to diminish oxidative stress. We investigated how the ratio of the two main islet cell types (alpha and beta cells) and their culture in three-dimensional aggregates could protect against oxidative stress. Monolayer and aggregate cultures were established by seeding the alphaTC1 (alpha) and INS1E (beta) cell lines in varying ratios, and hydrogen peroxide was applied to induce oxidative stress. Viability, oxidative stress, and the level of the antioxidant glutathione were measured. Both aggregation and an increasing prevalence of INS1E cells in the co-cultures conferred greater resistance to cell death induced by oxidative stress. Increasing the prevalence of INS1E cells also decreased the number of alphaTC1 cells experiencing oxidative stress in the monolayer culture. In 3D aggregates, culturing the alphaTC1 and INS1E cells in a ratio of 50:50 prevented oxidative stress in both cell types. Together, the results of this study lead to new insight into how modulating the composition and dimensionality of a co-culture can influence the oxidative stress levels experienced by the cells.

Neuroprotective substances: are they able to protect the pancreatic beta-cells too?

BACKGROUND

Growing evidences demonstrate a close relationship between type 2 diabetes (T2D) and neurodegenerative disorders such as Alzheimer's disease. The similarity of physiological and pathological processes, occurring in pancreatic β-cells and neurons over the course of these pathologies, allows to raise the question of the practicability of studying neuroprotective substances for their potential antidiabetic activity.

OBJECTIVE

This review analyzes studies of antidiabetic and cytoprotective action on pancreatic β-cells of the neuroprotective compounds that can attenuate the oxidative stress and enhance the expression of neurotrophins: low-molecular-weight NGF mimetic compound GK-2, selective anxiolytic afobazole, antidepressants lithium chloride and lithium carbonate on the rat streptozotocin model of T2D.

RESULTS

It was found that all above-listed neuroprotective substances have a pronounced antidiabetic activity. The decrease in the β-cells number, the average area of the pancreatic islets, as well as the violation of their morphological structure caused by the streptozotocin was significantly weakened by the therapy with the investigated neuroprotective substances. The extent of these morphological changes clearly correlates with the antihyperglycemic effect of these compounds.

CONCLUSION

The presented data indicate that the neuroprotective substances attenuating the damaging effect of oxidative stress and neurotrophins deficit cannot only protect neurons but also exert their cytoprotective effect towards pancreatic β-cells. These data may provide a theoretical basis for the further study of neuroprotective drugs as potential therapeutic options for T2D prevention and treatment.

Analysis of the transcriptome and metabolome of pancreatic spheroids derived from human induced pluripotent stem cells and matured in an organ-on-a-chip

The differentiation of pancreatic cells from hiPSC is one of the emerging strategies to achieve an in vitro pancreas model. Here, hiPSC-derived β-like-cells spheroids were cultured in microfluidic environment and characterized using omics analysis.

Leveraging the strengths of mice, human stem cells, and organoids to model pancreas development and diabetes

Diabetes is an epidemic with increasing incidence across the world. Most individuals who are afflicted by this disease have type 2 diabetes, but there are many who suffer from type 1, an autoimmune disorder. Both types of diabetes have complex genetic underpinnings that are further complicated by epigenetic and environmental factors. A less prevalent and often under diagnosed subset of diabetes cases are characterized by single genetic mutations and include Maturity Onset Diabetes of the Young (MODY) and Neonatal Diabetes Mellitus (NDM). While the mode of action and courses of treatment for all forms of diabetes are distinct, the diseases all eventually result in the dysfunction and/or death of the pancreatic β cell - the body's source of insulin. With loss of β cell function, blood glucose homeostasis is disrupted, and life-threatening complications arise. In this review, we focus on how model systems provide substantial insights into understanding β cell biology to inform our understanding of all forms of diabetes. The strengths and weaknesses of animal, hPSC derived β-like cell, and organoid models are considered along with discussion of GATA6, a critical transcription factor frequently implicated in pancreatic dysfunction with developmental origins; experimental studies of GATA6 have highlighted the advantages and disadvantages of how each of these model systems can be used to inform our understanding of β cell specification and function in health and disease.

Drivers of transcriptional variance in human intestinal epithelial organoids

Human intestinal epithelial organoids (enteroids and colonoids) are tissue cultures used for understanding the physiology of the human intestinal epithelium. Here, we explored the effect on the transcriptome of common variations in culture methods, including extracellular matrix substrate, format, tissue segment, differentiation status, and patient heterogeneity. RNA-sequencing datasets from 276 experiments performed on 37 human enteroid and colonoid lines from 29 patients were aggregated from several groups in the Texas Medical Center. DESeq2 and gene set enrichment analysis (GSEA) were used to identify differentially expressed genes and enriched pathways. PERMANOVA, Pearson's correlation, and dendrogram analysis of the data originally indicated three tiers of influence of culture methods on transcriptomic variation: substrate (collagen vs. Matrigel) and format (3-D, transwell, and monolayer) had the largest effect; segment of origin (duodenum, jejunum, ileum, colon) and differentiation status had a moderate effect; and patient heterogeneity and specific experimental manipulations (e.g., pathogen infection) had the smallest effect. GSEA identified hundreds of pathways that varied between culture methods, such as IL1 cytokine signaling enriched in transwell versus monolayer cultures and E2F target genes enriched in collagen versus Matrigel cultures. The transcriptional influence of the format was furthermore validated in a synchronized experiment performed with various format-substrate combinations. Surprisingly, large differences in organoid transcriptome were driven by variations in culture methods such as format, whereas experimental manipulations such as infection had modest effects. These results show that common variations in culture conditions can have large effects on intestinal organoids and should be accounted for when designing experiments and comparing results between laboratories. Our data constitute the largest RNA-seq dataset interrogating human intestinal epithelial organoids.

Engineering islets from stem cells for advanced therapies of diabetes

Diabetes mellitus is a metabolic disorder that affects more than 460 million people worldwide. Type 1 diabetes (T1D) is caused by autoimmune destruction of β-cells, whereas type 2 diabetes (T2D) is caused by a hostile metabolic environment that leads to β-cell exhaustion and dysfunction. Currently, first-line medications treat the symptomatic insulin resistance and hyperglycaemia, but do not prevent the progressive decline of β-cell mass and function. Thus, advanced therapies need to be developed that either protect or regenerate endogenous β-cell mass early in disease progression or replace lost β-cells with stem cell-derived β-like cells or engineered islet-like clusters. In this Review, we discuss the state of the art of stem cell differentiation and islet engineering, reflect on current and future challenges in the area and highlight the potential for cell replacement therapies, disease modelling and drug development using these cells. These efforts in stem cell and regenerative medicine will lay the foundations for future biomedical breakthroughs and potentially curative treatments for diabetes.

Disruption of O-Linked N-Acetylglucosamine Signaling in Placenta Induces Insulin Sensitivity in Female Offspring

Placental dysfunction can lead to fetal growth restriction which is associated with perinatal morbidity and mortality. Fetal growth restriction increases the risk of obesity and diabetes later in life. Placental O-GlcNAc transferase (OGT) has been identified as a marker and a mediator of placental insufficiency in the setting of prenatal stress, however, its role in the fetal programming of metabolism and glucose homeostasis remains unknown. We aim to determine the long-term metabolic outcomes of offspring with a reduction in placental OGT. Mice with a partial reduction and a full knockout of placenta-specific OGT were generated utilizing the Cre-Lox system. Glucose homeostasis and metabolic parameters were assessed on a normal chow and a high-fat diet in both male and female adult offspring. A reduction in placental OGT did not demonstrate differences in the metabolic parameters or glucose homeostasis compared to the controls on a standard chow. The high-fat diet provided a metabolic challenge that revealed a decrease in body weight gain (p = 0.02) and an improved insulin tolerance (p = 0.03) for offspring with a partially reduced placental OGT but not when OGT was fully knocked out. Changes in body weight were not associated with changes in energy homeostasis. Offspring with a partial reduction in placental OGT demonstrated increased hepatic Akt phosphorylation in response to insulin treatment (p = 0.02). A partial reduction in placental OGT was protective from weight gain and insulin intolerance when faced with the metabolic challenge of a high-fat diet. This appears to be, in part, due to increased hepatic insulin signaling. The findings of this study contribute to the greater understanding of fetal metabolic programming and the effect of placental OGT on peripheral insulin sensitivity and provides a target for future investigation and clinical applications.

Molecular mechanisms of transcription factor mediated cell reprogramming: conversion of liver to pancreas

Transdifferentiation is a type of cellular reprogramming involving the conversion of one differentiated cell type to another. This remarkable phenomenon holds enormous promise for the field of regenerative medicine. Over the last 20 years techniques used to reprogram cells to alternative identities have advanced dramatically. Cellular identity is determined by the transcriptional profile which comprises the subset of mRNAs, and therefore proteins, being expressed by a cell at a given point in time. A better understanding of the levers governing transcription factor activity benefits our ability to generate therapeutic cell types at will. One well-established example of transdifferentiation is the conversion of hepatocytes to pancreatic β-cells. This cell type conversion potentially represents a novel therapy in T1D treatment. The identification of key master regulator transcription factors (which distinguish one body part from another) during embryonic development has been central in developing transdifferentiation protocols. Pdx1 is one such example of a master regulator. Ectopic expression of vector-delivered transcription factors (particularly the triumvirate of Pdx1, Ngn3 and MafA) induces reprogramming through broad transcriptional remodelling. Increasingly, complimentary cell culture techniques, which recapitulate the developmental microenvironment, are employed to coax cells to adopt new identities by indirectly regulating transcription factor activity via intracellular signalling pathways. Both transcription factor-based reprogramming and directed differentiation approaches ultimately exploit transcription factors to influence cellular identity. Here, we explore the evolution of reprogramming and directed differentiation approaches within the context of hepatocyte to β-cell transdifferentiation focussing on how the introduction of new techniques has improved our ability to generate β-cells.

Culture, differentiation, and transduction of mouse E12.5 pancreatic spheres: an in vitro model for the secondary transition of pancreas development

During the secondary transition of rodent pancreatic development, mainly between E12.5 and E15.5 in mice, exocrine and endocrine populations differentiate from pancreatic progenitors. Here we describe an experimental system for its study in vitro. First, we show that spheres derived from dissociated E12.5 mouse pancreases differentiate within 7 days into most pancreatic exocrine and endocrine cell types, including beta cells. The proportion and spatial repartition of the different endocrine populations mirror those observed during normal development. Thus, dissociation and culture do not impair the developmental events affecting pancreatic progenitors during the secondary transition. Moreover, dissociated cells from mouse E12.5 pancreas were transduced with ecotropic MLV-based retroviral vectors or, though less efficiently, with a mixture of ALV(A)-based retroviral vectors and gesicles containing the TVA (Tumor Virus A) receptor. As an additional improvement, we also created a transgenic mouse line expressing TVA under the control of the 4.5 kB pdx1 promoter (pdx1-TVA). We demonstrate that pancreatic progenitors from dissociated pdx1-TVA pancreas can be specifically transduced by ALV(A)-based retroviral vectors. Using this model, we expressed an activated mutant of the YAP transcriptional co-activator in pancreatic progenitors. These experiments indicate that deregulated YAP activity reduces endocrine and exocrine differentiation in the resulting spheres, confirming and extending previously published data. Thus, our experimental model recapitulates in vitro the crucial developmental decisions arising at the secondary transition and provides a convenient tool to study their genetic control.

Hypoxia-inducible factors and diabetes

Hypoxia can be defined as a relative deficiency in the amount of oxygen reaching the tissues. Hypoxia-inducible factors (HIFs) are critical regulators of the mammalian response to hypoxia. In normal circumstances, HIF-1α protein turnover is rapid, and hyperglycemia further destabilizes the protein. In addition to their role in diabetes pathogenesis, HIFs are implicated in development of the microvascular and macrovascular complications of diabetes. Improving glucose control in people with diabetes increases HIF-1α protein and has wide-ranging benefits, some of which are at least partially mediated by HIF-1α. Nevertheless, most strategies to improve diabetes or its complications via regulation of HIF-1α have not currently proven to be clinically useful. The intersection of HIF biology with diabetes is a complex area in which many further questions remain, especially regarding the well-conducted studies clearly describing discrepant effects of different methods of increasing HIF-1α, even within the same tissues. This Review presents a brief overview of HIFs; discusses the range of evidence implicating HIFs in β cell dysfunction, diabetes pathogenesis, and diabetes complications; and examines the differing outcomes of HIF-targeting approaches in these conditions.

Response of Pluripotent Stem Cells to Environmental Stress and Its Application for Directed Differentiation

Simple Summary

Environmental changes in oxygen concentration, temperature, and mechanical stimulation lead to the activation of specific transcriptional factors and induce the expression of each downstream gene. In general, these responses are protective machinery against such environmental stresses, while these transcriptional factors also regulate cell proliferation, differentiation, and organ development in mammals. In the case of pluripotent stem cells, similar response mechanisms normally work and sometimes stimulate the differentiation cues. Up to now, differentiation protocols utilizing such environmental stresses have been reported to obtain various types of somatic cells from pluripotent stem cells. Basically, environmental stresses as hypoxia (low oxygen), hyperoxia, (high oxygen) and mechanical stress from cell culture plates are relatively safer than chemicals and gene transfers, which affect the genome irreversibly. Therefore, protocols designed with such environments in mind could be useful for the technology development of cell therapy and regenerative medicine. In this manuscript, we summarize recent findings of environmental stress-induced differentiation protocols and discuss their mechanisms.

Abstract

Pluripotent stem cells have unique characteristics compared to somatic cells. In this review, we summarize the response to environmental stresses (hypoxic, oxidative, thermal, and mechanical stresses) in embryonic stem cells (ESCs) and their applications in the differentiation methods directed to specific lineages. Those stresses lead to activation of each specific transcription factor followed by the induction of downstream genes, and one of them regulates lineage specification. In short, hypoxic stress promotes the differentiation of ESCs to mesodermal lineages via HIF-1α activation. Concerning mechanical stress, high stiffness tends to promote mesodermal differentiation, while low stiffness promotes ectodermal differentiation via the modulation of YAP1. Furthermore, each step in the same lineage differentiation favors each appropriate stiffness of culture plate; for example, definitive endoderm favors high stiffness, while pancreatic progenitor favors low stiffness during pancreatic differentiation of human ESCs. Overall, treatments utilizing those stresses have no genotoxic or carcinogenic effects except oxidative stress; therefore, the differentiated cells are safe and could be useful for cell replacement therapy. In particular, the effect of mechanical stress on differentiation is becoming attractive for the field of regenerative medicine. Therefore, the development of a stress-mediated differentiation protocol is an important matter for the future.

Unbiased approach for the identification of molecular mechanisms sensitive to chemical exposures

Targeted methods that dominated toxicological research until recently did not allow for screening of all molecular changes involved in toxic response. Therefore, it is difficult to infer if all major mechanisms of toxicity have already been discovered, or if some of them are still overlooked. We used data on 591,084 unique chemical-gene interactions to identify genes and molecular pathways most sensitive to chemical exposures. The list of identified pathways did not change significantly when analyses were done on different subsets of data with non-overlapping lists of chemical compounds indicative that our dataset is saturated enough to provide unbiased results. One of the most important findings of this study is that almost every known molecular mechanism may be affected by chemical exposures. Predictably, xenobiotic metabolism pathways, and mechanisms of cellular response to stress and damage were among the most sensitive. Additionally, we identified highly sensitive molecular pathways, which are not widely recognized as major targets of toxicants, including lipid metabolism pathways, longevity regulation cascade, and cytokine-mediated signaling. These mechanisms are relevant to significant public health problems, such as aging, cancer, metabolic and autoimmune disease. Thus, public health field will benefit from future focus of toxicological research on identified sensitive mechanisms.

Human Pluripotent Stem Cells to Model Islet Defects in Diabetes

Diabetes mellitus is characterized by elevated levels of blood glucose and is ultimately caused by insufficient insulin production from pancreatic beta cells. Different research models have been utilized to unravel the molecular mechanisms leading to the onset of diabetes. The generation of pancreatic endocrine cells from human pluripotent stem cells constitutes an approach to study genetic defects leading to impaired beta cell development and function. Here, we review the recent progress in generating and characterizing functional stem cell-derived beta cells. We summarize the diabetes disease modeling possibilities that stem cells offer and the challenges that lie ahead to further improve these models.

Non-xenogeneic expansion and definitive endoderm differentiation of human pluripotent stem cells in an automated bioreactor

Scalable processes are requisite for the robust biomanufacturing of human pluripotent stem cell (hPSC)-derived therapeutics. Toward this end, we demonstrate the xeno-free expansion and directed differentiation of human embryonic and induced pluripotent stem cells to definitive endoderm (DE) in a controlled stirred suspension bioreactor (SSB). Based on previous work on converting hPSCs to insulin-producing progeny, differentiation of two hPSC lines was optimized in planar cultures yielding up to 87% FOXA2⁺ /SOX17⁺ cells. Next, hPSCs were propagated in an SSB with controlled pH and dissolved oxygen. Cultures displayed a 10- to 12-fold increase in cell number over 5-6 days with the maintenance of pluripotency (>85% OCT4⁺ ) and viability (>85%). For differentiation, SSB cultures yielded up to 89% FOXA2⁺ /SOX17⁺ cells or ~ 8 DE cells per seeded hPSC. Specification to DE cell fate was consistently more efficient in the bioreactor compared to planar cultures. Hence, a tunable strategy is established that is suitable for the xeno-free manufacturing of DE cells from different hPSC lines in scalable SSBs. This study advances bioprocess development for producing a wide gamut of human DE cell-derived therapeutics.

Developmentally-Inspired Biomimetic Culture Models to Produce Functional Islet-Like Cells From Pluripotent Precursors

Insulin-producing beta cells sourced from pluripotent stem cells hold great potential as a virtually unlimited cell source to treat diabetes. Directed pancreatic differentiation protocols aim to mimic various stimuli present during embryonic development through sequential changes of in vitro culture conditions. This is commonly accomplished by the timed addition of soluble signaling factors, in conjunction with cell-handling steps such as the formation of 3D cell aggregates. Interestingly, when stem cells at the pancreatic progenitor stage are transplanted, they form functional insulin-producing cells, suggesting that in vivo microenvironmental cues promote beta cell specification. Among these cues, biophysical stimuli have only recently emerged in the context of optimizing pancreatic differentiation protocols. This review focuses on studies of cell–microenvironment interactions and their impact on differentiating pancreatic cells when considering cell signaling, cell–cell and cell–ECM interactions. We highlight the development of in vitro cell culture models that allow systematic studies of pancreatic cell mechanobiology in response to extracellular matrix proteins, biomechanical effects, soluble factor modulation of biomechanics, substrate stiffness, fluid flow and topography. Finally, we explore how these new mechanical insights could lead to novel pancreatic differentiation protocols that improve efficiency, maturity, and throughput.

Emerging routes to the generation of functional β-cells for diabetes mellitus cell therapy

Diabetes mellitus, which affects more than 463 million people globally, is caused by the autoimmune ablation or functional loss of insulin-producing β-cells, and prevalence is projected to continue rising over the next decades. Generating β-cells to mitigate the aberrant glucose homeostasis manifested in the disease has remained elusive. Substantial advances have been made in producing mature β-cells from human pluripotent stem cells that respond appropriately to dynamic changes in glucose concentrations in vitro and rapidly function in vivo following transplantation in mice. Other potential avenues to produce functional β-cells include: transdifferentiation of closely related cell types (for example, other pancreatic islet cells such as α-cells, or other cells derived from endoderm); the engineering of non-β-cells that are capable of modulating blood sugar; and the construction of synthetic 'cells' or particles mimicking functional aspects of β-cells. This Review focuses on the current status of generating β-cells via these diverse routes, highlighting the unique advantages and challenges of each approach. Given the remarkable progress in this field, scalable bioengineering processes are also discussed for the realization of the therapeutic potential of derived β-cells.

Transient FOXO1 inhibition in pancreatic endoderm promotes the generation of NGN3+ endocrine precursors from human iPSCs

In the multi-step differentiation protocol used to generate pancreatic endocrine cells from human pluripotent stem cells, the induction of NGN3+ endocrine precursors from the PDX1+/NKX6.1+ pancreatic endoderm is crucial for efficient endocrine cell production. Here, we demonstrate that transient, not prolonged FOXO1 inhibition results in enhanced NGN3+ endocrine precursors and hormone-producing cell production. FOXO1 inhibition does not directly induce NGN3 expression but stimulates PDX1+/NKX6.1+ cell proliferation. NOTCH activity, whose suppression is important for Ngn3 expression, is not suppressed but Wnt signaling is stimulated by FOXO1 inhibition. Reversely, Wnt inhibition suppresses the effects of FOXO1 inhibitor. These findings indicate that FOXO1 and Wnt are involved in regulating the proliferation of PDX1+/NKX6.1+ pancreatic endoderm that gives rise to NGN3+ endocrine precursors.

Molecular Mechanisms Linking Oxidative Stress and Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is the most prevalent metabolic disorder characterized by chronic hyperglycemia and an inadequate response to circulatory insulin by peripheral tissues resulting in insulin resistance. Insulin resistance has a complex pathophysiology, and it is contributed to by multiple factors including oxidative stress. Oxidative stress refers to an imbalance between free radical production and the antioxidant system leading to a reduction of peripheral insulin sensitivity and contributing to the development of T2DM via several molecular mechanisms. In this review, we present the molecular mechanisms by which the oxidative milieu contributes to the pathophysiology of insulin resistance and diabetes mellitus.

Mesenchymal stem cell-derived exosomes protect beta cells against hypoxia-induced apoptosis via miR-21 by alleviating ER stress and inhibiting p38 MAPK phosphorylation

Background

Hypoxia is a major cause of beta cell death and dysfunction after transplantation. The aim of this study was to investigate the effect of exosomes derived from mesenchymal stem cells (MSCs) on beta cells under hypoxic conditions and the potential underlying mechanisms.

Methods

Exosomes were isolated from the conditioned medium of human umbilical cord MSCs and identified by WB, NTA, and transmission electron microscopy. Beta cells (βTC-6) were cultured in serum-free medium in the presence or absence of exosomes under 2% oxygen conditions. Cell viability and apoptosis were analysed with a CCK-8 assay and a flow cytometry-based annexin V-FITC/PI apoptosis detection kit, respectively. Endoplasmic reticulum stress (ER stress) proteins and apoptosis-related proteins were detected by the WB method. MiRNAs contained in MSC exosomes were determined by Illumina HiSeq, and treatment with specific miRNA mimics or inhibitors of the most abundant miRNAs was used to reveal the underlying mechanism of exosomes.

Results

Exosomes derived from MSC-conditioned culture medium were 40–100 nm in diameter and expressed the exosome markers CD9, CD63, CD81, HSP70, and Flotillin 1, as well as the MSC markers CD73, CD90, and CD105. Hypoxia significantly induced beta cell apoptosis, while MSC exosomes remarkably improved beta cell survival. The WB results showed that ER stress-related proteins, including GRP78, GRP94, p-eIF2α and CHOP, and the apoptosis-related proteins cleaved caspase 3 and PARP, were upregulated under hypoxic conditions but were inhibited by MSC exosomes. Moreover, the p38 MAPK signalling pathway was activated by hypoxia and was inhibited by MSC exosomes. The Illumina HiSeq results show that MSC exosomes were rich in miR-21, let-7 g, miR-1246, miR-381, and miR-100. After transfection with miRNA mimics, the viability of beta cells under hypoxia was increased significantly by miR-21 mimic, and the p38 MAPK and ER stress-related proteins in beta cells were downregulated. These changes were reversed after exosomes were pretreated with miR-21 inhibitor.

Conclusions

Exosomes derived from MSCs could protect beta cells against apoptosis induced by hypoxia, largely by carrying miR-21, alleviating ER stress and inhibiting p38 MAPK signalling. This result indicated that MSC exosomes might improve encapsulated islet survival and benefit diabetes patients.

Combination treatment of autologous bone marrow stem cell transplantation and hyperbaric oxygen therapy for type 2 diabetes mellitus: A randomized controlled trial

The objective of this study was to compare standard treatment versus the combination of intrapancreatic autologous stem cell (ASC) infusion and hyperbaric oxygen treatment (HBOT) before and after ASC in the metabolic control of patients with type 2 diabetes mellitus (T2DM). This study was a prospective, randomized controlled trial. The combined intervention consisted of 10 sessions of HBOT before the intrapancreatic infusion of ASC and 10 sessions afterwards. ASCs were infused into the main arterial supply of the pancreas to maximize the presence of the stem cells where the therapeutic effect is most desired. A total of 23 patients were included (control group = 10, intervention group = 13). Age, gender, diabetes duration, number of medications taken, body weight and height, and insulin requirements were recorded at baseline and every three months. Also, body mass index, fasting plasma glucose, C-peptide, and HbA1c, C-peptide/glucose ratio (CPGR) were measured every three months for one year. HbA1c was significantly lower in the intervention group compared with control throughout follow-up. Overall, 77% of patients in the intervention group and 30% of patients in the control group demonstrated a decrease of HbA1c at 180 days (compared with baseline) of at least 1 unit. Glucose levels were significantly lower in the intervention group at all timepoints during follow-up. C-peptide levels were significantly higher in the intervention group during follow-up and at one year: 1.9 ± 1.0 ng/mL versus 0.7 ± 0.4 ng/mL in intervention versus control groups, respectively, p = 0.0021. CPGR was higher in the intervention group at all controls during follow-up. The requirement for insulin was significantly lower in the intervention group at 90, 180, 270, and 365 days. Combined therapy of intrapancreatic ASC infusion and HBOT showed increased metabolic control and reduced insulin requirements in patients with T2DM compared with standard treatment.

Stem Cells, Self-Renewal, and Lineage Commitment in the Endocrine System

The endocrine system coordinates a wide array of body functions mainly through secretion of hormones and their actions on target tissues. Over the last decades, a collective effort between developmental biologists, geneticists, and stem cell biologists has generated a wealth of knowledge related to the contribution of stem/progenitor cells to both organogenesis and self-renewal of endocrine organs. This review provides an up-to-date and comprehensive overview of the role of tissue stem cells in the development and self-renewal of endocrine organs. Pathways governing crucial steps in both development and stemness maintenance, and that are known to be frequently altered in a wide array of endocrine disorders, including cancer, are also described. Crucially, this plethora of information is being channeled into the development of potential new cell-based treatment modalities for endocrine-related illnesses, some of which have made it through clinical trials.

Relevance of Oxygen Concentration in Stem Cell Culture for Regenerative Medicine

The key hallmark of stem cells is their ability to self-renew while keeping a differentiation potential. Intrinsic and extrinsic cell factors may contribute to a decline in these stem cell properties, and this is of the most importance when culturing them. One of these factors is oxygen concentration, which has been closely linked to the maintenance of stemness. The widely used environmental 21% O₂ concentration represents a hyperoxic non-physiological condition, which can impair stem cell behaviour by many mechanisms. The goal of this review is to understand these mechanisms underlying the oxygen signalling pathways and their negatively-associated consequences. This may provide a rationale for culturing stem cells under physiological oxygen concentration for stem cell therapy success, in the field of tissue engineering and regenerative medicine.

Vegfa/vegfr2 signaling is necessary for zebrafish islet vessel development, but is dispensable for beta-cell and alpha-cell formation

The mechanisms underlying zebrafish pancreatic islet vascularization have not been well characterized. We sought to determine the angiogenic factors responsible for islet vascularization and assess whether an absence of endothelial cells affects beta-cell and alpha-cell formation. We used a double transgenic zebrafish Tg(fli1:EGFP; insa:tagRFP) to label endothelial cells and beta-cells, respectively. Beta-cells developed adjacent to endothelial cells and by 72 hours post fertilization (hpf) the zebrafish pancreatic islet was highly vascularized. Zebrafish beta-cells express vascular endothelial growth factors (vegf), vegfaa and vegfab. Double knockdown of vegfaa and vegfab or the primary Vegfa receptors (Vegfr2), kdr and kdrl, resulted in vessel deficient islets. While beta-cell and alpha-cell numbers remained unchanged in vessel deficient islets, insulina expression was downregulated relative to controls. Vegfaa/Vegfab-Vegfr2 signaling is necessary for proper islet vessel development, but not for the initial formation of beta-cells and alpha-cells.

A Novel Dipeptide NGF Mimetic GK-2 Selectively Activating the PI3K/AKT Signaling Pathway Promotes the Survival of Pancreatic β-Cells in a Rat Model of Diabetes

We investigated the cytoprotective effect of a novel low-molecular-weight NGF mimetic, GK-2 (hexamethylenediamide bis-N-monosuccinyl-L-glutamyl-L-lysine), on pancreatic β-cells. The neuroprotective effect of GK-2 had been previously shown to be associated with selective activation of the PI3K/Akt signaling pathway. In this study, rats with streptozotocin (STZ)-induced type 2 diabetes mellitus were used. Metformin was used as a reference drug. STZ was immunohistochemically demonstrated to reduce the number of β-cells and affect their morphological structure. Treatment of diabetic animals with GK-2 (at a dose of 0.5 mg/kg intraperitoneally or 5 mg/kg orally) or metformin (300 mg/kg orally) for 28 days reduced the damaging effect of STZ. The effect of GK-2 on manifestations of STZ-induced diabetes, such as hyperglycemia, weight loss, polyphagia, and polydipsia, was comparable to that of metformin, while the cytoprotective activity of GK-2 was slightly stronger than that of metformin. A strong positive correlation between morphometric parameters and the blood glucose level was revealed. The GK-2 cytoprotective effect on β-cells is supposed to manifest through the PI3K/Akt signaling pathway.

Fetal undernutrition, placental insufficiency, and pancreatic β-cell development programming in utero

The prevalence of obesity and type 2 (T2D) diabetes is a major health concern in the United States and around the world. T2D is a complex disease characterized by pancreatic β-cell failure in association with obesity and insulin resistance in peripheral tissues. Although several genes associated with T2D have been identified, it is speculated that genetic variants account for only <10% of the risk for this disease. A strong body of data from both human epidemiological and animal studies shows that fetal nutrient factors in utero confer significant susceptibility to T2D. Numerous studies done in animals have shown that suboptimal maternal environment or placental insufficiency causes intrauterine growth restriction (IUGR) in the fetus, a critical factor known to predispose offspring to obesity and T2D, in part by causing permanent consequences in total functional β-cell mass. This review will focus on the potential contribution of the placenta in fetal programming of obesity and TD and its likely impact on pancreatic β-cell development and growth.

Expression kinetics reveal the self-adaptive role of β cells during the progression of diabetes

OBJECTIVE

To determine the histopathological and molecular changes in β-cells at different time intervals following streptozotocin (STZ)-induced diabetes.

METHODS

STZ (65 mg/kg body weight) was given to overnight fasted rats that were sacrificed after 1, 3, and 10 days of injection. Changes in islet morphology and in the expression of various factors involved in β-cell proliferation, inflammation and apoptosis were analyzed.

RESULTS

Superoxide dismutase (Sod) expression was completely reduced and that of NF-kB and iNOS were significantly increased, along with lymphocytic infiltration in the islets within 24 h of STZ injection. In addition, the β-cell protective markers Bcl-2, IL-6, Ki67, Hif-1α, VEGF and insulin were also enhanced, indicating a compensatory response of the β-cells to the initial damaging effects. Lymphocytic infiltration decreased after 3 days of injection, accompanied by enhanced expression of both GLP-1R and GIP R. The unresponsiveness of the incretin ligands after STZ administration further suggested a compensatory approach by the incretin receptors independent of glucose regulation. After 10 days, lymphocytic infiltration and inflammatory markers again increased, along with a concomitant reduction in the expression of incretin receptors, and upregulation of the protective markers. Furthermore, the saturation peak of blood glucose indicated progressive diabetes.

CONCLUSIONS

The β-cells follow a biphasic pattern of expression of certain factors in order to achieve a balance between apoptosis, autophagy, neo-genesis, hypoxia and proliferation, and achieve homeostatic protection before the onset of diabetes. The drug interventions at an early stage, which are specific to these pathways, could be beneficial in preventing the progression of diabetes pathogenesis.

Enhanced oxygen permeability in membrane-bottomed concave microwells for the formation of pancreatic islet spheroids

Oxygen availability is a critical factor in regulating cell viability that ultimately contributes to the normal morphogenesis and functionality of human tissues. Among various cell culture platforms, construction of 3D multicellular spheroids based on microwell arrays has been extensively applied to reconstitute in vitro human tissue models due to its precise control of tissue culture conditions as well as simple fabrication processes. However, an adequate supply of oxygen into the spheroidal cellular aggregation still remains one of the main challenges to producing healthy in vitro spheroidal tissue models. Here, we present a novel design for controlling the oxygen distribution in concave microwell arrays. We show that oxygen permeability into the microwell is tightly regulated by varying the poly-dimethylsiloxane (PDMS) bottom thickness of the concave microwells. Moreover, we validate the enhanced performance of the engineered microwell arrays by culturing non-proliferated primary rat pancreatic islet spheroids on varying bottom thickness from 10 μm to 1050 μm. Morphological and functional analyses performed on the pancreatic islet spheroids grown for 14 days prove the long-term stability, enhanced viability, and increased hormone secretion under the sufficient oxygen delivery conditions. We expect our results could provide knowledge on oxygen distribution in 3-dimensional spheroidal cell structures and critical design concept for tissue engineering applications.

STATEMENT OF SIGNIFICANCE

In this study, we present a noble design to control the oxygen distribution in concave microwell arrays for the formation of highly functional pancreatic islet spheroids by engineering the bottom of the microwells. Our new platform significantly enhanced oxygen permeability that turned out to improve cell viability and spheroidal functionality compared to the conventional thick-bottomed 3-D culture system. Therefore, we believe that this could be a promising medical biotechnology platform to further develop high-throughput tissue screening system as well as in vivo-mimicking customised 3-D tissue culture systems.

Pancreatic HIF2α Stabilization Leads to Chronic Pancreatitis and Predisposes to Mucinous Cystic Neoplasm

BACKGROUND & AIMS

Tissue hypoxia controls cell differentiation in the embryonic pancreas, and promotes tumor growth in pancreatic cancer. The cellular response to hypoxia is controlled by the hypoxia-inducible factor (HIF) proteins, including HIF2α. Previous studies of HIF action in the pancreas have relied on loss-of-function mouse models, and the effects of HIF2α expression in the pancreas have remained undefined.

METHODS

We developed several transgenic mouse models based on the expression of an oxygen-stable form of HIF2α, or indirect stabilization of HIF proteins though deletion of von Hippel-Lindau, thus preventing HIF degradation. Furthermore, we crossed both sets of animals into mice expressing oncogenic KrasG12D in the pancreas.

RESULTS

We show that HIF2α is not expressed in the normal human pancreas, however, it is up-regulated in human chronic pancreatitis. Deletion of von Hippel-Lindau or stabilization of HIF2α in mouse pancreata led to the development of chronic pancreatitis. Importantly, pancreatic HIF1α stabilization did not disrupt the pancreatic parenchyma, indicating that the chronic pancreatitis phenotype is specific to HIF2α. In the presence of oncogenic Kras, HIF2α stabilization drove the formation of cysts resembling mucinous cystic neoplasm (MCN) in humans. Mechanistically, we show that the pancreatitis phenotype is linked to expression of multiple inflammatory cytokines and activation of the unfolded protein response. Conversely, MCN formation is linked to activation of Wnt signaling, a feature of human MCN.

CONCLUSIONS

We show that pancreatic HIF2α stabilization disrupts pancreatic homeostasis, leading to chronic pancreatitis, and, in the context of oncogenic Kras, MCN formation. These findings provide new mouse models of both chronic pancreatitis and MCN, as well as illustrate the importance of hypoxia signaling in the pancreas.

Oxidative Stress in Pancreatic Beta Cell Regeneration

Pancreatic β cell neogenesis and proliferation during the neonatal period are critical for the generation of sufficient pancreatic β cell mass/reserve and have a profound impact on long-term protection against type 2 diabetes (T2D). Oxidative stress plays an important role in β cell neogenesis, proliferation, and survival under both physiological and pathophysiological conditions. Pancreatic β cells are extremely susceptible to oxidative stress due to a high endogenous production of reactive oxygen species (ROS) and a low expression of antioxidative enzymes. In this review, we summarize studies describing the critical roles and the mechanisms of how oxidative stress impacts β cell neogenesis and proliferation. In addition, the effects of antioxidant supplements on reduction of oxidative stress and increase of β cell proliferation are discussed. Exploring the roles and the potential therapeutic effects of antioxidants in the process of β cell regeneration would provide novel perspectives to preserve and/or expand pancreatic β cell mass for the treatment of T2D.

Air-liquid interface enhances oxidative phosphorylation in intestinal epithelial cell line IPEC-J2

The intestinal porcine epithelial cell line IPEC-J2, cultured under the air-liquid interface (ALI) conditions, develops remarkable morphological characteristics close to intestinal epithelial cells in vivo. Improved oxygen availability has been hypothesised to be the leading cause of this morphological differentiation. We assessed oxygen availability in ALI cultures and examined the influence of this cell culture method on glycolysis and oxidative phosphorylation in IPEC-J2 using the submerged membrane culture (SMC) and ALI cultures. Furthermore, the role of HIF-1 as mediator of oxygen availability was analysed. Measurements of oxygen tension confirmed increased oxygen availability at the medium-cell interface and demonstrated reduced oxygen extraction at the basal compartment in ALI. Microarray analysis to determine changes in the genetic profile of IPEC-J2 in ALI identified 2751 modified transcripts. Further examinations of candidate genes revealed reduced levels of glycolytic enzymes hexokinase II and GAPDH, as well as lactate transporting monocarboxylate transporter 1 in ALI, whereas expression of the glucose transporter GLUT1 remained unchanged. Cytochrome c oxidase (COX) subunit 5B protein analysis was increased in ALI, although mRNA level remained at constant level. COX activity was assessed using photometric quantification and a three-fold increase was found in ALI. Quantification of glucose and lactate concentrations in cell culture medium revealed significantly reduced glucose levels and decreased lactate production in ALI. In order to evaluate energy metabolism, we measured cellular adenosine triphosphate (ATP) aggregation in homogenised cell suspensions showing similar levels. However, application of the uncoupling agent FCCP reduced ATP levels in ALI but not in SMC. In addition, HIF showed reduced mRNA levels in ALI. Furthermore, HIF-1α protein was reduced in the nuclear compartment of ALI when compared to SCM as confirmed by confocal microscopy. These results indicate a metabolic switch in IPEC-J2 cultured under ALI conditions enhancing oxidative phosphorylation and suppressing glycolysis. ALI-induced improvement of oxygen supply reduced nuclear HIF-1α, demonstrating a major change in the transcriptional response.

A synopsis of factors regulating beta cell development and beta cell mass

The insulin-secreting beta cells in the endocrine pancreas regulate blood glucose levels, and loss of functional beta cells leads to insulin deficiency, hyperglycemia (high blood glucose) and diabetes mellitus. Current treatment strategies for type-1 (autoimmune) diabetes are islet transplantation, which has significant risks and limitations, or normalization of blood glucose with insulin injections, which is clearly not ideal. The type-1 patients can lack insulin counter-regulatory mechanism; therefore, hypoglycemia is a potential risk. Hence, a cell-based therapy offers a better alternative for the treatment of diabetes. Past research was focused on attempting to generate replacement beta cells from stem cells; however, recently there has been an increasing interest in identifying mechanisms that will lead to the conversion of pre-existing differentiated endocrine cells into beta cells. The goal of this review is to provide an overview of several of the key factors that regulate new beta cell formation (neogenesis) and beta cell proliferation.

Xeno-Transplantation of macro-encapsulated islets and Pluripotent Stem Cell-Derived Pancreatic Progenitors without Immunosuppression

Islet transplantation effectively treats diabetes but relies on immune suppression and is practically limited by the number of cadaveric islets available. An alternative cellular source is insulin-producing cells derived from pluripotent cell sources. Three animal cohorts were used in the current study to evaluate whether an oxygen-providing macro-encapsulation device, 'βAIR', could function in conjunction with human embryonic stem cells (hESCs) and their derivatives. The first cohort received macro-encapsulated undifferentiated hESCs, a second cohort received hESCs differentiated to a pancreatic progenitor state with limited endocrine differentiation. A reference cohort received human islets. Macro-encapsulation devices were implanted subcutaneously and monitored for up to 4 months. Undifferentiated pluripotent stem cells did not form teratoma but underwent cell death following implantation. Human C-peptide (hC- peptide) was detectable in host serum one week after implantation for both other cohorts. hC-peptide levels decreasing over time but remained detectable up to the end of the study. Key factors associated with mature endocrine cells were observed in grafts recovered from cohorts containing islets and hESC-derivatives including C-peptide, insulin, glucagon and urocortin 3. We conclude that the 'βAIR' macroencapsulation device is compatible with both human islets and pluripotent derivatives, but has a limited capability of sustaining undifferentiated pluripotent cells.

Three-dimensional pancreas organogenesis models

A rediscovery of three-dimensional culture has led to the development of organ biogenesis, homeostasis and disease models applicable to human tissues. The so-called organoids that have recently flourished serve as valuable models bridging between cell lines or primary cells grown on the bottom of culture plates and experiments performed in vivo. Though not recapitulating all aspects of organ physiology, the miniature organs generated in a dish are useful models emerging for the pancreas, starting from embryonic progenitors, adult cells, tumour cells and stem cells. This review focusses on the currently available systems and their relevance to the study of the pancreas, of β-cells and of several pancreatic diseases including diabetes. We discuss the expected future developments for studying human pancreas development and function, for developing diabetes models and for producing therapeutic cells.

Aggregation of Engineered Human β-Cells Into Pseudoislets: Insulin Secretion and Gene Expression Profile in Normoxic and Hypoxic Milieu

Innovative treatments to cure type 1 diabetes are being actively researched. Among the different strategies, the replacement of β-cells has given promising results. Classically, islets from cadaveric donors are transplanted into diabetic patients, but recently phase I clinical trials that use stem cell-derived β-cells have been started. Such protocols require either an immunosuppressive treatment or the macroencapsulation of the β-cells. They involve cell aggregation and the exposure of the cells to hypoxia. Using an engineered human β-cell, we have addressed these two problems: a novel human β-cell line called EndoC-βH3 was cultured as single cells or aggregated clusters. EndoC-βH3 cells were also cultured at normal atmospheric oxygen tension (pO₂ = 21%) or hypoxia (pO₂ = 3%) in the presence or absence of modulators of the hypoxia-inducible factor 1α (HIF1α) pathway. Cell aggregation improved glucose-stimulated insulin secretion, demonstrating the benefit of cell-cell contacts. Low oxygen tension decreased β-cell viability and their sensitivity to glucose, but did not alter insulin production nor the insulin secretion capacity of the remaining cells. To investigate the role of HIF1α, we first used a HIF stabilizer at pO₂ = 21%. This led to a mild decrease in cell viability, impaired glucose sensitivity, and altered insulin secretion. Finally, we used a HIF inhibitor on EndoC-βH3 pseudoislets exposed to hypoxia. Such treatment considerably decreased cell viability. In conclusion, aggregation of the EndoC-βH3 cells seems to be important to improve their function. A fraction of the EndoC-βH3 cells are resistant to hypoxia, depending on the level of activity of HIF1α. Thus, these cells represent a good human cell model for future investigations on islet cell transplantation analysis.

Concise reviews: In vitro-produced pancreas organogenesis models in three dimensions: self-organization from few stem cells or progenitors

Three-dimensional models of organ biogenesis have recently flourished. They promote a balance between stem/progenitor cell expansion and differentiation without the constraints of flat tissue culture vessels, allowing for autonomous self-organization of cells. Such models allow the formation of miniature organs in a dish and are emerging for the pancreas, starting from embryonic progenitors and adult cells. This review focuses on the currently available systems and how these allow new types of questions to be addressed. We discuss the expected advancements including their potential to study human pancreas development and function as well as to develop diabetes models and therapeutic cells.

Endothelium-derived essential signals involved in pancreas organogenesis

Endothelial cells (ECs) are essential for pancreas differentiation, endocrine specification, and endocrine function. They are also involved in the physiopathology of type 1 and type 2 diabetes. During embryogenesis, aortic ECs provide specific factors that maintain the expression of key genes for pancreas development such as pancreatic and duodenal homeobox-1. Other unknown factors are also important for pancreatic endocrine specification and formation of insulin-producing beta cells. Endocrine precursors proliferate interspersed with ductal cells and exocrine precursors and, at some point of development, these endocrine precursors migrate to pancreatic mesenchyme and start forming the islets of Langerhans. By the end of the gestation and close to birth, these islets contain immature beta cells with the capacity to express vascular endothelial growth factor and therefore to recruit ECs from the surrounding microenvironment. ECs in turn produce factors that are essential to maintain insulin secretion in pancreatic beta cells. Once assembled, a cross talk between endocrine cells and ECs maintain the integrity of islets toward an adequate function during the whole life of the adult individual. This review will focus in the EC role in the differentiation and maturation of pancreatic beta cells during embryogenesis as well as the current knowledge about the involvement of endothelium to derive pancreatic beta cells in vitro from mouse or human pluripotent stem cells.

Fetal Erythroblastosis May Be an Indicator of Neonatal Transient Hyperinsulinism

BACKGROUND

Small for gestational age and birth asphyxia are associated with neonatal transient hyperinsulinism (THI). Some newborns with THI showed marked erythroblastosis on admission to our neonatal intensive care unit.

OBJECTIVE

This study was designed to test our hypothesis that fetal erythroblastosis may be a risk factor for developing THI.

METHODS

The records of all babies admitted to our neonatal intensive care unit within 24 h of birth between January 2010 and May 2014, and who were born after 34 weeks of gestation, were retrospectively reviewed. Hyperinsulinism was diagnosed as hypoglycemia concomitant with high serum insulin in babies requiring >6 mg/kg/min intravenous glucose and THI as hyperinsulinism without maternal diabetes or genetic disorders. The following three possible risk factors for THI were evaluated: (1) birth weight z-score, (2) 1-min Apgar score and (3) absolute nucleated red blood cell (aNRBC) count on admission.

RESULTS

Of 705 infants, 8 were diagnosed with THI. Multivariate logistic regression analysis revealed that the aNRBC count was the most significant risk factor for THI. The median aNRBC count was 181/µl (interquartile range 0-538/µl), and 8 of 71 infants (11.3%) having an aNRBC count >1,413/µl (90th percentile in this study) had THI. The aNRBC counts in the 8 cases with THI were significantly higher than those in the 5 cases with hyperinsulinism caused by maternal diabetes or genetic disorders.

CONCLUSIONS

This study showed that the aNRBC count was strongly associated with subsequent THI. Fetal erythroblastosis, characterized by chronic fetal hypoxia, may be an indicator of perinatal stress sufficient to cause THI.

von Hippel-Lindau gene disruption in mouse pancreatic progenitors and its consequences on endocrine differentiation in vivo: importance of HIF1-α and VEGF-A upregulation

AIM/HYPOTHESIS

Different studies have linked hypoxia to embryonic development. Specifically, when embryonic pancreases are cultured ex vivo under hypoxic conditions (3% O2), beta cell development is impaired. Different cellular signalling pathways are involved in adaptation to hypoxia, including the ubiquitous hypoxia-inducible-factor 1-α (HIF1-α) pathway. We aimed to analyse the effects of HIF1-α stabilisation on fetal pancreas development in vivo.

METHODS

We deleted the Vhl gene, which encodes von Hippel-Lindau protein (pVHL), a factor necessary for HIF1-α degradation, by crossing Vhl-floxed mice with Sox9-Cre mice.

RESULTS

HIF1-α was stabilised in pancreatic progenitor cells in which the HIF pathway was induced. The number of neurogenin-3 (NGN3)-expressing cells was reduced and consequently endocrine development was altered in Vhl knockout pancreases. HIF1-α stabilisation induced Vegfa upregulation, leading to increased vascularisation. To investigate the impact of increased vascularisation on NGN3 expression, we used a bioassay in which Vhl mutant pancreases were cultured with or without vascular endothelial growth factor (VEGF) receptor 2 (VEGF-R2) inhibitors (e.g. Ki8751). Ex vivo analysis showed that Vhl knockout pancreases developed fewer NGN3-positive cells compared with controls. Interestingly, this effect was blocked when vascularisation was inhibited in the presence of VEGF-R2 inhibitors.

CONCLUSIONS/INTERPRETATION

Our data demonstrate that HIF1-α negatively controls beta cell differentiation in vivo by regulating NGN3 expression, and that this effect is mediated by signals from blood vessels.