Concise review: in search of unlimited sources of functional human pancreatic beta cells

Terpenoids and steroids from the whole plants of Euphorbia wallichii and their protective effects on STZ-induced damage in INS-1 cells

The research on the whole plant of Euphorbia wallichii led to the identification of two undescribed compounds, (1R,4S,5S,10S)-10-hydroxyacorenone B and (5R,9R,18S,20S,25R,26S,27S,28R)-D:C-friedolupane-3-oxo-7-ene, together with 32 known compounds. Their chemical structures were determined through detailed spectroscopic data analyses and electronic circular dichroism measurements. The terpenoids and steroids found in Euphorbia wallichii have been identified to exhibit a diverse array of biological activities. However, their underlying antidiabetic effects have not yet been examined. In this study, the effects of terpenoid and steroid compounds on promoting the proliferation of INS-1 cells and protecting STZ-induced pancreatic β-cell damage were evaluated. Bioassays have demonstrated that compounds 32 and 33 exhibited a noteworthy protective effect on INS-1 cells against STZ-induced injury, as well as promoted the proliferation of INS-1 cells. As a whole, compounds 32 and 33 might be potentially beneficial for the treatment of diabetes.

Glucose controls co-translation of structurally related mRNAs via the mTOR and eIF2 pathways in human pancreatic beta cells

Pancreatic beta cell response to glucose is critical for the maintenance of normoglycemia. A strong transcriptional response was classically described in rodent models but, interestingly, not in human cells. In this study, we exposed human pancreatic beta cells to an increased concentration of glucose and analysed at a global level the mRNAs steady state levels and their translationalability. Polysome profiling analysis showed an early acute increase in protein synthesis and a specific translation regulation of more than 400 mRNAs, independently of their transcriptional regulation. We clustered the co-regulated mRNAs according to their behaviour in translation in response to glucose and discovered common structural and sequence mRNA features. Among them mTOR- and eIF2-sensitive elements have a predominant role to increase mostly the translation of mRNAs encoding for proteins of the translational machinery. Furthermore, we show that mTOR and eIF2α pathways are independently regulated in response to glucose, participating to a translational reshaping to adapt beta cell metabolism. The early acute increase in the translation machinery components prepare the beta cell for further protein demand due to glucose-mediated metabolism changes.

The efficiency of insulin production and its content in insulin-expressing model β-cells correlate with their Zn2+ levels

Insulin is produced and stored inside the pancreatic β-cell secretory granules, where it is assumed to form Zn2+-stabilized oligomers. However, the actual storage forms of this hormone and the impact of zinc ions on insulin production in vivo are not known. Our initial X-ray fluorescence experiment on granules from native Langerhans islets and insulinoma-derived INS-1E cells revealed a considerable difference in the zinc content. This led our further investigation to evaluate the impact of the intra-granular Zn2+ levels on the production and storage of insulin in different model β-cells. Here, we systematically compared zinc and insulin contents in the permanent INS-1E and BRIN-BD11 β-cells and in the native rat pancreatic islets by flow cytometry, confocal microscopy, immunoblotting, specific messenger RNA (mRNA) and total insulin analysis. These studies revealed an impaired insulin production in the permanent β-cell lines with the diminished intracellular zinc content. The drop in insulin and Zn2+ levels was paralleled by a lower expression of ZnT8 zinc transporter mRNA and hampered proinsulin processing/folding in both permanent cell lines. To summarize, we showed that the disruption of zinc homeostasis in the model β-cells correlated with their impaired insulin and ZnT8 production. This indicates a need for in-depth fundamental research about the role of zinc in insulin production and storage.

Lipid Droplet Accumulation in Human Pancreatic Islets Is Dependent On Both Donor Age and Health

Human but not mouse islets transplanted into immunodeficient NSG mice effectively accumulate lipid droplets (LDs). Because chronic lipid exposure is associated with islet β-cell dysfunction, we investigated LD accumulation in the intact human and mouse pancreas over a range of ages and states of diabetes. Very few LDs were found in normal human juvenile pancreatic acinar and islet cells, with numbers subsequently increasing throughout adulthood. While accumulation appeared evenly distributed in postjuvenile acinar and islet cells in donors without diabetes, LDs were enriched in islet α- and β-cells from donors with type 2 diabetes (T2D). LDs were also found in the islet β-like cells produced from human embryonic cell-derived β-cell clusters. In contrast, LD accumulation was nearly undetectable in the adult rodent pancreas, even in hyperglycemic and hyperlipidemic models or 1.5-year-old mice. Taken together, there appear to be significant differences in pancreas islet cell lipid handling between species, and the human juvenile and adult cell populations. Moreover, our results suggest that LD enrichment could be impactful to T2D islet cell function.

The supply chain of human pancreatic β cell lines

Patients with type 1 or type 2 diabetes have an insufficiency in their functional β cell mass. To advance diabetes treatment and to work toward a cure, a better understanding of how to protect the pancreatic β cells against autoimmune or metabolic assaults (e.g., obesity, gestation) will be required. Over the past decades, β cell protection has been extensively investigated in rodents both in vivo and in vitro using isolated islets or rodent β cell lines. Transferring these rodent data to humans has long been challenging, at least partly for technical reasons: primary human islet preparations were scarce and functional human β cell lines were lacking. In 2011, we described a robust protocol of targeted oncogenesis in human fetal pancreas and produced the first functional human β cell line, and in subsequent years additional lines with specific traits. These cell lines are currently used by more than 150 academic and industrial laboratories worldwide. In this Review, we first explain how we developed the human β cell lines and why we think we succeeded where others, despite major efforts, did not. Next, we discuss the use of such functional human β cell lines and share some perspectives on their use to advance diabetes research.

MondoA Is an Essential Glucose-Responsive Transcription Factor in Human Pancreatic β-Cells

Although the mechanisms by which glucose regulates insulin secretion from pancreatic β-cells are now well described, the way glucose modulates gene expression in such cells needs more understanding. Here, we demonstrate that MondoA, but not its paralog carbohydrate-responsive element-binding protein, is the predominant glucose-responsive transcription factor in human pancreatic β-EndoC-βH1 cells and in human islets. In high-glucose conditions, MondoA shuttles to the nucleus where it is required for the induction of the glucose-responsive genes arrestin domain-containing protein 4 (ARRDC4) and thioredoxin interacting protein (TXNIP), the latter being a protein strongly linked to β-cell dysfunction and diabetes. Importantly, increasing cAMP signaling in human β-cells, using forskolin or the glucagon-like peptide 1 mimetic Exendin-4, inhibits the shuttling of MondoA and potently inhibits TXNIP and ARRDC4 expression. Furthermore, we demonstrate that silencing MondoA expression improves glucose uptake in EndoC-βH1 cells. These results highlight MondoA as a novel target in β-cells that coordinates transcriptional response to elevated glucose levels.

Reconstructing human pancreatic differentiation by mapping specific cell populations during development

Information remains scarce on human development compared to animal models. Here, we reconstructed human fetal pancreatic differentiation using cell surface markers. We demonstrate that at 7weeks of development, the glycoprotein 2 (GP2) marks a multipotent cell population that will differentiate into the acinar, ductal or endocrine lineages. Development towards the acinar lineage is paralleled by an increase in GP2 expression. Conversely, a subset of the GP2⁺ population undergoes endocrine differentiation by down-regulating GP2 and CD142 and turning on NEUROG3, a marker of endocrine differentiation. Endocrine maturation progresses by up-regulating SUSD2 and lowering ECAD levels. Finally, in vitro differentiation of pancreatic endocrine cells derived from human pluripotent stem cells mimics key in vivo events. Our work paves the way to extend our understanding of the origin of mature human pancreatic cell types and how such lineage decisions are regulated.

DOI:http://dx.doi.org/10.7554/eLife.27564.001

Dynamics of Insulin Secretion from EndoC-βH1 β-Cell Pseudoislets in Response to Glucose and Other Nutrient and Nonnutrient Secretagogues

The dynamics of insulin secretion were characterized in response to a variety of physiological and pharmacological stimulators and other compounds in perifused pseudoislets generated from cells of the EndoC-βH1 β-cell line. Perifusion of EndoC-βH1 pseudoislets with the physiological stimulus glucose (16.7 mM) induced sustained insulin secretion, which was inhibited by mannoheptulose. The adenylate cyclase activators IBMX and forskolin strongly potentiated this secretion. Glibenclamide, a Kir 6.2 potassium channel blocker, and Bay K 8644, an opener of the voltage-sensitive Ca²⁺ channel, also potentiated glucose-induced insulin secretion. The dynamics of insulin secretion from EndoC-βH1 pseudoislets were characterized by an insulin secretory response to glucose starting within 1-2 min and passing over without interruption into a sustained phase of insulin release for the whole stimulation period. This lack of a transient decline between the first and the second phases of insulin release is an indication for a quick supply of insulin secretory granules from the reserve pool to the docking sites below the plasma membrane. Thereby, new secretory granules are directly made available for sustained exocytosis of insulin in EndoC-βH1 β-cells. The study shows that EndoC-βH1 β-cell pseudoislets are well suited for kinetic analyses of insulin secretion.

Mass production of functional human pancreatic β-cells: why and how?

Diabetes (either type 1 or type 2) is due to insufficient functional β-cell mass. Research has, therefore, aimed to discover new ways to maintain or increase either β-cell mass or function. For this purpose, rodents have mainly been used as model systems and a large number of discoveries have been made. Meanwhile, although we have learned that rodent models represent powerful systems to model β-cell development, function and destruction, we realize that there are limitations when attempting to transfer the data to what is occurring in humans. Indeed, while human β-cells share many similarities with rodent β-cells, they also differ on a number of important parameters. In this context, developing ways to study human β-cell development, function and death represents an important challenge. This review will describe recent data on the development and use of convenient sources of human β-cells that should be useful tools to discover new ways to modulate functional β-cell mass in humans.

Extracellular acidification stimulates GPR68 mediated IL-8 production in human pancreatic β cells

Acute or chronic metabolic complications such as diabetic ketoacidosis are often associated with extracellular acidification and pancreatic β-cell dysfunction. However, the mechanisms by which human β-cells sense and respond to acidic pH remain elusive. In this study, using the recently developed human β-cell line EndoC-βH2, we demonstrate that β-cells respond to extracellular acidification through GPR68, which is the predominant proton sensing receptor of human β-cells. Using gain- and loss-of-function studies, we provide evidence that the β-cell enriched transcription factor RFX6 is a major regulator of GPR68. Further, we show that acidic pH stimulates the production and secretion of the chemokine IL-8 by β-cells through NF-кB activation. Blocking of GPR68 or NF-кB activity severely attenuated acidification induced IL-8 production. Thus, we provide mechanistic insights into GPR68 mediated β-cell response to acidic microenvironment, which could be a new target to protect β-cell against acidosis induced inflammation.

Cystine accumulation attenuates insulin release from the pancreatic β-cell due to elevated oxidative stress and decreased ATP levels

The pancreatic β-cell has reduced antioxidant defences making it more susceptible to oxidative stress. In cystinosis, a lysosomal storage disorder, an altered redox state may contribute to cellular dysfunction. This rare disease is caused by an abnormal lysosomal cystine transporter, cystinosin, which causes excessive accumulation of cystine in the lysosome. Cystinosis associated kidney damage and dysfunction leads to the Fanconi syndrome and ultimately end-stage renal disease. Following kidney transplant, cystine accumulation in other organs including the pancreas leads to multi-organ dysfunction. In this study, a Ctns gene knockdown model of cystinosis was developed in the BRIN-BD11 rat clonal pancreatic β-cell line using Ctns-targeting siRNA. Additionally there was reduced cystinosin expression, while cell cystine levels were similarly elevated to the cystinotic state. Decreased levels of chronic (24 h) and acute (20 min) nutrient-stimulated insulin secretion were observed. This decrease may be due to depressed ATP generation particularly from glycolysis. Increased ATP production and the ATP/ADP ratio are essential for insulin secretion. Oxidised glutathione levels were augmented, resulting in a lower [glutathione/oxidised glutathione] redox potential. Additionally, the mitochondrial membrane potential was reduced, apoptosis levels were elevated, as were markers of oxidative stress, including reactive oxygen species, superoxide and hydrogen peroxide. Furthermore, the basal and activated phosphorylated forms of the redox-sensitive transcription factor NF-κB were increased in cells with silenced Ctns. From this study, the cystinotic-like pancreatic β-cell model demonstrated that the altered oxidative status of the cell, resulted in depressed mitochondrial function and pathways of ATP production, causing reduced nutrient-stimulated insulin secretion.

Genes affecting β-cell function in type 1 diabetes

Type 1 diabetes (T1D) is a multifactorial disease resulting from an immune-mediated destruction of the insulin-producing pancreatic β cells. Several environmental and genetic risk factors predispose to the disease. Genome-wide association studies (GWAS) have identified around 50 genetic regions that affect the risk of developing T1D, but the disease-causing variants and genes are still largely unknown. In this review, we discuss the current status of T1D susceptibility loci and candidate genes with focus on the β cell. At least 40 % of the genes in the T1D susceptibility loci are expressed in human islets and β cells, where they according to recent studies modulate the β-cell response to the immune system. As most of the risk variants map to noncoding regions of the genome, i.e., promoters, enhancers, intergenic regions, and noncoding genes, their possible involvement in T1D pathogenesis as gene regulators will also be addressed.

A human beta cell line with drug inducible excision of immortalizing transgenes

Objectives

Access to immortalized human pancreatic beta cell lines that are phenotypically close to genuine adult beta cells, represent a major tool to better understand human beta cell physiology and develop new therapeutics for Diabetes. Here we derived a new conditionally immortalized human beta cell line, EndoC-βH3 in which immortalizing transgene can be efficiently removed by simple addition of tamoxifen.

Methods

We used lentiviral mediated gene transfer to stably integrate a tamoxifen inducible form of CRE (CRE-ERT2) into the recently developed conditionally immortalized EndoC βH2 line. The resulting EndoC-βH3 line was characterized before and after tamoxifen treatment for cell proliferation, insulin content and insulin secretion.

Results

We showed that EndoC-βH3 expressing CRE-ERT2 can be massively amplified in culture. We established an optimized tamoxifen treatment to efficiently excise the immortalizing transgenes resulting in proliferation arrest. In addition, insulin expression raised by 12 fold and insulin content increased by 23 fold reaching 2 μg of insulin per million cells. Such massive increase was accompanied by enhanced insulin secretion upon glucose stimulation. We further observed that tamoxifen treated cells maintained a stable function for 5 weeks in culture.

Conclusions

EndoC βH3 cell line represents a powerful tool that allows, using a simple and efficient procedure, the massive production of functional non-proliferative human beta cells. Such cells are close to genuine human beta cells and maintain a stable phenotype for 5 weeks in culture.

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EndoC-βH3: a conditionally immortalized human pancreatic beta cell line.

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Proliferation arrest upon removal of immortalizing transgenes with Tamoxifen.

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Enhancement of beta cell function upon removal of immortalizing transgenes.

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Tamoxifen-treated EndoC-βH3 maintain a stable phenotype for 5 weeks in culture.

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EndoC-βH3: a unique tool for large-scale drug discovery and proliferation studies.

Co-Culture of α TC-6 Cells and β TC-1 Cells: Morphology and Function

BACKGROUND

In vitro experiments using only β-cell lines instead of islets are limited because pancreatic islets are composed of four different types of endocrine cells. Several recent studies have focused on cellular interactions among these cell types, especially α- and β-cells. Because islet isolation needs time and experience, we tested a simple co-culture system with α- and β-cells. Their morphology and function were assessed by comparison to each single cell culture and pancreatic islets.

METHODS

α TC-6 cells and β TC-1 cells were maintained in Dulbecco's Minimal Essential Medium containing 5 mM glucose and 10% fetal bovine serum. Cells were mixed at a 1:1 ratio (5×10⁵) in 6-well plates and cultured for 24, 48, and 72 hours. After culture, cells were used for insulin and glucagon immunoassays and tested for glucose-stimulated insulin secretion (GSIS).

RESULTS

α TC-6 and β TC-1 cells became condensed by 24 hours and were more strongly compacted after 48 hours. β TC-1 cells showed both β-β and β-α cell contacts. GSIS increased with increasing glucose concentration in co-cultured cells, which showed lower secreted insulin levels than β TC-1 cells alone. The increase in the secreted insulin/insulin content ratio was significantly lower for co-cultured cells than for β-cells alone (P=0.04). Compared to islets, the α-/β-cell co-culture showed a higher ratio of GSIS to insulin content, but the difference was not statistically significant (P=0.09).

CONCLUSION

α TC-6 and β TC-1 cells in the co-culture system showed cell-to-cell contacts and a similar stimulated insulin secretion pattern to islets. The co-culture system may be used to better mimic pancreatic islets in in vitro assessments.

Characterization of stimulus-secretion coupling in the human pancreatic EndoC-βH1 beta cell line

Aims/Hypothesis

Studies on beta cell metabolism are often conducted in rodent beta cell lines due to the lack of stable human beta cell lines. Recently, a human cell line, EndoC-βH1, was generated. Here we investigate stimulus-secretion coupling in this cell line, and compare it with that in the rat beta cell line, INS-1 832/13, and human islets.

Methods

Cells were exposed to glucose and pyruvate. Insulin secretion and content (radioimmunoassay), gene expression (Gene Chip array), metabolite levels (GC/MS), respiration (Seahorse XF24 Extracellular Flux Analyzer), glucose utilization (radiometric), lactate release (enzymatic colorimetric), ATP levels (enzymatic bioluminescence) and plasma membrane potential and cytoplasmic Ca²⁺ responses (microfluorometry) were measured. Metabolite levels, respiration and insulin secretion were examined in human islets.

Results

Glucose increased insulin release, glucose utilization, raised ATP production and respiratory rates in both lines, and pyruvate increased insulin secretion and respiration. EndoC-βH1 cells exhibited higher insulin secretion, while plasma membrane depolarization was attenuated, and neither glucose nor pyruvate induced oscillations in intracellular calcium concentration or plasma membrane potential. Metabolite profiling revealed that glycolytic and TCA-cycle intermediate levels increased in response to glucose in both cell lines, but responses were weaker in EndoC-βH1 cells, similar to those observed in human islets. Respiration in EndoC-βH1 cells was more similar to that in human islets than in INS-1 832/13 cells.

Conclusions/Interpretation

Functions associated with early stimulus-secretion coupling, with the exception of plasma membrane potential and Ca²⁺ oscillations, were similar in the two cell lines; insulin secretion, respiration and metabolite responses were similar in EndoC-βH1 cells and human islets. While both cell lines are suitable in vitro models, with the caveat of replicating key findings in isolated islets, EndoC-βH1 cells have the advantage of carrying the human genome, allowing studies of human genetic variants, epigenetics and regulatory RNA molecules.

In search of a surrogate: engineering human beta cell lines for therapy

Replacement of insulin-producing cells is a promising therapy for the restoration of the beta cell mass that is destroyed in patients with type 1 diabetes (T1D). However, the use of large amounts of islets per transplant, coupled with the scarcity of donor tissue, diminishes its feasibility. Here we briefly discuss current progress in developing ideal functional beta cells as well as the rationale for developing renewable sources of insulin-producing cells that can be transplanted.

Development of a conditionally immortalized human pancreatic β cell line

Diabetic patients exhibit a reduction in β cells, which secrete insulin to help regulate glucose homeostasis; however, little is known about the factors that regulate proliferation of these cells in human pancreas. Access to primary human β cells is limited and a challenge for both functional studies and drug discovery progress. We previously reported the generation of a human β cell line (EndoC-βH1) that was generated from human fetal pancreas by targeted oncogenesis followed by in vivo cell differentiation in mice. EndoC-βH1 cells display many functional properties of adult β cells, including expression of β cell markers and insulin secretion following glucose stimulation; however, unlike primary β cells, EndoC-βH1 cells continuously proliferate. Here, we devised a strategy to generate conditionally immortalized human β cell lines based on Cre-mediated excision of the immortalizing transgenes. The resulting cell line (EndoC-βH2) could be massively amplified in vitro. After expansion, transgenes were efficiently excised upon Cre expression, leading to an arrest of cell proliferation and pronounced enhancement of β cell-specific features such as insulin expression, content, and secretion. Our data indicate that excised EndoC-βH2 cells are highly representative of human β cells and should be a valuable tool for further analysis of human β cells.

A synergistic therapeutic scheme for hyperglycemia and nephrotic disorders in diabetes

We previously demonstrated that the utilization of an electrospun scaffold could boost functional outputs of transplanted islets. In this study, we aim to develop a drug-eluting scaffold with a payload of pioglitazone to simultaneously rein in hyperglycemia and recoup lost renal functions in diabetic mice that underwent islet transplantation. The in vivo proliferation of islets was measured by a non-invasive bio-imaging technology whereas the blood insulin, blood glucose and renal proteins were assayed. The local stimulation of transplanted islets by pioglitazone saw an accelerated in vivo proliferation without apoptosis caused by the drug-eluting scaffold. In addition, pioglitazone contributed to an increased secretion of insulin and C-peptide 2, giving rise to an accelerated rein-in of hyperglycemia and enhanced tolerance of sudden oral glucose challenge. Moreover, the accelerated decrease of blood creatinine, urine creatinine and blood urea nitrogen suggested that pioglitazone contributed to the recovery of renal functions compromised by diabetes. Our bioengineering strategy effectively ameliorated hyperglycemia and associated nephrotic disorders, and shed a new light on an engineering approach to combat diabetes.

Mouse muscle as an ectopic permissive site for human pancreatic development

While sporadic human genetic studies have permitted some comparisons between rodent and human pancreatic development, the lack of a robust experimental system has not permitted detailed examination of human pancreatic development. We previously developed a xenograft model of immature human fetal pancreas grafted under the kidney capsule of immune-incompetent mice, which allowed the development of human pancreatic β-cells. Here, we compared the development of human and murine fetal pancreatic grafts either under skeletal muscle epimysium or under the renal capsule. We demonstrated that human pancreatic β-cell development occurs more slowly (weeks) than murine pancreas (days) both by differentiation of pancreatic progenitors and by proliferation of developing β-cells. The superficial location of the skeletal muscle graft and its easier access permitted in vivo lentivirus-mediated gene transfer with a green fluorescent protein-labeled construct under control of the insulin or elastase gene promoter, which targeted β-cells and nonendocrine cells, respectively. This model of engraftment under the skeletal muscle epimysium is a new approach for longitudinal studies, which allows localized manipulation to determine the regulation of human pancreatic development.