Role of the AMP kinase in cytokine-induced human EndoC-βH1 cell death

GDF15 Protects Insulin-Producing Beta Cells against Pro-Inflammatory Cytokines and Metabolic Stress via Increased Deamination of Intracellular Adenosine

It has been proposed that antidiabetic drugs, such as metformin and imatinib, at least in part, promote improved glucose tolerance in type 2 diabetic patients via increased production of the inflammatory cytokine GDF15. This is supported by studies, performed in rodent cell lines and mouse models, in which the addition or production of GDF15 improved beta-cell function and survival. The aim of the present study was to determine whether human beta cells produce GDF15 in response to antidiabetic drugs and, if so, to further elucidate the mechanisms by which GDF15 modulates the function and survival of such cells. The effects and expression of GDF15 were analyzed in human insulin-producing EndoC-betaH1 cells and human islets. We observed that alpha and beta cells exhibit considerable heterogeneity in GDF15 immuno-positivity. The predominant form of GDF15 present in islet and EndoC-betaH1 cells was pro-GDF15. Imatinib, but not metformin, increased pro-GDF15 levels in EndoC-betaH1 cells. Under basal conditions, exogenous GDF15 increased human islet oxygen consumption rates. In EndoC-betaH1 cells and human islets, exogenous GDF15 partially ameliorated cytokine- or palmitate + high-glucose-induced loss of function and viability. GDF15-induced cell survival was paralleled by increased inosine levels, suggesting a more efficient disposal of intracellular adenosine. Knockdown of adenosine deaminase, the enzyme that converts adenosine to inosine, resulted in lowered inosine levels and loss of protection against cytokine- or palmitate + high-glucose-induced cell death. It is concluded that imatinib-induced GDF15 production may protect human beta cells partially against inflammatory and metabolic stress. Furthermore, it is possible that the GDF15-mediated activation of adenosine deaminase and the increased disposal of intracellular adenosine participate in protection against beta-cell death.

The selective NOX4 inhibitor GLX7013159 decreases blood glucose concentrations and human beta-cell apoptotic rates in diabetic NMRI nu/nu mice transplanted with human islets

NADPH oxidase 4 (NOX4) inhibition has been reported to mitigate diabetes-induced beta-cell dysfunction and improve survival in vitro, as well as counteract high-fat diet-induced glucose intolerance in mice. We investigated the antidiabetic effects of the selective NOX4 inhibitor GLX7013159 in vivo in athymic diabetic mice transplanted with human islets over a period of 4 weeks. The GLX7013159-treated mice achieved lower blood glucose and water consumption throughout the treatment period. Furthermore, GLX7013159 treatment resulted in improved insulin and c-peptide levels, better insulin secretion capacity, as well as in greatly reduced apoptotic rates of the insulin-positive human cells, measured as colocalization of insulin and cleaved caspase-3. We conclude that the antidiabetic effects of NOX4 inhibition by GLX7013159 are observed also during a prolonged study period in vivo and are likely to be due to an improved survival and function of the human beta-cells.

Proinflammatory cytokines induce rapid, NO-independent apoptosis, expression of chemotactic mediators and interleukin-32 secretion in human pluripotent stem cell-derived beta cells

AIMS/HYPOTHESIS

The aim of this study was to examine the effects of proinflammatory cytokines on cells of different developmental stages during the generation of stem cell-derived beta cells (SC-beta cells) from human pluripotent stem cells (hPSCs). We wanted to find out to what extent human SC-beta cells are suitable as an experimental cellular model and, with regard to a possible therapeutic use, whether SC-beta cells have a comparable vulnerability to cytokines as bona fide beta cells.

METHODS

hPSCs were differentiated towards pancreatic organoids (SC-organoids) using a 3D production protocol. SC-beta cells and non-insulin-producing cells were separated by FACS and differential gene expression profiles of purified human SC-beta cells, progenitor stages and the human beta cell line EndoC-βH1, as a reference, were determined after 24 h incubation with the proinflammatory cytokines IL-1β, TNF-α and IFN-γ via a transcriptome microarray. Furthermore, we investigated apoptosis based on caspase cleavage, the generation of reactive oxygen species and activation of mitogen-activated protein-kinase (MAPK) stress-signalling pathways.

RESULTS

A 24 h exposure of SC-beta cells to proinflammatory cytokines resulted in significant activation of caspase 3/7 and apoptosis via the extrinsic and intrinsic apoptosis signalling pathways. At this time point, SC-beta cells showed a markedly higher sensitivity towards proinflammatory cytokines than non-insulin-producing cells and EndoC-βH1 cells. Furthermore, we were able to demonstrate the generation of reactive oxygen species and rule out the involvement of NO-mediated stress. A transient activation of stress-signalling pathways p38 mitogen-activated protein kinases (p38) and c-Jun N-terminal kinase (JNK) was already observed after 10 min of cytokine exposure. The transcriptome analysis revealed that the cellular response to proinflammatory cytokines increased with the degree of differentiation of the cells. Cytokines induced the expression of multiple inflammatory mediators including IL-32, CXCL9 and CXCL10 in SC-beta cells and in non-insulin-producing cells.

CONCLUSIONS/INTERPRETATION

Our results indicate that human SC-beta cells respond to proinflammatory cytokines very similarly to human islets. Due to the fast and fulminant cellular response of SC-beta cells, we conclude that SC-beta cells represent a suitable model for diabetes research. In light of the immaturity of SC-beta cells, they may be an attractive model for developmentally young beta cells as they are, for example, present in patients with early-onset type 1 diabetes. The secretion of chemotactic signals may promote communication between SC-beta cells and immune cells, and non-insulin-producing cells possibly participate in the overall immune response and are thus capable of amplifying the immune response and further stimulating inflammation. We demonstrated that cytokine-treated SC-organoids secrete IL-32, which is considered a promising candidate for type 1 diabetes onset. This underlines the need to ensure the survival of SC-beta cells in an autoimmune environment such as that found in type 1 diabetes.

Are off-target effects of imatinib the key to improving beta-cell function in diabetes?

The small tyrosine kinase (TK) inhibitor imatinib mesylate (Gleevec, STI571) protects against both type 1 and type 2 diabetes, but as it inhibits many TKs and other proteins, it is not clear by which mechanisms it acts. This present review will focus on the possibility that imatinib acts, at least in part, by improving beta-cell function and survival via off-target effects on beta-cell signaling/metabolic flow events. Particular attention will be given to the possibility that imatinib and other TK inhibitors function as inhibitors of mitochondrial respiration. A better understanding of how imatinib counteracts diabetes will possibly help to clarify the pathogenic role of beta-cell signaling events and mitochondrial function, and hopefully leading to improved treatment of the disease.

Imatinib protects against human beta-cell death via inhibition of mitochondrial respiration and activation of AMPK

The protein tyrosine kinase inhibitor imatinib is used in the treatment of various malignancies but may also promote beneficial effects in the treatment of diabetes. The aim of the present investigation was to characterize the mechanisms by which imatinib protects insulin producing cells. Treatment of non-obese diabetic (NOD) mice with imatinib resulted in increased beta-cell AMP-activated kinase (AMPK) phosphorylation. Imatinib activated AMPK also in vitro, resulting in decreased ribosomal protein S6 phosphorylation and protection against islet amyloid polypeptide (IAPP)-aggregation, thioredoxin interacting protein (TXNIP) up-regulation and beta-cell death. 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) mimicked and compound C counteracted the effect of imatinib on beta-cell survival. Imatinib-induced AMPK activation was preceded by reduced glucose/pyruvate-dependent respiration, increased glycolysis rates, and a lowered ATP/AMP ratio. Imatinib augmented the fractional oxidation of fatty acids/malate, possibly via a direct interaction with the beta-oxidation enzyme enoyl coenzyme A hydratase, short chain, 1, mitochondrial (ECHS1). In non-beta cells, imatinib reduced respiratory chain complex I and II-mediated respiration and acyl-CoA carboxylase (ACC) phosphorylation, suggesting that mitochondrial effects of imatinib are not beta-cell specific. In conclusion, tyrosine kinase inhibitors modestly inhibit mitochondrial respiration, leading to AMPK activation and TXNIP down-regulation, which in turn protects against beta-cell death.

ZBED6 counteracts high-fat diet-induced glucose intolerance by maintaining beta cell area and reducing excess mitochondrial activation

AIMS/HYPOTHESIS

ZBED6 (zinc finger, BED-type containing 6) is known to regulate muscle mass by suppression of Igf2 gene transcription. In insulin-producing cell lines, ZBED6 maintains proliferative capacity at the expense of differentiation and beta cell function. The aim was to study the impact of Zbed6 knockout on beta cell function and glucose tolerance in C57BL/6 mice.

METHODS

Beta cell area and proliferation were determined in Zbed6 knockout mice using immunohistochemical analysis. Muscle and fat distribution were assessed using micro-computed tomography. Islet gene expression was assessed by RNA sequencing. Effects of a high-fat diet were analysed by glucose tolerance and insulin tolerance tests. ZBED6 was overexpressed in EndoC-βH1 cells and human islet cells using an adenoviral vector. Beta cell cell-cycle analysis, insulin release and mitochondrial function were studied in vitro using propidium iodide staining and flow cytometry, ELISA, the Seahorse technique, and the fluorescent probes JC-1 and MitoSox.

RESULTS

Islets from Zbed6 knockout mice showed lowered expression of the cell cycle gene Pttg1, decreased beta cell proliferation and decreased beta cell area, which occurred independently from ZBED6 effects on Igf2 gene expression. Zbed6 knockout mice, but not wild-type mice, developed glucose intolerance when given a high-fat diet. The high-fat diet Zbed6 knockout islets displayed upregulated expression of oxidative phosphorylation genes and genes associated with beta cell differentiation. In vitro, ZBED6 overexpression resulted in increased EndoC-βH1 cell proliferation and a reduced glucose-stimulated insulin release in human islets. ZBED6 also reduced mitochondrial JC-1 J-aggregate formation, mitochondrial oxygen consumption rates (OCR) and mitochondrial reactive oxygen species (ROS) production, both at basal and palmitate + high glucose-stimulated conditions. ZBED6-induced inhibition of OCR was not rescued by IGF2 addition. ZBED6 reduced levels of the mitochondrial regulator PPAR-γ related coactivator 1 protein (PRC) and bound its promoter/enhancer region. Knockdown of PRC resulted in a lowered OCR.

CONCLUSIONS/INTERPRETATION

It is concluded that ZBED6 is required for normal beta cell replication and also limits excessive beta cell mitochondrial activation in response to an increased functional demand. ZBED6 may act, at least in part, by restricting PRC-mediated mitochondrial activation/ROS production, which may lead to protection against beta cell dysfunction and glucose intolerance in vivo.

The central role of glutathione peroxidase 4 in the regulation of ferroptosis and its implications for pro-inflammatory cytokine-mediated beta-cell death

Pro-inflammatory cytokines are crucial mediators of beta-cell destruction in type 1 diabetes mellitus (T1DM). The involvement of ferroptosis as a form of oxidative non-apoptotic cell death in T1DM pathogenesis has not been elucidated so far. Moreover, the role of glutathione peroxidase 4 (GPx4) as an antioxidative enzyme and a major regulator of ferroptosis remains elusive. Assessment of GPx4 expression in different pancreatic islet cell types revealed a predominant expression in beta-cells. Silencing of GPx4 by RNA interference and exposure to tert-butyl hydroperoxide (tert-BHP) caused ferroptosis in rat pancreatic beta-cells as evidenced by non-apoptotic cell death in association with increased lipid peroxidation, disturbed ATP synthesis, reduced GSH content, and GPx4 degradation. GPx4 overexpression as well as the ferroptosis inhibitor ferrostatin-1 effectively attenuated beta-cell death induced by tert-BHP. Notably, beta-cell toxic cytokines did not induce ferroptosis although beta-cells underwent cell death. Inhibition of iNOS by Nω-nitro-L-arginine however led to a massive lipid peroxidation upon exposure to pro-inflammatory cytokines. Hence, nitric oxide produced during pro-inflammatory cytokine action prevents the induction of ferroptosis, thereby favouring apoptosis as a primary cell death mechanism. The extraordinarily high abundance of the phospholipid hydroperoxidase GPx4 in beta-cells in contrast to the very low expression in other islet cell types points to a susceptibility of beta-cells to the accumulation of toxic lipid peroxides. Overall, these data strongly suggest that GPx4 is indispensable for beta-cell function under physiological conditions. On the other hand, our results exclude an involvement of ferroptosis as an alternative beta-cell death mode under pro-inflammatory cytokine attack.

Zinc transporters and their functional integration in mammalian cells

Zinc is a ubiquitous biological metal in all living organisms. The spatiotemporal zinc dynamics in cells provide crucial cellular signaling opportunities, but also challenges for intracellular zinc homeostasis with broad disease implications. Zinc transporters play a central role in regulating cellular zinc balance and subcellular zinc distributions. The discoveries of two complementary families of mammalian zinc transporters (ZnTs and ZIPs) in the mid-1990s spurred much speculation on their metal selectivity and cellular functions. After two decades of research, we have arrived at a biochemical description of zinc transport. However, in vitro functions are fundamentally different from those in living cells, where mammalian zinc transporters are directed to specific subcellular locations, engaged in dedicated macromolecular machineries, and connected with diverse cellular processes. Hence, the molecular functions of individual zinc transporters are reshaped and deeply integrated in cells to promote the utilization of zinc chemistry to perform enzymatic reactions, tune cellular responsiveness to pathophysiologic signals, and safeguard cellular homeostasis. At present, the underlying mechanisms driving the functional integration of mammalian zinc transporters are largely unknown. This knowledge gap has motivated a shift of the research focus from in vitro studies of purified zinc transporters to in cell studies of mammalian zinc transporters in the context of their subcellular locations and protein interactions. In this review, we will outline how knowledge of zinc transporters has been accumulated from in-test-tube to in-cell studies, highlighting new insights and paradigm shifts in our understanding of the molecular and cellular basis of mammalian zinc transporter functions.

Down-regulation of the islet-specific zinc transporter-8 (ZnT8) protects human insulinoma cells against inflammatory stress

Zinc transporter-8 (ZnT8) primarily functions as a zinc-sequestrating transporter in the insulin-secretory granules (ISGs) of pancreatic β-cells. Loss-of-function mutations in ZnT8 are associated with protection against type-2 diabetes (T2D), but the protective mechanism is unclear. Here, we developed an in-cell ZnT8 assay to track endogenous ZnT8 responses to metabolic and inflammatory stresses applied to human insulinoma EndoC-βH1 cells. Unexpectedly, high glucose and free fatty acids did not alter cellular ZnT8 levels, but proinflammatory cytokines acutely, reversibly, and gradually down-regulated ZnT8. Approximately 50% of the cellular ZnT8 was localized to the endoplasmic reticulum (ER), which was the primary target of the cytokine-mediated ZnT8 down-regulation. Transcriptome profiling of cytokine-exposed β-cells revealed an adaptive unfolded protein response (UPR) including a marked immunoproteasome activation that coordinately degraded ZnT8 and insulin over a 1,000-fold cytokine concentration range. RNAi-mediated ZnT8 knockdown protected cells against cytokine cytotoxicity, whereas inhibiting immunoproteasomes blocked cytokine-induced ZnT8 degradation and triggered a transition of the adaptive UPR to cell apoptosis. Hence, cytokine-induced down-regulation of the ER ZnT8 level promotes adaptive UPR, acting as a protective mechanism that decongests the ER burden of ZnT8 to protect β-cells from proapoptotic UPR during chronic low-grade inflammation.

Structure-toxicity relationships of saturated and unsaturated free fatty acids for elucidating the lipotoxic effects in human EndoC-βH1 beta-cells

Lipotoxicity has been considered a major cause for beta-cell dysfunction in type 2 diabetes mellitus. However, the underlying mechanisms are still unclear. To achieve a better understanding of the toxicity a wide range of structurally different free fatty acids (FFAs) has been analyzed in human EndoC-βH1 beta-cells. Exposure of human EndoC-βH1 beta-cells to physiological saturated and monounsaturated long-chain FFAs induced apoptosis. Particularly noteworthy was that the toxicity increased more rapidly with increasing chain length of saturated than of unsaturated FFAs. The highest toxicity was observed in the presence of very long-chain FFAs (C20-C22), whereas polyunsaturated FFAs were not toxic. Long-chain FFAs increased peroxisomal hydrogen peroxide generation slightly, while very long-chain FFAs increased hydrogen peroxide generation more potently in both peroxisomes and mitochondria. The greater toxicity of very long-chain FFAs was accompanied by hydroxyl radical formation, along with cardiolipin peroxidation and ATP depletion. Intriguingly, only saturated very long-chain FFAs activated ER stress. On the other hand saturated very long-chain FFAs did not induce lipid droplet formation in contrast to long-chain FFAs and unsaturated very long-chain FFAs. The present data highlight the importance of structure-activity relationship analyses for the understanding of the mechanisms of lipotoxicity. Chain length and degree of saturation of FFAs are crucial factors for the toxicity of FFAs, with peroxisomal, mitochondrial, and ER stress representing the major pathogenic factors for induction of lipotoxicity. The results might provide a guide for the composition of a healthy beta-cell protective diet.

Electrophysiological properties of human beta-cell lines EndoC-βH1 and -βH2 conform with human beta-cells

Limited access to human islets has prompted the development of human beta cell models. The human beta cell lines EndoC-βH1 and EndoC-βH2 are increasingly used by the research community. However, little is known of their electrophysiological and secretory properties. Here, we monitored parameters that constitute the glucose-triggering pathway of insulin release. Both cell lines respond to glucose (6 and 20 mM) with 2- to 3-fold stimulation of insulin secretion which correlated with an elevation of [Ca²⁺]_i, membrane depolarisation and increased action potential firing. Similar to human primary beta cells, K_ATP channel activity is low at 1 mM glucose and is further reduced upon increasing glucose concentration; an effect that was mimicked by the K_ATP channel blocker tolbutamide. The upstroke of the action potentials reflects the activation of Ca²⁺ channels with some small contribution of TTX-sensitive Na⁺ channels. The repolarisation involves activation of voltage-gated Kv2.2 channels and large-conductance Ca²⁺-activated K⁺ channels. Exocytosis presented a similar kinetics to human primary beta cells. The ultrastructure of these cells shows insulin vesicles composed of an electron-dense core surrounded by a thin clear halo. We conclude that the EndoC-βH1 and -βH2 cells share many features of primary human β-cells and thus represent a useful experimental model.

The novel NADPH oxidase 4 selective inhibitor GLX7013114 counteracts human islet cell death in vitro

It has been proposed that pancreatic beta-cell dysfunction in type 2 diabetes is promoted by oxidative stress caused by NADPH oxidase (Nox) over-activity. The aim of the present study was to evaluate the efficacy of novel Nox inhibitors as protective agents against cytokine- or high glucose + palmitate-induced human beta-cell death. The Nox2 protein was present mainly in the cytoplasm and was induced by cytokines. Nox4 protein immunoreactivity, with some nuclear accumulation, was observed in human islet cells, and was not affected by islet culture in the presence of cytokines or high glucose + palmitate. Nox inhibitors with partial or no isoform selectivity (DPI, dapsone, GLX351322, and GLX481372) all reduced ROS production of human islet cells exposed to high glucose + palmitate. This was paralleled by improved viability and reduced caspase 3 activation. The Nox1 selective inhibitor ML171 failed to reduce human islet cell death in response to both cytokines and high glucose + palmitate. The selective Nox2 inhibitor Phox-I2 also failed to protect against cytokines, but protected partially against high glucose + palmitate-induced cellular death. The highly selective Nox4 inhibitor GLX7013114 protected islet cells against both cytokines and high glucose + palmitate. However, as no osmotic control for high glucose was used, we cannot exclude the possibility that the high glucose effect was due to osmosis. It is concluded that Nox4 may participate in stress-induced islet cell death in human islets in vitro. We propose that Nox4 mediates pro-apoptotic effects in intact islets under stressful conditions and that selective Nox4-inhibition may be a therapeutic strategy in type 2 diabetes.

BRICHOS domain of Bri2 inhibits islet amyloid polypeptide (IAPP) fibril formation and toxicity in human beta cells

Accumulation of islet amyloid polypeptide (IAPP)-containing amyloid fibrils is the main pathological finding in pancreatic islets in type 2 diabetes. The formation of these IAPP amyloid fibrils is considered toxic and may constitute a major cause for the loss of insulin-producing beta cells. The protein domain BRICHOS is present in several different proproteins and possesses antiamyloid chaperone activity. This study demonstrates expression of the BRICHOS-containing protein Bri2 in human pancreatic beta cells and its colocalization with IAPP. The Bri2 BRICHOS domain effectively prevents IAPP from forming fibrils and protects cells from the toxicity associated with IAPP fibrillation. It is concluded that the Bri2 BRICHOS domain may act as an endogenous inhibitor of IAPP amyloid formation in pancreatic beta cells.

Aggregation of islet amyloid polypeptide (IAPP) into amyloid fibrils in islets of Langerhans is associated with type 2 diabetes, and formation of toxic IAPP species is believed to contribute to the loss of insulin-producing beta cells. The BRICHOS domain of integral membrane protein 2B (Bri2), a transmembrane protein expressed in several peripheral tissues and in the brain, has recently been shown to prevent fibril formation and toxicity of Aβ42, an amyloid-forming peptide in Alzheimer disease. In this study, we demonstrate expression of Bri2 in human islets and in the human beta-cell line EndoC-βH1. Bri2 colocalizes with IAPP intracellularly and is present in amyloid deposits in patients with type 2 diabetes. The BRICHOS domain of Bri2 effectively inhibits fibril formation in vitro and instead redirects IAPP into formation of amorphous aggregates. Reduction of endogenous Bri2 in EndoC-βH1 cells with siRNA increases sensitivity to metabolic stress leading to cell death while a concomitant overexpression of Bri2 BRICHOS is protective. Also, coexpression of IAPP and Bri2 BRICHOS in lateral ventral neurons of Drosophila melanogaster results in an increased cell survival. IAPP is considered to be the most amyloidogenic peptide known, and described findings identify Bri2, or in particular its BRICHOS domain, as an important potential endogenous inhibitor of IAPP aggregation and toxicity, with the potential to be a possible target for the treatment of type 2 diabetes.

Chemistry and biology of reactive species with special reference to the antioxidative defence status in pancreatic β-cells

BACKGROUND

Diabetes mellitus is a serious metabolic disease. Dysfunction and subsequent loss of the β-cells in the islets of Langerhans through apoptosis ultimately cause a life-threatening insulin deficiency. The underlying reason for the particular vulnerability of the β-cells is an extraordinary sensitivity to the toxicity of reactive oxygen and nitrogen species (ROS and RNS) due to its low antioxidative defense status.

SCOPE REVIEW

This review considers the different aspects of the chemistry and biology of the biologically most important reactive species and their chemico-biological interactions in the β-cell toxicity of proinflammatory cytokines in type 1 diabetes and of lipotoxicity in type 2 diabetes development.

MAJOR CONCLUSION

The weak antioxidative defense equipment in the different subcellular organelles makes the β-cells particularly vulnerable and prone to mitochondrial, peroxisomal and ER stress. Looking upon the enzyme deficiencies which are responsible for the low antioxidative defense status of the pancreatic β-cells it is the lack of enzymatic capacity for H₂O₂ inactivation at all major subcellular sites.

GENERAL SIGNIFICANCE

Diabetes is the most prevalent metabolic disorder with a steadily increasing incidence of both type 1 and type 2 diabetes worldwide. The weak protection of the pancreatic β-cells against oxidative stress is a major reason for their particular vulnerability. Thus, careful protection of the β-cells is required for prevention of the disease.

EndoC-βH1 cells display increased sensitivity to sodium palmitate when cultured in DMEM/F12 medium

Aims - Human pancreatic islets are known to die in response to the free fatty acid of sodium palmitate when cultured in vitro. This is in contrast to EndoC-βH1 cells, which in our hands are not sensitive to the cell death-inducing effects sodium palmitate, making these cells seemingly unsuitable for lipotoxicity studies. However, the EndoC-βH1 cells are routinely cultured in a nutrient mixture based on Dulbecco's Modified Eagle Medium (DMEM), which may not be the optimal choice for studies dealing with lipotoxicity. The aim of the present investigation was to define culture conditions that render EndoC-βH1 cells sensitive to toxic effects of sodium palmitate. Methods - EndoC-βH1 cells were cultured at standard conditions in either DMEM or DMEM/F12 culture medium. Cell death was analyzed using propidium iodide staining and flow cytometry. Insulin release and content was quantified using a human insulin ELISA. Results - We presently observe that substitution of DMEM for a DMEM/Ham's F12 mixture (50%/50% vol/vol) renders the cells sensitive to the apoptotic effects of sodium palmitate and sodium palmitate + high glucose leading to an increased cell death. Supplementation of the DMEM culture medium with linoleic acid partially mimicked the effect of DMEM/F12. Culture of EndoC-βH1 cells in DMEM/F12 resulted also in increased proliferation, ROS production and insulin contents, but markers for metabolic stress, autophagy or amyloid deposits were unaffected. Conclusions - The culture conditions for EndoC-βH1 cells can be modified so these cells display signs of lipotoxicity in response to sodium palmitate.

Sensitivity profile of the human EndoC-βH1 beta cell line to proinflammatory cytokines

AIMS/HYPOTHESIS

The aim of this study was to perform a detailed analysis of cytokine toxicity in the new human EndoC-βH1 beta cell line.

METHODS

The expression profile of the antioxidative enzymes in the new human EndoC-βH1 beta cells was characterised and compared with that of primary beta cells in the human pancreas. The effects of proinflammatory cytokines on reactive oxygen species formation, insulin secretory responsiveness and apoptosis of EndoC-βH1 beta cells were determined.

RESULTS

EndoC-βH1 beta cells were sensitive to the toxic action of proinflammatory cytokines. Glucose-dependent stimulation of insulin secretion and an increase in the ATP/ADP ratio was abolished by proinflammatory cytokines without induction of IL-1β expression. Cytokine-mediated caspase-3 activation was accompanied by reactive oxygen species formation and developed more slowly than in rodent beta cells. Cytokines transiently increased the expression of unfolded protein response genes, without inducing endoplasmic reticulum stress-marker genes. Cytokine-mediated NFκB activation was too weak to induce inducible nitric oxide synthase expression. The resultant lack of nitric oxide generation in EndoC-βH1 cells, in contrast to rodent beta cells, makes these cells dependent on exogenously generated nitric oxide, which is released from infiltrating immune cells in human type 1 diabetes, for full expression of proinflammatory cytokine toxicity.

CONCLUSIONS/INTERPRETATION

EndoC-βH1 beta cells are characterised by an imbalance between H2O2-generating and -inactivating enzymes, and react to cytokine exposure in a similar manner to primary human beta cells. They are a suitable beta cell surrogate for cytokine-toxicity studies.

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.

Claes Hellerström and Cartesian diver microrespirometry

Cartesian diver microrespirometry was introduced by Claes Hellerström at the Department of Histology/Medical Cell Biology at Uppsala University, Sweden, to determine rates of oxygen consumption in islets of Langerhans. The theory behind this method is touched upon and the main findings described. Glucose-stimulated beta cell respiration significantly contributes to increased ATP generation, which is a prerequisite for stimulated insulin secretion and synthesis. This has had major implications for understanding the beta cell stimulus-secretion coupling.