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Aims Stevia rebaudiana Bertoni leaf extracts have gained increasing attention for their potential protection against type 2 diabetes. In this study, we have evaluated the possible beneficial effects of Stevia rebaudiana leaf extracts on beta-cells exposed to lipotoxicity and explored some of the possible mechanisms involved. Methods Extracts, deriving from six different chemotypes (ST1 to ST6), were characterized in terms of steviol glycosides, total phenols, flavonoids, and antioxidant activity. INS-1E beta cells and human pancreatic islets were incubated 24 h with 0.5 mM palmitate with or without varying concentrations of extracts. Beta-cell/islet cell features were analyzed by MTT assay, activated caspase 3/7 measurement, and/or nucleosome quantification. In addition, the proteome of INS-1E cells was assessed by bi-dimensional electrophoresis (2-DE). Results The extracts differed in terms of antioxidant activity and stevioside content. As expected, 24 h exposure to palmitate resulted in a significant decrease of INS-1E cell metabolic activity, which was counteracted by all the Stevia extracts at 200 μg/ml. However, varying stevioside only concentrations were not able to protect palmitate-exposed cells. ST3 extract was also tested with human islets, showing an anti-apoptotic effect. Proteome analysis showed several changes in INS-1E beta-cells exposed to ST3, mainly at the endoplasmic reticulum and mitochondrial levels. Conclusions Stevia rebaudiana leaf extracts have beneficial effects on beta cells exposed to lipotoxicity; this effect does not seem to be mediated by stevioside alone (suggesting a major role of the leaf phytocomplex as a whole) and might be due to actions on the endoplasmic reticulum and the mitochondrion.

BACKGROUND: Identification of islet β cell death prior to the onset of type 1 diabetes (T1D) or type 2 diabetes (T2D) might allow for interventions to protect β cells and reduce diabetes risk. Circulating unmethylated DNA fragments arising from the human INS gene have been proposed as biomarkers of β cell death, but this gene alone may not be sufficiently specific to report β cell death. RESULTS: To identify new candidate genes whose CpG sites may show greater specificity for β cells, we performed unbiased DNA methylation analysis using the Infinium HumanMethylation 450 array on 64 human islet preparations and 27 non-islet human tissues. For verification of array results, bisulfite DNA sequencing of human β cells and 11 non-β cell tissues was performed on 5 of the top 10 CpG sites that were found to be differentially methylated. We identified the CHTOP gene as a candidate whose CpGs show a greater frequency of unmethylation in human islets. A digital PCR strategy was used to determine the methylation pattern of CHTOP and INS CpG sites in primary human tissues. Although both INS and CHTOP contained unmethylated CpG sites in non-islet tissues, they occurred in a non-overlapping pattern. Based on Naïve Bayes classifier analysis, the two genes together report 100% specificity for islet damage. Digital PCR was then performed on cell-free DNA from serum from human subjects. Compared to healthy controls (N = 10), differentially methylated CHTOP and INS levels were higher in youth with new onset T1D (N = 43) and, unexpectedly, in healthy autoantibody-negative youth who have first-degree relatives with T1D (N = 23). When tested in lean (N = 32) and obese (N = 118) youth, increased levels of unmethylated INS and CHTOP were observed in obese individuals. CONCLUSION: Our data suggest that concurrent measurement of circulating unmethylated INS and CHTOP has the potential to detect islet death in youth at risk for both T1D and T2D. Our data also support the use of multiple parameters to increase the confidence of detecting islet damage in individuals at risk for developing diabetes., SCOPUS: ar.j, info:eu-repo/semantics/published

Pancreatic β-cell failure is key to type 2 diabetes (T2D) onset and progression. We assessed whether human β-cell dysfunction induced by metabolic stress is reversible, evaluated the molecular pathways underlying persistent or transient damage, and explored the relationships with T2D islet traits. Twenty-six human islet preparations were exposed to several lipo- and/or glucotoxicity conditions, some of which impaired insulin release depending on stressor type, concentration and combination. Interestingly, reversal of dysfunction occurred after wash out for some, but not for all, of the lipoglucotoxic insults. Islet transcriptomes assessed by RNA-sequencing and eQTL analysis identified specific pathways underlying β-cell failure and recovery. Notably, comparison of a large number of human T2D islet transcriptomes with those of persistent or reversible β-cell lipoglucotoxicity showed shared gene expression signatures. The identification of mechanisms associated with human β-cell dysfunction and recovery, and their overlap with T2D islet traits provide novel insights into T2D pathogenesis and should foster the development of improved β-cell targeted therapeutic strategies.

Statins are a class of drugs widely prescribed as frontline therapy for lowering plasma LDL-cholesterol in cardiovascular risk prevention. Several clinical reports have recently suggested an increased risk of type 2 diabetes associated with chronic use of these drugs. The pathophysiology of this effect remains to be fully elucidated but impaired β-cell function constitutes a potential mechanism. The aim of this study was to explore the effect of a chronic treatment with lipophilic and hydrophilic statins on β-cell function, using human pancreatic islets and rat insulin-secreting INS-1 cells; we particularly focused on the role of mitochondria and oxidative stress. The present study demonstrates, for the first time, that atorvastatin (lipophilic) but not pravastatin (hydrophilic) affected insulin release and mitochondrial metabolism due to the suppression of antioxidant defense system and induction of ROS production in pancreatic β-cell models. Mevalonate addition and treatment with a specific antioxidant (N-AcetylCysteine) effectively reversed the observed defects. These data demonstrate that mitochondrial oxidative stress is a key element in the pathogenesis of statin-related diabetes and may have clinical relevance to design strategies for prevention or reduction of statin induced β-cell dysfunction and diabetes in patients treated with lipophilic statins.

To improve the efficiency of pancreatic islet transplantation, we performed in-vitro and in-vivo experiments with isolated human pancreatic islets coated by multi-layer nano-encapsulation using differently charged polymers [chitosan and poly(sodium styrene sulfonate)] to obtain up to 9 layers. The islet coating (thickness: 104.2 ± 4.2 nm) was uniform, with ≥ 90% cell viability and well preserved beta- and alpha-cell ultrastructure. Nano-encapsulated islets maintained physiological glucose-stimulated insulin secretion by both static incubation and perifusion studies. Notably, palmitate- or cytokine-induced toxicity was significantly reduced in nano-coated islets. Xenotransplantation of nano-encapsulated islets under the kidney capsule of streptozotocin-induced C57Bl/6J diabetic mice allowed long term normal or near normal glycemia, associated with minimal infiltration of immune cell into the grafts, well preserved islet morphology and signs of re-vascularization. In summary, the multi-layer nano-encapsulation approach described in the present study provides a promising tool to effectively protect human islets both in-vitro and in-vivo conditions.

Progressive failure of insulin-producing beta cells is the central event leading to diabetes, but the signalling networks controlling beta cell fate remain poorly understood. Here we show that SRp55, a splicing factor regulated by the diabetes susceptibility gene GLIS3, has a major role in maintaining function and survival of human beta cells. RNA-seq analysis revealed that SRp55 regulates the splicing of genes involved in cell survival and death, insulin secretion and JNK signalling. Specifically, SRp55-mediated splicing changes modulate the function of the pro-apoptotic proteins BIM and BAX, JNK signalling and endoplasmic reticulum stress, explaining why SRp55 depletion triggers beta cell apoptosis. Furthermore, SRp55 depletion inhibits beta cell mitochondrial function, explaining the observed decrease in insulin release. These data unveil a novel layer of regulation of human beta cell function and survival, namely alternative splicing modulated by key splicing regulators such as SRp55 that may crosstalk with candidate genes for diabetes., SCOPUS: ar.j, info:eu-repo/semantics/published

Insulin, acting in an autocrine manner, promotes β-cell survival and growth and its own biosynthesis and secretion. Prolonged exposure of β-cells to high levels of saturated fatty acids (SFAs) impairs insulin signaling, reducing the ability of insulin to promote its release. The p66Shc protein is an inducer of cellular oxidative stress and apoptosis, and its mRNA levels are increased in pancreatic islets from overweight/obese subjects. Here we evaluated the role of p66Shc in pancreatic β-cell insulin resistance (IR) occurring in obesity and lipotoxic conditions. Insulin effects on its own content and C-peptide secretion were studied in pancreatic islets from overweight/obese (BMI ≥25 kg/m2) compared to lean (BMI In conclusion, the protein p66Shc exerts an inhibitory effect on β-cell insulin signaling and can mediate the ability of SFAs and excess body fat to cause β-cell IR, which results in both reduced survival and impaired secretory function. Disclosure L. Dipaola: None. A. Natalicchio: Other Relationship; Self; Novo Nordisk Inc., Sanofi-Aventis. G. Biondi: None. N. Marrano: None. M. Bugliani: None. A. Cignarelli: Consultant; Self; Eli Lilly and Company. Speaker's Bureau; Self; Merck Sharp & Dohme Corp., Novo Nordisk A/S. S. Perrini: None. P. Marchetti: None. L. Laviola: Advisory Panel; Self; Abbott, Boehringer Ingelheim Pharmaceuticals, Inc., Lilly Diabetes, Novo Nordisk Inc. Board Member; Self; AstraZeneca, Roche Diabetes Care, Sanofi-Aventis. Speaker's Bureau; Self; Medtronic, Mundipharma, Takeda Pharmaceutical Company Limited. F. Giorgino: Advisory Panel; Self; Aegerion Pharmaceuticals, AstraZeneca, Boehringer Ingelheim International GmbH, Eli Lilly and Company, MedImmune, Merck Sharp & Dohme Corp., Novo Nordisk A/S, Roche Diabetes Care, Sanofi. Consultant; Self; Roche Diabetes Care, Sanofi. Research Support; Self; Eli Lilly and Company, LifeScan, Inc., Takeda Pharmaceutical Company Limited. Other Relationship; Self; AstraZeneca, Eli Lilly and Company, Sanofi.

Little information is available on adipose tissue features in the human pancreas (AdTP). In the present study we performed morphologic and morphometric studies on AdTP of 9 overweight/obese nondiabetic (ND, age: 65±5 years; 4M/5F; BMI: 31.3±0.4 Kg/m2, mean±SEM) and 13 matched type 2 diabetic (T2D, age: 70±2 years, 8M/5F; BMI: 30.0±0.8 kg/m2) organ donors. Adipocytes were identified and quantified on a fluorescence DM5500 Leica microscope, using the MetaMorph v 1.8.0 software with a tresholded mask applied in exclusive mode. Macrophages were identified by immunohistochemistry using anti-CD68 (Dako) antibody. Assessment of insulin (Abcam Ab) and glucagon (Sigma Ab) positive cells was also performed. The number of adipocytes trended higher (+32.8%) in T2D (8.9±1.4/mm2) compared to ND (6.7±2.1/mm2) and their size was greater in T2D (9,319±1,028 μm2) than ND (5,639±639 μm2, p=0.01). AdTP area in relation to acinar tissue was 90.4% higher (p=0.07) in T2D (7.6±1.3%) than ND (3.9±1.5%). The amount of adipocytes with adjacent ≥ 3 CD68+ cells was higher (p=0.048) in T2D (31/281, 11%) than ND (7/147, 5%). Insulin positive area (T2D: 0.49±0.06%; ND: 0.55±0.09%) as well as glucagon positive area (T2D: 0.24±0.03%; ND: 0.32±0.07%) did not differ significantly between the two groups. Adipocyte size was negatively associated with islet number in ND+T2D (p=0.06) and positively with insulin area in ND (p=0.058); there was a significant, positive relationship between the amount of adipocytes and the number of islets in T2D (p=0.017). In conclusion, we found significant differences in the AdTP of T2D as compared to ND, including increased adypocite size and presence of adipocyte adjacent CD68+ cells; some of these parameters correlated with islet morphometric indices. Disclosure M. Suleiman: None. C. De Luca: None. P. De Simone: None. U. Boggi: None. F. Grano: None. M. Bugliani: None. P. Marchetti: None. L. Marselli: None. Funding Innovative Medicines Initiative 2 Joint Undertaking (115881); European Union; European Federation of Pharmaceutical Industries and Associations; Swiss State Secretariat for Education, Research and Innovation (16.0097-2)

Autophagy is the major mechanism involved in degradation and recycling of intracellular components, and its alterations have been proposed to cause beta cell dysfunction. In this study, we explored the effects of autophagy modulation in human islets under conditions associated to endoplasmic reticulum (ER) stress. Human pancreatic islets were isolated by enzymatic digestion and density gradient purification from pancreatic samples of non-diabetic (ND; n, info:eu-repo/semantics/published

miRNAs are a class of small non-coding RNAs that regulate gene expression. Type 1 diabetes is an autoimmune disease characterized by insulitis (islets inflammation) and pancreatic beta cell destruction. The pro-inflammatory cytokines interleukin 1 beta (IL1B) and interferon gamma (IFNG) are released during insulitis and trigger endoplasmic reticulum (ER) stress and expression of pro-apoptotic members of the BCL2 protein family in beta cells, thus contributing to their death. The nature of miRNAs that regulate ER stress and beta cell apoptosis remains to be elucidated. We have performed a global miRNA expression profile on cytokine-treated human islets and observed a marked downregulation of miR-211-5p. By real-time PCR and Western blot analysis, we confirmed cytokine-induced changes in the expression of miR-211-5p and the closely related miR-204-5p and downstream ER stress related genes in human beta cells. Blocking of endogenous miRNA-211-5p and miR-204-5p by the same inhibitor (it is not possible to block separately these two miRs) increased human beta cell apoptosis, as measured by Hoechst/propidium Iodide staining and by determination of cleaved caspase-3 activation. Interestingly, miRs-211-5p and 204-5p regulate the expression of several ER stress markers downstream of PERK, particularly the pro-apoptotic protein DDIT3 (also known as CHOP). Blocking CHOP expression by a specific siRNA partially prevented the increased apoptosis observed following miR-211-5p/miR-204-5p inhibition. These observations identify a novel crosstalk between miRNAs, ER stress and beta cell apoptosis in early type 1 diabetes., SCOPUS: ar.j, info:eu-repo/semantics/published

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The intracellular life of insulin secretory granules (ISGs) from biogenesis to secretion depends on their structural (e.g. size) and dynamic (e.g. diffusivity, mode of motion) properties. Thus, it would be useful to have rapid and robust measurements of such parameters in living β-cells. To provide such measurements, we have developed a fast spatiotemporal fluctuation spectroscopy. We calculate an imaging-derived Mean Squared Displacement (iMSD), which simultaneously provides the size, average diffusivity, and anomalous coefficient of ISGs, without the need to extract individual trajectories. Clustering of structural and dynamic quantities in a multidimensional parametric space defines the ISGs’ properties for different conditions. First, we create a reference using INS-1E cells expressing proinsulin fused to a fluorescent protein (FP) under basal culture conditions and validate our analysis by testing well-established stimuli, such as glucose intake, cytoskeleton disruption, or cholesterol overload. After, we investigate the effect of FP-tagged ISG protein markers on the structural and dynamic properties of the granule. While iMSD analysis produces similar results for most of the lumenal markers, the transmembrane marker phogrin-FP shows a clearly altered result. Phogrin overexpression induces a substantial granule enlargement and higher mobility, together with a partial de-polymerization of the actin cytoskeleton, and reduced cell responsiveness to glucose stimulation. Our data suggest a more careful interpretation of many previous ISG-based reports in living β-cells. The presented data pave the way to high-throughput cell-based screening of ISG structure and dynamics under various physiological and pathological conditions.

The presence of islet cells double positive for insulin and glucagon (Ins+/Glu+) has been described in the pancreas from both type 2 (T2D) and type 1 (T1D) diabetic subjects. We studied the role of pro-inflammatory cytokines on the occurrence, trajectory, and characteristics of Ins+/Glu+ cells in human pancreatic islets. Pancreas samples, isolated islets, and dispersed islet cells from 3 T1D and 11 non-diabetic (ND) multi-organ donors were studied by immunofluorescence, confocal microscopy, and/or electron microscopy. ND islet cells were exposed to interleukin-1β and inter-feron-γ for up to 120 h. In T1D islets, we confirmed an increased prevalence of Ins+/Glu+ cells. Cyto-kine-exposed islets showed a progressive increase of Ins+/Glu+ cells that represented around 50% of endocrine cells after 120h. Concomitantly, cells expressing insulin granules only decreased significantly over time, whereas those containing only glucagon granules remained stable. Interestingly, Ins+/Glu+ cells were less prone to cytokine-induced apoptosis than cells containing only insulin. Cy-tokine-exposed islets showed down-regulation of β-cell identity genes. In conclusion, pro-inflam-matory cytokines induce Ins+/Glu+ cells in human islets, possibly due to a switch from a β-to a β-/α-cell phenotype. These Ins+/Glu+ cells appear to be resistant to cytokine-induced apoptosis., SCOPUS: ar.j, info:eu-repo/semantics/published

Pancreatic β cell failure is key to type 2 diabetes (T2D) onset and progression. Here, we assess whether human β cell dysfunction induced by metabolic stress is reversible, evaluate the molecular pathways underlying persistent or transient damage, and explore the relationships with T2D islet traits. Twenty-six islet preparations are exposed to several lipotoxic/glucotoxic conditions, some of which impair insulin release, depending on stressor type, concentration, and combination. The reversal of dysfunction occurs after washout for some, although not all, of the lipoglucotoxic insults. Islet transcriptomes assessed by RNA sequencing and expression quantitative trait loci (eQTL) analysis identify specific pathways underlying β cell failure and recovery. Comparison of a large number of human T2D islet transcriptomes with those of persistent or reversible β cell lipoglucotoxicity show shared gene expression signatures. The identification of mechanisms associated with human β cell dysfunction and recovery and their overlap with T2D islet traits provide insights into T2D pathogenesis, fostering the development of improved β cell-targeted therapeutic strategies. Published version

The β-cell has become recognized as a central player in the pathogenesis of type 1 diabetes with the generation of neoantigens as potential triggers for breaking immune tolerance. We report that posttranslationally modified glucose-regulated protein 78 (GRP78) is a novel autoantigen in human type 1 diabetes. When human islets were exposed to inflammatory stress induced by interleukin-1β, tumor necrosis factor-α, and interferon-γ, arginine residue R510 within GRP78 was converted into citrulline, as evidenced by liquid chromatography-tandem mass spectrometry. This conversion, known as citrullination, led to the generation of neoepitopes, which effectively could be presented by HLA-DRB1*04:01 molecules. With the use of HLA-DRB1*04:01 tetramers and ELISA techniques, we demonstrate enhanced antigenicity of citrullinated GRP78 with significantly increased CD4+ T-cell responses and autoantibody titers in patients with type 1 diabetes compared with healthy control subjects. Of note, patients with type 1 diabetes had a predominantly higher percentage of central memory cells and a lower percentage of effector memory cells directed against citrullinated GRP78 compared with the native epitope. These results strongly suggest that citrullination of β-cell proteins, exemplified here by the citrullination of GRP78, contributes to loss of self-tolerance toward β-cells in human type 1 diabetes, indicating that β-cells actively participate in their own demise. ispartof: DIABETES vol:67 issue:11 pages:2337-2348 ispartof: location:United States status: published

Dietary n-3 polyunsaturated fatty acids, especially docosahexaenoic acid (DHA), are known to influence glucose homeostasis. We recently showed that Elovl2 expression in beta cells, which regulates synthesis of endogenous DHA, was associated with glucose tolerance and played a key role in insulin secretion. The present study aimed to examine the role of the very long chain fatty acid elongase 2 (ELOVL2)/DHA axis on the adverse effects of palmitate with high glucose, a condition defined as glucolipotoxicity, on beta cells. We detected ELOVL2 in INS-1 beta cells and mouse and human islets using quantitative PCR and western blotting. Downregulation and adenoviral overexpression of Elovl2 was carried out in beta cells. Ceramide and diacylglycerol levels were determined by radio-enzymatic assay and lipidomics. Apoptosis was quantified using caspase-3 assays and poly (ADP-ribose) polymerase cleavage. Palmitate oxidation and esterification were determined by [U-14C]palmitate labelling. We found that glucolipotoxicity decreased ELOVL2 content in rodent and human beta cells. Downregulation of ELOVL2 drastically potentiated beta cell apoptosis induced by glucolipotoxicity, whereas adenoviral Elovl2 overexpression and supplementation with DHA partially inhibited glucolipotoxicity-induced cell death in rodent and human beta cells. Inhibition of beta cell apoptosis by the ELOVL2/DHA axis was associated with a decrease in ceramide accumulation. However, the ELOVL2/DHA axis was unable to directly alter ceramide synthesis or metabolism. By contrast, DHA increased palmitate oxidation but did not affect its esterification. Pharmacological inhibition of AMP-activated protein kinase and etomoxir, an inhibitor of carnitine palmitoyltransferase 1 (CPT1), the rate-limiting enzyme in fatty acid β-oxidation, attenuated the protective effect of the ELOVL2/DHA axis during glucolipotoxicity. Downregulation of CPT1 also counteracted the anti-apoptotic action of the ELOVL2/DHA axis. By contrast, a mutated active form of Cpt1 inhibited glucolipotoxicity-induced beta cell apoptosis when ELOVL2 was downregulated. Our results identify ELOVL2 as a critical pro-survival enzyme for preventing beta cell death and dysfunction induced by glucolipotoxicity, notably by favouring palmitate oxidation in mitochondria through a CPT1-dependent mechanism.

Cobo-Vuilleumier, Nadia et al., Type 1 diabetes mellitus (T1DM) is due to the selective destruction of islet beta cells by immune cells. Current therapies focused on repressing the immune attack or stimulating beta cell regeneration still have limited clinical efficacy. Therefore, it is timely to identify innovative targets to dampen the immune process, while promoting beta cell survival and function. Liver receptor homologue-1 (LRH-1) is a nuclear receptor that represses inflammation in digestive organs, and protects pancreatic islets against apoptosis. Here, we show that BL001, a small LRH-1 agonist, impedes hyperglycemia progression and the immune-dependent inflammation of pancreas in murine models of T1DM, and beta cell apoptosis in islets of type 2 diabetic patients, while increasing beta cell mass and insulin secretion. Thus, we suggest that LRH-1 agonism favors a dialogue between immune and islet cells, which could be druggable to protect against diabetes mellitus., This work was funded by grants from the Juvenile Diabetes Research Foundation (17-2013-372 to B.R.G.), the Consejeria de Salud, Fundacion Publica Andaluza Progreso y Salud, Junta de Andalucia (PI-0727-2010 to B.R.G. and P10CTS6505 to B.S.), Consejeria de Economia, Innovacion y Ciencia (P10.CTS.6359 to B.R.G.), the Ministerio de Economia y Competidividad co-funded by Fondos FEDER (PI10/00871, PI13/00593, and BFU2017-83588-P to B.R.G.; PI14/01015, RD12/0019/0028, and RD16/0011/0034 to B.S.; PI16/00259 to A.H.) and Deutsche Forschungsgemeinschaft (GRK-1789 ´CEMMA´ and DFG SCHI-505/6-1 to R.S.). Special thanks to the families of the DiabetesCero Foundation that graciously supported this work (to B.R.G.). A.M.M. is a recipient of a Miguel Servet grant (CP14/00105) from the Instituto de Salud Carlos III co-funded by Fondos FEDER whereas E.F.M. is a recipient of a Juan de la Cierva Fellowship. I.G.H.G. is supported by a fellowship from Amarna Therapeutics. In some instances, human islets were procured through the European Consortium for Islet Transplantation funded by Juvenile Diabetes Research Foundation (3-RSC-2016-162-I-X).

Type 1 diabetes (T1D) is a chronic disease characterized by an autoimmune-mediated destruction of insulin-producing pancreatic β cells. Environmental factors such as viruses play an important role in the onset of T1D and interact with predisposing genes. Recent data suggest that viral infection of human islets leads to a decrease in insulin production rather than β cell death, suggesting loss of β cell identity. We undertook this study to examine whether viral infection could induce human β cell dedifferentiation. Using the functional human β cell line EndoC-βH1, we demonstrate that polyinosinic-polycytidylic acid (PolyI:C), a synthetic double-stranded RNA that mimics a byproduct of viral replication, induces a decrease in β cell-specific gene expression. In parallel with this loss, the expression of progenitor-like genes such as SOX9 was activated following PolyI:C treatment or enteroviral infection. SOX9 was induced by the NF-κB pathway and also in a paracrine non-cell-autonomous fashion through the secretion of IFN-α. Lastly, we identified SOX9 targets in human β cells as potentially new markers of dedifferentiation in T1D. These findings reveal that inflammatory signaling has clear implications in human β cell dedifferentiation.

Aims/hypothesis Pancreatic islet beta cell failure causes type 2 diabetes in humans. To identify transcriptomic changes in type 2 diabetic islets, the Innovative Medicines Initiative for Diabetes: Improving beta-cell function and identification of diagnostic biomarkers for treatment monitoring in Diabetes (IMIDIA) consortium (www.imidia.org) established a comprehensive, unique multicentre biobank of human islets and pancreas tissues from organ donors and metabolically phenotyped pancreatectomised patients (PPP). Methods Affymetrix microarrays were used to assess the islet transcriptome of islets isolated either by enzymatic digestion from 103 organ donors (OD), including 84 non-diabetic and 19 type 2 diabetic individuals, or by laser capture microdissection (LCM) from surgical specimens of 103 PPP, including 32 non-diabetic, 36 with type 2 diabetes, 15 with impaired glucose tolerance (IGT) and 20 with recent-onset diabetes (

It has been reported that the incretin system, including regulated GLP-1 secretion and locally expressed DPP-4, is present in pancreatic islets. In this study we comprehensively evaluated the expression and role of DPP-4 in islet alpha and beta cells from non-diabetic (ND) and type 2 diabetic (T2D) individuals, including the effects of its inhibition on beta cell function and survival. Isolated islets were prepared from 25 ND and 18 T2D organ donors; studies were also performed with the human insulin-producing EndoC-βH1 cells. Morphological (including confocal microscopy), ultrastructural (electron microscopy, EM), functional (glucose-stimulated insulin secretion), survival (EM and nuclear dyes) and molecular (RNAseq, qPCR and western blot) studies were performed under several different experimental conditions. DPP-4 co-localized with glucagon and was also expressed in human islet insulin-containing cells. Furthermore, DPP-4 was expressed in EndoC-βH1 cells. The proportions of DPP-4 positive alpha and beta cells and DPP-4 gene expression were significantly lower in T2D islets. A DPP-4 inhibitor protected ND human beta cells and EndoC-βH1 cells against cytokine-induced toxicity, which was at least in part independent from GLP1 and associated with reduced NFKB1 expression. Finally, DPP-4 inhibition augmented glucose-stimulated insulin secretion, reduced apoptosis and improved ultrastructure in T2D beta cells. These results demonstrate the presence of DPP-4 in human islet alpha and beta cells, with reduced expression in T2D islets, and show that DPP-4 inhibition has beneficial effects on human ND and T2D beta cells. This suggests that DPP-4, besides playing a role in incretin effects, directly affects beta cell function and survival.

Light scattering was recently demonstrated to serve as an intrinsic indicator for pancreatic islet cell mass and secretion. The insulin secretory granule (ISG), in particular, was proposed to be a reasonable candidate as the main intracellular source of scattered light due to the densely-packed insulin semi-crystal in the granule lumen. This scenario, if confirmed, would in principle open new perspectives for label-free single-granule imaging, tracking, and analysis. Contrary to such expectations, here we demonstrate that ISGs are not a primary source of scattering in primary human β-cells, as well as in immortalized β-like cells, quantitatively not superior to other intracellular organelles/structures, such as lysosomes and internal membranes. This result is achieved through multi-channel imaging of scattered light along with fluorescence arising from selectively-labelled ISGs. Co-localization and spatiotemporal cross-correlation analysis is performed on these signals, and compared among different cell lines. Obtained results suggest a careful re-thinking of the possibility to exploit intrinsic optical properties originating from ISGs for single-granule imaging purposes.

Mellado-Gil, José Manuel et al., HMG20A (also known as iBRAF) is a chromatin factor involved in neuronal differentiation and maturation. Recently small nucleotide polymorphisms (SNPs) in the HMG20A gene have been linked to type 2 diabetes mellitus (T2DM) yet neither expression nor function of this T2DM candidate gene in islets is known. Herein we demonstrate that HMG20A is expressed in both human and mouse islets and that levels are decreased in islets of T2DM donors as compared to islets from non-diabetic donors. In vitro studies in mouse and human islets demonstrated that glucose transiently increased HMG20A transcript levels, a result also observed in islets of gestating mice. In contrast, HMG20A expression was not altered in islets from diet-induced obese and pre-diabetic mice. The T2DM-associated rs7119 SNP, located in the 3′ UTR of the HMG20A transcript reduced the luciferase activity of a reporter construct in the human beta 1.1E7 cell line. Depletion of Hmg20a in the rat INS-1E cell line resulted in decreased expression levels of its neuronal target gene NeuroD whereas Rest and Pax4 were increased. Chromatin immunoprecipitation confirmed the interaction of HMG20A with the Pax4 gene promoter. Expression levels of Mafa, Glucokinase, and Insulin were also inhibited. Furthermore, glucose-induced insulin secretion was blunted in HMG20A-depleted islets. In summary, our data demonstrate that HMG20A expression in islet is essential for metabolism-insulin secretion coupling via the coordinated regulation of key islet-enriched genes such as NeuroD and Mafa and that depletion induces expression of genes such as Pax4 and Rest implicated in beta cell de-differentiation. More importantly we assign to the T2DM-linked rs7119 SNP the functional consequence of reducing HMG20A expression likely translating to impaired beta cell mature function., This work was supported by the Consejería de Salud, Fundación Pública Andaluza Progreso y Salud, Junta de Andalucía (PI-0727-2010 to B.R.G., PI-0085-2013 to P.I.L., PI-0006-2016 to E.F.-M. and PI-0574-2012 to S.Y.R.-Z.), the Consejería de Economía, Innovación y Ciencia (P10.CTS.6359 to B.R.G. and P09-CTS-5445 to A.C.-C.), the Ministerio de Economía y Competitividad, Instituto de Salud Carlos III co-funded by Fondos FEDER (PI10/00871 and PI13/00593 to B.R.G., and BFU2014-5343-P to J.C.R.) and the Red TerCel program (RD12/0019/0028 to B.S. and K.H.). E.F.M. is recipient of a Juan de la Cierva Incorporación Fellowship from the Ministerio de Economía y Competitividad (IJCI-2015-26238). S.Y.R.Z is a recipient of a postdoctoral fellowship from Consejería de Salud, Junta de Andalucía (RH-0070-2013). F.J.B.S. is recipient of a “Nicolás Monardes” research contract from Consejería de Salud Junta de Andalucía, (C-0070-2012). A.M.M. is supported by CP14/00105 and PI15/00134 from the Instituto de Salud Carlos III co-funded by Fondes FEDER. CIBERDEM is an initiative of the Instituto de Salud Carlos III.

SCOPUS: ar.j, info:eu-repo/semantics/published

We investigated whether improving 25-hydroxyvitamin D status in young type 1A diabetic patients reduces reactivity of peripheral blood mononuclear cells against islet autoantigens and associates with beta-cell functional changes.Eight patients with 25-hydroxyvitamin D deficiency (20 ng/ml), out of 15 consecutive young type 1A diabetic subjects received 25-hydroxyvitamin D3 to achieve and maintain levels above 50 ng/ml for up to one year. Peripheral blood mononuclear cell reactivity (Interferon-γ spots) against beta-cell autoantigens (glutamic acid decarboxylase 65-kD isoform, proinsulin and tyrosine phosphatase-like protein IA-2) and C-peptide during mixed meal were assessed before and after 25-hydroxyvitamin D3 replenishment.Target 25-hydroxyvitamin D blood levels were safely reached and maintained. Peripheral blood mononuclear cell reactivity against glutamic acid decarboxylase 65-kD isoform (3.8 ± 4.0 vs. 45 ± 16) and proinsulin (3.5 ± 3.2 vs. 75 ± 51) decreased significantly (p 0.001 and p 0.02) upon 25-hydroxyvitamin D3 replenishment, which was correlated with 25-hydroxyvitamin D concentrations. C-peptide values remained stable after one year of treatment.Safely restored and maintained 25-hydroxyvitamin D levels associated with reduced peripheral blood mononuclear cell reactivity against beta-cell autoantigens with no significant decrease of beta-cell function in this cohort of patients.

Background: Diabetes mellitus (DM) is a multifactorial disease orphan of a cure. Regenerative medicine has been proposed as novel strategy for DM therapy. Human fibroblast growth factor (FGF)-2b controls β-cell clusters via autocrine action, and human placental lactogen (hPL)-A increases functional β-cells. We hypothesized whether FGF-2b/hPL-A treatment induces β-cell differentiation from ductal/non-endocrine precursor(s) by modulating specific genes expression. Methods: Human pancreatic ductal-cells (PANC-1) and non-endocrine pancreatic cells were treated with FGF-2b plus hPL-A at 500 ng/mL. Cytofluorimetry and Immunofluorescence have been performed to detect expression of endocrine, ductal and acinar markers. Bromodeoxyuridine incorporation and annexin-V quantified cells proliferation and apoptosis. Insulin secretion was assessed by RIA kit, and electron microscopy analyzed islet-like clusters. Results: Increase in PANC-1 duct cells de-differentiation into islet-like aggregates was observed after FGF-2b/hPL-A treatment showing ultrastructure typical of islets-aggregates. These clusters, after stimulation with FGF-2b/hPL-A, had significant (p < 0.05) increase in insulin, C-peptide, pancreatic and duodenal homeobox 1 (PDX-1), Nkx2.2, Nkx6.1, somatostatin, glucagon, and glucose transporter 2 (Glut-2), compared with control cells. Markers of PANC-1 (Cytokeratin-19, MUC-1, CA19-9) were decreased (p < 0.05). These aggregates after treatment with FGF-2b/hPL-A significantly reduced levels of apoptosis. Conclusions: FGF-2b and hPL-A are promising candidates for regenerative therapy in DM by inducing de-differentiation of stem cells modulating pivotal endocrine genes.

Cytokine-induced endoplasmic reticulum (ER) stress is one of the molecular mechanisms underlying pancreatic β-cell demise in type 1 diabetes. Thrombospondin 1 (THBS1) was recently shown to promote β-cell survival during lipotoxic stress. Here we show that ER-localized THBS1 is cytoprotective to rat, mouse, andhumanβ-cells exposed to cytokines or thapsigargininduced ER stress. THBS1 confers cytoprotection by maintaining expression of mesencephalic astrocyte-derived neutrotrophic factor (MANF) in β-cells and thereby prevents the BH3-only protein BIM (BCL2-interacting mediator of cell death)-dependent triggering of the mitochondrial pathway of apoptosis. Prolonged exposure ofβ-cells to cytokines or thapsigargin leads to THBS1 and MANF degradation and loss of this prosurvival mechanism. Approaches that sustain intracellular THBS1 and MANF expression in β-cells should be explored as a cytoprotective strategy in type 1 diabetes., SCOPUS: ar.j, info:eu-repo/semantics/published

Pancreatic beta cells uniquely synthetize, store, and release insulin. Specific molecular, functional as well as ultrastructural traits characterize their insulin secretion properties and survival phentoype. In this review we focus on human islet/beta cells, and describe the changes that occur in type 2 diabetes and could play roles in the disease as well as represent possible targets for therapeutical interventions. These include transcription factors, molecules involved in glucose metabolism and insulin granule handling. Quantitative and qualitative insulin release patterns and their changes in type 2 diabetes are also associated with ultrastructural features involving the insulin granules, the mitochondria, and the endoplasmic reticulum.

Background Both types of diabetes are characterized by beta-cell failure and death, leading to insulin insufficiency. Very limited information is currently available about the ultrastructural alterations of beta cells in human diabetes. Our aim was to provide a comprehensive ultrastructural analysis of human pancreatic islets in type 1 (T1D) and type 2 (T2D) diabetic patients. Methods We performed a morphometric electron microscopy evaluation of beta cells obtained from the pancreas of 8 nondiabetic (ND), 5 T1D, and 8 T2D organ donors. Results A lower amount of beta cells was found in both T1D and T2D than in ND islets, whereas alpha cells were increased only in T2D. An increased number of bi-hormonal cells (showing both insulin and glucagon granules in their cytoplasm) were found in T1D. Insulin granules were less represented in T2D than in ND beta cells, whereas no significant changes were found in T1D. Volume density of the endoplasmic reticulum was increased in T2D and unchanged in T1D; mitochondria number and volume were significantly higher in T2D than in ND beta cells, whereas no significant differences were found in T1D. In both T1D and T2D, more beta cells showed signs of apoptosis than in ND. Conclusions Our results show that in each type of diabetes, beta cells exhibit specific ultrastructural alterations, whose better understanding might improve therapeutic strategies.

Statins are a class of drugs widely prescribed as frontline therapy for lowering plasma LDL-cholesterol in cardiovascular risk prevention. Several clinical reports have recently suggested an increased risk of type 2 diabetes associated with chronic use of these drugs. The pathophysiology of this effect remains to be fully elucidated but impaired β-cell function constitutes a potential mechanism. The aim of this study was to explore the effect of a chronic treatment with lipophilic and hydrophilic statins on β-cell function, using human pancreatic islets and rat insulin-secreting INS-1 cells; we particularly focused on the role of mitochondria and oxidative stress. The present study demonstrates, for the first time, that atorvastatin (lipophilic) but not pravastatin (hydrophilic) affected insulin release and mitochondrial metabolism due to the suppression of antioxidant defense system and induction of ROS production in pancreatic β-cell models. Mevalonate addition and treatment with a specific antioxidant (N-AcetylCysteine) effectively reversed the observed defects. These data demonstrate that mitochondrial oxidative stress is a key element in the pathogenesis of statin-related diabetes and may have clinical relevance to design strategies for prevention or reduction of statin induced β-cell dysfunction and diabetes in patients treated with lipophilic statins.

Type 2 diabetes is characterized by progressive β cell dysfunction, with lipotoxicity playing a possible pathogenetic role. Palmitate is often used to examine the direct effects of lipotoxicity and it may cause mitochondrial alterations by activating protein acetylation. However, it is unknown whether palmitate influences protein acetylation in β cells. We investigated lysine acetylation in mitochondrial proteins from INS-1E β cells (INS-1E) and in proteins from human pancreatic islets (HPI) after 24 h palmitate exposure. First, we confirmed that palmitate damages β cells and demonstrated that chemical inhibition of deacetylation also impairs INS-1E function and survival. Then, by 2-D gel electrophoresis, Western Blot and Liquid Chromatography-Mass Spectrometry we evaluated the effects of palmitate on protein acetylation. In mitochondrial preparations from palmitate-treated INS-1E, 32 acetylated spots were detected, with 13 proteins resulting over-acetylated. In HPI, 136 acetylated proteins were found, of which 11 were over-acetylated upon culture with palmitate. Interestingly, three proteins, glutamate dehydrogenase, mitochondrial superoxide dismutase, and SREBP-1, were over-acetylated in both INS-1E and HPI. Therefore, prolonged exposure to palmitate induces changes in β cell protein lysine acetylation and this modification could play a role in causing β cell damage. Dysregulated acetylation may be a target to counteract palmitate-induced β cell lipotoxicity., SCOPUS: ar.j, info:eu-repo/semantics/published

MicroRNAs are a class of negative regulators of gene expression, which have been shown to be involved in the development of endocrine pancreas and in the regulation of insulin secretion. Since type 2 diabetes (T2D) is characterized by beta cell dysfunction, we aimed at evaluating expression levels of miR-124a and miR-375, both involved in the control of beta cell function, in human pancreatic islets obtained from T2D and from age-matched non-diabetic organ donors. We analyzed miR-124a and miR-375 expression by real-time qRT-PCR in human pancreatic islets and evaluated the potential role of miR-124a by overexpressing or silencing such miRNA in MIN6 pseudoislets. We identified a major miR-124a hyperexpression in T2D human pancreatic islets with no differential expression of miR-375. Of note, miR-124a overexpression in MIN6 pseudoislets resulted in an impaired glucose-induced insulin secretion. In addition, miR-124a silencing in MIN6 pseudoislets resulted in increased expression of predicted target genes (Mtpn, Foxa2, Flot2, Akt3, Sirt1 and NeuroD1) involved in beta cell function. For Mtpn and Foxa2, we further demonstrated the actual binding of miR-124a to their 3UTR sequences by luciferase assay. We uncovered a major hyperexpression of miR-124a in T2D islets, whose silencing resulted in increased expression of target genes of major importance for beta cell function and whose overexpression impaired glucose-stimulated insulin secretion, leading to the hypothesis that an altered miR-124a expression may contribute to beta cell dysfunction in type 2 diabetes.

Zinc (Zn2+) ions are increasingly recognized as playing an important role in cellular physiology. Whereas the free Zn2+ concentration in the cytosol has been established to be 0.1-1 nM, the free Zn2+ concentration in subcellular organelles is not well-established. Here, we extend the eCALWY family of genetically encoded Forster Resonance Energy Transfer (FRET) Zn2+ probes to permit measurements in the endo(sarco)plasmic reticulum (ER) and mitochondria! matrix. Deployed in a variety of mammalian cell types, these probes reveal resting mitochondrial free [Zn2+] values of similar to 300 pM, somewhat lower than in the cytosol but 3 orders of magnitude higher than recently reported using an alternative FRET-based sensor. By contrast, free ER [Zn2+] was found to be >= 5 nM, which is >= 5000-fold higher than recently reported but consistent with the proposed role of the ER as a mobilizable Zn2+ store. Treatment of beta-cells or cardiomyocytes with sarco(endo)plasmic reticulum Ca2+-ATPase inhibitors, mobilization of ER Ca2+ after purinergic stimulation with ATP, or manipulation of ER redox, exerted no detectable effects on [Zn2+](ER). These findings question the previously proposed role of Ca2+ in Zn2+ mobilization from the ER and suggest that high ER Zn2+ levels may be an important aspect of cellular homeostasis.

Incretins such as glucagon-like peptide 1 (GLP-1) are released from the gut and potentiate insulin release in a glucose-dependent manner. Although this action is generally believed to hinge on cAMP and protein kinase A signaling, up-regulated beta cell intermediary metabolism may also play a role in incretin-stimulated insulin secretion. By employing recombinant probes to image ATP dynamically in situ within intact mouse and human islets, we sought to clarify the role of GLP-1-modulated energetics in beta cell function. Using these techniques, we show that GLP-1 engages a metabolically coupled subnetwork of beta cells to increase cytosolic ATP levels, an action independent of prevailing energy status. We further demonstrate that the effects of GLP-1 are accompanied by alterations in the mitochondrial inner membrane potential and, at elevated glucose concentration, depend upon GLP-1 receptor-directed calcium influx through voltage-dependent calcium channels. Lastly, and highlighting critical species differences, beta cells within mouse but not human islets respond coordinately to incretin stimulation. Together, these findings suggest that GLP-1 alters beta cell intermediary metabolism to influence ATP dynamics in a species-specific manner, and this may contribute to divergent regulation of the incretin-axis in rodents and man.