Multi-omics analysis reveals drivers of loss of ß-cell function after newly diagnosed autoimmune type 1 diabetes: An INNODIA multicenter study.

AIMS: Heterogeneity in the rate of ß-cell loss in newly diagnosed type 1 diabetes patients is poorly understood and creates a barrier to designing and interpreting disease-modifying clinical trials. Integrative analyses of baseline multi-omics data obtained after the diagnosis of type 1 diabetes may provide mechanistic insight into the diverse rates of disease progression after type 1 diabetes diagnosis. METHODS: We collected samples in a pan-European consortium that enabled the concerted analysis of five different omics modalities in data from 97 newly diagnosed patients. In this study, we used Multi-Omics Factor Analysis to identify molecular signatures correlating with post-diagnosis decline in ß-cell mass measured as fasting C-peptide. RESULTS: Two molecular signatures were significantly correlated with fasting C-peptide levels. One signature showed a correlation to neutrophil degranulation, cytokine signalling, lymphoid and non-lymphoid cell interactions and G-protein coupled receptor signalling events that were inversely associated with a rapid decline in ß-cell function. The second signature was related to translation and viral infection was inversely associated with change in ß-cell function. In addition, the immunomics data revealed a Natural Killer cell signature associated with rapid ß-cell decline. CONCLUSIONS: Features that differ between individuals with slow and rapid decline in ß-cell mass could be valuable in staging and prediction of the rate of disease progression and thus enable smarter (shorter and smaller) trial designs for disease modifying therapies as well as offering biomarkers of therapeutic effect.

Intra-islet insulin synthesis defects are associated with endoplasmic reticulum stress and loss of beta cell identity in human diabetes.

AIMS/HYPOTHESIS: Endoplasmic reticulum (ER) stress and beta cell dedifferentiation both play leading roles in impaired insulin secretion in overt type 2 diabetes. Whether and how these factors are related in the natural history of the disease remains, however, unclear. METHODS: In this study, we analysed pancreas biopsies from a cohort of metabolically characterised living donors to identify defects in in situ insulin synthesis and intra-islet expression of ER stress and beta cell phenotype markers. RESULTS: We provide evidence that in situ altered insulin processing is closely connected to in vivo worsening of beta cell function. Further, activation of ER stress genes reflects the alteration of insulin processing in situ. Using a combination of 17 different markers, we characterised individual pancreatic islets from normal glucose tolerant, impaired glucose tolerant and type 2 diabetic participants and reconstructed disease progression. CONCLUSIONS/INTERPRETATION: Our study suggests that increased beta cell workload is accompanied by a progressive increase in ER stress with defects in insulin synthesis and loss of beta cell identity.

Angiotensin I-converting enzyme type 2 expression is increased in pancreatic islets of type 2 diabetic donors.

AIMS: Angiotensin I-converting enzyme type 2 (ACE2), a pivotal SARS-CoV-2 receptor, has been shown to be expressed in multiple cells, including human pancreatic beta-cells. A putative bidirectional relationship between SARS-CoV-2 infection and diabetes has been suggested, confirming the hypothesis that viral infection in beta-cells may lead to new-onset diabetes or worse glycometabolic control in diabetic patients. However, whether ACE2 expression levels are altered in beta-cells of diabetic patients has not yet been investigated. Here, we aimed to elucidate the in situ expression pattern of ACE2 in Type 2 diabetes (T2D) with respect to non-diabetic donors which may account for a higher susceptibility to SARS-CoV-2 infection in beta-cells. MATERIAL AND METHODS: Angiotensin I-converting enzyme type 2 immunofluorescence analysis using two antibodies alongside insulin staining was performed on formalin-fixed paraffin embedded pancreatic sections obtained from n = 20 T2D and n = 20 non-diabetic (ND) multiorgan donors. Intensity and colocalisation analyses were performed on a total of 1082 pancreatic islets. Macrophage detection was performed using anti-CD68 immunohistochemistry on serial sections from the same donors. RESULTS: Using two different antibodies, ACE2 expression was confirmed in beta-cells and in pancreas microvasculature. Angiotensin I-converting enzyme type 2 expression was increased in pancreatic islets of T2D donors in comparison to ND controls alongside with a higher colocalisation rate between ACE2 and insulin using both anti-ACE2 antibodies. CD68+ cells tended to be increased in T2D pancreata, in line with higher ACE2 expression observed in serial sections. CONCLUSIONS: Higher ACE2 expression in T2D islets might increase their susceptibility to SARS-CoV-2 infection during COVID-19 in T2D patients, thus worsening glycometabolic outcomes and disease severity.

Crosstalk between MicroRNA and Oxidative Stress in Physiology and Pathology 2.0.

MicroRNAs (miRNAs) are a class of small non-coding RNAs around 22 nucleotides long that regulate gene expression by binding specific sequences within target messenger RNA (mRNA) [...].

Identification and Validation of miR-222-3p and miR-409-3p as Plasma Biomarkers in Gestational Diabetes Mellitus Sharing Validated Target Genes Involved in Metabolic Homeostasis.

Gestational diabetes mellitus (GDM) causes both maternal and fetal adverse outcomes. The deregulation of microRNAs (miRNAs) in GDM suggests their involvement in GDM pathogenesis and complications. Exosomes are extracellular vesicles (EVs) of endosomal origin, released via exocytosis into the extracellular compartment. Through EVs, miRNAs are delivered in distant target cells and are able to affect gene expression. In this study, miRNA expression was analyzed to find new miRNAs that could improve GDM classification and molecular characterization. MiRNA were profiled in total plasma and EVs in GDM patients and normal glucose tolerance (NGT) women. Samples were collected at third trimester of gestation from two diabetes centers. MiRNA expression was profiled in a discovery cohort using the multiplexed NanoString nCounter Human v3 miRNA. Validation analysis was performed in a second independent cohort using RT-qPCR. A set of miRNAs resulted to be differentially expressed (DE) in total plasma and EVs in GDM. Among them, total plasma miR-222-3p and miR-409-3p were validated in the independent cohort. MiR-222-3p levels correlated with fasting plasma glucose (FPG) (p < 0.001) and birth weight (p = 0.012), whereas miR-409-3p expression correlated with FPG (p < 0.001) and inversely with gestational age (p = 0.001). The major validated target genes of the deregulated miRNAs were consistently linked to type 2 diabetes and GDM pathophysiology. MiR-222-3p and miR-409-3p are two circulating biomarkers that could improve GDM classification power and act in the context of the molecular events leading to the metabolic alterations observed in GDM.

Immunoregulated insulitis and slow-progressing type 1 diabetes after duodenopancreatectomy.

AIMS/HYPOTHESIS: We report the case of a woman who underwent a partial pancreatectomy for a serous cystadenoma when aged 56 years. She had been diagnosed with diabetes 6 years before and had Hashimoto's thyroiditis. Despite positive anti-GAD autoantibodies (GADA) and previous surgery, she was transiently weaned off long-acting insulin. Blood glucose levels remained well controlled with low-dose long-acting insulin. Insulin needs eventually increased 8 years after surgery, in conjunction with anti-zinc transporter 8 (ZnT8) seroconversion and decreasing residual C-peptide. We hypothesised that the surgical pancreas specimens and blood autoimmune T cell responses may provide correlates of this indolent clinical course. METHODS: Beta and alpha cell area and insulitis were quantified on pancreas head tissue sections obtained at surgery. Blood T cell responses against beta cell antigens were analysed by enzyme-linked immunospot. RESULTS: Pancreas sections displayed reduced beta cell and normal alpha cell area (0.27% and 0.85% of section area, respectively). High-grade insulitis was observed, mostly in insulin-containing islets, with a peri-insulitis pattern enriched in T cells positive for regulatory forkhead box protein 3 (FOXP3). In vitro challenge with beta cell antigens of circulating T cells collected 4 and 9 years after surgery revealed dominant and persistent IL-10 responses; IFN-γ responses increasing at 9 years, after anti-ZnT8 seroconversion, was observed. CONCLUSIONS/INTERPRETATION: Despite persistent GADA and the histopathological finding of insulitis and decreased beta cell area 6 years after diabetes diagnosis, glycaemic control was maintained with low-dose insulin up to 8 years after surgery. Regulated T cell responses towards beta cell antigens and FOXP3-positive peri-insulitis suggest spontaneous long-term regulation of islet autoimmunity after substantial beta cell loss, and eventual autoimmune progression upon anti-ZnT8 seroconversion.

Regulatory T cell monitoring in severe eosinophilic asthma patients treated with mepolizumab.

Severe eosinophilic asthma (SEA) has been associated with T-helper type 2 (Th2) inflammatory response. A good understanding of T cell functions in asthma is important for therapy, especially in the choice of biological treatments for severe cases. Mepolizumab, an IL-5 antagonist, is indicated for the treatment of severe asthma. Regulatory T cells (Tregs) suppress inflammation by secreting cytokines that inhibit Th2 cell proliferation. We investigated peripheral Treg, CD4, CD8, CD19 and NK cell percentages and their relationship to clinical and functional parameters, including peripheral eosinophils, before and after anti-IL5 treatment. Subjects were 14 adult SEA patients (9 male, 54.1 ± 11.6 years), treated with mepolizumab, and 10 controls. T cells (CD4 and CD8), CD19, NK and Tregs were evaluated by flow cytometry. Comparison of lung function parameters before and after treatment with mepolizumab (T0 and T1) showed an increase in FEV1, FEV1/FVC ratio and a reduction in blood eosinophil percentages. CD8 and CD16/56+ CD3+ were significantly higher in SEA patients than controls (P = .04 and P = .03, respectively). A decrease in CD45+, CD8 + and CD16/56+ CD3+ cell percentages was observed between T0 and T1 (P = .02, P = .04, P = .03, respectively). A significant increase in Treg percentages (P = .0001) was recorded between T0 and T1. Mepolizumab therapy was found to modulate immune response, restoring immune balance in patients with SEA.

The Landscape of microRNAs in ßCell: Between Phenotype Maintenance and Protection.

Diabetes mellitus is a group of heterogeneous metabolic disorders characterized by chronic hyperglycaemia mainly due to pancreatic ß cell death and/or dysfunction, caused by several types of stress such as glucotoxicity, lipotoxicity and inflammation. Different patho-physiological mechanisms driving ß cell response to these stresses are tightly regulated by microRNAs (miRNAs), a class of negative regulators of gene expression, involved in pathogenic mechanisms occurring in diabetes and in its complications. In this review, we aim to shed light on the most important miRNAs regulating the maintenance and the robustness of ß cell identity, as well as on those miRNAs involved in the pathogenesis of the two main forms of diabetes mellitus, i.e., type 1 and type 2 diabetes. Additionally, we acknowledge that the understanding of miRNAs-regulated molecular mechanisms is fundamental in order to develop specific and effective strategies based on miRNAs as therapeutic targets, employing innovative molecules.

Non-Coding RNAs: Novel Players in Insulin Resistance and Related Diseases.

The rising prevalence of metabolic diseases related to insulin resistance (IR) have stressed the urgent need of accurate and applicable tools for early diagnosis and treatment. In the last decade, non-coding RNAs (ncRNAs) have gained growing interest because of their potential role in IR modulation. NcRNAs are variable-length transcripts which are not translated into proteins but are involved in gene expression regulation. Thanks to their stability and easy detection in biological fluids, ncRNAs have been investigated as promising diagnostic and therapeutic markers in metabolic diseases, such as type 2 diabetes mellitus (T2D), obesity and non-alcoholic fatty liver disease (NAFLD). Here we review the emerging role of ncRNAs in the development of IR and related diseases such as obesity, T2D and NAFLD, and summarize current evidence concerning their potential clinical application.

Circulating microRNAs Signature for Predicting Response to GLP1-RA Therapy in Type 2 Diabetic Patients: A Pilot Study.

Type 2 diabetes (T2D) represents one of the major health issues of this century. Despite the availability of an increasing number of anti-hyperglycemic drugs, a significant proportion of patients are inadequately controlled, thus highlighting the need for novel biomarkers to guide treatment selection. MicroRNAs (miRNAs) are small non-coding RNAs, proposed as useful diagnostic/prognostic markers. The aim of our study was to identify a miRNA signature occurring in responders to glucagon-like peptide 1 receptor agonists (GLP1-RA) therapy. We investigated the expression profile of eight T2D-associated circulating miRNAs in 26 prospectively evaluated diabetic patients in whom GLP1-RA was added to metformin. As expected, GLP1-RA treatment induced significant reductions of HbA1c and body weight, both after 6 and 12 months of therapy. Of note, baseline expression levels of the selected miRNAs revealed two distinct patient clusters: "high expressing" and "low expressing". Interestingly, a significantly higher percentage of patients in the high expression group reached the glycemic target after 12 months of treatment. Our findings suggest that the evaluation of miRNA expression could be used to predict the likelihood of an early treatment response to GLP1-RA and to select patients in whom to start such treatment, paving the way to a personalized medicine approach.

miR-409-3p is reduced in plasma and islet immune infiltrates of NOD diabetic mice and is differentially expressed in people with type 1 diabetes.

AIMS/HYPOTHESIS: MicroRNAs (miRNAs) are a novel class of potential biomarkers emerging in many diseases, including type 1 diabetes. Here, we aim to analyse a panel of circulating miRNAs in non-obese diabetic (NOD) mice and individuals with type 1 diabetes. METHODS: We adopted standardised methodologies for extracting miRNAs from small sample volumes to evaluate a profiling panel of mature miRNAs in paired plasma and laser-captured microdissected immune-infiltrated islets of recently diabetic and normoglycaemic NOD mice. Moreover, we validated the findings during disease progression and remission after anti-CD3 therapy in NOD mice, as well as in individuals with type 1 diabetes. RESULTS: Plasma levels of five miRNAs were downregulated in diabetic vs normoglycaemic mice. Of those, miR-409-3p was also downregulated in situ in the immune islet infiltrates of diabetic mice, suggesting an association with disease pathogenesis. Target-prediction tools linked miR-409-3p to immune- and metabolism-related signalling molecules. In situ miR-409-3p expression correlated with insulitis severity, and CD8+ central memory T cells were found to be enriched in miR-409-3p. Plasma miR-409-3p levels gradually decreased during diabetes development and improved with disease remission after anti-CD3 antibody therapy. Finally, plasma miR-409-3p levels were lower in people recently diagnosed with type 1 diabetes compared with a non-diabetic control group, and levels were inversely correlated with HbA1c levels. CONCLUSIONS/INTERPRETATION: We propose that miR-409-3p may represent a new circulating biomarker of islet inflammation and type 1 diabetes severity.

From immunohistological to anatomical alterations of human pancreas in type 1 diabetes: New concepts on the stage.

The histological analysis of human pancreatic samples in type 1 diabetes (T1D) has been proven essential to move forward in the evaluation of in situ events characterizing T1D. Increasing availability of pancreatic tissues collected from diabetic multiorgan donors by centralized biorepositories, which have shared tissues among researchers in the field, has allowed a deeper understanding of T1D pathophysiology, using novel immunohistological and high-throughput methods. In this review, we provide a comprehensive update of the main recent advancements in the characterization of cellular and molecular events involving endocrine and exocrine pancreas as well as the immune system in the onset and progression of T1D. Additionally, we underline novel elements, which provide evidence that T1D pathological changes affect not only islet ß-cells but also the entire pancreas.

Crosstalk between MicroRNA and Oxidative Stress in Physiology and Pathology.

MicroRNAs (miRNA), are short regulatory RNA molecules that regulate gene expression by binding specific sequences within target messenger RNA (mRNA) [...].

MicroRNA Expression in the Aqueous Humor of Patients with Diabetic Macular Edema.

We identified and compared secreted microRNA (miRNA) expression in aqueous humor (AH) and plasma samples among patients with: type 2 diabetes mellitus (T2D) complicated by non-proliferative diabetic retinopathy (DR) associated with diabetic macular edema (DME) (DME group: 12 patients); T2D patients without DR (D group: 8 patients); and non-diabetic patients (CTR group: 10 patients). Individual patient AH samples from five subjects in each group were profiled on TaqMan Low Density MicroRNA Array Cards. Differentially expressed miRNAs identified from profiling were then validated in single assay for all subjects. The miRNAs validated in AH were then evaluated in single assay in plasma. Gene Ontology (GO) analysis was conducted. From AH profiling, 119 mature miRNAs were detected: 86 in the DME group, 113 in the D group and 107 in the CTR group. miRNA underexpression in the DME group was confirmed in single assay for let-7c-5p, miR-200b-3p, miR-199a-3p and miR-365-3p. Of these four, miR-199a-3p and miR-365-3p were downregulated also in the plasma of the DME group. GO highlighted 54 validated target genes of miR-199a-3p, miR-200b-3p and miR-365-3p potentially implied in DME pathogenesis. Although more studies are needed, miR-200b-3p, let-7c-5p, miR-365-3p and miR-199a-3p represent interesting molecules in the study of DME pathogenesis.

Molecular Dysfunction and Phenotypic Derangement in Diabetic Cardiomyopathy.

The high incidence and poor prognosis of heart failure (HF) patients affected with diabetes (DM) is in part related to a specific cardiac remodeling currently recognized as diabetic cardiomyopathy (DCM). This cardiac frame occurs regardless of the presence of coronary artery diseases (CAD) and it can account for 15-20% of the total diabetic population. The pathogenesis of DCM remains controversial, and several molecular and cellular alterations including myocardial hypertrophy, interstitial fibrosis, oxidative stress and vascular inflammation, have been postulated. The main cardio-vascular alterations associated with hyperglycemia comprise endothelial dysfunction, adverse effects of circulating free fatty acids (FFA) and increased systemic inflammation. High glucose concentrations lead to a loss of mitochondrial networks, increased reactive oxygen species (ROS), endothelial nitric oxide synthase (eNOS) activation and a reduction in cGMP production related to protein kinase G (PKG) activity. Current mechanisms enhance the collagen deposition with subsequent increased myocardial stiffness. Several concerns regarding the exact role of DCM in HF development such as having an appearance as either dilated or as a concentric phenotype and whether diabetes could be considered a causal factor or a comorbidity in HF, remain to be clarified. In this review, we sought to explain the different DCM subtypes and the underlying pathophysiological mechanisms. Therefore, the traditional and new molecular and signal alterations and their relationship with macroscopic structural abnormalities are described.

Targeting microRNAs as a Therapeutic Strategy to Reduce Oxidative Stress in Diabetes.

Diabetes mellitus is a group of heterogeneous metabolic disorders characterized by chronic hyperglycaemia as a consequence of pancreatic ß cell loss and/or dysfunction, also caused by oxidative stress. The molecular mechanisms involved inß cell dysfunction and in response to oxidative stress are also regulated by microRNAs (miRNAs). miRNAs are a class of negative gene regulators, which modulate pathologic mechanisms occurring in diabetes and its complications. Although several pharmacological therapies specifically targeting miRNAs have already been developed and brought to the clinic, most previous miRNA-based drug delivery methods were unable to target a specific miRNA in a single cell type or tissue, leading to important off-target effects. In order to overcome these issues, aptamers and nanoparticles have been described as non-cytotoxic vehicles for miRNA-based drug delivery. These approaches could represent an innovative way to specifically target and modulate miRNAs involved in oxidative stress in diabetes and its complications. Therefore, the aims of this review are: (i) to report the role of miRNAs involved in oxidative stress in diabetes as promising therapeutic targets; (ii) to shed light onto the new delivery strategies developed to modulate the expression of miRNAs in diseases.

Unexpected subcellular distribution of a specific isoform of the Coxsackie and adenovirus receptor, CAR-SIV, in human pancreatic beta cells.

AIMS/HYPOTHESIS: The Coxsackie and adenovirus receptor (CAR) is a transmembrane cell-adhesion protein that serves as an entry receptor for enteroviruses and may be essential for their ability to infect cells. Since enteroviral infection of beta cells has been implicated as a factor that could contribute to the development of type 1 diabetes, it is often assumed that CAR is displayed on the surface of human beta cells. However, CAR exists as multiple isoforms and it is not known whether all isoforms subserve similar physiological functions. In the present study, we have determined the profile of CAR isoforms present in human beta cells and monitored the subcellular localisation of the principal isoform within the cells. METHODS: Formalin-fixed, paraffin-embedded pancreatic sections from non-diabetic individuals and those with type 1 diabetes were studied. Immunohistochemistry, confocal immunofluorescence, electron microscopy and western blotting with isoform-specific antisera were employed to examine the expression and cellular localisation of the five known CAR isoforms. Isoform-specific qRT-PCR and RNA sequencing (RNAseq) were performed on RNA extracted from isolated human islets. RESULTS: An isoform of CAR with a terminal SIV motif and a unique PDZ-binding domain was expressed at high levels in human beta cells at the protein level. A second isoform, CAR-TVV, was also present. Both forms were readily detected by qRT-PCR and RNAseq analysis in isolated human islets. Immunocytochemical studies indicated that CAR-SIV was the principal isoform in islets and was localised mainly within the cytoplasm of beta cells, rather than at the plasma membrane. Within the cells it displayed a punctate pattern of immunolabelling, consistent with its retention within a specific membrane-bound compartment. Co-immunofluorescence analysis revealed significant co-localisation of CAR-SIV with zinc transporter protein 8 (ZnT8), prohormone convertase 1/3 (PC1/3) and insulin, but not proinsulin. This suggests that CAR-SIV may be resident mainly in the membranes of insulin secretory granules. Immunogold labelling and electron microscopic analysis confirmed that CAR-SIV was localised to dense-core (insulin) secretory granules in human islets, whereas no immunolabelling of the protein was detected on the secretory granules of adjacent exocrine cells. Importantly, CAR-SIV was also found to co-localise with protein interacting with C-kinase 1 (PICK1), a protein recently demonstrated to play a role in insulin granule maturation and trafficking. CONCLUSIONS/INTERPRETATION: The SIV isoform of CAR is abundant in human beta cells and is localised mainly to insulin secretory granules, implying that it may be involved in granule trafficking and maturation. We propose that this subcellular localisation of CAR-SIV contributes to the unique sensitivity of human beta cells to enteroviral infection.

MicroRNAs as Regulators of Insulin Signaling: Research Updates and Potential Therapeutic Perspectives in Type 2 Diabetes.

The insulin signaling pathway is composed of a large number of molecules that positively or negatively modulate insulin specific signal transduction following its binding to the cognate receptor. Given the importance of the final effects of insulin signal transduction, it is conceivable that many regulators are needed in order to tightly control the metabolic or proliferative functional outputs. MicroRNAs (miRNAs) are small non-coding RNA molecules that negatively modulate gene expression through their specific binding within the 3'UTR sequence of messenger RNA (mRNA), thus causing mRNA decoy or translational inhibition. In the last decade, miRNAs have been addressed as pivotal cellular rheostats which control many fundamental signaling pathways, including insulin signal transduction. Several studies demonstrated that multiple alterations of miRNAs expression or function are relevant for the development of insulin resistance in type 2 diabetes (T2D); such alterations have been highlighted in multiple insulin target organs including liver, muscles, and adipose tissue. Indirectly, miRNAs have been identified as modulators of inflammation-derived insulin resistance, by controlling/tuning the activity of innate immune cells in insulin target tissues. Here, we review main findings on miRNA functions as modulators of insulin signaling in physiologic- or in T2D insulin resistance- status. Additionally, we report the latest hypotheses of prospective therapies involving miRNAs as potential targets for future drugs in T2D.

MicroRNA Expression Analysis of In Vitro Dedifferentiated Human Pancreatic Islet Cells Reveals the Activation of the Pluripotency-Related MicroRNA Cluster miR-302s.

ß-cell dedifferentiation has been recently suggested as an additional mechanism contributing to type-1 and to type-2 diabetes pathogenesis. Moreover, several studies demonstrated that in vitro culture of native human pancreatic islets derived from non-diabetic donors resulted in the generation of an undifferentiated cell population. Additional evidence from in vitro human ß-cell lineage tracing experiments, demonstrated that dedifferentiated cells derive from ß-cells, thus representing a potential in vitro model of ß-cell dedifferentiation. Here, we report the microRNA expression profiles analysis of in vitro dedifferentiated islet cells in comparison to mature human native pancreatic islets. We identified 13 microRNAs upregulated and 110 downregulated in islet cells upon in vitro dedifferentiation. Interestingly, among upregulated microRNAs, we observed the activation of microRNA miR-302s cluster, previously defined as pluripotency-associated. Bioinformatic analysis indicated that miR-302s are predicted to target several genes involved in the control of ß-cell/epithelial phenotype maintenance; accordingly, such genes were downregulated upon human islet in vitro dedifferentiation. Moreover, we uncovered that cell-cell contacts are needed to maintain low/null expression levels of miR-302. In conclusion, we showed that miR-302 microRNA cluster genes are involved in in vitro dedifferentiation of human pancreatic islet cells and inhibits the expression of multiple genes involved in the maintenance of ß-cell mature phenotype.

Mast cells infiltrate pancreatic islets in human type 1 diabetes.

AIMS/HYPOTHESIS: Beta cell destruction in human type 1 diabetes occurs through the interplay of genetic and environmental factors, and is mediated by immune cell infiltration of pancreatic islets. In this study, we explored the role of mast cells as an additional agent in the pathogenesis of type 1 diabetes insulitis. METHODS: Pancreatic tissue from donors without diabetes and with type 1 and 2 diabetes was studied using different microscopy techniques to identify islet-infiltrating cells. The direct effects of histamine exposure on isolated human islets and INS-1E cells were assessed using cell-survival studies and molecular mechanisms. RESULTS: A larger number of mast cells were found to infiltrate pancreatic islets in samples from donors with type 1 diabetes, compared with those from donors without diabetes or with type 2 diabetes. Evidence of mast cell degranulation was observed, and the extent of the infiltration correlated with beta cell damage. Histamine, an amine that is found at high levels in mast cells, directly contributed to beta cell death in isolated human islets and INS-1E cells via a caspase-independent pathway. CONCLUSIONS/INTERPRETATION: These findings suggest that mast cells might be responsible, at least in part, for immune-mediated beta cell alterations in human type 1 diabetes. If this is the case, inhibition of mast cell activation and degranulation might act to protect beta cells in individuals with type 1 diabetes.