The miRNAs miR-211-5p and miR-204-5p modulate ER stress in human beta cells.

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.

SRp55 Regulates a Splicing Network That Controls Human Pancreatic ß-Cell Function and Survival.

Progressive failure of insulin-producing ß-cells is the central event leading to diabetes, but the signaling networks controlling ß-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 the function and survival of human ß-cells. RNA sequencing analysis revealed that SRp55 regulates the splicing of genes involved in cell survival and death, insulin secretion, and c-Jun N-terminal kinase (JNK) signaling. In particular, SRp55-mediated splicing changes modulate the function of the proapoptotic proteins BIM and BAX, JNK signaling, and endoplasmic reticulum stress, explaining why SRp55 depletion triggers ß-cell apoptosis. Furthermore, SRp55 depletion inhibits ß-cell mitochondrial function, explaining the observed decrease in insulin release. These data unveil a novel layer of regulation of human ß-cell function and survival, namely alternative splicing modulated by key splicing regulators such as SRp55, that may cross talk with candidate genes for diabetes.

Pancreatic ß-cell protection from inflammatory stress by the endoplasmic reticulum proteins thrombospondin 1 and mesencephalic astrocyte-derived neutrotrophic factor (MANF).

Cytokine-induced endoplasmic reticulum (ER) stress is one of the molecular mechanisms underlying pancreatic ß-cell demise in type 1 diabetes. Thrombospondin 1 (THBS1) was recently shown to promote ß-cell survival during lipotoxic stress. Here we show that ER-localized THBS1 is cytoprotective to rat, mouse, and human ß-cells exposed to cytokines or thapsigargin-induced ER stress. THBS1 confers cytoprotection by maintaining expression of mesencephalic astrocyte-derived neutrotrophic factor (MANF) in ß-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 of ß-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 ß-cells should be explored as a cytoprotective strategy in type 1 diabetes.

MicroRNAs miR-23a-3p, miR-23b-3p, and miR-149-5p Regulate the Expression of Proapoptotic BH3-Only Proteins DP5 and PUMA in Human Pancreatic ß-Cells.

Type 1 diabetes (T1D) is an autoimmune disease leading to ß-cell destruction. MicroRNAs (miRNAs) are small noncoding RNAs that control gene expression and organ formation. They participate in the pathogenesis of several autoimmune diseases, but the nature of miRNAs contributing to ß-cell death in T1D and their target genes remain to be clarified. We performed an miRNA expression profile on human islet preparations exposed to the cytokines IL-1ß plus IFN-γ. Confirmation of miRNA and target gene modification in human ß-cells was performed by real-time quantitative PCR. Single-stranded miRNAs inhibitors were used to block selected endogenous miRNAs. Cell death was measured by Hoechst/propidium iodide staining and activation of caspase-3. Fifty-seven miRNAs were detected as modulated by cytokines. Three of them, namely miR-23a-3p, miR-23b-3p, and miR-149-5p, were downregulated by cytokines and selected for further studies. These miRNAs were found to regulate the expression of the proapoptotic Bcl-2 proteins DP5 and PUMA and consequent human ß-cell apoptosis. These results identify a novel cross talk between a key family of miRNAs and proapoptotic Bcl-2 proteins in human pancreatic ß-cells, broadening our understanding of cytokine-induced ß-cell apoptosis in early T1D.

Ubiquitin D Regulates IRE1α/c-Jun N-terminal Kinase (JNK) Protein-dependent Apoptosis in Pancreatic Beta Cells.

Pro-inflammatory cytokines contribute to pancreatic beta cell apoptosis in type 1 diabetes at least in part by inducing endoplasmic reticulum (ER) stress and the consequent unfolded protein response (UPR). It remains to be determined what causes the transition from "physiological" to "apoptotic" UPR, but accumulating evidence indicates that signaling by the ER transmembrane protein IRE1α is critical for this transition. IRE1α activation is regulated by both intra-ER and cytosolic cues. We evaluated the role for the presently discovered cytokine-induced and IRE1α-interacting protein ubiquitin D (UBD) on the regulation of IRE1α and its downstream targets. UBD was identified by use of a MAPPIT (mammalian protein-protein interaction trap)-based IRE1α interactome screen followed by comparison against functional genomic analysis of human and rodent beta cells exposed to pro-inflammatory cytokines. Knockdown of UBD in human and rodent beta cells and detailed signal transduction studies indicated that UBD modulates cytokine-induced UPR/IRE1α activation and apoptosis. UBD expression is induced by the pro-inflammatory cytokines interleukin (IL)-1ß and interferon (IFN)-γ in rat and human pancreatic beta cells, and it is also up-regulated in beta cells of inflamed islets from non-obese diabetic mice. UBD interacts with IRE1α in human and rodent beta cells, modulating IRE1α-dependent activation of JNK and cytokine-induced apoptosis. Our data suggest that UBD provides a negative feedback on cytokine-induced activation of the IRE1α/JNK pro-apoptotic pathway in cytokine-exposed beta cells.

A combined "omics" approach identifies N-Myc interactor as a novel cytokine-induced regulator of IRE1 protein and c-Jun N-terminal kinase in pancreatic beta cells.

Type 1 diabetes is an autoimmune disease with a strong inflammatory component. The cytokines interleukin-1ß and interferon-γ contribute to beta cell apoptosis in type 1 diabetes. These cytokines induce endoplasmic reticulum stress and the unfolded protein response (UPR), contributing to the loss of beta cells. IRE1α, one of the UPR mediators, triggers insulin degradation and inflammation in beta cells and is critical for the transition from "physiological" to "pathological" UPR. The mechanisms regulating inositol-requiring protein 1α (IRE1α) activation and its signaling for beta cell "adaptation," "stress response," or "apoptosis" remain to be clarified. To address these questions, we combined mammalian protein-protein interaction trap-based IRE1α interactome and functional genomic analysis of human and rodent beta cells exposed to pro-inflammatory cytokines to identify novel cytokine-induced regulators of IRE1α. Based on this approach, we identified N-Myc interactor (NMI) as an IRE1α-interacting/modulator protein in rodent and human pancreatic beta cells. An increased expression of NMI was detected in islets from nonobese diabetic mice with insulitis and in rodent or human beta cells exposed in vitro to the pro-inflammatory cytokines interleukin-1ß and interferon-γ. Detailed mechanistic studies demonstrated that NMI negatively modulates IRE1α-dependent activation of JNK and apoptosis in rodent and human pancreatic beta cells. In conclusion, by using a combined omics approach, we identified NMI induction as a novel negative feedback mechanism that decreases IRE1α-dependent activation of JNK and apoptosis in cytokine-exposed beta cells

Viral infections and diabetes.

Type 1 diabetes mellitus (T1DM) is a multi-factorial autoimmune disease determined by the interaction of genetic, environmental and immunologic factors. One of the environmental risk factors identified by a series of independent studies is represented by viral infection, with strong evidence showing that viruses can indeed infect pancreatic beta cells with consequent effects ranging from functional damage to cell death. In this chapter we review the data obtained both in man and in experimental animal models in support of the potential participation of viral infections to Type 1 diabetes pathogenesis, with a particular emphasis on virus-triggered islet inflammation, beta-cell dysfunction and autoimmunity.

Increased expression of microRNA miR-326 in type 1 diabetic patients with ongoing islet autoimmunity.

BACKGROUND: The current paradigm that microRNAs represent a new layer of gene regulation has generated much interest in this field. MicroRNAs have emerged as important regulatory factors involved in the developmental processes and in the regulation of insulin secretion and signalling. Furthermore, recent studies revealed an altered microRNA profiling in lymphocytes of patients with autoimmune diseases like multiple sclerosis, in which a hyperexpression of miR-326 was reported. Here, we analysed the expression levels of miR-326 in peripheral blood lymphocytes from type 1 diabetic (T1D) patients in relationship with ongoing islet autoimmunity. METHODS: Peripheral blood lymphocytes were obtained from 19 T1D patients; 4/19 patients were positive for both glutamic acid decarboxylase (GAD) and islet cell antigen 512 autoantibodies; 10/19 were single GAD or IA-2 Ab positive and 5/19 were GAD antibodies and IA-2 antibodies (IA-2A) negative. Quantitative analysis of miR-326 was performed using specific stem-loop primers followed by real-time polymerase chain reaction. All values were normalized to endogenous control U6. RESULTS: miR-326 resulted increased in Ab-positive versus Ab-negative T1D subjects. Its expression levels were 2.05±0.38-fold increased in peripheral blood lymphocytes from patients expressing both GADA and IA-2A and 2.93±0.46-fold increased in single Ab-positive versus Ab-negative individuals (p<0.05). CONCLUSION: In conclusion, we have shown that miR-326 is expressed at higher levels in T1D subjects with ongoing islet autoimmunity, similar to what has been observed in multiple sclerosis, in which levels of this microRNA were highly correlated with disease severity. Interestingly, an online search of miR-326 predicted targets revealed vitamin D receptor and Erythroblastosis virus E26 oncogene homologue 1, two molecules highly involved in immune regulation.

Innate immunity and the pathogenesis of type 1 diabetes.

Type 1 diabetes mellitus is an autoimmune disease caused by the immune-mediated destruction of insulin-producing pancreatic beta cells occurring in genetically predisposed individuals, with consequent hyperglycemia and serious chronic complications. Studies in man and in experimental animal models have shown that both innate and adaptive immune responses participate to disease pathogenesis, possibly reflecting the multifactorial pathogenetic nature of this autoimmune disorder, with the likely involvement of environmental factors occurring at least in a subset of individuals. As a consequence, components of both innate and adaptive immune response should be considered as potential targets of therapeutic strategies for disease prevention and cure. Here we review the contribution of innate immune response to type 1 diabetes, with a particular emphasis to Toll-like receptors (TLR) and NK cells.

Hedgehog signaling during expansion of human pancreatic islet-derived precursors.

A detailed understanding of the molecular process involved in the proliferation of pancreatic precursor cells would provide key elements for developing new therapeutic strategies to cure type 1 diabetes. In the present study we investigated the potential involvement of hedgehog signaling in proliferating human pancreatic islet-derived mesenchymal (hPIDM) cells, a population of cells that can be successfully expanded and induced to differentiate into an insulin-secreting phenotype. Here we report that in these precursor cells a hedgehog signaling pathway is activated, as shown by Gli1 expression, and that a dose-dependent inhibition of such a pathway by cyclopamine results in a significant reduction of cell proliferation.