Novel Insights into the Global Proteome Responses of Insulin-Producing INS-1E Cells To Different Degrees of Endoplasmic Reticulum Stress

The Role of Galectin 3 in the Pathogenesis of Diabetes Mellitus: Focus on Β-Cell Function and Survival

Galectin 3 is a lectin expressed in many tissues with a significant biological role in physiological and pathological processes. Our review aims to sublimate the effects of galectin 3 on the β-cells function and survival. Data about the effect of galectin 3 on β- cells are scarce and contradictory. Several studies have shown that reduced activity of the galectin 3 gene reduces the risk of developing type 1 diabetes in an experimental model of diabetes in galectin 3 deficient mice. On the other side, in an experimental model of type 1 diabetes with mice with selectively enhanced expression of galectin 3 in β-cells, was shown that increased expression of this lectin has a protective role. Unlike type 1 diabetes where the autoimmune process plays a dominant role in pathogenesis, the pathogenesis of type 2 diabetes is multifactorial. One of the main factors which contribute to type 2 diabetes, the insulin resistance, is related to the concentration of soluble galectin 3. The effect of galectin 3 is very important for β-cell function. When a harmful factor acts on a β-cell, its intracellular concentration increases to preserve the function of β-cells and prevent their apoptosis, by blocking the internal path of apoptosis. However, excessive accumulation of galectin 3 inside the cell leads to its secretion, which encourages tissue inflammation. Based on all the above, galectin 3 has a double effect on β-cells.

Pancreatic INS-1 β-Cell Response to Thapsigargin and Rotenone: A Comparative Proteomics Analysis Uncovers Key Pathways of β-Cell Dysfunction

Insulin-secreting β-cells in the pancreatic islets are exposed to various endogenous and exogenous stressing conditions, which may lead to β-cell dysfunction or apoptosis and ultimately to diabetes mellitus. However, the detailed molecular mechanisms underlying β-cell's inability to survive under severe stresses remain to be explored. This study used two common chemical stressors, thapsigargin and rotenone, to induce endoplasmic reticulum (ER) and mitochondria stress in a rat insuloma INS-1 832/13 β-cell line, mimicking the conditions experienced by dysfunctional β-cells. Proteomic changes of cells upon treatment with stressors at IC₅₀ were profiled with TMT-based quantitative proteomics and further verified using label-free quantitive proteomics. The differentially expressed proteins under stress conditions were selected for in-depth bioinformatic analysis. Thapsigargin treatment specifically perturbed unfolded protein response (UPR) related pathways; in addition, 58 proteins not previously linked to the UPR related pathways were identified with consistent upregulation under stress induced by thapsigargin. Conversely, rotenone treatment resulted in significant proteome changes in key mitochondria regulatory pathways such as fatty acid β-oxidation, cellular respiration, citric acid cycle, and respiratory electron transport. Our data also demonstrated that both stressors increased reactive oxygen species production and depleted adenosine triphosphate synthesis, resulting in significant dysregulation of oxidative phosphorylation signaling pathways. These novel dysregulated proteins may suggest an alternative mechanism of action in β-cell dysfunction and provide potential targets for probing ER- and mitochondria stress-induced β-cell death.

HSPB1 influences mitochondrial respiration in ER-stressed beta cells

Beta-cell death and dysfunction are involved in the development of type 1 and 2 diabetes. ER-stress impairs beta-cells function resulting in pro-apoptotic stimuli that promote cell death. Hence, the identification of protective mechanisms in response to ER-stress could lead to novel therapeutic targets and insight in the pathology of these diseases. Here, we report the identification of proteins involved in dysregulated pathways upon thapsigargin treatment of MIN6 cells. Utilizing quantitative proteomics we identified upregulation of proteins involved in protein folding, unfolded protein response, redox homeostasis, proteasome processes associated with endoplasmic reticulum and downregulation of TCA cycle, cellular respiration, lipid metabolism and ribosome assembly processes associated to mitochondria and eukaryotic initiation translation factor components. Subsequently, pro-inflammatory cytokine treatment was performed to mimic pathological changes observed in beta-cells during diabetes. Cytokines induced ER stress and impaired mitochondrial function in beta-cells corroborating the results obtained with the proteomic approach. HSPB1 levels are increased by prolactin on pancreatic beta-cells and this protein is a key factor for cytoprotection although its role has not been fully elucidated. Here we show that while up-regulation of HSPB1 was able to restore the mitochondrial dysfunction induced by beta-cells' exposure to inflammatory cytokines, silencing of this chaperone abrogated the beneficial effects promoted by PRL. Taken together, our results outline the importance of HSPB1 to mitigate beta-cell dysfunction. Further studies are needed to elucidate its role in diabetes.

Extracellular Vesicles in Type 1 Diabetes: Messengers and Regulators

PURPOSE OF REVIEW

Theories about the pathogenesis of type 1 diabetes (T1D) refer to the potential of primary islet inflammatory signaling as a trigger for the loss of self-tolerance leading to disease onset. Emerging evidence suggests that extracellular vesicles (EV) may represent the missing link between inflammation and autoimmunity. Here, we review the evidence for a role of EV in the pathogenesis of T1D, as well as discuss their potential value in the clinical sphere, as biomarkers and therapeutic agents.

RECENT FINDINGS

EV derived from β cells are enriched in diabetogenic autoantigens and miRNAs that are selectively sorted and packaged. These EV play a pivotal role in antigen presentation and cell to cell communication leading to activation of autoimmune responses. Furthermore, recent evidence suggests the potential of EV as novel tools in clinical diagnostics and therapeutic interventions. In-depth analysis of EV cargo using modern multi-parametric technologies may be useful in enhancing our understanding of EV-mediated immune mechanisms and in identifying robust biomarkers and therapeutic strategies for T1D.

The role of proteomics in assessing beta-cell dysfunction and death in type 1 diabetes

Introduction: Type 1 diabetes (T1D) is characterized by autoimmune-induced dysfunction and destruction of the pancreatic beta cells. Unfortunately, this process is poorly understood, and the current best treatment for type 1 diabetes is the administration of exogenous insulin. To better understand these mechanisms and to develop new therapies, there is an urgent need for biomarkers that can reliably predict disease stage. Areas covered: Mass spectrometry (MS)-based proteomics and complementary techniques play an important role in understanding the autoimmune response, inflammation and beta-cell death. MS is also a leading technology for the identification of biomarkers. This, and the technical difficulties and new technologies that provide opportunities to characterize small amounts of sample in great depth and to analyze large sample cohorts will be discussed in this review. Expert opinion: Understanding disease mechanisms and the discovery of disease-associated biomarkers are highly interconnected goals. Ideal biomarkers would be molecules specific to the different stages of the disease process that are released from beta cells to the bloodstream. However, such molecules are likely to be present in trace amounts in the blood due to the small number of pancreatic beta cells in the human body and the heterogeneity of the target organ and disease process.

T1D Autoantibodies: room for improvement?

PURPOSE OF REVIEW

Type 1 diabetes (T1D) is now predictable by measuring major islet autoantibodies (IAbs) against insulin and other pancreatic β cells proteins including GAD65 (GADA), islet antigen 2 (IA-2A), and zinc transporter 8 (ZnT8A). The assay technology for IAbs has made great progress; however, several important aspects still need to be addressed and improved.

RECENT FINDINGS

Currently a radio-binding assay has been well established as the 'gold' standard assay for all four IAbs. New generation of nonradioactive IAb assay with electrochemiluminescence technology has been shown to further improve sensitivity and disease specificity. Recently, multiplexed assays have opened the possibility of more efficient screening in large populations. Identification of potential new autoantibodies to neo-antigens or neo-epitopes posttranslational modification is a new important field to be explored.

SUMMARY

Individuals having a single positive autoantibody are at low risk for progression to T1D, whereas individuals expressing two or more positive autoantibodies, especially on multiple tests over time, have nearly 100% risk of developing clinical T1D when followed for over two decades. More efficient and cost effective IAb assays will hopefully lead to point-of-care screening in the general population.

Dissociation of NSC606985 induces atypical ER-stress and cell death in prostate cancer cells

Castration-resistant prostate cancer (CRPC) is a major cause of prostate cancer (Pca) death. Chemotherapy is able to improve the survival of CRPC patients. We previously found that NSC606985 (NSC), a highly water-soluble camptothecin analog, induced cell death in Pca cells via interaction with topoisomerase 1 and activation of the mitochondrial apoptotic pathway. To further elucidate the role of NSC, we studied the effect of NSC on ER-stress and its association with NSC-induced cell death in Pca cells. NSC produced a time- and dose-dependent induction of GRP78, CHOP and XBP1s mRNA, and CHOP protein expression in Pca cells including DU145, indicating an activation of ER-stress. However, unlike conventional ER-stress in which GRP78 protein is increased, NSC produced a time- and dose-dependent U-shape change in GRP78 protein in DU145 cells. The NSC-induced decrease in GRP78 protein was blocked by protease inhibitors, N-acetyl-L-leucyl-L-leucylnorleucinal (ALLN), a lysosomal protease inhibitor, and epoxomicin (EPO), a ubiquitin-protease inhibitor. ALLN, but not EPO, also partially inhibited NSC-induced cell death. However, both 4-PBA and TUDCA, two chemical chaperons that effectively reduced tunicamycin-induced ER-stress, failed to attenuate NSC-induced GRP78, CHOP and XBP1s mRNA expression and cell death. Moreover, knockdown of NSC induction of CHOP expression using a specific siRNA had no effect on NSC-induced cytochrome c release and NSC-induced cell death. These results suggest that NSC produced an atypical ER-stress that is dissociated from NSC-induced activation of the mitochondrial apoptotic pathway and NSC-induced cell death in DU145 prostate cancer cells.

The beta-cell in type 1 diabetes: What have we learned from proteomic studies?

Pancreatic beta-cells have a crucial role in the regulation of blood glucose homeostasis by the production and secretion of insulin. In type 1 diabetes (T1D), an autoimmune reaction against the beta-cells together with the presence of inflammatory cytokines and ROS in the islets leads to beta-cell dysfunction and death. This review gives an overview of proteomic studies that lead to better understanding of beta-cell functioning in T1D. Protein profiling of isolated islets and beta-cell lines in health and T1D contributed to the unraveling of pathways involved in cytokine-induced cell death. In addition, by studying the serological proteome of T1D patients, new biomarkers and beta-cell autoantigens were discovered, which may improve screening tests and follow-up of T1D development. Interestingly, an important role for PTMs was demonstrated in the generation of beta-cell autoantigens. To conclude, proteomic techniques are of indispensable value to improve the knowledge on beta-cell function in T1D and the search toward therapeutic targets.

Citrullinated glucose-regulated protein 78 is an autoantigen in type 1 diabetes

Posttranslational modifications of self-proteins play a substantial role in the initiation or propagation of the autoimmune attack in several autoimmune diseases, but their contribution to type 1 diabetes is only recently emerging. In the current study, we demonstrate that inflammatory stress, induced by the cytokines interleukin-1β and interferon-γ, leads to citrullination of GRP78 in β-cells. This is coupled with translocation of this endoplasmic reticulum chaperone to the β-cell plasma membrane and subsequent secretion. Importantly, expression and activity of peptidylarginine deiminase 2, one of the five enzymes responsible for citrullination and a candidate gene for type 1 diabetes in mice, is increased in islets from diabetes-prone nonobese diabetic (NOD) mice. Finally, (pre)diabetic NOD mice have autoantibodies and effector T cells that react against citrullinated GRP78, indicating that inflammation-induced citrullination of GRP78 in β-cells generates a novel autoantigen in type 1 diabetes, opening new avenues for biomarker development and therapeutic intervention.

A proteomic approach on the effects of TX527, a 1α,25-dihydroxyvitamin D3 analog, in human T lymphocytes

1α,25-Dihydroxyvitamin D3 (1α,25(OH)2D3), and its analogs (i.e. 14,20-bis-epi-19-nor-23-yne-1α,25(OH)2D3 - TX527) have been shown to prevent autoimmunity and prolong islet graft survival in the non-obese diabetic (NOD) mouse. Their effects are mediated by their action on various immune cell types, such as dendritic cells (DC) and T cells. We have previously reported important direct effects of TX527 on human T cells, on their cytokine/chemokine profiles, T regulatory cell markers, homing characteristics and chemotaxis. In order to fully understand the molecular mechanisms underlying the beneficial properties of TX527 on human T cells, we applied here 2-dimensional difference gel electrophoresis (2-D DIGE) to analyze the global protein alterations induced by TX527 on human synchronized T cells. We detected differential expression of 64 protein spots upon TX527 treatment, of which 65.6% could be successfully identified using tandem mass spectrometry (MALDI-TOF/TOF). The identified proteins function in various processes, such as metabolism and energy pathways, cytoskeleton and protein metabolism. When comparing the proteomics data to our previously performed microarray data on the same set of cells, we found an overlap of 17 different mRNAs/proteins. For some of these (e.g. PSME2, HSPA8), the direction of regulation was not similar, hereby reinforcing the important role of post-transcriptional/translational processes in the functionality of proteins. In addition, although 2-D DIGE offers the possibility of picking up post-translational processes, it lacks the ability to detect molecules with extreme molecular weight (MW) and isoelectrical point (pI) values, or very low abundant/hydrophobic proteins. This study highlights therefore the importance of combining different experimental approaches to obtain a complete picture of the underlying mechanisms and general processes being affected in T cells upon TX527 treatment. These processes lead altogether to the generation of T cells with interesting immunomodulatory features for clinical applications in the treatment of autoimmune diseases or in the prevention of graft rejection. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Taurine may not alleviate hyperglycemia-mediated endoplasmic reticulum stress in human adipocytes

In obesity and diabetes, adipocytes show significant endoplasmic reticulum (ER) stress. Hyperglycemia-induced ER stress has not been studied in adipocyte differentiation and adipokine expression. Taurine has been known to protect the cells against ER stress. This study examined the effect of taurine on ER stress-induced adipocyte differentiation and adipokine expression to explain the therapeutic effect of taurine on diabetes and obesity. To do this, human preadipocytes were differentiated into adipocytes, in the presence or absence of taurine, under ER stress conditions. Changes in adipokine expression in adipocytes stimulated with IL-1β were investigated in the presence or absence of taurine. Human preadipocytes were treated with thapsigargin (10 nM) or high glucose concentrations (100 mM) as ER stress inducers during differentiation into adipocytes. Thapsigargin inhibited the differentiation of adipocytes in a dose-dependent manner, but the high glucose concentration treatment did not. Taurine 100 mM treatment did not block the inhibition of differentiation of preadipcytes into adipocytes. Furthermore, the high glucose concentration treatment inhibited the expression of adiponectin and increased the expression of leptin in human adipocytes. However, taurine treatment did not affect the expression of two adipokines. In conclusion, the therapeutic mechanism of taurine in diabetes and obesity does not appear to occur by alleviating hyperglycemia-mediated ER stress. To clarify the molecular mechanism by which taurine improves diabetic symptoms and obesity in animal models, the protective effect of taurine against hyperglycemia- or overnutrition-mediated ER stress should be further evaluated under various conditions or types of ER stress.

Proteome changes in auricular lymph nodes and serum after dermal sensitization to toluene diisocyanate in mice

Some reactive chemicals, such as diisocyanates, are capable of initiating an allergic response, which can lead to occupational asthma after a latency period. Clinical symptoms such as cough, wheezing, and dyspnea occur only late, making it difficult to intervene at an early stage. So far, most studies using proteomics in lung research have focused on comparisons of healthy versus diseased subjects. Here, using 2D-DIGE, we explored proteome changes in the local draining lymph nodes and serum of mice dermally sensitized once or twice with toluene-2,4-diisocyanate (TDI) before asthma is induced. In the lymph nodes, we found 38 and 58 differentially expressed proteins after one and two treatments, respectively, between TDI-treated and vehicle-treated mice. In serum, seven and 16 differentially expressed proteins were detected after one and two treatments, respectively. We identified 80-85% of the differentially expressed proteins by MS. Among them, lymphocyte-specific protein-1, coronin 1a, and hemopexin were verified by Western blotting or ELISA in an independent group of mice. This study revealed alterations in the proteomes early during sensitization in a mouse model before the onset of chemical-induced asthma. If validated in humans, these changes could lead to earlier diagnosis of TDI-exposed workers.

Posttranslational modifications of proteins in type 1 diabetes: the next step in finding the cure?

The overall role of modification of β-cell antigens in type 1 diabetes has not been elucidated and was the focus of a recent workshop on posttranslational modification of proteins in type 1 diabetes. The prevailing opinion of the workshop attendees was that novel insights into the mechanism of loss of immune tolerance might be gained and that novel diagnostic and therapeutic approaches could be developed for type 1 diabetes if protein modifications were shown to play a critical role in the disease.

Optimal elevation of β-cell 11β-hydroxysteroid dehydrogenase type 1 is a compensatory mechanism that prevents high-fat diet-induced β-cell failure

Type 2 diabetes ultimately results from pancreatic β-cell failure. Abnormally elevated intracellular regeneration of glucocorticoids by the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in fat or liver may underlie pathophysiological aspects of the metabolic syndrome. Elevated 11β-HSD1 is also found in pancreatic islets of obese/diabetic rodents and is hypothesized to suppress insulin secretion and promote diabetes. To define the direct impact of elevated pancreatic β-cell 11β-HSD1 on insulin secretion, we generated β-cell-specific, 11β-HSD1-overexpressing (MIP-HSD1) mice on a strain background prone to β-cell failure. Unexpectedly, MIP-HSD1(tg/+) mice exhibited a reversal of high fat-induced β-cell failure through augmentation of the number and intrinsic function of small islets in association with induction of heat shock, protein kinase A, and extracellular signal-related kinase and p21 signaling pathways. 11β-HSD1(-/-) mice showed mild β-cell impairment that was offset by improved glucose tolerance. The benefit of higher β-cell 11β-HSD1 exhibited a threshold because homozygous MIP-HSD1(tg/tg) mice and diabetic Lep(db/db) mice with markedly elevated β-cell 11β-HSD1 levels had impaired basal β-cell function. Optimal elevation of β-cell 11β-HSD1 represents a novel biological mechanism supporting compensatory insulin hypersecretion rather than exacerbating metabolic disease. These findings have immediate significance for current therapeutic strategies for type 2 diabetes.

The role of endoplasmic reticulum stress in autoimmune-mediated beta-cell destruction in type 1 diabetes

Unlike type 2 diabetes which is caused by the loss of insulin sensitivity, type 1 diabetes (T1D) is manifested by the absolute deficiency of insulin secretion due to the loss of β mass by autoimmune response against β-cell self-antigens. Although significant advancement has been made in understanding the pathoetiology for type 1 diabetes, the exact mechanisms underlying autoimmune-mediated β-cell destruction, however, are yet to be fully addressed. Accumulated evidence demonstrates that endoplasmic reticulum (ER) stress plays an essential role in autoimmune-mediated β-cell destruction. There is also evidence supporting that ER stress regulates the functionality of immune cells relevant to autoimmune progression during T1D development. In this paper, we intend to address the role of ER stress in autoimmune-mediated β-cell destruction during the course of type 1 diabetes. The potential implication of ER stress in modulating autoimmune response will be also discussed. We will further dissect the possible pathways implicated in the induction of ER stress and summarize the potential mechanisms underlying ER stress for mediation of β-cell destruction. A better understanding of the role for ER stress in T1D pathoetiology would have great potential aimed at developing effective therapeutic approaches for the prevention/intervention of this devastating disorder.