Mitochondrial Networking Protects β-Cells From Nutrient-Induced Apoptosis

OBJECTIVE: Previous studies have reported that β-cell mitochondria exist as discrete organelles that exhibit heterogeneous bioenergetic capacity. To date, networking activity, and its role in mediating β-cell mitochondrial morphology and function, remains unclear. In this article, we investigate β-cell mitochondrial fusion and fission in detail and report alterations in response to various combinations of nutrients. RESEARCH DESIGN AND METHODS: Using matrix-targeted photoactivatable green fluorescent protein, mitochondria were tagged and tracked in β-cells within intact islets, as isolated cells and as cell lines, revealing frequent fusion and fission events. Manipulations of key mitochondrial dynamics proteins OPA1, DRP1, and Fis1 were tested for their role in β-cell mitochondrial morphology. The combined effects of free fatty acid and glucose on β-cell survival, function, and mitochondrial morphology were explored with relation to alterations in fusion and fission capacity. RESULTS: β-Cell mitochondria are constantly involved in fusion and fission activity that underlies the overall morphology of the organelle. We find that networking activity among mitochondria is capable of distributing a localized green fluorescent protein signal throughout an isolated β-cell, a β-cell within an islet, and an INS1 cell. Under noxious conditions, we find that β-cell mitochondria become fragmented and lose their ability to undergo fusion. Interestingly, manipulations that shift the dynamic balance to favor fusion are able to prevent mitochondrial fragmentation, maintain mitochondrial dynamics, and prevent apoptosis. CONCLUSIONS: These data suggest that alterations in mitochondrial fusion and fission play a critical role in nutrient-induced β-cell apoptosis and may be involved in the pathophysiology of type 2 diabetes.National Institutes of Health (R01HL071629-03, R01DK074778, 5T32DK007201

Lipopolysaccharides Impair Insulin Gene Expression in Isolated Islets of Langerhans via Toll-Like Receptor-4 and NF-κB Signalling

BACKGROUND:Type 2 diabetes is characterized by pancreatic β-cell dysfunction and is associated with low-grade inflammation. Recent observations suggest that the signalling cascade activated by lipopolysaccharides (LPS) binding to Toll-Like Receptor 4 (TLR4) exerts deleterious effects on pancreatic β-cell function; however, the molecular mechanisms of these effects are incompletely understood. In this study, we tested the hypothesis that LPS alters insulin gene expression via TLR4 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in islets. METHODOLOGY/PRINCIPAL FINDINGS:A 24-h exposure of isolated human, rat and mouse islets of Langerhans to LPS dose-dependently reduced insulin gene expression. This was associated in mouse and rat islets with decreased mRNA expression of pancreas-duodenum homebox-1 (PDX-1) and mammalian homologue of avian MafA/l-Maf (MafA). Accordingly, LPS exposure also decreased glucose-induced insulin secretion. LPS repression of insulin, PDX-1 and MafA expression, as well as its inhibition of insulin secretion, were not observed in islets from TLR4-deficient mice. LPS inhibition of β-cell gene expression in rat islets was prevented by inhibition of the NF-κB pathway, but not the p38 mitogen-activated protein kinase (p38 MAPK) pathway. CONCLUSIONS/SIGNIFICANCE:Our findings demonstrate that LPS inhibit β-cell gene expression in a TLR4-dependent manner and via NF-κB signaling in pancreatic islets, suggesting a novel mechanism by which the gut microbiota might affect pancreatic β-cell function

Whole-body imaging of the musculoskeletal system: the value of MR imaging

In clinical practice various modalities are used for whole-body imaging of the musculoskeletal system, including radiography, bone scintigraphy, computed tomography, magnetic resonance imaging (MRI), and positron emission tomography-computed tomography (PET-CT). Multislice CT is far more sensitive than radiographs in the assessment of trabecular and cortical bone destruction and allows for evaluation of fracture risk. The introduction of combined PET-CT scanners has markedly increased diagnostic accuracy for the detection of skeletal metastases compared with PET alone. The unique soft-tissue contrast of MRI enables for precise assessment of bone marrow infiltration and adjacent soft tissue structures so that alterations within the bone marrow may be detected before osseous destruction becomes apparent in CT or metabolic changes occur on bone scintigraphy or PET scan. Improvements in hard- and software, including parallel image acquisition acceleration, have made high resolution whole-body MRI clinically feasible. Whole-body MRI has successfully been applied for bone marrow screening of metastasis and systemic primary bone malignancies, like multiple myeloma. Furthermore, it has recently been proposed for the assessment of systemic bone diseases predisposing for malignancy (e.g., multiple cartilaginous exostoses) and muscle disease (e.g., muscle dystrophy). The following article gives an overview on state-of-the-art whole-body imaging of the musculoskeletal system and highlights present and potential future applications, especially in the field of whole-body MRI

Hepatitis C Virus Induced a Novel Apoptosis-Like Death of Pancreatic Beta Cells through a Caspase 3-Dependent Pathway

Epidemiological and experimental studies have suggested that Hepatitis C virus (HCV) infection is associated with the development of type 2 diabetes. Pancreatic beta cell failure is central to the progression of type 2 diabetes. Using virus infection system, we investigate the influence of HCV infection on the fate of the insulinoma cell line, MIN6. Our experiments demonstrate that the HCV virion itself is indispensable and has a dose- and time-dependent cytopathic effect on the cells. HCV infection inhibits cell proliferation and induces death of MIN6 cells with apoptotic characteristics, including cell surface exposure of phosphatidylserine, decreased mitochondrial membrane potential, activation of caspase 3 and poly (ADP-ribose) polymerase, and DNA fragmentation in the nucleus. However, the fact that HCV-infected cells exhibit a dilated, low-density nucleus with intact plasma and nuclear membrane indicates that a novel apoptosis-like death occurs. HCV infection also causes endoplasmic reticulum (ER) stress. Further, HCV RNA replication was detected in MIN6 cells, although the infection efficiency is very low and no progeny virus particle generates. Taken together, our data suggest that HCV infection induces death of pancreatic beta cells through an ER stress-involved, caspase 3-dependent, special pathway

Microbial Diversity in the Midguts of Field and Lab-Reared Populations of the European Corn Borer Ostrinia nubilalis

Background: Insects are associated with microorganisms that contribute to the digestion and processing of nutrients. The European Corn Borer (ECB) is a moth present world-wide, causing severe economical damage as a pest on corn and other crops. In the present work, we give a detailed view of the complexity of the microorganisms forming the ECB midgut microbiota with the objective of comparing the biodiversity of the midgut-associated microbiota and explore their potential as a source of genes and enzymes with biotechnological applications. Methodological/Principal Findings: A high-throughput sequencing approach has been used to identify bacterial species, genes and metabolic pathways, particularly those involved in plant-matter degradation, in two different ECB populations (field-collected vs. lab-reared population with artificial diet). Analysis of the resulting sequences revealed the massive presence of Staphylococcus warneri and Weissella paramesenteroides in the lab-reared sample. This enabled us to reconstruct both genomes almost completely. Despite the apparently low diversity, 208 different genera were detected in the sample, although most of them at very low frequency. By contrast, the natural population exhibited an even higher taxonomic diversity along with a wider array of cellulolytic enzyme families. However, in spite of the differences in relative abundance of major taxonomic groups, not only did both metagenomes share a similar functional profile but also a similar distribution of non-redundant genes in different functional categories. Conclusions/Significance: Our results reveal a highly diverse pool of bacterial species in both O. nubilalis populations, with major differences: The lab-reared sample is rich in gram-positive species (two of which have almost fully sequenced genomes) while the field sample harbors mainly gram-negative species and has a larger set of cellulolytic enzymes. We have found a clear relationship between the diet and the midgut microbiota, which reveals the selection pressure of food on the community of intestinal bacteria. © 2011 Belda et al.The research was funded by the Spanish Ministerio de Ciencia e Innovacion, under grant agreement CIT-010000-2008-5 and by a MICINN (Ministerio de Ciencia e Innovacion) TIN2009-12359 ArtBioCom project. Arnau Montagud acknowledges Generalitat Valenciana grant BFPI/2007/283. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Belda Cuesta, EA.; Pedrola, L.; Peretó Magraner, J.; Martinez Blanch, JF.; Montagud Aquino, A.; Navarro-Peris, E.; Urchueguía Schölzel, JF.... (2011). Microbial Diversity in the Midguts of Field and Lab-Reared Populations of the European Corn Borer Ostrinia nubilalis. PLoS ONE. 6(6):21751-21751. https://doi.org/10.1371/journal.pone.0021751S21751217516

Glucose Amplifies Fatty Acid-Induced Endoplasmic Reticulum Stress in Pancreatic β-Cells via Activation of mTORC1

BACKGROUND: Palmitate is a potent inducer of endoplasmic reticulum (ER) stress in beta-cells. In type 2 diabetes, glucose amplifies fatty-acid toxicity for pancreatic beta-cells, leading to beta-cell dysfunction and death. Why glucose exacerbates beta-cell lipotoxicity is largely unknown. Glucose stimulates mTORC1, an important nutrient sensor involved in the regulation of cellular stress. Our study tested the hypothesis that glucose augments lipotoxicity by stimulating mTORC1 leading to increased beta-cell ER stress. PRINCIPAL FINDINGS: We found that glucose amplifies palmitate-induced ER stress by increasing IRE1alpha protein levels and activating the JNK pathway, leading to increased beta-cell apoptosis. Moreover, glucose increased mTORC1 activity and its inhibition by rapamycin decreased beta-cell apoptosis under conditions of glucolipotoxicity. Inhibition of mTORC1 by rapamycin did not affect proinsulin and total protein synthesis in beta-cells incubated at high glucose with palmitate. However, it decreased IRE1alpha expression and signaling and inhibited JNK pathway activation. In TSC2-deficient mouse embryonic fibroblasts, in which mTORC1 is constitutively active, mTORC1 regulated the stimulation of JNK by ER stressors, but not in response to anisomycin, which activates JNK independent of ER stress. Finally, we found that JNK inhibition decreased beta-cell apoptosis under conditions of glucolipotoxicity. CONCLUSIONS/SIGNIFICANCE: Collectively, our findings suggest that mTORC1 mediates glucose amplification of lipotoxicity, acting through activation of ER stress and JNK. Thus, mTORC1 is an important transducer of ER stress in beta-cell glucolipotoxicity. Moreover, in stressed beta-cells mTORC1 inhibition decreases IRE1alpha protein expression and JNK activity without affecting ER protein load, suggesting that mTORC1 regulates the beta-cell stress response to glucose and fatty acids by modulating the synthesis and activity of specific proteins involved in the execution of the ER stress response. This novel paradigm may have important implications for understanding beta-cell failure in type 2 diabetes

TRPM2-mediated rise in mitochondrial Zn2+ promotes palmitate-induced mitochondrial fission and pancreatic β-cell death in rodents

Rise in plasma free fatty acids (FFAs) represents a major risk factor for obesity-induced type 2 diabetes. Saturated FFAs cause a progressive decline in insulin secretion by promoting pancreatic β-cell death through increased production of reactive oxygen species (ROS). Recent studies have demonstrated that palmitate (a C16-FFA)-induced rise in ROS causes β-cell death by triggering mitochondrial fragmentation, but the underlying mechanisms are unclear. Using the INS1-832/13 β-cell line, here we demonstrate that palmitate generates the ROS required for mitochondrial fission by activating NOX (NADPH oxidase)-2. More importantly, we show that chemical inhibition, RNAi-mediated silencing and knockout of ROS-sensitive TRPM (transient receptor potential melastatin)-2 channels prevent palmitate-induced mitochondrial fission. Although TRPM2 activation affects the intracellular dynamics of Ca2+ and Zn2+, chelation of Zn2+ alone was sufficient to prevent mitochondrial fission. Consistent with the role of Zn2+, palmitate caused a rise in mitochondrial Zn2+, leading to Zn2+-dependent mitochondrial recruitment of Drp-1 (a protein that catalyses mitochondrial fission) and loss of mitochondrial membrane potential. In agreement with the previous reports, Ca2+ caused Drp-1 recruitment, but it failed to induce mitochondrial fission in the absence of Zn2+. These results indicate a novel role for Zn2+ in mitochondrial dynamics. Inhibition or knockout of TRPM2 channels in mouse islets and RNAi-mediated silencing of TRPM2 expression in human islets prevented FFA/cytokine-induced β-cell death, findings that are consistent with the role of abnormal mitochondrial fission in cell death. To conclude, our results reveal a novel, potentially druggable signalling pathway for FFA-induced β-cell death. The cascade involves NOX-2-dependent production of ROS, activation of TRPM2 channels, rise in mitochondrial Zn2+, Drp-1 recruitment and abnormal mitochondrial fission

The prevalence of diabetes and prediabetes in the adult population of Jeddah, Saudi Arabia- a community-based survey

BACKGROUND: Type 2 (T2DM) is believed to be common in Saudi Arabia, but data are limited. In this population survey, we determined the prevalence of T2DM and prediabetes. MATERIALS AND METHODS: A representative sample among residents aged ≥ 18 years of the city of Jeddah was obtained comprising both Saudi and non-Saudi families (N = 1420). Data on dietary, clinical and socio-demographic characteristics were collected and anthropometric measurements taken. Fasting plasma glucose and glycated hemoglobin (HbA1c) were used to diagnose diabetes and prediabetes employing American Diabetes Association criteria. Multiple logistic regression analysis was used to identify factors associated with T2DM. RESULTS: Age and sex standardized prevalence of prediabetes was 9.0% (95% CI 7.5-10.5); 9.4% (7.1-11.8) in men and 8.6% (6.6-10.6) in women. For DM it was 12.1% (10.7-13.5); 12.9% (10.7-13.5) in men and 11.4% (9.5-13.3) in women. The prevalence based on World Population as standard was 18.3% for DM and 11.9% for prediabetes. The prevalence of DM and prediabetes increased with age. Of people aged ≥50 years 46% of men and 44% of women had DM. Prediabetes and DM were associated with various measures of adiposity. DM was also associated with and family history of dyslipidemia in women, cardiovascular disease in men, and with hypertension, dyslipidemia and family history of diabetes in both sexes. DISCUSSION: Age was the strongest predictor of DM and prediabetes followed by obesity. Of people aged 50 years or over almost half had DM and another 10-15% had prediabetes leaving only a small proportion of people in this age group with normoglycemia. Since we did not use an oral glucose tolerance test the true prevalence of DM and prediabetes is thus likely to be even higher than reported here. These results demonstrate the urgent need to develop primary prevention strategies for type 2 diabetes in Saudi Arabia