Intracellular pathways of pancreatic β-cell apoptosis in type 1 diabetes

Phytoconstituents and Pharmacological Activities of Indian Camphorweed (Pluchea indica): A Multi-Potential Medicinal Plant of Nutritional and Ethnomedicinal Importance

Pluchea indica (L.) Less. (Asteraceae) commonly known as Indian camphorweed, pluchea, or marsh fleabane has gained great importance in various traditional medicines for its nutritional and medicinal benefits. It is utilized to cure several illnesses such as lumbago, kidney stones, leucorrhea, inflammation, gangrenous and atonic ulcer, hemorrhoids, dysentery, eye diseases, itchy skin, acid stomach, dysuria, abdominal pain, scabies, fever, sore muscles, dysentery, diabetes, rheumatism, etc. The plant or its leaves in the form of tea are commonly used for treating diabetes and rheumatism. The plant is a rich source of calcium, vitamin C, dietary fiber, and β-carotene. Various biomolecules have been isolated from P. indica, including thiophenes, terpenes, quinic acids, sterols, lignans, phenolics, and flavonoids. The current review reports detailed information about the phytoconstituents and pharmacological relevance of P. indica and the link to its traditional uses. The reported studies validated the efficacy and safety of P. indica, as well as supported its traditional uses for treating various ailments and promoting health and well-being. Thus, this could encourage the development of this plant into a healthy food supplement or medicine for the prevention and treatment of various diseases. However, further studies on the drug interactions, mechanism of action, pharmacokinetics, toxicology, and metabolism, as well as clinical trials, should be carried out.

Beta Cell Therapies for Preventing Type 1 Diabetes: From Bench to Bedside

Type 1 diabetes (T1D) is a chronic metabolic disease characterized by insulin deficiency, generally resulting from progressive autoimmune-mediated destruction of pancreatic beta cells. While the phenomenon of beta cell autoimmunity continues to be an active area of investigation, recent evidence suggests that beta cell stress responses are also important contributors to disease onset. Here we review the pathways driving different kinds of beta cell dysfunction and their respective therapeutic targets in the prevention of T1D. We discuss opportunities and important open questions around the effectiveness of beta cell therapies and challenges for clinical utility. We further evaluate ways in which beta cell drug therapy could be combined with immunotherapy for preventing T1D in light of our growing appreciation of disease heterogeneity and patient endotypes. Ultimately, the emergence of pharmacologic beta cell therapies for T1D have armed us with new tools and closing the knowledge gaps in T1D etiology will be essential for maximizing the potential of these approaches.

Ethanolic extracts of Pluchea indica (L.) leaf pretreatment attenuates cytokine-induced β-cell apoptosis in multiple low-dose streptozotocin-induced diabetic mice

Loss of β-cell mass and function is a fundamental feature of pathogenesis for type 1 and type 2 diabetes. Increasing evidence indicates that apoptosis is one of the main mechanisms of β-cell death in both types. Ethanolic extracts of Pluchea indica leaf (PILE) have been reported to possess blood glucose lowering actions in vivo. Nevertheless, further study is required to determine the underlying mechanisms. In this report, we have investigated the preventive effects of PILE on multiple low doses of streptozotocin (MLDS)-induced β-cell apoptosis. Mice were pre-treated with PILE at 50 mg/kg (PILE 50) or 100 mg/kg (PILE 100) for 2 weeks before streptozotocin (STZ) stimulation, and the treatment continued for 4 or 8 weeks. Results revealed that PILE 100 mice exhibited improved blood biochemistry, maintained a higher body weight, had decreased hyperglycemia, and restored islet architectures compared to non-treated STZ mice. Significantly, PILE 100 decreased levels of inflammatory response markers interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and interlukin1-β (IL-1β), concomitant with the inhibition of caspase-3, caspase-8, capsepase-9, phosphorylation of signal transducer and activator of transcription 1 (pSTAT1), nuclear factor-κBp65 (NF-κBp65), and inducible nitric oxide synthase (iNOS). Additionally, survival and proliferative ability of β-cells was mediated by up-regulated Bcl-2 and Ki67, respectively. These results provide strong evidence that pretreatment with PILE 100 effectively attenuated STZ-induced diabetes-related symptoms and these effects could be associated with the inhibition of cytokine-induced β-cell apoptosis.

The transcription factor STAT6 plays a critical role in promoting beta cell viability and is depleted in islets of individuals with type 1 diabetes

AIMS/HYPOTHESIS

In type 1 diabetes, selective beta cell loss occurs within the inflamed milieu of insulitic islets. This milieu is generated via the enhanced secretion of proinflammatory cytokines and by the loss of anti-inflammatory molecules such as IL-4 and IL-13. While the actions of proinflammatory cytokines have been well-studied in beta cells, the effects of their anti-inflammatory counterparts have received relatively little attention and we have addressed this.

METHODS

Clonal beta cells, isolated human islets and pancreas sections from control individuals and those with type 1 diabetes were employed. Gene expression was measured using targeted gene arrays and by quantitative RT-PCR. Protein expression was monitored in cell extracts by western blotting and in tissue sections by immunocytochemistry. Target proteins were knocked down selectively with interference RNA.

RESULTS

Cytoprotection achieved with IL-4 and IL-13 is mediated by the early activation of signal transducer and activator of transcription 6 (STAT6) in beta cells, leading to the upregulation of anti-apoptotic proteins, including myeloid leukaemia-1 (MCL-1) and B cell lymphoma-extra large (BCLXL). We also report the induction of signal regulatory protein-α (SIRPα), and find that knockdown of SIRPα is associated with reduced beta cell viability. These anti-apoptotic proteins and their attendant cytoprotective effects are lost following siRNA-mediated knockdown of STAT6 in beta cells. Importantly, analysis of human pancreas sections revealed that STAT6 is markedly depleted in the beta cells of individuals with type 1 diabetes, implying the loss of cytoprotective responses.

CONCLUSIONS/INTERPRETATION

Selective loss of STAT6 may contribute to beta cell demise during the progression of type 1 diabetes.

miR15a and miR16 in Chilean type 1 diabetes patients: possible association with apoptosis, inflammatory, or autoimmunity markers

AIM

Type 1 diabetes mellitus (T1D) is an autoimmune disease characterized by the progressive destruction of β cells, mediated by the interaction between T cells and several cytokines. The pathogenesis of T1D has established its possible relationship with miRNAs. In this study, we analyze the expression profile of miR-15a and miR-16 in peripheral blood mononuclear cells (PBMCs) and their possible association with apoptosis, inflammation, or autoimmunity markers.

PATIENTS AND METHODOLOGY

38 T1D patients and 41 control subjects were recruited. mRNAs were analyzed by means of qPCR and TaqMan probes. PBMCs were treated with different concentrations of glucose (baseline, 11 and 25 mM) with or without an inflammatory stimulus as TNF-α (10 ng/ml).

RESULTS

A decrease in the levels of the miR-15a expression in basal conditions is observed in T1D patients compared to healthy control subjects (relative units 0.5 vs. 1.8, p < 0.05). This change in miR-15a and miR-16 is not affected by the addition of TNF-α. No association is observed with inflammatory markers (IL-6, TNF-α, vCAM) or apoptosis (bcl2 expression). The relationship with immunological markers shows an interaction effect between miR16 and IA-2 (p < 0.03).

CONCLUSION

TNF-α does not affect the expression profile of miR-15a and miR16 in PBMCs. A weak correlation is observed between miR-16 and with the autoimmunity profile (IA-2 autoantibody).

An SCFFBXO28 E3 Ligase Protects Pancreatic β-Cells from Apoptosis

Loss of pancreatic β-cell function and/or mass is a central hallmark of all forms of diabetes but its molecular basis is incompletely understood. β-cell apoptosis contributes to the reduced β-cell mass in diabetes. Therefore, the identification of important signaling molecules that promote β-cell survival in diabetes could lead to a promising therapeutic intervention to block β-cell decline during development and progression of diabetes. In the present study, we identified F-box protein 28 (FBXO28), a substrate-recruiting component of the Skp1-Cul1-F-box (SCF) ligase complex, as a regulator of pancreatic β-cell survival. FBXO28 was down-regulated in β-cells and in isolated human islets under diabetic conditions. Consistently, genetic silencing of FBXO28 impaired β-cell survival, and restoration of FBXO28 protected β-cells from the harmful effects of the diabetic milieu. Although FBXO28 expression positively correlated with β-cell transcription factor NEUROD1 and FBXO28 depletion also reduced insulin mRNA expression, neither FBXO28 overexpression nor depletion had any significant impact on insulin content, glucose-stimulated insulin secretion (GSIS) or on other genes involved in glucose sensing and metabolism or on important β-cell transcription factors in isolated human islets. Consistently, FBXO28 overexpression did not further alter insulin content and GSIS in freshly isolated islets from patients with type 2 diabetes (T2D). Our data show that FBXO28 improves pancreatic β-cell survival under diabetogenic conditions without affecting insulin secretion, and its restoration may be a novel therapeutic tool to promote β-cell survival in diabetes.

The Hippo Signaling Pathway in Pancreatic β-Cells: Functions and Regulations

Hippo signaling is an evolutionarily conserved pathway that critically regulates development and homeostasis of various tissues in response to a wide range of extracellular and intracellular signals. As an emerging important player in many diseases, the Hippo pathway is also involved in the pathophysiology of diabetes on the level of the pancreatic islets. Multiple lines of evidence uncover the importance of Hippo signaling in pancreas development as well as in the regulation of β-cell survival, proliferation, and regeneration. Hippo therefore represents a potential target for therapeutic agents designed to improve β-cell function and survival in diabetes. In this review, we summarize recent data on the regulation of the Hippo signaling pathway in the pancreas/in pancreatic islets, its functions on β-cell homeostasis in physiology and pathophysiology, and its contribution toward diabetes progression. The current knowledge related to general mechanisms of action and the possibility of exploiting the Hippo pathway for therapeutic approaches to block β-cell failure in diabetes is highlighted.

miR15a and miR16 in Chilean type 1 diabetes patients: possible association with apoptosis, inflammatory, or autoimmunity markers

AIM

Type 1 diabetes mellitus (T1D) is an autoimmune disease characterized by the progressive destruction of β cells, mediated by the interaction between T cells and several cytokines. The pathogenesis of T1D has established its possible relationship with miRNAs. In this study, we analyze the expression profile of miR-15a and miR-16 in peripheral blood mononuclear cells (PBMCs) and their possible association with apoptosis, inflammation, or autoimmunity markers.

PATIENTS AND METHODOLOGY

38 T1D patients and 41 control subjects were recruited. mRNAs were analyzed by means of qPCR and TaqMan probes. PBMCs were treated with different concentrations of glucose (baseline, 11 and 25 mM) with or without an inflammatory stimulus as TNF-α (10 ng/ml).

RESULTS

A decrease in the levels of the miR-15a expression in basal conditions is observed in T1D patients compared to healthy control subjects (relative units 0.5 vs. 1.8, p < 0.05). This change in miR-15a and miR-16 is not affected by the addition of TNF-α. No association is observed with inflammatory markers (IL-6, TNF-α, vCAM) or apoptosis (bcl2 expression). The relationship with immunological markers shows an interaction effect between miR16 and IA-2 (p < 0.03).

CONCLUSION

TNF-α does not affect the expression profile of miR-15a and miR16 in PBMCs. A weak correlation is observed between miR-16 and with the autoimmunity profile (IA-2 autoantibody).

Human islet cells are killed by BID-independent mechanisms in response to FAS ligand

Cell death via FAS/CD95 can occur either by activation of caspases alone (extrinsic) or by activation of mitochondrial death signalling (intrinsic) depending on the cell type. The BH3-only protein BID is activated in the BCL-2-regulated or mitochondrial apoptosis pathway and acts as a switch between the extrinsic and intrinsic cell death pathways. We have previously demonstrated that islets from BID-deficient mice are protected from FAS ligand-mediated apoptosis in vitro. However, it is not yet known if BID plays a similar role in human beta cell death. We therefore aimed to test the role of BID in human islet cell apoptosis immediately after isolation from human cadaver donors, as well as after de-differentiation in vitro. Freshly isolated human islets or 10-12 day cultured human islet cells exhibited BID transcript knockdown after BID siRNA transfection, however they were not protected from FAS ligand-mediated cell death in vitro as determined by DNA fragmentation analysis using flow cytometry. On the other hand, the same cells transfected with siRNA for FAS-associated via death domain (FADD), a molecule in the extrinsic cell death pathway upstream of BID, showed significant reduction in cell death. De-differentiated islets (human islet-derived progenitor cells) also demonstrated similar results with no difference in cell death after BID knockdown as compared to scramble siRNA transfections. Our results indicate that BID-independent pathways are responsible for FAS-dependent human islet cell death. These results are different from those observed in mouse islets and therefore demonstrate potentially alternate pathways of FAS ligand-induced cell death in human and mouse islet cells.

Life and death of β cells in Type 1 diabetes: A comprehensive review

Type 1 diabetes (T1D) is an autoimmune disorder characterized by the destruction of insulin-producing pancreatic β cells. Immune modulators have achieved some success in modifying the course of disease progression in T1D. However, there are parallel declines in C-peptide levels in treated and control groups after initial responses. In this review, we discuss mechanisms of β cell death in T1D that involve necrosis and apoptosis. New technologies are being developed to enable visualization of insulitis and β cell mass involving positron emission transmission that identifies β cell ligands and magnetic resonance imaging that can identify vascular leakage. Molecular signatures that identify β cell derived insulin DNA that is released from dying cells have been described and applied to clinical settings. We also consider changes in β cells that occur during disease progression including the induction of DNA methyltransferases that may affect the function and differentiation of β cells. Our findings from newer data suggest that the model of chronic long standing β cell killing should be reconsidered. These studies indicate that the pathophysiology is accelerated in the peridiagnosis period and manifest by increased rates of β cell killing and insulin secretory impairments over a shorter period than previously thought. Finally, we consider cellular explanations to account for the ongoing loss of insulin production despite continued immune therapy that may identify potential targets for treatment. The progressive decline in β cell function raises the question as to whether β cell failure that is independent of immune attack may be involved.

Quantitative Genetics of Food Intake in Drosophila melanogaster

Food intake is an essential animal activity, regulated by neural circuits that motivate food localization, evaluate nutritional content and acceptance or rejection responses through the gustatory system, and regulate neuroendocrine feedback loops that maintain energy homeostasis. Excess food consumption in people is associated with obesity and metabolic and cardiovascular disorders. However, little is known about the genetic basis of natural variation in food consumption. To gain insights in evolutionarily conserved genetic principles that regulate food intake, we took advantage of a model system, Drosophila melanogaster, in which food intake, environmental conditions and genetic background can be controlled precisely. We quantified variation in food intake among 182 inbred, sequenced lines of the Drosophila melanogaster Genetic Reference Panel (DGRP). We found significant genetic variation in the mean and within-line environmental variance of food consumption and observed sexual dimorphism and genetic variation in sexual dimorphism for both food intake traits (mean and variance). We performed genome wide association (GWA) analyses for mean food intake and environmental variance of food intake (using the coefficient of environmental variation, CV_E, as the metric for environmental variance) and identified molecular polymorphisms associated with both traits. Validation experiments using RNAi-knockdown confirmed 24 of 31 (77%) candidate genes affecting food intake and/or variance of food intake, and a test cross between selected DGRP lines confirmed a SNP affecting mean food intake identified in the GWA analysis. The majority of the validated candidate genes were novel with respect to feeding behavior, and many had mammalian orthologs implicated in metabolic diseases.

Regulation of Bim in Health and Disease

The BH3-only Bim protein is a major determinant for initiating the intrinsic apoptotic pathway under both physiological and pathophysiological conditions. Tight regulation of its expression and activity at the transcriptional, translational and post-translational levels together with the induction of alternatively spliced isoforms with different pro-apoptotic potential, ensure timely activation of Bim. Under physiological conditions, Bim is essential for shaping immune responses where its absence promotes autoimmunity, while too early Bim induction eliminates cytotoxic T cells prematurely, resulting in chronic inflammation and tumor progression. Enhanced Bim induction in neurons causes neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. Moreover, type I diabetes is promoted by genetically predisposed elevation of Bim in β-cells. On the contrary, cancer cells have developed mechanisms that suppress Bim expression necessary for tumor progression and metastasis. This review focuses on the intricate network regulating Bim activity and its involvement in physiological and pathophysiological processes.

A soluble activin receptor type IIB does not improve blood glucose in streptozotocin-treated mice

Type 1 diabetes mellitus (T1DM), or insulin dependent DM, is accompanied by decreased muscle mass. The growth factor myostatin (MSTN) is a negative regulator of muscle growth, and a loss of MSTN signaling has been shown to increase muscle mass and prevent the development of obesity, insulin resistance and lipodystrophic diabetes in mice. The effects of MSTN inhibition in a T1DM model on muscle mass and blood glucose are unknown. We asked whether MSTN inhibition would increase muscle mass and decrease hyperglycemia in mice treated with streptozotocin (STZ) to destroy pancreatic beta cells. After diabetes developed, mice were treated with a soluble MSTN/activin receptor fused to Fc (ACVR2B:Fc). ACVR2B:Fc increased body weight and muscle mass compared to vehicle treated mice. Unexpectedly, ACVR2B:Fc reproducibly exacerbated hyperglycemia within approximately one week of administration. ACVR2B:Fc treatment also elevated serum levels of the glucocorticoid corticosterone. These results suggest that although MSTN/activin inhibitors increased muscle mass, they may be counterproductive in improving health in patients with T1DM.

β-Cell responses to nitric oxide

Autoimmune diabetes is characterized by the selective destruction of insulin-secreting β-cells that occurs during an inflammatory reaction in and around pancreatic islets of Langerhans. Cytokines such as interleukin-1, released by activated immune cells, have been shown to inhibit insulin secretion from pancreatic β-cells and cause islet destruction. In response to cytokines, β-cells express inducible nitric oxide synthase and produce micromolar levels of the free radical nitric oxide. Nitric oxide inhibits the mitochondrial oxidation of glucose resulting in an impairment of insulin secretion. Nitric oxide is also responsible for cytokine-mediated DNA damage in β-cells. While nitric oxide mediates the inhibitory and toxic effects of cytokines, it also activates protective pathways that allow β-cells to recover from this damage. This review will focus on the dual role of nitric oxide as a mediator of cytokine-induced damage and the activator of repair mechanisms that protect β-cells from cytokine-mediated injury.

Genetic and epigenetic factors in etiology of diabetes mellitus type 1

Diabetes mellitus type 1 (T1D) is a complex disease resulting from the interplay of genetic, epigenetic, and environmental factors. Recent progress in understanding the genetic basis of T1D has resulted in an increased recognition of childhood diabetes heterogeneity. After the initial success of family-based linkage analyses, which uncovered the strong linkage and association between HLA gene variants and T1D, genome-wide association studies performed with high-density single-nucleotide polymorphism genotyping platforms provided evidence for a number of novel loci, although fine mapping and characterization of these new regions remains to be performed. T1D is one of the most heritable common diseases, and among autoimmune diseases it has the largest range of concordance rates in monozygotic twins. This fact, coupled with evidence of various epigenetic modifications of gene expression, provides convincing proof of the complex interplay between genetic and environmental factors. In T1D, epigenetic phenomena, such as DNA methylation, histone modifications, and microRNA dysregulation, have been associated with altered gene expression. Increasing epidemiologic and experimental evidence supports the role of genetic and epigenetic alterations in the etiopathology of diabetes. We discuss recent results related to the role of genetic and epigenetic factors involved in development of T1D.

Diabetes in Friedreich ataxia

Diabetes is a common metabolic disorder in patients with Friedreich ataxia. In this Supplement article, we review the clinical data on diabetes in Friedreich ataxia, and the experimental data from rodent and in vitro models of the disease. Increased body adiposity and insulin resistance are frequently present in Friedreich ataxia, but pancreatic β cell dysfunction and death are a conditio sine qua non for the loss of glucose tolerance and development of diabetes. The loss of frataxin function in mitochondria accounts for these pathogenic processes in Friedreich ataxia. Mitochondria are essential for the sensing of nutrients by the β cell and for the generation of signals that trigger and amplify insulin secretion, known as stimulus-secretion coupling. Moreover, in the intrinsic pathway of apoptosis, pro-apoptotic signals converge on mitochondria, resulting in mitochondrial Bax translocation, membrane permeabilization, cytochrome c release and caspase cleavage. How and at which level frataxin deficiency impacts on these processes in β cells is only partially understood. A better understanding of the molecular mechanisms mediating β cell demise in Friedreich ataxia will pave the way for new therapeutic approaches.

The role of reactive oxygen species and proinflammatory cytokines in type 1 diabetes pathogenesis

Type 1 diabetes (T1D) is a T cell–mediated autoimmune disease characterized by the destruction of insulin-secreting pancreatic β cells. In humans with T1D and in nonobese diabetic (NOD) mice (a murine model for human T1D), autoreactive T cells cause β-cell destruction, as transfer or deletion of these cells induces or prevents disease, respectively. CD4⁺ and CD8⁺ T cells use distinct effector mechanisms and act at different stages throughout T1D to fuel pancreatic β-cell destruction and disease pathogenesis. While these adaptive immune cells employ distinct mechanisms for β-cell destruction, one central means for enhancing their autoreactivity is by the secretion of proinflammatory cytokines, such as IFN-γ, TNF-α, and IL-1. In addition to their production by diabetogenic T cells, proinflammatory cytokines are induced by reactive oxygen species (ROS) via redox-dependent signaling pathways. Highly reactive molecules, proinflammatory cytokines are produced upon lymphocyte infiltration into pancreatic islets and induce disease pathogenicity by directly killing β cells, which characteristically possess low levels of antioxidant defense enzymes. In addition to β-cell destruction, proinflammatory cytokines are necessary for efficient adaptive immune maturation, and in the context of T1D they exacerbate autoimmunity by intensifying adaptive immune responses. The first half of this review discusses the mechanisms by which autoreactive T cells induce T1D pathogenesis and the importance of ROS for efficient adaptive immune activation, which, in the context of T1D, exacerbates autoimmunity. The second half provides a comprehensive and detailed analysis of (1) the mechanisms by which cytokines such as IL-1 and IFN-γ influence islet insulin secretion and apoptosis and (2) the key free radicals and transcription factors that control these processes.