Mild endoplasmic reticulum stress augments the proinflammatory effect of IL-1β in pancreatic rat β-cells via the IRE1α/XBP1s pathway

IRE1 RNase controls CD95-mediated cell death

Signalling by the Unfolded Protein Response (UPR) or by the Death Receptors (DR) are frequently activated towards pro-tumoral outputs in cancer. Herein, we demonstrate that the UPR sensor IRE1 controls the expression of the DR CD95/Fas, and its cell death-inducing ability. Both genetic and pharmacologic blunting of IRE1 activity increased CD95 expression and exacerbated CD95L-induced cell death in glioblastoma (GB) and Triple-Negative Breast Cancer (TNBC) cell lines. In accordance, CD95 mRNA was identified as a target of Regulated IRE1-Dependent Decay of RNA (RIDD). Whilst CD95 expression is elevated in TNBC and GB human tumours exhibiting low RIDD activity, it is surprisingly lower in XBP1s-low human tumour samples. We show that IRE1 RNase inhibition limited CD95 expression and reduced CD95-mediated hepatic toxicity in mice. In addition, overexpression of XBP1s increased CD95 expression and sensitized GB and TNBC cells to CD95L-induced cell death. Overall, these results demonstrate the tight IRE1-mediated control of CD95-dependent cell death in a dual manner through both RIDD and XBP1s, and they identify a novel link between IRE1 and CD95 signalling.

Compound A attenuates proinflammatory cytokine-induced endoplasmic reticulum stress in beta cells and displays beneficial therapeutic effects in a mouse model of autoimmune diabetes

Type 1 diabetes (T1D) is characterized by an immune-mediated progressive destruction of the insulin-producing β-cells. Proinflammatory cytokines trigger endoplasmic reticulum (ER) stress and subsequent insulin secretory deficiency in cultured β-cells, mimicking the islet microenvironment in T1D. β-cells undergo physiologic ER stress due to the high rate of insulin production and secretion under stimulated conditions. Severe and uncompensated ER stress in β-cells is induced by several pathological mechanisms before onset and during T1D. We previously described that the small drug Compound A (CpdA), a selective glucocorticoid receptor (GR/NR3C1, nuclear receptor subfamily 3, group C, member 1) ligand with demonstrated inflammation-suppressive activity in vivo, is an effective modulator of effector T and dendritic cells and of macrophages, yet, in a GR-independent manner. Here, we focus on CpdA's therapeutic potential in T1D cellular and animal models. We demonstrate that CpdA improves the unfolded protein response (UPR) by attenuating ER stress and favoring the survival and function of β-cells exposed to an environment of proinflammatory cytokines. CpdA administration to NODscid mice adoptively transferred with diabetogenic splenocytes (from diabetic NOD mice) led to a delay of disease onset and reduction of diabetes incidence. Histological analysis of the pancreas showed a reduction in islet leukocyte infiltration (insulitis) and preservation of insulin expression in CpdA-treated normoglycemic mice in comparison with control group. These new findings together with our previous reports justify further studies on the administration of this small molecule as a novel therapeutic strategy with dual targets (effector immune and β-cells) during autoimmune diabetes.

Bromocriptine-QR Therapy Reduces Sympathetic Tone and Ameliorates a Pro-Oxidative/Pro-Inflammatory Phenotype in Peripheral Blood Mononuclear Cells and Plasma of Type 2 Diabetes Subjects

Bromocriptine-QR is a sympatholytic dopamine D2 agonist for the treatment of type 2 diabetes that has demonstrated rapid (within 1 year) substantial reductions in adverse cardiovascular events in this population by as yet incompletely delineated mechanisms. However, a chronic state of elevated sympathetic nervous system activity and central hypodopaminergic function has been demonstrated to potentiate an immune system pro-oxidative/pro-inflammatory condition and this immune phenotype is known to contribute significantly to the advancement of cardiovascular disease (CVD). Therefore, the possibility exists that bromocriptine-QR therapy may reduce adverse cardiovascular events in type 2 diabetes subjects via attenuation of this underlying chronic pro-oxidative/pro-inflammatory state. The present study was undertaken to assess the impact of bromocriptine-QR on a wide range of immune pro-oxidative/pro-inflammatory biochemical pathways and genes known to be operative in the genesis and progression of CVD. Inflammatory peripheral blood mononuclear cell biology is both a significant contributor to cardiovascular disease and also a marker of the body’s systemic pro-inflammatory status. Therefore, this study investigated the effects of 4-month circadian-timed (within 2 h of waking in the morning) bromocriptine-QR therapy (3.2 mg/day) in type 2 diabetes subjects whose glycemia was not optimally controlled on the glucagon-like peptide 1 receptor agonist on (i) gene expression status (via qPCR) of a wide array of mononuclear cell pro-oxidative/pro-inflammatory genes known to participate in the genesis and progression of CVD (OXR1, NRF2, NQO1, SOD1, SOD2, CAT, GSR, GPX1, GPX4, GCH1, HMOX1, BiP, EIF2α, ATF4, PERK, XBP1, ATF6, CHOP, GSK3β, NFkB, TXNIP, PIN1, BECN1, TLR2, TLR4, TLR10, MAPK8, NLRP3, CCR2, GCR, L-selectin, VCAM1, ICAM1) and (ii) humoral measures of sympathetic tone (norepinephrine and normetanephrine), whole-body oxidative stress (nitrotyrosine, TBARS), and pro-inflammatory factors (IL-1β, IL-6, IL-18, MCP-1, prolactin, C-reactive protein [CRP]). Relative to pre-treatment status, 4 months of bromocriptine-QR therapy resulted in significant reductions of mRNA levels in PBMC endoplasmic reticulum stress-unfolded protein response effectors [GRP78/BiP (34%), EIF2α (32%), ATF4 (29%), XBP1 (25%), PIN1 (14%), BECN1 (23%)], oxidative stress response proteins [OXR1 (31%), NRF2 (32%), NQO1 (39%), SOD1 (52%), CAT (26%), GPX1 (33%), GPX4 (31%), GCH1 (30%), HMOX1 (40%)], mRNA levels of TLR pro-inflammatory pathway proteins [TLR2 (46%), TLR4 (20%), GSK3β (19%), NFkB (33%), TXNIP (18%), NLRP3 (32%), CCR2 (24%), GCR (28%)], mRNA levels of pro-inflammatory cellular receptor proteins CCR2 and GCR by 24% and 28%, and adhesion molecule proteins L-selectin (35%) and VCAM1 (24%). Relative to baseline, bromocriptine-QR therapy also significantly reduced plasma levels of norepinephrine and normetanephrine by 33% and 22%, respectively, plasma pro-oxidative markers nitrotyrosine and TBARS by 13% and 10%, respectively, and pro-inflammatory factors IL-18, MCP1, IL-1β, prolactin, and CRP by 21%,13%, 12%, 42%, and 45%, respectively. These findings suggest a unique role for circadian-timed bromocriptine-QR sympatholytic dopamine agonist therapy in reducing systemic low-grade sterile inflammation to thereby reduce cardiovascular disease risk.

Progress in Research on the Alleviation of Glucose Metabolism Disorders in Type 2 Diabetes Using Cyclocarya paliurus

Globally, the incidence of diabetes is increasing annually, and China has the largest number of patients with diabetes. Patients with type 2 diabetes need lifelong medication, with severe cases requiring surgery. Diabetes treatment may cause complications, side-effects, and postoperative sequelae that could lead to adverse health problems and significant social and economic burdens; thus, more efficient hypoglycemic drugs have become a research hotspot. Glucose metabolism disorders can promote diabetes, a systemic metabolic disease that impairs the function of other organs, including the heart, liver, and kidneys. Cyclocarya paliurus leaves have gathered increasing interest among researchers because of their effectiveness in ameliorating glucose metabolism disorders. At present, various compounds have been isolated from C. paliurus, and the main active components include polysaccharides, triterpenes, flavonoids, and phenolic acids. C. paliurus mainly ameliorates glucose metabolism disorders by reducing glucose uptake, regulating blood lipid levels, regulating the insulin signaling pathway, reducing β-cell apoptosis, increasing insulin synthesis and secretion, regulating abundances of intestinal microorganisms, and exhibiting α-glucosidase inhibitor activity. In this paper, the mechanism of glucose metabolism regulation by C. paliurus was reviewed to provide a reference to prevent and treat diabetes, hyperlipidaemia, obesity, and other metabolic diseases.

To Be or Not to Be: The Divergent Action and Metabolism of Sphingosine-1 Phosphate in Pancreatic Beta-Cells in Response to Cytokines and Fatty Acids

Sphingosine-1 phosphate (S1P) is a bioactive sphingolipid with multiple functions conveyed by the activation of cell surface receptors and/or intracellular mediators. A growing body of evidence indicates its important role in pancreatic insulin-secreting beta-cells that are necessary for maintenance of glucose homeostasis. The dysfunction and/or death of beta-cells lead to diabetes development. Diabetes is a serious public health burden with incidence growing rapidly in recent decades. The two major types of diabetes are the autoimmune-mediated type 1 diabetes (T1DM) and the metabolic stress-related type 2 diabetes (T2DM). Despite many differences in the development, both types of diabetes are characterized by chronic hyperglycemia and inflammation. The inflammatory component of diabetes remains under-characterized. Recent years have brought new insights into the possible mechanism involved in the increased inflammatory response, suggesting that environmental factors such as a westernized diet may participate in this process. Dietary lipids, particularly palmitate, are substrates for the biosynthesis of bioactive sphingolipids. Disturbed serum sphingolipid profiles were observed in both T1DM and T2DM patients. Many polymorphisms were identified in genes encoding enzymes of the sphingolipid pathway, including sphingosine kinase 2 (SK2), the S1P generating enzyme which is highly expressed in beta-cells. Proinflammatory cytokines and free fatty acids have been shown to modulate the expression and activity of S1P-generating and S1P-catabolizing enzymes. In this review, the similarities and differences in the action of extracellular and intracellular S1P in beta-cells exposed to cytokines or free fatty acids will be identified and the outlook for future research will be discussed.

Molecular Mechanisms of Apoptosis Induction and Its Regulation by Fatty Acids in Pancreatic β-Cells

Pancreatic β-cell failure and death contribute significantly to the pathogenesis of type 2 diabetes. One of the main factors responsible for β-cell dysfunction and subsequent cell death is chronic exposure to increased concentrations of FAs (fatty acids). The effect of FAs seems to depend particularly on the degree of their saturation. Saturated FAs induce apoptosis in pancreatic β-cells, whereas unsaturated FAs are well tolerated and are even capable of inhibiting the pro-apoptotic effect of saturated FAs. Molecular mechanisms of apoptosis induction by saturated FAs in β-cells are not completely elucidated. Saturated FAs induce ER stress, which in turn leads to activation of all ER stress pathways. When ER stress is severe or prolonged, apoptosis is induced. The main mediator seems to be the CHOP transcription factor. Via regulation of expression/activity of pro- and anti-apoptotic Bcl-2 family members, and potentially also through the increase in ROS production, CHOP switches on the mitochondrial pathway of apoptosis induction. ER stress signalling also possibly leads to autophagy signalling, which may activate caspase-8. Saturated FAs activate or inhibit various signalling pathways, i.e., p38 MAPK signalling, ERK signalling, ceramide signalling, Akt signalling and PKCδ signalling. This may lead to the activation of the mitochondrial pathway of apoptosis, as well. Particularly, the inhibition of the pro-survival Akt signalling seems to play an important role. This inhibition may be mediated by multiple pathways (e.g., ER stress signalling, PKCδ and ceramide) and could also consequence in autophagy signalling. Experimental evidence indicates the involvement of certain miRNAs in mechanisms of FA-induced β-cell apoptosis, as well. In the rather rare situations when unsaturated FAs are also shown to be pro-apoptotic, the mechanisms mediating this effect in β-cells seem to be the same as for saturated FAs. To conclude, FA-induced apoptosis rather appears to be preceded by complex cross talks of multiple signalling pathways. Some of these pathways may be regulated by decreased membrane fluidity due to saturated FA incorporation. Few data are available concerning molecular mechanisms mediating the protective effect of unsaturated FAs on the effect of saturated FAs. It seems that the main possible mechanism represents a rather inhibitory intervention into saturated FA-induced pro-apoptotic signalling than activation of some pro-survival signalling pathway(s) or metabolic interference in β-cells. This inhibitory intervention may be due to an increase of membrane fluidity.

Type I interferons as key players in pancreatic β-cell dysfunction in type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by pancreatic islet inflammation (insulitis) and specific pancreatic β-cell destruction by an immune attack. Although the precise underlying mechanisms leading to the autoimmune assault remain poorly understood, it is well accepted that insulitis takes place in the context of a conflicting dialogue between pancreatic β-cells and the immune cells. Moreover, both host genetic background (i.e., candidate genes) and environmental factors (e.g., viral infections) contribute to this inadequate dialogue. Accumulating evidence indicates that type I interferons (IFNs), cytokines that are crucial for both innate and adaptive immune responses, act as key links between environmental and genetic risk factors in the development of T1D. This chapter summarizes some relevant pathways involved in β-cell dysfunction and death, and briefly reviews how enteroviral infections and genetic susceptibility can impact insulitis. Moreover, we present the current evidence showing that, in β-cells, type I IFN signaling pathway activation leads to several outcomes, such as long-lasting major histocompatibility complex (MHC) class I hyperexpression, endoplasmic reticulum (ER) stress, epigenetic changes, and induction of posttranscriptional as well as posttranslational modifications. MHC class I overexpression, when combined with ER stress and posttranscriptional/posttranslational modifications, might lead to sustained neoantigen presentation to immune system and β-cell apoptosis. This knowledge supports the concept that type I IFNs are implicated in the early stages of T1D pathogenesis. Finally, we highlight the promising therapeutic avenues for T1D treatment directed at type I IFN signaling pathway.

MicroRNA-24 promotes pancreatic beta cells toward dedifferentiation to avoid endoplasmic reticulum stress-induced apoptosis

Current research indicates that beta cell loss in type 2 diabetes may be attributed to beta cell dedifferentiation rather than apoptosis; however, the mechanisms by which this occurs remain poorly understood. Our previous study demonstrated that elevation of microRNA-24 (miR-24) in a diabetic setting caused beta cell dysfunction and replicative deficiency. In this study, we focused on the role of miR-24 in beta cell apoptosis and dedifferentiation under endoplasmic reticulum (ER) stress conditions. We found that miR-24 overabundance protected beta cells from thapsigargin-induced apoptosis at the cost of accelerating the impairment of glucose-stimulated insulin secretion (GSIS) and enhancing the presence of dedifferentiation markers. Ingenuity® Pathway Analysis (IPA) revealed that elevation of miR-24 had an inhibitory effect on XBP1 and ATF4, which are downstream effectors of two key branches of ER stress, by inhibiting its direct target, Ire1α. Notably, elevated miR-24 initiated another pathway that targeted Mafa and decreased GSIS function in surviving beta cells, thus guiding their dedifferentiation under ER stress conditions. Our results demonstrated that the elevated miR-24, to the utmost extent, preserves beta cell mass by inhibiting apoptosis and inducing dedifferentiation. This study not only provides a novel mechanism by which miR-24 dominates beta cell turnover under persistent metabolic stress but also offers a therapeutic consideration for treating diabetes by inducing dedifferentiated beta cells to re-differentiation.

Recent Insights Into Mechanisms of β-Cell Lipo- and Glucolipotoxicity in Type 2 Diabetes

The deleterious effects of chronically elevated free fatty acid (FFA) levels on glucose homeostasis are referred to as lipotoxicity, and the concurrent exposure to high glucose may cause synergistic glucolipotoxicity. Lipo- and glucolipotoxicity have been studied for over 25 years. Here, we review the current evidence supporting the role of pancreatic β-cell lipo- and glucolipotoxicity in type 2 diabetes (T2D), including lipid-based interventions in humans, prospective epidemiological studies, and human genetic findings. In addition to total FFA quantity, the quality of FFAs (saturation and chain length) is a key determinant of lipotoxicity. We discuss in vitro and in vivo experimental models to investigate lipo- and glucolipotoxicity in β-cells and describe experimental pitfalls. Lipo- and glucolipotoxicity adversely affect many steps of the insulin production and secretion process. The molecular mechanisms underpinning lipo- and glucolipotoxic β-cell dysfunction and death comprise endoplasmic reticulum stress, oxidative stress and mitochondrial dysfunction, impaired autophagy, and inflammation. Crosstalk between these stress pathways exists at multiple levels and may aggravate β-cell lipo- and glucolipotoxicity. Lipo- and glucolipotoxicity are therapeutic targets as several drugs impact the underlying stress responses in β-cells, potentially contributing to their glucose-lowering effects in T2D.

Immune privilege in corneal transplantation

Corneal transplantation is the most successful solid organ transplantation performed in humans. The extraordinary success of orthotopic corneal allografts, in both humans and experimental animals, is related to the phenomenon of "immune privilege". Inflammation is self-regulated to preserve ocular functions because the eye has immune privilege. At present, three major mechanisms are considered to provide immune privilege in corneal transplantation: 1) anatomical, cellular, and molecular barriers in the cornea; 2) tolerance related to anterior chamber-associated immune deviation and regulatory T cells; and 3) an immunosuppressive intraocular microenvironment. This review describes the mechanisms of immune privilege that have been elucidated from animal models of ocular inflammation, especially those involving corneal transplantation, and its relevance for the clinic. An update on molecular, cellular, and neural interactions in local and systemic immune regulation is provided. Therapeutic strategies for restoring immune privilege are also discussed.

An SFTPC BRICHOS mutant links epithelial ER stress and spontaneous lung fibrosis

Alveolar type 2 (AT2) cell endoplasmic reticulum (ER) stress is a prominent feature in adult and pediatric interstitial lung disease (ILD and ChILD), but in vivo models linking AT2 cell ER stress to ILD have been elusive. Based on a clinical ChILD case, we identified a critical cysteine residue in the surfactant protein C gene (SFTPC) BRICHOS domain whose mutation induced ER stress in vitro. To model this in vivo, we generated a knockin mouse model expressing a cysteine-to-glycine substitution at codon 121 (C121G) in the Sftpc gene. SftpcC121G expression during fetal development resulted in a toxic gain-of-function causing fatal postnatal respiratory failure from disrupted lung morphogenesis. Induced SftpcC121G expression in adult mice resulted in an ER-retained pro-protein causing AT2 cell ER stress. SftpcC121G AT2 cells were a source of cytokines expressed in concert with development of polycellular alveolitis. These cytokines were subsequently found in a high-dimensional proteomic screen of bronchoalveolar lavage fluid from ChILD patients with the same class of SFTPC mutations. Following alveolitis resolution, SftpcC121G mice developed spontaneous pulmonary fibrosis and restrictive lung impairment. This model provides proof of concept linking AT2 cell ER stress to fibrotic lung disease coupled with translationally relevant biomarkers.

Coxsackievirus B Tailors the Unfolded Protein Response to Favour Viral Amplification in Pancreatic β Cells

Type 1 diabetes (T1D) is an autoimmune disease characterized by islet inflammation and progressive pancreatic β cell destruction. The disease is triggered by a combination of genetic and environmental factors, but the mechanisms leading to the triggering of early innate and late adaptive immunity and consequent progressive pancreatic β cell death remain unclear. The insulin-producing β cells are active secretory cells and are thus particularly sensitive to endoplasmic reticulum (ER) stress. ER stress plays an important role in the pathologic pathway leading to autoimmunity, islet inflammation, and β cell death. We show here that group B coxsackievirus (CVB) infection, a putative causative factor for T1D, induces a partial ER stress in rat and human β cells. The activation of the PERK/ATF4/CHOP branch is blunted while the IRE1α branch leads to increased spliced XBP1 expression and c-Jun N-terminal kinase (JNK) activation. Interestingly, JNK1 activation is essential for CVB amplification in both human and rat β cells. Furthermore, a chemically induced ER stress preceding viral infection increases viral replication, in a process dependent on IRE1α activation. Our findings show that CVB tailors the unfolded protein response in β cells to support their replication, preferentially triggering the pro-viral IRE1α/XBP1s/JNK1 pathway while blocking the pro-apoptotic PERK/ATF4/CHOP pathway.

Impaired Store-Operated Calcium Entry and STIM1 Loss Lead to Reduced Insulin Secretion and Increased Endoplasmic Reticulum Stress in the Diabetic β-Cell

Store-operated Ca2+ entry (SOCE) is a dynamic process that leads to refilling of endoplasmic reticulum (ER) Ca2+ stores through reversible gating of plasma membrane Ca2+ channels by the ER Ca2+ sensor Stromal Interaction Molecule 1 (STIM1). Pathogenic reductions in β-cell ER Ca2+ have been observed in diabetes. However, a role for impaired SOCE in this phenotype has not been tested. We measured the expression of SOCE molecular components in human and rodent models of diabetes and found a specific reduction in STIM1 mRNA and protein levels in human islets from donors with type 2 diabetes (T2D), islets from hyperglycemic streptozotocin-treated mice, and INS-1 cells (rat insulinoma cells) treated with proinflammatory cytokines and palmitate. Pharmacologic SOCE inhibitors led to impaired islet Ca2+ oscillations and insulin secretion, and these effects were phenocopied by β-cell STIM1 deletion. STIM1 deletion also led to reduced ER Ca2+ storage and increased ER stress, whereas STIM1 gain of function rescued β-cell survival under proinflammatory conditions and improved insulin secretion in human islets from donors with T2D. Taken together, these data suggest that the loss of STIM1 and impaired SOCE contribute to ER Ca2+ dyshomeostasis under diabetic conditions, whereas efforts to restore SOCE-mediated Ca2+ transients may have the potential to improve β-cell health and function.

Inflammatory stress in islet β-cells: therapeutic implications for type 2 diabetes?

Type 2 diabetes is a common complex disease. Relatively little is known about the underlying pathophysiology. Mild islet inflammation has been suggested to play a pathogenic role; here we review the available evidence. Mild islet inflammation is histologically detected in pancreas sections of type 2 diabetic patients. In experimental models, it can be triggered by excess nutrients, amyloid, lipopolysaccharide, and endoplasmic reticulum and oxidative stress. Transcriptome studies do not consistently identify pro-inflammatory gene expression signatures in type 2 diabetic islets, and genetic evidence calls into question the causality of inflammation. Several anti-inflammatory medications confer a modest glucose-lowering effect, supporting the role for inflammation in type 2 diabetes. Whether these anti-inflammatory therapies target inflammation in islets or in other metabolically relevant tissues remains unknown.

IRE1α Implications in Endoplasmic Reticulum Stress-Mediated Development and Pathogenesis of Autoimmune Diseases

Inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α) is the most prominent and evolutionarily conserved endoplasmic reticulum (ER) membrane protein. This transduces the signal of misfolded protein accumulation in the ER, named as ER stress, to the nucleus as “unfolded protein response (UPR).” The ER stress-mediated IRE1α signaling pathway arbitrates the yin and yang of cell life. IRE1α has been implicated in several physiological as well as pathological conditions, including immune disorders. Autoimmune diseases are caused by abnormal immune responses that develop due to genetic mutations and several environmental factors, including infections and chemicals. These factors dysregulate the cell immune reactions, such as cytokine secretion, antigen presentation, and autoantigen generation. However, the mechanisms involved, in which these factors induce the onset of autoimmune diseases, are remaining unknown. Considering that these environmental factors also induce the UPR, which is expected to have significant role in secretory cells and immune cells. The role of the major UPR molecule, IRE1α, in causing immune responses is well identified, but its role in inducing autoimmunity and the pathogenesis of autoimmune diseases has not been clearly elucidated. Hence, a better understanding of the role of IRE1α and its regulatory mechanisms in causing autoimmune diseases could help to identify and develop the appropriate therapeutic strategies. In this review, we mainly center the discussion on the molecular mechanisms of IRE1α in the pathophysiology of autoimmune diseases.

Association between corneal endothelial cell densities and elevated cytokine levels in the aqueous humor

Annual reduction rate of corneal endothelial cell density (ECD) varies among etiologies, however, the cause of chronic endothelial cell loss is still unknown. We recently reported the elevation of inflammatory cytokines in the aqueous humor (AqH) in eyes with bullous keratopathy and low ECD. To evaluate the association between ECD and aqueous cytokine levels, we collected a total of 157 AqH samples prospectively. The AqH levels of cytokines were measured and multivariate analyses were conducted to find the correlation between ECD, aqueous cytokine levels and clinical factors, such as number of previous intraocular surgeries and protein concentration in AqH. As a result, ECD was negatively correlated with specific cytokine levels, including IL-1α, IL-4, IL-13, MIP-1β, TNF-α and E-selectin (all P < 0.05). The aqueous cytokine levels showed different correlations with these clinical factors; the number of previous intraocular surgeries was associated with all cytokines except MIP-1α. The AqH protein concentration and the status of intraocular lens showed similar patterns of elevation of IL-1α, IL-4, IL-6, IL-8, IL-10, IL-13, IL-17A, MIP-1β, MCP-1, E-selectin, P-selectin and sICAM-1. In conclusion, elevation of AqH cytokine levels was associated with reduced ECDs. AqH cytokine levels showed significant correlations with clinical factors associated with low ECDs.

Targeting Cellular Calcium Homeostasis to Prevent Cytokine-Mediated Beta Cell Death

Pro-inflammatory cytokines are important mediators of islet inflammation, leading to beta cell death in type 1 diabetes. Although alterations in both endoplasmic reticulum (ER) and cytosolic free calcium levels are known to play a role in cytokine-mediated beta cell death, there are currently no treatments targeting cellular calcium homeostasis to combat type 1 diabetes. Here we show that modulation of cellular calcium homeostasis can mitigate cytokine- and ER stress-mediated beta cell death. The calcium modulating compounds, dantrolene and sitagliptin, both prevent cytokine and ER stress-induced activation of the pro-apoptotic calcium-dependent enzyme, calpain, and partly suppress beta cell death in INS1E cells and human primary islets. These agents are also able to restore cytokine-mediated suppression of functional ER calcium release. In addition, sitagliptin preserves function of the ER calcium pump, sarco-endoplasmic reticulum Ca²⁺-ATPase (SERCA), and decreases levels of the pro-apoptotic protein thioredoxin-interacting protein (TXNIP). Supporting the role of TXNIP in cytokine-mediated cell death, knock down of TXNIP in INS1-E cells prevents cytokine-mediated beta cell death. Our findings demonstrate that modulation of dynamic cellular calcium homeostasis and TXNIP suppression present viable pharmacologic targets to prevent cytokine-mediated beta cell loss in diabetes.

Interferon-α mediates human beta cell HLA class I overexpression, endoplasmic reticulum stress and apoptosis, three hallmarks of early human type 1 diabetes

AIMS/HYPOTHESIS

Three hallmarks of the pancreatic islets in early human type 1 diabetes are overexpression of HLA class I, endoplasmic reticulum (ER) stress and beta cell apoptosis. The mediators of these phenomena remain to be defined. The type I interferon IFNα is expressed in human islets from type 1 diabetes patients and mediates HLA class I overexpression. We presently evaluated the mechanisms involved in IFNα-induced HLA class I expression in human beta cells and determined whether this cytokine contributes to ER stress and apoptosis.

METHODS

IFNα-induced inflammation, ER stress and apoptosis were evaluated by RT-PCR, western blot, immunofluorescence and nuclear dyes, and proteins involved in type I interferon signalling were inhibited by small interfering RNAs. All experiments were performed in human islets or human EndoC-βH1 cells.

RESULTS

IFNα upregulates HLA class I, inflammation and ER stress markers in human beta cells via activation of the candidate gene TYK2, and the transcription factors signal transducer and activator of transcription 2 and IFN regulatory factor 9. Furthermore, it acts synergistically with IL-1β to induce beta cell apoptosis.

CONCLUSIONS/INTERPRETATION

The innate immune effects induced by IFNα may induce and amplify the adaptive immune response against human beta cells, indicating that IFNα has a central role in the early phases of diabetes.

Type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM), also known as autoimmune diabetes, is a chronic disease characterized by insulin deficiency due to pancreatic β-cell loss and leads to hyperglycaemia. Although the age of symptomatic onset is usually during childhood or adolescence, symptoms can sometimes develop much later. Although the aetiology of T1DM is not completely understood, the pathogenesis of the disease is thought to involve T cell-mediated destruction of β-cells. Islet-targeting autoantibodies that target insulin, 65 kDa glutamic acid decarboxylase, insulinoma-associated protein 2 and zinc transporter 8 - all of which are proteins associated with secretory granules in β-cells - are biomarkers of T1DM-associated autoimmunity that are found months to years before symptom onset, and can be used to identify and study individuals who are at risk of developing T1DM. The type of autoantibody that appears first depends on the environmental trigger and on genetic factors. The pathogenesis of T1DM can be divided into three stages depending on the absence or presence of hyperglycaemia and hyperglycaemia-associated symptoms (such as polyuria and thirst). A cure is not available, and patients depend on lifelong insulin injections; novel approaches to insulin treatment, such as insulin pumps, continuous glucose monitoring and hybrid closed-loop systems, are in development. Although intensive glycaemic control has reduced the incidence of microvascular and macrovascular complications, the majority of patients with T1DM are still developing these complications. Major research efforts are needed to achieve early diagnosis, prevent β-cell loss and develop better treatment options to improve the quality of life and prognosis of those affected.

Endoplasmic reticulum stress in beta cells and autoimmune diabetes

Type 1 diabetes results from the autoimmune destruction of pancreatic β cells, leading to insulin deficiency and hyperglycemia. Although multiple attempts have been made to slow the autoimmune process using immunosuppressive or immunomodulatory agents, there are still no effective treatments that can delay or reverse the progression of type 1 diabetes in humans. Recent studies support endoplasmic reticulum (ER) as a novel target for preventing the initiation of the autoimmune reaction, propagation of inflammation, and β cell death in type 1 diabetes. This review highlights recent findings on ER stress in β cells and development of type 1 diabetes and introduces potential new treatments targeting the ER to combat this disorder.

Endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

Insulin-secreting pancreatic β-cells are extremely dependent on their endoplasmic reticulum (ER) to cope with the oscillatory requirement of secreted insulin to maintain normoglycemia. Insulin translation and folding rely greatly on the unfolded protein response (UPR), an array of three main signaling pathways designed to maintain ER homeostasis and limit ER stress. However, prolonged or excessive UPR activation triggers alternative molecular pathways that can lead to β-cell dysfunction and apoptosis. An increasing number of studies suggest a role of these pro-apoptotic UPR pathways in the downfall of β-cells observed in diabetic patients. Particularly, the past few years highlighted a cross talk between the UPR and inflammation in the context of both type 1 (T1D) and type 2 diabetes (T2D). In this article, we describe the recent advances in research regarding the interplay between ER stress, the UPR, and inflammation in the context of β-cell apoptosis leading to diabetes.

Cytokines and Pancreatic β-Cell Apoptosis

The discovery 30 years ago that inflammatory cytokines cause a concentration, activity, and time-dependent bimodal response in pancreatic β-cell function and viability has been a game-changer in the fields of research directed at understanding inflammatory regulation of β-cell function and survival and the causes of β-cell failure and destruction in diabetes. Having until then been confined to the use of pathophysiologically irrelevant β-cell toxic chemicals as a model of β-cell death, researchers could now mimic endocrine and paracrine effects of the cytokine response in vitro by titrating concentrations in the low to the high picomolar-femtomolar range and vary exposure time for up to 14-16h to reproduce the acute regulatory effects of systemic inflammation on β-cell secretory responses, with a shift to inhibition at high picomolar concentrations or more than 16h of exposure to illustrate adverse effects of local, chronic islet inflammation. Since then, numerous studies have clarified how these bimodal responses depend on discrete signaling pathways. Most interest has been devoted to the proapoptotic response dependent upon mainly nuclear factor κ B and mitogen-activated protein kinase activation, leading to gene expressional changes, endoplasmic reticulum stress, and triggering of mitochondrial dysfunction. Preclinical studies have shown preventive effects of cytokine antagonism in animal models of diabetes, and clinical trials demonstrating proof of concept are emerging. The full clinical potential of anticytokine therapies has yet to be shown by testing the incremental effects of appropriate dosing, timing, and combinations of treatments. Due to the considerable translational importance of enhancing the precision, specificity, and safety of antiinflammatory treatments of diabetes, we review here the cellular, preclinical, and clinical evidence of which of the death pathways recently proposed in the Nomenclature Committee on Cell Death 2012 Recommendations are activated by inflammatory cytokines in the pancreatic β-cell to guide the identification of antidiabetic targets. Although there are still scarce human data, the cellular and preclinical studies point to the caspase-dependent intrinsic apoptosis pathway as the prime effector of inflammatory β-cell apoptosis.

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)-1β 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.

Endoplasmic Reticulum Stress Response in Non-alcoholic Steatohepatitis: The Possible Role of Physical Exercise

Sedentary lifestyle coupled with excessive consumption of high caloric food has been related to the epidemic increase of non-alcoholic fatty liver disease, which can progress from simple steatosis to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis and, eventually, may culminate in hepatocellular carcinoma. Although the precise mechanisms underlying the progression of NASH are not completely understood, endoplasmic reticulum (ER) dysfunction seems to play a key role in the process. Hepatic ER stress has been associated to hepatic steatosis, insulin resistance, inflammation, oxidative stress and hepatocyte death, contributing to liver dysfunction. Physical exercise seems to be the most effective preventive and therapeutic non-pharmacological strategy to mitigate several features related to NASH, possibly targeting most of the referred mechanisms associated with the pathophysiology of ER-related NASH. Nevertheless, little is known about the impact of physical exercise on NASH-related ER stress. In this review, we will discuss the ER stress associated to NASH conditions and highlight the possible benefits of physical exercise in the attenuation and/or reversion of NASH-related ER stress.

Involvement of the IRE1α-XBP1 pathway and XBP1s-dependent transcriptional reprogramming in metabolic diseases

The X-box binding protein 1 (XBP1) is not only an important component of the unfolded protein response (UPR), but also an important nuclear transcription factor. Upon endoplasmic reticulum stress, XBP1 is spliced by inositol-requiring enzyme 1 (IRE1), thereby generating functional spliced XBP1 (XBP1s). XBP1s functions by translocating into the nucleus to initiate transcriptional programs that regulate a subset of UPR- and non-UPR-associated genes involved in the pathophysiological processes of various diseases. Recent reports have implicated XBP1 in metabolic diseases. This review summarizes the effects of XBP1-mediated regulation on lipid metabolism, glucose metabolism, obesity, and atherosclerosis. Additionally, for the first time, we present XBP1s-dependent transcriptional reprogramming in metabolic diseases under different conditions, including pathology and physiology. Understanding the function of XBP1 in metabolic diseases may provide a basic knowledge for the development of novel therapeutic targets for ameliorating these diseases.

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-1β 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-1β 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

Targeting inflammation in diabetes: Newer therapeutic options

Inflammation has been recognised to both decrease beta cell insulin secretion and increase insulin resistance. Circulating cytokines can affect beta cell function directly leading to secretory dysfunction and increased apoptosis. These cytokines can also indirectly affect beta cell function by increasing adipocyte inflammation.The resulting glucotoxicity and lipotoxicity further enhance the inflammatory process resulting in a vicious cycle. Weight reduction and drugs such as metformin have been shown to decrease the levels of C-Reactive Protein by 31% and 13%, respectively. Pioglitazone, insulin and statins have anti-inflammatory effects. Interleukin 1 and tumor necrosis factor-α antagonists are in trials and NSAIDs such as salsalate have shown an improvement in insulin sensitivity. Inhibition of 12-lipo-oxygenase, histone de-acetylases, and activation of sirtuin-1 are upcoming molecular targets to reduce inflammation. These therapies have also been shown to decrease the conversion of pre-diabetes state to diabetes. Drugs like glicazide, troglitazone, N-acetylcysteine and selective COX-2 inhibitors have shown benefit in diabetic neuropathy by decreasing inflammatory markers. Retinopathy drugs are used to target vascular endothelial growth factor, angiopoietin-2, various proteinases and chemokines. Drugs targeting the proteinases and various chemokines are pentoxifylline, inhibitors of nuclear factor-kappa B and mammalian target of rapamycin and are in clinical trials for diabetic nephropathy. Commonly used drugs such as insulin, metformin, peroxisome proliferator-activated receptors, glucagon like peptide-1 agonists and dipeptidyl peptidase-4 inhibitors also decrease inflammation. Anti-inflammatory therapies represent a potential approach for the therapy of diabetes and its complications.

A molecular web: endoplasmic reticulum stress, inflammation, and oxidative stress

Execution of fundamental cellular functions demands regulated protein folding homeostasis. Endoplasmic reticulum (ER) is an active organelle existing to implement this function by folding and modifying secretory and membrane proteins. Loss of protein folding homeostasis is central to various diseases and budding evidences suggest ER stress as being a major contributor in the development or pathology of a diseased state besides other cellular stresses. The trigger for diseases may be diverse but, inflammation and/or ER stress may be basic mechanisms increasing the severity or complicating the condition of the disease. Chronic ER stress and activation of the unfolded-protein response (UPR) through endogenous or exogenous insults may result in impaired calcium and redox homeostasis, oxidative stress via protein overload thereby also influencing vital mitochondrial functions. Calcium released from the ER augments the production of mitochondrial Reactive Oxygen Species (ROS). Toxic accumulation of ROS within ER and mitochondria disturbs fundamental organelle functions. Sustained ER stress is known to potentially elicit inflammatory responses via UPR pathways. Additionally, ROS generated through inflammation or mitochondrial dysfunction could accelerate ER malfunction. Dysfunctional UPR pathways have been associated with a wide range of diseases including several neurodegenerative diseases, stroke, metabolic disorders, cancer, inflammatory disease, diabetes mellitus, cardiovascular disease, and others. In this review, we have discussed the UPR signaling pathways, and networking between ER stress-induced inflammatory pathways, oxidative stress, and mitochondrial signaling events, which further induce or exacerbate ER stress.

Lipotoxicity in the pancreatic beta cell: not just survival and function, but proliferation as well?

Free fatty acids (FFAs) exert both positive and negative effects on beta cell survival and insulin secretory function, depending on concentration, duration, and glucose abundance. Lipid signals are mediated not only through metabolic pathways, but also through cell surface and nuclear receptors. Toxicity is modulated by positive signals arising from circulating factors such as hormones, growth factors and incretins, as well as negative signals such as inflammatory mediators and cytokines. Intracellular mechanisms of lipotoxicity include metabolic interference and cellular stress responses such as oxidative stress, endoplasmic reticulum (ER) stress, and possibly autophagy. New findings strengthen an old hypothesis that lipids may also impair compensatory beta cell proliferation. Clinical observations continue to support a role for lipid biology in the risk and progression of both type 1 (T1D) and type 2 diabetes (T2D). This review summarizes recent work in this important, rapidly evolving field.

Role of the unfolded protein response in β cell compensation and failure during diabetes

Pancreatic β cell failure leads to diabetes development. During disease progression, β cells adapt their secretory capacity to compensate the elevated glycaemia and the peripheral insulin resistance. This compensatory mechanism involves a fine-tuned regulation to modulate the endoplasmic reticulum (ER) capacity and quality control to prevent unfolded proinsulin accumulation, a major protein synthetized within the β cell. These signalling pathways are collectively termed unfolded protein response (UPR). The UPR machinery is required to preserve ER homeostasis and β cell integrity. Moreover, UPR actors play a key role by regulating ER folding capacity, increasing the degradation of misfolded proteins, and limiting the mRNA translation rate. Recent genetic and biochemical studies on mouse models and human UPR sensor mutations demonstrate a clear requirement of the UPR machinery to prevent β cell failure and increase β cell mass and adaptation throughout the progression of diabetes. In this review we will highlight the specific role of UPR actors in β cell compensation and failure during diabetes.

The unfolded protein response and diabetic retinopathy

Diabetic retinopathy, a common complication of diabetes, is the leading cause of blindness in adults. Diabetes chronically damages retinal blood vessels and neurons likely through multiple pathogenic pathways such as oxidative stress, inflammation, and endoplasmic reticulum (ER) stress. To relieve ER stress, the cell activates an adaptive mechanism known as the unfolded protein response (UPR). The UPR coordinates the processes of protein synthesis, protein folding, and degradation to ensure proteostasis, which is vital for cell survival and activity. Emerging evidence suggests that diabetes can activate all three UPR branches in retinal cells, among which the PERK/ATF4 pathway is the most extensively studied in the development of diabetic retinopathy. X-box binding protein 1 (XBP1) is a major transcription factor in the core UPR pathway and also regulates a variety of genes involved in cellular metabolism, redox state, autophagy, inflammation, cell survival, and vascular function. The exact function and implication of XBP1 in the pathogenesis of diabetic retinopathy remain elusive. Focusing on this less studied pathway, we summarize recent progress in studies of the UPR pertaining to diabetic changes in retinal vasculature and neurons, highlighting the perspective of XBP1 as a potential therapeutic target in diabetic retinopathy.

Endoplasmic reticulum stress sensitizes pancreatic beta cells to interleukin-1β-induced apoptosis via Bim/A1 imbalance

We have recently shown that the crosstalk between mild endoplasmic reticulum (ER) stress and low concentrations of the pro-inflammatory cytokine interleukin (IL)-1β exacerbates beta cell inflammatory responses via the IRE1α/XBP1 pathway. We presently investigated whether mild ER stress also sensitizes beta cells to cytokine-induced apoptosis. Cyclopiazonic acid (CPA)-induced ER stress enhanced the IL-1β apoptosis in INS-1E and primary rat beta cells. This was not prevented by XBP1 knockdown (KD), indicating the dissociation between the pathways leading to inflammation and cell death. Analysis of the role of pro- and anti-apoptotic proteins in cytokine-induced apoptosis indicated a central role for the pro-apoptotic BH3 (Bcl-2 homology 3)-only protein Bim (Bcl-2-interacting mediator of cell death), which was counteracted by four anti-apoptotic Bcl-2 (B-cell lymphoma-2) proteins, namely Bcl-2, Bcl-XL, Mcl-1 and A1. CPA+IL-1β-induced beta cell apoptosis was accompanied by increased expression of Bim, particularly the most pro-apoptotic variant, small isoform of Bim (Bim_S), and decreased expression of A1. Bim silencing protected against CPA+IL-1β-induced apoptosis, whereas A1 KD aggravated cell death. Bim inhibition protected against cell death caused by A1 silencing under all conditions studied. In conclusion, mild ER stress predisposes beta cells to the pro-apoptotic effects of IL-1β by disrupting the balance between pro- and anti-apoptotic Bcl-2 proteins. These findings link ER stress to exacerbated apoptosis during islet inflammation and provide potential mechanistic targets for beta cell protection, namely downregulation of Bim and upregulation of A1.

Islet inflammation: a unifying target for diabetes treatment?

In the past decade, islet inflammation has emerged as a contributor to the loss of functional β cell mass in both type 1 (T1D) and type 2 diabetes (T2D). Evidence supports the idea that overnutrition and insulin resistance result in the production of proinflammatory mediators by β cells. In addition to compromising β cell function and survival, cytokines may recruit macrophages into islets, thus augmenting inflammation. Limited but intriguing data imply a role of adaptive immune response in islet dysfunction in T2D. Clinical trials have validated anti-inflammatory therapies in T2D, whereas immune therapy for T1D remains challenging. Further research is required to improve our understanding of islet inflammatory pathways and to identify more effective therapeutic targets for T1D and T2D.

Posttranscriptional regulation of PER1 underlies the oncogenic function of IREα

Growing evidence supports a role for the unfolded protein response (UPR) in carcinogenesis; however, the precise molecular mechanisms underlying this phenomenon remain elusive. Herein, we identified the circadian clock PER1 mRNA as a novel substrate of the endoribonuclease activity of the UPR sensor IRE1α. Analysis of the mechanism shows that IRE1α endoribonuclease activity decreased PER1 mRNA in tumor cells without affecting PER1 gene transcription. Inhibition of IRE1α signaling using either siRNA-mediated silencing or a dominant-negative strategy prevented PER1 mRNA decay, reduced tumorigenesis, and increased survival, features that were reversed upon PER1 silencing. Clinically, patients showing reduced survival have lower levels of PER1 mRNA expression and increased splicing of XBP1, a known IRE-α substrate, thereby pointing toward an increased IRE1α activity in these patients. Hence, we describe a novel mechanism connecting the UPR and circadian clock components in tumor cells, thereby highlighting the importance of this interplay in tumor development.

The role of the unfolded protein response in diabetes mellitus

The endoplasmic reticulum (ER) plays a key role in the synthesis and modification of secretory and membrane proteins in all eukaryotic cells. Under normal conditions, these proteins are correctly folded and assembled in the ER. However, when cells are exposed to environmental factors such as overproduction of ER proteins, viral infections, or glucose deprivation, the secretory and membrane proteins can accumulate in unfolded or misfolded forms in the lumen of the ER, and consequently, cause stress in the ER. To maintain cellular homeostasis, cells induce several responses to ER stress. In mammalian cells, ER stress responses are induced by a diversity of signal pathways. There are three ER-located transmembrane proteins that play important roles in mammalian ER stress responses: activating transcription factor 6, inositol-requiring protein 1, and protein kinase RNA-like endoplasmic reticulum kinase. ER stress is linked to various diseases, including diabetes. This review highlights the particular importance of ER stress-responsive molecules in insulin biosynthesis, glyconeogenesis, insulin resistance, glucose intolerance, and pancreatic β-cell apoptosis. An understanding of the pathogenic mechanism of diabetes from the aspect of ER stress is crucial in formulating therapeutic strategies.

Signalling danger: endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

Protein synthesis is increased by several-fold in stimulated pancreatic beta cells. Synthesis and folding of (pro)insulin takes place in the endoplasmic reticulum (ER), and beta cells trigger the unfolded protein response (UPR) to upgrade the functional capacity of the ER. Prolonged or excessive UPR activation contributes to beta cell dysfunction and death in type 2 diabetes, but there is another side of the UPR that may be of particular relevance for autoimmune type 1 diabetes, namely, the cross-talk between the UPR and innate immunity/inflammation. Recent evidence, discussed in this review, indicates that both saturated fats and inflammatory mediators such as cytokines trigger the UPR in pancreatic beta cells. The UPR potentiates activation of nuclear factor κB, a key regulator of inflammation. Two branches of the UPR, namely IRE1/XBP1s and PERK/ATF4/CHOP, mediate the UPR-induced sensitisation of pancreatic beta cells to the proinflammatory effects of cytokines. This can contribute to the upregulation of local inflammatory mechanisms and the aggravation of insulitis. The dialogue between the UPR and inflammation may provide an explanation for the parallel increase in the prevalence of childhood obesity and type 1 diabetes.

Obesity and endoplasmic reticulum (ER) stresses

In obesity, the adipose cells behave as inflammatory source and result to low grade inflammation. This systemic inflammation along with oxidative stress is a silent killer and damages other vital organs also. High metabolic process, induced due to high nutritional intake, results to endoplasmic reticulum (ER) stress and mitochondrial stress. This review describes the triggering factor and basic mechanism behind the obesity mediated these stresses in relation to inflammation. Efforts have been made to describe the effect-response cycle between adipocytes and non-adipocyte cells with reference to metabolic syndrome (MS).