Signs Of Endoplasmic Reticulum Stress Research Articles

Neuromolecular responses in disrupted mutualistic cleaning interactions under future environmental conditions

BackgroundMutualistic interactions, which constitute some of the most advantageous interactions among fish species, are highly vulnerable to environmental changes. A key mutualistic interaction is the cleaning service rendered by the cleaner wrasse, Labroides dimidiatus, which involves intricate processes of social behaviour to remove ectoparasites from client fish and can be altered in near-future environmental conditions. Here, we evaluated the neuromolecular mechanisms behind the behavioural disruption of cleaning interactions in response to future environments. We subjected cleaner wrasses and surgeonfish (Acanthurus leucosternon, serving as clients) to elevated temperature (warming, 32 °C), increased levels of CO2 (high CO2, 1000 ppm), and a combined condition of elevated CO2 and temperature (warming and high CO2, 32 °C, and 1000 ppm) for 28 days.ResultsEach of these conditions resulted in behavioural disruptions concerning the motivation to interact and the quality of interaction (high CO2 − 80.7%, warming − 92.6%, warming and high CO2 − 79.5%, p < 0.001). Using transcriptomics of the fore-, mid-, and hindbrain, we discovered that most transcriptional reprogramming in both species under warming conditions occurred primarily in the hind- and forebrain. The associated functions under warming were linked to stress, heat shock proteins, hypoxia, and behaviour. In contrast, elevated CO2 exposure affected a range of functions associated with GABA, behaviour, visual perception, thyroid hormones and circadian rhythm. Interestingly, in the combined warming and high CO2 condition, we did not observe any expression changes of behaviour. However, we did find signs of endoplasmic reticulum stress and apoptosis, suggesting not only an additive effect of the environmental conditions but also a trade-off between physiological performance and behaviour in the cleaner wrasse.ConclusionsWe show that impending environmental shifts can affect the behaviour and molecular processes that sustain mutualistic interactions between L. dimidiatus and its clients, which could have a cascading effect on their adaptation potential and possibly cause large-scale impacts on coral reef ecosystems.

Accumulation and neuroprotective effects of lithium on hepatocellular carcinoma mice model

AimThe peripheral tumor growth is accompanied by the accumulation of inflammatory mediators in the blood that can negatively influence blood-brain barrier function and neuronal structure and develop the cancer-associated depression. The aim of the study was to evaluate the neurobiological effects of lithium on hepatocellular carcinoma mice model. MethodsIn this study we analyzed the locomotor activity of lithium-treated tumor-bearing mice using the Phenomaster instrument. Inductively coupled plasma mass-spectral analysis was used to determine lithium levels in blood, brain, liver, kidneys, tumors and muscle tissues. The prefrontal cortex neurons ultrastructure was assessed by transmission electron microscopy. Expression of BDNF, GRP78, EEA1, LAMP1, and LC3 beta in neurons was determined by immunohistochemical analysis. ResultsA decrease in locomotor activity was found in animals with tumors. At the same time, the low expression levels of the neurotrophic factor BDNF and early endosomal marker EEA1 were revealed, as well as the decreased amount of synaptic vesicles and synapses was shown. Signs of endoplasmic reticulum stress and autophagy development in neurons of animals with tumors were noted. Lithium carbonate administration had a corrective effect on animal’s behavior and the prefrontal cortex neurons structure. ConclusionsIn summary, lithium can restore the neuronal homeostasis in tumor-bearing mice.

Induction of Oxidative Stress and Alteration of Synaptic Gene Expression in Newborn Hippocampal Granule Cells after Developmental Exposure to Aroclor 1254

Introduction: Hippocampal newborn neurons integrate into functional circuits where they play an important role in learning and memory. We previously showed that perinatal exposure to Aroclor 1254, a commercial mixture of polychlorinated biphenyls (PCBs) associated with alterations of cognitive function in children, disrupted the normal maturation of excitatory synapses in the dentate gyrus. We hypothesized that hippocampal immature neurons underlie some of the cognitive effects of PCBs. Methods: We used newly generated neurons to examine the effects of PCBs in mice following maternal exposure. Newborn dentate granule cells were tagged with enhanced green fluorescent protein using a transgenic mouse line. The transcriptome of the newly generated granule cells was assessed using RNA sequencing. Results: Gestational and lactational exposure to 6 mg/kg/day of Aroclor 1254 disrupted the mRNA expression of 1,308 genes in newborn granule cells. Genes involved in mitochondrial functions were highly enriched with 154 genes significantly increased in exposed compared to control mice. The upregulation of genes involved in oxidative phosphorylation was accompanied by signs of endoplasmic reticulum stress and an increase in lipid peroxidation, a marker of oxidative stress, in the subgranular zone of the dentate gyrus but not in mature granule cells in the granular zone. Aroclor 1254 exposure also disrupted the expression of synaptic genes. Using laser-captured subgranular and granular zones, this effect was restricted to the subgranular zone, where newborn neurons are located. Conclusion: Our data suggest that gene expression in newborn granule cells is disrupted by Aroclor 1254 and provide clues to the effects of endocrine-disrupting chemicals on the brain.

Temporal Transcript Profiling Identifies a Role for Unfolded Protein Stress in Human Gut Ischemia-Reperfusion Injury.

Background & AimsIntestinal ischemia-reperfusion injury is a serious and life-threatening condition. A better understanding of molecular mechanisms related to intestinal ischemia-reperfusion injury in human beings is imperative to find therapeutic targets and improve patient outcome.MethodsFirst, the in vivo dynamic modulation of mucosal gene expression of the ischemia-reperfusion–injured human small intestine was studied. Based on functional enrichment analysis of the changing transcriptome, one of the predominantly regulated pathways was selected for further investigation in an in vitro human intestinal organoid model.ResultsIschemia-reperfusion massively changed the transcriptional landscape of the human small intestine. Functional enrichment analysis based on gene ontology and pathways pointed to the response to unfolded protein as a predominantly regulated process. In addition, regulatory network analysis identified hypoxia-inducing factor 1A as one of the key mediators of ischemia-reperfusion–induced changes, including the unfolded protein response (UPR). Differential expression of genes involved in the UPR was confirmed using quantitative polymerase chain reaction analysis. Electron microscopy showed signs of endoplasmic reticulum stress. Collectively, these findings point to a critical role for unfolded protein stress in intestinal ischemia-reperfusion injury in human beings. In a human intestinal organoid model exposed to hypoxia-reoxygenation, attenuation of UPR activation with integrated stress response inhibitor strongly reduced pro-apoptotic activating transcription factor 4 (ATF4)-CCAAT/enhancer-binding protein homologous protein (CHOP) signaling.ConclusionsTranscriptome analysis showed a crucial role for unfolded protein stress in the response to ischemia-reperfusion in human small intestine. UPR inhibition during hypoxia-reoxygenation in an intestinal organoid model suggests that downstream protein kinase R-like ER kinase (PERK) signaling may be a promising target to reduce intestinal ischemia-reperfusion injury. Microarray data are available in GEO (https://www.ncbi.nlm.nih.gov/gds, accession number GSE37013).

Induction of Premature Cell Senescence Stimulated by High Doses of Antioxidants Is Mediated by Endoplasmic Reticulum Stress.

In our previous study, we found that high doses of several substances with antioxidant capacities (Tempol, resveratrol, diphenyleneiodonium) can cause genotoxic stress and induce premature senescence in the human mesenchymal stem cells (MSCs). Here, using whole-transcriptome analysis, we revealed the signs of endoplasmic reticulum stress and unfolded protein response (UPR) in MSCs stressed with Tempol and resveratrol. In addition, we found the upregulation of genes, coding the UPR downstream target APC/C, and E3 ubiquitin ligase that regulate the stability of cell cycle proteins. We performed the molecular analysis, which further confirmed the untimely degradation of APC/C targets (cyclin A, geminin, and Emi1) in MSCs treated with antioxidants. Human fibroblasts responded to antioxidant applications similarly. We conclude that endoplasmic reticulum stress and impaired DNA synthesis regulation can be considered as potential triggers of cell damage and premature senescence stimulated by high-dose antioxidant treatments.

A TRANSLATIONAL PHASE I STUDY OF TAUROURSODEOXYCHOLIC ACID (TUDCA) TO REDUCE SYMPTOMS AND ER STRESS IN ACTIVE ULCERATIVE COLITIS

Abstract Background Emerging evidence has demonstrated that protein misfolding in the endoplasmic reticulum (ER), i.e., ER stress, plays fundamental roles in IBD development in humans. Patients with active Crohn’s disease and ulcerative colitis exhibit signs of ER stress in their ileal and/or colonic epithelium. Human genetic studies of IBD have identified primary genetic abnormalities in several genes that encode proteins associated with ER stress. We recently reported that oral delivery of tauroursodeoxycholic acid (TUDCA), a naturally occurring bile salt proven to reduce ER stress both in vitro and in vivo, dramatically decreases the clinical, histological and biochemical signs of inflammation in four different IBD mouse models through reducing ER stress in colonic epithelial cells. Aim Based on this, our aim was to test the efficacy and safety of TUDCA in an open label, Phase I trial for patients with symptomatic ulcerative colitis. Methods TUDCA was administered at 2000 mg divided TID for 6 weeks. Baseline and 6 week colonoscopy/flexible sigmoidoscopy with biopsy was performed. Outcome measures include safety, tolerability, Mayo score, and change in markers of ER stress from colon biopsies. Results To date, complete data is available on 9 of a planned 12 patients. TUDCA was well tolerated and safe with no Grade 3 or greater CTCAE adverse events and no Serious Adverse Events. A significant reduction of 4.6 points on the complete Mayo score was observed from baseline to week 6 (Avg. 8.6 ± 2.5 → 4.00 ± 2.7, P=0.004) with 100% of patients seeing a decrease. Clinical remission, clinical response and mucosal healing were observed in 22%, 67% and 56% respectively. Fecal calprotectin decreased in 67% of patients. As diarrhea can be a side effect of TUDCA treatment at these doses, we also assessed the Partial Mayo Score at two weeks after completion of the trial (8 weeks from baseline). At this time point the Partial Mayo Score significantly decreased by 3.8 points (Avg. 6.2 ± 2.1 → 2.4 ± 1.9, P=0.004) with 67% achieving clinical response and 56% remission. The Robarts Histopathology Index decreased in 8 of 9 patients with a mean reduction of 2.67 points (Avg. 6.4 ± 3.2 → 3.8 ± 2.9, P=0.003). Total serum bile acid profiles changed, but not significantly so, from Wk0 to Wk6. ER stress markers Bip, eIF2a and p-eIF2a were increased in inflamed colon tissue and were lowered post TUDCA treatment in a subset of patients. Conclusions Preliminary results from a Phase I clinical trial demonstrate that the dietary supplement TUDCA is safe, well tolerated and is associated with significant clinical improvement in a majority of patients with moderate to severely active ulcerative colitis. Mucosal healing and reductions in markers of ER stress were observed in a subset of patients. Study completion and analysis of gene expression and microbiome are underway.

2120-P: The Protein Phosphatase M1K Connects Glucose Sensing to Protein Translation in Pancreatic Beta Cells

The protein phosphatase m1K (PPm1K) dephosphorylates and activates the rate limiting enzyme in the branched-chain amino acid (BCAA) catabolism pathway, branched chain a-keto acid dehydrogenase (BCKDH). A common single nucleotide polymorphism upstream of the gene for PPm1K is associated with elevated circulating levels of BCAA and increased risk for development of type 2 diabetes; however, the function of PPm1K in the pancreatic beta cell has not been assessed. In line with our previous observations in liver, we found that increasing glucose concentrations in INS1 cells results in elevated expression of the ChREBP β isoform and lower PPM1K mRNA expression. SiRNA-mediated knockdown (KD) of PPm1K to levels achieved by glucose in INS1 cells lead to robust phosphorylation of the ribosomal protein S6 on its regulatory phosphosites ser235/236 and ser240/s244. Notably, this occurred absent any effect on the phosphorylation of the upstream proteins mammalian target of rapamycin (mTOR) or p70 S6 Kinase (S6K) and could not be reversed by inhibiting BCKDH phosphorylation with the small molecule, BT2. Thus Ppm1K appears to regulate S6 independently of mTOR, S6K, and BCKDH. Surface sensing of translation (SUnSET) studies revealed that the increase in S6 phosphorylation in PPm1K KD INS1 cells is associated with a 2-fold increase in protein translation rate. Accordingly, PPm1K KD increased both insulin content and glucose stimulated insulin secretion in INS1 cells. In line with the higher translation rate, PPm1K KD cells displayed signs of endoplasmic reticulum stress including increased expression of spliced xbp1 and Bip mRNA. In conclusion, our data highlight a new role for PPm1K in pancreatic beta cells, as a mechanism connecting glucose sensing to protein translation via modulation of S6 phosphorylation. Disclosure Y. Deleye: None. J. Herring: None. K.H. Hess: None. B. Leininger: None. R.W. McGarrah: None. J.S. Tessem: None. P.J. White: None. Funding American Diabetes Association/Pathway to Stop Diabetes (1-16-INI-17 to P.J.W.)

The neuroprotective role of microglial cells against amyloid beta-mediated toxicity in organotypic hippocampal slice cultures.

During Alzheimer’s disease (AD) progression, microglial cells play complex roles and have potentially detrimental as well as beneficial effects. The use of appropriate model systems is essential for characterizing and understanding the roles of microglia in AD pathology. Here, we used organotypic hippocampal slice cultures (OHSCs) to investigate the impact of microglia on amyloid beta (Aβ)‐mediated toxicity. Neurons in OHSCs containing microglia were not vulnerable to cell death after 7 days of repeated treatment with Aβ1‐42 oligomer‐enriched preparations. However, when clodronate was used to remove microglia, treatment with Aβ1‐42 resulted in significant neuronal death. Further investigations indicated signs of endoplasmic reticulum stress and caspase activation after Aβ1‐42 challenge only when microglia were absent. Interestingly, microglia provided protection without displaying any classic signs of activation, such as an amoeboid morphology or the release of pro‐inflammatory mediators (e.g., IL‐6, TNF‐α, NO). Furthermore, depleting microglia or inhibiting microglial uptake mechanisms resulted in significant more Aβ deposition compared to that observed in OHSCs containing functional microglia, suggesting that microglia efficiently cleared Aβ. Because inhibiting microglial uptake increased neuronal cell death, the ability of microglia to engulf Aβ is thought to contribute to its protective properties. Our study argues for a beneficial role of functional ramified microglia whereby they act against the accumulation of neurotoxic forms of Aβ and support neuronal resilience in an in situ model of AD pathology.

EIF2α phosphorylation is pathognomonic for immunogenic cell death.

The phosphorylation of eIF2α is essential for the endoplasmic reticulum (ER) stress response, the formation of stress granules, as well as macroautophagy. Several successful anticancer chemotherapeutics have the property to induce immunogenic cell death (ICD), thereby causing anticancer immune responses. ICD is accompanied by the translocation of calreticulin (CALR) from the ER lumen to the plasma membrane, which facilitates the transfer of tumor-associated antigens to dendritic cells. Here we systematically investigated the capacity of anticancer chemotherapeutics to induce signs of ER stress. ICD inducers including anthracyclines and agents that provoke tetraploidization were highly efficient in enhancing the phosphorylation of eIF2α, yet failed to stimulate other signs of ER stress including the transcriptional activation of activating transcription factor 4 (ATF4), the alternative splicing of X-box binding protein 1 (XBP1s) mRNA and the proteolytic cleavage of activating transcription factor 6 (ATF6) both in vitro and in cancers established in mice. Systematic analyses of clinically used anticancer chemotherapeutics revealed that only eIF2α phosphorylation, but none of the other signs of ER stress, correlated with CALR exposure. eIF2α phosphorylation induced by mitoxantrone, a prototype ICD-inducing anthracyline, was mediated by eIF2α kinase-3 (EIF2AK3). Machine-learning approaches were used to determine the physicochemical properties of drugs that induce ICD, revealing that the sole ER stress response relevant to the algorithm is eIF2α phosphorylation with its downstream consequences CALR exposure, stress granule formation and autophagy induction. Importantly, this approach could reduce the complexity of compound libraries to identify ICD inducers based on their physicochemical and structural characteristics. In summary, it appears that eIF2α phosphorylation constitutes a pathognomonic characteristic of ICD.

Development of Endoplasmic Reticulum Stress during Experimental Oxalate Nephrolithiasis.

Morphological and ultrastructural study of the kidney was performed in rats with oxalate nephrolithiasis. Specific features of endoplasmic reticulum stress were evaluated during nephrolithiasis and treatment with α-tocopherol. We observed the signs of endoplasmic reticulum stress with activation of proapoptotic pathways and injury to the cell lining in nephron tubules and collecting ducts. Ultrastructural changes were found in the organelles, nuclei, and cell membranes of epitheliocytes. A relationship was revealed between endoplasmic reticulum stress and oxidative damage, which developed at the early state of lithogenesis.

Effect of Calreticulin on Ca2+/CaM KinaseIIα and Endoplasmic Reticulum Stress in Hippocampal in a Rat Model of Post-traumatic Stress Disorder

The purpose of the present study was to examine the changes in the molecular chaperone calreticulin (CRT), calcium signaling pathway Ca(2+)-calmodulin (CaM)-CaM kinaseIIα (CaMKIIα), and the endoplasmic reticulum (ER) apoptotic modulator caspase-12 in hippocampal neurons of rats exposed to single-prolonged stress (SPS), a model of post-traumatic stress disorder (PTSD). Molecular markers and proteins were assessed using immunohistochemistry, western blot and reverse transcript-polymerase chain reaction in rats exposed to SPS at 1 day (1d), 4 and 7 days post-stress and time matched controls. We found that at 7 days, SPS rats had the highest CRT expression. The intracellular free Ca(2+) and the CaM expression reached peak at 1 day post-SPS whereas the CaMKIIα had the opposite trend. Caspase-12 was most active at 4 days and was found to decrease thereafter. Signs of apoptosis were identified using transmission electron microscopy in the rats exposed to SPS. The results indicate that signs of ER stress in the hippocampus of rats exposed to SPS trigger the molecular changes in the intracellular cytoplasm which in turn activate the apoptotic pathway through caspase-12. Therefore, we propose that the hippocampal apoptosis could be one of the pathological mechanisms related to the memory disorders in PTSD.

COL4A2 mutation associated with familial porencephaly and small-vessel disease

Familial porencephaly, leukoencephalopathy and small-vessel disease belong to the spectrum of disorders ascribed to dominant mutations in the gene encoding for type IV collagen alpha-1 (COL4A1). Mice harbouring mutations in either Col4a1 or Col4a2 suffer from porencephaly, hydrocephalus, cerebral and ocular bleeding and developmental defects. We observed porencephaly and white matter lesions in members from two families that lack COL4A1 mutations. We hypothesized that COL4A2 mutations confer genetic predisposition to porencephaly, therefore we sequenced COL4A2 in the family members and characterized clinical, neuroradiological and biochemical phenotypes. Genomic sequencing of COL4A2 identified the heterozygous missense G1389R in exon 44 in one family and the c.3206delC change in exon 34 leading to frame shift and premature stop, in the second family. Fragmentation and duplication of epidermal basement membranes were observed by electron microscopy in a c.3206delC patient skin biopsy, consistent with abnormal collagen IV network. Collagen chain accumulation and endoplasmic reticulum (ER) stress have been proposed as cellular mechanism in COL4A1 mutations. In COL4A2 (3206delC) fibroblasts we detected increased rates of apoptosis and no signs of ER stress. Mutation phenotypes varied, including porencephaly, white matter lesions, cerebellar and optic nerve hypoplasia and unruptured carotid aneurysm. In the second family however, we found evidence for additional factors contributing to the phenotype. We conclude that dominant COL4A2 mutations are a novel major risk factor for familial cerebrovascular disease, including porencephaly and small-vessel disease with reduced penetrance and variable phenotype, which might also be modified by other contributing factors.

바우미 상황버섯 추출물의 항염증 효과에 관한 연구

This study is to characterize the postulated anti-inflammatory effect of the hot water extracts from the Phellinus baumii. RAW264.7, macrophage cell line, was activated by lipopolysaccharide (LPS) and, further, treated with Phellinus baumii`s aqueous extract. When the cultured macrophage cells were treated with LPS, they show typical signs of endoplasmic reticulum stress (ERS) and an increment in secretion of inflammatory cytokine compared to the non-treated control: The expression of glucose-regulated protein78 (Grp78), Grp94, and C/EBP homologous protein/GADD 153 (CHOP) increased along with augmented secretion of interlukin-6. Cellular nitric oxide content also significantly went up in comparison to the non-LPS treatment. When the LPS-treated RAW264.7 was treated with the aqueous Phellinus baumii extracts, however, the expression of ERS markers markedly reduced and the release of nitric oxide declined. Also, the expression of induced nitric oxide synthase (iNOS) notably diminished similarly as the NO content. In conclusion, this study strongly indicated that aqueous Phellinus baumii extract can be utilized directly as anti-inflammation agent and serves as a source of functional ingredient to lessen the inflammation.

Cellular Response to Cigarette Smoke and Oxidants: Adapting to Survive

The gaseous and soluble phases of cigarette smoke are sources of oxidants that contribute to the pathogenesis of chronic obstructive pulmonary disease (COPD). Chronic oxidative stress of cigarette smoking induces mucus secretion and inhibits cystic fibrosis transmembrane conductance regulator function. The increased mucus viscosity renders the airways susceptible to bacterial infections, a hallmark of chronic bronchitis. Furthermore, lungs chronically exposed to the toxic mixture of oxidants in cigarette smoke show signs of endoplasmic reticulum stress, unfolded protein response, altered ceramide metabolism, and apoptosis. Fortunately, the respiratory tract has developed effective adaptive cellular mechanisms to limit oxidant damage. Numerous antioxidant enzymes and glutathione-dependent detoxification systems are increased in healthy smokers. The regulation of the antioxidant response is largely dependent on the nuclear factor erythroid 2-related factor-2 (Nrf2) pathway. However, patients with COPD have defective Nrf2 responses. Novel therapies such as 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) to correct defective Nrf2-dependent cellular response may hold promise for patients with COPD.

Amyotrophic Lateral Sclerosis Pathogenesis: A Journey Through the Secretory Pathway

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motoneuron degenerative disease characterized by the selective loss of motoneurons in the spinal ventral horn, most brainstem nuclei, and the cerebral cortex. Although approximately 90% of ALS cases are sporadic (sALS), analyses of familial ALS (fALS)-causative genes have generated relevant insight into molecular events involved in the pathology. Here we overview an emerging concept indicating the occurrence of secretory pathway stress in the disease process. These alterations include a failure in the protein folding machinery at the endoplasmic reticulum (ER), engagement of the unfolded protein response (UPR), modifications of the Golgi apparatus network, impaired vesicular trafficking, inhibition of protein quality control mechanisms, oxidative damage to ER proteins, and sustained activation of degradative pathways such as autophagy. A common feature predicted for most of these alterations is abnormal protein homeostasis associated with the accumulation of misfolded proteins at the ER, possibly leading to chronic ER stress and neuronal dysfunction. Signs of ER stress are observed even during presymptomatic stages in fALS mouse models, and pharmacological strategies to alleviate protein misfolding slow disease progression. Because the secretory pathway stress occurs in both sALS and several forms of fALS, it may offer a unique common target for possible therapeutic strategies to treat this devastating disease.

Intraluminal hydrogen peroxide induces a permeability change of the endoplasmic reticulum membrane

Gulonolactone treatment of mice resulted in the elevation of hepatic ascorbate and hydrogen peroxide levels accompanied by transient liver swelling and reversible dilatation of endoplasmic reticulum cisternae. Although a decrease in glutathione (reduced form)/total glutathione ratio was observed in microsomes, the redox state of luminal foldases remained unchanged and the signs of endoplasmic reticulum stress were absent. Increased permeability of the microsomal membrane to various compounds of low molecular weight was substantiated. It is assumed that Gulonolactone-dependent luminal hydrogen peroxide formation in the endoplasmic reticulum provokes a temporary increase in non-selective membrane permeability, which results in the dilation of the organelle and in enhanced transmembrane fluxes of small molecules.

Rosiglitazone protects against beta cell destruction in ZDF (Type 2) diabetic rats

The progression of type 2 diabetes involves insulin resistance, impairment in insulin secretion, and eventual loss of β‐cell mass. Current therapies largely address insulin sensitivity and secretion but it is also important that therapies be found which protect against β‐cell loss. Finegood et al (2000) have reported that rosiglitazone (RSG) treatment largely prevents loss of β‐cell mass. We have confirmed this observation and present new information on islet morphology during this process. Examination of pancreas sections from 6 week‐old ZDF fa/fa rats, by means of double immunofluorescence staining for insulin and glucagon, revealed the normal oval morphology of islets with a mantle of α‐cells at the periphery and β‐cells in the central region. Six weeks of treatment with RSG (10 μmol/kg BW/day) maintained this structure whereas, in untreated rats, the islets had lost their normal architecture. After another 6 weeks, atrophy of the islets, fibrosis and loss of insulin‐positive cells was observed in the untreated rats whereas in the treated group, the islets were larger with numerous insulin‐positive cells. However, at this time point, islets from both groups showed diffusion into exocrine tissue and loss of the α‐cell mantle. The appearance of signs of endoplasmic reticulum stress during the loss of islet integrity was also protected against by RSG. (Supported by CIHR and Canadian Diabetes Association).

Nitric oxide selectively depletes macrophages in atherosclerotic plaques via induction of endoplasmic reticulum stress

Macrophages in atherosclerotic plaques have a tremendous impact on atherogenesis and plaque destabilization. We previously demonstrated that treatment of plaques in cholesterol-fed rabbits with the nitric oxide (NO) donor molsidomine preferentially eliminates macrophages, thereby favouring features of plaque stability. In this study, we investigated the underlying mechanism. Macrophages and smooth muscle cells (SMCs) were treated in vitro with the NO donors, spermine NONOate or S-nitroso-N-acetylpenicillamine (SNAP) as well as with the well-known endoplasmic reticulum (ER) stress inducers thapsigargin, tunicamycin, dithiothreitol or brefeldin A. Cell viability was analysed by Neutral Red viability assays. Cleavage of caspase-3, DNA fragmentation and ultrastructural changes were examined to characterize the type of macrophage death. Induction of ER stress was evaluated by measuring C/EBP homologous protein (CHOP) expression, phosphorylation of eukaryotic initiation factor 2 alpha (eIF2a), splicing of X-box binding protein 1 (XBP1) and inhibition of protein synthesis. Macrophages and SMCs treated with spermine NONOate or SNAP showed several signs of ER stress, including upregulation of CHOP expression, hyperphosphorylation of eIF2 alpha, inhibition of de novo protein synthesis and splicing of XBP1 mRNA. These effects were similar in macrophages and SMCs, yet only macrophages underwent apoptosis. Plaques from molsidomine-treated atherosclerotic rabbits showed a 2.7-fold increase in CHOP expression as compared to placebo. Beside NO, selective induction of macrophage death could be initiated with thapsigargin and tunicamycin. Induction of ER stress explains selective depletion of macrophages in atherosclerotic plaques by a NO donor, probably via inhibition of protein synthesis.