The unfolding tale of the unfolded protein response

Glucose sensing and the unfolded protein response

The unfolded protein response (UPR) is activated primarily upon alteration of protein folding in the endoplasmic reticulum (ER). This occurs under physiological situations that cause an abrupt increase in protein synthesis, or under redox and metabolic stresses. Among the latter, hyperglycemia and glucose scarcity have been identified as major modulators of UPR signaling. Indeed, the first mammalian UPR effector, the glucose-regulated protein 78, also known as BiP, was identified in response to glucose deprivation. Tunicamycin, arguably the most commonly used drug to induce ER stress responses in vitro and in vivo, is an inhibitor of N-glycosylation. We compile here evidence that the UPR is activated upon physiological and pathological conditions that alter glucose levels and that this is mostly mediated by alterations of protein N-glycosylation, ATP levels, or redox balance. The three branches of the UPR transduced by PERK/ATF4, IRE1/XBP1s, and ATF6, as well as non-canonical ER sensors such as SCAP/SREBP, sense ER protein glycosylation status driven by glucose and other glucose-derived metabolites. The outcomes of UPR activation range from restoring protein N-glycosylation and protein folding flux to stimulating autophagy, organelle recycling, and mitochondrial respiration, and in some cases, cell death. Anabolic responses to glucose levels are also stimulated by glucose through components of the UPR. Therefore, the UPR should be further studied as a potential biomarker and mediator of glucose-associated diseases.

AMX0035 Mitigates Oligodendrocyte Apoptosis and Ameliorates Demyelination in MCAO Rats by Inhibiting Endoplasmic Reticulum Stress and Mitochondrial Dysfunction

Post-stroke cognitive impairment (PSCI) is a common complication of strokes and is associated with the demyelination of nerve fibers. AMX0035, a drug currently used to treat motor neuron diseases, may aid in preventing oligodendrocyte apoptosis and alleviating demyelination by targeting the pathways involved in ERS and mitochondrial dysfunction. All animals were randomly divided into four groups: the sham, sham+AMX0035, middle cerebral artery occlusion (MCAO), and MCAO+AMX0035 group. The Morris water maze was used to test cognitive function, and changes in myelin structure in the brain were investigated using transmission electron microscopy (TEM), Luxol fast blue (LFB) staining, and myelin basic protein (MBP) immunofluorescence staining. Western blot was performed to detect proteins associated with ER stress and mitochondrial dysfunction, and double-labeling immunofluorescence was utilized to localize oligodendrocytes and apoptosis-related proteins. Neurological function scores and TTC staining confirmed the successful establishment of the MCAO rat model. The Morris water maze experiment revealed impaired cognitive function in MCAO rats, which significantly improved following the AMX0035 intervention. TEM and LFB staining showed the disrupted myelin structure in the MCAO group, while AMX0035 effectively ameliorated this myelin damage. Immunofluorescence examination and Western blot revealed the decreased expression of MBP in MCAO rats, increasing with AMX0035 treatment. TUNEL staining demonstrated increased cell apoptosis in MCAO rats, which was reduced following AMX0035 therapy. Western blot detected significant increases in proteins associated with the ER stress pathway and proteins linked to mitochondrial dysfunction in the MCAO group, all of which were downregulated after AMX0035 intervention. Double-labeling immunofluorescence staining revealed a significant increase in the number of cytochrome c+ and caspase 12+ oligodendrocyte cells in MCAO rats, which decreased after AMX0035 administration. The activation of ER stress and mitochondrial dysfunction pathways following MCAO led to oligodendrocyte damage and apoptosis. AMX0035 can inhibit these pathways, reduce oligodendrocyte apoptosis, and alleviate demyelination, thereby improving PSCI.

Lipid droplets in the nervous system: involvement in cell metabolic homeostasis

Lipid droplets serve as primary storage organelles for neutral lipids in neurons, glial cells, and other cells in the nervous system. Lipid droplet formation begins with the synthesis of neutral lipids in the endoplasmic reticulum. Previously, lipid droplets were recognized for their role in maintaining lipid metabolism and energy homeostasis; however, recent research has shown that lipid droplets are highly adaptive organelles with diverse functions in the nervous system. In addition to their role in regulating cell metabolism, lipid droplets play a protective role in various cellular stress responses. Furthermore, lipid droplets exhibit specific functions in neurons and glial cells. Dysregulation of lipid droplet formation leads to cellular dysfunction, metabolic abnormalities, and nervous system diseases. This review aims to provide an overview of the role of lipid droplets in the nervous system, covering topics such as biogenesis, cellular specificity, and functions. Additionally, it will explore the association between lipid droplets and neurodegenerative disorders. Understanding the involvement of lipid droplets in cell metabolic homeostasis related to the nervous system is crucial to determine the underlying causes and in exploring potential therapeutic approaches for these diseases.

A statistical mechanics investigation of unfolded protein response across organisms

Living systems rely on coordinated molecular interactions, especially those related to gene expression and protein activity. The Unfolded Protein Response is a crucial mechanism in eukaryotic cells, activated when unfolded proteins exceed a critical threshold. It maintains cell homeostasis by enhancing protein folding, initiating quality control, and activating degradation pathways when damage is irreversible. This response functions as a dynamic signaling network, with proteins as nodes and their interactions as edges. We analyze these protein-protein networks across different organisms to understand their intricate intra-cellular interactions and behaviors. In this work, analyzing twelve organisms, we assess how fundamental measures in network theory can individuate seed proteins and specific pathways across organisms. We employ network robustness to evaluate and compare the strength of the investigated protein-protein interaction networks, and the structural controllability of complex networks to find and compare the sets of driver nodes necessary to control the overall networks. We find that network measures are related to phylogenetics, and advanced network methods can identify main pathways of significance in the complete Unfolded Protein Response mechanism.

Antifungal Tetrahydrocarbazole Compound CAR-8 Induces Endoplasmic Reticulum Stress in Candida albicans

The development of new effective antifungal agents is essential to combat fungal infections. Tetrahydrocarbazole has been exploited as a promising skeleton against various pathogenic microorganisms and is used to search for novel active antifungal compounds. In this study, a library composed of small tetrahydrocarbazole compounds was screened, and a potent antifungal agent, CAR-8, was identified with a minimum inhibitory concentration of 2-4 μg/mL against Candida albicans. CAR-8 showed strong fungicidal activities and killed almost all C. albicans within 3 h at a concentration of 16 μg/mL. At concentrations of 2 and 8 μg/mL, CAR-8 significantly inhibited the formation of hyphae and biofilms. Moreover, CAR-8 at 10 and 20 mg/kg reduced the fungal load and improved the survival in the C. albicans infection model in the invertebrate Galleria mellonella. Transcriptome analysis revealed significant changes in the expression of genes associated with protein processing in the endoplasmic reticulum (ER), ER-associated degradation, and unfolded protein response (UPR), which suggested that CAR-8 treatment induced ER stress. Moreover, CAR-8 treatment resulted in various phenotypes similar to tunicamycin, a classical ER stress inducer. These included nonconventional splicing of HAC1 mRNA, the fragmented morphology of ER, the distribution changes of GFP-Snc1 in Saccharomyces cerevisiae, and cell apoptosis probably caused by ER stress. More importantly, the disruption of IRE1 or HAC1 increased the sensitivity of C. albicans to CAR-8, confirming that the UPR signaling pathway was critical for CAR-8 resistance. Overall, our study identifies a potent ER stress-induced antifungal compound that will help the discovery of new antifungal drugs.

Drug-induced ER stress leads to induction of programmed cell death pathways of the malaria parasite

The rapid emergence of drug resistance against the mainstream antimalarial drugs has increased the need for development of novel drugs. Recent approaches have embarked on the repurposing of existing drugs to induce cell death via programmed cell death pathways. However, little is known about the ER stress response and programmed cell death pathways of the malaria parasite. In this study, we treated ex vivo Plasmodium berghei cultures with tunicamycin, 5-fluorouracil, and chloroquine as known stress inducer drugs to probe the transcriptional changes of autophagy and apoptosis-related genes (PbATG5, PbATG8, PbATG12, and PbMCA2). Treatments with 5-fluorouracil and chloroquine resulted in the upregulation of all analyzed markers, yet the levels of PbATG5 and PbATG12 were dramatically higher in chloroquine-treated ex vivo cultures. In contrast, tunicamycin treatment resulted in the downregulation of both PbATG8 and PbATG12, and upregulation of PbMCA2. Our results indicate that the malaria parasite responds to various ER stressors by inducing autophagy- and/or apoptosis-like pathways.

sUPRa is a dual-color reporter for unbiased quantification of the unfolded protein response with cellular resolution

The unfolded protein response (UPR) maintains proteostasis upon endoplasmic reticulum (ER) stress, and is initiated by a range of physiological and pathological processes. While there have been advances in developing fluorescent reporters for monitoring individual signaling pathways of the UPR, this approach may not capture a cell's overall UPR activity. Here we describe a novel sensor of UPR activity, sUPRa, which is designed to report the global UPR. sUPRa displays excellent response characteristics, outperforms reporters of individual UPR pathways in terms of sensitivity and kinetics, and responds to a range of different ER stress stimuli. Furthermore, sUPRa's dual promoter and fluorescent protein design ensures that both UPR-active and inactive cells are detected, and controls for reporter copy number. Using sUPRa, we reveal UPR activation in layer 2/3 pyramidal neurons of mouse cerebral cortex following a period of sleep deprivation. sUPRa affords new opportunities for quantifying physiological UPR activity with cellular resolution.

The Interplay Between Endoplasmic Reticulum Stress and Oxidative Stress in Chondrocyte Catabolism

OBJECTIVE

Oxidative stress and endoplasmic reticulum (ER) stress play pivotal roles in disrupting the homeostasis of chondrocytes by producing catalytic proteases and enhancing chondrocyte senescence, consequently contributing to the progression of osteoarthritis (OA). Despite their close interaction, the underlying molecular mechanisms remain poorly understood. Here, we show that ER stress and oxidative stress reciprocally modulate each other to promote cartilage degradation.

METHODS

Primary chondrocytes were obtained from the articular cartilage of 5-day-old C57BL/6J mice by excising distal femur and proximal tibia. Tunicamycin was applied to induce ER stress in primary chondrocytes. Surgical OA was induced in 12-week-old male C57BL/6J mice by destabilizing the medial meniscus (DMM).

RESULTS

Tunicamycin-induced ER stress led to an increase in the production of reactive oxygen species (ROS) and catalytic proteases, including MMP13 and Adamts5, in primary chondrocytes, and it was primarily dependent on the NADPH oxidase (NOX) system. ER stress directly increased the expression of NOX2, NOX3, NOX4, and p22phox. Specifically, the protein kinase RNA-like ER kinase (PERK) pathway is involved in the expression of NOX4 and p22phox, the inositol-requiring enzyme 1 alpha (IRE1α) pathway in NOX2 and NOX3 expression, and the activating transcription factor 6 (ATF6) pathway influences NOX3 expression in chondrocytes. Conversely, inhibiting NOX function significantly reduced both ER stress sensor-related signaling and chondrocyte catabolism, thereby decelerating the progression of surgically induced OA in vivo.

CONCLUSIONS

Our findings highlight the positive feedback loop between ER stress and oxidative stress in OA pathogenesis, suggesting that targeting NOX isoforms is a promising therapeutic strategy for OA.

The Multiple Roles of Autophagy in Neural Function and Diseases

Autophagy involves the sequestration and delivery of cytoplasmic materials to lysosomes, where proteins, lipids, and organelles are degraded and recycled. According to the way the cytoplasmic components are engulfed, autophagy can be divided into macroautophagy, microautophagy, and chaperone-mediated autophagy. Recently, many studies have found that autophagy plays an important role in neurological diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, neuronal excitotoxicity, and cerebral ischemia. Autophagy maintains cell homeostasis in the nervous system via degradation of misfolded proteins, elimination of damaged organelles, and regulation of apoptosis and inflammation. AMPK-mTOR, Beclin 1, TP53, endoplasmic reticulum stress, and other signal pathways are involved in the regulation of autophagy and can be used as potential therapeutic targets for neurological diseases. Here, we discuss the role, functions, and signal pathways of autophagy in neurological diseases, which will shed light on the pathogenic mechanisms of neurological diseases and suggest novel targets for therapies.

Autophagy as an Anti-senescent in Aging Neurocytes

Neuron homeostasis is crucial for the organism, and its maintenance is multifactorial, including autophagy. The turnover of aberrant intracellular components is a fundamental pathogenetic mechanism for cell aging. Autophagy is involved in the acceleration of the neurocyte aging process and the modification of cell longevity. Neurocyte aging is a process of loss of cell identity through cellular and subcellular changes that include molecular loss of epigenetics, transcriptomic, proteomic, and autophagy dysfunction. Autophagy dysfunction is the hallmark of neurocyte aging. Cell aging is the credential feature of neurodegenerative diseases. Pathophysiologically, aged neurocytes are characterized by dysregulated autophagy and subsequently neurocyte metabolic stress, resulting in accelerated neurocyte aging. In particular, chaperone- mediated autophagy perturbation results in upregulated expression of aging and apoptosis genes. Aged neurocytes are also characterized by the down-regulation of autophagy-related genes, such as ATG5-ATG12, LC3-II / LC3-I ratio, Beclin-1, and p62. Slowing aging through autophagy targeting is sufficient to improve prognosis in neurodegenerative diseases. Three primary anti-senescent molecules are involved in the aging process: mTOR, AMPK, and Sirtuins. Autophagy therapeutic effects can be applied to reverse and slow aging. This article discusses current advances in the role of autophagy in neurocyte homeostasis, aging, and potential therapeutic strategies to reduce aging and increase cell longevity.

Grp78 is required for intestinal Kras-dependent glycolysis proliferation and adenomagenesis

In development of colorectal cancer, mutations in APC are often followed by mutations in oncogene KRAS The latter changes cellular metabolism and is associated with the Warburg phenomenon. Glucose-regulated protein 78 (Grp78) is an important regulator of the protein-folding machinery, involved in processing and localization of transmembrane proteins. We hypothesize that targeting Grp78 in Apc and Kras (AK)-mutant intestines interferes with the metabolic phenotype imposed by Kras mutations. In mice with intestinal epithelial mutations in Apc, Kras G12D and heterozygosity for Grp78 (AK-Grp78 HET ) adenoma number and size is decreased compared with AK-Grp78 WT mice. Organoids from AK-Grp78 WT mice exhibited a glycolysis metabolism which was completely rescued by Grp78 heterozygosity. Expression and correct localization of glucose transporter GLUT1 was diminished in AK-Grp78 HET cells. GLUT1 inhibition restrained the increased growth observed in AK-mutant organoids, whereas AK-Grp78 HET organoids were unaffected. We identify Grp78 as a critical factor in Kras-mutated adenomagenesis. This can be attributed to a critical role for Grp78 in GLUT1 expression and localization, targeting glycolysis and the Warburg effect.

The Role of NMDA Receptor Partial Antagonist, Carbamathione, as a Therapeutic Agent for Transient Global Ischemia

Carbamathione (Carb), an NMDA glutamate receptor partial antagonist, has potent neuroprotective functions against hypoxia- or ischemia-induced neuronal injury in cell- or animal-based stroke models. We used PC-12 cell cultures as a cell-based model and bilateral carotid artery occlusion (BCAO) for stroke. Whole-cell patch clamp recording in the mouse retinal ganglion cells was performed. Key proteins involved in apoptosis, endoplasmic reticulum (ER) stress, and heat shock proteins were analyzed using immunoblotting. Carb is effective in protecting PC12 cells against glutamate- or hypoxia-induced cell injury. Electrophysiological results show that Carb attenuates NMDA-mediated glutamate currents in the retinal ganglion cells, which results in activation of the AKT signaling pathway and increased expression of pro-cell survival biomarkers, e.g., Hsp 27, P-AKT, and Bcl2 and decreased expression of pro-cell death markers, e.g., Beclin 1, Bax, and Cleaved caspase 3, and ER stress markers, e.g., CHOP, IRE1, XBP1, ATF 4, and eIF2α. Using the BCAO animal stroke model, we found that Carb reduced the brain infarct volume and decreased levels of ER stress markers, GRP 78, CHOP, and at the behavioral level, e.g., a decrease in asymmetric turns and an increase in locomotor activity. These findings for Carb provide promising and rational strategies for stroke therapy.

Effects of GRP78 on Endoplasmic Reticulum Stress and Inflammatory Response in Macrophages of Large Yellow Croaker (Larimichthys crocea)

Endoplasmic reticulum (ER) homeostasis plays a vital role in cell physiological functions. Various factors can destroy the homeostasis of the ER and cause ER stress. Moreover, ER stress is often related to inflammation. Glucose-regulated protein 78 (GRP78) is an ER chaperone, which plays a vital role in maintaining cellular homeostasis. Nevertheless, the potential effects of GRP78 on ER stress and inflammation is still not fully elucidated in fish. In the present study, ER stress and inflammation was induced by tunicamycin (TM) or palmitic acid (PA) in the macrophages of large yellow croakers. GRP78 was treated with an agonist/inhibitor before or after the TM/PA treatment. The results showed that the TM/PA treatment could significantly induce ER stress and an inflammatory response in the macrophages of large yellow croakers whereas the incubation of the GRP78 agonist could reduce TM/PA-induced ER stress and an inflammatory response. Moreover, the incubation of the GRP78 inhibitor could further induce TM/PA-induced ER stress and an inflammatory response. These results provide an innovative idea to explain the relationship between GRP78 and TM/PA-induced ER stress or inflammation in large yellow croakers.

Co-chaperones of the Human Endoplasmic Reticulum: An Update

In mammalian cells, the rough endoplasmic reticulum (ER) plays central roles in the biogenesis of extracellular plus organellar proteins and in various signal transduction pathways. For these reasons, the ER comprises molecular chaperones, which are involved in import, folding, assembly, export, plus degradation of polypeptides, and signal transduction components, such as calcium channels, calcium pumps, and UPR transducers plus adenine nucleotide carriers/exchangers in the ER membrane. The calcium- and ATP-dependent ER lumenal Hsp70, termed immunoglobulin heavy-chain-binding protein or BiP, is the central player in all these activities and involves up to nine different Hsp40-type co-chaperones, i.e., ER membrane integrated as well as ER lumenal J-domain proteins, termed ERj or ERdj proteins, two nucleotide exchange factors or NEFs (Grp170 and Sil1), and NEF-antagonists, such as MANF. Here we summarize the current knowledge on the ER-resident BiP/ERj chaperone network and focus on the interaction of BiP with the polypeptide-conducting and calcium-permeable Sec61 channel of the ER membrane as an example for BiP action and how its functional cycle is linked to ER protein import and various calcium-dependent signal transduction pathways.

Sec61 complex/translocon: The role of an atypical ER Ca2+-leak channel in health and disease

The heterotrimeric Sec61 protein complex forms the functional core of the so-called translocon that forms an aqueous channel in the endoplasmic reticulum (ER). The primary role of the Sec61 complex is to allow protein import in the ER during translation. Surprisingly, a completely different function in intracellular Ca2+ homeostasis has emerged for the Sec61 complex, and the latter is now accepted as one of the major Ca2+-leak pathways of the ER. In this review, we first discuss the structure of the Sec61 complex and focus on the pharmacology and regulation of the Sec61 complex as a Ca2+-leak channel. Subsequently, we will pay particular attention to pathologies that are linked to Sec61 mutations, such as plasma cell deficiency and congenital neutropenia. Finally, we will explore the relevance of the Sec61 complex as a Ca2+-leak channel in various pathophysiological (ER stress, apoptosis, ischemia-reperfusion) and pathological (type 2 diabetes, cancer) settings.

Integrative Transcriptomics and Proteomics Analysis Provide a Deep Insight Into Bovine Viral Diarrhea Virus-Host Interactions During BVDV Infection

Bovine viral diarrhea virus (BVDV) is the causative agent of bovine viral diarrhea-mucosal disease (BVD-MD), an important viral disease in cattle that is responsible for extensive economic losses to the cattle industry worldwide. Currently, several underlying mechanisms involved in viral replication, pathogenesis, and evading host innate immunity of BVDV remain to be elucidated, particularly during the early stage of virus infection. To further explore the mechanisms of BVDV-host interactions, the transcriptomics and proteomics profiles of BVDV-infected MDBK cells were sequenced using RNA-seq and iTRAQ techniques, respectively, and followed by an integrative analysis. Compared with mock-infected MDBK cells, a total of 665 differentially expressed genes (DEGs) (391 down-regulated, 274 up-regulated) and 725 differentially expressed proteins (DEPs) (461 down-regulated, 264 up-regulated) were identified. Among these, several DEGs and DEPs were further verified using quantitative RT-PCR and western blot. Following gene ontology (GO) annotation and KEGG enrichment analysis, we determined that these DEGs and DEPs were significantly enriched in multiple important cellular signaling pathways including NOD-like receptor, Toll-like receptor, TNF, NF-κB, MAPK, cAMP, lysosome, protein processing in endoplasmic reticulum, lipid metabolism, and apoptosis signaling pathways. Significantly, the down-regulated DEGs and DEPs were predominantly associated with apoptosis-regulated elements, inflammatory factors, and antiviral elements that were involved in innate immunity, thus, indicating that BVDV could inhibit apoptosis and the expression of host antiviral genes to facilitate viral replication. Meanwhile, up-regulated DEGs and DEPs were primarily involved in metabolism and autophagy signaling pathways, indicating that BVDV could utilize the host metabolic resources and cell autophagy to promote replication. However, the potential mechanisms BVDV-host interactions required further experimental validation. Our data provide an overview of changes in transcriptomics and proteomics profiles of BVDV-infected MDBK cells, thus, providing an important basis for further exploring the mechanisms of BVDV-host interactions.

Endothelial Intracellular ANG (Angiogenin) Protects Against Atherosclerosis by Decreasing Endoplasmic Reticulum Stress

BACKGROUND

ANG (angiogenin) is essential for cellular adaptation to endoplasmic reticulum (ER) stress, a process closely associated with cardiovascular diseases, including atherosclerosis. We aimed to investigate the role of ANG in the progression of atherosclerosis and elucidate its underlying molecular mechanisms.

METHODS

We constructed adenoassociated virus 9 ANG overexpression vectors and endothelial ANG- and ApoE (apolipoprotein E)-deficient mice to determine the effects of ANG on ER stress and atherosclerotic lesions. RNA sequencing of endothelial ANG- and ApoE-deficient mice identified ANG-dependent downregulation of ST3GAL5 (ST3 beta-galactoside alpha-2,3-sialyltransferase 5) expression, and the direct regulation of ST3GAL5 by ANG was verified by chromatin immunoprecipitation sequencing and luciferase reporter assay results.

RESULTS

Reanalysis of expression profiling datasets indicated decreased ANG levels in patients' atherosclerotic lesions, and these data were validated in aortas from ApoE^-/- mice. ER stress marker and adhesion molecule levels, aortic root lesions and macrophage deposition were substantially reduced in ApoE^-/- mice injected with an adenoassociated virus 9 ANG without signal peptide (ANG-ΔSP) overexpression vector compared with empty and full-length ANG overexpression vectors. Endothelial ANG deficiency significantly elevated ER stress and increased adhesion molecule expression, which aggravated atherosclerotic lesions and enhanced THP-1 monocyte adhesion to endothelial cells in vivo and in vitro, respectively. Furthermore, ANG-ΔSP overexpression significantly attenuated oxidized low-density lipoprotein-induced ER stress and THP-1 monocyte adhesion to endothelial cells, which were reversed by ST3GAL5 inhibition.

CONCLUSIONS

These results suggest that endothelial intracellular ANG is a novel therapeutic against atherosclerosis and exerts atheroprotective effects via ST3GAL5-mediated ER stress suppression.

Granulocyte colony-stimulating factor reduces the endoplasmic reticulum stress in a rat model of diabetic cardiomyopathy

Prolonged endoplasmic reticulum (ER) stress contributes to the apoptosis of cardiomyocytes, which leads to the development of diabetic cardiomyopathy. Previously, we reported that the granulocyte colony-stimulating factor (G-CSF) reduces the cardiomyocyte apoptosis in diabetic cardiomyopathy; however, the precise mechanisms associated with this process are not yet fully understood. Therefore, in this study, we investigated whether the mechanism of the anti-apoptotic effect of G-CSF was associated with ER stress in a rat model of diabetic cardiomyopathy. Diabetic cardiomyopathy was induced in rats using a high-fat diet combined with the administration of a low-dose of streptozotocin. Diabetic rats were treated with G-CSF or saline for 5 days. Cardiac function was evaluated using serial echocardiography before and 4 weeks after treatment. The rate of cardiomyocyte apoptosis and the expression levels of proteins related to ER stress, including glucose-regulated protein 78 (GRP78), caspase-9, and caspase-12 were analyzed in the cardiac tissue. G-CSF treatment significantly reduced cardiomyocyte apoptosis in the diabetic myocardium and downregulated the expression levels of these proteins in diabetic rats treated with low-dose streptozotocin when compared to that in rats treated with saline. In addition, G-CSF treatment significantly downregulated the expression levels of proteins related to ER stress, such as GRP78, inositol-requiring enzyme-1α (IRE-1α), and C/EBP homologous protein (CHOP) in H9c2 cells under high glucose (HG) conditions. Moreover, G-CSF treatment significantly improved the diastolic dysfunction in serial echocardiography assessments. In conclusion, the anti-apoptotic effect of G-CSF may be associated with the downregulation of ER stress.

Characterization, Stress Response and Functional Analyses of Giant River Prawn (Macrobrachium rosenbergii) Glucose-Regulated Protein 78 (Mr-grp78) under Temperature Stress and during Aeromonas hydrophila Infection

Simple Summary

Glucose-regulated protein 78 (grp78) is classified as a member of the Hsp70 subfamily. This protein functions as a key factor in signal transduction associated with the unfolded protein response (UPR) in the endoplasmic reticulum (ER) during cellular stress and protects against cell damage caused by toxic chemicals, oxidative stress, Ca²⁺ depletion, programmed cell death and various infectious conditions. To investigate this crucial mechanism in giant river prawn (Macrobrachium rosenbergii), we analyzed the biological function of prawn grp78 at the molecular level in this study. The regulation of this gene was intensively analyzed under normal bacterial infection and heat/cold-shock inductions. A functional analysis of this gene under heat and infectious stress conditions was performed by gene knockdown. The information obtained in the current study clearly indicates the crucially significant roles of grp78 in the cellular stress responses of the target experimental animal under various stress conditions.

Abstract

The endoplasmic reticulum (ER) is an organelle important for several functions of cellular physiology. This study identified the giant river prawn’s glucose-regulated protein 78 (Mr-grp78), which is important for ER stress mechanisms. Nucleotide and amino acid analyses of Mr-grp78, as compared with other species, revealed the highest similarity scores with the grp78 genes of crustaceans. An expression analysis by quantitative RT-PCR indicated that Mr-grp78 was expressed in all tissues and presented its highest expression in the ovary (57.64 ± 2.39-fold), followed by the gills (42.25 ± 1.12), hindgut (37.15 ± 2.47), thoracic ganglia (28.55 ± 2.45) and hemocytes (28.45 ± 2.26). Expression analysis of Mr-grp78 mRNA levels under Aeromonas hydrophila induction and heat/cold-shock exposure was conducted in the gills, hepatopancreas and hemocytes. The expression levels of Mr-grp78 in these tissues were highly upregulated 12 h after bacterial infection. In contrast, under heat- and cold-shock conditions, the expression of Mr-grp78 was significantly suppressed in the gills at 24–96 h and in the hepatopancreas at 12 h (p < 0.05). A functional analysis via Mr-grp78 gene knockdown showed that Mr-grp78 transcription in the gills, hepatopancreas and muscle strongly decreased from 6 to 96 h. Furthermore, the silencing of this gene effectively increased the sensitivity of the tested prawns to heat- and pathogenic-bacterium-induced stress. The results of this study clearly demonstrate the significant functional roles of Mr-grp78 in response to both temperature and pathogen treatments.

PERK in POMC neurons connects celastrol with metabolism

ER stress and activation of the unfolded protein response in the periphery as well as the central nervous system have been linked to various metabolic abnormalities. Chemically lowering protein kinase R–like ER kinase (PERK) activity within the hypothalamus leads to decreased food intake and body weight. However, the cell populations required in this response remain undefined. In the current study, we investigated the effects of proopiomelanocortin-specific (POMC-specific) PERK deficiency on energy balance and glucose metabolism. Male mice deficient for PERK in POMC neurons exhibited improvements in energy balance on a high-fat diet, showing decreased food intake and body weight, independent of changes in glucose and insulin tolerances. The plant-based inhibitor of PERK, celastrol, increases leptin sensitivity, resulting in decreased food intake and body weight in a murine model of diet-induced obesity (DIO). Our data extend these observations by demonstrating that celastrol-induced improvements in leptin sensitivity and energy balance were attenuated in mice with PERK deficiency in POMC neurons. Altogether, these data suggest that POMC-specific PERK deficiency in male mice confers protection against DIO, possibly providing a new therapeutic target for the treatment of diabetes and metabolic syndrome.

The regulation of Ero1-alpha in homocysteine-induced macrophage apoptosis and vulnerable plaque formation in atherosclerosis

BACKGROUND AND AIMS

Hyperhomocysteinemia (HHcy) is an independent risk factor for atherosclerosis and plaque vulnerability. Macrophage apoptosis mediated by endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of HHcy-aggravated atherosclerosis. Endoplasmic reticulum oxidoreductase 1α (Ero1α) is critical for ER stress-induced apoptosis. We hypothesized that Ero1α may contribute to ER-stress induced macrophage apoptosis and plaque stability in advanced atherosclerotic lesions by HHcy.

METHODS

Apoe^-/- mice were maintained on drinking water containing homocysteine (Hcy, 1.8 g/L) to establish HHcy atherosclerotic models. The role of Ero1α in atherosclerotic plaque stability, macrophage apoptosis and ER stress were monitored in the plaque of aortic roots in HHcy Apoe^-/- mice with or without silence or overexpression of Ero1α through lentivirus. Mouse peritoneal macrophages were used to confirm the regulation of Ero1α on ER stress dependent apoptosis in the presence of HHcy.

RESULTS

Atherosclerotic plaque vulnerability and macrophage apoptosis were promoted in Apoe^-/- mice by high Hcy diet, accompanied by the upregulation of Ero1α expression and ER stress. Inhibition of Ero1α prevented macrophage apoptosis and atherosclerotic plaque vulnerability, and vice versa. Consistently, in mouse peritoneal macrophages, ER stress and apoptosis were attenuated by Ero1α deficiency, but enhanced by Ero1α overexpression.

CONCLUSIONS

Hcy, via upregulation of Ero1α expression, activates ER stress-dependent macrophage apoptosis to promote vulnerable plaque formation in atherosclerosis. Ero1α may be a potential therapeutic target for atherosclerosis induced by Hcy.

Cardiomyocyte Stim1 Deficiency Exacerbates Doxorubicin Cardiotoxicity by Magnification of Endoplasmic Reticulum Stress

INTRODUCTION

Doxorubicin (Dox) is an effective anticancer agent; however, its cardiotoxicity remains a challenge. Dysfunction of intracellular calcium ion (Ca2+) is implicated in the process of Dox-induced cardiomyocyte apoptosis. Although store-operated Ca2+ entry (SOCE) is suggested to be responsible for Ca2+ entry in cardiomyocytes, the direct role of store-operated Ca2+ channels in Dox-related cardiomyocyte apoptosis is unknown.

MATERIALS AND METHODS

Cardiomyocyte Stim1-specific knockout or overexpression mice were treated with Dox. Cardiomyocytes were pretreated with Stim1 adenovirus or siRNA followed by Dox incubation in vitro. Cardiac function and underlying mechanisms echocardiography were assessed via immunofluorescence, flow cytometry, real-time PCR, Western blotting and immunoprecipitation.

RESULTS

We observed the inhibition of Stim1 expression, association of Stim1 to Orai1 or Trpc1, and SOCE in Dox-treated mouse myocardium and cardiomyocytes. Orai1 and Trpc1 expression remained unchanged. Cardiomyocyte-specific deficiency of Stim1 exacerbated Dox-induced cardiac dysfunction and myocardial apoptosis. However, specific overexpression of Stim1 in the myocardium was associated with amelioration of cardiac dysfunction and myocardial apoptosis. In vitro, STIM1 knockdown potentiated Dox-induced AC16 human cardiomyocyte apoptosis. This apoptosis was attenuated by STIM1 upregulation. Moreover, STIM1 downregulation enhanced Dox-induced endoplasmic reticulum (ER) stress in cardiomyocytes. In contrast, STIM1 overexpression inhibited the activation of the above molecular markers of ER stress. Immunoprecipitation assay showed that STIM1 interacted with GRP78 in cardiomyocytes. This interaction was attenuated in response to Dox treatment.

CONCLUSION

Our data demonstrate that cardiomyocyte STIM1 binding to GRP78 ameliorates Dox cardiotoxicity by inhibiting pro-apoptotic ER stress.

Nodal modulator (NOMO) is required to sustain endoplasmic reticulum morphology

The endoplasmic reticulum (ER) is a membrane-bound organelle responsible for protein folding, lipid synthesis, and calcium homeostasis. Maintenance of ER structural integrity is crucial for proper function, but much remains to be learned about the molecular players involved. To identify proteins that support the structure of the ER, we performed a proteomic screen and identified nodal modulator (NOMO), a widely conserved type I transmembrane protein of unknown function, with three nearly identical orthologs specified in the human genome. We found that overexpression of NOMO1 imposes a sheet morphology on the ER, whereas depletion of NOMO1 and its orthologs causes a collapse of ER morphology concomitant with the formation of membrane-delineated holes in the ER network positive for the lysosomal marker lysosomal-associated protein 1. In addition, the levels of key players of autophagy including microtubule-associated protein light chain 3 and autophagy cargo receptor p62/sequestosome 1 strongly increase upon NOMO depletion. In vitro reconstitution of NOMO1 revealed a "beads on a string" structure likely representing consecutive immunoglobulin-like domains. Extending NOMO1 by insertion of additional immunoglobulin folds results in a correlative increase in the ER intermembrane distance. Based on these observations and a genetic epistasis analysis including the known ER-shaping proteins Atlastin2 and Climp63, we propose a role for NOMO1 in the functional network of ER-shaping proteins.

Murine Factor H Co-Produced in Yeast With Protein Disulfide Isomerase Ameliorated C3 Dysregulation in Factor H-Deficient Mice

Recombinant human factor H (hFH) has potential for treating diseases linked to aberrant complement regulation including C3 glomerulopathy (C3G) and dry age-related macular degeneration. Murine FH (mFH), produced in the same host, is useful for pre-clinical investigations in mouse models of disease. An abundance of FH in plasma suggests high doses, and hence microbial production, will be needed. Previously, Pichia pastoris produced useful but modest quantities of hFH. Herein, a similar strategy yielded miniscule quantities of mFH. Since FH has 40 disulfide bonds, we created a P. pastoris strain containing a methanol-inducible codon-modified gene for protein-disulfide isomerase (PDI) and transformed this with codon-modified DNA encoding mFH under the same promoter. What had been barely detectable yields of mFH became multiple 10s of mg/L. Our PDI-overexpressing strain also boosted hFH overproduction, by about tenfold. These enhancements exceeded PDI-related production gains reported for other proteins, all of which contain fewer disulfide-stabilized domains. We optimized fermentation conditions, purified recombinant mFH, enzymatically trimmed down its (non-human) N-glycans, characterised its functions in vitro and administered it to mice. In FH-knockout mice, our de-glycosylated recombinant mFH had a shorter half-life and induced more anti-mFH antibodies than mouse serum-derived, natively glycosylated, mFH. Even sequential daily injections of recombinant mFH failed to restore wild-type levels of FH and C3 in mouse plasma beyond 24 hours after the first injection. Nevertheless, mFH functionality appeared to persist in the glomerular basement membrane because C3-fragment deposition here, a hallmark of C3G, remained significantly reduced throughout and beyond the ten-day dosing regimen.

Life as a Vector of Dengue Virus: The Antioxidant Strategy of Mosquito Cells to Survive Viral Infection

Dengue fever is a mosquito-borne viral disease of increasing global importance. The disease has caused heavy burdens due to frequent outbreaks in tropical and subtropical areas of the world. The dengue virus (DENV) is generally transmitted between human hosts via the bite of a mosquito vector, primarily Aedes aegypti and Ae. albopictus as a minor species. It is known that the virus needs to alternately infect mosquito and human cells. DENV-induced cell death is relevant to the pathogenesis in humans as infected cells undergo apoptosis. In contrast, mosquito cells mostly survive the infection; this allows infected mosquitoes to remain healthy enough to serve as an efficient vector in nature. Overexpression of antioxidant genes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), glutaredoxin (Grx), thioredoxin (Trx), and protein disulfide isomerase (PDI) have been detected in DENV2-infected mosquito cells. Additional antioxidants, including GST, eukaryotic translation initiation factor 5A (eIF5a), and p53 isoform 2 (p53-2), and perhaps some others, are also involved in creating an intracellular environment suitable for cell replication and viral infection. Antiapoptotic effects involving inhibitor of apoptosis (IAP) upregulation and subsequent elevation of caspase-9 and caspase-3 activities also play crucial roles in the ability of mosquito cells to survive DENV infection. This article focused on the effects of intracellular responses in mosquito cells to infection primarily by DENVs. It may provide more information to better understand virus/cell interactions that can possibly elucidate the evolutionary pathway that led to the mosquito becoming a vector.

Zonisamide, an antiepileptic drug, alleviates diabetic cardiomyopathy by inhibiting endoplasmic reticulum stress

Endoplasmic reticulum stress (ER stress) plays a key role in the development of cardiac hypertrophy and diabetic cardiomyopathy (DCM). Zonisamide (ZNS) was originally developed as an antiepileptic drug. Studies have shown that ZNS suppresses ER stress-induced neuronal cell damage in the experimental models of Parkinson's disease. Herein, we investigated whether ZNS improved DCM by attenuating ER stress-induced apoptosis. C57BL/6J mice were fed with high-fat diet (HFD) and intraperitoneally injected with low-dose streptozotocin (STZ) to induce type 2 diabetes mellitus (T2DM), and then treated with ZNS (40 mg·kg-1·d-1, i.g.) for 16 weeks. We showed that ZNS administration slightly ameliorated the blood glucose levels, but significantly alleviated diabetes-induced cardiac dysfunction and hypertrophy. Furthermore, ZNS administration significantly inhibited the Bax and caspase-3 activity, upregulated Bcl-2 activity, and decreased the proportion of TUNEL-positive cells in heart tissues. We analyzed the hallmarks of ER stress in heart tissues, and revealed that ZNS administration significantly decreased the protein levels of GRP78, XBP-1s, ATF6, PERK, ATF4, and CHOP, and elevated Hrd1 protein. In high glucose (HG)-treated primary cardiomyocytes, application of ZNS (3 μM) significantly alleviated HG-induced cardiomyocyte hypertrophy and apoptosis. ZNS application also suppressed activated ER stress in HG-treated cardiomyocytes. Moreover, preapplication of the specific ER stress inducer tunicamycin (10 ng/mL) eliminated the protective effects of ZNS against HG-induced cardiac hypertrophy and ER stress-mediated apoptosis. Our findings suggest that ZNS improves the cardiac diastolic function in diabetic mice and prevents T2DM-induced cardiac hypertrophy by attenuating ER stress-mediated apoptosis.

Stress response pathways in the male germ cells and gametes

The unfolded protein response (UPR) is a conserved and essential cellular pathway involved in protein quality control that is activated in response to several cellular stressors such as diseases states, ageing, infection and toxins. The cytosol, endoplasmic reticulum (ER) and mitochondria are continuously exposed to new proteins and in situations of aberrant protein folding; one of three lines of defence may be activated: (i) heat-shock response, (ii) mitochondrial UPR and (iii) ER UPR. These pathways lead to different signal transduction mechanisms that activate or upregulate transcription factors that, in turn, regulate genes that increase the cell's ability to correct the conformation of poorly folded proteins or, ultimately, lead to apoptosis. Despite the recent progress in understanding such biological processes, few studies have focused on the implications of the UPR in male infertility, highlighting the need for a first approach concerning the presence of these components in the male reproductive system. In testis, there is a high rate of protein synthesis, and the UPR mechanisms are well described. However, the presence of these mechanisms in spermatozoa, apparently transcriptionally inactive cells, is contentious, and it is unclear how sperm cells deal with stress. Here, we review current concepts and mechanisms of the UPR and highlight the relevance of these stress response pathways in male fertility, especially the presence and functional activation of those components in male germinal cells and spermatozoa.

Cardinal role of eukaryotic initiation factor 2 (eIF2α) in progressive dopaminergic neuronal death & DNA fragmentation: Implication of PERK:IRE1α:ATF6 axis in Parkinson's pathology

The study was conducted to assess the role of eukaryotic initiation factor 2 (eIF2α) in progressive dopaminergic neuronal death employing various interventions (YM08, 4μ8C, AEBSF, salubrinal, ursolic acid) of endoplasmic reticulum (ER) stress signaling. The protein level of all the ER stress related signaling factors (GRP78, IRE1α, ATF6, eIF2α, ATF4, XBP-1, GADD153) were estimated after 3 and 7 day of experiment initiation. Findings with single administration of interventions showed that salubrinal exhibited significant protection against rotenone induced adverse alterations in comparison to other interventions. Therefore, further study was expanded with repeat dose of salubrinal. Rotenone administration in rat brain caused the significant biochemical alterations, dose dependent progressive neuronal apoptosis and altered neuronal morphology which was significantly attenuated with salubrinal treatment. In conclusion, findings showed that rotenone administration caused the dose dependent progressive neuronal death including cardinal role of eIF2α, suggesting the potential pharmacological utilization of salubrinal or salubrinal like molecules in therapeutics of Parkinson's diseases.

Salvianolic Acid B Protects Against Fatty Acid-Induced Renal Tubular Injury via Inhibition of Endoplasmic Reticulum Stress

Background/Aims: Obesity-related kidney disease is associated with elevated levels of saturated free fatty acids (SFA). SFA lipotoxicity in tubular cells contributes to significant cellular apoptosis and injury. Salvianolic acid B (SalB) is the most abundant bioactive molecule from Radix Salviae Miltiorrhizae. In this study, we investigated the effect of SalB on SFA-induced renal tubular injury and endoplasmic reticulum (ER) stress, in vivo and in vitro. Methods: C57BL/6 mice were assigned to five groups: a control group with normal diet (Nor), high-fat diet group (HFD), and HFD with three different SalB treatment doses, low (SalBL; 3 mg/kg), medium (SalBM; 6.25 mg/kg), and high (SalBH; 12.5 mg/kg) doses. SalB was intraperitoneally injected daily for 4 weeks after 8 weeks of HFD. After 12 weeks, mice were sacrificed and kidneys and sera were collected. Apoptosis and ER stress were induced in human proximal tubule epitelial (HK2) cells by palmitic acid (PA, 0.6 mM), tunicamycin (TM, 1 μg/ml), or thapsigargin (TG, 200 nM) in vitro. Results: C57BL/6 mice fed a high-fat diet (HFD) for 12 weeks exhibited increased apoptosis (Bax and cleaved caspase-3) and ER stress (BIP, P-eIF2α, ATF4, CHOP, ATF6, IRE1α, and XBP1s) markers expression in the kidney, compared with control mice, which were remarkably suppressed by SalB treatment. In vitro studies showed that PA (0.6 mM) induced apoptosis and ER stress in cultured HK2 cells. SalB treatment attenuated all the adverse effects of PA. However, SalB failed to inhibit TM or TG-induced ER stress in HK2 cells. Conclusion: The study indicated that SalB may play an important role in obesity-related kidney injury via mediating SFA-induced ER stress.

Histone deacetylase inhibitor valproic acid attenuates high glucose‑induced endoplasmic reticulum stress and apoptosis in NRK‑52E cells

Previous studies have demonstrated that valproic acid (VPA), a histone deacetylase inhibitor, alleviates diabetic nephropathy (DN). However, the biological mechanisms underlying this protective effect remains unclear. This study aimed to investigate the effects of histone deacetylase inhibitor VPA on hyperglycemic induction of NRK‑52E cell ERS and apoptosis. Endoplasmic reticulum stress (ERS)‑related apoptosis is involved in DN, and improving ERS may delay the symptoms of DN. Histone deacetylase regulates gene transcription or expression of ERS‑related proteins. The present study established an ERS model by treating the rat renal tubular epithelial cells NRK‑52E with high glucose (HG) and investigated the effects of VPA on the apoptosis of the NRK‑52E cells. HG stimulation significantly increased the protein levels of the ERS‑related proteins including glucose regulated protein 78 (GRP78), activating transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), caspase‑12 and phosphorylated (p)‑JNK. VPA treatment further upregulated GRP78 expression and attenuated the levels of ATF4, CHOP, caspase‑12 and p‑JNK. Notably, HG markedly promoted apoptosis of NRK‑52E cells by regulating the protein levels of Bax, cleaved caspase‑3 and Bcl‑2, which was attenuated by simultaneous VPA treatment. Mechanistically, VPA increased the total acetylation levels of histone H4 in NRK‑52E cells and increased the histone H4 acetylation of the GRP78 promoter region. In conclusion, VPA attenuated HG‑induced ERS and apoptosis in NRK‑52E cells, which may be due to the regulation of acetylation levels of ERS‑related proteins. In addition, the present study suggested that HDACIs are promising drugs for treating patients with DN.

Curcumin attenuates angiotensin II-induced podocyte injury and apoptosis by inhibiting endoplasmic reticulum stress

Podocytes are an important component of the glomerular filtration barrier in the kidneys. The dysfunction and apoptosis of podocytes are important factors that can lead to the progression of chronic kidney disease (CKD). In CKD, angiotensin II is continuously elevated in circulation and is considered to have key roles in inducing podocyte injury and apoptosis. Curcumin is a hydrophobic polyphenolic compound extracted from turmeric. Increasing evidence demonstrates that curcumin has a protective effect on the kidneys in CKD. However, the mechanisms mediating this protective effect remain unclear. The aim of this study was to explore whether curcumin could protect against angiotensin II‐induced injury and apoptosis of podocytes. We performed western blotting, immunofluorescence, phalloidin staining, and terminal deoxynucleotidyl transferase nick‐end labeling staining to observe the expression level of podocyte‐specific proteins, apoptosis‐related proteins, and the arrangement of F‐actin. We found that curcumin could reverse angiotensin II‐induced podocyte injury and apoptosis in a dose‐dependent manner. In addition, curcumin dose‐dependently attenuated a pro‐apoptotic pathway, activated by angiotensin II‐induced endoplasmic reticulum stress. Conversely, the protective effects of curcumin were impaired upon addition of tunicamycin, an activator of endoplasmic reticulum stress. Thus, we speculate that curcumin protects against angiotensin II‐induced podocyte injury and apoptosis, at least partly by inhibiting endoplasmic reticulum stress.

A cell cycle checkpoint for the endoplasmic reticulum

The generation of new cells is one of the most fundamental aspects of cell biology. Proper regulation of the cell cycle is critical for human health, as underscored by many diseases associated with errors in cell cycle regulation, including both cancer and hereditary diseases. A large body of work has identified regulatory mechanisms and checkpoints that ensure accurate and timely replication and segregation of chromosomal DNA. However, few studies have evaluated the extent to which similar checkpoints exist for the division of cytoplasmic components, including organelles. Such checkpoint mechanisms might be crucial for compartments that cannot be generated de novo, such as the endoplasmic reticulum (ER). In this review, we highlight recent work in the model organism Saccharomyces cerevisiae that led to the discovery of such a checkpoint that ensures that cells inherit functional ER into the daughter cell.

Qualitative and Quantitative Study of the Changes in the Ultrastructure of Mammalian Adrenal Cortex Caused by the Venezuelan Tigra Mariposa (Bothrops venezuelensis) Snake Venom

The damage of the adrenal gland by snake venoms needs to be clarified. Lethality (LD50) of Bothrops venezuelensis (Bv) venom was established by intraperitoneally mice injections. Preparation of specimens for transmission electron microscopy samples from cortex adrenal gland biopsies at 3, 6, and 24 h was processed. The quantitative description by the principal component analysis (PCA) of the adrenal gland was as follows: thickening of the capillary endothelium, area of the capillary lumen, cell nucleus area, enlargement of the perinuclear space, number of mitochondria, area of the mitochondria, number of mitochondrial cristae, number of cristae per mitochondrial unit, and tubular diameter of the smooth endoplasmic reticulum (SER). Sections of the adrenal cortex, after 3 h postinjection with Bv venom showed in the cortical cells: mitochondria with tubular cristae and slightly swollen SER cisternae, nucleus with variable heterochromatin content, irregular edges, and swollen nuclear envelope. After 6 h, cells with swollen nucleus envelope, electron dense lipids and mitochondria with loss of their cristae were observed. Myelin figures, close to the microvilli of the cortical cell, multivesicular bodies, swollen profiles of the SER, and electron dense lipid drops were noticed. After 24 h, thickening of the endothelial wall, fenestrae and projections into the capillary lumen, loss of the mitochondrial cristae, destruction of the capillary and the plasma membrane of the cortical cell, multivesicular body, SER loss, and an enlargement of the perinuclear space were detected. In the quantitative PCA, there were significant changes after the venom treatments.

Mitogen-Activated Protein Kinase (MAPK) and Obesity-Related Cancer

Obesity is a major public health concern worldwide. The increased risk of certain types of cancer is now an established deleterious consequence of obesity, although the molecular mechanisms of this are not completely understood. In this review, we aim to explore the links between MAPK signalling and obesity-related cancer. We focus mostly on p38 and JNK MAPK, as the role of ERK remains unclear. These links are seen through the implication of MAPK in obesity-related immune paralysis as well as through effects on the endoplasmic reticulum stress response and activation of aromatase. By way of example, we highlight areas of interest and possibilities for future research in endometrioid endometrial cancer and hepatocellular carcinoma associated with non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH) and MAPK.

Endoplasmic Reticulum Stress Pathway, the Unfolded Protein Response, Modulates Immune Function in the Tumor Microenvironment to Impact Tumor Progression and Therapeutic Response

Despite advances in cancer therapy, several persistent issues remain. These include cancer recurrence, effective targeting of aggressive or therapy-resistant cancers, and selective treatments for transformed cells. This review evaluates the current findings and highlights the potential of targeting the unfolded protein response to treat cancer. The unfolded protein response, an evolutionarily conserved pathway in all eukaryotes, is initiated in response to misfolded proteins accumulating within the lumen of the endoplasmic reticulum. This pathway is initially cytoprotective, allowing cells to survive stressful events; however, prolonged activation of the unfolded protein response also activates apoptotic responses. This balance is key in successful mammalian immune response and inducing cell death in malignant cells. We discuss how the unfolded protein response affects cancer progression, survival, and immune response to cancer cells. The literature shows that targeting the unfolded protein response as a monotherapy or in combination with chemotherapy or immunotherapies increases the efficacy of these drugs; however, systemic unfolded protein response targeting may yield deleterious effects on immune cell function and should be taken into consideration. The material in this review shows the promise of both approaches, each of which merits further research.

Perforated vesicles composed of amphiphilic diblock copolymer: new artificial biomembrane model of nuclear envelope

With the aim of creating a new artificial model of a biomembrane for the nuclear envelope, perforated vesicles were prepared employing an amphiphilic diblock copolymer of poly(methacrylic acid)-block-poly(methyl methacrylate-random-methacrylic acid-random-2,2,6,6-tetramethyl-4-piperidyl methacrylate), PMAA-b-P(MMA-r-MAA-r-TPMA), by polymerization-induced self-assembly through photo nitroxide-mediated controlled/living radical polymerization (photo NMP). The photo NMP in an aqueous methanol solution produced spherical vesicles perforated with various holes and pores in the surface. The perforation of the vesicles was prevented by trifluoroacetic acid based on the disturbance of the MAA-TPMA interaction in the hydrophobic block chain. The investigation of the morphology changes by the polymerization progress revealed that the perforated spherical vesicles were produced within the membrane of contorted huge vesicles that were formed during the early stage of the polymerization due to the extension of the hydrophobic block chain. The perforated vesicles were found to show a reversible thermo-responsive behavior in the range of 25-50 °C based on dynamic light scattering and transmittance measurements. The vesicles were fused and divided into much smaller vesicles at high temperature, but were restored by cooling. However, the restored vesicles only had a few holes and no pores in the surface. The rearrangement of the MAA-TPMA interaction at high temperature produced more morphologically stable non-perforated vesicles.

Role of Podocyte Injury in Glomerulosclerosis

Finding new therapeutic targets of glomerulosclerosis treatment is an ongoing quest. Due to a living environment of various stresses and pathological stimuli, podocytes are prone to injuries; moreover, as a cell without proliferative potential, loss of podocytes is vital in the pathogenesis of glomerulosclerosis. Thus, sufficient understanding of factors and underlying mechanisms of podocyte injury facilitates the advancement of treating and prevention of glomerulosclerosis. The clinical symptom of podocyte injury is proteinuria, sometimes with loss of kidney functions progressing to glomerulosclerosis. Injury-induced changes in podocyte physiology and function are actually not a simple passive process, but a complex interaction of proteins that comprise the anatomical structure of podocytes at molecular levels. This chapter lists several aspects of podocyte injuries along with potential mechanisms, including glucose and lipid metabolism disorder, hypertension, RAS activation, micro-inflammation, immune disorder, and other factors. These aspects are not technically separated items, but intertwined with each other in the pathogenesis of podocyte injuries.

Translation deregulation in human disease

Advances in sequencing and high-throughput techniques have provided an unprecedented opportunity to interrogate human diseases on a genome-wide scale. The list of disease-causing mutations is expanding rapidly, and mutations affecting mRNA translation are no exception. Translation (protein synthesis) is one of the most complex processes in the cell. The orchestrated action of ribosomes, tRNAs and numerous translation factors decodes the information contained in mRNA into a polypeptide chain. The intricate nature of this process renders it susceptible to deregulation at multiple levels. In this Review, we summarize current evidence of translation deregulation in human diseases other than cancer. We discuss translation-related diseases on the basis of the molecular aberration that underpins their pathogenesis (including tRNA dysfunction, ribosomopathies, deregulation of the integrated stress response and deregulation of the mTOR pathway) and describe how deregulation of translation generates the phenotypic variability observed in these disorders.

Salubrinal enhances eIF2α phosphorylation and improves fertility in a mouse model of Classic Galactosemia

Loss of galactose-1 phosphate uridylyltransferase (GALT) activity in humans results in Classic Galactosemia, and the GalT-deficient (GalT^-/-) mouse mimics the patient condition. GalT^-/- ovaries display elevated endoplasmic reticulum (ER) stress marker, BiP, and downregulated canonical phosphatidylinositol 3-kinase (Pi3k)/protein kinase B (Akt) growth/pro-survival signaling. Numbers of primordial follicles are reduced in the mutants, recapitulating the accelerated ovarian aging seen in human patients. We previously found that oral administration of the compound Salubrinal (an eIF2α phosphatase inhibitor), resulted in reduction of ovarian BiP expression, rescued Pi3k/Akt signaling, and a doubling of primordial follicles in GalT^-/- adults. Here, we further characterized galactosemic stress in GalT^-/- mice versus wild-type (WT) controls, and examined whether Salubrinal treatment improved broader reproductive parameters. We assessed the expression levels of factors of the unfolded protein response (UPR), and found that BiP, phospho-Perk, and phospho-eIF2α were all elevated in GalT^-/- ovaries. However, neither IKK activation (NFκB pathway) nor alternative Xbp1 splicing downstream of ER membrane protein Ire1α activation was induced, suggesting an Xbp1-independent UPR in galactosemic stress. Moreover, Salubrinal treatment significantly increased the number of ovulated eggs in mutant animals after gonadotrophic superovulation. Salubrinal treatment also normalized estrus cycle stage lengths and resulted in significantly larger litter sizes than vehicle-treated mutants. Overall, we show that Salubrinal protects against galactosemia-induced primordial follicle loss in a fashion that includes suppressing the de-phosphorylation of eIF2α, and that intervention in this way significantly improves and extends ovarian function, fertility, and fecundity.

Expression of UPR effector proteins ATF6 and XBP1 reduce colorectal cancer cell proliferation and stemness by activating PERK signaling

The unfolded protein response (UPR) acts through its downstream branches, PERK-eIF2α signaling, IRE1α-XBP1 signaling and ATF6 signaling. In the intestine, activation of the UPR through the kinase PERK results in differentiation of intestinal epithelial stem cells and colon cancer stem cells, whereas deletion of XBP1 results in increased stemness and adenomagenesis. How downstream activation of XBP1 and ATF6 influences intestinal stemness and proliferation remains largely unknown. We generated colorectal cancer cells (LS174T) that harbor doxycycline inducible expression of the active forms of either XBP1(s) or ATF61-373. Activation of either XBP1 or ATF6 resulted in reduced cellular proliferation and reduced expression of markers of intestinal epithelial stemness. Moreover, XBP1 and ATF6 activation reduced global protein synthesis and lowered the threshold for UPR activation. XBP1-mediated loss of stemness and proliferation resulted from crossactivation of PERK-eIF2α signaling and could be rescued by constitutive expression of eIF2α phosphatase GADD34. We thus find that enforced activation of XBP1 and ATF6 results in reduction of stemness and proliferation. We expose a novel interaction between XBP1 and PERK-eIF2α signaling.

Sec62 Suppresses Foot-and-Mouth Disease Virus Proliferation by Promotion of IRE1α-RIG-I Antiviral Signaling

Foot-and-mouth disease virus (FMDV) is highly infectious and causes a major plague in animal farming. Unfolded protein response is one of the major cellular responses to pathogenic infections, which performs a crucial role in cell survival, apoptosis, and antiviral innate immune response. In this study, we showed that FMDV infection activated two unfolded protein response branches (PERK-eIF2α and ATF6 signaling) in both baby hamster kidney cells (BHK-21) and porcine kidney (PK-15) cells, whereas it suppressed the IRE1α-XBP1 signaling by decreasing IRE1α level. Further study revealed IRE1α signaling as an important antiviral innate immune mechanism against FMDV. Sec62, the transport protein, was greatly decreased at the late stages of FMDV infection. By overexpression and knockdown study, we also found that the expression of Sec62 was positively involved in the levels of IRE1α and RIG-I and subsequent activation of downstream antiviral signaling pathways in FMDV-infected PK-15 cells. Taken together, our study demonstrates that Sec62 is an important antiviral factor that upregulates IRE1α-RIG-I-dependent antiviral innate immune responses, and FMDV evades antiviral host defense mechanism by downregulating Sec62-IRE1α/RIG-I.

Vph2 is required for protection against a reductive stress in Candida albicans

Vph2 is a putative V-ATPase assembly factor. Our previous study has characterized its roles in localization of V-ATPase subunit, cell wall composition, hyphal development and virulence. In this study, our results further demonstrated that Vph2 was localized around the nucleus and in patches close to the periphery of the cell, indicating that Vph2 was located to the endoplasmic reticulum (ER), which was consistent with that in Saccharomyces cerevisiae. Disruption of VPH2 led to hypersensitivity to reducing stresses induced by dithiothreitol (DTT) and β-mercaptoethanol (β-ME), and displayed increased GSH content and up-regulation of unfolded protein response (UPR)-related genes, such as PRB1 and PMT4. However, the induced UPR and growth defect on β-ME plates of vph2Δ/Δ mutant could be partly alleviated by the GSH-specific scavenger 1-chloro-2, 4-dinitrobenzene (CDNB). These results indicated that loss of VPH2 led to an increase in GSH levels, which induced the UPR and caused the defective growth on reductive stress induced by β-ME. In summary, Vph2 is necessary to maintain resistance against reductive stresses.

Arctigenin ameliorates renal impairment and inhibits endoplasmic reticulum stress in diabetic db/db mice

AIMS

Diabetic nephropathy (DN) is the most common complication of diabetes mellitus. Endoplasmic reticulum (ER) plays an important role in the development and progression of DN. Arctigenin (ATG), a lignan extract from Fructus Arctii, exhibits anti-inflammatory, anticarcinogenic, anti-oxidative stress and immunomodulatory properties. The present research aimed to investigate whether ATG could protect against diabetes-related renal injury and inhibit ER stress in db/db mice.

MAIN METHODS

Male db/db mice were randomly divided into two groups: DN group and ATG treatment group (DN + ATG). db/m mice were defined as the normal control group (NC). ATG was dissolved in 0.5% carboxymethyl cellulose sodium salt solution and administered orally at a dose of 80 mg/kg to mice in the DN + ATG group once daily for 8 consecutive weeks. HK2 cells were used to determine the effects of ATG on ER stress and cell apoptosis in vitro.

KEY FINDINGS

ATG administration significantly reduced blood glucose, urine albumin excretion, and urine albumin to creatinine ratio, and attenuated renal pathological injury when compared with untreated db/db mice. These changes were accompanied by decreased expression of both ER stress-related markers and caspase 12 level in the kidneys of db/db mice. In vitro, high glucose activated ER stress signal transduction pathway and induced cell apoptosis in HK2 cells, which were blocked by ATG.

SIGNIFICANCE

Our results suggest that ATG exerts renoprotective effects on diabetes-related renal injury in db/db mice and cytoprotective effects on high glucose induced cell apoptosis and inhibits ER stress.

Mechanisms of disordered neurodegenerative function: concepts and facts about the different roles of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)

Neurodegenerative diseases, such as Alzheimer's disease, Huntington's disease, Parkinson's disease, prion disease, and amyotrophic lateral sclerosis, are a dissimilar group of disorders that share a hallmark feature of accumulation of abnormal intraneuronal or extraneuronal misfolded/unfolded protein and are classified as protein misfolding disorders. Cellular and endoplasmic reticulum (ER) stress activates multiple signaling cascades of the unfolded protein response (UPR). Consequently, translational and transcriptional alterations in target gene expression occur in response directed toward restoring the ER capacity of proteostasis and reestablishing the cellular homeostasis. Evidences from in vitro and in vivo disease models indicate that disruption of ER homeostasis causes abnormal protein aggregation that leads to synaptic and neuronal dysfunction. However, the exact mechanism by which it contributes to disease progression and pathophysiological changes remains vague. Downstream signaling pathways of UPR are fully integrated, yet with diverse unexpected outcomes in different disease models. Three well-identified ER stress sensors have been implicated in UPR, namely, inositol requiring enzyme 1, protein kinase RNA-activated-like ER kinase (PERK), and activating transcription factor 6. Although it cannot be denied that each of the involved stress sensor initiates a distinct downstream signaling pathway, it becomes increasingly clear that shared pathways are crucial in determining whether or not the UPR will guide the cells toward adaptive prosurvival or proapoptotic responses. We review a body of work on the mechanism of neurodegenerative diseases based on oxidative stress and cell death pathways with emphasis on the role of PERK.

Mitochondrial stress management: a dynamic journey

Mitochondria undergo continuous challenges in the course of their life, from their generation to their degradation. These challenges include the management of reactive oxygen species, the proper assembly of mitochondrial respiratory complexes and the need to balance potential mutations in the mitochondrial DNA. The detection of damage and the ability to keep it under control is critical to fine-tune mitochondrial function to the organismal energy needs. In this review, we will analyze the multiple mechanisms that safeguard mitochondrial function in light of in crescendo damage. This sequence of events will include initial defense against excessive reactive oxygen species production, compensation mechanisms by the unfolded protein response (UPR^mt), mitochondrial dynamics and elimination by mitophagy.

Magnolol exerts anticancer activity in hepatocellular carcinoma cells through regulating endoplasmic reticulum stress-mediated apoptotic signaling

Introduction

Magnolol (Mag), a biologically active compound isolated from the root and stem bark of Magnolia officinalis, has been reported to induce apoptosis in several cancer cell lines in vitro. In the present study, we aimed to determine the anticancer effects of Mag on hepatocellular carcinoma (HCC) cells.

Materials and methods

The HepG2 cells were treated with varying concentrations of Mag (10, 20, and 30 μM) for 48 hours. The effects of Mag on the proliferation, migration, invasion, apoptosis and cell cycle progression of HepG2 cells were respectively detected by MTT assay, transwell assays, and flow cytometric analysis. A HepG2 cell-based tumor-bearing model was established to evaluate the effect of Mag on HCC tumor growth in vivo. The protein expression levels were determined by Western blot analysis.

Results

Our results showed that Mag inhibited the proliferation, migration, and invasion of HepG2 cells in vitro in a dose-dependent manner. In addition, Mag reduced the HCC tumor volume and weight in the mouse xenograft model. Subsequent studies showed that Mag induced apoptosis in HepG2 cells, accompanied by a loss in mitochondrial membrane potential, cytochrome c release, and induction of endoplasmic reticulum stress. Furthermore, inhibition of the endoplasmic reticulum stress by CHOP knockdown restored the effects of Mag in HepG2 cells.

Conclusion

The present study highlighted the possibility of using Mag as a novel therapeutic drug for HCC treatment.

The UPR Activator ATF6 Responds to Proteotoxic and Lipotoxic Stress by Distinct Mechanisms

The unfolded protein response (UPR) is induced by proteotoxic stress of the endoplasmic reticulum (ER). Here we report that ATF6, a major mammalian UPR sensor, is also activated by specific sphingolipids, dihydrosphingosine (DHS) and dihydroceramide (DHC). Single mutations in a previously undefined transmembrane domain motif that we identify in ATF6 incapacitate DHS/DHC activation while still allowing proteotoxic stress activation via the luminal domain. ATF6 thus possesses two activation mechanisms: DHS/DHC activation and proteotoxic stress activation. Reporters constructed to monitor each mechanism show that phenobarbital-induced ER membrane expansion depends on transmembrane domain-induced ATF6. DHS/DHC addition preferentially induces transcription of ATF6 target lipid biosynthetic and metabolic genes over target ER chaperone genes. Importantly, ATF6 containing a luminal achromatopsia eye disease mutation, unresponsive to proteotoxic stress, can be activated by fenretinide, a drug that upregulates DHC, suggesting a potential therapy for this and other ATF6-related diseases including heart disease and stroke.

The exposure to uteroplacental insufficiency is associated with activation of unfolded protein response in postnatal life

Early life events are associated with the susceptibility to chronic diseases in adult life. Perturbations of endoplasmic reticulum (ER) homeostasis activate the unfolded protein response (UPR), which contributes to the development of metabolic alterations. Our aim was to evaluate liver UPR in an animal model of intrauterine growth restriction (IUGR). A significantly increased expression of X-box binding protein-1 spliced (XBP1s) mRNA (p<0.01), Endoplasmic Reticulum-localized DnaJ homologue (Erdj4) mRNA (p<0.05) and Bip/GRP78-glucose-regulated protein 78 (Bip) mRNA (p<0.05) was observed in the liver of IUGR rats at birth. Furthermore, the expression of gluconeogenesis genes and lipogenesis genes were significantly upregulated (p<0.05) in IUGR pups. At 105 d, IUGR male rats showed significantly reduced glucose tolerance (p<0.01). A significant decreased expression of XBP1s mRNA (p<0.01) and increased expression of double-stranded RNA-dependent protein kinase-like ER kinase (PERK) and Asparagine synthetase (ASNS) (p<0.05) was observed in the liver of IUGR male adult rats. Liver focal steatosis and periportal fibrosis were observed in IUGR rats. These findings show for the first time that fetal exposure to uteroplacental insufficiency is associated with the activation of hepatic UPR and suggest that UPR signaling may play a role in the metabolic risk.