Perk is essential for translational regulation and cell survival during the unfolded protein response

Sleep deficiency as a driver of cellular stress and damage in neurological disorders

Neurological disorders encompass an extremely broad range of conditions, including those that present early in development and those that progress slowly or manifest with advanced age. Although these disorders have distinct underlying etiologies, the activation of shared pathways, e.g., integrated stress response (ISR) and the development of shared phenotypes (sleep deficits) may offer clues toward understanding some of the mechanistic underpinnings of neurologic dysfunction. While it is incontrovertibly complex, the relationship between sleep and persistent stress in the brain has broad implications in understanding neurological disorders from development to degeneration. The convergent nature of the ISR could be a common thread linking genetically distinct neurological disorders through the dysregulation of a core cellular homeostasis pathway.

Effect of Propionic Acid on Diabetes-Induced Impairment of Unfolded Protein Response Signaling and Astrocyte/Microglia Crosstalk in Rat Ventromedial Nucleus of the Hypothalamus

Background

The aim was to investigate the influence of propionic acid (PA) on the endoplasmic reticulum (ER), unfolded protein response (UPR) state, and astrocyte/microglia markers in rat ventromedial hypothalamus (VMH) after type 2 diabetes mellitus (T2DM).

Methods

Male Wistar rats were divided: (1) control, (2) T2DM, and groups that received the following (14 days, orally): (3) metformin (60 mg/kg), (4) PA (60 mg/kg), and (5) PA+metformin. Western blotting, RT-PCR, transmission electron microscopy, and immunohistochemical staining were performed.

Results

We found T2DM-associated enlargement of ER cisterns, while drug administration slightly improved VMH ultrastructural signs of damage. GRP78 level was 2.1-fold lower in T2DM vs. control. Metformin restored GRP78 to control, while PA increased it by 2.56-fold and metformin+PA—by 3.28-fold vs. T2DM. PERK was elevated by 3.61-fold in T2DM, after metformin—by 4.98-fold, PA—5.64-fold, and metformin+PA—3.01-fold vs. control. A 2.45-fold increase in ATF6 was observed in T2DM. Metformin decreased ATF6 content vs. T2DM. Interestingly, PA exerted a more pronounced lowering effect on ATF6, while combined treatment restored ATF6 to control. IRE1 increased in T2DM (2.4-fold), metformin (1.99-fold), and PA (1.45-fold) groups vs. control, while metformin+PA fully normalized its content. The Iba1 level was upregulated in T2DM (5.44-fold) and metformin groups (6.88-fold). Despite PA treatment leading to a further 8.9-fold Iba1 elevation, PA+metformin caused the Iba1 decline vs. metformin and PA treatment. GFAP level did not change in T2DM but rose in metformin and PA groups vs. control. PA+metformin administration diminished GFAP vs. PA. T2DM-induced changes were associated with dramatically decreased ZO-1 levels, while PA treatment increased it almost to control values.

Conclusions

T2DM-induced UPR imbalance, activation of microglia, and impairments in cell integrity may trigger VMH dysfunction. Drug administration slightly improved ultrastructural changes in VMH, normalized UPR, and caused an astrocyte activation. PA and metformin exerted beneficial effects for counteracting diabetes-induced ER stress in VMH.

Peroxisomal Stress Response and Inter-Organelle Communication in Cellular Homeostasis and Aging

Peroxisomes are key regulators of cellular and metabolic homeostasis. These organelles play important roles in redox metabolism, the oxidation of very-long-chain fatty acids (VLCFAs), and the biosynthesis of ether phospholipids. Given the essential role of peroxisomes in cellular homeostasis, peroxisomal dysfunction has been linked to various pathological conditions, tissue functional decline, and aging. In the past few decades, a variety of cellular signaling and metabolic changes have been reported to be associated with defective peroxisomes, suggesting that many cellular processes and functions depend on peroxisomes. Peroxisomes communicate with other subcellular organelles, such as the nucleus, mitochondria, endoplasmic reticulum (ER), and lysosomes. These inter-organelle communications are highly linked to the key mechanisms by which cells surveil defective peroxisomes and mount adaptive responses to protect them from damages. In this review, we highlight the major cellular changes that accompany peroxisomal dysfunction and peroxisomal inter-organelle communication through membrane contact sites, metabolic signaling, and retrograde signaling. We also discuss the age-related decline of peroxisomal protein import and its role in animal aging and age-related diseases. Unlike other organelle stress response pathways, such as the unfolded protein response (UPR) in the ER and mitochondria, the cellular signaling pathways that mediate stress responses to malfunctioning peroxisomes have not been systematically studied and investigated. Here, we coin these signaling pathways as "peroxisomal stress response pathways". Understanding peroxisomal stress response pathways and how peroxisomes communicate with other organelles are important and emerging areas of peroxisome research.

Endoplasmic reticulum stress affects mouse salivary protein secretion induced by chronic administration of an α1-adrenergic agonist

Stress stimulates both the sympathetic-adrenomedullary and hypothalamus-pituitary-adrenal axes. Activation of these axes results in the release of catecholamines, which in turn affects salivary secretion. Thus, repetitive stimulation of the α₁-adrenergic receptor could be useful for studying the effects of chronic stress on the salivary gland. Salivary protein concentration and kallikrein activity were significantly lower in mice following chronic phenylephrine (PHE) administration. Chronic PHE administration led to significantly increased expression of the 78-kDa glucose-regulated protein, activating transcription factor 4, and activating transcription factor 6. Histological analyses revealed a decrease in the size of the serous cell and apical cytoplasm. These results suggest that repetitive pharmacological stimulation of the sympathetic nervous system elicits ER stress and translational suppression. In addition, PHE-treated mice exhibited a decrease in intracellular Ca²⁺ influx elicited by carbachol, a muscarine receptor agonist in the submandibular gland. The present findings suggest that chronic psychological, social, and physical stress could adversely affect Ca²⁺ regulation.

Resveratrol protected acrolein-induced ferroptosis and insulin secretion dysfunction via ER-stress- related PERK pathway in MIN6 cells

Acrolein is a typical food and environmental pollutant and a risk factor for diabetes. The primary pathogenesis of diabetes is insulin deficiency and resistance. Ferroptosis is an iron-dependent cell death type, accompanying by lipid peroxide accumulation. Here, 25 μM acrolein-induced ferroptosis is observed in mouse pancreatic β-cell MIN6 cells as indicated by ferroptosis-related indicators, including GPX4 exhaustion, lipid peroxides accumulation, and insulin secretion impairment. Additionally, acrolein-induced ferroptosis could be reversed by Ferrostatin-1. Furthermore, endoplasmic reticulum stress (ER stress) is involved in acrolein-induced ferroptosis. The ER stress inhibits the expression of PPARγ, an essential gene in glucose and lipid metabolism, and facilitates lipid peroxide accumulation, leading to MIN6 cells ferroptosis and dysfunction. Moreover, resveratrol, an antioxidant natural product, may relieve ER stress and upregulate PPARγ expression, thereby inhibiting acrolein-induced ferroptosis. Thus, this study demonstrated a new perspective for the cytotoxic mechanism of acrolein on pancreatic β-cell and the protective effect of resveratrol.

Impact of ER Stress and ER-Mitochondrial Crosstalk in Huntington's Disease

Accumulation of misfolded proteins is a common phenomenon of several neurodegenerative diseases. The misfolding of proteins due to abnormal polyglutamine (PolyQ) expansions are linked to the development of PolyQ diseases including Huntington's disease (HD). Though the genetic basis of PolyQ repeats in HD remains prominent, the primary molecular basis mediated by PolyQ toxicity remains elusive. Accumulation of misfolded proteins in the ER or disruption of ER homeostasis causes ER stress and activates an evolutionarily conserved pathway called Unfolded protein response (UPR). Protein homeostasis disruption at organelle level involving UPR or ER stress response pathways are found to be linked to HD. Due to dynamic intricate connections between ER and mitochondria, proteins at ER-mitochondria contact sites (mitochondria associated ER membranes or MAMs) play a significant role in HD development. The current review aims at highlighting the most updated information about different UPR pathways and their involvement in HD disease progression. Moreover, the role of MAMs in HD progression has also been discussed. In the end, the review has focused on the therapeutic interventions responsible for ameliorating diseased states via modulating either ER stress response proteins or modulating the expression of ER-mitochondrial contact proteins.

Targeting Endoplasmic Reticulum Stress as an Effective Treatment for Alcoholic Pancreatitis

Pancreatitis and alcoholic pancreatitis are serious health concerns with an urgent need for effective treatment strategies. Alcohol is a known etiological factor for pancreatitis, including acute pancreatitis (AP) and chronic pancreatitis (CP). Excessive alcohol consumption induces many pathological stress responses; of particular note is endoplasmic reticulum (ER) stress and adaptive unfolded protein response (UPR). ER stress results from the accumulation of unfolded/misfolded protein in the ER and is implicated in the pathogenesis of alcoholic pancreatitis. Here, we summarize the possible mechanisms by which ER stress contributes to alcoholic pancreatitis. We also discuss potential approaches targeting ER stress and UPR in developing novel therapeutic strategies for the disease.

Polyhexamethylene guanidine phosphate increases stress granule formation in human 3D lung organoids under respiratory syncytial virus infection

Polyhexamethylene guanidine phosphate (PHMG-p), a humidifier disinfectant, is known to cause lung toxicity, including inflammation and pulmonary fibrosis. In this study, we aimed to investigate the effect of PHMG-p on human lung tissue models (2D epithelial cells and 3D organoids) under conditions of oxidative stress and viral infection. The effect of PHMG-p was studied by evaluating the formation of stress granules (SGs), which play a pivotal role in cellular adaptation to various stress conditions. Under oxidative stress and respiratory syncytial virus (RSV) infection, exposure to PHMG-p remarkably increased eIF2α phosphorylation, which is essential for SG-related signalling, and significantly increased SG formation. Furthermore, PHMG-p induced fibrotic gene expression and caused cell death due to severe DNA damage, which was further increased under oxidative stress and RSV infection, indicating that PHMG-p induces severe lung toxicity under stress conditions. Taken together, toxicity evaluation under various stressful conditions is necessary to accurately predict potential lung toxicity of chemicals affecting the respiratory tract.

Protein Preparation for Proteomic Analysis of the Unfolded Protein Response in Arabidopsis thaliana

Excessive accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) leads to a potentially cytotoxic condition known as the ER stress. Upon ER stress, cells initiate a homeostatic response called unfolded protein response (UPR) to assist proper folding the unfolded or misfolded proteins. Proteomics have been broadly used in plants with Liquid Chromatography coupled to tandem MS (LC-MS/MS) technologies. LC-MS/MS techniques have also been a great tool for studies of posttranslational modifications (PTMs). Here we describe our protocol of a fast method for large amount of seedling treatment and collection for UPR study in Arabidopsis thaliana and the preparation of total proteins for proteomic analysis.

An Overview of Methods for Detecting eIF2α Phosphorylation and the Integrated Stress Response

Phosphorylation of the translation initiation factor eIF2α is an adaptive signaling event that is essential for cell and organismal survival from yeast to humans. It is central to the integrated stress response (ISR) that maintains cellular homeostasis in the face of threats ranging from viral infection, amino acid, oxygen, and heme deprivation to the accumulation of misfolded proteins in the endoplasmic reticulum. Phosphorylation of eIF2α has broad physiological, pathological, and therapeutic relevance. However, despite more than two decades of research and growing pharmacological interest, phosphorylation of eIF2α remains difficult to detect and quantify, because of its transient nature and because substoichiometric amounts of this modification are sufficient to profoundly reshape cellular physiology. This review aims to provide a roadmap for facilitating a robust evaluation of eIF2α phosphorylation and its downstream consequences in cells and organisms.

Endoplasmic reticulum stress associates with the development of intervertebral disc degeneration

Endoplasmic reticulum (ER) is an important player in various intracellular signaling pathways that regulate cellular functions in many diseases. Intervertebral disc degeneration (IDD), an age-related degenerative disease, is one of the main clinical causes of low back pain. Although the pathological development of IDD is far from being fully elucidated, many studies have been shown that ER stress (ERS) is involved in IDD development and regulates various processes, such as inflammation, cellular senescence and apoptosis, excessive mechanical loading, metabolic disturbances, oxidative stress, calcium homeostasis imbalance, and extracellular matrix (ECM) dysregulation. This review summarizes the formation of ERS and the potential link between ERS and IDD development. ERS can be a promising new therapeutic target for the clinical management of IDD.

Canary in a coal mine: collided ribosomes as sensors of cellular conditions

The recent discovery that collision of ribosomes triggers quality control and stress responses in eukaryotes has shifted the perspective of the field. Collided eukaryotic ribosomes adopt a unique structure, acting as a ubiquitin signaling platform for various response factors. While several of the signals that determine which downstream pathways are activated have been uncovered, we are only beginning to learn how the specificity for the activation of each process is achieved during collisions. This review will summarize those findings and how ribosome-associated factors act as molecular sentinels, linking aberrations in translation to the overall cellular state. Insights into how cells respond to ribosome collision events will provide greater understanding of the role of the ribosome in the maintenance of cellular homeostasis.

CRISPR-Based Screening for Stress Response Factors in Mammalian Cells

In the presence of different physiological and environmental stresses, cells rapidly initiate stress responses to re-establish cellular homeostasis. Stress responses usually orchestrate both transcriptional and translational programs via distinct mechanisms. With the advance of transcriptomics and proteomics technologies, transcriptional and translational outputs to a particular stress condition have become easier to measure; however, these technologies lack the ability to reveal the upstream regulatory pathways. Unbiased genetic screens based on a transcriptional or translational reporter are powerful approaches to identify regulatory factors of a specific stress response. CRISPR/Cas-based technologies, together with next-generation sequencing, enable genome-scale pooled screens to systematically elucidate gene function in mammalian cells, with a significant reduction in the rate of off-target effects compared to the previously used RNAi technology. Here, we describe our fluorescence-activated cell sorting (FACS)-based CRISPR interference (CRISPRi) screening platform using a translational reporter to identify novel genetic factors of the mitochondrial stress response in mammalian cells. This protocol provides a general framework for scientists who wish to establish a reporter-based CRISPRi screening platform to address questions in their area of research.

Ischemic brain injury in diabetes and endoplasmic reticulum stress

Diabetes is a widespread disease characterized by high blood glucose levels due to abnormal insulin activity, production, or both. Chronic diabetes causes many secondary complications including cardiovascular disease: a life-threatening complication. Cerebral ischemia-related mortality, morbidity, and the extent of brain injury are high in diabetes. However, the mechanism of increase in ischemic brain injury during diabetes is not well understood. Multiple mechanisms mediate diabetic hyperglycemia and hypoglycemia-induced increase in ischemic brain injury. Endoplasmic reticulum (ER) stress mediates both brain injury as well as brain protection after ischemia-reperfusion injury. The pathways of ER stress are modulated during diabetes. Free radical generation and mitochondrial dysfunction, two of the prominent mechanisms that mediate diabetic increase in ischemic brain injury, are known to stimulate the pathways of ER stress. Increased ischemic brain injury in diabetes is accompanied by a further increase in the activation of ER stress. As there are many metabolic changes associated with diabetes, differential activation of the pathways of ER stress may mediate pronounced ischemic brain injury in subjects suffering from diabetes. We presently discuss the literature on the significance of ER stress in mediating increased ischemia-reperfusion injury in diabetes.

The unfolded protein response: An emerging therapeutic target for pancreatitis and pancreatic ductal adenocarcinoma

Pancreatitis is a debilitating disease involving inflammation and fibrosis of the exocrine pancreas. Recurrent or chronic forms of pancreatitis are a significant risk factor for pancreatic ductal adenocarcinoma. While genetic factors have been identified for both pathologies, environmental stresses play a large role in their etiology. All cells have adapted mechanisms to handle acute environmental stress that alters energy demands. A common pathway involved in the stress response involves endoplasmic reticulum stress and the unfolded protein response (UPR). While rapidly activated by many external stressors, in the pancreas the UPR plays a fundamental biological role, likely due to the high protein demands in acinar cells. Despite this, increased UPR activity is observed in response to acute injury or following exposure to risk factors associated with pancreatitis and pancreatic cancer. Studies in animal and cell cultures models show the importance of affecting the UPR in the context of both diseases, and inhibitors have been developed for several specific mediators of the UPR. Given the importance of the UPR to normal acinar cell function, efforts to affect the UPR in the context of disease must be able to specifically target pathology vs. physiology. In this review, we highlight the importance of the UPR to normal and pathological conditions of the exocrine pancreas. We discuss recent studies suggesting the UPR may be involved in the initiation and progression of pancreatitis and PDAC, as well as contributing to chemoresistance that occurs in pancreatic cancer. Finally, we discuss the potential of targeting the UPR for treatment.

GADD34-mediated dephosphorylation of eIF2α facilitates pseudorabies virus replication by maintaining de novo protein synthesis

Viruses have evolved multiple strategies to manipulate their host's translational machinery for the synthesis of viral proteins. A common viral target is the alpha subunit of eukaryotic initiation factor 2 (eIF2α). In this study, we show that global protein synthesis was increased but the eIF2α phosphorylation level was markedly decreased in porcine kidney 15 (PK15) cells infected with pseudorabies virus (PRV), a swine herpesvirus. An increase in the eIF2α phosphorylation level by salubrinal treatment or transfection of constructs expressing wild-type eIF2α or an eIF2α phosphomimetic [eIF2α(S51D)] attenuated global protein synthesis and suppressed PRV replication. To explore the mechanism involved in the inhibition of eIF2α phosphorylation during PRV infection, we examined the phosphorylation status of protein kinase R-like endoplasmic reticulum kinase (PERK) and double-stranded RNA-dependent protein kinase R (PKR), two kinases that regulate eIF2α phosphorylation during infection with numerous viruses. We found that the level of neither phosphorylated (p)-PERK nor p-PKR was altered in PRV-infected cells or the lungs of infected mice. However, the expression of growth arrest and DNA damage-inducible protein 34 (GADD34), which promotes eIF2α dephosphorylation by recruiting protein phosphatase 1 (PP1), was significantly induced both in vivo and in vitro. Knockdown of GADD34 and inhibition of PP1 activity by okadaic acid treatment led to increased eIF2α phosphorylation but significantly suppressed global protein synthesis and inhibited PRV replication. Collectively, these results demonstrated that PRV induces GADD34 expression to promote eIF2α dephosphorylation, thereby maintaining de novo protein synthesis and facilitating viral replication.

Dihydrocapsaicin induces translational repression and stress granule through HRI-eIF2α phosphorylation axis

Stress granules (SGs) are cytoplasmic biomolecular condensates that are formed against a variety of stress conditions when translation initiation is perturbed. SGs form through the weak protein-protein, protein-RNA, and RNA-RNA interactions, as well as through the intrinsically disordered domains and post-translation modifications within RNA binding proteins (RBPs). SGs are known to contribute to cell survivability by minimizing the stress-induced damage to the cells by delaying the activation of apoptosis. Here, we find that dihydrocapsaicin (DHC), an analogue of capsaicin, is a SG inducer that promotes polysome disassembly and reduces global protein translation via phosphorylation of eIF2α. DHC-mediated SG assembly is controlled by the phosphorylation of eIF2α at serine 51 position and is controlled by all four eIF2α stress kinases (i.e., HRI, PKR, PERK, and GCN2) with HRI showing maximal effect. We demonstrate that DHC is a bonafide compound that induces SG assembly, disassembles polysome, phosphorylates eIF2α in an HRI dependent manner, and thereby arrest global translation. Together, our results suggest that DHC is a novel SG inducer and an alternate to sodium arsenite to study SG dynamics.

TiO2 NPs induce the reproductive toxicity in mice with gestational diabetes mellitus through the effects on the endoplasmic reticulum stress signaling pathway

The effect of one of the most widely studied nanomaterials at present, TiO₂ nanoparticles (NPs), on pregnancy-related diseases is not clear. In this study, the adverse effects of TiO₂ NPs on mice with gestational diabetes mellitus (GDM) and their possible mechanism were investigated. GDM mice were orally administered 0, 10, 50 and 250 mg/kg TiO₂ NPs for 14 days. GDM reduced the weight of pregnant mice, destroyed the placental structure and caused abnormal fetal development. After exposure to increasing doses of TiO₂ NPs, blood glucose levels increased significantly and body weight further decreased in GDM mice. The accumulation of the Ti content was detected in the placenta and fetus, which may further damage the placental structure in GDM mice, thereby exacerbating abnormal fetal development. In addition, the MDA and SOD activities were obviously increased, and the expression of genes associated with endoplasmic reticulum stress (ERS) (PERK, eIF2α, AFT4, IRE1α, and XBP1s) and apoptosis (CHOP, JNK, Bax/Bcl-2, Caspase-12, Caspase-9, and Caspase-3) were also obviously increased in the placenta, which reflected the possible activation of apoptosis. It could be speculated that the reproductive toxicity of TiO₂ NPs in GDM mice triggered oxidative stress that subsequently activated ERS pathways to induce cell apoptosis.

Mechanistic studies of PEG-asparaginase-induced liver injury and hepatic steatosis in mice

PEGylated-l-asparaginase (PEG-ASNase) is a chemotherapeutic agent used to treat pediatric acute lymphoblastic leukemia (ALL). Its use is avoided in adults due to its high risk of liver injury including hepatic steatosis, with obesity and older age considered risk factors of the injury. Our study aims to elucidate the mechanism of PEG-ASNase-induced liver injury. Mice received 1500 U/kg of PEG-ASNase and were sacrificed 1, 3, 5, and 7 days after drug administration. Liver triglycerides were quantified, and plasma bilirubin, ALT, AST, and non-esterified fatty acids (NEFA) were measured. The mRNA and protein levels of genes involved in hepatic fatty acid synthesis, β-oxidation, very low-density lipoprotein (VLDL) secretion, and white adipose tissue (WAT) lipolysis were determined. Mice developed hepatic steatosis after PEG-ASNase, which associated with increases in bilirubin, ALT, and AST. The hepatic genes Ppara, Lcad/Mcad, Hadhb, Apob100, and Mttp were upregulated, and Srebp-1c and Fas were downregulated after PEG-ASNase. Increased plasma NEFA, WAT loss, and adipose tissue lipolysis were also observed after PEG-ASNase. Furthermore, we found that PEG-ASNase-induced liver injury was exacerbated in obese and aged mice, consistent with clinical studies of ASNase-induced liver injury. Our data suggest that PEG-ASNase-induced liver injury is due to drug-induced lipolysis and lipid redistribution to the liver.

Dexmedetomidine Preconditioning Reduces Myocardial Ischemia-Reperfusion Injury in Rats by Inhibiting the PERK Pathway

BACKGROUND

Ischemic heart disease has attracted much attention due to its high mortality rates, treatment costs and the increasing morbidity in the young population. Strategies for reperfusion have reduced mortality. However, reperfusion can lead to cardiomyocyte death and subsequent irreversible myocardial damage. At present, the timely and targeted treatment of ischemia-reperfusion (I/R) injury is often lacking.

OBJECTIVES

To evaluate if dexmedetomidine (DEX) has a protective effect in myocardiual I/R and explore the possible mechanism behind it.

METHODS

Rat hearts were perfused with a Langendorff perfusion system, and randomly assigned to five groups: control group, perfused with Krebs-Henseleit (K-H) solution for 205 minutes without ischemia; and four test groups that underwent 40 minutes of global ischemia and 120 min of reperfusion. The DEX group, the yohimbine (YOH) group and the DEX + YOH group were perfused with DEX (10 nM), YOH (1 μM) or the combination of DEX and YOH prior to reperfusion, respectively. Cardiac hemodynamics, myocardial infarct size, and myocardial histology were evaluated. The expression of glucose-related protein 78 (GRP78), protein kinase R-like ER kinase (PERK), phosphorylated PERK, eukaryotic initiation factor 2α (eIF2α), phosphorylated eIF2α, activating transcription factor 4 (ATF4), and CCAAT/enhancer-binding protein homologous protein (CHOP) were assessed. P<0.05 was considered to indicate a statistically significant difference.

RESULTS

DEX preconditioning improved the cardiac function of I/R hearts, reduced myocardial infarction, myocardial apoptosis, and the expression of GRP78, p-PERK, eIF2α, p-eIF2α, ATF4 and CHOP.

CONCLUSIONS

DEX pretreatment reduced myocardial I/R injury by suppressing apoptosis, which was induced by the PERK pathway.

Therapeutic Targeting of Autophagy in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease characterized by early metastasis, late detection, and poor prognosis. Progress towards effective therapy has been slow despite significant efforts. Novel treatment approaches are desperately needed and autophagy, an evolutionary conserved process through which proteins and organelles are recycled for use as alternative energy sources, may represent one such target. Although incompletely understood, there is growing evidence suggesting that autophagy may play a role in PDAC carcinogenesis, metastasis, and survival. Early clinical trials involving autophagy inhibiting agents, either alone or in combination with chemotherapy, have been disappointing. Recently, evidence has demonstrated synergy between the MAPK pathway and autophagy inhibitors in PDAC, suggesting a promising therapeutic intervention. In addition, novel agents, such as ONC212, have preclinical activity in pancreatic cancer, in part through autophagy inhibition. We discuss autophagy in PDAC tumorigenesis, metabolism, modulation of the immune response, and preclinical and clinical data with selected autophagy modulators as therapeutics.

High Glucose Concentrations Impair the Processing and Presentation of Mycobacterium tuberculosis Antigens In Vitro

Type 2 diabetes is an established risk factor for tuberculosis, but the underlying mechanisms are largely unknown. We established an in vitro model to analyze the effect of high glucose concentrations in antigen processing and presentation in antigen-presenting cells. Human monocyte-derived macrophages (MDMs) were exposed to high (11 mM and 30 mM) and low (5.5 mM) glucose concentrations and infected with Mycobacterium tuberculosis (Mtb). Flow cytometry was used to analyze the effect of high glucose concentrations in histocompatibility complex (MHC) class II molecules (HLA-DR) and co-stimulatory molecules (CD80 and CD86), indispensable for an adequate antigenic presentation and CD4+ T cell activation. HLA-DR and CD86 were significantly decreased by high glucose concentrations compared with low glucose concentrations. Confocal microscopy was used to detect Rab 5 and Lamp-1, proteins involved in the kinetics of antigen processing as early markers, and Rab 7 and cathepsin D as late markers. We observed a delay in the dynamics of the acquisition of Rab 7 and cathepsin D in high glucose concentrations. Moreover, the kinetics of the formation M. tuberculosis peptide-MHC II complexes in MDMs was decreased under high glucose concentrations, reducing their capacity for T cell activation. These findings suggest that high glucose concentrations directly affect antigenic processing, and therefore antigenic presentation.

Integrated stress response restricts macrophage necroptosis

Stress inhibits necroptosis in a PERK-dependent manner via reduced RIPK1-RIPK3-MLKL signaling, showing an integral mechanistic connection between stress responses and programmed cell death.

The integrated stress response (ISR) regulates cellular homeostasis and cell survival following exposure to stressors. Cell death processes such as apoptosis and pyroptosis are known to be modulated by stress responses, but the role of the ISR in necroptosis is poorly understood. Necroptosis is an inflammatory, lytic form of cell death driven by the RIPK3-MLKL signaling axis. Here, we show that macrophages that have induced the ISR are protected from subsequent necroptosis. Consistent with a reduction in necroptosis, phosphorylation of RIPK1, RIPK3, and MLKL is reduced in macrophages pre-treated with ISR-inducing agents that are challenged with necroptosis-inducing triggers. The stress granule component DDX3X, which is involved in ISR-mediated regulation of pyroptosis, is not required for protecting ISR-treated cells from necroptosis. Disruption of stress granule assembly or knockdown of Perk restored necroptosis in pre-stressed cells. Together, these findings identify a critical role for the ISR in limiting necroptosis in macrophages.

Targeting UPR branches, a potential strategy for enhancing efficacy of cancer chemotherapy

Cancer cells are often exposed to cell intrinsic stresses and environmental perturbations that may lead to accumulation of unfolded and/or misfolded proteins in the lumen of endoplasmic reticulum (ER), a cellular condition known as ER stress. In response to ER stress, the cells elicit an adaptive process called unfolded protein response (UPR) to cope with the stress, supporting cellular homeostasis and survival. The ER stress sensors inositol requiring protein 1α (IRE1α), eukaryotic translation initiation factor 2 alpha kinase 3 (EIF2AK3, also called PERK), and activating transcription factor 6 (ATF6) constitute the three branches of UPR to resolve ER stress. IRE1α, PERK, and ATF6 play an important role in tumor cell growth and survival. They are also involved in chemotherapy resistance of cancers. These have generated widespread interest in targeting these UPR branches for cancer treatment. In this review, we provide an overview of the role of IRE1α, PERK, and ATF6 in cancer progression and drug resistance and we summarize the research advances in targeting these UPR branches to enhance the efficacy of chemotherapy of cancers.

Transcriptional Control of Metastasis by Integrated Stress Response Signaling

As a central cellular program to sense and transduce stress signals, the integrated stress response (ISR) pathway has been implicated in cancer initiation and progression. Depending on the genetic mutation landscape, cellular context, and differentiation states, there are emerging pieces of evidence showing that blockage of the ISR can selectively and effectively shift the balance of cancer cells toward apoptosis, rendering the ISR a promising target in cancer therapy. Going beyond its pro-survival functions, the ISR can also influence metastasis, especially via proteostasis-independent mechanisms. In particular, ISR can modulate metastasis via transcriptional reprogramming, in the help of essential transcription factors. In this review, we summarized the current understandings of ISR in cancer metastasis from the perspective of transcriptional regulation.

The Interplay between the Unfolded Protein Response, Inflammation and Infection in Cystic Fibrosis

In cystic fibrosis (CF), p.Phe508del is the most frequent mutation in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. The p.Phe508del-CFTR protein is retained in the ER and rapidly degraded. This retention likely triggers an atypical Unfolded Protein Response (UPR) involving ATF6, which reduces the expression of p.Phe508del-CFTR. There are still some debates on the role of the UPR in CF: could it be triggered by the accumulation of misfolded CFTR proteins in the endoplasmic reticulum as was proposed for the most common CFTR mutation p.Phe508del? Or, is it the consequence of inflammation and infection that occur in the disease? In this review, we summarize recent findings on UPR in CF and show how infection, inflammation and UPR act together in CF. We propose to rethink their respective role in CF and to consider them as a whole.

The first presentation of Wolcott-Rallison syndrome in a four-month-old infant with diabetic ketoacidosis (DKA) precipitating by COVID-19: A case report

Monogenic diabetes mellitus (eg, Wolcott-Rallison syndrome) is a rare condition. It associates with neonatal or early-infancy insulin-dependent diabetes. We reported DKA in the four-month infant as the first presentation of monogenic diabetes that has accelerated by COVID-19 infection. Therefore, considering the concurrency of COVID-19 and DKA is crucial.

The Unfolded Protein Response as a Guardian of the Secretory Pathway

The endoplasmic reticulum (ER) is the major site of membrane biogenesis in most eukaryotic cells. As the entry point to the secretory pathway, it handles more than 10,000 different secretory and membrane proteins. The insertion of proteins into the membrane, their folding, and ER exit are affected by the lipid composition of the ER membrane and its collective membrane stiffness. The ER is also a hotspot of lipid biosynthesis including sterols, glycerophospholipids, ceramides and neural storage lipids. The unfolded protein response (UPR) bears an evolutionary conserved, dual sensitivity to both protein-folding imbalances in the ER lumen and aberrant compositions of the ER membrane, referred to as lipid bilayer stress (LBS). Through transcriptional and non-transcriptional mechanisms, the UPR upregulates the protein folding capacity of the ER and balances the production of proteins and lipids to maintain a functional secretory pathway. In this review, we discuss how UPR transducers sense unfolded proteins and LBS with a particular focus on their role as guardians of the secretory pathway.

Increased Post-Hypoxic Oxidative Stress and Activation of the PERK Branch of the UPR in Trap1-Deficient Drosophila melanogaster Is Abrogated by Metformin

Hypoxia is known to impair mitochondrial and endoplasmic reticulum (ER) homeostasis. Post-hypoxic perturbations of the ER proteostasis result in the accumulation of misfolded/unfolded proteins leading to the activation of the Unfolded Protein Response (UPR). Mitochondrial chaperone TNF receptor-associated protein 1 (TRAP1) is reported to preserve mitochondrial membrane potential and to impede reactive oxygen species (ROS) production thereby protecting cells from ER stress as well as oxidative stress. The first-line antidiabetic drug Metformin has been attributed a neuroprotective role after hypoxia. Interestingly, Metformin has been reported to rescue mitochondrial deficits in fibroblasts derived from a patient carrying a homozygous TRAP1 loss-of-function mutation. We sought to investigate a putative link between Metformin, TRAP1, and the UPR after hypoxia. We assessed post-hypoxic/reperfusion longevity, mortality, negative geotaxis, ROS production, metabolic activity, gene expression of antioxidant proteins, and activation of the UPR in Trap1-deficient flies. Following hypoxia, Trap1 deficiency caused higher mortality and greater impairments in negative geotaxis compared to controls. Similarly, post-hypoxic production of ROS and UPR activation was significantly higher in Trap1-deficient compared to control flies. Metformin counteracted the deleterious effects of hypoxia in Trap1-deficient flies but had no protective effect in wild-type flies. We provide evidence that TRAP1 is crucially involved in the post-hypoxic regulation of mitochondrial/ER stress and the activation of the UPR. Metformin appears to rescue Trap1-deficiency after hypoxia mitigating ROS production and downregulating the pro-apoptotic PERK (protein kinase R-like ER kinase) arm of the UPR.

Proteostasis deregulation as a driver of C9ORF72 pathogenesis

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two related neurodegenerative disorders that display overlapping features. The hexanucleotide repeat expansion GGGGCC (G₄ C₂ ) in C9ORF72 gene has been causally linked to both ALS and FTD emergence, thus opening a novel potential therapeutic target for disease intervention. The main driver of C9ORF72 pathology is the disruption of distinct cellular processes involved in the function of the proteostasis network. Here we discuss main findings relating to the induction of neurodegeneration by C9ORF72 mutation and proteostasis deregulation, highlighting the role of the endoplasmic reticulum stress, nuclear transport, and autophagy in the disease process. We further discuss possible points of intervention to target proteostasis mediators to treat C9ORF72-linked ALS/FTD.

Interactions between Endoplasmic Reticulum Stress and Autophagy: Implications for Apoptosis and Neuroplasticity-Related Proteins in Palmitic Acid-Treated Prefrontal Cells

Lipotoxicity of palmitic acid (PA) or high-fat diets has been reported to increase endoplasmic reticulum (ER) stress and autophagy in peripheral tissue as well as apoptotic cell death. It also can lead to an AD-like pathological pattern. However, it has been unknown that PA-induced ER stress and autophagy are involved in the regulation of neuroplastic abnormalities. Here, we investigated the roles of ER stress and autophagy in apoptosis and neuroplasticity-related protein expression in PA-treated prefrontal cells. Prefrontal cells dissected from newborn Sprague-Dawley rats were treated with PA compound with ER stress inhibitor 4-phenylbutyric acid (4-PBA) and autophagy inhibitor 3-methyladenine (3-MA) or PA alone. PA promoted ER stress and autophagy and also cause apoptosis as well as a decline in the expression of neuroplasticity-related proteins. Inhibition of ER stress decreased the expressions of neuroplasticity-related proteins and reduced autophagy activation and apoptosis in PA-treated prefrontal cells. Inhibition of autophagy exacerbated apoptosis and enhanced ER stress in PA-treated prefrontal cells. The present study illustrated that both ER stress and autophagy could be involved in apoptosis and decreased neuroplasticity-related proteins, and the interaction between ER stress and autophagy may play a critical role in apoptosis in PA-treated prefrontal cells. Our results provide new insights into the molecular mechanisms in vitro of lipotoxicity in obesity-related cognitive dysfunction.

Gut bacterial metabolites modulate endoplasmic reticulum stress

Background

The endoplasmic reticulum (ER) is a membranous organelle that maintains proteostasis and cellular homeostasis, controlling the fine balance between health and disease. Dysregulation of the ER stress response has been implicated in intestinal inflammation associated with inflammatory bowel disease (IBD), a chronic condition characterized by changes to the mucosa and alteration of the gut microbiota. While the microbiota and microbially derived metabolites have also been implicated in ER stress, examples of this connection remain limited to a few observations from pathogenic bacteria. Furthermore, the mechanisms underlying the effects of bacterial metabolites on ER stress signaling have not been well established.

Results

Utilizing an XBP1s-GFP knock-in reporter colorectal epithelial cell line, we screened 399 microbiome-related metabolites for ER stress pathway modulation. We find both ER stress response inducers (acylated dipeptide aldehydes and bisindole methane derivatives) and suppressors (soraphen A) and characterize their activities on ER stress gene transcription and translation. We further demonstrate that these molecules modulate the ER stress pathway through protease inhibition or lipid metabolism interference.

Conclusions

Our study identified novel links between classes of gut microbe-derived metabolites and the ER stress response, suggesting the potential for these metabolites to contribute to gut ER homeostasis and providing insight into the molecular mechanisms by which gut microbes impact intestinal epithelial cell homeostasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-021-02496-8.

Human Amnion Membrane-Derived Mesenchymal Stem Cells and Conditioned Medium Can Ameliorate X-Irradiation-Induced Testicular Injury by Reducing Endoplasmic Reticulum Stress and Apoptosis

Today, infertility affects 15% of couples and half of this rate is due to reproductive problems in men. Radiation-induced damage to the testicles causes sterility depending on the dose. Radiation causes endoplasmic reticulum (ER) stress and ER stress induces apoptosis. In this study, the effect of human amniotic membrane-derived mesenchymal stem cells (hAMSCs) and conditioned medium (hAMSCs-CM) on testicular damage induced by ionizing radiation is aimed to be elucidated through ER stress and apoptosis mechanisms. Six gray scrotal irradiation was used to create a testicular injury model. hAMSCs isolated and characterized with immunofluorescence and flow cytometry, while 2.5 × 10⁵ hAMSCs were transplanted into testis and hAMSCs-CM was applied. Fertility assessment was performed. Expressions of ER stress markers GRP78, Ire1, Chop and Caspase-12, and Caspase-3 were determined. TUNEL was performed. Serum FSH, LH, and testosterone were measured. After hAMSC transplantation and administration of hAMSCs-CM, offsprings were obtained. Seminiferous tubule diameter and seminiferous epithelial height increased. The expression of GRP78, IRE1α, CHOP, Caspase-12, and Caspase-3 decreased. Percentages of tunel positive cells decreased. While FSH and LH levels decreased, testosterone increased. After irradiation, both hAMSCs transplantation and paracrine activity of hAMSCs may have a role in reducing ER stress by suppressing the UPR response. Decrease in FSH and LH and increase in testosterone level after MSCs transplantation may have contributed to the improvement of spermatogenesis. Thus, it can be said that MSCs derived from human amniotic membrane can improve ionized radiation-induced testicular damage by reducing ER stress and apoptosis.

Pharmacological Inhibition of Inositol-Requiring Enzyme 1α RNase Activity Protects Pancreatic Beta Cell and Improves Diabetic Condition in Insulin Mutation-Induced Diabetes

β-cell ER stress plays an important role in β-cell dysfunction and death during the pathogenesis of diabetes. Proinsulin misfolding is regarded as one of the primary initiating factors of ER stress and unfolded protein response (UPR) activation in β-cells. Here, we found that the ER stress sensor inositol-requiring enzyme 1α (IRE1α) was activated in the Akita mice, a mouse model of mutant insulin gene-induced diabetes of youth (MIDY), a monogenic diabetes. Normalization of IRE1α RNase hyperactivity by pharmacological inhibitors significantly ameliorated the hyperglycemic conditions and increased serum insulin levels in Akita mice. These benefits were accompanied by a concomitant protection of functional β-cell mass, as shown by the suppression of β-cell apoptosis, increase in mature insulin production and reduction of proinsulin level. At the molecular level, we observed that the expression of genes associated with β-cell identity and function was significantly up-regulated and ER stress and its associated inflammation and oxidative stress were suppressed in islets from Akita mice treated with IRE1α RNase inhibitors. This study provides the evidence of the in vivo efficacy of IRE1α RNase inhibitors in Akita mice, pointing to the possibility of targeting IRE1α RNase as a therapeutic direction for the treatment of diabetes.

Longxuetongluo Capsule protects against cerebral ischemia/reperfusion injury through endoplasmic reticulum stress and MAPK-mediated mechanisms

Introduction

Longxuetongluo Capsule (LTC) is wildly applied to treat ischemic stroke in clinical practice in China. However, the pharmacological mechanism of LTC on ischemic stroke is still unstated.

Objective

Our research was designed to study the protective effect of LTC against cerebral ischemia–reperfusion (I/R) injury and reveal the underlying mechanism both in vivo and in vitro.

Methods

PC12 cells treated with glucose deprivation/reperfusion (OGD/R) were used to simulate in vitro ischemia/reperfusion (I/R) injury. The cell viability, apoptosis rate, and protein expressions of PC12 cells were evaluated. In vivo validation of the protective effect of LTC was carried out by middle cerebral artery occlusion (MCAO)/reperfusion treatment, and the underlying mechanism of its anti-apoptosis ability was further revealed by immunohistochemistry staining and Western blotting.

Results

In the current study, we observed that LTC effectively inhibited oxygen-glucose deprivation/reperfusion (OGD/R) induced apoptosis of PC12 cells through suppressing the cleavage of poly ADP-ribose polymerase (PARP), caspase-3, and caspase-9. Further investigation revealed that OGD/R insult remarkably triggered the endoplasmic reticulum stress responses (ER stress) to induce PC12 cell apoptosis. LTC treatment alleviated OGD/R induced ER stress by inhibiting the activation of protein kinase RNA (PKR)-like ER kinase (PERK)/eukaryotic translation initiation factor 2 (eIF2α) and inositol requiring enzyme 1 (IRE1)/tumor necrosis factor receptor-associated factor 2 (TRAF2) pathways. Additionally, LTC also restrained the OGD/R-induced PC12 cell apoptosis by reversing the activated mitogen-activated protein kinase (MAPK) through IRE1/TRAF2 pathway. Animal studies demonstrated LTC significantly restricted the infarct region induced by middle cerebral artery occlusion (MCAO)/reperfusion, the activation of ER stress and apoptosis of neuronal cells had also been suppressed by LTC in the penumbra region.

Conclusion

LTC protects the cerebral neuronal cell against ischemia/reperfusion injury through ER stress and MAPK-mediated mechanisms.

Endoplasmic reticulum unfolded protein response modulates the adaptation of Trachemys scripta elegans in salinity water

Trachemys scripta elegans, as a freshwater invasive species, can survive and lay eggs in brackish water, which may lead to the expansion of its potential invasion range due to freshwater salinization. Our previous studies have shown that high salinity leads to the accumulation of serum lipid content, which may induce endoplasmic reticulum stress (ERS) in the turtle. To better understand whether ERS is triggered by salinity, and in turn whether the turtles promote the protection mechanism, we exposed the turtles to the freshwater (CK), 5‰ salinity water (S5) and 15‰ salinity water (S15), and sampled at 6 h, 24 h and 30 d. 13 differentially expressed genes (DEGs) related to ERS pathways were found in the comparison of CK vs. S15 by transcriptomics analysis. Then, the mRNA and protein expression of ERS and its related activation pathways were further investigated. ERS marker glucose regulated protein 78 kD (GRP78) increased significantly (p < 0.05) in both the transcript and protein levels after exposure to 15‰ salinity water, which clearly indicated that salinity could induce ERS in T. s. elegans. Meanwhile, the three unfolded protein response (UPR) including transducers protein kinase RNA (PKR)-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α) and activating transcription factor-6 (ATF6) were promoted by salinity, suggesting that the turtle might promote physiological process to eliminate damaged cells and cope with unfolded proteins accumulation induced by ERS. Our results provide new insight into the mechanism of salinity adaptation in T. s. elegans and salt-tolerant biological invasion.

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.

Salubrinal Enhances Cancer Cell Death during Glucose Deprivation through the Upregulation of xCT and Mitochondrial Oxidative Stress

Cancer cells have the metabolic flexibility to adapt to heterogeneous tumor microenvironments. The integrated stress response (ISR) regulates the cellular adaptation response during nutrient stress. However, the issue of how the ISR regulates metabolic flexibility is still poorly understood. In this study, we activated the ISR using salubrinal in cancer cells and found that salubrinal repressed cell growth, colony formation, and migration but did not induce cell death in a glucose-containing condition. Under a glucose-deprivation condition, salubrinal induced cell death and increased the levels of mitochondrial reactive oxygen species (ROS). We found that these effects of salubrinal and glucose deprivation were associated with the upregulation of xCT (SLC7A11), which functions as an antiporter of cystine and glutamate and maintains the level of glutathione to maintain redox homeostasis. The upregulation of xCT did not protect cells from oxidative stress-mediated cell death but promoted it during glucose deprivation. In addition, the supplementation of ROS scavenger N-acetylcysteine and the maintenance of intracellular levels of amino acids via sulfasalazine (xCT inhibitor) or dimethyl-α-ketoglutarate decreased the levels of mitochondrial ROS and protected cells from death. Our results suggested that salubrinal enhances cancer cell death during glucose deprivation through the upregulation of xCT and mitochondrial oxidative stress.

Tardigrada: An Emerging Animal Model to Study the Endoplasmic Reticulum Stress Response to Environmental Extremes

Tardigrada (also known as "water bears") are hydrophilous microinvertebrates with a bilaterally symmetrical body and four pairs of legs usually terminating with claws. Water bears are quite complex animals and range from 50 to 1200 μm in length. Their body is divided into a head segment and four trunk segments, each bearing a pair of legs. They inhabit almost all terrestrial and aquatic environments, from the ocean depths to highest mountains ranges. However, one of their best known and unusual features is their capability for cryptobiosis. In this state tardigrades are able to survive extremely low and high temperatures and atmospheric pressures, complete lack of water, high doses of radiation, high concentrations of toxins and even a cosmic vacuum. The cellular mechanisms enabling cryptobiosis are poorly understood, although it appears the synthesis of certain types of molecules (sugars and proteins) enable the prevention of cellular damage at different levels. The endoplasmic reticulum (ER) is a morphologically and functionally diverse organelle able to integrate multiple extracellular and internal signals and generate adaptive cellular responses. However, the ER morphology and activity in the case of tardigrades has been studied rarely and in the context of oogenesis, functioning of the digestive system, and in the role and function of storage cells. Thus, there are no direct studies on the contribution of the ER in the ability of this organism to cope with environmental stress during cryptobiosis. Nevertheless, it is highly probable that the ER has a crucial role in this uncommon process. Since water bears are easy to handle laboratory animals, they may represent an ideal model organism to uncover the important role of the ER in the cell response to extreme environmental stress conditions.

Developing Therapies for Neurodegenerative Disorders: Insights from Protein Aggregation and Cellular Stress Responses

As the world's population ages, neurodegenerative disorders are poised to become the commonest cause of death. Despite this, they remain essentially untreatable. Characterized pathologically both by the aggregation of disease-specific misfolded proteins and by changes in cellular stress responses, to date, therapeutic approaches have focused almost exclusively on reducing misfolded protein load-notably amyloid beta (Aβ) in Alzheimer's disease. The repeated failure of clinical trials has led to despondency over the possibility that these disorders will ever be treated. We argue that this is in fact a time for optimism: Targeting various generic stress responses is emerging as an increasingly promising means of modifying disease progression across these disorders. New treatments are approaching clinical trials, while novel means of targeting aggregates could eventually act preventively in early disease.

The special unfolded protein response in plasma cells

The high rate of antibody production places considerable metabolic and folding stress on plasma cells (PC). Not surprisingly, they rely on the unfolded protein response (UPR), a universal signaling, and transcriptional network that monitors the health of the secretory pathway and mounts cellular responses to stress. Typically, the UPR utilizes three distinct stress sensors in the ER membrane, each regulating a subset of targets to re-establish homeostasis. PC use a specialized UPR scheme-they preemptively trigger the UPR via developmental signals and suppress two of the sensors, PERK and ATF6, relying on IRE1 alone. The specialized PC UPR program is tuned to the specific needs at every stage of development-from early biogenesis of secretory apparatus, to massive immunoglobulin expression later. Furthermore, the UPR in PC integrates with other pathways essential in a highly secretory cell-mTOR pathway that ensures efficient synthesis, autophagosomes that recycle components of the synthetic machinery, and apoptotic signaling that controls cell fate in the face of excessive folding stress. This specialized PC program is not shared with other secretory cells, for reasons yet to be defined. In this review, we give a perspective into how and why PC need such a unique UPR program.

Membraneless organelles restructured and built by pandemic viruses: HIV-1 and SARS-CoV-2

Viruses hijack host functions to invade their target cells and spread to new cells. Specifically, viruses learned to usurp liquid‒liquid phase separation (LLPS), a newly exploited mechanism, used by the cell to concentrate enzymes to accelerate and confine a wide variety of cellular processes. LLPS gives rise to actual membraneless organelles (MLOs), which do not only increase reaction rates but also act as a filter to select molecules to be retained or to be excluded from the liquid droplet. This is exactly what seems to happen with the condensation of SARS-CoV-2 nucleocapsid protein to favor the packaging of intact viral genomes, excluding viral subgenomic or host cellular RNAs. Another older pandemic virus, HIV-1, also takes advantage of LLPS in the host cell during the viral cycle. Recent discoveries highlighted that HIV-1 RNA genome condensates in nuclear MLOs accompanied by specific host and viral proteins, breaking the dogma of retroviruses that limited viral synthesis exclusively to the cytoplasmic compartment. Intriguing fundamental properties of viral/host LLPS remain still unclear. Future studies will contribute to deeply understanding the role of pathogen-induced MLOs in the epidemic invasion of pandemic viruses.

DYT-TOR1A subcellular proteomics reveals selective vulnerability of the nuclear proteome to cell stress

TorsinA is a AAA⁺ ATPase that shuttles between the ER lumen and outer nuclear envelope in an ATP-dependent manner and is functionally implicated in nucleocytoplasmic transport. We hypothesized that the DYT-TOR1A dystonia disease-causing variant, ΔE TorsinA, may therefore disrupt the normal subcellular distribution of proteins between the nuclear and cytosolic compartments. To test this hypothesis, we performed proteomic analysis on nuclear and cytosolic subcellular fractions from DYT-TOR1A and wildtype mouse embryonic fibroblasts (MEFs). We further examined the compartmental proteomes following exposure to thapsigargin (Tg), an endoplasmic reticulum (ER) stressor, because DYT-TOR1A dystonia models have previously shown abnormalities in cellular stress responses. Across both subcellular compartments, proteomes of DYT-TOR1A cells showed basal state disruptions consistent with an activated stress response, and in response to thapsigargin, a blunted stress response. However, the DYT-TOR1A nuclear proteome under Tg cell stress showed the most pronounced and disproportionate degree of protein disruptions - 3-fold greater than all other conditions. The affected proteins extended beyond those typically associated with stress responses, including enrichments for processes critical for neuronal synaptic function. These findings highlight the advantage of subcellular proteomics to reveal events that localize to discrete subcellular compartments and refine thinking about the mechanisms and significance of cell stress in DYT-TOR1A pathogenesis.

Acrylamide inhibits vaccinia virus through vimentin-independent anti-viral granule formation

The replication and assembly of vaccinia virus (VACV), the prototypic poxvirus, occurs exclusively in the cytoplasm of host cells. While the role of cellular cytoskeletal components in these processes remains poorly understood, vimentin-a type III intermediate filament-has been shown to associate with viral replication sites and to be incorporated into mature VACV virions. Here, we employed chemical and genetic approaches to further investigate the role of vimentin during the VACV lifecycle. The collapse of vimentin filaments, using acrylamide, was found to inhibit VACV infection at the level of genome replication, intermediate- and late-gene expression. However, we found that CRISPR-mediated knockout of vimentin did not impact VACV replication. Combining these tools, we demonstrate that acrylamide treatment results in the formation of anti-viral granules (AVGs) known to mediate translational inhibition of many viruses. We conclude that vimentin is dispensable for poxvirus replication and assembly and that acrylamide, as a potent inducer of AVGs during VACV infection, serves to bolster cell's anti-viral response to poxvirus infection.

Evolution of the unfolded protein response in plants

The unfolded protein response (UPR) in plants is elicited by endoplasmic reticulum stress, which can be brought about by adverse environmental conditions. The response is mediated by a conserved signalling network composed of two branches - one branch involving inositol requiring enzyme1- basic leucine zipper60 (IRE1-bZIP60) signalling pathway and another branch involving the membrane transcription factors, bZIP17 and -28. The UPR has been reported in Chlamydomonas reinhardtii, a unicellular green alga, which lacks some canonical UPR signalling components found in vascular plants, raising the question whether C. reinhardtii uses other means such as oxidative signalling or Regulated IRE1-Dependent Decay to activate the UPR. In vascular plants, IRE1 splices bZIP60 mRNA in response to endoplasmic reticulum stress by cutting at a site in the RNA that is highly conserved in structure and sequence. Monocots have a single IRE1 gene required for viability in rice, while dicots have two IRE1 genes, IRE1a and -b. Brassicas have a third IRE1 gene, IRE1c, which lacks a lumenal domain, but is required in combination with IRE1b for gametogenesis. Vascular and non-vascular plants upregulate a similar set of genes in response to endoplasmic reticulum stress despite differences in the complexity of their UPR signalling networks.

The Role of PERK in Understanding Development of Neurodegenerative Diseases

Neurodegenerative diseases are an ever-increasing problem for the rapidly aging population. Despite this, our understanding of how these neurodegenerative diseases develop and progress, is in most cases, rudimentary. Protein kinase RNA (PKR)-like ER kinase (PERK) comprises one of three unfolded protein response pathways in which cells attempt to manage cellular stress. However, because of its role in the cellular stress response and the far-reaching implications of this pathway, error within the PERK pathway has been shown to lead to a variety of pathologies. Genetic and clinical studies show a correlation between failure of the PERK pathway in neural cells and the development of neurodegeneration, but the wide array of methodology of these studies is presenting conflicting narratives about the role of PERK in these affected systems. Because of the connection between PERK and pathology, PERK has become a high value target of study for understanding neurodegenerative diseases and potentially how to treat them. Here, we present a review of the literature indexed in PubMed of the PERK pathway and some of the complexities involved in investigating the protein's role in the development of neurodegenerative diseases as well as how it may act as a target for therapeutics.

Pathological mechanisms of vacuolar aggregate myopathy arising from a Casq1 mutation

Mice with a mutation (D244G, DG) in calsequestrin 1 (CASQ1), analogous to a human mutation in CASQ1 associated with a delayed onset human myopathy (vacuolar aggregate myopathy), display a progressive myopathy characterized by decreased activity, decreased ability of fast twitch muscles to generate force and low body weight after one year of age. The DG mutation causes CASQ1 to partially dissociate from the junctional sarcoplasmic reticulum (SR) and accumulate in the endoplasmic reticulum (ER). Decreased junctional CASQ1 reduces SR Ca²⁺ release. Muscles from older DG mice display ER stress, ER expansion, increased mTOR signaling, inadequate clearance of aggregated proteins by the proteasomes, and elevation of protein aggregates and lysosomes. This study suggests that the myopathy associated with the D244G mutation in CASQ1 is driven by CASQ1 mislocalization, reduced SR Ca²⁺ release, CASQ1 misfolding/aggregation and ER stress. The subsequent maladaptive increase in protein synthesis and decreased protein aggregate clearance are likely to contribute to disease progression.

Amyotrophic Lateral Sclerosis (ALS): Stressed by Dysfunctional Mitochondria-Endoplasmic Reticulum Contacts (MERCs)

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which there is currently no cure. Progress in the characterization of other neurodegenerative mechanisms has shifted the spotlight onto an intracellular structure called mitochondria-endoplasmic reticulum (ER) contacts (MERCs) whose ER portion can be biochemically isolated as mitochondria-associated membranes (MAMs). Within the central nervous system (CNS), these structures control the metabolic output of mitochondria and keep sources of oxidative stress in check via autophagy. The most relevant MERC controllers in the ALS pathogenesis are vesicle-associated membrane protein-associated protein B (VAPB), a mitochondria-ER tether, and the ubiquitin-specific chaperone valosin containing protein (VCP). These two systems cooperate to maintain mitochondrial energy output and prevent oxidative stress. In ALS, mutant VAPB and VCP take a central position in the pathology through MERC dysfunction that ultimately alters or compromises mitochondrial bioenergetics. Intriguingly, both proteins are targets themselves of other ALS mutant proteins, including C9orf72, FUS, or TDP-43. Thus, a new picture emerges, where different triggers cause MERC dysfunction in ALS, subsequently leading to well-known pathological changes including endoplasmic reticulum (ER) stress, inflammation, and motor neuron death.