The ORF8 protein of SARS-CoV-2 induced endoplasmic reticulum stress and mediated immune evasion by antagonizing production of interferon beta.

The open reading frame 8 (orf8) is an accessory protein of SARS-CoV-2. It has 121 amino acids with two genotypes, orf8L and orf8S. In this study, we overexpressed the orf8L and orf8S of SARS-CoV-2 as well as the orf8b of SARS-CoV to investigate their roles in the regulation of endoplasmic reticulum (ER) stress and the inhibition of interferon beta (IFNß) production. We found that the two genotypes of SARS-CoV-2 orf8 are capable of inducing ER stress without significant difference by triggering the activating transcription factor 6 (ATF6) and inositol-requiring enzymes 1 (IRE1) branches of the ER stress pathway. However, the third branch of ER stress pathway, i.e. the protein kinase-like ER kinase (PERK), was unaffected by the overexpression of SARS-CoV-2 orf8L or orf8S. Moreover, both orf8L and orf8S of SARS-CoV-2 are capable of down regulating the production of IFNß and interferon-stimulated genes (ISG), ISG15 and ISG56 induced by polyinosinic-polycytidylic acid (poly (I:C)). Moreover, we also found decreased nuclear translocation of Interferon regulatory factor 3 (IRF3), after overexpressing orf8L and orf8S induced by poly (I:C). Our data demonstrated that SARS-CoV-2 orf8 protein could induce ER stress by activating the ATF6 and IRE1 pathways, but not the PERK pathway, and functions as an interferon antagonist to inhibit the production of IFNß. However, these functions appeared not to be affected by the genotypes of SARS-CoV-2 orf8L and orf8S.

The role of activating transcription factor 6 in hydroxycamptothecin-induced fibroblast autophagy and apoptosis.

BACKGROUND: The over-proliferation of fibroblasts is considered to be the main cause of scar adhesion after joint surgery. Hydroxycamptothecin (HCPT), though as a potent antineoplastic drug, shows preventive effects on scar adhesion. This study aimed to investigate the role of activating transcription factor 6 (ATF-6) in the HCPT-induced inhibition of fibroblast viability. METHODS: The cell counting kit-8 (CCK-8) assay, western blot analysis, lentivirus-mediated gene silencing, transmission electron microscopy (TEM) analysis, immunofluorescent staining for autophagy-related protein light chain 3 (LC3) were used to explore the effect of HCPT on triggering fibroblast apoptosis and inhibiting fibroblast proliferation, and the involvement of possible signaling pathways. RESULTS: It was found that HCPT exacerbated fibroblast apoptosis and repressed its proliferation. Subsequently, endoplasmic reticulum stress (ERS)-related proteins were determined by western blot prior to ATF6 p50 was screened out and reexamined after it was silenced. As a result, ATF6-mediated ERS played a role in HCPT-induced fibroblast apoptosis. Autophagy-related proteins and autophagosomes were detected after the HCPT administration using western blot and TEM analyses, respectively. Autophagy was activated after the HCPT treatment. With the co-treatment of autophagy inhibitor 3-methyladenine (3-MA), both the western blot analysis and the CCK-8 assay showed inhibited autophagy, which indicated that the effect of HCPT on fibroblast proliferation was partially reversed. Besides, the LC3 immunofluorescence staining revealed suppressed autophagy after silencing ATF6 p50. CONCLUSION: Our results demonstrate that HCPT acts as a facilitator of fibroblast apoptosis and inhibitor of fibroblast proliferation for curbing the postoperative scar adhesion, in which the ATF6-mediated ERS pathway and autophagy are involved.

Endoplasmic reticulum stress, an important factor in the development of Parkinson's disease.

Similar to other types of neuronal degeneration, Parkinson's disease (PD) is characterized by the aggregation of a pathological protein, α-synuclein. The endoplasmic reticulum (ER) is the principal site of protein synthesis, quality control and degradation. Genetic mutants, environmental insults and other factors disturb ER balance and induce the accumulation of misfolded/unfolded proteins, which initiate ER stress and disturb normal cell function. ER stress perturbs Ca2+ homeostasis and initiates the activation of autophagy and inflammasomes, which have been identified as risk factors for the development of PD. However, the mechanisms by which ER stress contributes to the processed of PD pathogenesis and development remain unclear. This review summarizes current knowledge of ER stress and highlights the principal role of ER stress in PD pathogenesis which may help reveal novel sight to illustrate the pathomechanism of PD.

Establishment and validation of an endoplasmic reticulum stress reporter to monitor zebrafish ATF6 activity in development and disease.

Induction of endoplasmic reticulum (ER) stress is associated with diverse developmental and degenerative diseases. Modified ER homeostasis causes activation of conserved stress pathways at the ER called the unfolded protein response (UPR). ATF6 is a transcription factor activated during ER stress as part of a coordinated UPR. ATF6 resides at the ER and, upon activation, is transported to the Golgi apparatus, where it is cleaved by proteases to create an amino-terminal cytoplasmic fragment (ATF6f). ATF6f translocates to the nucleus to activate transcriptional targets. Here, we describe the establishment and validation of zebrafish reporter lines for ATF6 activity. These transgenic lines are based on a defined and multimerized ATF6 consensus site, which drives either eGFP or destabilized eGFP, enabling dynamic study of ATF6 activity during development and disease. The results show that the reporter is specific for the ATF6 pathway, active during development and induced in disease models known to engage UPR. Specifically, during development, ATF6 activity is highest in the lens, skeletal muscle, fins and gills. The reporter is also activated by common chemical inducers of ER stress, including tunicamycin, thapsigargin and brefeldin A, as well as by heat shock. In models for amyotrophic lateral sclerosis and cone dystrophy, ATF6 reporter expression is induced in spinal cord interneurons or photoreceptors, respectively, suggesting a role for ATF6 response in multiple neurodegenerative diseases. Collectively our results show that these ATF6 reporters can be used to monitor ATF6 activity changes throughout development and in zebrafish models of disease.This article has an associated First Person interview with the first author of the paper.

An ATF6-tPA pathway in hepatocytes contributes to systemic fibrinolysis and is repressed by DACH1.

Tissue-type plasminogen activator (tPA) is a major mediator of fibrinolysis and, thereby, prevents excessive coagulation without compromising hemostasis. Studies on tPA regulation have focused on its acute local release by vascular cells in response to injury or other stimuli. However, very little is known about sources, regulation, and fibrinolytic function of noninjury-induced systemic plasma tPA. We explore the role and regulation of hepatocyte-derived tPA as a source of basal plasma tPA activity and as a contributor to fibrinolysis after vascular injury. We show that hepatocyte tPA is downregulated by a pathway in which the corepressor DACH1 represses ATF6, which is an inducer of the tPA gene Plat Hepatocyte-DACH1-knockout mice show increases in liver Plat, circulating tPA, fibrinolytic activity, bleeding time, and time to thrombosis, which are reversed by silencing hepatocyte Plat Conversely, hepatocyte-ATF6-knockout mice show decreases in these parameters. The inverse correlation between DACH1 and ATF6/PLAT is conserved in human liver. These findings reveal a regulated pathway in hepatocytes that contributes to basal circulating levels of tPA and to fibrinolysis after vascular injury.

Activated ATF6 Induces Intestinal Dysbiosis and Innate Immune Response to Promote Colorectal Tumorigenesis.

BACKGROUND & AIMS: Activating transcription factor 6 (ATF6) regulates endoplasmic reticulum stress. We studied whether ATF6 contributes to the development of colorectal cancer (CRC) using tissue from patients and transgenic mice. METHODS: We analyzed data from 541 patients with CRC in The Cancer Genome Atlas database for genetic variants and aberrant expression levels of unfolded protein response genes. Findings were validated in a cohort of 83 patients with CRC in Germany. We generated mice with intestinal epithelial cell-specific expression of the active form of Atf6 (nATF6IEC) from 2 alleles (homozygous), mice with expression of nATF6IEC from 1 allele (heterozygous), and nATF6IECfl/fl mice (controls). All nATF6IEC mice were housed under either specific-pathogen-free or germ-free conditions. Cecal microbiota from homozygous nATF6IEC mice or control mice was transferred into homozygous nATF6IEC mice or control mice. nATF6IEC mice were crossed with mice with disruptions in the myeloid differentiation primary response gene 88 and toll-like receptor adaptor molecule 1 gene (Myd88/Trif-knockout mice). Intestinal tissues were collected from mice and analyzed by histology, immunohistochemistry, immunoblots, gene expression profiling of unfolded protein response and inflammatory genes, array-based comparative genome hybridization, and 16S ribosomal RNA gene sequencing. RESULTS: Increased expression of ATF6 was associated with reduced disease-free survival times of patients with CRC. Homozygous nATF6IEC mice developed spontaneous colon adenomas at 12 weeks of age. Compared with controls, homozygous nATF6IEC mice had changes in the profile of their cecal microbiota, increased proliferation of intestinal epithelial cells, and loss of the mucus barrier-all preceding tumor formation. These mice had increased penetration of bacteria into the inner mucus layer and activation of signal transducer and activator of transcription 3, yet inflammation was not observed at the pretumor or tumor stages. Administration of antibiotics to homozygous nATF6IEC mice greatly reduced tumor incidence, and germ-free housing completely prevented tumorigenesis. Analysis of nATF6IEC MyD88/TRIF-knockout mice showed that tumor initiation and growth required MyD88/TRIF-dependent activation of signal transducer and activator of transcription 3. Transplantation of cecal microbiota from nATF6IEC mice and control mice, collected before tumor formation, caused tumor formation in ex-germ-free nATF6IEC mice. CONCLUSIONS: In patients with CRC, ATF6 was associated with reduced time of disease-free survival. In studies of nATF6IEC mice, we found sustained intestinal activation of ATF6 in the colon to promote dysbiosis and microbiota-dependent tumorigenesis.

Endoplasmic reticulum stress signalling and the pathogenesis of non-alcoholic fatty liver disease.

The global epidemic of obesity has been accompanied by a rising burden of non-alcoholic fatty liver disease (NAFLD), with manifestations ranging from simple steatosis to non-alcoholic steatohepatitis, potentially developing into hepatocellular carcinoma. Although much attention has focused on NAFLD, its pathogenesis remains largely obscure. The hallmark of NAFLD is the hepatic accumulation of lipids, which subsequently leads to cellular stress and hepatic injury, eventually resulting in chronic liver disease. Abnormal lipid accumulation often coincides with insulin resistance in steatotic livers and is associated with perturbed endoplasmic reticulum (ER) proteostasis in hepatocytes. In response to chronic ER stress, an adaptive signalling pathway known as the unfolded protein response is triggered to restore ER proteostasis. However, the unfolded protein response can cause inflammation, inflammasome activation and, in the case of non-resolvable ER stress, the death of hepatocytes. Experimental data suggest that the unfolded protein response influences hepatic tumour development, aggressiveness and response to treatment, offering novel therapeutic avenues. Herein, we provide an overview of the evidence linking ER stress to NAFLD and discuss possible points of intervention.

ER Protein Quality Control and the Unfolded Protein Response in the Heart.

Cardiac myocytes are the cells responsible for the robust ability of the heart to pump blood throughout the circulatory system. Cardiac myocytes grow in response to a variety of physiological and pathological conditions; this growth challenges endoplasmic reticulum-protein quality control (ER-PQC), a major feature of which includes the unfolded protein response (UPR). ER-PQC and the UPR in cardiac myocytes growing under physiological conditions, including normal development, exercise, and pregnancy, are sufficient to support hypertrophic growth of each cardiac myocyte. However, the ER-PQC and UPR are insufficient to respond to the challenge of cardiac myocyte growth under pathological conditions, including myocardial infarction and heart failure. In part, this insufficiency is due to a continual decline in the expression levels of important adaptive UPR components as a function of age and during myocardial pathology. This chapter will discuss the physiological and pathological conditions unique to the heart that involves ER-PQC, and whether the UPR is adaptive or maladaptive under these circumstances.

[Activating transcription factor 6-C/EBP homologous protein pathway mediates advanced glycated albumin-induced macrophage apoptosis].

The purpose of this study was to investigate whether activating transcription factor 6 (ATF6), a sensor to endoplasmic reticulum stress (ERS), would mediate advanced glycated albumin (AGE-alb)-induced macrophage apoptosis and to elucidate the possible molecular mechanisms. RAW264.7 macrophages were cultured in vitro and treated with AGE-alb (2, 4 and 6 g/L), normal control albumin or tunicamycin (TM, 4 mg/L) for 24 h. ATF6 small interfering RNA (siRNA) was transfected to RAW264.7 cells by Lipofectamine 2000. Cell viability and apoptosis were determined by MTT method and Annexin V-FITC/propidium iodide apoptosis detection kit, respectively. The activities of lactate dehydrogenase (LDH) in medium and caspase-3 in cells were measured by corresponding detection kits. ATF6 nuclear translocation was detected by Western blot and immunofluorescence cytochemistry. Protein and mRNA levels of C/EBP homologous protein (CHOP, a key-signaling component of ERS-induced apoptosis) were detected by Western blot and real-time fluorescence quantitative PCR, respectively. The results showed that similar to TM, AGE-alb increased the expression of CHOP at both the protein and mRNA levels in a concentration dependent manner. ATF6, as a factor that positively regulates CHOP expression, was activated by AGE-alb in a concentration dependent manner. siRNA-mediated knockdown of ATF6 significantly inhibited AGE-alb-induced macrophage injury, as indicated by the increased cell viability and the decreased LDH release, apoptosis and caspase-3 activation. Additionally, ATF6 siRNA attenuated AGE-alb-induced CHOP upregulation at both the protein and mRNA levels. These results suggest that ATF6 and its downstream molecule CHOP are involved in AGE-alb-induced macrophage apoptosis.

Avian metapneumovirus subgroup C induces autophagy through the ATF6 UPR pathway.

An increasing number of studies have demonstrated that macroautophagy/autophagy plays an important role in the infectious processes of diverse pathogens. However, it remains unknown whether autophagy is induced in avian metapneumovirus (aMPV)-infected host cells, and, if so, how this occurs. Here, we report that aMPV subgroup C (aMPV/C) induces autophagy in cultured cells. We demonstrated this relationship by detecting classical autophagic features, including the formation of autophagsomes, the presence of GFP-LC3 puncta and the conversation of LC3-I into LC3-II. Also, we used pharmacological regulators and siRNAs targeting ATG7 or LC3 to examine the role of autophagy in aMPV/C replication. The results showed that autophagy is required for efficient replication of aMPV/C. Moreover, infection with aMPV/C promotes autophagosome maturation and induces a complete autophagic process. Finally, the ATF6 pathway, of which one component is the unfolded protein response (UPR), becomes activated in aMPV/C-infected cells. Knockdown of ATF6 inhibited aMPV/C-induced autophagy and viral replication. Collectively, these results not only show that autophagy promotes aMPV/C replication in the cultured cells, but also reveal that the molecular mechanisms underlying aMPV/C-induced autophagy depends on regulation of the ER stress-related UPR pathway.

Pathogenic Mechanism of Diabetes Development Due to Dysfunction of Unfolded Protein Response.

The endoplasmic reticulum (ER) is an organelle in which newly synthesized secretory and membrane proteins are folded and assembled. Various stresses cause the accumulation of unfolded or misfolded proteins in the ER, resulting in ER dysfunction. This condition is termed ER stress. To cope with ER stress, cells activate a signaling pathway termed the unfolded protein response (UPR). Recently, accumulating evidence suggests that the UPR plays a pivotal role in pancreatic ß cells. Pancreatic ß cells producing a large amount of insulin are highly sensitive when the UPR is impaired. In mammalian cells, three principal ER stress sensors, PERK, IRE1, and ATF6, initiate the UPR. Activated PERK attenuates protein translation through eIF2α phosphorylation to cope with the ER stress. PERK KO mice develop diabetes by 2-4 weeks of age due to progressive ß-cell loss. IRE1α noncanonically splices the XBP1 mRNA, leading to the upregulation of the ERAD components and ER molecular chaperones. This pathway is constitutively activated in pancreatic ß cells. To clarify the physiological role of the IRE1α pathway in ß cells, we generated pancreatic-ß-cell-specific IRE1α-conditional KO (cKO) mice and IRE1α-cKO insulinoma cell lines. Here, we show that IRE1α is required for the upregulation of insulin-folding enzymes in pancreatic ß cells to balance insulin-folding enzymes with insulin.

ATF6a, a Runx2-activable transcription factor, is a new regulator of chondrocyte hypertrophy.

Our previous research has shown that the spliced isoform of XBP1 (XBP1s) is an important downstream mediator of BMP2 and is involved in BMP2-stimulated chondrocyte differentiation. Herein, we report that ATF6 and its cleaved N-terminal cytoplasmic domain (known as ATF6a) are expressed in growth plate chondrocytes. We find that these proteins are differentially induced during BMP2-triggered chondrocyte differentiation. This differential expression probably results from the activation of the ATF6 gene by Runx2 and its repression by the Sox6 transcription factor. Runx2 and Sox6 act through their respective binding elements on the ATF6 gene. When overexpressed, ATF6 and ATF6a intensify chondrogenesis; our studies demonstrate that under the stimulation of ATF6 and ATF6a, chondrocytes tend to be hypertrophied and mineralized, a process leading to bone formation. By contrast, lowering expression of ATF6a by use of its specific siRNA suppresses chondrocyte differentiation. Moreover, ATF6a interacts with Runx2 and augments the Runx2-mediated hypertrophication of chondrocytes. Importantly, overexpression and knockdown of ATF6a during the chondrocyte hypertrophy process also led to altered expressions of IHH and PTHrP (also known as PTHLH). Taken together, these findings indicate that ATF6a favorably controls chondrogenesis and bone formation (1) by acting as a co-factor of Runx2 and enhancing Runx2-incited hypertrophic chondrocyte differentiation, and (2) by affecting IHH and PTHrP signaling.

Insulin demand regulates ß cell number via the unfolded protein response.

Although stem cell populations mediate regeneration of rapid turnover tissues, such as skin, blood, and gut, a stem cell reservoir has not been identified for some slower turnover tissues, such as the pancreatic islet. Despite lacking identifiable stem cells, murine pancreatic ß cell number expands in response to an increase in insulin demand. Lineage tracing shows that new ß cells are generated from proliferation of mature, differentiated ß cells; however, the mechanism by which these mature cells sense systemic insulin demand and initiate a proliferative response remains unknown. Here, we identified the ß cell unfolded protein response (UPR), which senses insulin production, as a regulator of ß cell proliferation. Using genetic and physiologic models, we determined that among the population of ß cells, those with an active UPR are more likely to proliferate. Moreover, subthreshold endoplasmic reticulum stress (ER stress) drove insulin demand-induced ß cell proliferation, through activation of ATF6. We also confirmed that the UPR regulates proliferation of human ß cells, suggesting that therapeutic UPR modulation has potential to expand ß cell mass in people at risk for diabetes. Together, this work defines a stem cell-independent model of tissue homeostasis, in which differentiated secretory cells use the UPR sensor to adapt organ size to meet demand.

ENDOPLASMIC RETICULUM STRESS IN SEPSIS.

Sepsis is an enormous public health issue and the leading cause of death in critically ill patients in intensive care units. Overwhelming inflammation, characterized by cytokine storm, oxidative threats, and neutrophil sequestration, is an underlying component of sepsis-associated organ failure. Despite recent advances in sepsis research, there is still no effective treatment available beyond the standard of care and supportive therapy. To reduce sepsis-related mortality, a better understanding of the biological mechanism associated with sepsis is essential. Endoplasmic reticulum (ER), a subcellular organelle, is responsible for the facilitation of protein folding and assembly and involved in several other physiological activities. Under stress and inflammatory conditions, ER loses homeostasis in its function, which is termed ER stress. During ER stress, unfolded protein response (UPR) is activated to restore ER function to its normal balance. However, once stress is beyond the compensatory capacity of UPR or protracted, apoptosis would be initiated by triggering cell injuries, even cell death. As such, ER stress and UPR are reported to be implicated in several pathological and inflammatory conditions. Although the detrimental role of ER stress during infections has been demonstrated, there is growing evidence that ER stress participates in the pathogenesis of sepsis. In this review, we summarize current research in the context of ER stress and UPR signaling associated with sepsis and its related clinical conditions, such as trauma-hemorrhage and ischemia/reperfusion injury. We also discuss the potential implications of ER stress as a novel therapeutic target and prognostic marker in patients with sepsis.

Unfolding the promise of translational targeting in neurodegenerative disease.

With the rise of aging populations, new challenges for health care systems are emerging. Degenerative conditions of the central nervous system share a strikingly great deal of similarities, particularly the production and buildup of malfolded proteins. As a result, stress pathways within the endoplasmic reticulum become activated, triggering widespread neuronal apoptosis. New pharmacological compounds targeting this response are emerging as promising treatment strategies. This review examines the current evidence for protein aggregation in neurodegenerative disease states and discusses future mechanisms of therapeutically targeting the endoplasmic reticulum.

ER Stress Response in Human Cellular Models of Senescence.

The aging process is characterized by progressive accumulation of damaged biomolecules in the endoplasmic reticulum, as result of increased oxidative stress accompanying cellular senescence. In agreement, we hypothesized that WI-38 human cellular models of replicative senescence and stress-induced premature senescence (SIPS) induced by hydrogen peroxide (H2O2-SIPS) or copper sulfate (CuSO4-SIPS) would present endoplasmic reticulum chaperoning mechanisms impairment and unfolded protein response activation. Results show that in replicative senescence and CuSO4-SIPS, immunoglobulin binding protein, calnexin, protein disulfide isomerase, and ER oxireductin-1 levels adjust to restore proteostasis and inositol-requiring enzyme-1 (IRE1)-, activating transcription factor 6 (ATF6)-, and pancreatic ER kinase (PERK)-mediated unfolded protein response are activated. However, H2O2-SIPS does not exhibit IRE1 and ATF6 pathways activation but a PERK-mediated upregulation of CCAAT/enhancer-binding protein homologous protein, showing that CuSO4-SIPS mimics better the endoplasmic reticulum molecular events of replicative senescence than H2O2-SIPS. Moreover, unfolded protein response activation is required for both SIPS models induction, because PERK and IRE1 inhibitors decreased senescence-associated beta-galactosidase appearance. In CuSO4-SIPS, the decrease in senescence levels is associated with PERK-driven, but IRE1 independent, cell cycle arrest while in H2O2-SIPS cell proliferation is PERK independent. These results add a step further on the molecular mechanisms that regulate senescence induction; moreover, they validate CuSO4-SIPS model as a useful tool to study cellular stress responses during aging, hoping to postpone age-related health decline.

Deletion of Atf6α impairs astroglial activation and enhances neuronal death following brain ischemia in mice.

To dissect the role of endoplasmic reticulum (ER) stress and unfolded protein response in brain ischemia, we investigated the relevance of activating transcription factor 6α (ATF6α), a master transcriptional factor in the unfolded protein response, after permanent middle cerebral artery occlusion (MCAO) in mice. Enhanced expression of glucose-regulated protein78, a downstream molecular chaperone of ATF6α, was observed in both neurons and glia in the peri-infarct region of wild-type mice after MCAO. Analysis using wild-type and Atf6α(-/-) mice revealed a larger infarct volume and increased cell death in the peri-ischemic region of Atf6α(-/-) mice 5 days after MCAO. These phenotypes in Atf6α(-/-) mice were associated with reduced levels of astroglial activation/glial scar formation, and a spread of tissue damage into the non-infarct area. Further analysis in mice and cultured astrocytes revealed that signal transducer and activator of transcription 3 (STAT3)-glial fibrillary acidic protein signaling were diminished in Atf6α(-/-) astrocytes. A chemical chaperone, 4-phenylbutyrate, restored STAT3-glial fibrillary acidic protein signaling, while ER stressors, such as tunicamycin and thapsigargin, almost completely abolished signaling in cultured astrocytes. Furthermore, ER stress-induced deactivation of STAT3 was mediated, at least in part, by the ER stress-responsive tyrosine phosphatase, TC-PTP/PTPN2. These results suggest that ER stress plays critical roles in determining the level of astroglial activation and neuronal survival after brain ischemia.

Single-prolonged stress activates the transcription factor ATF6α branch of the unfolded protein response in rat neurons of dorsal raphe nucleus.

In our previous studies, we have found that endoplasmic reticulum (ER) stress is associated with post-traumatic stress disorder (PTSD), however, the activation of ER stress sensors in PTSD remains unclear. ATF6 alpha (ATF6α) is an ER-membrane-bound transcription factor and functions as a critical sensor and regulator of ER stress in mammalian cells. The goal of this study is to detect whether there is activation of the transcription factor ATF6α branch of the unfolded protein response in the dorsal raphe nucleus neurons of the rats exposed to single-prolonged stress (SPS), which is a model employed extensively in PTSD study. Our results have demonstrated that SPS activated the ER transmembrane protein ATF6α via its cleavage; and induced the up-regulation of the downstream targets of ATF6α, the mRNA of XBP1 and GRP94. To the best of our knowledge, this is the first study to investigate the relationship between the ATF6α pathways and PTSD, and our results show that SPS activates the ATF6α branch of the ER stress response, which may be contributed to the pathogenesis of PTSD.

Activating transcription factor 6α is required for the vasopressin neuron system to maintain water balance under dehydration in male mice.

Activating transcription factor 6α (ATF6α) is a sensor of endoplasmic reticulum (ER) stress and increases the expression of ER chaperones and molecules related to the ER-associated degradation of unfolded/misfolded proteins. In this study, we used ATF6α knockout (ATF6α(-/-)) mice to clarify the role of ATF6α in the arginine vasopressin (AVP) neuron system. Although urine volumes were not different between ATF6α(-/-) and wild-type (ATF6α(+/+)) mice with access to water ad libitum, they were increased in ATF6α(-/-) mice compared with those in ATF6α(+/+) mice under intermittent water deprivation (WD) and accompanied by less urine AVP in ATF6α(-/-) mice. The mRNA expression of immunoglobulin heavy chain binding protein, an ER chaperone, was significantly increased in the supraoptic nucleus in ATF6α(+/+) but not ATF6α(-/-) mice after WD. Electron microscopic analyses demonstrated that the ER lumen of AVP neurons was more dilated in ATF6α(-/-) mice than in ATF6α(+/+) mice after WD. ATF6α(-/-) mice that were mated with mice possessing a mutation causing familial neurohypophysial diabetes insipidus (FNDI), which is characterized by progressive polyuria and AVP neuronal loss due to the accumulation of mutant AVP precursor in the ER, manifested increased urine volume under intermittent WD. The aggregate formation in the ER of AVP neurons was further impaired in FNDI/ATF6α(-/-) mice compared with that in FNDI mice, and AVP neuronal loss was accelerated in FNDI/ATF6α(-/-) mice under WD. These data suggest that ATF6α is required for the AVP neuron system to maintain water balance under dehydration.