Roles for ATF6 and the sarco/endoplasmic reticulum protein quality control system in the heart

Valosin-containing protein: A potential therapeutic target for cardiovascular diseases

Valosin-containing protein (VCP), also known as p97, plays a crucial role in various cellular processes, including protein degradation, endoplasmic reticulum-associated degradation, and cell cycle regulation. While extensive research has been focused on VCP's involvement in protein homeostasis and its implications in neurodegenerative diseases, emerging evidence suggests a potential link between VCP and cardiovascular health. VCP is a key regulator of mitochondrial function, and its overexpression or mutations lead to pathogenic diseases and cellular stress responses. The present review explores VCP's roles in numerous cardiovascular disorders including myocardial ischemia/reperfusion injury, cardiac hypertrophy, and heart failure. The review dwells on the roles of VCP in modifying mitochondrial activity, promoting S-nitrosylation, regulating mTOR signalling and demonstrating cardioprotective effects. Further research into VCP might lead to novel interventions for cardiovascular disease, particularly those involving ischemia/reperfusion injury and hypertrophy.

Potential role of endoplasmic reticulum stress in doxorubicin-induced cardiotoxicity-an update

As a chemotherapy agent, doxorubicin is used to combat cancer. However, cardiotoxicity has limited its use. The existing strategies fail to eliminate doxorubicin-induced cardiotoxicity, and an in-depth exploration of its pathogenesis is in urgent need to address the issue. Endoplasmic reticulum stress (ERS) occurs when Endoplasmic Reticulum (ER) dysfunction results in the accumulation of unfolded or misfolded proteins. Adaptive ERS helps regulate protein synthesis to maintain cellular homeostasis, while prolonged ERS stimulation may induce cell apoptosis, leading to dysfunction and damage to tissue and organs. Numerous studies on doxorubicin-induced cardiotoxicity strongly link excessive activation of the ERS to mechanisms including oxidative stress, calcium imbalance, autophagy, ubiquitination, and apoptosis. The researchers also found several clinical drugs, chemical compounds, phytochemicals, and miRNAs inhibited doxorubicin-induced cardiotoxicity by targeting ERS. The present review aims to outline the interactions between ERS and other mechanisms in doxorubicin-induced cardiotoxicity and summarize ERS's role in this type of cardiotoxicity. Additionally, the review enumerates several clinical drugs, phytochemicals, chemical compounds, and miRNAs targeting ERS for considering therapeutic regimens that address doxorubicin-induced cardiotoxicity.

Peroxiredoxin I and II as novel therapeutic molecular targets in cervical cancer treatment through regulation of endoplasmic reticulum stress induced by bleomycin

Cervical cancer, significantly affecting women worldwide, often involves treatment with bleomycin, an anticancer agent targeting breast, ovarian, and cervical cancers by generating reactive oxygen species (ROS) to induce cancer cell death. The Peroxiredoxin (PRDX) family, particularly PRDX1 and 2, plays a vital role in maintaining cellular balance by scavenging ROS, thus mitigating the damaging effects of bleomycin-induced mitochondrial and cellular oxidative stress. This process reduces endoplasmic reticulum (ER) stress and prevents cell apoptosis. However, reducing PRDX1 and 2 levels reverses their protective effect, increasing apoptosis. This research highlights the importance of PRDX1 and 2 in cervical cancer treatments with bleomycin, showing their potential to enhance treatment efficacy by managing ROS and ER stress and suggesting a therapeutic strategy for improving outcomes in cervical cancer treatment.

Doxorubicin‑induced cardiomyopathy is mitigated by empagliflozin via the modulation of endoplasmic reticulum stress pathways

Doxorubicin (Dox) exhibits a high efficacy in the treatment of numerous types of cancer. However, the beneficial cytotoxic effects of Dox are often accompanied by an increase in the risk of cardiotoxicity. Oxidative stress (OS) plays a key role in Dox‑induced cardiomyopathy (DIC). OS in cardiomyocytes disrupts endoplasmic reticulum (ER) function, leading to the accumulation of misfolded/unfolded proteins known as ER stress. ER stress acts as an adaptive mechanism; however, prolonged ER stress together with OS may lead to the initiation of cardiomyocyte apoptosis. The present study aimed to explore the potential of an anti‑diabetic drug, empagliflozin (EMPA), in mitigating Dox‑induced ER stress and cardiomyocyte apoptosis. In the present study, the effects of 1 h pretreatment of EMPA on Dox‑treated cardiomyocytes isolated from Sprague‑Dawley rats were investigated. After 24 h, EMPA pre‑treatment promoted cell survival in the EMPA + Dox group compared with the Dox group. Results of the present study also demonstrated that EMPA mitigated overall ER stress, as the increased expression of ER stress markers was reduced in the EMPA + Dox group. Additionally, OS, inflammation and expression of ER stress apoptotic proteins were also significantly reduced following EMPA pre‑treatment in the EMPA + Dox group. Thus, EMPA may exert beneficial effects on Dox‑induced ER stress and may exhibit potential changes that can be utilised to further evaluate the role of EMPA in mitigating DIC.

Molecular mechanism of ATF6 in unfolded protein response and its role in disease

Activating transcription factor 6 (ATF6), an important signaling molecule in unfolded protein response (UPR), plays a role in the pathogenesis of several diseases, including diseases such as congenital retinal disease, liver fibrosis and ankylosing spondylitis. After endoplasmic reticulum stress (ERS), ATF6 is activated after separation from binding immunoglobulin protein (GRP78/BiP) in the endoplasmic reticulum (ER) and transported to the Golgi apparatus to be hydrolyzed by site 1 and site 2 proteases into ATF6 fragments, which localize to the nucleus and regulate the transcription and expression of ERS-related genes. In these diseases, ERS leads to the activation of UPR, which ultimately lead to the occurrence and development of diseases by regulating the physiological state of cells through the ATF6 signaling pathway. Here, we discuss the evidence for the pathogenic importance of ATF6 signaling in different diseases and discuss preclinical results.

Cardiac proteostasis in obesity and cardiovascular disease

Cardiovascular diseases (CVD) are closely linked to protein homeostasis (proteostasis) and its failure. Beside genetic mutations that impair cardiac protein quality control, obesity is a strong risk factor for heart disease. In obesity, adipose tissue becomes dysfunctional and impacts heart function and CVD progression by releasing cytokines that contribute to systemic insulin resistance and cardiovascular dysfunction. In addition, chronic inflammation and lipotoxicity compromise endoplasmic reticulum (ER) function, eliciting stress responses that overwhelm protein quality control beyond its capacity. Impairment of proteostasis-including dysfunction of the ubiquitin-proteasome system (UPS), autophagy, and the depletion of chaperones-is intricately linked to cardiomyocyte dysfunction. Interventions targeting UPS and autophagy pathways are new potential strategies for re-establishing protein homeostasis and improving heart function. Additionally, lifestyle modifications such as dietary interventions and exercise have been shown to promote cardiac proteostasis and overall metabolic health. The pursuit of future research dedicated to proteostasis and protein quality control represents a pioneering approach for enhancing cardiac health and addressing the complexities of obesity-related cardiac dysfunction.

KCNH2A561V Heterozygous Mutation Inhibits KCNH2 Protein Expression via The Activation of UPR Mediated by ATF6

The potassium channel protein KCNH2 is encoded by KCNH2 gene, and there are more than 300 mutations of KCNH2. Unfolded protein response (UPR) is typically initiated in response to an accumulation of unfolded and/or misfolded proteins in the endoplasmic reticulum (ER). The present study aimed to explore the UPR process and the role of activating transcription factor 6 (ATF6) in the abnormal expression of potassium voltage-gated channel subfamily H member 2 (KCNH2)A561V. The wild-type (wt) KCNH2 and A561V mutant KCNH2 was constructed with his-tag. The 293 cells were used and divided into KCNH2wt+KCNH2A561V, KCNH2wt and KCNH2A561V groups. The expression levels of ATF6 and KCNH2 in different groups were detected by Western blotting, reverse transcription-quantitative PCR, immunofluorescence and immuno-coprecipitation assays. The protein types and abundance of immuno-coprecipitation samples were analyzed by mass spectrometry. The proteomic analysis of the mass spectrometry results was carried out by using the reactome database and GO (Gene Ontology) tool. The mRNA expression levels of KCNH2 and ATF6 in the KCNH2wt+KCNH2A561V group were higher compared with the KCNH2A561V group. However, the full-length protein expression of ATF6 was inhibited, indicating that ATF6 was highly activated and a substantial number of ATF6 was sheared in KCNH2wt+KCNH2A561V group compared with control group. Furthermore, A561V-KCNH2 mutation leading to the accumulation of the immature form of KCNH2 (135 kDa bands) in ER, resulting in the reduction of the ratio of 155 kDa/135 kDa. In addition, the abundance of UPR-related proteins in the KCNH2A561V group was higher compared with the KCNH2wt+KCNH2A561V group. The 'cysteine biosynthetic activity' of GO:0019344 process and the 'positive regulation of cytoplasmic translation activity' of GO:2000767 process in the KCNH2A561V group were higher compared with the KCNH2wt+KCNH2A561V group. Hence, co-expression of wild-type and A561V mutant KCNH2 in 293 cells activated the UPR process, which led to the inhibition of protein translation and synthesis, in turn inhibiting the expression of KCNH2. These results provided a theoretical basis for clinical treatment of Long QT syndrome.

Role of the ER-induced UPR pathway, apoptosis, and autophagy in colorectal cancer

When large amounts of misfolded or unfolded proteins accumulate in the endoplasmic reticulum (ER) in response to stress, a process called unfolded protein response (UPR) is activated. The disruption of this process leads to many diseases including diabetes, neurodegenerative diseases, and many cancers. In the process of UPR in response to stress and unfolded proteins, specific signaling pathways are induced in the endoplasmic reticulum and subsequently transmitted to the nucleus and cytoplasm, causing homeostasis and restoring the cell's normal condition with reducing protein translation and synthesis. The UPR response followed by stress enhancement balances cell survival with death, therefore in this condition cells decide either to survive or have the path of apoptosis ahead. However, in some cases, this balance is disturbed and the UPR pathway is chronically activated or not activated and the cell conditions lead to cancer. This study aimed to briefly investigate the association between ER stress, UPR, apoptosis, and autophagy in colorectal cancer (CRC). Moreover, in current study, we will try to demonstrate canonical ways and methods for the treatment of CRC cells with attenuated ER stress.

Melatonin as an Antioxidant Agent in Stroke: An Updated Review

Stroke is a devastating disease associated with high mortality and disability worldwide, and is generally classified as ischemic or hemorrhagic, which share certain similar pathophysiological processes. Oxidative stress is a critical factor involved in stroke-induced injury, which not only directly damages brain tissue, but also enhances a series of pathological signaling cascades, contributing to inflammation, brain edema, and neuronal death. To alleviate these serious secondary brain injuries, neuroprotective agents targeting oxidative stress inhibition may serve as a promising treatment strategy. Melatonin is a hormone secreted by the pineal gland, and has various properties, such as antioxidation, anti-inflammation, circadian rhythm modulation, and promotion of tissue regeneration. Numerous animal experiments studying stroke have confirmed that melatonin exerts considerable neuroprotective effects, partially via anti-oxidative stress. In this review, we introduce the possible role of melatonin as an antioxidant in the treatment of stroke based on the latest published studies of animal experiments and clinical research.

ER stress and calcium-dependent arrhythmias

The sarcoplasmic reticulum (SR) plays the key role in cardiac function as the major source of Ca²⁺ that activates cardiomyocyte contractile machinery. Disturbances in finely-tuned SR Ca²⁺ release by SR Ca²⁺ channel ryanodine receptor (RyR2) and SR Ca²⁺ reuptake by SR Ca²⁺-ATPase (SERCa2a) not only impair contraction, but also contribute to cardiac arrhythmia trigger and reentry. Besides being the main Ca²⁺ storage organelle, SR in cardiomyocytes performs all the functions of endoplasmic reticulum (ER) in other cell types including protein synthesis, folding and degradation. In recent years ER stress has become recognized as an important contributing factor in many cardiac pathologies, including deadly ventricular arrhythmias. This brief review will therefore focus on ER stress mechanisms in the heart and how these changes can lead to pro-arrhythmic defects in SR Ca²⁺ handling machinery.

Development and validation of a prognosis prediction model based on 18 endoplasmic reticulum stress-related genes for patients with lung adenocarcinoma

Background

Endoplasmic reticulum (ER) stress had a crucial impact on cell survival, proliferation, and metastasis in various cancers. However, the role of ER stress in lung adenocarcinoma remains unclear.

Method

Gene expression and clinical data of lung adenocarcinoma (LUAD) samples were extracted from The Cancer Genome Atlas (TCGA) and three Gene Expression Omnibus (GEO) datasets. ER stress score (ERSS) was constructed based on hub genes selected from 799 ER stress-related genes by least absolute shrinkage and selection operator (LASSO) regression. A Cox regression model, integrating ERSS and the TNM stage, was developed to predict overall survival (OS) in TCGA cohort and was validated in GEO cohorts. Gene set enrichment analysis (GSEA), single-sample GSEA (ssGSEA), and gene mutation analyses were performed to further understand the molecular features of ERSS. The tumor immune infiltration was evaluated by ESTIMATE, CIBERSORT, and xCell algorithms. The receiver operating characteristic (ROC) curves were used to evaluate the predictive value of the risk model. p< 0.05 was considered statistically significant.

Results

One hundred fifty-seven differentially expressed genes (DEGs) were identified between tumor and para-carcinoma tissues, and 45 of them significantly correlated with OS. Next, we identified 18 hub genes and constructed ERSS by LASSO regression. Multivariate analysis demonstrated that higher ERSS (p< 0.0001, hazard ratio (HR) = 3.8, 95%CI: 2.8–5.2) and TNM stage (p< 0.0001, HR = 1.55, 95%CI: 1.34–1.8) were independent predictors for worse OS. The prediction model integrating ERSS and TNM stage performed well in TCGA cohort (area under the curve (AUC) at five years = 0.748) and three GEO cohorts (AUC at 5 years = 0.658, 0.717, and 0.739). Pathway enrichment analysis showed that ERSS significantly correlated with unfolded protein response. Meanwhile, pathways associated with the cell cycle, growth, and metabolism were significantly enriched in the high ERSS group. Patients with SMARCA4, TP53, and EGFR mutations showed significantly higher ERSS (p = 4e−04, 0.0027, and 0.035, respectively). Tissues with high ERSS exhibited significantly higher infiltration of M1 macrophages, activated dendritic cells, and lower infiltration of CD8+ T cells and B cells, which indicate an activated tumor antigen-presenting but suppressive immune response status.

Conclusion

We developed and validated an ER stress-related risk model that exhibited great predictive value for OS in patients with LUAD. Our work also expanded the understanding of the role of ER stress in LUAD.

Myocardial ischemia/reperfusion injury: Mechanisms of injury and implications for management (Review)

Myocardial infarction is one of the primary causes of mortality in patients with coronary heart disease worldwide. Early treatment of acute myocardial infarction restores blood supply of ischemic myocardium and decreases the mortality risk. However, when the interrupted myocardial blood supply is recovered within a certain period of time, it causes more serious damage to the original ischemic myocardium; this is known as myocardial ischemia/reperfusion injury (MIRI). The pathophysiological mechanisms leading to MIRI are associated with oxidative stress, intracellular calcium overload, energy metabolism disorder, apoptosis, endoplasmic reticulum stress, autophagy, pyroptosis, necroptosis and ferroptosis. These interplay with one another and directly or indirectly lead to aggravation of the effect. In the past, apoptosis and autophagy have attracted more attention but necroptosis and ferroptosis also serve key roles. However, the mechanism of MIRI has not been fully elucidated. The present study reviews the mechanisms underlying MIRI. Based on current understanding of the pathophysiological mechanisms of MIRI, the association between cell death-associated signaling pathways were elaborated, providing direction for investigation of novel targets in clinical treatment.

Interleukin-10 Mitigates Doxorubicin-Induced Endoplasmic Reticulum Stress as Well as Cardiomyopathy

The use of doxorubicin (Dox) in cancer patients carries the risk of cardiotoxicity via an increase in oxidative stress, mitochondrial dysfunction, and disturbed endoplasmic reticulum (ER) homeostasis in cardiomyocytes. The present study explores which of the ER transmembrane sensors is involved in Dox-induced apoptosis and whether interleukin-10 (IL-10) has any mitigating effect. There was a time-related increase in apoptosis in cardiomyocytes exposed to 5.43 µg/mL Dox for 0 to 48 h. Dox treatment for 24 h significantly upregulated glucose-regulated proteins 78 and 94, protein disulfide isomerase, cleavage of activating transcription factor 6α, and X-box binding protein 1. These Dox-induced changes in ER stress proteins as well as apoptosis were blunted by IL-10 (10 ng/mL). In Dox-exposed cardiomyocytes, IL-10 also promoted expression of protein kinase-like endoplasmic reticulum kinase and inositol-requiring kinase 1α, which helped in maintaining ER homeostasis. Additionally, under Dox-treatment, IL-10 downregulated caspase-12 activation as well as phosphorylation of c-JUN NH2-terminal kinase, thereby promoting cardiomyocyte survival. IL-10 was able to reduce the overexpression of mitochondrial apoptotic proteins caspase-3 as well as Bax, which were upregulated upon Dox treatment. Thus, a reduction in Dox-induced ER stress as well as apoptosis through IL-10 may provide a significant benefit in improving cardiac function.

The Antioxidant Selenoprotein T Mimetic, PSELT, Induces Preconditioning-like Myocardial Protection by Relieving Endoplasmic-Reticulum Stress

Oxidative stress and endoplasmic reticulum stress (ERS) are strictly involved in myocardial ischemia/reperfusion (MI/R). Selenoprotein T (SELENOT), a vital thioredoxin-like selenoprotein, is crucial for ER homeostasis and cardiomyocyte differentiation and protection, likely acting as a redox-sensing protein during MI/R. Here, we designed a small peptide (PSELT), encompassing the redox site of SELENOT, and investigated whether its pre-conditioning cardioprotective effect resulted from modulating ERS during I/R. The Langendorff rat heart model was employed for hemodynamic analysis, while mechanistic studies were performed in perfused hearts and H9c2 cardiomyoblasts. PSELT improved the post-ischemic contractile recovery, reducing infarct size and LDH release with and without the ERS inducer tunicamycin (TM). Mechanistically, I/R and TM upregulated SELENOT expression, which was further enhanced by PSELT. PSELT also prevented the expression of the ERS markers CHOP and ATF6, reduced cardiac lipid peroxidation and protein oxidation, and increased SOD and catalase activities. An inert PSELT (I-PSELT) lacking selenocysteine was ineffective. In H9c2 cells, H₂O₂ decreased cell viability and SELENOT expression, while PSELT rescued protein levels protecting against cell death. In SELENOT-deficient H9c2 cells, H₂O₂ exacerbated cell death, that was partially mitigated by PSELT. Microscopy analysis revealed that a fluorescent form of PSELT was internalized into cardiomyocytes with a perinuclear distribution. Conclusions: The cell-permeable PSELT is able to induce pharmacological preconditioning cardioprotection by mitigating ERS and oxidative stress, and by regulating endogenous SELENOT.

Transcriptomic and Lipidomic Mapping of Macrophages in the Hub of Chronic Beta-Adrenergic-Stimulation Unravels Hypertrophy-, Proliferation-, and Lipid Metabolism-Related Genes as Novel Potential Markers of Early Hypertrophy or Heart Failure

Sympathetic nervous system overdrive with chronic release of catecholamines is the most important neurohormonal mechanism activated to maintain cardiac output in response to heart stress. Beta-adrenergic signaling behaves first as a compensatory pathway improving cardiac contractility and maladaptive remodeling but becomes dysfunctional leading to pathological hypertrophy and heart failure (HF). Cardiac remodeling is a complex inflammatory syndrome where macrophages play a determinant role. This study aimed at characterizing the temporal transcriptomic evolution of cardiac macrophages in mice subjected to beta-adrenergic-stimulation using RNA sequencing. Owing to a comprehensive bibliographic analysis and complementary lipidomic experiments, this study deciphers typical gene profiles in early compensated hypertrophy (ECH) versus late dilated remodeling related to HF. We uncover cardiac hypertrophy- and proliferation-related transcription programs typical of ECH or HF macrophages and identify lipid metabolism-associated and Na⁺ or K⁺ channel-related genes as markers of ECH and HF macrophages, respectively. In addition, our results substantiate the key time-dependent role of inflammatory, metabolic, and functional gene regulation in macrophages during beta-adrenergic dependent remodeling. This study provides important and novel knowledge to better understand the prevalent key role of resident macrophages in response to chronically activated beta-adrenergic signaling, an effective diagnostic and therapeutic target in failing hearts.

Zonisamide alleviates cardiac hypertrophy in rats by increasing Hrd1 expression and inhibiting endoplasmic reticulum stress

Antiepileptic drug zonisamide has been shown to be curative for Parkinson's disease (PD) through increasing HMG-CoA reductase degradation protein 1 (Hrd1) level and mitigating endoplasmic reticulum (ER) stress. Hrd1 is an ER-transmembrane E3 ubiquitin ligase, which is involved in cardiac dysfunction and cardiac hypertrophy in a mouse model of pressure overload. In this study, we investigated whether zonisamide alleviated cardiac hypertrophy in rats by increasing Hrd1 expression and inhibiting ER stress. The beneficial effects of zonisamide were assessed in two experimental models of cardiac hypertrophy: in rats subjected to abdominal aorta constriction (AAC) and treated with zonisamide (14, 28, 56 mg · kg-1 · d-1, i.g.) for 6 weeks as well as in neonatal rat cardiomyocytes (NRCMs) co-treated with Ang II (10 μM) and zonisamide (0.3 μM). Echocardiography analysis revealed that zonsiamide treatment significantly improved cardiac function in AAC rats. We found that zonsiamide treatment significantly attenuated cardiac hypertrophy and fibrosis, and suppressed apoptosis and ER stress in the hearts of AAC rats and in Ang II-treated NRCMs. Importantly, zonisamide markedly increased the expression of Hrd1 in the hearts of AAC rats and in Ang II-treated NRCMs. Furthermore, we demonstrated that zonisamide accelerated ER-associated protein degradation (ERAD) in Ang II-treated NRCMs; knockdown of Hrd1 abrogated the inhibitory effects of zonisamide on ER stress and cardiac hypertrophy. Taken together, our results demonstrate that zonisamide is effective in preserving heart structure and function in the experimental models of pathological cardiac hypertrophy. Zonisamide increases Hrd1 expression, thus preventing cardiac hypertrophy and improving the cardiac function of AAC rats.

Current Status of Endoplasmic Reticulum Stress in Type II Diabetes

The endoplasmic reticulum (ER) plays a multifunctional role in lipid biosynthesis, calcium storage, protein folding, and processing. Thus, maintaining ER homeostasis is essential for cellular functions. Several pathophysiological conditions and pharmacological agents are known to disrupt ER homeostasis, thereby, causing ER stress. The cells react to ER stress by initiating an adaptive signaling process called the unfolded protein response (UPR). However, the ER initiates death signaling pathways when ER stress persists. ER stress is linked to several diseases, such as cancer, obesity, and diabetes. Thus, its regulation can provide possible therapeutic targets for these. Current evidence suggests that chronic hyperglycemia and hyperlipidemia linked to type II diabetes disrupt ER homeostasis, thereby, resulting in irreversible UPR activation and cell death. Despite progress in understanding the pathophysiology of the UPR and ER stress, to date, the mechanisms of ER stress in relation to type II diabetes remain unclear. This review provides up-to-date information regarding the UPR, ER stress mechanisms, insulin dysfunction, oxidative stress, and the therapeutic potential of targeting specific ER stress pathways.

Pharmacological Activating Transcription Factor 6 Activation Is Beneficial for Liver Retrieval With ex vivo Normothermic Mechanical Perfusion From Cardiac Dead Donor Rats

Background: Normothermic machine perfusion (NMP) could be beneficial for organ retrieval from donors after cardiac death (DCD). Activating transcription factor 6 (ATF6) was recently shown to mitigate liver ischemia/reperfusion injury and confer protection. The aims of this study were to assess the implication of ATF6 in liver retrieval from DCD rat livers with NMP and explore the effect of pharmacologic ATF-6 activation on liver retrieval. Methods: The livers from DCD rats were exposed to 30 min of warm ischemia and 8 h cold preservation followed by 2 h NMP with or without an ATF6 activator in the perfusate. Perfusates and livers were harvested to detect ATF6 expression, liver function, and inflammation. Results: DCD livers with NMP were associated with ATF6 overexpression and activation based on IHC and WB (P < 0.05). The ATF6 activator downregulated perfusate aminotransferases, decreased the Suzuki score, downregulated CD68 and MPO based on IHC, induced the expression of cytochrome c in mitochondria and inhibited the expression of cytochrome c in cytoplasm based on WB, reduced TNFα and IL-6 levels based on ELISA, decreased levels of MDA, GSSG and ATP, and increased SOD activity and GSH levels in the perfused livers (P < 0.05). Conclusion: ATF6 is important for liver retrieval, and an exogenous ATF6 activator accelerates liver retrieval from DCD rats in an ex vivo NMP model.

Activation of the ATF6 (Activating Transcription Factor 6) Signaling Pathway in Neurons Improves Outcome After Cardiac Arrest in Mice

Background Ischemia/reperfusion injury impairs proteostasis, and triggers adaptive cellular responses, such as the unfolded protein response (UPR), which functions to restore endoplasmic reticulum homeostasis. After cardiac arrest (CA) and resuscitation, the UPR is activated in various organs including the brain. However, the role of the UPR in CA has remained largely unknown. Here we aimed to investigate effects of activation of the ATF6 (activating transcription factor 6) UPR branch in CA. Methods and Results Conditional and inducible sATF6-KI (short-form ATF6 knock-in) mice and a selective ATF6 pathway activator 147 were used. CA was induced in mice by KCl injection, followed by cardiopulmonary resuscitation. We first found that neurologic function was significantly improved, and neuronal damage was mitigated after the ATF6 pathway was activated in neurons of sATF6-KI mice subjected to CA/cardiopulmonary resuscitation. Further RNA sequencing analysis indicated that such beneficial effects were likely attributable to increased expression of pro-proteostatic genes regulated by ATF6. Especially, key components of the endoplasmic reticulum-associated degradation process, which clears potentially toxic unfolded/misfolded proteins in the endoplasmic reticulum, were upregulated in the sATF6-KI brain. Accordingly, the CA-induced increase in K48-linked polyubiquitin in the brain was higher in sATF6-KI mice relative to control mice. Finally, CA outcome, including the survival rate, was significantly improved in mice treated with compound 147. Conclusions This is the first experimental study to determine the role of the ATF6 UPR branch in CA outcome. Our data indicate that the ATF6 UPR branch is a prosurvival pathway and may be considered as a therapeutic target for CA.

The aftermath of the interplay between the endoplasmic reticulum stress response and redox signaling

The endoplasmic reticulum (ER) is an essential organelle of eukaryotic cells. Its main functions include protein synthesis, proper protein folding, protein modification, and the transportation of synthesized proteins. Any perturbations in ER function, such as increased demand for protein folding or the accumulation of unfolded or misfolded proteins in the ER lumen, lead to a stress response called the unfolded protein response (UPR). The primary aim of the UPR is to restore cellular homeostasis; however, it triggers apoptotic signaling during prolonged stress. The core mechanisms of the ER stress response, the failure to respond to cellular stress, and the final fate of the cell are not yet clear. Here, we discuss cellular fate during ER stress, cross talk between the ER and mitochondria and its significance, and conditions that can trigger ER stress response failure. We also describe how the redox environment affects the ER stress response, and vice versa, and the aftermath of the ER stress response, integrating a discussion on redox imbalance-induced ER stress response failure progressing to cell death and dynamic pathophysiological changes.

The endoplasmic reticulum (ER), a cellular organelle responsible for protein folding, is sensitive to chemical imbalances that can induce stress, leading to cell death and disease. Researchers in South Korea, led by Han-Jung Chae from Jeonbuk National University in Jeonju and Hyung-Ryong Kim from Dankook University in Cheonan, review how the ER counters changes in its environment that spur protein folding defects by activating a series of signaling pathways, known collectively as the unfolded protein response. Redox imbalance, may fail adaptive ER stress response that can damage the ER and surrounding mitochondria by modifying cysteine residues. The interaction between the two stress systems, ER stress and oxidative stress, has profound negative impacts on normal physiology. Targeting one or both of these stress mechanisms may therefore be an effective means of treating disease.

Up-regulated DERL3 in fibroblast-like synoviocytes exacerbates inflammation of rheumatoid arthritis

Endoplasmic reticulum (ER) stress associated proteins contribute to the pathogenesis of rheumatoid arthritis (RA) through affecting synoviocyte proliferation and proinflammatory cytokine production. The role of DERL3, an ER-associated degradation component, in joint inflammation of RA was explored. Synovial tissues from RA and osteoarthritis (OA) patients were collected, and in RA synovial tissue, DERL3 showed up-regulation and significantly positive correlation with the expression of tumor necrosis factor alpha (TNF-α), interleukin (IL)-6 and matrix metalloproteinase (MMP)-1. Immunofluorescence result suggested DERL3 was located in fibroblast-like synoviocytes (FLS). Among different inflammatory stimuli, DERL3 could be up-regulated by TNF-α stimulation in FLS. Under TNF-α stimulation, knocking down DERL3, the expression of IL-6, IL-8, MMP-1, MMP-13 was reduced and the activation of nuclear factor kappa B (NF-κB) signaling pathway was inhibited. In pristane-induced arthritis (PIA) rat model, Derl3 was up-regulated in synovial tissue and disease was attenuated after intraarticular injection of siDerl3. Overall, we conclude that TNF-α inducing DERL3 expression promotes the inflammation of FLS through activation of NF-κB signaling pathway, suggesting DERL3 plays important roles in the pathogenesis of RA and is a promising therapeutic target.

ATF6 as a Nodal Regulator of Proteostasis in the Heart

Proteostasis encompasses a homeostatic cellular network in all cells that maintains the integrity of the proteome, which is critical for optimal cellular function. The components of the proteostasis network include protein synthesis, folding, trafficking, and degradation. Cardiac myocytes have a specialized endoplasmic reticulum (ER) called the sarcoplasmic reticulum that is well known for its role in contractile calcium handling. However, less studied is the proteostasis network associated with the ER, which is of particular importance in cardiac myocytes because it ensures the integrity of proteins that are critical for cardiac contraction, e.g., ion channels, as well as proteins necessary for maintaining myocyte viability and interaction with other cell types, e.g., secreted hormones and growth factors. A major aspect of the ER proteostasis network is the ER unfolded protein response (UPR), which is initiated when misfolded proteins in the ER activate a group of three ER transmembrane proteins, one of which is the transcription factor, ATF6. Prior to studies in the heart, ATF6 had been shown in model cell lines to be primarily adaptive, exerting protective effects by inducing genes that encode ER proteins that fortify protein-folding in this organelle, thus establishing the canonical role for ATF6. Subsequent studies in isolated cardiac myocytes and in the myocardium, in vivo, have expanded roles for ATF6 beyond the canonical functions to include the induction of genes that encode proteins outside of the ER that do not have known functions that are obviously related to ER protein-folding. The identification of such non-canonical roles for ATF6, as well as findings that the gene programs induced by ATF6 differ depending on the stimulus, have piqued interest in further research on ATF6 as an adaptive effector in cardiac myocytes, underscoring the therapeutic potential of activating ATF6 in the heart. Moreover, discoveries of small molecule activators of ATF6 that adaptively affect the heart, as well as other organs, in vivo, have expanded the potential for development of ATF6-based therapeutics. This review focuses on the ATF6 arm of the ER UPR and its effects on the proteostasis network in the myocardium.

Susceptibility to Cardiac Arrhythmias and Sympathetic Nerve Growth in VEGF-B Overexpressing Myocardium

VEGF-B gene therapy is a promising proangiogenic treatment for ischemic heart disease, but, unexpectedly, we found that high doses of VEGF-B promote ventricular arrhythmias (VAs). VEGF-B knockout, alpha myosin heavy-chain promoter (αMHC)-VEGF-B transgenic mice, and pigs transduced intramyocardially with adenoviral (Ad)VEGF- B186 were studied. Immunostaining showed a 2-fold increase in the number of nerves per field (76 vs. 39 in controls, p < 0.001) and an abnormal nerve distribution in the hypertrophic hearts of 11- to 20-month-old αMHC-VEGF-B mice. AdVEGF-B186 gene transfer (GT) led to local sprouting of nerve endings in pig myocardium (141 vs. 78 nerves per field in controls, p < 0.05). During dobutamine stress, 60% of the αMHC-VEGF-B hypertrophic mice had arrhythmias as compared to 7% in controls, and 20% of the AdVEGF-B186-transduced pigs and 100% of the combination of AdVEGF-B186- and AdsVEGFR-1-transduced pigs displayed VAs and even ventricular fibrillation. AdVEGF-B186 GT significantly increased the risk of sudden cardiac death in pigs when compared to any other GT with different VEGFs (hazard ratio, 500.5; 95% confidence interval [CI] 46.4-5,396.7; p < 0.0001). In gene expression analysis, VEGF-B induced the upregulation of Nr4a2, ATF6, and MANF in cardiomyocytes, molecules previously linked to nerve growth and differentiation. Thus, high AdVEGF-B186 overexpression induced nerve growth in the adult heart via a VEGFR-1 signaling-independent mechanism, leading to an increased risk of VA and sudden cardiac death.

Sledgehammer to Scalpel: Broad Challenges to the Heart and Other Tissues Yield Specific Cellular Responses via Transcriptional Regulation of the ER-Stress Master Regulator ATF6α

There are more than 2000 transcription factors in eukaryotes, many of which are subject to complex mechanisms fine-tuning their activity and their transcriptional programs to meet the vast array of conditions under which cells must adapt to thrive and survive. For example, conditions that impair protein folding in the endoplasmic reticulum (ER), sometimes called ER stress, elicit the relocation of the ER-transmembrane protein, activating transcription factor 6α (ATF6α), to the Golgi, where it is proteolytically cleaved. This generates a fragment of ATF6α that translocates to the nucleus, where it regulates numerous genes that restore ER protein-folding capacity but is degraded soon after. Thus, upon ER stress, ATF6α is converted from a stable, transmembrane protein, to a rapidly degraded, nuclear protein that is a potent transcription factor. This review focuses on the molecular mechanisms governing ATF6α location, activity, and stability, as well as the transcriptional programs ATF6α regulates, whether canonical genes that restore ER protein-folding or unexpected, non-canonical genes affecting cellular functions beyond the ER. Moreover, we will review fascinating roles for an ATF6α isoform, ATF6β, which has a similar mode of activation but, unlike ATF6α, is a long-lived, weak transcription factor that may moderate the genetic effects of ATF6α.

Mechanical Regulation of Protein Translation in the Cardiovascular System

The cardiovascular system can sense and adapt to changes in mechanical stimuli by remodeling the physical properties of the heart and blood vessels in order to maintain homeostasis. Imbalances in mechanical forces and/or impaired sensing are now not only implicated but are, in some cases, considered to be drivers for the development and progression of cardiovascular disease. There is now growing evidence to highlight the role of mechanical forces in the regulation of protein translation pathways. The canonical mechanism of protein synthesis typically involves transcription and translation. Protein translation occurs globally throughout the cell to maintain general function but localized protein synthesis allows for precise spatiotemporal control of protein translation. This Review will cover studies on the role of biomechanical stress -induced translational control in the heart (often in the context of physiological and pathological hypertrophy). We will also discuss the much less studied effects of mechanical forces in regulating protein translation in the vasculature. Understanding how the mechanical environment influences protein translational mechanisms in the cardiovascular system, will help to inform disease pathogenesis and potential areas of therapeutic intervention.

microRNAs in Cardiovascular Disease: Small Molecules but Big Roles

microRNAs (miRNAs) are an evolutionarily conserved class of small single-stranded noncoding RNAs. The aberrant expression of specific miRNAs has been implicated in the development and progression of diverse cardiovascular diseases. For many decades, miRNA therapeutics has flourished, taking advantage of the fact that miRNAs can modulate gene expression and control cellular phenotypes at the posttranscriptional level. Genetic replacement or knockdown of target miRNAs by chemical molecules, referred to as miRNA mimics or inhibitors, has been used to reverse their abnormal expression as well as their adverse biological effects in vitro and in vivo in an effort to fully implement the therapeutic potential of miRNA-targeting treatment. However, the limitations of the chemical structure and delivery systems are hindering progress towards clinical translation. Here, we focus on the regulatory mechanisms and therapeutic trials of several representative miRNAs in the context of specific cardiovascular diseases; from this basic perspective, we evaluate chemical modifications and delivery vectors of miRNA-based chemical molecules and consider the underlying challenges of miRNA therapeutics as well as the clinical perspectives on their applications.

ATF6 Regulates Cardiac Hypertrophy by Transcriptional Induction of the mTORC1 Activator, Rheb

RATIONALE

Endoplasmic reticulum (ER) stress dysregulates ER proteostasis, which activates the transcription factor, ATF6 (activating transcription factor 6α), an inducer of genes that enhance protein folding and restore ER proteostasis. Because of increased protein synthesis, it is possible that protein folding and ER proteostasis are challenged during cardiac myocyte growth. However, it is not known whether ATF6 is activated, and if so, what its function is during hypertrophic growth of cardiac myocytes.

OBJECTIVE

To examine the activity and function of ATF6 during cardiac hypertrophy.

METHODS AND RESULTS

We found that ER stress and ATF6 were activated and ATF6 target genes were induced in mice subjected to an acute model of transverse aortic constriction, or to free-wheel exercise, both of which promote adaptive cardiac myocyte hypertrophy with preserved cardiac function. Cardiac myocyte-specific deletion of Atf6 (ATF6 cKO [conditional knockout]) blunted transverse aortic constriction and exercise-induced cardiac myocyte hypertrophy and impaired cardiac function, demonstrating a role for ATF6 in compensatory myocyte growth. Transcript profiling and chromatin immunoprecipitation identified RHEB (Ras homologue enriched in brain) as an ATF6 target gene in the heart. RHEB is an activator of mTORC1 (mammalian/mechanistic target of rapamycin complex 1), a major inducer of protein synthesis and subsequent cell growth. Both transverse aortic constriction and exercise upregulated RHEB, activated mTORC1, and induced cardiac hypertrophy in wild type mouse hearts but not in ATF6 cKO hearts. Mechanistically, knockdown of ATF6 in neonatal rat ventricular myocytes blocked phenylephrine- and IGF1 (insulin-like growth factor 1)-mediated RHEB induction, mTORC1 activation, and myocyte growth, all of which were restored by ectopic RHEB expression. Moreover, adeno-associated virus 9- RHEB restored cardiac growth to ATF6 cKO mice subjected to transverse aortic constriction. Finally, ATF6 induced RHEB in response to growth factors, but not in response to other activators of ATF6 that do not induce growth, indicating that ATF6 target gene induction is stress specific.

CONCLUSIONS

Compensatory cardiac hypertrophy activates ER stress and ATF6, which induces RHEB and activates mTORC1. Thus, ATF6 is a previously unrecognized link between growth stimuli and mTORC1-mediated cardiac growth.

Endoplasmic Reticulum Stress Activates Unfolded Protein Response Signaling and Mediates Inflammation, Obesity, and Cardiac Dysfunction: Therapeutic and Molecular Approach

Obesity has been implicated as a risk factor for insulin resistance and cardiovascular diseases (CVDs). Although the association between obesity and CVD is a well-established phenomenon, the precise mechanisms remain incompletely understood. This has led to a relative paucity of therapeutic measures for the prevention and treatment of CVD and associated metabolic disorders. Recent studies have shed light on the pivotal role of prolonged endoplasmic reticulum stress (ERS)-initiated activation of the unfolded protein response (UPR), the ensuing chronic low-grade inflammation, and altered insulin signaling in promoting obesity-compromised cardiovascular system (CVS). In this aspect, potential ways of attenuating ERS-initiated UPR signaling seem a promising avenue for therapeutic interventions. We review intersecting role of obesity-induced ERS, chronic inflammation, insulin resistance, and oxidative stress in the discovery of targeted therapy. Moreover, this review highlights the current progress and strategies on therapeutics being explored in preclinical and clinical research to modulate ERS and UPR signaling.

Psoralen induces hepatic toxicity through PERK and ATF6 related ER stress pathways in HepG2 cells

Psoralen has potential hepatotoxicity and has a certain promoting effect on the clinical liver injury of Psoralea corylifolia L (Fructus Psoraleae). This study investigated the underlying mechanisms of psoralen-induced hepatotoxicity in vitro. HepG2 cells were treated with psoralen for 6, 12, 24, or 48 h, and an endoplasmic reticulum (ER) stress-specific inhibitor, 4-PBA, was employed to investigate the mechanism of psoralen on ER stress and unfolded protein response (UPR). Cell viability was tested by MTT assay, ATP assay, and cell death by LDH. The apoptosis was reflected by the flow cytometry, caspase-8, and caspase-3 activates. The expression of ER stress-related markers was determined by RT-PCR and western blot. We found that psoralen significantly decreased cell viability, increased activities of caspase-8 and caspase-3, and upregulated expression of CHOP and BAX in a time- and dose-dependent manner. Moreover, psoralen significantly increased the expression and transcription levels of ER stress-related markers, including Grp78, PERK, eIF2α, ATF4, and ATF6, while IRE1α was not significantly affected. And 4-PBA could effectively inhibit psoralen-induced cell death and apoptosis along with the inhibition of ER stress responses. These results suggested that psoralen causes liver injury due to the induction of the ER stress-mediated apoptosis via PERK-eIF2α-ATF4-CHOP and ATF6-CHOP related pathways.

Heparanase protects the heart against chemical or ischemia/reperfusion injury

Although cancer cells use heparanase for tumor metastasis, favourable effects of heparanase have been reported in the management of Alzheimer's disease and diabetes. Indeed, we previously established a protective function for heparanase in the acutely diabetic heart, where it conferred cardiomyocyte resistance to oxidative stress and apoptosis by provoking changes in gene expression. In this study, we tested if overexpression of heparanase can protect the heart against chemically induced or ischemia/reperfusion (I/R) injury. Transcriptomic analysis of Hep-tg hearts reveal that 240 genes related to the stress response, immune response, cell death, and development were altered in a pro-survival direction encompassing genes promoting the unfolded protein response (UPR) and autophagy, as well as those protecting against oxidative stress. The observed UPR activation was adaptive and not apoptotic, was mediated by activation of ATF6α, and when combined with mTOR inhibition, induced autophagy. Subjecting wild type (WT) mice to increasing concentrations of the ER stress inducer thapsigargin evoked a transition from adaptive to apoptotic UPR, an effect that was attenuated in Hep-tg mouse hearts. Consistent with these observations, when exposed to I/R, the infarct size and markers of apoptosis were significantly lower in the Hep-tg heart compared to WT. Finally, UPR and autophagy inhibitors reduced the protective effects of heparanase overexpression during I/R. Our data suggest that the mechanisms that underlie the role of heparanase in promoting cell survival could be uniquely beneficial to the heart by providing protection against cellular stresses, and could be useful for exploitation as a therapeutic target for the treatment of heart disease.

Unfolded Protein Response as a Therapeutic Target in Cardiovascular Disease

Cardiovascular disease is the leading cause of death worldwide. Despite overwhelming socioeconomic impact and mounting clinical needs, our understanding of the underlying pathophysiology remains incomplete. Multiple forms of cardiovascular disease involve an acute or chronic disturbance in cardiac myocytes, which may lead to potent activation of the Unfolded Protein Response (UPR), a cellular adaptive reaction to accommodate protein-folding stress. Accumulation of unfolded or misfolded proteins in the Endoplasmic Reticulum (ER) elicits three signaling branches of the UPR, which otherwise remain quiescent. This ER stress response then transiently suppresses global protein translation, augments production of protein-folding chaperones, and enhances ER-associated protein degradation, with an aim to restore cellular homeostasis. Ample evidence has established that the UPR is strongly induced in heart disease. Recently, the mechanisms of action and multiple pharmacological means to favorably modulate the UPR are emerging to curb the initiation and progression of cardiovascular disease. Here, we review the current understanding of the UPR in cardiovascular disease and discuss existing therapeutic explorations and future directions.

Stress Coping Strategies in the Heart: An Integrated View

The heart is made up of an ordered amalgam of cardiac cell types that work together to coordinate four major processes, namely energy production, electrical conductance, mechanical work, and tissue remodeling. Over the last decade, a large body of information has been amassed regarding how different cardiac cell types respond to cellular stress that affect the functionality of their elaborate intracellular membrane networks, the cellular reticular network. In the context of the heart, the manifestations of stress coping strategies likely differ depending on the coping strategy outcomes of the different cardiac cell types, and thus may underlie the development of distinct cardiac disorders. It is not clear whether all cardiac cell types have similar sensitivity to cellular stress, how specific coping response strategies modify their unique roles, and how their metabolic status is communicated to other cells within the heart. Here we discuss our understanding of the roles of specialized cardiac cells that together make the heart function as an organ with the ability to pump blood continuously and follow a regular rhythm.

Network pharmacology-based identification of major component of Angelica sinensis and its action mechanism for the treatment of acute myocardial infarction

Background: To decipher the mechanisms of Angelica sinensis for the treatment of acute myocardial infarction (AMI) using network pharmacology analysis. Methods: Databases were searched for the information on constituents, targets, and diseases. Cytoscape software was used to construct the constituent–target–disease network and screen the major targets, which were annotated with the DAVID (Database for Annotation, Visualization and Integrated Discovery) tool. The cardioprotective effects of Angelica sinensis polysaccharide (ASP), a major component of A. sinensis, were validated both in H9c2 cells subjected to simulated ischemia by oxygen and glucose deprivation and in rats with AMI by ligation of the left anterior coronary artery. Results: We identified 228 major targets against AMI injury for A. sinensis, which regulated multiple pathways and hit multiple targets involved in several biological processes. ASP significantly decreased endoplasmic reticulum (ER) stress-induced cell death both in vitro and in vivo. In ischemia injury rats, ASP treatment reduced infarct size and preserved heart function. ASP enhanced activating transcription factor 6 (ATF6) activity, which improved ER-protein folding capacity. ASP activated the expression of p-AMP-activated protein kinase (p-AMPK) and peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α). Additionally, ASP attenuated levels of proinflammatory cytokines and maintained a balance in the oxidant/antioxidant levels after AMI. Conclusion:In silico analysis revealed the associations between A. sinensis and AMI through multiple targets and several key signaling pathways. Experimental data indicate that ASP protects the heart against ischemic injury by activating ATF6 to ameliorate the detrimental ER stress. ASP’s effects could be mediated via the activation of AMPK-PGC1α pathway.

Inadequate ubiquitination-proteasome coupling contributes to myocardial ischemia-reperfusion injury

The ubiquitin-proteasome system (UPS) degrades a protein molecule via 2 main steps: ubiquitination and proteasomal degradation. Extraproteasomal ubiquitin receptors are thought to couple the 2 steps, but this proposition has not been tested in vivo with vertebrates. More importantly, impaired UPS performance plays a major role in cardiac pathogenesis, including myocardial ischemia-reperfusion injury (IRI), but the molecular basis of UPS impairment remains poorly understood. Ubiquilin1 is a bona fide extraproteasomal ubiquitin receptor. Here, we report that mice with a cardiomyocyte-restricted knockout of Ubiquilin1 (Ubqln1-CKO mice) accumulated a surrogate UPS substrate (GFPdgn) and increased myocardial ubiquitinated proteins without altering proteasome activities, resulting in late-onset cardiomyopathy and a markedly shortened life span. When subject to regional myocardial ischemia-reperfusion, young Ubqln1-CKO mice showed substantially exacerbated cardiac malfunction and enlarged infarct size, and conversely, mice with transgenic Ubqln1 overexpression displayed attenuated IRI. Furthermore, Ubqln1 overexpression facilitated proteasomal degradation of oxidized proteins and the degradation of a UPS surrogate substrate in cultured cardiomyocytes without increasing autophagic flux. These findings demonstrate that Ubiquilin1 is essential to cardiac ubiquitination-proteasome coupling and that an inadequacy in the coupling represents a major pathogenic factor for myocardial IRI; therefore, strategies to strengthen coupling have the potential to reduce IRI.

Melatonin Protects Against Neuronal Apoptosis via Suppression of the ATF6/CHOP Pathway in a Rat Model of Intracerebral Hemorrhage

Neuronal apoptosis is an important factor accounting for the poor outcomes of intracerebral hemorrhage (ICH). This study first showed that inhibition of activating transcription factor 6 (ATF6) could alleviate secondary brain injury through anti-apoptosis after ICH in rats. Melatonin, ATF6 and CCAAT/enhancer-binding protein homologous protein (CHOP) siRNAs were applied in this study. Brain edema, neurological functions, blood-brain barrier (BBB) integrity were evaluated at 24 h after ICH. Western blot analysis was used to evaluate the protein level of target proteins (ATF6, CHOP, Bip, Bcl-2, Bax, and cleaved caspase-3). Reverse transcription-polymerase chain reaction (RT-PCR) was used to assess the mRNA level of ATF6, CHOP and cleaved caspase-3. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and caspase-3 immunofluorescence staining were applied to evaluate the neuronal cell death. The results suggested that the levels of ATF6 and its downstream protein, CHOP, were upregulated and reached the peak at 24 h after ICH. ATF6 was highly expressed in neurons. The administration of melatonin significantly decreased the mRNA and protein levels of ATF6, and its downstream targets, CHOP and cleaved caspase-3, but increased the Bcl-2/Bax ratio, which ameliorated the neurological functions. The CHOP siRNA significantly reversed the pro-apoptotic effect induced by the increased ATF6 level after ICH. Melatonin could protect against neuronal apoptosis via suppression of ATF6/CHOP arm of ER-stress-response pathway.

MiR-155 aggravated septic liver injury by oxidative stress-mediated ER stress and mitochondrial dysfunction via targeting Nrf-2

OBJECTIVE

Liver is uniquely vulnerable during sepsis. MicroRNA-155 (miR-155) is confirmed to play crucial roles in septic liver injury. The present study aims to investigate the mechanisms of miR-155 in septic liver injury.

METHODS

The sepsis model was established by intraperitoneal injection of lipopolysaccharide (LPS) in mice. Mice were divided into four groups: Vehicle, miR-155 antagomir, LPS, LPS+ miR-155 antagomir. The survival rate and body weight were monitored. Liver injury was assessed by H&E staining. The levels of serum ALT and inflammatory cytokines were determined by ELISA kits. Oxidative stress was detected by MDA and SOD detection kits. The miR-155, Nrf-2, and markers related to oxidative stress, endoplasmic reticulum (ER) stress, mitochondrial injury and apoptosis were detected by western blotting and qPCR. Apoptosis in liver tissues was detected by TUNELstaining.

RESULTS

MiR-155 antagomir alleviated liver injury as evidenced by enhancing survival rate and body weight, inhibiting inflammatory cell infiltration, liver cells necrosis and decreasing ALT level. The productions of TNF-α, IL-6 were suppressed, while anti-inflammatory cytokine IL-10 was promoted by miR-155 antagomir. Oxidative stress was inhibited by miR-155 antagomir via enhancing nuclear factor, erythroid 2-like 2 (Nrf-2) expression. ER stress and Cytochrome C (Cyto-C) release were restrained by miR-155 antagomir. Sepsis-induced apoptosis was repressed by miR-155 antagomir as manifested by the decreased levels of Bax, cleaved caspase-12, 9 and 3, and increased levels of Bcl-2 and uncleaved PARP.

CONCLUSION

MiR-155 antagomir relieved septic liver injury through inhibiting oxidative stress-mediated ER stress, mitochondrial dysfunction and apoptosis via targeting Nrf-2, suggesting miR-155 as a therapeutic target for septic liver injury.

Lutein and Zeaxanthin Isomers Protect against Light-Induced Retinopathy via Decreasing Oxidative and Endoplasmic Reticulum Stress in BALB/cJ Mice

Oxidative stress (OS) and endoplasmic reticulum stress (ERS) are the major factors underlying photoreceptor degeneration. Lutein, RR-zeaxanthin (3R,3’R-zeaxanthin) and RS (meso)-zeaxanthin (3R,3’S-RS- zeaxanthin) (L/Zi) could protect against cell damage by ameliorating OS in retina. In this study, we examined the effect of L/Zi supplementation in a mouse model of photoreceptor degeneration and investigated whether the treatment of L/Zi ameliorated OS and ERS. BALB/cJ mice after light exposure were used as the animal model. The protective effects of L/Zi were observed by electroretinography (ERG) and terminal deoxyuridine triphosphate nick-end labeling (TUNEL) analysis. The underlying mechanisms related to OS and ERS were explored by Western blotting. After L/Zi treatment, the ERG amplitudes were significantly higher, and the number of TUNEL-positive cells was significantly reduced compared to that of the vehicle group. Western blotting results revealed that OS was ameliorated according to the significant downregulation of phosphorylated c-Jun N-terminal kinase (p-JNK), and significant upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2). In addition, ERS was reduced according to the significant downregulation of 78 kDa glucose-regulated protein (GRP78), phosphorylated protein kinase RNA-like endoplasmic reticulum kinase (p-PERK), activating transcription factor 4 (ATF4) and activating transcription factor (ATF6). Our data shows that L/Zi provided functional and morphological preservation of photoreceptors against light damage, which is probably related to its mitigation of oxidative and endoplasmic reticulum stress.

A lifetime of stress: ATF6 in development and homeostasis

BACKGROUND

Activating transcription factor 6 (ATF6) is an endoplasmic reticulum (ER)-localised protein and member of the leucine zipper family of transcription factors. Best known for its role in transducing signals linked to stress to the endoplasmic reticulum, the 50 kDa activated form of ATF6 is now emerging as a major regulator of organogenesis and tissue homeostasis. Responsible for the correct folding, secretion and membrane insertion of a third of the proteome in eukaryotic cells, the ER encompasses a dynamic, labyrinthine network of regulators, chaperones, foldases and cofactors. Such structures are crucial to the extensive protein synthesis required to undergo normal development and maintenance of tissue homeostasis. When an additional protein synthesis burden is placed on the ER, ATF6, in tandem with ER stress transducers inositol requiring enzyme 1 (IRE1) and PKR-like endoplasmic reticulum kinase (PERK), slows the pace of protein translation and induces the production of stress-reducing chaperones and foldases.

MAIN TEXT

In the context of development and tissue homeostasis, however, distinct cellular impacts have been attributed to ATF6. Drawing on data published from human, rodent, fish, goat and bovine research, this review first focuses on ATF6-mediated regulation of osteo- and chondrogenesis, ocular development as well as neuro- and myelinogenesis. The purported role of ATF6 in development of the muscular and reproductive systems as well as adipo- and lipogenesis is then described. With relevance to cardiac disease, cancer and brain disorders, the importance of ATF6 in maintaining tissue homeostasis is the subject of the final section.

CONCLUSION

In conclusion, the review encourages further elucidation of ATF6 regulatory operations during organogenesis and tissue homeostasis, to spawn the development of ATF6-targeted therapeutic strategies.

Endoplasmic Reticulum Chaperone GRP78 Protects Heart From Ischemia/Reperfusion Injury Through Akt Activation

RATIONALE

Restoration of coronary artery blood flow is the most effective means of ameliorating myocardial damage triggered by ischemic heart disease. However, coronary reperfusion elicits an increment of additional injury to the myocardium. Accumulating evidence indicates that the unfolded protein response (UPR) in cardiomyocytes is activated by ischemia/reperfusion (I/R) injury. Xbp1s (spliced X-box binding protein 1), the most highly conserved branch of the unfolded protein response, is protective in response to cardiac I/R injury. GRP78 (78 kDa glucose-regulated protein), a master regulator of the UPR and an Xbp1s target, is upregulated after I/R. However, its role in the protective response of Xbp1s during I/R remains largely undefined.

OBJECTIVE

To elucidate the role of GRP78 in the cardiomyocyte response to I/R using both in vitro and in vivo approaches.

METHODS AND RESULTS

Simulated I/R injury to cultured neonatal rat ventricular myocytes induced apoptotic cell death and strong activation of the UPR and GRP78. Overexpression of GRP78 in neonatal rat ventricular myocytes significantly protected myocytes from I/R-induced cell death. Furthermore, cardiomyocyte-specific overexpression of GRP78 ameliorated I/R damage to the heart in vivo. Exploration of underlying mechanisms revealed that GRP78 mitigates cellular damage by suppressing the accumulation of reactive oxygen species. We go on to show that the GRP78-mediated cytoprotective response involves plasma membrane translocation of GRP78 and interaction with PI3 kinase, culminating in stimulation of Akt. This response is required as inhibition of the Akt pathway significantly blunted the antioxidant activity and cardioprotective effects of GRP78.

CONCLUSIONS

I/R induction of GRP78 in cardiomyocytes stimulates Akt signaling and protects against oxidative stress, which together protect cells from I/R damage.

Glucose-regulated protein 78 is essential for cardiac myocyte survival

Secretory and transmembrane proteins rely on proper function of the secretory pathway for folding, posttranslational modification, assembly, and secretion. Accumulation of misfolded proteins in the endoplasmic reticulum (ER) stimulates the unfolded protein response (UPR), which communicates between the ER and other organelles to enhance ER-folding capacity and restore cellular homeostasis. Glucose-regulated protein of 78 kDa (GRP78), an ER-resident protein chaperone, is a master regulator of all UPR signaling branches. Accumulating studies have established a fundamental role of GRP78 in protein folding, ER stress response, and cell survival. However, role of GRP78 in the heart remains incompletely characterized. Here we showed that embryos lacking GRP78 specifically in cardiac myocytes manifest cardiovascular malformations and die in utero at late gestation. We went further to show that inducible knockout of GRP78 in adult cardiac myocytes causes early mortality due to cardiac cell death and severe decline in heart performance. At the cellular level, we found that loss of GRP78 increases apoptotic cell death, which is accompanied by reduction in AKT signaling and augmentation of production for reactive oxygen species. Importantly, enhancing AKT phosphorylation and activity leads to decreases in oxidative stress and increases in cardiac myocyte survival. Collectively, our results demonstrate an essential role of GRP78 in ensuring normal cardiogenesis and maintaining cardiac contractility and function.

Essential role for smooth muscle cell stromal interaction molecule-1 in myocardial infarction

OBJECTIVES

Stromal interacting molecule-1 (STIM1) plays a role in coordinating calcium signaling in different cell types. The increase or deletion of STIM1 expression in cardiomyocyte causes cardiac complication. Moreover, the deletion of STIM1 in endothelial cell causes vascular endothelial dysfunction. However, the disruption of STIM1 in smooth muscle cells (SMC) has no effect on endothelial function but protects vascular function when mice are infused with angiotensin-II. Nevertheless, the role of SMC-STIM1 in acute and chronic myocardial infarction (MI) induced by acute ischemia-reperfusion injury and permanent coronary artery occlusion is unknown.

METHODS AND RESULTS

Stim1 were generated and crossed into the SM22α-Cre backgrounds. SM22α-Cre causes deletion of STIM1 floxed genes in adult SMC (Stim1). Control and Stim1 mice were subjected to acute ischemia-reperfusion injury. Hearts were then harvested and incubated with triphenyltetrazolium chloride to determine the infarct size. In control mice which are subjected to ischemia-reperfusion, the heart developed a significant infarct associated with an increase in STIM1 expression. Interestingly, the infarct size was substantially reduced in Stim1 mice. The protection in Stim1 mice against ischemia-reperfusion injury involves the modulation of endoplasmic reticulum stress, apoptosis, oxidative stress, protein kinase B, and mitogen-activated protein (MAP) kinase (ERK1/2 and p38) signaling, and inflammation. Furthermore, in another model of chronic MI induced by permanent coronary artery occlusion, SMC-STIM1 disruption significantly reduced myocardial infarct size and improved cardiac function.

CONCLUSION

Our results provide new evidence that SMC-STIM1 disruption is a novel mechanism that protects the heart from MI through reduction of endoplasmic reticulum stress, oxidative stress, MAP-Kinase, apoptosis, and inflammation.

What role does the stress response have in congestive heart failure?

This review is concerned with cardiac malfunction as a result of an imbalance in protein proteostasis, the homeostatic balance between protein removal and regeneration in a long remodeling process involving the endoplasmic reticulum (ER) and the unfolded protein response (UPR). The importance of this is of special significance with regard to cardiac function as a high energy requiring muscular organ that has a high oxygen requirement and is highly dependent on mitochondria. The importance of mitochondria is not only concerned with high energy dependence on mitochondrial electron transport, but it also has a role in the signaling between the mitochondria and the ER under stress. Proteins made in the ER are folded as a result of sulfhydryl groups (-SH) and attractive and repulsive reactions in the tertiary structure. We discuss how this matters with respect to an imbalance between muscle breakdown and repair in a stressful environment, especially as a result of oxidative and nitrosative byproducts of mitochondrial activity. The normal repair is a remodeling, but under this circumstance, the cell undergoes or even lysosomal "self eating" autophagy, or even necrosis instead of apoptosis. We shall discuss the relationship of the UPR pathway to chronic congestive heart failure (CHF).